StemCell Therapy

Cystic fibrosis (CF) is a genetic disorder that affects mostly the lungs but also the pancreas, liver, kidneys, and intestine.[1][2] Long-term issues include difficulty breathing and coughing up mucus as a result of frequent lung infections. Other signs and symptoms include sinus infections, poor growth, fatty stool, clubbing of the fingers and toes, and infertility in males, among others. Different people may have different degrees of symptoms.[1]

CF is inherited in an autosomal recessive manner. It is caused by the presence of mutations in both copies of the gene for the cystic fibrosis transmembrane conductance regulator (CFTR) protein.[1] Those with a single working copy are carriers and otherwise mostly normal.[3] CFTR is involved in production of sweat, digestive fluids, and mucus.[4] When CFTR is not functional, secretions which are usually thin instead become thick.[5] The condition is diagnosed by a sweat test and genetic testing.[1] Screening of infants at birth takes place in some areas of the world.[1]

There is no cure for cystic fibrosis.[3] Lung infections are treated with antibiotics which may be given intravenously, inhaled, or by mouth. Sometimes the antibiotic azithromycin is used long term. Inhaled hypertonic saline and salbutamol may also be useful. Lung transplantation may be an option if lung function continues to worsen. Pancreatic enzyme replacement and fat-soluble vitamin supplementation are important, especially in the young.[1]Airway clearance techniques such as chest physiotherapy have some short term benefit but long term effects are unclear.[6] The average life expectancy is between 42 and 50 years in the developed world.[7][8] Lung problems are responsible for death in 80% of people with cystic fibrosis.[1]

CF is most common among people of Northern European ancestry and affects about one out of every 3,000 newborns.[1] About one in 25 people are carriers.[3] It is least common in Africans and Asians.[1] It was first recognized as a specific disease by Dorothy Andersen in 1938, with descriptions that fit the condition occurring at least as far back as 1595.[2] The name cystic fibrosis refers to the characteristic fibrosis and cysts that form within the pancreas.[2][9]

The main signs and symptoms of cystic fibrosis are salty-tasting skin,[10] poor growth, and poor weight gain despite normal food intake,[11] accumulation of thick, sticky mucus,[12] frequent chest infections, and coughing or shortness of breath.[13] Males can be infertile due to congenital absence of the vas deferens.[14] Symptoms often appear in infancy and childhood, such as bowel obstruction due to meconium ileus in newborn babies.[15] As the children grow, they exercise to release mucus in the alveoli.[16]Ciliated epithelial cells in the person have a mutated protein that leads to abnormally viscous mucus production.[12] The poor growth in children typically presents as an inability to gain weight or height at the same rate as their peers and is occasionally not diagnosed until investigation is initiated for poor growth. The causes of growth failure are multifactorial and include chronic lung infection, poor absorption of nutrients through the gastrointestinal tract, and increased metabolic demand due to chronic illness.[11]

In rare cases, cystic fibrosis can manifest itself as a coagulation disorder. Vitamin K is normally absorbed from breast milk, formula, and later, solid foods. This absorption is impaired in some cystic fibrosis patients. Young children are especially sensitive to vitamin K malabsorptive disorders because only a very small amount of vitamin K crosses the placenta, leaving the child with very low reserves and limited ability to absorb vitamin K from dietary sources after birth. Because factors II, VII, IX, and X (clotting factors) are vitamin Kdependent, low levels of vitamin K can result in coagulation problems. Consequently, when a child presents with unexplained bruising, a coagulation evaluation may be warranted to determine whether there is an underlying disease.[17]

Lung disease results from clogging of the airways due to mucus build-up, decreased mucociliary clearance, and resulting inflammation.[18][19] Inflammation and infection cause injury and structural changes to the lungs, leading to a variety of symptoms. In the early stages, incessant coughing, copious phlegm production, and decreased ability to exercise are common. Many of these symptoms occur when bacteria that normally inhabit the thick mucus grow out of control and cause pneumonia. In later stages, changes in the architecture of the lung, such as pathology in the major airways (bronchiectasis), further exacerbate difficulties in breathing. Other signs include coughing up blood (hemoptysis), high blood pressure in the lung (pulmonary hypertension), heart failure, difficulties getting enough oxygen to the body (hypoxia), and respiratory failure requiring support with breathing masks, such as bilevel positive airway pressure machines or ventilators.[20]Staphylococcus aureus, Haemophilus influenzae, and Pseudomonas aeruginosa are the three most common organisms causing lung infections in CF patients.[19] In addition to typical bacterial infections, people with CF more commonly develop other types of lung disease. Among these is allergic bronchopulmonary aspergillosis, in which the body's response to the common fungus Aspergillus fumigatus causes worsening of breathing problems. Another is infection with Mycobacterium avium complex (MAC), a group of bacteria related to tuberculosis, which can cause a lot of lung damage and does not respond to common antibiotics.[21]

Mucus in the paranasal sinuses is equally thick and may also cause blockage of the sinus passages, leading to infection. This may cause facial pain, fever, nasal drainage, and headaches. Individuals with CF may develop overgrowth of the nasal tissue (nasal polyps) due to inflammation from chronic sinus infections.[22] Recurrent sinonasal polyps can occur in as many as 10% to 25% of CF patients.[19] These polyps can block the nasal passages and increase breathing difficulties.[23][24]

Cardiorespiratory complications are the most common cause of death (~80%) in patients at most CF centers in the United States.[19]

Prior to prenatal and newborn screening, cystic fibrosis was often diagnosed when a newborn infant failed to pass feces (meconium). Meconium may completely block the intestines and cause serious illness. This condition, called meconium ileus, occurs in 510%[19][25] of newborns with CF. In addition, protrusion of internal rectal membranes (rectal prolapse) is more common, occurring in as many as 10% of children with CF,[19] and it is caused by increased fecal volume, malnutrition, and increased intraabdominal pressure due to coughing.[26]

The thick mucus seen in the lungs has a counterpart in thickened secretions from the pancreas, an organ responsible for providing digestive juices that help break down food. These secretions block the exocrine movement of the digestive enzymes into the duodenum and result in irreversible damage to the pancreas, often with painful inflammation (pancreatitis).[27] The pancreatic ducts are totally plugged in more advanced cases, usually seen in older children or adolescents.[19] This causes atrophy of the exocrine glands and progressive fibrosis.[19]

The lack of digestive enzymes leads to difficulty absorbing nutrients with their subsequent excretion in the feces, a disorder known as malabsorption. Malabsorption leads to malnutrition and poor growth and development because of calorie loss. Resultant hypoproteinemia may be severe enough to cause generalized edema.[19] Individuals with CF also have difficulties absorbing the fat-soluble vitamins A, D, E, and K.

In addition to the pancreas problems, people with cystic fibrosis experience more heartburn, intestinal blockage by intussusception, and constipation.[28] Older individuals with CF may develop distal intestinal obstruction syndrome when thickened feces cause intestinal blockage.[29]

Exocrine pancreatic insufficiency occurs in the majority (85% to 90%) of patients with CF.[19] It is mainly associated with "severe" CFTR mutations, where both alleles are completely nonfunctional (e.g. F508/F508).[19] It occurs in 10% to 15% of patients with one "severe" and one "mild" CFTR mutation where there still is a little CFTR activity, or where there are two "mild" CFTR mutations.[19] In these milder cases, there is still sufficient pancreatic exocrine function so that enzyme supplementation is not required.[19] There are usually no other GI complications in pancreas-sufficient phenotypes, and in general, such individuals usually have excellent growth and development.[19] Despite this, idiopathic chronic pancreatitis can occur in a subset of pancreas-sufficient individuals with CF, and is associated with recurrent abdominal pain and life-threatening complications.[19]

Thickened secretions also may cause liver problems in patients with CF. Bile secreted by the liver to aid in digestion may block the bile ducts, leading to liver damage. Over time, this can lead to scarring and nodularity (cirrhosis). The liver fails to rid the blood of toxins and does not make important proteins, such as those responsible for blood clotting.[30][31] Liver disease is the third most common cause of death associated with CF.[19]

The pancreas contains the islets of Langerhans, which are responsible for making insulin, a hormone that helps regulate blood glucose. Damage of the pancreas can lead to loss of the islet cells, leading to a type of diabetes that is unique to those with the disease.[32] This cystic fibrosis-related diabetes (CFRD) shares characteristics that can be found in type 1 and type 2 diabetics, and is one of the principal nonpulmonary complications of CF.[33]Vitamin D is involved in calcium and phosphate regulation. Poor uptake of vitamin D from the diet because of malabsorption can lead to the bone disease osteoporosis in which weakened bones are more susceptible to fractures.[34] In addition, people with CF often develop clubbing of their fingers and toes due to the effects of chronic illness and low oxygen in their tissues.[35][36]

Infertility affects both men and women. At least 97% of men with cystic fibrosis are infertile, but not sterile and can have children with assisted reproductive techniques.[37] The main cause of infertility in men with cystic fibrosis is congenital absence of the vas deferens (which normally connects the testes to the ejaculatory ducts of the penis), but potentially also by other mechanisms such as causing no sperm, teratospermia, and few sperm with poor motility.[38] Many men found to have congenital absence of the vas deferens during evaluation for infertility have a mild, previously undiagnosed form of CF.[39] Approximately 20% of women with CF have fertility difficulties due to thickened cervical mucus or malnutrition. In severe cases, malnutrition disrupts ovulation and causes a lack of menstruation.[40]

CF is caused by a mutation in the gene cystic fibrosis transmembrane conductance regulator (CFTR). The most common mutation, F508, is a deletion ( signifying deletion) of three nucleotides[41] that results in a loss of the amino acid phenylalanine (F) at the 508th position on the protein. This mutation accounts for two-thirds (6670%[19]) of CF cases worldwide and 90% of cases in the United States; however, there are over 1500 other mutations that can produce CF.[42] Although most people have two working copies (alleles) of the CFTR gene, only one is needed to prevent cystic fibrosis. CF develops when neither allele can produce a functional CFTR protein. Thus, CF is considered an autosomal recessive disease.

The CFTR gene, found at the q31.2 locus of chromosome 7, is 230,000 base pairs long, and creates a protein that is 1,480 amino acids long. More specifically the location is between base pair 117,120,016 to 117,308,718 on the long arm of chromosome 7, region 3, band 1, sub-band 2, represented as 7q31.2. Structurally, CFTR is a type of gene known as an ABC gene. The product of this gene (the CFTR) is a chloride ion channel important in creating sweat, digestive juices and mucus. This protein possesses two ATP-hydrolyzing domains, which allows the protein to use energy in the form of ATP. It also contains two domains comprising 6 alpha helices apiece, which allow the protein to cross the cell membrane. A regulatory binding site on the protein allows activation by phosphorylation, mainly by cAMP-dependent protein kinase.[20] The carboxyl terminal of the protein is anchored to the cytoskeleton by a PDZ domain interaction.[43]

In addition, there is increasing evidence that genetic modifiers besides CFTR modulate the frequency and severity of the disease. One example is mannan-binding lectin, which is involved in innate immunity by facilitating phagocytosis of microorganisms. Polymorphisms in one or both mannan-binding lectin alleles that result in lower circulating levels of the protein are associated with a threefold higher risk of end-stage lung disease, as well as an increased burden of chronic bacterial infections.[19]

There are several mutations in the CFTR gene, and different mutations cause different defects in the CFTR protein, sometimes causing a milder or more severe disease. These protein defects are also targets for drugs which can sometimes restore their function. F508-CFTR, which occurs in >90% of patients in the U.S., creates a protein that does not fold normally and is not appropriately transported to the cell membrane, resulting in its degradation. Other mutations result in proteins that are too short (truncated) because production is ended prematurely. Other mutations produce proteins that: do not use energy normally, do not allow chloride, iodide, and thiocyanate to cross the membrane appropriately,[44] degrade at a faster rate than normal. Mutations may also lead to fewer copies of the CFTR protein being produced.[20]

The protein created by this gene is anchored to the outer membrane of cells in the sweat glands, lungs, pancreas, and all other remaining exocrine glands in the body. The protein spans this membrane and acts as a channel connecting the inner part of the cell (cytoplasm) to the surrounding fluid. This channel is primarily responsible for controlling the movement of halogens from inside to outside of the cell; however, in the sweat ducts, it facilitates the movement of chloride from the sweat duct into the cytoplasm. When the CFTR protein does not resorb ions in sweat ducts, chloride and thiocyanate[45] released from sweat glands are trapped inside the ducts and pumped to the skin. Additionally hypothiocyanite, OSCN, cannot be produced by the immune defense system.[46][47] Because chloride is negatively charged, this modifies the electrical potential inside and outside the cell that normally causes cations to cross into the cell. Sodium is the most common cation in the extracellular space. The excess chloride within sweat ducts prevents sodium resorption by epithelial sodium channels and the combination of sodium and chloride creates the salt, which is lost in high amounts in the sweat of individuals with CF. This lost salt forms the basis for the sweat test.[20]

Most of the damage in CF is due to blockage of the narrow passages of affected organs with thickened secretions. These blockages lead to remodeling and infection in the lung, damage by accumulated digestive enzymes in the pancreas, blockage of the intestines by thick faeces, etc. There are several theories on how the defects in the protein and cellular function cause the clinical effects. The most current theory suggests that defective ion transport leads to dehydration in the airway epithelia, thickening mucus. In airway epithelial cells, the cilia exist in between the cell's apical surface and mucus in a layer known as Airway Surface Liquid (ASL). The flow of ions from the cell and into this layer is determined by ion channels like CFTR. CFTR not only allows Chloride ions to be drawn from the cell and into the ASL, but it also regulates another channel called ENac. ENac allows sodium ions to leave the ASL and enter the respiratory epithelium. CFTR normally inhibits this channel, but if the CFTR is defective, then sodium will flow freely from the ASL and into the cell. As water follows sodium, the depth of ASL will be depleted and the cilia will be left in the mucous layer.[48] As cilia cannot effectively move in a thick viscous environment, there is deficient mucociliary clearance and a buildup of mucus, clogging small airways.[49] The accumulation of more viscous, nutrient-rich mucus in the lungs allows bacteria to hide from the body's immune system, causing repeated respiratory infections. The presence of the same CFTR proteins in pancreatic duct and skin cells are what cause symptoms in these systems.

The lungs of individuals with cystic fibrosis are colonized and infected by bacteria from an early age. These bacteria, which often spread among individuals with CF, thrive in the altered mucus, which collects in the small airways of the lungs. This mucus leads to the formation of bacterial microenvironments known as biofilms that are difficult for immune cells and antibiotics to penetrate. Viscous secretions and persistent respiratory infections repeatedly damage the lung by gradually remodeling the airways, which makes infection even more difficult to eradicate.[50]

Over time, both the types of bacteria and their individual characteristics change in individuals with CF. In the initial stage, common bacteria such as Staphylococcus aureus and Haemophilus influenzae colonize and infect the lungs.[19] Eventually, Pseudomonas aeruginosa (and sometimes Burkholderia cepacia) dominates. By 18 years of age, 80% of patients with classic CF harbor P. aeruginosa, and 3.5% harbor B. cepacia.[19] Once within the lungs, these bacteria adapt to the environment and develop resistance to commonly used antibiotics. Pseudomonas can develop special characteristics that allow the formation of large colonies, known as "mucoid" Pseudomonas, which are rarely seen in people that do not have CF.[50] Scientific evidences suggest that Interleukin 17 pathway plays a key role in resistance and modulation of the inflammatory response during P. aeruginosa infection in CF.[51] In particular, Interleukin 17 -mediated immunity plays a double-edged activity during chronic airways infection: on one side, it contributes to the control of P. aeruginosa burden while, on the other, it propagates exacerbated pulmonary neutrophilia and tissue remodeling.[51]

One way infection spreads is by passing between different individuals with CF.[52] In the past, people with CF often participated in summer "CF Camps" and other recreational gatherings.[53][54] Hospitals grouped patients with CF into common areas and routine equipment (such as nebulizers)[55] was not sterilized between individual patients.[56] This led to transmission of more dangerous strains of bacteria among groups of patients. As a result, individuals with CF are now routinely isolated from one another in the healthcare setting, and healthcare providers are encouraged to wear gowns and gloves when examining patients with CF to limit the spread of virulent bacterial strains.[57]

CF patients may also have their airways chronically colonized by filamentous fungi (such as Aspergillus fumigatus, Scedosporium apiospermum, Aspergillus terreus) and/or yeasts (such as Candida albicans); other filamentous fungi less commonly isolated include Aspergillus flavus and Aspergillus nidulans (occur transiently in CF respiratory secretions) and Exophiala dermatitidis and Scedosporium prolificans (chronic airway-colonizers); some filamentous fungi like Penicillium emersonii and Acrophialophora fusispora are encountered in patients almost exclusively in the context of CF.[58] Defective mucociliary clearance characterizing CF is associated with local immunological disorders. In addition, the prolonged therapy with antibiotics and the use of corticosteroid treatments may also facilitate fungal growth. Although the clinical relevance of the fungal airway colonization is still a matter of debate, filamentous fungi may contribute to the local inflammatory response and therefore to the progressive deterioration of the lung function, as often happens with allergic broncho-pulmonary aspergillosis (ABPA) the most common fungal disease in the context of CF, involving a Th2-driven immune response to Aspergillus.[58][59]

Cystic fibrosis may be diagnosed by many different methods including newborn screening, sweat testing, and genetic testing.[60] As of 2006 in the United States, 10 percent of cases are diagnosed shortly after birth as part of newborn screening programs. The newborn screen initially measures for raised blood concentration of immunoreactive trypsinogen.[61] Infants with an abnormal newborn screen need a sweat test to confirm the CF diagnosis. In many cases, a parent makes the diagnosis because the infant tastes salty.[19]Trypsinogen levels can be increased in individuals who have a single mutated copy of the CFTR gene (carriers) or, in rare instances, in individuals with two normal copies of the CFTR gene. Due to these false positives, CF screening in newborns can be controversial.[62][63] Most states and countries do not screen for CF routinely at birth. Therefore, most individuals are diagnosed after symptoms (e.g. sinopulmonary disease and GI manifestations[19]) prompt an evaluation for cystic fibrosis. The most commonly used form of testing is the sweat test. Sweat-testing involves application of a medication that stimulates sweating (pilocarpine). To deliver the medication through the skin, iontophoresis is used to, whereby one electrode is placed onto the applied medication and an electric current is passed to a separate electrode on the skin. The resultant sweat is then collected on filter paper or in a capillary tube and analyzed for abnormal amounts of sodium and chloride. People with CF have increased amounts of sodium and chloride in their sweat. In contrast, people with CF have less thiocyanate and hypothiocyanite in their saliva[64] and mucus (Banfi et al.). CF can also be diagnosed by identification of mutations in the CFTR gene.[65]

People with CF may be listed in a disease registry that allows researchers and doctors to track health results and identify candidates for clinical trials.[66]

Couples who are pregnant or planning a pregnancy can have themselves tested for the CFTR gene mutations to determine the risk that their child will be born with cystic fibrosis. Testing is typically performed first on one or both parents and, if the risk of CF is high, testing on the fetus is performed. The American College of Obstetricians and Gynecologists (ACOG) recommends testing for couples who have a personal or close family history of CF, and they recommend that carrier testing be offered to all Caucasian couples and be made available to couples of other ethnic backgrounds.[67]

Because development of CF in the fetus requires each parent to pass on a mutated copy of the CFTR gene and because CF testing is expensive, testing is often performed initially on one parent. If testing shows that parent is a CFTR gene mutation carrier, the other parent is tested to calculate the risk that their children will have CF. CF can result from more than a thousand different mutations.[68] As of 2016 typically only the most common mutations are tested for, such as F508[68] Most commercially available tests look for 32 or fewer different mutations. If a family has a known uncommon mutation, specific screening for that mutation can be performed. Because not all known mutations are found on current tests, a negative screen does not guarantee that a child will not have CF.[69]

During pregnancy, testing can be performed on the placenta (chorionic villus sampling) or the fluid around the fetus (amniocentesis). However, chorionic villus sampling has a risk of fetal death of 1 in 100 and amniocentesis of 1 in 200;[70] a recent study has indicated this may be much lower, approximately 1 in 1,600.[71]

Economically, for carrier couples of cystic fibrosis, when comparing preimplantation genetic diagnosis (PGD) with natural conception (NC) followed by prenatal testing and abortion of affected pregnancies, PGD provides net economic benefits up to a maternal age of approximately 40 years, after which NC, prenatal testing, and abortion has higher economic benefit.[72]

While there are no cures for cystic fibrosis, there are several treatment methods. The management of cystic fibrosis has improved significantly over the past 70 years. While infants born with cystic fibrosis 70 years ago would have been unlikely to live beyond their first year, infants today are likely to live well into adulthood. Recent advances in the treatment of cystic fibrosis have meant that an individual with cystic fibrosis can live a fuller life less encumbered by their condition. The cornerstones of management are the proactive treatment of airway infection, and encouragement of good nutrition and an active lifestyle. Pulmonary rehabilitation as a management of cystic fibrosis continues throughout a person's life, and is aimed at maximizing organ function, and therefore the quality of life. At best, current treatments delay the decline in organ function. Because of the wide variation in disease symptoms, treatment typically occurs at specialist multidisciplinary centers and is tailored to the individual. Targets for therapy are the lungs, gastrointestinal tract (including pancreatic enzyme supplements), the reproductive organs (including assisted reproductive technology (ART)) and psychological support.[61]

The most consistent aspect of therapy in cystic fibrosis is limiting and treating the lung damage caused by thick mucus and infection, with the goal of maintaining quality of life. Intravenous, inhaled, and oral antibiotics are used to treat chronic and acute infections. Mechanical devices and inhalation medications are used to alter and clear the thickened mucus. These therapies, while effective, can be extremely time-consuming.

Many people with CF are on one or more antibiotics at all times, even when healthy, to prophylactically suppress infection. Antibiotics are absolutely necessary whenever pneumonia is suspected or there has been a noticeable decline in lung function, and are usually chosen based on the results of a sputum analysis and the person's past response. This prolonged therapy often necessitates hospitalization and insertion of a more permanent IV such as a peripherally inserted central catheter (PICC line) or Port-a-Cath. Inhaled therapy with antibiotics such as tobramycin, colistin, and aztreonam is often given for months at a time to improve lung function by impeding the growth of colonized bacteria.[73][74][75] Inhaled antibiotic therapy helps lung function by fighting infection, but also has significant drawbacks like development of antibiotic resistance, tinnitus and changes in the voice.[76] Oral antibiotics such as ciprofloxacin or azithromycin are given to help prevent infection or to control ongoing infection.[77] The aminoglycoside antibiotics (e.g. tobramycin) used can cause hearing loss, damage to the balance system in the inner ear or kidney problems with long-term use.[78] To prevent these side-effects, the amount of antibiotics in the blood is routinely measured and adjusted accordingly.

Several mechanical techniques are used to dislodge sputum and encourage its expectoration. In the hospital setting, chest physiotherapy (CPT) is utilized; a respiratory therapist percusses an individual's chest with his or her hands several times a day, to loosen up secretions. Devices that recreate this percussive therapy include the ThAIRapy Vest and the intrapulmonary percussive ventilator (IPV). Newer methods such as Biphasic Cuirass Ventilation, and associated clearance mode available in such devices, integrate a cough assistance phase, as well as a vibration phase for dislodging secretions. These are portable and adapted for home use.[79][needs update]Ivacaftor is an oral medication for the treatment of cystic fibrosis due to a number of specific mutations.[80][81] It improves lung function by about 10%; however, as of 2014 is expensive.[80]

Aerosolized medications that help loosen secretions include dornase alfa and hypertonic saline.[82] Dornase is a recombinant human deoxyribonuclease, which breaks down DNA in the sputum, thus decreasing its viscosity.[83]Denufosol is an investigational drug that opens an alternative chloride channel, helping to liquefy mucus.[84] It is unclear if inhaled corticosteroids are useful.[85]

As lung disease worsens, mechanical breathing support may become necessary. Individuals with CF may need to wear special masks at night that help push air into their lungs. These machines, known as bilevel positive airway pressure (BiPAP) ventilators, help prevent low blood oxygen levels during sleep. BiPAP may also be used during physical therapy to improve sputum clearance.[86][needs update] During severe illness, a tube may be placed in the throat (a procedure known as a tracheostomy) to enable breathing supported by a ventilator.

For children, preliminary studies show massage therapy may help people and their families quality of life.[87] It is unclear what effect pneumococcal vaccination has as it has not been studied as of 2014.[88]

Lung transplantation often becomes necessary for individuals with cystic fibrosis as lung function and exercise tolerance decline. Although single lung transplantation is possible in other diseases, individuals with CF must have both lungs replaced because the remaining lung might contain bacteria that could infect the transplanted lung. A pancreatic or liver transplant may be performed at the same time in order to alleviate liver disease and/or diabetes.[89] Lung transplantation is considered when lung function declines to the point where assistance from mechanical devices is required or someone's survival is threatened.[90]

Newborns with intestinal obstruction typically require surgery, whereas adults with distal intestinal obstruction syndrome typically do not. Treatment of pancreatic insufficiency by replacement of missing digestive enzymes allows the duodenum to properly absorb nutrients and vitamins that would otherwise be lost in the feces. However, the best dosage and form of pancreatic enzyme replacement is unclear, as are the risks and long-term effectiveness of this treatment.[91]

So far, no large-scale research involving the incidence of atherosclerosis and coronary heart disease in adults with cystic fibrosis has been conducted. This is likely due to the fact that the vast majority of people with cystic fibrosis do not live long enough to develop clinically significant atherosclerosis or coronary heart disease.

Diabetes is the most common non-pulmonary complication of CF. It mixes features of type 1 and type 2 diabetes, and is recognized as a distinct entity, cystic fibrosis-related diabetes (CFRD).[33][92] While oral anti-diabetic drugs are sometimes used, the only recommended treatment is the use of insulin injections or an insulin pump,[93][needs update] and, unlike in type 1 and 2 diabetes, dietary restrictions are not recommended.[33]

Development of osteoporosis can be prevented by increased intake of vitamin D and calcium, and can be treated by bisphosphonates, although adverse effects can be an issue.[94][needs update] Poor growth may be avoided by insertion of a feeding tube for increasing calories through supplemental feeds or by administration of injected growth hormone.[95]

Sinus infections are treated by prolonged courses of antibiotics. The development of nasal polyps or other chronic changes within the nasal passages may severely limit airflow through the nose, and over time reduce the person's sense of smell. Sinus surgery is often used to alleviate nasal obstruction and to limit further infections. Nasal steroids such as fluticasone are used to decrease nasal inflammation.[96]

Female infertility may be overcome by assisted reproduction technology, particularly embryo transfer techniques. Male infertility caused by absence of the vas deferens may be overcome with testicular sperm extraction (TESE), collecting sperm cells directly from the testicles. If the collected sample contains too few sperm cells to likely have a spontaneous fertilization, intracytoplasmic sperm injection can be performed.[97]Third party reproduction is also a possibility for women with CF. It is unclear if taking antioxidants affects outcomes.[98]

The prognosis for cystic fibrosis has improved due to earlier diagnosis through screening, better treatment and access to health care. In 1959, the median age of survival of children with cystic fibrosis in the United States was six months.[99] In 2010, survival is estimated to be 37 years for women and 40 for men.[100] In Canada, median survival increased from 24 years in 1982 to 47.7 in 2007.[101]

Of those with cystic fibrosis who are more than 18 years old as of 2009, 92% had graduated from high school, 67% had at least some college education, 15% were disabled and 9% were unemployed, 56% were single and 39% were married or living with a partner.[102]

Chronic illnesses can be very difficult to manage. Cystic fibrosis (CF) is a chronic illness that affects the "digestive and respiratory tracts resulting in generalized malnutrition and chronic respiratory infections".[103] The thick secretions clog the airways in the lungs, which often cause inflammation and severe lung infections.[104][105] If it is compromised, it affects the quality of life of someone with CF and their ability to complete such tasks as everyday chores. It is important for CF patients to understand the detrimental relationship that chronic illnesses place on the quality of life. According to Schmitz and Goldbeck (2006), the fact that cystic fibrosis significantly increases emotional stress on both the individual and the family, "and the necessary time-consuming daily treatment routine may have further negative effects on quality of life (QOL)".[106] However, Havermans and colleagues (2006) have shown that young outpatients with CF who have participated in the CFQ-R (Cystic Fibrosis Questionnaire-Revised) "rated some QOL domains higher than did their parents".[107] Consequently, outpatients with CF have a more positive outlook for themselves. Furthermore, there are many ways to improve the QOL in CF patients. Exercise is promoted to increase lung function. Integrating an exercise regimen into the CF patients daily routine can significantly improve the quality of life.[108] There is no definitive cure for cystic fibrosis. However, there are diverse medications used, such as mucolytics, bronchodilators, steroids, and antibiotics, that have the purpose of loosening mucus, expanding airways, decreasing inflammation, and fighting lung infections.[109]

Cystic fibrosis is the most common life-limiting autosomal recessive disease among people of European heritage.[111] In the United States, approximately 30,000 individuals have CF; most are diagnosed by six months of age. In Canada, there are approximately 4,000 people with CF.[112] Approximately 1 in 25 people of European descent, and one in 30 of Caucasian Americans,[113] is a carrier of a cystic fibrosis mutation. Although CF is less common in these groups, approximately 1 in 46 Hispanics, 1 in 65 Africans and 1 in 90 Asians carry at least one abnormal CFTR gene.[114][115] Ireland has the world's highest prevalence of cystic fibrosis, at 1:1353.[116]

Although technically a rare disease, cystic fibrosis is ranked as one of the most widespread life-shortening genetic diseases. It is most common among nations in the Western world. An exception is Finland, where only one in 80 people carry a CF mutation.[117] The World Health Organization states that "In the European Union, 1 in 20003000 newborns is found to be affected by CF".[118] In the United States, 1 in 3,500 children are born with CF.[119] In 1997, about 1 in 3,300 caucasian children in the United States was born with cystic fibrosis. In contrast, only 1 in 15,000 African American children suffered from cystic fibrosis, and in Asian Americans the rate was even lower at 1 in 32,000.[120]

Cystic fibrosis is diagnosed in males and females equally. For reasons that remain unclear, data has shown that males tend to have a longer life expectancy than females,[121][122] however recent studies suggest this gender gap may no longer exist perhaps due to improvements in health care facilities,[123][124] while a recent study from Ireland identified a link between the female hormone estrogen and worse outcomes in CF.[125]

The distribution of CF alleles varies among populations. The frequency of F508 carriers has been estimated at 1:200 in northern Sweden, 1:143 in Lithuanians, and 1:38 in Denmark. No F508 carriers were found among 171 Finns and 151 Saami people.[126] F508 does occur in Finland, but it is a minority allele there. Cystic fibrosis is known to occur in only 20 families (pedigrees) in Finland.[127]

The F508 mutation is estimated to be up to 52,000 years old.[128] Numerous hypotheses have been advanced as to why such a lethal mutation has persisted and spread in the human population. Other common autosomal recessive diseases such as sickle-cell anemia have been found to protect carriers from other diseases, a concept known as heterozygote advantage. Resistance to the following have all been proposed as possible sources of heterozygote advantage:

It is supposed that CF appeared about 3,000 BC because of migration of peoples, gene mutations, and new conditions in nourishment.[137] Although the entire clinical spectrum of CF was not recognized until the 1930s, certain aspects of CF were identified much earlier. Indeed, literature from Germany and Switzerland in the 18th century warned "Wehe dem Kind, das beim Ku auf die Stirn salzig schmekt, er ist verhext und muss bald sterbe" or "Woe to the child who tastes salty from a kiss on the brow, for he is cursed and soon must die," recognizing the association between the salt loss in CF and illness.[137]

In the 19th century, Carl von Rokitansky described a case of fetal death with meconium peritonitis, a complication of meconium ileus associated with cystic fibrosis. Meconium ileus was first described in 1905 by Karl Landsteiner.[137] In 1936, Guido Fanconi published a paper describing a connection between celiac disease, cystic fibrosis of the pancreas, and bronchiectasis.[138]

In 1938 Dorothy Hansine Andersen published an article, "Cystic Fibrosis of the Pancreas and Its Relation to Celiac Disease: a Clinical and Pathological Study," in the American Journal of Diseases of Children. She was the first to describe the characteristic cystic fibrosis of the pancreas and to correlate it with the lung and intestinal disease prominent in CF.[9] She also first hypothesized that CF was a recessive disease and first used pancreatic enzyme replacement to treat affected children. In 1952 Paul di SantAgnese discovered abnormalities in sweat electrolytes; a sweat test was developed and improved over the next decade.[139]

The first linkage between CF and another marker (Paroxonase) was found in 1985 by Hans Eiberg, indicating that only one locus exists for CF. In 1988 the first mutation for CF, F508 was discovered by Francis Collins, Lap-Chee Tsui and John R. Riordan on the seventh chromosome. Subsequent research has found over 1,000 different mutations that cause CF.

Because mutations in the CFTR gene are typically small, classical genetics techniques had been unable to accurately pinpoint the mutated gene.[140] Using protein markers, gene-linkage studies were able to map the mutation to chromosome 7. Chromosome-walking and -jumping techniques were then used to identify and sequence the gene.[141] In 1989 Lap-Chee Tsui led a team of researchers at the Hospital for Sick Children in Toronto that discovered the gene responsible for CF. Cystic fibrosis represents a classic example of how a human genetic disorder was elucidated strictly by the process of forward genetics.

Gene therapy has been explored as a potential cure for cystic fibrosis. Results from trials have shown limited success as of 2013.[142] A small study published in 2015 found a small benefit.[143]

The focus of much cystic fibrosis gene therapy research is aimed at trying to place a normal copy of the CFTR gene into affected cells. Transferring the normal CFTR gene into the affected epithelium cells would result in the production of functional CFTR in all target cells, without adverse reactions or an inflammation response. Studies have shown that to prevent the lung manifestations of cystic fibrosis, only 510% the normal amount of CFTR gene expression is needed.[144] Multiple approaches have been tested for gene transfer, such as liposomes and viral vectors in animal models and clinical trials. However, both methods were found to be relatively inefficient treatment options.[145] The main reason is that very few cells take up the vector and express the gene, so the treatment has little effect. Additionally, problems have been noted in cDNA recombination, such that the gene introduced by the treatment is rendered unusable.[146] There has been a functional repair in culture of CFTR by CRISPR/Cas9 in intestinal stem cell organoids of cystic fibrosis patients.[147]

A number of small molecules that aim at compensating various mutations of the CFTR gene are under development. One approach is to develop drugs that get the ribosome to overcome the stop codon and synthesize a full-length CFTR protein. About 10% of CF result from a premature stop codon in the DNA, leading to early termination of protein synthesis and truncated proteins. These drugs target nonsense mutations such as G542X, which consists of the amino acid glycine in position 542 being replaced by a stop codon. Aminoglycoside antibiotics interfere with protein synthesis and error-correction. In some cases, they can cause the cell to overcome a premature stop codon by inserting a random amino acid, thereby allowing expression of a full-length protein.[148] The aminoglycoside gentamicin has been used to treat lung cells from CF patients in the laboratory to induce the cells to grow full-length proteins.[149] Another drug targeting nonsense mutations is ataluren, which is undergoing Phase III clinical trials as of October 2011[update].[150]

It is unclear as of 2014 if ursodeoxycholic acid is useful for those with cystic fibrosis-related liver disease.[151]

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Cystic fibrosis - Wikipedia, the free encyclopedia

What Is Gene Therapy?

Explore the what's and why's of gene therapy research, includingan in-depth look at the genetic disorder cystic fibrosis and how gene therapy could potentially be used to treat it.

Gene Delivery: Tools of the Trade

Explore the methods for delivering genes into cells.

Space Doctor

You are the doctor! Design and test gene therapy treatments with ailing aliens.

Challenges In Gene Therapy

Researchers hoping to bring gene therapy to the clinic face unique challenges.

Approaches To Gene Therapy

Beyond adding a working copy of a broken gene, gene therapy can also repair or eliminate broken genes.

Gene Therapy Successes

The future of gene therapy is bright. Learn about some of its most encouraging success stories.

Gene Therapy Case Study: Cystic Fibrosis

APA format:

Genetic Science Learning Center. (2012, December 1) Gene Therapy. Retrieved August 09, 2016, from http://learn.genetics.utah.edu/content/genetherapy/

CSE format:

Gene Therapy [Internet]. Salt Lake City (UT): Genetic Science Learning Center; 2012 [cited 2016 Aug 9] Available from http://learn.genetics.utah.edu/content/genetherapy/

Chicago format:

Genetic Science Learning Center. "Gene Therapy." Learn.Genetics. December 1, 2012. Accessed August 9, 2016. http://learn.genetics.utah.edu/content/genetherapy/.

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Gene Therapy - Learn Genetics

Editor-in-Chief: Terence R. Flotte, MD Deputy Editor, Europe: Thierry VandenDriessche, PhD Deputy Editor, U.S.: Barry J. Byrne, MD, PhD Human Gene Therapy Editor: Guangping Gao, PhD Methods Editor: Hildegard Bning, PhD Clinical Development Editor: James M. Wilson, MD, PhD

Latest Impact Factor* is 3.755 *2014 Journal Citation Reports published by Thomson Reuters, 2015

Human Gene Therapy is the premier, multidisciplinary journal covering all aspects of gene therapy. The Journal publishes in-depth coverage of DNA, RNA, and cell therapies by delivering the latest breakthroughs in research and technologies. Human Gene Therapy provides a central forum for scientific and clinical information, including ethical, legal, regulatory, social, and commercial issues, which enables the advancement and progress of therapeutic procedures leading to improved patient outcomes, and ultimately, to curing diseases.

The Journal is divided into three parts. Human Gene Therapy, the flagship, is published 12 times per year. HGT Methods, a bimonthly journal, focuses on the applications of gene therapy to product testing and development. HGT Clinical Development, a quarterly journal, serves as a venue for publishing data relevant to the regulatory review and commercial development of cell and gene therapy products.

Human Gene Therapy was voted one of the most influential journals in Biology and Medicine over the last 100 years by the Biomedical & Life Sciences Division of the Special Libraries Association.

Human Gene Therapy, HGT Methods, and HGT Clinical Development are under the editorial leadership of Editor-in-Chief Terence R. Flotte, MD, University of Massachusetts Medical School; Deput Editor Europe Thierry VandenDriessche, PhD, Free University of Brussels (VUB); Deputy Editor U.S. Barry J. Byrne, MD, PhD,Powell Gene Therapy Center, University of Florida, College of Medicine; Human Gene Therapy Editor Guangping Gao, PhD, University of Massachusetts Medical School; Methods Editor Hildegard Bning, PhD, University of Cologne; Clinical Development Editor James M. Wilson, MD, PhD,University of Pennsylvania School of Medicine, Gene Therapy Program; and other leading investigators. View the entire editorial board.

Audience: Geneticists, medical geneticists, molecular biologists, virologists, experimental researchers, and experimental medicine specialists, among others.

Human Gene Therapy and HGT Methods provide Instant Online publication 72 hours after acceptance

The views, opinions, findings, conclusions and recommendations set forth in any Journal article are solely those of the authors of those articles and do not necessarily reflect the views, policy or position of the Journal, its Publisher, its editorial staff or any affiliated Societies and should not be attributed to any of them.

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Human Gene Therapy

Gene therapy is an experimental treatment that involves inserting genetic material into your cells to give them a new function or restore a missing function, as cancer may be caused by damaged or missing genes, also known as gene mutations. Although gene therapy may be one way to overcome these changes and treat or prevent cancer, it is currently only available through clinical trials.

Cancer is caused by changes in our genes. Genes are inherited from our parents, and determine our traits and characteristics. They are made of biological molecules called deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). DNA and RNA are responsible for making proteins, which have many functions, such as helping a cell to maintain its shape or controlling its growth and division. Changes or mutations in genes can affect the proteins and may sometimes lead to diseases, such as cancer.

Gene therapy is designed to modify cancer cells at the molecular level and replace a missing or bad gene with a healthy one. The new gene is delivered to the target cell via a vector, which is usually an inactive virus or liposome, a tiny fat bubble.

Gene therapy can be done in two ways: outside (ex vivo) or inside (in vivo) your body. Ex-vivo techniques involve taking some of the cancer cells out of your body, injecting them with good genes, and then putting them back into your body. The in-vivo process requires that good genes be put directly into a tumor, which may be difficult depending on its location or if the cancer has spread. Scientists generally use two types of cells in gene therapy the tumor cells themselves and immune system cells that attack the tumors.

Researchers from Moores Cancer Center at UC San Diego Health System are studying several gene therapy techniques for breast cancer, melanoma, leukemia and pancreatic cancer.

For example, they have been integrally involved in the development of Herceptin, a targeted therapy that is proving to be effective in curing localized human epidermal growth factor receptor-2 (HER2) breast cancer. HER2 controls how cells grow, divide and repair themselves.

Researchers have also been injecting a modified herpes virus into melanoma tumors, with the intention of improving the bodys immune defenses against the disease.

Gene therapy called TNFerade Biologic involves a DNA carrier containing the gene for tumor necrosis factor-alpha, an immune system protein with potent and well-documented anti-cancer effects. TNFerade is being studied in combination with radiation therapy for first-time treatment of inoperable pancreatic cancer.

TNFerade and the herpes strategies use gene therapy to enhance the killing effect of the primary mechanism radiation in TNFerade and viral induced cell lysis, or splitting, in the herpes virus.

When will gene therapy be available? Gene therapy is only available as a cancer treatment through clinical trials.

Are there any risks associated with gene therapy clinical trials? Yes. Viral vectors might infect healthy cells as well as cancer cells, a new gene might be inserted in the wrong location in the DNA, or the transferred genes could be overexpressed and produce too much of the missing protein, causing harm. All risks for any procedure should be discussed with your doctor.

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Gene Therapy - Cancer Treatments - Moores Cancer Center ...

In Lung Cancer, Not All HER2 Alterations Are Created Equal Jan. 28, 2016 Study shows two distinct causes of HER2 activation in lung cancer: mutation of the gene and amplification of the gene. In patient samples of lung adenocarcinoma, 3 percent were found to have HER2 ... read more Dec. 12, 2015 Results from a long-term clinical trial conducted by cancer researchers show that combining radiation treatment with 'suicide gene therapy' provides a safe and effective one-two punch ... read more Gene Therapy Used to Extend Estrogen's Protective Effects on Memory Dec. 8, 2015 The hormone estrogen helps protect memory and promote a healthy brain, but this effect wanes as women age, and even estrogen replacement therapy stops working in humans after age 65. Now researchers ... read more Shrinking Tumors With an RNA Triple-Helix Hydrogel Glue Dec. 7, 2015 An efficient and effective delivery vehicle for gene therapy has been developed by researchers who have used it to shrink tumors by nearly 90 percent in a pre-clinical model of triple-negative breast ... read more Characteristics That May Increase a Breast Cancer Survivor's Risk of Developing Leukemia Following Treatment Identified Dec. 7, 2015 A new analysis indicates that certain characteristics may increase a breast cancer survivor's risk of developing leukemia after undergoing chemotherapy and/or radiation. The findings are a first ... read more Early Gene Therapy Results in Wiskott-Aldrich Syndrome Promising Dec. 6, 2015 Researchers reported promising preliminary outcomes for the first four children enrolled in a US gene therapy trial for Wiskott-Aldrich syndrome (WAS), a life-threatening genetic blood and immune ... read more Gene Therapy Restores Immunity in Children and Young Adults With Rare Immunodeficiency Dec. 6, 2015 Gene therapy can safely rebuild the immune systems of older children and young adults with X-linked severe combined immunodeficiency (SCID-X1), a rare inherited disorder that primarily affects males, ... read more MECP2 Duplication Syndrome Is Reversible, Study Suggests Nov. 25, 2015 The MECP2 Duplication Syndrome is reversible, say researchers. Importantly their study paves the way for treating duplication patients with an antisense oligonucleotide ... read more Gene Therapy: Promising Candidate for Cystic Fibrosis Treatment Nov. 16, 2015 An improved gene therapy treatment can cure mice with cystic fibrosis (CF). Cell cultures from CF patients, too, respond well to the treatment, suggest new encouraging ... read more Link Found Between Genetic Mutations, Proliferation, Immune Surveillance in Lung Cancer Nov. 11, 2015 There are four gene mutations (KRAS, TP53, STK11, and EGFR) that most commonly occur in lung cancer; however, there are limited effective therapies to target these mutations. With this in mind, ... read more Nov. 9, 2015 Genome editing techniques for blood stem cells just got better, thanks to a team of researchers. In a new article, they describe a new, more efficient way to edit genes in blood-forming or ... read more Nov. 2, 2015 Eye drops have been used to deliver the gene for a growth factor called granulocyte colony stimulating factor (G-CSF) in a mouse model of brain ischemia. The treatment led to a significant reduction ... read more Oct. 21, 2015 Delivering the hormone leptin directly to the brain through gene therapy aids weight loss without the significant side effect of bone loss, according to new ... read more New Study Explains Why You Bulk Up With Resistance Training, Not Endurance Training Oct. 20, 2015 Resistance and endurance exercises activate the same gene, PGC-1?, but the processes stimulated for the muscles to adapt depend on the exercise type. A new study offers insight into why the physical ... read more Researchers Identify Gene That Increases Risk of Sudden Death in Patients With Mild Epilepsy Oct. 15, 2015 A gene mutation that increases the risk of sudden unexpected death in epilepsy (SUDEP) in patients with mild forms of the disease has been discovered by a group of ... read more Oct. 8, 2015 Compared with direct gene injection, cell-mediated GDNF gene delivery led to considerably more pronounced preservation of myelinated fibers in the remote segments of the spinal cord (5 vs 3 mm from ... read more 'Alarm Clock' of a Leukemia-Causing Oncogene Identified Oct. 8, 2015 Mutations in DNMT3A gene cause MEIS1 activacion, triggering leukemia, a research team ... read more Oct. 5, 2015 A novel mouse model for the vision disorder Leber hereditary optic neuropathy (LHON) has been developed by researchers who have found that they can use gene therapy to improve visual function in the ... read more Genetic Polymorphism Associated With Lung Cancer Progression Oct. 5, 2015 Genetic polymorphisms associated with cancer progression lead to variations in gene expression and may serve as prognostic markers for lung cancer, researchers show. They found that in patients with ... read more New Hope for Lou: Unexplored Therapeutic Targets for ALS Sep. 3, 2015 No cures exist for amyotrophic lateral sclerosis (ALS), and the only approved therapy slows the progression by only a few months. A new study identifies a promising unexplored avenue of treatment for ... read more

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Originally posted here:
Gene Therapy News -- ScienceDaily

A few years ago, a clinical trial began in France in the hope of curing children with a type of genetic immune deficiency called SCID-X1. Children with this disease have a defective gene, called gamma-c, which prevents a subset of the cells of the immune system from forming, and predisposes the children to life-threatening infections. In an attempt to cure the childrenwho would otherwise die at a young agephysicians used gene therapy to provide them with normal gamma-c genes.

This particular trial has had striking success as well as tragedy. Eight of the eleven children are currently thriving. However, in two cases the therapy successfully introduced gamma-c genes, but these children have since developed leukemia. In both children, a gamma-c gene inserted next to another gene, called LMO2. The LMO2 gene has previously been linked to leukemia, and scientists speculate that the insertion of the gamma-c gene next to LMO2 may have overstimulated the gene, causing T cells to proliferate in excess. An LMO2 effect, in combination with the proliferation-inducing effects of the gamma-c gene itself, may be the cause of the leukemia in these two patients. Scientists are still investigating other possible causes.

From this single trial, it is clear that gene therapy holds significant promise, yet it is also clear that it poses significant risks. To learn more about the application of gene therapy in SCID, view the accompanying animation.

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Gene Therapy - Sumanas, Inc.

The mission of the Center for Gene Therapy is to investigate and employ the use of gene and cell based therapeutics for prevention and treatment of human diseases including: neuromuscular and neurodegenerative diseases, lysosomal storage disorders, ischemia and re-perfusion injury, neonatal hypertension, cancer and infectious diseases.

Learn about our areas of focus and featured research projects.

The National Institutes of Health has designated the Center for Gene Therapy as a Paul D. Wellstone Muscular Dystrophy Cooperative Research Center (MDCRC). MDCRCs promote basic, translational and clinical research and provide important resources that can be shared within the national muscle biology and neuromuscular research communities.

The MDCRC will allow Nationwide Children's researchers to further develop methods to overcome immune barriers to gene correction for Duchenne muscular dystrophy.

View the Nationwide Children's Wellstone Center page.

The Center for Gene Therapy and the Viral Vector Core are home to a Good Manufacturing Practice (GMP) production facility for manufacture of clinical-grade rAAV vectors.

View the Viral Vector Core & Clinical Manufacturing Facility site.

TheOSU and Nationwide Children's Muscle Groupbrings together investigators with diverse research interests in skeletal muscle, cardiac muscle, and neuromuscular biology.

Hosted by Kevin Flanigan, MD,"This Month in Muscular Dystrophy" podcastshighlight the latest in muscular dystrophy and other inherited neuromuscular disease research.During each podcast, authors of recent publications discuss how their work improves our understanding of inherited neuromuscular diseases, and what their work might mean for treatment of these diseases.

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Center for Gene Therapy :: The Research Institute at ...

Gene therapy is the insertion of genes into an individual's cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one.

Although the technology is still in its infancy, it has been used with some success.

Antisense therapy is not strictly a form of gene therapy, but is a genetically-mediated therapy and is often considered together with other methods.

In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene.

A carrier called a vector must be used to deliver the therapeutic gene to the patient's target cells.

Currently, the most common type of vectors are viruses that have been genetically altered to carry normal human DNA.

Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner.

Scientists have tried to harness this ability by manipulating the viral genome to remove disease-causing genes and insert therapeutic ones.

Target cells such as the patient's liver or lung cells are infected with the vector.

The vector then unloads its genetic material containing the therapeutic human gene into the target cell.

The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state.

In theory it is possible to transform either somatic cells (most cells of the body) or cells of the germline (such as sperm cells, ova, and their stem cell precursors).

All gene therapy to date on humans has been directed at somatic cells, whereas germline engineering in humans remains controversial.

For the introduced gene to be transmitted normally to offspring, it needs not only to be inserted into the cell, but also to be incorporated into the chromosomes by genetic recombination.

Somatic gene therapy can be broadly split in to two categories: ex vivo, which means exterior (where cells are modified outside the body and then transplanted back in again) and in vivo, which means interior (where genes are changed in cells still in the body).

Recombination-based approaches in vivo are especially uncommon, because for most DNA constructs recombination has a very low probability.

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Gene therapy - ScienceDaily

The Center for Biologics Evaluation and Research (CBER) regulates cellular therapy products, human gene therapy products, and certain devices related to cell and gene therapy. CBER uses both the Public Health Service Act and the Federal Food Drug and Cosmetic Act as enabling statutes for oversight.

Cellular therapy products include cellular immunotherapies, and other types of both autologous and allogeneic cells for certain therapeutic indications, including adult and embryonic stem cells. Human gene therapy refers to products that introduce genetic material into a persons DNA to replace faulty or missing genetic material, thus treating a disease or abnormal medical condition.

Although some cellular therapy products have been approved, CBER has not yet approved any human gene therapy product for sale. However, the amount of cellular and gene therapy-related research and development occurring in the United States continues to grow at a fast rate. CBER has received many requests from medical researchers and manufacturers to study cellular and gene therapies and to develop cellular and gene therapy products. In addition to regulatory oversight of clinical studies, CBER provides proactive scientific and regulatory advice to medical researchers and manufacturers in the area of novel product development.

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Cellular & Gene Therapy Products

noun, Medicine/Medical. 1.

the application of genetic engineering to the transplantation of genes into human cells in order to cure a disease caused by a genetic defect, as a missing enzyme.

British Dictionary definitions for gene therapy Expand

the replacement or alteration of defective genes in order to prevent the occurrence of such inherited diseases as haemophilia. Effected by genetic engineering techniques, it is still at the experimental stage

gene therapy in Medicine Expand

gene therapy n. A technique for the treatment of genetic disease in which a gene that is absent or defective is replaced by a healthy gene.

gene therapy in Science Expand

gene therapy in Culture Expand

A promising technology that involves replacing a defective gene in the body with a healthy one. This can be done by removing cells from the body, using genetic engineering techniques to change defective sequences in the DNA, and then reinserting the cells. This technique has been carried out successfully, for example, on bone marrow cells, in which defective cells were successfully replaced with healthy, genetically engineered cells. Scientists hope to find an agent, such as a therapeutic virus, that will be able to correct defective DNA in situ. (See cloning vector.)

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Gene therapy | Define Gene therapy at Dictionary.com

Dry Needling Course presented by Myopain Seminars

Dates: March 15-17, May 3-5, Sept 27-29, and Dec 6-8, 2013

Location: Physical Therapy First 5005 Signal Bell Lane #202 Clarksville, MD 21029

Click here for more information.

Click here for map and directions.

Jan Dommerholt, PT, DPT, MPS, DAAPM, is a Dutch-trained physical therapist who holds a Master of Professional Studies degree with a concentration in biomechanical trauma and health care administration, and a Doctorate in Physical Therapy from the University of St. Augustine for Health Sciences. Dr. Dommerholt has taught many courses and lectured at conferences throughout the United States, Europe, South America, and the Middle East while maintaining an active clinical practice. He is on the editorial board of the Journal of Musculoskeletal Pain (editor Dr. I. Jon Russell), the Journal of Bodywork and Movement Therapies (editor Dr. Leon Chaitow), the Journal of Manual and Manipulative Therapy (editor Chad Cook, PT, PhD), and Cuestiones de Fisioterapia.

He has authored many chapters and articles on myofascial pain, fibromyalgia, complex regional pain syndrome, and performing arts physical therapy, and prepares a quarterly literature review column on myofascial pain for the Journal of Musculoskeletal Pain. Read "Treating the Trigger" (PDF), a 2008 interview with Dr. Dommerholt published in Advance magazine. Dr. Dommerholt is the president of Bethesda Physiocare and editor of several books on myofascial trigger points.

Robert Gerwin, MD, FAAN, is Co-Founder, Vice President, and Co-Director of Myopain Seminars. He is a Board Certified Neurologist and a Fellow of the American Academy of Neurology. He is also a Diplomate of the American Board of Pain Medicine and a member of the American Academy of Pain Medicine. Dr. Gerwin graduated from the University of Chicago School of Medicine. He had two years of Internal Medicine post-graduate training at New York University--Bellevue Hospital and did his Neurology Residency at Case-Western Reserve University/Cleveland Metropolitan General Hospital, Cleveland, Ohio. He had a two year special fellowship at NIH in neurology and immunology. He has been in private practice in the Washington DC area for many years. Dr. Gerwin has been working in the area of Myofascial Pain and Fibromyalgia for many years. Dr. Janet G. Travell was his mentor while she lived in Washington DC. Dr. Gerwin is former President of the International Myopain Society. He was the Scientific Program Chairman for the 2007 International Congress of the Myopain Society.

He is the author of over 30 peer reviewed articles, reviews, book chapters and consensus statements. He reviews articles for over a dozen medical journals. He is on the editorial board of the Journal of Musculoskeletal Pain. He is co-editor of the books Tension-Type and Cervicogenic Headache: Pathophysiology, Diagnosis, and Management and Clinical Mastery in the Treatment of Myofascial Pain (see Books). He has been teaching courses and seminars worldwide in the field of neuromuscular and myofascial pain for many years. He founded the Focus on Pain series of neuromuscular and myofascial pain conferences in 1990. His interests lie in the area of Myofascial Pain and Fibromyalgia, and in the related issues of chronic headache, low back pain, and pelvic region pain, in addition to practicing neurological medicine. He is particularly concerned with the problem of persistent or chronic pain, and why some persons do not recover as expected. Dr. Gerwin is the Medical Director of Pain and Rehabilitation Medicine in Bethesda, MD and is an associate professor in the Department of Neurology at Johns Hopkins University School of Medicine.

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Physical Therapy First

This article is about the heritable unit for transmission of biological traits. For other uses, see Gene (disambiguation).

A gene is a locus (or region) of DNA which is made up of nucleotides and is the molecular unit of heredity.[1][2]:Glossary The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. Most biological traits are under the influence of polygenes (many different genes) as well as the geneenvironment interactions. Some genetic traits are instantly visible, such as eye colour or number of limbs, and some are not, such as blood type, risk for specific diseases, or the thousands of basic biochemical processes that comprise life.

Genes can acquire mutations in their sequence, leading to different variants, known as alleles, in the population. These alleles encode slightly different versions of a protein, which cause different phenotype traits. Colloquial usage of the term "having a gene" (e.g., "good genes," "hair colour gene") typically refers to having a different allele of the gene. Genes evolve due to natural selection or survival of the fittest of the alleles.

The concept of a gene continues to be refined as new phenomena are discovered.[3] For example, regulatory regions of a gene can be far removed from its coding regions, and coding regions can be split into several exons. Some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. Therefore, a broad, modern working definition of a gene is any discrete locus of heritable, genomic sequence which affect an organism's traits by being expressed as a functional product or by regulation of gene expression.[4][5]

The existence of discrete inheritable units was first suggested by Gregor Mendel (18221884).[6] From 1857 to 1864, he studied inheritance patterns in 8000 common edible pea plants, tracking distinct traits from parent to offspring. He described these mathematically as 2ncombinations where n is the number of differing characteristics in the original peas. Although he did not use the term gene, he explained his results in terms of discrete inherited units that give rise to observable physical characteristics. This description prefigured the distinction between genotype (the genetic material of an organism) and phenotype (the visible traits of that organism). Mendel was also the first to demonstrate independent assortment, the distinction between dominant and recessive traits, the distinction between a heterozygote and homozygote, and the phenomenon of discontinuous inheritance.

Prior to Mendel's work, the dominant theory of heredity was one of blending inheritance, which suggested that each parent contributed fluids to the fertilisation process and that the traits of the parents blended and mixed to produce the offspring. Charles Darwin developed a theory of inheritance he termed pangenesis, from Greek pan ("all, whole") and genesis ("birth") / genos ("origin").[7][8] Darwin used the term gemmule to describe hypothetical particles that would mix during reproduction.

Mendel's work went largely unnoticed after its first publication in 1866, but was rediscovered in the late 19th-century by Hugo de Vries, Carl Correns, and Erich von Tschermak, who (claimed to have) reached similar conclusions in their own research.[9] Specifically, in 1889, Hugo de Vries published his book Intracellular Pangenesis,[10] in which he postulated that different characters have individual hereditary carriers and that inheritance of specific traits in organisms comes in particles. De Vries called these units "pangenes" (Pangens in German), after Darwin's 1868 pangenesis theory.

Sixteen years later, in 1905, the word genetics was first used by William Bateson,[11] while Eduard Strasburger, amongst others, still used the term pangene for the fundamental physical and functional unit of heredity.[12] In 1909 the Danish botanist Wilhelm Johannsen shortened the name to "gene".[13]

Advances in understanding genes and inheritance continued throughout the 20th century. Deoxyribonucleic acid (DNA) was shown to be the molecular repository of genetic information by experiments in the 1940s to 1950s.[14][15] The structure of DNA was studied by Rosalind Franklin using X-ray crystallography, which led James D. Watson and Francis Crick to publish a model of the double-stranded DNA molecule whose paired nucleotide bases indicated a compelling hypothesis for the mechanism of genetic replication.[16][17] Collectively, this body of research established the central dogma of molecular biology, which states that proteins are translated from RNA, which is transcribed from DNA. This dogma has since been shown to have exceptions, such as reverse transcription in retroviruses. The modern study of genetics at the level of DNA is known as molecular genetics.

In 1972, Walter Fiers and his team at the University of Ghent were the first to determine the sequence of a gene: the gene for Bacteriophage MS2 coat protein.[18] The subsequent development of chain-termination DNA sequencing in 1977 by Frederick Sanger improved the efficiency of sequencing and turned it into a routine laboratory tool.[19] An automated version of the Sanger method was used in early phases of the Human Genome Project.[20]

The theories developed in the 1930s and 1940s to integrate molecular genetics with Darwinian evolution are called the modern evolutionary synthesis, a term introduced by Julian Huxley.[21] Evolutionary biologists subsequently refined this concept, such as George C. Williams' gene-centric view of evolution. He proposed an evolutionary concept of the gene as a unit of natural selection with the definition: "that which segregates and recombines with appreciable frequency."[22]:24 In this view, the molecular gene transcribes as a unit, and the evolutionary gene inherits as a unit. Related ideas emphasizing the centrality of genes in evolution were popularized by Richard Dawkins.[23][24]

The vast majority of living organisms encode their genes in long strands of DNA (deoxyribonucleic acid). DNA consists of a chain made from four types of nucleotide subunits, each composed of: a five-carbon sugar (2'-deoxyribose), a phosphate group, and one of the four bases adenine, cytosine, guanine, and thymine.[2]:2.1

Two chains of DNA twist around each other to form a DNA double helix with the phosphate-sugar backbone spiralling around the outside, and the bases pointing inwards with adenine base pairing to thymine and guanine to cytosine. The specificity of base pairing occurs because adenine and thymine align to form two hydrogen bonds, whereas cytosine and guanine form three hydrogen bonds. The two strands in a double helix must therefore be complementary, with their sequence of bases matching such that the adenines of one strand are paired with the thymines of the other strand, and so on.[2]:4.1

Due to the chemical composition of the pentose residues of the bases, DNA strands have directionality. One end of a DNA polymer contains an exposed hydroxyl group on the deoxyribose; this is known as the 3'end of the molecule. The other end contains an exposed phosphate group; this is the 5'end. The two strands of a double-helix run in opposite directions. Nucleic acid synthesis, including DNA replication and transcription occurs in the 5'3'direction, because new nucleotides are added via a dehydration reaction that uses the exposed 3'hydroxyl as a nucleophile.[25]:27.2

The expression of genes encoded in DNA begins by transcribing the gene into RNA, a second type of nucleic acid that is very similar to DNA, but whose monomers contain the sugar ribose rather than deoxyribose. RNA also contains the base uracil in place of thymine. RNA molecules are less stable than DNA and are typically single-stranded. Genes that encode proteins are composed of a series of three-nucleotide sequences called codons, which serve as the "words" in the genetic "language". The genetic code specifies the correspondence during protein translation between codons and amino acids. The genetic code is nearly the same for all known organisms.[2]:4.1

The total complement of genes in an organism or cell is known as its genome, which may be stored on one or more chromosomes. A chromosome consists of a single, very long DNA helix on which thousands of genes are encoded.[2]:4.2 The region of the chromosome at which a particular gene is located is called its locus. Each locus contains one allele of a gene; however, members of a population may have different alleles at the locus, each with a slightly different gene sequence.

The majority of eukaryotic genes are stored on a set of large, linear chromosomes. The chromosomes are packed within the nucleus in complex with storage proteins called histones to form a unit called a nucleosome. DNA packaged and condensed in this way is called chromatin.[2]:4.2 The manner in which DNA is stored on the histones, as well as chemical modifications of the histone itself, regulate whether a particular region of DNA is accessible for gene expression. In addition to genes, eukaryotic chromosomes contain sequences involved in ensuring that the DNA is copied without degradation of end regions and sorted into daughter cells during cell division: replication origins, telomeres and the centromere.[2]:4.2 Replication origins are the sequence regions where DNA replication is initiated to make two copies of the chromosome. Telomeres are long stretches of repetitive sequence that cap the ends of the linear chromosomes and prevent degradation of coding and regulatory regions during DNA replication. The length of the telomeres decreases each time the genome is replicated and has been implicated in the aging process.[27] The centromere is required for binding spindle fibres to separate sister chromatids into daughter cells during cell division.[2]:18.2

Prokaryotes (bacteria and archaea) typically store their genomes on a single large, circular chromosome. Similarly, some eukaryotic organelles contain a remnant circular chromosome with a small number of genes.[2]:14.4 Prokaryotes sometimes supplement their chromosome with additional small circles of DNA called plasmids, which usually encode only a few genes and are transferable between individuals. For example, the genes for antibiotic resistance are usually encoded on bacterial plasmids and can be passed between individual cells, even those of different species, via horizontal gene transfer.[28]

Whereas the chromosomes of prokaryotes are relatively gene-dense, those of eukaryotes often contain regions of DNA that serve no obvious function. Simple single-celled eukaryotes have relatively small amounts of such DNA, whereas the genomes of complex multicellular organisms, including humans, contain an absolute majority of DNA without an identified function.[29] This DNA has often been referred to as "junk DNA". However, more recent analyses suggest that, although protein-coding DNA makes up barely 2% of the human genome, about 80% of the bases in the genome may be expressed, so the term "junk DNA" may be a misnomer.[5]

The structure of a gene consists of many elements of which the actual protein coding sequence is often only a small part. These include DNA regions that are not transcribed as well as untranslated regions of the RNA.

Firstly, flanking the open reading frame, all genes contain a regulatory sequence that is required for their expression. In order to be expressed, genes require a promoter sequence. The promoter is recognized and bound by transcription factors and RNA polymerase to initiate transcription.[2]:7.1 A gene can have more than one promoter, resulting in messenger RNAs (mRNA) that differ in how far they extend in the 5'end.[30] Promoter regions have a consensus sequence, however highly transcribed genes have "strong" promoter sequences that bind the transcription machinery well, whereas others have "weak" promoters that bind poorly and initiate transcription less frequently.[2]:7.2Eukaryotic promoter regions are much more complex and difficult to identify than prokaryotic promoters.[2]:7.3

Additionally, genes can have regulatory regions many kilobases upstream or downstream of the open reading frame. These act by binding to transcription factors which then cause the DNA to loop so that the regulatory sequence (and bound transcription factor) become close to the RNA polymerase binding site.[31] For example, enhancers increase transcription by binding an activator protein which then helps to recruit the RNA polymerase to the promoter; conversely silencers bind repressor proteins and make the DNA less available for RNA polymerase.[32]

The transcribed pre-mRNA contains untranslated regions at both ends which contain a ribosome binding site, terminator and start and stop codons.[33] In addition, most eukaryotic open reading frames contain untranslated introns which are removed before the exons are translated. The sequences at the ends of the introns, dictate the splice sites to generate the final mature mRNA which encodes the protein or RNA product.[34]

Many prokaryotic genes are organized into operons, with multiple protein-coding sequences that are transcribed as a unit.[35][36] The products of operon genes typically have related functions and are involved in the same regulatory network.[2]:7.3

Defining exactly what section of a DNA sequence comprises a gene is difficult.[3]Regulatory regions of a gene such as enhancers do not necessarily have to be close to the coding sequence on the linear molecule because the intervening DNA can be looped out to bring the gene and its regulatory region into proximity. Similarly, a gene's introns can be much larger than its exons. Regulatory regions can even be on entirely different chromosomes and operate in trans to allow regulatory regions on one chromosome to come in contact with target genes on another chromosome.[37][38]

Early work in molecular genetics suggested the model that one gene makes one protein. This model has been refined since the discovery of genes that can encode multiple proteins by alternative splicing and coding sequences split in short section across the genome whose mRNAs are concatenated by trans-splicing.[5][39][40]

A broad operational definition is sometimes used to encompass the complexity of these diverse phenomena, where a gene is defined as a union of genomic sequences encoding a coherent set of potentially overlapping functional products.[11] This definition categorizes genes by their functional products (proteins or RNA) rather than their specific DNA loci, with regulatory elements classified as gene-associated regions.[11]

In all organisms, two steps are required to read the information encoded in a gene's DNA and produce the protein it specifies. First, the gene's DNA is transcribed to messenger RNA (mRNA).[2]:6.1 Second, that mRNA is translated to protein.[2]:6.2 RNA-coding genes must still go through the first step, but are not translated into protein.[41] The process of producing a biologically functional molecule of either RNA or protein is called gene expression, and the resulting molecule is called a gene product.

The nucleotide sequence of a gene's DNA specifies the amino acid sequence of a protein through the genetic code. Sets of three nucleotides, known as codons, each correspond to a specific amino acid.[2]:6 Additionally, a "start codon", and three "stop codons" indicate the beginning and end of the protein coding region. There are 64possible codons (four possible nucleotides at each of three positions, hence 43possible codons) and only 20standard amino acids; hence the code is redundant and multiple codons can specify the same amino acid. The correspondence between codons and amino acids is nearly universal among all known living organisms.[42]

Transcription produces a single-stranded RNA molecule known as messenger RNA, whose nucleotide sequence is complementary to the DNA from which it was transcribed.[2]:6.1 The mRNA acts as an intermediate between the DNA gene and its final protein product. The gene's DNA is used as a template to generate a complementary mRNA. The mRNA matches the sequence of the gene's DNA coding strand because it is synthesised as the complement of the template strand. Transcription is performed by an enzyme called an RNA polymerase, which reads the template strand in the 3' to 5'direction and synthesizes the RNA from 5' to 3'. To initiate transcription, the polymerase first recognizes and binds a promoter region of the gene. Thus, a major mechanism of gene regulation is the blocking or sequestering the promoter region, either by tight binding by repressor molecules that physically block the polymerase, or by organizing the DNA so that the promoter region is not accessible.[2]:7

In prokaryotes, transcription occurs in the cytoplasm; for very long transcripts, translation may begin at the 5'end of the RNA while the 3'end is still being transcribed. In eukaryotes, transcription occurs in the nucleus, where the cell's DNA is stored. The RNA molecule produced by the polymerase is known as the primary transcript and undergoes post-transcriptional modifications before being exported to the cytoplasm for translation. One of the modifications performed is the splicing of introns which are sequences in the transcribed region that do not encode protein. Alternative splicing mechanisms can result in mature transcripts from the same gene having different sequences and thus coding for different proteins. This is a major form of regulation in eukaryotic cells and also occurs in some prokaryotes.[2]:7.5[43]

Translation is the process by which a mature mRNA molecule is used as a template for synthesizing a new protein.[2]:6.2 Translation is carried out by ribosomes, large complexes of RNA and protein responsible for carrying out the chemical reactions to add new amino acids to a growing polypeptide chain by the formation of peptide bonds. The genetic code is read three nucleotides at a time, in units called codons, via interactions with specialized RNA molecules called transfer RNA (tRNA). Each tRNA has three unpaired bases known as the anticodon that are complementary to the codon it reads on the mRNA. The tRNA is also covalently attached to the amino acid specified by the complementary codon. When the tRNA binds to its complementary codon in an mRNA strand, the ribosome attaches its amino acid cargo to the new polypeptide chain, which is synthesized from amino terminus to carboxyl terminus. During and after synthesis, most new proteins must folds to their active three-dimensional structure before they can carry out their cellular functions.[2]:3

Genes are regulated so that they are expressed only when the product is needed, since expression draws on limited resources.[2]:7 A cell regulates its gene expression depending on its external environment (e.g. available nutrients, temperature and other stresses), its internal environment (e.g. cell division cycle, metabolism, infection status), and its specific role if in a multicellular organism. Gene expression can be regulated at any step: from transcriptional initiation, to RNA processing, to post-translational modification of the protein. The regulation of lactose metabolism genes in E. coli (lac operon) was the first such mechanism to be described in 1961.[44]

A typical protein-coding gene is first copied into RNA as an intermediate in the manufacture of the final protein product.[2]:6.1 In other cases, the RNA molecules are the actual functional products, as in the synthesis of ribosomal RNA and transfer RNA. Some RNAs known as ribozymes are capable of enzymatic function, and microRNA has a regulatory role. The DNA sequences from which such RNAs are transcribed are known as non-coding RNA genes.[41]

Some viruses store their entire genomes in the form of RNA, and contain no DNA at all.[45][46] Because they use RNA to store genes, their cellular hosts may synthesize their proteins as soon as they are infected and without the delay in waiting for transcription.[47] On the other hand, RNA retroviruses, such as HIV, require the reverse transcription of their genome from RNA into DNA before their proteins can be synthesized. RNA-mediated epigenetic inheritance has also been observed in plants and very rarely in animals.[48]

Organisms inherit their genes from their parents. Asexual organisms simply inherit a complete copy of their parent's genome. Sexual organisms have two copies of each chromosome because they inherit one complete set from each parent.[2]:1

According to Mendelian inheritance, variations in an organism's phenotype (observable physical and behavioral characteristics) are due in part to variations in its genotype (particular set of genes). Each gene specifies a particular trait with different sequence of a gene (alleles) giving rise to different phenotypes. Most eukaryotic organisms (such as the pea plants Mendel worked on) have two alleles for each trait, one inherited from each parent.[2]:20

Alleles at a locus may be dominant or recessive; dominant alleles give rise to their corresponding phenotypes when paired with any other allele for the same trait, whereas recessive alleles give rise to their corresponding phenotype only when paired with another copy of the same allele. For example, if the allele specifying tall stems in pea plants is dominant over the allele specifying short stems, then pea plants that inherit one tall allele from one parent and one short allele from the other parent will also have tall stems. Mendel's work demonstrated that alleles assort independently in the production of gametes, or germ cells, ensuring variation in the next generation. Although Mendelian inheritance remains a good model for many traits determined by single genes (including a number of well-known genetic disorders) it does not include the physical processes of DNA replication and cell division.[49][50]

The growth, development, and reproduction of organisms relies on cell division, or the process by which a single cell divides into two usually identical daughter cells. This requires first making a duplicate copy of every gene in the genome in a process called DNA replication.[2]:5.2 The copies are made by specialized enzymes known as DNA polymerases, which "read" one strand of the double-helical DNA, known as the template strand, and synthesize a new complementary strand. Because the DNA double helix is held together by base pairing, the sequence of one strand completely specifies the sequence of its complement; hence only one strand needs to be read by the enzyme to produce a faithful copy. The process of DNA replication is semiconservative; that is, the copy of the genome inherited by each daughter cell contains one original and one newly synthesized strand of DNA.[2]:5.2

After DNA replication is complete, the cell must physically separate the two copies of the genome and divide into two distinct membrane-bound cells.[2]:18.2 In prokaryotes(bacteria and archaea) this usually occurs via a relatively simple process called binary fission, in which each circular genome attaches to the cell membrane and is separated into the daughter cells as the membrane invaginates to split the cytoplasm into two membrane-bound portions. Binary fission is extremely fast compared to the rates of cell division in eukaryotes. Eukaryotic cell division is a more complex process known as the cell cycle; DNA replication occurs during a phase of this cycle known as S phase, whereas the process of segregating chromosomes and splitting the cytoplasm occurs during M phase.[2]:18.1

The duplication and transmission of genetic material from one generation of cells to the next is the basis for molecular inheritance, and the link between the classical and molecular pictures of genes. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parents' cells. In asexually reproducing organisms, the offspring will be a genetic copy or clone of the parent organism. In sexually reproducing organisms, a specialized form of cell division called meiosis produces cells called gametes or germ cells that are haploid, or contain only one copy of each gene.[2]:20.2 The gametes produced by females are called eggs or ova, and those produced by males are called sperm. Two gametes fuse to form a diploid fertilized egg, a single cell that has two sets of genes, with one copy of each gene from the mother and one from the father.[2]:20

During the process of meiotic cell division, an event called genetic recombination or crossing-over can sometimes occur, in which a length of DNA on one chromatid is swapped with a length of DNA on the corresponding sister chromatid. This has no effect if the alleles on the chromatids are the same, but results in reassortment of otherwise linked alleles if they are different.[2]:5.5 The Mendelian principle of independent assortment asserts that each of a parent's two genes for each trait will sort independently into gametes; which allele an organism inherits for one trait is unrelated to which allele it inherits for another trait. This is in fact only true for genes that do not reside on the same chromosome, or are located very far from one another on the same chromosome. The closer two genes lie on the same chromosome, the more closely they will be associated in gametes and the more often they will appear together; genes that are very close are essentially never separated because it is extremely unlikely that a crossover point will occur between them. This is known as genetic linkage.[51]

DNA replication is for the most part extremely accurate, however errors (mutations) do occur.[2]:7.6 The error rate in eukaryotic cells can be as low as 108 per nucleotide per replication,[52][53] whereas for some RNA viruses it can be as high as 103.[54] This means that each generation, each human genome accumulates 12 new mutations.[54] Small mutations can be caused by DNA replication and the aftermath of DNA damage and include point mutations in which a single base is altered and frameshift mutations in which a single base is inserted or deleted. Either of these mutations can change the gene by missense (change a codon to encode a different amino acid) or nonsense (a premature stop codon).[55] Larger mutations can be caused by errors in recombination to cause chromosomal abnormalities including the duplication, deletion, rearrangement or inversion of large sections of a chromosome. Additionally, the DNA repair mechanisms that normally revert mutations can introduce errors when repairing the physical damage to the molecule is more important than restoring an exact copy, for example when repairing double-strand breaks.[2]:5.4

When multiple different alleles for a gene are present in a species's population it is called polymorphic. Most different alleles are functionally equivalent, however some alleles can give rise to different phenotypic traits. A gene's most common allele is called the wild type, and rare alleles are called mutants. The genetic variation in relative frequencies of different alleles in a population is due to both natural selection and genetic drift.[56] The wild-type allele is not necessarily the ancestor of less common alleles, nor is it necessarily fitter.

Most mutations within genes are neutral, having no effect on the organism's phenotype (silent mutations). Some mutations do not change the amino acid sequence because multiple codons encode the same amino acid (synonymous mutations). Other mutations can be neutral if they lead to amino acid sequence changes, but the protein still functions similarly with the new amino acid (e.g. conservative mutations). Many mutations, however, are deleterious or even lethal, and are removed from populations by natural selection. Genetic disorders are the result of deleterious mutations and can be due to spontaneous mutation in the affected individual, or can be inherited. Finally, a small fraction of mutations are beneficial, improving the organism's fitness and are extremely important for evolution, since their directional selection leads to adaptive evolution.[2]:7.6

Genes with a most recent common ancestor, and thus a shared evolutionary ancestry, are known as homologs.[57] These genes appear either from gene duplication within an organism's genome, where they are known as paralogous genes, or are the result of divergence of the genes after a speciation event, where they are known as orthologous genes,[2]:7.6 and often perform the same or similar functions in related organisms. It is often assumed that the functions of orthologous genes are more similar than those of paralogous genes, although the difference is minimal.[58][59]

The relationship between genes can be measured by comparing the sequence alignment of their DNA.[2]:7.6 The degree of sequence similarity between homologous genes is called conserved sequence. Most changes to a gene's sequence do not affect its function and so genes accumulate mutations over time by neutral molecular evolution. Additionally, any selection on a gene will cause its sequence to diverge at a different rate. Genes under stabilizing selection are constrained and so change more slowly whereas genes under directional selection change sequence more rapidly.[60] The sequence differences between genes can be used for phylogenetic analyses to study how those genes have evolved and how the organisms they come from are related.[61][62]

The most common source of new genes in eukaryotic lineages is gene duplication, which creates copy number variation of an existing gene in the genome.[63][64] The resulting genes (paralogs) may then diverge in sequence and in function. Sets of genes formed in this way comprise a gene family. Gene duplications and losses within a family are common and represent a major source of evolutionary biodiversity.[65] Sometimes, gene duplication may result in a nonfunctional copy of a gene, or a functional copy may be subject to mutations that result in loss of function; such nonfunctional genes are called pseudogenes.[2]:7.6

De novo or "orphan" genes, whose sequence shows no similarity to existing genes, are extremely rare. Estimates of the number of de novo genes in the human genome range from 18[66] to 60.[67] Such genes are typically shorter and simpler in structure than most eukaryotic genes, with few if any introns.[63] Two primary sources of orphan protein-coding genes are gene duplication followed by extremely rapid sequence change, such that the original relationship is undetectable by sequence comparisons, and formation through mutation of "cryptic" transcription start sites that introduce a new open reading frame in a region of the genome that did not previously code for a protein.[68][69]

Horizontal gene transfer refers to the transfer of genetic material through a mechanism other than reproduction. This mechanism is a common source of new genes in prokaryotes, sometimes thought to contribute more to genetic variation than gene duplication.[70] It is a common means of spreading antibiotic resistance, virulence, and adaptive metabolic functions.[28][71] Although horizontal gene transfer is rare in eukaryotes, likely examples have been identified of protist and alga genomes containing genes of bacterial origin.[72][73]

The genome is the total genetic material of an organism and includes both the genes and non-coding sequences.[74]

The genome size, and the number of genes it encodes varies widely between organisms. The smallest genomes occur in viruses (which can have as few as 2 protein-coding genes),[83] and viroids (which act as a single non-coding RNA gene).[84] Conversely, plants can have extremely large genomes,[85] with rice containing >46,000 protein-coding genes.[86] The total number of protein-coding genes (the Earth's proteome) is estimated to be 5million sequences.[87]

Although the number of base-pairs of DNA in the human genome has been known since the 1960s, the estimated number of genes has changed over time as definitions of genes, and methods of detecting them have been refined. Initial theoretical predictions of the number of human genes were as high as 2,000,000.[88] Early experimental measures indicated there to be 50,000100,000 transcribed genes (expressed sequence tags).[89] Subsequently, the sequencing in the Human Genome Project indicated that many of these transcripts were alternative variants of the same genes, and the total number of protein-coding genes was revised down to ~20,000[82] with 13 genes encoded on the mitochondrial genome.[80] Of the human genome, only 12% consists of protein-coding genes,[90] with the remainder being 'noncoding' DNA such as introns, retrotransposons, and noncoding RNAs.[90][91]Every organism has all his genes in all cells of his body but it is not important that every gene must function in every cell .

Essential genes are the set of genes thought to be critical for an organism's survival.[93] This definition assumes the abundant availability of all relevant nutrients and the absence of environmental stress. Only a small portion of an organism's genes are essential. In bacteria, an estimated 250400 genes are essential for Escherichia coli and Bacillus subtilis, which is less than 10% of their genes.[94][95][96] Half of these genes are orthologs in both organisms and are largely involved in protein synthesis.[96] In the budding yeast Saccharomyces cerevisiae the number of essential genes is slightly higher, at 1000 genes (~20% of their genes).[97] Although the number is more difficult to measure in higher eukaryotes, mice and humans are estimated to have around 2000 essential genes (~10% of their genes).[98] The synthetic organism, Syn 3, has a minimal genome of 473 essential genes and quasi-essential genes (necessary for fast growth), although 149 have unknown function.[92]

Essential genes include Housekeeping genes (critical for basic cell functions)[99] as well as genes that are expressed at different times in the organisms development or life cycle.[100] Housekeeping genes are used as experimental controls when analysing gene expression, since they are constitutively expressed at a relatively constant level.

Gene nomenclature has been established by the HUGO Gene Nomenclature Committee (HGNC) for each known human gene in the form of an approved gene name and symbol (short-form abbreviation), which can be accessed through a database maintained by HGNC. Symbols are chosen to be unique, and each gene has only one symbol (although approved symbols sometimes change). Symbols are preferably kept consistent with other members of a gene family and with homologs in other species, particularly the mouse due to its role as a common model organism.[101]

Genetic engineering is the modification of an organism's genome through biotechnology. Since the 1970s, a variety of techniques have been developed to specifically add, remove and edit genes in an organism.[102] Recently developed genome engineering techniques use engineered nuclease enzymes to create targeted DNA repair in a chromosome to either disrupt or edit a gene when the break is repaired.[103][104][105][106] The related term synthetic biology is sometimes used to refer to extensive genetic engineering of an organism.[107]

Genetic engineering is now a routine research tool with model organisms. For example, genes are easily added to bacteria[108] and lineages of knockout mice with a specific gene's function disrupted are used to investigate that gene's function.[109][110] Many organisms have been genetically modified for applications in agriculture, industrial biotechnology, and medicine.

For multicellular organisms, typically the embryo is engineered which grows into the adult genetically modified organism.[111] However, the genomes of cells in an adult organism can be edited using gene therapy techniques to treat genetic diseases.

Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). Molecular Biology of the Cell (Fourth ed.). New York: Garland Science. ISBN978-0-8153-3218-3. A molecular biology textbook available free online through NCBI Bookshelf.

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Gene - Wikipedia, the free encyclopedia

Gene therapy is a way of inserting genes into a patient's cells and replacing the preexisting alleles, or gene variants, to perform some therapeutic function. It has been used thus far primarily to replace mutant defective genes, or alleles, with normal alleles, but could in theory be used to edit the human genome arbitrarily. If gene therapy were applied to reproductive cells in the gonads (the germline), these genetic changes would be heritable. This process has never been performed, but it has a name: germline genetic engineering.

Since the early 1980s, gene therapy has been used to produce medicines. Say that a human being needs a certain protein as a medicine. This therapy uses a viral vector, that is, a virus modified to contain the DNA to be introduced. Large quantities of the virus are injected to the target area, or, sometimes tissue is removed, infected with the virus, and then implanted again. The viruses are modified such that the vast majority are not capable of independent self-replication - providing little chance for pathogenic infection. The virus introduced the new DNA into the genome of human cells, much in the same way normal viruses introduce their own genetic material into human cells, hijacking the cellular machinery.

After the new DNA is integrated into the target cell, the cell begins to manufacture proteins specified by the new genetic material, which in some instances, can be lifesaving. For example, patients with severe diabetes may be given the cellular machinery to produce insulin, obviating the need for regular injections. The benefits of the therapy can last for weeks, months, or even years or a lifetime.

Gene therapy has been used successfully to treat inherited retinal disease, thalassaemia, cystic fibrosis, severe combined immunodeficiency, and some cancers. Medical miracles not possible with any other approach have been demonstrated by gene therapy, such as reprogramming the body's natural sentinels, T-cells, to attack cancer cells. Gene therapy shows promise for treating afflictions such as Huntington's disease and sickle cell anemia. As the therapy continues to mature, it could save millions of lives.

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What is Gene Therapy? (with pictures) - wiseGEEK

For 26 years, doctors could not piece together the medical puzzle of Stewart Altman's symptoms -- as a child growing up on Long Island, he was uncoordinated and slurred his speech. Later, as a volunteer fireman, he kept falling down and had trouble climbing the ladders.

It seemed unrelated at the time, but his older sister, who had a history of psychological symptoms, was hospitalized in a mental institution. Her psychiatrist suspected a physical disorder and consulted a geneticist who eventually connected the dots.

In 1978, Altman and his sister Roslyn Vaccaro were given a stunning diagnosis: Tay-Sachs -- an inherited neurological disease that typically affects babies, killing them between the ages of 3 and 5. Only several hundred cases exist in the United States.

Altman, now 58, has a non-fatal, adult form of the disease, late onset Tay-Sachs (LOTS), and depends on his wife and a service dog to perform most daily tasks.

"I am devastated," Altman said of the disease that has robbed him of much of his speech and muscle strength, confining him to a wheelchair. "But the alternative is much worse."

His sister died in 2000 after battling LOTS-related bipolar disorder and schizophrenia -- which occurs in 50 to 60 percent of all adult cases -- and Altman and his wife raised her two sons.

Now scientists are hopeful that gene therapy may help late-onset patients like Altman and look forward to human trials.

Tay-Sachs is caused by gene mutation results in the absence or insufficient levels of the enzyme, hexosamindase A or Hex A. Without it, a fatty substance or lipids accumulates in the cells, mostly in the brain. It comes in three forms: infantile, juvenile or adult onset.

Doctors say there can be great variations in the presentation of Tay-Sachs, even in the same family with the same mutations. Babies born with Tay-Sachs appear normal at first, but by 3 or 4 years old, their nerve cells deteriorate and they eventually die. Those with LOTS can live a long life, but, like Altman, are progressively disabled.

The story of Tay-Sachs is a miraculous one. It was first identified in the late 1800s by British ophthalmologist Warren Tay and New York neurologist Bernard Sachs, who noticed the disease was prevalent in Jews of Eastern European origin.

In the 1970s and 1980s, when genetic testing became available, synagogues launched public education campaigns encouraging prospective parents to be tested, and the disease was virtually eliminated in those of Jewish ancestry.

Now, mostly non-Jews, though their risk is not as great, are among the 100 American children who have the disease, according to the National Tay-Sachs and Allied Diseases Association (NTSAD), which leads the fight for a cure.

Altman's speech is difficult to understand, so his wife Lorrie said her husband of 37 years wanted the public to know, "it's not just an infant's disease."

"Tay-Sachs is also in the general population and people don't know," she said. "He thinks we need to get the word out. One in 250 Americans carries the gene."

French Canadians, Louisiana Cajuns and even those of English-Irish ancestry have a greater chance of carrying the recessive gene that causes the disease.

Tay-Sachs is an autosomal recessive disorder, which means each parent must carry the gene. Their children have a 25 percent chance of developing Tay-Sachs, 50 percent chance of being a carrier and a 25 percent chance of being free of that recessive gene.

Altman was born in 1952, before genetic testing was available. Both his parents were carriers of the recessive gene that causes Tay-Sachs and both he and sister were stricken with the mildest form of the disease. Two of their brothers were unaffected, although one is a carrier.

The Massapequa, N.Y., couple have two healthy sons, who are carriers, but whose wives are not, and four healthy grandchildren.

For years, Altman was able to get around with a walker until he had to drop out of a clinical trial for a new drug because of debilitating side effects. After that, he said he lost 40 pounds and so much muscle that he could no longer stand on his own.

"Between the two of us we handle it and we lead kind of a normal life," said Lorrie. "But we have no idea what the future will bring."

Altman works at Nassau University Medical Center in the security monitoring department. He raises funds for about 11 different non-profit organizations, including NTSAD, and has given presentations to the Boy Scouts and senior citizens.

Much of the public work has now ended, as his speech has become more incomprehensible because the degeneration of the nerves that control his respiratory muscles.

"Stewart has a good way of just living in the moment," said his wife, who met Altman in college. "But the worst part for him is his speech. He is such a social, outgoing person."

He has faced discrimination along the way, especially after leaving a Manhattan engineering job because he couldn't climb the subway stairs.

"He has such a hard time getting a job -- it was devastating," said Lorrie Altman. "On paper, he looked so good, but his speech was terrible. He has a college degree and isn't stupid, but all people see is the wheelchair."

Doctors say that many with the milder adult form of Tay-Sachs can lead full lives, despite their disability. And science is getting closer to finding treatments for this devastating disease.

Dr. Edwin Kolodny, former department chair and now professor of neurology at New York University School of Medicine, has been a leader in the field for 30 years. He first helped identify the role of the enzyme Hex-A and later tested more than 30,000 young adults in the 1970s and 1980s.

Today, he and others are involved in the promising gene therapy studies involving first mice, then cats and now sheep. Injecting genes into the brains of Jacob lambs has doubled their life span.

Clinical trials on humans are set to begin as soon as researchers can raise another $700,000 -- in addition to a grant from the National Institutes of Health -- to manufacture the vectors required to insert the genes into the body.

"It seems like every parent in the world would like to be part of the trial," said Kolodny. "And there are reasons to think there will be success here, especially for children who have a slightly later onset and not the classic form Tay-Sachs."

In the past, infantile Tay-Sachs has seen most of the medical attention. "These children have zero quality of life," he said.

Those with mild mutations, like Altman, who have 5 to 10 percent of Hex A enzyme activity, "sometimes lead full lives," according to Kolodny. "Intellectually, most of their cognitive function is retained. We have patients who are lawyers and accountants."

Pre-conception testing is still the gold standard for fighting the disease. "If your parents don't have the same recessive genes, you are home free," he said.

Those identified as at risk for having a child with Tay-Sachs can decide to adopt or conceive through in vitro fertilization, where geneticists can test the embryos before implantation to ensure the child will be disease-free.

Doctors can also do prenatal genetic testing and if the fetus is affected, the decision is up to the parents whether or not they want to terminate the pregnancy. "Three out of four times, they are reassured they have a normal child," said Kolodny.

Doctors say such testing -- at a cost of around $100 -- should be done routinely for 18 autosomal recessive disorders, including the gene for cystic fibrosis, which occurs in one in 20 caucasians, said Kolodny. Even with advances in Tay-Sachs testing in the Jewish community, public education must continue.

"The problem is each generation forgets what happened in the prior generation -- the grandmothers die out, " said Kolodny. "We need to educate health care professionals. Each new group of students graduating from medical school isn't prepared to ask the right questions."

Susan Kahn, NTSAD's executive director, who is involved in fundraising for research, agrees that along with a fight for a cure, genetic testing is critical.

"When there is a genetic disease, it's not just about that person, there is a whole implication for the rest of the family and how they deal with it," she said.

Stewart Altman sits on the association's board of directors and is a tireless crusader for a cure.

"He's got some disabilities that make it difficult for him to do certain things, but of all the board members asking for money to support, he is probably the boldest in our group," said Kahn. "He does have a lot of limitations, but he is still very energetic and wants to do something important. Not everyone responds with the same attitude."

His wife Lorrie backed that up with a laugh. "He is persistent," she said. "He carries these little envelopes around and will ask anyone he meets for a donation. It's almost embarrassing. He's not afraid to ask."

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Gene Therapy in Sheep May Bring Hope to Adults With Tay ...

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Summary Clinical characteristics.

If untreated, young children with profound biotinidase deficiency usually exhibit neurologic abnormalities including seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities (e.g., alopecia, skin rash, candidiasis). Older children and adolescents with profound biotinidase deficiency often exhibit motor limb weakness, spastic paresis, and decreased visual acuity. Once vision problems, hearing loss, and developmental delay occur, they are usually irreversible, even with biotin therapy. Individuals with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress.

The diagnosis of biotinidase deficiency is established in a proband whose newborn screening or biochemical findings indicate multiple carboxylase deficiency based on either detection of deficient biotinidase enzyme activity in serum/plasma OR identification of biallelic pathogenic variants in BTD on molecular genetic testing.

Treatment of manifestations: All symptomatic children with profound biotinidase deficiency improve when treated with 5-10 mg of oral biotin per day. All individuals with profound biotinidase deficiency, even those who have some residual enzymatic activity, should have lifelong treatment with biotin. Children with vision problems may benefit from vision aids; those with hearing loss will usually benefit from hearing aids or cochlear implants, and those with developmental deficits from appropriate interventions.

Prevention of primary manifestations: Children with biotinidase deficiency identified by newborn screening should remain asymptomatic if biotin therapy is instituted early and continuously lifelong.

Surveillance: Annual vision and hearing evaluation, physical examination, and periodic assessment by a metabolic specialist.

Agents/circumstances to avoid: Raw eggs because they contain avidin, an egg-white protein that binds biotin and decreases the bioavailability of the vitamin.

Evaluation of relatives at risk: Testing of asymptomatic sibs of a proband ensures that biotin therapy for affected sibs can be instituted in a timely manner.

Biotinidase deficiency is inherited in an autosomal recessive manner. With each pregnancy, a couple who has had one affected child has a 25% chance of having an affected child, a 50% chance of having a child who is an asymptomatic carrier, and a 25% chance of having an unaffected child who is not a carrier. Carrier testing for at-risk family members and prenatal testing for pregnancies at increased risk are options if the pathogenic variants in the family are known.

Clinical issues and frequently asked questions regarding biotinidase deficiency have been addressed in a review [Wolf 2010].

Biotinidase deficiency should be suspected in infants with positive newborn screening results, untreated individuals with clinical findings, and persons with suggestive preliminary laboratory findings [Wolf 2012]:

Virtually 100% of infants with either profound biotinidase deficiency or partial biotinidase deficiency can be detected in the US by newborn screening (see National Newborn Screening Status Report).

Newborn screening utilizes a small amount of blood obtained from a heel prick for a colorimetric test for biotinidase activity:

Children or adults with untreated profound biotinidase deficiency usually exhibit one or more of the following non-specific features (which are also observed in many other inherited metabolic disorders):

Seizures

Hypotonia

Respiratory problems including hyperventilation, laryngeal stridor, and apnea

Developmental delay

Hearing loss

Vision problems, such as optic atrophy

Features more specific to profound biotinidase deficiency include the following:

Eczematous skin rash

Alopecia

Conjunctivitis

Candidiasis

Ataxia

Older children and adolescents may exhibit limb weakness, paresis, and scotomata. Some have exhibited findings suggestive of a myelopathy and have been initially incorrectly diagnosed and treated as having another disorder before biotinidase deficiency is correctly diagnosed [Wolf 2015].

Children or adults with untreated partial biotinidase deficiency may exhibit any of the above signs and symptoms, but the manifestations are mild and occur only when the person is stressed, such as with a prolonged infection.

The following findings are sugggestive of biotinidase deficiency:

Metabolic ketolactic acidosis

Organic aciduria (usually with the metabolites commonly seen in multiple carboxylase deficiency; however, 3-hydroxyisovalerate may be the only metabolite present). Note: Urinary organic acids can be normal even in individuals with biotinidase deficiency who are symptomatic.

Hyperammonemia

The diagnosis of biotinidase deficiency is established in a proband whose newborn screening or biochemical findings indicate multiple carboxylase deficiency based on either:

Biotinidase enzyme activity in serum. The working group of the American College of Medical Genetics Laboratory Quality Assurance Committee has established technical standards and guidelines for the diagnosis of biotinidase deficiency [Cowan et al 2010] (full text).

Molecular genetic testing is performed by single-gene testing. Sequence analysis of BTD is performed first, followed by gene-targeted deletion/duplication analysis if only one or no pathogenic variant is found.

Molecular Genetic Testing Used in Biotinidase Deficiency

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Test characteristics. See Clinical Utility Gene Card [Kry et al 2012] for information on test characteristics including sensitivity and specificity.

Individuals with biotinidase deficiency who are diagnosed before they have developed symptoms (e.g., by newborn screening) and who are treated with biotin have normal development [Mslinger et al 2001, Weber et al 2004] (see also Management, Prevention of Primary Manifestations). Neurologic problems occur only in those individuals with biotinidase deficiency who have recurrent symptoms and metabolic compromise prior to biotin treatment.

Early onset. Symptoms of untreated profound biotinidase deficiency (<10% mean normal serum biotinidase activity) usually appear between ages one week and ten years, with a mean age of three and one-half months [Wolf et al 1985b].

Some children with biotinidase deficiency manifest only a single finding, whereas others exhibit multiple neurologic and cutaneous findings.

The most common neurologic features in individuals with untreated, profound biotinidase deficiency are seizures and hypotonia [Wolf et al 1983a, Wolf et al 1985b, Wastell et al 1988, Wolf 1995, Wolf 2011]. The seizures are usually myoclonic but may be grand mal and focal; some children have infantile spasms [Salbert et al 1993b]. Some untreated children have exhibited spinal cord involvement characterized by progressive spastic paresis and myelopathy [Chedrawi et al 2008]. Older affected children often have ataxia and developmental delay.

Many symptomatic children with biotinidase deficiency exhibit a variety of central nervous system abnormalities on brain MRI or CT [Wolf et al 1983b, Wastell et al 1988, Lott et al 1993, Salbert et al 1993b, Grnewald et al 2004]. These findings may improve or become normal after biotin treatment.

Sensorineural hearing loss and eye problems (e.g., optic atrophy) have also been described in untreated children [Wolf et al 1983b, Taitz et al 1985, Salbert et al 1993a, Weber et al 2004]. Approximately 76% of untreated symptomatic children with profound biotinidase deficiency have sensorineural hearing loss that usually does not resolve or improve but remains static with biotin treatment [Wolf et al 2002].

Cutaneous manifestations include skin rash, alopecia, and recurrent viral or fungal infections caused by immunologic dysfunction.

Respiratory problems including hyperventilation, laryngeal stridor, and apnea can occur.

One death initially thought to be caused by sudden infant death syndrome was subsequently attributed to biotinidase deficiency [Burton et al 1987].

Late onset. A number of children with profound biotinidase deficiency were asymptomatic until adolescence, when they developed sudden loss of vision with progressive optic neuropathy and spastic paraparesis [Ramaekers et al 1992, Lott et al 1993, Ramaekers et al 1993]. After several months of biotin therapy, the eye findings resolved and the spastic paraparesis improved. In other individuals with enzyme deficiency, paresis and eye problems have occurred during early adolescence [Tokatli et al 1997, Wolf et al 1998, Wolf 2015].

Individuals with partial biotinidase deficiency (10%-30% of mean normal serum biotinidase activity) may develop symptoms only when stressed, such as during infection.

One child with partial biotinidase deficiency who was not treated with biotin exhibited hypotonia, skin rash, and hair loss during an episode of gastroenteritis at approximately age six months. When treated with biotin, the symptoms resolved.

Genotype/phenotype correlations are not well established. Deletions, insertions, or nonsense variants usually result in complete absence of biotinidase enzyme activity, whereas missense variants may or may not result in complete loss of biotinidase enzyme activity. Those with absence of all biotinidase enzyme activity are likely to be at increased risk for earlier onset of symptoms.

Although genotype-phenotype correlations are not well established, in one study, children with symptoms of profound biotinidase deficiency with null variants were more likely to develop hearing loss than those with missense variants, even if not treated for a period of time [Sivri et al 2007].

Certain genotypes correlate with complete biotinidase deficiency and others with partial biotinidase deficiency:

Profound biotinidase deficiency (<10% mean normal serum biotinidase activity):

Most BTD pathogenic variants cause complete loss or near-complete loss of biotinidase enzyme activity. These alleles are considered profound biotinidase deficiency alleles; a combination of two such alleles, whether homozygous or compound heterozygous, results in profound biotinidase deficiency. Affected individuals are likely to develop symptoms if not treated with biotin.

Partial biotinidase deficiency (10%-30% of mean normal serum biotinidase activity)

Heterozygotes

Individuals with one profound or one partial biotinidase deficiency BTD variant are carriers of biotinidase deficiency and do not exhibit symptoms [B Wolf, personal observation]. Such individuals do not require biotin therapy.

Individuals who are homozygous for the p.Asp444His pathogenic variant are expected to have approximately 45%-50% of mean normal serum biotinidase enzyme activity (which is similar to the activity of heterozygotes for profound biotinidase deficiency) and do not require biotin therapy.

Almost all children with profound biotinidase deficiency become symptomatic or are at risk of becoming symptomatic if not treated.

Several reports describe adults with profound biotinidase deficiency who have offspring who also have profound biotinidase deficiency identified by newborn screening, but who have never had symptoms [Wolf et al 1997, Baykal et al 2005]. In addition, several enzyme-deficient sibs of symptomatic children have apparently never exhibited symptoms. It is possible that these individuals would become symptomatic if stressed, such as with a prolonged infection.

Profound and partial biotinidase deficiency is the accepted nomenclature for this disorder.

Individuals with partial biotinidase deficiency were previously described as having late-onset or juvenile multiple or combined carboxylase deficiency.

Biotinidase deficiency should not be confused with holocarboxylase synthetase deficiency (see Differential Diagnosis), previously refered to as early-onset or infantile multiple or combined carboxylase deficiency.

Based on the results of worldwide screening of biotinidase deficiency [Wolf 1991], the incidence of the disorder is:

One in 137,401 for profound biotinidase deficiency;

One in 109,921 for partial biotinidase deficiency;

One in 61,067 for the combined incidence of profound and partial biotinidase deficiency.

The incidence of biotinidase deficiency is generally higher in populations with a high rate of consanguinity (e.g., Turkey, Saudi Arabia).

The incidence appears to be increased in the Hispanic population [Cowan et al 2012] and it may be lower in the African American population.

Carrier frequency in the general population is approximately one in 120.

Clinical features including vomiting, hypotonia, and seizures accompanied by metabolic ketolactic acidosis or mild hyperammonemia are often observed in inherited metabolic diseases. Individuals with biotinidase deficiency may exhibit clinical features that are misdiagnosed as other disorders (e.g., isolated carboxylase deficiency) before they are correctly identified [Suormala et al 1985, Wolf & Heard 1989]. Other symptoms that are more characteristic of biotinidase deficiency (e.g., skin rash, alopecia) can also occur in children with nutritional biotin deficiency, holocarboxylase synthetase deficiency, zinc deficiency, or essential fatty acid deficiency. See .

The biotin cycle

Free biotin enters the cycle from dietary sources or from the cleavage of biocytin or biotinyl-peptides by the action of biotinidase. The free biotin is then covalently attached to the various apocarboxylases, propionyl-CoA (more...)

Biotin deficiency. Biotin deficiency can usually be diagnosed by dietary history. Individuals with biotin deficiency may have a diet containing raw eggs or protracted parenteral hyperalimentation without biotin supplementation.

Low-serum biotin concentrations are useful in differentiating biotin and biotinidase deficiencies from holocarboxylase synthetase deficiency; however, it is important to know the method used for determining the biotin concentration as only methods that distinguish biotin from biocytin or bound biotin yield reliable estimates of free biotin concentrations.

Isolated carboxylase deficiency. Urinary organic acid analysis is useful for differentiating isolated carboxylase deficiencies from the multiple carboxylase deficiencies that occur in biotinidase deficiency and holocarboxylase synthetase deficiency:

The multiple carboxylase deficiencies are biotin responsive, whereas the isolated carboxylase deficiencies are not. A trial of biotin can be useful for discriminating between the disorders.

Isolated carboxylase deficiency can be diagnosed by demonstrating deficient enzyme activity of one of the three mitochondrial carboxylases in peripheral blood leukocytes (prior to biotin therapy) or in cultured fibroblasts grown in low biotin-containing medium, and normal activity of the other two carboxylases.

Holocarboxylase synthetase deficiency (OMIM). Both biotinidase deficiency and holocarboxylase synthetase deficiency are characterized by deficient activities of the three mitochondrial carboxylases in peripheral blood leukocytes prior to biotin treatment. In both disorders, these activities increase to near-normal or normal after biotin treatment.

The symptoms of biotinidase deficiency and holocarboxylase synthetase deficiency are similar, and clinical differentiation is often difficult.

The age of onset of symptoms may be useful for distinguishing between holocarboxylase synthetase deficiency and biotinidase deficiency. Holocarboxylase synthetase deficiency usually presents with symptoms before age three months, whereas biotinidase deficiency usually presents after age three months; however, there are exceptions for both disorders.

Organic acid abnormalities in biotinidase deficiency and holocarboxylase synthetase deficiency are similar and may be reported as consistent with multiple carboxylase deficiency. However, the tandem mass spectroscopic methodology that is being incorporated into many newborn screening programs should identify metabolites that are consistent with multiple carboxylase deficiency. Because most children with holocarboxylase synthetase deficiency excrete these metabolites in the newborn period, the disorder should be identifiable using this technology.

Definitive enzyme determinations are required to distinguish between the two disorders:

Individuals with holocarboxylase synthetase deficiency have deficient activities of the three mitochondrial carboxylases in extracts of fibroblasts that are incubated in medium containing only the biotin contributed by fetal calf serum (low biotin), whereas individuals with biotinidase deficiency have normal carboxylase activities in fibroblasts. The activities of the carboxylases in fibroblasts of individuals with holocarboxylase synthetase deficiency become near-normal to normal when cultured in medium supplemented with biotin (high biotin).

Sensorineural hearing loss (see Deafness and Hereditary Hearing Loss Overview). Sensorineural hearing loss has many causes. Biotinidase deficiency can be excluded as a cause by determining biotinidase enzyme activity in serum. This test should be performed specifically on children with hearing loss who are exhibiting other clinical features consistent with biotinidase deficiency.

To establish the extent of disease and needs in a symptomatic individual diagnosed with biotinidase deficiency, the following evaluations are recommended:

History of seizures, balance problems, feeding problems, breathing problems, loss of hair, fungal infections, skin rash, conjunctivitis

Physical examination for hypotonia, ataxia, eye findings such as optic atrophy, eczematous skin rash, alopecia, conjunctivitis, breathing abnormalities such as stridor, thrush, and/or candidiasis

Evaluation for psychomotor deficits

Evaluation for sensorineural hearing loss

Ophthalmologic examination

Identification of cellular immunologic abnormalities because of the increased risk of recurrent viral or fungal infections caused by immunologic dysfunction

Consultation with a metabolic specialist or clinical geneticist

To establish the extent of disease and needs in infants or children diagnosed with biotinidase deficiency following newborn screening, the following evaluations are recommended:

Physical examination for neurologic findings (e.g., hypotonia, ataxia), eye findings (e.g., conjunctivitis), skin findings (eczematous rash, alopecia), breathing abnormalities (e.g., stridor) and fungal infections caused by immunologic dysfunction (thrush and/or candidiasis).

Evaluation for psychomotor deficits

Evaluation for sensorineural hearing loss

Ophthalmologic examination (for finding such as optic atrophy)

Consultation with a metabolic specialist or clinical geneticist

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Biotinidase Deficiency - GeneReviews - NCBI Bookshelf

This is an illustration of SRM peaks and a human face. Reporting in the journal Cell, Senior Research Scientist Dr. Ulrike Kusebauch, of Institute for Systems Biology (ISB), describes the results of a collaboration between scientists at ISB, ETH Zurich and a number of other contributing institutes to develop the Human SRMAtlas, a compendium of proteomic assays for any human protein. The Human SRMAtlas is a compendium of highly specific mass spectrometry assays for the targeted identification and reproducible quantification of any protein in the predicted human proteome, including assays for many spliced variants, non-synonymous mutations and post-translational modifications. Using the technique called selected reaction monitoring, assays were developed with the use of 166,174 well-characterized, chemically synthesized proteotypic peptides. The SRMAtlas resource is freely publicly available at http://www.srmatlas.org and will equally benefit focused, hypothesis-driven and large proteome-scale studies. We expect this resource will significantly advance protein-based experimental biology to understand disease transitions and wellness trajectories because any human protein can now, in principle, be identified and quantified in any sample.

Link:
Biology News Net - Latest Biology Articles, News & Current ...

A treatment for Cystic Fibrosis. A cure for AIDS. The end of cancer. That's what the newspapers promised us in the early 1990's. Gene therapy was the answer to what ailed us. Scientists had at last learned how to insert healthy genes into unhealthy people. And those healthy genes would either replace the bad genes causing diseases like CF, sickle-cell anemia and hemophilia or stimulate the body's own immune system to rid itself of HIV and some forms of cancer. A decade later, none of these treatments have come to fruition and research into gene therapy has become politically unpopular, making clinical trials hard to approve and research dollars hard to come by. But some researchers who are taking a different approach to gene therapy could be on the road to more success than ever before. - - - - - - - - - - - -

Early Promise

Almost as soon as Watson and Crick unwound the double helix in the 1950's, researchers began considering the possibility- and ethics- of gene therapy. The goals were lofty- to fix inherited genetic diseases such as Cystic Fibrosis and hemophilia forever.

Gene therapists planned to isolate the relevant gene in question, prepare good copies of that gene, then deliver them to patients' cells. The hope was that the treated cells would give rise to new generations of healthy cells for the rest of the patient's life. The concept was elegant, but would require decades of research to locate the genes that cause illnesses.

By 1990, it was working in the lab. By inserting healthy genes into cells from CF patients, scientists were able to transmogrify the sick cells as if by magic into healthy cells.

That same year, four-year-old Ashanti DeSilva became the first person in history to receive gene therapy. Dr. W. French Anderson of the National Heart, Lung and Blood Institute and Dr. Michael Blaese and Dr. Kenneth Culver, both of the National Cancer Institute, performed the historic and controversial experiment.

DeSilva suffered from a rare immune disorder known as ADA deficiency that made her vulnerable to even the mildest infections. A single genetic defect- like a typo in a novel- left DeSilva unable to produce an important enzyme. Without that enzyme, DeSilva was likely to die a premature death.

Anderson, Blaese and Culver drew the girl's blood and treated her defective white blood cells with the gene she lacked. The altered cells were then injected back into the girl, where- the scientists hoped- they would produce the enzyme she needed as well as produce future generations of normal cells.

Though the treatment proved safe, its efficacy is still in question. The treated cells did produce the enzyme, but failed to give rise to healthy new cells. DeSilva, who is today relatively healthy, still receives periodic gene therapy to maintain the necessary levels of the enzyme in her blood. She also takes doses of the enzyme itself, in the form of a drug called PEG-ADA, which makes it difficult to tell how well the gene therapy would have worked alone.

"It was a very logical approach," says Dr. Jeffrey Isner, Chief of Vascular Medicine and Cardiovascular Research at St. Elizabeth's Medical Center in Boston as well as Professor of Medicine at Tufts University School of Medicine. "But in most cases the strategy failed, because the vectors we have today are not ready for prime time." - - - - - - - - - - - - 4 pages: | 1 | 2 | 3 | 4 |

Photo: Dr. W. French Anderson

See the article here:
Gene therapy - PBS

Researchers are looking at different ways of using gene therapy, including

Some types of gene therapy aim to boost the body's natural ability to attack cancer cells. Our immune system has cells that recognise and kill harmful things that can cause disease, such as cancer cells.

There are many different types of immune cell. Some of them produce proteins that encourage other immune cells to destroy cancer cells. Some types of therapy add genes to a patient's immune cells to make them better at finding or destroying particular types of cancer. There are a few trials using this type of gene therapy in the UK.

Some gene therapies put genes into cancer cells to make the cells more sensitive to particular treatments such as chemotherapy or radiotherapy. This type of gene therapy aims to make the other cancer treatments work better.

Some types of gene therapy deliver genes into the cancer cells that allow the cells to change drugs from an inactive form to an active form. The inactive form of the drug is called a pro drug.

After giving the carrier containing the gene, the doctor gives the patient the pro drug. The pro drug may be a tablet or capsule that you swallow, or you may have it into the bloodstream.

The pro drug circulates in the body and doesn't harm normal cells. But when it reaches the cancer cells, the gene activates it and the drug kills the cancer cells.

Some gene therapies block processes that cancer cells use to survive. For example, most cells in the body are programmed to die if their DNA is damaged beyond repair. This is called programmed cell death or apoptosis. But cancer cells block this process so they don't die even when they are supposed to. Some gene therapy strategies aim to reverse this blockage. Doctors hope that these new types of treatment will make the cancer cells die.

Some viruses infect and kill cells. Researchers are working on ways to change these viruses so that they only target and kill cancer cells, leaving healthy cells alone. This sort of treatment uses the viruses to kill cancer cells directly rather than to deliver genes. So it is not cancer gene therapy in the true sense of the word. But doctors sometimes refer to it as gene therapy.

One example of this type of research uses the cold sore virus (herpes simplex virus). The changed virus is called Oncovex. It has been tested in early clinical trials for advanced melanoma, pancreatic cancer and head and neck cancers.

Read the rest here:
Gene therapy | Cancer Research UK

The general approach of gene therapy is nothing more than an extension of the technique for clone selection by functional complementation (Chapter 12). The functions absent in the recipient as a result of a defective gene are introduced on a vector that inserts into one of the recipients chromosomes and thereby generates a transgenic animal that has been genetically cured. The technique is of great potential in humans because it offers the hope of correcting hereditary diseases. However, gene therapy is also being applied to mammals other than humans.

The first example of gene therapy in a mammal was the correction of a growth-hormone deficiency in mice. The recessive mutation little (lit) results in dwarf mice. Even though a mouses growth-hormone gene is present and apparently normal, no mRNA for this gene is produced. The initial step in correcting this deficiency was to inject homozygous lit/lit eggs with about 5000 copies of a 5-kb linear DNA fragment that contained the rat growth-hormone structural gene (RGH) fused to a regulatorpromoter sequence from a mouse metallothionein gene (MP). The normal job of metallothionein is to detoxify heavy metals, so the regulatory sequence is responsive to the presence of heavy metals in the animal. The eggs were then implanted into pseudopregnant mice, and the baby mice were raised. About 1 percent of these babies turned out to be transgenic, showing increased size when heavy metals were administered in the course of development. A representative transgenic mouse was then crossed with a homozygous lit/lit female. The ensuing pedigree is shown in . We can see in that mice two to three times the weight of their lit/lit relatives are produced in subsequent generations, with the rat growth-hormone transgene acting as a dominant allele, always heterozygous in this pedigree. The rat growth-hormone transgene also makes lit+ mice bigger ().

The rat growth-hormone gene (RGH), under the control of a mouse promoter region that is responsive to heavy metals, is inserted into a plasmid and used to produce a transgenic mouse. RGH compensates for the inherent dwarfism (lit/lit) in the mouse. RGH (more...)

Transgenic mouse. The mice are siblings, but the mouse on the left was derived from an egg transformed by injection with a new gene composed of the mouse metallothionein promoter fused to the rat growth-hormone structural gene. (This mouse weighs 44g, (more...)

The site of insertion of the introduced DNA in mammals is highly variable, and the DNA is generally not found at the homologous locus. Hence, gene therapy most often provides not a genuine correction of the original problem but a masking of it.

Similar technology has been used to develop transgenic fast-growing strains of Pacific salmon, with spectacular results. A plasmid containing a growth-hormone gene placed next to a metallothionein promoter (all derived from salmon) was microinjected into salmon eggs. A small proportion of the resulting fish proved to be transgenic, testing positive when their DNA was probed with the plasmid construct. These fish were on average 11-fold heavier than the nontransgenic controls (). Progeny inherited the transgene in the same manner as the mice in the earlier example.

Effect of introducing a hormone transgene complex with a strong promoter into Pacific salmon. All salmon shown are the same age. (R. H. Devlin, T. Y. Yesaki, C. A. Biagi, E. M. Donaldson, P. Swanson, and W.-K. Chan, Extraordinary Growth, (more...)

Perhaps the most exciting and controversial application of transgenic technology is in human gene therapy, the treatment and alleviation of human genetic disease by adding exogenous wild-type genes to correct the defective function of mutations. We have seen that the first case of gene therapy in mammals was to cure a genotypically dwarf fertilized mouse egg by injecting the appropriate wild-type allele for normal growth. This technique () has little application in humans, because it is currently impossible to diagnose whether a fertilized egg cell carries a defective genotype without destroying the cell. (However, in an early embryo containing only a few cells, one cell can be removed and analyzed with no ill effects on the remainder.)

Two basic types of gene therapy can be applied to humans, germ line and somatic. The goal of germ-line gene therapy () is the more ambitious: to introduce transgenic cells into the germ line as well as into the somatic cell population. Not only should this therapy achieve a cure of the person treated, but some gametes could also carry the corrected genotype. We have seen that such germinal therapy has been achieved by injecting mice eggs. However, the protocol that is relevant for application to humans is the removal of an early embryo (blastocyst) with a defective genotype from a pregnant mouse and injection with transgenic cells containing the wild-type allele. These cells become part of many tissues of the body, often including the germ line, which will give rise to the gonads. Then the gene can be passed on to some or all progeny, depending on the size of the clone of transgenic cells that lodges in the germinal area. However, no human germ-line gene therapy has been performed to date.

We have seen that most transforming fragments will insert ectopically throughout the genome. This is a disadvantage in human gene therapy not only because of the possibility of the ectopic insert causing gene disruption, but also because, even if the disease phenotype is reversed, the defective allele is still present and can segregate away from the transgene in future generations. Therefore, for effective germinal gene therapy, an efficient targeted gene replacement will be necessary, in which case the wild-type transgene replaces the resident defective copy by a double crossover.

Somatic gene therapy () focuses only on the body (soma). The approach is to attempt to correct a disease phenotype by treating some somatic cells in the affected person. At present, it is not possible to render an entire body transgenic, so the method addresses diseases whose phenotype is caused by genes that are expressed predominantly in one tissue. In such cases, it is likely that not all the cells of that tissue need to become transgenic; a percentage of cells being transgenic can ameliorate the overall disease symptoms. The method proceeds by removing some cells from a patient with the defective genotype and making these cells transgenic through the introduction of copies of the cloned wild-type gene. The transgenic cells are then reintroduced into the patients body, where they provide normal gene function.

Currently, there are two ways of getting the transgene into the defective somatic cells. Both methods use viruses. The older method uses a disarmed retrovirus with the transgene spliced into its genome, replacing most of the viral genes. The natural cycle of retroviruses includes the integration of the viral genome at some location in one of the host cells chromosomes. The recombinant retrovirus will carry the transgene along with it into the chromosome. This type of vector poses a potential problem, because the integrating virus can act as an insertional mutagen and inactivate some unknown resident gene, causing a mutation. Another problem with this type of vector is that a retrovirus attacks only proliferating cells such as blood cells. This procedure has been used for somatic gene therapy of severe combined immunodeficiency disease (SCID), otherwise known as bubble-boy disease. This disease is caused by a mutation in the gene encoding the blood enzyme adenosine deaminase (ADA). In an attempt at gene therapy, blood stem cells are removed from the bone marrow, the transgene is added, and the transgenic cells are reintroduced into the blood system. Prognosis for such patients is currently good.

Even solid tissues seem to be accessible to somatic gene therapy. In a dramatic case, gene therapy was administered to a patient homozygous for a recessive mutant allele of the LDLR gene for low-density-lipoprotein receptor (genotype LDLR/LDLR). This mutant allele increases the risk of atherosclerosis and coronary disease. The receptor protein is made in liver cells, so 15 percent of the patients liver was removed, and the liver cells were dissociated and treated with retrovirus carrying the LDLR+ allele. Transgenic cells were reintroduced back into the body by injection into the portal venous system, which takes blood from the intestine to the liver. The transgenic cells took up residence in the liver. The latest reports are that the procedure seems to be working and the patients lipid profile has improved.

The other vector used in human gene therapy is the adenovirus. This virus normally attacks respiratory epithelia, injecting its genome into the epithelial cells. The viral genome does not integrate into a chromosome but persists extrachromosomally in the cells, which eliminates the problem of insertional mutagenesis by the vector. Another advantage of the adenovirus as a vector is that it attacks nondividing cells, making most tissues susceptible in principle. Inasmuch as cystic fibrosis is a disease of the respiratory epithelium, adenovirus is an appropriate choice of vector for treating this disease, and gene therapy for cystic fibrosis is currently being attempted with the use of this vector. Viruses bearing the wild-type cystic fibrosis allele are introduced through the nose as a spray. It is also possible to use the adenovirus to attack cells of the nervous system, muscle, and liver.

A promising type of construct that should find use in gene therapy is the human artificial chromosome (HAC). HACs contain essentially the same components as YACs. They were made by mixing human telomeric DNA, genomic DNA, and arrays of repetitive -satellite DNA (thought to have centrometric activity). To this unjoined mixture was added lipofectin, a substance needed for passage through the membrane, and the complete mixture was added to cultured cells. Some cells were observed to contain small new chromosomes that seemed to have assembled de novo inside the cell from the added components (). When the technology has been perfected, these HACs should be potent vectors capable of transferring large amounts of human DNA into cells in a stable replicating form.

An artificial human chromosome (at arrow). (John J. Harrington, G. Van Bokkelen, R. W. Mays, K. Gustashaw, and H. F. Willard, Formation of de Novo Centromeres and Construction of First-Generation Human Artificial Microchromosomes, Nature (more...)

Gene therapy introduces transgenic cells either into somatic tissue to correct defective function (somatic therapy) or into the germ line for transmission to descendants (germ-line therapy).

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Gene therapy - An Introduction to Genetic Analysis - NCBI ...