J Diabetes Sci Technol. 2009 Jul; 3(4): 781788.
Published online 2009 Jul.
Institute for Genome Sciences and Policy, Duke University, Durham, North Carolina
With the rising number of individuals affected with diabetes and the significant health care costs of treatment, the emphasis on prevention is key to controlling the health burden of this disease. Several genetic and genomic studies have identified genetic variants associated with increased risk to diabetes. As a result, commercial testing is available to predict an individual's genetic risk. Although the clinical benefits of testing have not yet been demonstrated, it is worth considering some of the ethical implications of testing for this common chronic disease. In this article, I discuss several issues that should be considered during the translation of predictive testing for diabetes, including familial implications, improvement of risk communication, implications for behavioral change and health outcomes, the Genetic Information Nondiscrimination Act, direct-to-consumer testing, and appropriate age of testing.
Keywords: ethics, genetic testing, risk
Type 2 diabetes mellitus (T2DM) is a prevalent, chronic condition associated with extensive morbidity, decreased quality of life, and increased utilization of health services.1 Approximately 23 million people in the United States are affected with diabetes, and more than twice that number are prediabetic.2 The annual risk of developing T2DM for the average person living in the United States with normal glucose levels is approximately 0.7% per year.3
The polygenic nature of T2DM has been a major challenge to identifying genes involved in the pathogenesis of this diseaseknowledge that could give rise to new treatments and tests. However, following the completion of the Human Genome Project and HapMap and the development of high-throughput technologies, scientists are in a much better position to tackle the complex genetic underpinnings of T2DM.4 The rise of genetic and genomic studies has aligned with the increasing incidence rate of T2DM (). A number of commercial tests have already been developed that assay a panel of genetic variants in several genes identified from genome-wide association studies of T2DM. Among the best studied of these are two very closely linked single nucleotide polymorphisms (SNPs) in the transcription factor 7-like 2 (TCF7L2) gene.5 More than 20 studies have replicated the association between these two SNPs in TCF7L2 and increased T2DM risk. The largest pooled analysis reported an overall odds ratio of 1.37 with a single copy of the higher-risk allele at one of the TCF7L2SNPs.6 In comparison, individuals with a positive family history for T2DM are at a 26 times increased risk compared to those without a family history.710
Unlike single-gene testing for Mendelian disorders that produce a relatively certain prediction of disease, genomic testing for complex diseases like T2DM will generate disease riskinformation. Some of the ethical issues of genome risk profiling or predispositional testing overlap with single-gene testing used primarily for diagnosis, although additional issues related to predispositional testing include challenges of communicating risk information (particularly low risks), uncertainty of disease risk and psychosocial impact of at-risk status, and ensuring patient comprehension. Of substantial importance is that individuals are informed about these and other issues when they are deciding if the test is appropriate for them. Although written informed consent may not be warranted, a discussion with a physician or other professional such as a genetic counselor can serve to educate and encourage careful consideration of the benefits and risks of testing as well as alternatives to testing. This article presents an overview of several issues that should be considered as genome risk profiling for T2DM becomes integrated into clinical care.
As with any type of genetic testing, it is important to consider the impact of testing on family members. Predisposition testing for T2DM and other chronic diseases raises familial implications on two levels. The implication of test results for biological family members raises the issue of whether and how to discuss the results with other family members.12 Tested individuals may be reluctant to share the results due to fear it will disrupt relationships, be hesitant of having to contact estranged and distant family members, and feel guilt.1316 Those who opt to share the results with family members may have difficulty accurately communicating the results17,18 or minimize the seriousness of the finding.19 Although a positive test result could be inferred from changes in lifestyle and preventive medical procedures, individuals undergoing testing should ascertain the wishes of other family members prior to discussing their test results.20 Furthermore, as many individuals choose to undergo genetic testing for the sake of their children, they will need to understand when and how best to discuss the results with their children.21,22 Family members who decide to learn of their relative's results must also decide how they'll act upon them (e.g., getting themselves tested), if at all.
Second, given that environment can substantially influence risk for T2DM and other complex diseases, a positive result of one individual can affect the lifestyle of the entire family. For example, adoption of healthy eating habits may be better achieved if the entire family is involved in promoting healthy living.2326 Special treatment of a child found to be at increased genetic risk may lead to feelings of ostracism, stigmatization, and inferiority.
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Personalized Medicine for Diabetes: Ethical Issues of ...