Genetic Testing for Neurological Diseases

January 21, 2016
Anna B. Boyum, PhD

What implications does genetic testing have for people at risk of neurological diseases and for the physicians treating these patients?

The personal genetics company 23andMe has recently resumed providing its customers with health reports.1 What implications does this have for both people at risk of neurological diseases and physicians to whom they reach out for answers?

Currently, 23andMe is the only company whose reports meet U.S. Food and Drug Administration (FDA) standards. As many know, this has not always been the case. In a widely publicized struggle with the FDA, 23andMe lost the right to provide health reports to its customers in November of 2013. Less than 2 years later, the company is back to reporting genetic traits and carrier status for heritable diseases. At the moment, the company does not report the risk of common neurological conditions like stroke, Parkinson disease, and Alzheimer disease, but it is working with the FDA to expand its repertoire of reports in the future.

What has been driving the tedious and costly effort to resume health information reporting? Since 23andMe is a for-profit company, albeit with a noble mission, the answer is customer demand. People want to have access to health information: some are just curious while others intend to use it. But how can it be used?

One example is to help plan a family. Turning out to be a carrier of a mutation linked to an inherited form of muscular dystrophy or peripheral neuropathy can prompt a person to have their partner tested. The company recommends that all concerned customers consult a geneticist.

But can personal genetic information be used to detect increased risk for and ultimately prevent a disease with a complex mode of inheritance, such as stroke? Although 23andMe does not explicitly report the risk of stroke, it provides a test taker with raw genetic data, which can be easily interpreted using the Browse Raw Data tool on the company’s website. A search for a single nucleotide polymorphism (SNP) will return one’s personal variant, allele, which may be linked to an increased risk of disease. For example, each adenine in rs12425791 SNP increases the risk of total and ischemic stroke roughly 1.3 times.2 Another SNP, rs2231137, is also linked to an increased risk of ischemic stroke.3 This information is freely available on websites geared towards a lay audience (23andMe blog, SNPedia), so a test taker without medical training can learn about the risk of stroke with little help from 23andMe and without FDA approval. On the web, stories about the role of personal genetic testing in helping someone understand mysterious symptoms are common.

I have said that these data are easy to interpret, but they are just as easy to misinterpret. Much evidence exists that disease phenotype is the result of complex interactions of multiple genes and environmental factors; 23andMe mentions this in the disclaimer. While discussing the limitations of personal genetics testing, Janssens and Duijn, researchers from Erasmus University Medical Center, Netherlands, refer to the value of these tests as minimal.4 Currently, American Heart Association/American Stroke Association does not recommend genetic screening of the general population for the prevention of first stroke.5

Not surprisingly, 23andMe refers to the information it provides as “highly relevant,” and public interest remains high.1 Equipped with this information and inspired by the company’s messages and customers’ stories, people may be more likely to initiate a conversation with clinicians about prevention and treatment of a disease of concern. How well are clinicians prepared to respond? Also, the subjects of conversation may vary from stroke to Alzheimer disease. To someone at risk (real or not) of stroke, a clinician may recommend positive lifestyle changes including diet, exercise, and smoking status adjustments. But what options exist for those concerned about an increased risk of a disease which cannot be prevented? What experience did you have with follow-up on direct-to-consumer genetic testing?

References:

1. 23andMe Launches New Customer Experience – Reports Include Carrier Status That Meet FDA Standards, Wellness, Traits, and Ancestry [press release]. Mountain View, CA: 23andMe Media Center Web site, October 21, 2015. http://mediacenter.23andme.com/blog/2015/10/21/new-23andme/

2. Ikram MA, et al. Genomewide association studies of stroke. N Engl J Med. 2009;360(17):1718-1728.

3. Luke MM, et al. Gene variants associated with ischemic stroke: the cardiovascular health study. Stroke. 2009;40(2):363-368.

4. Janssens AC, van Duijn CM. An epidemiological perspective on the future of direct-to-consumer personal genome testing. Investig Genet. 2010;1(1):10.

5. Meschia JF, et al. Guidelines for the primary prevention of stroke: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014;45(12):3754-3832.