What are the challenges involved in genetic testing?
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The perspective of a genetic counselor
As genetic counselors, we help patients to make informed decisions about genetic testing.
We talk to them about what we know about the genetics of the condition and answer any questions, and then we order genetic testing for them, if that is something they want to do.
When the results come back, we share those results with the patients, help them to correctly interpret them, and offer support in making medical and personal decisions. I work specifically with retinal dystrophy patients, and most of them are interested in genetic testing. Some patients, however, are reluctant to order testing. Because the clinical diagnosis has already been made by an ophthalmologist, they are not sure the test would make a difference and do not see the value of a genetic diagnosis. They may feel there is not much to do in terms of treatment, and although we do explain that there is one FDA-approved gene therapy treatment at this time and several clinical trials, including gene therapy and stem cell therapy, it is still the case that most people are not going to be eligible for clinical trials at this time. They may feel the same about their family members: Why have them tested if there is nothing they can do? Some patients are afraid of having a genetic test for fear of discovering other health conditions. We clarify that all testing we order is targeted to genes associated with retinal dystrophies, but some of these genes do cause syndromic retinal dystrophies when mutated, and we may therefore learn about other related health concerns unexpectedly.
Another problem may be the cost because not all health insurance plans cover, or cover entirely, the costs of genetic testing. However, we do have the ability to have most patients order testing at no charge through the My Retina Tracker program from Foundation Fighting Blindness.
Sometimes we have patients referred to us from ophthalmologists outside our institution who may have ordered genetic testing upfront. If they are not so familiar with retinal dystrophies, they may order tests that are less comprehensive than what we would have ordered. At that point, the patient may not be eligible for further testing at no charge. Ophthalmic genetics is a specialized field, and patients should be referred to specialized centers or to genetics clinics to help interpret test results, it at all possible. Particularly if the results are inconclusive or hard to interpret, ophthalmologists who do not have a background in genetics will have a hard time explaining them to the patients and providing correct information about the implications for them and their families, the options, the follow-up, and answering their many questions.
Dana Schlegel, MS, MPH, CGC, is a genetic counselor at University of Michigan Kellogg Eye Center.
The perspective of a retina specialist
Genetic testing can provide important insights for the diagnosis, prognosis and treatment of specific conditions (eg, Luxturna for treatment of Leber congenital amaurosis due to biallelic RPE65 mutation) as well as enrollment in clinical trials that target a specific genetic mutation (eg, choroideremia associated with CHM genotype). There are, however, some limitations, potential drawbacks and unanswered questions.
Genetic testing can be misleading because sometimes, due to limitations of the assay, other genetic abnormalities may go undetected. So, a specific test result may give an incomplete explanation of the cause of a retinal dystrophy. Also, a “positive” result might affect insurance eligibility and coverage. Some genetic testing services may not be able to provide the level of confidentiality that ensures the information is protected from disclosure.
Employment issues also might arise. A normally sighted 20-year-old with Usher syndrome type 3, which is associated with variable, relatively late-onset sensory neural hearing loss and retinal degeneration, might not be eligible for some types of employment. (On the other hand, this information might be useful in assisting that individual in making a career choice.)
From a psychological standpoint, people’s attitudes and feelings concerning test results can be quite diverse. Some may be relieved to know what their genetic abnormality is, but others may not find that information useful or even desirable. Woody Guthrie, for example, had Huntington’s chorea, a relatively late-onset degenerative neurological disease associated with paroxysmal choreoathetosis and can be associated with cognitive dysfunction. His son, Arlo, chose not to be tested because he did not feel that information would influence how he lived his life, eg, deciding to have children.
Something to bear in mind is that a test can tell you what might happen, but it may not tell you what will happen. In many cases, there is more to what happens than just what your genes are. Clinical outcome can be influenced by the penetrance of the gene, by the presence of modifier genes, by how introns affect gene expression and by environmental exposure (ie, epigenetics). So, knowing one’s genetic code is not, in all cases, going to predict one’s clinical future. At this point in time, genetic testing should be used in a targeted manner, ideally after appropriate counseling by the patient’s physician. In addition, patients undergoing such testing should receive guidance from a genetic counselor once the results are available.
- Reference:
- Abbott J. Arlo Guthrie talks to Pete Fornatale about Huntington’s disease and life. YouTube. https://www.youtube.com/watch?v=1RyeOYYa6w0. Published Jan. 14, 2014.
Marco A. Zarbin, MD, PhD, is professor and chair, Institute of Ophthalmology and Visual Science, Rutgers New Jersey Medical School.
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