At present, a positive family history carries greater specificity and sensitivity than most laboratory genetic tests. Even with all the DNA mutations currently known for diseases, the vast majority of mutations remains to be identified, and the full hand of genetic cards dealt to each person is not known. Genetics is important in every ophthalmic consultation, from those involving rare inborn errors of metabolism or congenital malformations to common eye diseases, such as myopia, glaucoma, cataract, and age-related macular degeneration (AMD). Even susceptibility to infection and trauma can be genetic. An understanding of the genetic basis of a disease may be particularly useful for arriving at a correct diagnosis when another family member has a similar disease. In addition, it is important for clinicians to recognize that a patient presenting with a particular eye problem may be at increased risk for an unrelated disease, such as glaucoma, because of an affected parent.
The ophthalmologist has an important obligation to patients with genetic eye diseases—either to provide genetic counseling or to arrange for referral to a geneticist or genetic counselor. Clinicians now have patients presenting with DNA test results for themselves or their families. The results may range from the identification of high-risk retinoblastoma gene mutations (which would significantly influence the management of at-risk children within the family) to genetic associations that are of no more value than iridology (genes have been associated with iris crypts and furrows). It is important to understand the clinical settings in which a genetic test is crucial, useful, or irrelevant to patient management. These distinctions will change in the future as new clinical trials define treatments based on genetic background.
When a patient presents with a DNA result for a disease for which no effective treatment based on such results is currently available, the clinician may be asked the following question: “What should we do about this?” The best answer is: “Participate in, or help fund, research so we can find out what the best treatments are.” The US National Institutes of Health (NIH) website ClinicalTrials.gov is a good place to refer these patients.
The key recommendations of the AAO Task Force on Genetic Testing policy are given at the end of this chapter. When faced with the option of ordering genetic tests, clinicians should ask the same question they ask before ordering any tests: How will this change management? The best utilization of genetic testing comes from knowledge of the family history. An accurate family history might help an ophthalmologist save not only a patient’s sight but also, in cases of retinoblastoma or Marfan syndrome, the patient’s life.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.