The association of open-angle glaucoma and family history has been known for years. The lifetime risk for first-degree relatives of affected individuals to develop open-angle glaucoma is 22 % when compared with a 2 % risk in controls, but clinicians routinely overlook this fact when interviewing and evaluating patients. Patients are rarely accurate in reporting family history. Three genetic loci for glaucoma were first found in a single glaucoma practice in Portland, Oregon – GLC1C, GLC1F, and GLC1G – because of repeated and persistent inquiries about affected relatives. Asking a patient only once about his or her family history is rarely effective; patients tend to confuse macular degeneration, cataracts, and glaucoma.The purpose of this chapter is to call attention to family history as a critical risk factor and provide a basis for those interested in gaining a basic understanding of the currently known genetics of glaucoma and its implications on patient care. Perhaps the most important concept in discussing glaucoma genetics is to point out that it is both monogenic and polygenic. Instances where a single gene causes glaucoma (monogenic) have emerged (e.g., the myocilin and optineurin genes), but in other instances, glaucoma is much more likely the result of multiple genes (polygenic). Being polygenic makes a disease such as glaucoma more difficult to study and explains why much remains to be learned about the inheritance of this condition.
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