Hereditary considerations in common disorders.

We have reviewed the approach of the modern clinical geneticist to the genetics of common diseases. The importance of considering genetic heterogeneity within these groups of disorders has been emphasized. The physician should recognize our present inability to deliver exact recurrence risks for most families with these common disorders. As our knowledge improves, we must constantly update our counseling. Until then, in most cases, we can only utilize the empirical risk data presently available and provide an idea of the magnitude of risk, which in many of these disorders appears low. However, continued utilization of imprecise risk data must not impede recognition of potential and demonstrated heterogeneity within these disorders, or retard the development of new and improved risk data based on knowledge of the heterogeneity within common diseases.