The field of medical genetics has traditionally focused on chromosomal abnormalities (Chap. 63) and Mendelian disorders (Chap. 62). However, there is genetic susceptibility to many common adult-onset diseases, including atherosclerosis, cardiac disorders, asthma, hypertension, autoimmune diseases, diabetes mellitus, macular degeneration, Alzheimer's disease, psychiatric disorders, and many forms of cancer. Genetic contributions to these common disorders involve more than the ultimate expression of an illness; these genes can also influence the severity of infirmity, effect of treatment, and progression of disease. The primary care clinician is now faced with the role of recognizing and counseling patients at risk for a number.
