Genetics and psychiatry: past discoveries, current dilemmas, and future directions.

Family, twin, and adoption studies have suggested an important role for hereditary factors in the etiology and pathogenesis of several psychiatric disorders. Advances in molecular and statistical genetics may very well reveal the identity of these factors, which may include single genes. Linked markers, critical to the discovery of abnormal genes in several medical conditions, have been reported for Huntington's disease, Alzheimer's disease, bipolar disorder, and schizophrenia. Psychiatric disorders pose particular problems (etiologic heterogeneity, incomplete penetrance, variable expressivity) for genetic research. New practical and ethical questions also arise. Nevertheless, knowledge may emerge that will suggest new approaches to diagnosis, prevention, and treatment.