Genetic epidemiology.

Studies of families, twins, and adoptees have helped to quantify the genetic contributions to and overlaps between depression, anxiety, phobias and alcoholism, and to refine the boundaries of the schizophrenia spectrum. Analyses of covariance structures in twin data have confirmed genetic susceptibility and recent life stresses as the major determinants of depression. Genetic modelling of family data on schizophrenia and bipolar disorder indicates three or more common genes each having a small multiplicative effect on risk, although rare major genes may be present in some families. Linkage studies have localised genes for familial Alzheimer's disease on chromosomes 14 and 21; disease mutations on these chromosomes have since been isolated. Association studies have identified susceptibility (or protective) genes for Alzheimer's disease and alcoholism. Several tentative linkage and association findings in schizophrenia and bipolar disorder require further study.