Genetic studies of affective disorders and schizophrenia.

The evidence on transmission of the major psychoses in adoption studies and their aggregation within a limited number of families in population studies strongly suggests genetic transmission. In schizophrenia there have been relatively few pedigree studies or studies of pathophysiologic markers. The mode of genetic transmission is generally unknown. In the affective disorders, the frequency of expression of illness varies significantly between comparable populations and even between generations and between geographical regions in the same population. No genetic transmission model applies to all data sets collected. Linkage to chromosomal markers has been reported but the reports have been questioned and there have been failures of replication. It appears that clinical diagnosis alone will not serve for precise phenotype identification. Further progress may require identification of a pathophysiologic vulnerability or linkage marker for at least a subgroup of patients.