The role of genetic factors in the etiology of the affective disorders.

Recent application of genetic linkage analysis to the affective disorders has suggested that there are at least three genotypic forms. This is an important step toward defining the genetic etiology involved, as it had previously been suggested that the complex nature of the clinical phenotype would preclude any attempt to apply such a technique. However, to date no clinical evidence exists to discriminate these genotypes at the phenotypic level. Molecular geneticists now face a formidable task of identifying the aberrant gene and relating the gene product, a protein, to the observed psychopathology. Current molecular genetic research in the affective disorders is discussed and similar work applied to the study of nonpsychiatric disorders such as cystic fibrosis and Duchenne muscular dystrophy is reviewed. The clinical value of genetic risk analysis for individuals with a family history of the affective disorders is also considered.