Genetics of affective disorders. II. Morbidity risk and genetic transmission.

Morbidity risk and genetic transmission data on a small population of bipolar, unipolar and schizo-affective outpatients suggest a possible genetic overlap between bipolar and schizo-affective patients. There is a conspicuous absence of a homologous illness in the relatives of schizo-affective probands, although the incidence of schizophrenia was higher in these relatives as compared to the relatives of either bipolar or unipolar probands. The data, although tentative because of the relatively small numbers involved, suggest a multifactorial mode of transmission in some affective illnesses. These disease entities appear familial rather than 'genetically transmitted'. There are select families who show the heritable genetic penetrance previously recorded for these mental disorders.