Affective illness and schizophrenia in families with multiple schizophrenic members: independent illnesses or variant gene(s)?

Affective disorder occurs in some families with schizophrenia, and schizophrenic patients often describe concurrent episode(s) of depression that may lead them to be diagnosed schizoaffective. The present study examines the pattern of affective disorder in families with two or more members with schizophrenia or schizoaffective disorder. We find that affective disorders are more frequently inherited from the same parental side of the family as schizophrenia-like psychosis. When unipolar, it more often is expressed in female than male relatives (particularly mothers), and when bipolar it is more likely in males. In contrast, schizophrenia with and without depression is equally prevalent in both sexes. Unipolar illness was more common in relatives of schizophrenics whose illnesses are characterized by recurrent episodes of depression than in those whose are not. These data are consistent with the hypothesis that the same genes could contribute to susceptibility to both schizophrenia and affective disorder in some families, and that sex and phenotypic expression are in some way related. However, the phenomenon of high rates of depression in mothers of schizophrenic patients needs explanation.