Schizophrenic individuals with bipolar first-degree relatives: analysis of two pedigrees.

During the course of a family-interview study of probands with psychotic disorders, the authors encountered two pedigrees in which schizophrenic individuals had first-degree relatives with bipolar disorder. The authors describe the members of both families in detail and discuss several hypotheses that might account for the co-occurrence of schizophrenia and bipolar disorder in the same family.