It is unknown whether intellectual disability (ID) is more familially related to psychotic mood disorders or schizophrenia. L. S. Penrose's large sample of families with two or more members admitted to psychiatric hospitals provided a unique opportunity to investigate the familial relationship between mild ID, schizophrenia and psychotic affective disorders.
Clinical Genetics Research Program, Queen Street Site, Centre for Addiction and Mental Health, 1001 Queen Street West, Toronto, Ontario M6J 1H4, Canada.