Lack of gender differences in age at onset in familial schizophrenia.

One of the most consistent findings in the epidemiology of schizophrenia is that males are younger at the onset of schizophrenia than females. However, the vast majority of studies focussing on gender differences have not considered the potential influence of genetic factors on age at onset. We investigated the impact of familial loading on gender differences in age at onset in families with at least two siblings with RDC/DSM-III-R schizophrenia or chronic schizoaffective disorder. A total of 106 sib pairs, including 38 male-male pairs, 29 female-female pairs and 39 mixed-sex pairs of siblings as well as 260 male and 221 female isolated cases with no relative of first, second or third degree suffering from psychotic or major affective illness were investigated. We found no gender differences in age at onset in familial cases. An earlier age at onset in males compared to females was observed only in isolated cases. Our data strongly support the assumption that gender differences in age at onset of schizophrenia is not consistent across all subgroups of schizophrenics.