Frequency of non-right-handedness in bipolar disorder and schizophrenia.

Increased non-right-handedness (NRH) probably reflects neurodevelopmental abnormalities in psychiatric disorders. Past studies of NRH have focused more on schizophrenia (SZ) than bipolar disorder (BPD). We report results on NRH in two large studies. In (1), NRH was compared among BPD patients with psychosis, SZ patients, and healthy controls (HC). NRH was elevated in BPD with psychosis and SZ patients relative to HC, but not SZ relative to BPD. In (2), NRH was compared between BPD patients with and without psychosis. NRH was similarly elevated in both. The findings suggest that NRH may reflect shared brain anomalies in SZ and BPD.