Mixed handedness in familial and non-familial schizophrenia

Abstract

An excess of mixed handedness has been reported in schizophrenia but it is not clear whether this reflects a genetic or environmental aetiology. We sought to clarify this issue by examining mixed handedness in families likely to be enriched or depleted for schizophrenia genes. We assessed rates of mixed handedness in a group of patients with DSM-IIIR schizophrenia from multiply affected families (n=43), their unaffected first degree relatives (n=69), nonfamilial cases of schizophrenia (n =46), their first degree relatives (n = 79) and controls (n = 72). Handedness was measured using the Annett Questionnaire. Measures of developmental disturbance included the Lewis-Murray scale for obstetric complications and the Premorbid Social Adjustment scale. The data were analysed using logistic regression and controlling for gender and age. There was a significant excess of broadly defined mixed handedness (Annett class 2-7) in patients with non-familial schizophrenia compared to controls (OR 4.19, 95% CI 1.61 10.89, p=0.003). There were no significant differences in rates of mixed handedness between controls and patients with familial schizophrenia (OR 1.65, 95% CI 0.634.33, p =0.31 ), familial relatives (OR 1.23, 95% CI 0.49-3.06, p=0.66) or nonfamilial relatives (OR 1.93, 95% CI 0.71-5.24, p=0.20). There were no significant findings for narrowly defined mixed handedhess (Annett class 5-6). There was no relationship between mixed handedness and obstetric complications or poor premorbid social adjustment. Our results suggest that environmental factors may contribute to the presence of mixed handedness in schizophrenia. Such factors do not appear to be linked to obstetric complications or abnormalities of premorbid personality.