Movement disorders in nonpsychotic siblings of patients with nonaffective psychosis

Movement disorders such as dyskinesia and Parkinsonism have frequently been reported in (drug-naïve) patients with nonaffective psychosis. Therefore movement disorders may be related to schizophrenia. Siblings of patients with nonaffective psychosis also appear to have subtle forms of movement disorders. This suggests that motor abnormalities may also be related to the risk of developing the disease. Subtle forms are not always detected with the use of the standard observation-based clinical rating scales, which are less sensitive than mechanical instrument measurement. This study compared the presence and severity of dyskinesia and Parkinsonism in 42 non-psychotic siblings of patients with nonaffective psychosis and in 38 controls as measured by mechanical instruments and clinical rating scales. There were no significant differences in movement disorders between siblings and controls on the basis of clinical assessments. However, mechanical measurements indicated that siblings compared to controls displayed significantly more dyskinesia and Parkinsonism signs. These results suggest that motor signs could be markers of vulnerability for psychosis or schizophrenia. In addition this study shows that mechanical instrument measurement of movement disorders is more sensitive than assessment with clinical rating scales. Therefore, it may be used in screening programs for populations at risk for psychosis.