Relative risk of neurological signs in siblings of patients with schizophrenia

Objective: First-degree relatives of patients with schizophrenia appear to have subtle neurological signs, suggesting that these measures could serve as intermediate phenotypes in genetic studies of schizophrenia. The strength of a possible genetic component is unknown, however, leaving it uncertain whether such traits could increase the power to find schizophrenia susceptibility loci. The authors' goal was to investigate the strength of this possible genetic component. Method: They estimated the relative risk of neurological impairments in a large group of siblings of patients with schizophrenia. Two standard neurological scales (the Neurological Evaluation Scale and the Woods Scale) were used to examine 115 patients, 185 of their siblings, and 88 normal comparison subjects. Results: There were significant differences between the siblings of patients with schizophrenia and the normal comparison subjects only on the Woods Scale. Relative risk of neurological impairment was significantly increased in the sibling group, but the significance was weak to moderate. Neurological impairment was not redundant with several other intermediate phenotypic measures based on cognitive impairment. Conclusions: These data suggest that neurological signs cluster in patients with schizophrenia and their families and could possibly identify a unique component of genetic variance for risk of schizophrenia. However, the fairly low relative risk and the uncertain pathophysiology of such signs may limit their usefulness.