Smooth pursuit eye movements (SPEM) have been found to be disturbed in schizophrenic patients and their unaffected relatives raising the hypothesis that SPEM abnormalities may be a genetic marker of vulnerability for schizophrenia. Of particular relevance for this hypothesis is the question of specificity. Psychiatric controls as well as their unaffected family members should show better SPEM performance than schizophrenics and their relatives. Previous results were inconsistent. We conducted a family study to further evaluate the familial specificity of SPEM dysfunction. A sample of 263 subjects (54 schizophrenia spectrum patients, 46 affective psychotics, 43 healthy first-degree relatives of schizophrenics, 36 healthy first-degree relatives of affective psychotics, 84 healthy controls) were examined. Horizontal eye movements were recorded by electro-oculography. Five trials were presented. Pursuit gain was calculated as the ratio of average eye velocity to target velocity.

Both schizophrenia spectrum patients and affective psychotics had lower overall pursuit gain than healthy controls (p < 0.001) whereas the patient groups did not differ from each other (p > 0.5). Comparison of the bipolar and the major depression patients did not reveal differences in eye tracking performance. Both relatives of the schizophrenia spectrum patients and of the affective psychotics showed worse smooth pursuit than healthy controls (p < 0.05). No difference was found between groups of relatives (p > 0.5). It is concluded that SPEM dysfunction is not limited to schizophrenia spectrum families. Pursuit impairment may reflect a genetically based vulnerability for the development of various forms of major psychotic illness.(Supported by DFG grant Bo 710/2).