Deficits in gain of smooth pursuit eye movements in schizophrenia and affective disorder patients and their unaffected relatives.

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Disturbance of smooth pursuit eye movements has been discussed as marking a putative endophenotype closely associated with the genetic basis of schizophrenia. Previous studies are not conclusive in regard to the specificity of this marker. Therefore, oculomotor pursuit was evaluated in unaffected family members of index probands diagnosed as having either schizophrenia or affective disorders. A series of eye tracking tasks were performed by 54 patients with schizophrenia or schizoaffective disorder, 46 patients with an affective disorder, 43 unaffected first-degree relatives of the schizophrenia patients, 36 unaffected first-degree relatives of the affective disorder patients, and 84 healthy comparison subjects. The gain, which relates the velocity of the eye movement to the velocity of the target, was determined to index the intactness of the oculomotor pursuit system. Mean pursuit gain was significantly lower in the schizophrenia and affective disorder patients than in the healthy comparison subjects. Moreover, the relatives of both the schizophrenia and affective disorder patients showed significant gain deficits of about one-half the size of those observed in the patients. Gain deficits are present in psychotic patients and in their unaffected biological relatives. This finding supports a genetic origin of eye tracking disturbances in major psychotic disorders. There is no evidence for diagnostic or familial specificity. The weak sensitivity of the marker suggests that it refers to a nonnecessary genetic factor in schizophrenic and affective disorders.