Familial Aggregation Of Eye-Tracking Endophenotypes In Families Of Schizophrenic Patients

Background: Abnormal smooth pursuit eye movements (SPEMs) are some of the most reproducible biological changes associated with the susceptibility for schizophrenia. Recent studies have suggested that deficit in predictive pursuit, a specific component of the SPEMs, marks schizophrenia susceptibility.Objective: To test whether predictive pursuit contains less extraneous noise and may be under more direct genetic control than the traditional measure of overall pursuit performance using maintenance pursuit gain.Design: Familial aggregation estimation of the predictive pursuit measure and the traditional maintenance pursuit measure in sibling pairs from families of schizophrenic patients.Setting: Outpatient clinics.Participants: Patients with schizophrenia and their full siblings were recruited, provided that at least 1 sibling pair could be formed per family. Ninety-two siblings were recruited into the study. They formed 70 sibling pairs. Ninety healthy control subjects were also recruited using targeted local community advertisements based on patients' county of residence, aiming to capture the basic demographics of the regions from which the patients were recruited.Main Outcome Measures: Familial correlations and heritability estimates of 2 SPEM measures: maintenance pursuit gain and predictive pursuit gain.Results: The sibling intraclass correlation coefficient of the predictive pursuit gain (r=0.45-0.48) was significantly higher than that of maintenance pursuit gain (r=0.02-0.20) (P=.005-.007). Variance component analysis suggested a high genetic loading for predictive pursuit (heritability=0.90, SE= 0.22; P <. 001) but relatively low heritability in the traditional maintenance pursuit measure (heritability=0.27, SE= 0.21; P=. 08).Conclusion: These results suggest that predictive pursuit may index stronger genetic effect and may be better suited for genetic studies than the traditional SPEM measure of maintenance pursuit gain.