Smooth pursuit in twins before and after alcohol ingestion.

PURPOSE The influence of genetic factors on characteristics of smooth pursuit were evaluated in young adult monozygotic (MZ) and dizygotic (DZ) twins before and after the administration of a single dose of ethanol. METHODS Sinusoidal pursuit was recorded using a scleral search coil at frequencies of 0.25 and 0.5 Hz before and after alcohol consumption. Pursuit gain, interval between saccades, saccadic accuracy, and saccadic amplitude were quantified. RESULTS Alcohol consumption reduced pursuit gain and saccadic accuracy and increased the rate and amplitude of saccades. Before and after alcohol consumption, the intraclass correlations for MZ twins (rMZ) were highly significant for pursuit gain, interval between saccades, and saccade amplitude. Corresponding correlations for DZ twins (rDZ) were not significant. Heritability values were similar before and after alcohol ingestion. CONCLUSIONS The disparity between rMZ and rDZ suggests either multiple gene interactions or common environmental influences for MZ twins, greater than those for DZ twins.