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An earlier study of smooth-pursuit eye movements (SPEMs) in monozygotic (MZ) and dizygotic (DZ) twins discordant for functional psychosis reported high concordance of pursuit abnormalities in MZ pairs and moderate concordance in DZ pairs. That study was repeated with younger pairs of twins and with some quantitative refinements in scoring. Results show the same levels of concordance for pursuit dysfunctions, thus replicating the earlier study. The data support an interpretation of genetic factors contributing to variability in SPEMs.
Philip S. Holzman (Sun,) studied this question.