The genetic transmission of schizophrenia: application of Mendelian latent structure analysis to eye tracking dysfunctions in schizophrenia and affective disorder.

The first-degree relatives of probands with schizophrenia tend to have abnormal smooth pursuit eye tracking, even when the proband's smooth pursuit is normal. In order to account for this finding, we propose that schizophrenia and disturbed eye tracking are independent expressions of an underlying "latent" trait which is genetically transmitted. The data on manic-depressive illness, but not schizophrenia, fit a simpler model in which abnormal smooth pursuit is a consequence of the psychiatric illness, rather than an independent expression of an underlying trait.