Eye Tracking Dysfunction is Associated With Partial Trisomy of Chromosome 5 and Schizophrenia: A Response

To the Editor.—  In their letter that appeared in the December 1988 issue of the Archives, Iacono et al¹ presented interesting data showing the co-occurrence of schizophrenia and eye movement dysfunctions (EMDs) in a proband and his schizophrenic maternal uncle, both of whom also had a partial trisomy of chromosome 5. Iacono et al interpret these data as supporting the latent trait hypothesis, and we agree. We have, however, some reservations and concerns.Iacono et al give the impression that one-to-one co-occurrence of EMDs and schizophrenia is predicted by the latent trait model. If readers will examine Fig 2 of our article that appeared in the July 1988 issue of the Archives,² which we reprint here (Figure) and in which we present a validation of the model using offspring of discordant twins, they will see that in this representative family EMDs and schizophrenia did not occur jointly in