Eye movement dysfunction in schizophrenia: A heritable characteristic for enhancing phenotype definition

The occurrence of ocular motor dysfunction in schizophrenia patients and th eir first-degree biological relatives is remarkably consistent, suggesting that abnormal smooth pursuit and saccadic oculomotion are heritable charact eristics that can be used to identify gene carriers for schizophrenia. Sacc adic system dysfunction probably reflects a generalized deficit in prefront at cortical functioning, rather than a specific deficit in saccade system f unctioning. Although abnormal smooth pursuit has also been associated with impaired frontal functioning, it is unclear whether these two types of dysf unction arise from the same neural pathology. Therefore, deviant smooth pur suit and saccadic oculomotian may constitute unrelated factors identifying two different types of genetic risk. Alternatively, they may derive from a single risk factor that causes (a) both types of deficits to be expressed t ogether or (b) each type to be expressed separately as pleiotropic manifest ations of the underlying genotype. Although a full complement of pursuit an d saccade measures has not been examined together in family studies of schi zophrenia, there is obvious value in determining how these measures relate to one another in schizophrenia families and whether they can be used in co mbination to enhance phenotype definition to facilitate the search for schi zophrenia susceptibility genes. (C) 2000 Wiley-Liss. inc.