Neurobiological deficits that serve as informative endophenotype markers have been demonstrated in schizophrenia by a number of different paradigms. Neurophysiological deficits are prominent in P50 event related suppression, prepulse inhibition (PPI) of the startle response, and the antisaccade (AS) task for eye movement dysfunction. Neurocognitive deficits in schizophrenia are revealed by poor performance on the CPT, verbal memory, and tests of working memory. Each of these deficits has also been demonstrated in clinically unaffected relatives of schizophrenia patients, which is evidence that they may reflect part of the heritable risk for the illness. This conclusion is reinforced by findings of deficits in non-psychotic, unmedicated schizophrenia patients, and schizotypal patients. The null hypothesis is that all 6 deficits reflect a single, common underlying heritable dysfunction in all schizophrenia patients. A test of that hypothesis requires measurement of all of these deficits in the same group of schizophrenia patient probands and their relatives. If they are all manifestations of the same genetic dysfunction (although perhaps expressed in different brain areas), then a multivariate analysis would show that they all contribute to a single dimension in both relatives and schizophrenia patients. An alternative hypothesis is that only one or a small subset of deficits is present in each family, which is consistent with the heterogeneity found in current genetic linkage studies. In that case, the multivariate analysis would show the different measures or subsets of them loading onto different dimensions. Schizophrenia itself is likely to be the result of multiple deficits in any individual. Therefore, the analysis is performed in the same cohort of schizophrenia patient probands and their relatives to take advantage of Mendel's second law, which holds that genetically independent deficits segregate independently. Hence, although schizophrenia patient probands themselves have multiple deficits, if the deficits are caused by different genetic factors, then they will segregate to different groups of relatives. This 7 site collaborative RO1 project will gather a combined total of 420 pedigrees (1680 subjects) and 525 normal subjects over 5 years (each site will contribute 1/7th of these totals). Findings of heritable deficits in specific measures will be used to guide the next generation of studies of the genetics of schizophrenia.
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