Schizophrenia is substantially heritable, but specific susceptibility genes remain to be identified. Progress in this endeavor has been hindered by non-Mendelian transmission patterns, probable genetic heterogeneity, and an inability to detect premorbid and nonpenetrant carriers of predisposing genes. To circumvent these complexities, this study employed quantitative measures of liability, or "endophenotypes," within a sample of twins discordant for schizophrenia, drawn from the relatively genetically isolated population of Finland. A region on the distal portion of chromosome 1 has shown evidence for linkage to schizophrenia in two prior studies using Finnish patient samples. To elucidate further the nature and location of this potential susceptibility gene, linkage and association analyses were carried out across the chromosome 1 region of interest using quantitative neuropsychological measures of liability. Analyses with a composite measure of liability yielded suggestive evidence for linkage at marker D1S2833 (P = 0.04). Follow-up analyses of the individual trait measures showed that the Visual Span subtest of the Wechsler Memory Scale (WMS), an indicator of spatial working memory function, was uniquely sensitive to marker D1S2833 (P = 0.007). Association analysis confirmed that allelic variation in D1S2833 is associated with variation in spatial working memory performance as measured by the Visual Span subtest (P = 0.003), the significance of which was confirmed in an analysis of 10,000 Monte Carlo permutations. These data support the utility of this approach and provide evidence for a gene affecting spatial working memory function in schizophrenia patients and their unaffected co-twins.
Copyright 2002 Wiley-Liss, Inc.