Genome-wide linkage scan, fine mapping, and haplotype analysis in a large, inbred, Arab Israeli pedigree suggest a schizophrenia susceptibility locus on chromosome 20p13.

Linkage and association studies in schizophrenia have repeatedly drawn attention to several chromosomal regions and to genes within them. Conflicting patterns of association and the lack of a clear functional significance of the associated variants limit the interpretation of these results. The use of rare pedigrees, where genes with a major effect cause the disorder, has been proven beneficial in studies of other complex disorders. Our objective was to use this advantage by performing a genome wide linkage analysis for schizophrenia in a large, multiplex Israeli Arab pedigree. We genotyped 346 microsatellite markers in 24 pedigree members affected with schizophrenia spectrum disorders and 32 unaffected relatives. Two-point linkage analysis with SUPERLINK demonstrated a LOD score of 2.47 for D20S116 on chromosome 20p13 under an autosomal dominant mode of inheritance. Further fine mapping yielded a two-point LOD score of 2.56 for the adjacent marker D20S193 and narrowed down the linked region to 2-5 cM. A haplotype containing the markers D20S193, D20S889, and D20S116, 0.7 Mb in length, was found to be shared by most affected pedigree members. Genotyping of 43 SNPs in the interval supported these results with a multipoint LOD score of 2.7 around D20S193. We were also able to better define the boundaries of the shared haplotype which contains strong candidate genes for schizophrenia. Our study exemplifies the power of rare and unique pedigrees in drawing attention to novel regions for genetic studies of schizophrenia.