Cytogenetic analysis of 477 psoriatics revealed an increased frequency of aberrations involving chromosome region 11q

Psoriasis is an inflammatory skin disorder affecting approximately 3% of th e population. Genetic studies published so far have shown a complex genetic inheritance with heterogeneity and a putative major susceptibility locus i n the HLA region on chromosome 6. We have collected a large amount of mater ial consisting mostly of small nuclear families in order to perform a genom e-nide scan for psoriasis-associated genes. In order to focus the scan prop erly on possible candidate regions, we performed a cytogenetic analysis of 477 unrelated psoriatics. We divided our findings into sporadic, affecting a minor fraction of the cells, and constitutional, ie they were present in all cells examined. We found three cases of balanced translocation, all of which involved chromosome 11q. Two of these had a breakpoint in q12-13, whi lst one involved the telomeric part of chromosome 11q. In order to characte rise further the breakpoint on 11q12-13, we used bacterial artificial chrom osomes (BACs) analysed by fluorescent in situ hybridisation (FISH). We were able to show that the persons had a close, but not identical breakpoints; they were separated by at least 5 cM. The major atopy locus is located in t his region, as well as a locus for insulin-dependent diabetes mellitus, bot h being conditions with a pathogenetic mechanism involving antigen presenta tion.