Association scan of the novel psoriasis susceptibility region on chromosome 19: evidence for both susceptible and protective loci

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Abstract
To follow up the novel psoriasis susceptibility region on chromosome 19 (PSORS6), we performed an association scan for psoriasis vulgaris using 45 evenly spaced DNA microsatellite markers. For this study, a new independent sample of 210 nuclear psoriasis families (trio design) from Northern Germany was recruited. We used the family based association test (FBAT) for an association scan over the chromosome 19 region encompassing 50.8 cM. We obtained a positive association for the markers D19S922 (allele 5, P = 0.008) and D19S916 (allele 13, P = 0.016), which correspond to the peak of the region identified in a previously performed scan. We identified two novel regions by a single marker, each showing negative association at D19S917 on 19p13.1 (allele 8, P = 0.0034) and at D19S425 (allele 9, P = 0.0005), compatible with the hypothesis of protective loci. These two novel regions were explored in more detail using novel microsatellite markers at an average distance of 100 kb. A separate analysis distinguishing between familial (n = 137) and sporadic (n = 73) psoriasis families showed that the familial trios contribute strongly in the region around D19S425 (P = 0.004), while the comparably small subset of 73 sporadic trios has a stronger effect at the locus around D19S917 (P = 0.026). These studies confirm the existence of a psoriasis susceptibility locus on chromosome 19 and give first evidence for the existence of both susceptible and protective loci in this region. Analysis of a dense marker set from these refined regions will eventually allow identification of the underlying susceptibility alleles.