Fine mapping of a psoriasis-susceptibility locus within the HLA class II region by using microsatellite markers in an association study of Japanese cases and controls.

BACKGROUND The association between psoriasis and the HLA antigens encoded by the Major Histocompatibility Complex (MHC) genomic region is well known, but the role of the HLA class II region in susceptibility to psoriasis is unclear. OBJECTIVE The purpose of this study is to map the psoriasis-susceptibility locus within the HLA class II region. METHODS Three hundred seventy five unrelated Japanese patients with psoriasis vulgaris and 375 unrelated Japanese healthy controls were studied by an association analysis using 15 polymorphic microsatellite markers. RESULTS Statistically significant differences were found at three microsatellite loci. The most significant association of psoriasis vulgaris with the microsatellite markers was found with DRA_CA (pc=0.0000135), the second with DQCARII (pc=0.0000840) and the third with G5_11525 (pc=0.0240). These significant microsatellite markers are in close vicinity to the DQA2, DQB1, DRB1, DRA and BTNL2 genes. CONCLUSION The results suggest that there are psoriasis susceptibility genes located within the HLA class II region and therefore strongly support previous findings of a positive association between psoriasis and certain alleles of the DQB1 and DRB1 genes.