HLA-C and psoriasis: Hence, the haplotype analysis determined a 369-kb critical region for the PSORS1. However, due to the strong linkage disequilibrium within this region, association evidences observed at the HLA-Cw6 and CDSN*TTC alleles as well as other 5 marker alleles are not independent from each other, and the haplotype-based analysis can not discriminate which alleles is the primary cause of association with psoriasis observed within the PSORS1 locus.