HLA-C and psoriasis: The human leukocyte antigen (HLA) region on chromosome 6p21 is well known to carry the most important genetic factors in the susceptibility to psoriasis, whereas the critical segment appears to be a 300-kb interval at the centromeric end of HLA class I, named PSORS1 (Nair et al. 2000; Martinez-Borra et al. 2003).