HLA-B and psoriasis: The PSORS1 risk variant, carried by more than half and about one third of the patients with psoriasis and PsA, respectively, was later identified to be the HLA-C*06:02 (corresponding to the HLA-Cw6 serotype) [30] and other polymorphisms in the major histocompatibility complex (MHC) class I region such as HLA-B*27, -B*38, and -B*39 have repeatedly been noted in PsA but not in psoriasis [9–11,13–17,29].