On the contrary, significant differences were noted when each of the two subsets was compared with population controls, namely a strong positive association of HLA-C*06 with psoriasis with the presence of PsA (OR = 3.94, Pcor < 0.0001) and a slightly weaker association with psoriasis alone (OR = 3.72, Pcor < 0.0001). This evidence concerns the gene HLA-C and psoriasis.