Within this subgroup of samples, HLA-C*06:02 is significantly associated with a protective effect on PsA (p=4.17×10−15, OR 0.52, 95% CI 0.44 to 0.61); however, when conditioning on age of psoriasis onset, there was no evidence of association between HLA-C*06:02 and PsA (p=0.07), suggesting the previously observed protective effect was the result of confounding due to the different age of psoriasis onset in the disease subgroup strata. This evidence concerns the gene HLA-C and psoriasis.