Previous studies comparing PsA and PsC have suggested that HLA-C∗06:02 shows increased PsC risk but decreased PsA risk,13,14 and our study replicated this finding in a concordant directional effect (p = 9.4 × 10−6 for PsA versus PsC individuals). However, the differential impact of HLA-C∗06:02 on PsA and PsC risk disappeared after we conditioned on HLA-B amino acid position 45 (p = 0.12), suggesting that this reduced effect was the result of linkage to HLA-B. In contrast, the effect of HLA-B amino acid position 45 with respect to PsA versus PsC risk retained significance even after we conditioned on HLA-C∗06:02 (pomnibus = 2.2 × 10−7).