HLA-C∗06:02 has the strongest association with PsV risk, as reported previously.7–12,17,18 We demonstrated that no single HLA-C amino acid polymorphism was more strongly associated than the HLA-C∗06:02 classical allele, suggesting that the haplotype sequence including HLA-C∗06:02 itself should be the origin of PsV risk. Several hypotheses might explain this. Clop et al. reported noncoding regulatory variants that are located in enhancer motifs and that are unique to the HLA-C∗06:02 haplotype.34 A combination of the polymorphisms in multiple HLA-C amino acid sites could effectively tag HLA-C∗06:02.35 We did observe a more modest independent effect at HLA-C∗12:03 in addition to the large HLA-C∗06:02 effect; Helms et al. reported that HLA-C∗06:02 and HLA-C∗12:03 share several functional domains and peptide-binding pockets of HLA-C.5 We note that HLA-C∗12:03 did not show an independent association signal after we conditioned on HLA-C∗06:02 and every classical HLA-B allele (p = 0.12), suggesting the possibility that the observed HLA-C∗12:03 association might reflect risk at other HLA-B alleles in LD. Further functional studies will be necessary for elucidating the role of HLA-C in PsV risk.