HLA-DRB1 and systemic sclerosis: While conditioning on 13 independent C4A exclusive eQTL SNPs had a similar effect on the residual association profile, conditioning on 12 C4B exclusive eQTL SNPs had a smaller effect with residual association (P < 5 × 10−8) to SSc in three regions centered on HLA-DPB1, HLA-DRB1, and HLA-B (Supplementary Fig. 4B, C), which suggests a stronger contribution of C4A to SSc.