HLA-DRB1 and systemic sclerosis: In addition to associations with ATA + SSc discussed above, significantly increased frequencies of the class II alleles HLA-DQA1*01:01, DQB1*05:01, and DRB1*01:01 were seen with ACA + relative to ACA − disease, confirming published findings from smaller studies comparing patient subgroups across multiple ethnicities (Kuwana et al., 1995; Fanning et al., 1998; Simeon et al., 2009).