HLA-DRB1 and dermatomyositis: Analyses of amino acid positions within HLA-DRB1 indicated that the strongest association was at position 37 (omnibus P = 3.3 × 10−19), with suggestive evidence this association was independent of position 74 (omnibus P = 5.1 × 10−5), the position most strongly associated with adult-onset DM.