The closely linked <i>HLA-DPA1</i> and <i>HLA-DPB1</i> genes were associated with OP-MG subjects (gene-based <i>p</i> < 0.05) and the frequency of a functional A > G SNP (rs9277534) in the <i>HLA-DPB1</i> 3'UTR, which increases <i>HLA-DPB1</i> expression, differed between the two groups (<i>G</i>-allele 0.30 in OP-MG vs. 0.60 in control MG; <i>p</i> = 0.04).