The SNP with the highest associated MS risk, HLA-DRB1*15:01 tag SNP rs9271069 (OR = 2.77), had a significantly higher frequency in Orkney controls (RAF = 0.23) and Shetland controls (RAF = 0.21) than mainland Scotland controls (RAF = 0.17: respective p values of 8 × 10–13 and 2.3 × 10–6). Here, HLA-DRB1 is linked to myeloid sarcoma.