The etiology of MS is complex and largely unknown and influenced by genetic and environmental factors.1,2 One of the major environmental risk factors is exposure to tobacco smoke, where daily smokers have an estimated odds ratio (OR) of 1.5 for the risk of developing MS compared to non-smokers.3 This risk is being further increased (OR ~ 14) in carriers of the major MS risk variants (HLA-DRB1*15:01+/HLA-A*02−), that is, three times more than risk of haplotype-matched non-smokers.4,5 Notably, exposure to cigarette smoke has also been associated with MS disease progression and severity.1 This evidence concerns the gene HLA-DRB1 and myeloid sarcoma.