Vitamin D deficiency has already been associated with risk of MS and controls the expression of HLA-DRB1*1501, the key genetic risk factor in MS.[10], [16] However, it is likely that MS prevalence will be explained only by considering a complex interplay of genetic and environmental risk factors, some of which may not yet have been identified [8]. The gene discussed is HLA-DRB1; the disease is myeloid sarcoma.