Host genetics strongly influence gut microbiome composition, highlighted by twin studies where the gut microbiome of monozygotic twins showed more similarity than dizygotic twins’ microbiome.9,53,54 The importance of host genes on the microbiome was further validated by large genome-wide association studies (mGWAS), which cataloged the association between host gene variants and the gut microbiome.55,56 Among all the genetic factors linked with MS, major histocompatibility complex (MHC) or HLA genes show the strongest association with MS susceptibility. The gene discussed is HLA-C; the disease is myeloid sarcoma.