Changes in the composition and function of commensal microbes can trigger inflammation and abnormal immune activation, contributing to disorders such as multiple sclerosis (MS), neuromyelitis optica spectrum disorder (NMOSD), myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), autoimmune encephalitis (AIE), neuropsychiatric lupus (NPSLE), and narcolepsy. The gene discussed is OMG; the disease is multiple sclerosis.