The broad armamentarium of available DMT comprises, on the one hand, highly efficient drugs such as natalizumab, fingolimod, and alemtuzumab, which bear substantial risk of progressive multifocal leukoencephalopathy (PML) or secondary autoimmunity and, on the other, moderately efficient options with favorable long-term safety profiles such as interferon beta, glatiramer acetate, dimethyl fumarate, and teriflunomide. The gene discussed is IFNB1; the disease is progressive multifocal leukoencephalopathy.