IFNB1 and progressive multifocal leukoencephalopathy: IFN-β: interferon-beta; DMT: disease-modifying therapy; AMP: adenosine monophosphate; RRMS: relapsing-remitting multiple sclerosis; SPMS: secondary progressive multiple sclerosis; CIS: clinically isolated syndrome; JC: John Cunningham; PML: progressive multifocal leukoencephalopathy; Nrf-2: nuclear factor (erythroid-derived 2)-like 2