It is likely that different areas of the brain have varying remyelination capacities, and that some areas of the brain might retain the ability to remyelinate even at advanced ages, particularly cortical grey matter regions.27,28 Recent work has compared lesion biopsies from people with ‘normal’-onset MS (mean age at biopsy 29) to late-onset MS (mean age 69); this found that older patients have fewer ramified oligodendrocytes, suggesting a lower level of active remyelination.30 Similarly, BCAS1+ newly generated oligodendrocytes were more abundant in lesions from the younger patients. This evidence concerns the gene BCAS1 and myeloid sarcoma.