Fig. 1

PRISMA diagram. ^aThe reference lists from these publications were cross-checked against lists of included references to ensure that all relevant data were identified. Data from SLRs/meta-analyses were not extracted. ^bFour references were data-extracted, but data were either not reported separately for patients with MLD, or no relevant data were reported in the publication. ^cOf the 120 publications from which data were extracted, 108 related to the natural history and burden of illness of MLD (i.e., non-treatment related). MLD: metachromatic leukodystrophy; PRISMA: Preferred Reporting Items for Systematic review and Meta-Analysis; SLR: systematic literature review