Table 1 Eligibility criteria for inclusion of all sources (full-text articles and conference abstracts)

Studies conducted in humans

Non-interventional (observational) studies (e.g. cohort studies, cross-sectional studies, case series, registries)

Studies that included patients with MLD either as the study population or as a subgroup analysis

Studies that reported on outcomes of interest (PICOTS)

Original research articles published as full text or conference proceedings (i.e. posters, abstracts)

Reviews (systematic or non-systematic) and meta-analyses (for snowballing only)

For studies with multiple publications, only the latest publication on each outcome was retained

Publications written in English, French, Italian, Portuguese or Spanish

Editorials, letters to the editors or opinions

Case reports

Clinical trials (phases 1–3)

Non-clinical and experimental studies

Studies reporting preliminary results (if later published as full text)