FIGURE S1 Median age at LOA by genotype from IPD from DMD patients who had lost ambulation— overall and corticosteroid-treated. Abbreviations: DMD, Duchenne muscular dystrophy; IPD, individual patient data; LOA, loss of ambulation; SCR, stop-codon readthrough. Patients from the study by Goemans et al (2017) had been treated previously with drisapersen (n = 3)⁴⁸. One patient from the study by Kulshreshtha et al (2019) had been treated previously with ataluren (n = 1)⁴⁴.

FIGURE S2 Estimates of mean percent predicted 6MWT over time by genotype, age, and use of other disease-modifying treatments. Abbreviations: 6MWD, 6-minute walk distance; SCR, stop-codon readthrough. References and baseline ambulatory status: Bushby et al (2014), 6MWD ≥75 m⁵⁶; Goemans et al (2011), ambulatory⁵⁸; Goemans et al (2018), 6MWD ≥75 m⁵⁷; McDonald et al (2013), 6MWD ≥75 m²⁷; McDonald et al (2017), 6MWD ≥150 m²⁵; McDonald et al (2018), 6MWD ≥75 m⁶⁰; Mercuri et al (2016), ambulatory²⁶; Pane et al (2014), could walk ≥100 m¹¹; Vill et al (2015), 6MWD >200 m⁶³; and Voit et al (2014), 6MWD ≥75 m.⁶⁴

TABLE S1 Search strategy

TABLE S2 Population, Exposure, Comparator, Outcomes, Study design (PECOS) criteria

*Except for mortality, only data for measures reported in at least one study or with more than 50 patients are presented. Extracted data for all outcomes are available from the researchers upon request.

TABLE S3 Pathogenic variants in the DMD gene included in the systematic review analyses and corresponding exon skipping or stop-codon readthrough amenability

TABLE S4 Characteristics of 54 studies included in the manuscript

Abbreviations: 6MWT, 6-minute walk test; AHF, acute heart failure; CINRG, Cooperative International Neuromuscular Research Group; DB, database; DMD, Duchenne muscular dystrophy; FSIQ, full-scale intelligence quotient; FVC, forced vital capacity; HMV, home mechanical ventilation; LOA, loss of ambulation; LVEF, left ventricular ejection fraction; MD, muscular dystrophy; NMRC, Neuromuscular Reference Centre; NR, not reported; NTR, Netherlands National Trial Register; STRIDE NMD, Strategic Targeting of Registries and International Database for Excellence—neuromuscular disorders; TREAT-NMD, Translational Research in Europe—Assessment & Treatment of Neuromuscular Diseases; UDP, United Dystrophinopathy Project; UMD, Universal Mutation Database; y, year.

*Total number of DMD patients from study; the number included varies by number of classifiable genotypes and by number reported for each outcome.

**35 (natural history); 523 (UMD/DMD-Cochin DB).

TABLE S5 Quality assessment of the 54 studies included in the article

Note: Observational studies were assessed using STrengthening the Reporting of Observational studies in Epidemiology (STROBE) statement,²⁰ Case studies assessed using the CARE (CAse REport) statement and checklist,²¹ randomized clinical trials assessed using the Revised Cochrane Risk of Bias Tool for Randomized Trials (RoB 2),²² and nonrandomized clinical studies assessed using the Methodological Index for Non-Randomized Studies (MINORS).²³