Loss of ambulation in SMA III at the time of disease-modifying treatments: an international study

Treatment in type III reduced the risk of ambulation loss by 50%, extending median ambulation by 12 years, with the greatest benefit in type IIIA. Later onset, female sex and higher SMN2 copy number were also protective but did not modify treatment effect. These findings underscore the value of early treatment and support its broad use to preserve ambulation across clinical subgroups.