Duchenne muscular dystrophy has a severe disease course, though variability exists. Case reports suggest a milder disease course of patients amenable to exon 44 skipping. In this study, we analyzed this and show that age at wheelchair dependence in patients with a dystrophin deletion requiring exon 44 skipping is postponed compared to patients with a deletion skippable by exon 45, 51 and 53 (10.8 versus 9.8 years; P 0.020). This may be explained by more frequent spontaneous exon 44 skipping in patients with a deletion flanking exon 44. This finding has important implications for the development of future Duchenne trials.