Increase in Full-Length Dystrophin by Exon Skipping in Duchenne Muscular Dystrophy Patients with Single Exon Duplications: An Open-label Study

Abstract

Single exon duplications account for disease in a minority of Duchenne muscular dystrophy patients. Exon skipping in these patients has the potential to be highly therapeutic through restoration of full-length dystrophin expression. We conducted a 48-week open label study of casimersen and golodirsen in 3 subjects with an exon 45 or 53 duplication. Two subjects (aged 18 and 23 years) were non-ambulatory at baseline. Upper limb, pulmonary, and cardiac function appeared stable in the 2 subjects in whom they could be evaluated. Dystrophin expression increased from 0.94 % ±0.59% (mean±SD) of normal to 5.1% ±2.9% by western blot. Percent dystrophin positive fibers also rose from 14% ±17% at baseline to 50% ±42% . Our results provide initial evidence that the use of exon-skipping drugs may increase dystrophin levels in patients with single-exon duplications.

Keywords: Muscular dystrophy; antisense; clinical trial; duchenne; dystrophin; oligonucleotides.

Fig.1

Exon skipping and dystrophin expression. A–C. The PROMIS score, FVC, and ejection fraction remained stable over the duration of the study. D. There was an increase in full-length DMD transcripts (relative to total DMD transcripts) in subjects 1 and 3. Deletion transcripts (i.e. skipping both copies of the target exon) were only observed at very low frequencies. E-F. Dystrophin expression increased in all subjects, as did PDPF. G. Representative western blots from each sample are shown as a composite. A 0.25% –8% standard curve prepared from healthy control tissue was included on each blot. H. Representative regions of interest stained for dystrophin are shown, along with dystrophin positivity analysis. Scale bar = 100μm. 48w, 48 weeks; BL, baseline; FVC, forced vital capacity; PDPF, percent dystrophin positive fibers.