Systemic deletion of DMD exon 51 rescues clinically severe Duchenne muscular dystrophy in a pig model lacking DMD exon 52.

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease caused by mutations in the DMD gene, leading to complete absence of dystrophin and progressive degeneration of skeletal musculature and myocardium. In DMD patients and in a corresponding pig model with a deletion of DMD exon 52 ( DMD Δ52), expression of an internally shortened dystrophin can be achieved by skipping of DMD exon 51 to reframe the transcript. To predict the best possible outcome of this strategy, we generated DMD Δ51-52 pigs, additionally representing a model for Becker muscular dystrophy (BMD). DMD Δ51-52 skeletal muscle and myocardium samples stained positive for dystrophin and did not show the characteristic dystrophic alterations observed in DMD Δ52 pigs. Western blot analysis confirmed the presence of dystrophin in the skeletal muscle and myocardium of DMD Δ51-52 pigs and its absence in DMD Δ52 pigs. The proteome profile of skeletal muscle, which showed a large number of abundance alterations in DMD Δ52 vs. wild-type (WT) samples, was normalized in DMD Δ51-52 samples. Cardiac function at age 3.5 mo was significantly reduced in DMD Δ52 pigs (mean left ventricular ejection fraction 58.8% vs. 70.3% in WT) but completely rescued in DMD Δ51-52 pigs (72.3%), in line with normalization of the myocardial proteome profile. Our findings indicate that ubiquitous deletion of DMD exon 51 in DMD Δ52 pigs largely rescues the rapidly progressing, severe muscular dystrophy and the reduced cardiac function of this model. Long-term follow-up studies of DMD Δ51-52 pigs will show if they develop symptoms of the milder BMD.