Amondys 45 and Vyondys 53 do not meet main goal in Duchenne muscular dystrophy trial

7 November 2025

A clinical trial testing two exon-skipping drugs for Duchenne muscular dystrophy (DMD) did not show a clear benefit in helping people with DMD walk better.

DMD is caused by changes in a gene that stop the body from making dystrophin, a protein that protects muscles. Without dystrophin, muscles weaken over time.

The gene for dystrophin is like a set of instructions made up of pieces called exons. If some exons are missing, the instructions don’t make sense. Exon-skipping treatments aim to “skip” over certain exons so the instructions fit together again, making a shorter but still working version of dystrophin.

The ESSENCE trial tested two potential treatments:

• Amondys 45 (casimersen) – skips exon 45
• Vyondys 53 (golodirsen) – skips exon 53

Results showed patients on these treatments tended to walk a little faster than those receiving the placebo (dummy drug). However, the difference wasn’t big enough to prove the drugs were working. Scientists call this “not statistically significant,” meaning the change could have happened by chance.

The company behind the treatments, Sarepta, said disruptions caused by the COVID-19 pandemic may have affected the trial results. These treatments already have conditional (accelerated) approval from the U.S. Food and Drug Administration (FDA). This means they were approved but needed to confirm benefits through this trial. The FDA may withdraw a product if a study fails to confirm it is beneficial.

Sarepta plans to seek full approval in the U.S. using these results and data from people taking the drugs outside of clinical trials. We are not aware of any plans to seek approval in the UK at this time.