Exondys 51 (eteplirsen) is an injectable solution developed by Sarepta Therapeutics, indicated for the treatment of Duchenne muscular dystrophy (DMD) in patients who have a confirmed mutation of the DMD gene that is amenable to exon 51 skipping. Exondys 51 is the first approved treatment designed to target the underlying cause of Duchenne muscular dystrophy (DMD) approved by the FDA.

DMD is a genetic disorder estimated to affect one in 3,500-5,000 males born worldwide. It is a severe type of muscular dystrophy caused by mutation of the dystrophin protein in the muscles, which acts as a protective layer.

The dystrophin gene is the largest occurring in nature, containing 79 exons. Research carried out in DMD patients found a common cause for mutation was due to deletion of exon 51 during the dystrophin protein’s creation. This occurred in 13% of males.

Exondys 51 is an antisense oligonucleotide produced using Sarepta’s phosphorodiamidate morpholin oligomer (PMO) technology. The drug binds to exon 51 of dystrophin gene to enable exclusion of the exon during expression of the dystrophin gene. Skipping of the exon 51 enables the truncated production of the dystrophin protein. As a result, a shorter dystrophin protein is produced, which slows the progression of DMD in patients.

Exondys 51 can potentially lessen the severe muscle weakness and atrophy caused by this mutation.

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