FDA gives orphan drug status to Avidity’s rare muscular dystrophy treatment

The US Food and Drug Administration (FDA) has granted Orphan Drug Designation (ODD) to Avidity Biosciences’ AOC 1020 for the potential treatment of facioscapulohumeral muscular dystrophy (FSHD), a rare muscle-weakening condition for which there are no approved treatments for.

The candidate will now benefit from the incentives given to those drugs granted orphan status through the FDA’s ODD programme, introduced by the organisation to improve the availability of treatments for rare diseases.

FSHD is characterised by the life-long, progressive loss of muscle function that typically causes weakness in muscles in the face, shoulders, arms and trunk, before progressing to muscles in the lower body.

Avidity’s AOC 1020 is designed to treat the underlying cause of FSHD, which is caused by the abnormal expression of a gene called double homeobox 4 or DUX4.

A murine version of the candidate has already been shown in preclinical studies to prevent the development of muscle weakness.

Now, AOC 1020 is being evaluated in the phase 1/2 FORTITUDE clinical trial in adults with FSHD, with the company expecting to share preliminary data from around half of the trial’s participants in the first half of 2024.

Commenting on the new designation, Avidity’s chief medical officer, Steve Hughes, said: "We are pleased that the FDA has granted ODD to AOC 1020, reinforcing the importance of finding an effective treatment option for people living with FSHD… We look forward to advancing AOC 1020 and bringing this much-needed therapy to patients."

Avidity's proprietary AOCs are designed to combine the specificity of monoclonal antibodies with the precision of oligonucleotide therapies to target the root cause of diseases previously untreatable with RNA therapeutics.

In addition to AOC 1020, the company has two other distinct rare disease programmes: AOC 1001 for myotonic dystrophy type 1 and AOC 1044 for Duchenne muscular dystrophy mutations amenable to exon 44 skipping.

Avidity announced positive results from its phase 1/2 trial of AOC 1001 in December 2022, which also demonstrated the first ever successful targeted delivery of RNA into muscle.

The trial is currently placed under partial clinical hold on new participant enrolment by the FDA due to a serious adverse event reported in a single participant, though the company says it is working to resolve this “as swiftly as possible”.