Del-desiran for myotonic dystrophy type 1

Last updated Aug. 11, 2025, by Andrea Lobo, PhD
Fact-checked by José Lopes, PhD

What is del-desiran for myotonic dystrophy?

Del-desiran, previously known as AOC 1001, is a small interfering RNA (siRNA)-based therapy being developed to treat people with myotonic dystrophy type 1 (DM1).

Available as an intravenous, or into the vein, infusion, del-desiran works to target and reduce the levels of abnormally long messenger RNA (mRNA), an intermediary molecule needed for protein production. The longer mRNA, which is caused by mutations in the DMPK gene, forms toxic clumps and causes cellular dysfunction, particularly in muscle cells, thereby driving the disease’s symptoms. To help gain access to muscle cells, the siRNA molecule is fused with an antibody that binds to the transferrin 1 receptor in muscle cells.

Del-desiran is being developed by Avidity Biosciences, and is expected to ease symptoms and slow down disease progression.

Therapy snapshot

How will del-desiran be administered?

Del-desiran is administered by intravenous infusion. In clinical trials enrolling people with DM1, the therapy has most recently been given at a dose of 4 mg/kg once every three months, and will be given and tested once every eight weeks (about two months).

Del-desiran in clinical trials

Del-desiran was investigated in the Phase 1/2 trial MARINA trial (NCT05027269) that tested it against a placebo in 38 adults with DM1.

• Results demonstrated the treatment had a favorable safety profile, was successfully delivered to muscle cells, and reduced levels of mRNA DMPK, which means it addressed the underlying cause of the condition. Treatment also eased myotonia, which is when muscles are unable to relax after a contraction. Participants were followed for about six months.
• Patients who completed the trial could join the open-label extension MARINA-OLE study (NCT05479981). At one year, treatment with 4 mg/kg of del-desiran once every three months continued to be safe and effective, reducing myotonia, and improving muscle strength and activities of daily living (such as taking a shower, climbing stairs, or visiting family or friends). Results suggested a reversal of DM1 disease progression relative to a natural history study of myotonic dystrophy.

A global Phase 3 clinical trial called HARBOR (NCT06411288) is testing del-desiran’s safety, tolerability, and efficacy in more than 150 DM1 patients, ages 16-65. The treatment is being compared to a placebo and given every eight weeks for a total of seven doses, for approximately 12.5 months. Myotonia, muscle strength, and activities of daily living will be assessed. All participants will have the option to join a subsequent open-label extension study.

Del-desiran side effects

The most common side effects of del-desiran seen in clinical trials included:

• procedural pain
• anemia (lacking enough healthy red blood cells or hemoglobin to carry oxygen to the body’s tissues)
• headache
• pain in the extremities
• nausea
• COVID-19.

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