Claimed effect · Follistatin 344

Does Follistatin 344 help with muscle function in Becker muscular dystrophy?

D
Grade D — no human evidence1 open-label phase 1/2a (n=6) · effect size: small
Short answerNo human evidence. As of 10 September 2026, only 1 open-label phase 1/2a (n=6) exists for Follistatin 344 for muscle function in Becker muscular dystrophy. A follistatin gene delivered by AAV into the quadriceps of six patients: four walked further on the six-minute test, two did not change, with no control group. Encouraging as proof of principle; not evidence for the injected protein, and not evidence in healthy people.

What the studies show

A follistatin gene delivered by AAV into the quadriceps of six patients: four walked further on the six-minute test, two did not change, with no control group. Encouraging as proof of principle; not evidence for the injected protein, and not evidence in healthy people.

“AAV1.CMV.FS344 was delivered to six BMD patients by direct bilateral intramuscular quadriceps injections.”

Verbatim, from the abstractMendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy. Mol Ther, 2015

Animal studies, cell studies, or anecdotes only. This is where almost every viral peptide sits. Promising and proven are different words for a reason.

  1. 1
    Mendell JR, Sahenk Z, Malik V, et al. A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy.Mol Ther, 2015Six patients; AAV1.CMV.FS344 injected into the quadriceps; no control group.

In context

Follistatin is a natural protein that binds and blocks myostatin, the signal that limits muscle growth; animals engineered to overexpress it become dramatically muscular. 'Follistatin 344' is the full-length form, sold as a lyophilised injectable for muscle. No human trial has ever tested injecting it. The only clinical data is a 2015 gene-therapy study in six men with Becker muscular dystrophy, in which a virus carrying the follistatin gene was injected into the thigh muscles — some walked further, some did not, and it is not the product being sold. It is prohibited in sport.

Follistatin 344 is not approved; research reagent. Legal status differs by country — see the regulation section or the jurisdiction pages.

Questions

Is Follistatin 344 proven to help with muscle function in Becker muscular dystrophy?
No. There is no human evidence for it (1 open-label phase 1/2a (n=6)); the claim rests on animal or cell studies and LYO grades it D.
What studies are behind the grade?
A follistatin gene delivered by AAV into the quadriceps of six patients: four walked further on the six-minute test, two did not change, with no control group. Encouraging as proof of principle; not evidence for the injected protein, and not evidence in healthy people.
Is Follistatin 344 approved for this?
No. Follistatin 344 is not approved; research reagent; it is not an approved medicine for any indication in the jurisdictions LYO covers.

Other outcomes for Follistatin 344

Written and maintained by LYO Research — how pages are written and checked. Reviewed 10 September 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →