Summary
Follistatin is a natural protein that binds and neutralizes myostatin and activin, two signals that limit muscle growth. Mice overexpressing follistatin develop dramatically larger muscles, and a small gene therapy trial in Becker muscular dystrophy reported improved walking distance in some patients.
Structure
The 344-residue precursor isoform of follistatin, which is processed to FS-315 in circulation.
How it works
Follistatin traps members of the TGF-β superfamily, chiefly myostatin (GDF-8) and activin A, preventing them from signalling through activin type II receptors.
Research use cases
Areas where Follistatin-344 has been studied. Inclusion here does not mean it works for that purpose.
- Muscular dystrophy (gene therapy)
- Muscle wasting
- Reproductive biology (activin regulation)
What the research found
Mouse muscle growth
Transgenic mice overexpressing follistatin had muscle mass increases greater than myostatin knockout mice, suggesting it blocks more than myostatin alone.1
Becker muscular dystrophy
In a phase 1/2a trial, intramuscular AAV1 delivery of the FS344 gene improved six-minute walk distance in four of six patients, without serious adverse events.2
Safety and open questions
The gene therapy trial did not report serious adverse events. Research-grade protein is large and difficult to produce reliably; supplier products may not contain active, correctly folded protein.
Regulatory status
Not approved. Studied as gene therapy (AAV-delivered) in muscular dystrophy.
Status was accurate when this page was last reviewed on October 26, 2026. Regulations change; check with the relevant authority before relying on it.
Follistatin-344: common questions
Can follistatin be made as a synthetic peptide?
Not easily. At 344 residues with complex folding and glycosylation, it is a recombinant protein, not a short synthetic peptide. Product quality is a real concern.
Is Follistatin-344 approved for human use?
Not approved. Studied as gene therapy (AAV-delivered) in muscular dystrophy.
References
- Lee SJ, McPherron AC. (2001). Regulation of myostatin activity and muscle growth. Proceedings of the National Academy of Sciences.
- Mendell JR, Sahenk Z, Malik V, et al. (2015). A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy. Molecular Therapy.
Links open a PubMed search for the exact title, or the original source where one is given.