Follistatin-344

Last Updated: July 2026

Follistatin-344 (FS-344) is a specific isoform of follistatin — a single-chain glycoprotein encoded by the FST gene that binds and neutralizes members of the TGF-β superfamily, most notably myostatin and activin A. It is a more specific entry alongside the general Follistatin profile: FS-344 is the 344-amino-acid precursor form used in most injectable and gene-therapy research, processed in the body toward the freely circulating FS-315 isoform. It is not approved and is supplied for research use only.

What is Follistatin-344 and how does it differ from other follistatin isoforms?

The FST gene produces several splice variants — FS-288 (tissue-bound, gonad-concentrated), FS-315 (circulating, muscle-targeting), and the FS-344 precursor that is processed toward FS-315 — and FS-344 is favored in research because it generates the bioactive circulating form once introduced into a biological system. Its 27-residue C-terminal extension affects tissue retention relative to the shorter FS-315.

How does Follistatin-344 build muscle?

By binding myostatin (and activin A) with high (picomolar) affinity, FS-344 prevents them from activating ActRIIB and the downstream SMAD2/3 cascade that normally suppresses muscle protein synthesis — releasing the brake and permitting hypertrophy and satellite-cell-driven growth. Because it also suppresses activin, it can affect pituitary FSH signaling — a reproductive-endocrine consideration.

What does the research on Follistatin-344 show?

The strongest human evidence is a gene-therapy trial (AAV1-FS344) in Becker muscular dystrophy and inclusion body myositis, reporting increased muscle volume and strength over ~2 years without serious adverse events; preclinical data in mice, primates, and dogs consistently show large (2–3×) muscle-mass increases. Human data for injectable follistatin peptide (as opposed to the gene therapy) is minimal. Evidence level: Gene-therapy human trial + strong preclinical; injectable-peptide human data minimal.

What are the safety concerns and regulatory status?

Follistatin-344 is not approved, its long-term human safety as an injectable is not established, and it is prohibited in sport (WADA); activin suppression also carries reproductive-endocrine implications. See the legal status guide.

Why does vendor verification matter, and how does Peptigrity verify?

Follistatin is an expensive recombinant protein, so implausibly cheap "follistatin-344" is a red flag, and counterfeits (including His-tagged constructs) are common — HPLC purity and mass-spec identity are the objective checks. Peptigrity buys it anonymously, tests it at independent ISO-accredited labs, and publishes the unedited COA; the trust score weights lab purity and reviews equally (50/50). See the COA red-flags guide.

Educational information only; not medical advice. Follistatin-344 is not approved for human use. Consult a qualified healthcare provider. Peptigrity does not sell, endorse, or recommend products or vendors.