Follistatin-344 is the 344-amino-acid precursor form of human follistatin, a natural glycoprotein that binds myostatin and activins. Nearly all published research delivers it as a gene (AAV vector) rather than as a peptide, in mice, monkeys and one small human trial.
Follistatin is established as a binding protein that neutralizes myostatin and activins, members of the TGF-beta family that limit muscle growth [1]. In mice, reducing the body's own follistatin produced smaller muscles, and the effect persisted partly without myostatin, supporting a role for activin A as well [1]. FS344 is processed in the body to the shorter FS315 form; gene-delivery studies inject an AAV vector so muscle cells make the protein locally [2][3].
| Study | Model | Reported result | Source |
|---|---|---|---|
| Primate gene-delivery study [2] | Other animal Six cynomolgus macaques given AAV1-FS344 into the quadriceps (two promoter groups) vs untreated controls, up to 15 months | Quadriceps circumference up ~10-15%; fiber diameter 87.7 vs 65.5 µm (CMV group vs controls); no organ, immune or reproductive-hormone changes reported | Peer-reviewed Sci Transl Med 2009 |
| Phase 1/2a gene-delivery trial [3] | Human 6 adults with a dystrophin gene variant, open-label, two ascending-level cohorts of 3, AAV1.CMV.FS344 into quadriceps | Primary endpoint: 6-minute walk distance. Published | Peer-reviewed Mol Ther 2015 |
| Follistatin knockout study [1] | Mouse Mice with one copy of the follistatin gene removed, including on a myostatin-null background; cardiotoxin muscle model | Smaller muscles, shift toward oxidative fibers, lower tetanic force; effect partly retained without myostatin | Peer-reviewed Mol Endocrinol 2010 |
| AAV1-follistatin in TIC-DUX4 mice [4] | Mouse TIC-DUX4 transgenic mouse model given AAV1-follistatin into leg muscles | Researchers reported larger muscle size and higher strength measures | Peer-reviewed JCI Insight 2018 |
Human trials are listed for research context only; outcomes are reported in the linked publications. Animal and lab results do not establish effects in humans.
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