Follistatin 344

Why scientists study it

• It is one of the two main natural forms of follistatin, and it binds and shuts off myostatin (GDF-8) and activin, two TGF-beta family signals that limit muscle size.
• Scientists delivered its gene with an AAV1 virus in mice and monkeys, and those animals gained muscle mass and strength. Pigs bred to carry the gene also gained muscle.
• One early human gene therapy trial (phase 1/2a) in people with a muscular dystrophy is finished, and animal work on the same pathway continues for muscle wasting and cachexia.

Three studies to know

Lee & McPherron, 2001 · Proceedings of the National Academy of Sciences

Mice bred to make extra follistatin overcame the limit myostatin puts on growth and gained a large amount of muscle. This well-known paper made follistatin a tool for studying the myostatin pathway. Read the paper

Kota et al., 2009 · Science Translational Medicine

Kota and colleagues gave cynomolgus macaques the Follistatin 344 gene by AAV1 virus. The monkeys gained muscle mass and strength, which gave large-animal data before any human study. Read the paper

Mendell et al., 2015 · Molecular Therapy

Mendell and colleagues ran the first published human study, a phase 1/2a gene therapy trial in adults with Becker muscular dystrophy. It looked at how safe the AAV1 treatment was and how well people tolerated it. Read the paper

Safety and legal status

• As of 2026 it is not approved by the FDA, the EMA or the MHRA for any medical use in people. It is still an experimental research compound.
• The World Anti-Doping Agency names follistatin as a banned myostatin blocker (class S4.3). Most of the research uses gene delivery, so it also falls under WADA’s ban on gene and cell doping (class M3).
• For laboratory research use only. It is not for human use.