Follistatin-344

It is like reading that surgeons fitted an experimental "brake-removal kit" to a handful of specific cars with real results, then buying an unlabelled bottle online that claims to do the same thing if you pour it in the fuel tank. The underlying engineering is sound (myostatin really is a brake on muscle), but the human proof exists only for the surgical version in those few cars, not for the bottle you can buy.

Follistatin binds and sequesters myostatin (GDF-8) and activin A with high affinity, preventing them from engaging the ActRIIB receptor complex. This blocks the downstream SMAD2/3 signalling cascade that normally restrains skeletal-muscle protein synthesis and satellite-cell proliferation, effectively releasing a negative brake on muscle growth. The FS-315 isoform (from the FS344 transcript) is the soluble, circulating form with weak heparin-binding, versus the cell-surface-anchored FS-288. In preclinical models, muscle hypertrophy has been achieved largely through gene transfer or transgenic/knockout manipulation of myostatin signalling rather than through injected follistatin protein.

Research contexts. Not proven uses, and not recommendations.

Genuinely thin and easily overstated. The only meaningful human evidence is a small, open-label, uncontrolled early-phase gene-therapy programme led by Mendell and colleagues at Nationwide Children's Hospital, delivering the follistatin gene (AAV1.CMV.FS344) by direct intramuscular injection into the quadriceps of six Becker muscular dystrophy patients (the trial also enrolled sporadic inclusion body myositis patients), with a parallel Duchenne cohort. Several patients showed improved six-minute walk distance and histological signs of better muscle regeneration and less fibrosis, but responses were variable and some showed no improvement. This was uncontrolled, tiny and disease-specific. There are essentially no controlled human trials of injected follistatin protein for building muscle in healthy people; the popular muscle-growth claims rest on animal data. Some follistatin gene-therapy efficacy claims, particularly in inclusion body myositis, were later publicly disputed.

• !The injectable 'Follistatin-344 peptide' sold online is an unlicensed research chemical with no human efficacy or safety data for muscle building. It is not the validated gene-therapy product.
• !Marketing routinely conflates a small disease-specific gene-therapy trial with the grey-market peptide. They are biologically and practically different interventions.
• !Myostatin/activin inhibition is not muscle-selective. Activin and TGF-beta signalling affect reproduction, fibrosis, the ovarian/pituitary axis and tumour biology, so chronic systemic suppression carries theoretical risks that are unstudied in healthy humans.
• !Some published follistatin gene-therapy efficacy claims were subsequently challenged in the literature, so even the disease-specific human data should be read cautiously.
• !Grey-market products carry no guarantee of identity, purity, sterility, correct protein folding or biological activity. Injected proteins also carry immunogenicity and infection risks.
• !Often sold 'for research use only / not for human consumption' to sidestep medicines regulation.
• !Muscle growth in preclinical models was largely achieved by gene transfer or genetic knockout, which does not translate to a self-administered injectable protein.

Not a licensed medicine in the UK. There is no MHRA marketing authorisation for follistatin in any form. The AAV follistatin construct exists only as an investigational gene therapy in early-stage trials (conducted in the US) and is not an approved product anywhere. The injectable "Follistatin-344" peptide is an unlicensed substance typically sold as a "research chemical / not for human consumption", a label intended to keep it outside medicines law on paper. In practice, marketing or supplying it for human use would engage the Human Medicines Regulations 2012 and could attract MHRA enforcement. It is not a controlled drug under the Misuse of Drugs Act, but it cannot lawfully be marketed for human use.

• NCT01519349· Phase 1/2a· Completed

  Follistatin Gene Transfer to Patients With Becker Muscular Dystrophy and Sporadic Inclusion Body Myositis

  rAAV1.CMV.huFollistatin344 intramuscular delivery (Mendell/Nationwide Children's); six BMD patients, some with improved six-minute walk distance. Open-label, uncontrolled.

• NCT02354781· Phase 1/2· Completed

  Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 in Duchenne Muscular Dystrophy

  Parallel follistatin gene-therapy cohort in DMD patients.

1. 01
   A Phase 1/2a Follistatin Gene Therapy Trial for Becker Muscular Dystrophy — Mendell JR, Sahenk Z, Al-Zaidy S, et al., Molecular Therapy (2015)

   Landmark first-in-human follistatin (AAV1.CMV.FS344) intramuscular gene therapy; variable functional and histological improvement in six BMD patients.

2. 02
   Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy — Al-Zaidy SA, Sahenk Z, Rodino-Klapac LR, Kaspar B, Mendell JR, Journal of Neuromuscular Diseases (2015)

   Follow-up reporting six-minute walk distance gains in the BMD cohort.

3. 03
   Regulation of myostatin activity and muscle growth — Lee SJ, McPherron AC, PNAS (2001)

   Foundational preclinical evidence: follistatin overexpression in transgenic mice produced dramatic muscle hypertrophy, exceeding the myostatin-knockout phenotype.

4. 04
   Clinical Intramuscular Gene Transfer of rAAV1.CMV.huFollistatin344 to Patients With Duchenne Muscular Dystrophy, ClinicalTrials.gov (2015)

   Trial protocol record for the parallel Duchenne cohort, NCT02354781.