Follistatin-344
Evidence: A/E — Established Human EvidenceRepair / Tissue Healing
Evidence Snapshot
What this grade covers
A/B for molecular identity and the AAV1.CMV.FS344 gene-therapy clinical program; E for any unverified commercial "Follistatin-344" injectable vial's efficacy or safety, since that is a distinct, unstudied product category from the AAV gene-therapy construct.
Regulatory Context
No FDA-approved recombinant Follistatin-344 injectable product was identified. AAV1.CMV.FS344 gene therapy is investigational only.
Research Takeaway
Follistatin-344 (FS344) is an alternatively spliced follistatin precursor isoform; after cellular processing, the longer circulating protein is commonly described as FS315. FS344 and FS315 are distinct forms and must not be conflated.
Evidence boundary: This is an identity statement based on the molecular biology literature, not an efficacy or safety claim.
See all 5 evidence claims →Quick Summary
Follistatin-344 (FS344) is an alternatively spliced follistatin precursor isoform. Its clinical evidence comes from AAV-mediated gene therapy (AAV1.CMV.FS344) in small trials for Becker muscular dystrophy and sporadic inclusion body myositis -- an approach that drives sustained endogenous follistatin expression, not an injected recombinant protein. A commercial vendor vial labeled "Follistatin-344" is not automatically equivalent to this gene-therapy construct, to the processed FS315 circulating isoform, to FS288, to generic follistatin, to myostatin, or to ACE-031.
Mechanism & Research Overview
Follistatin broadly antagonizes activin, myostatin, and growth/differentiation factor 11 (GDF-11) -- a pleiotropic, non-selective mechanism rather than myostatin-selective inhibition. The FS344 gene-therapy program uses an AAV1 vector to deliver the FS344-coding sequence intramuscularly, producing sustained local and circulating follistatin expression; the longer circulating protein produced after cellular processing is commonly referred to as FS315.
Evidence Claims
Individual scientific statements drawn from the sources cited below, each shown with the specific evidence boundary that statement does not establish.
Supported
Follistatin-344 (FS344) is an alternatively spliced follistatin precursor isoform; after cellular processing, the longer circulating protein is commonly described as FS315. FS344 and FS315 are distinct forms and must not be conflated.
Does not establish
Evidence boundary: This is an identity statement based on the molecular biology literature, not an efficacy or safety claim.
Sources: Follistatin Gene Therapy Improves Ambulation in Becker Muscular Dystrophy
Supported
AAV1.CMV.FS344 gene therapy produced pharmacodynamic and functional-outcome signals (including improved ambulation) in small early-phase trials for Becker muscular dystrophy and sporadic inclusion body myositis.
Does not establish
Evidence boundary: These are small, early-phase gene-therapy trial outcomes and describe a gene-therapy vector, not an injected recombinant Follistatin-344 protein; they must not be presented as evidence for a commercial injectable vial.
Sources: A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy; Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes
Supported
Follistatin broadly and non-selectively antagonizes activin, myostatin, and GDF-11, which is a pleiotropic mechanism with reproductive, endocrine, and tumor-biology relevance.
Does not establish
Evidence boundary: Broad-mechanism antagonism is a preclinical/mechanistic finding, not a demonstration of net clinical benefit or a quantified safety profile in any population.
Sources: Differential antagonism of activin, myostatin and growth and differentiation factor 11 by wild-type and mutant follistatin; Follistatin is a novel therapeutic target and biomarker in FLT3/ITD acute myeloid leukemia
Supported
No FDA-approved recombinant Follistatin-344 injectable product was identified; the AAV1.CMV.FS344 gene therapy is an investigational clinical-trial program, and neither its evidence nor its regulatory status extends to unverified commercial injectable vials.
Does not establish
Evidence boundary: Absence of an approved injectable product does not, by itself, characterize the quality or safety of any specific vendor vial; it establishes only that no such approval exists.
Supported
Follistatin-344 must not be conflated with ACE-031, a separate broad ActRIIB ligand trap that also antagonizes myostatin and related TGF-beta-family ligands but is a structurally distinct receptor-fusion protein rather than a follistatin isoform.
Does not establish
Evidence boundary: This is an identity-separation statement between two compounds in the same activin/myostatin-pathway family, not a claim of comparative efficacy or safety.
Safety & Evidence Limitations
Considerations reported in the sources cited on this page — not a complete list of every possible risk, and not medical advice.
Safety Consideration
Clinical outcomes from the AAV1.CMV.FS344 gene-therapy trials must not be presented as safety or efficacy evidence for a commercial injectable "Follistatin-344" vendor product.Safety Consideration
These are distinct molecular entities; evidence for one must not be transferred to another.Safety Consideration
Activin signaling has roles in reproduction, endocrine function, and has been implicated in some cancer biology (e.g. FST317/FST344 in FLT3/ITD AML models); this is mechanistic/preclinical safety context, not a quantified human risk.Safety Consideration
No FDA-approved recombinant Follistatin-344 injectable product was identified.Safety Consideration
Only dosing explicitly reported in the cited gene-therapy trials may appear as Study/Trial Dosing; no reconstitution, cycling, or injection protocol is supported.
Research Areas Being Studied
Research areas discussed on this page reflect the Repair / Tissue Healing category and the sources cited below.
Findings Reported in Studies
Educational summary only — reported in cited studies, not a claim of proven benefit.
No Human Study Findings Listed Yet
See preclinical, regulatory, and review sources below.
Study Tables by Evidence Type
No Sources Listed Yet
Human, preclinical, regulatory, and review sources will appear here as they are added.
Anecdotal Reported Patterns — Not Medical Advice
Anecdotal Reported Patterns — Not Medical Advice
Reported dosing patterns are included for educational context only. They are self-reported, unverified, not medical advice, and not instructions for human use. Community-submitted patterns are not yet available in this Phase 1 prototype; this section is a placeholder reserved for moderated, aggregated community data.
Lab Markers to Discuss With a Clinician
Educational topics only — not self-monitoring instructions.
FAQ
Disclaimer
Educational information only. This page summarizes published research and does not provide medical advice, a recommendation, or instructions for human use.
Educational use only. This content is provided for informational and research-summary purposes only. It is not medical advice, not a treatment recommendation, not a dosing guide, and not a substitute for care from a licensed medical professional. Nothing here is intended to diagnose, treat, cure, prevent, or mitigate disease. Reported dosing patterns, when shown elsewhere on the site, must be labeled either as Study / Trial Dosing or Anecdotal Reported Patterns — Not Medical Advice. Community reports are self-reported, unverified, and not scientific proof.
Community-reported experiences, once enabled, must be displayed only as moderated, anonymized, or aggregated data. They are anecdotal, self-reported, unverified, and should never be presented as proof of safety, efficacy, or expected results.
Content status: Content pending review. Last updated .
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