Follistatin-344

What it is

“Follistatin” is doing too much work online. Follistatin-344, FS344, or FST-344 is the 344-amino-acid precursor used as a transgene in the cited programs; processing produces circulating FS315. It is not FS288, FS317, generic follistatin, or every product carrying the class name.

AAV gene transfer encoding huFollistatin344, plasmid gene transfer encoding Follistatin-344, and administration of a recombinant protein are materially different interventions. Vector, promoter, manufacturing, tissue expression, duration, formulation, and route must remain attached to the evidence.

Why people care

Follistatin can bind activin-family ligands and inhibit myostatin signaling, which drives muscle-growth and longevity claims. Human gene-transfer studies and strong animal phenotypes attract attention, but they are often blurred across FS344, processed FS315, AAV vectors, plasmids, recombinant proteins, patient populations, and healthy-use claims.

What humans actually show

Follistatin-344 is a follistatin precursor and transgene identity, not one interchangeable finished product. The identified administered-human evidence consists of very small open-label AAV gene-transfer studies in neuromuscular disease, not injections of an FS344 protein. FDA's orphan record says the cited AAV-delivered follistatin is not approved for its orphan indication, and a completed plasmid registry has no posted results.

• other human — Six men with Becker muscular dystrophy in an open-label gene-transfer study; Route: Bilateral quadriceps rAAV1.CMV.FS344 gene transfer; Outcome: Six-minute walk performance and safety observations: Four participants improved on six-minute walk testing and two did not; the paper reported no treatment-attributed adverse effects. The seam: Six participants and no randomized comparator; Participants received peri-procedural prednisone; The intervention was muscle-targeted AAV gene transfer, not FS344 protein administration; The result does not establish benefit in healthy people; The sample cannot characterize a complete safety profile.
• other human — Six men with sporadic inclusion-body myositis in an open-label gene-transfer study; Route: rAAV1.CMV.huFollistatin344 gene transfer with a prescribed exercise program and peri-procedural prednisone; Outcome: Annualized six-minute walk change versus a nonconcurrent clinic comparator: The investigators reported improved walk distance in treated participants compared with a nonconcurrent clinic group matched for age, sex, and baseline walking performance. The seam: Open-label and nonrandomized; Six treated participants; Exercise and prednisone were cointerventions; Comparator participants were matched on selected variables but were nonconcurrent and not randomized; The study cannot isolate FS344 effect or establish healthy-population benefit.
• other human — Three boys with Duchenne muscular dystrophy in a completed gene-transfer study; Route: rAAV1.CMV.huFollistatin344 gene transfer; Outcome: Dose-limiting toxicity, six-minute walk, and North Star Ambulatory Assessment registry outcomes: The registry reports no dose-limiting toxicities, no participants with increased six-minute walk distance at two years, and one participant with an improved North Star score. Planned biopsy assessments were canceled because of disease progression. The seam: Three participants; Registry results rather than a peer-reviewed randomized comparison; No participant improved the reported long-term walk outcome; Canceled biopsies limited planned biologic assessment; Tiny samples cannot establish broad safety.
• other human — Forty-three healthy adults in a completed open-label phase 1 study in Honduras; Route: Follistatin-344 plasmid gene therapy; Outcome: Safety, serum follistatin, body composition, and exploratory aging measures: ClinicalTrials.gov lists completion and actual enrollment but has no posted results. The seam: No posted results means no efficacy or safety conclusion can be assigned; Open-label design; Registry marks the study as not FDA regulated; Plasmid gene therapy is not AAV gene transfer or an FS344 protein product; Completion does not establish approval.

Mechanistic and nonhuman evidence

• mechanistic — Cell-based ligand-binding systems and mouse myostatin models; Route: Experimental follistatin expression or exposure; Outcome: Myostatin binding or signaling and skeletal-muscle mass: The original work reported that follistatin inhibited myostatin activity and that experimental overexpression increased muscle mass in mice. The seam: Cell and mouse findings are not human clinical outcomes; Follistatin interacts with activin-family ligands beyond myostatin; Mechanism does not establish a safe exposure or product; Animal phenotype does not establish human efficacy.
• animal — Nonhuman primates in an AAV1-FS344 gene-transfer study; Route: Muscle-targeted AAV1-FS344 gene transfer; Outcome: Muscle size and strength: The paper reported increased muscle size and strength in the studied animals. The seam: Nonhuman-primate outcomes cannot establish human benefit; The intervention was AAV gene transfer, not protein administration; Small preclinical samples cannot establish long-term human safety; Vector and expression context are product-specific.
• mechanistic — Seventeen products labeled as follistatin in an analytical laboratory study; Route: Laboratory content and structural analysis; no human administration; Outcome: Presence and structural characteristics of labeled follistatin: The study found substantial label-content and structural discrepancies among tested materials. The seam: Analytical findings are not clinical outcomes; The study does not characterize every product; No vendor or purchasing conclusion is supported; The result supports identity caution rather than efficacy.

FDA and U.S. status

FDA's orphan-drug record for an AAV-delivered follistatin transgene in inclusion-body myositis states that it is not FDA approved for the orphan indication. An exact openFDA active-ingredient query for FOLLISTATIN returned no match. ClinicalTrials.gov lists small completed AAV gene-transfer studies and a completed Honduras plasmid study that is marked not FDA regulated and has no posted results. No FDA-approved Follistatin-344 prescribing information was identified; the exact database no-match is not used alone.

Risks and warning limits

• human trial: The Becker muscular dystrophy paper reported no treatment-attributed adverse effects among six participants, and the Duchenne registry reported no dose-limiting toxicities among three participants.
• not characterized: These very small gene-transfer studies cannot characterize uncommon, long-term, immune, reproductive, endocrine, vector-related, tumor, or off-target risks.
• not characterized: No FDA-approved Follistatin-344 prescribing information was identified, so this draft assigns no FDA-labeled contraindications, warnings, or adverse-reaction frequencies.
• theoretical: Because follistatin binds activin-family ligands as well as myostatin, endocrine and reproductive effects are mechanistically plausible but are not adequately characterized by the tiny human studies.

What remains unknown

• The results of the 43-participant Follistatin-344 plasmid study remain unknown because the registry has no posted results.
• Whether any FS344 intervention improves a patient-important outcome in an adequately randomized and controlled trial remains unestablished.
• Long-term vector, immune, reproductive, endocrine, tumor, and off-target risks remain inadequately characterized.
• No bridge was identified that transfers AAV or plasmid gene-transfer findings to an administered recombinant FS344 protein.
• The identity and quality of any material outside a controlled research program cannot be inferred from an FST-344 or follistatin label.

Product identity and quality limits

• FS344 is a precursor and transgene identity; processed FS315 and alternate FST isoforms are not interchangeable labels.
• AAV gene transfer, plasmid gene transfer, and recombinant-protein administration are materially different interventions whose evidence cannot be pooled without a bridge.
• An analytical survey found substantial content and structural discrepancies among tested products labeled as follistatin, so a label alone cannot establish the studied identity.
• A name or certificate does not establish sequence, vector genome, promoter, expression, concentration, purity, sterility, aggregation state, stability, or clinical equivalence.

What has been studied together

• rAAV1.CMV.FS344 gene transfer with prednisone — coadministration studied: The Becker muscular dystrophy and inclusion-body-myositis studies used peri-procedural prednisone. These small uncontrolled designs do not isolate a pharmacologic interaction or establish general combination safety.
• rAAV1.CMV.huFollistatin344 gene transfer with exercise — coadministration studied: The inclusion-body-myositis study paired gene transfer with a prescribed exercise program. The cointervention complicates outcome attribution and does not establish a product stack.
• Follistatin-344 with other peptides, anabolic agents, or hormone-related products — no direct evidence: No adequate direct human interaction program was identified for an FS344 protein or gene-transfer product with these categories. Missing evidence does not establish compatibility.

What people are hearing

These are claims this profile checks, not established conclusions.

• Claim under review: “Human AAV-FS344 studies prove the effects of an injected Follistatin-344 protein or plasmid product.”
• Claim under review: “A completed healthy-adult plasmid study proves safety, effectiveness, or FDA acceptance.”
• Claim under review: “An FST-344 or follistatin label establishes the studied molecule and product quality.”

Questions readers raise

• No reproducible community sample was collected for this profile.

The community-signal layer is not efficacy or safety evidence. Its current limits are:

• No reproducible community sample has been collected for this profile.
• Self-reports would be subject to selection and reporting bias.
• The exact identity, vector, or protein product described in a self-report could not be verified.
• Concurrent medicines, exercise, health conditions, diet, and behavior could confound an anecdote.
• Reported outcomes could not be independently verified.
• Anecdotes cannot establish efficacy, safety, approval, product identity, or interaction compatibility.

What would change this answer

• Posted results from the plasmid study would change the present no-results boundary for that exact non-FDA-regulated study but would not automatically transfer to an AAV or protein product.
• An adequately randomized controlled human trial with exact intervention identity and patient-important outcomes could change the current small open-label gene-transfer evidence boundary.
• An FDA approval action and final prescribing information would change the unapproved status and establish product-specific identity, indication, warnings, and interactions.
• Direct comparative pharmacology and clinical evidence could establish whether findings bridge between AAV, plasmid, and recombinant-protein interventions; none was identified.

Sources and records

• WADA — 2026 Prohibited List

• FST follistatin gene record — National Center for Biotechnology Information
• Drugs@FDA API exact active-ingredient search for follistatin — U.S. Food and Drug Administration
• Orphan Drug Designations and Approvals: AAV-delivered follistatin transgene for inclusion-body myositis — U.S. Food and Drug Administration
• rAAV1.CMV.huFollistatin344 gene transfer in Becker muscular dystrophy and sporadic inclusion-body myositis — ClinicalTrials.gov
• rAAV1.CMV.huFollistatin344 gene transfer in Duchenne muscular dystrophy — ClinicalTrials.gov
• Follistatin-344 plasmid gene therapy in healthy adults — ClinicalTrials.gov
• A phase 1/2a follistatin gene therapy trial for Becker muscular dystrophy — PubMed
• Follistatin gene therapy for sporadic inclusion body myositis improves functional outcomes — PubMed
• Regulation of muscle growth by multiple ligands signaling through activin type II receptors — PubMed
• Follistatin gene delivery enhances muscle growth and strength in nonhuman primates — PubMed Central
• Detection of black market follistatin 344 — PubMed