Follistatin Gene Therapy FST-344
TL;DR
⚠️ FST-344 is not FDA-approved and has no peer-reviewed human trial in healthy adults. All published human evidence is in two tiny Phase 1/2a trials (N=6 each) in degenerative muscle diseases — Becker muscular dystrophy (BMD) and sporadic inclusion body myositis (sIBM). Every claim of anti-aging, body recomposition, or longevity efficacy in healthy adults is extrapolated from animal data or unpublished industry preprints. FST-344 is not available as an approved therapeutic anywhere in the world.
Critical limitations that must precede any discussion:
- ⚠️ All published trials enrolled males only — safety and efficacy in females are completely unstudied
- ⚠️ Every myostatin inhibitor class has failed in human muscular dystrophy trials — human myostatin is ~10× lower than in mice (PMID 33322031), leaving little pharmacologic room to suppress an already-low signal
- ⚠️ Myostatin inhibition causes fast-glycolytic hypertrophy at the expense of oxidative capacity (PMID 33460149) — the opposite of what’s optimal for aging muscle
- ⚠️ The NCT05806221 trial identifier cited in some sources does not exist — the active combination trial is NCT07285629 (FST-344 + Klotho, age 50–80, recruiting as of 2026)
- ⚠️ Minicircle plasmid results (NCT06411366) are unpublished in peer-reviewed literature — the 1.96 lbs lean mass gain claim comes from a company preprint, not a confirmed clinical result
Established standard of care for muscle preservation: Resistance training (≥3×/week, progressive overload) + adequate protein intake (1.6–2.4 g/kg/day). This remains the evidence-backed anchor regardless of any pharmacologic intervention.
Why it matters for Vitals
FST-344 appears in biohacking and longevity communities as a muscle-growth intervention, including self-experimentation by prominent figures (Bryan Johnson’s “Blueprint”). Vitals users may encounter it via:
- Biohacking podcasts and forums
- Peptide clinic marketing (often offshore)
- Claims of “myostatin inhibition for longevity”
Vitals relevance is currently zero for healthy adults — there is no peer-reviewed evidence, no approved product, and no established safety profile in the target population. The biologically plausible benefits are undermined by:
- Fundamental species translation failure (human myostatin biology differs from rodents)
- Oxidative capacity trade-off (worsens metabolic health in aging)
- Male-only evidence base
- Complete absence of healthy-adult trial data
The only context where human evidence exists (degenerative muscle disease) is fundamentally different from age-related sarcopenia or body recomposition goals.
Key facts
| Item | Detail |
|---|---|
| Composition | Full-length follistatin isoform (FST-344) delivered via AAV1 viral vector or Minicircle non-viral plasmid |
| Target pathway | Myostatin + activin A/B → ActRIIB receptor → Smad2/3 → mTORC1 inhibition |
| Unique differentiator | Also directly activates Smad3/Akt/mTOR/S6K pathway — not just myostatin blockade |
| FDA status | ❌ No approved product (confirmed FDA database, April 2026) |
| Investigational IND | IND 14845 (Nationwide Children’s Hospital) |
| Published human trials | 2 (both Phase 1/2a, N=6 each, males only) |
| Healthy-adult trial | Gap — no peer-reviewed published trial |
| Active trial | NCT07285629 (FST-344 + Klotho, age 50–80, recruiting) |
| Minicircle trial | NCT06411366 (completed Aug 2022, results unpublished) |
Mechanism summary
Primary pathway
FST-344 (gene therapy) → Secreted follistatin protein
↓
Binds myostatin, activin A, activin B (high affinity)
↓
Blocks ActRIIB receptor on skeletal muscle
↓
Removes Smad2/3-mediated inhibition on mTORC1
↓
Net muscle hypertrophy
Dual mechanism advantage (claimed)
Unlike monoclonal antibodies targeting myostatin (bimagrumab), FST-344 also directly activates Smad3/Akt/mTOR/S6K signaling — the same core anabolic pathway engaged by resistance training and amino acids. This is the key mechanistic differentiator cited by proponents.
Evidence grade for dual mechanism: Preclinical only — human mechanistic data absent.
The oxidative capacity trade-off
Myostatin normally promotes slow oxidative fiber identity. Blocking it shifts muscle toward fast glycolytic phenotype. This has been confirmed in multiple preclinical models:
- Kramerova et al. (2020), Journal of Physiology 598:3927-3939, PMID 33460149: In a limb-girdle muscular dystrophy R1 model, follistatin overexpression produced muscle hypertrophy but exacerbated exercise intolerance with reduced oxidative fibers and decreased AMPK activation. The authors concluded: muscle hypertrophy induced by myostatin inhibition leads to loss of oxidative capacity, which further compromises metabolically impaired muscles.
For Vitals users focused on metabolic health, cardiovascular fitness, and healthy aging: this trade-off means FST-344 may worsen the metabolic profile of aging muscle even if it increases lean mass.
Relationship to ActRII/Myostatin Pathway
FST-344 acts on the same ActRII Myostatin Pathway targeted by bimagrumab — both block the ActRIIB receptor. However:
- Bimagrumab is a monoclonal antibody (protein, not gene therapy)
- Bimagrumab has Phase 2 human trial data in obesity (lean mass gain confirmed)
- Bimagrumab’s obesity Phase 3 path is uncertain after 2025 trial termination
- FST-344 has no healthy-adult trial data, different delivery mechanism, and the oxidative capacity trade-off
See ActRII Myostatin Pathway for the full mechanism note.
What the current evidence suggests
Human evidence by indication
Becker Muscular Dystrophy (BMD) — AAV1.CMV.FS344
PMID 25322757 | Phase 1/2a open-label dose-escalation | N=6 males, ages 24–37
- 4/6 patients improved 6-minute walk test (6MWT): +58 m, +125 m, +29 m, +108 m
- 2/6 patients showed no improvement (both had high baseline MRI-detected quadriceps fibrosis)
- Significant shift toward larger mean fiber diameter on histology (e.g., Patient 05: 40.1 µm → 59.3 µm, P<0.0001)
- No gene-transfer-related serious adverse events up to 12 months
- Evidence grade: Confirmed (BMD population, N=6, open-label, no control arm)
⚠️ Critical population caveat: BMD is a dystrophin-deficient state — fundamentally different from age-related sarcopenia. Dystrophic muscle has chronic inflammation, ongoing degeneration, and fibrosis. These patients may be MORE, not less, responsive to follistatin than healthy aging muscle.
Sporadic Inclusion Body Myositis (sIBM) — AAV1.CMV.huFS344
PMID 28279643 | Open-label with matched untreated comparator | N=6 males, median age 65.9
- Annualized median 6MWT: +56.0 m/year (treated) vs −25.8 m/year (untreated controls, N=8, p=0.01)
- 4/6 treated subjects improved 58–153 m; 2/6 showed minimal improvement (5–23 m)
- Methodology critique (Greenberg, PMID 28927986): Trial was unblinded; untreated comparator vs. sham-treated control; exercise regimen was a confounding variable
- Evidence grade: Supported (sIBM population; methodological concerns acknowledged)
⚠️ sIBM is an inflammatory myopathy — pathology involves autoimmune inflammation AND muscle degeneration. FST-344’s mechanism in sIBM may primarily address the degenerative component — a different context than healthy aging.
Minicircle FST344 Plasmid — Healthy Adults
NCT06411366 | Phase 1 open-label single-dose | N=43, ages 22–88 | Completed August 2022
- Reported results (from company preprint only — NOT peer-reviewed):
- Lean mass gain: +1.96 lbs at 90 days (DEXA)
- Body fat: −0.87%
- Visceral fat reduction
- CRP and homocysteine decreases
- Epigenetic age reversal: up to 7 years
- Critical limitations: Unpublished preprint circulated via marketing. No peer-reviewed primary publication. No dose-response data, no control arm description, no statistical methods in public record.
- Evidence grade: Gap (unpublished; claims require independent replication)
Active Combination Trial: FST-344 + Klotho (NCT07285629)
- Adults age 50–80 | Recruiting as of April 2026
- Outcome measures: physical strength, cognitive function, kidney function, body composition, epigenetic age
- Correct trial identifier — NCT05806221 cited in some sources does NOT exist
- Evidence grade: Gap (no published results)
Evidence summary table
| Claim | Evidence Grade | Source |
|---|---|---|
| AAV1-FS344 improved 6MWT in 4/6 BMD patients | Confirmed | PMID 25322757 |
| AAV1-FS344 improved 6MWT in sIBM vs. untreated controls | Supported (contested) | PMID 28279643; PMID 28927986 |
| No gene-transfer SAEs in AAV1-FS344 trials (up to 12 mo) | Confirmed | PMID 25322757, 28279643 |
| Myostatin inhibition reduces oxidative capacity | Confirmed (preclinical) | PMID 33460149 |
| All myostatin inhibitor classes failed in DMD human trials | Confirmed | PMID 33322031 |
| Human myostatin is ~10× lower than mice | Confirmed | PMID 33322031 |
| FST-344 is FDA-approved | Refuted | FDA database (April 2026) |
| FST-344 improves strength in healthy aging adults | Gap | No peer-reviewed human data |
| Minicircle FST-344 anti-frailty outcomes | Gap | Preprint only, unpublished |
| FST-344 safe/effective for female users | Gap | No female subjects studied |
| FST-344 + GLP-1 preserves muscle (human) | Gap | No trial has tested this combination |
| Oral follistatin-315 supplements ≈ FST-344 | Refuted | Different molecule; no oral bioavailability |
| NCT05806221 exists | Refuted | Trial not found; correct is NCT07285629 |
Likely wearable / Vitals relevance
Evidence-backed monitoring (in trial context only)
- DEXA lean mass: Primary body composition endpoint in trials — not a Vitals actionable outside investigator protocols
- 6MWT: Standardized functional capacity test — not wearable-accessible
- Grip strength dynamometry: Objective strength measurement
- Creatine kinase (CK): Muscle turnover/injury monitoring
- CRP: Safety signal for immune response to plasmid
Vitals operational status: Not actionable
FST-344 has no place in Vitals coaching or biometric interpretation protocols until:
- A peer-reviewed Phase 2 trial in healthy adults is published
- An FDA-approved product exists
- Safety profile is characterized in the target population
What this means for the GLP-1 muscle preservation context
The hypothesis that FST-344 could prevent GLP-1–induced muscle loss has never been tested in any animal or human trial. Evidence-based alternatives with actual human data include:
- Trevogrumab + garetosmab + semaglutide (COURAGE trial, Phase 2): GDF8/activin A blockade + GLP-1
- Bimagrumab + semaglutide (BELIEVE trial, Phase 2b): ActRIIB blockade + GLP-1 — Bimagrumab Semaglutide Combo Obesity is the note to watch
- Resistance training + protein 1.6–2.4 g/kg/day — the established standard of care
Vitals should not operationalize any FST-344 monitoring recommendation. Any body composition changes during FST-344 “therapy” should be interpreted as investigational only.
⚠️ Human sign-off required before FST-344 monitoring is embedded in Vitals coaching protocols.
Risks and uncertainty
Fundamental translation problem
Human myostatin levels are ~10× lower than in mice. Pharmacological myostatin inhibition therefore has “little room to further suppress an already-low signal” in humans. Every pharmacologic myostatin inhibitor class — domagrozumab, ACE-031, taldefgrobep — has failed in human muscular dystrophy trials. This establishes a strong class-level prior against efficacy.
Oxidative capacity trade-off
Confirmed in preclinical models: myostatin inhibition produces fast-glycolytic hypertrophy at the expense of oxidative capacity. For aging populations where metabolic health and cardiovascular fitness are primary concerns, this trade-off may worsen, not improve, overall health trajectory.
All trials male-only
No female subjects in any published FST-344 trial. Safety and efficacy in females are completely unstudied.
Durability unknown
Long-term expression beyond 6–12 months in humans is uncharacterized. Non-viral plasmids are episomal and do not integrate — they progressively dilute in dividing cells. In post-mitotic muscle, persistence may be longer, but actual kinetics remain unknown.
Safety profile limitations
- Follow-up only 6–12 months in published trials — delayed adverse events unknown
- No cardiac safety data specifically in FST-344 recipients
- Immunosuppression required for AAV delivery (prednisone used in trials) — immune profile in non-immunosuppressed healthy individuals unknown
- PEI delivery agent in Minicircle plasmid introduces incompletely characterized separate risk
Minicircle safety gap
The PEI (polyethylenimine) ratio is undisclosed and GMP specifications are unpublished for commercial Minicircle products. Products administered in Honduras, Panama, or other offshore jurisdictions operate outside FDA oversight with undefined quality and safety standards.
Comparison with Bimagrumab (the only ActRIIB blocker with human data)
| Dimension | Bimagrumab | FST-344 |
|---|---|---|
| Class | Monoclonal antibody (protein) | Gene therapy (viral or plasmid) |
| Mechanism | ActRIIB blockade | ActRIIB blockade + Smad3/Akt/mTOR activation |
| Human lean mass data | +3.6% at 48 weeks (Phase 2, T2D/obesity) | None in healthy adults |
| FDA status | Not approved; Phase 2 data published | Not approved; no healthy-adult trial data |
| Oxidative capacity | Not reported as impaired | Impaired in preclinical models |
| Female subjects | Not female-specifically studied | No female subjects in any trial |
| GLP-1 combo trial | BELIEVE trial (Phase 2b, published) | No human combo trial exists |
| Evidence grade | Supported (Phase 2) | Gap (healthy adults) |
Bottom line: Bimagrumab is the evidence-backed pharmacologic option for ActRIIB/myostatin pathway engagement in humans. FST-344 is investigational with a weaker evidence profile.
Related notes
Mechanism
- ActRII Myostatin Pathway — the shared myostatin/activin pathway; bimagrumab mechanism; FST-344 and bimagrumab both target this axis
- mTOR AMPK Muscle Catabolism — complementary catabolic pathway; both ultimately suppress mTORC1
GLP-1 muscle preservation
- GLP-1 Muscle Preservation — the hub note for GLP-1–induced muscle loss; FST-344 has zero human evidence in this context
- Bimagrumab Semaglutide Combo Obesity — the only pharmacologic with human ActRIIB + GLP-1 combo data
Standard of care
- Resistance Training for Longevity — the established, evidence-backed anchor for muscle preservation
Peptides MOC
- Peptides MOC — FST-344 gene therapy listed here for completeness; investigational status must be prominent
Vitals Knowledge Map
- Vitals Knowledge Map — this note is indexed under Substances / Investigational / Muscle
Sources: PMID 25322757 · PMID 28279643 · PMID 28927986 · PMID 28939086 · PMID 33322031 · PMID 33460149 · NCT06411366 · NCT07285629 · NCT07443826 · FDA database (April 2026)