What is Trofinetide?
Trofinetide (brand name DAYBUE, formerly NNZ-2566) is a synthetic analogue of the N-terminal tripeptide of insulin-like growth factor-1 (IGF-1). It is structurally based on glycine-proline-glutamate (GPE, or glypromate), a natural cleavage product of IGF-1, with a methyl substitution on the proline residue to improve oral bioavailability and metabolic stability.
It became the first therapy of any kind approved for Rett syndrome when the FDA granted approval on March 10, 2023 for use in patients aged 2 years and older.
Mechanism of Action
The exact mechanism by which trofinetide produces clinical benefit in Rett syndrome remains incompletely characterized, but preclinical work suggests several converging effects:
- Microglial modulation — restores normal microglial morphology and reduces neuroinflammatory cytokine release
- Synaptic maturation — promotes dendritic spine formation and functional excitatory/inhibitory balance
- IGF-1-like trophic signaling — though trofinetide does not bind the IGF-1 receptor directly, downstream effects overlap with IGF-1 pathways implicated in Rett pathobiology
- Reduced astrogliosis — normalizes GFAP expression in MeCP2-deficient mouse models
Rett syndrome is caused by loss-of-function mutations in the X-linked MECP2 gene. Trofinetide does not correct the underlying genetic defect; rather, it appears to address the downstream synaptic and inflammatory consequences.
Clinical Evidence — LAVENDER Trial
The pivotal LAVENDER Phase 3 trial (NCT04181723, published Nature Medicine 2023) randomized 187 girls and women (ages 5–20) with classic Rett syndrome to oral trofinetide twice daily or placebo for 12 weeks.
Primary endpoints (both significant vs placebo):
- Rett Syndrome Behaviour Questionnaire (RSBQ) — caregiver-rated behavioral and motor symptoms
- Clinical Global Impression-Improvement (CGI-I) — physician-rated overall improvement
The most common adverse events were diarrhea (82% vs 20% placebo) and vomiting (29% vs 12%), leading to discontinuation in approximately 17% of trofinetide-treated patients.
Place in Therapy
Trofinetide is administered as an oral solution twice daily, dosed by weight (typically 5 g to 12 g per dose). It is not curative but produces clinically meaningful improvement in core Rett behaviors — communication, hand stereotypies, mood, and breathing abnormalities — across age groups previously without any approved therapy.
Relationship to Other IGF-1 Peptides
Trofinetide should not be confused with the various IGF-1 analogues tracked in research peptide circles:
- IGF-1 LR3 (Long R3 IGF-1) — a 70-amino-acid full-length IGF-1 analogue
- MGF (IGF-1Ec) — a splice variant of IGF-1 expressed after muscle damage
- Trofinetide — a 3-residue (tripeptide) N-terminal cleavage product analogue of IGF-1
These are structurally and pharmacologically distinct, and trofinetide does not act through the IGF-1 receptor.
Sponsor and Development History
Originally developed by Neuren Pharmaceuticals (Australia) for traumatic brain injury and fragile X syndrome, trofinetide was licensed to Acadia Pharmaceuticals in 2018 specifically for Rett syndrome. Acadia retains North American rights; Neuren retains rights in the rest of the world.