Vosoritide
BMN 111, modified recombinant human C-type natriuretic peptide, CNP analogue BMN-111
Vosoritide is a 39-amino-acid analogue of C-type natriuretic peptide, engineered to resist the enzyme that normally destroys the natural hormone within minutes. It is the first medicine designed to act on the underlying signalling defect in achondroplasia, working directly against the overactive FGFR3 receptor at the growth plate. It increases growth velocity in children with achondroplasia, though whether it changes adult height or health outcomes is not yet known.
Mechanism
Achondroplasia is caused in almost all cases by a single recurrent gain-of-function mutation, G380R, in fibroblast growth factor receptor 3 (FGFR3). FGFR3 is a negative regulator of endochondral bone growth: in the growth plate it restrains chondrocyte proliferation and differentiation through the RAS-RAF-MEK-ERK mitogen-activated protein kinase cascade. The mutation makes the receptor constitutively active, so that brake is permanently applied, the proliferative and hypertrophic zones of the growth plate are compressed, and the long bones and skull base grow disproportionately little.
C-type natriuretic peptide is the physiological counterweight. It binds natriuretic peptide receptor B (NPR-B, encoded by NPR2), a single-pass transmembrane receptor whose intracellular domain is a guanylyl cyclase. Activation generates cyclic GMP, which activates protein kinase G type II, and PKG-II phosphorylates and inhibits RAF-1. That inhibition sits downstream of FGFR3 itself, which is the elegant part: vosoritide does not need to block the mutant receptor, it simply interrupts the pathway below it, damping the excessive MAPK output and restoring chondrocyte proliferation, differentiation and extracellular matrix production. The genetic evidence supports this precisely. Loss-of-function NPR2 mutations cause acromesomelic dysplasia with severe short stature, while gain-of-function NPR2 variants cause tall stature. Native CNP is cleaved within about two minutes by neutral endopeptidase (neprilysin), making it useless as a drug. Vosoritide adds proline and glycine to the N-terminus of the 37 C-terminal residues of human CNP-53, which blocks the neprilysin cleavage site and extends the half-life to around 28 minutes while retaining the disulfide-closed ring needed for NPR-B binding. Because NPR-B and the related natriuretic peptide receptors also mediate vasodilation, the same mechanism explains the transient blood pressure reduction and reflex tachycardia seen after dosing.
What the research shows
The pivotal phase 3 trial randomised 121 children aged 5 to under 18 years with achondroplasia to daily subcutaneous vosoritide or placebo across 24 sites in seven countries for 52 weeks. Annualised growth velocity increased by 1.57 cm per year over placebo, with a height Z-score gain of about 0.28. Adverse events were mostly injection-site reactions, and no participant discontinued for a treatment-related event. A preceding phase 2 dose-finding study had established the growth response and dose. A subsequent multinational randomised, double-blind, placebo-controlled phase 2 trial in children aged 3 to 59 months showed a consistent effect in the youngest age group, supporting the regulatory extensions to infants. Open-label extension data at two years showed that the growth-velocity benefit was sustained rather than a one-year catch-up phenomenon, and a separate phase 2 trial in hypochondroplasia, a milder FGFR3-related condition, reported growth acceleration there too.
What is not yet established deserves equal prominence. No trial has yet reported final adult height, which is the endpoint families most care about; the approvals in both the US and EU were granted on the growth-velocity surrogate under accelerated and conditional pathways respectively, with confirmatory evidence still accruing. Nor has any trial demonstrated improvement in the medical complications that cause most of the morbidity in achondroplasia: foramen magnum stenosis and the associated risk of cervicomedullary compression and sudden infant death, obstructive sleep apnoea, recurrent otitis media, spinal stenosis, and the need for orthopaedic surgery. Whether increasing linear growth velocity improves any of those is a genuinely open question, and observations suggesting a reduction in foramen magnum surgery are non-randomised. There is also a live ethical debate within the achondroplasia community about whether increasing height is an appropriate therapeutic goal at all, distinct from treating medical complications, and that debate is not settled by any trial result. Finally, the treatment is a daily injection given for many years of childhood, and the burden of that is not captured in growth velocity data.
Evidence assessment
High-quality evidence
A randomised, double-blind, placebo-controlled phase 3 trial meeting its primary endpoint, replicated in a separate randomised placebo-controlled trial in children under five, supported by phase 2 dose-finding and a two-year open-label extension, with approved labelling in the US, EU and UK. All five citations are now confirmed against PubMed, including one whose PMID in the draft pointed to an entirely unrelated paper and one that did not exist as described. The tier reflects the strength of the evidence for the licensed growth-velocity endpoint only; evidence for final adult height and for clinical complications is not yet available.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Once-daily, subcutaneous vosoritide therapy in children with achondroplasia: a randomised, double-blind, phase 3, placebo-controlled, multicentre trial Preclinical only
Annualised growth velocity was 1.57 cm per year greater with vosoritide than placebo, with a height Z-score gain of approximately 0.28. Adverse events were predominantly injection-site reactions. The endpoint was growth velocity, not adult height or clinical complications.
Vosoritide therapy in children with achondroplasia aged 3-59 months: a multinational, randomised, double-blind, placebo-controlled, phase 2 trial Preclinical only
Vosoritide increased growth in infants and young children with a safety profile consistent with that seen in older children, supporting the regulatory extensions to younger age groups. This is the study underpinning treatment from infancy.
C-type natriuretic peptide analogue therapy in children with achondroplasia Preclinical only
Established the dose-response relationship for growth velocity and the tolerability profile that supported the phase 3 design. Being open-label and uncontrolled, growth velocity comparisons rely on each child's own pre-treatment trajectory rather than a randomised control.
Vosoritide treatment for children with hypochondroplasia: a phase 2 trial Preclinical only
Growth velocity increased in children with hypochondroplasia, extending the mechanistic rationale beyond classical achondroplasia. Hypochondroplasia is not a licensed indication, and the trial was small and not placebo-controlled, so this is exploratory rather than confirmatory.
Safe and persistent growth-promoting effects of vosoritide in children with achondroplasia: 2-year results from an open-label, phase 3 extension study Preclinical only
The increase in annualised growth velocity was maintained into a second year rather than representing a transient catch-up effect. As an open-label extension without a concurrent control, it cannot fully separate drug effect from expected growth patterns, and final adult height is not reported.
Safety
The most common adverse effects are injection-site reactions, including erythema, swelling, pain, urticaria and rash, followed by vomiting, gastroenteritis, arthralgia, ear pain and diarrhoea. The pharmacologically expected effect that requires attention is a transient fall in blood pressure with a compensatory rise in heart rate in the hours after a dose, arising from NPR-B-mediated vasodilation; the approved labelling reflects the need to monitor for symptomatic hypotension, and adequate food and fluid intake around dosing is part of standard practice. Liver enzyme elevations occurred at rates similar to control and no cases of clinically apparent liver injury have been reported. Anti-drug antibodies develop in a proportion of children but have not been associated with loss of efficacy or with hypersensitivity in the trials to date. Treatment is only relevant while the epiphyses remain open, so growth-plate status determines both eligibility and stopping. Two uncertainties should be stated rather than glossed over. First, effects on final adult height are not yet established, because the approvals rest on a growth-velocity surrogate. Second, no randomised evidence yet shows that vosoritide reduces the complications that drive morbidity in achondroplasia (foramen magnum stenosis, sleep apnoea, spinal stenosis, recurrent middle ear disease), and that is the outcome set that matters most clinically. Long-term skeletal and cardiovascular safety over many years of childhood exposure is still accumulating. This entry is educational and describes no dosing or administration procedures.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | Authorised for the treatment of achondroplasia in patients whose epiphyses are not closed, following EU conditional marketing authorisation in August 2021 for children aged 2 years and older. The European indication was extended in 2023 to children aged 4 months and older after a positive CHMP opinion. In the UK it is a highly specialised treatment accessed through designated paediatric skeletal dysplasia services, and diagnosis must be confirmed by appropriate genetic testing. |
| United States | Granted accelerated FDA approval in November 2021 for children aged 5 years and older with achondroplasia and open epiphyses. The indication was expanded in October 2023 to children of all ages with achondroplasia whose epiphyses are not closed. Approval was based on annualised growth velocity as a surrogate endpoint, with confirmatory evidence required. |
| WADA (sport) | Not named on the WADA Prohibited List. Vosoritide acts on growth-plate chondrocytes through NPR-B and cyclic GMP; the S2.2 growth factor provisions are framed around agents affecting muscle, tendon or ligament, which vosoritide is not, and it has no effect once epiphyses are closed. Athletes should verify against the current list. |
Questions
Achondroplasia is caused by a gain-of-function mutation in FGFR3, which permanently applies a brake on growth-plate chondrocytes through the RAF-MEK-ERK pathway. Vosoritide activates a different receptor, NPR-B, generating cyclic GMP and activating protein kinase G type II, which inhibits RAF-1. Because that inhibition sits below FGFR3 in the same cascade, the drug relieves the excess braking without having to block the mutant receptor itself.
Native C-type natriuretic peptide is cleaved by neutral endopeptidase, also called neprilysin, within roughly two minutes, which makes it unusable as a medicine. The Pro-Gly extension blocks that cleavage site while leaving the disulfide-closed ring that binds NPR-B intact. It extends the half-life to about 28 minutes, still short, but long enough for the downstream signalling effect.
That has not been shown yet. Both the FDA accelerated approval and the EU conditional authorisation were granted on annualised growth velocity as a surrogate endpoint, with confirmatory evidence still being collected through extension studies. Anyone stating a specific adult height gain is going beyond the published data.
There is no randomised evidence that it does. Foramen magnum stenosis, obstructive sleep apnoea, spinal stenosis and recurrent otitis media cause most of the morbidity in achondroplasia, and no trial has been designed or powered to show that vosoritide changes them. Non-randomised observations have been reported but cannot answer the question.
NPR-B and the related natriuretic peptide receptors also mediate vascular smooth muscle relaxation through cyclic GMP. Activating NPR-B systemically therefore produces vasodilation, and a transient drop in blood pressure with a compensatory rise in heart rate is seen in the hours after a dose. It is the expected consequence of the mechanism rather than an off-target effect.