Children with Achondroplasia Treated with TransCon CNP Showed Continued Improvements in Lower Extremity Alignment at Week 104 of the Pivotal ApproaCH Trial

TransCon CNP Shows Continued Lower Limb Alignment Improvements in Achondroplasia

Ascendis Pharma announced new radiographic data from Week 104 of the pivotal ApproaCH Trial for once-weekly TransCon CNP (navepegritide) in children with achondroplasia. The data, presented at ICCBH 2026, showed continued improvements in lower extremity alignment, specifically tibial-femoral angle (TFA), through up to two years of treatment. Children treated with TransCon CNP demonstrated a mean absolute change of -2.2 degrees in TFA over two years, with greater improvements (-3.8 degrees) observed in those with preexisting genu varum. The drug was generally well tolerated, with a low rate of mild injection site reactions and no symptomatic hypotension or accelerated bone age. TransCon CNP, approved by the U.S. FDA in February 2026 as YUVIWEL® for pediatric achondroplasia, aims to counteract overactive FGFR3 signaling.

• The ApproaCH Trial demonstrated that TransCon CNP led to continued and significant improvements in lower extremity alignment, as measured by tibial-femoral angle (TFA), through Week 104. The average TFA decreased by 2.2 degrees over two years in all treated children, with a more pronounced reduction of 3.8 degrees in the subgroup with preexisting genu varum (baseline TFA ≥ 5°), highlighting its potential to address skeletal dysplasia complications.
• TransCon CNP exhibited a generally well-tolerated safety profile over two years of treatment. Adverse events were predominantly mild or moderate, with a low incidence of injection site reactions, all of which were mild. Importantly, no symptomatic hypotension or acceleration of bone age was observed, and no adverse events led to treatment discontinuation, reinforcing its potential for long-term use in pediatric patients.
• The positive outcomes, including improved TFA and stable fibula-to-tibia length ratio, suggest TransCon CNP's ability to support healthy and proportional growth. By continuously exposing tissues to active C-type natriuretic peptide, the drug counteracts overactive FGFR3 signaling, potentially mitigating serious complications like chronic pain, altered mobility, and the need for surgical interventions associated with achondroplasia.
• TransCon CNP, marketed as YUVIWEL®, received U.S. FDA approval in February 2026 for increasing linear growth in pediatric patients aged 2 years and older with achondroplasia and open epiphyses. A Marketing Authorisation Application is currently under review by the European Medicines Agency, with a regulatory decision anticipated in the fourth quarter of 2026, indicating its global regulatory progress.

Addressing Key Challenges in Achondroplasia Treatment

Current treatment approaches for achondroplasia span targeted pharmacotherapy, hormonal intervention, and surgical procedures — each carrying distinct limitations that temper their clinical utility. Evidence gaps, compliance burdens, and the absence of long-term outcomes data collectively underscore the need for more rigorous, large-scale investigation across all modalities.

• Vosoritide evidence maturity: Despite its status as the first approved targeted therapy for achondroplasia, vosoritide data remain limited in scope. Studies with longer duration (through puberty), larger sample sizes, and assessment of effects on medical complications are required to establish definitive effectiveness. Its requirement for daily subcutaneous injections also introduces a compliance burden comparable to growth hormone regimens.

• Growth hormone (GH) therapy limitations: Long-term effects of GH therapy remain unclear, and efficacy is not consistent across underlying diagnoses. Adherence to daily injection schedules is a recognized barrier that can directly compromise therapeutic outcomes; long-acting formulations and oral secretagogues have been developed to address this, though caveats remain before these can be introduced into routine practice.

• Limb lengthening complications: Surgical limb lengthening is associated with functional risks beyond standard procedural complications. The intervention can alter postural control — evidenced by amplified linear sway and reduced movement variability — and disproportionate trunk lengthening has caused severe functional impairment in documented cases, necessitating additional corrective procedures to restore limb-trunk proportions.

• Surgical risks in thoracolumbar kyphosis (TLK) correction: Vertebral column resection carries high complication risk, including intraoperative malpositioned instrumentation near vital structures and postoperative sequelae such as neurogenic bladder, wound leakage, and infection. The literature currently lacks clear thresholds for intervention based on symptom onset or deformity progression angles.

• Systemic evidence and cost-effectiveness gaps: Management guidelines varied widely in scope prior to the 2021 International Achondroplasia Consensus Statement. There remains a lack of utility and cost-effectiveness data across treatments, while the health-related quality of life (HRQoL) and healthcare resource utilization (HCRU) burden on patients and families — particularly in emotional wellbeing and hospitalization costs — is substantial. Most therapies for rare diseases carry high costs, making clear indications for treatment initiation, monitoring, and duration an urgent unmet need.

Unpacking the ApproaCH Trial Design and Radiographic Outcomes

The key clinical trials in achondroplasia span Phase 2 through Phase 3 designs, evaluating vosoritide as monotherapy and, more recently, in combination regimens, across a broad pediatric age range from infancy through adolescence. Endpoints consistently centre on annualised growth velocity (AGV) and height Z-score, with safety and tolerability as co-primary or secondary assessments depending on the study phase.

TransCon CNP's Safety Profile and Long-Term Clinical Impact

Across its clinical development program, TransCon CNP has demonstrated a consistently favorable safety and tolerability profile. In a Phase 1 randomized, placebo-controlled, single-ascending dose trial conducted in 45 healthy adult males at two sites in Australia, TransCon CNP was well tolerated across all dose cohorts (3, 10, 25, 75, and 150 μg CNP/kg), with no serious treatment-emergent adverse events (TEAEs) and no discontinuations. Comprehensive cardiac safety assessments revealed no clinically relevant effects on electrocardiogram parameters, including heart rate, PR, QRS, and QTcF intervals. The pharmacokinetic profile emerging from this trial was judged compatible with a once-weekly dosing regimen, supporting progression into pediatric studies.

In the Phase 2 ACcomplisH trial — a global, randomized, double-blind, placebo-controlled, dose-escalation study — 42 prepubertal children aged 2–10 years with genetically confirmed achondroplasia received TransCon CNP at doses of 6, 20, 50, or 100 μg CNP/kg/week over 52 weeks. All TEAEs were mild or moderate in severity, with no Grade 3 or 4 events reported. Two serious TEAEs occurred but were assessed as unrelated to study treatment. Injection site reactions were infrequent, occurring in 8 participants across 11 events, and no symptomatic hypotension was observed — a clinically important finding given the vasodilatory potential of CNP. All participants completed the randomized period and transitioned into the ongoing open-label extension at the 100 μg CNP/kg/week dose.

The cardiovascular tolerability advantage of TransCon CNP is further substantiated by preclinical data generated in mice and cynomolgus monkeys. At exposure levels exceeding the expected clinical therapeutic range, TransCon CNP produced no adverse cardiovascular effects, in contrast to unconjugated CNP-38 and the daily CNP-39 molecule — which shares its amino acid sequence with vosoritide — both of which induced reductions in blood pressure and/or increases in heart rate at equivalent dose levels. This differentiation is mechanistically attributed to the prolonged, controlled release of CNP-38 from the TransCon platform: in cynomolgus monkeys, the half-life of released CNP-38 was approximately 90 hours versus 20 minutes for CNP-39, and the C_max associated with 100 μg/kg TransCon CNP was approximately 100-fold lower than that of CNP-39 at 20 μg/kg. Systemic CNP-38 exposure following TransCon CNP administration persisted for at least seven days post-dose, compared to just two hours for the daily CNP-39 molecule, supporting both improved therapeutic coverage and a reduced hypotension risk.

Shaping the Future of Achondroplasia Treatment

The treatment landscape for achondroplasia has undergone a fundamental transformation over the past five years, transitioning from purely symptomatic management to mechanism-targeted precision therapy. Vosoritide, a C-type natriuretic peptide (CNP) analog that acts on the underlying FGFR3-mediated impairment of endochondral ossification, became the first approved disease-modifying therapy for achondroplasia, receiving EU approval in August 2021 for patients aged ≥2 years with open epiphyses. Phase II and III trials established that daily subcutaneous administration at 15 μg/kg increases annualized growth velocity (AGV) by approximately 1.5–2.0 cm/year versus placebo, with extension data out to seven years demonstrating sustained efficacy. In children randomized to vosoritide in a two-year extension study, AGV rose from 4.26 cm/year at baseline to 5.52 cm/year at week 104, with crossover participants achieving comparable gains. A subsequent Phase 2 trial in infants and young children (aged 0–59 months; n=75 across 16 international centers) demonstrated a least-squares mean difference in height Z-score change of 0.25 (95% CI: −0.02 to 0.53) versus placebo over 52 weeks, with an adverse event profile dominated by transient injection-site reactions. Real-world corroboration has emerged from multiple national programs: the French Early Access Program (n=62) recorded a mean AGV of 6.0 cm/year and a mean height gain of 6.2 cm after 12 months, with no treatment discontinuations. Registry data from CrescNet (n=186 vosoritide-treated individuals across 32 tertiary centers) confirmed mean height SDS increases at 1, 2, and 3 years post-initiation (P≤0.0001), consistent with trial findings. Notably, a prospective single-center study (n=17; mean age 7.6 years) reported statistically significant reductions in lumbar lordosis (−5.2°) and improvements in mechanical axis angle (−3.4°) after one year, indicating benefits extending beyond linear growth.

Beyond vosoritide, the pipeline has expanded meaningfully with two additional precision agents generating Phase 2 data. Infigratinib, an orally bioavailable FGFR1–3 selective tyrosine kinase inhibitor, was evaluated in the PROPEL2 dose-finding study (NCT04265651) across five sequential cohorts in 72 children aged 3–11 years. At the highest dose cohort (0.25 mg/kg/day), the mean change from baseline in AGV at 18 months was 2.50 cm/year (95% CI: 1.22–3.79; P=0.001), with a mean height Z-score improvement of 0.54 (95% CI: 0.35–0.72) relative to an untreated achondroplasia reference population, alongside a mean reduction of 0.12 in the upper-to-lower body segment ratio. TransCon CNP (navepegritide), a long-acting pegylated CNP prodrug designed to enable once-weekly dosing, was assessed in the 52-week Phase 2 ACcomplisH trial (n=42 active, n=15 placebo; ages 2–10 years). At the 100 μg CNP/kg/week dose, AGV significantly improved versus placebo (5.42 vs. 4.35 cm/year; p=0.0218), with a corresponding achondroplasia-specific height SDS gain of 0.22 versus −0.08 (p=0.0283). Both agents demonstrated mild-to-moderate adverse event profiles with no Grade 3/4 treatment-emergent events, and all ACcomplisH participants transitioned into an ongoing open-label extension.

A critical theme emerging across this body of evidence is the prognostic importance of treatment timing. Expert consensus data show 100% agreement that earlier treatment initiation will likely result in greater final height, and 92% agreement that earlier initiation more likely improves body proportionality. At least 75% of panelists consider it plausible that prolonged early treatment reduces lifetime incidence of symptomatic spinal stenosis, kyphosis, obstructive sleep apnea, and foramen magnum stenosis, with 90% expecting a reduction in surgical burden. However, current standard-of-care initiation at age 2 years does not address cranial malformations such as midface hypoplasia and foramen magnum stenosis; preclinical mouse model data suggest that immediate postnatal therapy—rather than treatment beginning at an equivalent of ~5 months of age—is required to normalize cranial base development, providing a scientific rationale for ongoing investigation of prenatal therapeutic strategies. Despite these advances, key evidence gaps remain, including the absence of long-term data on medical complication rates, health-related quality of life outcomes, and formal cost-effectiveness analyses, all of which will be essential for guiding reimbursement and clinical positioning decisions as this therapeutic class matures.

TransCon CNP: Sustained Impact on Achondroplasia Limb Alignment

The latest radiographic data from the ApproaCH Trial for TransCon CNP (navepegritide) marks a significant milestone in the treatment of achondroplasia, offering a clearer picture of the drug's enduring impact. The sustained improvements in lower extremity alignment, specifically the tibial-femoral angle, observed through two years of treatment, are particularly compelling. For children living with achondroplasia, limb deformities like genu varum are not merely cosmetic concerns; they can lead to pain, functional limitations, and often necessitate complex and invasive surgical corrections. The data showing greater improvements in those with pre-existing genu varum suggests that TransCon CNP could play a pivotal role in mitigating these orthopedic challenges, potentially reducing the need for such surgeries and significantly enhancing the quality of life for patients.

This long-term evidence, following the drug's recent FDA approval, solidifies its position as a foundational therapy. By continuously counteracting overactive FGFR3 signaling, TransCon CNP addresses a core mechanism of the disease. The favorable safety profile, characterized by a low rate of mild injection site reactions and no symptomatic hypotension or accelerated bone age, further supports its utility as a chronic treatment in a pediatric population. Strategically, this robust data strengthens the drug's differentiation in the rare disease market, providing a strong argument for its use as an early intervention to prevent or reduce the severity of skeletal complications.

However, as with any newly approved chronic therapy, certain considerations remain. While the trial data is encouraging, continued real-world monitoring will be crucial to fully understand the long-term safety and efficacy in a broader patient population. The emergence of any rare or delayed adverse events, not apparent in the trial, will need careful observation. Furthermore, while limb alignment is a critical outcome, the comprehensive impact on all aspects of skeletal development and overall health in achondroplasia warrants ongoing assessment. This data also lays a strong groundwork for future research into combination therapies, as existing evidence suggests navepegritide may enhance the growth plate's responsiveness to other growth-promoting agents, potentially unlocking even greater therapeutic benefits.