YUVIWEL's Week 104 Data Confirm Durability but Leave Cost-Effectiveness Unresolved Against a Brutal HTA Precedent

Ascendis Presents Positive Long-Term Navepegritide Data in Achondroplasia

Ascendis Pharma announced an oral presentation of Week 104 data from its pivotal ApproaCH Trial of once-weekly TransCon CNP (navepegritide) in children with achondroplasia at ISDS 2026. The data reinforced durable improvements in height, lower-extremity alignment, body proportionality, spinal canal dimensions, muscle function, and physical functioning. The drug demonstrated a safety and tolerability profile similar to placebo with a low rate of injection site reactions. TransCon CNP, approved by the FDA in February 2026 as YUVIWEL, is also under EMA review with a decision anticipated in Q4 2026.

• Ascendis Pharma presented Week 104 data from the open-label extension of its pivotal ApproaCH Trial for TransCon CNP (navepegritide) in children with achondroplasia. The data highlighted durable improvements across multiple physical parameters, including height, lower-extremity alignment, body proportionality, spinal canal dimensions, muscle function, and overall physical functioning.
• The long-term data reinforced a favorable safety and tolerability profile for once-weekly TransCon CNP, showing results similar to placebo and a low incidence of injection site reactions. These outcomes are consistent with improvements in health-related quality of life identified as important by the achondroplasia community.
• TransCon CNP, marketed as YUVIWEL, received U.S. Food & Drug Administration (FDA) approval in February 2026 for pediatric patients aged 2 years and older with achondroplasia and open epiphyses. The Marketing Authorisation Application for YUVIWEL is currently under review by the European Medicines Agency (EMA), with a regulatory decision expected in the fourth quarter of 2026.

ApproaCH Trial: Unpacking Week 104 Data for Navepegritide

Recent clinical investigations in achondroplasia have evaluated a range of interventions — from CNP analogues to FGFR3 inhibitors — across both controlled trial and real-world settings. The studies below represent the current leading edge of evidence, spanning Phase 2/3 trial data and post-authorization experience.

• ACcomplisH Trial (TransCon CNP / Navepegritide): Evaluated once-weekly subcutaneous navepegritide at doses of 6–100 μg CNP/kg/week. Safety was favorable — all treatment-emergent adverse events were mild or moderate, with no Grade 3/4 events, no symptomatic hypotension, and only 11 injection site reactions across 8 participants. At 52 weeks, the 100 μg/kg/week dose significantly improved annualized growth velocity versus placebo (5.42 vs. 4.35 cm/year; p = 0.0218), with dose-dependent effects observed, and a meaningful improvement in achondroplasia-specific height SDS (0.22 vs. −0.08; p = 0.0283).

• APPROACH Trial (Navepegritide): Assessed navepegritide at 100 μg/kg/week via once-weekly subcutaneous injection. No treatment-related serious adverse events or deaths were reported, with low injection site reaction rates and no symptomatic hypotension or fractures. At Week 52, navepegritide demonstrated a least-squares mean treatment difference in annualized growth velocity of 1.49 cm/year versus placebo (95% CI, 1.05–1.93; p < 0.001). Secondary endpoints also favored treatment, including improvements in tibial-femoral angle (−1.81°), mechanical axis deviation (−2.78 mm), fibula-to-tibia length ratio (−0.016), and Achondroplasia Child Experience Measures–Physical Functioning scores (−11.1) in children under 5 years.

• PROPEL 2 Trial (Infigratinib): Investigated oral infigratinib across ascending dose cohorts (0.016–0.25 mg/kg/day). All participants experienced at least one adverse event, though the majority were mild to moderate in severity with no treatment discontinuations and no major safety signals identified. At the highest dose cohort (0.25 mg/kg/day; Cohort 5), mean change from baseline in annualized height velocity 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, and a mean reduction in upper-to-lower body segment ratio of −0.12 (95% CI, −0.18 to −0.06).

• Real-World Vosoritide Study (Portugal): Examined vosoritide at 15 μg/kg/day via daily subcutaneous injection in a post-authorization real-world cohort. Injection site reactions were the most commonly reported adverse drug reaction (n = 14); no serious adverse drug reactions or treatment discontinuations were observed. At 24 months, mean annualized growth velocity was 5.87 cm/year (95% CI, 5.14–6.60), representing an increase of +1.62 cm/year from baseline (p ≤ 0.0001), alongside a height SDS increase of +0.95 SD versus an untreated achondroplasia-specific population (p ≤ 0.0001) and +0.56 SD relative to average-stature peers (p ≤ 0.0001).

Addressing the Complexities and Unmet Needs in Achondroplasia

Current treatment approaches for achondroplasia—ranging from pharmacological intervention with vosoritide to surgical limb lengthening—carry significant limitations that constrain their clinical utility. These challenges span tolerability, procedural complexity, long-term outcome uncertainty, and the progression of skeletal and craniofacial complications that persist despite available interventions.

• Vosoritide tolerability and uncertain long-term efficacy: Adverse events occurred in 100% of participants (75/75) in the 3–59 month age cohort, with an annual rate of 204.5 events per patient in the vosoritide group versus 73.6 in the placebo group—predominantly transient injection-site reactions and erythema. Critically, the long-term impact on final adult height and comprehensive skeletal outcomes remains to be fully established, with ongoing studies still needed to clarify effects on skeletal deformities and quality of life.

• Procedural burden and high complication rates with limb lengthening: Limb lengthening is a prolonged, psychologically demanding process, with a mean time in frame of 8 months (range: 4–14 months) and an average healing index of 48 days/cm of lengthening. Complication rates are substantial (0.6 per bone segment overall), including pin tract infections, transient joint stiffness, femoral fractures requiring surgical intervention, equinus deformities, and premature fibular consolidation. Among patients undergoing crossed lengthening, limb length discrepancy ≥1.0 cm was observed in 5 of 12 patients.

• Progressive skeletal deformities and functional decline: Thoracolumbar kyphosis, scoliosis, hip dysplasia, and genua valga can progress despite treatment. At last follow-up, 47% of patients were partially wheelchair dependent, 10% were wheelchair bound, and 25% experienced regular pain in the spine, hips, and lower extremities attributable to orthopedic complications.

• Worsening craniofacial phenotype and respiratory risk: 3D morphometric analyses demonstrate increasingly severe craniofacial phenotypes with patient age, characterized by progressive maxillary retrusion and closure of the spheno-occipital angle. Severity of maxillo-mandibular retrusion correlates significantly with obstructive sleep apnea syndrome (p < 0.01). Foramen magnum stenosis poses additional risk, with severe cord compression potentially leading to sleep apnea, sudden respiratory arrest, or death—yet surgical decompression practice varies considerably across centers.

Durable Benefits: TransCon CNP Reshapes Achondroplasia Treatment

The latest Week 104 data from the pivotal ApproaCH trial for TransCon CNP (navepegritide) marks a significant milestone in the evolving treatment landscape for achondroplasia. Historically, management for this genetic disorder has been largely supportive, with limited options to address its profound multisystemic effects. The sustained efficacy and safety profile demonstrated by TransCon CNP, now approved by the FDA as YUVIWEL, suggest a paradigm shift in how this condition can be managed.

Beyond simply increasing height, the data highlight durable improvements across a spectrum of critical clinical outcomes. Children receiving TransCon CNP showed enhanced lower-extremity alignment, improved body proportionality, and beneficial changes in spinal canal dimensions. Crucially, gains in muscle function and overall physical functioning were also observed, directly impacting the daily lives and health-related quality of life for patients. This comprehensive benefit addresses the broader pathology of achondroplasia, moving beyond a focus solely on stature.

The once-weekly subcutaneous administration of TransCon CNP, leveraging its sustained-release C-type natriuretic peptide prodrug design, offers a significant advantage. This approach ensures continuous therapeutic exposure while avoiding the high peak concentrations that have been associated with cardiovascular side effects, such as symptomatic hypotension, seen with shorter-acting C-type natriuretic peptide molecules. The safety and tolerability profile, reported as similar to placebo with a low incidence of injection site reactions, further supports its long-term use in a pediatric population.

However, as with any emerging therapy, strategic considerations and potential risks remain. While TransCon CNP presents a compelling profile, the absence of head-to-head comparative data against other targeted therapies like Vosoritide or Infigratinib means its definitive competitive positioning will continue to be evaluated. Furthermore, while initial data are promising for various comorbidities, the long-term impact on critical issues such as foramen magnum stenosis and sleep apnea requires ongoing investigation. Successfully navigating market access and reimbursement discussions will also be crucial, given the therapy's innovative nature and the rare disease context. Nevertheless, these durable Week 104 results solidify TransCon CNP's role as a transformative option, offering hope for a more comprehensive and sustained improvement in the lives of children with achondroplasia.