TransCon CNP Durability Data Credible But Numerical Gaps Prevent Definitive Benchmark Clearance Against Vosoritide

Ascendis Reports Positive COACH & ApproaCH Trial Data for Achondroplasia

Ascendis Pharma provided updates on its achondroplasia programs, highlighting durable efficacy and consistent safety from both combination therapy and monotherapy. Week 78 data from the Phase 2 COACH Trial for TransCon CNP and TransCon hGH combination therapy showed mean annualized growth velocity (AGV) meeting or exceeding the 97th percentile of children of average stature, with sustained increases in ACH height Z-score. Week 104 data from the pivotal ApproaCH Trial for TransCon CNP monotherapy demonstrated durable improvements in height, body proportionality, and lower-limb alignment. Additionally, Ascendis completed target enrollment for the pivotal reACHin Trial for infants. In the U.S., YUVIWEL (TransCon CNP) has achieved over 170 unique patient enrollments, with more than 65% approved for reimbursement through June 30, 2026.

• The Phase 2 COACH Trial's Week 78 results for TransCon CNP and TransCon hGH combination therapy in children with achondroplasia demonstrated sustained, healthy, and proportional growth. Mean annualized growth velocity (AGV) remained at or above the 97th percentile of children of average stature, with a tripling of efficacy compared to TransCon CNP monotherapy, and significant increases in ACH height Z-score, indicating robust and durable treatment benefits.
• Week 104 data from the pivotal ApproaCH Trial for TransCon CNP monotherapy showed durable improvements in height, including significant gains for those switching from placebo. Crucially, it also demonstrated benefits beyond height, such as improved lower-limb alignment and body proportionality, with a consistent safety profile similar to placebo over two years of treatment, highlighting comprehensive skeletal growth improvements.
• Ascendis completed target enrollment for the pivotal reACHin Trial for infants with achondroplasia, supporting future regulatory filings. In the U.S., YUVIWEL (TransCon CNP) has achieved significant commercial uptake with over 170 unique patient enrollments by approximately 90 prescribing healthcare providers, and more than 65% approved for reimbursement through June 30, 2026, underscoring its differentiated profile and patient access.

COACH Trial: Unprecedented Growth with TransCon Combination Therapy

The phase 2, proof-of-concept COACH trial (NCT05598320) is investigating a novel combination approach in children with achondroplasia aged 2 to 11 years, pairing navepegritide with lonapegsomatropin, both administered weekly. Navepegritide is a prodrug of C-type natriuretic peptide, while lonapegsomatropin is a prodrug of somatropin. The scientific rationale underpinning this combination is that navepegritide continuously relieves the pre-hypertrophic block characteristic of achondroplasia, thereby enhancing growth plate receptivity to the complementary, strong growth-promoting effect of lonapegsomatropin — a mechanism hypothesized to deliver benefits beyond those achievable with either monotherapy alone.

The trial enrolled 21 children, stratified into two cohorts: 12 treatment-naive (TN) children and 9 navepegritide-experienced (NE) children who had received navepegritide monotherapy for more than one year prior to combination therapy initiation. At Week 52, TN children on combination therapy achieved a least squares mean annualized growth velocity (AGV) of 8.69 cm/year, compared to 5.95 cm/year in matched children receiving navepegritide monotherapy — a statistically significant difference of 2.74 cm/year (p<0.0001), which served as the trial's primary efficacy endpoint versus AGV data from the ApproaCH trial (NCT05598320). Observed mean AGV for TN children was 8.80 cm/year, reflecting a +3.89 cm/year increase from baseline (p=0.0015), while NE children demonstrated an observed mean AGV of 8.42 cm/year, a +3.28 cm/year increase from their navepegritide-treated baseline (p<0.0001).

Beyond linear growth gains, combination therapy was associated with improved body proportionality, with substantial increases in arm span (+9.4 cm in TN children and +7.9 cm in NE children) that paralleled height gains. Importantly, the combination regimen was well-tolerated across both cohorts, with adverse events generally mild in severity and no treatment discontinuations reported, supporting the feasibility of this dual-mechanism approach for further clinical development in achondroplasia.

Durable Benefits and Expanding Reach of TransCon CNP Monotherapy

Recent clinical evidence continues to reinforce the durability and expanding clinical applicability of TransCon CNP (navepegritide) as a once-weekly precision therapy for achondroplasia, while parallel data on vosoritide and other modalities provide valuable comparative context. Below is a synthesis of the most relevant recent studies, highlighting intervention specifics and key efficacy and safety findings.

• Navepegritide (TransCon CNP) Phase 2 Trial (2026): A multicenter, double-blind, randomized, placebo-controlled, dose-escalation trial (NCT04085523; EudraCT 2019-002754-22) enrolled 57 children with achondroplasia aged 2 to <12 years, receiving navepegritide once weekly. Trial data were leveraged to psychometrically evaluate the Achondroplasia Child Experience Measures (ACEM-OSM [8-item] and ACEM-Impact [25-item]), confirming these tools as reliable, valid, and responsive instruments for capturing disease signs and impact in this age group. Explicit safety outcomes were not detailed in this analysis.

• CrescNet Registry Achondroplasia Module (2026): This real-world registry, active in 10 of 11 participating CrescNet countries, enrolled 486 participants across 32 tertiary centers as of May 2025, including 73 untreated and 186 vosoritide-treated individuals with genetically confirmed achondroplasia. Vosoritide treatment was associated with a statistically significant increase in mean height standard deviation score at 1, 2, and 3 years post-initiation (P≤0.0001), with growth trends consistent with pivotal trial and other real-world data.

• Vosoritide Systematic Review and Meta-Analysis (2026): Pooled data from 6 studies (752 records screened; n=156 across pediatric ages 3 months–18 years) confirmed significant improvements in annualized growth velocity, height Z-score, and standing height versus placebo. Safety findings across all 156 patients showed adverse events were predominantly mild (Grade 1), self-limiting, and largely confined to injection-site reactions.

• Vosoritide Single-Arm Meta-Analysis in Children (2026): Across 13 studies (RCTs, cohort studies, case reports/series), vosoritide (15 μg/kg/day) produced an annualized growth velocity of 5.72 cm/year (95% CI: 5.51–5.94) at 12 months and a mean height Z-score improvement of 0.28 (95% CI: 0.16–0.4), with no sex-based differences. The most frequently reported adverse events were injection-site reactions (51%) and gastrointestinal symptoms (50%), generally mild to moderate in severity.

• Limb Lengthening Systematic Review and Meta-Analysis (2026): As a comparator to pharmacologic approaches, this analysis of 14 studies (1,149 patients) reported substantial limb-length gains (femoral: 8.85 cm; tibial: 7.36 cm; humeral: 8.38 cm) and moderate quality-of-life improvement (PedsQL score: 75.69), but at the cost of a high overall complication rate (56.1%) and prolonged fixation duration (mean 7.71 months), underscoring the comparatively favorable risk-benefit profile of emerging pharmacotherapies like TransCon CNP.

The Burden of Achondroplasia and the Need for New Therapies

Achondroplasia management remains constrained by significant gaps in long-term efficacy data, high complication rates associated with surgical interventions, and treatment burdens that impact patient quality of life. While emerging therapies like vosoritide represent meaningful progress, clinicians and researchers must navigate several unresolved challenges before these approaches can be considered fully optimized.

• Vosoritide (VOXZOGO®) data limitations: Despite promising growth velocity outcomes, evidence stems from a limited number of studies with daily subcutaneous dosing (15 μg/kg) required; adverse events were recorded in all 156 enrolled patients (typically mild, grade 1, self-limiting injection site reactions and transient hypotension in infants), and longer-duration studies through puberty with larger sample sizes are needed to establish definitive effectiveness and clarify effects on adult height, skeletal deformities, and quality of life.

• Growth hormone (GH) therapy uncertainties: Long-term effects of GH therapy remain unclear, efficacy is inconsistent across underlying diagnoses (including achondroplasia versus conditions like Turner syndrome), and daily injection compliance presents a persistent barrier that can directly compromise treatment efficacy.

• Limb lengthening complication burden: This approach carries a high complication risk, with an overall complication rate of 56.1% (95% CI: 26.9-85.2) and prolonged treatment courses (mean fixation duration of 7.71 months; mean fixator index of 37.1 days/cm). Beyond physical risks, the procedure alters postural control variability and adaptability compared to natural development, and disproportionate correction—such as excessive trunk lengthening (13 cm) without preserving limb-trunk proportions—can cause severe functional impairment, including loss of independent toileting and dressing capability.

• Surgical correction risks: Vertebral column resection, while sometimes necessary for severe thoracolumbar kyphosis with hypoplastic vertebrae, carries substantial complication risk and should be reserved for experienced surgical teams. Intraoperative risks include malpositioned screws breaching cortex near vital structures (e.g., the aorta), while postoperative complications encompass neurogenic bladder, wound leakage, and urinary tract infections.

• Emerging therapy caveats: Long-acting growth hormone formulations and oral secretagogues—developed to address compliance challenges with daily injections—carry their own limitations that clinicians must understand before broader clinical adoption.

• Critical evidence gaps: The field lacks robust cost-effectiveness data for achondroplasia treatments, clear clinical thresholds for symptom onset or progressive deformity angles in thoracolumbar kyphosis, and standardized frameworks for outcome reporting and long-term quality-of-life assessment.