Ascendis Pharma A/S (ASND) hit a regulatory speed bump this week as the FDA extended its review timeline for TransCon CNP (navepegritide), a potential treatment for children with achondroplasia. The new target decision date is February 28, 2026—three months later than originally expected.

The delay stems from information Ascendis submitted on November 5, 2025, related to post-marketing study requirements. The FDA classified this submission as a major amendment to the New Drug Application, triggering an automatic extension of the PDUFA target action date.

Understanding Achondroplasia

Achondroplasia is a genetic disorder that causes dwarfism, characterized by short limbs, a normal-sized torso, and a large head. It's the most common form of skeletal dysplasia, resulting from a mutation in the FGFR3 gene. This mutation impairs the process of cartilage converting into bone, particularly affecting the long bones in the arms and legs.

Company Response

"We have responded to all outstanding requests from the FDA, including the request for a revised protocol for the post-marketing study, which we received as the lone item for discussion at our late-cycle meeting," said Jan Mikkelsen, President and CEO at Ascendis Pharma.

Promising Trial Results

The regulatory delay comes despite encouraging clinical data. In November, Ascendis announced that pivotal week 52 results from its ApproaCH Trial were published in JAMA Pediatrics, a journal of the American Medical Association.

The published results showed that treatment with TransCon CNP led to significantly higher annualized growth velocity at week 52 compared to placebo—the trial's primary endpoint. Beyond growth improvements, the treatment also improved lower-limb alignment and body proportionality, along with positive changes in health-related quality of life. The safety and tolerability profile was similar to placebo, which is obviously what you want to see.

Other Pipeline Developments

Earlier in November, the company shared a new pooled analysis of TransCon PTH (palopegteriparatide) in adults with hypoparathyroidism. The data, drawn from the Phase 2 PaTH Forward and Phase 3 PaTHway trials, showed sustained and clinically meaningful improvements in renal function through year three.

At the three-year mark, at least 91% of patients receiving palopegteriparatide in both trials were independent from conventional therapy, and at least 84% of patients achieved normocalcemia. Sustained and clinically meaningful improvements in eGFR (at least 5 mL/min/1.73 m2) were observed in 70.3% of patients, with numerically greater improvements in those with lower baseline eGFR.

Ascendis Pharma stock was up 1.44% at $213.03 following the announcement.