FDA Delays Decision on Ascendis' Dwarfism Drug, Intensifying Competition with BioMarin

The U.S. Food and Drug Administration (FDA) has extended its review period for Ascendis Pharma's achondroplasia treatment, TransCon CNP, by three months. This delay pushes the target action date from November 30, 2025, to February 28, 2026, following the submission of additional information regarding post-marketing requirements.

Regulatory Developments and Market Implications

Ascendis Pharma's CEO, Jan Mikkelsen, stated that the company has addressed "all outstanding requests from the FDA" and will continue to work with the regulator to bring TransCon CNP to patients "as soon as possible." The delay comes after Ascendis filed supplementary information on November 5, 2025, which the FDA deemed a "major amendment," necessitating an extended review period.

If approved, TransCon CNP, also known as navepegritide, would become the second FDA-approved therapy for achondroplasia, a genetic condition affecting bone development that impacts 15,000 to 40,000 newborns globally. The drug works by providing patients with C-type natriuretic peptide (CNP), counteracting the effects of the mutated FGFR3 gene responsible for impaired bone growth.

Clinical Efficacy and Market Competition

Data from Ascendis' Phase II ACcomplisH study, published in The Lancet in November 2023, demonstrated improved growth rates in patients with achondroplasia treated with TransCon CNP. The drug's once-weekly administration could provide a competitive advantage over BioMarin's Voxzogo, the current market leader approved in November 2021, which requires daily injections.

BioMarin has expressed concerns about incoming competition, abandoning its previously announced goal of reaching $4 billion in revenue by 2027. The company is now racing to defend its market position, having shared Phase 1 data on a once-weekly successor to Voxzogo in August 2025.

Future Outlook and Industry Impact

While the regulatory delay for TransCon CNP provides temporary relief for BioMarin, it also intensifies the competition in the achondroplasia treatment landscape. Analysts from TD Cowen remain optimistic about TransCon CNP's approval prospects, noting that the FDA's request for a revised protocol for the post-marketing study was "the lone item for discussion" at the late-cycle meeting.

As the pharmaceutical industry awaits the FDA's decision, the potential approval of TransCon CNP could significantly reshape the treatment options for individuals with achondroplasia, offering a new choice for patients and healthcare providers in managing this rare genetic condition.