FDA Delays Denali’s Hunter Syndrome Therapy Decision by Three Months

The FDA has extended its review of Denali Therapeutics' Biologics License Application (BLA) for tividenofusp alfa, a potential treatment for mucopolysaccharidosis type II (Hunter syndrome), by three months—from January 5, 2026 to April 5, 20262 3 1 6 13 15.

The extension was prompted by Denali’s submission of updated clinical pharmacology information after a request from the FDA as part of the review process2 3 1 6.

The additional information submitted was not related to the therapy’s efficacy, safety, or biomarker data; rather, it was procedural and addressed clinical pharmacology questions2 6 9.

The FDA classified Denali’s submission as a Major Amendment to the application, which by regulation results in a three-month extension of the review period2 6 1.

No extra clinical data were requested by the FDA as part of this amendment2 3 15.

Denali asserts that the new data do not alter the clinical pharmacology or the benefit-risk assessment that supports approval of tividenofusp alfa2 3 6 9.

Tividenofusp alfa, also known as DNL310, is an investigational enzyme replacement therapy designed to address the neurological and systemic symptoms of Hunter syndrome by delivering the IDS enzyme across the blood-brain barrier9.

The BLA is being reviewed under the accelerated approval pathway, and tividenofusp alfa has been granted Fast Track and Breakthrough Therapy designations by the FDA9 12.

Denali continues to prepare for potential FDA approval and commercial launch despite the review delay2 1 15.