The FDA has postponed its decision date for Regenxbio’s Hunter syndrome gene therapy to review additional longer-term clinical data for the asset.
The FDA has pushed back its target action date for Regenxbio’s Hunter syndrome gene therapy clemidsogene lanparvovec by three months. The company now expects a decision by Feb. 8, 2026.
The delay comes after Regenxbio filed longer-term clinical data from its pivotal study of the therapy after the FDA asked for more information. Extending the review period will allow the FDA to review the new submission. The regulator was originally scheduled to release its verdict for clemidsogene lanparvovec on Nov. 9.
There doesn’t appear to be an issue with the submission itself. The company said in a news release Monday that the FDA completed a pre-license inspection this month, which returned “no observations” and “no safety-related concerns.”
Even as the review for clemidsogene lanparvovec has been extended, Regenxbio remains “on track” in its launch preparations for the gene therapy, CEO Curran Simpson said in a prepared statement on Monday.
Also known as mucopolysaccharidosis type II, Hunter syndrome is a rare, X-linked genetic disease that mutates a gene called IDS, leading to the build-up glycosaminoglycans and heparan sulfate in various tissues across the body, culminating in organ damage. Hunter syndrome also affects the central nervous system and in its severe forms, leads to developmental delays apparent by 2 years of age.
Regenxbio’s clemidsogene lanparvovec addresses Hunter syndrome by delivering a functional copy of the IDS gene to the central nervous system, which helps clear the toxic buildup that causes the disease. The FDA has granted the gene therapy its orphan drug product, rare pediatric disease and regenerative medicine advanced therapy designations, as per the Monday release.
To support its application, Regenxbio submitted data from a Phase I/II/III study that in February 2024 showed an 86% reduction in a key disease biomarker in the cerebrospinal fluid of patients 16 weeks after treatment. Long-term follow-up findings at the time also found a “high rate” of patients receiving Regenxbio’s drug being taken off of the standard enzyme replacement therapy.
Regenxbio’s delay adds to the growing number of regulatory challenges faced by gene therapies. In July, for instance, the FDA turned down Ultragenyx’s UX111 for Sanfilippo syndrome type A, though not for its efficacy and safety data. The regulator instead pointed mainly to manufacturing issues. And in May, the regulator slapped a clinical hold on Rocket Therapeutics’ RP-A501 for Danon disease after the biotech reported a patient death.
