Regenxbio’s clemidsogene lanparvovec has a plausible pathway to FDA approval in Hunter syndrome, although the decision will likely hinge on whether biomarker reductions can be convincingly linked to meaningful clinical outcomes, experts tell the Insights Investigative News team at GlobalData, a leading intelligence and productivity platform.

Clemidsogene lanparvovec is a CNS-directed gene therapy designed to address the root cause of Hunter syndrome by restoring the functional IDS gene and reducing the accumulation of toxic glycosaminoglycans.

If approved, the therapy could become a first-in-class, potentially life-changing option for early-stage patients, while also stabilizing disease in more advanced cases.

The FDA accepted Regenxbio’s biologics license application (BLA) and initially set a Prescription Drug User Fee Act (PDUFA) decision date of November 9, 2025, which has since been extended to February 8, 2026. The extension follows heightened regulatory scrutiny of biomarker-based approvals in rare diseases, highlighted by recent reassessments of accelerated approvals such as Sarepta Therapeutics’ gene therapy Elevidys in Duchenne muscular dystrophy.

A detailed analysis of the publicly available data on clemidsogene lanparvovec, its upcoming approval decision date, and expert insights on other material events is included in the “Catalyst Monitor Q1 2026” report, which covers a total of 13 significant events that are expected to occur in Q1 2026.

Some of the catalysts covered in the report, include Aldeyra Therapeutics’ US approval for reproxalap in dry eye disease, Japan’s regulatory approval for GSK’s depemokimab, EU regulatory approval for Omeros Corp’s narsoplimab in thrombotic microangiopathy and Phase III trial results for Xenon Pharmaceuticals’ azetukalner in Focal Onset Seizures (FOS).

Omeros Corp’s narsoplimab is a first-in-class therapy for stem cell transplant–associated thrombotic microangiopathy (TA-TMA), which is an area with high unmet need. The asset faced a prior FDA rejection in 2021 due to reliance on a small, single-arm Phase II study (NCT02222545). However, in its updated approval package, the company strengthened its submission with data from an expanded access study (NCT04247906) and a comparison against an external untreated TA-TMA cohort. The asset received its first FDA approval on December 24, 2025, as the first and only treatment TA-TMA in adults and children two years and older, and approval in the EU is estimated to occur in Q1 2026. Narsoplimab is projected to yield $446 million in 2031, according to GlobalData consensus forecasts.

Irena Maragkou, Senior Healthcare Researcher at GlobalData says: “Narsoplimab’s future in stem cell transplant-associated thrombotic microangiopathy (TA-TMA) is unclear as experts have mixed views on whether benefits shown over external controls are enough to sway the FDA to reverse its prior rejection.”

The report also includes journalist coverage of other catalysts like Cerevel’s Phase III trial completion for tavapadon in Parkinson’s Disease and Sangamo Therapeutics’ BLA filing for isaralgagene civaparvovec in Fabry Disease, amongst others. 

The Catalyst Monitor report is published on a quarterly basis. The data presented in this report reflects the database as of December 24, 2025.