FDA places second hold on Regenxbio gene therapy trial for Hunter syndrome

The US Food and Drug Administration (FDA) has placed a second clinical hold on a Regenxbio gene therapy trial targeting Hunter syndrome (mucopolysaccharidosis type II, MPS II), according to reporting by STAT News on 24 August 2026. The full details of the safety concerns have not been disclosed publicly; Regenxbio confirmed the hold in response to new safety information that emerged during the trial.

Hunter syndrome is a rare, X-linked lysosomal storage disorder caused by pathogenic variants in the IDS gene, which encodes iduronate-2-sulfatase. Without functional enzyme activity, glycosaminoglycans accumulate in multiple organ systems, causing progressive multi-system disease. Gene therapy approaches aim to deliver a functional IDS transgene, typically via an adeno-associated virus (AAV) vector.

The recurrence of a clinical hold is notable in the context of broader scrutiny of AAV-based gene therapies, where dose-dependent hepatotoxicity and immune-mediated adverse events have been documented across several programmes. The FDA's willingness to place repeated holds reflects the agency's caution in the rare-disease gene therapy space following a series of serious adverse events reported across different sponsors and indications in recent years.

The STAT News article is behind a paywall and full clinical details are not available from public sources. This summary is based on the available lede text. Researchers, clinicians, and policy-watchers with an interest in gene therapy safety and regulatory science will wish to monitor further disclosures from Regenxbio and the FDA.