FDA agrees to reconsider Regenxbio's gene therapy for Hunter syndrome after earlier rejection

The US Food and Drug Administration (FDA) has agreed to reconsider its approval decision for Regenxbio's experimental gene therapy navsunli (RGX-121), which targets Hunter syndrome—also known as mucopolysaccharidosis type II (MPS II). The agency had rejected the therapy approximately four months ago; it will now re-examine the application, according to reporting by Stat News.

Hunter syndrome is a rare X-linked lysosomal storage disorder caused by deficiency of the enzyme iduronate-2-sulfatase (IDS), which leads to progressive accumulation of glycosaminoglycans in cells throughout the body, including the central nervous system. In its severe form, the condition causes significant neurological deterioration and is life-limiting in childhood. Current approved treatments, including enzyme replacement therapy, do not adequately address CNS manifestations.

Gene therapy approaches for MPS II aim to deliver a functional copy of the IDS gene, potentially providing a durable correction that standard enzyme replacement cannot. The FDA's decision to reconsider follows a pattern seen with other rare-disease gene therapy applications where applicants have engaged in dialogue with the agency following an initial Complete Response Letter.

The full basis for the FDA's reconsideration was not detailed in the available feed item; Stat News reporting is behind a paywall. Researchers, genetic counsellors, and those working with rare metabolic disease families will wish to follow primary regulatory communications from the FDA and Regenxbio for the specific grounds and timeline.