FDA pauses Regenxbio gene therapy trial for Hunter syndrome after spinal masses found

The Food and Drug Administration has placed another hold on Regenxbio's gene-therapy trial for mucopolysaccharidosis type II, also known as Hunter syndrome, after new safety concerns emerged.

Five participants were reported to have small, asymptomatic masses on their spines. The company said the patients showed no related symptoms.

The pause follows a previous incident in which a similar therapy for MPS type I was linked to a brain tumor, the first tumor conclusively tied to AAV-based gene therapy.

Regulators and investors are watching the development closely, as the action may extend timelines for the experimental treatment and highlights broader safety questions for viral-vector gene therapies.