The U.S. Food and Drug Administration has again halted testing of Regenxbio's experimental gene therapy for Hunter syndrome, a rare inherited disorder.
According to BioPharma Dive, investigators detected masses on the spines of five patients who had received the treatment. That finding triggered the program's second clinical hold this year.
A clinical hold is the FDA's order to stop dosing patients in a trial until safety questions are resolved. It is one of the bluntest tools the agency has, and getting hit with two in a single year on the same program is an unusually rough stretch for a drug developer.
According to Endpoints News, Regenxbio said it no longer expects to file for FDA approval of the Hunter syndrome therapy in the near future. That is a significant reversal: filing for approval is the final step before a treatment can reach patients commercially, and pushing it back means an indefinite delay for families waiting on the therapy.
Hunter syndrome is a rare genetic disease, and gene therapy — which aims to fix the underlying genetic defect rather than manage symptoms — has been one of the most closely watched approaches for treating such conditions. It has also been one of the most safety-scrutinized, because the effects of altering a patient's genes can be difficult to reverse.
The sources here do not specify what the spinal masses are, whether they are cancerous, or whether they were caused by the therapy itself. Those are exactly the questions the hold is designed to force answers to before more patients are dosed.
Why it matters: gene therapy promises one-time cures for devastating rare diseases, and each safety setback like this one slows the path for patients who have few other options while regulators work out how much risk these treatments actually carry.