US FDA declines to approve Regenxbio’s gene therapy for rare disease

Feb 9 (Reuters) – Regenxbio said on Monday the U.S. Food and Drug Administration had declined to approve its gene therapy for a rare disease called Hunter syndrome, citing uncertainty regarding the trial design.

Shares of the drug developer tumbled about 19% to $8.31 in aftermarket trading.

The company, which was seeking approval for RGX-121 to treat Mucopolysaccharidosis II, an ultra-rare neurodegenerative disease also known as Hunter syndrome, said the FDA had outlined several reasons in its so-called complete response letter.

They included uncertainty regarding the study’s eligibility criteria, as well as if a particular surrogate endpoint was reasonably likely to predict clinical benefit, the company disclosed.

“We are concerned about FDA’s feedback regarding the overall development path and evaluation of the data in the context of the urgent need for this irreversible ultra-rare disease,” said CEO Curran Simpson.

The health regulator last month placed a clinical hold on two of its experimental gene therapy programs that included RGX-121.

The potential next steps, which include a new study, treating additional patients and conducting longer-term follow up, “would be challenging in an ultra-rare disease population, like MPS II”, the company said.

The company plans to seek a meeting with the FDA on resubmitting its marketing application to provide further evidence on the patient population and additional longer-term clinical data.

Hunter Syndrome is a genetic disorder in which the body cannot break down certain sugar molecules, which can affect physical and mental development.

RGX-121 is a potential one-time gene therapy for the treatment of boys with MPS II, designed to deliver the gene which helps in breaking down complex sugar molecules.

(Reporting by Sneha S K in Bengaluru; Editing by Alan Barona and Sriraj Kalluvila)