The FDA approved PTC Therapeutics' gene therapy to treat a potential fatal enzyme deficiency disorder, the company said.

The therapy, sold under the brand name Kebilidi, is a one-time treatment for children and adults with an ultra rare inherited disorder called aromatic l-amino acid decarboxylase (AADC) deficiency.

The disorder is estimated to affect fewer than 1,000 people in the U.S., according to data from the National Institutes of Health.

So far, there have been no U.S.-approved treatments for the condition, and doctors often treat patients with a variety of drugs, including those that activate dopamine receptors in the brain.

Kebilidi is delivered into the putamen and is designed to use a modified virus to carry the AADC gene into nerve cells. This allows them to produce the missing AADC enzyme that can help produce dopamine and treat the condition.

In three very small studies with a total of 28 patients, the therapy helped improve their ability to control their head movement and sit unassisted two years after treatment.

PTC Therapeutics' gene therapy is already approved in the European Union, Great Britain, and Israel.

The drugmaker will also get the FDA's priority review voucher, which allows a drug developer to expedite the review process of its product even if it does not fit the agency's requirements.

The voucher is transferable. The company said it plans to monetize the voucher.