An 11-year-old boy who was born deaf can hear after receiving an experimental gene therapy, developer Eli Lilly reported on Tuesday.

The boy, identified as Aissam Dam by The New York Times, was the first participant treated in a small study Lilly is running to test the therapy, which is designed to correct a particular type of inherited hearing loss.

While only from one person, the result is a striking example of gene therapy’s potential. According to Lilly, Dam experienced restored hearing across sound frequencies within a month of treatment. In some frequencies, Dam’s hearing was within the normal range at day 30, Lilly said.

Lilly plans to present full data from Dam, as well as a second participant in its study, at a medical conference in early February.

“Gene therapy for hearing loss is something physicians and scientists around the world have been working toward for over 20 years,” said John Germiller, a director of clinical research at the Children’s Hospital of Philadelphia who administered Lilly’s gene therapy to Dam.

“These initial results show that it may restore hearing better than many thought possible,” he added in a statement provided by the company.

Lilly’s success spotlights advancing research around a gene called otoferlin. Mutations in this gene disrupt production of functional otoferlin protein, which is needed for so-called hair cells in the inner ear to transmit sound signals to the brain. Lilly’s therapy delivers, via an engineered virus, copies of the otoferlin gene into the ear, resulting in the needed protein.

Otoferlin-mediated hearing loss is estimated to affect around 200,000 people worldwide, according to Lilly.

Other groups are working on a similar approach. In China, several deaf children have been successfully treated by gene therapies developed there, as MIT Technology Review has documented. Last year, Regeneron Pharmaceuticals acquired Decibel Therapeutics for its otoferlin-directed gene therapy, and a study of that treatment is currently recruiting participants, according to a federal database.

In France, meanwhile, a company called Sensorion recently received a green light from regulators to proceed with an otoferlin gene therapy it’s developing.

Lilly’s treatment, dubbed AK-OTOF-101, came via a $610 million acquisition of Akuous in late 2022.

The expanding otoferlin treatment pipeline comes as the broader gene therapy field sees setbacks as well as successes. Many young biotech companies working on genetic medicines have struggled to secure sufficient funding, leading to layoffs, while clinical trial delays have stalled others’ progress.

But the field has delivered approved medicines that can deliver dramatic results for diseases like spinal muscular atrophy, sickle cell disease and beta thalassemia. The first gene therapy approved in the U.S., Luxturna, can help correct an inherited cause of blindness.

Alongside progress for otoferlin-directed treatments, companies working on other types of hearing loss drugs have struggled. Otonomy shut down in December 2022 after years of setbacks, while Frequency Therapeutics merged with Korro Bio after a clinical trial failure in February last year.