Quick Facts

• Gene therapy restored hearing in 90% of 42 patients with rare genetic deafness in international trial
• Treatment results lasted up to 2.5 years with no serious safety concerns reported
• Some patients can now hear whispers and learn to speak after being born deaf

An experimental gene therapy restored hearing in 90% of patients born with a rare form of deafness, according to results from the largest clinical trial of its kind published Wednesday in Nature.

The international study tracked 42 children and adults with autosomal recessive deafness 9 (DFNB9) for up to 2.5 years. Participants ranged from 0.8 to 32.3 years old and received treatment at eight medical centers.

The condition affects about 50 babies born each year in the United States. It stems from mutations in the OTOF gene, which provides instructions to make otoferlin protein. This protein allows hair cells in the inner ear to transmit sound signals to the brain.

Researchers used an adeno-associated virus to deliver a healthy version of the gene directly into patients’ ears. The virus carried the gene split in half to fit inside, then reassembled to produce working otoferlin protein.

“The results are really remarkable,” said Dr. Zheng-Yi Chen, an associate scientist at Mass Eye and Ear in Boston who led the study. “This is really for the first time in the whole field a brand-new treatment option for genetic hearing loss.”

Some patients experienced dramatic improvements. “Now they could hear very well,” Chen said. “In some patients, they can even hear even a whisper.” Patients who benefited could start learning to speak, enabling easier communication with others.

The treatment showed no dose-limiting toxicities. The primary adverse event was decreased neutrophil count, classified as Grade 3.

Dr. Lawrence Lustig, who chairs the Department of Otolaryngology-Head & Neck Surgery at Columbia University, called the development transformative. “Being able to restore natural hearing, I think, is a game changer for our field.”

The results could represent a one-time treatment lasting a lifetime. However, researchers note patients need longer follow-up to confirm lasting safety and benefits.

A competing therapy from Regeneron Pharmaceuticals could become the first FDA-approved gene therapy for deafness. Their treatment, DB-OTO, helped nine patients reach hearing levels that typically no longer require cochlear implants.

These advances are spurring increased interest in screening babies for genetic deafness to enable treatment as early as possible. Researchers hope gene therapy may eventually treat more common hearing loss from aging and noise exposure.

Read more: Gene therapy for a rare type of deafness shows lasting results