Single Injection Gene Therapy Restores Hearing in All 10 Congenitally Deaf Patients

A single injection of gene therapy has restored meaningful hearing in all ten participants of a landmark clinical trial, including a seven-year-old girl who regained near-full hearing just four months after treatment — a result that researchers say could transform the lives of millions of people born with profound deafness worldwide.

The study, published April 3 in the prestigious journal Nature Medicine, was conducted at five hospitals across China under the lead of Dr. Maoli Duan, a consultant and docent at the Karolinska Institutet in Sweden. All ten participants — ranging in age from one to 24 years old — had been born with deafness or severe hearing loss caused by mutations in the OTOF gene, which normally produces a protein called otoferlin, critical for transmitting sound signals from the inner ear to the brain.

The therapy works by delivering a corrected copy of the OTOF gene directly into the cochlea — the spiral-shaped, fluid-filled cavity of the inner ear responsible for converting sound vibrations into electrical signals. Scientists used a synthetic adeno-associated virus, or AAV, as the delivery vehicle, injecting the therapeutic payload through the round window membrane at the base of the cochlea in a single outpatient procedure. Unlike systemic gene therapies that must reach multiple organs, the inner ear's relative isolation makes it an ideal target: the gene stays local, the treatment bypasses most of the body, and the risk of immune reaction is lower.

The results were striking. Before treatment, participants had an average hearing threshold of 106 decibels — a level of loss so profound that even a jet engine passing nearby would be barely perceptible. At six months, that average had improved to 52 decibels, a level classified as moderate hearing impairment at which conversation becomes possible with some effort. Most patients began regaining hearing within one month of receiving the injection. The most dramatic improvements occurred in children between the ages of five and eight, whose auditory systems retained significant developmental plasticity. The highlighted case — a seven-year-old girl — was able to have everyday conversations within four months, her family reporting a transformation that went far beyond the clinical charts.

Safety results were equally encouraging. The most common side effect was a temporary, mild decrease in neutrophils, a type of white blood cell, which resolved without intervention. No serious adverse events were recorded during the six-to-twelve month follow-up period. The funding for the trial came from Chinese national research programs and Otovia Therapeutics Inc., which holds commercialization rights in several markets.

The OTOF gene causes only a small fraction of all genetic deafness — perhaps two to eight percent of cases. But Dr. Duan said the trial represents a proof of concept for a much broader application. "OTOF is just the beginning," she said. "We are already expanding our work to other, more common genes that cause deafness, such as GJB2 and TMC1." Mutations in GJB2 alone account for up to half of all cases of hereditary hearing loss in some populations, affecting tens of millions of people globally. Researchers and patient advocates say that if the AAV delivery platform proves as flexible as early results suggest, gene therapy could within a decade become a routine treatment for the most common forms of inherited deafness — making cochlear implants, which require lifelong maintenance and only approximate normal hearing, a last resort rather than a first-line option.