In the largest and longest trial of its kind, 90% of patients receiving an experimental gene therapy for congenital deafness showed significant and lasting improvements in hearing.
The study, conducted across eight sites in China, involved 42 participants, including 39 children and teenagers aged 9 months to 18 years, and three adults. All participants had complete hearing loss at the start. While children showed greater improvement, two of the three adults also responded well, suggesting the treatment may benefit a broader age range.
Hearing improvements began within weeks of treatment, continued over time, and generally stabilized after about one year. Ten participants have now been followed for at least two years. All can hear normal conversation levels (50–60 decibels), and five are able to hear whispers.
Congenital hearing loss affects about 1.5 in 1,000 children, and up to 8% of cases are linked to mutations in the OTOF gene. This gene produces otoferlin, a protein essential for inner ear hair cells that convert sound vibrations into signals for the brain.
The therapy works by using harmless viruses to deliver functional copies of the OTOF gene into the inner ear, restoring the function of these hair cells. Unlike cochlear implants, which rely on mechanical sound processing and require ongoing maintenance, this treatment targets the underlying genetic cause and is designed as a one-time procedure.
Most participants received the therapy in one ear, often because they already had a cochlear implant in the other, while six were treated in both ears.
No serious side effects were reported. Some participants experienced temporary immune changes, mild vertigo, or minor inner ear inflammation.
Hearing improved steadily in 38 treated ears. Among the 15 ears monitored for two years, all could detect conversational speech and 60% could detect whispers. Younger patients showed stronger outcomes, and researchers believe the condition of outer hair cells, which amplify sound, may influence recovery, particularly in long-term hearing loss.
Improved hearing also enhanced speech perception. Some participants began developing speech, including an 11-year-old girl who had never used a cochlear implant and was able to speak simple words after treatment.
Researchers are now exploring whether multiple doses could further improve results and are planning longer-term studies to assess durability and understand why some patients do not respond.
Early findings suggest the therapy may outperform cochlear implants in areas such as music perception and hearing in noisy environments. However, cochlear implants are expected to remain widely used, and gene therapy may not be suitable for ears that have already undergone implant surgery due to potential inner ear damage.
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