An experimental gene therapy for congenital deafness has achieved promising results, showing a marked improvement in hearing in 90% of participants in the largest and longest study of its kind to date.
This achievement strengthens hopes that some cases of hereditary deafness can be cured permanently, rather than relying solely on cochlear implantation.
The trial, conducted at eight medical centers in China, included 42 patients, mostly children, along with three adults, all of whom had been born with profound hearing loss due to mutations in a gene known as OTOF. The results showed that most patients began to regain their hearing within weeks of receiving treatment, with improvement continuing gradually until it peaked after about a year.
The researchers explained that some patients were able to restore their hearing to a degree very close to normal, while some became able to hear whispers, and a number of children were even able to learn to speak for the first time.
Zheng Yi Chen, a co-author of the study and associate professor at Harvard Medical School, said some of the improvements were exceptional, explaining that the restoration of hearing in some patients was "similar to a blind person regaining their full sight."
The OTOF gene is responsible for producing a protein called autofeberlin, which is essential for the function of the inner ear's hair cells that convert sound vibrations into signals the brain can understand. When a child is born with two mutated copies of this gene, they suffer from severe or profound hearing loss, which significantly impacts speech and language development.
Treatment for these conditions typically involves cochlear implantation, which is effective in improving hearing, but it remains a mechanical device that does not provide completely natural sound quality and requires maintenance over time. The new gene therapy, however, targets the underlying cause directly by delivering a healthy copy of the gene to the inner ear using harmless viruses, thus helping to restore the function of the cells responsible for hearing.
The study included 39 children and adolescents ranging in age from 9 months to 18 years, as well as three adults in their twenties and thirties. Most participants received treatment in only one ear, while six received treatment in both ears.
The results showed that 38 out of 42 patients responded to the treatment, while four patients showed no improvement, and the reason for this remains unclear. A two-year follow-up of 15 ears treated with gene therapy showed that all of them were able to hear normal speech, while 60% were able to hear whispers.
The improvement was more pronounced in children than in adults, but the researchers emphasized that the results also suggest older patients could benefit. The team also noted that the condition of the outer ear's hair cells may influence the degree of response to treatment, as these cells act as natural sound amplifiers and may deteriorate over time in those with long-term hearing loss.
The study did not record any serious side effects, although some temporary symptoms appeared, such as mild dizziness or limited changes in some immune cells, in addition to one case of inner ear inflammation.
Researchers believe these results represent the beginning of a new phase in the treatment of hereditary deafness, especially since the treatment may be a one-time procedure, instead of continuous reliance on assistive devices.
Chen, a co-founder of Salubritas Therapeutics, a company specializing in developing regenerative therapies, said: "We are at the beginning of a historic phase, and in the coming years we will see many trials to treat different types of hereditary hearing loss."
The team is currently working on studying the possibility of giving additional doses of the treatment to improve results, as well as understanding the reasons why some patients do not respond, and determining how long the improvement lasts.
Initial tests also indicate that gene therapy may outperform cochlear implantation in some aspects, such as music perception and speech comprehension in crowded places. However, researchers emphasize that cochlear implantation will remain the primary treatment option for a long time, especially since some patients may not be suitable for this type of treatment.
The treatment is expected to undergo further trials before its official approval in China is completed, with the possibility of additional trials later in the United States in preparation for obtaining approval from the US Food and Drug Administration.
The study was published in the journal Nature.
