A new study shows that gene therapy can significantly improve hearing in people born with congenital deafness or severe hearing loss. Researchers at Karolinska Institutet, working with hospitals and universities in China, treated ten patients and saw hearing improve in every case. The therapy was also well-tolerated. The findings were published in the journal Nature Medicine.
"This is a huge step forward in the genetic treatment of deafness, one that can be life-changing for children and adults," says Maoli Duan, consultant and docent at the Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Sweden, and one of the study's corresponding authors.
The trial included ten patients between the ages of 1 and 24 who were treated at five hospitals in China. All had a genetic form of deafness linked to mutations in a gene called OTOF. These mutations prevent the body from producing enough of the protein otoferlin, which is essential for sending sound signals from the inner ear to the brain.
To address this, researchers used a synthetic adeno-associated virus (AAV) to deliver a working version of the OTOF gene directly into the inner ear. The treatment was given as a single injection through a membrane at the base of the cochlea known as the round window.
The effects appeared quickly. Most patients began to regain some hearing within one month. After six months, all participants showed clear improvement. On average, the level of sound they could detect improved from 106 decibels to 52.
Children showed the most dramatic responses, especially those between the ages of five and eight. One seven-year-old girl regained nearly full hearing and was able to have everyday conversations with her mother just four months after treatment. At the same time, the therapy also produced meaningful improvements in adult patients.
"Smaller studies in China have previously shown positive results in children, but this is the first time that the method has been tested in teenagers and adults, too," says Dr. Duan. "Hearing was greatly improved in many of the participants, which can have a profound effect on their life quality. We will now be following these patients to see how lasting the effect is."
The therapy was shown to be safe and well-tolerated. The most commonly reported side effect was a decrease in neutrophils, which are a type of white blood cell. No serious adverse reactions were observed during the follow-up period of 6 to 12 months.
"OTOF is just the beginning," says Dr. Duan. "We and other researchers are expanding our work to other, more common genes that cause deafness, such as GJB2 and TMC1. These are more complicated to treat, but animal studies have so far returned promising results. We are confident that patients with different kinds of genetic deafness will one day be able to receive treatment."
The research involved multiple institutions, including Zhongda Hospital at Southeast University in China. Funding came from several Chinese research programs as well as Otovia Therapeutics Inc., the company that developed the gene therapy and employs many of the researchers involved. A full list of disclosures and conflicts of interest is available in the published paper.
