BY THE OPTIMIST DAILY EDITORIAL TEAM

A girl born without the ability to hear was having everyday conversations with her mother four months after a single injection into her inner ear. She was seven years old. The treatment did not give her a hearing aid or implant. It gave her a gene she had been missing.

Researchers at Karolinska Institutet, working with hospitals across China, published results in Nature Medicine last month from a trial involving ten patients with congenital deafness caused by mutations in a gene called OTOF. Every patient showed measurable improvement. Most started noticing changes within one month. By six months, the average level at which participants could detect sound had shifted from 106 decibels to 52, roughly the difference between a jackhammer and a normal conversation.

What OTOF does and why its absence silences people

The OTOF gene encodes a protein called otoferlin, which functions as a molecular switch at the inner hair cells of the cochlea. When sound waves cause those cells to vibrate, otoferlin triggers the release of neurotransmitters that carry the signal to the auditory nerve and on to the brain. Without it, the mechanical process of hearing is physically intact. The ear can receive sound, but nothing gets transmitted. The signal stops before it begins.

The therapy used a synthetic adeno-associated virus (AAV) to deliver a working copy of OTOF directly into the cochlea through a single injection at the round window, a thin membrane at the base of the inner ear. The AAV acts as a delivery vehicle, carrying the corrected gene into the hair cells without altering the surrounding tissue.

Younger patients showed the sharpest gains

Children between the ages of five and eight responded most dramatically to the treatment. The auditory cortex in younger patients appears better able to reorganize itself around newly available signals. Even so, the trial’s defining detail is that adults improved, too.

“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,” said Dr. Maoli Duan of Karolinska Institutet, one of the study’s corresponding authors. “Hearing was greatly improved in many of the participants, which can have a profound effect on their life quality.”

The youngest patient in the trial was one year old. The oldest was 24.

Safety findings and what comes next

No serious adverse reactions were observed during a follow-up period of six to twelve months. The most frequently reported side effect was a temporary drop in neutrophils, a type of white blood cell that plays a role in immune response.

OTOF mutations account for a relatively small share of genetic hearing loss. GJB2 mutations are considerably more common and are among the leading causes of congenital deafness worldwide. TMC1 mutations affect a different protein critical to the mechanical function of hair cells. Both are harder to treat than OTOF, partly because of how they interact with surrounding tissue and partly due to the size of the proteins involved.

“OTOF is just the beginning,” said 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 was funded in part by Otovia Therapeutics Inc., the company that developed the therapy and employs several of the researchers involved. Full disclosures are available in the published paper. Long-term follow-up is ongoing, and the research team is monitoring how durable the effects prove to be. What the current data shows is that every person enrolled in this trial heard more after treatment than before it.

Source study: Nature Medicine– AAV gene therapy for autosomal recessive deafness 9: a single-arm trial

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