A Single Injection Gave Ten People With an Inherited Deafness Their Hearing

For the ten patients in this study, the problem started with a single gene. All of them were born with congenital deafness or severe hearing impairment traced to mutations in a gene called OTOF. That gene is supposed to make otoferlin, a protein whose job is to relay the signal of sound onward from the inner ear toward the brain. Without enough of it, the ear can gather sound and still fail to pass the message along. The machinery is mostly intact. One relay is missing.

So the researchers set out to supply the missing part. They loaded a functioning version of the OTOF gene into a synthetic adeno-associated virus, a harmless courier, and delivered it with one injection through the round window, the thin membrane at the cochlea’s base. One dose, aimed at the inner ear. According to the Karolinska Institutet team behind the work, published in Nature Medicine, that was enough to change what these patients could hear.

The response came faster than the timeline usually allows. Most of the ten began to hear within the first month, and by the six-month mark all of them had improved considerably. On average, the quietest sound anyone in the group could still register fell from about 106 decibels to 52. A 106-decibel threshold is the territory of a chainsaw or a rock concert, roughly the only things loud enough to register. A 52-decibel threshold reaches down into the range of ordinary conversation.

A seven-year-old’s four months

The patients ranged in age from 1 to 24, treated at five Chinese hospitals. The biggest gains went to the youngest, and to the five-to-eight-year-olds in particular. One girl of seven got back nearly all of what she had been missing; within four months she was chatting with her mother as easily as any child. The researchers keep her unnamed, and hers is the kind of audiogram the whole field has been working toward.

The adults benefited too, and that is what set this trial apart. Smaller studies in China had already shown the method could help young children. This was the first time it was tried in teenagers and adults, the first evidence that a nervous system further from infancy could still take up the correction and use it.

What the safety data showed

Across six to twelve months of follow-up, there were no serious adverse reactions. Its main side effect was a brief fall in one kind of white blood cell, the neutrophils. The team is continuing to track all ten patients to learn how long the effect holds, which is the open question a single follow-up window cannot answer yet.

This is not a cure, and it does not speak to deafness in general. OTOF-related hearing loss is one specific genetic cause among many, and this therapy was built to address that one. It works precisely because it targets a single, well-understood break in the chain.

That specificity is also the reason the researchers are optimistic about what comes next. Maoli Duan of Karolinska Institutet, a corresponding author on the study, put the scope of the result plainly. “This is a huge step forward in the genetic treatment of deafness, one that can be life-changing for children and adults,” he said. And then he pointed past it: “OTOF is just the beginning.”

The team has already named its next two targets, GJB2 and TMC1. Both are more common causes of genetic hearing loss than OTOF, and both are more complicated to correct. Early animal studies have been encouraging, which is where the OTOF story started too.

The study also comes with a disclosure. It was financed in part by Otovia Therapeutics Inc., which developed the therapy and employs a number of the scientists behind it. That tie belongs alongside any early result this hopeful. It does not change what the audiograms recorded: ten people who could not hear, and then could, after a single injection aimed at one small gene.