6 deaf children can now hear after a single injection

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To get the new genetic material into cells, they created harmless viruses to carry it. Doctors carefully injected a small amount of liquid containing the virus into a part of the children's inner ear called the cochlea, a spiral-shaped chamber that contains hair cells. The first patient in the trial received the gene therapy in December 2022. Researchers followed the participants, who ranged in age from 1 to 6 years, for 23 weeks after treatment.

While the gene therapy didn't give the children “normal” levels of hearing, they went from hearing nothing below 95 decibels — about as loud as a food processor or a motorcycle — to perceiving sounds at about 45 decibels — the level of a normal conversation. Or the hum of the refrigerator.

“Families are very, very excited,” says Yilai Xu, a head and neck surgeon at the Eye and ENT Hospital of Fudan University and an author of the paper. For some parents, this is the first time they have heard their children called “mama” or “baba” (“papa” in Chinese).

Other children in the study had previously been fitted with a cochlear implant in one ear and had already learned to speak. In those cases, doctors injected the gene therapy into their other ear. Cochlear implants are surgically implanted devices that provide the wearer with the sensation of sound by stimulating the auditory nerve. However, implants do not reproduce natural hearing. The resulting sound may sound robotic or distorted. And when they're turned off, the wearer can't hear at all.

With gene therapy, researchers are aiming to provide a natural sense of hearing. When they contacted the patients after the injections, they took off the cochlear implants to assess how well the therapy was working in the children.

“They became more engaged and responsive. It's like a change in personality,” says Zheng-Yi Chen, an associate scientist at Mass Eye & Ear who co-led the study.

One child's hearing did not improve at all. Shu says one explanation is that the child already had immunity to the type of virus used to carry the new gene into inner ear cells — meaning the treatment would be effective. Must have been destroyed by their immune system first. It's also possible that the dose was too low to be effective, Lustig says.

Many companies are pursuing gene therapy for this very reason for deafness. Boston-based Akous, which was acquired by Eli Lilly in 2022, has treated two subjects in a clinical trial that started last year. Eli Lilly announced this week that one of those participants, an 11-year-old boy, could hear within 30 days of receiving otoferlin gene therapy.

And in October, Regeneron's Decibel Therapeutics in Boston reported improved auditory responses in a patient as part of an ongoing clinical trial. Otovia Therapeutics in China and France's Sensorion are working on similar treatments. The Fudan University trial reported today was funded by Shanghai's RefreshGene Therapeutics.

Colin Johnson, a biochemist at Oregon State University who studies otoferlin, calls the results of the Chinese and American studies a “dramatic development.” Scientists have been interested in restoring otoferlin for years, but have struggled with how to get the gene inside virus particles. The otoferlin gene is large – about 6,000 DNA letters long – and does not fit into viruses used for gene therapy. Scientists eventually discovered that they could split the gene into two parts and distribute the pieces differently. When tested in mice, the genes came together in the inner ear and allowed them to hear.