Five children born deaf can now hear, thanks to just one injection

Five children born deaf can now hear, thanks to just one injection

Six children who were born deaf were given a revolutionary gene therapy treatment in the form of an injection in the ear. Now, five of them have regained their hearing.

Written by Sethu Pradeep

Kochi | Updated: January 27, 2024 10:09 IST

The snail-shaped cochlea of the inner ear (Katelyn Comeau/Harvard Medical School)

After receiving an experimental treatment consisting of an injection into the ear, six children who were born deaf can now hear. The researchers behind the novel gene therapy approach believe that it may be useful in other treatments as well.

The research was conducted in Fudan, China but the team was co-led by Harvard Medical School researchers at the Massachusetts Eye and Ear. They treated six children between the ages of one and seven suffering from a type of inherited deafness. This was caused by the mutation of the OTOF gene, which manufactures a protein that plays an important role in transmitting signals from the ear to the brain.

Over the course of the 26-week trial, five of the six children showed signs of improved hearing, with the researchers describing four of the outcomes as “robust,” according to Harvard Medical School. The results of the study were published in the journal Lancet on Wednesday. Hearing ability is a critical factor in language learning. For the study, the researchers also measured speech perception, which is the ability to recognise sounds as speech. All five of the children who responded showed improvement there.

“This really opens the door to developing other treatments for different kinds of genetic deafness,” said co-senior author Zheng-Yi Chen in a press statement. Chen is an HMS associate professor of otolaryngology, head and neck surgery, and a researcher at Mass Eye and Ear’s Eaton-Peabody Laboratories.

The OTOF gene is responsible for the otoferlin protein, which is produced by cells in the snail-shaped part of the inner ear called the cochlea. The cochlea is the place where sound waves are translated into electric pulses carried to the brain by nerve cells. Otoferling helps transmit pulses from cochlear cells to nerves. Without it, sound would be translated to electric signals but they would never reach the brain.

The OTOF gene mutation the children had is an attractive target for gene therapy because it is a relatively simple condition caused by a single mutation. It also involves no physical damage to the cochlear cells.

When the researchers requested for study partners, they received a large response of 425 potential participants. According to Chen, this reflects the need for improved treatment for such congenital deafness that has no approved drugs. After screening the participants, the researchers enrolled just six at the end.

Among the six, four children had cochlear implants. With training, these implants allowed for the interpretation of speech and sound. The youngest two participants were aged one and two and had no implants. And when the implants were switched off, all the participants were completely deaf.

The procedure used by the researchers called for the gene to be inserted into the cochlea using a type of virus often used for this kind of treatment. The virus will insert the gene into the DNA of the target cells, causing them to manufacture the missing protein. But there was a problem — the OTOF gene was too big for the virus to hold.

They got past this problem by dividing the gene into two and then containing the halves in two different viruses. After that, they injected the mixture with both halves of the gene into the cochlea. Even though the viruses inserted the gene halves into different spots on the cells’ DNA, cellular machinery assembled the complete protein when the halves were expressed.

This special mixture was injected into the fluid of the inner ear, and from there, the viruses made their way to the target cells just like you would expect in a normal injection. The researchers and the participants waited for four to six weeks in each case to see the first signs of hearing being restored.

Five of the six participants displayed signs of progressive improvement. When the three older children had their cochlear implants turned off, they could understand and respond to speech by 26 weeks, with two among them able to recognise speech in a noisy room and even have a telephone conversation. The youngest children also showed improvements but they were too young for the tests.

Only one of the participants showed no signs of improvements. The researchers are not entirely sure about the cause, but they say it may have been because of an immune reaction to the viral vector.

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First uploaded on: 27-01-2024 at 09:32 IST