Gene therapy involves administering normal copies of the mutated gene that causes a particular disease.
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Five Chinese children born deaf have received gene therapy that provides them with a healthy copy of a mutated gene, allowing them to hear in both ears. Although the children have varying degrees of hearing loss, all can now hear and localize sounds at conversational volume.
Six months after treatment, the five children’s hearing was about 50 to 60 percent of normal levels, team members say. Chen Yi Chen “They get confused when we whisper, but normal conversation is fine,” he said at the Massachusetts Eye and Ear Infirmary in Boston. “We’re very happy.”
In the first phase of the trial, which began in 2022, the team gave another group of six children in China the gene therapy in just one ear. Five of the six children had their hearing restored in the treated ear, with continued improvement, Chen said.
The team expects to see further progress in the second group of five children. “The progress we’re seeing now isn’t the peak,” Chen says. “We expect to see even more progress.”
The trial in China is the first of several ongoing trials around the world. She lives in the UK with her two children. There have also been reports in the United States of people regaining hearing in one ear after undergoing gene therapy.
“The tests are all pretty much the same.” Manohar Bans Doctors from Cambridge University treated two children in the UK.
All of the children in these trials were born with hearing loss because they carry a mutation in both copies of the gene for a protein called otoferin, which plays a key role in synapses, or connections, between the hair cells in the ear that detect sound and the nerves that transmit signals to the brain. The mutation affects the protein, blocking the transmission of signals.
Between 2 and 8 percent of children worldwide who are born with hearing loss are thought to have this condition, known as DFNB9.
Both parents of a child with DFNB9 have normal hearing if they each have just one mutant copy of otoferlin. These couples are often unaware that they have a one in four chance of having a child that is born deaf.
Gene therapy relies on the help of a virus called AAV to deliver a working version of the otoferlin gene to hair cells. Due to the gene’s large size, it needs to be split and put into two separate viruses.
The virus cocktail is injected into the inner ear, and the complete gene is reconstituted in cells that receive both halves. The DFNB9 trial marks the first time that so-called dual AAV gene therapy has been used to treat humans.
“This is a major technological advance,” Chen says, “and we hope that this technology will be widely used to treat other genetic diseases.”
The clinical trials will begin by treating one ear at a time because half the dose of AAV is needed, reducing the chance of adverse events, he says. No serious adverse events have been reported in any of the trials.
Chen’s team now plans to treat the other ears of the first group of children. This could be difficult because an immune response to the initial AAV injection could block gene delivery, but Chen believes it is possible.
Treating other inherited hearing loss is more difficult because some of the structures inside the ear degenerate. With DFNB9, all of the structures remain intact. “You only need to repair one element,” Chen says.
Some people believe that hearing loss is not a disease that needs treatment, Martin MacLean The position of the National Society for Deaf Children. Families should be free to make their own informed decisions.
“Parents and young people need to be aware of all the risks and, above all, understand that hearing loss in itself does not prevent people from living a happy and fulfilling life,” he says.
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Source: www.newscientist.com
