All five children taking part in a Shanghai-led clinical trial of a gene therapy to treat congenital hearing loss showed significant restoration of hearing in both ears, researchers said on Wednesday.

Their speech function and ability to locate the sources of sound were also greatly improved, researchers from the Eye and ENT Hospital of Fudan University in Shanghai said.

It was the world's first clinical trial of a gene therapy for both ears, they said.

The children, aged between 1 and 11, all have autosomal recessive deafness 9, mainly caused by mutation of a particular gene, OTOF. The research team injected gene therapy medicine developed in its previous studies into both ears of the patients in the same session, using minimally invasive and microscopic injection methods.

"Good safety of the therapy was demonstrated during their follow-up observations, proving that the binaural gene therapy with the treatment known as AAV1-hOTOF was safe and effective," said Shu Yilai, one of the leading researchers and director of the inherited deafness diagnosis and treatment center affiliated with the Shanghai hospital.

A paper about their research, a joint effort with Harvard Medical School associate professor Zheng-Yi Chen, was published recently in the journal Nature Medicine.

There are an estimated 26 million people with congenital hearing loss worldwide, and approximately 30,000 infants are born with the condition in China each year. Experts said that 60 percent of them are related to genetic factors, which severely damage their speech, cognition and intellectual development. There is, as yet, no effective clinical therapy.

People with the OTOF mutation usually suffer from severe or even complete hearing loss and speech impairment. In China, among the infants and young children diagnosed with auditory neuropathy spectrum disorder, up to 41 percent have a mutation in the OTOF gene.

Gene therapy is widely considered by experts to be one of the most promising strategies for curing hereditary deafness. It can deliver genes with normal function directly to the inner ear through a delivery vehicle, fundamentally restoring or improving hearing for such patients, the research team said.

It began recruiting participants from China for the clinical trial to receive treatment in one ear in October 2022, and completed the treatment of the first patient outside China in December that year.

Six patients were included in the trial to receive gene therapy in one ear, and the longest follow-up time for a participant has now reached 17 months, with the young patient later able to hold daily conversations.

Shu shared the clinical trial data at the annual conference of the European Society of Gene and Cell Therapy, one of the world's most authoritative international academic conferences in the field of gene and cell therapy, in Belgium in October.

The results of the clinical research that used gene therapy in one ear were published in The Lancet in January. International peers said it could open a new era for treating hearing impairment and even more diseases through gene therapy.

The clinical trial of the gene therapy in both ears began recruiting participants in July last year.

"We took a step further to try to restore the natural ability of human hearing in both ears for the patients," Shu said. "It'll also help to restore their ability to hear three-dimensional sound, locate sound sources, and distinguish speech in the context of noise."

He shared the latest progress in the trial with experts and scholars from around the world during the annual conference of the American Society of Gene& Cell Therapy held last month in Baltimore in the United States.

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