Aissam Dam, an 11-year-old boy, grew up in a world of profound silence. He was born deaf and never heard anything. While living in a poor community in Morocco, he expressed himself with a sign language that he had invented and had not received schooling.

Last year, after moving to Spain, his family took him to a hearing specialist, who made a surprising suggestion: Aissam might be eligible for a clinical trial using gene therapy.

On October 4, Aissam was treated at Children’s Hospital of Philadelphia, becoming the first person to benefit from gene therapy in the United States for congenital deafness. The goal was to allow him to hear, but researchers didn’t know whether the treatment would work or, if it did, how well he would hear.

The treatment was a success, introducing a new world to a child who knew nothing about sounds.

“There’s no sound I don’t like,” Aissam said, with the help of interpreters, in an interview last week. “They are all good.”

While hundreds of millions of people around the world live with hearing loss defined as disabling, Aissam is one of those whose deafness is congenital. This is an extremely rare form, caused by a mutation in a single gene, otoferlin. Otoferline deafness affects approximately 200,000 people worldwide.

The goal of gene therapy is to replace the mutated otoferlin gene in patients’ ears with a functional gene.

Although it will take years for doctors to recruit many more patients – and younger ones – to further test the therapy, researchers said the success of patients like Aissam could lead to gene therapies targeting other forms of congenital deafness.

This is a “groundbreaking” study, said Dr. Dylan K. Chan, a pediatric otolaryngologist at the University of California, San Francisco and director of its Children’s Communication Center; he was not involved in the trial.

The one Aissam participated in is backed by Eli Lilly and a small biotech company he owns, Akouos. Investigators hope to eventually expand the study to six centers across the United States.

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