A clinical trial led by Chinese scientists has successfully treated a type of congenital deafness, with a 100% response rate among children aged 6 months to 3 years.

The study, published April 22 in Nature, was led by the Eye & ENT Hospital of Fudan University in Shanghai, with collaborators including Harvard Medical School in the U.S. and Peking Union Medical College Hospital in Beijing. 

Around two to three in every 1,000 newborns worldwide are affected by hearing loss, with up to 60% of cases linked to genetic mutations. Until now, treatment has predominantly relied on hearing aids or cochlear implants, which offer limited improvements.

Launched in 2022, the trial is both the first and largest in congenital deafness gene therapy, researchers said. It enrolled 42 patients aged 9 months to 32 years and followed them for up to two and a half years — the longest period reported so far — while comparing outcomes across age groups. 

The trial targets deafness caused by a specific mutation in the OTOF gene, which disrupts sound transmission from the inner ear to the brain, said Shu Yilai, leader of the research team and chief physician at the Eye & ENT Hospital of Fudan University.

Such individuals are typically born with severe-to-profound hearing loss in both ears, preventing normal language development and affecting cognition.

The therapy uses a viral vector — a modified virus — to deliver a functional copy of the defective gene into inner-ear cells through minimally invasive surgery.

Test subjects showed an overall response rate of 90%. Among successfully treated patients observed for 30 months following surgery, all reported being able to hear everyday conversation and more than half detecting sounds at a library-level volume. Just under half could hear whispered voices.

Younger patients benefited most. All patients aged 6 months to 3 years reported 100% hearing restoration, while two-thirds of patients over the age of 20 also reported hearing improvement.

The study also outlines which biomarkers could help predict who will benefit most from treatment. “The more cochlear function is preserved before treatment, the better the therapeutic outcome,” the research team told Sixth Tone. 

The team described one young patient diagnosed with OTOF-related deafness at 18 months. “He showed no response to sound and was slow to begin speaking,” they said. “When imitating others crying, he would open his mouth wide but make no sound.”

But after treatment, he gained hearing and speech.

“Seeing children and their families transformed — from living in a silent world to having clear speech — is the driving force behind more than a decade of persistence and countless technical challenges,” the team said.

A day after the paper went online, the U.S. Food and Drug Administration approved a separate in vivo gene therapy for OTOF-related hearing loss for clinical use — the world’s first — made by American biotech giant Regeneron. The drug’s clinical trial was launched a year after the Chinese trial and used a different drug design.

Editor: Marianne Gunnarsson.

(Header image: Visuals from VCG, reedited by Sixth Tone)