Regeneron Pharmaceuticals said on Monday its experimental gene therapy showed improved hearing in 10 of 11 children between 10 months and 16 years old born with hearing loss caused by gene mutations.

The first child in the study to receive Regeneron's therapy, who was dosed at 10 months of age, showed improvement in hearing which was at normal levels in most speech-relevant sound frequencies, the company added.

The updated data, which was presented at Association for Research in Otolaryngology's 48th Annual MidWinter Meeting, adds to growing evidence of the efficacy of such treatments in children who have profound deafness caused by mutations of the OTOF (otoferlin) gene.

Other developers such as China's Refreshgene and Eli Lilly have also developed therapies that have restored hearing in children in early trials.

"It's an ultra rare condition," said Jonathon Whitton, global program head of Regeneron's genetic medicines unit, adding that less than 50 children are born yearly with the mutation.

Otoferlin is a protein found in the ear's inner hair cells which vibrate to transmit sound signals to the brain. The therapy works by sending instructions encoded in DNA for the cells to produce the otoferlin protein, Whitton said.

Among 11 children with at least one post-treatment assessment, 10 showed improved hearing at various decibel levels, Regeneron said.

Additionally, of the five patients that underwent 24-week assessments, three experienced improvements to "nearly normal" or "normal" hearing levels. The first patient, 48 weeks after dosing, correctly identified words including "mommy," "cookies" and "airplane" at a conversational level without visual cues, Regeneron said. Regeneron had said last year the therapy helped the first patient reach normal hearing levels within 24 weeks and that a second child saw hearing improvements at 6 weeks.