The therapy delivers a working copy of the OTOF gene using an adeno-associated virus as the carrier. Injected into the cochlear fluid through the round window at the base of the cochlea, the virus infects the hair cells and delivers its genetic payload. The cells begin producing otoferlin, the calcium-sensing protein at the synapse where sound is converted into the nerve signal the brain reads, and a junction that never worked begins to function.
The trial enrolled six children aged one to eleven, all with confirmed mutations in both copies of OTOF and profound hearing loss. Five of the six showed measurable restoration of hearing after a single injection. Two progressed to functional speech comprehension and conversational ability. For families of children with this condition, the baseline is a child who has never heard speech, music, or their own name; two of these children cleared the trial's threshold so thoroughly that they can now hold a conversation.
Outcome tracked closely with age. The auditory cortex is most plastic in early childhood, the window when the brain reorganizes itself around sound, and the youngest patients showed the strongest responses. That mirrors what is known about cochlear implants and underlines the value of early diagnosis, achievable through newborn genetic screening. The OTOF coding sequence sits near the upper limit of what an AAV can carry, which is why earlier attempts faced manufacturing hurdles; the team used a single optimized vector with a serotype that preferentially infects cochlear hair cells.
The durability question remains open. AAV delivers its payload to cells that do not divide, and inner hair cells, once differentiated, are stable, so in theory the benefit should persist. In practice the longest cochlear-gene-therapy follow-up is about three years, and the field is waiting for more.
Regeneron is expanding the trial with longer follow-up and studying whether the approach helps adults, whose reduced cortical plasticity may still allow partial restoration. Regulatory filings have not been made; the trial remains Phase 1/2. The larger implication is the platform: this condition affects an estimated 200,000 people, but the same delivery mechanism applies to the 200-plus other identified genetic causes of congenital hearing loss. The first one is the hardest. The second is faster.