Dual AAV Gene Therapy Restores Hearing in Children With OTOF Deafness
Quick Facts
How Does OTOF Gene Therapy Restore Hearing?
Mutations in the OTOF gene disrupt production of otoferlin, a protein essential for releasing neurotransmitters at the ribbon synapses of inner hair cells. Without otoferlin, sound vibrations are detected mechanically by hair cells, but the electrical signal never reaches the auditory nerve — a condition called auditory synaptopathy, or DFNB9. Affected children are typically born profoundly deaf despite having structurally intact cochleae, which is precisely why they are strong candidates for gene replacement.
Because the OTOF coding sequence exceeds the packaging capacity of a single adeno-associated virus (AAV) vector, researchers use a dual-AAV strategy: the gene is split across two viral particles that recombine inside the target cells. The therapy is administered via a single intracochlear injection through the round window membrane under general anesthesia, allowing the vectors to transduce inner hair cells and reconstitute otoferlin expression.
What Have Clinical Trials Shown in Treated Children?
Results published in The Lancet in 2024 by investigators at Fudan University and collaborators at Mass Eye and Ear reported that a majority of children receiving AAV1-hOTOF experienced clinically meaningful hearing recovery, with auditory brainstem response thresholds improving from profound deafness toward moderate or mild hearing loss. Parallel trials sponsored by Regeneron, Eli Lilly, Sensorion, and Otovia have reported consistent findings across sites in the United States, Europe, and Asia.
Clinically, the most striking observation has been speech development. Children treated before the critical window for language acquisition closes — generally before age five — are beginning to recognize voices, respond to their names, and produce words. Families who had prepared for a lifetime of sign language or cochlear implants are now navigating an unanticipated milestone: their children learning to speak. Researchers caution that long-term durability, bilateral dosing strategies, and immune responses to AAV capsids remain active areas of study.
Who Is Eligible and What Are the Limitations?
OTOF-related deafness represents an estimated 1 to 8 percent of congenital genetic hearing loss, depending on the population studied. Eligibility requires genetic confirmation of pathogenic variants in both OTOF alleles, and current protocols focus on children with structurally normal cochleae and intact auditory nerves. Patients with hearing loss due to hair cell death, cochlear malformation, or other gene mutations — such as GJB2, the most common cause of genetic deafness — are not candidates for this specific therapy.
The broader implication, however, is a proof of concept that the inner ear is a tractable target for gene therapy. Programs aimed at other deafness genes, including STRC, GJB2, and TMC1, are moving through preclinical and early clinical stages. If those efforts succeed, the landscape of pediatric hearing loss — long dominated by cochlear implants and hearing aids — could shift toward molecular repair of the underlying cause.
Frequently Asked Questions
Current trials have primarily enrolled children, but some protocols now include older adolescents and adults with OTOF mutations. Benefit in adults may be more limited for speech acquisition because critical periods for language development have passed, though restoration of hearing itself remains possible.
Early follow-up data show sustained hearing improvement for several years after a single injection, but long-term durability is still being studied. Researchers are monitoring whether AAV-delivered transgene expression persists across decades or whether re-dosing will eventually be required.
Cochlear implants bypass damaged hair cells by electrically stimulating the auditory nerve and remain the standard of care for many forms of profound deafness. Gene therapy restores natural hearing through the cochlea's own anatomy, which may offer more natural sound perception — but only for specific genetic causes like OTOF mutations.
Reported adverse events in trials have generally been mild, including transient inflammation and vestibular symptoms. Serious complications have been uncommon, though immune responses to AAV capsids and the possibility of inner ear injury from surgery are ongoing safety considerations.
References
- Lv J, Wang H, Cheng X, et al. AAV1-hOTOF gene therapy for autosomal recessive deafness 9: a single-arm trial. The Lancet. 2024.
- The New York Times. New Gene Therapy Enables Children With a Rare Form of Deafness to Hear. April 2026.
- National Institute on Deafness and Other Communication Disorders (NIDCD). Genetics of Hearing Loss. NIH.
- U.S. Food and Drug Administration. Cellular & Gene Therapy Products.