In a groundbreaking advance for the treatment of hereditary deafness, researchers have reported promising long-term outcomes from a multicentre gene therapy trial targeting autosomal recessive deafness 9 (DFNB9), a severe form of congenital hearing loss caused by mutations in the OTOF gene. This study, published in Nature in 2026, highlights the sustained safety and efficacy of an adeno-associated virus 1 (AAV1) vector delivering a human OTOF transgene, offering new hope for patients whose deafness was previously considered irreversible.
Autosomal recessive deafness 9 is characterized by profound and congenital hearing impairment due to biallelic mutations in OTOF, a gene encoding otoferlin, a crucial protein for synaptic transmission in inner hair cells. This synaptic disruption severely impairs auditory signaling, leading to little or no functional hearing from birth. Traditional interventions like cochlear implants offer limited success for some patients but do not restore the underlying synaptic physiology. Gene therapy, aiming to replace or correct the defective gene within cochlear hair cells, has emerged as a transformative approach, yet previous trials were limited in size, age range, and follow-up duration.
The recently completed open-label, multicentre clinical trial enrolled 42 participants spanning a remarkably broad age range—from infancy to young adulthood (0.8 to 32.3 years)—to assess the safety, tolerability, and efficacy of AAV1-hOTOF gene therapy. Participants were stratified into three vector dose groups and monitored for adverse events and auditory improvement over an extended 2.5-year period. This comprehensive follow-up provided robust longitudinal data rarely captured in gene therapy trials for sensory disorders.
A critical primary outcome of the trial was dose-limiting toxicity within the first six weeks post-injection, a key milestone for evaluating safety in vivo gene transfer. Impressively, no dose-limiting toxicities emerged, and adverse effects were generally mild with only some Grade 3 events such as decreased neutrophil counts, manageable under clinical care. The favorable safety profile across different age groups and doses lays important groundwork for further development and regulatory approval.
Efficacy endpoints revealed remarkably durable improvement in auditory function following treatment. Measurement of auditory brainstem response (ABR) thresholds demonstrated progressive reductions from near-complete hearing loss at baseline (97±1 dB normalized hearing level) to substantial recovery—down to 42±5 dB normalized hearing level at 2.5 years. Behavioral audiometry corroborated these findings, showing mean thresholds improved from profound hearing deficits to mild hearing loss levels, a transformative functional gain for individuals who were previously deaf.
Notably, younger participants, particularly those aged 0.5 to 18 years, showed greater auditory gains compared to adults, suggesting that earlier intervention may capitalize on residual cochlear plasticity and maximize gene therapy outcomes. However, even adult patients displayed meaningful hearing improvements, challenging prior assumptions that gene therapy benefits wane with age in hereditary deafness.
Baseline biomarkers also appeared predictive of therapeutic response. A higher number of present distortion product otoacoustic emissions (DPOAEs)—indicators of hair cell activity—and the presence of biallelic non-truncating OTOF variants were correlated with more robust hearing recovery. These findings may inform patient selection criteria and prognostication in future clinical applications.
Beyond pure-tone thresholds, participants who experienced auditory improvement also demonstrated gradual enhancement in speech perception abilities over the follow-up period. This neurosensory and functional recovery indicates that gene therapy not only restores cochlear electrophysiology but translates to meaningful improvements in communication and quality of life.
This study marks a significant leap in translating gene editing tools from bench to bedside for sensory neural disorders. The use of AAV1 serotype vectors, optimized for cochlear hair cell tropism, combined with codon-optimized human OTOF transgenes, exemplifies precision molecular engineering adapted for therapeutic efficiency and durability.
While this trial was open-label and single-arm, the outcomes reflect breakthrough progress in overcoming prior limitations associated with narrow age cohorts and short-term follow-up. Multi-institutional collaboration across eight centers armed the study with the statistical power and diversity needed to validate gene therapy applicability across a broader patient population.
Looking forward, the success of AAV1-hOTOF gene therapy paves the way for regulatory submissions and future randomized controlled trials to underscore comparative efficacy and establish standardized protocols. The extended follow-up of 2.5 years is particularly encouraging for the durability of benefits in a condition traditionally deemed untreatable by molecular interventions.
The promising safety and efficacy demonstrated offer a new horizon for individuals with autosomal recessive deafness 9 and underscore the growing potential of gene therapy approaches in treating inherited sensory disorders. With continued advancements in vector technology and patient stratification, gene therapy for hereditary deafness may soon become a mainstream clinical option, reducing dependence on prosthetic devices and profoundly enhancing patient outcomes.
As gene therapy for OTOF-related deafness moves toward wider clinical implementation, researchers emphasize the importance of early diagnosis and genetic screening to identify candidates who can benefit most from these interventions. The identification of biomarkers predictive of response will further personalize treatment, ensuring optimal therapeutic outcomes.
This landmark study’s findings were registered in the Chinese Clinical Trial Registry (ChiCTR2200063181), highlighting the increasing global collaboration in advancing gene therapy treatments. The successful translation of molecular genetics into clinical success stories represents a major victory not only for deafness research but for the broader field of inherited neurosensory diseases.
In summary, the multicentre gene therapy trial for OTOF-related deafness has demonstrated a compelling blend of safety, precision, and long-term efficacy, reinforcing the remarkable potential of modern molecular medicine to rewrite the narrative of congenital sensory impairments. Sustained hearing restoration over years in children and adults alike sustains optimism that gene therapy can bridge the gap once thought insurmountable in irreversible genetic deafness.
Subject of Research:
Gene therapy for autosomal recessive deafness 9 caused by OTOF gene mutations
Article Title:
Multicentre gene therapy for OTOF-related deafness followed up to 2.5 years
Article References:
Jiang, L., Cheng, X., Lv, J. et al. Multicentre gene therapy for OTOF-related deafness followed up to 2.5 years. Nature (2026). https://doi.org/10.1038/s41586-026-10393-y
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