Gene therapy for hearing loss has transitioned from a theoretical concept into a transformative clinical reality, albeit limited to specific cases of genetic hearing loss—for now.
This first breakthrough targeted autosomal recessive deafness 9 (DFNB9), caused by an OTOF gene variant. The OTOF gene produces otoferlin, a protein enabling inner hair cells to transmit sound signals. Sixty percent of deafness in newborns has genetic causes, with the OTOF gene variant responsible for 2 to 8 percent of cases.
Because the sensory hair cells of the cochlea (inner ear) in DFNB9 remain structurally intact but “silent,” the condition was an ideal candidate for genetic intervention. Since the OTOF gene is too large for a single viral shell, the researchers pioneered a “dual-vector” approach, splitting the gene into two halves that recombine once inside the cell to restore function. This dual-AAV (adeno-associated virus) vector strategy successfully delivers functional OTOF to the cochlea.
In a major milestone, in April 2026 the U.S. Food & Drug Administration approved Otarmeni (lunsotogene parvec-cwha), the first-ever dual-AAV vector-based gene therapy for the treatment of OTOF-related hearing loss under the National Priority Voucher program. The FDA noted that in clinical trials, about 80 percent of treated children with profound OTOF‑related deafness regained meaningful hearing, with 42 percent reaching typical hearing that included whispers and with improvements lasting up to 2.5 years (when the study concluded).
However, many genetic causes of hearing loss are not monogenic but polygenic, involving complex interactions of multiple genes that cannot be resolved by a single gene replacement. In addition, unlike in DFNB9, many types of genetic hearing loss stem from problems with hair cells: They are malformed, fail to develop, or degenerate progressively before or shortly after birth.
Additionally, the great majority of hearing loss is due to hair cells damaged by non-genetic factors, including exposure to loud sounds, accumulated noise damage with age, and ototoxic drugs (such as chemotherapy). As a result, future gene therapy is focusing on regenerative medicine and using genetic triggers to reprogram supporting cells into new, functional hair cells. This is the focus of the Hearing Restoration Program (HRP) consortium that is supported by Hearing Health Foundation (HHF).
Key Roles and Discoveries
HHF-funded scientists played key roles in gene therapy for hearing loss: HHF board member and former Emerging Research Grants (ERG) scientist Anil K. Lalwani, M.D., pioneered the use of AAV as a gene delivery method in the 1990s; former ERG scientists John Germiller, M.D., led OTOF-related gene therapy research at Children’s Hospital of Philadelphia, and Zheng-Yi Chen, D.Phil., led OTOF-related gene therapy studies in China. Former ERG scientists Jason Riggs, Ph.D., Au.D., and Renjie Chai, Ph.D., also contributed to the research.
The HRP’s Andy Groves, Ph.D., and Litao Tao, Ph.D., studied DNA near the gene Lunatic Fringe (Lfng), which is specific to inner ear supporting cells, and identified three potential "switches" (enhancers) that could activate genes in these cells. They inserted these switches into an adeno-associated virus (AAV) and injected it into newborn mice. The experiment demonstrated that the switches effectively activated genes exclusively in the ear's supporting cells, with no activity detected elsewhere. Credit: Seist et al./Hearing Research
Here are additional recent discoveries from HRP and ERG scientists in this area:
The HRP’s Andy Groves, Ph.D., along with ERG scientists Melissa McGovern, Ph.D., and Bradley Walters, Ph.D., showed that in the mouse inner ear, mature cochlear supporting cells could be reprogrammed into sensory hair cells, providing a possible target for hair cell regeneration in mammals. Groves, a 1996–1997 and 2012 ERG scientist, in a paper coauthored by the HRP’s Litao Tao, Ph.D., also showed it is possible to design gene therapies for the ear that are carefully targeted at supporting cells (see illustration above).
The HRP’s Ksenia Gnedeva, Ph.D., revealed a class of DNA control elements known as “enhancers” that, after injury, amplify the production of a protein called ATOH1, which in turn induces a suite of genes required to create sensory cells of the inner ear in zebrafish.
The HRP’s Tatjana Piotrowski, Ph.D., a 2007 ERG scientist, identified how two distinct genes guide the regeneration of sensory cells in zebrafish, which may help guide regenerative medicine in mammals, including humans. She also showed that the transcription factor prdm1a plays a key role in determining hair cell fate in the zebrafish lateral line.
HRP member Stefan Heller, Ph.D., a 2001–2002 ERG scientist, showed that supporting cells in the avian inner ear uses two regeneration strategies: Some divide to create new hair cells, while other supporting cells transform directly into functional hair cells without cell division. Mammals possess nearly identical cell types, but these fail to activate.
And finally HRP member Yehoash Raphael, Ph.D., in the 2025 Annual Review of Genetics, discussed the challenges and future directions of the field of hair cell regeneration, pointing toward the use of genomics and epigenetics to decode gene expression and its epigenetic regulation. Raphael is a 1991–92, 1993, and 1997 ERG scientist.
Gene therapy for DFNB9 provided a foundational proof of concept. Now the next frontier lies in addressing structural and multigene complexities to treat other genetic causes of sensorineural hearing loss.
The Latest Blog Posts
Gene therapy for hearing loss has transitioned from a theoretical concept into a transformative clinical reality, albeit limited to specific cases of genetic hearing loss—for now.