Laying the foundation for gene editing for inherited progressive deafness in adults, DFNA41

(Press-News.org) Zheng-Yi Chen, DPhil, associate scientist at the Eaton-Peabody Laboratories, and Ines and Fredrick Yeatts Chair in Otolaryngology, at Mass Eye and Ear, is the senior and co-corresponding author of a paper published in the Journal of Clinical Investigation, “Single Dose Genome Editing Therapy Rescues Auditory and Vestibular Functions in Adult Mice with DFNA41 Deafness.”

Q: How would you summarize your study for a lay audience?

This study provides an example of a successful use of gene editing technology to treat a mouse model of human genetic hearing loss.

We developed a one-time, gene editing treatment that restored hearing and balance in adult mice with a genetic form of hearing loss called DFNA41, which is also found in humans.

We used a viral vector with a harmless adeno-associated virus (AAV) to deliver precise gene editing tools into the mouse inner ear. This editing specifically removed the harmful genetic mutation while keeping the healthy gene intact.

As a result, the treated mice regained long-term hearing and balance. The gene editing treatment further protected mice from hypersensitivity to noise-induced hearing loss.

In light of our recent success using gene therapy to treat a different form of genetic hearing loss in children (in one and both ears), we believe this work has potential to become a treatment for patients with DFNA41.

Q: What question were you investigating?

We were investigating whether a single-dose, gene editing therapy could safely and effectively correct a specific genetic mutation (P2RX2 V60L) that causes DFNA41, and whether this therapy could restore hearing in adult animal models, which better mimic human treatment conditions.

We wanted to find out if there is greater benefit if the intervention is carried out earlier. We also wanted to determine if this approach could protect against further damage from loud noise and vestibular dysfunction. These are crucial steps towards our ultimate goal of being able to safely translate this treatment to humans.

Q: What methods or approach did you use?

We used a gene editing approach based on CRISPR-Cas9 technology, delivered by a AAV2 vector directly into the inner ear of adult mouse model with DFNA41. Our goal was to selectively disable the mutant copy of the P2RX2 gene without affecting the healthy one. This is very challenging to accomplish as there is only a single nucleotide difference between the normal and mutant gene sequences.

To achieve this, we designed highly specific gene-editing tools (SaCas9 with a mutation-targeting guide RNA) that we then delivered using a minimally invasive injection through the round window of the ear. This surgical, delivery approach that has been successfully used in humans.

We verified editing accuracy and safety through genetic sequencing and tissue analysis by monitoring changes in hearing and balance over time using standard auditory and vestibular tests. We also compared the treatment effects from the interventions at different time points.

Lastly, we sought to validate a similar editing strategy in human patient–derived stem cells to assess its potential for clinical translation.

Q: What did you find?

We found that a single injection of our gene-editing therapy into the inner ear of adult mice with DFNA41 successfully and specifically disabled the harmful mutation in the P2RX2 gene while preserving the normal gene. Treating this mutation led to restored long-term hearing and balance in adult mice.

This study also showed that our approach is safe by minimizing risk factors such as off-target effect – or the therapy affecting genes other than the specific one it is targeting -- or viral DNA integration.

We also found the therapy prevented further hearing loss caused by loud noise exposure. That finding is important because this increased hearing-loss risk from noise exposure is a known risk for DFNA41 patients.

Our research also demonstrated better treatment effects from early intervention, suggesting a similar strategy should be applied to humans. We were able to show this approach may have promise as a human treatment, as we identified an effective and specific editing strategy in patient-derived stem cells carrying the same human mutation (P2RX2 V60L).

Q: What are the implications?

Our study shows that gene editing can be used as a one-time, lasting treatment to rescue hearing and balance in adults with genetic inner ear disorders—something previously thought to be possible only during early development.

 This finding has several key implications and may pave the way for future trials testing gene editing approaches for hearing and balance disorders.

First, there is potential for a therapeutic breakthrough, showing for the first time, that precise gene editing can effectively treat dominant, progressive hearing loss in fully mature ears—bringing us closer to real-world applications in humans.

 Current trials have been in children born with deafness. This study showed that our approach can be applied to patients who develop delayed-onset hearing loss, from childhood to adulthood. The study also found a dual benefit of rescuing balance function and protecting against noise-induced hearing loss, offering additional protection for people with genetic susceptibility.

This work lays the groundwork for first-in-human trials for DFNA41, by showing safety, long-term benefit, and success in human stem cells carrying the same mutation. This foundation may also be feasible for other forms of inherited deafness in adults. The mutation-specific design of the therapy highlights the growing potential of precision medicine—tailoring treatments to an individual’s specific genetic mutation.

Q: What are the next steps?

Building on our proof‑of‑concept successes in mice and human stem cells, we are now moving toward clinical translation through a series of IND‑enabling studies, with support from a grant from the NIH Somatic Cell Genome Editing (SCGE) program.

The grant supports two IND-enabling programs of editing therapy for genetic hearing loss, DFNA41 due to P2RX2 mutations and DFNA2 due to KCNQ4 mutations. We aim to complete the biodistribution and toxicity studies in order to initial clinical trials in a few years.

We are working in conjunction with Mass General Brigham’s Gene and Cell Therapy Institute on this grant as well as research efforts to develop platforms and vectors that would speed up the research process, making it easier to test the gene therapy approaches on new genes.

Authorship: In addition to Chen, study co-authors include Wei Wei, Wenliang Zhu, Stewart Silver, Ariel M Armstrong, Fletcher S Robbins, Arun Prabhu Rameshbabu, Katherina Walz, Yizhou Quan, Wan Du, Yehree Kim, Artur A. Indzhykulian, Yilai Shu, and Xue-Zhong Liu.

Funding: This work was supported by the fundings from National Institutes of Health grants: R01DC006908, R56DC006908, UG3TR002636, U01TR005352 (Z-Y.C.), and R01DC022239, R01DC017264, R01DC005575, R25 DC020726 (X-Z.L.); R01DC020190, R01DC021795, and R01DC017166 (A.A.I.); Department of Defense grant: W81XWH181033; and RH220053-W81XWH-22-HRRP-FRA (X-Z.L.), Fredrick and Ines Yeatts hair cell regeneration fellowship (Z-Y.C).

Paper cited: Wei, W, et. al. “Single-Dose Genome Editing Therapy 1 Rescues Auditory and Vestibular Functions in Adult Mice with DFNA41 Deafness.” Journal of Clinical Investigation DOI: XXX

Disclosures: Chen is a co-founder of Salubritas Therapeutics and has a financial interest in Regeneron Pharmaceuticals. Chen, Wei and Zhu have filed patent applications based on this work. Liu is a SAB member of Rescue Hearing Inc, and Salubritas Therapeutics. The other authors declare no competing interests.

END