RNA base editing therapy cures hearing loss induced by OTOF gene mutation

Otoferlin (OTOF) gene mutations represent the primary cause of hearing impairment and deafness in auditory neuropathy. The c.2485C>T (p. Q829X) mutation variant is responsible for approximately 3% of recessive prelingual deafness cases within the Spanish population. Previous studies have used two recombinant AAV vectors to overexpress OTOF, albeit with limited efficacy. In this study, we introduce an enhanced mini-dCas13X RNA base editor (emxABE) delivered via an AAV9 variant, achieving nearly 100% transfection efficiency in inner hair cells. This approach is aimed at treating OTOF^Q829X, resulting in an approximately 80% adenosine-to-inosine conversion efficiency in humanized Otof^Q829X/Q829X mice. Following a single scala media injection of emxABE targeting OTOF^Q829X (emxABE-T) administered during the postnatal day 0-3 period in Otof^Q829X/Q829X mice, we observed OTOF expression restoration in nearly 100% of inner hair cells. Moreover, auditory function was significantly improved, reaching similar levels as in wild-type mice. This enhancement persisted for at least 7 months. We also investigated P5-P7 and P30 Otof^Q829X/Q829X mice, achieving auditory function restoration through round window injection of emxABE-T. These findings not only highlight an effective therapeutic strategy for potentially addressing OTOF^Q829X-induced hearing loss but also underscore emxABE as a versatile toolkit for treating other monogenic diseases characterized by premature termination codons.