PAM-flexible adenine base editing rescues hearing loss in a humanized MPZL2 mouse model harboring an East Asian founder mutation

Hearing loss is one of the most prevalent sensory disorders, but no commercial biological treatments are currently available. Here, we identify an East Asia-specific founder mutation, the homozygous c.220C>T mutation in MPZL2, that contributes to a significant proportion of hereditary deafness cases in our cohort study. We find that the disease-causing mutation can be targetable by adenine base editors (ABEs) that enable A·T-to-G·C base corrections without DNA double-strand breaks. To demonstrate this, we develop a humanized mouse model (hMPZL2Q74X/Q74X) that recapitulates human MPZL2 deafness and leads to progressive hearing loss. A PAM-flexible ABE variant with reduced bystander and off-target effects (ABE8eWQ-SpRY:sgRNA3) is packaged in dual adeno-associated viruses (AAVs) and injected into the inner ear of hMPZL2Q74X/Q74X mice and effectively corrects the mutation. This treatment significantly restores hearing function, improves inner ear structural integrity, and reverses altered gene expression. Base editing may hold therapeutic potential for hereditary deafness, including most cases of MPZL2 deafness. RNA-seq profiling of mouse cochlear membranous labyrinth tissue from hMPZL2Q74X/Q74X, Mpzl2 WT, and hMPZL2Q74X/Q74X treated with AAV-ie-ABE8eWQ-SpRY:sgRNA3 at P28 to explore the molecular pathways involved in the cochlear histopathology caused by the MPZL2 c.220C>T mutation.