Gene supplementation with precise transgene expression rescues hearing loss in a mouse model with an Mpzl2 East Asian founder variant.

Hearing loss is the most common sensory organ disorder, with genetic factors substantially contributing to the disease. Among the 87 genes responsible for autosomal recessive nonsyndromic hearing loss, mutations in MPZL2 have been frequently linked to mild-to-moderate autosomal recessive hearing loss (DFNB111). Here, we present multiple families whose hearing loss arose from biallelic mutations in the MPZL2 gene and found that the MPZL2 p.Q74* mutation may be a founder allele among East Asians. Furthermore, we generated an Mpzl2 p.Q74* knock-in mouse model that exhibited autosomal recessive, progressive, ski-sloping hearing loss with Deiter's cell degeneration. Gene supplementation using AAV-DJ or AAV-PHP.eB to deliver human MPZL2 (hMPZL2) under control of the CAG promoter induced ototoxicity, whereas employing an alternative EF1α promoter with AAV-DJ (DJ-EF1α-hMPZL2) circumvented this issue, restoring long-term auditory function and Deiter's cell survival in Mpzl2Q74∗/Q74∗ mice for up to 24 weeks. Overall, this study provides the foundational steps for developing a safe and effective biological treatment for DFNB111 and underscores the importance of precise regulation of target cells and transgene expression in AAV-based treatments.