# Generation of marmoset monkeys with a non-mosaic disruption of the OTOF gene as a model of human deafness

## TL;DR

Scientists created marmoset monkeys with a genetic mutation causing hearing loss, to study and develop gene therapies for human deafness.

## Contribution

A non-mosaic marmoset model of OTOF-related auditory synaptopathy was generated and characterized.

## Key findings

- Marmosets with biallelic OTOF-KO were born and raised normally.
- Auditory synaptopathy was confirmed via brainstem recordings and lack of otoferlin in IHCs.
- The model will help study gene therapy efficacy and longevity in non-human primates.

## Abstract

Disabling hearing impairment is a common human sensory deficit. OTOF is a major deafness gene. It codes for the synaptic protein otoferlin and is essential for transmitter release by inner hair cells (IHCs). Upon genetic loss of otoferlin, cochlear structure and function remain intact up to the IHC synapses, which fail to encode sound. Building on preclinical hearing restoration by AAV-mediated cochlear gene transfer in mice, clinical OTOF-gene-therapy trials are now targeting the pediatric population. However, preclinical optimization and characterization remain urgent needs for the development of OTOF-gene-therapy. Here, we report on the generation and characterization of a marmoset KO that models OTOF-related auditory synaptopathy and can thus address these needs. Following ovary stimulation, harvesting, in vitro maturation and fertilization of oocytes, we injected the zygotes with Cas9 and guide RNAs to disrupt OTOF. Mutant embryos were transferred into the uterus of foster mothers. Marmosets with biallelic, non-mosaic OTOF-KO were normally born and raised by their respective foster parents. Auditory brainstem recordings and otoacoustic emissions revealed profound auditory synaptopathy and OTOF-KO was further validated by the lack of otoferlin expression in IHCs. The new non-human primate model of OTOF-related auditory synaptopathy will serve studies of specificity, efficacy, and longevity of novel inner ear therapies.

Advancing our understanding of hereditary hearing loss and the development of gene therapies requires disease models in non-human primates. Here, the authors report on the generation and characterization of a non-mosaic marmoset model of OTOF-related auditory synaptopathy.