Genetic hearing loss accounts for up to 50% of prelingual deafness worldwide, yet there are no biologic treatments currently available. To investigate gene therapy as a potential biologic strategy for restoration of auditory function in patients with genetic hearing loss, we tested a gene augmentation approach in mouse models of genetic deafness. We focused on DFNB7/11 and DFNA36, which are autosomal recessive and dominant deafnesses, respectively, caused by mutations in transmembrane channel-like 1 (TMC1). Mice that carry targeted deletion of Tmc1 or a dominant Tmc1 point mutation, known as Beethoven, are good models for human DFNB7/11 and DFNA36. We screened several adeno-associated viral (AAV) serotypes and promoters and identified AAV2/1 and the chicken β-actin (Cba) promoter as an efficient combination for driving the expression of exogenous Tmc1 in inner hair cells in vivo. Exogenous Tmc1 or its closely related ortholog, Tmc2, were capable of restoring sensory transduction, auditory brainstem responses, and acoustic startle reflexes in otherwise deaf mice, suggesting that gene augmentation with Tmc1 or Tmc2 is well suited for further development as a strategy for restoration of auditory function in deaf patients who carry TMC1 mutations.

Gene therapy, or the treatment of human disease using genetic material, for inner ear dysfunction is coming of age. Recent progress in developing gene therapy treatments for genetic hearing loss has demonstrated tantalizing proof-of-principle in animal models. While successful translation of this progress into treatments for humans awaits, there is growing interest from patients, scientists, clinicians, and industry. Nonetheless, it is clear that a number of hurdles remain, and expectations for total restoration of auditory function should remain tempered until these challenges have been overcome. Here, we review progress, prospects, and challenges for gene therapy in the inner ear. We focus on technical aspects, including routes of gene delivery to the inner ear, choice of vectors, promoters, inner ear targets, therapeutic strategies, preliminary success stories, and points to consider for translating of these successes to the clinic.

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The occurrence of ESS in adult patients with CF was predicted by previous ESS intervention as well as the severity of CFTR mutation.

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