Gene therapy for hearing loss.

Sensorineural hearing loss (SNHL) is the most common sensory disorder. Its underlying etiologies include a broad spectrum of genetic and environmental factors that can lead to hearing loss that is congenital or late onset, stable or progressive, drug related, noise induced, age related, traumatic or post-infectious. Habilitation options typically focus on amplification using wearable or implantable devices; however exciting new gene-therapy-based strategies to restore and prevent SNHL are actively under investigation. Recent proof-of-principle studies demonstrate the potential therapeutic potential of molecular agents delivered to the inner ear to ameliorate different types of SNHL. Correcting or preventing underlying genetic forms of hearing loss is poised to become a reality. Herein, we review molecular therapies for hearing loss such as gene replacement, antisense oligonucleotides, RNA interference and CRISPR-based gene editing. We discuss delivery methods, techniques and viral vectors employed for inner ear gene therapy and the advancements in this field that are paving the way for basic science research discoveries to transition to clinical trials.

Targeted Allele Suppression Prevents Progressive Hearing Loss in the Mature Murine Model of Human TMC1 Deafness.

Hearing loss is the most common human sensory deficit. Its correction has been the goal of several gene-therapy based studies exploring a variety of interventions. Although these studies report varying degrees of success, all treatments have targeted developing inner ears in neonatal mice, a time point in the structural maturation of the cochlea prior to 26 weeks gestational age in humans. It is unclear whether cochlear gene therapy can salvage hearing in the mature organ of Corti. Herein, we report the first study to test gene therapy in an adult murine model of human deafness. Using a single intracochlear injection of an artificial microRNA carried in an AAV vector, we show that RNAi-mediated gene silencing can slow progression of hearing loss, improve inner hair cell survival, and prevent stereocilia bundle degeneration in the mature Beethoven mouse, a model of human TMC1 deafness. The ability to study gene therapy in mature murine ears constitutes a significant step toward its translation to human subjects.

RNA Interference Prevents Autosomal-Dominant Hearing Loss.

Hearing impairment is the most common sensory deficit. It is frequently caused by the expression of an allele carrying a single dominant missense mutation. Herein, we show that a single intracochlear injection of an artificial microRNA carried in a viral vector can slow progression of hearing loss for up to 35 weeks in the Beethoven mouse, a murine model of non-syndromic human deafness caused by a dominant gain-of-function mutation in Tmc1 (transmembrane channel-like 1). This outcome is noteworthy because it demonstrates the feasibility of RNA-interference-mediated suppression of an endogenous deafness-causing allele to slow progression of hearing loss. Given that most autosomal-dominant non-syndromic hearing loss in humans is caused by this mechanism of action, microRNA-based therapeutics might be broadly applicable as a therapy for this type of deafness.

HOMER2, a stereociliary scaffolding protein, is essential for normal hearing in humans and mice.

Hereditary hearing loss is a clinically and genetically heterogeneous disorder. More than 80 genes have been implicated to date, and with the advent of targeted genomic enrichment and massively parallel sequencing (TGE+MPS) the rate of novel deafness-gene identification has accelerated. Here we report a family segregating post-lingual progressive autosomal dominant non-syndromic hearing loss (ADNSHL). After first excluding plausible variants in known deafness-causing genes using TGE+MPS, we completed whole exome sequencing in three hearing-impaired family members. Only a single variant, p.Arg185Pro in HOMER2, segregated with the hearing-loss phenotype in the extended family. This amino acid change alters a highly conserved residue in the coiled-coil domain of HOMER2 that is essential for protein multimerization and the HOMER2-CDC42 interaction. As a scaffolding protein, HOMER2 is involved in intracellular calcium homeostasis and cytoskeletal organization. Consistent with this function, we found robust expression in stereocilia of hair cells in the murine inner ear and observed that over-expression of mutant p.Pro185 HOMER2 mRNA causes anatomical changes of the inner ear and neuromasts in zebrafish embryos. Furthermore, mouse mutants homozygous for the targeted deletion of Homer2 present with early-onset rapidly progressive hearing loss. These data provide compelling evidence that HOMER2 is required for normal hearing and that its sequence alteration in humans leads to ADNSHL through a dominant-negative mode of action.

Comprehensive genetic testing in the clinical evaluation of 1119 patients with hearing loss.

Hearing loss is the most common sensory deficit in humans, affecting 1 in 500 newborns. Due to its genetic heterogeneity, comprehensive diagnostic testing has not previously been completed in a large multiethnic cohort. To determine the aggregate contribution inheritance makes to non-syndromic hearing loss, we performed comprehensive clinical genetic testing with targeted genomic enrichment and massively parallel sequencing on 1119 sequentially accrued patients. No patient was excluded based on phenotype, inheritance or previous testing. Testing resulted in identification of the underlying genetic cause for hearing loss in 440 patients (39%). Pathogenic variants were found in 49 genes and included missense variants (49%), large copy number changes (18%), small insertions and deletions (18%), nonsense variants (8%), splice-site alterations (6%), and promoter variants (<1%). The diagnostic rate varied considerably based on phenotype and was highest for patients with a positive family history of hearing loss or when the loss was congenital and symmetric. The spectrum of implicated genes showed wide ethnic variability. These findings support the more efficient utilization of medical resources through the development of evidence-based algorithms for the diagnosis of hearing loss.

TBC1D24 mutation causes autosomal-dominant nonsyndromic hearing loss.

Hereditary hearing loss is extremely heterogeneous. Over 70 genes have been identified to date, and with the advent of massively parallel sequencing, the pace of novel gene discovery has accelerated. In a family segregating progressive autosomal-dominant nonsyndromic hearing loss (NSHL), we used OtoSCOPE® to exclude mutations in known deafness genes and then performed segregation mapping and whole-exome sequencing to identify a unique variant, p.Ser178Leu, in TBC1D24 that segregates with the hearing loss phenotype. TBC1D24 encodes a GTPase-activating protein expressed in the cochlea. Ser178 is highly conserved across vertebrates and its change is predicted to be damaging. Other variants in TBC1D24 have been associated with a panoply of clinical symptoms including autosomal recessive NSHL, syndromic hearing impairment associated with onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS syndrome), and a wide range of epileptic disorders.

Ergonomics of Various Modalities for Ear Surgery.

Objective: Evaluate ergonomic differences of various modalities for performing middle ear surgery. Study Design: Observational study. Setting: Two academic tertiary care centers. Methods: Attending physicians and residents performing middle ear surgery were photographed intraoperatively. Intraoperative photographs were analyzed using the validated Rapid Upper Limb Assessment (RULA) tool to measure musculoskeletal disease (MSD) risk. Descriptive statistics and significance testing were used to characterize and compare ergonomic differences between surgical modalities. Multivariable ordinal regression was performed to assess factors associated with increased MSD risk, as determined by the final RULA score. Results: Most of our 110 intraoperative photos featured attendings (82.7%) performing combined middle ear surgery and mastoidectomy (60.0%). Body angles and the final RULA score varied significantly among modalities. On subset analysis, microscopic surgery exhibited significantly worse wrist, trunk, and neck angles compared to endoscopic and exoscopic surgery. Exoscopic surgery had significantly lower final RULA scores than both endoscopic and microscopic surgery, indicating significantly lower MSD risk. Microscopic and endoscopic surgery final scores did not vary significantly. In a multivariable ordinal regression of factors associated with increased RULA score, exoscopic surgery had statistically significantly less ergonomic risk relative to microscopic surgery (odds ratio = 0.12, 95% confidence interval = [0.03-0.43]). Conclusion: Exoscopic, endoscopic, and microscopic surgery all featured low ergonomic risk, although exoscopic middle ear surgery demonstrated the lowest risk profile among studied surgical modalities. This demonstrates the importance of using each modality in combination with other ergonomic interventions to provide meaningful musculoskeletal benefits.

Incidence of Postoperative CSF Leaks in Class III Obese Patients Undergoing Middle Cranial Fossa Approach for Spontaneous CSF Leak Repair.

OBJECTIVE: To determine the safety and effectiveness of the middle cranial fossa (MCF) approach for spontaneous cerebrospinal fluid leak (sCSF-L) repair in class III obese patients. To also assess the need for prophylactic lumbar drain (LD) placement in this patient population. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary Academic Center. PATIENTS: All patients older than 18 years undergoing sCSF-L repair with an MCF approach. INTERVENTION: An MCF craniotomy for sCSF-L repair. MAIN OUTCOME MEASURE: Rate of complications and postoperative leaks. RESULTS: There were no perioperative complications in 78.9% (56/71) of cases. The surgical complication rate was 12.5% (2/16), 10% (2/20), and 22.2% (6/27) in class I, class II, and class III obese patients. There was no statistically significant difference in complications among these three groups. The most common postoperative complication was a persistent CSF leak in the acute postoperative period with an overall rate of 9.9% (7/71) with six of the seven patients requiring postoperative LD placement. The percentage of postoperative CSF leaks in nonobese, class I, class II, and class III patients were 25% (2/8), 12.5% (2/16), 0% (0/20), and 11.1% (3/27), respectively. There was no statistically significant difference in the rate of postoperative CSF leaks among the four groups (chi-square, p = 0.48). In all cases, the acute postoperative CSF leaks resolved in the long term and did not require further surgical repair. CONCLUSIONS: We determine that MCF craniotomy repair for sCSF-Ls is safe in patients with class III obesity, and the incidence of postoperative CSF leaks did not vary among other obesity classes. We also find that prophylactic placement of LDs is not routinely needed in this population.

Neomycin-induced deafness in neonatal mice.

BACKGROUND: Hearing impairment is a rising public health issue, and current therapeutics fail to restore normal auditory sensation. Animal models are essential to a better understanding of the pathophysiology of deafness and developing therapeutics to restore hearing. NEW METHODS: Wild-type CBA/CaJ neonatal mice P2-5 were used in this study. Neomycin suspension (500 nl of 50 or 100 mg/ml) was micro-injected into the endolymphatic space. Cochlear morphology was examined 3 and 7 days after injection; hair cell (HC) loss, supporting cell morphology, and neurite denervation pattern were assessed with whole-mounts. At 2 and 4 weeks post-injection, the spiral ganglion neuron (SGN) density was analyzed with cryostat sections. Audiometric responses were measured with auditory brain response (ABR) at 4 weeks. RESULTS: Rapid and complete degeneration of the inner and outer HCs occurred as early as 3 days post-injection. Subsequently, time- and dose-dependent degeneration patterns were observed along the axis of the cochlear membranous labyrinth forming a flat epithelium. Likewise, the SGN histology demonstrated significant cell density reduction at 2 and 4 weeks. The ABR threshold measurements confirmed profound deafness at 4 weeks. COMPARISON WITH EXISTING METHODS: Compared to previously described local and systemic aminoglycoside injections, this method provides a reliable, robust, and rapid deafening model with a single infusion of neomycin in neonatal mice. This model also allows for investigating the effects of inner ear damage during auditory maturation. CONCLUSIONS: A single injection of neomycin into the endolymphatic space induces robust HC loss and denervation in neonatal mice.

Mutation-agnostic RNA interference with engineered replacement rescues Tmc1-related hearing loss.

Hearing loss is the most common sensory deficit, of which genetic etiologies are a frequent cause. Dominant and recessive mutations in TMC1, a gene encoding the pore-forming subunit of the hair cell mechanotransduction channel, cause DFNA36 and DFNB7/11, respectively, accounting for ∼2% of genetic hearing loss. Previous work has established the efficacy of mutation-targeted RNAi in treatment of murine models of autosomal dominant non-syndromic deafness. However, application of such approaches is limited by the infeasibility of development and validation of novel constructs for each variant. We developed an allele-non-specific approach consisting of mutation-agnostic RNAi suppression of both mutant and WT alleles, co-delivered with a knockdown-resistant engineered WT allele with or without the use of woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) to augment transgene expression. This therapeutic construct was delivered into the mature murine model of DFNA36 with an AAV vector and achieved robust hair cell and auditory brainstem response preservation. However, WPRE-enhanced Tmc1 expression resulted in inferior outcomes, suggesting a role for gene dosage optimization in future TMC1 gene therapy development.

Reduction of sporadic and neurofibromatosis type 2-associated vestibular schwannoma growth in vitro and in vivo after treatment with the c-Jun N-terminal kinase inhibitor AS602801.

OBJECTIVE: Vestibular schwannomas (VSs) are benign nerve sheath tumors that result from mutation in the tumor suppressor gene NF2, with functional loss of the protein merlin. The authors have previously shown that c-Jun N-terminal kinase (JNK) is constitutively active in human VS cells and plays a central role in their survival by suppressing accumulation of mitochondrial superoxides, implicating JNK inhibitors as a potential systemic treatment for VS. Thus, the authors hypothesized that the adenosine 5'-triphosphate-competitive JNK inhibitor AS602801 would demonstrate antitumor activity in multiple VS models. METHODS: Treatment with AS602801 was tested in primary human VS cultures, human VS xenografts, and a genetic mouse model of schwannoma (Postn-Cre;Nf2flox/flox). Primary human VS cell cultures were established from freshly obtained surgical tumor specimens; treatment group media was enriched with AS602801. VS xenograft tumors were established in male athymic nude mice from freshly collected human tumor. Four weeks postimplantation, a pretreatment MRI scan was obtained, followed by 65 days of AS602801 (n = 18) or vehicle control (n = 19) treatment. Posttreatment MRI scans were used to measure final tumor volume. Tumors were then harvested. Finally, Postn-Cre;Nf2flox/flox mice were treated with AS602801 (n = 10) or a vehicle (n = 13) for 65 days. Posttreatment auditory brainstem responses were obtained. Dorsal root ganglia from Postn-Cre;Nf2flox/flox mice were then harvested. In all models, schwannoma identity was confirmed with anti-S100 staining, cell proliferation was measured with the EdU assay, and cell death was measured with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. All protocols were approved by the local institutional review board and Institutional Animal Care and Use Committees. RESULTS: Treatment with AS602801 decreased cell proliferation and increased apoptosis in primary human VS cultures. The systemic administration of AS602801 in mice with human VS xenografts reduced tumor volume and cell proliferation. Last, the AS602801-treated Postn-Cre;Nf2flox/flox mice demonstrated decreased cell proliferation in glial cells in the dorsal root ganglia. However, AS602801 did not significantly delay hearing loss in Postn-Cre;Nf2flox/flox mice up to 3 months posttreatment. CONCLUSIONS: The data suggest that JNK inhibition with AS602801 suppresses growth of sporadic and neurofibromatosis type 2-associated VSs. As such, AS602801 is a potential systemic therapy for VS and warrants further investigation.

Neuralgia and Atypical Facial, Ear, and Head Pain.

Though there have been considerable strides in the diagnosis and care of orofacial pain disorders, facial neuralgias, and myofascial pain dysfunction syndrome remain incredibly cumbersome for patients and difficult to manage for providers. Cranial neuralgias, myofascial pain syndromes, temporomandibular dysfunction (TMD), dental pain, tumors, neurovascular pain, and psychiatric diseases can all present with similar symptoms. As a result, a patient's quest for the treatment of their orofacial pain often begins on the wrong foot, with a misdiagnosis or unnecessary procedure, which makes it all the more frustrating for them. Understanding the natural history, clinical presentation, and management of facial neuralgias and myofascial pain dysfunction syndrome can help clinicians better recognize and treat these conditions. In this article, we review updated knowledge on the pathophysiology, incidence, clinical features, diagnostic criteria, and medical management of TN, GPN, GN, and MPDS.

Comparative Analysis of Robotics-Assisted and Manual Insertions of Cochlear Implant Electrode Arrays.

HYPOTHESIS: Robotics-assisted cochlear implant (CI) insertions will result in reduced intracochlear trauma when compared with manual, across multiple users. BACKGROUND: Whether intracochlear trauma and translocations are two factors that may contribute to significant variability in CI outcomes remains to be seen. To address this issue, we have developed a robotics-assisted insertion system designed to aid the surgeon in inserting electrode arrays with consistent speeds and reduced variability. This study evaluated the effect of robotics-assisted insertions on the intracochlear trauma as compared with manual insertions in cadaveric cochleae in a simulated operative environment. METHODS: Twelve neurotologists performed bilateral electrode insertions into cochleae of full cadaveric heads using both the robotics-assisted system and manual hand insertion. Lateral wall electrodes from three different manufacturers (n = 24) were used and randomized between surgeons. Insertion angle of the electrode and trauma scoring were evaluated using high-resolution three-dimensional x-ray microscopy and compared between robotics-assisted and manual insertions. RESULTS: Three-dimensional x-ray microscopy provided excellent resolution to characterize the in situ trauma and insertion angle. Robotics-assisted insertions significantly decreased insertional intracochlear trauma as measured by reduced trauma scores compared with manual insertions (average: 1.3 versus 2.2, device versus manual, respectively; p < 0.05). There was no significant difference between insertion angles observed for manual and robotics-assisted techniques (311 ± 131° versus 307 ± 96°, device versus manual, respectively). CONCLUSIONS: Robotics-assisted insertion systems enable standardized electrode insertions across individual surgeons and experience levels. Clinical trials are necessary to investigate whether insertion techniques that reduce insertional variability and the likelihood of intracochlear trauma also improve CI auditory outcomes.

The biological underpinnings of radiation therapy for vestibular schwannomas: Review of the literature.

OBJECTIVE: Radiation therapy is a mainstay in the treatment of numerous neoplasms. Numerous publications have reported good clinical outcomes for primary radiation therapy for Vestibular Schwannomas (VS). However, there are relatively few pathologic specimens of VSs available to evaluate post-radiation, which has led to a relative dearth in research on the cellular mechanisms underlying the effects of radiation therapy on VSs. METHODS: Here we review the latest literature on the complex biological effects of radiation therapy on these benign tumors-including resistance to oxidative stress, mechanisms of DNA damage repair, alterations in normal growth factor pathways, changes in surrounding vasculature, and alterations in immune responses following radiation. RESULTS: Although VSs are highly radioresistant, radiotherapy is often successful in arresting their growth. CONCLUSION: By better understanding the mechanisms underlying these effects, we could potentially harness such mechanisms in the future to potentiate the clinical effects of radiotherapy on VSs. LEVEL OF EVIDENCE: N/A.

Transmastoid and Transtemporal Drainage of Petrous Apicitis with Otitis Media.

BACKGROUND: Petrous apicitis (PA) is a serious infection involving the apical portion of the petrous temporal bone. The classic triad of purulent otorrhea, ipsilateral abducens nerve palsy and retroorbital pain is rarely seen due to early detection and widespread use of antibiotics. Medical management is the primary treatment modality with surgery reserved for cases of recalcitrant petrous apex abscess. METHODS AND RESULTS: We presented a case of PA with previously untreated otitis media. After multidisciplinary evaluation, the patient was initially treated with intravenous antibiotics followed by drainage of the abscess using a combined transmastoid and middle cranial fossa (MCF) approach. The patient recovered well with no recurrence of the infection based on imaging and symptoms. DISCUSSION: While a variety of different surgical approaches can be used in treatment of PA, we recommend the MCF approach in cases where access to the anterior petrous apex may be challenging via transcanal or transmastoid approach.

Effects of Neurod1 Expression on Mouse and Human Schwannoma Cells.

OBJECTIVES: The objective was to explore the effect of the proneuronal transcription factor neurogenic differentiation 1 (Neurod1, ND1) on Schwann cells (SC) and schwannoma cell proliferation. METHODS: Using a variety of transgenic mouse lines, we investigated how expression of Neurod1 effects medulloblastoma (MB) growth, schwannoma tumor progression, vestibular function, and SC cell proliferation. Primary human vestibular schwannoma (VS) cell cultures were transduced with adenoviral vectors expressing Neurod1. Cell proliferation was assessed by 5-ethynyl-2'-deoxyuridine (EdU) uptake. STUDY DESIGN: Basic science investigation. RESULTS: Expression of Neurod1 reduced the growth of slow-growing but not fast-growing MB models. Gene transfer of Neurod1 in human schwannoma cultures significantly reduced cell proliferation in dose-dependent way. Deletion of the neurofibromatosis type 2 (Nf2) tumor-suppressor gene via Cre expression in SCs led to increased intraganglionic SC proliferation and mildly reduced vestibular sensory-evoked potentials (VsEP) responses compared to age-matched wild-type littermates. The effect of Neurod1-induced expression on intraganglionic SC proliferation in animals lacking Nf2 was mild and highly variable. Sciatic nerve axotomy significantly increased SC proliferation in wild-type and Nf2-null animals, and expression of Neurod1 reduced the proliferative capacity of both wild-type and Nf2-null SCs following nerve injury. CONCLUSION: Expression of Neurod1 reduces slow-growing MB progression and reduces human SC proliferation in primary VS cultures. In a genetic mouse model of schwannomas, we find some effects of Neurod1 expression; however, the high variability indicates that more tightly regulated Neurod1 expression levels that mimic our in vitro data are needed to fully validate Neurod1 effects on schwannoma progression. LEVEL OF EVIDENCE: NA Laryngoscope, 131:E259-E270, 2021.

Hair Cell Transduction Efficiency of Single- and Dual-AAV Serotypes in Adult Murine Cochleae.

Gene delivery is a key component for the treatment of genetic hearing loss. To date, a myriad of adeno-associated virus (AAV) serotypes and surgical approaches have been employed to deliver transgenes to cochlear hair cells, but the efficacy of dual transduction remains unclear. Herein, we investigated cellular tropism of single injections of AAV serotype 1 (AAV1), AAV2, AAV8, AAV9, and Anc80L65, and quantitated dual-vector co-transduction rates following co-injection of AAV2 and AAV9 vectors in adult murine cochlea. We used the combined round window membrane and canal fenestration (RWM+CF) injection technique for vector delivery. Single AAV2 injections were most robust and transduced 96.7% ± 1.1% of inner hair cells (IHCs) and 83.9% ± 2.0% of outer hair cells (OHCs) throughout the cochlea without causing hearing impairment or hair cell loss. Dual AAV2 injection co-transduced 96.9% ± 1.7% of IHCs and 65.6% ± 8.95% of OHCs. Together, RWM+CF-injected single or dual AAV2 provides the highest auditory hair cell transduction efficiency of the AAV serotypes we studied. These findings broaden the application of cochlear gene therapy targeting hair cells.

Gene therapy for hair cell regeneration: Review and new data.

Hair cells (HCs) in the cochlea are responsible for transducing mechanical sound energy into neural impulses which lead to the perception of sound. Loss of these sensory cells is the most common cause of sensorineural hearing loss, and spontaneous HC regeneration does not occur in mature mammals. Among the future potential treatment modalities is gene therapy, which is defined as the administration of either DNAs or RNAs as active pharmaceutical ingredients for inducing a clinically-beneficial response. Gene therapy is being envisioned and evaluated as a potential tool for addressing a number of human inner ear disorders. This paper is a hybrid Review and Research Paper, including unpublished data and a review of HC regeneration studies in live animal models. Current gene therapeutic approaches for replacing lost HC populations have been aimed at converting supporting cells surviving within the neuro-epithelium to new HCs by inducing upregulation of bHLH transcription factors such as Atoh1 or reciprocal silencing of Notch signaling with siRNAs, to tip the balance of transcriptional regulation toward a HC fate. Development of one or more of these techniques may yield a path to effective restoration of inner ear form and function. This review also describes other approaches and molecular targets that may prove efficacious and provides perspectives on future clinical challenges and opportunities for gene therapy to become a valuable weapon for the long-anticipated realization of this regenerative treatment.

Enhanced viral-mediated cochlear gene delivery in adult mice by combining canal fenestration with round window membrane inoculation.

Cochlear gene therapy holds promise for the treatment of genetic deafness. Assessing its impact in adult murine models of hearing loss, however, has been hampered by technical challenges that have made it difficult to establish a robust method to deliver transgenes to the mature murine inner ear. Here in we demonstrate the feasibility of a combined round window membrane injection and semi-circular canal fenestration technique in the adult cochlea. Injection of both AAV2/9 and AAV2/Anc80L65 via this approach in P15-16 and P56-60 mice permits robust eGFP transduction of virtually all inner hair cells throughout the cochlea with variable transduction of vestibular hair cells. Auditory thresholds are not compromised. Transduction rate and cell tropism is primarily influenced by viral titer and AAV serotype but not age at injection. This approach is safe, versatile and efficient. Its use will facilitate studies using cochlear gene therapy in murine models of hearing loss over a wide range of time points.

Intravenous rAAV2/9 injection for murine cochlear gene delivery.

Gene therapy for genetic deafness is a promising approach by which to prevent hearing loss or to restore hearing after loss has occurred. Although a variety of direct approaches to introduce viral particles into the inner ear have been described, presumed physiological barriers have heretofore precluded investigation of systemic gene delivery to the cochlea. In this study, we sought to characterize systemic delivery of a rAAV2/9 vector as a non-invasive means of cochlear transduction. In wild-type neonatal mice (postnatal day 0-1), we show that intravenous injection of rAAV2/9 carrying an eGFP-reporter gene results in binaural transduction of inner hair cells, spiral ganglion neurons and vestibular hair cells. Transduction efficiency increases in a dose-dependent manner. Inner hair cells are transduced in an apex-to-base gradient, with transduction reaching 96% in the apical turn. Hearing acuity in treated animals is unaltered at postnatal day 30. Transduction is influenced by viral serotype and age at injection, with less efficient cochlear transduction observed with systemic delivery of rAAV2/1 and in juvenile mice with rAAV2/9. Collectively, these data validate intravenous delivery of rAAV2/9 as a novel and atraumatic technique for inner ear transgene delivery in early postnatal mice.