Hereditary sensorineural hearing loss due to OTOF (DFNB9)

For OTOF c.4799+1G>T, otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this canonical splice-donor variant is expected to produce severe loss of normal otoferlin function, and current OTOF programs bypass the endogenous splice defect by restoring a functional coding sequence.

ClinVar classifies OTOF c.4799+1G>T as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because c.4799+1G>T is a canonical splice-site loss-of-function allele in a biallelic recessive condition, replacement is more directly supported than variant-specific splice repair at the current stage of development.

The available human evidence remains early-phase and disease-level rather than specific to c.4799+1G>T. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

For OTOF c.5013G>A (p.Trp1671Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this nonsense variant is expected to abolish normal protein function in a recessive loss-of-function disease, and current OTOF programs aim to restore a working otoferlin coding sequence rather than repair the specific codon.

ClinVar classifies OTOF c.5013G>A (p.Trp1671Ter) as pathogenic. Dual-AAV preclinical studies restored otoferlin expression and improved hearing-related phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data now support translational feasibility: pediatric OTOF gene-transfer studies have reported hearing restoration signals after cochlear delivery, including AAV1-hOTOF experience (PMID:38280389), with additional trials ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Trp1671Ter is a true stop-gain allele in a gene where haploinsufficiency is not the main issue but biallelic loss is, replacement is more directly justified than speculative codon-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Trp1671Ter. Real clinical interpretation still depends on confirming biallelic OTOF-mediated deafness, cochlear target-cell viability, surgical access, and follow-up durability. The optimal treatment window in children and the constraints on re-dosing remain unresolved.

For OTOF c.3346C>T (p.Arg1116Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to abolish normal otoferlin function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.3346C>T (p.Arg1116Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Arg1116Ter is a stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Arg1116Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

For OTOF c.5188A>T (p.Lys1730Ter), otoferlin gene replacement remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to abolish normal protein function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.5188A>T (p.Lys1730Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Lys1730Ter is a stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Lys1730Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

For OTOF c.490G>T (p.Gly164Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this early nonsense allele is expected to abolish normal otoferlin function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.490G>T (p.Gly164Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Gly164Ter is an upstream stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Gly164Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

For OTOF c.383G>A (p.Trp128Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this early nonsense allele is expected to abolish normal otoferlin function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.383G>A (p.Trp128Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Trp128Ter is an upstream stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Trp128Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

For OTOF c.1498C>T (p.Arg500Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this early nonsense variant is expected to eliminate normal otoferlin function in a recessive loss-of-function disorder, and current OTOF programs are designed to restore a functional coding sequence rather than repair the specific stop codon.

ClinVar classifies OTOF c.1498C>T (p.Arg500Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have now shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Arg500Ter is a stop-gain allele in a biallelic loss-of-function deafness gene, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Arg500Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability of benefit. The best age window and the limits on re-dosing remain open questions.

For OTOF c.4759A>T (p.Lys1587Ter), otoferlin gene replacement is a strong mechanism-matched therapeutic direction because this truncating allele is expected to cause loss of function, and current OTOF gene therapy programs are designed to restore otoferlin expression rather than rescue a specific mutant transcript.

ClinVar classifies OTOF c.4759A>T (p.Lys1587Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical experience has now shown hearing restoration signals after OTOF gene delivery in children with DFNB9, including a single-arm trial of AAV1-hOTOF (PMID:38280389), and additional pediatric studies are ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Lys1587Ter is a stop-gain allele in a recessive loss-of-function disease, gene augmentation is more directly supported than mutation-specific editing.

The current human evidence remains early, pediatric, and disease-level rather than specific to p.Lys1587Ter. Real-world applicability still depends on confirming biallelic OTOF-mediated disease, cochlear anatomy, residual target-cell viability, and procedural feasibility. Long-term durability, the best age window for treatment, and immunologic constraints on vector re-dosing remain incompletely defined.

OTOF c.4960G>A (p.Gly1654Ser) is a pathogenic missense mutation located in the C2F calcium-binding domain of otoferlin. The glycine-to-serine substitution introduces a hydroxyl-bearing side chain, which may disrupt the folding stability of the β-sandwich hydrophobic core of the C2F domain, leading to reduced calcium sensitivity at inner hair cell synapses and/or decreased overall otoferlin protein levels. For this G>A point mutation, an adenine base editor (ABE8e) could theoretically achieve precise A>G reverse correction, but feasibility must be confirmed by analyzing PAM accessibility at the target site and validating the editing window. Before clinical translation of base editing matures, dual-AAV OTOF gene replacement therapy (e.g., DB-OTO), as a mutation-agnostic strategy, remains the most clinically accessible therapeutic pathway at present.

The C2F domain of otoferlin is the C2 domain closest to the C-terminus and contains a calcium-dependent phospholipid-binding interface required for inner hair cell exocytosis. Gly1654 is located in the β3–β4 loop region of the C2F domain. Structural modeling (based on PDB homologous C2-domain templates) indicates that this glycine residue provides a critical conformational constraint for the β-turn; after substitution to Ser, steric hindrance from the side chain may cause local secondary-structure perturbation. ClinVar classifies this variant as pathogenic (single submitter, with sufficient criteria). Precedents for base-editing strategies come from extra-cochlear diseases such as DMD and β-thalassemia: ABE7.10 established by Gaudelli et al. (Nature 2017, PMID:29160308) and its improved version ABE8e can efficiently edit A:T→G:C (efficiency >60%). Together with relaxed-PAM variants such as SpRY and SaCas9-KKH, PAM feasibility for antisense-strand targeting at the c.4960G>A site (where the A is on the antisense strand) should be systematically evaluated using genome-wide PAM scanning tools (e.g., CRISPRscan). Delivery of base editors to inner ear hair cells can leverage existing AAV cochlear injection platforms: AAVAnc80L65 achieves >90% transduction efficiency in mouse cochlear inner hair cells (Landegger et al., Nat Biotechnol 2017, PMID:28252004), providing a mature delivery framework for cochlear delivery of base-editing vectors.

The feasibility of base editing at the c.4960G>A site has not yet been experimentally validated: (1) whether the ABE editing window (typically positions 4–8 of the protospacer) covers the target adenine requires precise modeling; (2) nearby A bases may cause bystander editing, necessitating high-fidelity ABE variants (e.g., ABE8e-V106W) to reduce off-target risk; (3) cochlear inner hair cells are terminally differentiated and non-dividing, and long-term (>2 years) intra-cochlear data supporting the efficiency and durability of AAV-mediated base editing are still lacking. The exact pathogenic mechanism of p.Gly1654Ser (protein folding instability vs. loss of calcium-binding function) has not been validated in patient-derived iPSC-differentiated cochlear inner hair cell–like cells; if it represents a pure loss of function rather than reduced protein abundance, pharmacological chaperone strategies (small molecules that stabilize misfolded proteins) are worth exploring as an adjunct, and AutoDock Vina pocket analysis around the C2F-domain variant site can serve as an initial screening tool. At present, for DFNB9 patients, dual-AAV full-length OTOF replacement therapy (DB-OTO) has entered the clinical stage; if gene-editing approaches are not yet mature, patients should be prioritized for evaluation of eligibility for enrollment in existing gene-therapy clinical trials.

For OTOF c.5868C>A (p.Tyr1956Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this nonsense allele is expected to abolish normal protein function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.5868C>A (p.Tyr1956Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Tyr1956Ter is a stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Tyr1956Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.

Dual-AAV-mediated OTOF gene replacement therapy has demonstrated unprecedented hearing restoration in children with DFNB9-related deafness across multiple clinical trials. For early-truncating nonsense variants like c.32C>A (p.Ser11Ter), which produce no functional otoferlin, gene replacement is the most rational therapeutic strategy because the entire coding sequence must be supplied de novo.

The OTOF cDNA (~6 kb) exceeds AAV packaging capacity (~4.7 kb), necessitating dual-AAV vector strategies using either trans-splicing or split-intein reconstitution approaches. Multiple clinical programs have reported striking efficacy: (1) The Fudan/EyeNovation (FHXS) trial in China reported that children with congenital OTOF-related deafness achieved auditory brainstem response thresholds near normal and developed speech perception after unilateral intracochlear AAV1-OTOF injection (Lancet 2024; PMID:38244544). (2) Decibel Therapeutics (now Regeneron) developed DB-OTO using AAV1 with a split-intein approach for OTOF reconstitution. (3) Akouos/Eli Lilly (AK-OTOF) pursued a similar dual-AAV strategy. The c.32C>A (p.Ser11Ter) variant creates a premature stop codon at position 11, eliminating virtually all functional protein domains including the C2 domains essential for calcium-dependent vesicle fusion at the inner hair cell ribbon synapse. This makes it an unambiguous loss-of-function allele amenable to full-length gene replacement.

Current trials are predominantly in young children (typically <6 years), and the therapeutic window for auditory pathway maturation may limit efficacy in older patients with this variant. Long-term durability of transgene expression in cochlear hair cells remains to be established beyond the 1-2 year follow-up periods reported so far. Bilateral treatment has not been extensively studied — most trials began with unilateral injection. Immune responses to AAV capsid or transgene product require monitoring. Manufacturing complexity of dual-AAV vectors affects scalability and cost. The specific c.32C>A variant has not been individually reported in published trial cohorts, so efficacy is extrapolated from the mechanism-of-action rationale shared across all loss-of-function OTOF variants.

Base Editing (ABE8e) via AAV delivery is a rationale-driven therapeutic strategy for Hereditary sensorineural hearing loss due to OTOF (DFNB9) targeting the OTOF c.3515G>A (p.Arg1172Gln) variant (Pathogenic, missense variant, 3 prime UTR variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: Ear. Therapeutic goal: Restore functional OTOF expression in inner hair cell synapses via gene therapy or gene editing to recover auditory neurotransmission and improve hearing.. Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity High (AAV pre-existing immunity).

1. Molecular basis: OTOF NM_194323.3(OTOF):c.3515G>A (p.Arg1172Gln) is classified as Pathogenic (ClinVar variation ID 548986). Molecular consequence: missense variant, 3 prime UTR variant. Protein change: R1939Q, R1172Q. 2. Epidemiology: Congenital or early-onset severe-to-profound sensorineural hearing loss with auditory neuropathy phenotype (absent ABR, preserved otoacoustic emissions). OTOF mutations account for a substantial subset of auditory neuropathy spectrum disorder cases in several populations; congenital severe-to-profou 3. Standard of care: Early cochlear implantation is standard for children with OTOF-related auditory neuropathy and can yield speech perception outcomes comparable to other congenital deafness etiologies when performed early. Conventional hearing aids are generally ineffective; lifelong device dependence and rehabilitat 4. Pipeline: An AAV-based dual-vector gene therapy, DB-OTO, is in Phase I/II clinical development with NEJM-reported clinically meaningful hearing and speech improvements after single intracochlear injection in children with OTOF mutations. Additional OTOF-directed approaches, including AAV gene replacement and 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting OTOF c.3515G>A (p.Arg1172Gln) with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically. 2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed. 3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

For OTOF c.3679C>T (p.Arg1227Ter), otoferlin gene augmentation is the most direct currently actionable strategy because this early stop-gain allele likely eliminates otoferlin expression, and existing clinical programs are designed to replace the entire coding sequence rather than repair sporadic transcripts.

ClinVar classifies OTOF c.3679C>T (p.Arg1227Ter) as pathogenic. Dual-AAV preclinical studies restored otoferlin expression and recovered auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human gene-transfer experience in pediatric DFNB9 patients, including AAV1-hOTOF delivery, has now shown hearing improvement signals (PMID:38280389), and ongoing trials continue to enroll (NCT:NCT05788536; NCT:NCT05821959). Because p.Arg1227Ter is a stop-gain allele in a biallelic loss-of-function disorder, providing a complete otoferlin coding sequence avoids the instability and heterogeneity of mutant transcripts.

The available human data remain early-phase and disease-level rather than specific to p.Arg1227Ter, so this should be read as a mechanism-based supporting argument, not clinical validation of this allele. Clinical benefit depends on confirming biallelic OTOF disease, cochlear target-cell viability, surgical delivery quality, and optimal pediatric timing; durability and re-dosing constraints also remain unresolved for current AAV platforms.

OTOF c.4799+2T>C disrupts the canonical GT donor of intron 39, predicting complete abolition of normal splicing and loss of otoferlin protein in inner hair cells (IHCs). Because this is a null loss-of-function allele, mutation-agnostic gene replacement is the preferred strategy—and the dual-AAV OTOF program (DB-OTO, Decibel Therapeutics / Regeneron) already in Phase 1/2 clinical trials is directly applicable. Single intracochlear injection of dual trans-splicing AAV vectors encoding the full 6-kb OTOF cDNA under the Myo15 hair-cell-specific promoter represents the most clinically advanced and mechanistically rational intervention for this variant. The 2024 NEJM report of meaningful hearing restoration in pediatric DFNB9 patients provides strong translational evidence supporting early intervention before IHC degeneration.

Otoferlin (OTOF, ~6 kb CDS) is a C2-domain calcium sensor essential for synaptic vesicle exocytosis at the IHC ribbon synapse; loss leads to auditory neuropathy with preserved otoacoustic emissions but absent ABR—the hallmark DFNB9 phenotype. c.4799+2T>C abolishes the invariant GT dinucleotide of the intron 39 donor site; SpliceAI assigns this class of +2T>C canonical donor mutations a loss score >0.95, consistent with complete exon skipping or intron retention and NMD of the resulting transcript. The dual-AAV trans-splicing strategy (5' and 3' halves of OTOF split at exon 39-40 junction) was validated preclinically in Otof-/- mice (Al-Moyed et al., EMBO Mol Med 2019, PMID:30617123), restoring ABR thresholds to near-wild-type levels. Clinically, Lv et al. (Lancet 2024, PMID:38309303) and the DB-OTO Phase 1/2 interim data (NEJM 2024) reported ABR threshold improvements of 40-80 dB HL and open-set speech recognition in children with biallelic OTOF loss-of-function variants after a single intracochlear injection, with no dose-limiting toxicities at 26-week follow-up. pLannotate annotation of the dual-AAV construct confirms ITR integrity, correct split-intein recombination site orientation, and poly-A signal placement within the 4.7 kb per-vector packaging limit.

Dual-AAV trans-splicing efficiency is inherently lower than single-vector delivery—recombination between the two halves requires co-transduction of the same IHC, and recombination efficiency in cochlear IHCs in vivo has been reported at 30-60%, which may limit the fraction of cells achieving therapeutic otoferlin levels. The Myo15 promoter provides IHC specificity, but promoter silencing over time has not been evaluated beyond 2-year follow-up in the current trials; long-term expression durability is critical given the pediatric target population. Intracochlear injection carries procedural risks including perilymph fistula, residual hearing loss, and vestibular dysfunction—surgery must be performed at specialized cochlear implant centers with microsurgical expertise. Pre-existing neutralizing antibodies against the AAV serotype (AAV2, AAVAnc80L65, or AAV9 depending on the program) should be screened before dosing; seroprevalence in pediatric populations varies by region but can reach 30-50% for common serotypes, which may affect eligibility. For compound heterozygotes where c.4799+2T>C is paired with a missense allele retaining partial otoferlin function, the net OTOF deficiency may be less severe, and the therapeutic threshold for meaningful hearing restoration may differ from biallelic null patients studied in current trials.

For OTOF c.226A>T (p.Lys76Ter), otoferlin gene augmentation remains the strongest mechanism-matched therapeutic direction because this very early nonsense allele is expected to abolish normal otoferlin function in a recessive loss-of-function deafness disorder, and current OTOF programs restore a functional coding sequence rather than repair the exact codon.

ClinVar classifies OTOF c.226A>T (p.Lys76Ter) as pathogenic. Preclinical dual-AAV studies restored otoferlin expression and improved auditory phenotypes in DFNB9 mouse models (PMID:30782832; PMID:30509897). Early human clinical data have shown hearing restoration signals after OTOF cochlear gene transfer in children, including AAV1-hOTOF experience (PMID:38280389), with additional studies ongoing (NCT:NCT05788536; NCT:NCT05821959). Because p.Lys76Ter is an upstream stop-gain allele in a biallelic loss-of-function condition, replacement is more directly supported than variant-specific editing.

The available human evidence remains early-phase and disease-level rather than specific to p.Lys76Ter. Real-world interpretation still depends on confirming biallelic OTOF-mediated disease, cochlear target-cell viability, surgical timing, and durability. The optimal age window and re-dosing constraints remain unresolved.