NM_194248.3(OTOF):c.32C>A (p.Ser11Ter)

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.