Eli Lilly and Company / Seamless Therapeutics GmbH

Genetic (inherited) hearing loss

1-5% Share of sensorineural hearing loss attributable to OTOF mutations

Disease Overview

Hearing loss is identified in two to three of every 1,000 US newborns, and the CDC attributes 50-60% of congenital cases to genetic causes -- roughly 70% of affected children have non-syndromic disease and about 20% of the genetic cases carry a co-occurring syndrome. More than a hundred genes are implicated, and many of the causal lesions are structural: large deletions, duplications and inversions that conventional base or prime editing cannot repair. Cochlear implants remain the standard of care for profound loss and restore useful hearing without restoring physiological hearing. That combination -- a defined monogenic population, a surgically accessible and immune-privileged target organ, and a standard of care that is functional rather than curative -- is why the cochlea has become one of the most active genetic-medicine settings of the past three years.

Genetic Medicine Landscape

The field's proof point is OTOF. Regeneron's Otarmeni (lunsotogene parvec-cwha, formerly DB-OTO), an AAV gene-replacement therapy delivering a functional otoferlin gene to inner hair cells, is now FDA-approved as the first and only gene therapy for genetic hearing loss; in the pivotal CHORD trial 11 of 12 participants showed clinically meaningful improvement and three reached normal hearing. Lilly is already in the same lane with AK-OTOF, acquired in its US$610m purchase of Akouos in 2022, which restored an 11-year-old's hearing to the normal range within a month of a single administration. Sensorion's SENS-501 is in Phase I/II in European sites in children aged six to 31 months. OTOF accounts for only about 1-5% of sensorineural hearing loss, however, and AAV gene replacement is limited by cargo capacity and by lesion type. Seamless's programmable recombinases are aimed squarely at that residual: engineered site-specific enzymes that perform large insertions, excisions and inversions without nuclease-induced double-strand breaks -- the structural mutation classes AAV replacement and base editing leave behind. The collaboration therefore extends rather than duplicates Lilly's existing AK-OTOF position.