OTOF encodes multiple long and short isoforms: Genetic evidence that the long ones underlie recessive deafness DFNB9

We have recently reported that OTOF underlies an autosomal recessive form o f prelingual sensorineural deafness, DFNB9. The isolated 5-kb cDNA predicte d a 1,230 amino acid (aa) C-terminus membrane-anchored cytosolic protein wi th three C2 domains. This protein belongs to a family of mammalian proteins sharing homology with the Caenorhabditis elegans fer-1. The two other know n members of this family, dysferlin and myoferlin, both have six predicted C2 domains. By northern blot analysis, a 7-kb otoferlin mRNA could be detec ted in the human brain. We isolated the corresponding cDNA, which is expect ed to encode a 1,977-aa-long form of otoferlin with six C2 domains. A 7-kb cDNA derived from the murine orthologous gene, Otof, was also identified in the inner ear and the brain. The determination of the exon-intron structur e of the human and murine genes showed that they are composed of 48 coding exons and extend similar to 90 kb and similar to 80 kb, respectively. Alter natively spliced transcripts could be detected that predict several long is oforms (six C2 domains) in humans and mice and short isoforms (three C2 dom ains) only in humans. Primers were designed to explore the first 19 OTOF ex ons, henceforth permitting exploration of the complete coding sequence of t he gene in DFNB9 patients. In a southwestern Indian family affected by DFNB 9, a mutation in the acceptor splice site of intron 8 was detected, which d emonstrates that the long otoferlin isoforms are required for inner ear fun ction.