Mutations in a novel cochlear gene cause DFNA9, a human nonsyndromic deafness with vestibular dysfunction


DFNA9 is an autosomal dominant, nonsyndromic, progressive sensorineural hearing loss with vestibular pathology. Here we report three missense mutations in human COCH (previously described as Coch5b2), a novel cochlear gene, in three unrelated kindreds with DFNA9. All three residues mutated in DFNA9 are conserved in mouse and chicken Coch, and are found in a region containing four conserved cysteines with homology to a domain in factor C, a lipopolysaccharide-binding coagulation factor in Limulus polyphemus. COCH message, found at high levels in human cochlear and vestibular organs, occurs in the chicken inner ear in the regions of the auditory and vestibular nerve fibres, the neural and abneural limbs adjacent to the cochlear sensory epithelium and the stroma of the crista ampullaris of the vestibular labyrinth. These areas correspond to human inner ear structures which show histopathological findings of acidophilic ground substance in DFNA9 patients.

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Figure 1: DFNA9 histopathology and Coch expression.
Figure 2: Pedigrees of three DFNA9 kindreds (circles, females; squares, males; slash, deceased; filled, hearing-impaired; open, hearing) showing segregation of each mutation only with hearing-impaired family members.
Figure 3: Structure and amino acid sequence of COCH showing missense mutations.
Figure 4: Allele-specific oligonucleotide (ASO) hybridization and AvaII digests assess segregation of mutant allele in individuals showing hearing loss (HL) or normal hearing (H).

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The authors are grateful to the three families for their collaboration in this study. We thank S. Blacklow, S. Maxwell, B. McDonough, M. Miri and H. Niimura for their invaluable assistance. This work was supported by NIH grants DC03402 (C.C.M.) and DC00317 (A.J.H.) and by Howard Hughes Medical Institute (A.J.H., C.E.S. and J.G.S.).

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Correspondence to Cynthia C. Morton.

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