A novel missense mutation in a C2 domain of OTOF results in autosomal recessive auditory neuropathy.

Division of Pediatric Molecular Genetics, Ankara University School of Medicine, Ankara, Turkey.
American Journal of Medical Genetics Part A (Impact Factor: 2.05). 09/2005; 138(1):6-10. DOI: 10.1002/ajmg.a.30907
Source: PubMed

ABSTRACT Screening of 12 Turkish families with apparently autosomal recessive nonsyndromic sensorineural deafness without GJB2 and mtDNA m.1555A > G mutations for 11 previously mapped recessive deafness loci showed a family in which hearing loss cosegregated with the DFNB9 (OTOF) locus. Three affected children were later found to carry a novel homozygous c.3032T > C (p.Leu1011Pro) mutation in the OTOF gene. Both parents were heterozygous for the mutation. p.Leu1011Pro alters a conserved leucine residue in the C2D domain of otoferlin. Pure tone audiometry of the family showed severe to profound sensorineural hearing loss (with U-shape audiograms) in children, and normal hearing in the parents. Otoacoustic emissions and auditory brainstem response (ABR) suggested the presence of auditory neuropathy in affected individuals.

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    ABSTRACT: Objective The aim of this study is to evaluate the auditory phenotype in subjects with OTOF gene mutations to describe genotype-phenotype correlations. Material- methods; Twenty-two affected members from three families with homozygous OTOF mutations were included. Nine subjects were evaluated audiologically with otoscopic examination, pure-tone audiometry, tympanometry with acoustic reflex testing, auditory brain stem responses, and otoacoustic emission tests. Results Homozygous c.4718T > C (p.Ile1573Thr) mutation was associated with the auditory neuropathy/auditory dys-synchrony (AN/AD) phenotype and with progressive sensorineural hearing loss in four siblings in one family, while homozygous c.4467dupC (p.I1490HfsX19) was associated with severe to profound sensorineural hearing loss without AN/AD in four relatives in another family. Homozygous c.1958delC (p.Pro653LeufsX13) mutation was associated with moderate sensorineural hearing loss without AN/AD in one affected person in an additional family. Conclusions The audiological phenotype associated with different OTOF mutations appears to be consistently different suggesting the presence of a genotype-phenotype correlation.
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    ABSTRACT: We characterize a novel otoferlin mutation discovered in a sibling pair diagnosed with auditory neuropathy spectrum disorder and investigate auditory nerve function through their cochlear implants. Genetic sequencing revealed a homozygous mutation at the otoferlin splice donor site of exon 28 (IVS28 + 1G>T) in both siblings. Functional investigation showed that the intronic sequence between exons 28 and 29 was retained in the mutated minigenes that were expressed in 293T cells. Auditory nerve compound action potential recovery functions in the siblings demonstrated different rates of neural recovery, with sibling AN1 showing rapid recovery (1.14 ms) and AN2 showing average recovery (0.78 ms) compared to subjects with sensorineural hearing loss (average: adults 0.71 ms, children 0.85 ms). Differences in neural recovery were consistent with speech perception differences between the siblings. Genotype information may indicate site of lesion in hearing loss; however, additional, as yet, unknown factors may impact clinical outcomes and must be considered. © 2013 S. Karger AG, Basel.
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    ABSTRACT: Mutations in otoferlin, a C2-domain-containing ferlin family protein, cause non-syndromic hearing loss in humans (DFNB9 deafness). Furthermore, transmitter secretion of cochlear inner hair cells is compromised in mice lacking otoferlin. In the present study we show that the C2F domain of otoferlin directly binds calcium (KD = 267 μM) with diminished binding in a pachanga (Asp1767Gly) C2F mouse mutation. Calcium is found to regulate differentially binding of otoferlin C2 domains to t-SNARE proteins and phospholipids. C2D-F domains interact with the syntaxin-1 t-SNARE motif, with a maximum binding within the range of 20-50 μM Ca(2+). At 20 μM Ca(2+), the dissociation rate is substantially lower, indicating increased binding (KD = ~10(-9)), compared to 0 μM Ca(2+) (KD = ~10(-8)), suggesting a calcium-mediated stabilization of the C2 domain-t-SNARE complex. C2A and C2B interactions with t-SNAREs are insensitive to calcium. The C2F domain also directly binds the t-SNARE, SNAP-25, maximally at 100 μM and with reduction at 0 μM Ca(2+), a pattern repeated for C2F domain interactions with PIP2. In contrast, C2F does not bind the v-SNARE protein synaptobrevin-1 (VAMP-1). Moreover, an antibody targeting otoferlin immunoprecipitates syntaxin-1 and SNAP-25 but not synaptobrevin-1. As opposed to an increase in binding with increased calcium, interactions between otoferlin C2F domain and intramolecular C2 domains occur in the absence of calcium, consistent with intra-C2 domain interactions forming a ″closed″ tertiary structure at low calcium that ″opens″ as calcium increases. These results suggest a direct role for otoferlin in exocytosis and modulation of calcium-dependent membrane fusion.
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