Autosomal recessive nonsyndromic hearing impairment (NSHI) is a heterogeneous condition, for which 53 genetic loci have been reported, and 29 genes have been identified to date. One of these, OTOF, encodes otoferlin, a membrane‐anchored calcium‐binding protein that plays a role in the exocytosis of synaptic vesicles at the auditory inner hair cell ribbon synapse. We have investigated the prevalence and spectrum of deafness‐causing mutations in the OTOF gene. Cohorts of 708 Spanish, 83 Colombian, and 30 Argentinean unrelated subjects with autosomal recessive NSHI were screened for the common p.Gln829X mutation. In compound heterozygotes, the second mutant allele was identified by DNA sequencing. In total, 23 Spanish, two Colombian and two Argentinean subjects were shown to carry two mutant alleles of OTOF. Of these, one Colombian and 13 Spanish subjects presented with auditory neuropathy. In addition, a cohort of 20 unrelated subjects with a diagnosis of auditory neuropathy, from several countries, was screened for mutations in OTOF by DNA sequencing. A total of 11 of these subjects were shown to carry two mutant alleles of OTOF. In total, 18 pathogenic and four neutral novel alleles of the OTOF gene were identified. Haplotype analysis for markers close to OTOF suggests a common founder for the novel c.2905_2923delinsCTCCGAGCGCA mutation, frequently found in Argentina. Our results confirm that mutation of the OTOF gene correlates with a phenotype of prelingual, profound NSHI, and indicate that OTOF mutations are a major cause of inherited auditory neuropathy. Hum Mutat 29(6), 823–831, 2008.

Diagnostic problems in identifying congenital infection cases in infancy have thus far impaired the assessment of the role of congenital cytomegalovirus (CMV) infection in the etiology of sensorineural hearing loss (SNHL). To estimate the impact of congenital infection in children with SNHL by detection of CMV DNA in stored samples of neonatal dried blood (dried blood spots test). The Guthrie cards of 130 children with hearing loss >40 dB hearing loss were retrieved from the regional screening center. CMV DNA was extracted by thermal shock and amplified by PCR. The percentage of SNHL cases attributable to congenital CMV infection was 10% (9 of 87) in infants whose SNHL had been diagnosed in their first 2 months of life and 34.2% (13 of 38) in children with deafness of unidentified cause that was diagnosed in early childhood. In the latter group 42.7% (12 of 28) of the children with a hearing loss of >70 dB were CMV-positive. The results suggest that congenital CMV infection has a more relevant role in the etiology of SNHL than previously reported. The data obtained in both groups suggest that 20 to 30% of all deafness cases are caused by CMV. The percent of congenital CMV cases alone appears to account for all the cases previously attributed to all congenital infections. More than 40% of deafness cases with an unknown cause, needing rehabilitation, are caused by congenital CMV.

The miR-96, miR-182 and miR-183 microRNA (miRNA) family is essential for differentiation and function of the vertebrate inner ear. Recently, point mutations within the seed region of miR-96 were reported in two Spanish families with autosomal dominant non-syndromic sensorineural hearing loss (NSHL) and in a mouse model of NSHL. We screened 882 NSHL patients and 836 normal-hearing Italian controls and identified one putative novel mutation within the miR-96 gene in a family with autosomal dominant NSHL. Although located outside the mature miR-96 sequence, the detected variant replaces a highly conserved nucleotide within the companion miR-96*, and is predicted to reduce the stability of the pre-miRNA hairpin. To evaluate the effect of the detected mutation on miR-96/mir-96* biogenesis, we investigated the maturation of miR-96 by transient expression in mammalian cells, followed by real-time reverse-transcription polymerase chain reaction (PCR). We found that both miR-96 and miR-96* levels were significantly reduced in the mutant, whereas the precursor levels were unaffected. Moreover, miR-96 and miR-96* expression levels could be restored by a compensatory mutation that reconstitutes the secondary structure of the pre-miR-96 hairpin, demonstrating that the mutation hinders precursor processing, probably interfering with Dicer cleavage. Finally, even though the mature miR-96 sequence is not altered, we demonstrated that the identified mutation significantly impacts on miR-96 regulation of selected targets. In conclusion, we provide further evidence of the involvement of miR-96 mutations in human deafness and demonstrate that a quantitative defect of this miRNA may contribute to NSHL.