Mutations in the Cx26 gene have been shown to cause autosomal recessive nonsyndromic hearing loss (ARNSHL) at the DFNB1 locus on chromosome 13q12. Using direct sequencing, we screened the Cx26 coding region of affected and nonaffected members from seven ARNSHL families either linked to the DFNB1 locus or in which the ARNSHL phenotype cosegregated with markers from chromosome 13q12. Cx26 mutations were found in six of the seven families and included two previously described mutations (W24X and W77X) and two novel Cx26 mutations: a single base pair deletion of nucleotide 35 resulting in a frameshift and a C‐to‐T substitution at nucleotide 370 resulting in a premature stop codon (Q124X). We have developed and optimized allele‐specific PCR primers for each of the four mutations to rapidly determine carrier and noncarrier status within families. We also have developed a single stranded conformational polymorphism (SSCP) assay which covers the entire Cx26 coding region. This assay can be used to screen individuals with nonsyndromic hearing loss for mutations in the CX26 gene. Hum Mutat 11:387–394, 1998. © 1998 Wiley‐Liss, Inc.

Sensorineural hearing loss affects the quality of life and communication of millions of people, but the underlying molecular mechanisms remain elusive. Here, we identify mutations in Gipc3 underlying progressive sensorineural hearing loss (age-related hearing loss 5, ahl5) and audiogenic seizures (juvenile audiogenic monogenic seizure 1, jams1) in mice and autosomal recessive deafness DFNB15 and DFNB95 in humans. Gipc3 localizes to inner ear sensory hair cells and spiral ganglion. A missense mutation in the PDZ domain has an attenuating effect on mechanotransduction and the acquisition of mature inner hair cell potassium currents. Magnitude and temporal progression of wave I amplitude of afferent neurons correlate with susceptibility and resistance to audiogenic seizures. The Gipc3343A allele disrupts the structure of the stereocilia bundle and affects long-term function of auditory hair cells and spiral ganglion neurons. Our study suggests a pivotal role of Gipc3 in acoustic signal acquisition and propagation in cochlear hair cells.

Among white adults otosclerosis is the single most common cause of hearing impairment. Although the genetics of this disease are controversial, the majority of studies indicate autosomal dominant inheritance with reduced penetrance. We studied a large multi-generational family in which otosclerosis has been inherited in an autosomal dominant pattern. Five of16 affected persons have surgically confirmed otosclerosis; the remaining nine have a conductive hearing loss but have not undergone corrective surgery. To locate the disease-causing gene we completed genetic linkage analysis using short tandem repeat polymorphisms (STRPs) distributed over the entire genome. Multipoint linkage analysis showed that only one genomic region, on chromosome 15q, generated a lod score >2.0. Additional STRPs were typed in this area, resulting in a lod score of 3.4. STRPs FES (centromeric) and D15S657 (telomeric) flank the 14. 5 cM region that contains an otosclerosis gene.

In a study of 530 individuals with non-syndromic, sensorineural hearing loss, we identified 18 mutations at connexin 26 (Cx26), four of which are novel (À23G4T, I33T, 377_383dupTCCGCAT, W172R) and the remaining 14 (ivs1 þ 1G4A, M1V, 35delG, W24X, I35S, V37I, R75W, W77X, 312del14, E120del, Q124X, Y136X, R143W, R184P) being mutations previously described. To gain insight into functional consequences of these mutations, cellular localization of the mutant proteins and their ability to permit lucifer yellow transfer between cells was studied in seven of them (W24X, I33T, I35S, R75W, E120del, W172R and R184P). I35S and R184P showed impaired trafficking of the protein to the plasma membrane. I33T, R75W, E120del and W172R showed predominantly membrane localization but did not form functional gap junction channels. Surprisingly, W24X, a protein-truncating mutation, apparently permits formation of a full-length protein, perhaps due to a stop codon read-through mechanism. These results provide further evidence that Cx26 mutations affect gap junction activity by mis-regulation at multiple levels.

Mutations in the autosomal genes TMPRSS3, TMC1, USHIC, CDH23 and TMIE are known to cause hereditary hearing loss. To study the contribution of these genes to autosomal recessive, non-syndromic hearing loss (ARNSHL) in India, we examined 374 families with the disorder to identify potential mutations. We found four mutations in TMPRSS3, eight in TMC1, ten in USHIC, eight in CDH23 and three in TMIE. Of the 33 potentially pathogenic variants identified in these genes, 23 were new and the remaining have been previously reported. Collectively, mutations in these five genes contribute to about one-tenth of ARNSHL among the families examined. New mutations detected in this study extend the allelic heterogeneity of the genes and provide several additional variants for structure-function correlation studies. These findings have implications for early DNA-based detection of deafness and genetic counseling of affected families in the Indian subcontinent.

Autosomal recessive non-syndromic hearing loss (ARNSHL) is the most common form of prelingual inherited hearing impairment. A small consanguineous family with this disorder was ascertained through the Institute of Basic Medical Sciences in Madras, India. Conditions such as rubella, prematurity, drug use during pregnancy, perinatal trauma, and meningitis were eliminated by history. Audiometry was performed to confirm severe-to-profound hearing impairment in affected persons. After excluding linkage to known DFNB genes, two genomic DNA pools, one from the affected persons and the other from their non-affected siblings and the parents, were used to screen 165 polymorphic markers evenly spaced across the autosomal human genome. Two regions showing homozygosity-by-descent in the affected siblings were identified on chromosomes 3q21.3-q25.2 and 19p13.3-p13.1, identifying one (or possibly both) as the site of a novel ARNSHL gene.

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A locus for recessive neurosensory nonsyndromic hearing impairment maps to chromosome 9q13-q21 in two regionally separate consanguineous families from India. Each family demonstrates a LOD score greater than 4.5 to this region. D9S15, tightly linked to the Friedreich's ataxia locus, a region that has been defined with over 1 Mb of YAC contig information and several expressed sequences, is one of the flanking markers. In mice, the deafness (dn) locus maps to mouse chromosome 19 and flanking loci are syntenic to human chromosome 9q11-q21. The dn mouse is a potential model for the hearing impairment found in both these families.