A missense mutation of Gipc3 was previously reported to cause age-related hearing loss in mice. Point mutations of human GIPC3 were found in two small families, but association with hearing loss was not statistically significant. Here, we describe one frameshift and six missense mutations in GIPC3 cosegregating with DFNB72 hearing loss in six large families that support statistically significant evidence for genetic linkage. However, GIPC3 is not the only nonsyndromic hearing impairment gene in this region; no GIPC3 mutations were found in a family cosegregating hearing loss with markers of chromosome 19p. Haplotype analysis excluded GIPC3 from the obligate linkage interval in this family and defined a novel locus spanning 4.08 Mb and 104 genes. This closely linked but distinct nonsyndromic hearing loss locus was designated DFNB81.

Mutations in the CLDN14 gene are known to cause autosomal recessive (AR) non-sydromic hearing loss (NSHL) at the DFNB29 locus on chromosome 21q22.13. As part of an ongoing study to localize and identify NSHL genes, the ARNSHL segregating in four Pakistani consanguineous families were mapped to the 21q22.13 region with either established or suggestive linkage. Given the known involvement of CLDN14 gene in NSHL, DNA samples from hearing-impaired members from the four families were sequenced to potentially identify causal variants within this gene. Three novel CLDN14 mutations, c.167G>A (p.Trp56★), c.242G>A (p.Arg81His), and c.694G>A (p.Gly232Arg), segregate with hearing loss (HL) in three of the families. The previously reported CLDN14 mutation c.254T>A (p.Val85Asp) was observed in the fourth family. None of the mutations were detected in 400 Pakistani control chromosomes and all were deemed damaging based on bioinformatics analyses. The nonsense mutation c.167G>A (p.Trp56★) is the first stop codon mutation in CLDN14 gene to be identified to cause NSHL. The c.242G>A (p.Arg81His) and c.694G>A (p.Gly232Arg) mutations were identified within the first extracellular loop and the carboxyl-tail of claudin-14, respectively, which highlights the importance of the extracellular domains and phosphorylation of cytoplasmic tail residues to claudin function within the inner ear. The HL due to novel CLDN14 mutations is prelingual, severe-to-profound with greater loss in the high frequencies.

Mutations in the TMPRSS3 gene are known to cause autosomal recessive nonsyndromic hearing impairment (ARNSHI). After undergoing a genome scan, ten consanguineous Pakistani families with ARNSHI were found to have significant or suggestive evidence of linkage to the TMPRSS3 region. In order to elucidate if the TMPRSS3 gene is responsible for ARNSHI in these families, the gene was sequenced using DNA samples from these families. Six TMPRSS3 variants were found to co-segregate in ten families. None of these variants were detected in 500 control chromosomes. Four novel variants, three of which are missense [c.310G>A (p.Glu104Lys), c.767C>T (p.Ala256Val) and c.1273T>C (p.Cys425Arg)] and one nonsense [c.310G>T (p.Glu104Stop)], were identified. The pathogenicity of novel missense variants was investigated through bioinformatics analyses. Additionally, the previously reported deletion c.208delC (p.His70ThrfsX19) was identified in one family and the known mutation c.1219T>C (p.Cys407Arg) was found in five families, which makes c.1219T>C (p.Cys407Arg) the most common TMPRSS3 mutation within the Pakistani population. Identification of these novel variants lends support to the importance of elements within the low-density lipoprotein receptor A (LDLRA) and serine protease domains in structural stability, ligand binding and proteolytic activity for proper TMPRSS3 function within the inner ear.

No abstract

Hearing impairment is the most prevalent sensorial deficit in the general population. Congenital deafness occurs in about 1 in 1000 live births, of which approximately 50% has hereditary cause in development countries. Non-syndromic deafness can be caused by mutations in both nuclear and mitochondrial genes. Mutations in mtDNA have been associated with aminoglycoside-induced and non-syndromic deafness in many families worldwide. However, the nuclear background influences the phenotypic expression of these pathogenic mutations. Indeed, it has been proposed that nuclear modifier genes modulate the phenotypic manifestation of the mitochondrial A1555G mutation in the MTRNR1 gene. The both putative nuclear modifiers genes TRMU and MTO1 encoding a highly conserved mitochondrial related to tRNA modification. It has been hypothesizes that human TRMU and also MTO1 nuclear genes may modulate the phenotypic manifestation of deafness-associated mitochondrial mutations. The aim of this work was to elucidate the contribution of mitochondrial mutations, nuclear modifier genes mutations and aminoglycoside exposure in the deafness phenotype. Our findings suggest that the genetic background of individuals may play an important role in the pathogenesis of deafness-associated with mitochondrial mutation and aminoglycoside-induced.