Genetic variants of CDH23 associated with noise-induced hearing loss.

OBJECTIVES: Noise-induced hearing loss (NIHL) is a complex disease resulting from the interaction between external and intrinsic/genetic factors. Based on mice studies, one of the most interesting candidate gene for NIHL susceptibility is CDH23-encoding cadherin 23, a component of the stereocilia tip links. The aim of this study was to analyze selected CDH23 single nucleotide polymorphisms (SNPs) and to evaluate their interaction with environmental and individual factors in respect to susceptibility for NIHL in humans. METHODS: A study group consisted of 314 worst-hearing and 313 best-hearing subjects exposed to occupational noise, selected out of 3,860 workers database. Five SNPs in CDH23 were genotyped using real-time PCR. Subsequently, the main effect of genotype and its interaction with selected environmental and individual factors were evaluated. RESULTS: The significant results within the main effect of genotype were obtained for the SNP rs3752752, localized in exon 21. The effect was observed in particular in the subgroup of young subjects and in those exposed to impulse noise; CC genotype was more frequent among susceptible subjects, whereas genotype CT appeared more often among resistant to noise subjects. The effect of this polymorphism was not modified by none of environmental/individual factors except for blood pressure; however, the latter one should be further investigated. Smoking was shown as an independent factor determining NIHL development. CONCLUSION: The results of this study confirm that CDH23 genetic variant may modify the susceptibility to NIHL development in humans, as it was earlier proven in mice. Because the differences between the 2 study groups were not necessarily related to susceptibility to noise but they also were prone to age-related cochlear changes, these results should be interpreted with caution until replication in another population.

Single nucleotide polymorphisms in the cadherin 23 (CDH23) gene in Polish workers exposed to industrial noise.

Single nucleotide polymorphisms (SNPs) are the most frequent type of variation in the human genome and may underlie differential susceptibility to common genetic diseases. A candidate gene for susceptibility to noise-induced hearing loss (NIHL) is Cadherin 23 (CDH23). This study aimed to analyze genetic variation in the CDH23 gene in a group of 10 individuals derived from a cohort of 949 workers exposed to noise, and consisted of five persons from each of the resistant and susceptible extremes. DNA samples were collected and the coding exons of CDH23 were sequenced. We identified a total of 35 SNPs: 11 amino acid substitutions, 8 silent nucleotide changes, and 16 substitutions in intervening sequences. Ten of the 11 amino acid substitutions were previously shown also to segregate in a Cuban population. The nonsynonymous SNPs localized to the part of the gene encoding the extracellular domain of Cadherin 23, in particular ectodomains 5, 13, 14, 15, 16, 17, 19, and 22. One amino acid change occurred at a conserved position in ectodomain 5. Our results provide a framework for future study of polymorphisms in CDH23 as risk factor for NIHL.

[Genetic factors in susceptibility to age- and noise-related hearing loss]. / Genetyczne uwarunkowania indywidualnej podatnosci na uszkodzenie sluchu zwiazane z wiekiem i narazeniem na halas.

Individual susceptibility to age-related hearing loss (AHL) and noise-induced hearing loss (NIHL) varies greatly, and this inter-individual variation is due to an interaction of environmental factors, individual factors, and susceptibility genes. Majority of studies on susceptibility genes for AHL and NIHL have been performed in mice model. These findings suggest the role of the same genes in the development of AHL and NIHL, the more so as the pathogenesis of both diseases is similar with a crucial role of oxidative stress. The alleles responsible for AHL have been localized to the chromosome 10 (Ahl gene). Ahl-/- mice develop hearing impairment at early age and are also oversensitive to noise. Ahl gene is a recessive gene and it is probably responsible for the synthesis of cell junction proteins. In mice ahl codes for cadherin (CDH) proteins. The cadherin of interest is named otocadherin or CDH23, and it is localized to the links between stereocilia of hair cells. A hypomorphic 753G>A single nucleotide polymorphism (SNP) in Cdh 23 is associated with AHL, and the 753A variant is also correlated with susceptibility to NIHL. An increased susceptibility to AHL and NIHL may rely on the SNPs of several other genes, including the groups of oxidative stress genes, K+ ions recycling genes, monogenic deafness genes (including Connexin 26 gene, which mutation is responsible for the most frequent hereditary deafness in Caucasians), as well as mitochondrial genes. Several oxidative stress enzyme (sod1-/-, gpx -/-) knock-out mice have been shown to be more susceptible to NIHL than wild strains. Current large-scale cohort studies on AHL and NIHL performed under the European projects in between-lab collaboration along with a dynamic progress in the field of genetics of deafness open up new opportunities to find human AHL and NIHL susceptibility genes and develop methods for AHUNIHL treatment.