Nonsyndromic deafness is a condition related to changes in mitochondrial DNA.
Mutations in the ACTG1, CDH23, CLDN14, COCH, COL11A2, DFNA5, DFNB31, DFNB59, ESPN, EYA4, GJB2, GJB6, KCNQ4, LHFPL5, MT-TS1, MYO15A, MYO6, MYO7A, OTOF, PCDH15, POU3F4, SLC26A4, STRC, TECTA, TMC1, TMIE, TMPRSS3, TRIOBP, USH1C, and WFS1 genes cause nonsyndromic deafness.
Variations of the MT-RNR1 gene increase the risk of developing nonsyndromic deafness.
Variations in the ATP2B2 gene modify the course of nonsyndromic deafness.
The GJB3 and MYO1A genes are associated with nonsyndromic deafness.
The causes of nonsyndromic deafness are complex. Researchers have identified more than 30 genes that, when mutated, may cause nonsyndromic deafness; however, some of these genes have not been fully characterized. Many genes related to deafness are involved in the development and function of the inner ear. Mutations in these genes result in hearing loss by interfering with critical steps in processing sound. Different mutations in the same gene can cause different types of hearing loss, and some genes are associated with both syndromic and nonsyndromic deafness. In many affected families, the gene responsible for hearing loss has not been found.
Mutations in the GJB2 gene are a major cause of prelingual nonsyndromic deafness. This gene provides instructions for making a protein called connexin 26. The GJB6 gene also provides instructions for making a connexin protein, connexin 30. These proteins form parts (subunits) of channels called gap junctions, which allow communication between neighboring cells. Mutations in connexin proteins that make up gap junctions may affect the function or survival of cells that are needed for hearing.
DFN3 deafness is caused by mutations in the POU3F4 gene, which is located on the X chromosome. In people with this condition, one of the small bones in the middle ear (the stapes) cannot move normally, which interferes with hearing. This characteristic sign of DFN3 is called stapes fixation. At least four other regions of the X chromosome are involved in hearing loss, but the responsible genes have not been discovered.
Alterations in the MT-RNR1 and MT-TS1 genes have been found to increase the risk of developing nonsyndromic deafness. These genes are found in mitochondria, which are structures within cells that convert the energy from food into a form that cells can use. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA (called mitochondrial DNA). People with particular mutations in the MT-RNR1 gene have an increased risk of hearing loss if they are exposed to certain antibiotic medications called aminoglycosides; however, some people with a mutation in the MT-RNR1 gene develop hearing loss even without exposure to these antibiotics.
Deafness can also result from environmental factors or a combination of genetic and environmental factors. Environmental causes of hearing loss include certain medications, specific infections before or after birth, and exposure to loud noise over an extended period.
Read more about the ACTG1, ATP2B2, CDH23, CLDN14, COCH, COL11A2, DFNA5, DFNB31, DFNB59, ESPN, EYA4, GJB2, GJB3, GJB6, KCNQ4, LHFPL5, MT-RNR1, MT-TS1, MYO15A, MYO1A, MYO6, MYO7A, OTOF, PCDH15, POU3F4, SLC26A4, STRC, TECTA, TMC1, TMIE, TMPRSS3, TRIOBP, USH1C, and WFS1 genes and mitochondrial DNA.