 | This article needs more reliable medical references for verification or relies too heavily on primary sources. (November 2016) |  |
| Nonsyndromic deafness | |
|---|---|
| Other names | Non-syndromic genetic deafness |
Nonsyndromic deafness is hearing loss that is not associated with other signs and symptoms. In contrast, syndromic deafness involves hearing loss that occurs with abnormalities in other parts of the body. Nonsyndromic deafness constitutes 75% of all hearing loss cases, and an estimated 100 genes are thought to be linked to this condition. About 80% are linked to autosomal recessive inheritance, 15% to autosomal dominant inheritance, 1-3% through the X chromosome, and 0.5-1% are associated with mitochondrial inheritance.[1][2]
Genetic changes are related to the following types of nonsyndromic deafness:
- DFNA: nonsyndromic deafness, autosomal dominant
- DFNB: nonsyndromic deafness, autosomal recessive
- DFNX: nonsyndromic deafness, X-linked
- nonsyndromic deafness, mitochondrial
Each type is numbered in the order in which it was described. For example, DFNA1 was the first described autosomal dominant type of nonsyndromic deafness. Mitochondrial nonsyndromic deafness involves changes to the small amount of DNA found in mitochondria, the energy-producing centers within cells.[3]
Most forms of nonsyndromic deafness are associated with permanent hearing loss caused by damage to structures in the inner ear. The inner ear consists of three parts: a snail-shaped structure called the cochlea that helps process sound, nerves that send information from the cochlea to the brain, and structures involved with balance. Loss of hearing caused by changes in the inner ear is called sensorineural deafness. Hearing loss that results from changes in the middle ear is called conductive hearing loss. The middle ear contains three tiny bones that help transfer sound from the eardrum to the inner ear. Some forms of nonsyndromic deafness involve changes in both the inner ear and the middle ear; this combination is called mixed hearing loss.
The severity of hearing loss varies and can change over time. It can affect one ear (unilateral) or both ears (bilateral). Degrees of hearing loss range from mild (difficulty understanding soft speech) to profound (inability to hear even very loud noises). The loss may be stable, or it may progress as a person gets older. Particular types of nonsyndromic deafness often show distinctive patterns of hearing loss. For example, the loss may be more pronounced at high, middle, or low tones.
- ^ Guilford, Parry; Arab, Saida Ben; Blanchard, Stéphane; Levilliers, Jacqueline; Weissenbach, Jean; Belkahia, Ali; Petit, Christine (1994). "A non–syndromic form of neurosensory, recessive deafness maps to the pericentromeric region of chromosome 13q". Nature Genetics. 6 (1): 24–28. doi:10.1038/ng0194-24. ISSN 1061-4036. PMID 8136828. S2CID 19240967.
- ^ Kalatzis, V (1998-09-01). "The fundamental and medical impacts of recent progress in research on hereditary hearing loss". Human Molecular Genetics. 7 (10): 1589–1597. doi:10.1093/hmg/7.10.1589. ISSN 1460-2083. PMID 9735380.
- ^ Reference, Genetics Home. "nonsyndromic hearing loss". Genetics Home Reference. Retrieved 14 April 2017.