Talk:Hearing impairment/Deafness

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Deafness is a physical condition characterized by lack of sensitivity to sound. That is, deaf people are unable to hear all or some sounds. Deafness is a form of hearing impairment.

Contents

[edit] Demographics

The global deaf population is roughly estimated to be 0.1% of the total population (1 in 1000).[1] The figure is likely to be higher in developing countries than developed countries due to restricted access to health care, and, in some cultures, due to the high rate of intrafamilial marriages. The great majority of people with less than average hearing are elderly or developed hearing loss after leaving school.[2] According to the U.S. National Center for Health statistics, approximately three quarters of deaf and hard-of-hearing Americans experienced the onset of hearing loss after age 18.[2]

Most deaf people, at least in developed countries, have some knowledge of the dominant language of their country. This may include the ability to lip read, to speak, or to read and write. Having some knowledge of both the dominant language and sign language is called bimodal bilingualism.

[edit] Categories of deafness

Further information: Hearing impairment#Categories of hearing impairment

Deafness can be classified according to type, severity, and age of onset.[3]

[edit] Type

[edit] Severity

  • Partial – limited hearing loss
  • Profound – complete or near-complete inability to hear

[edit] Age of onset

  • Congenital - deafness at birth
  • Pre-lingual – deafness beginning before language is learned
  • Peri-lingual – deafness beginning while in the midst of learning a first language
  • Post-lingual – beginning after a language has been learned

[edit] Other classifications

  • Progressive – hearing loss which increases over time
  • Tinnitus – Perception of a ringing sound in the ears which may be associated with conditions with hearing loss
  • Unilateral – loss of hearing in one ear only

[edit] Causes of deafness

[edit] Genetic causes

Genetic disorders are responsible for at least half of the cases of congenital deafness, with the other half caused by environmental factors.[4] Approximately 70% of genetic deafness is nonsyndromic deafness, meaning that the hearing loss is isolated and not associated with other physical features. The remaining 30% of genetic deafness is caused by a genetic syndrome.[5]

[edit] Non-syndromic

Main article: Nonsyndromic deafness

The majority (~80%) of nonsyndromic deafness is autosomal recessive, approximately 20% is autosomal dominant, about 1% is X-linked, and less than 1% is mitochondrial.[4][5]

  • GJB2 - Changes in the GJB2 gene are the most common genetic cause of hearing loss, accounting for approximately one third of all genetic hearing loss.[6] This gene encodes the Connexin 26 protein. Changes in GJB2 typically cause congenital, mild to profound hearing loss which is inherited in an autosomal recessive manner.[7]
  • GJB6 - This gene encodes the Connexin 30 protein. Individuals with a change in one of their GJB6 genes and one of their GJB2 genes will have hearing loss.[7]

[edit] Syndromic deafness

Over 400 syndromes have been identified as being associated with deafness.[5] The following are some of the more common syndromes which cause deafness:[5][6]

Syndrome Other common features Type of hearing loss Inheritance
Alport syndrome (Hereditary nephritis)[8] Kidney disease, visual problems Bilateral, high frequency, sensorineural 80% X-linked, 15% autosomal recessive, 5% autosomal dominant
Branchio-oto-renal syndrome (BOR syndrome)[9] Branchial fistula (small passageway between the inside of the throat and outside the skin on the neck) or cyst, ear and kidney malformations Mild to profound; conductive, sensorineural, or mixed Autosomal dominant
CHARGE syndrome[10] Coloboma, heart defects, choanal atresia, developmental retardation, genital abnormalities, ear defects Mild to profound, mixed Autosomal dominant or sporadic
Jervell and Lange-Nielsen syndrome[11] Long QT interval on ECG, fainting spells, sudden death Congenital, profound, bilateral, sensorineural Autosomal recessive
Pendred syndrome[12] Enlarged vestibular aqueduct (feature diagnosed on CT scan), goiter Congenital, severe to profound Autosomal recessive
Stickler syndrome[13] Cataracts, detached retina, near-sightedness, cleft palate, underdeveloped midface, flexible joints Sensorineural or conductive Autosomal dominant
Treacher Collins syndrome[14] Outer ear defects, small jaw, flat cheekbones, difference in eye shape Conductive Autosomal dominant
Usher syndrome[15] Retinitis pigmentosa, balance problems Varies with different types - profound congenital to progressive hearing loss in adulthood Autosomal recessive
Waardenburg syndrome[16] Different colored eyes (heterochromia), premature gray hair, white forelock in hair Autosomal dominant

[edit] Environmental causes

[edit] Congenital infections

Congenital infections that can cause deafness include:[17][18][19]

[edit] Postnatal infections

Postnatal infections that can cause deafness include:

[edit] Ototoxic

Exposure to many ototoxic substances can cause deafness, such as:[22]

[edit] Physical trauma

Types of physical trauma that can cause deafness include:

[edit] Occupational

Occupational hazards can cause deafness. Any occupation with exposure to loud noises on a continuous day-to-day basis can result in hearing loss due to nerve end damage. Increased attention to conditions in the work environment has markedly decreased the likelihood of work-related hearing loss. See Noise-induced hearing loss.

[edit] Other causes

Other causes of deafness include

[edit] Temporary hearing loss

Temporary hearing loss can be caused by:

  • The build-up of wax in the ear canal
  • Foreign body lodged in the ear canal
  • Injury to the head
  • Allergy
  • Blocked Eustachian tubes
  • Scarred or perforated eardrum
  • Ear infections (chronic otitis externa, chronic otitis media, malignant otitis externa)
  • Reaction to medication such as aminoglycosides, chloroquine, quinidine