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.
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[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
- Sensorineural hearing loss - hearing loss caused by damage to the inner ear or the acoustic nerve
- Conductive hearing loss - hearing loss due to a problem with the outer or middle ear
- Mixed hearing loss - combination of sensorineural and conductive hearing loss
[edit] Severity
[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
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]
- Congenital rubella syndrome
- Congenital cytomegalovirus
- Congenital toxoplasmosis
- Congenital herpes
- Congenital syphillis
[edit] Postnatal infections
Postnatal infections that can cause deafness include:
- Meningitis[20]
- Mumps
- Measles
- Ear infection (otitis media)[21]
- Scarlet fever
[edit] Ototoxic
Exposure to many ototoxic substances can cause deafness, such as:[22]
- Aminoglycoside antibiotics - including gentamicin
- Loop diuretics - including ethacrynic acid
- Salicylates - including Aspirin
- Chloroquine
- Quinidine
[edit] Physical trauma
Types of physical trauma that can cause deafness include:
- Noise-induced hearing loss such as from explosions, fireworks, gunfire, rock concerts, extraordinary passionate kissing on the ear, slaps and earphones
- Traumatic perforation of the eardrum,Horizonatal fracture of the temporal bone
- Barotrauma (differences in pressure)
[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
- Age-related hearing loss (presbycusis)
- Meniere's disease
- Acoustic neuroma
- Otosclerosis
[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