<unk>  may be genetic or acquired (i.e. as a consequence of disease, noise, trauma, etc.). People may have a<unk>  loss from birth (congenital) or the<unk>  loss may come on later. Many cases are related to old age (age-related). Genetic<unk>  loss can be inherited. More than 40 genes have been implicated in the cause of deafness. There are 300 syndromes with related<unk>  loss, and each syndrome may have causative genes. Recessive, dominant, X-linked, or mitochondrial genetic mutations can affect the structure or metabolism of the inner ear. Some may be single point mutations, whereas others are due to chromosomal abnormalities. Some genetic causes give rise to a late onset<unk>  loss. Mitochondrial mutations can cause<unk>  i.e. m.1555A>G, which makes the individual sensitive to the ototoxic effects of aminoglycoside antibiotics. * The most common cause of recessive genetic congenital<unk>  impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness. * The most common syndromic forms of<unk>  impairment include (dominant) Stickler syndrome and Waardenburg syndrome, and (recessive) Pendred syndrome and Usher syndrome. * Mitochondrial mutations causing deafness are rare: MT-TL1 mutations cause MIDD (Maternally inherited deafness and diabetes) and other conditions which may include deafness as part of the picture. * TMPRSS3 gene was identified by its association with both congenital and childhood onset autosomal recessive deafness. This gene is expressed in fetal cochleae and many other tissues, and is thought to be involved in the development and maintenance of the inner ear or the contents of the perilymph and endolymph. It was also identified as a tumor associated gene that is overexpressed in ovarian tumors. * Charcot–Marie–Tooth disease an inherited neurological disorder with delayed onset that can affect the ears as well as other organs. The<unk>  loss in this condition is often ANSD (auditory neuropathy spectrum disorder) a neural cause of<unk>  loss. * Muckle–Wells syndrome, a rare inherited autoinflammatory disorder, can lead to<unk>  loss. * Autoimmune disease: although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Granulomatosis with polyangiitis, an autoimmune condition, may precipitate<unk>  loss. Congenital * Infections: *Congenital rubella syndrome, CRS, results from transplacental transmission of the rubella virus during pregnancy. CRS has been controlled by universal vaccination (MMR or MMRV vaccine). *Cytomegalovirus (CMV) infection is the most common cause of progressive<unk>  in children. It is a common viral infection contracted by contact with infected bodily fluids such as saliva or urine and easily transmitted in nurseries and thus from toddlers to expectant mothers. CMV infection during pregnancy can affect the developing foetus and lead to learning difficulties as well as<unk>  loss. *Toxoplasmosis, a parasitic disease affecting 23% of the population in the U.S., can cause<unk>  deafness to the fetus in utero. * Hypoplastic auditory nerves or abnormalities of the cochlea. Abnormal development of the inner ear can occur in some genetic syndromes such as LAMM syndrome (labyrinthine aplasia, microtia and microdontia), Pendred syndrome, branchio-oto-renal syndrome, CHARGE syndrome * GATA2 deficiency, a grouping of several disorders caused by common defect, viz., familial or sporadic inactivating mutations in one of the two parental GATA2 genes. These autosomal dominant mutations cause a reduction, i.e. a haploinsufficiency, in the cellular levels of the gene's product, GATA2. The GATA2 protein is a transcription factor critical for the embryonic development, maintenance, and functionality of blood-forming, lympathic-forming, and other tissue-forming stem cells. In consequence of these mutations, cellular levels of GATA2 are deficient and individuals develop over time hematological, immunological, lymphatic, and/or other disorders. GATA2 deficiency-induced abnormalities in the lymphatic system are proposed to be responsible for a failure in generating the perilymphatic space around the inner ear's semicircular canals, which in turn underlies the development of<unk> . Presbycusis Progressive age-related loss of<unk>  acuity or sensitivity can start as early as age 18, primarily affecting the high frequencies, and men more than women. Such losses may not become apparent until much later in life. Presbycusis is by far the dominant cause of<unk>  in industrialized societies. A study conducted in Sudan, with a population free from loud noise exposures, found significantly less cases of<unk>  loss when compared with age-matched cases from an industrialized country. Similar findings were reported by a study conducted of a population from Easter island, which reported worse<unk>  among those that spent time in industrialized countries when compared with those that never left the island. Researchers have argued that factors other than differences in noise exposure, such as genetic make up, might also have contributed to the findings.<unk>  loss that worsens with age but is caused by factors other than normal aging, such as noise-induced<unk>  loss, is not presbycusis, although differentiating the individual effects of multiple causes of<unk>  loss can be difficult. One in three persons have significant<unk>  loss by age 65; by age 75, one in two. Age-related<unk>  loss is neither preventable nor reversible. Noise Most people living in modern society suffer from some degree of progressive<unk>  (i.e. permanent) noise-induced<unk>  loss (NIHL) resulting from overloading and damaging the sensory or neural apparatus of<unk>  in the inner ear. NIHL is typically a drop-out or notch centered at 4000 Hz. Both intensity (SPL) and duration of exposure, and repetitive exposure to unsafe levels of noise contribute to cochlear damage that results in<unk>  loss. The louder the noise is, the shorter the safe amount of exposure is. NIHL can be either permanent or temporary, called a threshold shift. Unsafe levels of noise can be as little as 70 dB (about twice as loud as normal conversation) if there is prolonged (24-hour) or continuous exposure. 125 dB (a loud rock concert is ~120 dB) is the pain level; sounds above this level cause instant and permanent ear damage. Noise and ageing are the primary causes of presbycusis, or age-related<unk>  loss, the most common kind of<unk>  loss in industrial society. The dangers of environmental and occupational noise exposure are widely recognized. Numerous national and international organizations have established standards for safe levels of exposure to noise in industry, the environment, military, transportation, agriculture, mining and other areas. Sound intensity or sound pressure level (SPL) is measured in decibels (dB). For reference: + db Level Example 45 dB Ambient noise level around the home 60 dB Quiet office 60–65 dB Normal conversation 70 dB City street noise at 25' or average TV audio 80 dB Noisy office 95–104 dB Nightclub dance floor 120 dB Close-by thunder or a loud rock concert 150–160 dB Gunshot from a handheld gun An increase of 6 dB represents a doubling of the SPL, or energy of the sound wave, and therefore its propensity to cause ear damage. Because human ears hear logarithmically, not linearly, it takes an increase of 10 dB to produce a sound that is perceived to be twice as loud. Ear damage due to noise is proportional to sound intensity, not perceived loudness, so it's misleading to rely on subjective perception of loudness as an indication of the risk to<unk> , i.e. it can significantly underestimate the danger. While the standards differ moderately in levels of intensity and duration of exposure considered safe, some guidelines can be derived. The safe amount of exposure is reduced by a factor of 2 for every exchange rate (3 dB for NIOSH standard or 5 dB for OSHA standard) increase in SPL. For example, the safe daily exposure amount at 85 dB (90 dB for OSHA) is 8 hours, while the safe exposure at 94 dB(A) (nightclub level) is only 1 hour. Noise trauma can also cause a reversible<unk>  loss, called a temporary threshold shift. This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event (tinnitus). * Ambient environmental noise: Populations living near airports, railyards and train stations, freeways and industrial areas are exposed to levels of noise typically in the 65 to 75 dBA range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade<unk> . U.S. Dept. of Housing and Urban Development sets standards for noise impact in residential and commercial construction zones. HUD’s noise standards may be found in 24 CFR Part 51, Subpart B. Environmental noise above 65 dB defines a noise-impacted area. * Personal audio electronics: Personal audio equipment such as iPods (iPods often reach 115 decibels or higher), can produce powerful enough sound to cause significant NIHL. * Acoustic trauma: Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent<unk>  loss. A typical source of acoustic trauma is a too-loud music concert. * Workplace noise: The OSHA standards 1910.95 General Industry Occupational Noise Exposure and 1926.52 Construction Industry Occupational Noise Exposure identify the level of 90 dB(A) for 8 hour exposure as the level necessary to protect workers from<unk>  loss.
Sensorineural hearing loss
Conductive hearing loss
Prelingual deafness
Spatial hearing loss
Unilateral hearing loss
Hemifacial hypertrophy
Cortical deafness
Ocular dysmetria