Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). SNHL accounts for about 90% of reported hearing loss. SNHL is usually permanent and can be mild, moderate, severe, profound, or total. Various other descriptors can be used depending on the shape of the audiogram, such as high frequency, low frequency, U-shaped, notched, peaked, or flat. Sensory hearing loss often occurs as a consequence of damaged or deficient cochlear hair cells. Hair cells may be abnormal at birth or damaged during the lifetime of an individual. There are both external causes of damage, including infection, and ototoxic drugs, as well as intrinsic causes, including genetic mutations. A common cause or exacerbating factor in SNHL is prolonged exposure to environmental noise, or noise-induced hearing loss. Exposure to a single very loud noise such as a gun shot or bomb blast can cause noise-induced hearing loss. Using headphones at high volume over time, or being in loud environments regularly, such as a loud workplace, sporting events, concerts, and using noisy machines can also be a risk for noise-induced hearing loss. Neural, or "retrocochlear", hearing loss occurs because of damage to the cochlear nerve (CVIII). This damage may affect the initiation of the nerve impulse in the cochlear nerve or the transmission of the nerve impulse along the nerve into the brainstem.
m.1555A>G, which makes the individual sensitive to the ototoxic effects of aminoglycoside antibiotics. The most common cause of recessive genetic congenital hearing impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness. The most common syndromic forms of hearing 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 hearing loss in this condition is often ANSD (auditory neuropathy spectrum disorder) a neural cause of hearing loss. Muckle–Wells syndrome, a rare inherited autoinflammatory disorder, can lead to hearing 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 hearing loss. Congenital
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Congenital rubella syndrome, CRS, results from transplacental transmission of the rubella virus during pregnancy.