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
Infections:
Congenital rubella syndrome, CRS, results from transplacental transmission of the rubella virus during pregnancy.
Acoustic neuroma (vestibular schwannoma) – benign neoplasm of Schwann cells affecting the vestibulocochlear nerve
Meningioma – benign tumour of the pia and arachnoid mater
Ménières disease – causes sensorineural hearing loss in the low frequency range (125 Hz to 1000 Hz). Ménières disease is characterized by sudden attacks of vertigo, lasting minutes to hours preceded by tinnitus, aural fullness, and fluctuating hearing loss. It is relatively rare and commonly over diagnosed. Bacterial meningitis e.g. pneumococcal, meningococcal, haemophilus influenzae may damage the cochlea – Hearing loss is one of the most common after-effects of bacterial meningitis. It has been estimated that 30% of bacterial meningitis cases result in mild to profound hearing loss. Children are most at risk: seventy percent of all bacterial meningitis occurs in young children under the age of five. Viral
AIDS and ARC patients frequently experience auditory system anomalies. Mumps(epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilaterally (one ear) or bilaterally (both ears). Measles may result in auditory nerve damage but more commonly gives a mixed (sensorineural plus conductive) hearing loss, and can be bilaterally. Ramsay Hunt syndrome type II (herpes zoster oticus)
Bacterial
Syphilis is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf. Ototoxic and neurotoxic drugs and chemicals
Some over-the-counter as well as prescription drugs and certain industrial chemicals are ototoxic. Exposure to these can result in temporary or permanent hearing loss. Some medications cause irreversible damage to the ear, and are limited in their use for this reason.