Mitochondrial non-syndromic sensorineural deafness with susceptibility to aminoglycoside exposure

Mitochondrial non-syndromic sensorineural deafness with susceptibility to aminoglycoside exposure is a maternally inherited form of hearing loss caused by specific mutations in mitochondrial DNA, most commonly the m.1555A>G mutation in the MT-RNR1 gene encoding the 12S ribosomal RNA. Individuals carrying this mutation may develop mild to profound bilateral sensorineural hearing loss either spontaneously or, more characteristically, after exposure to aminoglycoside antibiotics (such as gentamicin, streptomycin, tobramycin, or amikacin). The hearing loss is termed 'non-syndromic' because it occurs in isolation without other organ system involvement typically seen in syndromic mitochondrial disorders. The onset of hearing loss can be rapid and irreversible following even a single standard dose of aminoglycosides, though some carriers may develop progressive hearing loss without any aminoglycoside exposure. The condition affects the cochlea of the inner ear, where the mitochondrial ribosomal RNA mutation makes the human mitochondrial ribosome structurally more similar to bacterial ribosomes — the intended target of aminoglycoside antibiotics. This molecular mimicry leads to aminoglycoside-induced damage to cochlear hair cells, resulting in permanent sensorineural hearing loss. The severity of hearing loss is variable, ranging from mild high-frequency loss to profound deafness across all frequencies. Penetrance is incomplete, meaning not all carriers of the mutation will develop hearing loss, particularly in the absence of aminoglycoside exposure. There is currently no curative treatment for this condition. Management focuses primarily on prevention — specifically, avoidance of aminoglycoside antibiotics in known carriers and their maternal relatives. Genetic testing for the m.1555A>G and other MT-RNR1 variants (such as m.1494C>T) is recommended before aminoglycoside administration when feasible. For individuals who have already developed hearing loss, rehabilitation options include hearing aids for mild to moderate loss and cochlear implantation for severe to profound deafness. Genetic counseling is important to inform maternal family members of their carrier status and associated risks.

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