Themitochondrial12SrRNAhasbeenshowntobethehotspotformutationsassociatedwithbothaminoglycoside-inducedandnon-syndromichearingloss.Ofallthemutations,thehomoplasmicA1555GandC1494Tmutationsatahighlyconserveddecodingregioninthe12SrRNAhavebeenassociatedwithaminoglycoside-inducedandnon-syndromichearinglossinmanyfamiliesworldwide.TheA1555GorC1494Tmutationisexpectedtoformnovel1494C-G1555or1494U-A1555base-pairatthehighlyconservedA-siteof12SrRNA.ThesetransitionsmakethesecondarystructureofthisRNAmorecloselyresemblethecorrespondingregionofbacterial16SrRNA.Thus,thenewU-AorG-Cpairin12SrRNAcreatedbytheC1494TorA1555Gtransitionfacilitatesthebindingofaminoglycosides,therebyaccountingforthefactthattheexposuretoaminoglycosidescaninduceorworsenhearinglossininpidualscarryingthesemutations.Furthermore,thegrowthdefectandimpairmentofmitochondrialtranslationwereobservedincelllinescarryingtheA1555GorC1494Tmutationinthepresenceofhighconcentrationofaminoglycosides.Inaddition,nuclearmodifiergenesandmitochondrialhaplotypesmodulatethephenotypicmanifestationoftheA1555GandC1494Tmutations.TheseobservationsprovidethedirectgeneticandbiochemicalevidencesthattheA1555GorC1494TmutationisapathogenicmtDNAmutationassociatedwithaminoglycoside-inducedandnonsyndromichearingloss.Therefore,thesedatahavebeenprovidingvaluableinformationandtechnologytopredictwhichinpidualsareatriskforototoxicity,toimprovethesafetyofaminoglycosideantibiotictherapy,andeventuallytodecreasetheincidenceofdeafness.
