Aminoglycoside-Induced Hearing Loss

Mendelian MONDO:0010799 Pathograph 30 Show in embeddings browser Mitochondrial Disease Sensorineural Hearing Loss

This entry describes inherited susceptibility to aminoglycoside-induced sensorineural hearing loss associated with mitochondrial MT-RNR1 variants. The strongest prescribing evidence concerns m.1555A>G and m.1494C>T, with moderate evidence for m.1095T>C. Hearing loss can be bilateral, severe to profound and permanent after standard therapeutic exposure, sometimes after a single dose, but penetrance and severity are not uniform. Some families also have hearing loss without documented aminoglycoside exposure; population data do not establish inevitable hearing loss in carriers. For m.1555A>G and m.1494C>T, experimental ribosomes show altered decoding accuracy and increased aminoglycoside binding. The steps connecting these defects to selective human cochlear injury remain incompletely resolved. Avoiding aminoglycosides when an effective alternative exists is central to prevention. Genotype-guided prescribing must preserve timely treatment of serious infection: urgent therapy should not be delayed while awaiting a test. The general dose- and duration-related ototoxicity of aminoglycosides can also occur without an identified MT-RNR1 variant and is distinguished from inherited susceptibility here.

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Inheritance

Mitochondrial (maternal) inheritance HP:0001427

Predisposing mitochondrial variants are maternally transmitted. Children of a woman carrying a variant are at risk of inheritance; male carriers do not transmit their mitochondrial variant. Homoplasmy and heteroplasmy require different counseling, and inherited variant status does not by itself predict hearing-loss onset or severity.

Mitochondrial inheritance

Show evidence (3 references)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"All offspring of females with a mtDNA pathogenic variant are at risk of inheriting the pathogenic variant. Offspring of males with a mtDNA pathogenic variant are not at risk of inheriting the pathogenic variant."

Defines maternal transmission without guaranteeing phenotype or identical heteroplasmy in offspring.

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Furthermore, the presence of the mtDNA pathogenic variant does not predict the age of onset or severity of hearing loss."

Separates transmission from clinical penetrance.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/ SUPPORT REVIEW SYNTHESIS Other

"the presence of the mtDNA pathogenic variant does not predict the age of onset or severity of hearing loss."

Full GeneReviews chapter distinguishes inherited variant status from phenotype prediction.

◈

Mechanistic Hypotheses

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

mitoribosomal_dysfunction_to_cochlear_injury EMERGING

Evidence balance 2 support

Mutant ribosome biochemistry and selected family-derived cells support impaired translation and mitochondrial function. Connecting these findings to ATP limitation, oxidant stress and sensory-cell loss in exposed human carriers remains incompletely demonstrated. Generic drug-exposed fish, guinea-pig and mouse-explant systems do not encode the human susceptibility alleles; their drug-specific responses caution against a universal linear death pathway.

Pathograph links

Mitoribosomal Decoding Errors -> Reduced Mitochondrial Respiration INDIRECT UNKNOWN INTERMEDIATES Incorrectly translated mitochondrial proteins are proposed to impair respiratory function. The hybrid-ribosome study does not itself measure human respiratory complexes or prove mediation in cochlear cells.

Reduced Mitochondrial Protein Synthesis -> Reduced Mitochondrial Respiration INDIRECT KNOWN INTERMEDIATES Reduced synthesis of mitochondrial respiratory-chain components is a proposed route to impaired respiration. Supporting family-cell studies show both abnormalities, but do not isolate each mediator in human hair cells.

Reduced Mitochondrial Respiration -> Reduced Mitochondrial ATP Production INDIRECT KNOWN INTERMEDIATES Respiratory impairment is proposed to reduce mitochondrial ATP output. The measured mitochondrial ATP condition suppressed glycolysis; it does not demonstrate the same loss of total cellular ATP.

Reduced Mitochondrial Respiration -> Oxidative Stress INDIRECT UNKNOWN INTERMEDIATES Mitochondrial dysfunction may increase oxidant stress or reduce stress resistance. The selected cell studies and general drug models do not establish a uniform ROS mechanism in carrier cochleae.

Reduced Mitochondrial ATP Production -> Cochlear Hair Cell Loss INDIRECT UNKNOWN INTERMEDIATES Energy limitation could compromise mitochondrial integrity and activate downstream cell-death pathways. Its necessity or sufficiency for MT-RNR1-associated human hearing loss remains unresolved.

Oxidative Stress -> Cochlear Hair Cell Loss INDIRECT UNKNOWN INTERMEDIATES Oxidant injury can contribute to sensory-cell death, but the complete mitochondrial-variant-to-hair-cell pathway remains hypothetical. Antioxidant protection in one drug model does not establish a universal route.

Show evidence (2 references)

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood."

The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of the complete MT-RNR1 causal chain.

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death"

Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.

Discussions and Knowledge Gaps

Which exposures and modifiers explain clinical penetrance across actionable MT-RNR1 variants?

KNOWLEDGE GAP OPEN carrier_penetrance_and_exposure

Attached to

genetic#MT-RNR1 pathophysiology#Predisposing MT-RNR1 Variants

Severe loss after limited exposure is well documented, but selected maternal pedigrees and neonatal screening endpoints do not yield an unbiased lifetime risk. The British birth cohort had no individual aminoglycoside-exposure data and assessed better-ear thresholds at two frequencies in midlife. TRMU modifier families were selected and had no reported aminoglycoside exposure. General drug-resistant-tuberculosis ototoxicity estimates mix genetically unselected populations and cannot serve as prevalence of this inherited disorder.

Show evidence (3 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence"

The clinical susceptibility set is broader than the alleles tested in the structural experiments.

PMID:25155176 SUPPORT PRIMARY RESULT Human Clinical

"It is important to note, that most infants with failed newborn hearing screening do not develop permanent hearing loss."

A screening failure is not equivalent to permanent hearing impairment.

PMID:34015383 SUPPORT REVIEW SYNTHESIS Other

"aminoglycoside use results in high prevalence of ototoxic hearing loss"

Genetically unselected tuberculosis-treatment context, not Mendelian disease prevalence.

How do allele-specific mitoribosomal defects produce selective cochlear injury in exposed carriers?

KNOWLEDGE GAP OPEN human_cochlear_mechanistic_bridge

Attached to

pathophysiology#Mitoribosomal Decoding Errors pathophysiology#Cochlear Hair Cell Loss

Hybrid ribosomes isolate decoding-site effects and lymphoblasts establish cellular susceptibility, but neither reproduces the complete sensory-cell context. General drug models show multiple exposure-dependent injury responses, including delayed routes not protected by the tested mitochondrial antioxidant. A patient-genotype hair-cell system with allele correction and physiological drug exposure would help distinguish initiating defects from secondary stress.

Show evidence (2 references)

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood."

The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of the complete MT-RNR1 causal chain.

PMID:39610699 SUPPORT PRIMARY RESULT Model Organism

"The underlying mechanisms by which lysosomal accumulation of AGs result in delayed cell death remain unclear."

Even the delayed generic drug-injury mediator remains unresolved.

Can alternative antibiotics or otoprotective strategies preserve hearing in actionable-variant carriers without compromising infection treatment?

OPEN QUESTION OPEN clinical_otoprotection_and_testing_outcomes

Attached to

treatments#Avoidance or substitution of aminoglycoside antibiotics clinical_trials#NCT04105205

PALOH demonstrated prescribing change and similar mean antibiotic timing within its implementation comparison, not comparative long-term hearing protection. Apramycin has progressed beyond purely preclinical work to a healthy-volunteer phase I study, but that does not establish carrier safety. Antioxidant and other otoprotective findings in general drug models should not replace current genotype-guided avoidance.

Show evidence (2 references)

PMID:35311942 SUPPORT PRIMARY RESULT Human Clinical

"Three participants with the m.1555A>G variant were identified, all of whom avoided aminoglycoside antibiotics."

Observed implementation benefit; no measured comparative permanent-hearing outcome.

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"these protective results are mainly based on acute studies and the sustainability of therapeutic potential and safety remains to be evaluated in chronic exposure scenarios or in clinical trials."

Limits extrapolating experimental otoprotection to standard care.

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Pathophysiology

Predisposing MT-RNR1 Variants

Mechanism confidence: Established

Mitochondrial MT-RNR1 variants confer susceptibility to aminoglycoside ototoxicity. m.1555A>G and m.1494C>T are the best-supported alleles; m.1095T>C is also actionable with a lower level of evidence. Carriage can be homoplasmic or heteroplasmic. Variant status is a susceptibility state rather than a guarantee of hearing loss.

MT-RNR1 hgnc:7470

Downstream

Altered Mitoribosomal Decoding-Site Geometry This structural route concerns m.1555A>G and m.1494C>T. The same detailed geometry has not been demonstrated for every actionable MT-RNR1 variant.

Show evidence (1 reference)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence"

The clinical susceptibility set is broader than the alleles tested in the structural experiments.

Altered Mitoribosomal Decoding-Site Geometry

Mechanism confidence: Established

The m.1555A>G and m.1494C>T substitutions introduce a Watson–Crick pair that shortens the extended mitochondrial decoding-site loop. Hybrid-ribosome experiments support altered decoding behavior, but loop closure alone did not reproduce the fidelity defect. This is not wholesale conversion of a human mitoribosome into a bacterial ribosome.

Downstream

Aminoglycoside Binding to the Mitochondrial Ribosome The altered decoding environment increases aminoglycoside binding when drug is present. This interaction is supported by chemical footprinting of hybrid ribosomes.

Mitoribosomal Decoding Errors The mutant decoding site has reduced translational fidelity even without drug. The precise conformational sequence is inferred; simple loop closure alone was insufficient in a control construct.

Show evidence (1 reference)

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"Both the C1494U and the A1555G mutation replace the noncanonical C1494·A1555 interaction by a Watson–Crick base pairing, thus shortening the extended conformation of the mitochondrial loop."

Structural interpretation of the human-sequence decoding site in hybrid bacterial ribosomes; C1494U is the RNA equivalent of the DNA C1494T variant.

Cochlear Aminoglycoside Accumulation

Mechanism confidence: Established

Systemically administered aminoglycosides reach the inner ear and accumulate in sensory hair cells. Mechanotransduction channels are an important entry route in experimental systems. Uptake and intracellular localization vary with drug and exposure; this is general ototoxicity biology rather than a demonstrated MT-RNR1-specific uptake defect.

cochlear outer hair cell CL:0000601 cochlear inner hair cell CL:0000589

spiral organ of cochlea UBERON:0002227

Downstream

Aminoglycoside Binding to the Mitochondrial Ribosome Intracellular drug must reach the mitoribosomal target. The cited assays establish target susceptibility but do not resolve transport across every cellular and mitochondrial compartment.

Cochlear Hair Cell Loss Drug exposure causes sensory-cell injury through multiple routes. This aggregate edge preserves experimental toxicity outside the incompletely resolved mitochondrial-variant pathway.

RIPOR2 Redistribution in Hair Cells Gentamicin exposure drives rapid RIPOR2 redistribution in mouse cochlear explants with functional mechanotransduction. The intervening entry/signaling steps are not isolated by this experiment.

Show evidence (1 reference)

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"there is strong evidence that AGs enter hair cells through the MET channel located at the top of the stereocilia."

Review of experimental hair-cell entry mechanisms.

Aminoglycoside Binding to the Mitochondrial Ribosome

Mechanism confidence: Established

Aminoglycosides bind the mitochondrial decoding region, with enhanced susceptibility of A1555G/C1494T hybrid sites. Drug binding can both worsen decoding accuracy and inhibit protein synthesis; these are distinct readouts. The intrinsic variant-associated fidelity defect can exist before exposure.

Experimental models

Human-sequence mitochondrial decoding sites in bacterial hybrid ribosomes OTHER Chemical footprinting supports increased aminoglycoside interaction with variant decoding sites.

Downstream

Mitoribosomal Decoding Errors Drug binding aggravates miscoding by the mutant decoding apparatus.

Reduced Mitochondrial Protein Synthesis Aminoglycoside interaction with the translation machinery inhibits mitochondrial protein synthesis. In patient-derived lymphoblasts, drug-dependent labeling inhibition was greater in carriers.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/ SUPPORT PRIMARY RESULT In Vitro

"increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy."

Chemical footprinting and translation assays support enhanced drug binding plus inherent decoding infidelity in A1555G/C1494T hybrids.

Mitoribosomal Decoding Errors

Mechanism confidence: Established

A1555G/C1494T hybrid ribosomes misincorporate amino acids more frequently; aminoglycosides exacerbate the defect. Reduced reporter enzymatic activity despite comparable full-length protein output demonstrates why fidelity should be separated from a lower synthesis rate.

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

Experimental models

Human-sequence mitochondrial decoding sites in bacterial hybrid ribosomes OTHER Variant hybrid ribosomes show intrinsic and aminoglycoside-exacerbated miscoding.

Downstream

Reduced Mitochondrial Respiration Incorrectly translated mitochondrial proteins are proposed to impair respiratory function. The hybrid-ribosome study does not itself measure human respiratory complexes or prove mediation in cochlear cells.

Show evidence (2 references)

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation."

Direct comparative misincorporation assays distinguish accuracy from total protein output.

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"Mutant and wild-type mitochondrial hybrid ribosomes produced the same level of full-length protein"

The drug-free luciferase experiment distinguishes product quality from total protein output.

Reduced Mitochondrial Protein Synthesis

Mechanism confidence: Established

Aminoglycosides reduce mitochondrial protein synthesis in susceptible family-derived lymphoblasts. Separate unexposed TRMU modifier studies also show reduced mitochondrial protein labeling. These observations concern selected cultured cells and do not establish uniform translational arrest in every carrier.

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

mitochondrial translation GO:0032543 ↓ DECREASED

Experimental models

Paromomycin-exposed m.1555A>G family lymphoblasts CELL LINE Drug/no-drug mitochondrial translation-rate ratios were lower in carrier cells.

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL LINE Protein labeling was lower in the homozygous double-mutant lines.

Downstream

Reduced Mitochondrial Respiration Reduced synthesis of mitochondrial respiratory-chain components is a proposed route to impaired respiration. Supporting family-cell studies show both abnormalities, but do not isolate each mediator in human hair cells.

Show evidence (2 references)

PMID:10915767 SUPPORT PRIMARY RESULT In Vitro

"The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively),..."

Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high paromomycin concentration, not a clinical dose threshold.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

"the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%."

Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.

Reduced Mitochondrial Respiration

Mechanism confidence: Provisional

Reduced oxygen consumption is measured in m.1555A>G lymphoblasts, with larger reductions in selected TRMU A10S double-mutant lines. Extending these findings to drug-exposed carrier hair cells remains a mechanistic hypothesis. Non-isogenic family lines do not isolate the effect of one allele from every other background difference.

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

Experimental models

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL LINE Oxygen-consumption rates were reduced in selected mutant groups.

Downstream

Reduced Mitochondrial ATP Production Respiratory impairment is proposed to reduce mitochondrial ATP output. The measured mitochondrial ATP condition suppressed glycolysis; it does not demonstrate the same loss of total cellular ATP.

Oxidative Stress Mitochondrial dysfunction may increase oxidant stress or reduce stress resistance. The selected cell studies and general drug models do not establish a uniform ROS mechanism in carrier cochleae.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

"the average basal OCRs in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations, and only m.1555A→G mutation were 54, 76, and 88%, relative to the mean value measured in the control cell lines, respectively."

OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and controls; no drug exposure or hair cells.

Reduced Mitochondrial ATP Production

Mechanism confidence: Hypothetical

Mitochondrial ATP production was reduced in selected m.1555A>G/TRMU lymphoblast lines under conditions suppressing glycolysis. Total ATP was relatively preserved. ATP limitation in exposed human cochlear cells is proposed, not directly measured in these studies.

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

Experimental models

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL LINE ATP production was reduced with glycolysis suppressed.

Downstream

Cochlear Hair Cell Loss Energy limitation could compromise mitochondrial integrity and activate downstream cell-death pathways. Its necessity or sufficiency for MT-RNR1-associated human hearing loss remains unresolved.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

"the levels of ATP production in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations and only m.1555A→G mutation were 48, 61, and 83% of the mean value measured in the control cell lines, respectively."

ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this is not a global energy collapse.

Oxidative Stress

Mechanism confidence: Provisional

Oxidative stress is implicated in general aminoglycoside hair-cell toxicity and observed as an altered oxidant response in selected mitochondrial-variant lymphoblasts. Drug and exposure context matter: an antioxidant-sensitive acute larval-fish pathway differs from the tested delayed injury paradigm.

Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury

cellular response to oxidative stress GO:0034599 ↑ INCREASED

Downstream

Cochlear Hair Cell Loss Oxidant injury can contribute to sensory-cell death, but the complete mitochondrial-variant-to-hair-cell pathway remains hypothetical. Antioxidant protection in one drug model does not establish a universal route.

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

"the levels of ROS generation in the mutant cell lines cells carrying both m.1555A→G and homozygous TRMU A10S mutations ranged from 155 to 167%, with an average 161% of the mean value measured in the control cell lines"

Fluorescent-probe response under hydrogen-peroxide challenge in selected double-mutant lymphoblasts; not a direct measurement in human cochlea.

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death"

Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.

Cochlear Hair Cell Loss

Mechanism confidence: Established

Loss of cochlear sensory cells is a major structural substrate of aminoglycoside hearing impairment. Experimental gentamicin injury often has a basal-to-apical gradient. Apoptotic and other injury routes depend on model, dose and time; no single mode of death is established for all MT-RNR1-associated cases.

cochlear outer hair cell CL:0000601 cochlear inner hair cell CL:0000589

spiral organ of cochlea UBERON:0002227

Experimental models

Mouse cochlear explants exposed to gentamicin or apramycin PRIMARY CELL CULTURE Drug-dependent cochlear hair-cell loss was quantified in explants.

Animal models

Guinea-pig comparative aminoglycoside ototoxicity Guinea pig partially recapitulates In-vivo histology documents drug-associated cochlear sensory-cell loss.

Larval zebrafish acute and delayed aminoglycoside sensory-cell injury Zebrafish partially recapitulates Lateral-line sensory-cell loss provides a comparative drug-injury model for the cochlear injury node.

Downstream

Bilateral Sensorineural Hearing Loss Loss of sensory transduction contributes to persistent sensorineural hearing loss. Clinical laterality and severity are documented in affected humans; the tissue mechanism is supported mainly by general ototoxicity models.

High-Frequency Predominant Loss Preferential basal-cochlear injury offers an anatomical explanation for high-frequency loss in general aminoglycoside toxicity. Carrier audiograms are variable, so this is not a required sequence for every affected individual.

Show evidence (2 references)

PMID:22699498 SUPPORT PRIMARY RESULT Model Organism

"Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea."

In-vivo cochlear histology supports the structural injury pattern, with genotype extrapolation explicitly limited.

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood."

The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of the complete MT-RNR1 causal chain.

Reduced TRMU-Dependent tRNA Thiolation

Mechanism confidence: Provisional

The TRMU p.Ala10Ser modifier is associated with reduced 2-thiouridine modification of wobble U34 in selected mitochondrial tRNAs. Purified-protein thermal stability and cellular abundance were reduced in the 2017 study, but degradation kinetics were not measured and the earlier import assay was normal. This branch applies to the studied modifier genotypes, not all MT-RNR1 carriers.

TRMU hgnc:25481

Experimental models

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL LINE A10S-bearing lines have reduced tRNA thiolation.

Downstream

Reduced Mitochondrial tRNA Abundance Defective thiolation is proposed to impair tRNA stability and lower steady-state abundance. Northern blots measure abundance, without directly measuring degradation kinetics.

Show evidence (1 reference)

PMID:28049726 SUPPORT PRIMARY RESULT In Vitro

"The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln"

TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside treatment.

Reduced Mitochondrial tRNA Abundance

Mechanism confidence: Provisional

Several mitochondrial tRNAs were less abundant in homozygous TRMU A10S plus m.1555A>G lymphoblasts. This is a modifier-associated cellular observation in selected families; neither absent tRNA import nor uniformly decreased aminoacylation was demonstrated.

Experimental models

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL LINE Double-mutant lines have reduced mitochondrial tRNA steady-state abundance.

Downstream

Reduced Mitochondrial Protein Synthesis Lower availability of mitochondrial tRNAs can impair translation. The same family-derived lines show reduced mitochondrial protein labeling, but the contributions of thiolation, abundance and other background effects were not independently rescued.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

"the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls"

Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured, degradation kinetics were not.

RIPOR2 Redistribution in Hair Cells

Mechanism confidence: Provisional

Gentamicin induces reversible movement of RIPOR2 from the stereociliary base to the pericuticular region in mouse cochlear explants. Phosphatidylserine exposure occurs with different kinetics and is insufficient on its own to trigger this movement. This emerging drug-response branch has not been linked experimentally to the human MT-RNR1 variants in the cited study.

cochlear outer hair cell CL:0000601 cochlear inner hair cell CL:0000589

spiral organ of cochlea UBERON:0002227

Experimental models

Gentamicin and mechanotransduction perturbation in neonatal mouse cochlear explants PRIMARY CELL CULTURE Gentamicin induced reversible redistribution requiring an intact tested mechanotransduction context.

Show evidence (2 references)

PMID:40842562 SUPPORT PRIMARY RESULT In Vitro

"RIPOR2 translocated robustly from the stereocilia base to the pericuticular area"

Immunostaining response in P3–P5 mouse explants.

PMID:40842562 SUPPORT PRIMARY RESULT In Vitro

"These findings suggest that PS externalization alone is insufficient to trigger RIPOR2 translocation."

Benzamil induces surface phosphatidylserine without RIPOR2 movement; no inferred apoptosis or proven death-necessity edge is added.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

Bilateral Sensorineural Hearing Loss Auditory HP:0008619

Show evidence (1 reference)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound"

Supports the characteristic presentation, without assigning a frequency across all carriers.

High-Frequency Predominant Loss Auditory HP:0001757

Show evidence (2 references)

PMID:17698299 SUPPORT PRIMARY RESULT Human Clinical

"All affected individuals displayed the loss of the high frequencies and their hearing impairments were symmetric."

Observed in the WZD101 C1494T family; not an unselected carrier prevalence.

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"AG cochleotoxicity typically affects first the high frequency and then extends towards the lower frequency and ranges over time in a dose-dependent manner"

Context from general aminoglycoside toxicity, distinguished from the inherited phenotype.

🧬

Genetic Associations

MT-RNR1

Gene: MT-RNR1 hgnc:7470 gene page relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence"

Distinguishes evidence strength and clinical actionability.

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"there is not sufficient evidence to define a level of heteroplasmy where aminoglycoside administration becomes safe"

Supports precaution at any detected actionable variant level.

Variants (3)

m.1555A>G

The best-studied predisposing variant; high evidence for a drug-variant interaction. Hybrid-ribosome experiments show both intrinsic decoding errors and increased drug susceptibility.

Show evidence (1 reference)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"Some MT-RNR1 variants (i.e., m.1095T>C; m.1494C>T; m.1555A>G) more closely resemble the bacterial 16s rRNA subunit and result in increased risk of aminoglycoside-induced hearing loss."

CPIC includes this variant in its actionable susceptibility set; the detailed experimental mechanism is allele-dependent.

m.1494C>T

A decoding-site variant with high evidence for aminoglycoside susceptibility, including maternal pedigrees and hybrid-ribosome experiments. Clinical severity varies.

Show evidence (1 reference)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"additional variants with sufficient evidence to support a drug-variant interaction are m.1095T>C and m.1494C>T"

CPIC includes this variant in its actionable susceptibility set; the detailed experimental mechanism is allele-dependent.

m.1095T>C

An actionable susceptibility variant with moderate evidence. The detailed structural experiments on m.1555A>G and m.1494C>T should not be assumed to establish an identical molecular mechanism for this allele.

Show evidence (1 reference)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"additional variants with sufficient evidence to support a drug-variant interaction are m.1095T>C and m.1494C>T"

CPIC includes this variant in its actionable susceptibility set; the detailed experimental mechanism is allele-dependent.

TRMU

Gene: TRMU hgnc:25481 gene page relationship_type: MODIFIER

Show evidence (3 references)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT Human Clinical

"No subjects had a history of exposure to aminoglycosides."

The modifier study addresses hearing expression without drug exposure.

PMID:16826519 SUPPORT PRIMARY RESULT Human Clinical

"all 18 Arab-Israeli/Italian-Spanish matrilineal relatives carrying both the TRMU A10S and 12S rRNA A1555G mutations exhibited prelingual profound deafness."

Selected-family association; the full report specifies homozygous A10S, and other symptomatic relatives lacked it.

PMID:28049726 SUPPORT PRIMARY RESULT In Vitro

"The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln"

Functional modifier evidence from family-derived cell lines.

💊

Medical Actions

Avoidance or substitution of aminoglycoside antibiotics

Platform: Other

For carriers of an actionable MT-RNR1 variant, choose an effective non-aminoglycoside regimen when available. This reduces the drug-associated risk but does not eliminate all possible hearing loss. The precaution applies across the aminoglycoside class. Inhaled delivery can still produce systemic exposure; low-absorption topical/enteral use and damaged barriers require route-specific assessment.

Mechanism Target:

INHIBITS Cochlear Aminoglycoside Accumulation — Avoiding the drug prevents this exposure-dependent step; it does not correct the mitochondrial variant.

Show evidence (1 reference)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"aminoglycosides should be avoided unless the increased risk of hearing loss is outweighed by the severity of infection and lack of safe or effective alternative therapies"

Relative contraindication balances hearing risk against effective infection treatment.

Expert management when aminoglycosides are essential

Platform: Other

When no safe effective alternative exists, obtain infectious-disease/microbiology advice, document and discuss the risk-benefit decision, and use the shortest effective course with drug-level, renal and audiovestibular monitoring. If testing information is unavailable and clinical urgency is high, do not delay necessary antibiotic treatment.

Show evidence (2 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"an aminoglycoside used in patients at increased risk of AIHL due to the presence of an MT-RNR1 variant should be administered for the shortest possible period, under expert supervision, with therapeutic drug and ototoxicity monitoring"

Guideline precautions; monitoring does not guarantee prevention.

PMID:42524757 SUPPORT REVIEW SYNTHESIS Other

"Aminoglycoside treatment should not be delayed, and administration should proceed according to local microbiological guidance, as the benefit exceeds the risk."

Applies to the acute setting where genotype information is unavailable.

Hearing aids and auditory rehabilitation

Action: hearing-aid rehabilitation Ontology label: Rehabilitation NCIT:C15315

Platform: Device

Offer hearing aids and audiologic rehabilitation appropriate to residual hearing and communication needs. These improve functional access to sound; they do not regenerate damaged cochlear hair cells.

Mechanism Target:

BYPASSES Bilateral Sensorineural Hearing Loss — Amplification supports use of residual hearing without repairing the initiating molecular defect.

Show evidence (1 reference)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired)."

Mitochondrial-hearing-loss rehabilitation guidance.

Cochlear implantation and electric acoustic stimulation

Action: cochlear implantation Ontology label: Surgical Implantation NCIT:C201922

Platform: Surgery

Evaluate cochlear implantation for severe hearing loss according to standard candidacy assessment. Electric acoustic stimulation may be considered when usable low-frequency hearing remains. The GeneReviews recommendations address mitochondrial hearing loss generally, not a genotype-specific comparative trial.

Mechanism Target:

BYPASSES Bilateral Sensorineural Hearing Loss — Electrical stimulation bypasses impaired sensory transduction to support hearing.

Show evidence (3 references)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired)."

Includes cochlear implantation among rehabilitation options.

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Electric acoustic stimulation for individuals with mitochondrial hearing loss with residual hearing in the lower frequencies."

Qualifies the residual-hearing indication.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/ SUPPORT REVIEW SYNTHESIS Other

"Appropriate rehabilitation including hearing aids, speech therapy, culturally appropriate language training, and evaluation for eligibility for cochlear implantation"

Full chapter recommendation is evaluation for candidacy rather than universal implantation.

Communication, language and educational support

Action: Speech Language Therapy NCIT:C159273

Platform: Other

Provide speech/language therapy, culturally appropriate language support and educational accommodations according to the individual and family’s communication preferences and needs.

Show evidence (1 reference)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired)."

Guidance includes language, speech and educational support.

Maternal-family counseling and durable prescribing alerts

Action: Genetic Counseling NCIT:C15240

Platform: Other

Explain maternal transmission, variable penetrance and the importance of sharing drug-risk information with maternal relatives. Record the actionable result so future prescribers can retrieve it. The 2026 UK guideline considers maternal relatives of a homoplasmic carrier at risk without requiring confirmatory genotyping of each relative; testing first-degree maternal relatives can be considered for heteroplasmic findings. Prenatal variant detection does not predict hearing severity.

Show evidence (3 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"the advice to avoid aminoglycosides should be cascaded to the relevant individuals within the family."

Family risk communication.

PMID:42524757 SUPPORT REVIEW SYNTHESIS Other

"Where the variant detected is heteroplasmic, testing in first degree maternal relatives can be considered."

Heteroplasmy-specific family testing advice.

PMID:42524757 SUPPORT REVIEW SYNTHESIS Other

"The results should be recorded in the patient record (ideally in the electronic record in a format that is immediately available to inform future prescribing decisions)."

Durable pharmacogenetic communication, not a direct therapeutic action on the causal graph.

Hearing protection and routine vaccination

Platform: Other

Avoid excessive noise exposure as part of hearing preservation. Trace aminoglycosides in vaccines are not a reason to forgo recommended vaccination: the 2026 guideline considers vaccination benefits to outweigh the theoretical ototoxicity risk.

Show evidence (2 references)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Aminoglycosides and noise exposure, especially in those with normal hearing who have the m.1555A>G or m.1494C>T MT-RNR1 pathogenic variants."

Exposure-avoidance guidance.

PMID:42524757 SUPPORT REVIEW SYNTHESIS Other

"the benefits of vaccination far outweigh any theoretical risks of ototoxicity from vaccination in an individual with an AIHL associated MT‐RNR1 variant."

Distinguishes trace excipients from therapeutic aminoglycoside exposure.

🌍

Environmental Factors

Systemic aminoglycoside antibiotic administration

Systemic aminoglycoside treatment provides the drug exposure that can trigger hearing injury in genetically susceptible people. Therapeutic concentrations and even single doses have been associated with severe loss, but risk is not a universal dose-independent threshold. Duration, route and other clinical factors remain relevant, and ordinary drug-level monitoring does not eliminate inherited susceptibility.

Show evidence (2 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"The identification of an MT-RNR1 variant that is known to predispose to AIHL is sufficient to assign a phenotype status, but the absence of a variant does not indicate no risk of AIHL."

Distinguishes inherited susceptibility from the class’s broader ototoxicity.

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"occurring within a few days to weeks after administration of any amount (even a single dose) of an aminoglycoside antibiotic"

Documents potential severity after limited therapeutic exposure without assigning universal penetrance.

Mechanism Target:

TRIGGERS Cochlear Aminoglycoside Accumulation — Drug distribution into the inner ear and entry through hair-cell membranes precede intracellular accumulation.

Show evidence (1 reference)

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"there is strong evidence that AGs enter hair cells through the MET channel located at the top of the stereocilia."

General experimental uptake biology.

🔬

Diagnosis

Clinical audiologic and exposure assessment

Document hearing thresholds, onset, aminoglycoside history and the maternal family history. Age-appropriate audiometry and objective tests when needed characterize sensorineural loss; high-frequency testing can identify injury that conventional speech-frequency tests miss. A failed neonatal screening test alone is not proof of permanent aminoglycoside deafness.

audiometric test NCIT:C38036

Show evidence (2 references)

PMID:22121370 SUPPORT REVIEW SYNTHESIS Other

"patients should undergo a baseline hearing test including ultrahigh frequencies prior to AG administration to allow for early and unambiguous assessment of potential ototoxic damage."

General ototoxicity assessment guidance; obtain when feasible without delaying urgent treatment.

PMID:25155176 SUPPORT PRIMARY RESULT Human Clinical

"It is important to note, that most infants with failed newborn hearing screening do not develop permanent hearing loss."

Limits interpretation of newborn screening endpoints.

MT-RNR1 molecular testing

Assess the actionable m.1555A>G, m.1494C>T and m.1095T>C variants, with an assay whose variant coverage and heteroplasmy detection limit are understood. A negative targeted panel does not exclude all genetic susceptibility or general drug ototoxicity. Hearing loss and an appropriate molecular finding establish mitochondrial disease; an incidental positive result identifies susceptibility, not existing deafness.

genetic testing NCIT:C15709

Show evidence (3 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"The identification of an MT-RNR1 variant that is known to predispose to AIHL is sufficient to assign a phenotype status, but the absence of a variant does not indicate no risk of AIHL."

Here the assigned phenotype is pharmacogenetic risk, not measured hearing loss.

url:https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf SUPPORT REVIEW SYNTHESIS Other

"Laboratories should be aware of their lower heteroplasmy threshold and ensure results are reported with that context."

Laboratory interpretation requires a reported detection threshold.

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"The diagnosis of mitochondrial nonsyndromic hearing loss and deafness is established in a proband with hearing loss and identification of a pathogenic variant in MT-RNR1 or MT-TS1, or one of the eight additional mitochondrial genes known to cause nonsyndromic hearing loss and deafness."

The GeneReviews diagnostic criterion requires hearing loss together with a relevant pathogenic molecular finding. In this entry, an incidental MT-RNR1 result without hearing loss identifies susceptibility rather than established deafness; the broader chapter also covers other genes.

Pre-treatment and point-of-care genotyping

The 2026 UK CERSI-PGx guideline recommends testing before aminoglycoside treatment across ages and ancestries when a result is feasible within the clinical time frame. Planned treatment permits pre-emptive testing. A 26-minute m.1555A>G bedside assay changed prescribing in the 751-participant PALOH implementation study: 424/526 antibiotic-treated infants were successfully tested and three confirmed carriers avoided aminoglycosides. This was a workflow study, not a randomized demonstration of prevention of permanent hearing loss. It predominantly recruited from one center and excluded infants requiring immediate antibiotics with established intravenous access. Positive bedside results require laboratory confirmation; single-variant tests do not cover every actionable allele.

genetic testing NCIT:C15709

Show evidence (4 references)

PMID:42524757 SUPPORT REVIEW SYNTHESIS Other

"pharmacogenetic testing of variants in MT‐RNR1 should be undertaken in all individuals, of all age groups where this is possible in a clinically achievable time frame prior to use for all aminoglycosides"

Current UK guideline recommendation, contingent on feasible timing.

PMID:35311942 SUPPORT PRIMARY RESULT Human Clinical

"Overall, 424 infants (80.6%) receiving antibiotics were successfully tested for the variant, and the mean time to antibiotics was equivalent to previous practice."

Implementation outcome, with failed tests and incomplete coverage.

PMID:35311942 SUPPORT PRIMARY RESULT Human Clinical

"Three participants with the m.1555A>G variant were identified, all of whom avoided aminoglycoside antibiotics."

Demonstrated prescribing change, not a controlled hearing endpoint.

+ 1 more reference

Audiologic monitoring after exposure or established hearing loss

When aminoglycosides are unavoidable in an actionable-variant carrier, arrange frequent hearing/audiovestibular assessment during and after treatment alongside renal and therapeutic-drug monitoring. Annual audiometry is advised in established mitochondrial hearing loss to assess stability or progression. CPIC finds insufficient evidence to require additional hearing assessments solely because an asymptomatic carrier has never been exposed.

audiometric test NCIT:C38036

Show evidence (3 references)

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"with clinical audiovestibular assessment performed during and after treatment."

Exposure-related monitoring.

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Annual audiometric assessment to evaluate stability/progression of hearing loss."

Surveillance of established hearing impairment.

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"there is insufficient evidence to support additional hearing assessments in individuals with MT-RNR1 variants that predispose to AIHL if they have not been exposed to an aminoglycoside."

Prevents extrapolating an annual disease-surveillance schedule to every unexposed carrier.

📈

Progression

Exposure-associated onset and persistent hearing impairment

Hearing loss can begin within days to weeks after aminoglycoside exposure and is often severe and irreversible. Hearing level and age at recognition vary. A normal newborn screen or a previously tolerated course does not establish safety of subsequent exposure.

Show evidence (2 references)

PMID:20301595 SUPPORT REVIEW SYNTHESIS Other

"Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound, occurring within a few days to weeks after administration of any amount (even a single dose) of an aminoglycoside antibiotic"

Clinical synthesis of the characteristic presentation; not a universal penetrance estimate.

PMID:34032273 SUPPORT REVIEW SYNTHESIS Other

"Finally, if an individual with an actionable MT-RNR1 variant has previously received aminoglycosides and not developed AIHL, this does not preclude them from developing AIHL with subsequent doses."

Prior tolerance does not remove future risk.

Variable hearing expression without documented aminoglycoside exposure

Some MT-RNR1 families include congenital, progressive or later-onset hearing loss without documented exposure. This variable natural history should not be confused with inevitable deafness in an asymptomatic carrier or with a measured population penetrance estimate.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/ SUPPORT REVIEW SYNTHESIS Other

"The probability of hearing loss varies widely among reports and families"

Full GeneReviews clinical description of MT-RNR1 hearing loss independent of aminoglycoside exposure.

📊

Prevalence

United Kingdom, British 1958 birth cohort (m.1555A>G carriers)

Carrier Frequency 260.0 per 100,000 >1 in 1,000 (carriers)

m.1555A>G carrier frequency was 19/7350 (0.26%; 95% CI 0.14–0.38%) in successfully genotyped participants from the British 1958 birth cohort. This is neither hearing-loss prevalence nor a pooled frequency for every actionable variant. Audiometry at age 44–45 used better-ear thresholds at 1 and 4 kHz; individual aminoglycoside exposure was not recorded.

Show evidence (1 reference)

PMID:22223843 SUPPORT Human Clinical

"19 of 7350 individuals successfully genotyped had the m.1555A>G mutation, giving a prevalence of 0.26% (95% CI 0.14% to 0.38%) or 1 in 385"

Gives the carrier frequency with its confidence interval in an unselected birth cohort.

🔬

Clinical Trials

NCT04105205 PHASE_I

First-in-human single-ascending-dose apramycin safety, tolerability and pharmacokinetic study in healthy volunteers. The published analysis included 40 participants, of whom 30 received active drug. This is contextual antibiotic development, not a trial demonstrating prevention of hearing loss in MT-RNR1 carriers.

Show evidence (2 references)

clinicaltrials:NCT04105205 SUPPORT BACKGROUND Human Clinical

"This is a first-in-human study to assess the safety, tolerability and pharmacokinetics of escalating single doses of apramycin."

Registry summary establishes trial scope.

PMID:35849148 SUPPORT PRIMARY RESULT Human Clinical

"A total sample size of 40 subjects were enrolled in the trial and consecutively grouped into five sequential dose cohorts"

Small healthy-volunteer study; no carrier-specific otoprotection endpoint.

🧫

Experimental Models

Human-sequence mitochondrial decoding sites in bacterial hybrid ribosomes OTHER

A 34-nucleotide human mitochondrial decoding-site sequence was introduced into Mycobacterium smegmatis ribosomes, with wild-type, A1555G and C1494T variants. Cell-free amino-acid incorporation, luciferase and gentamicin-footprinting assays separate decoding fidelity, protein output and drug binding.

Pathograph links

Mitoribosomal Decoding Errors partially recapitulates observes: molecular Variant hybrid ribosomes show intrinsic and aminoglycoside-exacerbated miscoding.

Limitations: A human rRNA segment is tested in a bacterial ribosome. No hair cells, mitochondrial membrane transport or auditory outcome is represented.

Readouts

Translation accuracy

Near-cognate amino-acid misincorporation increased; reporter function fell without lower full-length protein output.

Direction: DECREASED

Show evidence (1 reference)

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation."

Direct comparative misincorporation assays distinguish accuracy from total protein output.

Show evidence (1 reference)

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation."

Direct comparative misincorporation assays distinguish accuracy from total protein output.

Aminoglycoside Binding to the Mitochondrial Ribosome partially recapitulates observes: molecular Chemical footprinting supports increased aminoglycoside interaction with variant decoding sites.

Limitations: Binding to hybrid ribosomes does not quantify drug entry into human cochlear mitochondria.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/ SUPPORT PRIMARY RESULT In Vitro

"increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy."

Chemical footprinting and translation assays support enhanced drug binding plus inherent decoding infidelity in A1555G/C1494T hybrids.

Structural interpretation is not a solved atomic structure of the complete human mutant mitoribosome. Loop closure alone was insufficient to reproduce the fidelity defect.

Show evidence (2 references)

PMID:18308926 SUPPORT PRIMARY RESULT In Vitro

"Both the C1494U and the A1555G mutation replace the noncanonical C1494·A1555 interaction by a Watson–Crick base pairing, thus shortening the extended conformation of the mitochondrial loop."

Structural interpretation of the human-sequence decoding site in hybrid bacterial ribosomes; C1494U is the RNA equivalent of the DNA C1494T variant.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/ SUPPORT PRIMARY RESULT In Vitro

"increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy."

Chemical footprinting and translation assays support enhanced drug binding plus inherent decoding infidelity in A1555G/C1494T hybrids.

Paromomycin-exposed m.1555A>G family lymphoblasts CELL_LINE

Lymphoblastoid lines from five deaf carriers, five hearing carriers and three married-in controls from an Arab-Israeli family were exposed to 2 mg/ml paromomycin. Carrier cells had greater drug-associated growth slowing and mitochondrial translation inhibition.

Pathograph links

Reduced Mitochondrial Protein Synthesis partially recapitulates observes: molecular Drug/no-drug mitochondrial translation-rate ratios were lower in carrier cells.

Limitations: Non-isogenic family lymphoblasts, high in-vitro exposure and abstract-only accessible report; not a hair-cell model or clinical dose threshold.

Readouts

Relative mitochondrial translation under paromomycin

The drug/no-drug ratios were lower than control ratios in both symptomatic- and asymptomatic-carrier lines.

Direction: DECREASED

Show evidence (1 reference)

PMID:10915767 SUPPORT PRIMARY RESULT In Vitro

Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high paromomycin concentration, not a clinical dose threshold.

Show evidence (1 reference)

PMID:10915767 SUPPORT PRIMARY RESULT In Vitro

Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high paromomycin concentration, not a clinical dose threshold.

The experiment supports drug susceptibility in hearing as well as deaf carriers, without showing that cellular response predicts individual future hearing outcome.

Show evidence (1 reference)

PMID:10915767 SUPPORT PRIMARY RESULT In Vitro

Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high paromomycin concentration, not a clinical dose threshold.

TRMU A10S and m.1555A>G family-derived lymphoblasts CELL_LINE

The 2006 study examined selected family lymphoblasts and controls for mitochondrial import, tRNA thiolation/abundance and protein labeling. The 2017 study used eight non-isogenic lines, two per group, for tRNA modification, mitochondrial protein abundance, respiration, ATP and oxidant-response assays. No aminoglycoside challenge was used in these modifier experiments.

Pathograph links

Reduced TRMU-Dependent tRNA Thiolation partially recapitulates observes: molecular A10S-bearing lines have reduced tRNA thiolation.

Limitations: Selected nuclear/mitochondrial genotype combinations, not an isogenic comparison or universal modifier effect.

Readouts

Wobble-uridine 2-thiouridine modification

Affected tRNA modification in selected modifier lines.

Direction: DECREASED

Show evidence (1 reference)

PMID:28049726 SUPPORT PRIMARY RESULT In Vitro

"The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln"

TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside treatment.

Show evidence (1 reference)

PMID:28049726 SUPPORT PRIMARY RESULT In Vitro

"The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln"

TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside treatment.

Reduced Mitochondrial tRNA Abundance partially recapitulates observes: molecular Double-mutant lines have reduced mitochondrial tRNA steady-state abundance.

Limitations: Reduced abundance does not directly establish accelerated degradation.

Readouts

Mitochondrial tRNA abundance

Northern-blot comparison to control cell lines.

Direction: DECREASED

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

"the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls"

Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured, degradation kinetics were not.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

"the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls"

Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured, degradation kinetics were not.

Reduced Mitochondrial Protein Synthesis partially recapitulates observes: molecular Protein labeling was lower in the homozygous double-mutant lines.

Limitations: The 2006 labeling assay measures synthesis; the 2017 immunoblots measure abundance and are not interchangeable.

Readouts

Mitochondrial protein labeling

A 44–57% decrease, averaging 51%, in the two homozygous double-mutant lines.

Direction: DECREASED

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.

Reduced Mitochondrial Respiration partially recapitulates observes: cellular Oxygen-consumption rates were reduced in selected mutant groups.

Limitations: Family background, two lines per group and lack of aminoglycoside exposure limit translation to carrier cochleae.

Readouts

Basal oxygen-consumption rate

Group means were 54%, 76% and 88% of control for homozygous modifier, heterozygous modifier and m.1555A>G-only lines.

Direction: DECREASED

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and controls; no drug exposure or hair cells.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and controls; no drug exposure or hair cells.

Reduced Mitochondrial ATP Production partially recapitulates observes: cellular ATP production was reduced with glycolysis suppressed.

Limitations: Total cellular ATP was relatively preserved; this assay does not establish whole-cell energy collapse or hearing-cell ATP levels.

Readouts

ATP under glycolysis-suppressed conditions

Group means were 48%, 61% and 83% of controls; these are assay-specific mitochondrial ATP values.

Direction: DECREASED

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this is not a global energy collapse.

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/ SUPPORT PRIMARY RESULT In Vitro

ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this is not a global energy collapse.

The 2017 oxidant assay used a fluorescent-probe response to hydrogen peroxide. Aminoacylation increased for some tRNAs, so reduced aminoacylation or measured mischarging should not be asserted. The original import assay did not detect an A10S import defect.

Show evidence (4 references)

PMID:28049726 SUPPORT PRIMARY RESULT In Vitro

"The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln"

TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside treatment.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

"the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls"

Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured, degradation kinetics were not.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/ SUPPORT PRIMARY RESULT In Vitro

Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.

+ 1 more reference

Mouse cochlear explants exposed to gentamicin or apramycin PRIMARY_CELL_CULTURE

Cochlear organ cultures were exposed to gentamicin and apramycin over a range of concentrations and assessed for sensory-cell loss and nitrotyrosine staining. Gentamicin caused greater loss; apramycin was less damaging, but sufficiently high exposure affected basal hair cells.

Pathograph links

Cochlear Hair Cell Loss partially recapitulates observes: cellular Drug-dependent cochlear hair-cell loss was quantified in explants.

Limitations: No human MT-RNR1 allele or clinical auditory endpoint; drug comparisons do not establish apramycin safety in carriers.

Readouts

Outer-hair-cell survival after gentamicin

Outer hair cells were eliminated at the stated explant concentration.

Direction: DECREASED

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT In Vitro

"complete elimination of outer hair cells was observed at 0.5 mM."

Gentamicin concentration-response assay.

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT In Vitro

"complete elimination of outer hair cells was observed at 0.5 mM."

Gentamicin explant response.

Nitrotyrosine staining supports an oxidative-injury association, not a complete causal epistasis test. Bacterial 30S crystallography in the same paper is not a human mitoribosomal structure.

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT In Vitro

"At 2 mM, apramycin begins to affect basal hair cells but does not cause a significant overall loss of hair cells"

Ex-vivo concentration-response finding; lower injury is not zero toxicity.

Gentamicin and mechanotransduction perturbation in neonatal mouse cochlear explants PRIMARY_CELL_CULTURE

P3–P5 cochlear explants were used to image RIPOR2 localization and Annexin-V phosphatidylserine signals after gentamicin, washout, benzamil or selected stereociliary mutations. Tmie-deficient cells lacked both gentamicin responses; benzamil caused phosphatidylserine exposure without RIPOR2 movement.

Pathograph links

RIPOR2 Redistribution in Hair Cells partially recapitulates observes: cellular Gentamicin induced reversible redistribution requiring an intact tested mechanotransduction context.

Limitations: No human MT-RNR1 variant, hearing outcome or newly demonstrated RIPOR2-mediated death rescue. Surface phosphatidylserine is not sufficient evidence of apoptosis.

Readouts

RIPOR2 subcellular localization

Movement from the stereociliary base to the pericuticular region and subsequent recovery.

Direction: ALTERED

Show evidence (1 reference)

PMID:40842562 SUPPORT PRIMARY RESULT In Vitro

"RIPOR2 translocated robustly from the stereocilia base to the pericuticular area"

Localization imaging.

Show evidence (2 references)

PMID:40842562 SUPPORT PRIMARY RESULT In Vitro

"RIPOR2 translocated robustly from the stereocilia base to the pericuticular area"

Drug-induced localization change.

+ 1 more reference

Phosphatidylserine exposure alone was insufficient for redistribution. Selective scramblase inhibition was not available to establish whether phosphatidylserine is necessary for death. Proposed TMC scramblase/TMIE roles and prior RIPOR2–GABARAP rescue results should not be treated as new assays here. Benzamil-associated uptake inhibition was inferred rather than measured.

Show evidence (1 reference)

PMID:40842562 SUPPORT PRIMARY RESULT In Vitro

"cochlear explants dissected from postnatal day 3 to 5 (P3-P5) wild-type C57/BL6 mice"

Defines the ex-vivo system.

🐁

Animal Models

Guinea-pig comparative aminoglycoside ototoxicity

Systemic gentamicin and apramycin were compared using auditory brainstem responses and cochlear histology. Apramycin produced less injury at tested doses. Gentamicin caused a basal-to-apical hair-cell-loss gradient and systemic toxicity; two of three animals at 160 mg/kg died early.

Species

Guinea pig

Publication

PMID:22699498

Pathograph links

Cochlear Hair Cell Loss partially recapitulates observes: cellular In-vivo histology documents drug-associated cochlear sensory-cell loss.

Limitations: Wild-type drug toxicity, not a human MT-RNR1 allele model; unequal dose responses and systemic toxicity limit extrapolation to safer human prescribing.

Readouts

Cochlear hair-cell survival with gentamicin

Complete basal-half loss at the specified 140 mg/kg treatment.

Direction: DECREASED

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT Model Organism

"Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea."

Whole-animal tissue outcome.

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT Model Organism

"Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea."

Guinea-pig cochlear histology.

Lower experimental ototoxicity does not establish clinical otoprotection or an exception to current class-wide precautions in actionable-variant carriers.

Show evidence (1 reference)

PMID:22699498 SUPPORT PRIMARY RESULT Model Organism

"at a dose of 160 mg/kg body weight, two of three animals died early during the experiments."

Important systemic-toxicity limitation of the comparator.

Larval zebrafish acute and delayed aminoglycoside sensory-cell injury

Living 5–8-day-postfertilization larvae were exposed to neomycin, gentamicin or G418, with acute imaging and survival after washout. Acute injury often involved mitochondrial calcium elevations and partial mitoTEMPO protection. Delayed injury correlated with lysosomal drug localization and responded to endolysosomal perturbation; G418 could also cause acute injury at higher doses.

Species

Zebrafish

Publication

PMID:39610699

Pathograph links

Cochlear Hair Cell Loss partially recapitulates observes: cellular Lateral-line sensory-cell loss provides a comparative drug-injury model for the cochlear injury node.

Limitations: Lateral-line rather than cochlear hair cells; no MT-RNR1 susceptibility allele, hearing test or human regeneration claim.

Readouts

Hair-cell survival after gentamicin washout

Delayed loss despite removal of extracellular drug after one hour.

Direction: DECREASED

Show evidence (1 reference)

PMID:39610699 SUPPORT PRIMARY RESULT Model Organism

"We found that 1 h exposure to 200 μM gentamicin was sufficient to cause damage comparable to that seen with neomycin if animals were incubated an additional 23 h in fresh medium"

Observed survival endpoint.

Show evidence (1 reference)

PMID:39610699 SUPPORT PRIMARY RESULT Model Organism

"We found that 1 h exposure to 200 μM gentamicin was sufficient to cause damage comparable to that seen with neomycin if animals were incubated an additional 23 h in fresh medium"

Delayed whole-larva sensory-cell injury after washout.

Notes

GPN altered intracellular distribution without lowering total fluorescent uptake, whereas bafilomycin reduced uptake and confounded a purely downstream lysosomal interpretation. Labeling efficiency prevented absolute between-drug concentration comparisons. Lysosomal membrane permeabilization, ferroptosis and pyroptosis were not established mediators. Calcium necessity/sufficiency was supported by cited prior work, not a new universal test in this study.

Show evidence (2 references)

PMID:39610699 SUPPORT PRIMARY RESULT Model Organism

"Experiments were conducted on 5–8 dpf (days postfertilization) larval zebrafish."

Whole-organism model scope.

PMID:39610699 SUPPORT PRIMARY RESULT Model Organism

"By contrast we observed no protection against 100 or 200 μM G418 using the 1+23 h exposure paradigm"

Limits transfer of the acute mitoTEMPO-sensitive pathway to delayed injury.

{ }

Source YAML

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name: Aminoglycoside-Induced Hearing Loss
creation_date: '2026-08-27T06:05:00Z'
category: Mendelian
description: >-
  This entry describes inherited susceptibility to aminoglycoside-induced sensorineural hearing loss associated
  with mitochondrial MT-RNR1 variants. The strongest prescribing evidence concerns m.1555A>G and m.1494C>T,
  with moderate evidence for m.1095T>C. Hearing loss can be bilateral, severe to profound and permanent
  after standard therapeutic exposure, sometimes after a single dose, but penetrance and severity are
  not uniform. Some families also have hearing loss without documented aminoglycoside exposure; population
  data do not establish inevitable hearing loss in carriers.

  For m.1555A>G and m.1494C>T, experimental ribosomes show altered decoding accuracy and increased aminoglycoside
  binding. The steps connecting these defects to selective human cochlear injury remain incompletely resolved.
  Avoiding aminoglycosides when an effective alternative exists is central to prevention. Genotype-guided
  prescribing must preserve timely treatment of serious infection: urgent therapy should not be delayed
  while awaiting a test. The general dose- and duration-related ototoxicity of aminoglycosides can also
  occur without an identified MT-RNR1 variant and is distinguished from inherited susceptibility here.
disease_term:
  preferred_term: deafness, aminoglycoside-induced
  term:
    id: MONDO:0010799
    label: deafness, aminoglycoside-induced
synonyms:
- aminoglycoside-induced deafness
- maternally inherited aminoglycoside-induced deafness
- mitochondrial isolated sensorineural deafness with susceptibility to aminoglycoside exposure
parents:
- Mitochondrial Disease
- Sensorineural Hearing Loss
inheritance:
- name: Mitochondrial (maternal) inheritance
  inheritance_term:
    preferred_term: Mitochondrial inheritance
    term:
      id: HP:0001427
      label: Mitochondrial inheritance
  description: >-
    Predisposing mitochondrial variants are maternally transmitted. Children of a woman carrying a variant
    are at risk of inheritance; male carriers do not transmit their mitochondrial variant. Homoplasmy
    and heteroplasmy require different counseling, and inherited variant status does not by itself predict
    hearing-loss onset or severity.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: All offspring of females with a mtDNA pathogenic variant are at risk of inheriting the pathogenic variant. Offspring of males with a mtDNA pathogenic variant are not at risk of inheriting the pathogenic variant.
    explanation: >-
      Defines maternal transmission without guaranteeing phenotype or identical heteroplasmy in offspring.
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Furthermore, the presence of the mtDNA pathogenic variant does not predict the age of onset or severity of hearing loss.
    explanation: >-
      Separates transmission from clinical penetrance.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: the presence of the mtDNA pathogenic variant does not predict the age of onset or severity of hearing loss.
    explanation: >-
      Full GeneReviews chapter distinguishes inherited variant status from phenotype prediction.
pathophysiology:
- name: Predisposing MT-RNR1 Variants
  biological_scale: MOLECULAR
  description: >-
    Mitochondrial MT-RNR1 variants confer susceptibility to aminoglycoside ototoxicity. m.1555A>G and
    m.1494C>T are the best-supported alleles; m.1095T>C is also actionable with a lower level of evidence.
    Carriage can be homoplasmic or heteroplasmic. Variant status is a susceptibility state rather than
    a guarantee of hearing loss.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence
    explanation: >-
      The clinical susceptibility set is broader than the alleles tested in the structural experiments.
  downstream:
  - target: Altered Mitoribosomal Decoding-Site Geometry
    description: >-
      This structural route concerns m.1555A>G and m.1494C>T. The same detailed geometry has not been
      demonstrated for every actionable MT-RNR1 variant.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:18308926
      reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: Both the C1494U and the A1555G mutation replace the noncanonical C1494·A1555 interaction by a Watson–Crick base pairing, thus shortening the extended conformation of the mitochondrial loop.
      explanation: >-
        Structural interpretation of the human-sequence decoding site in hybrid bacterial ribosomes;
        C1494U is the RNA equivalent of the DNA C1494T variant.
  genes:
  - preferred_term: MT-RNR1
    term:
      id: hgnc:7470
      label: MT-RNR1
- name: Altered Mitoribosomal Decoding-Site Geometry
  biological_scale: MOLECULAR
  description: >-
    The m.1555A>G and m.1494C>T substitutions introduce a Watson–Crick pair that shortens the extended
    mitochondrial decoding-site loop. Hybrid-ribosome experiments support altered decoding behavior,
    but loop closure alone did not reproduce the fidelity defect. This is not wholesale conversion of
    a human mitoribosome into a bacterial ribosome.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:18308926
    reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: Both the C1494U and the A1555G mutation replace the noncanonical C1494·A1555 interaction by a Watson–Crick base pairing, thus shortening the extended conformation of the mitochondrial loop.
    explanation: >-
      Structural interpretation of the human-sequence decoding site in hybrid bacterial ribosomes;
      C1494U is the RNA equivalent of the DNA C1494T variant.
  downstream:
  - target: Aminoglycoside Binding to the Mitochondrial Ribosome
    description: >-
      The altered decoding environment increases aminoglycoside binding when drug is present. This
      interaction is supported by chemical footprinting of hybrid ribosomes.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
      reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
      explanation: >-
        Chemical footprinting and translation assays support enhanced drug binding plus inherent
        decoding infidelity in A1555G/C1494T hybrids.
  - target: Mitoribosomal Decoding Errors
    description: >-
      The mutant decoding site has reduced translational fidelity even without drug. The precise conformational
      sequence is inferred; simple loop closure alone was insufficient in a control construct.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:18308926
      reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation.
      explanation: >-
        Direct comparative misincorporation assays distinguish accuracy from total protein output.
- name: Cochlear Aminoglycoside Accumulation
  biological_scale: CELLULAR
  description: >-
    Systemically administered aminoglycosides reach the inner ear and accumulate in sensory hair cells.
    Mechanotransduction channels are an important entry route in experimental systems. Uptake and intracellular
    localization vary with drug and exposure; this is general ototoxicity biology rather than a demonstrated
    MT-RNR1-specific uptake defect.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there is strong evidence that AGs enter hair cells through the MET channel located at the top of the stereocilia.  # codespell:ignore-line
    explanation: >-
      Review of experimental hair-cell entry mechanisms.
  downstream:
  - target: Aminoglycoside Binding to the Mitochondrial Ribosome
    description: >-
      Intracellular drug must reach the mitoribosomal target. The cited assays establish target susceptibility
      but do not resolve transport across every cellular and mitochondrial compartment.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
      reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
      explanation: >-
        Chemical footprinting and translation assays support enhanced drug binding plus inherent
        decoding infidelity in A1555G/C1494T hybrids.
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood.
      explanation: >-
        The tissue-selective link remains unresolved; generic aminoglycoside models are not proof
        of the complete MT-RNR1 causal chain.
  - target: Cochlear Hair Cell Loss
    description: >-
      Drug exposure causes sensory-cell injury through multiple routes. This aggregate edge preserves
      experimental toxicity outside the incompletely resolved mitochondrial-variant pathway.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22699498
      reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      snippet: Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea.
      explanation: >-
        Whole-animal gentamicin injury in guinea pigs, not a human susceptibility-allele model.
  - target: RIPOR2 Redistribution in Hair Cells
    description: >-
      Gentamicin exposure drives rapid RIPOR2 redistribution in mouse cochlear explants with functional
      mechanotransduction. The intervening entry/signaling steps are not isolated by this experiment.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:40842562
      reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: RIPOR2 translocated robustly from the stereocilia base to the pericuticular area
      explanation: >-
        Observed immunostaining redistribution in drug-treated explants.
  cell_types:
  - preferred_term: cochlear outer hair cell
    term:
      id: CL:0000601
      label: cochlear outer hair cell
  - preferred_term: cochlear inner hair cell
    term:
      id: CL:0000589
      label: cochlear inner hair cell
  locations:
  - preferred_term: spiral organ of cochlea
    term:
      id: UBERON:0002227
      label: spiral organ of cochlea
- name: Aminoglycoside Binding to the Mitochondrial Ribosome
  biological_scale: MOLECULAR
  description: >-
    Aminoglycosides bind the mitochondrial decoding region, with enhanced susceptibility of A1555G/C1494T
    hybrid sites. Drug binding can both worsen decoding accuracy and inhibit protein synthesis; these
    are distinct readouts. The intrinsic variant-associated fidelity defect can exist before exposure.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
    reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
    explanation: >-
      Chemical footprinting and translation assays support enhanced drug binding plus inherent decoding
      infidelity in A1555G/C1494T hybrids.
  downstream:
  - target: Mitoribosomal Decoding Errors
    description: >-
      Drug binding aggravates miscoding by the mutant decoding apparatus.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
      reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
      explanation: >-
        Chemical footprinting and translation assays support enhanced drug binding plus inherent
        decoding infidelity in A1555G/C1494T hybrids.
  - target: Reduced Mitochondrial Protein Synthesis
    description: >-
      Aminoglycoside interaction with the translation machinery inhibits mitochondrial protein synthesis.
      In patient-derived lymphoblasts, drug-dependent labeling inhibition was greater in carriers.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:10915767
      reference_title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively), compared with the ratios in the control cell lines.
      explanation: >-
        Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts;
        high paromomycin concentration, not a clinical dose threshold.
- name: Mitoribosomal Decoding Errors
  biological_scale: MOLECULAR
  description: >-
    A1555G/C1494T hybrid ribosomes misincorporate amino acids more frequently; aminoglycosides exacerbate
    the defect. Reduced reporter enzymatic activity despite comparable full-length protein output demonstrates
    why fidelity should be separated from a lower synthesis rate.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:18308926
    reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation.
    explanation: >-
      Direct comparative misincorporation assays distinguish accuracy from total protein output.
  - reference: PMID:18308926
    reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: Mutant and wild-type mitochondrial hybrid ribosomes produced the same level of full-length protein
    explanation: >-
      The drug-free luciferase experiment distinguishes product quality from total protein output.
  downstream:
  - target: Reduced Mitochondrial Respiration
    description: >-
      Incorrectly translated mitochondrial proteins are proposed to impair respiratory function. The
      hybrid-ribosome study does not itself measure human respiratory complexes or prove mediation
      in cochlear cells.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:18308926
      reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: This observation is compatible with our luciferase data in the mitochondrial hybrid ribosomes, which demonstrate that mutation-mediated misreading manifests primarily at the level of functional activity of the translated protein by missense rather than by nonsense decoding
      explanation: >-
        Authors connect reduced translation-product function with mitochondrial respiratory components;
        human cochlear mediation remains an inference.
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood.
      explanation: >-
        The tissue-selective link remains unresolved; generic aminoglycoside models are not proof
        of the complete MT-RNR1 causal chain.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
- name: Reduced Mitochondrial Protein Synthesis
  biological_scale: MOLECULAR
  description: >-
    Aminoglycosides reduce mitochondrial protein synthesis in susceptible family-derived lymphoblasts.
    Separate unexposed TRMU modifier studies also show reduced mitochondrial protein labeling. These
    observations concern selected cultured cells and do not establish uniform translational arrest in
    every carrier.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:10915767
    reference_title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively), compared with the ratios in the control cell lines.
    explanation: >-
      Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high
      paromomycin concentration, not a clinical dose threshold.
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
    reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%.
    explanation: >-
      Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.
  downstream:
  - target: Reduced Mitochondrial Respiration
    description: >-
      Reduced synthesis of mitochondrial respiratory-chain components is a proposed route to impaired
      respiration. Supporting family-cell studies show both abnormalities, but do not isolate each
      mediator in human hair cells.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: The defective translation resulted in the reduced activities of mitochondrial respiration chains.
      explanation: >-
        Authors’ mechanistic interpretation of linked translation and respiratory findings in selected
        lymphoblasts.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
  biological_processes:
  - preferred_term: mitochondrial translation
    term:
      id: GO:0032543
      label: mitochondrial translation
    modifier: DECREASED
- name: Reduced Mitochondrial Respiration
  biological_scale: CELLULAR
  description: >-
    Reduced oxygen consumption is measured in m.1555A>G lymphoblasts, with larger reductions in selected
    TRMU A10S double-mutant lines. Extending these findings to drug-exposed carrier hair cells remains
    a mechanistic hypothesis. Non-isogenic family lines do not isolate the effect of one allele from
    every other background difference.
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the average basal OCRs in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations, and only m.1555A→G mutation were 54, 76, and 88%, relative to the mean value measured in the control cell lines, respectively.
    explanation: >-
      OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and controls;
      no drug exposure or hair cells.
  downstream:
  - target: Reduced Mitochondrial ATP Production
    description: >-
      Respiratory impairment is proposed to reduce mitochondrial ATP output. The measured mitochondrial
      ATP condition suppressed glycolysis; it does not demonstrate the same loss of total cellular
      ATP.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the levels of ATP production in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations and only m.1555A→G mutation were 48, 61, and 83% of the mean value measured in the control cell lines, respectively.
      explanation: >-
        ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this
        is not a global energy collapse.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
  - target: Oxidative Stress
    description: >-
      Mitochondrial dysfunction may increase oxidant stress or reduce stress resistance. The selected
      cell studies and general drug models do not establish a uniform ROS mechanism in carrier cochleae.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the levels of ROS generation in the mutant cell lines cells carrying both m.1555A→G and homozygous TRMU A10S mutations ranged from 155 to 167%, with an average 161% of the mean value measured in the control cell lines
      explanation: >-
        Fluorescent-probe response under hydrogen-peroxide challenge in selected double-mutant lymphoblasts;
        not a direct measurement in human cochlea.
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death
      explanation: >-
        Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
- name: Reduced Mitochondrial ATP Production
  biological_scale: CELLULAR
  description: >-
    Mitochondrial ATP production was reduced in selected m.1555A>G/TRMU lymphoblast lines under conditions
    suppressing glycolysis. Total ATP was relatively preserved. ATP limitation in exposed human cochlear
    cells is proposed, not directly measured in these studies.
  mechanism_confidence: HYPOTHETICAL
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the levels of ATP production in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations and only m.1555A→G mutation were 48, 61, and 83% of the mean value measured in the control cell lines, respectively.
    explanation: >-
      ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this is
      not a global energy collapse.
  downstream:
  - target: Cochlear Hair Cell Loss
    description: >-
      Energy limitation could compromise mitochondrial integrity and activate downstream cell-death
      pathways. Its necessity or sufficiency for MT-RNR1-associated human hearing loss remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: With the decrease of energy production, the mitochondrial integrity is compromised and predispose to a leakage of cytochrome c and subsequent activation of the apoptotic cascades.
      explanation: >-
        Proposed energy-dependent mitochondrial injury route; omitted membrane and apoptotic intermediates
        are not established in carrier cochleae.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
- name: Oxidative Stress
  biological_scale: CELLULAR
  description: >-
    Oxidative stress is implicated in general aminoglycoside hair-cell toxicity and observed as an altered
    oxidant response in selected mitochondrial-variant lymphoblasts. Drug and exposure context matter:
    an antioxidant-sensitive acute larval-fish pathway differs from the tested delayed injury paradigm.
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the levels of ROS generation in the mutant cell lines cells carrying both m.1555A→G and homozygous TRMU A10S mutations ranged from 155 to 167%, with an average 161% of the mean value measured in the control cell lines
    explanation: >-
      Fluorescent-probe response under hydrogen-peroxide challenge in selected double-mutant lymphoblasts;
      not a direct measurement in human cochlea.
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death
    explanation: >-
      Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.
  downstream:
  - target: Cochlear Hair Cell Loss
    description: >-
      Oxidant injury can contribute to sensory-cell death, but the complete mitochondrial-variant-to-hair-cell
      pathway remains hypothetical. Antioxidant protection in one drug model does not establish a
      universal route.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death
      explanation: >-
        Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.
    hypothesis_groups:
    - mitoribosomal_dysfunction_to_cochlear_injury
  biological_processes:
  - preferred_term: cellular response to oxidative stress
    term:
      id: GO:0034599
      label: cellular response to oxidative stress
    modifier: INCREASED
- name: Cochlear Hair Cell Loss
  biological_scale: CELLULAR
  description: >-
    Loss of cochlear sensory cells is a major structural substrate of aminoglycoside hearing impairment.
    Experimental gentamicin injury often has a basal-to-apical gradient. Apoptotic and other injury
    routes depend on model, dose and time; no single mode of death is established for all MT-RNR1-associated
    cases.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:22699498
    reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea.
    explanation: >-
      In-vivo cochlear histology supports the structural injury pattern, with genotype extrapolation
      explicitly limited.
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood.
    explanation: >-
      The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of
      the complete MT-RNR1 causal chain.
  downstream:
  - target: Bilateral Sensorineural Hearing Loss
    description: >-
      Loss of sensory transduction contributes to persistent sensorineural hearing loss. Clinical
      laterality and severity are documented in affected humans; the tissue mechanism is supported
      mainly by general ototoxicity models.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301595
      reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound
      explanation: >-
        Human clinical syndrome.
    - reference: PMID:22699498
      reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      snippet: Loss of hair cells seen in cochlear surface preparations was consistent with the functional results obtained from the ABR measurements.
      explanation: >-
        Comparative experimental association of structural injury and auditory dysfunction; not
        proof of variant-specific mediation.
  - target: High-Frequency Predominant Loss
    description: >-
      Preferential basal-cochlear injury offers an anatomical explanation for high-frequency loss
      in general aminoglycoside toxicity. Carrier audiograms are variable, so this is not a required
      sequence for every affected individual.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: AG cochleotoxicity typically affects first the high frequency and then extends towards the lower frequency and ranges over time in a dose-dependent manner
      explanation: >-
        General ototoxicity pattern, qualified by variable human carrier audiograms.
  cell_types:
  - preferred_term: cochlear outer hair cell
    term:
      id: CL:0000601
      label: cochlear outer hair cell
  - preferred_term: cochlear inner hair cell
    term:
      id: CL:0000589
      label: cochlear inner hair cell
  locations:
  - preferred_term: spiral organ of cochlea
    term:
      id: UBERON:0002227
      label: spiral organ of cochlea
- name: Reduced TRMU-Dependent tRNA Thiolation
  biological_scale: MOLECULAR
  description: >-
    The TRMU p.Ala10Ser modifier is associated with reduced 2-thiouridine modification of wobble U34
    in selected mitochondrial tRNAs. Purified-protein thermal stability and cellular abundance were
    reduced in the 2017 study, but degradation kinetics were not measured and the earlier import assay
    was normal. This branch applies to the studied modifier genotypes, not all MT-RNR1 carriers.
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:28049726
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln
    explanation: >-
      TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside
      treatment.
  downstream:
  - target: Reduced Mitochondrial tRNA Abundance
    description: >-
      Defective thiolation is proposed to impair tRNA stability and lower steady-state abundance.
      Northern blots measure abundance, without directly measuring degradation kinetics.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
      reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls
      explanation: >-
        Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured,
        degradation kinetics were not.
  genes:
  - preferred_term: TRMU
    term:
      id: hgnc:25481
      label: TRMU
- name: Reduced Mitochondrial tRNA Abundance
  biological_scale: MOLECULAR
  description: >-
    Several mitochondrial tRNAs were less abundant in homozygous TRMU A10S plus m.1555A>G lymphoblasts.
    This is a modifier-associated cellular observation in selected families; neither absent tRNA import
    nor uniformly decreased aminoacylation was demonstrated.
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
    reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls
    explanation: >-
      Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured,
      degradation kinetics were not.
  downstream:
  - target: Reduced Mitochondrial Protein Synthesis
    description: >-
      Lower availability of mitochondrial tRNAs can impair translation. The same family-derived lines
      show reduced mitochondrial protein labeling, but the contributions of thiolation, abundance
      and other background effects were not independently rescued.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
      reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%.
      explanation: >-
        Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.
- name: RIPOR2 Redistribution in Hair Cells
  biological_scale: CELLULAR
  description: >-
    Gentamicin induces reversible movement of RIPOR2 from the stereociliary base to the pericuticular
    region in mouse cochlear explants. Phosphatidylserine exposure occurs with different kinetics and
    is insufficient on its own to trigger this movement. This emerging drug-response branch has not
    been linked experimentally to the human MT-RNR1 variants in the cited study.
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:40842562
    reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: RIPOR2 translocated robustly from the stereocilia base to the pericuticular area
    explanation: >-
      Immunostaining response in P3–P5 mouse explants.
  - reference: PMID:40842562
    reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: These findings suggest that PS externalization alone is insufficient to trigger RIPOR2 translocation.
    explanation: >-
      Benzamil induces surface phosphatidylserine without RIPOR2 movement; no inferred apoptosis or
      proven death-necessity edge is added.
  cell_types:
  - preferred_term: cochlear outer hair cell
    term:
      id: CL:0000601
      label: cochlear outer hair cell
  - preferred_term: cochlear inner hair cell
    term:
      id: CL:0000589
      label: cochlear inner hair cell
  locations:
  - preferred_term: spiral organ of cochlea
    term:
      id: UBERON:0002227
      label: spiral organ of cochlea
environmental:
- name: Systemic aminoglycoside antibiotic administration
  description: >-
    Systemic aminoglycoside treatment provides the drug exposure that can trigger hearing injury in
    genetically susceptible people. Therapeutic concentrations and even single doses have been associated
    with severe loss, but risk is not a universal dose-independent threshold. Duration, route and other
    clinical factors remain relevant, and ordinary drug-level monitoring does not eliminate inherited
    susceptibility.
  exposure_term:
    preferred_term: exposure to aminoglycoside antibiotic
  influences_mechanisms:
  - target: Cochlear Aminoglycoside Accumulation
    environmental_effect: TRIGGERS
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Drug distribution into the inner ear and entry through hair-cell membranes precede intracellular
      accumulation.
    evidence:
    - reference: PMID:22121370
      reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: there is strong evidence that AGs enter hair cells through the MET channel located at the top of the stereocilia.  # codespell:ignore-line
      explanation: >-
        General experimental uptake biology.
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The identification of an MT-RNR1 variant that is known to predispose to AIHL is sufficient to assign a phenotype status, but the absence of a variant does not indicate no risk of AIHL.
    explanation: >-
      Distinguishes inherited susceptibility from the class’s broader ototoxicity.
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: occurring within a few days to weeks after administration of any amount (even a single dose) of an aminoglycoside antibiotic
    explanation: >-
      Documents potential severity after limited therapeutic exposure without assigning universal
      penetrance.
phenotypes:
- category: Auditory
  name: Bilateral Sensorineural Hearing Loss
  description: >-
    Bilateral sensorineural hearing loss is the defining clinical manifestation in affected individuals.
    Severe or profound irreversible loss can follow ordinary therapeutic exposure, but variant carriage
    alone is not equivalent to this phenotype.
  phenotype_term:
    preferred_term: Bilateral sensorineural hearing impairment
    term:
      id: HP:0008619
      label: Bilateral sensorineural hearing impairment
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound
    explanation: >-
      Supports the characteristic presentation, without assigning a frequency across all carriers.
- category: Auditory
  name: High-Frequency Predominant Loss
  description: >-
    High-frequency involvement is documented in affected members of a C1494T pedigree, although audiometric
    configurations vary. General aminoglycoside cochleotoxicity commonly begins at higher frequencies;
    that broader pattern does not establish a pooled frequency or uniform sequence for MT-RNR1-associated
    disease.
  phenotype_term:
    preferred_term: High-frequency sensorineural hearing impairment
    term:
      id: HP:0001757
      label: High-frequency sensorineural hearing impairment
  evidence:
  - reference: PMID:17698299
    reference_title: Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation in three Han Chinese pedigrees.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: All affected individuals displayed the loss of the high frequencies and their hearing impairments were symmetric.
    explanation: >-
      Observed in the WZD101 C1494T family; not an unselected carrier prevalence.
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: AG cochleotoxicity typically affects first the high frequency and then extends towards the lower frequency and ranges over time in a dose-dependent manner
    explanation: >-
      Context from general aminoglycoside toxicity, distinguished from the inherited phenotype.
genetic:
- name: MT-RNR1
  gene_term:
    preferred_term: MT-RNR1
    term:
      id: hgnc:7470
      label: MT-RNR1
  relationship_type: CAUSATIVE
  notes: >-
    MT-RNR1 encodes mitochondrial 12S rRNA. m.1555A>G and m.1494C>T have high-level evidence for aminoglycoside
    susceptibility; m.1095T>C has moderate evidence and receives the same prescribing precaution. Other
    variants require variant-specific assessment; omission from these actionable variants does not prove
    benignity. There is no established heteroplasmy threshold below which an actionable variant makes
    aminoglycoside exposure safe.
  variants:
  - name: m.1555A>G
    description: >-
      The best-studied predisposing variant; high evidence for a drug-variant interaction. Hybrid-ribosome
      experiments show both intrinsic decoding errors and increased drug susceptibility.
    evidence:
    - reference: PMID:34032273
      reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: Some MT-RNR1 variants (i.e., m.1095T>C; m.1494C>T; m.1555A>G) more closely resemble the bacterial 16s rRNA subunit and result in increased risk of aminoglycoside-induced hearing loss.
      explanation: >-
        CPIC includes this variant in its actionable susceptibility set; the detailed experimental
        mechanism is allele-dependent.
      quote_role: REVIEW_SYNTHESIS
  - name: m.1494C>T
    description: >-
      A decoding-site variant with high evidence for aminoglycoside susceptibility, including maternal
      pedigrees and hybrid-ribosome experiments. Clinical severity varies.
    evidence:
    - reference: PMID:34032273
      reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: additional variants with sufficient evidence to support a drug-variant interaction are m.1095T>C and m.1494C>T
      explanation: >-
        CPIC includes this variant in its actionable susceptibility set; the detailed experimental
        mechanism is allele-dependent.
      quote_role: REVIEW_SYNTHESIS
  - name: m.1095T>C
    description: >-
      An actionable susceptibility variant with moderate evidence. The detailed structural experiments
      on m.1555A>G and m.1494C>T should not be assumed to establish an identical molecular mechanism
      for this allele.
    evidence:
    - reference: PMID:34032273
      reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: additional variants with sufficient evidence to support a drug-variant interaction are m.1095T>C and m.1494C>T
      explanation: >-
        CPIC includes this variant in its actionable susceptibility set; the detailed experimental
        mechanism is allele-dependent.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence
    explanation: >-
      Distinguishes evidence strength and clinical actionability.
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there is not sufficient evidence to define a level of heteroplasmy where aminoglycoside administration becomes safe
    explanation: >-
      Supports precaution at any detected actionable variant level.
- name: TRMU
  gene_term:
    preferred_term: TRMU
    term:
      id: hgnc:25481
      label: TRMU
  relationship_type: MODIFIER
  notes: >-
    TRMU p.Ala10Ser is a reported nuclear modifier in selected m.1555A>G families, not the primary mitochondrial
    susceptibility locus. Eighteen relatives homozygous for this allele and carrying m.1555A>G had prelingual
    profound deafness in the reported families, without aminoglycoside exposure. Other affected relatives
    lacked the modifier. Family-derived non-isogenic lymphoblast studies support altered tRNA modification
    and mitochondrial function, but do not establish a universal penetrance rule or a validated prescribing
    test.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
    reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: No subjects had a history of exposure to aminoglycosides.
    explanation: >-
      The modifier study addresses hearing expression without drug exposure.
  - reference: PMID:16826519
    reference_title: Mutation in TRMU related to transfer RNA modification modulates the phenotypic expression of the deafness-associated mitochondrial 12S ribosomal RNA mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: all 18 Arab-Israeli/Italian-Spanish matrilineal relatives carrying both the TRMU A10S and 12S rRNA A1555G mutations exhibited prelingual profound deafness.
    explanation: >-
      Selected-family association; the full report specifies homozygous A10S, and other symptomatic
      relatives lacked it.
  - reference: PMID:28049726
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln
    explanation: >-
      Functional modifier evidence from family-derived cell lines.
prevalence:
- population: United Kingdom, British 1958 birth cohort (m.1555A>G carriers)
  measure_type: CARRIER_FREQUENCY
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 260.0
  notes: >-
    m.1555A>G carrier frequency was 19/7350 (0.26%; 95% CI 0.14–0.38%) in successfully genotyped participants
    from the British 1958 birth cohort. This is neither hearing-loss prevalence nor a pooled frequency
    for every actionable variant. Audiometry at age 44–45 used better-ear thresholds at 1 and 4 kHz;
    individual aminoglycoside exposure was not recorded.
  evidence:
  - reference: PMID:22223843
    reference_title: 'Hearing in 44-45 year olds with m.1555A>G, a genetic mutation predisposing to aminoglycoside-induced deafness: a population based cohort study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 19 of 7350 individuals successfully genotyped had the m.1555A>G mutation, giving a prevalence of 0.26% (95% CI 0.14% to 0.38%) or 1 in 385
    explanation: Gives the carrier frequency with its confidence interval in an unselected birth cohort.
diagnosis:
- name: Clinical audiologic and exposure assessment
  description: >-
    Document hearing thresholds, onset, aminoglycoside history and the maternal family history. Age-appropriate
    audiometry and objective tests when needed characterize sensorineural loss; high-frequency testing
    can identify injury that conventional speech-frequency tests miss. A failed neonatal screening test
    alone is not proof of permanent aminoglycoside deafness.
  diagnosis_term:
    preferred_term: audiometric test
    term:
      id: NCIT:C38036
      label: Audiometric Test
  evidence:
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: patients should undergo a baseline hearing test including ultrahigh frequencies prior to AG administration to allow for early and unambiguous assessment of potential ototoxic damage.
    explanation: >-
      General ototoxicity assessment guidance; obtain when feasible without delaying urgent treatment.
  - reference: PMID:25155176
    reference_title: Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: It is important to note, that most infants with failed newborn hearing screening do not develop permanent hearing loss.
    explanation: >-
      Limits interpretation of newborn screening endpoints.
- name: MT-RNR1 molecular testing
  description: >-
    Assess the actionable m.1555A>G, m.1494C>T and m.1095T>C variants, with an assay whose variant coverage
    and heteroplasmy detection limit are understood. A negative targeted panel does not exclude all
    genetic susceptibility or general drug ototoxicity. Hearing loss and an appropriate molecular finding
    establish mitochondrial disease; an incidental positive result identifies susceptibility, not existing
    deafness.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The identification of an MT-RNR1 variant that is known to predispose to AIHL is sufficient to assign a phenotype status, but the absence of a variant does not indicate no risk of AIHL.
    explanation: >-
      Here the assigned phenotype is pharmacogenetic risk, not measured hearing loss.
  - reference: url:https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf
    reference_title: https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Laboratories should be aware of their lower heteroplasmy threshold and ensure results are reported with that context.
    explanation: >-
      Laboratory interpretation requires a reported detection threshold.
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The diagnosis of mitochondrial nonsyndromic hearing loss and deafness is established in a proband with hearing loss and identification of a pathogenic variant in MT-RNR1 or MT-TS1, or one of the eight additional mitochondrial genes known to cause nonsyndromic hearing loss and deafness.
    explanation: >-
      The GeneReviews diagnostic criterion requires hearing loss together with a relevant pathogenic
      molecular finding. In this entry, an incidental MT-RNR1 result without hearing loss identifies
      susceptibility rather than established deafness; the broader chapter also covers other genes.
- name: Pre-treatment and point-of-care genotyping
  description: >-
    The 2026 UK CERSI-PGx guideline recommends testing before aminoglycoside treatment across ages and
    ancestries when a result is feasible within the clinical time frame. Planned treatment permits pre-emptive
    testing. A 26-minute m.1555A>G bedside assay changed prescribing in the 751-participant PALOH implementation
    study: 424/526 antibiotic-treated infants were successfully tested and three confirmed carriers
    avoided aminoglycosides. This was a workflow study, not a randomized demonstration of prevention
    of permanent hearing loss. It predominantly recruited from one center and excluded infants requiring
    immediate antibiotics with established intravenous access. Positive bedside results require laboratory
    confirmation; single-variant tests do not cover every actionable allele.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: pharmacogenetic testing of variants in MT‐RNR1 should be undertaken in all individuals, of all age groups where this is possible in a clinically achievable time frame prior to use for all aminoglycosides
    explanation: >-
      Current UK guideline recommendation, contingent on feasible timing.
  - reference: PMID:35311942
    reference_title: Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: Overall, 424 infants (80.6%) receiving antibiotics were successfully tested for the variant, and the mean time to antibiotics was equivalent to previous practice.
    explanation: >-
      Implementation outcome, with failed tests and incomplete coverage.
  - reference: PMID:35311942
    reference_title: Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: Three participants with the m.1555A>G variant were identified, all of whom avoided aminoglycoside antibiotics.
    explanation: >-
      Demonstrated prescribing change, not a controlled hearing endpoint.
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Positive point‐of‐care results should be confirmed by laboratory testing.
    explanation: >-
      Confirmatory recommendation.
- name: Audiologic monitoring after exposure or established hearing loss
  description: >-
    When aminoglycosides are unavoidable in an actionable-variant carrier, arrange frequent hearing/audiovestibular
    assessment during and after treatment alongside renal and therapeutic-drug monitoring. Annual audiometry
    is advised in established mitochondrial hearing loss to assess stability or progression. CPIC finds
    insufficient evidence to require additional hearing assessments solely because an asymptomatic carrier
    has never been exposed.
  diagnosis_term:
    preferred_term: audiometric test
    term:
      id: NCIT:C38036
      label: Audiometric Test
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: with clinical audiovestibular assessment performed during and after treatment.
    explanation: >-
      Exposure-related monitoring.
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Annual audiometric assessment to evaluate stability/progression of hearing loss.
    explanation: >-
      Surveillance of established hearing impairment.
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there is insufficient evidence to support additional hearing assessments in individuals with MT-RNR1 variants that predispose to AIHL if they have not been exposed to an aminoglycoside.
    explanation: >-
      Prevents extrapolating an annual disease-surveillance schedule to every unexposed carrier.
treatments:
- name: Avoidance or substitution of aminoglycoside antibiotics
  therapeutic_modality: OTHER
  description: >-
    For carriers of an actionable MT-RNR1 variant, choose an effective non-aminoglycoside regimen when
    available. This reduces the drug-associated risk but does not eliminate all possible hearing loss.
    The precaution applies across the aminoglycoside class. Inhaled delivery can still produce systemic
    exposure; low-absorption topical/enteral use and damaged barriers require route-specific assessment.
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: aminoglycosides should be avoided unless the increased risk of hearing loss is outweighed by the severity of infection and lack of safe or effective alternative therapies
    explanation: >-
      Relative contraindication balances hearing risk against effective infection treatment.
  target_mechanisms:
  - target: Cochlear Aminoglycoside Accumulation
    treatment_effect: INHIBITS
    description: >-
      Avoiding the drug prevents this exposure-dependent step; it does not correct the mitochondrial
      variant.
- name: Expert management when aminoglycosides are essential
  therapeutic_modality: OTHER
  description: >-
    When no safe effective alternative exists, obtain infectious-disease/microbiology advice, document
    and discuss the risk-benefit decision, and use the shortest effective course with drug-level, renal
    and audiovestibular monitoring. If testing information is unavailable and clinical urgency is high,
    do not delay necessary antibiotic treatment.
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: an aminoglycoside used in patients at increased risk of AIHL due to the presence of an MT-RNR1 variant should be administered for the shortest possible period, under expert supervision, with therapeutic drug and ototoxicity monitoring
    explanation: >-
      Guideline precautions; monitoring does not guarantee prevention.
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Aminoglycoside treatment should not be delayed, and administration should proceed according to local microbiological guidance, as the benefit exceeds the risk.
    explanation: >-
      Applies to the acute setting where genotype information is unavailable.
- name: Hearing aids and auditory rehabilitation
  therapeutic_modality: DEVICE
  description: >-
    Offer hearing aids and audiologic rehabilitation appropriate to residual hearing and communication
    needs. These improve functional access to sound; they do not regenerate damaged cochlear hair cells.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired).
    explanation: >-
      Mitochondrial-hearing-loss rehabilitation guidance.
  target_mechanisms:
  - target: Bilateral Sensorineural Hearing Loss
    treatment_effect: BYPASSES
    description: >-
      Amplification supports use of residual hearing without repairing the initiating molecular defect.
  treatment_term:
    preferred_term: hearing-aid rehabilitation
    term:
      id: NCIT:C15315
      label: Rehabilitation
  notes: >-
    The action is bound to Rehabilitation rather than the Hearing Aid device class. Local OAK searches
    using t~Hearing Aid and t~Rehabilitation identified NCIT:C183182 as a device outside the TreatmentActionTerm
    procedure hierarchy and NCIT:C15315 as rehabilitation under Supportive Care.
- name: Cochlear implantation and electric acoustic stimulation
  therapeutic_modality: SURGERY
  description: >-
    Evaluate cochlear implantation for severe hearing loss according to standard candidacy assessment.
    Electric acoustic stimulation may be considered when usable low-frequency hearing remains. The GeneReviews
    recommendations address mitochondrial hearing loss generally, not a genotype-specific comparative
    trial.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired).
    explanation: >-
      Includes cochlear implantation among rehabilitation options.
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Electric acoustic stimulation for individuals with mitochondrial hearing loss with residual hearing in the lower frequencies.
    explanation: >-
      Qualifies the residual-hearing indication.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Appropriate rehabilitation including hearing aids, speech therapy, culturally appropriate language training, and evaluation for eligibility for cochlear implantation
    explanation: >-
      Full chapter recommendation is evaluation for candidacy rather than universal implantation.
  target_mechanisms:
  - target: Bilateral Sensorineural Hearing Loss
    treatment_effect: BYPASSES
    description: >-
      Electrical stimulation bypasses impaired sensory transduction to support hearing.
  treatment_term:
    preferred_term: cochlear implantation
    term:
      id: NCIT:C201922
      label: Surgical Implantation
  notes: >-
    The action is bound to Surgical Implantation rather than the Cochlear Implant device class. Local
    OAK searches using t~Cochlear Implant and t~Implantation identified NCIT:C157820 as a device outside
    the TreatmentActionTerm hierarchy and NCIT:C201922 as a surgical procedure; the name and description
    retain the cochlear indication.
- name: Communication, language and educational support
  therapeutic_modality: OTHER
  description: >-
    Provide speech/language therapy, culturally appropriate language support and educational accommodations
    according to the individual and family’s communication preferences and needs.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Appropriate rehabilitation (hearing aids, speech therapy, culturally appropriate language training, cochlear implantation, educational programs for the hearing impaired).
    explanation: >-
      Guidance includes language, speech and educational support.
  treatment_term:
    preferred_term: Speech Language Therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
- name: Maternal-family counseling and durable prescribing alerts
  therapeutic_modality: OTHER
  description: >-
    Explain maternal transmission, variable penetrance and the importance of sharing drug-risk information
    with maternal relatives. Record the actionable result so future prescribers can retrieve it. The
    2026 UK guideline considers maternal relatives of a homoplasmic carrier at risk without requiring
    confirmatory genotyping of each relative; testing first-degree maternal relatives can be considered
    for heteroplasmic findings. Prenatal variant detection does not predict hearing severity.
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: the advice to avoid aminoglycosides should be cascaded to the relevant individuals within the family.
    explanation: >-
      Family risk communication.
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Where the variant detected is heteroplasmic, testing in first degree maternal relatives can be considered.
    explanation: >-
      Heteroplasmy-specific family testing advice.
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The results should be recorded in the patient record (ideally in the electronic record in a format that is immediately available to inform future prescribing decisions).
    explanation: >-
      Durable pharmacogenetic communication, not a direct therapeutic action on the causal graph.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
- name: Hearing protection and routine vaccination
  therapeutic_modality: OTHER
  description: >-
    Avoid excessive noise exposure as part of hearing preservation. Trace aminoglycosides in vaccines
    are not a reason to forgo recommended vaccination: the 2026 guideline considers vaccination benefits
    to outweigh the theoretical ototoxicity risk.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Aminoglycosides and noise exposure, especially in those with normal hearing who have the m.1555A>G or m.1494C>T MT-RNR1 pathogenic variants.
    explanation: >-
      Exposure-avoidance guidance.
  - reference: PMID:42524757
    reference_title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: the benefits of vaccination far outweigh any theoretical risks of ototoxicity from vaccination in an individual with an AIHL associated MT‐RNR1 variant.
    explanation: >-
      Distinguishes trace excipients from therapeutic aminoglycoside exposure.
discussions:
- discussion_id: carrier_penetrance_and_exposure
  prompt: Which exposures and modifiers explain clinical penetrance across actionable MT-RNR1 variants?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - genetic#MT-RNR1
  - pathophysiology#Predisposing MT-RNR1 Variants
  rationale: >-
    Severe loss after limited exposure is well documented, but selected maternal pedigrees and neonatal
    screening endpoints do not yield an unbiased lifetime risk. The British birth cohort had no individual
    aminoglycoside-exposure data and assessed better-ear thresholds at two frequencies in midlife. TRMU
    modifier families were selected and had no reported aminoglycoside exposure. General drug-resistant-tuberculosis
    ototoxicity estimates mix genetically unselected populations and cannot serve as prevalence of this
    inherited disorder.
  evidence:
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: there was sufficient and consistent evidence to assign actionability to the m.1555A>G and m.1494C>T variants with high levels of evidence and the m.1095T>C variant with a moderate level of evidence
    explanation: >-
      The clinical susceptibility set is broader than the alleles tested in the structural experiments.
  - reference: PMID:25155176
    reference_title: Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: It is important to note, that most infants with failed newborn hearing screening do not develop permanent hearing loss.
    explanation: >-
      A screening failure is not equivalent to permanent hearing impairment.
  - reference: PMID:34015383
    reference_title: 'Prevalence of aminoglycoside-induced hearing loss in drug-resistant tuberculosis patients: A systematic review.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: aminoglycoside use results in high prevalence of ototoxic hearing loss
    explanation: >-
      Genetically unselected tuberculosis-treatment context, not Mendelian disease prevalence.
- discussion_id: human_cochlear_mechanistic_bridge
  prompt: How do allele-specific mitoribosomal defects produce selective cochlear injury in exposed carriers?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Mitoribosomal Decoding Errors
  - pathophysiology#Cochlear Hair Cell Loss
  rationale: >-
    Hybrid ribosomes isolate decoding-site effects and lymphoblasts establish cellular susceptibility,
    but neither reproduces the complete sensory-cell context. General drug models show multiple exposure-dependent
    injury responses, including delayed routes not protected by the tested mitochondrial antioxidant.
    A patient-genotype hair-cell system with allele correction and physiological drug exposure would
    help distinguish initiating defects from secondary stress.
  evidence:
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood.
    explanation: >-
      The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of
      the complete MT-RNR1 causal chain.
  - reference: PMID:39610699
    reference_title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: The underlying mechanisms by which lysosomal accumulation of AGs result in delayed cell death remain unclear.  # codespell:ignore-line
    explanation: >-
      Even the delayed generic drug-injury mediator remains unresolved.
- discussion_id: clinical_otoprotection_and_testing_outcomes
  prompt: Can alternative antibiotics or otoprotective strategies preserve hearing in actionable-variant carriers without compromising infection treatment?
  kind: OPEN_QUESTION
  status: OPEN
  attaches_to:
  - treatments#Avoidance or substitution of aminoglycoside antibiotics
  - clinical_trials#NCT04105205
  rationale: >-
    PALOH demonstrated prescribing change and similar mean antibiotic timing within its implementation
    comparison, not comparative long-term hearing protection. Apramycin has progressed beyond purely
    preclinical work to a healthy-volunteer phase I study, but that does not establish carrier safety.
    Antioxidant and other otoprotective findings in general drug models should not replace current genotype-guided
    avoidance.
  evidence:
  - reference: PMID:35311942
    reference_title: Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: Three participants with the m.1555A>G variant were identified, all of whom avoided aminoglycoside antibiotics.
    explanation: >-
      Observed implementation benefit; no measured comparative permanent-hearing outcome.
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: these protective results are mainly based on acute studies and the sustainability of therapeutic potential and safety remains to be evaluated in chronic exposure scenarios or in clinical trials.
    explanation: >-
      Limits extrapolating experimental otoprotection to standard care.
references:
- reference: PMID:20301595
  title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
  findings:
  - statement: >-
      GeneReviews indexed summary covers maternal inheritance, hearing manifestations, rehabilitation
      and counseling; the full NBK1422 chapter was also reviewed.
  tags:
  - GeneReviews
- reference: PMID:17698299
  title: Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation in three Han Chinese pedigrees.
  findings:
  - statement: >-
      Three C1494T maternal pedigrees show variable hearing phenotypes with and without exposure;
      high-frequency involvement is directly described in WZD101.
- reference: PMID:34015383
  title: 'Prevalence of aminoglycoside-induced hearing loss in drug-resistant tuberculosis patients: A systematic review.'
  findings:
  - statement: >-
      Genetically unselected tuberculosis-treatment systematic review is contextual drug-toxicity
      evidence, not prevalence of inherited susceptibility.
- reference: PMID:34032273
  title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
  findings:
  - statement: >-
      CPIC supplies variant-specific prescribing precautions, absence of a safe heteroplasmy threshold,
      limits of negative tests and prior tolerance, and monitoring when treatment is unavoidable.
- reference: PMID:37314952
  title: Clinical Pharmacogenomic MT-RNR1 Screening for Aminoglycoside-Induced Ototoxicity and the Post-Test Counseling Conundrum.
  findings:
  - statement: >-
      Pharmacogenetic counseling perspective provides context for communicating susceptibility rather
      than diagnosing inevitable deafness.
- reference: PMID:22223843
  title: 'Hearing in 44-45 year olds with m.1555A>G, a genetic mutation predisposing to aminoglycoside-induced deafness: a population based cohort study.'
  findings:
  - statement: >-
      British cohort carrier frequency was 19/7350; midlife hearing assessment did not record aminoglycoside
      exposure or establish lifetime penetrance.
- reference: PMID:35311942
  title: Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care.
  findings:
  - statement: >-
      PALOH established bedside workflow and prescribing change, with test failures and wide carrier-sensitivity
      uncertainty; it did not compare permanent hearing outcomes.
- reference: PMID:18308926
  title: Mitochondrial deafness alleles confer misreading of the genetic code.
  findings:
  - statement: >-
      Human-sequence bacterial hybrid ribosomes distinguish intrinsic decoding errors from protein
      output and drug-exacerbated miscoding.
- reference: PMID:16826519
  title: Mutation in TRMU related to transfer RNA modification modulates the phenotypic expression of the deafness-associated mitochondrial 12S ribosomal RNA mutations.
  findings:
  - statement: >-
      Selected TRMU A10S modifier families and lymphoblast assays; generated PMC1559489 full text
      establishes absent drug exposure and assay-specific findings.
- reference: PMID:28049726
  title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
  findings:
  - statement: >-
      Selected modifier lymphoblast and recombinant-protein study; generated PMC5314183 full text
      distinguishes tRNA modification, protein abundance, respiration and assay-specific ATP.
- reference: PMID:10915767
  title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
  findings:
  - statement: >-
      Abstract-only primary paromomycin study in family lymphoblasts; comparative translation-rate
      ratios support cellular susceptibility at a high experimental concentration.
- reference: PMID:22121370
  title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
  findings:
  - statement: >-
      Full review supplies general aminoglycoside entry and hair-cell injury biology while explicitly
      identifying the incomplete mitochondrial-genotype link.
- reference: PMID:19104050
  title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity.
  findings:
  - statement: >-
      Canonical abstract plus generated PMC2634874 full text supply gentamicin footprinting and mutant
      hybrid-ribosome susceptibility.
- reference: PMID:39610699
  title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
  findings:
  - statement: >-
      Whole-larva zebrafish study separates acute and delayed drug injury and identifies limits of
      mitochondrial-antioxidant and lysosomal-perturbation interpretations.
- reference: PMID:40842562
  title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
  findings:
  - statement: >-
      Mouse cochlear explants separate RIPOR2 movement from phosphatidylserine exposure; no new living-animal
      hearing rescue or human MT-RNR1 experiment.
- reference: PMID:22699498
  title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
  findings:
  - statement: >-
      Hybrid-ribosome, explant and guinea-pig comparisons show lower experimental apramycin ototoxicity
      without proving human carrier safety.
- reference: PMID:25155176
  title: Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants.
  findings:
  - statement: >-
      Preterm-neonate cohort links genotype/exposure to failed screening in a small carrier subset,
      not a validated estimate of permanent hearing loss.
- reference: PMID:35849148
  title: Population pharmacokinetics of apramycin from first-in-human plasma and urine data to support prediction of efficacious dose.
  findings:
  - statement: >-
      Healthy-volunteer phase I apramycin pharmacokinetics; simulated efficacy targets are not observed
      infection or carrier hearing outcomes.
- reference: PMID:42524757
  title: 'MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).'
  findings:
  - statement: >-
      2026 UK CERSI-PGx testing guidance extends beyond CPIC interpretation, including urgent-treatment
      timing, confirmatory testing, family communication and vaccine advice.
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/
  title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial - GeneReviews® - NCBI Bookshelf
  findings:
  - statement: >-
      Full GeneReviews scientific chapter read for clinical variability, differential diagnosis, molecular
      diagnosis, counseling, rehabilitation and surveillance; broader MT-TS1 features are outside
      this entry.
  tags:
  - GeneReviews
- reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
  title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
  findings:
  - statement: >-
      Genuine full text of PMID19104050, used for chemical-footprinting and translation experiments.
- reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
  title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
  findings:
  - statement: >-
      Genuine full text of PMID16826519, used for family ascertainment, absence of drug exposure and
      tRNA/protein-labeling assays.
- reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
  title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
  findings:
  - statement: >-
      Genuine full text of PMID28049726, used for non-isogenic design and thermal-stability, respiration,
      ATP and oxidant-assay limits.
- reference: url:https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf
  title: https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf
  findings:
  - statement: >-
      CPIC supplemental methods and variant-evidence table, including the October 2025 correction;
      heteroplasmy reporting does not imply a safe clinical threshold.
- reference: clinicaltrials:NCT04105205
  title: A Phase I, Randomized, Double-blind, Placebo-controlled, Single Ascending Dose Study to Assess the Safety, Tolerability, and Pharmacokinetics of Apramycin Administered Intravenously in Healthy Adults.
  findings:
  - statement: >-
      Canonical registry summary identifies a first-in-human apramycin single-dose safety and pharmacokinetic
      study.
notes: >-
  The entry concerns inherited MT-RNR1-associated susceptibility. General aminoglycoside ototoxicity is
  included only where it provides explicitly qualified experimental context. Hearing loss without documented
  exposure occurs in selected families; drug avoidance reduces exposure-associated risk without guaranteeing
  normal lifetime hearing. Vestibular toxicity of the drug class is not assigned as an established MT-RNR1-specific
  phenotype. The exact aminoglycoside-exposure concept is retained as free text because ECTO:9002231 has
  no label in the configured local ontology adapter. Full primary texts and the full GeneReviews chapter
  were reviewed; URL caches supply the scientific bodies where canonical PMID retrieval returned only
  an abstract.
progression:
- phase: Exposure-associated onset and persistent hearing impairment
  notes: >-
    Hearing loss can begin within days to weeks after aminoglycoside exposure and is often severe and
    irreversible. Hearing level and age at recognition vary. A normal newborn screen or a previously
    tolerated course does not establish safety of subsequent exposure.
  evidence:
  - reference: PMID:20301595
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Hearing loss associated with aminoglycoside ototoxicity is bilateral and severe to profound, occurring within a few days to weeks after administration of any amount (even a single dose) of an aminoglycoside antibiotic
    explanation: >-
      Clinical synthesis of the characteristic presentation; not a universal penetrance estimate.
  - reference: PMID:34032273
    reference_title: Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Finally, if an individual with an actionable MT-RNR1 variant has previously received aminoglycosides and not developed AIHL, this does not preclude them from developing AIHL with subsequent doses.
    explanation: >-
      Prior tolerance does not remove future risk.
- phase: Variable hearing expression without documented aminoglycoside exposure
  notes: >-
    Some MT-RNR1 families include congenital, progressive or later-onset hearing loss without documented
    exposure. This variable natural history should not be confused with inevitable deafness in an asymptomatic
    carrier or with a measured population penetrance estimate.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/
    reference_title: Nonsyndromic Hearing Loss and Deafness, Mitochondrial - GeneReviews® - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The probability of hearing loss varies widely among reports and families
    explanation: >-
      Full GeneReviews clinical description of MT-RNR1 hearing loss independent of aminoglycoside
      exposure.
mechanistic_hypotheses:
- hypothesis_group_id: mitoribosomal_dysfunction_to_cochlear_injury
  hypothesis_label: Mitoribosomal dysfunction, bioenergetic stress and selective cochlear injury
  status: EMERGING
  description: >-
    Mutant ribosome biochemistry and selected family-derived cells support impaired translation and
    mitochondrial function. Connecting these findings to ATP limitation, oxidant stress and sensory-cell
    loss in exposed human carriers remains incompletely demonstrated. Generic drug-exposed fish, guinea-pig
    and mouse-explant systems do not encode the human susceptibility alleles; their drug-specific responses
    caution against a universal linear death pathway.
  evidence:
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: The mechanism of involvement of mitochondrial mutations in ototoxic hair cell death is not completely understood.
    explanation: >-
      The tissue-selective link remains unresolved; generic aminoglycoside models are not proof of
      the complete MT-RNR1 causal chain.
  - reference: PMID:22121370
    reference_title: Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: Furthermore, it is hypothesized that the mitochondrial RNA mutations when exposed to AG cause an increased formation of ROS, which then promote apoptotic cell death
    explanation: >-
      Explicitly hypothetical mitochondrial-variant-to-oxidative-death route.
experimental_models:
- name: Human-sequence mitochondrial decoding sites in bacterial hybrid ribosomes
  experimental_model_type: OTHER
  description: >-
    A 34-nucleotide human mitochondrial decoding-site sequence was introduced into Mycobacterium smegmatis
    ribosomes, with wild-type, A1555G and C1494T variants. Cell-free amino-acid incorporation, luciferase
    and gentamicin-footprinting assays separate decoding fidelity, protein output and drug binding.
  modeled_mechanisms:
  - target: Mitoribosomal Decoding Errors
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Variant hybrid ribosomes show intrinsic and aminoglycoside-exacerbated miscoding.
    model_scale: MOLECULAR
    limitations: >-
      A human rRNA segment is tested in a bacterial ribosome. No hair cells, mitochondrial membrane
      transport or auditory outcome is represented.
    evidence:
    - reference: PMID:18308926
      reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation.
      explanation: >-
        Direct comparative misincorporation assays distinguish accuracy from total protein output.
    readouts:
    - name: Translation accuracy
      target: Mitoribosomal Decoding Errors
      direction: DECREASED
      description: >-
        Near-cognate amino-acid misincorporation increased; reporter function fell without lower
        full-length protein output.
      evidence:
      - reference: PMID:18308926
        reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: In contrast, the accuracy of mRNA translation was significantly reduced in the hybrid ribosomes carrying a deafness mutation.
        explanation: >-
          Direct comparative misincorporation assays distinguish accuracy from total protein output.
  - target: Aminoglycoside Binding to the Mitochondrial Ribosome
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Chemical footprinting supports increased aminoglycoside interaction with variant decoding sites.
    model_scale: MOLECULAR
    limitations: >-
      Binding to hybrid ribosomes does not quantify drug entry into human cochlear mitochondria.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
      reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
      explanation: >-
        Chemical footprinting and translation assays support enhanced drug binding plus inherent
        decoding infidelity in A1555G/C1494T hybrids.
  evidence:
  - reference: PMID:18308926
    reference_title: Mitochondrial deafness alleles confer misreading of the genetic code.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: Both the C1494U and the A1555G mutation replace the noncanonical C1494·A1555 interaction by a Watson–Crick base pairing, thus shortening the extended conformation of the mitochondrial loop.
    explanation: >-
      Structural interpretation of the human-sequence decoding site in hybrid bacterial ribosomes;
      C1494U is the RNA equivalent of the DNA C1494T variant.
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/
    reference_title: Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: increased drug binding to its target and excessive aggravation of the mutants' inherent deficiency in ribosomal accuracy.
    explanation: >-
      Chemical footprinting and translation assays support enhanced drug binding plus inherent decoding
      infidelity in A1555G/C1494T hybrids.
  notes: >-
    Structural interpretation is not a solved atomic structure of the complete human mutant mitoribosome.
    Loop closure alone was insufficient to reproduce the fidelity defect.
- name: Paromomycin-exposed m.1555A>G family lymphoblasts
  experimental_model_type: CELL_LINE
  description: >-
    Lymphoblastoid lines from five deaf carriers, five hearing carriers and three married-in controls
    from an Arab-Israeli family were exposed to 2 mg/ml paromomycin. Carrier cells had greater drug-associated
    growth slowing and mitochondrial translation inhibition.
  modeled_mechanisms:
  - target: Reduced Mitochondrial Protein Synthesis
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Drug/no-drug mitochondrial translation-rate ratios were lower in carrier cells.
    model_scale: MOLECULAR
    limitations: >-
      Non-isogenic family lymphoblasts, high in-vitro exposure and abstract-only accessible report;
      not a hair-cell model or clinical dose threshold.
    evidence:
    - reference: PMID:10915767
      reference_title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively), compared with the ratios in the control cell lines.
      explanation: >-
        Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts;
        high paromomycin concentration, not a clinical dose threshold.
    readouts:
    - name: Relative mitochondrial translation under paromomycin
      target: Reduced Mitochondrial Protein Synthesis
      direction: DECREASED
      description: >-
        The drug/no-drug ratios were lower than control ratios in both symptomatic- and asymptomatic-carrier
        lines.
      evidence:
      - reference: PMID:10915767
        reference_title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively), compared with the ratios in the control cell lines.
        explanation: >-
          Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts;
          high paromomycin concentration, not a clinical dose threshold.
  evidence:
  - reference: PMID:10915767
    reference_title: A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: The ratios of translation rates in the presence and absence of paromomycin, which reflected the effect of the drug on mitochondrial protein synthesis, were significantly decreased in the cell lines derived from symptomatic and asymptomatic individuals (by 30 and 28% on average, respectively), compared with the ratios in the control cell lines.
    explanation: >-
      Drug-dependent mitochondrial protein-labeling inhibition in family-derived lymphoblasts; high
      paromomycin concentration, not a clinical dose threshold.
  notes: >-
    The experiment supports drug susceptibility in hearing as well as deaf carriers, without showing
    that cellular response predicts individual future hearing outcome.
- name: TRMU A10S and m.1555A>G family-derived lymphoblasts
  experimental_model_type: CELL_LINE
  description: >-
    The 2006 study examined selected family lymphoblasts and controls for mitochondrial import, tRNA
    thiolation/abundance and protein labeling. The 2017 study used eight non-isogenic lines, two per
    group, for tRNA modification, mitochondrial protein abundance, respiration, ATP and oxidant-response
    assays. No aminoglycoside challenge was used in these modifier experiments.
  modeled_mechanisms:
  - target: Reduced TRMU-Dependent tRNA Thiolation
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      A10S-bearing lines have reduced tRNA thiolation.
    model_scale: MOLECULAR
    limitations: >-
      Selected nuclear/mitochondrial genotype combinations, not an isogenic comparison or universal
      modifier effect.
    evidence:
    - reference: PMID:28049726
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln
      explanation: >-
        TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside
        treatment.
    readouts:
    - name: Wobble-uridine 2-thiouridine modification
      target: Reduced TRMU-Dependent tRNA Thiolation
      direction: DECREASED
      description: >-
        Affected tRNA modification in selected modifier lines.
      evidence:
      - reference: PMID:28049726
        reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln
        explanation: >-
          TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside
          treatment.
  - target: Reduced Mitochondrial tRNA Abundance
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Double-mutant lines have reduced mitochondrial tRNA steady-state abundance.
    model_scale: MOLECULAR
    limitations: >-
      Reduced abundance does not directly establish accelerated degradation.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
      reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls
      explanation: >-
        Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured,
        degradation kinetics were not.
    readouts:
    - name: Mitochondrial tRNA abundance
      target: Reduced Mitochondrial tRNA Abundance
      direction: DECREASED
      description: >-
        Northern-blot comparison to control cell lines.
      evidence:
      - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
        reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls
        explanation: >-
          Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured,
          degradation kinetics were not.
  - target: Reduced Mitochondrial Protein Synthesis
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Protein labeling was lower in the homozygous double-mutant lines.
    model_scale: MOLECULAR
    limitations: >-
      The 2006 labeling assay measures synthesis; the 2017 immunoblots measure abundance and are not
      interchangeable.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
      reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%.
      explanation: >-
        Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.
    readouts:
    - name: Mitochondrial protein labeling
      target: Reduced Mitochondrial Protein Synthesis
      direction: DECREASED
      description: >-
        A 44–57% decrease, averaging 51%, in the two homozygous double-mutant lines.
      evidence:
      - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
        reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%.
        explanation: >-
          Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.
  - target: Reduced Mitochondrial Respiration
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Oxygen-consumption rates were reduced in selected mutant groups.
    model_scale: CELLULAR
    limitations: >-
      Family background, two lines per group and lack of aminoglycoside exposure limit translation
      to carrier cochleae.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the average basal OCRs in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations, and only m.1555A→G mutation were 54, 76, and 88%, relative to the mean value measured in the control cell lines, respectively.
      explanation: >-
        OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and
        controls; no drug exposure or hair cells.
    readouts:
    - name: Basal oxygen-consumption rate
      target: Reduced Mitochondrial Respiration
      direction: DECREASED
      description: >-
        Group means were 54%, 76% and 88% of control for homozygous modifier, heterozygous modifier
        and m.1555A>G-only lines.
      evidence:
      - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
        reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: the average basal OCRs in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations, and only m.1555A→G mutation were 54, 76, and 88%, relative to the mean value measured in the control cell lines, respectively.
        explanation: >-
          OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes
          and controls; no drug exposure or hair cells.
  - target: Reduced Mitochondrial ATP Production
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      ATP production was reduced with glycolysis suppressed.
    model_scale: CELLULAR
    limitations: >-
      Total cellular ATP was relatively preserved; this assay does not establish whole-cell energy
      collapse or hearing-cell ATP levels.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
      reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: the levels of ATP production in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations and only m.1555A→G mutation were 48, 61, and 83% of the mean value measured in the control cell lines, respectively.
      explanation: >-
        ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so this
        is not a global energy collapse.
    readouts:
    - name: ATP under glycolysis-suppressed conditions
      target: Reduced Mitochondrial ATP Production
      direction: DECREASED
      description: >-
        Group means were 48%, 61% and 83% of controls; these are assay-specific mitochondrial ATP
        values.
      evidence:
      - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
        reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: the levels of ATP production in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations and only m.1555A→G mutation were 48, 61, and 83% of the mean value measured in the control cell lines, respectively.
        explanation: >-
          ATP measured with glycolysis inhibited; total cellular ATP was much less affected, so
          this is not a global energy collapse.
  evidence:
  - reference: PMID:28049726
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: The A10S mutation caused marked decreases in 2-thiouridine modification of U34 of tRNALys, tRNAGlu and tRNAGln
    explanation: >-
      TRMU A10S-associated tRNA thiolation defect in family-derived cell lines, without aminoglycoside
      treatment.
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
    reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the average steady-state levels of those tRNAs were significantly decreased in the mutant cell lines carrying both A1555G and homozygous A10S mutations, relative to the controls
    explanation: >-
      Northern analysis in homozygous A10S plus A1555G lymphoblasts; tRNA abundance was measured,
      degradation kinetics were not.
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/
    reference_title: Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the decrease in the rate of mitochondrial-protein labeling in cell lines V-1 and V-3, carrying both A1555G and homozygous A10S mutations, relative to the controls had a range of 44%–57%, with an average of 51%.
    explanation: >-
      Mitochondrial protein-labeling readout in the selected double-mutant lymphoblasts.
  - reference: url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/
    reference_title: Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation - PMC
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: the average basal OCRs in mutant cell lines carrying both m.1555A→G and homozygous or heterozygous TRMU A10S mutations, and only m.1555A→G mutation were 54, 76, and 88%, relative to the mean value measured in the control cell lines, respectively.
    explanation: >-
      OCR measurements in eight non-isogenic lymphoblast lines, including modifier genotypes and controls;
      no drug exposure or hair cells.
  notes: >-
    The 2017 oxidant assay used a fluorescent-probe response to hydrogen peroxide. Aminoacylation increased
    for some tRNAs, so reduced aminoacylation or measured mischarging should not be asserted. The original
    import assay did not detect an A10S import defect.
- name: Mouse cochlear explants exposed to gentamicin or apramycin
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    Cochlear organ cultures were exposed to gentamicin and apramycin over a range of concentrations
    and assessed for sensory-cell loss and nitrotyrosine staining. Gentamicin caused greater loss; apramycin
    was less damaging, but sufficiently high exposure affected basal hair cells.
  modeled_mechanisms:
  - target: Cochlear Hair Cell Loss
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Drug-dependent cochlear hair-cell loss was quantified in explants.
    model_scale: CELLULAR
    limitations: >-
      No human MT-RNR1 allele or clinical auditory endpoint; drug comparisons do not establish apramycin
      safety in carriers.
    evidence:
    - reference: PMID:22699498
      reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: complete elimination of outer hair cells was observed at 0.5 mM.
      explanation: >-
        Gentamicin explant response.
    readouts:
    - name: Outer-hair-cell survival after gentamicin
      target: Cochlear Hair Cell Loss
      direction: DECREASED
      description: >-
        Outer hair cells were eliminated at the stated explant concentration.
      evidence:
      - reference: PMID:22699498
        reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: complete elimination of outer hair cells was observed at 0.5 mM.
        explanation: >-
          Gentamicin concentration-response assay.
  evidence:
  - reference: PMID:22699498
    reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: At 2 mM, apramycin begins to affect basal hair cells but does not cause a significant overall loss of hair cells
    explanation: >-
      Ex-vivo concentration-response finding; lower injury is not zero toxicity.
  notes: >-
    Nitrotyrosine staining supports an oxidative-injury association, not a complete causal epistasis
    test. Bacterial 30S crystallography in the same paper is not a human mitoribosomal structure.
- name: Gentamicin and mechanotransduction perturbation in neonatal mouse cochlear explants
  experimental_model_type: PRIMARY_CELL_CULTURE
  description: >-
    P3–P5 cochlear explants were used to image RIPOR2 localization and Annexin-V phosphatidylserine
    signals after gentamicin, washout, benzamil or selected stereociliary mutations. Tmie-deficient
    cells lacked both gentamicin responses; benzamil caused phosphatidylserine exposure without RIPOR2
    movement.
  modeled_mechanisms:
  - target: RIPOR2 Redistribution in Hair Cells
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Gentamicin induced reversible redistribution requiring an intact tested mechanotransduction
      context.
    model_scale: CELLULAR
    limitations: >-
      No human MT-RNR1 variant, hearing outcome or newly demonstrated RIPOR2-mediated death rescue.
      Surface phosphatidylserine is not sufficient evidence of apoptosis.
    evidence:
    - reference: PMID:40842562
      reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: RIPOR2 translocated robustly from the stereocilia base to the pericuticular area
      explanation: >-
        Drug-induced localization change.
    - reference: PMID:40842562
      reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      snippet: neither RIPOR2 translocation nor PS externalization was observed in hair cells lacking TMIE
      explanation: >-
        Genetic perturbation under the tested conditions.
    readouts:
    - name: RIPOR2 subcellular localization
      target: RIPOR2 Redistribution in Hair Cells
      direction: ALTERED
      description: >-
        Movement from the stereociliary base to the pericuticular region and subsequent recovery.
      evidence:
      - reference: PMID:40842562
        reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        snippet: RIPOR2 translocated robustly from the stereocilia base to the pericuticular area
        explanation: >-
          Localization imaging.
  evidence:
  - reference: PMID:40842562
    reference_title: Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    snippet: cochlear explants dissected from postnatal day 3 to 5 (P3-P5) wild-type C57/BL6 mice
    explanation: >-
      Defines the ex-vivo system.
  notes: >-
    Phosphatidylserine exposure alone was insufficient for redistribution. Selective scramblase inhibition
    was not available to establish whether phosphatidylserine is necessary for death. Proposed TMC scramblase/TMIE
    roles and prior RIPOR2–GABARAP rescue results should not be treated as new assays here. Benzamil-associated
    uptake inhibition was inferred rather than measured.
animal_models:
- name: Guinea-pig comparative aminoglycoside ototoxicity
  species: Guinea pig
  publication: PMID:22699498
  description: >-
    Systemic gentamicin and apramycin were compared using auditory brainstem responses and cochlear
    histology. Apramycin produced less injury at tested doses. Gentamicin caused a basal-to-apical hair-cell-loss
    gradient and systemic toxicity; two of three animals at 160 mg/kg died early.
  modeled_mechanisms:
  - target: Cochlear Hair Cell Loss
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      In-vivo histology documents drug-associated cochlear sensory-cell loss.
    model_scale: CELLULAR
    limitations: >-
      Wild-type drug toxicity, not a human MT-RNR1 allele model; unequal dose responses and systemic
      toxicity limit extrapolation to safer human prescribing.
    evidence:
    - reference: PMID:22699498
      reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      snippet: Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea.
      explanation: >-
        Guinea-pig cochlear histology.
    readouts:
    - name: Cochlear hair-cell survival with gentamicin
      target: Cochlear Hair Cell Loss
      direction: DECREASED
      description: >-
        Complete basal-half loss at the specified 140 mg/kg treatment.
      evidence:
      - reference: PMID:22699498
        reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        quote_role: PRIMARY_RESULT
        snippet: Treatment with 140 mg gentamicin/kg body weight resulted in a base-to-apex gradient of hair cell loss with a complete destruction of hair cells in the basal half of the cochlea.
        explanation: >-
          Whole-animal tissue outcome.
  evidence:
  - reference: PMID:22699498
    reference_title: Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: at a dose of 160 mg/kg body weight, two of three animals died early during the experiments.
    explanation: >-
      Important systemic-toxicity limitation of the comparator.
  notes: >-
    Lower experimental ototoxicity does not establish clinical otoprotection or an exception to current
    class-wide precautions in actionable-variant carriers.
- name: Larval zebrafish acute and delayed aminoglycoside sensory-cell injury
  species: Zebrafish
  publication: PMID:39610699
  description: >-
    Living 5–8-day-postfertilization larvae were exposed to neomycin, gentamicin or G418, with acute
    imaging and survival after washout. Acute injury often involved mitochondrial calcium elevations
    and partial mitoTEMPO protection. Delayed injury correlated with lysosomal drug localization and
    responded to endolysosomal perturbation; G418 could also cause acute injury at higher doses.
  modeled_mechanisms:
  - target: Cochlear Hair Cell Loss
    relationship: PARTIALLY_RECAPITULATES
    description: >-
      Lateral-line sensory-cell loss provides a comparative drug-injury model for the cochlear injury
      node.
    model_scale: CELLULAR
    limitations: >-
      Lateral-line rather than cochlear hair cells; no MT-RNR1 susceptibility allele, hearing test
      or human regeneration claim.
    evidence:
    - reference: PMID:39610699
      reference_title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      snippet: We found that 1 h exposure to 200 μM gentamicin was sufficient to cause damage comparable to that seen with neomycin if animals were incubated an additional 23 h in fresh medium
      explanation: >-
        Delayed whole-larva sensory-cell injury after washout.
    readouts:
    - name: Hair-cell survival after gentamicin washout
      target: Cochlear Hair Cell Loss
      direction: DECREASED
      description: >-
        Delayed loss despite removal of extracellular drug after one hour.
      evidence:
      - reference: PMID:39610699
        reference_title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        quote_role: PRIMARY_RESULT
        snippet: We found that 1 h exposure to 200 μM gentamicin was sufficient to cause damage comparable to that seen with neomycin if animals were incubated an additional 23 h in fresh medium
        explanation: >-
          Observed survival endpoint.
  evidence:
  - reference: PMID:39610699
    reference_title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: Experiments were conducted on 5–8 dpf (days postfertilization) larval zebrafish.
    explanation: >-
      Whole-organism model scope.
  - reference: PMID:39610699
    reference_title: Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    snippet: By contrast we observed no protection against 100 or 200 μM G418 using the 1+23 h exposure paradigm
    explanation: >-
      Limits transfer of the acute mitoTEMPO-sensitive pathway to delayed injury.
  notes: >-
    GPN altered intracellular distribution without lowering total fluorescent uptake, whereas bafilomycin
    reduced uptake and confounded a purely downstream lysosomal interpretation. Labeling efficiency
    prevented absolute between-drug concentration comparisons. Lysosomal membrane permeabilization,
    ferroptosis and pyroptosis were not established mediators. Calcium necessity/sufficiency was supported
    by cited prior work, not a new universal test in this study.
clinical_trials:
- name: NCT04105205
  phase: PHASE_I
  description: >-
    First-in-human single-ascending-dose apramycin safety, tolerability and pharmacokinetic study in
    healthy volunteers. The published analysis included 40 participants, of whom 30 received active
    drug. This is contextual antibiotic development, not a trial demonstrating prevention of hearing
    loss in MT-RNR1 carriers.
  evidence:
  - reference: clinicaltrials:NCT04105205
    reference_title: A Phase I, Randomized, Double-blind, Placebo-controlled, Single Ascending Dose Study to Assess the Safety, Tolerability, and Pharmacokinetics of Apramycin Administered Intravenously in Healthy Adults.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: This is a first-in-human study to assess the safety, tolerability and pharmacokinetics of escalating single doses of apramycin.
    explanation: >-
      Registry summary establishes trial scope.
  - reference: PMID:35849148
    reference_title: Population pharmacokinetics of apramycin from first-in-human plasma and urine data to support prediction of efficacious dose.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    snippet: A total sample size of 40 subjects were enrolled in the trial and consecutively grouped into five sequential dose cohorts
    explanation: >-
      Small healthy-volunteer study; no carrier-specific otoprotection endpoint.
  notes: >-
    The published pharmacokinetic dose projections are not clinical efficacy results. Active-drug participants
    were predominantly male and White. Lower preclinical ototoxicity does not establish apramycin safety
    in inherited susceptibility.

📚

References & Deep Research

References

PMID:20301595

Nonsyndromic Hearing Loss and Deafness, Mitochondrial.

1 finding

GeneReviews indexed summary covers maternal inheritance, hearing manifestations, rehabilitation and counseling; the full NBK1422 chapter was also reviewed.

PMID:17698299

Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation in three Han Chinese pedigrees.

1 finding

Three C1494T maternal pedigrees show variable hearing phenotypes with and without exposure; high-frequency involvement is directly described in WZD101.

PMID:34015383

Prevalence of aminoglycoside-induced hearing loss in drug-resistant tuberculosis patients: A systematic review.

1 finding

Genetically unselected tuberculosis-treatment systematic review is contextual drug-toxicity evidence, not prevalence of inherited susceptibility.

PMID:34032273

Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype.

1 finding

CPIC supplies variant-specific prescribing precautions, absence of a safe heteroplasmy threshold, limits of negative tests and prior tolerance, and monitoring when treatment is unavoidable.

PMID:37314952

Clinical Pharmacogenomic MT-RNR1 Screening for Aminoglycoside-Induced Ototoxicity and the Post-Test Counseling Conundrum.

1 finding

Pharmacogenetic counseling perspective provides context for communicating susceptibility rather than diagnosing inevitable deafness.

PMID:22223843

Hearing in 44-45 year olds with m.1555A>G, a genetic mutation predisposing to aminoglycoside-induced deafness: a population based cohort study.

1 finding

British cohort carrier frequency was 19/7350; midlife hearing assessment did not record aminoglycoside exposure or establish lifetime penetrance.

PMID:35311942

Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care.

1 finding

PALOH established bedside workflow and prescribing change, with test failures and wide carrier-sensitivity uncertainty; it did not compare permanent hearing outcomes.

PMID:18308926

Mitochondrial deafness alleles confer misreading of the genetic code.

1 finding

Human-sequence bacterial hybrid ribosomes distinguish intrinsic decoding errors from protein output and drug-exacerbated miscoding.

PMID:16826519

Mutation in TRMU related to transfer RNA modification modulates the phenotypic expression of the deafness-associated mitochondrial 12S ribosomal RNA mutations.

1 finding

Selected TRMU A10S modifier families and lymphoblast assays; generated PMC1559489 full text establishes absent drug exposure and assay-specific findings.

PMID:28049726

Biochemical Evidence for a Nuclear Modifier Allele (A10S) in TRMU (Methylaminomethyl-2-thiouridylate-methyltransferase) Related to Mitochondrial tRNA Modification in the Phenotypic Manifestation of Deafness-associated 12S rRNA Mutation.

1 finding

Selected modifier lymphoblast and recombinant-protein study; generated PMC5314183 full text distinguishes tRNA modification, protein abundance, respiration and assay-specific ATP.

PMID:10915767

A biochemical basis for the inherited susceptibility to aminoglycoside ototoxicity.

1 finding

Abstract-only primary paromomycin study in family lymphoblasts; comparative translation-rate ratios support cellular susceptibility at a high experimental concentration.

PMID:22121370

Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection.

1 finding

Full review supplies general aminoglycoside entry and hair-cell injury biology while explicitly identifying the incomplete mitochondrial-genotype link.

PMID:19104050

Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity.

1 finding

Canonical abstract plus generated PMC2634874 full text supply gentamicin footprinting and mutant hybrid-ribosome susceptibility.

PMID:39610699

Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action.

1 finding

Whole-larva zebrafish study separates acute and delayed drug injury and identifies limits of mitochondrial-antioxidant and lysosomal-perturbation interpretations.

PMID:40842562

Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms.

1 finding

Mouse cochlear explants separate RIPOR2 movement from phosphatidylserine exposure; no new living-animal hearing rescue or human MT-RNR1 experiment.

PMID:22699498

Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin.

1 finding

Hybrid-ribosome, explant and guinea-pig comparisons show lower experimental apramycin ototoxicity without proving human carrier safety.

PMID:25155176

Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants.

1 finding

Preterm-neonate cohort links genotype/exposure to failed screening in a small carrier subset, not a validated estimate of permanent hearing loss.

PMID:35849148

Population pharmacokinetics of apramycin from first-in-human plasma and urine data to support prediction of efficacious dose.

1 finding

Healthy-volunteer phase I apramycin pharmacokinetics; simulated efficacy targets are not observed infection or carrier hearing outcomes.

PMID:42524757

MT-RNR1 genotype testing for preventing aminoglycoside-mediated ototoxicity: A guideline developed by the UK Centre of Excellence in Regulatory Science and Innovation in Pharmacogenomics (CERSI-PGx).

1 finding

2026 UK CERSI-PGx testing guidance extends beyond CPIC interpretation, including urgent-treatment timing, confirmatory testing, family communication and vaccine advice.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1422/

Nonsyndromic Hearing Loss and Deafness, Mitochondrial - GeneReviews® - NCBI Bookshelf

1 finding

Full GeneReviews scientific chapter read for clinical variability, differential diagnosis, molecular diagnosis, counseling, rehabilitation and surveillance; broader MT-TS1 features are outside this entry.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634874/

Genetic analysis of interactions with eukaryotic rRNA identify the mitoribosome as target in aminoglycoside ototoxicity - PMC

1 finding

Genuine full text of PMID19104050, used for chemical-footprinting and translation experiments.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1559489/

Mutation in TRMU Related to Transfer RNA Modification Modulates the Phenotypic Expression of the Deafness-Associated Mitochondrial 12S Ribosomal RNA Mutations - PMC

1 finding

Genuine full text of PMID16826519, used for family ascertainment, absence of drug exposure and tRNA/protein-labeling assays.

url:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5314183/

1 finding

Genuine full text of PMID28049726, used for non-isogenic design and thermal-stability, respiration, ATP and oxidant-assay limits.

url:https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf

https://files.cpicpgx.org/data/guideline/publication/aminoglycosides/2021/34032273-supplement.pdf

1 finding

CPIC supplemental methods and variant-evidence table, including the October 2025 correction; heteroplasmy reporting does not imply a safe clinical threshold.

clinicaltrials:NCT04105205

A Phase I, Randomized, Double-blind, Placebo-controlled, Single Ascending Dose Study to Assess the Safety, Tolerability, and Pharmacokinetics of Apramycin Administered Intravenously in Healthy Adults.

1 finding

Canonical registry summary identifies a first-in-human apramycin single-dose safety and pharmacokinetic study.

Deep Research

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Review inherited aminoglycoside hearing-loss susceptibility and evidence scope · 2026-09-21T08:42:34Z · View source

Read all original cited sources and matching deep research, recovered the full GeneReviews chapter and genuine full experimental articles, and reviewed current CPIC/CERSI guidance plus PALOH. Replaced inevitable drug-triggered deafness and a direct universal oxidative-death chain with variant-specific susceptibility, distinct decoding-accuracy and synthesis nodes, and explicitly hypothetical cochlear bioenergetic links. Corrected carrier-versus-disease prevalence, selected-cohort screening endpoints, TRMU modifier scope, genotype testing and surveillance, and experimental model limitations. Added contextual phase I apramycin evidence without claiming carrier safety. Peer audits independently checked CPIC/PALOH and the new fish/explant studies. Reference caches were generated through fetch-reference; no frozen dataset cache was accessed. Authoritative schema/term/snippet validation and repository quality gates are recorded with the review PR.

Review response: CPIC guideline, structured variants, model mismatch · 2026-08-27T15:16:09Z · View source

Response to the first review round. Added the CPIC guideline PMID:34032273, which the entry needed and which the deep-research artifact's own Key Caveats for Curators had told me to cite - the one explicit curation instruction in that section I had not followed. It now carries the prescribing recommendation itself and the cascade-to-the-matriline sentence on the avoidance treatment. Added a structured variants list to the MT-RNR1 genetic entry covering m.1555A>G, m.1494C>T and m.1095T>C; the third is CPIC-actionable and was absent entirely, which made the actionable-variant list incomplete for prescribing, and the variants slot had been left unused so nothing was machine-queryable by variant. Added a HUMAN_MODEL_MISMATCH discussion explaining why the entry carries no animal model: the lesion makes a human mitochondrial rRNA resemble a bacterial one, species diverge at that sequence, and the research sweep did not surface a knock-in line reproducing the genotype-specific susceptibility - phrased as a limit of the search rather than a demonstrated absence. Added a notes sentence recording that vestibulotoxicity is deliberately out of scope as drug- and dose-dependent toxicity. 27/27 snippets verified and independently re-checked as raw substrings.

Claude Code ▸

Aminoglycoside-Induced Hearing Loss (AIHL) — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 42 citations 2026-08-27T14:24:25.412309

Aminoglycoside-Induced Hearing Loss (AIHL) — Comprehensive Research Report

1. Disease Information

Overview. Aminoglycoside-induced hearing loss (AIHL) is a form of ototoxic, mitochondrially-mediated sensorineural hearing loss (SNHL) that occurs when a person carrying a pathogenic variant in the mitochondrial 12S rRNA gene MT-RNR1 is exposed to aminoglycoside antibiotics (gentamicin, tobramycin, amikacin, streptomycin, kanamycin, neomycin). In susceptible individuals the hearing loss can be triggered by even a single, therapeutic-dose exposure and is typically bilateral, severe-to-profound, and irreversible. A separate, dose/duration-dependent form of ototoxicity also occurs in the general population (without a known MT-RNR1 variant) after cumulative or prolonged aminoglycoside courses, e.g., in cystic fibrosis (CF) or multidrug-resistant tuberculosis (MDR-TB) treatment.

Key identifiers: - OMIM: #580000 — DEAFNESS, AMINOGLYCOSIDE-INDUCED (OMIM.org) - Gene: MT-RNR1 (mitochondrial 12S rRNA), maternally inherited - GeneReviews: "Nonsyndromic Hearing Loss and Deafness, Mitochondrial" (PMID: 20301595) - ClinVar: RCV000010254/RCV000010255 (m.1555A>G); RCV001449811/RCV000010263 (m.1494C>T) - MeSH/ICD: classified under drug-induced/toxic sensorineural hearing loss (ICD-10 H91.0 Ototoxic hearing loss); MONDO term to be confirmed against the local MONDO release - Suggested MONDO search terms: "aminoglycoside-induced hearing loss," "aminoglycoside otototoxicity," "maternally inherited nonsyndromic hearing loss and deafness"

Synonyms: Aminoglycoside-induced deafness; maternally inherited aminoglycoside ototoxicity; MT-RNR1-related susceptibility to aminoglycoside ototoxicity; nonsyndromic mitochondrial deafness with aminoglycoside sensitivity.

Evidence base: Predominantly aggregated disease-level literature — pedigree studies of maternally-transmitted deafness (Prezant et al. 1993; Hutchin et al. 1993, foundational reports establishing MT-RNR1 m.1555A>G), population cohort studies (UK Biobank-linked cohort, PMID: 22223843), systematic reviews of ototoxicity in TB/CF populations, and structured pharmacogenomic guidance (CPIC). Individual EHR-level data exist mainly through CF and TB ototoxicity cohort studies.

2. Etiology

Disease Causal Factors

AIHL has two overlapping causal mechanisms: 1. Genetic (Mendelian/mitochondrial) susceptibility: A maternally inherited, usually homoplasmic, pathogenic variant in MT-RNR1 (12S rRNA) that structurally mimics bacterial 16S rRNA, allowing aminoglycosides to bind and disrupt mitochondrial ribosomal protein synthesis in cochlear hair cells upon drug exposure ("two-hit" gene-environment model). This is the classic Mendelian entry represented by OMIM #580000. 2. Non-genetic/dose-dependent ototoxicity: Cumulative aminoglycoside exposure (total dose, duration, peak/trough serum levels, concurrent nephrotoxicity) causes ototoxicity in genetically unselected patients, especially with repeated courses (CF, MDR-TB).

Genetic Risk Factors

MT-RNR1 m.1555A>G — the most common and best-characterized variant; population prevalence ~1 in 500 (UK) to 0.19–1.8% globally, with marked founder-effect enrichment in some populations (e.g., 20.2% in Buryat individuals of the Baikal Lake region, PMID pending; PMC: 11222474). Penetrance of hearing loss with aminoglycoside exposure is considered near-100% for homoplasmic carriers.
MT-RNR1 m.1494C>T — second most common variant, homoplasmic, reported in >20 Asian and 2 Spanish probands; average penetrance ~18% (range 0–77%) in the absence of documented aminoglycoside exposure, rising sharply with exposure.
MT-RNR1 m.1095T>C — third variant flagged by CPIC as high-risk.
Rarer variants at position 961 (961delT+Cn insertion, 961T>C) are also associated with nonsyndromic hearing loss with and without aminoglycoside exposure.
Nuclear modifier genes: TRMU (mitochondrial tRNA-modifying enzyme; A10S missense variant) modulates penetrance of m.1555A>G/m.1494C>T-associated deafness in Arab-Israeli, European, and Chinese pedigrees. Secondary mitochondrial variants (e.g., m.4394C>T tRNA-Gln, m.1584A m62A rRNA methylation site) have also been proposed as penetrance modifiers (PMC: 9602358; HMG: 617880).

Environmental/Clinical Risk Factors

Aminoglycoside class, dose, duration, and route (systemic vs. topical/otic) — cumulative dose is the dominant driver of non-genetic ototoxicity (CF cohorts: 4.5× higher odds of hearing loss with higher cumulative dosing).
Renal impairment (reduced clearance → higher serum trough levels).
Concurrent ototoxic drugs (loop diuretics, cisplatin/platinum chemotherapy, vancomycin).
Advanced age, pre-existing renal or hepatic dysfunction, prolonged treatment duration (TB regimens of 6–12 months show near-universal hearing loss in some series).
Noise exposure may synergize in genetically susceptible carriers even without drug exposure.

Protective Factors

Absence of the MT-RNR1 risk variant (genotype-guided antibiotic selection).
Use of alternative, non-ototoxic antimicrobials when genotype-positive.
Emerging "designer aminoglycosides" engineered to spare the mitochondrial ribosome (see Treatment/Prevention, §12–13).
Investigational otoprotectants (see below) — evidence base currently strongest for cisplatin, not aminoglycosides.

Gene-Environment Interaction

This is the defining feature of AIHL: the MT-RNR1 variant alone is often clinically silent (or produces only mild, late-onset, non-progressive/age-related hearing loss); the drug exposure is the "second hit" that converts genetic susceptibility into acute, severe, irreversible deafness. CPIC (2021, updated 2023) formalizes this as a pharmacogenomic gene-drug interaction (see §12).

3. Phenotypes

Phenotype	Type	Onset/Course	Frequency	Suggested HPO term
Bilateral sensorineural hearing loss	Clinical sign	Acute (hours–days) to subacute after exposure; can occur after a single dose in genotype-positive individuals	Near 100% penetrance in homoplasmic m.1555A>G + exposure; ~18% baseline for m.1494C>T without exposure	HP:0000407 (Sensorineural hearing impairment)
High-frequency-predominant hearing loss	Clinical sign / audiometric finding	Earliest detectable change (as soon as 4h post-treatment by high-frequency audiometry), progressing base-to-apex to affect speech frequencies	Common; a base-to-apex cochlear damage gradient is well documented	HP:0008625 (High-frequency sensorineural hearing impairment)
Progressive, severe-to-profound deafness	Clinical course	Progressive over days–weeks; permanent	Majority of homoplasmic-variant + exposure cases	HP:0008625; HP:0001730 (Progressive hearing impairment)
Tinnitus	Symptom	Subacute/chronic, often precedes or accompanies threshold shift	Frequently reported in cochleotoxicity monitoring	HP:0000360 (Tinnitus)
Vestibulotoxicity — gait ataxia, oscillopsia, dizziness, nystagmus	Clinical sign	Subacute bilateral vestibulopathy, may develop in parallel with cochleotoxicity	Variable, drug- and dose-dependent (higher with streptomycin/gentamicin)	HP:0002066 (Gait ataxia); HP:0000615 (Oscillopsia); HP:0002321 (Vertigo)
Multiorgan mitochondrial features (rare)	Systemic	Variable	Reported in some m.1555A>G carriers with syndromic presentations (PMC: 7015579)	context-dependent

Quality of life impact: Profound bilateral SNHL in infancy/early childhood (the population most likely to receive gentamicin for suspected sepsis) has major, well-documented effects on language acquisition, education, and social development; adult-onset cases affect communication, employment, and mental health, consistent with general SNHL QoL literature (EQ-5D/SF-36 not disease-specific for AIHL).

4. Genetic/Molecular Information

Causal gene: MT-RNR1 (mitochondrially encoded 12S rRNA), OMIM *561000; the deafness phenotype is OMIM #580000.

Key pathogenic variants (all mitochondrial, maternally inherited): | Variant | Classification | Notes | |---|---|---| | m.1555A>G | Pathogenic (ClinVar RCV000010254/255) | Most common; homoplasmic; near-complete penetrance with aminoglycoside exposure; population frequency ~0.1–1.8% depending on cohort/region | | m.1494C>T | Pathogenic (ClinVar RCV001449811/RCV000010263) | Second most common; incomplete penetrance (avg. ~18%, up to 77% in some pedigrees) | | m.1095T>C | Pathogenic, CPIC-flagged | Rarer | | m.961delT+Cn / m.961T>C | Associated, variable evidence | Reported with and without aminoglycoside exposure | | m.7444G>A (MT-CO1) | Co-segregating secondary variant | Reported alongside m.1555A>G in a 3-generation Chinese family, may modify phenotype |

Zygosity/heteroplasmy: These variants are typically found in the homoplasmic state in affected pedigrees; CPIC (2021) explicitly states there is not yet sufficient evidence to define a heteroplasmy threshold below which aminoglycoside use is safe, so any detectable variant is treated per the homoplasmic guidance.

Functional consequence: Gain-of-susceptibility, not a classic loss-of-function — the base substitution creates a new base pair at the terminus of the penultimate stem of the 12S rRNA decoding site, structurally converting it toward the ancestral bacterial-type 16S rRNA conformation. This increases the aminoglycoside-binding pocket, permitting aminoglycoside binding to the mitochondrial ribosome much as it would bind a bacterial ribosome, inhibiting mitochondrial protein synthesis in cochlear tissue.

Modifier genes: - TRMU (mitochondrial tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase) — nuclear-encoded modifier; the A10S variant increases penetrance of MT-RNR1-associated deafness. - Secondary mtDNA variants (m.4394C>T tRNA-Gln, m.1584 12S rRNA methylation site) proposed as additional modifiers of clinical expressivity.

Population/allele frequency resources: gnomAD (mitochondrial variant server) and MITOMAP catalog m.1555A>G and m.1494C>T frequencies across populations; GeneReviews Table 2 provides population-stratified prevalence of m.1555A>G (NCBI Bookshelf NBK1422).

Suggested gene/molecular ontology bindings: HGNC gene symbol MT-RNR1 (mitochondrial, note standard HGNC/NCBI Gene entry applies; dismech convention uses lowercase hgnc: CURIEs for nuclear genes — MT-RNR1 is mitochondrially encoded and may require special handling per dismech's mitochondrial-gene conventions).

5. Environmental Information

Primary environmental/pharmacologic trigger: Systemic aminoglycoside antibiotic exposure — gentamicin, tobramycin, amikacin, streptomycin, kanamycin, neomycin, and (in TB regimens) capreomycin/viomycin (technically cyclic peptides with similar ribosomal mechanism).
Clinical contexts of exposure: Neonatal suspected sepsis (empiric gentamicin), CF pulmonary exacerbations (inhaled/IV tobramycin prophylaxis every 3–4 months), MDR-TB intensive-phase injectable regimens (kanamycin, amikacin, capreomycin), and historically streptomycin for various infections.
Non-infectious environmental modifiers: Concurrent noise exposure may act synergistically with genetic susceptibility (reported in some m.1555A>G pedigrees even absent drug exposure) — supports possible G×E beyond drug exposure alone.
No infectious-agent etiology — this is a drug-toxicity disorder, though the underlying illness prompting aminoglycoside use (sepsis, TB, CF pulmonary infection) is itself infectious in most cases; the ontology ECTO "aminoglycoside antibiotic exposure" or an equivalent drug-exposure term is the appropriate environmental/exposure binding, not a pathogen taxon.

6. Mechanism / Pathophysiology

Causal chain (genotype-positive form): 1. Trigger: Systemic aminoglycoside administration in a carrier of a pathogenic MT-RNR1 variant (m.1555A>G most common). 2. Molecular lesion: The variant reconfigures the 12S rRNA decoding-site conformation to resemble bacterial 16S rRNA, permitting high-affinity aminoglycoside binding within the mitochondrial ribosome's small subunit. 3. Mitochondrial protein synthesis inhibition: Aminoglycoside binding at the decoding site causes mistranslation/inhibition of mitochondrially-encoded OXPHOS subunit synthesis, analogous to bacterial ribosome inhibition. 4. Mitochondrial dysfunction in cochlear hair cells: Disrupted protein synthesis leads to impaired oxidative phosphorylation, mitochondrial membrane potential collapse, and generation of reactive oxygen species (ROS). 5. Downstream cell-death signaling: ROS and stress-kinase activation (notably c-Jun N-terminal kinase, JNK) amplify mitochondrial injury; cytochrome c release triggers caspase-9 → caspase-3 activation (intrinsic apoptotic pathway). Calcium flux from the endoplasmic reticulum via IP3 receptors into mitochondria is a key acute step (documented in zebrafish lateral-line hair cells). 6. Distinct temporal/mechanistic pathways by drug: Neomycin exposure causes rapid (within ~1h) hair cell death associated with acute mitochondrial calcium flux (attenuated by the mitochondria-targeted antioxidant mitoTEMPO); gentamicin causes delayed (up to 24h) hair cell death via calcium-independent pathways (PMC: 11602426). 7. Cell death mechanisms beyond classical apoptosis: Necroptosis has also been implicated alongside apoptosis in aminoglycoside- and cisplatin-induced ototoxicity; RIPOR2 translocation and phosphatidylserine externalization occur via mechanistically distinct pathways from canonical apoptosis (PMC: 12364911). 8. Anatomical gradient: Cochlear damage follows a base-to-apex gradient — basal-turn (high-frequency-encoding) outer hair cells are damaged first and are most vulnerable, explaining the characteristic high-frequency-first audiometric pattern; inner hair cells appear especially vulnerable at low, non-antibacterial concentrations relevant to hidden hearing loss. 9. Clinical manifestation: Irreversible bilateral sensorineural hearing loss, high-frequency-predominant progressing to lower frequencies, ± tinnitus and vestibulotoxicity.

Cellular processes involved: Mitochondrial protein synthesis inhibition (GO:0032543, mitochondrial translation), oxidative stress response (GO:0006979/0034599), intrinsic apoptotic signaling (GO:0097193), regulated necrosis/necroptosis, calcium-mediated signaling between ER and mitochondria.

Protein/molecular target: MT-RNR1 12S rRNA decoding site of the mitochondrial small ribosomal subunit (28S) — a structural/RNA target rather than a protein per se.

Cell types involved: Cochlear outer hair cells (basal turn preferentially) and inner hair cells, spiral ganglion neurons (secondary degeneration), vestibular hair cells (type I/II) for the vestibulotoxic phenotype.

Suggested ontology terms: - GO: GO:0032543 (mitochondrial translation), GO:0006915 (apoptotic process), GO:0070997 (neuron death), GO:0055074 (calcium ion homeostasis), GO:0034599 (cellular response to oxidative stress) - CL: CL:0000601 (outer hair cell), CL:0000598 (inner hair cell), CL:0000101 (sensory neuron; for spiral ganglion neurons), CL:0000211 (vestibular hair cell where applicable) - CHEBI: CHEBI:41000 (aminoglycoside antibiotic) or specific drugs — CHEBI:17833 (gentamicin), CHEBI:28864 (tobramycin), CHEBI:2637 (amikacin), CHEBI:9334 (streptomycin)

Molecular profiling data: Direct disease-specific transcriptomic/proteomic/metabolomic datasets in humans are limited (ototoxicity research relies heavily on animal/organoid models); zebrafish lateral-line and mouse cochlear explant transcriptomic studies of aminoglycoside exposure are available in GEO but are model-system, not human-tissue, datasets.

7. Anatomical Structures Affected

Organ level: Inner ear (cochlea — primary; vestibular labyrinth — secondary/vestibulotoxicity). Systemic aminoglycoside toxicity also affects the kidney (nephrotoxicity) as a parallel, mechanistically related but anatomically distinct toxicity — relevant as a comorbid risk marker (nephrotoxicity often co-occurs and can indicate cumulative exposure).
Tissue/cell level: Organ of Corti sensory epithelium — outer hair cells (basal turn first), inner hair cells, supporting cells (Deiters', pillar cells), spiral ganglion neurons (stria vascularis less directly implicated than in some other ototoxic mechanisms); vestibular sensory epithelium (crista ampullaris, maculae) hair cells for the vestibular phenotype.
Subcellular level: Mitochondria (site of 12S rRNA target and ROS generation), endoplasmic reticulum (calcium release via IP3 receptors), cytosol (caspase cascade execution).
Localization/laterality: Bilateral and typically symmetric.

Suggested UBERON terms: UBERON:0001846 (cochlea), UBERON:0005988 (organ of Corti), UBERON:0009663 (spiral ganglion), UBERON:0001824 (vestibular organ), UBERON:0000362 (mitochondrion is GO cellular component, not UBERON — use GO:0005739 for mitochondrion instead).

8. Temporal Development

Onset: Can occur at any age when aminoglycoside is administered; clinically most consequential in neonates (empiric gentamicin for suspected sepsis) and in patients receiving prolonged/repeated courses (CF, MDR-TB). Onset relative to drug exposure is acute-to-subacute: earliest detectable ultra-high-frequency threshold shifts within hours (as early as 4h post-treatment in monitoring studies); clinically apparent hearing loss can appear within days to a few weeks of exposure.
Progression: Once triggered, hearing loss is typically progressive over days to weeks, following a base-to-apex cochlear gradient (high frequencies affected first, then progressively lower/speech frequencies). It then stabilizes as permanent, non-progressive residual deafness once the ototoxic insult resolves (unlike some other genetic SNHL that continues to progress with age).
Disease course pattern: Not relapsing-remitting — a single triggering exposure produces a step-wise, largely irreversible threshold shift. Genetically susceptible carriers not exposed to aminoglycosides may still show mild, later-onset, more gradual hearing decline in some pedigrees (independent low-penetrance expression), distinct from the acute triggered form.
Critical windows for intervention: The period between first aminoglycoside dose and onset of measurable ototoxicity (hours to days) is the key window for early detection (serial high-frequency/ultra-high-frequency audiometry, otoacoustic emissions) and for genotype-based pre-exposure avoidance (point-of-care testing before/at time of first dose, see §10, §13).

9. Inheritance and Population

Inheritance pattern: Maternal (mitochondrial) inheritance — MT-RNR1 variants are transmitted exclusively through the maternal line; male carriers do not transmit the variant to offspring.

Penetrance: - m.1555A>G: near-complete (approaching 100%) for hearing loss when a homoplasmic carrier receives aminoglycosides; lower baseline penetrance without exposure, historically reported 28%, 20%, 15% across different pedigree analyses when aminoglycoside-induced cases are included/excluded. - m.1494C>T: average penetrance ~18% (range 0–77%) across families, strongly modified by aminoglycoside exposure history and by nuclear modifier genes (e.g., TRMU).

Expressivity: Variable — ranges from no detectable hearing loss (silent carriers without exposure) to profound congenital-onset deafness, influenced by modifier genes, heteroplasmy (where present), and environmental co-factors (noise, drug exposure).

Genetic anticipation: Not a recognized feature (this is not a repeat-expansion disorder).

Founder effects: Strong founder effect documented in the Buryat population of the Baikal Lake region of Russia (m.1555A>G prevalence 20.2% vs. 1.3% in surrounding Russian population) — PMC: 11222474 / Sci Rep s41598-024-66254-z. Founder enrichment also reported in some Spanish, Chinese, and Arab-Israeli pedigrees.

Carrier/population frequency: - UK general population: ~0.26% (~1 in 385–500) for m.1555A>G. - European general population: ~0.19%. - Global pooled estimate (enriched cohorts, hearing-loss-ascertained): ~1.8% (863/47,328) — likely an overestimate of true general-population frequency due to ascertainment bias. - Wide regional variation, up to 20%+ in isolated founder populations.

Population demographics: - No strong sex bias in mitochondrial transmission itself (both sexes can be affected equally since inheritance is maternal but penetrance is independent of the child's sex); clinical exposure risk (e.g., neonatal sepsis treatment) is population-wide. - Geographic/ethnic enrichment as above (Han Chinese, Spanish, Arab-Israeli, Buryat/Siberian populations disproportionately represented in the literature for specific variants). - Age distribution of clinical presentation skews toward populations with high aminoglycoside exposure: neonates (NICU sepsis treatment), children/young adults with CF, and TB patients of any age receiving injectable second-line regimens.

Epidemiology of ototoxicity in exposed populations (non-genotype-specific dose-dependent toxicity): - CF: prevalence of SNHL 0–57% depending on cohort/definition; 3–24% with <10 IV aminoglycoside doses, rising to 40–44% with >10 doses (recurrent exposure); cumulative dose associated with 4.5× higher odds of hearing loss; adult CF prevalence up to 59%. - TB: incidence ranges from 3.2% in early-phase standard therapy up to near-universal with prolonged (6–12 month) treatment; MDR-TB incidence of ototoxicity ~22.9% in one cohort; a meta-analysis found pooled prevalence of ototoxic hearing loss of ~40.6% across drugs, with kanamycin highest at ~49.65% (J Infect systematic review, PMID: 34015383).

10. Diagnostics

Clinical/audiologic tests: - Pure-tone audiometry (standard + extended high-frequency/ultra-high-frequency audiometry, which detects the earliest threshold shifts before speech-frequency involvement). - Otoacoustic emissions (OAEs, especially distortion-product OAEs) for early, pre-symptomatic monitoring, particularly in infants and non-verbal patients. - Serial audiometric monitoring protocols are standard of care during prolonged aminoglycoside courses (CF, TB) to detect ototoxicity early and allow dose adjustment/discontinuation. - Newborn hearing screening (universal newborn hearing screening programs) — m.1555A>G has been specifically studied as a risk factor for failed newborn hearing screening in preterm infant cohorts (PMC: 4236616).

Genetic testing: - Targeted MT-RNR1 variant testing (m.1555A>G, m.1494C>T, m.1095T>C at minimum, per CPIC) — via standard clinical mtDNA sequencing/genotyping panels or dedicated hearing-loss gene panels. - Rapid point-of-care genotyping: The Genedrive MT-RNR1 ID Kit provides m.1555A>G genotyping in ~26 minutes with reported 100% sensitivity/specificity in preclinical validation, enabling real-time avoidance of gentamicin in NICU settings before first dose (the PALOH trial, PMC: 8211036 and PMC: 8938898). Deployed at Manchester University NHS Foundation Trust and now expanding to 14 NHS neonatal units across England, Scotland, Wales, and Northern Ireland (2024–2025 rollout). - Non-invasive prenatal MT-RNR1 pharmacogenetic testing is under active investigation (2026 medRxiv preprint) as a means of identifying at-risk neonates before birth. - Whole mitochondrial genome sequencing can identify rarer/novel MT-RNR1 variants and co-segregating secondary mtDNA variants (e.g., m.7444G>A, m.4394C>T) beyond the three CPIC-actionable variants.

Clinical criteria / differential diagnosis: Diagnosis relies on temporal association between aminoglycoside exposure and new-onset bilateral high-frequency-predominant SNHL, ideally confirmed by pre/post-exposure audiometric comparison; differential diagnosis includes other causes of SNHL (congenital, noise-induced, presbycusis, other syndromic/nonsyndromic genetic deafness, autoimmune inner ear disease) which the genetic test and exposure history help exclude/confirm.

Screening: CPIC and NHS guidance effectively function as a pharmacogenomic screening recommendation — genotype before first aminoglycoside exposure wherever feasible (especially neonatal/NICU and CF/TB populations with anticipated repeated courses).

11. Outcome/Prognosis

Reversibility: Hearing loss from AIHL, once established, is generally permanent and irreversible — this is a defining clinical feature distinguishing it from some other forms of drug ototoxicity.
Severity spectrum: Ranges from mild high-frequency threshold shifts (often subclinical, detected only by extended high-frequency audiometry) to bilateral profound deafness.
Functional/QoL impact: Congenital or early-childhood-onset profound deafness (as in genotype-positive neonates exposed to gentamicin) carries major lifelong implications for language development, education, and psychosocial functioning unless mitigated by early intervention (hearing aids, cochlear implantation, sign language/communication support).
Complications: Concurrent vestibulotoxicity contributes to falls risk, gait instability, and oscillopsia, compounding functional impact, especially in adults.
Mortality: Not directly disease-related; mortality risk in this population is driven by the underlying infection requiring aminoglycoside therapy (sepsis, MDR-TB), not by the ototoxicity itself.
Prognostic factors: Genotype (homoplasmic MT-RNR1 pathogenic variant = near-certain severe outcome with exposure), cumulative dose, concurrent nephrotoxicity/renal impairment (reduces drug clearance, raising exposure), and early detection/discontinuation of the ototoxic agent.

12. Treatment

There is no reversal treatment for established AIHL; management is preventive (avoidance, monitoring, dose optimization) and rehabilitative once hearing loss has occurred.

Pharmacogenomics (CPIC): The Clinical Pharmacogenetics Implementation Consortium (CPIC) published a formal guideline in 2021 (updated March 2023) — cpicpgx.org/guidelines/cpic-guideline-for-aminoglycosides-and-mt-rnr1:

Any individual carrying the m.1555A>G, m.1494C>T, or m.1095T>C variant should avoid aminoglycoside antibiotics unless the risk of permanent hearing loss is outweighed by the severity of the infection and lack of suitable alternatives. No heteroplasmy threshold has been established as "safe," so any detectable variant is managed as if homoplasmic. The 2023 update also addressed whether variant carriers should avoid vaccines manufactured using aminoglycosides (residual amounts are not considered clinically significant for this indication).

Rehabilitative/supportive care (NCIT terms suggested): - Hearing aids — NCIT:C50384 (Hearing Aid) or device-category equivalent. - Cochlear implantation — NCIT term for cochlear implant procedure (surgical intervention; suggest NCIT:C61509 Cochlear Implant or closest available surgical-device term). - Speech-language therapy — NCIT:C15302 (Physical Therapy)-adjacent; NCIT speech therapy term if available. - Genetic counseling — NCIT:C15240 (Genetic Counseling), critical given maternal transmission implications for family planning. - Audiologic monitoring/surveillance — NCIT:C25218 category (Clinical Intervention or Procedure), specific monitoring/audiometry term.

Avoidance/substitution strategy (primary "treatment" for genotype-positive individuals): substitution of non-aminoglycoside antimicrobials for suspected sepsis/infection when clinically appropriate — NCIT:C15986 (Pharmacotherapy) with a different therapeutic_agent.

Experimental/otoprotective strategies (evidence base still developing for aminoglycosides specifically): - Sodium thiosulfate — FDA-, EMA-, and MHRA-approved (2022–2023) as an otoprotectant, but specifically for cisplatin-induced ototoxicity in pediatric localized non-metastatic solid tumors (SIOPEL6 and COG ACCL0431 trials showed reduced hearing-loss incidence: 39% vs 68%, and 44% vs 58%, respectively). Not yet an approved indication for aminoglycoside ototoxicity, though mechanistic overlap (oxidative stress, ROS scavenging) makes it of research interest. - Mitochondria-targeted antioxidants (e.g., mitoTEMPO) — shown in zebrafish models to attenuate acute neomycin-induced hair cell death via mitigation of mitochondrial calcium flux; not yet in human trials for AIHL. - N-acetylcysteine and related antioxidants — investigated in CF and other cohorts as adjunctive otoprotection during aminoglycoside courses; evidence remains preliminary/mixed.

Designer aminoglycosides in development (address root cause by decoupling antibacterial activity from mitochondrial ribosome binding): - Apramycin — a 4-monosubstituted 2-deoxystreptamine aminoglycoside shown in guinea pig and cochlear explant models to have substantially lower ototoxicity than gentamicin while retaining potent activity against MDR pathogens including Mycobacterium tuberculosis; structural studies (3.5 Å resolution apramycin-ribosome complexes) provide a framework for further reduced-toxicity aminoglycoside design (PNAS: 10.1073/pnas.1204073109; PMC: 3390888, 6382871). - Gentamicin C1a — a specific gentamicin congener also identified as having lower ototoxicity and no evidence of "hidden hearing loss" in guinea pig round-window application studies. - ELX-02 — a synthetic, eukaryotic-ribosome-selective aminoglycoside-class "read-through" agent developed primarily for nonsense-mutation genetic diseases (e.g., CF); engineered to eliminate antibacterial activity and reduce nephro-/ototoxicity. Phase 1 trials showed no severe ototoxicity or nephrotoxicity signals across dose range 0.3–7.5 mg/kg.

Experimental clinical trials: Multiple registered trials on ClinicalTrials.gov address sodium thiosulfate otoprotection (mostly cisplatin-focused; e.g., NCT05129748, NCT04541355) and ELX-02 pharmacokinetics/safety (NCT03776539, NCT03309605). No large registered trial currently targets otoprotection specifically for genotype-positive AIHL beyond the genotyping-avoidance strategy itself (PALOH and related implementation trials).

13. Prevention

AIHL is one of the clearest examples of a primary-prevention-focused pharmacogenomic disorder — because the hearing loss is irreversible once triggered, prevention (avoiding the triggering exposure in genetically susceptible individuals) is the dominant clinical strategy, more so than treatment.

Primary prevention — genotype-guided prescribing: Pre-emptive or point-of-care MT-RNR1 genotyping before first aminoglycoside dose, especially in neonatal intensive care (NICU) settings where empiric gentamicin is common for suspected sepsis. The Manchester/NHS PALOH implementation trial demonstrated feasibility: 424/526 (80.6%) of eligible infants tested within the clinically actionable window using the Genedrive MT-RNR1 ID Kit (~26 min turnaround, 100% sensitivity/specificity in validation); identified variant carriers avoided aminoglycoside exposure entirely. This program is expanding to 14 NHS neonatal units UK-wide (2024–2025).
Screening — high-risk/repeated-exposure populations: Consider MT-RNR1 genotyping before starting long-term/repeated aminoglycoside regimens in CF and MDR-TB patients, in addition to serial audiometric monitoring throughout treatment.
Secondary prevention — early detection during ongoing therapy: Extended high-frequency/ultra-high-frequency audiometry and OAE monitoring at baseline and serially during aminoglycoside courses to detect subclinical threshold shifts before they progress into speech-frequency-affecting, functionally significant hearing loss; allows early drug discontinuation/dose adjustment.
Tertiary prevention: Once hearing loss occurs, prompt referral to audiology/otolaryngology for hearing aid fitting or cochlear implant evaluation, and early educational/communication intervention in pediatric cases to mitigate developmental impact.
Genetic counseling: Because inheritance is maternal, identification of an affected/carrier proband should prompt counseling and (ideally) cascade testing of maternal relatives, since all maternal-line relatives share the same variant and risk.
Non-invasive prenatal testing (emerging, 2026): Under active investigation as a way to identify at-risk MT-RNR1-carrier neonates before birth, allowing avoidance planning before any postnatal antibiotic exposure decision is needed.
Prescribing/stewardship policy: Clinical guideline bodies (CPIC; UK Genomics Education programs) now explicitly recommend genotype-informed antibiotic stewardship as formal policy, moving beyond individual clinician awareness to systematized point-of-care testing pathways.

14. Other Species / Natural Disease

No well-established naturally-occurring veterinary counterpart of MT-RNR1-mediated AIHL has been prominently reported in the literature surveyed (OMIA search recommended for confirmation); aminoglycoside ototoxicity itself is a recognized general veterinary drug-toxicity concern (e.g., in companion animals receiving aminoglycosides), but genotype-linked susceptibility analogous to human MT-RNR1 variants is not established as a common veterinary syndrome in the sources reviewed here.
The mitochondrial 12S rRNA target is deeply evolutionarily conserved (relationship to the bacterial 16S rRNA target is the entire basis of the mechanism), so cross-species susceptibility to aminoglycoside ototoxicity is a general pharmacological property of the drug class rather than being confined to genetically susceptible human carriers — this is why "designer aminoglycoside" research uses standard rodent (mouse, guinea pig) ototoxicity models even without introducing the human risk variant.
Note: This report did not identify strong evidence of natural (spontaneous) veterinary MT-RNR1-variant disease; recommend an OMIA database check during KB curation to confirm absence/presence before asserting a definitive negative.

15. Model Organisms

Zebrafish (lateral-line hair cells): Extensively used to dissect distinct temporal/mechanistic pathways of aminoglycoside-induced hair cell death — neomycin (rapid, ~1h, calcium-dependent via ER→mitochondria IP3-mediated calcium flux, rescued by mitoTEMPO) vs. gentamicin (delayed, up to 24h, calcium-independent) (PMC: 11602426, bioRxiv: 2024.05.30.596537). This model does not carry the human MT-RNR1 variant but demonstrates the general aminoglycoside-mitochondrial hair cell death mechanism and is used for mechanistic dissection and drug (designer-aminoglycoside/otoprotectant) screening.
Guinea pig (cochlear explant / in vivo chronic ototoxicity model): Used to compare ototoxicity profiles across aminoglycoside congeners — demonstrated gentamicin C1a and apramycin as substantially less ototoxic than standard gentamicin via round-window drug application and compound action potential/outer hair cell survival assays (PMC: 6382871).
Mouse (cochlear explants, in vivo dosing comparisons): Used to refine ototoxicity study protocols and compare different aminoglycoside dosing regimens in adult mice (Murillo-Cuesta et al., Lab Animals 2010).
Genotype-specific (MT-RNR1 variant knock-in) models: This search did not surface a well-established, widely-cited mouse or zebrafish knock-in line carrying the human m.1555A>G or m.1494C>T variant that recapitulates genotype-specific hypersensitivity; most mechanistic model-organism work uses wild-type animals to study general aminoglycoside ototoxicity pathways rather than modeling the specific human genetic susceptibility variant. This is a notable gap worth flagging in a knowledge-gap/discussion entry — direct modeling of the human-specific MT-RNR1 gain-of-susceptibility mutation in an animal ribosome is complicated by sequence divergence between species' mitochondrial rRNA.
Model limitations: Because the causal lesion is a single-nucleotide change in human mitochondrial 12S rRNA altering aminoglycoside binding affinity, and because most current animal ototoxicity models use wild-type (non-variant) rRNA, these models capture the general aminoglycoside-mitochondrial-ribosome-hair-cell-death mechanism well but do not directly recapitulate the human genotype-specific hypersusceptibility — this is a translational (human-model mismatch) gap appropriate for a HUMAN_MODEL_MISMATCH discussion entry in dismech curation, pending confirmation of whether a knock-in model has since been published.

Summary of Suggested Ontology Bindings for Curation

Category	Suggested term(s)
MONDO	(verify local release for exact ID; candidate labels: "aminoglycoside-induced hearing loss," "maternally-inherited nonsyndromic hearing loss and deafness")
OMIM	#580000
HPO	HP:0000407, HP:0008625, HP:0001730, HP:0000360, HP:0002066, HP:0000615, HP:0002321
GO (BP)	GO:0032543, GO:0006915, GO:0070997, GO:0034599, GO:0055074
CL	CL:0000601 (outer hair cell), CL:0000598 (inner hair cell), CL:0000211, CL:0000101
UBERON	UBERON:0001846 (cochlea), UBERON:0005988 (organ of Corti), UBERON:0009663 (spiral ganglion), UBERON:0001824 (vestibular organ)
CHEBI	CHEBI:17833 (gentamicin), CHEBI:28864 (tobramycin), CHEBI:2637 (amikacin), CHEBI:9334 (streptomycin), CHEBI:41000 (aminoglycoside antibiotic class)
NCIT (treatment)	NCIT:C15986 (Pharmacotherapy), NCIT:C15240 (Genetic Counseling), NCIT:C15747 (Supportive Care) + device/procedure terms for hearing aid/cochlear implant
Gene	MT-RNR1 (mitochondrial 12S rRNA)

Key Caveats for Curators

Snippet/quote verification required: This report synthesizes web-search summaries and secondary source excerpts; per dismech's evidence policy, every claim used in a KB entry must be re-verified with an exact quoted substring from the actual cached reference (PMID/OMIM/GeneReviews/CPIC) via just fetch-reference, not from this report's paraphrased summaries.
CPIC guideline citation: Cite the primary CPIC publication (2021, PMID needed — search PubMed directly for the exact PMID of "Clinical Pharmacogenetics Implementation Consortium Guideline for the Use of Aminoglycosides Based on MT-RNR1 Genotype") plus its March 2023 update supplement.
MONDO ID and precise HPO/GO term matches should be confirmed against the locally cached ontology versions before binding, per dismech's anti-hallucination term-validation workflow.
Founder-effect prevalence figures (Buryat 20.2%, etc.) and global pooled prevalence (1.8%) should be sourced to their specific primary publications (Scientific Reports 2024, PMC:11222474) rather than cited from this summary.

Sources: - NC_012920.1(MT-RNR1):m.1555A>G AND Mitochondrial non-syndromic sensorineural hearing loss - ClinVar - NC_012920.1(MT-RNR1):m.1555A>G AND Aminoglycoside-induced deafness - ClinVar - Clinical Pharmacogenomic MT-RNR1 Screening for Aminoglycoside-Induced Ototoxicity and the Post-Test Counseling Conundrum - PubMed - Gentamicin Therapy and MT-RNR1 Genotype - Medical Genetics Summaries - NCBI Bookshelf - Non-invasive Prenatal MT-RNR1 Pharmacogenetic Testing for the Prevention of Aminoglycoside-Induced Profound Hearing Loss - medRxiv - Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection - PubMed - Multiple mechanisms of aminoglycoside ototoxicity are distinguished by subcellular localization of action - PMC - Towards the Prevention of Aminoglycoside-Related Hearing Loss - PMC - Mechanisms of Aminoglycoside- and Cisplatin-Induced Ototoxicity - American Journal of Audiology - Aminoglycoside induces RIPOR2 translocation and phosphatidylserine externalization via distinct mechanisms - PMC - Entry - #580000 - DEAFNESS, AMINOGLYCOSIDE-INDUCED - OMIM - Maternally inherited aminoglycoside-induced and nonsyndromic hearing loss is associated with the 12S rRNA C1494T mutation - PubMed - CPIC® Guideline for Aminoglycosides and MT-RNR1 - MT-RNR1 CPIC Guidelines - Aminoglycoside antibiotics — Genomics Education Knowledge Hub - New developments in aminoglycoside therapy and ototoxicity - PMC - Aminoglycoside- and glycopeptide-induced ototoxicity in children: a systematic review - PMC - Prevalence of aminoglycoside-induced hearing loss in drug-resistant tuberculosis patients: A systematic review - PubMed - Nonsyndromic Hearing Loss and Deafness, Mitochondrial - PubMed (GeneReviews) - Mitochondrial tRNAGln 4394C>T Mutation May Contribute to the Clinical Expression of 1555A>G-Induced Deafness - PMC - Results: Patient with a known MT-RNR1 genotype requiring aminoglycoside antibiotics — In the Clinic - Use of Sodium Thiosulfate as an Otoprotectant in Patients With Cancer Treated With Platinum Compounds - JCO - FDA Approves Sodium Thiosulfate to Decrease Cisplatin-Associated Ototoxicity - CancerNetwork - Sodium Thiosulfate for Protection from Cisplatin-Induced Hearing Loss - NEJM - New Rapid genomic testing at Manchester University NHS Foundation Trust prevents at-risk neonates from potential lifelong hearing loss - BioSpace - Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care - PubMed - Pharmacogenetics to Avoid Loss of Hearing (PALOH) trial protocol - PMC - Rapid Point-of-Care Genotyping to Avoid Aminoglycoside-Induced Ototoxicity in Neonatal Intensive Care - PMC - Genotype testing to guide antibiotic use and prevent hearing loss - Scottish Health Technologies Group - Genetic test developed by Manchester researchers to prevent newborn babies going deaf, to be trialled across the UK - MFT NHS - Variant m.1555A>G in MT-RNR1 causes hearing loss and multiorgan mitochondrial disorder - PMC - High prevalence of m.1555A>G in patients with hearing loss in the Baikal Lake region of Russia as a result of founder effect - PMC / Scientific Reports - Lower ototoxicity and absence of hidden hearing loss point to gentamicin C1a and apramycin as promising antibiotics for clinical use - PMC - Dissociation of antibacterial activity and aminoglycoside ototoxicity in the 4-monosubstituted 2-deoxystreptamine apramycin - PNAS - ELX-02: an investigational read-through agent for the treatment of nonsense mutation-related genetic disease - Hearing in 44-45 year olds with m.1555A>G, a genetic mutation predisposing to aminoglycoside-induced deafness: a population based cohort study - PubMed - Table 2. Prevalence of MT-RNR1 Pathogenic Variant m.1555A>G by Population - GeneReviews, NCBI Bookshelf - Mitochondrial mutation m.1555A>G as a risk factor for failed newborn hearing screening in a large cohort of preterm infants - PMC - Mitochondrial m.1584A 12S rRNA methylation in families with m.1555A>G associated hearing loss - Human Molecular Genetics

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Aminoglycoside-Induced Hearing Loss (AIHL) — Comprehensive Research Report

1. Disease Information

2. Etiology

Disease Causal Factors

Genetic Risk Factors

Environmental/Clinical Risk Factors

Protective Factors

Gene-Environment Interaction

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Suggested Ontology Bindings for Curation

Key Caveats for Curators

Reference Validation