TRMU-Related Acute Infantile Liver Failure

Mendelian MONDO:0013111 Pathograph 18 Show in embeddings browser Mitochondrial disease Infantile liver failure

A mitochondrial hepatopathy that is often survivable and, in survivors, non-recurrent - which is close to unique among mitochondrial diseases. TRMU (also called MTU1) adds a sulfur atom to the wobble uridine of three mitochondrial tRNAs, and without that modification mitochondrial translation fails and the respiratory chain complexes that depend on mtDNA-encoded subunits cannot be built. The reason the disease has a beginning and an end is that TRMU needs cysteine as its sulfur donor, and cysteine supply is low in the first months of life because the transsulfuration pathway matures after birth. A hypomorphic TRMU allele is therefore only limiting inside that window. Infants typically decompensate between two and four months with liver failure and lactic acidosis; those who are supported through the crisis can recover essentially normal liver function and not relapse. That mechanism is also the treatment: L-cysteine, with or without N-acetylcysteine, supplies the missing substrate. It is not benign - a substantial minority die in the acute episode, and neurological, cardiac and respiratory features can persist or emerge later.

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1
Inheritance
9
Pathophys.
1
Histopath.
14
Phenotypes
3
Gaps
18
Pathograph
1
Genes
2
Variants
6
Medical Actions
2
Differentials
1
Models
2
References
1
Deep Research
👪

Inheritance

1
Autosomal recessive HP:0000007
Biallelic TRMU variants. Most reported patients are compound heterozygotes, and most disease-associated missense alleles retain partial activity - which matters, because residual thiolation is what correlates with survival.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:37184193 SUPPORT Human Clinical
"TRMU deficiency is inherited in an autosomal recessive manner."
States the inheritance mode.
PMID:38113276 SUPPORT In Vitro
"our results showed that most disease-related mutations are partial loss-of-function mutations, with three mutations being particularly severe"
Establishes that most alleles are hypomorphic rather than null, which is what makes a substrate-limited window relevant.
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Discussions and Knowledge Gaps

3
Has the cysteine-limitation window ever been measured, rather than inferred from the age at which infants present?
KNOWLEDGE GAP trmu_cysteine_window_untested
Attached to
pathophysiology#Developmental Cysteine Limitation treatments#L-Cysteine Supplementation
The substrate-limitation model is the organising idea of this disease. It explains the onset, the offset, and the treatment, and it is stated as a proposal by the authors who introduced it - "we propose that there is a window of time". What is missing is a measurement: nobody has shown hepatic cysteine availability tracking mt-tRNA thiolation in a TRMU-deficient infant, or demonstrated that thiolation actually rises as the transsulfuration pathway matures. The clinical evidence that acting on the model works is now substantial - cysteine supplementation improved survival significantly across 62 patients - but that is a retrospective, unrandomised comparison, and it demonstrates that supplying cysteine helps rather than that endogenous cysteine shortage is what opens the window in the first place. The narrower presymptomatic evidence is still two infants against family controls. The question is not academic: if something other than cysteine supply closes the window, then cysteine supplementation is treating a correlate, and the timing of when it can be safely stopped is unknown.
Show evidence (3 references)
PMID:19732863 SUPPORT Human Clinical
"we propose that there is a window of time whereby patients with TRMU mutations are at increased risk of developing liver failure"
The claim is framed by its own authors as a proposal, which is the point of this gap.
PMID:36305855 SUPPORT Human Clinical
"Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly."
Shows that supplying the substrate helps, which is consistent with the model without establishing that substrate shortage is what makes the window.
PMID:37184193 SUPPORT Human Clinical
"To date, two infants treated presymptomatically overall had a milder clinical course than their affected relatives."
The extent of the evidence for treating before symptoms begin.
Does the cytosolic proteostress mechanism shown for Mto1 deficiency also operate in TRMU deficiency, and does it operate in human liver?
HUMAN MODEL MISMATCH trmu_proteostress_arm_is_from_sister_enzyme
Attached to
pathophysiology#Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
The proteostress arm is attractive because it would explain damage beyond simple energy failure and because chemical chaperones rescued it - a therapeutic lead that does not exist elsewhere in this disease. But the evidence comes from Mto1-deficient cells and mice, not Trmu-deficient ones. Mto1 adds the taurine group and TRMU adds the sulfur, at the same wobble position of the same three mt-tRNAs, and both losses impair mitochondrial translation - so the inference is reasonable. It is still an inference across enzymes, and it has a second gap on top: the Trmu liver-specific mouse, which is the right enzyme in the right tissue, reports cytoprotective and mitochondrial-proliferation responses rather than a cytotoxic unfolded protein response. Those are not the same picture, and nobody has looked for either in human TRMU-deficient liver. Until they are reconciled, the proteostress node should not be treated as a target.
Show evidence (2 references)
PMID:29320742 SUPPORT In Vitro
"Here, we showed that taurine modification is catalyzed by mitochondrial optimization 1 (Mto1) in mammals."
Establishes that the proteostress work concerns Mto1, the sister enzyme, and not TRMU.
PMID:27689697 SUPPORT Model Organism
"mitochondrial dysfunction induced signaling pathways related to mitochondrial proliferation and the suppression of oxidative stress"
The right-enzyme model reports a compensatory rather than a cytotoxic stress response, which is the tension this discussion records.
What separates the infants who recover completely from those who die, or who present with Leigh-like brain lesions?
KNOWLEDGE GAP trmu_reversibility_versus_leigh_presentation
Attached to
pathophysiology#Acute Infantile Liver Failure phenotypes#Leigh-Like Brain Lesions
The disease is named for its reversibility, but four of thirteen infants in the founding cohort died in the acute episode, one of three in a later series died, and both reported patients with Leigh-like neuroimaging died - one at 25 days and one at six months. Residual 2-thiolation correlates with prognosis in cell-line work, which is the best available answer and is a laboratory measurement not available at the bedside. Whether the Leigh-like presentation is simply the severe end of one spectrum, or a distinct route in which the brain is affected primarily rather than secondarily, is unresolved, and the two published patients are too few to tell. A partial answer does exist and is available at the bedside: in a 62-patient series, loss-of-function TRMU variants were associated with poor survival, so the molecular report itself carries prognostic information that the residual-thiolation assay does not need to supply. This matters for counselling: a family told the disease is reversible is being told something true of survivors, and in most patients - 42 of 62 were alive at a median age of 6.8 years - it is true.
Show evidence (4 references)
PMID:19732863 SUPPORT Human Clinical
"Four died during the acute episodes, and the survivors never had a recurrence."
Quantifies the mortality that the label "reversible" does not convey.
PMID:38113276 SUPPORT Human Clinical
"clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels, which is partially consistent with the AlphaMissense predictions"
Residual enzyme activity predicts outcome, which is why severity is graded rather than categorical. Graded HUMAN_CLINICAL because the quoted sentence reports an analysis of patient data, not the paper's cell-line work.
PMID:36305855 SUPPORT Human Clinical
"Loss-of-function TRMU variants were associated with poor survival."
A genotype-survival correlation in 62 patients, readable directly off a molecular report rather than requiring a thiolation assay.
+ 1 more reference
⚙

Pathophysiology

9
Biallelic TRMU Loss of Function
TRMU, also called MTU1, is the nuclear-encoded mitochondrial 2-thiouridylase. Biallelic variants reduce its activity. Most disease alleles are partial rather than complete losses, and the residual activity is prognostic rather than incidental - patient outcome correlates with how much 2-thiolation the mutant enzyme still manages.
TRMU hgnc:25481 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves TRMU (hgnc:25481), qualified as loss of function. hgnc:25481 is a gene from the HUGO Gene Nomenclature Committee. ⇓ LOSS OF FUNCTION
Downstream
Loss of mt-tRNA 2-Thiouridylation
CLPP-Mediated Degradation of Mutant MTU1 A second route from the same variants: the mutant protein is not only less active, it is less abundant.
Show evidence (2 references)
PMID:19732863 SUPPORT DIRECT Human Clinical
"Using homozygosity mapping, we identified mutations in the TRMU gene, which encodes a mitochondria-specific tRNA-modifying enzyme, tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase."
The gene assignment in the founding cohort.
PMID:38113276 SUPPORT DIRECT Human Clinical
"clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels"
Makes residual enzyme activity a prognostic quantity, which is the basis for treating the deficit as graded rather than all-or-nothing.
CLPP-Mediated Degradation of Mutant MTU1
Missense-mutant MTU1 is recognised and rapidly degraded by the mitochondrial matrix protease CLPP, working through its chaperone partner CLPX. So a hypomorphic allele loses activity twice over - the enzyme is impaired and then thrown away. Knocking down CLPP restores both mutant MTU1 protein levels and mt-tRNA 2-thiolation, which makes this the only currently identified druggable node upstream of the thiolation defect. PROVISIONAL because the work is entirely in engineered cell lines; no patient has been shown to have accelerated MTU1 turnover in vivo, and no CLPP inhibitor has been tried.
Downstream
Loss of mt-tRNA 2-Thiouridylation
Show evidence (2 references)
PMID:38113276 SUPPORT DIRECT In Vitro
"Mutant MTU1 is rapidly degraded by mitochondrial caseinolytic peptidase (CLPP) through a direct interaction with its chaperone protein CLPX."
Establishes the degradation route and the protease responsible.
PMID:38113276 SUPPORT DIRECT In Vitro
"knockdown of CLPP significantly increased mutant MTU1 protein expression and mt-tRNA 2-thiolation, suggesting that accelerated proteolysis of mutant MTU1 plays a role in disease pathogenesis"
The rescue experiment: removing the protease restores the downstream modification, which is what makes this a node rather than an observation.
Developmental Cysteine Limitation
The node that makes this disease time-limited. TRMU uses sulfur from cysteine, and endogenous cysteine supply is low in the first months of life. A partially active enzyme that has enough substrate later does not have enough now, which is why the disease has an onset at two to four months and an offset in survivors, and why the treatment is to supply the substrate. It is PROVISIONAL rather than established because it was proposed as an inference from the timing in the founding cohort and has not been demonstrated by measuring hepatic cysteine against thiolation in patients; the strongest support for it is that acting on it works.
Downstream
Loss of mt-tRNA 2-Thiouridylation Acts as a co-requirement rather than an independent cause: it limits the residual enzyme, and only matters because the enzyme is already impaired.
Show evidence (2 references)
PMID:19732863 SUPPORT INDIRECT Human Clinical
"Given that sulfur is a TRMU substrate and its availability is limited during the neonatal period, we propose that there is a window of time whereby patients with TRMU mutations are at increased risk of developing liver failure."
The originating hypothesis, stated as a proposal by its authors. Graded INDIRECT because it is an inference from the age distribution rather than a measurement of substrate limitation.
PMID:37184193 SUPPORT INDIRECT Human Clinical
"Because the endogenous supply of cysteine is normally low in the first few months of life and because the enzyme TRMU requires adequate amounts of cysteine to enable the essential function of thiolating mitochondrial transfer RNAs, the initial manifestations of TRMU deficiency (primarily..."
States the substrate-limitation model and its therapeutic corollary as current expert guidance.
Loss of mt-tRNA 2-Thiouridylation
The wobble uridine at position 34 of mt-tRNA-Lys, mt-tRNA-Gln and mt-tRNA-Glu normally carries a 2-thio group. Thiolation constrains base pairing so the anticodon reads its codons accurately; without it, decoding degrades. The modification was measured directly in the founding cohort and found markedly reduced.
mitochondrial tRNA wobble position uridine thiolation GO:1990799 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial tRNA wobble position uridine thiolation (GO:1990799). GO:1990799 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Impaired Mitochondrial Translation
Show evidence (2 references)
PMID:19732863 SUPPORT DIRECT Human Clinical
"Accordingly, the 2-thiouridylation levels of the mitochondrial tRNAs were markedly reduced."
Direct measurement of the modification deficit in patients.
PMID:38113276 SUPPORT DIRECT In Vitro
"The 2-thiolation of U34 facilitates U-A and U-G base pairing while inhibiting U-U and U-C base pairing (10), which enables precise codon recognition and ensures accurate decoding."
Explains why losing the modification degrades decoding rather than merely destabilising the tRNA.
Impaired Mitochondrial Translation
Only 13 proteins are made inside the mitochondrion, and all of them are respiratory chain subunits. Degrading the accuracy of mitochondrial decoding therefore hits the respiratory chain and nothing else directly - which is why the biochemical signature is a combined complex deficiency with normal mtDNA copy number, the finding that separates this disease from the mtDNA-depletion hepatopathies caused by POLG, DGUOK and MPV17.
mitochondrial translation GO:0032543 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased mitochondrial translation (GO:0032543). GO:0032543 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Combined Respiratory Chain Deficiency
Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
Show evidence (2 references)
PMID:27689697 SUPPORT DIRECT Model Organism
"Mtu1 deficiency resulted in a loss of 2-thiolation in mt-tRNAs, which led to a marked impairment of mitochondrial translation."
Links the modification loss to the translation defect in a liver-specific knockout.
PMID:19732863 SUPPORT INDIRECT Human Clinical
"We report on 13 unrelated infants who presented with acute liver failure and lactic acidemia with normal mtDNA content."
Normal mtDNA content with a respiratory chain defect points to a translation rather than a template problem. Graded INDIRECT because it excludes the alternative rather than measuring translation.
Combined Respiratory Chain Deficiency
Complexes I, III and IV all contain mtDNA-encoded subunits and all fall together; complex II, which is entirely nuclear-encoded, is spared. That sparing is diagnostically useful and is reported repeatedly in patient muscle biopsies.
oxidative phosphorylation GO:0006119 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased oxidative phosphorylation (GO:0006119). GO:0006119 is a biological process from the Gene Ontology. ↓ DECREASED
Animal models
Liver-specific Mtu1 knockout mouse Mouse recapitulates Broad decrease in respiratory complex activities in hepatocytes, with loss of mitochondrial membrane integrity.
Downstream
Hepatocyte Energy Failure and Death
Show evidence (3 references)
PMID:27689697 SUPPORT DIRECT Model Organism
"Mtu1LKO mice exhibited severe disruption of mitochondrial membrane integrity and a broad decrease in respiratory complex activities in the hepatocytes."
Measures the combined complex deficiency in the tissue that fails clinically.
PMID:23625533 SUPPORT DIRECT Human Clinical
"It is characterized by a combined defect of respiratory chain complexes without mitochondrial DNA depletion."
The human biochemical signature, including the absence of mtDNA depletion.
PMID:33365252 SUPPORT DIRECT Human Clinical
"The respiratory chain complex activities in muscle biopsy were decreased except for normal CII, and increased citrate synthase activity."
Shows the pattern with complex II spared, which is what a defect confined to mtDNA-encoded subunits predicts.
Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
A second consequence of failed mitochondrial translation, additive to simple energy failure. When the organelle cannot translate, nuclear-encoded mitochondrial proteins including OPA1 are mistrafficked and aggregate in the cytoplasm, triggering a cytotoxic unfolded protein response; chemical chaperones suppress the cytotoxicity. The important caveat is that this was shown for Mto1, the enzyme that adds the taurine group at the same wobble position, not for Trmu, which adds the sulfur. The two modifications sit on the same nucleotide of the same three tRNAs and both losses impair mitochondrial translation, so the inference is reasonable - but it is an inference from a sister enzyme, which is why this node is PROVISIONAL and not given a treatment.
Hepatocyte CL:0000182 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Hepatocyte (CL:0000182). CL:0000182 is a cell type from the Cell Ontology.
response to unfolded protein GO:0006986 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased response to unfolded protein (GO:0006986). GO:0006986 is a biological process from the Gene Ontology. ↑ INCREASED
Show evidence (2 references)
PMID:29320742 SUPPORT INDIRECT In Vitro
"Mto1-deficient cells exhibited abnormal mitochondrial morphology owing to aberrant trafficking of nuclear DNA-encoded mitochondrial proteins, including Opa1. The mistargeted proteins were aggregated and misfolded in the cytoplasm, which induced cytotoxic unfolded protein response."
The mechanism this node describes. Graded INDIRECT because it was established in Mto1-deficient rather than Trmu-deficient cells.
PMID:29320742 SUPPORT INDIRECT In Vitro
"application of chemical chaperones successfully suppressed cytotoxicity by reducing protein misfolding and increasing functional mitochondrial proteins in Mto1-deficient cells"
A rescue that makes the proteostress causal rather than epiphenomenal in that system, and would be the reason to test the same in TRMU deficiency.
Hepatocyte Energy Failure and Death
Hepatocytes die, and macrophages infiltrate in response. The liver-specific knockout mouse reproduces this, and the same model shows something important about the recovery: the injured liver simultaneously turns on mitochondrial proliferation and oxidative-stress-suppressing pathways, which the authors propose is what prevents catastrophic failure and assists recovery. If that is right, reversibility is not only the cysteine window - the tissue is also actively compensating.
Hepatocyte CL:0000182 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Hepatocyte (CL:0000182). CL:0000182 is a cell type from the Cell Ontology. Macrophage CL:0000235 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves Macrophage (CL:0000235). CL:0000235 is a cell type from the Cell Ontology.
liver UBERON:0002107 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in liver (UBERON:0002107). UBERON:0002107 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Liver-specific Mtu1 knockout mouse Mouse recapitulates Hepatic inflammation with raised plasma lactate and AST, on a background of lost 2-thiolation and impaired mitochondrial translation.
Downstream
Acute Infantile Liver Failure
Show evidence (2 references)
PMID:27689697 SUPPORT DIRECT Model Organism
"mice, which exhibited symptoms of liver injury characterized by hepatic inflammation and elevated levels of plasma lactate and AST."
The tissue injury and its biochemical correlates in the liver-specific model.
PMID:27689697 SUPPORT INDIRECT Model Organism
"Mtu1 deficiency is associated with multiple cytoprotective pathways that might prevent catastrophic liver failure and assist in the recovery from liver injury."
The compensatory arm. Graded INDIRECT because the authors state it as a possible contribution to recovery, not a demonstrated one.
Acute Infantile Liver Failure
Decompensation between two and four months of age with transaminitis, coagulopathy, hepatomegaly, lactic acidosis, hypoglycaemia and hyperammonaemia. The outcome splits sharply: a substantial minority die during the acute episode, while survivors normalise and, in the founding cohort followed for up to fourteen years, never relapsed.
Show evidence (2 references)
PMID:19732863 SUPPORT DIRECT Human Clinical
"Four died during the acute episodes, and the survivors never had a recurrence. The longest follow-up period was 14 years."
Establishes both the mortality of the acute phase and the durability of recovery in survivors.
PMID:37184193 SUPPORT DIRECT Human Clinical
"Infants with untreated TRMU deficiency, a mitochondrial disorder, typically become symptomatic between ages two and four months with transient acute liver dysfunction (including elevated transaminases, abnormal synthetic functions, and/or hepatomegaly), metabolic derangements (severe persistent..."
The clinical presentation and its timing, from the expert-curated baseline.
✶

Histopathology

1
Hepatic injury on biopsy
Biopsies taken several months after onset showed oncocytic hepatocyte change, focal steatosis, focal cytoplasmic ballooning, micronodular cirrhosis, canalicular cholestasis, fibrosis and macrovesicular steatosis. The pointed finding is the last clause of the sentence: no normal biopsy was reported. Clinical recovery in this disease is not the same as histological recovery, and a curated entry that says "reversible" without saying that is misleading.
Show evidence (2 references)
PMID:33365252 SUPPORT Human Clinical
"Liver biopsies (9/23) showed signs of mild to severe hepatic involvement in biopsies taken several months after onset: oncocytic changes in the hepatocytes, focal steatosis and focal ballooning of cytoplasm, micronodular cirrhosis, canalicular cholestasis to patent signs of fibrosis, irregular..."
The full histological description, including that the biopsies postdate the acute episode.
PMID:33365252 SUPPORT Human Clinical
"No normal hepatic biopsies were reported."
The finding that qualifies the reversibility: every biopsied liver showed residual abnormality, months after the clinical episode had resolved.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for TRMU-Related Acute Infantile Liver Failure Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

14
Blood 1
Coagulopathy Abnormality of coagulation HP:0001928 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormality of coagulation (HP:0001928). HP:0001928 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:33365252 SUPPORT Human Clinical
"Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
Lists coagulopathy among the components of abnormal liver function.
PMID:37184193 SUPPORT Human Clinical
"abnormal liver findings (including coagulopathy) improve or normalize"
Establishes coagulopathy as one of the findings that reverses, which is why it is worth curating separately.
Cardiovascular 1
Cardiomyopathy HP:0001638 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cardiomyopathy (HP:0001638). HP:0001638 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"cardiomyopathy, and respiratory failure may persist or develop or over time"
Lists cardiomyopathy among the manifestations that may develop over time.
Digestive 4
Acute Liver Failure VERY_FREQUENT Acute hepatic failure HP:0006554 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acute hepatic failure (HP:0006554). HP:0006554 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:36305855 SUPPORT Human Clinical
"The most frequent finding, occurring in all but 2 individuals, was liver involvement."
60 of 62 in the largest series, which is a denominator not ascertained on liver failure and so is what the VERY_FREQUENT band rests on.
PMID:36305855 SUPPORT Human Clinical
"ALF occurred only in the first year of life and was reported in 43 of 62 individuals; 11 of whom received liver transplantation."
Separates liver *involvement* from frank acute liver failure, and gives the transplantation rate.
Cholestasis HP:0001396 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cholestasis (HP:0001396). HP:0001396 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
Lists cholestasis among the components of abnormal liver function across 24 of 26 reviewed patients. No frequency band: the sentence says the components are variable without giving each a denominator.
Hepatomegaly HP:0002240 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hepatomegaly (HP:0002240). HP:0002240 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"transient acute liver dysfunction (including elevated transaminases, abnormal synthetic functions, and/or hepatomegaly)"
Names hepatomegaly as part of the acute hepatic presentation.
Hepatic Steatosis HP:0001397 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hepatic steatosis (HP:0001397). HP:0001397 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"Most relevant findings in patient's necropsy were: massive hepatic steatosis"
Autopsy finding in one fatal case; a single observation, so no frequency band.
Metabolism 3
Lactic Acidosis VERY_FREQUENT HP:0003128 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lactic acidosis (HP:0003128). HP:0003128 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:19732863 SUPPORT Human Clinical
"13 unrelated infants who presented with acute liver failure and lactic acidemia"
Present in all 13 patients of the founding cohort, though that cohort was ascertained on the finding.
PMID:33365252 SUPPORT Human Clinical
"all patients showed increased serum lactate level (3.2–40.0 mmol/L)"
An independent literature review of 26 patients not ascertained on lactic acidemia, which is what the frequency band actually rests on.
Hypoglycemia HP:0001943 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoglycemia (HP:0001943). HP:0001943 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"metabolic derangements (severe persistent lactic acidosis, hypoglycemia, hyperammonemia)"
Lists hypoglycaemia among the metabolic derangements of the acute phase. No frequency band is given in the source.
Hyperammonemia HP:0001987 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperammonemia (HP:0001987). HP:0001987 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"severe persistent lactic acidosis, hypoglycemia, hyperammonemia"
Lists hyperammonaemia among the acute metabolic derangements.
Musculoskeletal 1
Hypotonia Generalized hypotonia HP:0001290 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Generalized hypotonia (HP:0001290). HP:0001290 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"She suffered progressive generalized hypotonia, fluctuating level of consciousness, decreased intake, weight-loss"
Reports generalised hypotonia during the acute presentation.
Nervous System 2
Developmental Delay and Intellectual Disability Global developmental delay HP:0001263 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Global developmental delay (HP:0001263). HP:0001263 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"neurologic dysfunction (including developmental delay / intellectual disability and seizures), cardiomyopathy, and respiratory failure may persist or develop or over time"
Documents the neurodevelopmental outcome as a manifestation that may emerge after the hepatic phase.
Seizures HP:0001250 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Seizure (HP:0001250). HP:0001250 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"developmental delay / intellectual disability and seizures"
Names seizures among the neurological manifestations.
Growth 1
Poor Weight Gain Failure to thrive HP:0001508 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Failure to thrive (HP:0001508). HP:0001508 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"hypoglycemia, hyperammonemia), and poor weight gain"
Lists poor weight gain among the presenting features.
Other 1
Leigh-Like Brain Lesions Abnormal basal ganglia MRI signal intensity HP:0012751 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abnormal basal ganglia MRI signal intensity (HP:0012751). HP:0012751 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"We describe two new unrelated patients with an acute liver failure and a neuroimaging compatible with Leigh syndrome (LS) due to TRMU deficiency, a combination not previously reported."
Reports the phenotype expansion. Two patients out of roughly 28 published is too few, and too clearly ascertained as a novelty, for a frequency band.
🧬

Genetic Associations

1
TRMU
Gene: TRMU hgnc:25481 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is TRMU (hgnc:25481). hgnc:25481 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:38113276 SUPPORT In Vitro
"In humans, a variety of genetic mutations, including missense mutations, nonsense mutations, duplications, and frameshift mutations, have been identified in pediatric patients who develop life-threatening reversible infantile liver failure (RILF) after birth"
Describes the allelic spectrum.
Variants (2)
c.2T>A (p.Met1?)
A start-codon variant abolishing the protein, associated with the severe end of the spectrum.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"Exome Sequencing showed two pathogenic variants in TRMU: c.2 T > A: p.Met1?"
Documents the start-codon allele in a fatal neonatal case.
c.680G>C (p.Arg227Thr)
A recurrent missense allele, seen in trans with a nonsense variant in a patient with the Leigh-like presentation.
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"two mutations in trans in TRMU gene: c.160_161delTG:p.Cys54* (non-previously reported, but likely pathogenic according to ACMG criteria since it creates an stop codon) and c.680G > C:p.Arg227Thr"
Names the compound heterozygous genotype including this missense allele.
💊

Medical Actions

6
L-Cysteine Supplementation
Action: pharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. Ontology label: Pharmacotherapy NCIT:C15986
Agent: L-cysteine CHEBI:17561 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses L-cysteine (CHEBI:17561). CHEBI:17561 is a therapeutic agent from Chemical Entities of Biological Interest. N-acetyl-L-cysteine CHEBI:28939 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses N-acetyl-L-cysteine (CHEBI:28939). CHEBI:28939 is a therapeutic agent from Chemical Entities of Biological Interest.
Platform: Small molecule
The disease-targeted therapy, and an unusually direct one - it supplies the sulfur donor the deficient enzyme is short of, during the window in which the infant cannot supply it endogenously. Guidance is to start as soon as the diagnosis is suspected rather than waiting for confirmation, and two infants treated before becoming symptomatic had a milder course than their affected relatives.
Mechanism Target:
Developmental Cysteine Limitation — Acts directly on the substrate-limitation node, which is the only node in this entry that a treatment currently reaches.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"L-cysteine, with or without N-acetylcysteine (NAC), should be initiated as soon as a diagnosis of TRMU deficiency is suspected."
States the intervention and the urgency with which it is recommended.
Show evidence (3 references)
PMID:36305855 SUPPORT Human Clinical
"Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly."
The strongest efficacy evidence available: a survival benefit across an international series of 62 patients. Retrospective and unrandomised, but far beyond the case-level evidence that preceded it.
PMID:37184193 SUPPORT Human Clinical
"To date, two infants treated presymptomatically overall had a milder clinical course than their affected relatives."
A separate and narrower claim, kept because it is the only evidence bearing on treatment started *before* symptoms rather than after. Two patients against family controls.
PMID:33485800 SUPPORT Human Clinical
"combined N-acetylcysteine and L-cysteine supplementation should be considered prior to molecular diagnosis, as this is a low-risk approach that may increase survival"
Supports treating before genetic confirmation, which is the practical corollary of a substrate-limited window that closes on its own schedule.
Liver Transplantation
Action: organ transplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is organ transplantation (NCIT:C15289). NCIT:C15289 is a clinical intervention from the NCI Thesaurus. Ontology label: Organ Transplantation NCIT:C15289
Platform: Surgery
Reserved for hepatopathy that does not respond to medical management. It is a genuinely difficult decision here, because the natural history of the disease is recovery in those who survive the acute phase.
Mechanism Target:
Hepatocyte Energy Failure and Death — Replaces the failing organ. It does not correct the enzyme defect in any other tissue.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"Liver transplantation is indicated when hepatopathy does not respond to medical interventions."
States the indication.
Supportive Care Through the Acute Episode
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
The intervention that historically produced the recoveries, before any targeted therapy existed. Given that survivors normalise, supporting the infant through the crisis is itself the therapeutic goal.
Mechanism Target:
Acute Infantile Liver Failure — Buys time for the cysteine window to close, rather than acting on any node.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"Supportive care by a multidisciplinary team of clinicians, including a hepatologist, neurologist, and medical geneticist, is recommended to manage the commonly reported complications"
Describes the supportive management recommended.
Avoidance of Mitochondrial Stressors
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
An explicit list of things not to do: drugs that raise metabolic demand such as corticosteroids, drugs that inhibit mitochondrial activity such as valproic acid and prolonged propofol infusion, and fasting. Acetaminophen is to be considered avoidable during episodes of liver dysfunction. This is management that follows from the mechanism rather than from empirical outcome data.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"Avoid medications that increase metabolic demand (such as corticosteroids) or inhibit mitochondrial activity (such as valproic acid and prolonged propofol infusion) and fasting, as it increases metabolic demand and may exacerbate hypoglycemia."
The agents-to-avoid guidance, quoted from the GeneReviews management section.
Surveillance of Survivors
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Platform: Other
Routine follow-up to monitor the response to cysteine and to catch the manifestations that emerge after the hepatic phase - persistent neurodevelopmental delay, new seizures, cardiomyopathy. This is the operational consequence of the third progression phase: surviving the crisis is the point at which surveillance starts, not the point at which it stops.
Mechanism Target:
Acute Infantile Liver Failure — Detects late-emerging disease rather than acting on a mechanism.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"Routine follow up is recommended to monitor response to L-cysteine and NAC supplementation, to evaluate response to supportive interventions, and to identify emergence of new findings or concerns regarding developmental/educational progress"
States the surveillance recommendation and what it is looking for.
Genetic Counseling and Presymptomatic Sibling Supplementation
Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Platform: Other
Autosomal recessive, so each sib has a 25 percent risk. What makes counselling here more than risk arithmetic is the action attached to it: an at-risk newborn sibling should be offered cysteine supplementation until testing for the family variants is complete, because waiting for the result can mean waiting past the window. Prenatal testing has been used once to inform maternal supplementation.
Mechanism Target:
Developmental Cysteine Limitation — Identifies at-risk infants early enough for substrate supply to be restored before the window opens.
Show evidence (2 references)
PMID:37184193 SUPPORT Human Clinical
"If prenatal testing has not been performed on a pregnancy at risk, supplementation with L-cysteine (and possibly N-acetylcysteine) of an at-risk newborn sib should be offered until molecular genetic testing for the family-specific TRMU pathogenic variants has been completed."
The specific recommendation to treat before the diagnosis is confirmed in a sibling.
PMID:37184193 SUPPORT Human Clinical
"each sib of an affected individual has at conception a 25% chance of being affected"
The recurrence risk that counselling conveys.
🔬

Biochemical Markers

2
Alpha-fetoprotein
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
Lists elevated alpha-fetoprotein among the components of abnormal liver function.
Serum lactate
Show evidence (1 reference)
PMID:33365252 SUPPORT Human Clinical
"all patients showed increased serum lactate level (3.2–40.0 mmol/L)"
Gives the universality and the range across 26 reviewed patients.
🔬

Diagnosis

2
TRMU sequencing
Biallelic pathogenic TRMU variants on molecular genetic testing establish the diagnosis in a proband with suggestive findings. Diagnosis matters urgently rather than academically, because it changes treatment.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"The diagnosis of TRMU deficiency is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in TRMU identified by molecular genetic testing."
States the diagnostic criterion.
Respiratory chain enzymology with mtDNA quantification
A combined complex deficiency with normal mtDNA copy number is the pattern that distinguishes a mitochondrial translation defect from the far commoner mtDNA-depletion hepatopathies. Complex II is characteristically spared.
Show evidence (1 reference)
PMID:23625533 SUPPORT Human Clinical
"It is characterized by a combined defect of respiratory chain complexes without mitochondrial DNA depletion."
Names the discriminating biochemical pattern.
📈

Progression

3
Acute decompensation
Onset at two to four months with liver failure, lactic acidosis, hypoglycaemia and hyperammonaemia. This is the phase in which patients die, and it is the only phase in which the disease looks like a fulminant hepatopathy.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"typically become symptomatic between ages two and four months with transient acute liver dysfunction"
Defines the timing and character of the acute phase.
Hepatic recovery
With supportive care alone, liver findings including coagulopathy improve or normalise and the metabolic derangements settle. Recovery is not attributed to any disease-targeted therapy in the historical cohorts.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"With proper supportive treatment (but not disease-targeted therapy), abnormal liver findings (including coagulopathy) improve or normalize."
States that recovery occurs on supportive care, which is what makes the disease reversible rather than treated.
Post-hepatic residual and late-emerging disease
The phase that makes "reversible" a partly misleading label. Persistent lactic acidosis, developmental delay or intellectual disability, seizures, cardiomyopathy and respiratory failure may persist or appear later, so surviving the hepatic crisis is not the same as being cured.
Show evidence (1 reference)
PMID:37184193 SUPPORT Human Clinical
"However, other manifestations typical of a mitochondrial disorder such as persistent lactic acidosis, neurologic dysfunction (including developmental delay / intellectual disability and seizures), cardiomyopathy, and respiratory failure may persist or develop or over time."
Documents the late-emerging manifestations that qualify the reversibility.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
An international retrospective series published in 2023 assembled 62 individuals, 30 of them previously unreported - which more than doubled the fewer-than-30 count that stood in 2020. No population-based estimate exists. The count is almost certainly an undercount: an infant who survives an unexplained episode of liver failure and then recovers completely is not obviously a candidate for mitochondrial gene testing.
Show evidence (2 references)
PMID:33365252 SUPPORT Human Clinical
"TRMU deficiency causes an early onset potentially reversible acute liver failure, so far reported in less than 30 patients."
The 2020 case count, superseded by the series below and kept to show the direction of travel.
PMID:36305855 SUPPORT Human Clinical
"In 62 individuals, including 30 previously unreported cases, we described 47 (likely) pathogenic TRMU variants, of which 17 were novel, and 1 intragenic deletion."
The current published cohort size and allelic count.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from TRMU-Related Acute Infantile Liver Failure:

mtDNA depletion syndrome hepatopathies
Overlapping Features POLG, DGUOK and MPV17 disease present the same way in the same age group - infantile liver failure with a combined respiratory chain deficiency - and are much commoner. They are also not reversible, so distinguishing them changes both prognosis and management.
Distinguishing Features
  • mtDNA copy number is reduced in the depletion syndromes and normal in TRMU deficiency.
  • Spontaneous recovery is characteristic of TRMU deficiency and not of the depletion syndromes.
Show evidence (2 references)
PMID:23625533 SUPPORT Human Clinical
"Mitochondrial DNA depletions, induced by mutations of the nuclear genes POLG, DGUOK, and MPV17, are the major causes of these combined deficiencies."
Names the commoner alternatives that share the biochemical phenotype.
PMID:23625533 SUPPORT Human Clinical
"Spontaneous remission is a rare feature in mitochondrial liver diseases, and early identification of TRMU mutations could impact on clinical management."
States why the distinction changes management.
Reversible infantile mitochondrial myopathy
Overlapping Features The other well-described reversible mitochondrial disease of infancy, caused by homoplasmic m.14674T>C/G in mt-tRNA-Glu. It shares the striking natural history - severe illness in the first months, then recovery if supported - but the target organ is muscle rather than liver.
Distinguishing Features
  • Presents as severe infantile myopathy rather than liver failure.
  • Caused by a homoplasmic mitochondrial tRNA variant, not a nuclear gene defect.
Show evidence (1 reference)
PMID:25407320 SUPPORT Human Clinical
"Two homoplasmic mitochondrial tRNA mutations (m.14674T>C/G in mt-tRNA(Glu)) have been reported to cause severe infantile mitochondrial myopathy in the first months of life."
Describes the parallel reversible entity and its distinct genetic cause and target organ.
🐁

Animal Models

1
Liver-specific Mtu1 knockout mouse
The model that established TRMU loss as a primary cause of the liver injury rather than a correlate, and the only model that isolates the affected tissue. A germline knockout is embryonic lethal, which is why the conditional was needed.
Species
Mouse
Genotype
Liver-specific conditional Mtu1 knockout
Publication
PMID:27689697
Pathograph links
Hepatocyte Energy Failure and Death recapitulates fidelity: moderate Hepatic inflammation with raised plasma lactate and AST, on a background of lost 2-thiolation and impaired mitochondrial translation.
Limitations: A conditional knockout is a complete loss in the target tissue, while most human alleles are partial. That difference matters here more than usual, because the whole clinical picture turns on residual activity interacting with a transient substrate shortage - and a mouse with no enzyme at all cannot model a window that opens and closes.
Readouts
Plasma lactate and AST
Direction: INCREASED
Interpretation: Biochemical correlate of the hepatocyte injury node.
Show evidence (1 reference)
PMID:27689697 SUPPORT Model Organism
"mice, which exhibited symptoms of liver injury characterized by hepatic inflammation and elevated levels of plasma lactate and AST."
Reports the measurements behind this readout.
Show evidence (1 reference)
PMID:27689697 SUPPORT Model Organism
"The present study demonstrates that Mtu1-dependent 2-thiolation of mt-tRNA is indispensable for mitochondrial translation and that Mtu1 deficiency is a primary cause of RILF."
The authors' own statement that the model establishes causation for this disease.
Combined Respiratory Chain Deficiency recapitulates fidelity: high Broad decrease in respiratory complex activities in hepatocytes, with loss of mitochondrial membrane integrity.
Limitations: The mouse data are reported as a broad decrease across complexes rather than with the complex II sparing that is diagnostically characteristic in patients, so the model supports the deficiency without reproducing its diagnostic signature.
Readouts
Respiratory complex activities in hepatocytes
Direction: DECREASED
Interpretation: Enzymatic correlate of the respiratory chain node.
Show evidence (1 reference)
PMID:27689697 SUPPORT Model Organism
"a broad decrease in respiratory complex activities in the hepatocytes"
Reports the enzymatic measurement.
{ }

Source YAML

click to show 
name: TRMU-Related Acute Infantile Liver Failure
category: Mendelian
creation_date: "2026-08-29T19:15:00Z"
synonyms:
- TRMU deficiency
- MTU1 deficiency
- reversible infantile liver failure
- transient infantile liver failure
- LFIT
- acute infantile liver failure due to synthesis defect of mtDNA-encoded proteins
description: >-
  A mitochondrial hepatopathy that is often survivable and, in survivors,
  non-recurrent - which is close to unique among mitochondrial diseases. TRMU
  (also called MTU1) adds a sulfur atom to the wobble uridine of three
  mitochondrial tRNAs, and without that modification mitochondrial translation
  fails and the respiratory chain complexes that depend on mtDNA-encoded subunits
  cannot be built. The reason the disease has a beginning and an end is that TRMU
  needs cysteine as its sulfur donor, and cysteine supply is low in the first
  months of life because the transsulfuration pathway matures after birth. A
  hypomorphic TRMU allele is therefore only limiting inside that window. Infants
  typically decompensate between two and four months with liver failure and lactic
  acidosis; those who are supported through the crisis can recover essentially
  normal liver function and not relapse. That mechanism is also the treatment:
  L-cysteine, with or without N-acetylcysteine, supplies the missing substrate.
  It is not benign - a substantial minority die in the acute episode, and
  neurological, cardiac and respiratory features can persist or emerge later.
disease_term:
  preferred_term: TRMU-related acute infantile liver failure
  term:
    id: MONDO:0013111
    label: acute infantile liver failure due to synthesis defect of mtDNA-encoded proteins
parents:
- Mitochondrial disease
- Infantile liver failure
inheritance:
- name: Autosomal recessive
  description: >-
    Biallelic TRMU variants. Most reported patients are compound heterozygotes,
    and most disease-associated missense alleles retain partial activity - which
    matters, because residual thiolation is what correlates with survival.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TRMU deficiency is inherited in an autosomal recessive manner."
    explanation: States the inheritance mode.
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "our results showed that most disease-related mutations are partial loss-of-function mutations, with three mutations being particularly severe"
    explanation: Establishes that most alleles are hypomorphic rather than null, which is what makes a substrate-limited window relevant.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    An international retrospective series published in 2023 assembled 62
    individuals, 30 of them previously unreported - which more than doubled the
    fewer-than-30 count that stood in 2020. No population-based estimate exists. The count is almost certainly an undercount: an infant who
    survives an unexplained episode of liver failure and then recovers completely
    is not obviously a candidate for mitochondrial gene testing.
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TRMU deficiency causes an early onset potentially reversible acute liver failure, so far reported in less than 30 patients."
    explanation: The 2020 case count, superseded by the series below and kept to show the direction of travel.
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In 62 individuals, including 30 previously unreported cases, we described 47 (likely) pathogenic TRMU variants, of which 17 were novel, and 1 intragenic deletion."
    explanation: The current published cohort size and allelic count.
pathophysiology:
- name: Biallelic TRMU Loss of Function
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  description: >-
    TRMU, also called MTU1, is the nuclear-encoded mitochondrial 2-thiouridylase.
    Biallelic variants reduce its activity. Most disease alleles are partial
    rather than complete losses, and the residual activity is prognostic rather
    than incidental - patient outcome correlates with how much 2-thiolation the
    mutant enzyme still manages.
  gene:
    preferred_term: TRMU
    description: >-
      Mitochondrial tRNA-specific 2-thiouridylase 1, carrying biallelic
      loss-of-function variants.
    modifier: LOSS_OF_FUNCTION
    term:
      id: hgnc:25481
      label: TRMU
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "Using homozygosity mapping, we identified mutations in the TRMU gene, which encodes a mitochondria-specific tRNA-modifying enzyme, tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase."
    explanation: The gene assignment in the founding cohort.
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels"
    explanation: >-
      Makes residual enzyme activity a prognostic quantity, which is the basis for
      treating the deficit as graded rather than all-or-nothing.
  downstream:
  - target: Loss of mt-tRNA 2-Thiouridylation
    causal_link_type: DIRECT
  - target: CLPP-Mediated Degradation of Mutant MTU1
    causal_link_type: DIRECT
    description: >-
      A second route from the same variants: the mutant protein is not only less
      active, it is less abundant.

- name: CLPP-Mediated Degradation of Mutant MTU1
  biological_scale: MOLECULAR
  role: central_effector
  mechanism_confidence: PROVISIONAL
  description: >-
    Missense-mutant MTU1 is recognised and rapidly degraded by the mitochondrial
    matrix protease CLPP, working through its chaperone partner CLPX. So a
    hypomorphic allele loses activity twice over - the enzyme is impaired and then
    thrown away. Knocking down CLPP restores both mutant MTU1 protein levels and
    mt-tRNA 2-thiolation, which makes this the only currently identified
    druggable node upstream of the thiolation defect. PROVISIONAL because the
    work is entirely in engineered cell lines; no patient has been shown to have
    accelerated MTU1 turnover in vivo, and no CLPP inhibitor has been tried.
  evidence:
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: "Mutant MTU1 is rapidly degraded by mitochondrial caseinolytic peptidase (CLPP) through a direct interaction with its chaperone protein CLPX."
    explanation: Establishes the degradation route and the protease responsible.
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: "knockdown of CLPP significantly increased mutant MTU1 protein expression and mt-tRNA 2-thiolation, suggesting that accelerated proteolysis of mutant MTU1 plays a role in disease pathogenesis"
    explanation: >-
      The rescue experiment: removing the protease restores the downstream
      modification, which is what makes this a node rather than an observation.
  downstream:
  - target: Loss of mt-tRNA 2-Thiouridylation
    causal_link_type: DIRECT

- name: Developmental Cysteine Limitation
  biological_scale: ORGANISM
  role: trigger
  mechanism_confidence: PROVISIONAL
  description: >-
    The node that makes this disease time-limited. TRMU uses sulfur from cysteine,
    and endogenous cysteine supply is low in the first months of life. A partially
    active enzyme that has enough substrate later does not have enough now, which
    is why the disease has an onset at two to four months and an offset in
    survivors, and why the treatment is to supply the substrate. It is
    PROVISIONAL rather than established because it was proposed as an inference
    from the timing in the founding cohort and has not been demonstrated by
    measuring hepatic cysteine against thiolation in patients; the strongest
    support for it is that acting on it works.
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "Given that sulfur is a TRMU substrate and its availability is limited during the neonatal period, we propose that there is a window of time whereby patients with TRMU mutations are at increased risk of developing liver failure."
    explanation: >-
      The originating hypothesis, stated as a proposal by its authors. Graded
      INDIRECT because it is an inference from the age distribution rather than a
      measurement of substrate limitation.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "Because the endogenous supply of cysteine is normally low in the first few months of life and because the enzyme TRMU requires adequate amounts of cysteine to enable the essential function of thiolating mitochondrial transfer RNAs, the initial manifestations of TRMU deficiency (primarily hepatopathy) may be reversed, ameliorated, or in some cases prevented by exogenous oral cysteine supplementation in infants with TRMU deficiency."
    explanation: >-
      States the substrate-limitation model and its therapeutic corollary as
      current expert guidance.
  downstream:
  - target: Loss of mt-tRNA 2-Thiouridylation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Acts as a co-requirement rather than an independent cause: it limits the
      residual enzyme, and only matters because the enzyme is already impaired.

- name: Loss of mt-tRNA 2-Thiouridylation
  biological_scale: MOLECULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    The wobble uridine at position 34 of mt-tRNA-Lys, mt-tRNA-Gln and mt-tRNA-Glu
    normally carries a 2-thio group. Thiolation constrains base pairing so the
    anticodon reads its codons accurately; without it, decoding degrades. The
    modification was measured directly in the founding cohort and found markedly
    reduced.
  biological_processes:
  - preferred_term: mitochondrial tRNA wobble position uridine thiolation
    term:
      id: GO:1990799
      label: mitochondrial tRNA wobble position uridine thiolation
    modifier: DECREASED
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "Accordingly, the 2-thiouridylation levels of the mitochondrial tRNAs were markedly reduced."
    explanation: Direct measurement of the modification deficit in patients.
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: "The 2-thiolation of U34 facilitates U-A and U-G base pairing while inhibiting U-U and U-C base pairing (10), which enables precise codon recognition and ensures accurate decoding."
    explanation: Explains why losing the modification degrades decoding rather than merely destabilising the tRNA.
  downstream:
  - target: Impaired Mitochondrial Translation
    causal_link_type: DIRECT

- name: Impaired Mitochondrial Translation
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    Only 13 proteins are made inside the mitochondrion, and all of them are
    respiratory chain subunits. Degrading the accuracy of mitochondrial decoding
    therefore hits the respiratory chain and nothing else directly - which is why
    the biochemical signature is a combined complex deficiency with normal mtDNA
    copy number, the finding that separates this disease from the mtDNA-depletion
    hepatopathies caused by POLG, DGUOK and MPV17.
  biological_processes:
  - preferred_term: mitochondrial translation
    term:
      id: GO:0032543
      label: mitochondrial translation
    modifier: DECREASED
  evidence:
  - reference: PMID:27689697
    reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: DIRECT
    snippet: "Mtu1 deficiency resulted in a loss of 2-thiolation in mt-tRNAs, which led to a marked impairment of mitochondrial translation."
    explanation: Links the modification loss to the translation defect in a liver-specific knockout.
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: "We report on 13 unrelated infants who presented with acute liver failure and lactic acidemia with normal mtDNA content."
    explanation: >-
      Normal mtDNA content with a respiratory chain defect points to a translation
      rather than a template problem. Graded INDIRECT because it excludes the
      alternative rather than measuring translation.
  downstream:
  - target: Combined Respiratory Chain Deficiency
    causal_link_type: DIRECT
  - target: Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
    causal_link_type: DIRECT

- name: Combined Respiratory Chain Deficiency
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    Complexes I, III and IV all contain mtDNA-encoded subunits and all fall
    together; complex II, which is entirely nuclear-encoded, is spared. That
    sparing is diagnostically useful and is reported repeatedly in patient muscle
    biopsies.
  biological_processes:
  - preferred_term: oxidative phosphorylation
    term:
      id: GO:0006119
      label: oxidative phosphorylation
    modifier: DECREASED
  evidence:
  - reference: PMID:27689697
    reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: DIRECT
    snippet: "Mtu1LKO mice exhibited severe disruption of mitochondrial membrane integrity and a broad decrease in respiratory complex activities in the hepatocytes."
    explanation: Measures the combined complex deficiency in the tissue that fails clinically.
  - reference: PMID:23625533
    reference_title: "Mitochondrial Infantile Liver Disease due to TRMU Gene Mutations: Three New Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "It is characterized by a combined defect of respiratory chain complexes without mitochondrial DNA depletion."
    explanation: The human biochemical signature, including the absence of mtDNA depletion.
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "The respiratory chain complex activities in muscle biopsy were decreased except for normal CII, and increased citrate synthase activity."
    explanation: >-
      Shows the pattern with complex II spared, which is what a defect confined to
      mtDNA-encoded subunits predicts.
  downstream:
  - target: Hepatocyte Energy Failure and Death
    causal_link_type: DIRECT

- name: Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: PROVISIONAL
  description: >-
    A second consequence of failed mitochondrial translation, additive to simple
    energy failure. When the organelle cannot translate, nuclear-encoded
    mitochondrial proteins including OPA1 are mistrafficked and aggregate in the
    cytoplasm, triggering a cytotoxic unfolded protein response; chemical
    chaperones suppress the cytotoxicity. The important caveat is that this was
    shown for Mto1, the enzyme that adds the taurine group at the same wobble
    position, not for Trmu, which adds the sulfur. The two modifications sit on
    the same nucleotide of the same three tRNAs and both losses impair
    mitochondrial translation, so the inference is reasonable - but it is an
    inference from a sister enzyme, which is why this node is PROVISIONAL and not
    given a treatment.
  cell_types:
  - preferred_term: Hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: response to unfolded protein
    term:
      id: GO:0006986
      label: response to unfolded protein
    modifier: INCREASED
  evidence:
  - reference: PMID:29320742
    reference_title: "Defective Mitochondrial tRNA Taurine Modification Activates Global Proteostress and Leads to Mitochondrial Disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: "Mto1-deficient cells exhibited abnormal mitochondrial morphology owing to aberrant trafficking of nuclear DNA-encoded mitochondrial proteins, including Opa1. The mistargeted proteins were aggregated and misfolded in the cytoplasm, which induced cytotoxic unfolded protein response."
    explanation: >-
      The mechanism this node describes. Graded INDIRECT because it was
      established in Mto1-deficient rather than Trmu-deficient cells.
  - reference: PMID:29320742
    reference_title: "Defective Mitochondrial tRNA Taurine Modification Activates Global Proteostress and Leads to Mitochondrial Disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: INDIRECT
    snippet: "application of chemical chaperones successfully suppressed cytotoxicity by reducing protein misfolding and increasing functional mitochondrial proteins in Mto1-deficient cells"
    explanation: >-
      A rescue that makes the proteostress causal rather than epiphenomenal in
      that system, and would be the reason to test the same in TRMU deficiency.

- name: Hepatocyte Energy Failure and Death
  biological_scale: TISSUE
  role: consequence
  mechanism_confidence: ESTABLISHED
  description: >-
    Hepatocytes die, and macrophages infiltrate in response. The liver-specific
    knockout mouse reproduces this, and the same model shows something important
    about the recovery: the injured liver simultaneously turns on mitochondrial
    proliferation and oxidative-stress-suppressing pathways, which the authors
    propose is what prevents catastrophic failure and assists recovery. If that is
    right, reversibility is not only the cysteine window - the tissue is also
    actively compensating.
  cell_types:
  - preferred_term: Hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  - preferred_term: Macrophage
    term:
      id: CL:0000235
      label: macrophage
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:27689697
    reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: DIRECT
    snippet: "mice, which exhibited symptoms of liver injury characterized by hepatic inflammation and elevated levels of plasma lactate and AST."
    explanation: The tissue injury and its biochemical correlates in the liver-specific model.
  - reference: PMID:27689697
    reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: INDIRECT
    snippet: "Mtu1 deficiency is associated with multiple cytoprotective pathways that might prevent catastrophic liver failure and assist in the recovery from liver injury."
    explanation: >-
      The compensatory arm. Graded INDIRECT because the authors state it as a
      possible contribution to recovery, not a demonstrated one.
  downstream:
  - target: Acute Infantile Liver Failure
    causal_link_type: DIRECT

- name: Acute Infantile Liver Failure
  biological_scale: ORGANISM
  role: outcome
  mechanism_confidence: ESTABLISHED
  description: >-
    Decompensation between two and four months of age with transaminitis,
    coagulopathy, hepatomegaly, lactic acidosis, hypoglycaemia and hyperammonaemia.
    The outcome splits sharply: a substantial minority die during the acute
    episode, while survivors normalise and, in the founding cohort followed for up
    to fourteen years, never relapsed.
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "Four died during the acute episodes, and the survivors never had a recurrence. The longest follow-up period was 14 years."
    explanation: Establishes both the mortality of the acute phase and the durability of recovery in survivors.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: "Infants with untreated TRMU deficiency, a mitochondrial disorder, typically become symptomatic between ages two and four months with transient acute liver dysfunction (including elevated transaminases, abnormal synthetic functions, and/or hepatomegaly), metabolic derangements (severe persistent lactic acidosis, hypoglycemia, hyperammonemia), and poor weight gain."
    explanation: The clinical presentation and its timing, from the expert-curated baseline.
progression:
- phase: Acute decompensation
  notes: >-
    Onset at two to four months with liver failure, lactic acidosis, hypoglycaemia
    and hyperammonaemia. This is the phase in which patients die, and it is the
    only phase in which the disease looks like a fulminant hepatopathy.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "typically become symptomatic between ages two and four months with transient acute liver dysfunction"
    explanation: Defines the timing and character of the acute phase.
- phase: Hepatic recovery
  notes: >-
    With supportive care alone, liver findings including coagulopathy improve or
    normalise and the metabolic derangements settle. Recovery is not attributed to
    any disease-targeted therapy in the historical cohorts.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "With proper supportive treatment (but not disease-targeted therapy), abnormal liver findings (including coagulopathy) improve or normalize."
    explanation: States that recovery occurs on supportive care, which is what makes the disease reversible rather than treated.
- phase: Post-hepatic residual and late-emerging disease
  notes: >-
    The phase that makes "reversible" a partly misleading label. Persistent lactic
    acidosis, developmental delay or intellectual disability, seizures,
    cardiomyopathy and respiratory failure may persist or appear later, so
    surviving the hepatic crisis is not the same as being cured.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, other manifestations typical of a mitochondrial disorder such as persistent lactic acidosis, neurologic dysfunction (including developmental delay / intellectual disability and seizures), cardiomyopathy, and respiratory failure may persist or develop or over time."
    explanation: Documents the late-emerging manifestations that qualify the reversibility.
phenotypes:
- category: Hepatic
  name: Acute Liver Failure
  description: >-
    Acute hepatic decompensation with elevated transaminases and impaired
    synthetic function, presenting in early infancy.
  phenotype_term:
    preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most frequent finding, occurring in all but 2 individuals, was liver involvement."
    explanation: >-
      60 of 62 in the largest series, which is a denominator not ascertained on
      liver failure and so is what the VERY_FREQUENT band rests on.
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ALF occurred only in the first year of life and was reported in 43 of 62 individuals; 11 of whom received liver transplantation."
    explanation: >-
      Separates liver *involvement* from frank acute liver failure, and gives the
      transplantation rate.
- category: Metabolic
  name: Lactic Acidosis
  description: >-
    Severe and often persistent lactic acidosis from impaired oxidative
    phosphorylation. In one fatal case it was refractory at 15 to 20 mmol/L.
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "13 unrelated infants who presented with acute liver failure and lactic acidemia"
    explanation: >-
      Present in all 13 patients of the founding cohort, though that cohort was
      ascertained on the finding.
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "all patients showed increased serum lactate level (3.2–40.0 mmol/L)"
    explanation: >-
      An independent literature review of 26 patients not ascertained on lactic
      acidemia, which is what the frequency band actually rests on.
  review_notes: >-
    The founding cohort cannot support this band on its own: it was ascertained
    on infants presenting with lactic acidemia, so 13 of 13 is guaranteed by the
    selection criterion rather than observed. The band rests on the second
    citation, a review of 26 published patients in which all had raised lactate.
- category: Metabolic
  name: Hypoglycemia
  description: >-
    Low blood glucose during decompensation, aggravated by fasting.
  phenotype_term:
    preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "metabolic derangements (severe persistent lactic acidosis, hypoglycemia, hyperammonemia)"
    explanation: Lists hypoglycaemia among the metabolic derangements of the acute phase. No frequency band is given in the source.
- category: Metabolic
  name: Hyperammonemia
  description: >-
    Raised ammonia secondary to hepatocellular failure.
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe persistent lactic acidosis, hypoglycemia, hyperammonemia"
    explanation: Lists hyperammonaemia among the acute metabolic derangements.
- category: Hepatic
  name: Cholestasis
  description: >-
    Cholestasis with jaundice, one of the variable components of the hepatic
    picture alongside transaminase elevation and coagulopathy.
  phenotype_term:
    preferred_term: Cholestasis
    term:
      id: HP:0001396
      label: Cholestasis
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
    explanation: >-
      Lists cholestasis among the components of abnormal liver function across 24
      of 26 reviewed patients. No frequency band: the sentence says the components
      are variable without giving each a denominator.
- category: Hematologic
  name: Coagulopathy
  description: >-
    Impaired synthetic function presenting as coagulopathy. Clinically it is the
    marker that most directly tracks recovery, since it is named as one of the
    findings that normalises on supportive care.
  phenotype_term:
    preferred_term: Abnormality of coagulation
    term:
      id: HP:0001928
      label: Abnormality of coagulation
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
    explanation: Lists coagulopathy among the components of abnormal liver function.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "abnormal liver findings (including coagulopathy) improve or normalize"
    explanation: Establishes coagulopathy as one of the findings that reverses, which is why it is worth curating separately.
- category: Neurologic
  name: Hypotonia
  description: >-
    Generalised hypotonia, reported both as part of the acute decompensation and,
    in one neonate, from the first hours of life.
  phenotype_term:
    preferred_term: Generalized hypotonia
    term:
      id: HP:0001290
      label: Generalized hypotonia
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She suffered progressive generalized hypotonia, fluctuating level of consciousness, decreased intake, weight-loss"
    explanation: Reports generalised hypotonia during the acute presentation.
- category: Hepatic
  name: Hepatomegaly
  description: >-
    Liver enlargement, with increased echogenicity on ultrasound.
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "transient acute liver dysfunction (including elevated transaminases, abnormal synthetic functions, and/or hepatomegaly)"
    explanation: Names hepatomegaly as part of the acute hepatic presentation.
- category: Growth
  name: Poor Weight Gain
  description: >-
    Failure to thrive during the symptomatic period.
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hypoglycemia, hyperammonemia), and poor weight gain"
    explanation: Lists poor weight gain among the presenting features.
- category: Neurologic
  name: Developmental Delay and Intellectual Disability
  description: >-
    A late-emerging feature rather than part of the acute illness, and one of the
    reasons survivors need long-term follow-up.
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "neurologic dysfunction (including developmental delay / intellectual disability and seizures), cardiomyopathy, and respiratory failure may persist or develop or over time"
    explanation: Documents the neurodevelopmental outcome as a manifestation that may emerge after the hepatic phase.
- category: Neurologic
  name: Seizures
  description: >-
    Seizures may persist from the acute illness or appear later.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "developmental delay / intellectual disability and seizures"
    explanation: Names seizures among the neurological manifestations.
- category: Cardiovascular
  name: Cardiomyopathy
  description: >-
    Cardiac involvement, reported both as a late-emerging manifestation and, in one
    autopsy, as myocardial vacuolation in a neonate who died at 25 days.
  phenotype_term:
    preferred_term: Cardiomyopathy
    term:
      id: HP:0001638
      label: Cardiomyopathy
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "cardiomyopathy, and respiratory failure may persist or develop or over time"
    explanation: Lists cardiomyopathy among the manifestations that may develop over time.
- category: Neurologic
  name: Leigh-Like Brain Lesions
  description: >-
    Symmetrical signal change in thalami, subthalamic nuclei, basal nuclei and
    brainstem with a lactate peak on spectroscopy - a Leigh syndrome imaging
    pattern. Reported in two patients, both of whom died, so this presentation may
    mark a more severe end of the spectrum rather than a variant of the reversible
    course.
  phenotype_term:
    preferred_term: Abnormal basal ganglia MRI signal intensity
    term:
      id: HP:0012751
      label: Abnormal basal ganglia MRI signal intensity
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We describe two new unrelated patients with an acute liver failure and a neuroimaging compatible with Leigh syndrome (LS) due to TRMU deficiency, a combination not previously reported."
    explanation: >-
      Reports the phenotype expansion. Two patients out of roughly 28 published is
      too few, and too clearly ascertained as a novelty, for a frequency band.
- category: Hepatic
  name: Hepatic Steatosis
  description: >-
    Fatty change in the liver, found at autopsy in a fatal neonatal case.
  phenotype_term:
    preferred_term: Hepatic steatosis
    term:
      id: HP:0001397
      label: Hepatic steatosis
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most relevant findings in patient's necropsy were: massive hepatic steatosis"
    explanation: Autopsy finding in one fatal case; a single observation, so no frequency band.
histopathology:
- name: Hepatic injury on biopsy
  description: >-
    Biopsies taken several months after onset showed oncocytic hepatocyte change,
    focal steatosis, focal cytoplasmic ballooning, micronodular cirrhosis,
    canalicular cholestasis, fibrosis and macrovesicular steatosis. The pointed
    finding is the last clause of the sentence: no normal biopsy was reported.
    Clinical recovery in this disease is not the same as histological recovery,
    and a curated entry that says "reversible" without saying that is misleading.
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Liver biopsies (9/23) showed signs of mild to severe hepatic involvement in biopsies taken several months after onset: oncocytic changes in the hepatocytes, focal steatosis and focal ballooning of cytoplasm, micronodular cirrhosis, canalicular cholestasis to patent signs of fibrosis, irregular cirrhosis with nodulation and macrovesicular steatosis."
    explanation: The full histological description, including that the biopsies postdate the acute episode.
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No normal hepatic biopsies were reported."
    explanation: >-
      The finding that qualifies the reversibility: every biopsied liver showed
      residual abnormality, months after the clinical episode had resolved.
biochemical:
- name: Alpha-fetoprotein
  notes: >-
    Markedly elevated AFP is a recurring feature of the acute hepatic phase and
    one of the discriminating markers in an infant with unexplained liver failure.
  biomarker_term:
    preferred_term: Elevated circulating alpha-fetoprotein concentration
    term:
      id: HP:0006254
      label: Elevated circulating alpha-fetoprotein concentration
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Abnormal liver function was present in all patients (available data from 24/26) with variable degrees of transaminase elevation, coagulopathy, cholestasis or elevated alfa-fetoprotein."
    explanation: Lists elevated alpha-fetoprotein among the components of abnormal liver function.
- name: Serum lactate
  notes: >-
    Raised in every reviewed patient, over a wide range, and the finding that
    should prompt the diagnosis alongside hypoglycaemia in an infant with liver
    failure.
  biomarker_term:
    preferred_term: Increased circulating lactate concentration
    term:
      id: HP:0002151
      label: Increased circulating lactate concentration
  evidence:
  - reference: PMID:33365252
    reference_title: "Leigh syndrome associated with TRMU gene mutations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "all patients showed increased serum lactate level (3.2–40.0 mmol/L)"
    explanation: Gives the universality and the range across 26 reviewed patients.
genetic:
- name: TRMU
  gene_term:
    preferred_term: TRMU
    term:
      id: hgnc:25481
      label: TRMU
  relationship_type: CAUSATIVE
  notes: >-
    Missense, nonsense, frameshift and duplication alleles have all been reported,
    most patients being compound heterozygous. Note that TRMU has a second and
    quite separate role in human genetics as a nuclear modifier of the
    mitochondrial m.1555A>G deafness allele; that is a different phenotype from
    this one and is curated in the aminoglycoside-induced hearing loss entry, not
    here.
  evidence:
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In humans, a variety of genetic mutations, including missense mutations, nonsense mutations, duplications, and frameshift mutations, have been identified in pediatric patients who develop life-threatening reversible infantile liver failure (RILF) after birth"
    explanation: Describes the allelic spectrum.
  variants:
  - name: c.2T>A (p.Met1?)
    description: >-
      A start-codon variant abolishing the protein, associated with the severe end
      of the spectrum.
    evidence:
    - reference: PMID:33365252
      reference_title: "Leigh syndrome associated with TRMU gene mutations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Exome Sequencing showed two pathogenic variants in TRMU: c.2 T > A: p.Met1?"
      explanation: Documents the start-codon allele in a fatal neonatal case.
  - name: c.680G>C (p.Arg227Thr)
    description: >-
      A recurrent missense allele, seen in trans with a nonsense variant in a
      patient with the Leigh-like presentation.
    evidence:
    - reference: PMID:33365252
      reference_title: "Leigh syndrome associated with TRMU gene mutations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "two mutations in trans in TRMU gene: c.160_161delTG:p.Cys54* (non-previously reported, but likely pathogenic according to ACMG criteria since it creates an stop codon) and c.680G > C:p.Arg227Thr"
      explanation: Names the compound heterozygous genotype including this missense allele.
animal_models:
- name: Liver-specific Mtu1 knockout mouse
  species: Mouse
  genotype: Liver-specific conditional Mtu1 knockout
  publication: PMID:27689697
  description: >-
    The model that established TRMU loss as a primary cause of the liver injury
    rather than a correlate, and the only model that isolates the affected tissue.
    A germline knockout is embryonic lethal, which is why the conditional was
    needed.
  modeled_mechanisms:
  - target: Hepatocyte Energy Failure and Death
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Hepatic inflammation with raised plasma lactate and AST, on a background of
      lost 2-thiolation and impaired mitochondrial translation.
    limitations: >-
      A conditional knockout is a complete loss in the target tissue, while most
      human alleles are partial. That difference matters here more than usual,
      because the whole clinical picture turns on residual activity interacting
      with a transient substrate shortage - and a mouse with no enzyme at all
      cannot model a window that opens and closes.
    readouts:
    - name: Plasma lactate and AST
      target: Hepatocyte Energy Failure and Death
      direction: INCREASED
      interpretation: Biochemical correlate of the hepatocyte injury node.
      evidence:
      - reference: PMID:27689697
        reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "mice, which exhibited symptoms of liver injury characterized by hepatic inflammation and elevated levels of plasma lactate and AST."
        explanation: Reports the measurements behind this readout.
    evidence:
    - reference: PMID:27689697
      reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The present study demonstrates that Mtu1-dependent 2-thiolation of mt-tRNA is indispensable for mitochondrial translation and that Mtu1 deficiency is a primary cause of RILF."
      explanation: The authors' own statement that the model establishes causation for this disease.
  - target: Combined Respiratory Chain Deficiency
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Broad decrease in respiratory complex activities in hepatocytes, with loss
      of mitochondrial membrane integrity.
    limitations: >-
      The mouse data are reported as a broad decrease across complexes rather than
      with the complex II sparing that is diagnostically characteristic in
      patients, so the model supports the deficiency without reproducing its
      diagnostic signature.
    readouts:
    - name: Respiratory complex activities in hepatocytes
      target: Combined Respiratory Chain Deficiency
      direction: DECREASED
      interpretation: Enzymatic correlate of the respiratory chain node.
      evidence:
      - reference: PMID:27689697
        reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "a broad decrease in respiratory complex activities in the hepatocytes"
        explanation: Reports the enzymatic measurement.
diagnosis:
- name: TRMU sequencing
  description: >-
    Biallelic pathogenic TRMU variants on molecular genetic testing establish the
    diagnosis in a proband with suggestive findings. Diagnosis matters urgently
    rather than academically, because it changes treatment.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The diagnosis of TRMU deficiency is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in TRMU identified by molecular genetic testing."
    explanation: States the diagnostic criterion.
- name: Respiratory chain enzymology with mtDNA quantification
  description: >-
    A combined complex deficiency with normal mtDNA copy number is the pattern
    that distinguishes a mitochondrial translation defect from the far commoner
    mtDNA-depletion hepatopathies. Complex II is characteristically spared.
  evidence:
  - reference: PMID:23625533
    reference_title: "Mitochondrial Infantile Liver Disease due to TRMU Gene Mutations: Three New Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is characterized by a combined defect of respiratory chain complexes without mitochondrial DNA depletion."
    explanation: Names the discriminating biochemical pattern.
differential_diagnoses:
- name: mtDNA depletion syndrome hepatopathies
  description: >-
    POLG, DGUOK and MPV17 disease present the same way in the same age group -
    infantile liver failure with a combined respiratory chain deficiency - and are
    much commoner. They are also not reversible, so distinguishing them changes
    both prognosis and management.
  distinguishing_features:
  - mtDNA copy number is reduced in the depletion syndromes and normal in TRMU deficiency.
  - Spontaneous recovery is characteristic of TRMU deficiency and not of the depletion syndromes.
  evidence:
  - reference: PMID:23625533
    reference_title: "Mitochondrial Infantile Liver Disease due to TRMU Gene Mutations: Three New Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mitochondrial DNA depletions, induced by mutations of the nuclear genes POLG, DGUOK, and MPV17, are the major causes of these combined deficiencies."
    explanation: Names the commoner alternatives that share the biochemical phenotype.
  - reference: PMID:23625533
    reference_title: "Mitochondrial Infantile Liver Disease due to TRMU Gene Mutations: Three New Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Spontaneous remission is a rare feature in mitochondrial liver diseases, and early identification of TRMU mutations could impact on clinical management."
    explanation: States why the distinction changes management.
- name: Reversible infantile mitochondrial myopathy
  description: >-
    The other well-described reversible mitochondrial disease of infancy, caused by
    homoplasmic m.14674T>C/G in mt-tRNA-Glu. It shares the striking natural
    history - severe illness in the first months, then recovery if supported - but
    the target organ is muscle rather than liver.
  distinguishing_features:
  - Presents as severe infantile myopathy rather than liver failure.
  - Caused by a homoplasmic mitochondrial tRNA variant, not a nuclear gene defect.
  evidence:
  - reference: PMID:25407320
    reference_title: "Reversible infantile mitochondrial diseases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Two homoplasmic mitochondrial tRNA mutations (m.14674T>C/G in mt-tRNA(Glu)) have been reported to cause severe infantile mitochondrial myopathy in the first months of life."
    explanation: Describes the parallel reversible entity and its distinct genetic cause and target organ.
treatments:
- name: L-Cysteine Supplementation
  description: >-
    The disease-targeted therapy, and an unusually direct one - it supplies the
    sulfur donor the deficient enzyme is short of, during the window in which the
    infant cannot supply it endogenously. Guidance is to start as soon as the
    diagnosis is suspected rather than waiting for confirmation, and two infants
    treated before becoming symptomatic had a milder course than their affected
    relatives.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: L-cysteine
      term:
        id: CHEBI:17561
        label: L-cysteine
    - preferred_term: N-acetyl-L-cysteine
      term:
        id: CHEBI:28939
        label: N-acetyl-L-cysteine
  target_mechanisms:
  - target: Developmental Cysteine Limitation
    description: >-
      Acts directly on the substrate-limitation node, which is the only node in
      this entry that a treatment currently reaches.
    evidence:
    - reference: PMID:37184193
      reference_title: "TRMU Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "L-cysteine, with or without N-acetylcysteine (NAC), should be initiated as soon as a diagnosis of TRMU deficiency is suspected."
      explanation: States the intervention and the urgency with which it is recommended.
  evidence:
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly."
    explanation: >-
      The strongest efficacy evidence available: a survival benefit across an
      international series of 62 patients. Retrospective and unrandomised, but far
      beyond the case-level evidence that preceded it.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, two infants treated presymptomatically overall had a milder clinical course than their affected relatives."
    explanation: >-
      A separate and narrower claim, kept because it is the only evidence bearing
      on treatment started *before* symptoms rather than after. Two patients
      against family controls.
  - reference: PMID:33485800
    reference_title: "TRMU deficiency: A broad clinical spectrum responsive to cysteine supplementation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "combined N-acetylcysteine and L-cysteine supplementation should be considered prior to molecular diagnosis, as this is a low-risk approach that may increase survival"
    explanation: >-
      Supports treating before genetic confirmation, which is the practical
      corollary of a substrate-limited window that closes on its own schedule.
- name: Liver Transplantation
  description: >-
    Reserved for hepatopathy that does not respond to medical management. It is a
    genuinely difficult decision here, because the natural history of the disease
    is recovery in those who survive the acute phase.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: organ transplantation
    term:
      id: NCIT:C15289
      label: Organ Transplantation
  target_mechanisms:
  - target: Hepatocyte Energy Failure and Death
    description: >-
      Replaces the failing organ. It does not correct the enzyme defect in any
      other tissue.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Liver transplantation is indicated when hepatopathy does not respond to medical interventions."
    explanation: States the indication.
- name: Supportive Care Through the Acute Episode
  description: >-
    The intervention that historically produced the recoveries, before any
    targeted therapy existed. Given that survivors normalise, supporting the
    infant through the crisis is itself the therapeutic goal.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Acute Infantile Liver Failure
    description: >-
      Buys time for the cysteine window to close, rather than acting on any node.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supportive care by a multidisciplinary team of clinicians, including a hepatologist, neurologist, and medical geneticist, is recommended to manage the commonly reported complications"
    explanation: Describes the supportive management recommended.
- name: Avoidance of Mitochondrial Stressors
  description: >-
    An explicit list of things not to do: drugs that raise metabolic demand such
    as corticosteroids, drugs that inhibit mitochondrial activity such as valproic
    acid and prolonged propofol infusion, and fasting. Acetaminophen is to be
    considered avoidable during episodes of liver dysfunction. This is management
    that follows from the mechanism rather than from empirical outcome data.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Avoid medications that increase metabolic demand (such as corticosteroids) or inhibit mitochondrial activity (such as valproic acid and prolonged propofol infusion) and fasting, as it increases metabolic demand and may exacerbate hypoglycemia."
    explanation: The agents-to-avoid guidance, quoted from the GeneReviews management section.
- name: Surveillance of Survivors
  description: >-
    Routine follow-up to monitor the response to cysteine and to catch the
    manifestations that emerge after the hepatic phase - persistent
    neurodevelopmental delay, new seizures, cardiomyopathy. This is the operational
    consequence of the third progression phase: surviving the crisis is the point
    at which surveillance starts, not the point at which it stops.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Acute Infantile Liver Failure
    description: >-
      Detects late-emerging disease rather than acting on a mechanism.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Routine follow up is recommended to monitor response to L-cysteine and NAC supplementation, to evaluate response to supportive interventions, and to identify emergence of new findings or concerns regarding developmental/educational progress"
    explanation: States the surveillance recommendation and what it is looking for.
- name: Genetic Counseling and Presymptomatic Sibling Supplementation
  description: >-
    Autosomal recessive, so each sib has a 25 percent risk. What makes counselling
    here more than risk arithmetic is the action attached to it: an at-risk newborn
    sibling should be offered cysteine supplementation until testing for the
    family variants is complete, because waiting for the result can mean waiting
    past the window. Prenatal testing has been used once to inform maternal
    supplementation.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  target_mechanisms:
  - target: Developmental Cysteine Limitation
    description: >-
      Identifies at-risk infants early enough for substrate supply to be restored
      before the window opens.
  evidence:
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If prenatal testing has not been performed on a pregnancy at risk, supplementation with L-cysteine (and possibly N-acetylcysteine) of an at-risk newborn sib should be offered until molecular genetic testing for the family-specific TRMU pathogenic variants has been completed."
    explanation: The specific recommendation to treat before the diagnosis is confirmed in a sibling.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "each sib of an affected individual has at conception a 25% chance of being affected"
    explanation: The recurrence risk that counselling conveys.
discussions:
- discussion_id: trmu_cysteine_window_untested
  kind: KNOWLEDGE_GAP
  prompt: >-
    Has the cysteine-limitation window ever been measured, rather than inferred
    from the age at which infants present?
  rationale: >-
    The substrate-limitation model is the organising idea of this disease. It
    explains the onset, the offset, and the treatment, and it is stated as a
    proposal by the authors who introduced it - "we propose that there is a window
    of time". What is missing is a measurement: nobody has shown hepatic cysteine
    availability tracking mt-tRNA thiolation in a TRMU-deficient infant, or
    demonstrated that thiolation actually rises as the transsulfuration pathway
    matures. The clinical evidence that acting on the model works is now
    substantial - cysteine supplementation improved survival significantly across
    62 patients - but that is a retrospective, unrandomised comparison, and it
    demonstrates that supplying cysteine helps rather than that endogenous
    cysteine shortage is what opens the window in the first place. The narrower
    presymptomatic evidence is still two infants against family controls. The question is not academic: if something
    other than cysteine supply closes the window, then cysteine supplementation is
    treating a correlate, and the timing of when it can be safely stopped is
    unknown.
  attaches_to:
  - pathophysiology#Developmental Cysteine Limitation
  - treatments#L-Cysteine Supplementation
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we propose that there is a window of time whereby patients with TRMU mutations are at increased risk of developing liver failure"
    explanation: The claim is framed by its own authors as a proposal, which is the point of this gap.
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Supplementation with at least 1 cysteine source, typically N-acetylcysteine, improved survival significantly."
    explanation: >-
      Shows that supplying the substrate helps, which is consistent with the model
      without establishing that substrate shortage is what makes the window.
  - reference: PMID:37184193
    reference_title: "TRMU Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, two infants treated presymptomatically overall had a milder clinical course than their affected relatives."
    explanation: The extent of the evidence for treating before symptoms begin.
- discussion_id: trmu_proteostress_arm_is_from_sister_enzyme
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Does the cytosolic proteostress mechanism shown for Mto1 deficiency also
    operate in TRMU deficiency, and does it operate in human liver?
  rationale: >-
    The proteostress arm is attractive because it would explain damage beyond
    simple energy failure and because chemical chaperones rescued it - a
    therapeutic lead that does not exist elsewhere in this disease. But the
    evidence comes from Mto1-deficient cells and mice, not Trmu-deficient ones.
    Mto1 adds the taurine group and TRMU adds the sulfur, at the same wobble
    position of the same three mt-tRNAs, and both losses impair mitochondrial
    translation - so the inference is reasonable. It is still an inference across
    enzymes, and it has a second gap on top: the Trmu liver-specific mouse, which
    is the right enzyme in the right tissue, reports cytoprotective and
    mitochondrial-proliferation responses rather than a cytotoxic unfolded protein
    response. Those are not the same picture, and nobody has looked for either in
    human TRMU-deficient liver. Until they are reconciled, the proteostress node
    should not be treated as a target.
  attaches_to:
  - pathophysiology#Cytosolic Proteostress from Mistargeted Mitochondrial Proteins
  evidence:
  - reference: PMID:29320742
    reference_title: "Defective Mitochondrial tRNA Taurine Modification Activates Global Proteostress and Leads to Mitochondrial Disease."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Here, we showed that taurine modification is catalyzed by mitochondrial optimization 1 (Mto1) in mammals."
    explanation: Establishes that the proteostress work concerns Mto1, the sister enzyme, and not TRMU.
  - reference: PMID:27689697
    reference_title: "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "mitochondrial dysfunction induced signaling pathways related to mitochondrial proliferation and the suppression of oxidative stress"
    explanation: >-
      The right-enzyme model reports a compensatory rather than a cytotoxic stress
      response, which is the tension this discussion records.
- discussion_id: trmu_reversibility_versus_leigh_presentation
  kind: KNOWLEDGE_GAP
  prompt: >-
    What separates the infants who recover completely from those who die, or who
    present with Leigh-like brain lesions?
  rationale: >-
    The disease is named for its reversibility, but four of thirteen infants in
    the founding cohort died in the acute episode, one of three in a later series
    died, and both reported patients with Leigh-like neuroimaging died - one at 25
    days and one at six months. Residual 2-thiolation correlates with prognosis in
    cell-line work, which is the best available answer and is a laboratory
    measurement not available at the bedside. Whether the Leigh-like presentation
    is simply the severe end of one spectrum, or a distinct route in which the
    brain is affected primarily rather than secondarily, is unresolved, and the
    two published patients are too few to tell. A partial answer does exist and is
    available at the bedside: in a 62-patient series, loss-of-function TRMU
    variants were associated with poor survival, so the molecular report itself
    carries prognostic information that the residual-thiolation assay does not
    need to supply. This matters for counselling: a family told the disease is
    reversible is being told something true of survivors, and in most patients -
    42 of 62 were alive at a median age of 6.8 years - it is true.
  attaches_to:
  - pathophysiology#Acute Infantile Liver Failure
  - phenotypes#Leigh-Like Brain Lesions
  evidence:
  - reference: PMID:19732863
    reference_title: "Acute infantile liver failure due to mutations in the TRMU gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four died during the acute episodes, and the survivors never had a recurrence."
    explanation: Quantifies the mortality that the label "reversible" does not convey.
  - reference: PMID:38113276
    reference_title: "Pathological mutations promote proteolysis of mitochondrial tRNA-specific 2-thiouridylase 1 (MTU1) via mitochondrial caseinolytic peptidase (CLPP)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "clinical data analysis underscores a significant correlation between patient prognosis and residual 2-thiolation levels, which is partially consistent with the AlphaMissense predictions"
    explanation: >-
      Residual enzyme activity predicts outcome, which is why severity is graded
      rather than categorical. Graded HUMAN_CLINICAL because the quoted sentence
      reports an analysis of patient data, not the paper's cell-line work.
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Loss-of-function TRMU variants were associated with poor survival."
    explanation: >-
      A genotype-survival correlation in 62 patients, readable directly off a
      molecular report rather than requiring a thiolation assay.
  - reference: PMID:36305855
    reference_title: "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of these 62 individuals, 42 were alive at a median age of 6.8 (0.6-22) years after a median follow-up of 3.6 (0.1-22) years."
    explanation: Gives the survival denominator that the word "reversible" is shorthand for.
references:
- reference: PMID:37184193
  title: "TRMU Deficiency."
  tags:
  - GeneReviews
- reference: PMID:19732863
  title: "Acute infantile liver failure due to mutations in the TRMU gene."
review_notes: >-
  Ten references are cited. Two of them, PMID:36305855 and PMID:33485800, were
  cached by the deep-research citation pass and initially left uncited, which was
  a mistake: PMID:36305855 is a 62-patient international series and is now the
  basis for the cysteine efficacy claim, the genotype-survival correlation, the
  survival denominator, and the acute liver failure frequency band. Two statements
  in the first version of this entry were wrong because it was not read - the
  efficacy evidence was described as two presymptomatically treated infants, and
  residual 2-thiolation was described as the best available prognostic marker when
  a bedside-readable genotype correlation exists. The remaining uncited files come
  from the same citation pass, and DOI_10.1093_nar_gkad1197.md is the same paper
  as the cited PMID:38113276, kept only because the report cites it in DOI form.

  Two snippets failed exact matching on first validation and were corrected
  against the cached text rather than reworded to fit. The first had been
  reconstructed as "Mtu1LKO mice exhibited symptoms of liver injury" where the
  source reads "(Mtu1LKO) mice, which exhibited"; the second carried a bracketed
  citation marker that the validator strips before matching. Both are recorded
  here because the failure mode - a snippet that is nearly right and reads
  perfectly - is the one worth being able to find later.
notes: >-
  Scope and modelling decisions.

  TRMU appears in three existing entries but never as the causal gene of its own
  disease: Aminoglycoside-Induced_Hearing_Loss, where it is a nuclear modifier of
  the m.1555A>G allele, MTO1_Deficiency, and
  Reversible_Infantile_Cytochrome_c_Oxidase_Deficiency. This entry does not
  duplicate any of them. Infantile_Liver_Failure_Syndrome_1 is LARS1, a different
  gene and a different entity, and is not a subtype of this.

  The modifier role is deliberately not curated here. TRMU variants modify
  penetrance of mitochondrial deafness, which is a different phenotype with a
  different mechanism, and folding it in would misrepresent one gene's two
  distinct disease roles as one.

  No environmental section, despite the disease being substrate-limited. Dietary
  cysteine is not an ECTO-style exposure acting on a mechanism node; it is the
  treatment, and it is curated as one. The developmental cysteine shortage is a
  property of infant physiology rather than of the environment, so it is modelled
  as a pathophysiology node.

  No conforms_to. No module in kb/modules covers mitochondrial translation
  failure or tRNA modification; a mitochondrial_translation_failure module would
  be a reasonable follow-up, since MTO1_Deficiency, GTPBP3 disease and this entry
  would all conform to it, but creating one is out of scope for a single curation.

  No clinical trials. Nothing is registered for TRMU deficiency; cysteine
  supplementation entered practice through case reports and expert consensus, not
  a trial, which is worth knowing when reading the treatment section.
📚

References & Deep Research

References

2
PMID:37184193
TRMU Deficiency.
No top-level findings curated for this source.
PMID:19732863
Acute infantile liver failure due to mutations in the TRMU gene.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
TRMU-Related Acute Infantile Liver Failure (TRMU Deficiency): Comprehensive Research Report
claude-haiku-4-5-20251001, claude-sonnet-5 12 citations 2026-08-29T19:41:21.056582

TRMU-Related Acute Infantile Liver Failure (TRMU Deficiency): Comprehensive Research Report

1. Disease Information

Overview

TRMU-related acute infantile liver failure — clinically termed TRMU deficiency — is an autosomal recessive mitochondrial disorder caused by biallelic pathogenic variants in TRMU (tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase, also called MTU1). It is characterized by transient, life-threatening acute liver failure presenting in infancy (classically ages 2–4 months), accompanied by severe lactic acidosis, hypoglycemia, hyperammonemia, and poor weight gain. A defining and clinically critical feature is that, unlike most mitochondrial hepatopathies, survivors of the acute episode typically show full clinical and biochemical resolution of liver disease with no recurrence — hence "transient" (GeneReviews, NBK591557, updated May 2023; OMIM #613070).

Key Identifiers

Resource ID Notes
OMIM (phenotype) #613070 — LIVER FAILURE, INFANTILE, TRANSIENT (LFIT) omim.org/entry/613070
OMIM (gene) *610230 — TRMU Chromosome 22q13.31 (omim.org/entry/610230)
MONDO MONDO:0009723 TRMU deficiency (autosomal recessive, Leigh-syndrome-spectrum related disorder)
Orphanet ORPHA:217371 — Acute infantile liver failure due to synthesis defect of mtDNA-encoded proteins; also cross-referenced under ORPHA:254864 (Mitochondrial myopathy with reversible cytochrome c oxidase deficiency) orpha.net/en/disease/detail/217371
HGNC HGNC:25481 (TRMU)
Gene symbol/aliases TRMU; formerly MTU1, SDO1, KIAA0812
GeneReviews NBK591557 Vogel et al, updated 2023

Synonyms

Reversible infantile liver failure (RILF); transient infantile liver failure due to TRMU mutations; mitochondrial DNA depletion-like syndrome due to TRMU deficiency; MTU1 deficiency.

Evidence base

Information is derived from aggregated disease-level resources (OMIM, Orphanet, GeneReviews, MalaCards) built from pooled case series and cohort studies (not raw EHR data) — most authoritatively the GeneReviews chapter (Vogel et al., 2023) and the largest published cohort to date, Murali et al. and colleagues' Genetics in Medicine study of 62 individuals from 56 families (Vogel CH et al., "Genotypic and phenotypic spectrum of infantile liver failure due to pathogenic TRMU variants," Genet Med 2022 Dec, PMID: 36305855).

2. Etiology

Disease Causal Factors

The sole known cause is biallelic (homozygous or compound heterozygous) pathogenic loss-of-function variants in TRMU (22q13.31), which abolish or reduce the enzyme's 2-thiolation activity on mitochondrial tRNAs. This is a purely genetic/mitochondrial-translation disease; there is no known infectious or purely environmental primary cause, though physiologic/metabolic stress is a key disease-triggering cofactor (see below).

Genetic Risk Factors

  • Causal variants: missense, nonsense, frameshift, splice-site, and small indel variants throughout TRMU; sequence analysis detects ~93% (26/28) of pathogenic alleles, with gene-targeted deletion/duplication analysis detecting the remainder (~7%, 2/28) (GeneReviews).
  • Founder variant: c.229T>C (p.Tyr77His) is a well-documented founder mutation in the Yemenite Jewish population, first described by Zeharia et al. (2009, Am J Hum Genet, PMID: 19732863), the paper that originally established TRMU as the causal gene for this syndrome.
  • Loss-of-function (nonsense/frameshift/splice) variants are significantly associated with worse survival than missense/in-frame indel variants (10/20 deaths in LOF carriers vs. 10/42 in missense/in-frame carriers; p=0.022; GeneReviews, citing Vogel et al. 2023).
  • c.2T>A (p.Met1?) (loss of the start codon) is specifically associated with early mortality despite aggressive management (observed in 5 deceased individuals).

Environmental / Physiologic Risk Factors

  • Age window of vulnerability: acute liver failure occurs almost exclusively within the first year of life (43/62 individuals in the largest cohort), with a specific window of increased risk around 1–4 months of age.
  • Intercurrent illness/physiologic stress: episodes are typically precipitated by febrile illness or other metabolic stress; patients are often well between episodes.
  • Low endogenous cysteine: infants have a physiologic nadir in cystathionase (cystathionine γ-lyase) activity, making cysteine a conditionally essential amino acid in the neonatal/infantile period — this is the key gene-environment (developmental) interaction underlying disease timing (Murali et al., Mol Genet Metab 2021, PMID: 33485800).
  • A case report documents cytomegalovirus infection aggravating/precipitating fatal hepatic dysfunction in a TRMU-mutation carrier (Cureus case report), illustrating infection as a secondary stressor rather than a primary cause.

Protective Factors

  • Presymptomatic/prenatal cysteine + N-acetylcysteine (NAC) supplementation in at-risk siblings (identified via prior affected sibling) is associated with a milder clinical course, less severe acidosis/liver dysfunction, and fewer hospitalizations (GeneReviews).
  • The p.Tyr77His founder allele itself appears relatively protective/lower-mortality compared with other genotypes (0/8 deaths in homozygotes; 1/9 in compound heterozygotes in the Vogel et al. cohort).

Gene-Environment Interaction

The central gene-environment interaction in this disease is the intersection of (1) genetically reduced TRMU thiolation capacity with (2) the developmentally programmed, transient physiologic deficiency of endogenous cysteine synthesis in infancy. This is why the disease is age-restricted and why exogenous cysteine/NAC supplementation is disease-modifying rather than merely supportive.

3. Phenotypes

Frequencies below are from the largest published cohort of 60 untreated symptomatic children (GeneReviews/Vogel et al. 2023):

Phenotype Frequency Onset Suggested HPO term
Liver disease (elevated transaminases/liver dysfunction) 58/60 (97%) 2–4 months typical HP:0001392 (Abnormality of the liver)
Lactic acidosis 44/60 (73%) Acute episodes HP:0003128 (Lactic acidosis)
Jaundice 34/60 (57%) With acute episodes HP:0000952 (Jaundice)
Failure to thrive 33/60 (55%) Progressive HP:0001508 (Failure to thrive)
Emesis/diarrhea 28/60 (47%) Acute episodes HP:0002013 (Vomiting) / HP:0002014 (Diarrhea)
Neurodevelopmental delay 24/60 (40%) Often resolves with liver recovery HP:0012758 (Neurodevelopmental delay)
Hypotonia 20/60 (33%) Acute/subacute HP:0001252 (Hypotonia)
Hypoglycemia 11/28 assessed (39%) Acute episodes HP:0001943 (Hypoglycemia)
Hepatomegaly 13/60 (22%) Acute episodes HP:0002240 (Hepatomegaly)
Cardiomyopathy 5/60 (8%) Variable HP:0001638 (Cardiomyopathy)
Seizures 4/60 (7%) Acute/severe cases HP:0001250 (Seizures)
Coagulopathy Common in acute episodes (specific % not separately tabulated) Acute HP:0001928 (Abnormal coagulation)
Hyperammonemia Reported as metabolic derangement Acute HP:0001987 (Hyperammonemia)
Sensorineural hearing loss Reported in a subset (broader clinical spectrum) Variable, can be later-onset HP:0000407 (Sensorineural hearing loss)
Ragged red fibers on muscle biopsy Subset (histologic finding) — HP:0003200 (Ragged-red muscle fibers)

Phenotype Characteristics

  • Onset: classically 2–4 months of age; presymptomatic/prenatally treated at-risk siblings can be identified and managed before symptom onset.
  • Course: episodic/acute and — in survivors — self-limited and reversible, distinguishing this from most other mitochondrial hepatopathies (e.g., DGUOK, MPV17, POLG-related disease), which are progressive. Genetics in Medicine cohort work also documents a broader phenotypic spectrum, including patients without overt liver failure, some presenting instead with Leigh-syndrome-like neuroimaging (symmetric restricted diffusion in thalami/putamen), chronic respiratory failure, or isolated myopathy (Murali et al. 2021, PMID: 33485800).
  • Severity/variability: highly variable — from fatal neonatal multiorgan failure to mild, self-resolving transaminitis; genotype (LOF vs. missense) and treatment timing are major severity modifiers.
  • Hepatic copper accumulation has been reported as a possible secondary, cholestasis-associated feature in at least one case (Grover et al., JIMD Reports, PMID: 25665837), postulated to be secondary to cholangiopathy rather than a primary TRMU effect.
  • Quality of life: for survivors, long-term outcomes are generally favorable; among 25 followed individuals in the GeneReviews cohort, 9 had full resolution of developmental delay following liver recovery, while 5 had persistent developmental delays — indicating QOL impact is concentrated in the acute period and in the minority with residual neurodevelopmental sequelae.

4. Genetic/Molecular Information

Causal Gene

  • TRMU (HGNC:25481; OMIM *610230), chromosome 22q13.31. Encodes tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase (also known as mitochondrial tRNA-specific 2-thiouridylase 1, MTU1).

Gene Function

TRMU is a nuclear-encoded, mitochondrially targeted enzyme that catalyzes 2-thiolation of uridine at the wobble (position 34) anticodon position of three mitochondrial tRNAs — mt-tRNA^Lys, mt-tRNA^Glu, and mt-tRNA^Gln — generating the modified nucleoside 5-taurinomethyl-2-thiouridine (τm5s2U). This modification is essential for accurate codon-anticodon pairing, translational fidelity, and structural stability of these tRNAs (PubMed 16513084; Suzuki lab reviews, WIREs RNA 2011).

Pathogenic Variants

  • Variant types: missense (most common), nonsense, frameshift, splice-site, small indels, and gene-level deletion/duplication (rare).
  • ACMG classification: cataloged in ClinVar (e.g., RCV001277295, RCV000351468) predominantly as Pathogenic/Likely Pathogenic when biallelic and segregating with disease.
  • Allele frequency: specific gnomAD population allele-frequency figures were not identified in available secondary sources beyond the qualitative statement that overall disease prevalence is <1 per 1,000,000 (OMIM) with founder-elevated frequency of c.229T>C (p.Tyr77His) in the Yemenite Jewish population.
  • Somatic vs. germline: exclusively germline (biallelic recessive); no somatic TRMU disease association reported.
  • Functional consequence: loss of function — reduced or absent thiolation activity leads to loss of τm5s2U modification, reduced steady-state levels of the three target mt-tRNAs, impaired mitochondrial translation of OXPHOS subunits, and downstream respiratory chain complex I, III, and IV deficiency (GeneReviews; muscle biopsy shows decreased complex I/III/IV activity and ragged red fibers).
  • A 2024 mechanistic paper (Nucleic Acids Research, doi:10.1093/nar/gkad1197) shows that pathological MTU1 mutations promote proteolysis of the MTU1 protein via mitochondrial caseinolytic peptidase (CLPP), providing a protein-stability mechanism for how missense variants cause loss of function.

Modifier Genes

  • TRMU acts as a nuclear modifier gene for the phenotypic expression of the deafness-associated mitochondrial 12S rRNA m.1555A>G mutation — i.e., TRMU variants can modulate penetrance/severity of aminoglycoside-induced and non-syndromic hearing loss in carriers of 12S rRNA mutations (Guan et al., PMID: 16513084). This is a related but mechanistically and clinically distinct TRMU-associated phenotype (maternally inherited deafness) from the infantile liver failure syndrome, and should not be conflated with it.
  • Related paralogous tRNA-thiolation pathway genes GTPBP3 and MTO1 cause overlapping/similar τm5s2U-modification-deficiency phenotypes (deafness, reversible liver failure, hypertrophic cardiomyopathy, lactic acidosis) and are relevant differential-diagnosis/pathway partners.

Epigenetic Information

A study describes microRNA-mediated differential expression of TRMU, GTPBP3, and MTO1 in cell models of mitochondrial-DNA disease (PMC5524753), suggesting post-transcriptional/epigenetic-adjacent regulation of this pathway, though this is not established as a primary disease mechanism in TRMU deficiency itself.

Chromosomal Abnormalities

No large-scale chromosomal rearrangements (aneuploidy, translocation) are reported as a cause; disease is driven by intragenic sequence-level variants.

5. Environmental Information

  • No toxic/occupational/pollutant etiology is established; this is a monogenic mitochondrial disease.
  • Nutritional/metabolic environment: the infant's transient physiologic cysteine deficiency (low cystathionase activity) functions as the key "environmental" (developmental-metabolic) permissive factor.
  • Infectious triggers: intercurrent viral illness (e.g., CMV, reported in one fatal case) can precipitate or worsen acute decompensation, acting as a physiologic stressor rather than a primary cause.
  • Drugs to avoid (iatrogenic environmental risk factors that worsen mitochondrial function or increase metabolic demand): corticosteroids, valproic acid, prolonged propofol infusion, fasting, and acetaminophen during liver dysfunction — all flagged in GeneReviews management guidance as agents that can exacerbate hepatic/mitochondrial decompensation.

6. Mechanism / Pathophysiology

Causal Chain

  1. Molecular trigger: Biallelic TRMU loss-of-function variants → loss of 2-thiouridylase activity on mt-tRNA^Lys, mt-tRNA^Glu, mt-tRNA^Gln (loss of τm5s2U wobble modification).
  2. RNA-level consequence: Reduced steady-state levels/stability of thio-modified mitochondrial tRNAs; impaired aminoacylation and codon-anticodon decoding fidelity.
  3. Translational consequence: Impaired mitochondrial protein synthesis — specifically of the 13 mtDNA-encoded OXPHOS subunits — causing combined respiratory chain deficiency (complexes I, III, IV, all of which contain mtDNA-encoded subunits reliant on these tRNAs).
  4. Cellular consequence — proteostress/UPR activation: A key mechanistic paper (Cell Reports, PMID: 29320742) shows that defective mt-tRNA taurine modification (via Mto1/Trmu loss) causes mistrafficking and cytoplasmic aggregation/misfolding of nuclear-DNA-encoded mitochondrial proteins (e.g., OPA1), which activates a cytotoxic unfolded protein response (UPR) and global proteostasis stress — a mechanism distinct from, and additive to, simple OXPHOS insufficiency.
  5. Tissue/organ consequence: Hepatocyte energy failure, cell death (apoptosis/necrosis), and macrophage infiltration. A liver-specific conditional Mtu1 knockout mouse model shows hepatocellular injury with karyomegaly/multinucleation, macrophage infiltration, and spotty necrosis, without fibrosis — closely recapitulating human RILF histology (PLOS Genetics, PMID: 27689697; follow-up NAR work).
  6. Clinical manifestation: Acute hepatic decompensation (jaundice, coagulopathy, transaminitis), systemic lactic acidosis (impaired oxidative phosphorylation → compensatory anaerobic glycolysis), hypoglycemia, and (in a subset) CNS involvement resembling Leigh syndrome (thalamic/putaminal restricted diffusion) and cardiomyopathy.
  7. Reversibility mechanism: Because the defect is a modifiable post-transcriptional RNA modification rather than a structural/genomic lesion, and because the developmental cysteine deficiency is time-limited, hepatocyte and mitochondrial function can recover once the infant ages past the vulnerable cysteine-deficient window and/or receives exogenous sulfur-donor supplementation — explaining the "transient" clinical hallmark unique among mitochondrial hepatopathies.

Molecular Pathways

  • Mitochondrial tRNA wobble-position modification pathway (τm5s2U biosynthesis: TRMU, GTPBP3, MTO1 cooperate).
  • Mitochondrial translation machinery (mitoribosome-dependent synthesis of OXPHOS subunits).
  • Oxidative phosphorylation / electron transport chain (Complexes I, III, IV).
  • Unfolded protein response (mitochondrial and cytosolic UPR) triggered by protein mistargeting.

Cellular Processes

Apoptosis/necrosis of hepatocytes; mitochondrial biogenesis impairment; proteostasis/UPR activation; inflammatory macrophage recruitment; (in bone-related studies) impaired osteogenic differentiation has also been linked to Mtu1 defects (Cell Death & Disease, PMC on osteogenic differentiation), suggesting a broader cell-differentiation impact of τm5s2U loss beyond hepatocytes.

Protein Dysfunction

Loss-of-function/reduced enzymatic activity of TRMU protein; some pathogenic missense variants additionally destabilize the protein and target it for proteolysis via mitochondrial CLPP protease, compounding the enzymatic defect with reduced protein abundance (NAR 2024, doi:10.1093/nar/gkad1197).

Metabolic Changes

Lactic acidosis (impaired pyruvate oxidation via ETC dysfunction); hypoglycemia (impaired hepatic gluconeogenesis/energy failure); hyperammonemia (impaired urea cycle function secondary to hepatocellular failure); disrupted sulfur amino acid (cysteine/taurine) metabolism as the central biochemical lever of both pathogenesis and treatment.

Immune System Involvement

Secondary innate immune activation — macrophage infiltration into injured liver tissue is a consistent histologic finding in both human liver biopsies and the mouse model, reflecting a response to hepatocyte injury rather than primary autoimmune/immunodeficiency pathology.

Tissue Damage Mechanisms

Hepatocellular necrosis/apoptosis, oxidative-phosphorylation failure-driven energy crisis, and proteostress-induced cytotoxicity converge on hepatocyte death; histologically the human liver shows bridging fibrosis, cirrhosis (in some cases), steatosis, and mitochondrial proliferation on biopsy (GeneReviews).

Biochemical Abnormalities

Specific enzymatic defect: loss of mitochondrial tRNA 2-thiouridylase activity (EC 2.8.1.-); combined respiratory chain complex I, III, IV deficiency on muscle biopsy enzymology.

Suggested Ontology Terms

  • GO (Biological Process): GO:0002143 (tRNA wobble position uridine thiolation), GO:0032543 (mitochondrial translation), GO:0006120 (mitochondrial electron transport, NADH to ubiquinone), GO:0034341 (response to type II interferon — not core), GO:0006986 (response to unfolded protein / UPR-related terms), GO:0006915 (apoptotic process).
  • GO (Cellular Component): GO:0005739 (mitochondrion), GO:0005759 (mitochondrial matrix), GO:0005743 (mitochondrial inner membrane).
  • CL (Cell Type): CL:0000182 (hepatocyte), CL:0000235 (macrophage), CL:0000187 (muscle cell — for the myopathic phenotype).

7. Anatomical Structures Affected

Organ Level

  • Primary organ: Liver (UBERON:0002107) — the dominant and most consistent manifestation.
  • Secondary/associated organ involvement: brain (Leigh-syndrome-like lesions in thalami, putamen, basal nuclei, pontine tracts — UBERON:0001897 thalamus, UBERON:0001874 putamen), heart (cardiomyopathy — UBERON:0000948), skeletal muscle (myopathy, ragged red fibers — UBERON:0001134), inner ear (sensorineural hearing loss, in the broader spectrum/related deafness phenotype — UBERON:0001846 cochlea).
  • Body systems: hepatic, metabolic/endocrine (hypoglycemia, lactic acidosis), hematologic (coagulopathy), neurologic, cardiovascular, and (in related phenotypes) audiologic.

Tissue and Cell Level

  • Hepatocytes (CL:0000182) — primary target of injury.
  • Kupffer cells/macrophages (CL:0000235) — secondary inflammatory infiltration.
  • Skeletal muscle fibers with ragged red fiber morphology (mitochondrial proliferation).
  • Cochlear hair cells (in zebrafish model and in human deafness-associated phenotype).

Subcellular Level

  • Mitochondrial matrix (GO:0005759) — site of tRNA modification defect and impaired translation.
  • Mitochondrial inner membrane (GO:0005743) — site of the respiratory chain complexes affected.
  • Cytoplasm — secondary site of misfolded/mistargeted protein aggregation (proteostress mechanism).

Localization

Diffuse/bilateral, symmetric involvement is typical for the brain lesions (symmetric thalamic/putaminal restricted diffusion) — not lateralized. Liver involvement is diffuse (whole-organ hepatocellular dysfunction), not focal.

8. Temporal Development

  • Onset: typically 2–4 months of age (infantile), occasionally as early as neonatal or as late as ~1 year; presymptomatic identification possible in at-risk siblings via prenatal/newborn testing.
  • Onset pattern: acute — episodes of decompensation are abrupt, often precipitated by intercurrent illness.
  • Disease course pattern: episodic and, in survivors, self-limited/monophasic — this is the disease's defining feature. Acute liver failure occurs only in the first year of life (43/62 in the largest cohort); survivors of the initial episode show clinical/biochemical resolution and no further episodes (OMIM #613070).
  • Progression rate: rapid during the acute episode (can progress to multiorgan failure and death within weeks); but the overall disease is not chronically progressive in survivors, unlike most mitochondrial hepatopathies.
  • Critical period: the first ~4–6 months of life, corresponding to the developmental nadir of endogenous cystathionase activity — the key window for both risk and for the protective effect of early cysteine/NAC supplementation.
  • Remission: spontaneous biochemical/clinical resolution occurs in survivors after the acute window passes, and is further improved by treatment (cysteine supplementation); this is not "treatment-induced remission" in the oncologic sense but genuine reversal of the acute hepatopathy.

9. Inheritance and Population

Epidemiology

  • Prevalence: <1 per 1,000,000 (OMIM), consistent with an ultra-rare disease.
  • Cohort size reported to date: 62 individuals from 56 families in the largest combined cohort (GeneReviews/Vogel et al. 2023, Genet Med, PMID: 36305855).

Inheritance Pattern

  • Autosomal recessive. For carrier parents: 25% risk of an affected child, 50% risk of a carrier child, 25% risk of an unaffected/non-carrier child per pregnancy (GeneReviews).

Penetrance / Expressivity

  • Penetrance and expressivity are variable — presentation ranges from asymptomatic/mild transaminitis to fatal multiorgan failure, with genotype (LOF vs. missense) as a major modifier of severity.

Founder Effects

  • c.229T>C (p.Tyr77His) is a well-established founder variant in the Yemenite Jewish population, first reported by Zeharia et al. (2009, PMID: 19732863).

Consanguinity

  • As an autosomal recessive disease, consanguineous unions increase risk in affected families/populations, consistent with the founder-population pattern described.

Population Demographics

  • Highest documented ancestry association: Yemenite Jewish founder population; cases are otherwise reported across diverse ethnicities/geographies (cohorts include patients from the US, China, and elsewhere), indicating global but very low-frequency distribution with no single dominant geographic endemic focus outside the noted founder population.
  • Sex ratio: no sex predilection reported (autosomal recessive; no data suggesting skew).
  • Age distribution of affected individuals: concentrated in the first year of life at symptom onset; median age at death (in fatal cases) reported as ~3 months.

10. Diagnostics

Clinical/Laboratory Tests

  • Liver function panel: elevated transaminases (AST/ALT), elevated bilirubin, coagulopathy (elevated INR/PT).
  • Metabolic panel: elevated serum/plasma lactate (HP:0002151), hypoglycemia, hyperammonemia.
  • Muscle biopsy: ragged red fibers; decreased respiratory chain complex I, III, IV enzyme activities.
  • Liver biopsy histology: bridging fibrosis, cirrhosis, steatosis, mitochondrial proliferation.
  • Brain MRI: variable lesions in thalami, putamen, basal ganglia, and pontine tracts (Leigh-syndrome-like), which may normalize after clinical recovery.

Genetic Testing

  • Diagnosis is established by molecular genetic testing identifying biallelic pathogenic TRMU variants.
  • Approach: mitochondrial disease, cholestasis, or acute infantile liver failure multigene panels; or comprehensive genomic testing (exome/genome sequencing) when the phenotype is broad/atypical.
  • Yield: sequence analysis detects ~93% of pathogenic alleles (26/28); deletion/duplication analysis detects the remainder (~7%, 2/28) (GeneReviews Table 2).
  • Prenatal/presymptomatic testing: feasible and clinically used in at-risk families with a known familial variant, enabling presymptomatic/prenatal cysteine supplementation (as documented in multiple case reports).

Differential Diagnosis (from GeneReviews)

Deoxyguanosine kinase (DGUOK) deficiency; Leigh syndrome (>90 causal genes); POLG-related Alpers-Huttenlocher syndrome; SERAC1 deficiency; other mtDNA maintenance disorders (MPV17, DGUOK); organic acidemias (propionic acidemia, methylmalonic acidemia); fatty acid oxidation disorders (MCAD, VLCAD, SCAD deficiency); glycogen storage disease type Ia. Related genes in the same τm5s2U-modification pathway — GTPBP3 and MTO1 — cause phenotypically overlapping disease (deafness, reversible liver failure, hypertrophic cardiomyopathy, lactic acidosis) and should specifically be considered/excluded.

Screening

No population-based newborn screening currently exists for TRMU deficiency specifically (it is not part of standard NBS panels); the recommended approach in suspected/at-risk cases is targeted familial variant testing and prenatal diagnosis once a proband is identified, combined with a low-risk empiric-treatment strategy (starting cysteine/NAC supplementation) in symptomatic infants with compatible biochemistry (persistent lactic acidosis + hypoglycemia) even before molecular confirmation, given its safety and time-critical benefit (Murali et al. 2021, PMID: 33485800).

11. Outcome/Prognosis

Survival and Mortality

  • Mortality among symptomatic children: 20/60 (33%) died in the largest reported cohort.
  • Causes: 8 from liver failure complications, 8 from multiorgan failure, 3 from cardiorespiratory failure, 1 from sepsis.
  • Median age at death: 3 months.
  • Overall cohort survival (all 62 individuals, symptomatic and presymptomatic combined): 42/62 alive at a median age of 6.8 years, median follow-up 3.6 years (Vogel et al. 2023 per WebSearch synthesis of GeneReviews/GIM data).
  • Impact of cysteine/NAC supplementation on survival: survival beyond acute decompensation was 84% in supplemented children vs. 61% in unsupplemented children (GeneReviews, citing Vogel et al. 2023) — a substantial, clinically actionable treatment effect.
  • Genotype effect on survival: LOF variants → 10/20 deaths; missense/in-frame indel variants → 10/42 deaths (p=0.022). The Yemenite founder variant p.Tyr77His is associated with the lowest mortality (0/8 homozygotes, 1/9 compound heterozygotes died).
  • Follow-up duration by variant class: nonsense/frameshift/splice variant carriers had shorter average follow-up (38 months) than missense/in-frame indel carriers (78 months), consistent with earlier mortality in the LOF group.

Morbidity / Functional Outcomes

  • Among 25 long-term followed individuals: 9 had full resolution of neurodevelopmental delay after liver recovery; 5 had persistent developmental delays.
  • Liver transplantation does not appear to improve overall survival: 11 children underwent orthotopic liver transplantation at a median age of 4 months, but two post-transplant deaths were reported, and GeneReviews states transplantation "did not influence overall survival" — an important finding given that this is otherwise a self-limited disease, meaning transplant may treat a transient problem with a permanent, high-risk intervention.

Prognostic Factors

  • Genotype (LOF vs. missense), timing of cysteine/NAC initiation (pre-symptomatic/early vs. late), and severity of the initial acute episode are the principal prognostic determinants identified to date.

12. Treatment

Targeted (Disease-Modifying) Therapy: Sulfur-Donor Supplementation

This is the only disease-specific/targeted therapy currently established, and represents a genuine precision-metabolic intervention aimed directly at the enzymatic substrate deficiency.

  • Regimen: combined L-cysteine (85–300 mg/kg/day, goal 300 mg/kg/day) and N-acetylcysteine (NAC) (70–150 mg/kg/day; proposed total combined goal 300 mg/kg/day with 150 mg/kg/day as NAC) (GeneReviews; Murali et al. 2021, PMID: 33485800).
  • Duration: minimum through the first year of life (the vulnerable cysteine-deficient developmental window).
  • Mechanism: provides exogenous sulfur donor to compensate for reduced TRMU enzymatic capacity and for the physiologic infantile cystathionase nadir, increasing thiouridylation of residual/partially functional mitochondrial tRNAs.
  • Evidence: multiple case reports (e.g., Sasarman et al., ScienceDirect S2214426918301332 — "L-Cysteine supplementation prevents liver transplantation in a patient with TRMU deficiency") and cohort data (84% vs. 61% survival, above) support benefit; presymptomatic/prenatal initiation produces the mildest courses.
  • NCIT term suggestion: NCIT:C15986 (Pharmacotherapy) as the treatment action, with therapeutic_agent bound to CHEBI for L-cysteine (CHEBI:17561) and N-acetylcysteine (CHEBI:47704).

Supportive Care

  • Management of hypoglycemia, lactic acidosis, coagulopathy, and hyperammonemia during acute episodes.
  • Feeding support (may require gastrostomy tube) for failure to thrive.
  • Seizure management as needed.
  • Cardiac monitoring (given cardiomyopathy risk).
  • Developmental/early intervention services (ages 0–3) and special education as needed for children with persistent neurodevelopmental delay.
  • NCIT terms: NCIT:C15747 (Supportive Care), NCIT:C15302 (Physical Therapy)/rehabilitation as applicable.

Surgical/Interventional

  • Orthotopic liver transplantation: has been performed (11 children at median age 4 months in the largest cohort) for hepatopathy unresponsive to medical management, but does not appear to improve overall survival compared with medical management given the disease's transient/reversible natural history — a critical nuance for clinical decision-making (avoid unless truly refractory, given the risk of transplanting a self-limited disease). NCIT:C15289 (Organ Transplantation).

Agents to Avoid (iatrogenic risk)

  • Corticosteroids (increase metabolic demand).
  • Valproic acid and prolonged propofol infusion (mitochondrial toxicity/inhibition).
  • Fasting (worsens hypoglycemia and metabolic demand).
  • Acetaminophen during active liver dysfunction.

Experimental/Research Directions

No gene therapy, RNA-based therapy, or targeted molecular therapy beyond sulfur-donor supplementation is currently in clinical trials specifically for TRMU deficiency, per available search results; mechanistic work on CLPP-mediated proteolysis of mutant MTU1 protein (NAR 2024) suggests a potential future therapeutic angle (e.g., CLPP inhibition to stabilize residual mutant protein), but this remains preclinical.

Treatment Strategy / Algorithm

Given the low risk and potential high benefit, GeneReviews and Murali et al. recommend empiric initiation of combined L-cysteine + NAC supplementation in any infant with persistent lactic acidosis and hypoglycemia suggestive of TRMU deficiency, even prior to molecular confirmation, alongside standard supportive metabolic/hepatic care, while genetic testing is pending.

13. Prevention

Primary Prevention

No population-level primary prevention (e.g., vaccination) applies to this genetic disease. The principal actionable "prevention" is presymptomatic identification and early/prenatal cysteine-NAC supplementation in at-risk siblings once a family's causal variant is known — documented to blunt disease severity substantially.

Screening and Early Detection

  • Genetic carrier screening / cascade testing: recommended in families with a known affected child, especially relevant in populations with elevated carrier frequency (e.g., Yemenite Jewish ancestry) — following the standard ACMG/genetic-counseling framework for autosomal recessive disease.
  • Prenatal diagnosis: has been used clinically (e.g., a documented case of prenatal L-cysteine initiation in the third trimester based on prenatal molecular diagnosis).
  • Not currently part of routine population newborn screening panels.

Genetic Counseling

Standard autosomal recessive counseling: 25%/50%/25% recurrence risk pattern per pregnancy for carrier couples; particular relevance for genetic counseling in Yemenite Jewish families given the founder variant.

Prophylaxis

Early/prophylactic cysteine + NAC supplementation in genetically identified at-risk (presymptomatic) infants functions as a form of secondary/tertiary prevention, reducing severity of the first (and typically only) disease episode.

14. Other Species / Natural Disease

  • No naturally occurring TRMU-deficiency disease has been reported in companion animals or wildlife in the literature surveyed; this appears to be a laboratory-model-only cross-species picture (see Model Organisms, below) rather than a naturally occurring veterinary disease.
  • Orthologous gene: Trmu/Mtu1 is conserved across vertebrates (mouse Trmu, NCBI Gene; zebrafish trmu/mtu1, ZFIN ZDB-GENE-050522-540), reflecting deep evolutionary conservation of the mitochondrial tRNA thiolation pathway.

15. Model Organisms

Zebrafish (Danio rerio)

  • mtu1 (trmu) knockout zebrafish (Zhou et al., Nucleic Acids Research 2018, PMID: 30137487; full text) show:
  • Abolished 2-thiouridine modification of mt-tRNA^Lys, mt-tRNA^Glu, mt-tRNA^Gln.
  • Impaired mitochondrial translation, respiratory complex activity reduced to 38–83% of wild-type, mitochondrial ATP production reduced to ~51% in homozygous mutants.
  • Auditory/vestibular phenotype: abnormal startle response and swimming behavior (~42% of larvae abnormal swimming, ~23% weak/absent startle), reduced saccular otolith size, reduced hair cell numbers and hair bundle density in inner ear structures — modeling the deafness component of the human TRMU-associated phenotypic spectrum, though this particular model did not recapitulate liver pathology at the stages examined.
  • A related zebrafish model of Mto1 ablation (pathway partner gene) shows hypertrophic cardiomyopathy via mitochondrial RNA maturation deficiency (PMC8096277), relevant as a comparative model for the cardiomyopathy phenotype seen in a subset of human TRMU-deficiency patients.

Mouse (Mus musculus)

  • Global Mtu1 (Trmu) knockout is embryonic lethal at a very early developmental stage, precluding study of postnatal disease in constitutive knockouts.
  • Liver-specific conditional knockout mice (Mtu1-LKO) show:
  • Severe liver injury with hepatocyte cell death, macrophage infiltration, and spotty necrosis.
  • Enlarged hepatocytes with karyomegaly and multinucleation.
  • Notably, no significant fibrosis, distinguishing the acute-injury mouse model from some human biopsy findings of fibrosis/cirrhosis in severe cases.
  • This model is described as closely resembling the histologic features of human RILF (PLOS Genetics, PMID: 27689697, "Mtu1-Mediated Thiouridine Formation of Mitochondrial tRNAs Is Required for Mitochondrial Translation and Is Involved in Reversible Infantile Liver Injury").
  • Additional mouse/cell-based work links Mtu1 defects to impaired osteogenic differentiation (Cell Death & Disease, doi:10.1038/s41419-020-03345-5), suggesting a broader tissue impact of the pathway beyond liver, ear, and heart that may be under-recognized clinically.

Model Recapitulation Assessment

  • Zebrafish model: high fidelity for the auditory/hair-cell and mitochondrial bioenergetic phenotype; does not recapitulate the hepatic phenotype at examined stages — a translational gap (candidate for a HUMAN_MODEL_MISMATCH-type annotation if curated into a knowledge base).
  • Liver-conditional mouse model: high fidelity for acute hepatocellular injury/macrophage infiltration; partially recapitulates human histology (misses fibrosis seen in some human cases) and, being an induced conditional knockout, does not model the transient/reversible natural history directly (the mouse model is not reported to spontaneously resolve).
  • Global mouse knockout: fails to recapitulate any postnatal phenotype due to embryonic lethality, underscoring that a full-body, physiological TRMU-null state is likely incompatible with life in mammals — a key mechanistic insight, since human patients rarely if ever carry complete null/null genotypes (most surviving patients carry at least one hypomorphic/missense allele).

Summary of Key Evidence-Grade Citations

Claim Source PMID/DOI
Original gene discovery, Yemenite founder mutation Zeharia et al. 2009, Am J Hum Genet PMID: 19732863
Largest cohort (62 individuals/56 families), genotype-phenotype, survival stats Vogel et al. 2023 (cited in GeneReviews); Genotypic/phenotypic spectrum paper PMID: 36305855; GeneReviews NBK591557
Cysteine/NAC treatment protocol and case outcomes Murali et al. 2021, Mol Genet Metab PMID: 33485800
Mechanism: proteostress/UPR activation Cell Reports 2017 PMID: 29320742
Zebrafish model (hearing, mito biogenesis) Zhou et al. 2018, NAR PMID: 30137487
Mouse liver-conditional knockout model PLOS Genetics 2016 PMID: 27689697
CLPP-mediated proteolysis mechanism NAR 2024 doi:10.1093/nar/gkad1197
Hepatic copper accumulation case Grover et al., JIMD Reports PMID: 25665837
TRMU as modifier of 12S rRNA deafness Guan et al. PMID: 16513084
OMIM phenotype/gene entries OMIM #613070; *610230

Notes on Information Gaps

  • Specific gnomAD population allele-frequency and carrier-frequency figures for individual TRMU pathogenic variants were not retrievable from the sources searched (beyond the qualitative OMIM prevalence estimate of <1/1,000,000 and the known Yemenite Jewish founder-variant enrichment); direct gnomAD/ClinVar query would be needed to populate this precisely.
  • Detailed transcriptomic/proteomic/metabolomic dataset accessions (GEO, MetaboLights, etc.) specific to TRMU-deficiency patient or model-organism samples were not identified in this search and may require a dedicated dataset-repository search (e.g., GEO query for "TRMU" or "Mtu1").
  • Full OMIM Clinical Synopsis (categorized organ-system checklist) and the complete Genetics in Medicine full-text (both paywalled/403 in this session) could supplement further granular phenotype-frequency and variant-table detail if full-text access is available in a curation environment (e.g., via institutional subscription or PubMed Central when eligible).

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 12
Resolved 12
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 12
On topic 8
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 45
Resolved 42
Unresolved (possible confabulation) 0
Obsolete 0
Unverifiable 3
Terms whose name was checked 33
Terms named correctly 25
Terms named as a different term 3
Terms whose name is worth a second look 5

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • MONDO:0009723 (1 mention) - the report calls it "MONDO"; MONDO calls it Leigh syndrome
  • CL:0000187 (1 mention) - the report calls it "muscle cell — for the myopathic phenotype"; CL calls it muscle cell
  • UBERON:0002107 (1 mention) - the report calls it "Liver", "Primary organ: Liver"; UBERON calls it liver

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • HP:0001928 (1 mention) - the report calls it "Abnormal coagulation"; HP calls it Abnormality of coagulation
  • GO:0034341 (1 mention) - the report calls it "response to type II interferon — not core"; GO calls it response to type II interferon
  • GO:0006986 (1 mention) - the report calls it "response to unfolded protein / UPR-related terms"; GO calls it response to unfolded protein
  • CL:0000235 (2 mentions) - the report calls it "macrophage", "Kupffer cells/macrophages"; CL calls it macrophage
  • HP:0002151 (1 mention) - the report calls it "Metabolic panel: elevated serum/plasma lactate"; HP calls it Increased circulating lactate concentration**, and lists "Increased serum lactate" among its other names

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • GO:0005759 - called "mitochondrial matrix", "Mitochondrial matrix"
  • GO:0005743 - called "mitochondrial inner membrane", "Mitochondrial inner membrane"
  • CL:0000182 - called "hepatocyte", "Hepatocytes"
  • CL:0000235 - called "macrophage", "Kupffer cells/macrophages"
  • UBERON:0002107 - called "Liver", "Primary organ: Liver"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.