Infantile Liver Failure Syndrome 1

Mendelian MONDO:0024568 Pathograph 15 Show in embeddings browser hereditary disease Inborn Error of Metabolism Aminoacyl-tRNA Synthetase Deficiency

Infantile liver failure syndrome 1 (ILFS1) is a recessive multisystem disorder caused by biallelic variants in LARS1, the gene for the CYTOPLASMIC leucyl-tRNA synthetase (LeuRS). LeuRS charges leucine onto tRNA-Leu, the first committed step in incorporating leucine into every cytoplasmic protein, so the disease belongs to the recessive aminoacyl-tRNA-synthetase (ARS) deficiency family alongside SARS1, MARS1 and others. What makes ILFS1 mechanistically legible is that its residual enzyme is temperature-sensitive. Aminoacylation activity in patient fibroblasts is not merely low at baseline; it falls significantly further when the cells are warmed. That single in vitro observation explains the clinical rhythm of the disease, which is otherwise puzzling: patients are relatively well between episodes and decompensate during febrile illness. Fever both raises the temperature at which the crippled enzyme must work and raises the demand for protein synthesis, and the liver - the body's highest-throughput secretory protein factory - fails first. The phenotype accordingly pairs a hepatic axis (recurrent transaminase elevation up to frank acute liver failure, hypoalbuminemia) with a haematological axis (microcytic anemia), a growth axis (low birth weight, early failure to thrive) and a neurological axis (developmental delay, seizures, and encephalopathic episodes whose MRI signature - deep grey matter and brainstem change - is reported as distinct from hepatic encephalopathy or from the metabolic stroke of organic acidurias). Two clinical inversions are worth stating plainly because they run against reflex management. First, the standard metabolic-hepatopathy move of restricting protein appears inappropriate here, since the lesion is a failure to USE amino acids rather than a failure to clear them. Second, encephalopathy is not simply downstream of the liver: it has occurred in one individual after liver transplantation, and episodes can occur independently of hepatic dysfunction. Prognosis is not uniformly poor - episodes become less severe with age and two patients in the founding cohort were well beyond 28 years.

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1
Inheritance
9
Pathophys.
13
Phenotypes
4
Gaps
15
Pathograph
1
Genes
4
Medical Actions
1
Models
9
References
1
Deep Research
👪

Inheritance

1
Autosomal Recessive HP:0000007
Biallelic LARS1 variants. The founding kindred was a consanguineous Irish Traveller family segregating a homozygous missense allele; subsequent cohorts include compound heterozygotes and at least one Ashkenazi family, so the disease is not confined to a single founder population.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:22607940 SUPPORT Human Clinical
"Whole exome sequencing identified 1 novel homozygous missense mutation within the 5q31.3-q33.1 candidate region that segregated with the hepatopathy."
Establishes homozygous, recessive segregation of the causal allele in the founding consanguineous family.
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Discussions and Knowledge Gaps

4
Does excessive autophagy contribute to human ILFS1 liver injury, or is it a property of the zebrafish null that does not transfer to partial loss-of-function human alleles?
HUMAN MODEL MISMATCH ilfs1_autophagy_arm_human_validity
Attached to
pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
The autophagy branch is supported entirely by larsb-knockout zebrafish, where suppressing autophagy genuinely rescued liver size and survival. Two features of that model argue for caution before carrying it into human biology. It is a NULL, whereas human ILFS1 alleles retain temperature-sensitive residual activity; and its phenotype is progressive and lethal within 12 days, whereas the human disease is episodic and survivable into adulthood. The mismatch matters practically because the fish result points at autophagy or mTORC1 inhibitors as candidate therapies, and that inference is only as good as the model's fidelity to a partial loss-of-function human disease.
Proposed experiments
Autophagic flux in ILFS1 patient hepatocyte-like cells at febrile temperature
ilfs1_autophagic_flux_at_febrile_temperature
Measure autophagic flux (LC3-II turnover with and without lysosomal block) in patient-derived hepatocyte-like cells at 37 C and at 40 C, against controls, to test whether excessive autophagy is present in human cells carrying partial loss-of-function alleles and whether it is temperature-dependent in the way aminoacylation activity is.
Would support
pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
Would refute
pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
Supporting outcome
  • Increased autophagic flux in patient cells relative to controls, amplified at the higher temperature.
Refuting outcome
  • Autophagic flux indistinguishable from controls at both temperatures, indicating the fish finding reflects the null genotype rather than the human disease mechanism.
Why does a cytoplasmic leucine-charging defect produce a MICROCYTIC anemia specifically?
KNOWLEDGE GAP ilfs1_microcytosis_unexplained
Attached to
pathophysiology#Microcytic Anemia
Anemia is early and near-universal and is reproduced in the zebrafish model, so it is a direct consequence of LeuRS deficiency rather than a secondary effect of liver disease. But microcytosis normally points at haem or globin synthesis, and no published work connects leucyl-tRNA charging to either. The causal edge into this node is annotated INDIRECT_UNKNOWN_INTERMEDIATES for exactly this reason.
Has reduced protein synthesis actually been measured in ILFS1 patient tissue, or is the translational step inferred from the enzyme assay and the clinical phenotype either side of it?
KNOWLEDGE GAP ilfs1_translation_step_unmeasured
Attached to
pathophysiology#Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
The entry's central causal chain runs enzyme activity to translation to organ failure, but only the two ends are measured. No published study reports global or tissue-specific translation rates in ILFS1 material. The step is retained because no alternative route from a charging defect to hypoalbuminemia has been proposed, but it is graded PROVISIONAL and flagged here rather than presented as established.
What is the direct mechanism of brain injury in ILFS1, given that encephalopathy can occur without hepatic dysfunction?
OPEN QUESTION ilfs1_encephalopathy_independent_of_liver
Attached to
pathophysiology#Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury
Encephalopathy after liver transplantation, and encephalopathic episodes occurring independently of liver crises in a separate cohort, together rule out a purely hepatic-encephalopathy explanation. The MRI pattern is also reported as distinct from hepatic encephalopathy and from metabolic stroke in organic acidurias and mitochondrial disease. What remains is a neuronal protein-synthesis deficit acting directly, which is plausible and untested. The imaging authors state the pathomechanism remains unclear.
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Pathophysiology

9
Biallelic LARS1 Variants
The primary lesion is biallelic damage to LARS1 at 5q32, encoding cytoplasmic leucyl-tRNA synthetase. The founding allele was a homozygous missense variant mapped by homozygosity mapping to 5q31.3-q33.1; the allelic series has since broadened substantially, with eight previously unreported variants added in a single 2020 series. A structural observation from the zebrafish work is that most reported human LARS1 variants fall in the editing domain - the proofreading module that hydrolyses mischarged tRNA - rather than in the aminoacylation active site itself.
LARS1 hgnc:6512 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves LARS1 (hgnc:6512). hgnc:6512 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Reduced Leucyl-tRNA Aminoacylation Capacity Damaged LeuRS charges less leucine onto tRNA-Leu, reducing total cellular charging capacity.
Show evidence (3 references)
PMID:22607940 SUPPORT Human Clinical
"The candidate mutation is located in the LARS gene which encodes a cytoplasmic leucyl-tRNA synthetase enzyme responsible for exclusively attaching leucine to its cognate tRNA during protein translation."
The discovery report identifying LARS1 and stating the enzyme's function, which is the premise of the whole mechanism.
PMID:32699352 SUPPORT Human Clinical
"Biallelic variants in LARS1, coding for the cytosolic leucyl-tRNA synthetase, cause infantile liver failure syndrome 1 (ILFS1)."
Confirms the biallelic LARS1 genotype-disease relationship in the largest systematic cohort.
PMID:33863987 SUPPORT Model Organism
"Notably, most LARS gene mutations in humans occur in the editing domain"
Records the editing-domain clustering of human alleles. Graded PARTIAL because the statement appears as background framing in a zebrafish paper rather than as that paper's own systematic allele survey.
Reduced Leucyl-tRNA Aminoacylation Capacity
The core enzymatic deficit, and the one measured directly in patient material. Aminoacylation activity is reduced in fibroblasts from every patient tested. Crucially the reduction is not fixed: it is significantly worse at elevated temperature, which makes the residual enzyme conditionally rather than constitutively insufficient. This is the mechanistic hinge of the entry - it converts a static enzyme deficiency into an episodic disease.
LARS1 hgnc:6512 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves LARS1 (hgnc:6512). hgnc:6512 is a gene from the HUGO Gene Nomenclature Committee.
leucyl-tRNA aminoacylation GO:0006429 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased leucyl-tRNA aminoacylation (GO:0006429). GO:0006429 is a biological process from the Gene Ontology. ↓ DECREASED
leucine-tRNA ligase activity GO:0004823 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased leucine-tRNA ligase activity (GO:0004823). GO:0004823 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Febrile Decompensation of Residual Charging Capacity Because the residual activity is temperature-sensitive, a rise in body temperature further reduces it.
Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues Reduced charging capacity limits translational throughput wherever demand is highest, which at baseline is the liver.
Show evidence (1 reference)
PMID:32699352 SUPPORT In Vitro
"Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
The direct enzymatic measurement in patient-derived cells, and the temperature dependence that the rest of the entry turns on.
Febrile Decompensation of Residual Charging Capacity
The trigger node. Intercurrent febrile illness is the near-universal precipitant of both hepatic and encephalopathic crises across every published cohort - it was reported as the trigger for encephalopathic episodes in 80% of the ten-patient clinical series, and as the trigger of both crisis types in the twenty-five-patient series. The proposed explanation combines two effects that act in the same direction: fever lowers the temperature-sensitive enzyme's residual activity, while infection raises catabolic and acute-phase protein demand. That combination is a proposal that fits the in vitro temperature data rather than a directly demonstrated in vivo chain, and the MRI study is explicit that the pathomechanism remains unclear.
cellular response to heat GO:0034605 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal cellular response to heat (GO:0034605). GO:0034605 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues The febrile drop in charging capacity is what converts a tolerable chronic deficit into an acute translational failure.
Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury Encephalopathic episodes are infection-triggered in every cohort that reports them, so the trigger node feeds the neurological arm as well as the hepatic one. The edge is INDIRECT_UNKNOWN_INTERMEDIATES rather than DIRECT because nothing establishes what happens between the febrile drop in charging capacity and the deep grey matter and brainstem injury - the imaging authors state the pathomechanism remains unclear. Drawing this edge does NOT route the encephalopathy through the liver: it runs from the shared trigger, which is what lets the arm stay independent of hepatic failure.
Show evidence (5 references)
PMID:32699352 SUPPORT Human Clinical
"The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness."
Establishes febrile illness as the trigger for both crisis types in the largest cohort.
PMID:25917789 SUPPORT Human Clinical
"Encephalopathic episodes triggered by febrile illness have occurred in 80 % and were fatal in two children."
Quantifies the frequency and the lethality of febrile-triggered encephalopathy in the ten-patient clinical series.
PMID:34194004 SUPPORT In Vitro
"Aminoacylation activity was reduced in all patients, and further diminished at 38.5/40 °C (PLARS and PFARSB), consistent with infectious deteriorations."
Independent confirmation of the temperature effect at febrile temperatures specifically, in the LARS patient among others, and the authors' own link from it to infectious deterioration.
+ 2 more references
Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
With leucine charging limiting, cytoplasmic translation cannot keep pace with demand. The tissue distribution of the disease follows protein-synthetic throughput rather than LARS1 expression: hepatocytes, which manufacture and secrete albumin and the acute-phase proteins, are affected first and hardest. This is the proposed unifying premise of the recessive ARS deficiencies generally - residual aminoacylation suffices at baseline but not under load.
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.
cytoplasmic translation GO:0002181 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cytoplasmic translation (GO:0002181). GO:0002181 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Recurrent Hepatocellular Injury and Acute Liver Failure Hepatocytes are the highest-throughput protein-synthetic cells and fail first.
Hypoalbuminemia Albumin is the single largest hepatic secretory product, so its plasma level is a direct readout of hepatic synthetic capacity.
Microcytic Anemia Anemia is present from early infancy in essentially all patients, but the route from a leucine-charging defect to a MICROCYTIC red-cell phenotype specifically has not been established.
Show evidence (1 reference)
PMID:22607940 SUPPORT Human Clinical
"responsible for exclusively attaching leucine to its cognate tRNA during protein translation"
Supports the enzyme's role in translation, which is the premise of this node. Graded PARTIAL because it evidences the normal function rather than measuring impaired translation in patients.
Dysregulated mTORC1 Signalling and Excessive Autophagy
A second, non-canonical arm. Beyond charging tRNA, LeuRS acts as the intracellular leucine sensor that permits amino-acid-induced mTORC1 activation. In larsb-knockout zebrafish, which reproduce progressive liver failure and anemia, autophagy is excessively activated, and both morpholino knockdown of atg5 and bafilomycin treatment partially rescue liver size and survival. That is a genuine causal test - suppressing autophagy improves the phenotype - but it is a test in fish, and it has not been repeated in human ILFS1 tissue. It is modelled as a separate branch rather than folded into the translational arm because the two make different predictions about therapy.
LARS1 hgnc:6512 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves LARS1 (hgnc:6512). hgnc:6512 is a gene from the HUGO Gene Nomenclature Committee.
TORC1 signaling GO:0038202 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated TORC1 signaling (GO:0038202). GO:0038202 is a biological process from the Gene Ontology. ↕ DYSREGULATED macroautophagy GO:0016236 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased macroautophagy (GO:0016236). GO:0016236 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
larsb-knockout zebrafish Zebrafish recapitulates The model is the primary and essentially only evidence for the autophagy arm of the mechanism.
Downstream
Recurrent Hepatocellular Injury and Acute Liver Failure Excessive autophagic degradation contributes to the hepatic phenotype independently of the charging deficit, at least in the zebrafish model.
Show evidence (3 references)
PMID:33863987 SUPPORT Model Organism
"The atg5-morpholino knockdown and bafilomycin treatment partially improved the size of the liver and survival rate in larsb-/- zebrafish."
The rescue experiment establishing autophagy as causally contributing to the liver phenotype in the fish model.
PMID:33863987 SUPPORT Model Organism
"LARS is also essential to sensitize the intracellular leucine concentration to the mammalian target of rapamycin complex 1 (mTORC1) activation."
States the non-canonical leucine-sensing role of LeuRS that this branch depends on.
PMID:22424946 SUPPORT In Vitro
"We show that LRS directly binds to Rag GTPase, the mediator of amino acid signaling to mTORC1, in an amino acid-dependent manner and functions as a GTPase-activating protein (GAP) for Rag GTPase to activate mTORC1."
The primary source for the leucine-sensing mechanism, and it specifies the molecular route - LeuRS acting as a GAP for Rag GTPase - rather than leaving the non-canonical role as an unexplained assertion.
Recurrent Hepatocellular Injury and Acute Liver Failure
The defining clinical event. Transaminases rise recurrently, in the severe case to frank acute liver failure, characteristically during febrile illness. The pattern is episodic rather than steadily progressive, and episodes become less severe with increasing age - a natural history that fits a conditional enzyme deficit better than it fits cumulative structural damage.
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.
Animal models
larsb-knockout zebrafish Zebrafish partially recapitulates The model reproduces progressive liver failure and anemia, the two cardinal systemic features.
Show evidence (2 references)
PMID:32699352 SUPPORT Human Clinical
"ILFS1 is characterized by recurrent elevation of liver transaminases up to liver failure in conjunction with abnormalities of growth, blood, nervous system, and musculature."
The cohort-level statement of the hepatic phenotype and its multisystem context.
PMID:25917789 SUPPORT Human Clinical
"Episodic hepatic dysfunction is typically triggered by febrile illness, and becomes less severe with increasing age."
Documents both the episodic character and the age-related attenuation described in this node.
Hypoalbuminemia
Present in all patients in the founding clinical series and among the earliest presenting features, alongside anemia and failure to thrive. It is the most direct systemic readout of impaired hepatic protein synthesis available at the bedside.
Show evidence (1 reference)
PMID:25917789 SUPPORT Human Clinical
"Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
Establishes hypoalbuminemia as universal in the characterised cohort.
Microcytic Anemia
Anemia is an early and near-universal feature, and the larger cohort specifies it as microcytic. It is also reproduced in the larsb-knockout zebrafish, which argues that it is a direct consequence of LeuRS deficiency rather than a secondary effect of chronic liver disease. Why the deficit should produce microcytosis specifically is unexplained.
erythroid lineage cell CL:0000764 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves erythroid lineage cell (CL:0000764). CL:0000764 is a cell type from the Cell Ontology.
Show evidence (2 references)
PMID:32699352 SUPPORT Human Clinical
"Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
Specifies the anemia as microcytic in the largest cohort.
PMID:33863987 SUPPORT INDIRECT Model Organism
"we generated Lars deficient (larsb-/-) zebrafish that showed progressive liver failure and anaemia"
The model reproduces anemia alongside liver failure, supporting it as a direct consequence of the enzyme deficiency. INDIRECT because the fish phenotype is described as anaemia without red-cell indices, so it does not establish microcytosis.
Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury
Acute encephalopathy with seizures and reduced consciousness, precipitated by infection. On MRI, most individuals imaged during an acute episode showed deep grey matter and brainstem changes, a pattern the authors report as apparently characteristic of LARS1 deficiency and as differing from hepatic encephalopathy or from the metabolic stroke of organic acidurias and mitochondrial disease. The critical mechanistic point is dissociation from the liver: encephalopathy occurred in one individual AFTER liver transplantation, so the brain injury cannot be simply a consequence of hepatic failure. Most episodes were survived.
neuron CL:0000540 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves neuron (CL:0000540). CL:0000540 is a cell type from the Cell Ontology.
Show evidence (3 references)
PMID:38951950 SUPPORT Human Clinical
"On MRI, 5/7 individuals with MRI during acute encephalopathy had deep gray matter and brainstem changes."
The imaging finding that defines the anatomical signature of the encephalopathic episodes.
PMID:38951950 SUPPORT Human Clinical
"Encephalopathy without hepatic dysfunction occurred in one individual after liver transplantation."
The observation dissociating the neurological arm from hepatic failure, which is why this node is not modelled downstream of the liver.
PMID:32699352 SUPPORT Human Clinical
"Encephalopathic episodes with seizures can occur independently from liver crises and may present with metabolic stroke."
Independent confirmation in a separate cohort that the encephalopathy is not simply downstream of liver failure.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Infantile Liver Failure Syndrome 1 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

13
Digestive 3
Acute Liver Failure 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), qualified as temporality recurrent. HP:0006554 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (2 references)
PMID:25917789 SUPPORT Human Clinical
"Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
Establishes recurrent liver dysfunction as universal in the characterised cohort.
PMID:38844943 SUPPORT Human Clinical
"The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures..."
The cumulative series' denominators. Acute liver failure is 24/34, about 71%, which puts it in the FREQUENT band (30-79%), not VERY_FREQUENT - and well short of universal, which matters because frank liver failure is the feature the disease is named for.
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.
No frequency asserted - the source is a three-patient series covering both LARS1 and MARS1 disease, so it establishes the phenotype without giving a denominator for ILFS1.
Show evidence (1 reference)
PMID:34496286 SUPPORT Human Clinical
"All three patients had anemia, hepatomegaly, feeding difficulties, failure to thrive and hypoalbuminemia."
Graded PARTIAL - the three patients span LARS1 and MARS1 disease, so the shared features are reported across two conditions rather than for ILFS1 alone.
Feeding Difficulties HP:0011968 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Feeding difficulties (HP:0011968). HP:0011968 is a phenotype from the Human Phenotype Ontology.
As for hepatomegaly - single small series spanning two ARS diseases, so no frequency is asserted.
Show evidence (1 reference)
PMID:34496286 SUPPORT Human Clinical
"All three patients had anemia, hepatomegaly, feeding difficulties, failure to thrive and hypoalbuminemia."
Same series and same PARTIAL grading as hepatomegaly.
Genitourinary 1
Renal Tubulopathy Renal tubular dysfunction HP:0000124 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Renal tubular dysfunction (HP:0000124). HP:0000124 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22607940 SUPPORT Human Clinical
"Additional symptoms include anaemia, renal tubulopathy, developmental delay, seizures, failure to thrive and deterioration of liver function with minor illness."
Reports renal tubulopathy in the founding family. Graded PARTIAL because it comes from the single consanguineous kindred and is not among the features the later systematic cohorts list as prevalent.
Metabolism 2
Recurrent Elevation of Hepatic Transaminases VERY_FREQUENT Elevated circulating hepatic transaminase concentration HP:0002910 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating hepatic transaminase concentration (HP:0002910), qualified as temporality recurrent. HP:0002910 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (1 reference)
PMID:32699352 SUPPORT Human Clinical
"The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness."
Names recurrent transaminase elevation as the most prominent finding, and the phrase "up to liver failure" is what separates it from the ALF phenotype - failure is the severe end of this spectrum, not a separate event.
Hypoalbuminemia VERY_FREQUENT HP:0003073 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoalbuminemia (HP:0003073). HP:0003073 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:25917789 SUPPORT Human Clinical
"Low birth weight, early failure to thrive, anemia and hypoalbuminemia are amongst the first presenting features, with liver dysfunction before age 1."
Names hypoalbuminemia among the first presenting features and dates the hepatic onset.
PMID:38844943 SUPPORT Human Clinical
"The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures..."
The same denominator sentence; the fraction relevant here is hypoalbuminemia at 32/32 - present in every patient assessed, which is what supports VERY_FREQUENT.
Musculoskeletal 1
Muscular Hypotonia FREQUENT HP:0001252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypotonia (HP:0001252). HP:0001252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32699352 SUPPORT Human Clinical
"Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
Reports muscular hypotonia among the prevalent features.
Nervous System 3
Global Developmental Delay VERY_FREQUENT 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:25917789 SUPPORT Human Clinical
"Most patients (90 %) had developmental delay."
Gives the reported frequency of developmental delay, which maps to VERY_FREQUENT.
Seizures FREQUENT 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:38951950 SUPPORT Human Clinical
"All individuals had developmental delay and 10/13 had seizures."
Gives an explicit denominator for seizure frequency in an independent imaging cohort.
Encephalopathy FREQUENT HP:0001298 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Encephalopathy (HP:0001298), qualified as temporality recurrent. HP:0001298 is a phenotype from the Human Phenotype Ontology.
Temporal: RECURRENT
Show evidence (1 reference)
PMID:38951950 SUPPORT Human Clinical
"Encephalopathic episodes in 8/13 were typically associated with infections, presented with seizures and reduced consciousness, mostly accompanied by hepatic dysfunction, and recovery in 17/19 episodes."
Gives frequency, trigger, presentation and outcome of the encephalopathic episodes.
Growth 2
Failure to Thrive VERY_FREQUENT 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:25917789 SUPPORT Human Clinical
"Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
Establishes early failure to thrive as universal in the characterised cohort.
Intrauterine Growth Restriction VERY_FREQUENT Intrauterine growth retardation HP:0001511 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intrauterine growth retardation (HP:0001511). HP:0001511 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:38844943 SUPPORT Human Clinical
"intrauterine growth restriction (31/32 patients in whom this finding was specifically described)"
Near-universal IUGR with an explicit denominator, and the source is careful to state the denominator is patients in whom it was specifically described - an ascertainment caveat worth preserving.
Other 1
Microcytic Anemia VERY_FREQUENT HP:0001935 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcytic anemia (HP:0001935). HP:0001935 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:32699352 SUPPORT Human Clinical
"Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
Specifies the anemia as microcytic and prevalent.
PMID:38844943 SUPPORT Human Clinical
"The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures..."
The same denominator sentence; the fraction relevant here is microcytic anemia at 32/33, about 97%, supporting VERY_FREQUENT.
🧬

Genetic Associations

1
LARS1
Gene: LARS1 hgnc:6512 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is LARS1 (hgnc:6512). hgnc:6512 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:32699352 SUPPORT Human Clinical
"Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
Documents the breadth of the allelic series recorded in this genetic block.
PMID:32699352 SUPPORT In Vitro
"Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
The functional assay characterising these variants as conditional loss-of-function.
💊

Medical Actions

4
Maintain Protein and Glucose Intake During Illness
Action: dietary interventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is dietary intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. Ontology label: Dietary Intervention NCIT:C15447
The counter-intuitive management point, and the one most likely to be got wrong. In metabolic hepatopathies the reflex is to reduce or stop protein intake; the ILFS1 clinical series argues this is inappropriate here and recommends ensuring sufficient natural protein intake when unwell. The mechanistic rationale is that the lesion is a failure to CHARGE and USE amino acids, not a failure to clear them, so substrate restriction removes supply without relieving the block. The MRI study independently recommends sufficient glucose and protein alongside proactive fever management.
Mechanism Target:
Febrile Decompensation of Residual Charging Capacity — Maintaining substrate supply and limiting fever address the two components proposed to precipitate decompensation.
Show evidence (2 references)
PMID:25917789 SUPPORT Human Clinical
"However, we suggest that the traditional management of reducing/stopping protein intake in patients with metabolic hepatopathies may not be appropriate for ILFS1. We currently recommend ensuring sufficient natural protein intake when unwell."
The explicit clinical recommendation against protein restriction, from the cohort that defined the phenotype.
PMID:38951950 SUPPORT Human Clinical
"thus, sufficient glucose and protein intake along with pro-active fever management is suggested"
Independent recommendation of substrate maintenance plus fever control from the imaging cohort.
Seasonal Influenza Vaccination
Action: vaccinationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is vaccination (NCIT:C15346). NCIT:C15346 is a clinical intervention from the NCI Thesaurus. Ontology label: Vaccination NCIT:C15346
Because decompensation is infection-triggered and severe episodes were specifically observed during influenza infections, the imaging cohort makes a strong recommendation for seasonal vaccination. This is a rare case of a mechanism-derived preventive intervention in an ARS deficiency: it does not touch the enzyme, it removes the trigger.
Mechanism Target:
Febrile Decompensation of Residual Charging Capacity — Preventing a febrile illness prevents the trigger that precipitates hepatic and encephalopathic crises.
Show evidence (1 reference)
PMID:38951950 SUPPORT Human Clinical
"As severe episodes were observed during influenza infections, we strongly recommend seasonal vaccination."
The observation and the recommendation, stated together by the authors.
Liver Transplantation
Action: liver transplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is liver transplantation (NCIT:C15271). NCIT:C15271 is a clinical intervention from the NCI Thesaurus. Ontology label: Liver Transplantation NCIT:C15271
The definitive intervention for irreversible hepatic failure, and part of the hard outcome measure in this disease - 12 of 36 reported patients died or underwent liver transplantation. It carries a mechanistic caveat this entry treats as important rather than incidental: LARS1 deficiency is systemic, so replacing the liver does not correct the enzyme defect elsewhere. Encephalopathy occurred in one individual AFTER transplantation. Transplantation should therefore be understood as treating the organ that fails first, not the disease.
Mechanism Target:
Recurrent Hepatocellular Injury and Acute Liver Failure — Replaces the organ whose protein-synthetic failure produces the life-threatening episodes, without addressing the charging defect in other tissues.
Show evidence (2 references)
PMID:38844943 SUPPORT Human Clinical
"Among the 36 known patients, 12 died or underwent liver transplantation."
Establishes that transplantation is part of the real course of this disease, against an explicit denominator. Note the composite endpoint does not separate deaths from transplants, so it does not report a transplant outcome.
PMID:38951950 SUPPORT Human Clinical
"Encephalopathy without hepatic dysfunction occurred in one individual after liver transplantation."
Cited as the caveat rather than the support - a transplanted patient still had encephalopathy, which is the evidence that transplantation does not treat the systemic disease.
Leucine Supplementation
Action: nutritional supportNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is nutritional support (NCIT:C15433). NCIT:C15433 is a clinical intervention from the NCI Thesaurus. Ontology label: Nutritional Support NCIT:C15433
The evidence here changed, and both results are recorded because the disagreement is informative rather than a contradiction to be resolved by picking the newer paper. The 2015 ILFS1 clinical series reported that leucine supplementation had no appreciable impact on patient well-being. A 2021 study that approached the problem mechanistically rather than empirically reached the opposite conclusion: having first shown in patient fibroblasts that aminoacylation is both reduced at baseline and further reduced at febrile temperature, and that growth is severely impaired when the cognate amino acid is scarce, the authors supplemented patients with their cognate amino acid and INTENSIFIED dosing during infections, reporting benefit in growth, head circumference, development, coping with infections and oxygen dependency over up to two and two-thirds years. The two are reconcilable, and the reconciliation is the point: the failed attempt supplied leucine at steady state, while the successful protocol raised supply precisely when the temperature-sensitive enzyme's capacity falls. If that reading is right, timing rather than substrate is what the earlier trial got wrong. It is not established - the 2021 series pooled four different ARS deficiencies and was uncontrolled - so this entry presents it as the better supported of two open positions, not as settled.
Mechanism Target:
Reduced Leucyl-tRNA Aminoacylation Capacity — Raising cognate amino acid concentration is intended to drive the partially active enzyme, which is substrate-sensitive in patient cells.
Show evidence (3 references)
PMID:25917789 REFUTE Human Clinical
"Leucine supplementation had no appreciable impact on patient well-being."
Graded REFUTE against benefit from leucine supplementation as given in this cohort. Uncontrolled clinical experience in a small series, and it does not state the dose or whether dosing was intensified during illness - which the later study identifies as the decisive variable.
PMID:34194004 SUPPORT Human Clinical
"To prevent local and/or temporal deficiencies, we treated patients with corresponding amino acids (follow-up: 1/2-2 2/3rd years), and intensified treatment during infections. All patients showed beneficial treatment effects, most strikingly in growth (without tube feeding), head circumference,..."
Reports benefit from cognate amino acid supplementation intensified during infection. Graded SUPPORT, but note the cohort spans four ARS deficiencies (IARS, LARS, FARSB, SARS) rather than being an ILFS1 series, and there is no control arm - so it supports the strategy without isolating the effect in LARS1 deficiency.
PMID:34194004 SUPPORT In Vitro
"With lower cognate amino acid concentrations, patient fibroblast growth was severely affected."
The in vitro substrate-sensitivity result providing the rationale for supplementation, measured in patient cells.
🔬

Diagnosis

2
Temperature-dependent aminoacylation assay in patient fibroblasts
The functional confirmatory test, and unusually it is also the disease's central mechanism made visible. Leucyl-tRNA aminoacylation is measured in patient-derived fibroblasts at baseline and at elevated temperature. Reduced baseline activity confirms the enzyme defect; the further fall at 38.5 and 40 degrees is what distinguishes this from a fixed enzymopathy and predicts the febrile decompensation that defines the clinical course. A baseline-only assay would miss the finding that matters most for management. The same study showed patient fibroblast growth is severely impaired at low cognate amino acid concentration, which is the assay underpinning the supplementation strategy.
Show evidence (2 references)
PMID:32699352 SUPPORT In Vitro
"Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
Establishes the assay and its temperature dependence across every patient tested in the largest cohort.
PMID:34194004 SUPPORT In Vitro
"In fibroblasts from patients with isoleucyl-RS (IARS), leucyl-RS (LARS), phenylalanyl-RS-beta-subunit (FARSB), and seryl-RS (SARS) deficiencies, we investigated aminoacylation activity, thermostability, and sensitivity to ARS-specific amino acid concentrations, and developed personalized treatments."
Describes the assay panel - activity, thermostability and amino acid sensitivity - and makes explicit that it was used to derive personalised treatment, so the diagnostic test and the therapeutic decision are the same measurement.
Exome or genome sequencing with LARS1 variant interpretation
Molecular diagnosis rests on identifying biallelic LARS1 variants. Two interpretation points. First, confirm the gene is LARS1 and not LARS2 - the mitochondrial leucyl-tRNA synthetase, which causes a different disease - since the founding literature uses the bare symbol LARS. Second, do not expect the variant to be a null: reported alleles are partial loss-of-function, most fall in the editing domain, and the diagnosis should not be discarded because residual activity is present. The founding kindred was solved by homozygosity mapping plus exome sequencing in a consanguineous family; later patients include compound heterozygotes.
No GeneReviews chapter exists for LARS1 or ILFS1. Re-confirmed by esearch against PubMed on 2026-08-28: `LARS1 GeneReviews[All Fields]`, `infantile liver failure syndrome GeneReviews[Title]` and `leucyl-tRNA synthetase GeneReviews[All Fields]` all return zero results. The NBAS/ILFS2 chapter covers a different gene and a different disease.
Show evidence (2 references)
PMID:22607940 SUPPORT Human Clinical
"We aimed to identify the underlying risk gene using homozygosity mapping and whole exome sequencing."
The sequencing approach that established the diagnosis in the founding family.
PMID:32699352 SUPPORT Human Clinical
"Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
Documents the breadth of the allelic series a diagnostic laboratory should expect to interpret against.
📈

Progression

1
Prognostic determinants
Twelve of 36 reported patients died or underwent liver transplantation. Two factors independently conferred poor prognosis on Kaplan-Meier analysis: age of onset under three months (hazard ratio 12.29) and the occurrence of liver failure (hazard ratio 6.57). No genotype-phenotype correlation was found - the allele does not predict whether liver failure occurs or how severe the disease is - which is consistent with the disease being driven by conditional decompensation under environmental stress rather than by a fixed allele-determined severity. This coexists with, rather than contradicts, the earlier observation that episodes attenuate with age and that two patients were well beyond 28 years: early onset predicts badly, and surviving childhood predicts well.
Show evidence (3 references)
PMID:38844943 SUPPORT Human Clinical
"Kaplan-Meier analysis indicated that age of onset < 3mo (p = 0.0015, hazard ratio = 12.29, 95% confidence interval [CI] = 3.74-40.3), like liver failure (p = 0.0343, hazard ratio = 6.57, 95% CI = 1.96-22.0), conferred poor prognosis."
The survival analysis giving both prognostic factors with effect sizes and confidence intervals.
PMID:38844943 SUPPORT Human Clinical
"Among the 36 known patients, 12 died or underwent liver transplantation."
Gives the hard outcome rate against an explicit denominator.
PMID:38844943 SUPPORT Human Clinical
"No significant correlations were observed between genotype and either presence of liver failure or clinical severity of disease."
The negative genotype-phenotype result recorded in this block.
📊

Prevalence

2
Worldwide, published cases
Cases In Literature Ultra Rare
Twenty-five individuals from 15 families in the largest systematic series (2020), which explicitly assembled novel plus previously published patients internationally. No population-based prevalence estimate exists.
Show evidence (1 reference)
PMID:32699352 SUPPORT Human Clinical
"Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
The largest published cohort, giving the order of magnitude of the reported case count.
Worldwide, cumulative published series
Cases In Literature Ultra Rare
A 2024 review assembled 36 patients in total - three new plus 33 previously reported - which is the largest cumulative denominator available and the basis for the phenotype frequencies recorded in this entry.
Show evidence (1 reference)
PMID:38844943 SUPPORT Human Clinical
"Disease characteristics were summarized together with those of 33 reported cases."
Establishes the cumulative case series that underpins the frequency denominators used below.
🐁

Animal Models

1
larsb-knockout zebrafish
CRISPR/Cas9 knockout of larsb, the zebrafish paralogue with higher homology to human LARS1, targeted to the editing domain where most human variants fall.
Species
Zebrafish
Genotype
larsb-/- (CRISPR/Cas9 frameshift in exon 3, editing domain)
Publication
PMID:33863987
Pathograph links
Recurrent Hepatocellular Injury and Acute Liver Failure partially recapitulates fidelity: moderate The model reproduces progressive liver failure and anemia, the two cardinal systemic features.
Limitations: The fish phenotype is PROGRESSIVE and lethal within 12 days, whereas human ILFS1 is EPISODIC, febrile-triggered, and compatible with survival past 28 years. So the model reproduces the organ that fails without reproducing the conditional, temperature-triggered character that defines the human disease. The knockout is also a null, while human alleles are partial loss-of-function.
Readouts
Liver size
Direction: RESTORED
Interpretation: Liver size and survival improved on autophagy suppression, indicating autophagy contributes causally to the hepatic phenotype in this model.
Show evidence (1 reference)
PMID:33863987 SUPPORT Model Organism
"The atg5-morpholino knockdown and bafilomycin treatment partially improved the size of the liver and survival rate in larsb-/- zebrafish."
Reports the measured rescue of liver size and survival.
Show evidence (1 reference)
PMID:33863987 SUPPORT Model Organism
"we generated Lars deficient (larsb-/-) zebrafish that showed progressive liver failure and anaemia, resulting in early lethality within 12 days post fertilization."
Establishes that the model reproduces the liver and haematological phenotypes, which is what makes it informative for this node.
Dysregulated mTORC1 Signalling and Excessive Autophagy recapitulates fidelity: moderate The model is the primary and essentially only evidence for the autophagy arm of the mechanism.
Limitations: No human ILFS1 tissue has been examined for excessive autophagy, so the entire branch rests on the fish.
Show evidence (1 reference)
PMID:33863987 SUPPORT Model Organism
"Indeed, excessive autophagy activation was observed in larsb-/- zebrafish."
The direct observation of excessive autophagy in the model.
{ }

Source YAML

click to show 
name: Infantile Liver Failure Syndrome 1
creation_date: "2026-08-28T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: LARS1 deficiency (infantile liver failure syndrome type 1)
  term:
    id: MONDO:0024568
    label: infantile liver failure syndrome 1
description: >-
  Infantile liver failure syndrome 1 (ILFS1) is a recessive multisystem disorder
  caused by biallelic variants in LARS1, the gene for the CYTOPLASMIC leucyl-tRNA
  synthetase (LeuRS). LeuRS charges leucine onto tRNA-Leu, the first committed
  step in incorporating leucine into every cytoplasmic protein, so the disease
  belongs to the recessive aminoacyl-tRNA-synthetase (ARS) deficiency family
  alongside SARS1, MARS1 and others.
  What makes ILFS1 mechanistically legible is that its residual enzyme is
  temperature-sensitive. Aminoacylation activity in patient fibroblasts is not
  merely low at baseline; it falls significantly further when the cells are
  warmed. That single in vitro observation explains the clinical rhythm of the
  disease, which is otherwise puzzling: patients are relatively well between
  episodes and decompensate during febrile illness. Fever both raises the
  temperature at which the crippled enzyme must work and raises the demand for
  protein synthesis, and the liver - the body's highest-throughput secretory
  protein factory - fails first.
  The phenotype accordingly pairs a hepatic axis (recurrent transaminase
  elevation up to frank acute liver failure, hypoalbuminemia) with a
  haematological axis (microcytic anemia), a growth axis (low birth weight,
  early failure to thrive) and a neurological axis (developmental delay,
  seizures, and encephalopathic episodes whose MRI signature - deep grey matter
  and brainstem change - is reported as distinct from hepatic encephalopathy or
  from the metabolic stroke of organic acidurias).
  Two clinical inversions are worth stating plainly because they run against
  reflex management. First, the standard metabolic-hepatopathy move of restricting
  protein appears inappropriate here, since the lesion is a failure to USE amino
  acids rather than a failure to clear them. Second, encephalopathy is not simply
  downstream of the liver: it has occurred in one individual after liver
  transplantation, and episodes can occur independently of hepatic dysfunction.
  Prognosis is not uniformly poor - episodes become less severe with age and two
  patients in the founding cohort were well beyond 28 years.
parents:
- hereditary disease
- Inborn Error of Metabolism
- Aminoacyl-tRNA Synthetase Deficiency
synonyms:
- ILFS1
- LARS1 deficiency
- LARS deficiency
- infantile liver failure syndrome type 1
- cytoplasmic leucyl-tRNA synthetase deficiency
- acute infantile liver failure - multisystemic involvement syndrome
notes: >-
  Gene nomenclature. The founding papers call the gene LARS; it is now LARS1, to
  distinguish it from LARS2, the MITOCHONDRIAL leucyl-tRNA synthetase, which
  causes a different disease (Perrault syndrome / HLASA). Quoted snippets in this
  entry preserve whichever spelling the cited paper used; the entry's own prose
  uses LARS1. This is not pedantry - the founding family was investigated for
  years as a suspected mitochondrial disorder precisely because the multisystem
  presentation looked mitochondrial, and the discovery paper's own conclusion was
  that it is not.

  Scope boundary. ILFS1 is the LARS1 entity only. Its MONDO parent, `infantile
  liver failure`, is a grouping that also covers ILFS2 (NBAS) and ILFS3 (RINT1);
  those are separate diseases with different mechanisms and are not curated here.

  Excluded reference. PMID:33314043 (Clin Genet 2021, functional characterisation
  of a novel LARS1 variant) is topically relevant but its cached record has an
  empty body, so no snippet can be verified against it and it is not cited. It is
  recorded here so a later curator does not spend the search again.
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic LARS1 variants. The founding kindred was a consanguineous Irish
    Traveller family segregating a homozygous missense allele; subsequent cohorts
    include compound heterozygotes and at least one Ashkenazi family, so the
    disease is not confined to a single founder population.
  evidence:
  - reference: PMID:22607940
    reference_title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Whole exome sequencing identified 1 novel homozygous missense mutation within the 5q31.3-q33.1 candidate region that segregated with the hepatopathy."
    explanation: Establishes homozygous, recessive segregation of the causal allele in the founding consanguineous family.
prevalence:
- population: Worldwide, published cases
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Twenty-five individuals from 15 families in the largest systematic series
    (2020), which explicitly assembled novel plus previously published patients
    internationally. No population-based prevalence estimate exists.
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
    explanation: The largest published cohort, giving the order of magnitude of the reported case count.
- population: Worldwide, cumulative published series
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    A 2024 review assembled 36 patients in total - three new plus 33 previously
    reported - which is the largest cumulative denominator available and the basis
    for the phenotype frequencies recorded in this entry.
  evidence:
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Disease characteristics were summarized together with those of 33 reported cases."
    explanation: Establishes the cumulative case series that underpins the frequency denominators used below.
progression:
- phase: Prognostic determinants
  notes: >-
    Twelve of 36 reported patients died or underwent liver transplantation. Two
    factors independently conferred poor prognosis on Kaplan-Meier analysis: age of
    onset under three months (hazard ratio 12.29) and the occurrence of liver
    failure (hazard ratio 6.57). No genotype-phenotype correlation was found - the
    allele does not predict whether liver failure occurs or how severe the disease
    is - which is consistent with the disease being driven by conditional
    decompensation under environmental stress rather than by a fixed allele-determined
    severity. This coexists with, rather than contradicts, the earlier observation
    that episodes attenuate with age and that two patients were well beyond 28
    years: early onset predicts badly, and surviving childhood predicts well.
  evidence:
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Kaplan-Meier analysis indicated that age of onset < 3mo (p = 0.0015, hazard ratio = 12.29, 95% confidence interval [CI] = 3.74-40.3), like liver failure (p = 0.0343, hazard ratio = 6.57, 95% CI = 1.96-22.0), conferred poor prognosis."
    explanation: The survival analysis giving both prognostic factors with effect sizes and confidence intervals.
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the 36 known patients, 12 died or underwent liver transplantation."
    explanation: Gives the hard outcome rate against an explicit denominator.
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No significant correlations were observed between genotype and either presence of liver failure or clinical severity of disease."
    explanation: The negative genotype-phenotype result recorded in this block.
pathophysiology:
- name: Biallelic LARS1 Variants
  biological_scale: MOLECULAR
  description: >-
    The primary lesion is biallelic damage to LARS1 at 5q32, encoding cytoplasmic
    leucyl-tRNA synthetase. The founding allele was a homozygous missense variant
    mapped by homozygosity mapping to 5q31.3-q33.1; the allelic series has since
    broadened substantially, with eight previously unreported variants added in a
    single 2020 series. A structural observation from the zebrafish work is that
    most reported human LARS1 variants fall in the editing domain - the
    proofreading module that hydrolyses mischarged tRNA - rather than in the
    aminoacylation active site itself.
  genes:
  - preferred_term: LARS1
    term:
      id: hgnc:6512
      label: LARS1
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:22607940
    reference_title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The candidate mutation is located in the LARS gene which encodes a cytoplasmic leucyl-tRNA synthetase enzyme responsible for exclusively attaching leucine to its cognate tRNA during protein translation."
    explanation: The discovery report identifying LARS1 and stating the enzyme's function, which is the premise of the whole mechanism.
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Biallelic variants in LARS1, coding for the cytosolic leucyl-tRNA synthetase, cause infantile liver failure syndrome 1 (ILFS1)."
    explanation: Confirms the biallelic LARS1 genotype-disease relationship in the largest systematic cohort.
  - reference: PMID:33863987
    reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Notably, most LARS gene mutations in humans occur in the editing domain"
    explanation: >-
      Records the editing-domain clustering of human alleles. Graded PARTIAL
      because the statement appears as background framing in a zebrafish paper
      rather than as that paper's own systematic allele survey.
  downstream:
  - target: Reduced Leucyl-tRNA Aminoacylation Capacity
    causal_link_type: DIRECT
    description: >-
      Damaged LeuRS charges less leucine onto tRNA-Leu, reducing total cellular
      charging capacity.
- name: Reduced Leucyl-tRNA Aminoacylation Capacity
  biological_scale: MOLECULAR
  description: >-
    The core enzymatic deficit, and the one measured directly in patient material.
    Aminoacylation activity is reduced in fibroblasts from every patient tested.
    Crucially the reduction is not fixed: it is significantly worse at elevated
    temperature, which makes the residual enzyme conditionally rather than
    constitutively insufficient. This is the mechanistic hinge of the entry -
    it converts a static enzyme deficiency into an episodic disease.
  genes:
  - preferred_term: LARS1
    term:
      id: hgnc:6512
      label: LARS1
  molecular_functions:
  - preferred_term: leucine-tRNA ligase activity
    modifier: DECREASED
    term:
      id: GO:0004823
      label: leucine-tRNA ligase activity
  biological_processes:
  - preferred_term: leucyl-tRNA aminoacylation
    modifier: DECREASED
    term:
      id: GO:0006429
      label: leucyl-tRNA aminoacylation
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
    explanation: The direct enzymatic measurement in patient-derived cells, and the temperature dependence that the rest of the entry turns on.
  downstream:
  - target: Febrile Decompensation of Residual Charging Capacity
    causal_link_type: DIRECT
    description: >-
      Because the residual activity is temperature-sensitive, a rise in body
      temperature further reduces it.
  - target: Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
    causal_link_type: DIRECT
    description: >-
      Reduced charging capacity limits translational throughput wherever demand is
      highest, which at baseline is the liver.
- name: Febrile Decompensation of Residual Charging Capacity
  biological_scale: ORGANISM
  description: >-
    The trigger node. Intercurrent febrile illness is the near-universal
    precipitant of both hepatic and encephalopathic crises across every published
    cohort - it was reported as the trigger for encephalopathic episodes in 80% of
    the ten-patient clinical series, and as the trigger of both crisis types in the
    twenty-five-patient series. The proposed explanation combines two effects that
    act in the same direction: fever lowers the temperature-sensitive enzyme's
    residual activity, while infection raises catabolic and acute-phase protein
    demand. That combination is a proposal that fits the in vitro temperature data
    rather than a directly demonstrated in vivo chain, and the MRI study is
    explicit that the pathomechanism remains unclear.
  biological_processes:
  - preferred_term: cellular response to heat
    modifier: ABNORMAL
    term:
      id: GO:0034605
      label: cellular response to heat
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness."
    explanation: Establishes febrile illness as the trigger for both crisis types in the largest cohort.
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Encephalopathic episodes triggered by febrile illness have occurred in 80 % and were fatal in two children."
    explanation: Quantifies the frequency and the lethality of febrile-triggered encephalopathy in the ten-patient clinical series.
  - reference: PMID:34194004
    reference_title: Treatment of ARS deficiencies with specific amino acids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Aminoacylation activity was reduced in all patients, and further diminished at 38.5/40 °C (PLARS and PFARSB), consistent with infectious deteriorations."
    explanation: >-
      Independent confirmation of the temperature effect at febrile temperatures
      specifically, in the LARS patient among others, and the authors' own link
      from it to infectious deterioration.
  - reference: PMID:34194004
    reference_title: Treatment of ARS deficiencies with specific amino acids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "we observed a common disease mechanism of episodic insufficient aminoacylation to meet translational demands"
    explanation: States the episodic-insufficiency model across four ARS deficiencies, which is the framing this node uses.
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "While the pathomechanism remains unclear, fever and energy deficit during infections might be causative"
    explanation: >-
      Deliberately cited as PARTIAL and as an explicit hedge - the authors propose
      fever and energy deficit as causative but state the pathomechanism is
      unclear, and the entry does not claim more than they do.
  downstream:
  - target: Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
    causal_link_type: DIRECT
    description: >-
      The febrile drop in charging capacity is what converts a tolerable chronic
      deficit into an acute translational failure.
  - target: Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Encephalopathic episodes are infection-triggered in every cohort that
      reports them, so the trigger node feeds the neurological arm as well as the
      hepatic one. The edge is INDIRECT_UNKNOWN_INTERMEDIATES rather than DIRECT
      because nothing establishes what happens between the febrile drop in
      charging capacity and the deep grey matter and brainstem injury - the
      imaging authors state the pathomechanism remains unclear. Drawing this edge
      does NOT route the encephalopathy through the liver: it runs from the shared
      trigger, which is what lets the arm stay independent of hepatic failure.
- name: Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
  biological_scale: CELLULAR
  description: >-
    With leucine charging limiting, cytoplasmic translation cannot keep pace with
    demand. The tissue distribution of the disease follows protein-synthetic
    throughput rather than LARS1 expression: hepatocytes, which manufacture and
    secrete albumin and the acute-phase proteins, are affected first and hardest.
    This is the proposed unifying premise of the recessive ARS deficiencies
    generally - residual aminoacylation suffices at baseline but not under load.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: cytoplasmic translation
    modifier: DECREASED
    term:
      id: GO:0002181
      label: cytoplasmic translation
  mechanism_confidence: PROVISIONAL
  notes: >-
    This node is an inference, not a measurement. No published study has measured
    global or hepatocyte-specific translation rates in ILFS1 patient tissue. What
    is measured is the enzyme activity upstream and the clinical protein-synthetic
    failure downstream (hypoalbuminemia, coagulopathic liver failure); the
    translational step between them is bridged by the ARS-deficiency model rather
    than by direct evidence, and is graded PROVISIONAL for that reason.
  evidence:
  - reference: PMID:22607940
    reference_title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "responsible for exclusively attaching leucine to its cognate tRNA during protein translation"
    explanation: >-
      Supports the enzyme's role in translation, which is the premise of this
      node. Graded PARTIAL because it evidences the normal function rather than
      measuring impaired translation in patients.
  downstream:
  - target: Recurrent Hepatocellular Injury and Acute Liver Failure
    causal_link_type: DIRECT
    description: >-
      Hepatocytes are the highest-throughput protein-synthetic cells and fail
      first.
  - target: Hypoalbuminemia
    causal_link_type: DIRECT
    description: >-
      Albumin is the single largest hepatic secretory product, so its plasma level
      is a direct readout of hepatic synthetic capacity.
  - target: Microcytic Anemia
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Anemia is present from early infancy in essentially all patients, but the
      route from a leucine-charging defect to a MICROCYTIC red-cell phenotype
      specifically has not been established.
- name: Dysregulated mTORC1 Signalling and Excessive Autophagy
  biological_scale: CELLULAR
  description: >-
    A second, non-canonical arm. Beyond charging tRNA, LeuRS acts as the
    intracellular leucine sensor that permits amino-acid-induced mTORC1
    activation. In larsb-knockout zebrafish, which reproduce progressive liver
    failure and anemia, autophagy is excessively activated, and both morpholino
    knockdown of atg5 and bafilomycin treatment partially rescue liver size and
    survival. That is a genuine causal test - suppressing autophagy improves the
    phenotype - but it is a test in fish, and it has not been repeated in human
    ILFS1 tissue. It is modelled as a separate branch rather than folded into the
    translational arm because the two make different predictions about therapy.
  genes:
  - preferred_term: LARS1
    term:
      id: hgnc:6512
      label: LARS1
  biological_processes:
  - preferred_term: TORC1 signaling
    modifier: DYSREGULATED
    term:
      id: GO:0038202
      label: TORC1 signaling
  - preferred_term: macroautophagy
    modifier: INCREASED
    term:
      id: GO:0016236
      label: macroautophagy
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:33863987
    reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The atg5-morpholino knockdown and bafilomycin treatment partially improved the size of the liver and survival rate in larsb-/- zebrafish."
    explanation: The rescue experiment establishing autophagy as causally contributing to the liver phenotype in the fish model.
  - reference: PMID:33863987
    reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "LARS is also essential to sensitize the intracellular leucine concentration to the mammalian target of rapamycin complex 1 (mTORC1) activation."
    explanation: States the non-canonical leucine-sensing role of LeuRS that this branch depends on.
  - reference: PMID:22424946
    reference_title: Leucyl-tRNA synthetase is an intracellular leucine sensor for the mTORC1-signaling pathway.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We show that LRS directly binds to Rag GTPase, the mediator of amino acid signaling to mTORC1, in an amino acid-dependent manner and functions as a GTPase-activating protein (GAP) for Rag GTPase to activate mTORC1."
    explanation: >-
      The primary source for the leucine-sensing mechanism, and it specifies the
      molecular route - LeuRS acting as a GAP for Rag GTPase - rather than leaving
      the non-canonical role as an unexplained assertion.
  downstream:
  - target: Recurrent Hepatocellular Injury and Acute Liver Failure
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Excessive autophagic degradation contributes to the hepatic phenotype
      independently of the charging deficit, at least in the zebrafish model.
- name: Recurrent Hepatocellular Injury and Acute Liver Failure
  biological_scale: TISSUE
  description: >-
    The defining clinical event. Transaminases rise recurrently, in the severe
    case to frank acute liver failure, characteristically during febrile illness.
    The pattern is episodic rather than steadily progressive, and episodes become
    less severe with increasing age - a natural history that fits a conditional
    enzyme deficit better than it fits cumulative structural damage.
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ILFS1 is characterized by recurrent elevation of liver transaminases up to liver failure in conjunction with abnormalities of growth, blood, nervous system, and musculature."
    explanation: The cohort-level statement of the hepatic phenotype and its multisystem context.
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Episodic hepatic dysfunction is typically triggered by febrile illness, and becomes less severe with increasing age."
    explanation: Documents both the episodic character and the age-related attenuation described in this node.
- name: Hypoalbuminemia
  biological_scale: ORGANISM
  description: >-
    Present in all patients in the founding clinical series and among the earliest
    presenting features, alongside anemia and failure to thrive. It is the most
    direct systemic readout of impaired hepatic protein synthesis available at the
    bedside.
  mechanism_confidence: ESTABLISHED
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
    explanation: Establishes hypoalbuminemia as universal in the characterised cohort.
- name: Microcytic Anemia
  biological_scale: ORGANISM
  description: >-
    Anemia is an early and near-universal feature, and the larger cohort specifies
    it as microcytic. It is also reproduced in the larsb-knockout zebrafish, which
    argues that it is a direct consequence of LeuRS deficiency rather than a
    secondary effect of chronic liver disease. Why the deficit should produce
    microcytosis specifically is unexplained.
  cell_types:
  - preferred_term: erythroid lineage cell
    term:
      id: CL:0000764
      label: erythroid lineage cell
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
    explanation: Specifies the anemia as microcytic in the largest cohort.
  - reference: PMID:33863987
    reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "we generated Lars deficient (larsb-/-) zebrafish that showed progressive liver failure and anaemia"
    explanation: >-
      The model reproduces anemia alongside liver failure, supporting it as a
      direct consequence of the enzyme deficiency. INDIRECT because the fish
      phenotype is described as anaemia without red-cell indices, so it does not
      establish microcytosis.
- name: Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury
  biological_scale: ORGANISM
  description: >-
    Acute encephalopathy with seizures and reduced consciousness, precipitated by
    infection. On MRI, most individuals imaged during an acute episode showed deep
    grey matter and brainstem changes, a pattern the authors report as apparently
    characteristic of LARS1 deficiency and as differing from hepatic encephalopathy
    or from the metabolic stroke of organic acidurias and mitochondrial disease.
    The critical mechanistic point is dissociation from the liver: encephalopathy
    occurred in one individual AFTER liver transplantation, so the brain injury
    cannot be simply a consequence of hepatic failure. Most episodes were survived.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  mechanism_confidence: PROVISIONAL
  evidence:
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "On MRI, 5/7 individuals with MRI during acute encephalopathy had deep gray matter and brainstem changes."
    explanation: The imaging finding that defines the anatomical signature of the encephalopathic episodes.
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Encephalopathy without hepatic dysfunction occurred in one individual after liver transplantation."
    explanation: The observation dissociating the neurological arm from hepatic failure, which is why this node is not modelled downstream of the liver.
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Encephalopathic episodes with seizures can occur independently from liver crises and may present with metabolic stroke."
    explanation: Independent confirmation in a separate cohort that the encephalopathy is not simply downstream of liver failure.
diagnosis:
- name: Temperature-dependent aminoacylation assay in patient fibroblasts
  description: >-
    The functional confirmatory test, and unusually it is also the disease's
    central mechanism made visible. Leucyl-tRNA aminoacylation is measured in
    patient-derived fibroblasts at baseline and at elevated temperature.
    Reduced baseline activity confirms the enzyme defect; the further fall at
    38.5 and 40 degrees is what distinguishes this from a fixed enzymopathy and
    predicts the febrile decompensation that defines the clinical course. A
    baseline-only assay would miss the finding that matters most for management.
    The same study showed patient fibroblast growth is severely impaired at low
    cognate amino acid concentration, which is the assay underpinning the
    supplementation strategy.
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
    explanation: Establishes the assay and its temperature dependence across every patient tested in the largest cohort.
  - reference: PMID:34194004
    reference_title: Treatment of ARS deficiencies with specific amino acids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In fibroblasts from patients with isoleucyl-RS (IARS), leucyl-RS (LARS), phenylalanyl-RS-beta-subunit (FARSB), and seryl-RS (SARS) deficiencies, we investigated aminoacylation activity, thermostability, and sensitivity to ARS-specific amino acid concentrations, and developed personalized treatments."
    explanation: >-
      Describes the assay panel - activity, thermostability and amino acid
      sensitivity - and makes explicit that it was used to derive personalised
      treatment, so the diagnostic test and the therapeutic decision are the same
      measurement.
- name: Exome or genome sequencing with LARS1 variant interpretation
  description: >-
    Molecular diagnosis rests on identifying biallelic LARS1 variants. Two
    interpretation points. First, confirm the gene is LARS1 and not LARS2 - the
    mitochondrial leucyl-tRNA synthetase, which causes a different disease - since
    the founding literature uses the bare symbol LARS. Second, do not expect the
    variant to be a null: reported alleles are partial loss-of-function, most fall
    in the editing domain, and the diagnosis should not be discarded because
    residual activity is present. The founding kindred was solved by homozygosity
    mapping plus exome sequencing in a consanguineous family; later patients
    include compound heterozygotes.
  evidence:
  - reference: PMID:22607940
    reference_title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We aimed to identify the underlying risk gene using homozygosity mapping and whole exome sequencing."
    explanation: The sequencing approach that established the diagnosis in the founding family.
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
    explanation: Documents the breadth of the allelic series a diagnostic laboratory should expect to interpret against.
  notes: >-
    No GeneReviews chapter exists for LARS1 or ILFS1. Re-confirmed by esearch
    against PubMed on 2026-08-28: `LARS1 GeneReviews[All Fields]`,
    `infantile liver failure syndrome GeneReviews[Title]` and
    `leucyl-tRNA synthetase GeneReviews[All Fields]` all return zero results. The
    NBAS/ILFS2 chapter covers a different gene and a different disease.
genetic:
- name: LARS1
  gene_term:
    preferred_term: LARS1
    term:
      id: hgnc:6512
      label: LARS1
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  notes: >-
    LARS1 at 5q32 encodes cytoplasmic leucyl-tRNA synthetase. Inheritance is
    autosomal recessive; the founding kindred was a consanguineous Irish Traveller
    family with a homozygous missense allele, and eight further previously
    unreported variants were added by the 2020 international series. Most reported
    human variants fall in the enzyme's editing (proofreading) domain. The
    functional consequence measured in patient fibroblasts is reduced
    aminoacylation activity that worsens with temperature - a partial,
    conditional loss of function rather than a null.
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants."
    explanation: Documents the breadth of the allelic series recorded in this genetic block.
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro."
    explanation: The functional assay characterising these variants as conditional loss-of-function.
phenotypes:
- category: Hepatic
  name: Acute Liver Failure
  description: >-
    Recurrent hepatic dysfunction progressing in severe episodes to acute liver
    failure, typically precipitated by febrile illness, with onset before age one.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
    temporality: RECURRENT
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
    explanation: Establishes recurrent liver dysfunction as universal in the characterised cohort.
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures (22/29), and muscular hypotonia (13/27)."
    explanation: >-
      The cumulative series' denominators. Acute liver failure is 24/34, about
      71%, which puts it in the FREQUENT band (30-79%), not VERY_FREQUENT - and
      well short of universal, which matters because frank liver failure is the
      feature the disease is named for.
- category: Hepatic
  name: Recurrent Elevation of Hepatic Transaminases
  description: >-
    The leading hepatic finding, and more common than frank liver failure -
    transaminases rise recurrently with febrile illness, reaching acute liver
    failure in only some episodes and some patients. Modelling it separately from
    Acute Liver Failure matters because it is the phenotype most patients actually
    have most of the time.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Elevated circulating hepatic transaminase concentration
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
    temporality: RECURRENT
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness."
    explanation: >-
      Names recurrent transaminase elevation as the most prominent finding, and
      the phrase "up to liver failure" is what separates it from the ALF phenotype
      - failure is the severe end of this spectrum, not a separate event.
- category: Hepatic
  name: Hepatomegaly
  description: Liver enlargement, reported in all three patients of a deep-phenotyping case series.
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  notes: >-
    No frequency asserted - the source is a three-patient series covering both
    LARS1 and MARS1 disease, so it establishes the phenotype without giving a
    denominator for ILFS1.
  evidence:
  - reference: PMID:34496286
    reference_title: "Deep phenotyping of MARS1 (interstitial lung and liver disease) and LARS1 (infantile liver failure syndrome 1) recessive multisystemic disease using Human Phenotype Ontology annotation: Overlap and differences. Case report and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All three patients had anemia, hepatomegaly, feeding difficulties, failure to thrive and hypoalbuminemia."
    explanation: >-
      Graded PARTIAL - the three patients span LARS1 and MARS1 disease, so the
      shared features are reported across two conditions rather than for ILFS1
      alone.
- category: Gastrointestinal
  name: Feeding Difficulties
  description: >-
    Feeding difficulties, contributing to the early failure to thrive and
    relevant to the supplementation strategy, which depends on maintaining
    substrate intake during illness.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  notes: >-
    As for hepatomegaly - single small series spanning two ARS diseases, so no
    frequency is asserted.
  evidence:
  - reference: PMID:34496286
    reference_title: "Deep phenotyping of MARS1 (interstitial lung and liver disease) and LARS1 (infantile liver failure syndrome 1) recessive multisystemic disease using Human Phenotype Ontology annotation: Overlap and differences. Case report and review of literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All three patients had anemia, hepatomegaly, feeding difficulties, failure to thrive and hypoalbuminemia."
    explanation: Same series and same PARTIAL grading as hepatomegaly.
- category: Hepatic
  name: Hypoalbuminemia
  description: One of the earliest presenting features, reflecting impaired hepatic protein synthesis.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Hypoalbuminemia
    term:
      id: HP:0003073
      label: Hypoalbuminemia
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Low birth weight, early failure to thrive, anemia and hypoalbuminemia are amongst the first presenting features, with liver dysfunction before age 1."
    explanation: Names hypoalbuminemia among the first presenting features and dates the hepatic onset.
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures (22/29), and muscular hypotonia (13/27)."
    explanation: >-
      The same denominator sentence; the fraction relevant here is hypoalbuminemia
      at 32/32 - present in every patient assessed, which is what supports
      VERY_FREQUENT.
- category: Hematologic
  name: Microcytic Anemia
  description: Anemia, specified as microcytic in the largest cohort, present from early infancy.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Microcytic anemia
    term:
      id: HP:0001935
      label: Microcytic anemia
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
    explanation: Specifies the anemia as microcytic and prevalent.
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures (22/29), and muscular hypotonia (13/27)."
    explanation: >-
      The same denominator sentence; the fraction relevant here is microcytic
      anemia at 32/33, about 97%, supporting VERY_FREQUENT.
- category: Growth
  name: Failure to Thrive
  description: Early failure to thrive, often preceded by low birth weight.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Early failure to thrive, recurrent liver dysfunction, anemia, hypoalbuminemia and seizures were present in all patients."
    explanation: Establishes early failure to thrive as universal in the characterised cohort.
- category: Growth
  name: Intrauterine Growth Restriction
  description: >-
    Reduced intrauterine growth, present in almost every patient in whom it was
    specifically looked for - which places the disease's onset before birth, before
    any febrile trigger can have acted.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Intrauterine growth retardation
    term:
      id: HP:0001511
      label: Intrauterine growth retardation
  evidence:
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "intrauterine growth restriction (31/32 patients in whom this finding was specifically described)"
    explanation: >-
      Near-universal IUGR with an explicit denominator, and the source is careful
      to state the denominator is patients in whom it was specifically described -
      an ascertainment caveat worth preserving.
- category: Neurologic
  name: Global Developmental Delay
  description: Developmental delay in the great majority of patients.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most patients (90 %) had developmental delay."
    explanation: Gives the reported frequency of developmental delay, which maps to VERY_FREQUENT.
- category: Neurologic
  name: Seizures
  description: >-
    Seizures, frequently infection-related, and a defining component of the
    encephalopathic episodes. Reported at 10/13 in the imaging cohort and 22/29
    in the cumulative series - about 77% either way, so FREQUENT rather than
    VERY_FREQUENT.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All individuals had developmental delay and 10/13 had seizures."
    explanation: Gives an explicit denominator for seizure frequency in an independent imaging cohort.
- category: Neurologic
  name: Encephalopathy
  description: >-
    Acute encephalopathic episodes with reduced consciousness, precipitated by
    infection and capable of occurring independently of hepatic dysfunction.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
    temporality: RECURRENT
  evidence:
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Encephalopathic episodes in 8/13 were typically associated with infections, presented with seizures and reduced consciousness, mostly accompanied by hepatic dysfunction, and recovery in 17/19 episodes."
    explanation: Gives frequency, trigger, presentation and outcome of the encephalopathic episodes.
- category: Musculoskeletal
  name: Muscular Hypotonia
  description: Hypotonia, reported as prevalent in the largest cohort.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:32699352
    reference_title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, growth retardation, microcytic anemia, neurodevelopmental delay, muscular hypotonia, and infection-related seizures are prevalent."
    explanation: Reports muscular hypotonia among the prevalent features.
- category: Renal
  name: Renal Tubulopathy
  description: >-
    Renal tubular dysfunction, reported in the founding kindred. Not confirmed as
    a consistent feature in later cohorts.
  phenotype_term:
    preferred_term: Renal tubular dysfunction
    term:
      id: HP:0000124
      label: Renal tubular dysfunction
  evidence:
  - reference: PMID:22607940
    reference_title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Additional symptoms include anaemia, renal tubulopathy, developmental delay, seizures, failure to thrive and deterioration of liver function with minor illness."
    explanation: >-
      Reports renal tubulopathy in the founding family. Graded PARTIAL because it
      comes from the single consanguineous kindred and is not among the features
      the later systematic cohorts list as prevalent.
treatments:
- name: Maintain Protein and Glucose Intake During Illness
  description: >-
    The counter-intuitive management point, and the one most likely to be got
    wrong. In metabolic hepatopathies the reflex is to reduce or stop protein
    intake; the ILFS1 clinical series argues this is inappropriate here and
    recommends ensuring sufficient natural protein intake when unwell. The
    mechanistic rationale is that the lesion is a failure to CHARGE and USE amino
    acids, not a failure to clear them, so substrate restriction removes supply
    without relieving the block. The MRI study independently recommends sufficient
    glucose and protein alongside proactive fever management.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  target_mechanisms:
  - target: Febrile Decompensation of Residual Charging Capacity
    description: >-
      Maintaining substrate supply and limiting fever address the two components
      proposed to precipitate decompensation.
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "However, we suggest that the traditional management of reducing/stopping protein intake in patients with metabolic hepatopathies may not be appropriate for ILFS1. We currently recommend ensuring sufficient natural protein intake when unwell."
    explanation: The explicit clinical recommendation against protein restriction, from the cohort that defined the phenotype.
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "thus, sufficient glucose and protein intake along with pro-active fever management is suggested"
    explanation: Independent recommendation of substrate maintenance plus fever control from the imaging cohort.
- name: Seasonal Influenza Vaccination
  description: >-
    Because decompensation is infection-triggered and severe episodes were
    specifically observed during influenza infections, the imaging cohort makes a
    strong recommendation for seasonal vaccination. This is a rare case of a
    mechanism-derived preventive intervention in an ARS deficiency: it does not
    touch the enzyme, it removes the trigger.
  therapeutic_modality: VACCINE
  treatment_term:
    preferred_term: vaccination
    term:
      id: NCIT:C15346
      label: Vaccination
  target_mechanisms:
  - target: Febrile Decompensation of Residual Charging Capacity
    description: >-
      Preventing a febrile illness prevents the trigger that precipitates hepatic
      and encephalopathic crises.
  evidence:
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As severe episodes were observed during influenza infections, we strongly recommend seasonal vaccination."
    explanation: The observation and the recommendation, stated together by the authors.
- name: Liver Transplantation
  description: >-
    The definitive intervention for irreversible hepatic failure, and part of the
    hard outcome measure in this disease - 12 of 36 reported patients died or
    underwent liver transplantation.
    It carries a mechanistic caveat this entry treats as important rather than
    incidental: LARS1 deficiency is systemic, so replacing the liver does not
    correct the enzyme defect elsewhere. Encephalopathy occurred in one individual
    AFTER transplantation. Transplantation should therefore be understood as
    treating the organ that fails first, not the disease.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: liver transplantation
    term:
      id: NCIT:C15271
      label: Liver Transplantation
  target_mechanisms:
  - target: Recurrent Hepatocellular Injury and Acute Liver Failure
    description: >-
      Replaces the organ whose protein-synthetic failure produces the
      life-threatening episodes, without addressing the charging defect in other
      tissues.
  evidence:
  - reference: PMID:38844943
    reference_title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among the 36 known patients, 12 died or underwent liver transplantation."
    explanation: >-
      Establishes that transplantation is part of the real course of this disease,
      against an explicit denominator. Note the composite endpoint does not
      separate deaths from transplants, so it does not report a transplant
      outcome.
  - reference: PMID:38951950
    reference_title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Encephalopathy without hepatic dysfunction occurred in one individual after liver transplantation."
    explanation: >-
      Cited as the caveat rather than the support - a transplanted patient still
      had encephalopathy, which is the evidence that transplantation does not
      treat the systemic disease.
- name: Leucine Supplementation
  description: >-
    The evidence here changed, and both results are recorded because the
    disagreement is informative rather than a contradiction to be resolved by
    picking the newer paper.
    The 2015 ILFS1 clinical series reported that leucine supplementation had no
    appreciable impact on patient well-being. A 2021 study that approached the
    problem mechanistically rather than empirically reached the opposite
    conclusion: having first shown in patient fibroblasts that aminoacylation is
    both reduced at baseline and further reduced at febrile temperature, and that
    growth is severely impaired when the cognate amino acid is scarce, the authors
    supplemented patients with their cognate amino acid and INTENSIFIED dosing
    during infections, reporting benefit in growth, head circumference,
    development, coping with infections and oxygen dependency over up to two and
    two-thirds years.
    The two are reconcilable, and the reconciliation is the point: the failed
    attempt supplied leucine at steady state, while the successful protocol raised
    supply precisely when the temperature-sensitive enzyme's capacity falls. If
    that reading is right, timing rather than substrate is what the earlier trial
    got wrong. It is not established - the 2021 series pooled four different ARS
    deficiencies and was uncontrolled - so this entry presents it as the better
    supported of two open positions, not as settled.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: nutritional support
    term:
      id: NCIT:C15433
      label: Nutritional Support
  target_mechanisms:
  - target: Reduced Leucyl-tRNA Aminoacylation Capacity
    description: >-
      Raising cognate amino acid concentration is intended to drive the partially
      active enzyme, which is substrate-sensitive in patient cells.
  evidence:
  - reference: PMID:25917789
    reference_title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Leucine supplementation had no appreciable impact on patient well-being."
    explanation: >-
      Graded REFUTE against benefit from leucine supplementation as given in this
      cohort. Uncontrolled clinical experience in a small series, and it does not
      state the dose or whether dosing was intensified during illness - which the
      later study identifies as the decisive variable.
  - reference: PMID:34194004
    reference_title: Treatment of ARS deficiencies with specific amino acids.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To prevent local and/or temporal deficiencies, we treated patients with corresponding amino acids (follow-up: 1/2-2 2/3rd years), and intensified treatment during infections. All patients showed beneficial treatment effects, most strikingly in growth (without tube feeding), head circumference, development, coping with infections, and oxygen dependency."
    explanation: >-
      Reports benefit from cognate amino acid supplementation intensified during
      infection. Graded SUPPORT, but note the cohort spans four ARS deficiencies
      (IARS, LARS, FARSB, SARS) rather than being an ILFS1 series, and there is no
      control arm - so it supports the strategy without isolating the effect in
      LARS1 deficiency.
  - reference: PMID:34194004
    reference_title: Treatment of ARS deficiencies with specific amino acids.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "With lower cognate amino acid concentrations, patient fibroblast growth was severely affected."
    explanation: The in vitro substrate-sensitivity result providing the rationale for supplementation, measured in patient cells.
animal_models:
- name: larsb-knockout zebrafish
  species: Zebrafish
  genotype: larsb-/- (CRISPR/Cas9 frameshift in exon 3, editing domain)
  publication: PMID:33863987
  description: >-
    CRISPR/Cas9 knockout of larsb, the zebrafish paralogue with higher homology to
    human LARS1, targeted to the editing domain where most human variants fall.
  modeled_mechanisms:
  - target: Recurrent Hepatocellular Injury and Acute Liver Failure
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      The model reproduces progressive liver failure and anemia, the two
      cardinal systemic features.
    limitations: >-
      The fish phenotype is PROGRESSIVE and lethal within 12 days, whereas human
      ILFS1 is EPISODIC, febrile-triggered, and compatible with survival past 28
      years. So the model reproduces the organ that fails without reproducing the
      conditional, temperature-triggered character that defines the human disease.
      The knockout is also a null, while human alleles are partial loss-of-function.
    readouts:
    - name: Liver size
      target: Recurrent Hepatocellular Injury and Acute Liver Failure
      direction: RESTORED
      interpretation: >-
        Liver size and survival improved on autophagy suppression, indicating
        autophagy contributes causally to the hepatic phenotype in this model.
      evidence:
      - reference: PMID:33863987
        reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "The atg5-morpholino knockdown and bafilomycin treatment partially improved the size of the liver and survival rate in larsb-/- zebrafish."
        explanation: Reports the measured rescue of liver size and survival.
    evidence:
    - reference: PMID:33863987
      reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "we generated Lars deficient (larsb-/-) zebrafish that showed progressive liver failure and anaemia, resulting in early lethality within 12 days post fertilization."
      explanation: Establishes that the model reproduces the liver and haematological phenotypes, which is what makes it informative for this node.
  - target: Dysregulated mTORC1 Signalling and Excessive Autophagy
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      The model is the primary and essentially only evidence for the autophagy arm
      of the mechanism.
    limitations: >-
      No human ILFS1 tissue has been examined for excessive autophagy, so the
      entire branch rests on the fish.
    evidence:
    - reference: PMID:33863987
      reference_title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Indeed, excessive autophagy activation was observed in larsb-/- zebrafish."
      explanation: The direct observation of excessive autophagy in the model.
discussions:
- discussion_id: ilfs1_autophagy_arm_human_validity
  kind: HUMAN_MODEL_MISMATCH
  attaches_to:
  - pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
  prompt: >-
    Does excessive autophagy contribute to human ILFS1 liver injury, or is it a
    property of the zebrafish null that does not transfer to partial
    loss-of-function human alleles?
  rationale: >-
    The autophagy branch is supported entirely by larsb-knockout zebrafish, where
    suppressing autophagy genuinely rescued liver size and survival. Two features
    of that model argue for caution before carrying it into human biology. It is a
    NULL, whereas human ILFS1 alleles retain temperature-sensitive residual
    activity; and its phenotype is progressive and lethal within 12 days, whereas
    the human disease is episodic and survivable into adulthood. The mismatch
    matters practically because the fish result points at autophagy or mTORC1
    inhibitors as candidate therapies, and that inference is only as good as the
    model's fidelity to a partial loss-of-function human disease.
  proposed_experiments:
  - experiment_id: ilfs1_autophagic_flux_at_febrile_temperature
    name: Autophagic flux in ILFS1 patient hepatocyte-like cells at febrile temperature
    description: >-
      Measure autophagic flux (LC3-II turnover with and without lysosomal block)
      in patient-derived hepatocyte-like cells at 37 C and at 40 C, against
      controls, to test whether excessive autophagy is present in human cells
      carrying partial loss-of-function alleles and whether it is temperature-dependent
      in the way aminoacylation activity is.
    would_support:
    - pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
    supporting_outcome:
    - >-
      Increased autophagic flux in patient cells relative to controls, amplified at
      the higher temperature.
    would_refute:
    - pathophysiology#Dysregulated mTORC1 Signalling and Excessive Autophagy
    refuting_outcome:
    - >-
      Autophagic flux indistinguishable from controls at both temperatures,
      indicating the fish finding reflects the null genotype rather than the human
      disease mechanism.
- discussion_id: ilfs1_microcytosis_unexplained
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Microcytic Anemia
  prompt: >-
    Why does a cytoplasmic leucine-charging defect produce a MICROCYTIC anemia
    specifically?
  rationale: >-
    Anemia is early and near-universal and is reproduced in the zebrafish model,
    so it is a direct consequence of LeuRS deficiency rather than a secondary
    effect of liver disease. But microcytosis normally points at haem or globin
    synthesis, and no published work connects leucyl-tRNA charging to either. The
    causal edge into this node is annotated INDIRECT_UNKNOWN_INTERMEDIATES for
    exactly this reason.
- discussion_id: ilfs1_translation_step_unmeasured
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Impaired Cytoplasmic Protein Synthesis in High-Demand Tissues
  prompt: >-
    Has reduced protein synthesis actually been measured in ILFS1 patient tissue,
    or is the translational step inferred from the enzyme assay and the clinical
    phenotype either side of it?
  rationale: >-
    The entry's central causal chain runs enzyme activity to translation to organ
    failure, but only the two ends are measured. No published study reports global
    or tissue-specific translation rates in ILFS1 material. The step is retained
    because no alternative route from a charging defect to hypoalbuminemia has been
    proposed, but it is graded PROVISIONAL and flagged here rather than presented
    as established.
- discussion_id: ilfs1_encephalopathy_independent_of_liver
  kind: OPEN_QUESTION
  attaches_to:
  - pathophysiology#Encephalopathic Episodes with Deep Grey Matter and Brainstem Injury
  prompt: >-
    What is the direct mechanism of brain injury in ILFS1, given that encephalopathy
    can occur without hepatic dysfunction?
  rationale: >-
    Encephalopathy after liver transplantation, and encephalopathic episodes
    occurring independently of liver crises in a separate cohort, together rule out
    a purely hepatic-encephalopathy explanation. The MRI pattern is also reported as
    distinct from hepatic encephalopathy and from metabolic stroke in organic
    acidurias and mitochondrial disease. What remains is a neuronal
    protein-synthesis deficit acting directly, which is plausible and untested. The
    imaging authors state the pathomechanism remains unclear.
references:
- reference: PMID:22607940
  title: Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
- reference: PMID:25917789
  title: "Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS."
- reference: PMID:32699352
  title: Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
- reference: PMID:33863987
  title: Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
- reference: PMID:38951950
  title: "MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration."
- reference: PMID:34194004
  title: Treatment of ARS deficiencies with specific amino acids.
- reference: PMID:38844943
  title: Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
- reference: PMID:22424946
  title: Leucyl-tRNA synthetase is an intracellular leucine sensor for the mTORC1-signaling pathway.
- reference: PMID:34496286
  title: "Deep phenotyping of MARS1 (interstitial lung and liver disease) and LARS1 (infantile liver failure syndrome 1) recessive multisystemic disease using Human Phenotype Ontology annotation: Overlap and differences. Case report and review of literature."
📚

References & Deep Research

References

9
PMID:22607940
Identification of a mutation in LARS as a novel cause of infantile hepatopathy.
No top-level findings curated for this source.
PMID:25917789
Clinical and genetic characterisation of infantile liver failure syndrome type 1, due to recessive mutations in LARS.
No top-level findings curated for this source.
PMID:32699352
Genotypic diversity and phenotypic spectrum of infantile liver failure syndrome type 1 due to variants in LARS1.
No top-level findings curated for this source.
PMID:33863987
Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish.
No top-level findings curated for this source.
PMID:38951950
MRI in LARS1 deficiency-Spectrum, patterns, and correlation with acute neurological deterioration.
No top-level findings curated for this source.
PMID:34194004
Treatment of ARS deficiencies with specific amino acids.
No top-level findings curated for this source.
PMID:38844943
Early onset and liver failure indicating poor prognosis of infant liver failure syndrome type 1.
No top-level findings curated for this source.
PMID:22424946
Leucyl-tRNA synthetase is an intracellular leucine sensor for the mTORC1-signaling pathway.
No top-level findings curated for this source.
PMID:34496286
Deep phenotyping of MARS1 (interstitial lung and liver disease) and LARS1 (infantile liver failure syndrome 1) recessive multisystemic disease using Human Phenotype Ontology annotation: Overlap and differences. Case report and review of literature.
No top-level findings curated for this source.

Deep Research

1
OpenScientist ▸
Infantile Liver Failure Syndrome 1 (ILFS1): A Comprehensive Disease Report
openscientist-autonomous 15 citations 2026-08-28T10:39:37.097243

Infantile Liver Failure Syndrome 1 (ILFS1): A Comprehensive Disease Report

Disease: Infantile Liver Failure Syndrome 1 (ILFS1) Gene: LARS1 (cytosolic leucyl-tRNA synthetase 1) Category: Mendelian, autosomal recessive Key identifiers: OMIM #615438 (disease); OMIM 151350 / HGNC:6512 (LARS1); Orphanet ORPHA:463328; UniProt Q9P2J5; NCBI Gene 51520; reference transcript NM_020117.11; locus 5q31.3–q33.1 (5q32); suggested MONDO: MONDO:0014220 Evidence base: Human clinical case series/reviews, patient-derived cellular assays, zebrafish models, and biochemical mechanistic studies. Synthesized from aggregated disease-level literature and case series* (not individual EHR data).

Summary

Infantile Liver Failure Syndrome type 1 (ILFS1; OMIM #615438) is a rare autosomal-recessive multisystem disorder caused by biallelic hypomorphic (predominantly missense) variants in LARS1, the gene encoding cytosolic leucyl-tRNA synthetase. The enzyme has two essential and mechanistically distinct roles: (1) it charges cytoplasmic tRNA^Leu with leucine to enable protein translation, and (2) it "moonlights" as the intracellular leucine sensor that activates the mechanistic target of rapamycin complex 1 (mTORC1) by acting as a GTPase-activating protein (GAP) for the Rag GTPase. Loss of function in both arms explains the disease's defining feature — fever-triggered, recurrent acute liver failure and encephalopathy superimposed on a background of intrauterine growth restriction, failure to thrive, hypoalbuminemia, and microcytic anemia.

The pathophysiology is dual and unified by a temperature-sensitivity mechanism. Patient-derived fibroblasts show aminoacylation activity that is reduced at baseline and further diminished at febrile temperatures (38.5–40 °C), rendering the mutant enzyme rate-limiting for translation precisely when protein-synthetic demand rises during infection. Simultaneously, loss of the LARS1 leucine-sensing/Rag-GAP function downregulates mTORC1 and drives excessive autophagy, a mechanism directly modeled in zebrafish larsb mutants. This convergence of "insufficient aminoacylation to meet translational demands" during febrile catabolic stress establishes infancy and fever episodes as the critical window of vulnerability and the primary target for intervention.

Prognosis is guided by early onset (<3 months) and the presence of liver failure, both of which confer significantly poorer survival. Management remains largely supportive, but a mechanism-based disease-modifying therapy — supplementation with the cognate amino acid L-leucine — has shown benefit in growth, development, and liver/lung disease in the majority of treated patients, though it does not rescue the most severe phenotypes. Liver transplantation is reserved for end-stage or recurrent liver failure. Diagnosis rests on whole-exome/whole-genome sequencing, supported by a characteristic biochemical profile and a confirmatory temperature-dependent fibroblast aminoacylation assay. This report synthesizes 12 confirmed findings drawn from 21 reviewed papers spanning human clinical cohorts, in vitro functional studies, and zebrafish models.

1. Disease Information

ILFS1 is a Mendelian, autosomal-recessive inborn error caused by biallelic variants in LARS1. It presents in infancy with recurrent, fever-triggered acute liver failure on a background of poor growth, hypoalbuminemia, and anemia, and it can involve the brain, kidney, muscle, and blood.

  • Key identifiers: OMIM #615438; Orphanet ORPHA:463328; suggested MONDO:0014220; MeSH — indexed under inborn errors/liver failure (no dedicated descriptor). ICD-10: no specific code (mapped under K72.– acute/subacute hepatic failure and P-codes for perinatal presentations); ICD-11: no dedicated code.
  • Synonyms / alternative names: ILFS1; Infantile liver failure syndrome type 1; LARS1 deficiency; Leucyl-tRNA synthetase deficiency (cytosolic); LARS-related infantile hepatopathy.
  • Information source type: Aggregated disease-level resources and published case series/reviews — not individual EHR data.

2. Etiology

Disease causal factors. The primary cause is genetic: biallelic (homozygous or compound heterozygous) hypomorphic variants in LARS1, encoding cytoplasmic leucyl-tRNA synthetase. The disorder is not mitochondrial — LARS knockdown in HEK293 cells does not impair mitochondrial function even under stress.

"The candidate mutation is located in the LARS gene which encodes a cytoplasmic leucyl-tRNA synthetase enzyme responsible for exclusively attaching leucine to its cognate tRNA during protein translation." — PMID: 22607940

"Knock-down of LARS in HEK293 cells did not impact on mitochondrial function even when the cells were put under physiological stress." — PMID: 22607940

Genetic risk factors. Consanguinity (homozygous variants in founder populations such as Irish Travellers); carrier parents (obligate heterozygotes). No modifier genes have been established, and there is no significant genotype–phenotype correlation with severity.

Environmental risk factors / triggers. Febrile infections are the principal precipitant of acute crises (see Section 5 and Finding 12). Catabolic stress (fasting, illness) likely lowers substrate availability and increases translational demand.

Protective factors. No genetic protective variants are described. Environmentally, cognate L-leucine supplementation and aggressive fever/sick-day management act as risk-modifying/protective interventions (see Section 12).

Gene–environment interaction. ILFS1 is a textbook GxE disorder: a temperature-sensitive hypomorphic enzyme becomes rate-limiting during fever (see Finding 12).

3. Phenotypes

Phenotypes combine episodic, fever-triggered hepatic and neurologic crises with a chronic multisystem background (growth failure, hypoalbuminemia, anemia). Onset is neonatal-to-infantile; severity is variable (mild-stabilizing to lethal neonatal); progression is episodic with a progressive baseline component.

Phenotype Type Frequency Suggested HPO
Intrauterine growth restriction Physical/lab 31/32 (~97%) HP:0001511
Failure to thrive Clinical sign 30/31 (~97%) HP:0001508
Hypoalbuminemia Lab abnormality 32/32 (100%) HP:0003073
Microcytic anemia Lab abnormality 32/33 (~97%) HP:0001935
Acute liver failure Clinical sign 24/34 (~71%) HP:0006554
Neurodevelopmental delay Behavioral/dev 25/30 (~83%) HP:0012758
Seizures Clinical sign 22/29 (~76%) HP:0001250
Muscular hypotonia Clinical sign 13/27 (~48%) HP:0001252
Recurrent transaminase elevation Lab abnormality Prominent HP:0002910
Encephalopathy / metabolic stroke Clinical sign Episodic HP:0001298
Hepatomegaly / splenomegaly Physical Reported HP:0002240 / HP:0001744
Coagulopathy Lab abnormality During crises HP:0001928

"The main clinical features of ILFS1 were intrauterine growth restriction (31/32 patients in whom this finding was specifically described), failure to thrive (30/31), hypoalbuminemia (32/32), microcytic anemia (32/33), acute liver failure (24/34), neurodevelopmental delay (25/30), seizures (22/29), and muscular hypotonia (13/27)." — PMID: 38844943

"The most prominent clinical findings are recurrent elevation of liver transaminases up to liver failure and encephalopathic episodes, both triggered by febrile illness." — PMID: 32699352

Quality of life impact. Recurrent hospitalizations for liver crises, chronic growth failure, developmental delay/seizures, and the constant need for infection vigilance impose a substantial burden on affected children and families. Disease-specific QoL instruments have not been applied; QoL data are qualitative.

4. Genetic / Molecular Information

Causal gene. LARS1 (HGNC:6512; OMIM *151350; NCBI Gene 51520; UniProt Q9P2J5), chromosome 5q32, reference transcript NM_020117.11.

Pathogenic variants. Predominantly biallelic missense, homozygous in consanguinity and compound heterozygous otherwise, with strong allelic (mostly private) heterogeneity and loss-of-function/hypomorphic, temperature-sensitive consequences. All are germline. There is no significant genotype–phenotype correlation with severity.

Study Variant(s) Zygosity PMID
Casey 2012 (Irish Traveller) homozygous missense homozygous 22607940
Chinese patient p.L712del + p.D395N compound het 28774368
ANE siblings c.83_88delinsAATGGGATA p.(Arg28_Phe30delinsLysTryAspIle) + c.1283C>T p.(Pro428Leu) compound het 38923116
Deep-phenotyping case c.1818dup + c.463A>G compound het 34496286
Lenz/Staufner 2020 8 previously unreported variants across 15 families mixed 32699352

"Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants." — PMID: 32699352

"Whole exome sequencing identified the compound heterozygous variants in LARS1 (NM_020117.11) as c.83_88delinsAATGGGATA, p.(Arg28_Phe30delinsLysTryAspIle) and c.1283C>T, p.(Pro428Leu) in both siblings." — PMID: 38923116

Variant classification (ACMG/AMP): ranges from pathogenic/likely pathogenic to VUS; functional aminoacylation assays provide supporting (PS3) evidence. Allele frequencies: individual variants are ultra-rare/absent in gnomAD (not systematically quantified here). Modifier genes / epigenetics / chromosomal abnormalities: none established for ILFS1.

5. Environmental Information

  • Environmental / lifestyle factors: Febrile illness and catabolic stress are the operative environmental exposures; there are no toxin, occupational, or lifestyle exposures implicated in disease causation (the cause is genetic).
  • Infectious agents (triggers, not causes): Documented crisis triggers include influenza type A and human herpesvirus 6 (HHV-6), each preceding fatal acute necrotizing encephalopathy in affected siblings.

"She presented with generalized seizure and liver dysfunction due to influenza type A infection." — PMID: 38923116

6. Mechanism / Pathophysiology

Molecular pathways. Two arms converge from a single gene defect:

  1. Canonical (translation): LARS1 charges cytoplasmic tRNA^Leu with leucine (GO:0004823 leucine-tRNA ligase activity; GO:0006429 leucyl-tRNA aminoacylation). Mutant enzyme is temperature-sensitive — aminoacylation drops at 38.5–40 °C.
  2. Non-canonical (mTORC1 signaling): LARS1 is the intracellular leucine sensor that binds Rag GTPase in a leucine-dependent manner and acts as a GAP for RagD, switching mTORC1 ON (GO:0038202 TORC1 signaling; GO:0032008 positive regulation of TOR signaling).

"Aminoacylation activity is significantly decreased in all patient cells studied upon temperature elevation in vitro." — PMID: 32699352

"leucyl-tRNA synthetase (LRS) plays a critical role in amino acid-induced mTORC1 activation by sensing intracellular leucine concentration and initiating molecular events leading to mTORC1 activation" — PMID: 22424946

"LRS directly binds to Rag GTPase, the mediator of amino acid signaling to mTORC1, in an amino acid-dependent manner and functions as a GTPase-activating protein (GAP) for Rag GTPase to activate mTORC1" — PMID: 22424946

A refined switch model casts LARS as the initiating "ON" switch via GTP hydrolysis of RagD, opposed by Sestrin2 as the "OFF" switch (PMID: 29784813).

Cellular processes. Loss of mTORC1 activation drives excessive autophagy (GO:0010506 regulation of autophagy; GO:0006914 autophagy), demonstrated systemically in zebrafish.

"Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish." — PMID: 33863987

Protein dysfunction: hypomorphic, thermolabile loss of function (not aggregation). Metabolic changes: impaired leucine handling and reduced anabolic mTORC1 signaling; catabolic vulnerability during fever. Tissue damage: hepatocyte translational failure → hepatocellular injury, fibrogenesis; neuronal injury (metabolic stroke, ANE). Biochemical abnormality: reduced leucyl-tRNA aminoacylation (enzyme deficiency). Immune involvement: none primary; infections act as triggers. Cell types: hepatocytes (CL:0000182) primarily; neurons; erythroid lineage; skeletal myocytes. Subcellular compartment: cytoplasm (GO:0005737); Rag/mTORC1 signaling at the lysosomal surface.

7. Anatomical Structures Affected

  • Primary organ: liver (UBERON:0002107) — recurrent transaminase elevation, acute liver failure, hepatomegaly; histology shows cirrhosis and fatty liver; autopsy shows fulminant hepatitis-like injury and fibrogenesis.
  • Secondary/multisystem: blood (UBERON:0000178; microcytic anemia ~97%), brain (UBERON:0000955; developmental delay, seizures, encephalopathy/metabolic stroke, ANE), skeletal muscle (UBERON:0001134; dysgenesis with disrupted striated fibers), kidney (UBERON:0002113; renal tubulopathy), and — by analogy within the ARS1 cluster — lung (UBERON:0002048).
  • Subcellular: cytoplasm (GO:0005737); lysosomal mTORC1 platform. Cells: hepatocyte (CL:0000182). Lateralization: bilateral/systemic.

"An autopsy showed fulminant hepatitis-like hepatocellular injury and fibrogenesis in the liver and a lack of uniformity in skeletal muscle, accompanied by the disruption of striated muscle fibers." — PMID: 33300650

"Additional symptoms include anaemia, renal tubulopathy, developmental delay, seizures, failure to thrive and deterioration of liver function with minor illness." — PMID: 22607940

Deep HPO phenotyping shows ILFS1 (LARS1) shares ~42% of phenotypic abnormalities with MARS1 disease (PMID: 34496286).

8. Temporal Development

  • Onset: congenital/neonatal-to-infantile; onset <3 months is common in severe cases. IUGR reflects prenatal onset of the growth phenotype.
  • Onset pattern: chronic baseline (growth failure, hypoalbuminemia, anemia) punctuated by acute, fever-triggered crises.
  • Progression: episodic/relapsing crises superimposed on a variably progressive course; some patients stabilize with age and management (e.g., a compound-heterozygous child stabilized by age 4 — PMID: 28774368), while severe neonatal cases are rapidly lethal.
  • Critical period: infancy and febrile episodes constitute the window of vulnerability and the key opportunity for intervention.

9. Inheritance and Population

  • Inheritance: autosomal recessive (OMIM #615438; ORPHA:463328). Penetrance appears complete in biallelic carriers; expressivity is variable. No anticipation, no reported germline mosaicism.
  • Epidemiology: ultra-rare; no established prevalence/incidence. Cumulative reported patients rose from 3 initial cases to 25 individuals/15 families (2020) to 36 patients (2024), plus additional case reports (~50+ total worldwide). Both sexes affected; no sex bias.
  • Founder effect / consanguinity: first described in a consanguineous Irish Traveller founder population; consanguinity is a key risk factor. Later reported in Caucasian and non-Caucasian (Chinese) patients.
  • Relative burden: among indeterminate pediatric acute liver failure, cytosolic aminoacyl-tRNA synthetase deficiencies (including LARS1) accounted for 10% of genetically solved cases.

"the most frequent were mitochondrial diseases (45%), disorders of vesicular trafficking (28%), and cytosolic aminoacyl-tRNA synthetase deficiencies (10%)" — PMID: 37976411

"Twenty-five individuals from 15 families were ascertained including 12 novel patients with eight previously unreported variants." — PMID: 32699352

10. Diagnostics

There is no specific biomarker; diagnosis rests on molecular genetic testing, supported by a characteristic biochemical profile.

  • Genetic testing (primary modality): WES/WGS established the diagnosis and is recommended for neonates/infants with unexplained early liver failure when metabolic testing is inconclusive. Gene panels for infantile cholestasis/liver failure that include LARS1 are appropriate; single-gene testing applies for known familial variants.

"Whole-exome sequencing may be useful for neonates with unexplained early liver failure if extensive genetic and metabolic testing is inconclusive." — PMID: 33300650

"WES established a genetic diagnosis in 37% of cases (97/260). Diagnostic yield was highest in children with PALF in the first year of life (41%), and in children with recurrent acute liver failure (64%)." — PMID: 37976411

  • Laboratory findings: episodic elevated transaminases (up to liver failure), hypoalbuminemia, coagulopathy, microcytic anemia, hyperammonemia during crises.
  • Functional confirmatory test: fibroblast aminoacylation assay showing reduced activity that worsens at 38.5–40 °C (PMID: 34194004).
  • Imaging: MRI may show metabolic stroke during encephalopathy; ultrasound may show hepatomegaly/splenomegaly.
  • Differential diagnosis: NBAS (ILFS2), MPV17/DGUOK and other mtDNA-depletion syndromes, citrin deficiency (SLC25A13), and other cytosolic aaRS deficiencies (IARS, MARS1). The Chinese case explicitly excluded citrin deficiency before diagnosing ILFS1 (PMID: 28774368).

11. Outcome / Prognosis

Prognosis is variable and driven by two factors. In the 36-patient cohort, 12 died or underwent liver transplantation, and Kaplan-Meier analysis identified:

Prognostic factor p-value Hazard ratio 95% CI
Age of onset < 3 months 0.0015 12.29 3.74–40.3
Presence of liver failure 0.0343 6.57 1.96–22.0

"Kaplan-Meier analysis indicated that age of onset < 3mo (p = 0.0015, hazard ratio = 12.29, 95% confidence interval [CI] = 3.74-40.3), like liver failure (p = 0.0343, hazard ratio = 6.57, 95% CI = 1.96-22.0), conferred poor prognosis." — PMID: 38844943

Severe neonatal disease can be lethal (hepatocellular injury, skeletal muscle dysgenesis; PMID: 33300650), and some patients develop fatal acute necrotizing encephalopathy (PMID: 38923116). Overall ARS1-deficiency mortality (a superset including LARS1) is ~22% (PMID: 40044141). Complications include end-stage liver disease, encephalopathy, chronic anemia, and developmental disability. Recovery/stabilization is possible with management (PMID: 28774368). Prognostic factors: early onset and liver failure (above); no prognostic biomarker is established.

12. Treatment

Mechanism-based pharmacotherapy — cognate L-leucine supplementation (CHEBI:15603; NCIT: Dietary Supplement Therapy). Supplying excess leucine helps the impaired enzyme meet translational demand and partly restores mTORC1 signaling.

"we observed a common disease mechanism of episodic insufficient aminoacylation to meet translational demands and illustrate the power of amino acid supplementation for the expanding ARS patient group" — PMID: 34194004

"Supplementation with cognate amino acids was described in 21 patients, with beneficial effects (e.g., improvements in growth, development, liver and lung disease) in the majority. Treatment did not alleviate the most severe phenotypes." — PMID: 40044141

Supportive care (NCIT: Supportive Care, C15277): aggressive fever/sick-day management, avoidance of catabolism, correction of hypoalbuminemia and coagulopathy, transfusion for anemia, nutritional support, seizure management.

Surgical/advanced: liver transplantation (NCIT: Liver Transplantation, C15360) for end-stage or recurrent liver failure (12/36 died or transplanted).

Experimental / strategy: All treatment data remain observational (case series, N-of-1); no controlled trials exist. Cognate amino acid supplementation is a shared, theoretically appealing strategy across the ARS deficiency family that requires controlled study. Pharmacogenomics: not applicable. Personalized approach: dosing guided by residual enzyme activity is a rational (untested) direction.

13. Prevention

  • Primary prevention: none for disease occurrence (genetic); genetic counseling and carrier/cascade screening in at-risk families (especially consanguineous kindreds and the Irish Traveller founder population); prenatal and preimplantation genetic testing available for known familial variants.
  • Secondary prevention: early molecular diagnosis via WES enables anticipatory management; there is no population newborn-screening test.
  • Tertiary prevention (preventing crises/complications): aggressive antipyresis and sick-day protocols during febrile illness, avoidance of catabolic stress, and cognate L-leucine supplementation to reduce crisis severity. Given fever as the defined critical trigger, prompt medical attention for febrile infections is the central preventive measure.

14. Other Species / Natural Disease

  • Taxonomy / orthologs: human LARS1 (NCBI Gene 51520) is conserved across vertebrates; zebrafish (Danio rerio, NCBI Taxon 7955) ortholog is larsb.
  • Natural disease in other species: no naturally occurring companion-animal or wildlife ILFS1 disease is documented in the reviewed literature; relevance is via engineered/mutant models. A bovine study shows LARS regulates casein synthesis via mTORC1-LAT1 (PMID: 40045634), underscoring conservation of the leucine-sensing function.
  • Comparative biology / evolutionary conservation: the dual aminoacylation + leucine-sensing/mTORC1 mechanism is conserved from fish to mammals, supporting translational relevance.

15. Model Organisms

  • Zebrafish (larsb): two independent larsb mutant lines recapitulate ILFS1-like features (liver dysfunction/hepatopathy), and larsb deficiency systemically induces excessive autophagy linked to mTORC1 downregulation — directly modeling the human mechanism.

"we obtained zebrafish larsb" — PMID: 30262142

"Leucyl-tRNA synthetase deficiency systemically induces excessive autophagy in zebrafish." — PMID: 33863987

  • In vitro / cellular: patient-derived fibroblasts (aminoacylation and thermostability assays; [PMIDs 32699352, 34194004]) and HEK293 LARS-knockdown cells (which excluded a primary mitochondrial defect; [PMID: 22607940]).
  • Model characteristics: zebrafish recapitulate hepatopathy and the autophagy/mTORC1 mechanism; limitations include incomplete capture of human hepatic failure, neurodevelopmental, and febrile-trigger dynamics. No mammalian (mouse) model is documented in the reviewed literature. Resources: ZFIN (zebrafish); patient fibroblast lines from published cohorts.

Mechanistic Model / Interpretation

     Biallelic hypomorphic LARS1 variants
                    │
      ┌─────────────────────┴─────────────────────┐
      ▼                                            ▼
   ARM 1: CANONICAL FUNCTION                   ARM 2: MOONLIGHTING FUNCTION
   Leu-tRNA aminoacylation                     Intracellular leucine sensor
      │                                            │
   Temperature-sensitive:                       Fails to bind Rag GTPase /
   activity ↓ at 38.5–40°C                      loss of GAP activity for RagD
      │                                            │
   FEVER (influenza A, HHV-6) ─────────►  Insufficient charged tRNA^Leu    mTORC1 activity ↓
      │                            to meet ↑ translational demand           │
      │                                            │              Excessive autophagy
      ▼                                            ▼                         ▼
┌──────────────────────────────────────────────────────────────────────────┐
│      Hepatocyte translational failure + catabolic stress + autophagy       │
└──────────────────────────────────────────────────────────────────────────┘
                    │
┌───────────────┬───────────┴───────────┬───────────────┐
▼               ▼                        ▼               ▼
  Acute liver      Encephalopathy /        Hypoalbuminemia   Growth failure
  failure          metabolic stroke / ANE  coagulopathy      (IUGR, FTT), anemia

Upstream vs downstream. The upstream trigger is febrile infection raising core temperature above the mutant enzyme's stability threshold, in an organ (liver) with high secretory translational load. Downstream, two parallel consequences unfold: (1) failed aminoacylation impairs synthesis of essential proteins (albumin, clotting factors) → hypoalbuminemia, coagulopathy, hepatocellular injury; and (2) failed leucine sensing collapses mTORC1 → excessive autophagy amplifying cell stress. The chronic non-febrile phenotype (IUGR, failure to thrive, anemia, developmental delay) reflects the constant baseline deficit. Why leucine helps: excess substrate partially restores both charged-tRNA production and the mTORC1 leucine signal — consistent with benefit in milder cases and failure in the most severe (residual activity too low). ILFS1 sits within the cytosolic ARS1 family sharing "episodic insufficient aminoacylation to meet translational demands," corroborated by ~42% HPO overlap with MARS1 disease.

Evidence Base

PMID Title (abbrev.) Evidence type Role
22607940 LARS as novel cause of infantile hepatopathy Human + in vitro Causal gene; excludes mitochondrial mechanism; multi-organ features
32699352 Genotypic/phenotypic spectrum of ILFS1 Human (25 pts) + functional Fever trigger; temperature-sensitive aminoacylation; allelic heterogeneity
38844943 Early onset & liver failure → poor prognosis Human (36 pts) Phenotype frequencies; Kaplan-Meier prognosis
33863987 LARS deficiency induces excessive autophagy Zebrafish Links LARS loss to mTORC1/autophagy
30262142 Loss of LARSb → ILFS1-like symptoms Zebrafish Disease-recapitulating model
38923116 Two siblings with ANE and LARS1 variants Human (case) Infectious triggers; severe ANE; compound-het variants
33300650 Severe neonatal course Human + autopsy Severe spectrum; WES recommendation; muscle pathology
34194004 Treatment of ARS deficiencies with amino acids In vitro + clinical Common mechanism; leucine therapy; temperature assay
40044141 ARS1-deficiencies phenotype & treatment review Review (438 pts) Cognate amino acid benefit/limits; 22% mortality
22424946 LARS is intracellular leucine sensor for mTORC1 Molecular Leucine-sensing/Rag-GAP mechanism
29784813 Coordination of Rag GTPase cycle by LARS Molecular LARS "ON" vs Sestrin2 "OFF" switch
28774368 First non-Caucasian ILFS1 child Human (case) Compound-het variants; differential dx; stabilization
37976411 Genetic landscape of pediatric ALF Human cohort (260) WES yield; cytosolic aaRS = 10% of solved cases
34496286 Deep phenotyping MARS1 vs LARS1 Human + review ~42% HPO overlap; shared multisystem features

Consistency and challenges. Human cohorts, in vitro assays, and zebrafish models converge on the dual aminoacylation/mTORC1 mechanism. The main tension is therapeutic — cognate amino acid supplementation benefits milder cases but fails in the most severe, and all treatment evidence is observational. The absence of genotype–phenotype correlation means variant identity alone does not predict severity.

Limitations and Knowledge Gaps

  1. Ultra-rare disease, small numbers (<~60 patients worldwide; max cohort 36) limit statistical power for genotype–phenotype and treatment analyses; no formal prevalence/incidence.
  2. No controlled treatment trials — all L-leucine/cognate amino acid data are observational or N-of-1; optimal dosing/timing and long-term efficacy undefined; no rescue of severe phenotypes.
  3. Absent genotype–phenotype correlation — determinants of lethal neonatal vs stabilizing courses unknown; modifiers/epigenetics unexplored.
  4. Mechanism partly inferred from models — the mTORC1/autophagy arm is best demonstrated in zebrafish/cell lines; direct human hepatocyte evidence and quantitative apportioning of the two arms are lacking.
  5. No mammalian (mouse) model documented in the reviewed literature.
  6. Biomarker gap — no specific circulating biomarker for diagnosis, crisis prediction, or monitoring; the fibroblast temperature assay is not widely available.
  7. Population genetics (carrier frequency, gnomAD variant frequencies, founder haplotype) not quantitatively established here.
  8. Citation caveat — the autophagy paper (PMID 33863987) snippet was flagged as an approximate match; the mechanistic claim is supported but exact wording should be verified against the source.

Proposed Follow-up Experiments / Actions

  1. Prospective international registry to capture natural history and enable powered genotype–phenotype and treatment-outcome analyses.
  2. Controlled/adaptive L-leucine trial with predefined endpoints (growth, crisis frequency, transaminase/albumin trajectories, neurodevelopment), stratified by residual enzyme activity.
  3. Conditional hepatocyte-specific Lars1 mouse model to test temperature-sensitivity and mTORC1/autophagy mechanisms in mammalian liver and as a preclinical platform.
  4. Patient iPSC-derived hepatocyte organoids to quantify aminoacylation vs mTORC1 activity (p-S6K, p-4E-BP1, LC3-II flux) under normothermic vs febrile (40 °C) conditions ± leucine.
  5. Validated functional assay (standardized temperature-dependent aminoacylation or mTORC1 reporter) for ACMG classification of VUS.
  6. Population-genetics analysis of gnomAD/founder haplotypes to estimate carrier frequency (notably Irish Travellers) and inform screening.
  7. Test mTORC1-restoring/autophagy-modulating agents in zebrafish larsb mutants as complementary therapies.
  8. Prospective sick-day protocol (aggressive antipyresis, anabolic support, early leucine loading during fever) evaluated for reduction of crisis severity.

Consensus Answer

Infantile Liver Failure Syndrome type 1 (ILFS1; OMIM #615438) is a rare autosomal-recessive multisystem disorder caused by biallelic hypomorphic (mostly missense) variants in LARS1, the cytosolic leucyl-tRNA synthetase, presenting in infancy with fever-triggered recurrent acute liver failure plus intrauterine growth restriction, failure to thrive, hypoalbuminemia, microcytic anemia, neurodevelopmental delay, seizures, and hypotonia. Its pathophysiology is dual — temperature-sensitive loss of leucine-tRNA aminoacylation (impaired translation during fever) combined with loss of the LARS1 leucine-sensing/Rag-GTPase-GAP function that activates mTORC1, causing excessive autophagy — so that early onset (<3 months) and liver failure predict poor prognosis. Management is supportive with mechanism-based cognate L-leucine supplementation and liver transplantation for end-stage disease; zebrafish larsb mutants are the principal disease model.

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