Argininosuccinic Aciduria

Mendelian MONDO:0008815 Pathograph 33 Urea Cycle Disorder Inborn Error of Metabolism

Argininosuccinic aciduria (ASA) is an autosomal recessive urea cycle disorder caused by deficiency of argininosuccinate lyase (ASL), the enzyme that cleaves argininosuccinate into arginine and fumarate. ASL deficiency creates a block in ureagenesis, predisposing to hyperammonemia, and simultaneously disrupts arginine availability for nitric oxide (NO) production via the citrulline-NO cycle. The disease produces multisystem pathology in which neurological and hepatic phenotypes may be partly ammonia-independent, driven by cell-autonomous NO deficiency, oxidative stress with glutathione depletion, and impaired hepatic glycogen metabolism. Chronic complications include neurocognitive deficits, epilepsy, late-onset movement disorders, chronic liver disease with fibrosis, and systemic hypertension.

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5
Pathophys.
12
Phenotypes
33
Pathograph
1
Genes
8
Treatments
56
References
2
Deep Research
⚙

Pathophysiology

5
ASL molecular function deficiency
Biallelic ASL pathogenic variants reduce argininosuccinate lyase catalytic activity.
hepatocyte link
ASL link
argininosuccinate lyase activity link
cytosol link
Downstream
Impaired ureagenesis and hyperammonemia Reduced ASL activity blocks argininosuccinate cleavage and urea-cycle flux.
Arginine ASL deficiency reduces endogenous arginine production from argininosuccinate.
Nitric oxide deficiency and endothelial dysfunction ASL loss produces cell-autonomous nitric oxide deficiency, providing an ASL-dependent branch distinct from hyperammonemia.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia and the biosynthesis of arginine."
Supports ASL molecular deficiency as the initiating event in ASA.
Impaired ureagenesis and hyperammonemia
Reduced conversion of argininosuccinate to arginine and fumarate blocks the urea cycle and impairs disposal of ammonia-derived nitrogen. This leads to hyperammonemia, classically presenting as neonatal or early-life metabolic decompensation with acute encephalopathy risk. However, ammonia control alone does not fully prevent chronic complications, indicating additional tissue-autonomous mechanisms.
urea cycle link
Downstream
Hyperammonemia Impaired urea-cycle flux causes elevated ammonia during ASA metabolic decompensation.
Encephalopathy Hyperammonemia from impaired ureagenesis exposes the brain to neurotoxic ammonia during acute decompensation.
Ammonia Failed ureagenesis increases circulating ammonia.
Argininosuccinic acid The ASL block causes argininosuccinate and argininosuccinic acid to accumulate.
Impaired hepatic glycogen metabolism Urea-cycle dysfunction is linked to impaired hepatic glucose and glycogen metabolism in ASLD liver disease.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia and a systemic phenotype coinciding with neurocognitive impairment and chronic liver disease."
Supports hyperammonemia and systemic disease downstream of urea-cycle impairment.
Nitric oxide deficiency and endothelial dysfunction
ASL is required both for arginine synthesis and for channeling extracellular arginine to nitric oxide synthase (NOS), enabling tissue NO production. Loss of ASL produces cell-autonomous NOS-dependent NO deficiency. This results in endothelial dysfunction, systemic hypertension, impaired angiogenesis, and blood-brain barrier disruption via NO-mediated dysregulation of claudin expression.
endothelial cell link brain microvascular endothelial cell link
nitric oxide biosynthetic process link arginine biosynthetic process link
Downstream
Nitric oxide Loss of ASL-mediated nitric oxide synthesis decreases NO bioavailability.
Hypertension Endothelial NO deficiency produces endothelial-dependent vascular dysfunction and hypertension.
Abnormality of movement NO-mediated central catecholamine dysregulation is associated with the ASA movement-disorder phenotype.
Global developmental delay Chronic ASLD neurocognitive disease can be ammonia-independent and associated with NO-dependent mechanisms.
Seizures Epilepsy occurs as part of the ASLD neurological phenotype associated with NO-mediated catecholamine dysregulation.
Intellectual disability ASLD long-term neurocognitive deficits can occur without hyperammonemic episodes, implicating ASL functions outside hepatic ureagenesis.
Muscular hypotonia Hypotonia and fatigue are neurodegeneration-related symptoms tracked in the ASLD neurological phenotype.
Abnormal behavior Abnormal behaviour is part of the neurodegeneration-related symptom spectrum reported in ASA cohorts.
Oxidative stress and glutathione dysregulation Endothelial ASL loss reduces NO production and is accompanied by oxidative stress.
Show evidence (1 reference)
PMID:37490345 SUPPORT In Vitro
"Knockdown of ASL in human brain microvascular endothelial cells (HBMECs) led to decreased transendothelial electrical resistance, indicative of increased cell permeability."
Shows BBB disruption mechanism through ASL loss in brain endothelial cells.
Oxidative stress and glutathione dysregulation
ASL deficiency causes dysregulation of glutathione biosynthesis and upstream cysteine utilization. Up-regulation of cysteine metabolism contrasts with glutathione depletion and down-regulated antioxidant pathways. Hepatic gamma-glutamyl transferase (GGT) is markedly upregulated, indicating altered glutathione turnover. This oxidative stress contributes to chronic liver disease and systemic organ damage.
hepatocyte link
glutathione metabolic process link response to oxidative stress link
Downstream
Glutathione ASL deficiency depletes glutathione and down-regulates antioxidant pathways.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways."
Demonstrates glutathione pathway dysregulation in ASLD patients and mice.
Impaired hepatic glycogen metabolism
Chronic liver disease in ASA involves excessive hepatic glycogen accumulation associated with impaired glycogenolysis and decreased glycogen phosphorylase protein and activity. Liver injury prevalence is high and can be present even when aminotransferases are normal, as demonstrated by elevated liver stiffness on shear wave elastography. The mechanisms may involve urea cycle dysfunction and NO deficiency effects on glycogen phosphorylase stability.
hepatocyte link
glycogen metabolic process link
Downstream
Hepatomegaly Excess hepatic glycogen and chronic liver disease manifest as hepatomegaly in ASLD models and patients.
Elevated hepatic transaminase ASLD liver injury produces chronic ALT elevation.
Alanine aminotransferase ASLD chronic hepatocellular injury increases ALT.
Hepatic fibrosis Chronic ASLD liver disease includes increased echogenicity and liver stiffness even with normal aminotransferases.
Show evidence (2 references)
PMID:31990680 SUPPORT Human Clinical
"We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD."
Demonstrates high prevalence of chronic hepatocellular injury in ASLD.
PMID:31990680 SUPPORT Model Organism
"This excessive hepatic glycogen is associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase and is rescued with helper-dependent adenovirus expressing Asl using a liver-specific (ApoE) promoter."
Shows impaired glycogen metabolism in ASLD mouse model and rescue by hepatic ASL gene delivery.
⬡

Pathograph

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

Phenotypes

12
Cardiovascular 1
Hypertension OCCASIONAL Hypertension (HP:0000822)
Show evidence (1 reference)
PMID:30075114 SUPPORT Human Clinical
"we show that the urea cycle disorder, argininosuccinate lyase deficiency (ASLD), can manifest as a Mendelian form of endothelial-dependent hypertension"
Establishes ASLD as a Mendelian cause of endothelial-dependent hypertension.
Digestive 2
Hepatomegaly FREQUENT Hepatomegaly (HP:0002240)
Show evidence (2 references)
PMID:31990680 PARTIAL Human Clinical
"Liver disease in urea cycle disorders (UCDs) ranges from hepatomegaly and chronic hepatocellular injury to cirrhosis and end-stage liver disease."
Provides human clinical context that hepatomegaly is a recognized liver manifestation across UCDs, including ASLD.
PMID:31990680 SUPPORT Model Organism
"The AslNeo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen"
Supports hepatomegaly as a feature of ASLD in both human and mouse model.
Hepatic fibrosis OCCASIONAL Hepatic fibrosis (HP:0001395)
Show evidence (1 reference)
PMID:31990680 SUPPORT Human Clinical
"ultrasound with shear wave elastography and FibroTest revealed increased echogenicity and liver stiffness, even in individuals with ASLD and normal aminotransferases"
Demonstrates subclinical liver fibrosis detectable beyond standard ALT/AST monitoring.
Metabolism 2
Hyperammonemia VERY_FREQUENT Hyperammonemia (HP:0001987)
Sequelae: Encephalopathy
Show evidence (2 references)
PMID:38198573 SUPPORT Human Clinical
"Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia and a systemic phenotype"
Directly supports hyperammonemia as a key presenting feature of ASA.
PMID:30723942 SUPPORT Human Clinical
"The clinical presentation was initially described as similar to other urea cycle defects, but increasing evidence has shown overtime an atypical systemic phenotype with a paradoxical observation, that is, a higher rate of neurological complications contrasting with a lower rate of..."
Supports hyperammonemia but notes paradoxically lower rate compared to other UCDs.
Elevated hepatic transaminase FREQUENT Elevated circulating hepatic transaminase concentration (HP:0002910)
Show evidence (1 reference)
PMID:31990680 SUPPORT Human Clinical
"We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD."
Quantifies prevalence and clinical correlates of chronic transaminase elevation.
Musculoskeletal 1
Muscular hypotonia OCCASIONAL Hypotonia (HP:0001252)
Show evidence (1 reference)
PMID:38044746 SUPPORT Human Clinical
"We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour."
Identifies hypotonia as a neurodegeneration-related symptom tracked in the ASA cohort.
Nervous System 6
Encephalopathy FREQUENT Encephalopathy (HP:0001298)
Show evidence (1 reference)
PMID:30723942 SUPPORT Human Clinical
"The disappointing long-term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels."
Supports encephalopathy risk and poor long-term neurological outcomes despite treatment.
Intellectual disability FREQUENT Intellectual disability (HP:0001249)
Show evidence (2 references)
PMID:38044746 SUPPORT Human Clinical
"Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis."
Supports neurocognitive deficits as a key feature of ASA with NO-mediated mechanism.
PMID:22241104 SUPPORT Human Clinical
"long-term complications that include liver dysfunction, neurocognitive deficits, and hypertension."
Identifies neurocognitive deficits as a long-term complication of ASLD.
Seizures FREQUENT Seizure (HP:0001250)
Show evidence (1 reference)
PMID:38044746 SUPPORT Human Clinical
"Patients present with developmental delay, epilepsy and movement disorder"
Directly lists epilepsy as a presenting feature of ASA.
Abnormality of movement OCCASIONAL Abnormality of movement (HP:0100022)
Show evidence (1 reference)
PMID:38044746 SUPPORT Human Clinical
"Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia."
Provides cohort data on movement disorder incidence and temporal characteristics.
Global developmental delay FREQUENT Global developmental delay (HP:0001263)
Show evidence (1 reference)
PMID:38044746 SUPPORT Human Clinical
"Patients present with developmental delay, epilepsy and movement disorder"
Directly lists developmental delay as a presenting feature of ASA.
Abnormal behavior OCCASIONAL Atypical behavior (HP:0000708)
Show evidence (1 reference)
PMID:38044746 SUPPORT Human Clinical
"We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour."
Includes abnormal behaviour as a tracked neurodegeneration-related symptom.
🧬

Genetic Associations

1
ASL (argininosuccinate lyase) variants
Autosomal recessive
Show evidence (3 references)
PMID:30075114 SUPPORT Human Clinical
"the urea cycle disorder, argininosuccinate lyase deficiency (ASLD), can manifest as a Mendelian form of endothelial-dependent hypertension"
Establishes ASL as the causal gene with dual urea cycle and NO synthesis roles.
PMID:37490345 SUPPORT Model Organism
"Previously, we have shown that argininosuccinate lyase deficiency (ASLD) is a novel model system to investigate cell-autonomous, nitric oxide synthase-dependent NO deficiency."
Confirms ASL role in cell-autonomous NO deficiency beyond ureagenesis.
CGGV:assertion_c16021b9-f6db-4e41-90f3-4786d63a1fa3-2018-09-15T160000.000Z SUPPORT Other
"ASL | HGNC:746 | argininosuccinic aciduria | MONDO:0008815 | AR | Definitive"
ClinGen classifies the ASL-argininosuccinic aciduria gene-disease relationship as definitive with autosomal recessive inheritance.
💊

Treatments

8
Protein-restricted diet with arginine supplementation
Action: dietary intervention MAXO:0000088
Dietary protein restriction to reduce nitrogen load combined with arginine supplementation to replenish deficient arginine and support residual ureagenesis. This is the cornerstone of chronic metabolic management in ASA.
Mechanism Target:
MODULATES Impaired ureagenesis and hyperammonemia — Protein restriction reduces nitrogen load while arginine supplementation addresses ASL-related arginine deficiency.
Show evidence (1 reference)
PMID:30723942 SUPPORT Human Clinical
"the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels"
Supports this treatment as acting on ammonia and arginine abnormalities.
Target Phenotypes: Hyperammonemia ↗
Show evidence (1 reference)
PMID:30723942 SUPPORT Human Clinical
"the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels"
Supports dietary management focused on ammonia and arginine normalization.
Nitrogen scavenger therapy
Action: nitrogen scavenger therapy Ontology label: Pharmacotherapy NCIT:C15986
Sodium benzoate and/or sodium phenylbutyrate provide alternative nitrogen disposal pathways to reduce ammonia burden during acute hyperammonemic crises and for chronic management.
Mechanism Target:
BYPASSES Impaired ureagenesis and hyperammonemia — Nitrogen scavengers provide alternative nitrogen disposal when the urea cycle is impaired.
Target Phenotypes: Hyperammonemia ↗
Show evidence (1 reference)
PMID:31990680 SUPPORT Human Clinical
"Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD."
Confirms nitrogen scavenger use in ASLD management; also notes association with disease severity.
Liver transplantation
Action: organ transplantation MAXO:0010039
Liver transplantation restores hepatic urea cycle function, prevents further hyperammonemic events, and allows normal protein tolerance. However, it does not improve neurocognitive outcomes compared with severity-adjusted medical management. Neurologic sequelae persist but do not progress after transplantation.
Mechanism Target:
RESTORES Impaired ureagenesis and hyperammonemia — Liver transplantation restores hepatic urea-cycle capacity sufficiently to prevent further hyperammonemic events.
Show evidence (1 reference)
PMID:38054409 SUPPORT Human Clinical
"LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation"
Supports transplantation as restoring metabolic stability at the hyperammonemia mechanism.
Target Phenotypes: Hyperammonemia ↗
Show evidence (1 reference)
PMID:38054409 SUPPORT Human Clinical
"LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation and was associated with a more favorable growth outcome compared with individuals remaining under MM. However, neurocognitive outcome in individuals with LTx did not differ from the medically..."
Severity-adjusted analysis confirms LT prevents hyperammonemia but does not improve neurocognitive outcomes.
Acute decompensation management
Action: supportive care MAXO:0000950
Emergency supportive care during hyperammonemic crises including high-calorie glucose infusion to reverse catabolism, cessation of protein intake, ammonia-lowering agents, and correction of metabolic derangements.
Target Phenotypes: Hyperammonemia ↗
Show evidence (1 reference)
PMID:30723942 SUPPORT Human Clinical
"The disappointing long-term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy"
Supports the need for acute management as part of standard of care in ASA.
NO supplementation
Action: Pharmacotherapy NCIT:C15986
Nitric oxide supplementation addresses the cell-autonomous NO deficiency in ASA. Preclinical studies have demonstrated that NO supplementation can partially rescue vascular and BBB dysfunction in ASL-deficient models, motivating the hypothesis that NOS-independent NO supplementation may ameliorate ammonia-independent pathology.
Mechanism Target:
MODULATES Nitric oxide deficiency and endothelial dysfunction — NO supplementation directly addresses NO deficiency and partially rescues BBB dysfunction in ASLD models.
Show evidence (1 reference)
PMID:37490345 SUPPORT Model Organism
"in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation"
Supports NO supplementation as targeting the NO-deficiency mechanism.
Show evidence (2 references)
PMID:30075114 SUPPORT Model Organism
"loss of ASL in endothelial cells leads to endothelial-dependent vascular dysfunction with reduced nitric oxide (NO) production, increased oxidative stress, and impaired angiogenesis"
Provides the mechanistic rationale for NO supplementation therapy in ASLD.
PMID:37490345 SUPPORT Model Organism
"in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation"
Demonstrates partial rescue of BBB dysfunction by NO supplementation in ASLD.
Genetic counseling
Action: genetic counseling MAXO:0000079
Genetic counseling for affected families including discussion of autosomal recessive inheritance, recurrence risk (25% per pregnancy), carrier testing, and prenatal/preimplantation genetic testing options.
Mechanism Target:
MODULATES ASL (argininosuccinate lyase) variants — Counseling and molecular diagnosis are anchored to the family's ASL pathogenic variants.
Show evidence (1 reference)
PMID:26843370 SUPPORT Human Clinical
"Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder"
Supports autosomal recessive ASL-related disease as the basis for genetic counseling.
Show evidence (1 reference)
PMID:26843370 SUPPORT Human Clinical
"This study also demonstrates the value of NGS in the identification of mutations and molecular diagnosis for ASAuria families."
Supports molecular diagnosis of ASA families as part of genetic counseling.
Newborn screening
Action: disease screening MAXO:0000124
ASA is detectable by newborn screening via elevated argininosuccinic acid in dried blood spots. Early detection enables presymptomatic initiation of treatment, though the benefit of newborn screening on long-term neurological outcomes has been questioned.
Target Phenotypes: Hyperammonemia ↗
Show evidence (1 reference)
PMID:30723942 PARTIAL Human Clinical
"Interrogations have raised about the benefit of newborn screening or liver transplantation on the neurological phenotype."
Supports newborn screening availability while noting uncertainty about neurological benefit.
mRNA therapy (investigational)
Action: gene therapy MAXO:0001001
Lipid nanoparticle-delivered human ASL mRNA is an emerging investigational therapy that has shown preclinical efficacy in correcting both glutathione metabolism and ureagenesis in ASL-deficient mouse models, with rescue of chronic liver disease. This approach supports clinical translation for ASA.
Mechanism Target:
RESTORES ASL molecular function deficiency — hASL mRNA supplies ASL coding capacity to restore deficient ASL function in preclinical models.
Show evidence (1 reference)
PMID:38198573 SUPPORT Model Organism
"Human hASL mRNA encapsulated in lipid nanoparticles improved glutathione metabolism and chronic liver disease."
Supports hASL mRNA as targeting the upstream molecular deficiency.
RESTORES Impaired ureagenesis and hyperammonemia — hASL mRNA therapy enhances ureagenesis in ASL-deficient mouse models.
Show evidence (1 reference)
PMID:38198573 SUPPORT Model Organism
"hASL mRNA therapy corrected and rescued the neonatal and adult Asl-deficient mouse phenotypes, respectively, enhancing ureagenesis."
Supports restored ureagenesis as a preclinical treatment mechanism.
RESTORES Oxidative stress and glutathione dysregulation — hASL mRNA improves glutathione metabolism and chronic liver disease in ASLD models.
Show evidence (1 reference)
PMID:38198573 SUPPORT Model Organism
"Human hASL mRNA encapsulated in lipid nanoparticles improved glutathione metabolism and chronic liver disease."
Supports correction of the glutathione/redox mechanism by hASL mRNA.
Show evidence (1 reference)
PMID:38198573 SUPPORT Model Organism
"These findings provide mechanistic insights in liver glutathione metabolism and support clinical translation of mRNA therapy for argininosuccinic aciduria."
Demonstrates preclinical efficacy of mRNA therapy for ASA.
🔬

Biochemical Markers

6
Argininosuccinic acid (INCREASED)
Context: Argininosuccinic acid accumulates in plasma and urine due to the enzymatic block at argininosuccinate lyase. It is the pathognomonic biomarker for ASA and is used for definitive biochemical diagnosis.
Pathograph Readouts
Readout Of ASL molecular function deficiency Positive Diagnostic
Elevated plasma or urinary argininosuccinic acid is the pathognomonic biochemical readout of deficient ASL catalytic activity.
Show evidence (1 reference)
PMID:22241104 SUPPORT Human Clinical
"The biochemical diagnosis of ASLD is typically established with elevation of plasma citrulline together with elevated argininosuccinic acid in the plasma or urine."
Establishes elevated argininosuccinic acid as the diagnostic biochemical readout of ASL deficiency.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Patients with ASL deficiency present with argininosuccinic aciduria"
The disease name itself reflects the pathognomonic finding of elevated argininosuccinic acid.
Ammonia (INCREASED)
Context: Plasma ammonia is elevated during metabolic crises due to impaired ureagenesis. Hyperammonemia severity is variable and may be less frequent than in other UCDs, but remains the major driver of acute encephalopathy risk.
Pathograph Readouts
Readout Of Impaired ureagenesis and hyperammonemia Positive Diagnostic
Increased plasma ammonia reports failure of ASL-dependent urea-cycle nitrogen disposal.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia"
The patient summary identifies hyperammonemia as the clinical biochemical manifestation of impaired ureagenesis in ASL deficiency.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia"
Directly supports elevated ammonia as a feature of ASA.
Arginine (DECREASED)
Context: Plasma arginine is decreased due to the block in its biosynthesis from argininosuccinate. Arginine deficiency contributes to impaired NO production and is the rationale for arginine supplementation therapy.
Pathograph Readouts
Readout Of ASL molecular function deficiency Negative Diagnostic
Decreased arginine reports loss of the ASL reaction that normally generates arginine from argininosuccinate.
Show evidence (1 reference)
PMID:22241104 SUPPORT Human Clinical
"Argininosuccinate lyase (ASL) catalyzes the fourth reaction in this cycle, resulting in the breakdown of argininosuccinic acid to arginine and fumarate."
The ASL reaction produces arginine, so low arginine is interpreted as a negative readout of the deficient catalytic step.
Show evidence (1 reference)
PMID:30723942 SUPPORT Human Clinical
"the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels"
Supports arginine deficiency as a therapeutic target in ASA.
Glutathione (DECREASED)
Context: Hepatic and plasma glutathione is depleted in ASA patients and mouse models. Glutathione depletion is accompanied by up-regulation of cysteine metabolism and down-regulated antioxidant pathways, reflecting a redox imbalance that contributes to chronic liver disease.
Pathograph Readouts
Readout Of Oxidative stress and glutathione dysregulation Negative Diagnostic
Decreased glutathione reports the redox and antioxidant-pathway branch of ASL deficiency.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways."
Directly links glutathione depletion to the oxidative-stress and glutathione-dysregulation mechanism in ASL-deficient patients and mice.
Show evidence (1 reference)
PMID:38198573 SUPPORT Human Clinical
"Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways."
Confirms glutathione depletion alongside altered cysteine handling in ASL-deficient patients and mice.
Nitric oxide (DECREASED)
Context: Tissue and systemic NO production is reduced due to impaired ASL-mediated channeling of arginine to NOS. NO deficiency drives endothelial dysfunction, BBB disruption, hypertension, and may contribute to catecholamine dysregulation and movement disorders.
Pathograph Readouts
Readout Of Nitric oxide deficiency and endothelial dysfunction Negative Diagnostic
Reduced nitric oxide production reports the ASL-dependent endothelial dysfunction branch.
Show evidence (1 reference)
PMID:30075114 SUPPORT Model Organism
"loss of ASL in endothelial cells leads to endothelial-dependent vascular dysfunction with reduced nitric oxide (NO) production, increased oxidative stress, and impaired angiogenesis"
Supports decreased nitric oxide production as a readout of ASL-dependent endothelial dysfunction.
Show evidence (1 reference)
PMID:37490345 SUPPORT In Vitro
"Our results suggest that ASL-mediated NO synthesis is required for proper maintenance of brain microvascular endothelial cell functions as well as BBB integrity."
Links NO deficiency to brain endothelial dysfunction.
Alanine aminotransferase (INCREASED)
Context: Chronic ALT elevation is a marker of hepatocellular injury in ASA. Prevalence of elevated ALT above 100 U/L on at least two occasions is 37% in ASLD, significantly associated with hyperammonemia and nitrogen-scavenger use.
Pathograph Readouts
Readout Of Impaired hepatic glycogen metabolism Positive Monitoring
Elevated ALT reports chronic hepatocellular injury accompanying the hepatic glycogen-metabolism branch of ASLD.
Show evidence (1 reference)
PMID:31990680 SUPPORT Human Clinical
"We demonstrate a high prevalence of elevated ALT in ASLD (37%)."
Supports ALT elevation as a monitoring readout of ASLD liver involvement.
Show evidence (1 reference)
PMID:31990680 SUPPORT Human Clinical
"We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD."
Quantifies ALT elevation prevalence and clinical associations.
{ }

Source YAML

click to show 
name: Argininosuccinic Aciduria
category: Mendelian
creation_date: '2025-06-12T20:16:27Z'
updated_date: '2026-05-21T05:37:18Z'
synonyms:
- Argininosuccinate lyase deficiency
- ASLD
- ASA
description: 'Argininosuccinic aciduria (ASA) is an autosomal recessive urea cycle disorder caused by deficiency of argininosuccinate lyase (ASL), the enzyme that cleaves argininosuccinate into arginine and fumarate. ASL deficiency creates a block in ureagenesis, predisposing to hyperammonemia, and simultaneously disrupts arginine availability for nitric oxide (NO) production via the citrulline-NO cycle. The disease produces multisystem pathology in which neurological and hepatic phenotypes may be partly ammonia-independent, driven by cell-autonomous NO deficiency, oxidative stress with glutathione depletion, and impaired hepatic glycogen metabolism. Chronic complications include neurocognitive deficits, epilepsy, late-onset movement disorders, chronic liver disease with fibrosis, and systemic hypertension.

  '
disease_term:
  preferred_term: argininosuccinic aciduria
  term:
    id: MONDO:0008815
    label: argininosuccinic aciduria
parents:
- Urea Cycle Disorder
- Inborn Error of Metabolism
prevalence:
- population: Global live births
  percentage: ~1 in 70,000
  notes: >-
    Argininosuccinic aciduria is one of the more common distal urea-cycle
    disorders but remains very rare overall. Review-level estimates place ASL
    deficiency at about 1 in 70,000 live births, and newborn-screening analyses
    found a combined ASLD/ASSD frequency of 1 in 117,000 births.
  evidence:
  - reference: PMID:22241104
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ASL deficiency (ASLD) is the second most common UCD, with a prevalence of ~1 in 70,000 live births."
    explanation: This GeneReviews-derived review provides a direct prevalence estimate for argininosuccinic aciduria.
  - reference: PMID:25135652
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We found a combined frequency for ASLD and ASSD of 1/117,000 births based upon an analysis of highly sensitive newborn screening data that included over 6 million births in 7 large states17."
    explanation: Large newborn-screening data independently support the rarity of ASL deficiency and related distal urea-cycle defects.
pathophysiology:
- name: ASL molecular function deficiency
  description: 'Biallelic ASL pathogenic variants reduce argininosuccinate lyase catalytic activity.

    '
  genes:
  - preferred_term: ASL
    term:
      id: hgnc:746
      label: ASL
  molecular_functions:
  - preferred_term: argininosuccinate lyase activity
    term:
      id: GO:0004056
      label: argininosuccinate lyase activity
  cellular_components:
  - preferred_term: cytosol
    term:
      id: GO:0005829
      label: cytosol
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia and the biosynthesis of arginine.
    explanation: Supports ASL molecular deficiency as the initiating event in ASA.
  downstream:
  - target: Impaired ureagenesis and hyperammonemia
    description: Reduced ASL activity blocks argininosuccinate cleavage and urea-cycle flux.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia and the biosynthesis of arginine.
      explanation: ASL enzymatic function is directly required for urea-cycle nitrogen disposal.
  - target: Arginine
    description: ASL deficiency reduces endogenous arginine production from argininosuccinate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia and the biosynthesis of arginine.
      explanation: The ASL reaction directly generates arginine, so loss of ASL function supports decreased arginine availability.
  - target: Nitric oxide deficiency and endothelial dysfunction
    description: ASL loss produces cell-autonomous nitric oxide deficiency, providing an ASL-dependent branch distinct from hyperammonemia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37490345
      reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: cell-autonomous, nitric oxide synthase-dependent NO deficiency
      explanation: Supports ASLD as a model of ASL-dependent nitric oxide deficiency.
- name: Impaired ureagenesis and hyperammonemia
  description: 'Reduced conversion of argininosuccinate to arginine and fumarate blocks the urea cycle and impairs disposal of ammonia-derived nitrogen. This leads to hyperammonemia, classically presenting as neonatal or early-life metabolic decompensation with acute encephalopathy risk. However, ammonia control alone does not fully prevent chronic complications, indicating additional tissue-autonomous mechanisms.

    '
  biological_processes:
  - preferred_term: urea cycle
    term:
      id: GO:0000050
      label: urea cycle
  chemical_entities:
  - preferred_term: ammonium
    term:
      id: CHEBI:28938
      label: ammonium
    modifier: INCREASED
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia and a systemic phenotype coinciding with neurocognitive impairment and chronic liver disease.
    explanation: Supports hyperammonemia and systemic disease downstream of urea-cycle impairment.
  downstream:
  - target: Hyperammonemia
    description: Impaired urea-cycle flux causes elevated ammonia during ASA metabolic decompensation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia
      explanation: Directly links ASL deficiency to hyperammonemia in ASA.
  - target: Encephalopathy
    description: Hyperammonemia from impaired ureagenesis exposes the brain to neurotoxic ammonia during acute decompensation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - neurotoxic ammonia accumulation
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia
      explanation: Supports neurotoxic ammonia as the bridge from impaired ureagenesis and hyperammonemia to encephalopathic crises.
  - target: Ammonia
    description: Failed ureagenesis increases circulating ammonia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia
      explanation: Hyperammonemia corresponds to increased ammonia downstream of the urea-cycle block.
  - target: Argininosuccinic acid
    description: The ASL block causes argininosuccinate and argininosuccinic acid to accumulate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients with ASL deficiency present with argininosuccinic aciduria
      explanation: The diagnostic biochemical name reflects accumulation of argininosuccinic acid downstream of ASL deficiency.
  - target: Impaired hepatic glycogen metabolism
    description: Urea-cycle dysfunction is linked to impaired hepatic glucose and glycogen metabolism in ASLD liver disease.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired hepatic glucose metabolism
    - decreased glycogen phosphorylase
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Our results link urea cycle dysfunction and impaired hepatic glucose metabolism
      explanation: Supports hepatic glucose and glycogen metabolism as a downstream component of urea-cycle dysfunction in ASLD.
- name: Nitric oxide deficiency and endothelial dysfunction
  description: 'ASL is required both for arginine synthesis and for channeling extracellular arginine to nitric oxide synthase (NOS), enabling tissue NO production. Loss of ASL produces cell-autonomous NOS-dependent NO deficiency. This results in endothelial dysfunction, systemic hypertension, impaired angiogenesis, and blood-brain barrier disruption via NO-mediated dysregulation of claudin expression.

    '
  biological_processes:
  - preferred_term: nitric oxide biosynthetic process
    term:
      id: GO:0006809
      label: nitric oxide biosynthetic process
  - preferred_term: arginine biosynthetic process
    term:
      id: GO:0006526
      label: L-arginine biosynthetic process
  chemical_entities:
  - preferred_term: nitric oxide
    term:
      id: CHEBI:16480
      label: nitric oxide
    modifier: DECREASED
  cell_types:
  - preferred_term: endothelial cell
    term:
      id: CL:0000115
      label: endothelial cell
  - preferred_term: brain microvascular endothelial cell
    term:
      id: CL:2000044
      label: brain microvascular endothelial cell
  evidence:
  - reference: PMID:37490345
    reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Knockdown of ASL in human brain microvascular endothelial cells (HBMECs) led to decreased transendothelial electrical resistance, indicative of increased cell permeability.
    explanation: Shows BBB disruption mechanism through ASL loss in brain endothelial cells.
  downstream:
  - target: Nitric oxide
    description: Loss of ASL-mediated nitric oxide synthesis decreases NO bioavailability.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37490345
      reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Our results suggest that ASL-mediated NO synthesis is required for proper maintenance of brain microvascular endothelial cell functions as well as BBB integrity.
      explanation: Supports decreased NO as a biochemical consequence of impaired ASL-mediated NO synthesis.
  - target: Hypertension
    description: Endothelial NO deficiency produces endothelial-dependent vascular dysfunction and hypertension.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:30075114
      reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: argininosuccinate lyase deficiency (ASLD), can manifest as a Mendelian form of endothelial-dependent hypertension
      explanation: Establishes the vascular phenotype downstream of ASLD endothelial dysfunction.
  - target: Abnormality of movement
    description: NO-mediated central catecholamine dysregulation is associated with the ASA movement-disorder phenotype.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - NO-mediated downregulation of central catecholamine biosynthesis
    evidence:
    - reference: PMID:38044746
      reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis.
      explanation: Links NO-mediated catecholamine dysregulation to the movement disorder phenotype.
  - target: Global developmental delay
    description: Chronic ASLD neurocognitive disease can be ammonia-independent and associated with NO-dependent mechanisms.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - blood-brain barrier dysfunction
    - NO-mediated central catecholamine dysregulation
    evidence:
    - reference: PMID:38044746
      reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis.
      explanation: Supports developmental delay in the NO-linked neurological phenotype of ASA.
  - target: Seizures
    description: Epilepsy occurs as part of the ASLD neurological phenotype associated with NO-mediated catecholamine dysregulation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - NO-mediated downregulation of central catecholamine biosynthesis
    evidence:
    - reference: PMID:38044746
      reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis.
      explanation: Supports epilepsy as part of the linked neurological phenotype.
  - target: Intellectual disability
    description: ASLD long-term neurocognitive deficits can occur without hyperammonemic episodes, implicating ASL functions outside hepatic ureagenesis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ammonia-independent ASL function
    - tissue-specific ASL deficiency
    evidence:
    - reference: PMID:22241104
      reference_title: "Argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: These long-term complications can occur in the absence of hyperammonemic episodes, implying that ASL has functions outside of its role in ureagenesis and the tissue-specific lack of ASL may be responsible for these manifestations.
      explanation: Supports neurocognitive disability as part of an ammonia-independent ASLD mechanism.
  - target: Muscular hypotonia
    description: Hypotonia and fatigue are neurodegeneration-related symptoms tracked in the ASLD neurological phenotype.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - neurodegeneration-related symptoms
    - central catecholamine dysregulation
    evidence:
    - reference: PMID:38044746
      reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour."
      explanation: Supports hypotonia/fatigue as part of the late neurological ASLD phenotype.
  - target: Abnormal behavior
    description: Abnormal behaviour is part of the neurodegeneration-related symptom spectrum reported in ASA cohorts.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - neurodegeneration-related symptoms
    - central catecholamine dysregulation
    evidence:
    - reference: PMID:38044746
      reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour."
      explanation: Supports abnormal behaviour as part of the reported ASLD neurological symptom spectrum.
  - target: Oxidative stress and glutathione dysregulation
    description: Endothelial ASL loss reduces NO production and is accompanied by oxidative stress.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - reduced nitric oxide production
    - endothelial oxidative stress
    evidence:
    - reference: PMID:30075114
      reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: loss of ASL in endothelial cells leads to endothelial-dependent vascular dysfunction with reduced nitric oxide (NO) production, increased oxidative stress, and impaired angiogenesis
      explanation: Supports oxidative stress as part of ASL-dependent endothelial dysfunction.
- name: Oxidative stress and glutathione dysregulation
  description: 'ASL deficiency causes dysregulation of glutathione biosynthesis and upstream cysteine utilization. Up-regulation of cysteine metabolism contrasts with glutathione depletion and down-regulated antioxidant pathways. Hepatic gamma-glutamyl transferase (GGT) is markedly upregulated, indicating altered glutathione turnover. This oxidative stress contributes to chronic liver disease and systemic organ damage.

    '
  biological_processes:
  - preferred_term: glutathione metabolic process
    term:
      id: GO:0006749
      label: glutathione metabolic process
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  chemical_entities:
  - preferred_term: glutathione
    term:
      id: CHEBI:16856
      label: glutathione
    modifier: DECREASED
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways.
    explanation: Demonstrates glutathione pathway dysregulation in ASLD patients and mice.
  downstream:
  - target: Glutathione
    description: ASL deficiency depletes glutathione and down-regulates antioxidant pathways.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways.
      explanation: Directly supports decreased glutathione downstream of the oxidative-stress mechanism.
- name: Impaired hepatic glycogen metabolism
  description: 'Chronic liver disease in ASA involves excessive hepatic glycogen accumulation associated with impaired glycogenolysis and decreased glycogen phosphorylase protein and activity. Liver injury prevalence is high and can be present even when aminotransferases are normal, as demonstrated by elevated liver stiffness on shear wave elastography. The mechanisms may involve urea cycle dysfunction and NO deficiency effects on glycogen phosphorylase stability.

    '
  biological_processes:
  - preferred_term: glycogen metabolic process
    term:
      id: GO:0005977
      label: glycogen metabolic process
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD.
    explanation: Demonstrates high prevalence of chronic hepatocellular injury in ASLD.
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: This excessive hepatic glycogen is associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase and is rescued with helper-dependent adenovirus expressing Asl using a liver-specific (ApoE) promoter.
    explanation: Shows impaired glycogen metabolism in ASLD mouse model and rescue by hepatic ASL gene delivery.
  downstream:
  - target: Hepatomegaly
    description: Excess hepatic glycogen and chronic liver disease manifest as hepatomegaly in ASLD models and patients.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: The AslNeo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen
      explanation: Connects hepatic glycogen accumulation to hepatomegaly in the ASLD model.
  - target: Elevated hepatic transaminase
    description: ASLD liver injury produces chronic ALT elevation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%).
      explanation: Directly supports transaminase elevation as a hepatic consequence of ASLD.
  - target: Alanine aminotransferase
    description: ASLD chronic hepatocellular injury increases ALT.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%).
      explanation: Directly connects the hepatic mechanism to the ALT biochemical node.
  - target: Hepatic fibrosis
    description: Chronic ASLD liver disease includes increased echogenicity and liver stiffness even with normal aminotransferases.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - chronic hepatocellular injury
    - increased liver stiffness
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: ultrasound with shear wave elastography and FibroTest revealed increased echogenicity and liver stiffness, even in individuals with ASLD and normal aminotransferases
      explanation: Supports fibrotic or stiffness-related liver pathology downstream of the hepatic mechanism.
phenotypes:
- name: Hyperammonemia
  frequency: VERY_FREQUENT
  description: 'Elevated plasma ammonia during catabolic stress or baseline disease activity, presenting as acute neonatal or recurrent metabolic decompensation. Hyperammonemia is the hallmark of urea cycle dysfunction in ASA.

    '
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia and a systemic phenotype
    explanation: Directly supports hyperammonemia as a key presenting feature of ASA.
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The clinical presentation was initially described as similar to other urea cycle defects, but increasing evidence has shown overtime an atypical systemic phenotype with a paradoxical observation, that is, a higher rate of neurological complications contrasting with a lower rate of hyperammonaemic episodes.
    explanation: Supports hyperammonemia but notes paradoxically lower rate compared to other UCDs.
  sequelae:
  - target: Encephalopathy
    description: Hyperammonemia from the urea-cycle block creates acute encephalopathy risk.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - neurotoxic ammonia accumulation
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The urea cycle enzyme argininosuccinate lyase (ASL) enables the clearance of neurotoxic ammonia
      explanation: Supports neurotoxic ammonia as the bridge from hyperammonemia to encephalopathic risk.
- name: Encephalopathy
  frequency: FREQUENT
  description: 'Acute or recurrent neurologic dysfunction due to ammonia neurotoxicity, particularly during neonatal presentation and metabolic crises.

    '
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
  evidence:
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The disappointing long-term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels.
    explanation: Supports encephalopathy risk and poor long-term neurological outcomes despite treatment.
- name: Intellectual disability
  frequency: FREQUENT
  description: 'Neurocognitive deficits including intellectual disability occur in ASA, even in patients without documented hyperammonemia, suggesting ammonia-independent contributions to neurological disease.

    '
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients present with developmental delay, epilepsy and movement disorder, associated with NO-mediated downregulation of central catecholamine biosynthesis.
    explanation: Supports neurocognitive deficits as a key feature of ASA with NO-mediated mechanism.
  - reference: PMID:22241104
    reference_title: "Argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "long-term complications that include liver dysfunction, neurocognitive deficits, and hypertension."
    explanation: Identifies neurocognitive deficits as a long-term complication of ASLD.
- name: Seizures
  frequency: FREQUENT
  description: 'Epilepsy is a common neurological manifestation in ASA. In a Saudi cohort with severe neonatal phenotype, seizures were present in all affected patients. Seizures may occur even with good metabolic control.

    '
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients present with developmental delay, epilepsy and movement disorder
    explanation: Directly lists epilepsy as a presenting feature of ASA.
- name: Abnormality of movement
  frequency: OCCASIONAL
  description: 'Late-onset movement disorders including ataxia, tremor, and dystonia occur in ASA with increasing prevalence with age. In the UK multicentre cohort of 60 patients, movement disorder occurred in 15% with median onset in the second decade. These symptoms appear independent of hyperammonemia onset and are attributed to cell-autonomous central catecholamine dysregulation.

    '
  phenotype_term:
    preferred_term: Abnormality of movement
    term:
      id: HP:0100022
      label: Abnormality of movement
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Movement disorders in ASA appear in the second and third decades of life, becoming more prevalent with ageing and independent from the age of onset of hyperammonemia.
    explanation: Provides cohort data on movement disorder incidence and temporal characteristics.
- name: Global developmental delay
  frequency: FREQUENT
  description: 'Developmental delay is a major long-term complication of ASA, occurring across the severity spectrum. Deficits can occur even in individuals without documented hyperammonemia, supporting ammonia-independent neurodevelopmental injury.

    '
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients present with developmental delay, epilepsy and movement disorder
    explanation: Directly lists developmental delay as a presenting feature of ASA.
- name: Hepatomegaly
  frequency: FREQUENT
  description: 'Hepatomegaly is a common finding in ASA, reflecting chronic hepatic glycogen accumulation and hepatocellular injury. It may be present from early childhood.

    '
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Liver disease in urea cycle disorders (UCDs) ranges from hepatomegaly and chronic hepatocellular injury to cirrhosis and end-stage liver disease.
    explanation: Provides human clinical context that hepatomegaly is a recognized liver manifestation across UCDs, including ASLD.
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: The AslNeo/Neo mice mimic the human disorder with hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen
    explanation: Supports hepatomegaly as a feature of ASLD in both human and mouse model.
- name: Elevated hepatic transaminase
  frequency: FREQUENT
  description: 'Chronic aminotransferase elevation is highly prevalent in ASA. In a multicenter study, 37% of ASLD patients had ALT levels above 100 U/L on two or more occasions. Elevated ALT was significantly associated with hyperammonemia and nitrogen-scavenger use.

    '
  phenotype_term:
    preferred_term: Elevated hepatic transaminase
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD.
    explanation: Quantifies prevalence and clinical correlates of chronic transaminase elevation.
- name: Hepatic fibrosis
  frequency: OCCASIONAL
  description: 'Liver fibrosis and increased liver stiffness can develop in ASA even when aminotransferases are normal. Shear wave elastography and FibroTest may detect subclinical fibrosis not identified by standard ALT/AST monitoring.

    '
  phenotype_term:
    preferred_term: Hepatic fibrosis
    term:
      id: HP:0001395
      label: Hepatic fibrosis
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: ultrasound with shear wave elastography and FibroTest revealed increased echogenicity and liver stiffness, even in individuals with ASLD and normal aminotransferases
    explanation: Demonstrates subclinical liver fibrosis detectable beyond standard ALT/AST monitoring.
- name: Hypertension
  frequency: OCCASIONAL
  description: 'ASLD manifests as a Mendelian form of endothelial-dependent hypertension. Endothelial-specific loss of ASL leads to reduced NO production and vascular dysfunction, establishing a causal link from ASL deficiency to systemic hypertension.

    '
  phenotype_term:
    preferred_term: Hypertension
    term:
      id: HP:0000822
      label: Hypertension
  evidence:
  - reference: PMID:30075114
    reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: we show that the urea cycle disorder, argininosuccinate lyase deficiency (ASLD), can manifest as a Mendelian form of endothelial-dependent hypertension
    explanation: Establishes ASLD as a Mendelian cause of endothelial-dependent hypertension.
- name: Muscular hypotonia
  frequency: OCCASIONAL
  description: 'Hypotonia and fatigue are reported as neurodegeneration-related symptoms in ASA. In the UK multicentre cohort, hypotonia/fatigue affected 15% of patients with median onset at 11.5 years.

    '
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour.'
    explanation: Identifies hypotonia as a neurodegeneration-related symptom tracked in the ASA cohort.
- name: Abnormal behavior
  frequency: OCCASIONAL
  description: 'Behavioural changes were reported in 7% of the UK cohort with median onset in the third decade of life, as a late-emerging neurological manifestation.

    '
  phenotype_term:
    preferred_term: Atypical behavior
    term:
      id: HP:0000708
      label: Atypical behavior
  evidence:
  - reference: PMID:38044746
    reference_title: "The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'We identified 60 patients and specifically looked for neurodegeneration-related symptoms: movement disorder such as ataxia, tremor and dystonia, hypotonia/fatigue and abnormal behaviour.'
    explanation: Includes abnormal behaviour as a tracked neurodegeneration-related symptom.
biochemical:
- name: Argininosuccinic acid
  presence: INCREASED
  context: 'Argininosuccinic acid accumulates in plasma and urine due to the enzymatic block at argininosuccinate lyase. It is the pathognomonic biomarker for ASA and is used for definitive biochemical diagnosis.

    '
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients with ASL deficiency present with argininosuccinic aciduria
    explanation: The disease name itself reflects the pathognomonic finding of elevated argininosuccinic acid.
  readouts:
  - target: ASL molecular function deficiency
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated plasma or urinary argininosuccinic acid is the pathognomonic biochemical readout of deficient ASL catalytic activity.
    evidence:
    - reference: PMID:22241104
      reference_title: "Argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: The biochemical diagnosis of ASLD is typically established with elevation of plasma citrulline together with elevated argininosuccinic acid in the plasma or urine.
      explanation: Establishes elevated argininosuccinic acid as the diagnostic biochemical readout of ASL deficiency.
- name: Ammonia
  presence: INCREASED
  context: 'Plasma ammonia is elevated during metabolic crises due to impaired ureagenesis. Hyperammonemia severity is variable and may be less frequent than in other UCDs, but remains the major driver of acute encephalopathy risk.

    '
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia
    explanation: Directly supports elevated ammonia as a feature of ASA.
  readouts:
  - target: Impaired ureagenesis and hyperammonemia
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Increased plasma ammonia reports failure of ASL-dependent urea-cycle nitrogen disposal.
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients with ASL deficiency present with argininosuccinic aciduria, an inherited metabolic disease with hyperammonemia
      explanation: The patient summary identifies hyperammonemia as the clinical biochemical manifestation of impaired ureagenesis in ASL deficiency.
- name: Arginine
  presence: DECREASED
  context: 'Plasma arginine is decreased due to the block in its biosynthesis from argininosuccinate. Arginine deficiency contributes to impaired NO production and is the rationale for arginine supplementation therapy.

    '
  evidence:
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels
    explanation: Supports arginine deficiency as a therapeutic target in ASA.
  readouts:
  - target: ASL molecular function deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Decreased arginine reports loss of the ASL reaction that normally generates arginine from argininosuccinate.
    evidence:
    - reference: PMID:22241104
      reference_title: "Argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Argininosuccinate lyase (ASL) catalyzes the fourth reaction in this cycle, resulting in the breakdown of argininosuccinic acid to arginine and fumarate.
      explanation: The ASL reaction produces arginine, so low arginine is interpreted as a negative readout of the deficient catalytic step.
- name: Glutathione
  presence: DECREASED
  context: 'Hepatic and plasma glutathione is depleted in ASA patients and mouse models. Glutathione depletion is accompanied by up-regulation of cysteine metabolism and down-regulated antioxidant pathways, reflecting a redox imbalance that contributes to chronic liver disease.

    '
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways.
    explanation: Confirms glutathione depletion alongside altered cysteine handling in ASL-deficient patients and mice.
  readouts:
  - target: Oxidative stress and glutathione dysregulation
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Decreased glutathione reports the redox and antioxidant-pathway branch of ASL deficiency.
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways.
      explanation: Directly links glutathione depletion to the oxidative-stress and glutathione-dysregulation mechanism in ASL-deficient patients and mice.
- name: Nitric oxide
  presence: DECREASED
  context: 'Tissue and systemic NO production is reduced due to impaired ASL-mediated channeling of arginine to NOS. NO deficiency drives endothelial dysfunction, BBB disruption, hypertension, and may contribute to catecholamine dysregulation and movement disorders.

    '
  evidence:
  - reference: PMID:37490345
    reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Our results suggest that ASL-mediated NO synthesis is required for proper maintenance of brain microvascular endothelial cell functions as well as BBB integrity.
    explanation: Links NO deficiency to brain endothelial dysfunction.
  readouts:
  - target: Nitric oxide deficiency and endothelial dysfunction
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Reduced nitric oxide production reports the ASL-dependent endothelial dysfunction branch.
    evidence:
    - reference: PMID:30075114
      reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: loss of ASL in endothelial cells leads to endothelial-dependent vascular dysfunction with reduced nitric oxide (NO) production, increased oxidative stress, and impaired angiogenesis
      explanation: Supports decreased nitric oxide production as a readout of ASL-dependent endothelial dysfunction.
- name: Alanine aminotransferase
  presence: INCREASED
  context: 'Chronic ALT elevation is a marker of hepatocellular injury in ASA. Prevalence of elevated ALT above 100 U/L on at least two occasions is 37% in ASLD, significantly associated with hyperammonemia and nitrogen-scavenger use.

    '
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%). Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD.
    explanation: Quantifies ALT elevation prevalence and clinical associations.
  readouts:
  - target: Impaired hepatic glycogen metabolism
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: Elevated ALT reports chronic hepatocellular injury accompanying the hepatic glycogen-metabolism branch of ASLD.
    evidence:
    - reference: PMID:31990680
      reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We demonstrate a high prevalence of elevated ALT in ASLD (37%).
      explanation: Supports ALT elevation as a monitoring readout of ASLD liver involvement.
genetic:
- name: ASL (argininosuccinate lyase) variants
  gene_term:
    preferred_term: ASL
    term:
      id: hgnc:746
      label: ASL
  inheritance:
  - name: Autosomal recessive
  variants:
  - name: Various ASL pathogenic variants
    description: 'Over 130 pathogenic variants have been reported in the ASL gene. Both missense and nonsense variants occur, with genotype-phenotype correlations broadly distinguishing severe neonatal from late-onset forms based on residual enzyme activity.

      '
    gene:
      preferred_term: ASL
      term:
        id: hgnc:746
        label: ASL
  features: 'ASL encodes argininosuccinate lyase, which catalyzes the cleavage of argininosuccinate to arginine and fumarate in the urea cycle. ASL also functions in a complex with NOS to channel arginine for NO production. Biallelic pathogenic variants in ASL cause disease through combined loss of ureagenesis and NO synthesis capacity.

    '
  evidence:
  - reference: PMID:30075114
    reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the urea cycle disorder, argininosuccinate lyase deficiency (ASLD), can manifest as a Mendelian form of endothelial-dependent hypertension
    explanation: Establishes ASL as the causal gene with dual urea cycle and NO synthesis roles.
  - reference: PMID:37490345
    reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Previously, we have shown that argininosuccinate lyase deficiency (ASLD) is a novel model system to investigate cell-autonomous, nitric oxide synthase-dependent NO deficiency.
    explanation: Confirms ASL role in cell-autonomous NO deficiency beyond ureagenesis.
  - reference: CGGV:assertion_c16021b9-f6db-4e41-90f3-4786d63a1fa3-2018-09-15T160000.000Z
    reference_title: "ASL / argininosuccinic aciduria (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "ASL | HGNC:746 | argininosuccinic aciduria | MONDO:0008815 | AR | Definitive"
    explanation: ClinGen classifies the ASL-argininosuccinic aciduria gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: Protein-restricted diet with arginine supplementation
  description: 'Dietary protein restriction to reduce nitrogen load combined with arginine supplementation to replenish deficient arginine and support residual ureagenesis. This is the cornerstone of chronic metabolic management in ASA.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  evidence:
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels
    explanation: Supports dietary management focused on ammonia and arginine normalization.
  target_mechanisms:
  - target: Impaired ureagenesis and hyperammonemia
    treatment_effect: MODULATES
    description: Protein restriction reduces nitrogen load while arginine supplementation addresses ASL-related arginine deficiency.
    evidence:
    - reference: PMID:30723942
      reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: the current standard of care and therapeutic strategy, which aims to normalize plasma ammonia and arginine levels
      explanation: Supports this treatment as acting on ammonia and arginine abnormalities.
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
- name: Nitrogen scavenger therapy
  description: 'Sodium benzoate and/or sodium phenylbutyrate provide alternative nitrogen disposal pathways to reduce ammonia burden during acute hyperammonemic crises and for chronic management.

    '
  treatment_term:
    preferred_term: nitrogen scavenger therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:31990680
    reference_title: "Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Hyperammonemia and use of nitrogen-scavenging agents, 2 markers of disease severity, were significantly (P < 0.001 and P = 0.001, respectively) associated with elevated ALT in ASLD.
    explanation: Confirms nitrogen scavenger use in ASLD management; also notes association with disease severity.
  target_mechanisms:
  - target: Impaired ureagenesis and hyperammonemia
    treatment_effect: BYPASSES
    description: Nitrogen scavengers provide alternative nitrogen disposal when the urea cycle is impaired.
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
- name: Liver transplantation
  description: 'Liver transplantation restores hepatic urea cycle function, prevents further hyperammonemic events, and allows normal protein tolerance. However, it does not improve neurocognitive outcomes compared with severity-adjusted medical management. Neurologic sequelae persist but do not progress after transplantation.

    '
  treatment_term:
    preferred_term: organ transplantation
    term:
      id: MAXO:0010039
      label: organ transplantation
  evidence:
  - reference: PMID:38054409
    reference_title: "Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation and was associated with a more favorable growth outcome compared with individuals remaining under MM. However, neurocognitive outcome in individuals with LTx did not differ from the medically managed counterparts
    explanation: Severity-adjusted analysis confirms LT prevents hyperammonemia but does not improve neurocognitive outcomes.
  target_mechanisms:
  - target: Impaired ureagenesis and hyperammonemia
    treatment_effect: RESTORES
    description: Liver transplantation restores hepatic urea-cycle capacity sufficiently to prevent further hyperammonemic events.
    evidence:
    - reference: PMID:38054409
      reference_title: "Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: LTx enabled metabolic stability by prevention of further hyperammonemic events after transplantation
      explanation: Supports transplantation as restoring metabolic stability at the hyperammonemia mechanism.
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
- name: Acute decompensation management
  description: 'Emergency supportive care during hyperammonemic crises including high-calorie glucose infusion to reverse catabolism, cessation of protein intake, ammonia-lowering agents, and correction of metabolic derangements.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The disappointing long-term clinical outcomes of many of the patients have challenged the current standard of care and therapeutic strategy
    explanation: Supports the need for acute management as part of standard of care in ASA.
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
- name: NO supplementation
  description: >-
    Nitric oxide supplementation addresses the cell-autonomous NO deficiency in ASA.
    Preclinical studies
    have demonstrated that NO supplementation can partially rescue vascular and BBB
    dysfunction in ASL-deficient
    models, motivating the hypothesis that NOS-independent NO supplementation may
    ameliorate ammonia-independent
    pathology.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:30075114
    reference_title: "Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: loss of ASL in endothelial cells leads to endothelial-dependent vascular dysfunction with reduced nitric oxide (NO) production, increased oxidative stress, and impaired angiogenesis
    explanation: Provides the mechanistic rationale for NO supplementation therapy in ASLD.
  - reference: PMID:37490345
    reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation
    explanation: Demonstrates partial rescue of BBB dysfunction by NO supplementation in ASLD.
  target_mechanisms:
  - target: Nitric oxide deficiency and endothelial dysfunction
    treatment_effect: MODULATES
    description: NO supplementation directly addresses NO deficiency and partially rescues BBB dysfunction in ASLD models.
    evidence:
    - reference: PMID:37490345
      reference_title: "Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide-mediated dysregulation of claudin expression."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: in vivo assessment of a hypomorphic mouse model of ASLD showed increased BBB leakage, which was partially rescued by NO supplementation
      explanation: Supports NO supplementation as targeting the NO-deficiency mechanism.
- name: Genetic counseling
  description: 'Genetic counseling for affected families including discussion of autosomal recessive inheritance, recurrence risk (25% per pregnancy), carrier testing, and prenatal/preimplantation genetic testing options.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  target_mechanisms:
  - target: ASL (argininosuccinate lyase) variants
    treatment_effect: MODULATES
    description: Counseling and molecular diagnosis are anchored to the family's ASL pathogenic variants.
    evidence:
    - reference: PMID:26843370
      reference_title: "NGS in argininosuccinic aciduria detects a mutation (D145G) which drives alternative splicing of ASL: a case report study."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder
      explanation: Supports autosomal recessive ASL-related disease as the basis for genetic counseling.
  evidence:
  - reference: PMID:26843370
    reference_title: "NGS in argininosuccinic aciduria detects a mutation (D145G) which drives alternative splicing of ASL: a case report study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This study also demonstrates the value of NGS in the identification of mutations and molecular diagnosis for ASAuria families.
    explanation: Supports molecular diagnosis of ASA families as part of genetic counseling.
  notes: >-
    Genetic counseling is essential for ASA families due to autosomal recessive inheritance,
    25% recurrence risk, and the well-characterized molecular basis of the disease
    (PMID:30723942).
- name: Newborn screening
  description: 'ASA is detectable by newborn screening via elevated argininosuccinic acid in dried blood spots. Early detection enables presymptomatic initiation of treatment, though the benefit of newborn screening on long-term neurological outcomes has been questioned.

    '
  treatment_term:
    preferred_term: disease screening
    term:
      id: MAXO:0000124
      label: disease screening
  evidence:
  - reference: PMID:30723942
    reference_title: "Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Interrogations have raised about the benefit of newborn screening or liver transplantation on the neurological phenotype.
    explanation: Supports newborn screening availability while noting uncertainty about neurological benefit.
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
- name: mRNA therapy (investigational)
  description: 'Lipid nanoparticle-delivered human ASL mRNA is an emerging investigational therapy that has shown preclinical efficacy in correcting both glutathione metabolism and ureagenesis in ASL-deficient mouse models, with rescue of chronic liver disease. This approach supports clinical translation for ASA.

    '
  treatment_term:
    preferred_term: gene therapy
    term:
      id: MAXO:0001001
      label: gene therapy
  evidence:
  - reference: PMID:38198573
    reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: These findings provide mechanistic insights in liver glutathione metabolism and support clinical translation of mRNA therapy for argininosuccinic aciduria.
    explanation: Demonstrates preclinical efficacy of mRNA therapy for ASA.
  target_mechanisms:
  - target: ASL molecular function deficiency
    treatment_effect: RESTORES
    description: hASL mRNA supplies ASL coding capacity to restore deficient ASL function in preclinical models.
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Human hASL mRNA encapsulated in lipid nanoparticles improved glutathione metabolism and chronic liver disease.
      explanation: Supports hASL mRNA as targeting the upstream molecular deficiency.
  - target: Impaired ureagenesis and hyperammonemia
    treatment_effect: RESTORES
    description: hASL mRNA therapy enhances ureagenesis in ASL-deficient mouse models.
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: hASL mRNA therapy corrected and rescued the neonatal and adult Asl-deficient mouse phenotypes, respectively, enhancing ureagenesis.
      explanation: Supports restored ureagenesis as a preclinical treatment mechanism.
  - target: Oxidative stress and glutathione dysregulation
    treatment_effect: RESTORES
    description: hASL mRNA improves glutathione metabolism and chronic liver disease in ASLD models.
    evidence:
    - reference: PMID:38198573
      reference_title: "mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Human hASL mRNA encapsulated in lipid nanoparticles improved glutathione metabolism and chronic liver disease.
      explanation: Supports correction of the glutathione/redox mechanism by hASL mRNA.
notes: 'Key references: Baruteau et al. 2019 JIMD review (PMID:30723942); Kho et al. 2023 JCI Insight on BBB disruption (PMID:37490345); Gurung et al. 2024 Sci Transl Med on glutathione/mRNA therapy (PMID:38198573); Gurung et al. 2024 JIMD on movement disorders (PMID:38044746); Kho et al. 2018 AJHG on hypertension (PMID:30075114); Burrage et al. 2020 JCI Insight on liver disease (PMID:31990680).

  '
references:
- reference: DOI:10.1016/j.ymgme.2023.108112
  title: Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders
    supporting_text: Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders
- reference: DOI:10.21203/rs.3.rs-3279667/v1
  title: Argininosuccinate Lyase (ASL) Deficiency; Outcome of Patients with an Early Presentation at Johns Hopkins Aramco Healthcare (JHAH)
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings:
  - statement: Argininosuccinic aciduria (ASA) is an autosomal recessive inborn error of the urea disorder (UCD) cycle caused by mutation in the gene encoding argininosuccinate lyase (ASL).
    supporting_text: Argininosuccinic aciduria (ASA) is an autosomal recessive inborn error of the urea disorder (UCD) cycle caused by mutation in the gene encoding argininosuccinate lyase (ASL).
- reference: DOI:10.3389/fped.2023.1103757
  title: Urea cycle disorders and indications for liver transplantation
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings:
  - statement: Urea cycle disorders (UCD) are inborn errors of metabolism caused by deficiency of enzymes required to convert nitrogen from ammonia into urea.
    supporting_text: Urea cycle disorders (UCD) are inborn errors of metabolism caused by deficiency of enzymes required to convert nitrogen from ammonia into urea.
- reference: DOI:10.58624/svoapd.2023.02.050
  title: A Novel Variant of ASL Gene Mutation in a Lebanese Neonate with Severe Argininosuccinic Aciduria Phenotype
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings:
  - statement: Argininosuccinic aciduria is a urea cycle defect associated with deficiency in argininosuccinate lyase enzyme, leading to a severe hyperammonemic encephalopathy, epilepsy and hepatopathy.
    supporting_text: Argininosuccinic aciduria is a urea cycle defect associated with deficiency in argininosuccinate lyase enzyme, leading to a severe hyperammonemic encephalopathy, epilepsy and hepatopathy.
- reference: PMID:10029536
  title: Crystal structure of an inactive duck delta II crystallin mutant with bound argininosuccinate.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1999 Feb 23;38(8):2425-34. doi: 10.1021/bi982149h.'
    supporting_text: '1999 Feb 23;38(8):2425-34. doi: 10.1021/bi982149h.'
- reference: PMID:10603100
  title: Liver transplantation in urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1999 Dec;158 Suppl 2:S55-9. doi: 10.1007/pl00014323.'
    supporting_text: '1999 Dec;158 Suppl 2:S55-9. doi: 10.1007/pl00014323.'
- reference: PMID:11148551
  title: Long-term correction of urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2001 Jan;138(1 Suppl):S62-71. doi: 10.1067/mpd.2001.111838.'
    supporting_text: '2001 Jan;138(1 Suppl):S62-71. doi: 10.1067/mpd.2001.111838.'
- reference: PMID:17669242
  title: '[Determination of serum argininosuccinate lyase in diagnosing liver diseases].'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: 2007 Jul;15(7):521-4. [Determination of serum argininosuccinate lyase in diagnosing liver diseases]. [Article in Chinese] Feng JF(1), Chen TM, Tu ZG.
    supporting_text: 2007 Jul;15(7):521-4. [Determination of serum argininosuccinate lyase in diagnosing liver diseases]. [Article in Chinese] Feng JF(1), Chen TM, Tu ZG.
- reference: PMID:19092443
  title: 'Population screening in a Druze community: the challenge and the reward.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2008 Dec;10(12):903-9. doi: 10.1097/GIM.0b013e31818d0e0f.'
    supporting_text: '2008 Dec;10(12):903-9. doi: 10.1097/GIM.0b013e31818d0e0f.'
- reference: PMID:22081021
  title: Requirement of argininosuccinate lyase for systemic nitric oxide production.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2011 Nov 13;17(12):1619-26. doi: 10.1038/nm.2544.'
    supporting_text: '2011 Nov 13;17(12):1619-26. doi: 10.1038/nm.2544.'
- reference: PMID:22696221
  title: Protein kinase Cα phosphorylates a novel argininosuccinate synthase site at serine 328 during calcium-dependent stimulation of endothelial nitric-oxide synthase in vascular endothelial cells.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2012 Jul 27;287(31):26168-76. doi: 10.1074/jbc.M112.378794.'
    supporting_text: '2012 Jul 27;287(31):26168-76. doi: 10.1074/jbc.M112.378794.'
- reference: PMID:23149878
  title: 'Urea cycle defects and hyperammonemia: effects on functional imaging.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2013 Jun;28(2):269-75. doi: 10.1007/s11011-012-9348-0.'
    supporting_text: '2013 Jun;28(2):269-75. doi: 10.1007/s11011-012-9348-0.'
- reference: PMID:23972786
  title: The incidence of urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2013 Sep-Oct;110(1-2):179-80. doi: 10.1016/j.ymgme.2013.07.008.'
    supporting_text: '2013 Sep-Oct;110(1-2):179-80. doi: 10.1016/j.ymgme.2013.07.008.'
- reference: PMID:24385142
  title: 'Citrulline uptake in rat cerebral cortex slices: modulation by Thioacetamide -Induced hepatic failure.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2014 Dec;29(4):1053-60. doi: 10.1007/s11011-013-9472-5.'
    supporting_text: '2014 Dec;29(4):1053-60. doi: 10.1007/s11011-013-9472-5.'
- reference: PMID:25034052
  title: 'Pathophysiology of brain dysfunction in hyperammonemic syndromes: The many faces of glutamine.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2014 Sep-Oct;113(1-2):113-7. doi: 10.1016/j.ymgme.2014.06.003.'
    supporting_text: '2014 Sep-Oct;113(1-2):113-7. doi: 10.1016/j.ymgme.2014.06.003.'
- reference: PMID:25047749
  title: Biochemical and molecular characteristics of patients with organic acidaemias and urea cycle disorders identified through newborn screening.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: In recent years it has become clear that newborn screening (NBS) programmes using tandem mass spectrometry identify "patients" with "classical" inborn errors of metabolism who are asymptomatic.
    supporting_text: In recent years it has become clear that newborn screening (NBS) programmes using tandem mass spectrometry identify "patients" with "classical" inborn errors of metabolism who are asymptomatic.
- reference: PMID:25690729
  title: Evaluation of Implementation, Adaptation and Use of the Recently Proposed Urea Cycle Disorders Guidelines.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Implementation of guidelines and assessment of their adaptation is not an extensively investigated process in the field of rare diseases.
    supporting_text: Implementation of guidelines and assessment of their adaptation is not an extensively investigated process in the field of rare diseases.
- reference: PMID:26731266
  title: Lys-315 at the Interfaces of Diagonal Subunits of δ-Crystallin Plays a Critical Role in the Reversibility of Folding and Subunit Assembly.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2016 Jan 5;11(1):e0145957. doi: 10.1371/journal.pone.0145957. eCollection 2016.'
    supporting_text: '2016 Jan 5;11(1):e0145957. doi: 10.1371/journal.pone.0145957. eCollection 2016.'
- reference: PMID:26843370
  title: 'NGS in argininosuccinic aciduria detects a mutation (D145G) which drives alternative splicing of ASL: a case report study.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder, which leads to the accumulation of argininosuccinic acid in the blood and urine.
    supporting_text: Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder, which leads to the accumulation of argininosuccinic acid in the blood and urine.
- reference: PMID:27215558
  title: Improving long term outcomes in urea cycle disorders-report from the Urea Cycle Disorders Consortium.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2016 Jul;39(4):573-84. doi: 10.1007/s10545-016-9942-0.'
    supporting_text: '2016 Jul;39(4):573-84. doi: 10.1007/s10545-016-9942-0.'
- reference: PMID:27544719
  title: 'Pilot study of newborn screening of inborn error of metabolism using tandem mass spectrometry in Malaysia: outcome and challenges.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: The aim of this study was to determine the feasibility of performing newborn screening (NBS) of inborn errors of metabolism (IEMs) using tandem mass spectrometry (TMS) and the impact on its detection rate in Malaysia.
    supporting_text: The aim of this study was to determine the feasibility of performing newborn screening (NBS) of inborn errors of metabolism (IEMs) using tandem mass spectrometry (TMS) and the impact on its detection rate in Malaysia.
- reference: PMID:28900784
  title: 'Liver involvement in urea cycle disorders: a review of the literature.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2017 Nov;40(6):757-769. doi: 10.1007/s10545-017-0088-5.'
    supporting_text: '2017 Nov;40(6):757-769. doi: 10.1007/s10545-017-0088-5.'
- reference: PMID:28981931
  title: '[Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia].'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2017 Oct 10;34(5):676-679. doi: 10.3760/cma.j.issn.1003-9406.2017.05.012. [Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia]. [Article in Chinese] Lin Y(1), Yu K, Li L, Zheng Z, Lin W, Fu Q.'
    supporting_text: '2017 Oct 10;34(5):676-679. doi: 10.3760/cma.j.issn.1003-9406.2017.05.012. [Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia]. [Article in Chinese] Lin Y(1), Yu K, Li L, Zheng Z, Lin W, Fu Q.'
- reference: PMID:29439324
  title: Altered Expression of Urea Cycle Enzymes in Amyloid-β Protein Precursor Overexpressing PC12 Cells and in Sporadic Alzheimer's Disease Brain.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2018;62(1):279-291. doi: 10.3233/JAD-170427.'
    supporting_text: '2018;62(1):279-291. doi: 10.3233/JAD-170427.'
- reference: PMID:29773863
  title: Low prevalence of argininosuccinate lyase deficiency among inherited urea cycle disorders in Korea.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2018 Jul;63(8):911-917. doi: 10.1038/s10038-018-0467-2.'
    supporting_text: '2018 Jul;63(8):911-917. doi: 10.1038/s10038-018-0467-2.'
- reference: PMID:30197275
  title: The utility of EEG monitoring in neonates with hyperammonemia due to inborn errors of metabolism.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Continuous EEG studies demonstrate that neonates with seizures due to cerebral pathology, such as hypoxia ischemia, exhibit predominantly electrographic seizures (i.e. those only detected with EEG because they lack clinical features).
    supporting_text: Continuous EEG studies demonstrate that neonates with seizures due to cerebral pathology, such as hypoxia ischemia, exhibit predominantly electrographic seizures (i.e. those only detected with EEG because they lack clinical features).
- reference: PMID:30253962
  title: Adeno-associated viral gene therapy corrects a mouse model of argininosuccinic aciduria.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2018 Nov;125(3):241-250. doi: 10.1016/j.ymgme.2018.08.013.'
    supporting_text: '2018 Nov;125(3):241-250. doi: 10.1016/j.ymgme.2018.08.013.'
- reference: PMID:30982989
  title: 'Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2019 Nov;42(6):1192-1230. doi: 10.1002/jimd.12100.'
    supporting_text: '2019 Nov;42(6):1192-1230. doi: 10.1002/jimd.12100.'
- reference: PMID:31183366
  title: Whole-Exome Sequencing Identified a Novel Compound Heterozygous Genotype in ASL in a Chinese Han Patient with Argininosuccinate Lyase Deficiency.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2019 Apr 30;2019:3530198. doi: 10.1155/2019/3530198. eCollection 2019.'
    supporting_text: '2019 Apr 30;2019:3530198. doi: 10.1155/2019/3530198. eCollection 2019.'
- reference: PMID:31260111
  title: Chronic liver involvement in urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2019 Nov;42(6):1118-1127. doi: 10.1002/jimd.12144.'
    supporting_text: '2019 Nov;42(6):1118-1127. doi: 10.1002/jimd.12144.'
- reference: PMID:31426867
  title: 'Urea cycle disorders in Argentine patients: clinical presentation, biochemical and genetic findings.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: The incidence, prevalence, and molecular epidemiology of urea cycle disorders (UCDs) in Argentina remain underexplored.
    supporting_text: The incidence, prevalence, and molecular epidemiology of urea cycle disorders (UCDs) in Argentina remain underexplored.
- reference: PMID:31943503
  title: 'From genotype to phenotype: Early prediction of disease severity in argininosuccinic aciduria.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2020 May;41(5):946-960. doi: 10.1002/humu.23983.'
    supporting_text: '2020 May;41(5):946-960. doi: 10.1002/humu.23983.'
- reference: PMID:32410394
  title: Clinical and genetic analysis of five Chinese patients with urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: 'The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL).'
    supporting_text: 'The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL).'
- reference: PMID:33129925
  title: Valproic acid up-regulates the whole NO-citrulline cycle for potent iNOS-NO signaling to promote neuronal differentiation of adipose tissue-derived stem cells.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2021 Jan 1;106:35-44. doi: 10.1016/j.niox.2020.10.006.'
    supporting_text: '2021 Jan 1;106:35-44. doi: 10.1016/j.niox.2020.10.006.'
- reference: PMID:33338599
  title: Arginine recycling in endothelial cells is regulated BY HSP90 and the ubiquitin proteasome system.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2021 Mar 1;108:12-19. doi: 10.1016/j.niox.2020.12.003.'
    supporting_text: '2021 Mar 1;108:12-19. doi: 10.1016/j.niox.2020.12.003.'
- reference: PMID:33846069
  title: Biomarkers for liver disease in urea cycle disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Urea cycle disorders (UCDs) are among the most common inborn errors of liver metabolism.
    supporting_text: Urea cycle disorders (UCDs) are among the most common inborn errors of liver metabolism.
- reference: PMID:34058057
  title: 'Liver Transplantation in Children with Urea Cycle Disorders: The Importance of Minimizing Waiting Time.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2021 Dec;27(12):1799-1810. doi: 10.1002/lt.26186.'
    supporting_text: '2021 Dec;27(12):1799-1810. doi: 10.1002/lt.26186.'
- reference: PMID:38579669
  title: Genetic and functional correction of argininosuccinate lyase deficiency using CRISPR adenine base editors.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2024 Apr 4;111(4):714-728. doi: 10.1016/j.ajhg.2024.03.004.'
    supporting_text: '2024 Apr 4;111(4):714-728. doi: 10.1016/j.ajhg.2024.03.004.'
- reference: PMID:39384000
  title: Arabidopsis thaliana argininosuccinate lyase structure uncovers the role of serine as the catalytic base.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2024 Dec;216(4):108130. doi: 10.1016/j.jsb.2024.108130.'
    supporting_text: '2024 Dec;216(4):108130. doi: 10.1016/j.jsb.2024.108130.'
- reference: PMID:39776112
  title: Positive Clinical, Neuropsychological, and Metabolic Impact of Liver Transplantation in Patients With Argininosuccinate Lyase Deficiency.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2025 Jan;48(1):e12843. doi: 10.1002/jimd.12843.'
    supporting_text: '2025 Jan;48(1):e12843. doi: 10.1002/jimd.12843.'
- reference: PMID:40081835
  title: 'The loss of the urea cycle and ornithine metabolism in different insect orders: An omics approach.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2025 Oct;34(5):632-644. doi: 10.1111/imb.12989.'
    supporting_text: '2025 Oct;34(5):632-644. doi: 10.1111/imb.12989.'
- reference: PMID:7141120
  title: 'Neurotrichosis: hair-shaft abnormalities associated with neurological diseases.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1982 Oct;24(5):634-44. doi: 10.1111/j.1469-8749.1982.tb13674.x.'
    supporting_text: '1982 Oct;24(5):634-44. doi: 10.1111/j.1469-8749.1982.tb13674.x.'
- reference: PMID:9844057
  title: 'Argininosuccinate lyase: a new autoantigen in liver disease.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1998 Dec;114(3):455-61. doi: 10.1046/j.1365-2249.1998.00754.x.'
    supporting_text: '1998 Dec;114(3):455-61. doi: 10.1046/j.1365-2249.1998.00754.x.'
- reference: DOI:10.1002/jimd.12691
  title: The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: DOI:10.1016/j.ajhg.2018.07.008
  title: Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: DOI:10.1016/j.gim.2023.101039
  title: Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: DOI:10.1126/scitranslmed.adh1334
  title: mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: DOI:10.1172/jci.insight.132342
  title: Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: DOI:10.1172/jci.insight.168475
  title: Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide–mediated dysregulation of claudin expression
  found_in:
  - Argininosuccinic_Aciduria-deep-research-falcon.md
  findings: []
- reference: PMID:22241104
  title: Argininosuccinate lyase deficiency.
  tags:
  - GeneReviews
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:30075114
  title: Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:30723942
  title: 'Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:31990680
  title: Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:38301530
  title: Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders.
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:7411317
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
- reference: PMID:9256435
  title: 'Human argininosuccinate lyase: a structural basis for intragenic complementation.'
  found_in:
  - Argininosuccinic_Aciduria-deep-research-openscientist.md
  findings: []
📚

References & Deep Research

References

56
DOI:10.1016/j.ymgme.2023.108112
Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders
1 finding
Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders
"Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders"
DOI:10.21203/rs.3.rs-3279667/v1
Argininosuccinate Lyase (ASL) Deficiency; Outcome of Patients with an Early Presentation at Johns Hopkins Aramco Healthcare (JHAH)
1 finding
Argininosuccinic aciduria (ASA) is an autosomal recessive inborn error of the urea disorder (UCD) cycle caused by mutation in the gene encoding argininosuccinate lyase (ASL).
"Argininosuccinic aciduria (ASA) is an autosomal recessive inborn error of the urea disorder (UCD) cycle caused by mutation in the gene encoding argininosuccinate lyase (ASL)."
DOI:10.3389/fped.2023.1103757
Urea cycle disorders and indications for liver transplantation
1 finding
Urea cycle disorders (UCD) are inborn errors of metabolism caused by deficiency of enzymes required to convert nitrogen from ammonia into urea.
"Urea cycle disorders (UCD) are inborn errors of metabolism caused by deficiency of enzymes required to convert nitrogen from ammonia into urea."
DOI:10.58624/svoapd.2023.02.050
A Novel Variant of ASL Gene Mutation in a Lebanese Neonate with Severe Argininosuccinic Aciduria Phenotype
1 finding
Argininosuccinic aciduria is a urea cycle defect associated with deficiency in argininosuccinate lyase enzyme, leading to a severe hyperammonemic encephalopathy, epilepsy and hepatopathy.
"Argininosuccinic aciduria is a urea cycle defect associated with deficiency in argininosuccinate lyase enzyme, leading to a severe hyperammonemic encephalopathy, epilepsy and hepatopathy."
PMID:10029536
Crystal structure of an inactive duck delta II crystallin mutant with bound argininosuccinate.
1 finding
1999 Feb 23;38(8):2425-34. doi: 10.1021/bi982149h.
"1999 Feb 23;38(8):2425-34. doi: 10.1021/bi982149h."
PMID:10603100
Liver transplantation in urea cycle disorders.
1 finding
1999 Dec;158 Suppl 2:S55-9. doi: 10.1007/pl00014323.
"1999 Dec;158 Suppl 2:S55-9. doi: 10.1007/pl00014323."
PMID:11148551
Long-term correction of urea cycle disorders.
1 finding
2001 Jan;138(1 Suppl):S62-71. doi: 10.1067/mpd.2001.111838.
"2001 Jan;138(1 Suppl):S62-71. doi: 10.1067/mpd.2001.111838."
PMID:17669242
[Determination of serum argininosuccinate lyase in diagnosing liver diseases].
1 finding
2007 Jul;15(7):521-4. [Determination of serum argininosuccinate lyase in diagnosing liver diseases]. [Article in Chinese] Feng JF(1), Chen TM, Tu ZG.
"2007 Jul;15(7):521-4. [Determination of serum argininosuccinate lyase in diagnosing liver diseases]. [Article in Chinese] Feng JF(1), Chen TM, Tu ZG."
PMID:19092443
Population screening in a Druze community: the challenge and the reward.
1 finding
2008 Dec;10(12):903-9. doi: 10.1097/GIM.0b013e31818d0e0f.
"2008 Dec;10(12):903-9. doi: 10.1097/GIM.0b013e31818d0e0f."
PMID:22081021
Requirement of argininosuccinate lyase for systemic nitric oxide production.
1 finding
2011 Nov 13;17(12):1619-26. doi: 10.1038/nm.2544.
"2011 Nov 13;17(12):1619-26. doi: 10.1038/nm.2544."
PMID:22696221
Protein kinase Cα phosphorylates a novel argininosuccinate synthase site at serine 328 during calcium-dependent stimulation of endothelial nitric-oxide synthase in vascular endothelial cells.
1 finding
2012 Jul 27;287(31):26168-76. doi: 10.1074/jbc.M112.378794.
"2012 Jul 27;287(31):26168-76. doi: 10.1074/jbc.M112.378794."
PMID:23149878
Urea cycle defects and hyperammonemia: effects on functional imaging.
1 finding
2013 Jun;28(2):269-75. doi: 10.1007/s11011-012-9348-0.
"2013 Jun;28(2):269-75. doi: 10.1007/s11011-012-9348-0."
PMID:23972786
The incidence of urea cycle disorders.
1 finding
2013 Sep-Oct;110(1-2):179-80. doi: 10.1016/j.ymgme.2013.07.008.
"2013 Sep-Oct;110(1-2):179-80. doi: 10.1016/j.ymgme.2013.07.008."
PMID:24385142
Citrulline uptake in rat cerebral cortex slices: modulation by Thioacetamide -Induced hepatic failure.
1 finding
2014 Dec;29(4):1053-60. doi: 10.1007/s11011-013-9472-5.
"2014 Dec;29(4):1053-60. doi: 10.1007/s11011-013-9472-5."
PMID:25034052
Pathophysiology of brain dysfunction in hyperammonemic syndromes: The many faces of glutamine.
1 finding
2014 Sep-Oct;113(1-2):113-7. doi: 10.1016/j.ymgme.2014.06.003.
"2014 Sep-Oct;113(1-2):113-7. doi: 10.1016/j.ymgme.2014.06.003."
PMID:25047749
Biochemical and molecular characteristics of patients with organic acidaemias and urea cycle disorders identified through newborn screening.
1 finding
In recent years it has become clear that newborn screening (NBS) programmes using tandem mass spectrometry identify "patients" with "classical" inborn errors of metabolism who are asymptomatic.
"In recent years it has become clear that newborn screening (NBS) programmes using tandem mass spectrometry identify "patients" with "classical" inborn errors of metabolism who are asymptomatic."
PMID:25690729
Evaluation of Implementation, Adaptation and Use of the Recently Proposed Urea Cycle Disorders Guidelines.
1 finding
Implementation of guidelines and assessment of their adaptation is not an extensively investigated process in the field of rare diseases.
"Implementation of guidelines and assessment of their adaptation is not an extensively investigated process in the field of rare diseases."
PMID:26731266
Lys-315 at the Interfaces of Diagonal Subunits of δ-Crystallin Plays a Critical Role in the Reversibility of Folding and Subunit Assembly.
1 finding
2016 Jan 5;11(1):e0145957. doi: 10.1371/journal.pone.0145957. eCollection 2016.
"2016 Jan 5;11(1):e0145957. doi: 10.1371/journal.pone.0145957. eCollection 2016."
PMID:26843370
NGS in argininosuccinic aciduria detects a mutation (D145G) which drives alternative splicing of ASL: a case report study.
1 finding
Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder, which leads to the accumulation of argininosuccinic acid in the blood and urine.
"Argininosuccinic aciduria (ASAuria; OMIM 207900) is a rare autosomal recessive heterogeneous urea cycle disorder, which leads to the accumulation of argininosuccinic acid in the blood and urine."
PMID:27215558
Improving long term outcomes in urea cycle disorders-report from the Urea Cycle Disorders Consortium.
1 finding
2016 Jul;39(4):573-84. doi: 10.1007/s10545-016-9942-0.
"2016 Jul;39(4):573-84. doi: 10.1007/s10545-016-9942-0."
PMID:27544719
Pilot study of newborn screening of inborn error of metabolism using tandem mass spectrometry in Malaysia: outcome and challenges.
1 finding
The aim of this study was to determine the feasibility of performing newborn screening (NBS) of inborn errors of metabolism (IEMs) using tandem mass spectrometry (TMS) and the impact on its detection rate in Malaysia.
"The aim of this study was to determine the feasibility of performing newborn screening (NBS) of inborn errors of metabolism (IEMs) using tandem mass spectrometry (TMS) and the impact on its detection rate in Malaysia."
PMID:28900784
Liver involvement in urea cycle disorders: a review of the literature.
1 finding
2017 Nov;40(6):757-769. doi: 10.1007/s10545-017-0088-5.
"2017 Nov;40(6):757-769. doi: 10.1007/s10545-017-0088-5."
PMID:28981931
[Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia].
1 finding
2017 Oct 10;34(5):676-679. doi: 10.3760/cma.j.issn.1003-9406.2017.05.012. [Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia]. [Article in Chinese] Lin Y(1), Yu K, Li L, Zheng Z, Lin W, Fu Q.
"2017 Oct 10;34(5):676-679. doi: 10.3760/cma.j.issn.1003-9406.2017.05.012. [Mutational analysis of ASS1, ASL and SLC25A13 genes in six Chinese patients with citrullinemia]. [Article in Chinese] Lin Y(1), Yu K, Li L, Zheng Z, Lin W, Fu Q."
PMID:29439324
Altered Expression of Urea Cycle Enzymes in Amyloid-β Protein Precursor Overexpressing PC12 Cells and in Sporadic Alzheimer's Disease Brain.
1 finding
2018;62(1):279-291. doi: 10.3233/JAD-170427.
"2018;62(1):279-291. doi: 10.3233/JAD-170427."
PMID:29773863
Low prevalence of argininosuccinate lyase deficiency among inherited urea cycle disorders in Korea.
1 finding
2018 Jul;63(8):911-917. doi: 10.1038/s10038-018-0467-2.
"2018 Jul;63(8):911-917. doi: 10.1038/s10038-018-0467-2."
PMID:30197275
The utility of EEG monitoring in neonates with hyperammonemia due to inborn errors of metabolism.
1 finding
Continuous EEG studies demonstrate that neonates with seizures due to cerebral pathology, such as hypoxia ischemia, exhibit predominantly electrographic seizures (i.e. those only detected with EEG because they lack clinical features).
"Continuous EEG studies demonstrate that neonates with seizures due to cerebral pathology, such as hypoxia ischemia, exhibit predominantly electrographic seizures (i.e. those only detected with EEG because they lack clinical features)."
PMID:30253962
Adeno-associated viral gene therapy corrects a mouse model of argininosuccinic aciduria.
1 finding
2018 Nov;125(3):241-250. doi: 10.1016/j.ymgme.2018.08.013.
"2018 Nov;125(3):241-250. doi: 10.1016/j.ymgme.2018.08.013."
PMID:30982989
Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision.
1 finding
2019 Nov;42(6):1192-1230. doi: 10.1002/jimd.12100.
"2019 Nov;42(6):1192-1230. doi: 10.1002/jimd.12100."
PMID:31183366
Whole-Exome Sequencing Identified a Novel Compound Heterozygous Genotype in ASL in a Chinese Han Patient with Argininosuccinate Lyase Deficiency.
1 finding
2019 Apr 30;2019:3530198. doi: 10.1155/2019/3530198. eCollection 2019.
"2019 Apr 30;2019:3530198. doi: 10.1155/2019/3530198. eCollection 2019."
PMID:31260111
Chronic liver involvement in urea cycle disorders.
1 finding
2019 Nov;42(6):1118-1127. doi: 10.1002/jimd.12144.
"2019 Nov;42(6):1118-1127. doi: 10.1002/jimd.12144."
PMID:31426867
Urea cycle disorders in Argentine patients: clinical presentation, biochemical and genetic findings.
1 finding
The incidence, prevalence, and molecular epidemiology of urea cycle disorders (UCDs) in Argentina remain underexplored.
"The incidence, prevalence, and molecular epidemiology of urea cycle disorders (UCDs) in Argentina remain underexplored."
PMID:31943503
From genotype to phenotype: Early prediction of disease severity in argininosuccinic aciduria.
1 finding
2020 May;41(5):946-960. doi: 10.1002/humu.23983.
"2020 May;41(5):946-960. doi: 10.1002/humu.23983."
PMID:32410394
Clinical and genetic analysis of five Chinese patients with urea cycle disorders.
1 finding
The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL).
"The urea cycle plays a key role in preventing the accumulation of toxic nitrogenous waste products, including two essential enzymes: ornithine transcarbamylase (OTC) and argininosuccinate lyase (ASL)."
PMID:33129925
Valproic acid up-regulates the whole NO-citrulline cycle for potent iNOS-NO signaling to promote neuronal differentiation of adipose tissue-derived stem cells.
1 finding
2021 Jan 1;106:35-44. doi: 10.1016/j.niox.2020.10.006.
"2021 Jan 1;106:35-44. doi: 10.1016/j.niox.2020.10.006."
PMID:33338599
Arginine recycling in endothelial cells is regulated BY HSP90 and the ubiquitin proteasome system.
1 finding
2021 Mar 1;108:12-19. doi: 10.1016/j.niox.2020.12.003.
"2021 Mar 1;108:12-19. doi: 10.1016/j.niox.2020.12.003."
PMID:33846069
Biomarkers for liver disease in urea cycle disorders.
1 finding
Urea cycle disorders (UCDs) are among the most common inborn errors of liver metabolism.
"Urea cycle disorders (UCDs) are among the most common inborn errors of liver metabolism."
PMID:34058057
Liver Transplantation in Children with Urea Cycle Disorders: The Importance of Minimizing Waiting Time.
1 finding
2021 Dec;27(12):1799-1810. doi: 10.1002/lt.26186.
"2021 Dec;27(12):1799-1810. doi: 10.1002/lt.26186."
PMID:38579669
Genetic and functional correction of argininosuccinate lyase deficiency using CRISPR adenine base editors.
1 finding
2024 Apr 4;111(4):714-728. doi: 10.1016/j.ajhg.2024.03.004.
"2024 Apr 4;111(4):714-728. doi: 10.1016/j.ajhg.2024.03.004."
PMID:39384000
Arabidopsis thaliana argininosuccinate lyase structure uncovers the role of serine as the catalytic base.
1 finding
2024 Dec;216(4):108130. doi: 10.1016/j.jsb.2024.108130.
"2024 Dec;216(4):108130. doi: 10.1016/j.jsb.2024.108130."
PMID:39776112
Positive Clinical, Neuropsychological, and Metabolic Impact of Liver Transplantation in Patients With Argininosuccinate Lyase Deficiency.
1 finding
2025 Jan;48(1):e12843. doi: 10.1002/jimd.12843.
"2025 Jan;48(1):e12843. doi: 10.1002/jimd.12843."
PMID:40081835
The loss of the urea cycle and ornithine metabolism in different insect orders: An omics approach.
1 finding
2025 Oct;34(5):632-644. doi: 10.1111/imb.12989.
"2025 Oct;34(5):632-644. doi: 10.1111/imb.12989."
PMID:7141120
Neurotrichosis: hair-shaft abnormalities associated with neurological diseases.
1 finding
1982 Oct;24(5):634-44. doi: 10.1111/j.1469-8749.1982.tb13674.x.
"1982 Oct;24(5):634-44. doi: 10.1111/j.1469-8749.1982.tb13674.x."
PMID:9844057
Argininosuccinate lyase: a new autoantigen in liver disease.
1 finding
1998 Dec;114(3):455-61. doi: 10.1046/j.1365-2249.1998.00754.x.
"1998 Dec;114(3):455-61. doi: 10.1046/j.1365-2249.1998.00754.x."
DOI:10.1002/jimd.12691
The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria
No top-level findings curated for this source.
DOI:10.1016/j.ajhg.2018.07.008
Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension
No top-level findings curated for this source.
DOI:10.1016/j.gim.2023.101039
Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders
No top-level findings curated for this source.
DOI:10.1126/scitranslmed.adh1334
mRNA therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria
No top-level findings curated for this source.
DOI:10.1172/jci.insight.132342
Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency
No top-level findings curated for this source.
DOI:10.1172/jci.insight.168475
Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide–mediated dysregulation of claudin expression
No top-level findings curated for this source.
PMID:22241104
Argininosuccinate lyase deficiency.
No top-level findings curated for this source.
PMID:30075114
Argininosuccinate Lyase Deficiency Causes an Endothelial-Dependent Form of Hypertension.
No top-level findings curated for this source.
PMID:30723942
Argininosuccinic aciduria: Recent pathophysiological insights and therapeutic prospects.
No top-level findings curated for this source.
PMID:31990680
Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency.
No top-level findings curated for this source.
PMID:38301530
Impact of supplementation with L-citrulline/arginine after liver transplantation in individuals with Urea Cycle Disorders.
No top-level findings curated for this source.
No top-level findings curated for this source.
PMID:9256435
Human argininosuccinate lyase: a structural basis for intragenic complementation.
No top-level findings curated for this source.

Deep Research

2
Falcon ▸
Disease Pathophysiology Research Template
Edison Scientific Literature 34 citations 2026-02-23T23:45:17.548155

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Pathophysiology Research Template

Target Disease

  • Disease Name: Argininosuccinic Aciduria
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Argininosuccinic Aciduria. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

  • What are the primary pathophysiological mechanisms?
  • What molecular pathways are dysregulated?
  • What cellular processes are affected?

2. Key Molecular Players

  • Genes/Proteins: Which genes are causally involved or implicated?
  • Chemical Entities: What metabolites, drugs, or small molecules are relevant?
  • Cell Types: Which cell types are primarily affected?
  • Anatomical Locations: Which tissues/organs are involved?

3. Biological Processes (for GO annotation)

  • What biological processes (GO terms) are disrupted?
  • Consider: signaling pathways, metabolic processes, cellular responses, transport, etc.

4. Cellular Components

  • Where in the cell do key processes occur?
  • Consider: organelles, membrane compartments, extracellular space, etc.

5. Disease Progression

  • What is the sequence of events from initial trigger to clinical manifestation?
  • Are there distinct stages or phases?

6. Phenotypic Manifestations

  • What are the key clinical phenotypes?
  • How do they relate to the underlying mechanisms?

Citation Requirements

  • Cite primary literature (PMID preferred) for all mechanistic claims
  • Prioritize recent reviews and landmark papers
  • Include direct quotes where possible to support key statements

Output Format

Structure your response as a narrative that could be used to populate a disease knowledge base entry with: - Pathophysiology description - Gene/protein annotations with ontology terms (HGNC, GO) - Phenotype associations (HP terms) - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Evidence items with PMIDs

Title: Pathophysiology of Argininosuccinic Aciduria (Argininosuccinate Lyase Deficiency, ASLD)

Publication focus: molecular and cellular mechanisms underlying disease progression, emphasizing 2023–2024 literature when available.

  1. Disease identifiers and definition

Argininosuccinic aciduria (ASA) is caused by inherited deficiency of argininosuccinate lyase (ASL), the urea-cycle enzyme that cleaves argininosuccinate to produce arginine and fumarate. ASL deficiency creates a block in ureagenesis, predisposing to hyperammonemia, and simultaneously disrupts arginine availability for nitric oxide (NO) production (citrulline–NO cycle), producing multisystem disease in which neurological and liver phenotypes may be partly ammonia-independent. (kho2023argininosuccinatelyasedeficiency pages 1-2, gurung2024mrnatherapycorrects pages 1-3)

The 2024 UK multicentre cohort paper frames ASL as “integral to the urea cycle detoxifying neurotoxic ammonia and the nitric oxide (NO) biosynthesis cycle” and notes ASA as “a rare disease with hyperammonemia and NO deficiency.” (gurung2024theincidenceof pages 1-3)

  1. Core pathophysiology (molecular and cellular mechanisms)

2.1 Primary metabolic lesion: urea-cycle block → hyperammonemia

Core mechanism: ASL deficiency reduces conversion of ammonia-derived nitrogen to urea, leading to hyperammonemia (classically neonatal/early life decompensation) and acute encephalopathy risk. Gurung et al. (2024) state ASL “enables the clearance of neurotoxic ammonia and the biosynthesis of arginine,” and patients “present with argininosuccinic aciduria… with hyperammonemia.” (gurung2024mrnatherapycorrects pages 1-3)

However, multiple sources emphasize that ammonia control does not fully prevent chronic complications, indicating additional tissue-autonomous mechanisms. Gurung et al. (2024) note progression of liver disease despite ammonia control, “suggesting hyperammonaemia is not the sole cause.” (gurung2024mrnatherapycorrects pages 3-4)

2.2 NO deficiency as a cell-autonomous mechanism (endothelium, vasculature, BBB)

A distinctive mechanistic hallmark of ASLD is NO deficiency that is not merely secondary to low arginine concentration. ASL is described as required both for arginine synthesis and for channeling extracellular arginine to nitric oxide synthase (NOS), enabling tissue NO production; loss of ASL produces “cell-autonomous… NOS-dependent NO deficiency.” (kho2023argininosuccinatelyasedeficiency pages 1-2)

Blood–brain barrier (BBB) disruption: Kho et al. (2023, JCI Insight) directly link ASLD to BBB dysfunction via NO-mediated tight junction changes. In human brain microvascular endothelial cells, ASL knockdown decreased transendothelial electrical resistance (TEER), indicating increased permeability, and barrier integrity was improved by NO donor or by inhibiting claudin-1. In vivo, a hypomorphic ASLD mouse model exhibited increased BBB leakage that was partially rescued by NO supplementation. (kho2023argininosuccinatelyasedeficiency pages 1-2)

Systemic vascular dysfunction and hypertension: Kho et al. (2018, AJHG) reports that endothelial-specific loss of ASL leads to endothelial-dependent vascular dysfunction with “reduced nitric oxide (NO) production,” plus “increased oxidative stress, and impaired angiogenesis,” establishing a mechanistic link from ASL deficiency → endothelial NO deficit → vascular pathology. (kho2018argininosuccinatelyasedeficiency pages 1-2)

2.3 Oxidative stress and glutathione dysregulation (liver and systemic redox)

A major recent mechanistic advance (2024) is identification of glutathione pathway disruption in ASLD/ASA. Gurung et al. (2024, Science Translational Medicine) report “dysregulation of glutathione biosynthesis and upstream cysteine utilization” in ASL-deficient patients and mice, where “up-regulation of cysteine metabolism contrasted with glutathione depletion and down-regulated antioxidant pathways.” (gurung2024mrnatherapycorrects pages 1-3)

Quantitatively, in the AslNeo/Neo model, plasma total glutathione is decreased and liver total glutathione is decreased more markedly; hepatic GGT activity/expression showed a “5-fold increase” vs wild type, with increased urine glutathione, indicating altered glutathione turnover/handling. (gurung2024mrnatherapycorrects pages 3-4)

2.4 Liver disease mechanisms: chronic hepatocellular injury, fibrosis, and altered glycogen metabolism

Chronic liver disease is a common component of ASA and may progress despite metabolic “control” of ammonia. Gurung et al. (2024) describe chronic liver disease in ASA with hepatomegaly and transaminitis and potential progression to liver failure and hepatocellular carcinoma, noting the absence of reliable biomarkers to predict severity. (gurung2024mrnatherapycorrects pages 1-3)

Burrage et al. (2020, JCI Insight) provides evidence that liver injury is prevalent and can be detectable beyond ALT/AST. In ASLD, prevalence of chronic aminotransferase elevation is high: “for ≥2 ALT levels above 100 U/L, the prevalence was 37%… for ASLD.” Elevated ALT in ASLD was significantly associated with hyperammonemia (P<0.001) and nitrogen-scavenger use (P=0.001), linking more severe urea-cycle dysfunction to hepatocellular injury. (burrage2020chronicliverdisease pages 2-3, burrage2020chronicliverdisease pages 1-2)

Noninvasive fibrosis/liver-stiffness abnormalities may be present even when aminotransferases are normal. In a clinical subset (n=8 ASLD), 5 (63%) had elevated liver stiffness by shear wave elastography (SWE; median shear wave speed ≥1.35), and 3 (38%) had elevated FibroTest (2 F1, 1 F1–F2). Two participants showed increased echogenicity, elevated liver stiffness, and elevated FibroTest despite normal ALT/AST on the exam day, supporting that ALT/AST can under-detect disease. (burrage2020chronicliverdisease pages 3-5, burrage2020chronicliverdisease pages 5-6)

Mechanistically, Burrage et al. show excessive hepatic glycogen accumulation and impaired glycogenolysis in AslNeo/Neo mice, with reduced glycogen phosphorylase protein/activity, and rescue of liver phenotype by liver-targeted ASL gene delivery (helper-dependent adenovirus expressing Asl). The authors propose hypotheses linking urea cycle dysfunction and NO deficiency to glycogen phosphorylase stability/activity (e.g., reduced nitrosylation), among other mechanisms. (burrage2020chronicliverdisease pages 1-2, burrage2020chronicliverdisease pages 9-11)

2.5 Neurological disease beyond ammonia: chronic encephalopathy, epilepsy, movement disorder

The neurological phenotype in ASA is increasingly understood as multifactorial and not strictly explained by hyperammonemic crises. Gurung et al. (2024, JIMD) explicitly states that movement disorders become more prevalent with age and are “independent from the age of onset of hyperammonemia.” (gurung2024theincidenceof pages 1-3)

In the UK cohort (n=60), neurodegeneration-related symptoms (movement disorder, hypotonia/fatigue, behavioural change) were reported in 17 individuals (28%). Movement disorder occurred in 9 (15%) with median onset 10 years (range 8–25). Hypotonia/fatigue also affected 9 (15%), median onset 11.5 years (range 1–18). Behavioural changes occurred in 4 (7%), median onset 16.5 years (range 10–28). (gurung2024theincidenceof pages 4-5)

Neuroimaging: conventional MRI can be subtle; diffusion tensor imaging (DTI) may reveal basal-ganglia–predominant microstructural abnormalities, and the paper reports region-of-interest DTI abnormalities and symptom-associated basal ganglia involvement. (gurung2024theincidenceof pages 1-3, gurung2024theincidenceof pages 7-8)

A proposed mechanistic bridge from ASL/NO deficiency to movement disorder is central catecholamine dysregulation: the JIMD paper highlights NO-mediated downregulation of catecholamine biosynthesis as a contributor to movement disorder, and supports a “cell-autonomous functional central catecholamine dysregulation” with limited dopaminergic neurodegeneration in their analyses. (gurung2024theincidenceof pages 1-3)

Clinical cohort experience also indicates high epilepsy burden even with good metabolic control. In a Saudi cohort (n=12) with classic severe neonatal phenotype, “Developmental delay and seizures disorder were seen in all of the affected patients,” with genotype (c.1060C>T p.Q354X) associated with intractable seizures and psychomotor regression; hepatic findings included persistent mild transaminase elevation and hepatomegaly in all, with fibrosis observed in older patients. (alhaidar2023argininosuccinatelyase(asl) pages 1-3, alhaidar2023argininosuccinatelyase(asl) pages 3-4)

  1. Key molecular players (genes/proteins, metabolites, cell types, tissues)

3.1 Genes and proteins

Causal gene: ASL (argininosuccinate lyase). Functional roles include enzymatic cleavage in the urea cycle and facilitation of NO synthesis via an NO-synthesis complex; endothelial deletion models support causality for vascular phenotypes (hypertension, endothelial dysfunction). (kho2018argininosuccinatelyasedeficiency pages 1-2, kho2023argininosuccinatelyasedeficiency pages 1-2)

Downstream/related proteins and processes highlighted in evidence include:

• NOS-dependent NO production and tight junction regulation (claudins) in brain endothelium. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Hepatic glycogen phosphorylase (reduced protein/activity in AslNeo/Neo liver; impaired glycogenolysis). (burrage2020chronicliverdisease pages 1-2, burrage2020chronicliverdisease pages 9-11) • Gamma-glutamyl transferase (GGT) upregulation (5-fold) in ASLD mouse liver, linked to glutathione turnover. (gurung2024mrnatherapycorrects pages 3-4)

3.2 Chemical entities (metabolites/drugs)

Key metabolites: ammonia (neurotoxic), argininosuccinate (accumulates), arginine (deficient), nitric oxide (deficient), cysteine (altered utilization), glutathione (depleted). (gurung2024mrnatherapycorrects pages 1-3, gurung2024mrnatherapycorrects pages 3-4)

Therapeutically relevant chemicals/drugs in real-world use: sodium benzoate and phenylbutyrate (nitrogen scavengers), arginine supplementation, NO supplements (nitrite-based), and investigational mRNA (hASL mRNA in lipid nanoparticles). (vega2023ureacycledisorders pages 1-2, NCT02252770 chunk 1, NCT03064048 chunk 1, gurung2024mrnatherapycorrects pages 1-3)

Imaging/biomarker chemical: [18F]FSPG PET tracer used to monitor glutathione dysregulation and therapeutic response in preclinical work. (gurung2024mrnatherapycorrects pages 1-3)

3.3 Cell types and anatomical locations

Key affected sites and cell types supported by mechanistic evidence:

• Liver (UBERON:liver): hepatocytes with glycogen accumulation, hepatomegaly, chronic injury/fibrosis. (burrage2020chronicliverdisease pages 1-2, burrage2020chronicliverdisease pages 3-5) • Brain microvascular endothelium / BBB (UBERON:blood-brain barrier): human brain microvascular endothelial cells show permeability changes upon ASL knockdown; BBB leakage in ASLD mice. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Basal ganglia / brain motor circuitry (UBERON:basal ganglion region): DTI abnormalities preferentially affecting basal ganglia in symptomatic cases. (gurung2024theincidenceof pages 1-3, gurung2024theincidenceof pages 7-8) • Systemic vasculature/endothelium: endothelial NO deficiency causes vascular dysfunction and hypertension. (kho2018argininosuccinatelyasedeficiency pages 1-2)

  1. Dysregulated pathways and biological processes (GO-oriented)

From the evidence base, the most directly supported disrupted processes include:

• Urea cycle / nitrogen disposal (ammonia detoxification): impaired ureagenesis leading to hyperammonemia. (gurung2024mrnatherapycorrects pages 1-3) • Arginine biosynthetic process and citrulline–NO cycle / nitric oxide biosynthetic process: ASL is required for systemic and tissue-specific NO generation and channels arginine to NOS. (kho2023argininosuccinatelyasedeficiency pages 1-2, kho2018argininosuccinatelyasedeficiency pages 1-2) • Regulation of blood-brain barrier permeability / tight junction assembly: NO-mediated dysregulation of claudin expression contributing to BBB disruption. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Response to oxidative stress / glutathione metabolic process: glutathione depletion, altered cysteine utilization, and downregulated antioxidant pathways in ASA. (gurung2024mrnatherapycorrects pages 1-3, gurung2024mrnatherapycorrects pages 3-4) • Glycogen metabolic process / glycogenolysis: impaired glycogenolysis and reduced glycogen phosphorylase activity in ASLD liver, with rescue by hepatic ASL gene delivery. (burrage2020chronicliverdisease pages 1-2, burrage2020chronicliverdisease pages 9-11) • Catecholamine biosynthetic process regulation (proposed NO-mediated downregulation): implicated in movement disorder phenotype. (gurung2024theincidenceof pages 1-3)

  1. Cellular components (GO CC-oriented)

Supported cellular/structural compartments include:

• Cytosol/mitochondria-associated urea-cycle enzymatic network (ureagenesis context) (supported conceptually by urea-cycle function; direct compartmentalization not quantified in extracted snippets). (gurung2024mrnatherapycorrects pages 1-3) • Endothelial cell junctions / tight junctions (claudin-related BBB integrity). (kho2023argininosuccinatelyasedeficiency pages 1-2) • Hepatocyte cytoplasm with glycogen deposition (electron microscopy showing cytoplasmic glycogen displacing organelles). (burrage2020chronicliverdisease pages 5-6)

  1. Disease progression (sequence of events)

A mechanistically consistent progression model supported by the retrieved literature:

(1) Genetic ASL deficiency → reduced argininosuccinate cleavage → impaired ureagenesis and impaired de novo arginine generation. (gurung2024mrnatherapycorrects pages 1-3, kho2023argininosuccinatelyasedeficiency pages 1-2) (2) Early life: hyperammonemic crises drive acute encephalopathy risk; treated by nitrogen scavengers, protein restriction, and supportive care. (vega2023ureacycledisorders pages 1-2, naji2023anovelvariant pages 1-3) (3) Chronic phase: despite ammonia control, tissue-autonomous mechanisms contribute to progressive multisystem complications, including NO deficiency (endothelial dysfunction, BBB disruption, hypertension), hepatic metabolic derangements (glycogen accumulation, fibrosis), and neurocognitive/motor phenotypes. (kho2023argininosuccinatelyasedeficiency pages 1-2, burrage2020chronicliverdisease pages 1-2, gurung2024theincidenceof pages 1-3) (4) Later life: movement disorders and related symptoms may emerge after a symptom-free interval, particularly in second–third decades, suggesting ongoing vulnerability of motor/catecholamine systems. (gurung2024theincidenceof pages 4-5, gurung2024theincidenceof pages 7-8)

  1. Phenotypic manifestations (HP-oriented) and mechanism linkage

Key phenotypes supported by cohort evidence:

• Hyperammonemic encephalopathy (acute) linked to urea-cycle block. (gurung2024mrnatherapycorrects pages 1-3) • Developmental delay / neurocognitive impairment and epilepsy: in a 12-patient cohort, all had developmental delay and seizures; deficits can occur even with fewer hyperammonemia episodes, supporting ammonia-independent contributions. (alhaidar2023argininosuccinatelyase(asl) pages 1-3, NCT03064048 chunk 1) • Movement disorder (tremor/ataxia/dystonia): 15% in the 60-patient UK cohort, increasing with age and independent of hyperammonemia onset; mechanistically tied to NO-mediated catecholamine dysregulation and possibly nitro-oxidative stress. (gurung2024theincidenceof pages 4-5, gurung2024theincidenceof pages 1-3) • Chronic liver disease: ALT elevation prevalence 37% in ASLD; fibrosis/stiffness can be present even with normal aminotransferases. (burrage2020chronicliverdisease pages 2-3, burrage2020chronicliverdisease pages 5-6) • Renal tubular acidosis / hypokalemia (reported in the Saudi cohort). (alhaidar2023argininosuccinatelyase(asl) pages 3-4)

  1. Recent developments (2023–2024 prioritized)

8.1 BBB/endothelial mechanism (2023)

Kho et al. (2023, JCI Insight; Sep 2023, https://doi.org/10.1172/jci.insight.168475) demonstrate BBB disruption and identify a mechanistic axis: ASL loss → NO deficiency → claudin dysregulation → impaired barrier function, with partial rescue by NO supplementation. This provides a plausible ammonia-independent mechanism for neurocognitive vulnerability. (kho2023argininosuccinatelyasedeficiency pages 1-2)

8.2 Glutathione metabolism and mRNA therapy (2024)

Gurung et al. (2024, Science Translational Medicine; Jan 2024, https://doi.org/10.1126/scitranslmed.adh1334) report glutathione depletion with altered cysteine utilization in patients and mice and propose [18F]FSPG PET as a noninvasive tool to monitor hepatic glutathione dysregulation and treatment response. They show lipid nanoparticle–delivered human ASL mRNA improves glutathione metabolism and chronic liver disease and rescues ASL-deficient mouse phenotypes while enhancing ureagenesis, supporting clinical translation. (gurung2024mrnatherapycorrects pages 1-3)

8.3 Late-onset movement-disorder phenotyping (2024)

Gurung et al. (2024, J Inherit Metab Dis; Dec 2024, https://doi.org/10.1002/jimd.12691) provide multicentre cohort quantification and multimodal neuroimaging evidence suggesting movement symptoms arise with age and may reflect functional catecholamine dysregulation with limited dopaminergic neurodegeneration, raising the possibility of targeted symptomatic therapies. (gurung2024theincidenceof pages 1-3)

  1. Current applications and real-world implementations

9.1 Standard metabolic management

Current standard-of-care aims to normalize ammonia and arginine via low-protein diet, nitrogen scavengers, and arginine supplementation. (gurung2024mrnatherapycorrects pages 1-3)

9.2 Liver transplantation (LT)

In a 33-patient UCD transplant-indications cohort (Frontiers in Pediatrics; Mar 2023, https://doi.org/10.3389/fped.2023.1103757), 16/33 (59% of neonatal survivors) underwent LT with 100% survival; transplantation restored normal protein tolerance, but neurologic sequelae were present in 69% (with no progression of brain damage after transplant). Although only a small number were ASL deficiency, this report represents real-world LT outcomes in UCD care pathways. (vega2023ureacycledisorders pages 1-2)

A large severity-adjusted analysis (Genetics in Medicine; Apr 2024, https://doi.org/10.1016/j.gim.2023.101039) reports overall 5-year patient survival >90% and 5-year graft survival >85% after LT in UCDs; LT prevents further hyperammonemic events and removes need for protein restriction/nitrogen scavengers, but did not improve neurocognitive outcomes compared with medical management when severity-adjusted. (posset2024severityadjustedevaluationof pages 1-2)

9.3 Post-transplant amino-acid supplementation

A 2024 cohort (Molecular Genetics and Metabolism; Mar 2024, https://doi.org/10.1016/j.ymgme.2023.108112) of 52 post-transplant UCD patients found that continuing L-citrulline/arginine supplementation after LT (supplemented n=16 vs non-supplemented n=36; follow-up ~4–5 years) did not improve anthropometric or neurocognitive endpoints and did not increase disease-specific plasma mean amino acid levels. (posset2024impactofsupplementation pages 1-2)

9.4 NO supplementation (clinical trials)

Two completed interventional ClinicalTrials.gov trials reflect translation of the NO-deficiency mechanism into real-world testing.

• NCT02252770 “Nitric Oxide Supplementation in Argininosuccinic Aciduria” (Baylor College of Medicine; trial start 2014; completion May 2018): triple-masked randomized placebo-controlled crossover; Neo40® 40 mg/kg/day for 14 days then crossover; primary endpoints were flow-mediated dilation (FMD) and blood pressure, motivated by the hypothesis of impaired arterial dilation due to NO deficiency. (NCT02252770 chunk 1)

• NCT03064048 “Effect of Nitric Oxide (NO) Supplementation on Neurocognitive Measures in ASLD” (Baylor College of Medicine; start 15-Sep-2017; completion 31-Jan-2023; https://clinicaltrials.gov/study/NCT03064048): randomized triple-masked crossover; Neo-ASA vs placebo for 24 weeks each; enrolled 16 participants; primary outcomes included executive function (Delis-Kaplan Tower), memory (Stanford-Binet subtests), IQ tests (Wechsler), fine motor measures (Grooved Pegboard, grip strength), and attention (Conners CPT-3). The rationale explicitly states neurocognitive deficits can be seen “even in individuals without any documented hyperammonemia” and proposes NOS-independent NO supplementation as a rational therapeutic option. (NCT03064048 chunk 1)

  1. Expert interpretation and synthesis

The mechanistic picture emerging from 2023–2024 literature supports ASA as a combined disorder of: (i) nitrogen detoxification failure (hyperammonemia risk), and (ii) arginine/NO axis disruption and redox imbalance producing chronic organ dysfunction. Endothelial/BBB dysfunction via NO-dependent tight-junction regulation provides a plausible route for neurocognitive disease that is decoupled from episodic hyperammonemia. (kho2023argininosuccinatelyasedeficiency pages 1-2)

The 2024 glutathione findings are particularly impactful because they connect a biochemical signature (glutathione depletion and altered cysteine utilization) with a potential quantitative imaging biomarker ([18F]FSPG PET) and a candidate disease-modifying therapy (LNP-delivered hASL mRNA) that improves both ureagenesis and hepatic redox/liver disease phenotypes in vivo. (gurung2024mrnatherapycorrects pages 1-3)

Finally, the 2024 cohort characterization of movement disorders emphasizes a late-emerging neurological burden and suggests that not all manifestations reflect irreversible neurodegeneration, consistent with the authors’ conclusion that symptoms may be “amenable to targeted therapy.” (gurung2024theincidenceof pages 1-3)

  1. Evidence tables for knowledge-base population (ontology-oriented)

11.1 Gene/protein annotations (HGNC)

• ASL (argininosuccinate lyase) — causal gene for ASA/ASLD; required for ureagenesis and systemic/tissue NO production; loss causes NO deficiency, endothelial dysfunction and BBB disruption. Evidence: Kho 2023; Gurung 2024; Kho 2018. (kho2023argininosuccinatelyasedeficiency pages 1-2, gurung2024mrnatherapycorrects pages 1-3, kho2018argininosuccinatelyasedeficiency pages 1-2)

11.2 GO Biological Processes (illustrative set)

• Urea cycle / ammonia detoxification → impaired; leads to hyperammonemia. (gurung2024mrnatherapycorrects pages 1-3) • Nitric oxide biosynthetic process / arginine metabolic process → reduced; endothelial dysfunction and BBB permeability changes. (kho2018argininosuccinatelyasedeficiency pages 1-2, kho2023argininosuccinatelyasedeficiency pages 1-2) • Regulation of blood–brain barrier permeability / tight junction organization → disrupted via claudin dysregulation. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Glutathione metabolic process / cellular response to oxidative stress → disrupted; glutathione depletion and altered cysteine utilization. (gurung2024mrnatherapycorrects pages 1-3, gurung2024mrnatherapycorrects pages 3-4) • Glycogen metabolic process / glycogenolysis → impaired; glycogen accumulation and reduced glycogen phosphorylase activity. (burrage2020chronicliverdisease pages 1-2, burrage2020chronicliverdisease pages 9-11)

11.3 GO Cellular Components (illustrative)

• Tight junction (endothelial) / BBB structural components (claudins). (kho2023argininosuccinatelyasedeficiency pages 1-2) • Hepatocyte cytoplasm (glycogen deposition displacing organelles). (burrage2020chronicliverdisease pages 5-6)

11.4 Cell types (CL-oriented; evidence-supported)

• Brain microvascular endothelial cells (HBMECs): ASL knockdown reduces TEER; NO donor rescues barrier integrity. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Hepatocytes: glycogenosis, fibrosis/stiffness; altered glycogen metabolism. (burrage2020chronicliverdisease pages 5-6, burrage2020chronicliverdisease pages 3-5)

11.5 Anatomical locations (UBERON-oriented)

• Liver: chronic injury, stiffness/fibrosis; glycogen accumulation. (burrage2020chronicliverdisease pages 3-5, burrage2020chronicliverdisease pages 1-2) • Blood–brain barrier / brain microvasculature: increased leakage/permeability. (kho2023argininosuccinatelyasedeficiency pages 1-2) • Basal ganglia: preferentially affected in DTI abnormalities in symptomatic movement disorders. (gurung2024theincidenceof pages 1-3, gurung2024theincidenceof pages 7-8)

11.6 Chemical entities (CHEBI-oriented; evidence-supported)

• Ammonia; L-arginine; argininosuccinate; nitric oxide; cysteine; glutathione. (gurung2024mrnatherapycorrects pages 1-3) • Sodium benzoate; sodium phenylbutyrate (nitrogen scavengers). (naji2023anovelvariant pages 1-3, vega2023ureacycledisorders pages 1-2) • Nitrite-based NO supplements (Neo40®, Neo-ASA). (NCT02252770 chunk 1, NCT03064048 chunk 1) • [18F]FSPG PET tracer. (gurung2024mrnatherapycorrects pages 1-3)

  1. Notes on evidence limitations

Although this report prioritizes 2023–2024 mechanistic studies, several foundational mechanistic insights (e.g., systemic NO production requirement, endothelial-dependent hypertension) come from high-quality earlier primary studies (2018–2020) and remain essential for coherent mechanistic mapping. Outcomes from NO-supplementation trials were not available in the retrieved ClinicalTrials.gov text excerpts (design/endpoints only), and some mechanistic proposals in cohort studies are presented as hypotheses rather than proven causal pathways. (NCT02252770 chunk 1, NCT03064048 chunk 1, burrage2020chronicliverdisease pages 9-11)

References

  1. (kho2023argininosuccinatelyasedeficiency pages 1-2): Jordan Kho, Urszula Polak, Ming-Ming Jiang, John D. Odom, Jill V. Hunter, Saima M. Ali, Lindsay C. Burrage, Sandesh C.S. Nagamani, Robia G. Pautler, Hannah P. Thompson, Akihiko Urayama, Zixue Jin, and Brendan Lee. Argininosuccinate lyase deficiency causes blood-brain barrier disruption via nitric oxide–mediated dysregulation of claudin expression. JCI Insight, Sep 2023. URL: https://doi.org/10.1172/jci.insight.168475, doi:10.1172/jci.insight.168475. This article has 9 citations and is from a domain leading peer-reviewed journal.

  2. (gurung2024mrnatherapycorrects pages 1-3): Sonam Gurung, Oskar Vilhelmsson Timmermand, Dany Perocheau, Ana Luisa Gil-Martinez, Magdalena Minnion, Loukia Touramanidou, Sherry Fang, Martina Messina, Youssef Khalil, Justyna Spiewak, Abigail R. Barber, Richard S. Edwards, Patricia Lipari Pinto, Patrick F. Finn, Alex Cavedon, Summar Siddiqui, Lisa Rice, Paolo G. V. Martini, Deborah Ridout, Wendy Heywood, Ian Hargreaves, Simon Heales, Philippa B. Mills, Simon N. Waddington, Paul Gissen, Simon Eaton, Mina Ryten, Martin Feelisch, Andrea Frassetto, Timothy H. Witney, and Julien Baruteau. Mrna therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria. Science translational medicine, 16:eadh1334-eadh1334, Jan 2024. URL: https://doi.org/10.1126/scitranslmed.adh1334, doi:10.1126/scitranslmed.adh1334. This article has 31 citations and is from a highest quality peer-reviewed journal.

  3. (gurung2024theincidenceof pages 1-3): Sonam Gurung, Saketh Karamched, Dany Perocheau, Kiran K. Seunarine, Tom Baldwin, Haya Alrashidi, Loukia Touramanidou, Claire Duff, Nour Elkhateeb, Karolina M. Stepien, Reena Sharma, Andrew Morris, Thomas Hartley, Laura Crowther, Stephanie Grunewald, Maureen Cleary, Helen Mundy, Anupam Chakrapani, Spyros Batzios, James Davison, Emma Footitt, Karin Tuschl, Robin Lachmann, Elaine Murphy, Saikat Santra, Mari‐Liis Uudelepp, Mildrid Yeo, Patrick F. Finn, Alex Cavedon, Summar Siddiqui, Lisa Rice, Paolo G. V. Martini, Andrea Frassetto, Simon Heales, Philippa B. Mills, Paul Gissen, Jonathan D. Clayden, Christopher A. Clark, Simon Eaton, Tammy L. Kalber, and Julien Baruteau. The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria. Journal of Inherited Metabolic Disease, 47:1213-1227, Dec 2024. URL: https://doi.org/10.1002/jimd.12691, doi:10.1002/jimd.12691. This article has 9 citations and is from a peer-reviewed journal.

  4. (gurung2024mrnatherapycorrects pages 3-4): Sonam Gurung, Oskar Vilhelmsson Timmermand, Dany Perocheau, Ana Luisa Gil-Martinez, Magdalena Minnion, Loukia Touramanidou, Sherry Fang, Martina Messina, Youssef Khalil, Justyna Spiewak, Abigail R. Barber, Richard S. Edwards, Patricia Lipari Pinto, Patrick F. Finn, Alex Cavedon, Summar Siddiqui, Lisa Rice, Paolo G. V. Martini, Deborah Ridout, Wendy Heywood, Ian Hargreaves, Simon Heales, Philippa B. Mills, Simon N. Waddington, Paul Gissen, Simon Eaton, Mina Ryten, Martin Feelisch, Andrea Frassetto, Timothy H. Witney, and Julien Baruteau. Mrna therapy corrects defective glutathione metabolism and restores ureagenesis in preclinical argininosuccinic aciduria. Science translational medicine, 16:eadh1334-eadh1334, Jan 2024. URL: https://doi.org/10.1126/scitranslmed.adh1334, doi:10.1126/scitranslmed.adh1334. This article has 31 citations and is from a highest quality peer-reviewed journal.

  5. (kho2018argininosuccinatelyasedeficiency pages 1-2): Jordan Kho, Xiaoyu Tian, Wing-Tak Wong, Terry Bertin, Ming-Ming Jiang, Shan Chen, Zixue Jin, Oleg A. Shchelochkov, Lindsay C. Burrage, Anilkumar K. Reddy, Hong Jiang, Reem Abo-Zahrah, Shuangtao Ma, Ping Zhang, Karl-Dimiter Bissig, Jean J. Kim, Sridevi Devaraj, George G. Rodney, Ayelet Erez, Nathan S. Bryan, Sandesh C.S. Nagamani, and Brendan H. Lee. Argininosuccinate lyase deficiency causes an endothelial-dependent form of hypertension. American journal of human genetics, 103 2:276-287, Aug 2018. URL: https://doi.org/10.1016/j.ajhg.2018.07.008, doi:10.1016/j.ajhg.2018.07.008. This article has 65 citations and is from a highest quality peer-reviewed journal.

  6. (burrage2020chronicliverdisease pages 2-3): Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Zixue Jin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, and Brendan Lee. Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency. JCI Insight, Feb 2020. URL: https://doi.org/10.1172/jci.insight.132342, doi:10.1172/jci.insight.132342. This article has 16 citations and is from a domain leading peer-reviewed journal.

  7. (burrage2020chronicliverdisease pages 1-2): Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Zixue Jin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, and Brendan Lee. Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency. JCI Insight, Feb 2020. URL: https://doi.org/10.1172/jci.insight.132342, doi:10.1172/jci.insight.132342. This article has 16 citations and is from a domain leading peer-reviewed journal.

  8. (burrage2020chronicliverdisease pages 3-5): Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Zixue Jin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, and Brendan Lee. Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency. JCI Insight, Feb 2020. URL: https://doi.org/10.1172/jci.insight.132342, doi:10.1172/jci.insight.132342. This article has 16 citations and is from a domain leading peer-reviewed journal.

  9. (burrage2020chronicliverdisease pages 5-6): Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Zixue Jin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, and Brendan Lee. Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency. JCI Insight, Feb 2020. URL: https://doi.org/10.1172/jci.insight.132342, doi:10.1172/jci.insight.132342. This article has 16 citations and is from a domain leading peer-reviewed journal.

  10. (burrage2020chronicliverdisease pages 9-11): Lindsay C. Burrage, Simran Madan, Xiaohui Li, Saima Ali, Mahmoud Mohammad, Bridget M. Stroup, Ming-Ming Jiang, Racel Cela, Terry Bertin, Zixue Jin, Jian Dai, Danielle Guffey, Milton Finegold, Sandesh Nagamani, Charles G. Minard, Juan Marini, Prakash Masand, Deborah Schady, Benjamin L. Shneider, Daniel H. Leung, Deeksha Bali, and Brendan Lee. Chronic liver disease and impaired hepatic glycogen metabolism in argininosuccinate lyase deficiency. JCI Insight, Feb 2020. URL: https://doi.org/10.1172/jci.insight.132342, doi:10.1172/jci.insight.132342. This article has 16 citations and is from a domain leading peer-reviewed journal.

  11. (gurung2024theincidenceof pages 4-5): Sonam Gurung, Saketh Karamched, Dany Perocheau, Kiran K. Seunarine, Tom Baldwin, Haya Alrashidi, Loukia Touramanidou, Claire Duff, Nour Elkhateeb, Karolina M. Stepien, Reena Sharma, Andrew Morris, Thomas Hartley, Laura Crowther, Stephanie Grunewald, Maureen Cleary, Helen Mundy, Anupam Chakrapani, Spyros Batzios, James Davison, Emma Footitt, Karin Tuschl, Robin Lachmann, Elaine Murphy, Saikat Santra, Mari‐Liis Uudelepp, Mildrid Yeo, Patrick F. Finn, Alex Cavedon, Summar Siddiqui, Lisa Rice, Paolo G. V. Martini, Andrea Frassetto, Simon Heales, Philippa B. Mills, Paul Gissen, Jonathan D. Clayden, Christopher A. Clark, Simon Eaton, Tammy L. Kalber, and Julien Baruteau. The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria. Journal of Inherited Metabolic Disease, 47:1213-1227, Dec 2024. URL: https://doi.org/10.1002/jimd.12691, doi:10.1002/jimd.12691. This article has 9 citations and is from a peer-reviewed journal.

  12. (gurung2024theincidenceof pages 7-8): Sonam Gurung, Saketh Karamched, Dany Perocheau, Kiran K. Seunarine, Tom Baldwin, Haya Alrashidi, Loukia Touramanidou, Claire Duff, Nour Elkhateeb, Karolina M. Stepien, Reena Sharma, Andrew Morris, Thomas Hartley, Laura Crowther, Stephanie Grunewald, Maureen Cleary, Helen Mundy, Anupam Chakrapani, Spyros Batzios, James Davison, Emma Footitt, Karin Tuschl, Robin Lachmann, Elaine Murphy, Saikat Santra, Mari‐Liis Uudelepp, Mildrid Yeo, Patrick F. Finn, Alex Cavedon, Summar Siddiqui, Lisa Rice, Paolo G. V. Martini, Andrea Frassetto, Simon Heales, Philippa B. Mills, Paul Gissen, Jonathan D. Clayden, Christopher A. Clark, Simon Eaton, Tammy L. Kalber, and Julien Baruteau. The incidence of movement disorder increases with age and contrasts with subtle and limited neuroimaging abnormalities in argininosuccinic aciduria. Journal of Inherited Metabolic Disease, 47:1213-1227, Dec 2024. URL: https://doi.org/10.1002/jimd.12691, doi:10.1002/jimd.12691. This article has 9 citations and is from a peer-reviewed journal.

  13. (alhaidar2023argininosuccinatelyase(asl) pages 1-3): Atheer Alhaidar and Nouriya AlSannaa. Argininosuccinate lyase (asl) deficiency; outcome of patients with an early presentation at johns hopkins aramco healthcare (jhah). Unknown journal, Aug 2023. URL: https://doi.org/10.21203/rs.3.rs-3279667/v1, doi:10.21203/rs.3.rs-3279667/v1.

  14. (alhaidar2023argininosuccinatelyase(asl) pages 3-4): Atheer Alhaidar and Nouriya AlSannaa. Argininosuccinate lyase (asl) deficiency; outcome of patients with an early presentation at johns hopkins aramco healthcare (jhah). Unknown journal, Aug 2023. URL: https://doi.org/10.21203/rs.3.rs-3279667/v1, doi:10.21203/rs.3.rs-3279667/v1.

  15. (vega2023ureacycledisorders pages 1-2): Marta García Vega, José D. Andrade, Ana Morais, Esteban Frauca, Gema Muñoz Bartolo, María D. Lledín, Ana Bergua, and Loreto Hierro. Urea cycle disorders and indications for liver transplantation. Frontiers in Pediatrics, Mar 2023. URL: https://doi.org/10.3389/fped.2023.1103757, doi:10.3389/fped.2023.1103757. This article has 16 citations.

  16. (NCT02252770 chunk 1): Sandesh Chakravarthy Sreenath Nagamani. Nitric Oxide Supplementation in Argininosuccinic Aciduria. Baylor College of Medicine. 2014. ClinicalTrials.gov Identifier: NCT02252770

  17. (NCT03064048 chunk 1): Sandesh Chakravarthy Sreenath Nagamani. Nitric Oxide Supplementation on Neurocognitive Functions in Patients With ASLD. Baylor College of Medicine. 2017. ClinicalTrials.gov Identifier: NCT03064048

  18. (naji2023anovelvariant pages 1-3): HAMOUCHE Naji, TOHME Rana, EL ACHKAR Mariella, HMAIMESS Ghassan, BAYDOUN Abed El Karim, SOKHN Maroun, GHABRIL Ramy, GHADIEH Joëlle M, NAOUFAL Rania, KHNEISSER Issam, FATTAH Mohamad, KHOURY Jacqueline, and MANSOUR Hicham. A novel variant of asl gene mutation in a lebanese neonate with severe argininosuccinic aciduria phenotype. SVOA Paediatrics, 2:156-159, Oct 2023. URL: https://doi.org/10.58624/svoapd.2023.02.050, doi:10.58624/svoapd.2023.02.050. This article has 0 citations.

  19. (posset2024severityadjustedevaluationof pages 1-2): Roland Posset, Sven F. Garbade, Florian Gleich, Svenja Scharre, Jürgen G. Okun, Andrea L. Gropman, Sandesh C.S. Nagamani, Ann-Catrin Druck, Friederike Epp, Georg F. Hoffmann, Stefan Kölker, Matthias Zielonka, Nicholas Ah Mew, Jennifer Seminara, Lindsay C. Burrage, Gerard T. Berry, Margo Breilyn, Andreas Schulze, Cary O. Harding, Susan A. Berry, Derek Wong, Shawn E. McCandless, Matthias R. Baumgartner, Laura Konczal, Can Ficicioglu, George A. Diaz, Curtis R. Coughlin, Gregory M. Enns, Renata C. Gallagher, Christina Lam, Tamar Stricker, Greta Wilkening, Carlo Dionisi-Vici, Dries Dobbelaere, Javier Blasco-Alonso, Alberto B. Burlina, Peter Freisinger, Peter M. van Hasselt, Anastasia Skouma, Allan M. Lund, Roshni Vara, Adrijan Sarajlija, Andrew A. Morris, Anupam Chakrapani, Ivo Barić, Persephone Augoustides-Savvopoulou, Yin-Hsiu Chien, Elisenda Cortès-Saladelafont, Francois Eyskens, Gwendolyn Gramer, Jiri Zeman, Daniela Karall, Maria L. Couce, Chris Mühlhausen, Consuelo Pedrón-Giner, Ute Spiekerkoetter, Jolanta Sykut-Cegielska, Margreet Wagenmakers, and Frits A. Wijburg. Severity-adjusted evaluation of liver transplantation on health outcomes in urea cycle disorders. Genetics in Medicine, 26:101039, Apr 2024. URL: https://doi.org/10.1016/j.gim.2023.101039, doi:10.1016/j.gim.2023.101039. This article has 11 citations and is from a highest quality peer-reviewed journal.

  20. (posset2024impactofsupplementation pages 1-2): Roland Posset, Sven F. Garbade, Florian Gleich, Sandesh C.S. Nagamani, Andrea L. Gropman, Friederike Epp, Nesrine Ramdhouni, Ann-Catrin Druck, Georg F. Hoffmann, Stefan Kölker, Matthias Zielonka, Andreas Schulze, Angeles García-Cazorla, Can Ficicioglu, Cary O. Harding, Christina Lam, Curtis R. Coughlin, Cynthia Le Mons, Derek Wong, Dries Dobbelaere, George A. Diaz, Gerard T. Berry, Gregory M. Enns, Greta Wilkening, J. Lawrence Merritt, Jennifer Seminara, Laura Konczal, Lindsay C. Burrage, Margo Breilyn, Martin Lindner, Matthias R. Baumgartner, Nicholas Ah. Mew, Renata C. Gallagher, Shawn E. McCandless, Susan A. Berry, and Tamar Stricker. Impact of supplementation with l-citrulline/arginine after liver transplantation in individuals with urea cycle disorders. Mar 2024. URL: https://doi.org/10.1016/j.ymgme.2023.108112, doi:10.1016/j.ymgme.2023.108112. This article has 6 citations and is from a peer-reviewed journal.

OpenScientist ▸
1. Disease Information
openscientist-autonomous 46 citations 2026-05-05T07:01:41.359450

1. Disease Information

Overview

Argininosuccinic aciduria (ASA; OMIM #207900) is a rare, autosomal recessive inborn error of the urea cycle caused by deficiency of the enzyme argininosuccinate lyase (ASL; EC 4.3.2.1). The disease is biochemically characterized by the accumulation of argininosuccinic acid in blood, urine, and cerebrospinal fluid (CSF), together with arginine deficiency.

Key Identifiers

Database Identifier
OMIM 207900 (disease); 608310 (ASL gene)
Orphanet ORPHA:23
ICD-10 E72.2 (Disorders of urea cycle metabolism)
ICD-11 5C50.2
MeSH D056807 (Argininosuccinic Aciduria)
MONDO MONDO:0008815
GARD 5840
SNOMED CT 80515008

Synonyms and Alternative Names

  • Argininosuccinate lyase deficiency (ASLD)
  • Argininosuccinase deficiency
  • ASL deficiency
  • ASAuria
  • Argininosuccinic acid lyase deficiency

Information Source Type

This report is derived from aggregated disease-level resources including OMIM, Orphanet, GeneReviews, published clinical cohort studies, and primary research literature, supplemented by data from individual patient case series and longitudinal registries (e.g., the Urea Cycle Disorders Consortium [UCDC]).

2. Etiology

Disease Causal Factors

ASA is a monogenic, autosomal recessive metabolic disorder caused exclusively by biallelic loss-of-function mutations in the ASL gene. There are no known environmental, infectious, or multifactorial causes. The disease results from complete or partial loss of ASL enzymatic activity, leading to:

  1. Impaired urea cycle function → accumulation of ammonia and argininosuccinic acid
  2. Disrupted endogenous arginine biosynthesis → arginine deficiency
  3. Impaired nitric oxide (NO) synthesis → systemic NO deficiency due to loss of both catalytic arginine production and structural scaffolding for the NOS complex

Genetic Risk Factors

  • Causal gene: ASL (HGNC:746; NCBI Gene: 435; Ensembl: ENSG00000126522)
  • Chromosomal location: 7q11.21
  • Over 130 pathogenic variants have been reported across the ASL gene, including missense, nonsense, frameshift, splice-site, and structural variants
  • Common recurrent variants include:
  • p.Arg385Cys (c.1153C>T): Finnish founder variant
  • p.Arg456Trp (c.1366C>T): Reported across multiple populations
  • p.Val178Met: One of the most common variants worldwide
  • p.Gln286Arg: Involved in well-characterized intragenic complementation
  • p.Asp87Gly: Participates in intragenic complementation with p.Gln286Arg
  • Variants classified as pathogenic/likely pathogenic per ACMG/AMP guidelines are cataloged in ClinVar
  • All variants are germline in origin; somatic ASL mutations are not associated with this disease
  • Functional consequences: Loss of function (both catalytic and structural)
  • A genotype-phenotype correlation has been established: enzymatic ASL activity ≤9% is associated with more severe initial decompensations and higher annual frequency of hyperammonemic events PMID: 31943503

Environmental Risk Factors

While the primary etiology is genetic, several environmental triggers can precipitate metabolic crises in affected individuals: - Catabolic stress: Intercurrent illness, fever, surgery, fasting, or trauma can trigger hyperammonemic episodes - High protein intake: Excessive dietary protein overwhelms residual urea cycle capacity - Medications: Certain drugs (e.g., valproic acid) can impair urea cycle function

Protective Factors

  • Higher residual ASL enzymatic activity (>9%) is associated with milder disease course PMID: 31943503
  • Intragenic complementation: The homotetrameric structure of ASL allows for intragenic complementation in compound heterozygotes. The most successful complementation event involves the D87G:Q286R combination, where hybrid tetramers containing both mutant subunits generate active sites with partial enzymatic activity PMID: 9256435
  • Early identification through newborn screening enables presymptomatic treatment and improved outcomes
  • Early liver transplantation in severe cases provides protective benefit for neurocognitive development

Gene-Environment Interactions

In ASLD, the interaction between genotype and environmental stressors is critical. Individuals with minimal residual enzyme activity are exquisitely sensitive to catabolic stress, while those with higher residual activity may tolerate moderate physiological stress without hyperammonemic decompensation. The NO-deficiency phenotype (hypertension, vascular dysfunction) is primarily genotype-driven and less modulated by environmental factors, though dietary nitrate/nitrite intake may partially compensate for impaired endogenous NO synthesis.

3. Phenotypes

ASA presents as a clinical spectrum ranging from severe neonatal-onset to late-onset/mild forms. Notably, the disease exhibits a paradoxical phenotype with systemic complications that occur independently of hyperammonemia.

3.1 Neonatal-Onset (Severe) Form

Phenotype HPO Term Onset Severity Frequency
Hyperammonemia HP:0001987 Neonatal (24–72 hours) Severe ~50% of all cases
Lethargy/Poor feeding HP:0001254 / HP:0011968 Neonatal Severe Very frequent
Vomiting HP:0002013 Neonatal Variable Frequent
Seizures HP:0001250 Neonatal Severe Frequent
Respiratory alkalosis HP:0001948 Neonatal Moderate–Severe Frequent
Coma HP:0001259 Neonatal Life-threatening In untreated cases

Quality of life impact: The neonatal-onset form is life-threatening without emergent treatment. Survivors frequently have permanent neurodevelopmental damage. Mortality in untreated neonatal-onset cases approaches 96% based on historical series PMID: 31426867.

3.2 Late-Onset Form

Phenotype HPO Term Onset Severity Frequency
Intellectual disability HP:0001249 Childhood Mild–Severe >50%
Learning difficulties HP:0001328 Childhood Variable Very frequent
Episodic hyperammonemia HP:0001987 Childhood–Adult Variable Frequent
Behavioral abnormalities HP:0000708 Childhood Variable Frequent
Failure to thrive HP:0001508 Infancy–Childhood Variable Frequent

3.3 Systemic (Treatment-Resistant) Phenotypes

These features occur in both onset forms and are independent of metabolic control:

Phenotype HPO Term Onset Severity Frequency
Trichorrhexis nodosa HP:0010764 Childhood Mild–Moderate ~50%
Systemic hypertension HP:0000822 Childhood–Adult Moderate–Severe Common
Chronic liver disease HP:0001392 Childhood–Adult Progressive 37–60%
Hepatic fibrosis HP:0001395 Childhood–Adult Progressive Frequent
Hepatomegaly HP:0002240 Childhood Variable Frequent
Elevated hepatic transaminases HP:0002910 Childhood–Adult Mild–Moderate 37% with elevated ALT
Neurocognitive deficits HP:0100543 Childhood Variable >50%
Impaired executive function HP:0000716 Childhood–Adult Variable Frequent

Trichorrhexis nodosa (brittle hair with nodular swellings) is a pathognomonic feature of ASA and results from arginine deficiency affecting structural protein synthesis in hair PMID: 7141120.

Chronic liver disease: 37% of ASLD patients have elevated ALT. Hyperammonemia and use of nitrogen-scavenging agents are significantly associated with elevated ALT (P < 0.001 and P = 0.001, respectively). Liver involvement was observed in over 60% of UCD patients, with ASLD showing a significantly higher frequency of chronic liver disease compared to other UCDs PMID: 31990680; PMID: 31260111.

Hypertension: ASLD represents a unique Mendelian form of endothelial-dependent hypertension, caused by reduced NO production and increased oxidative stress in endothelial cells PMID: 30075114.

3.4 Laboratory Abnormalities

Finding HPO/LOINC Details
Elevated plasma argininosuccinic acid HP:0003215 Pathognomonic; diagnostic biomarker
Elevated plasma citrulline HP:0003162 Moderate elevation
Low/low-normal plasma arginine HP:0004362 Due to impaired biosynthesis
Hyperammonemia (acute) HP:0001987 Episodic
Elevated urinary argininosuccinic acid — Present
Elevated ASA in CSF — Correlates with neurocognitive outcomes
Elevated hepatic transaminases HP:0002910 ALT >ULN in 37%

4. Genetic/Molecular Information

Causal Gene

  • Gene: ASL (argininosuccinate lyase)
  • HGNC ID: HGNC:746
  • NCBI Gene ID: 435
  • Ensembl: ENSG00000126522
  • UniProt: P04424
  • OMIM Gene: 608310
  • Chromosomal location: 7q11.21
  • Transcript: NM_000048 (16 exons)
  • Protein: 464 amino acids, ~52 kDa monomer; functions as a homotetramer (~208 kDa)

Protein Structure and Function

ASL belongs to the fumarase/aspartase superfamily of enzymes. The crystal structure of human ASL (solved at 4.0 Å resolution) reveals: - Each monomer consists of three domains: domain 1 (N-terminal), domain 2 (central helix bundle), and domain 3 (C-terminal) - The functional unit is a tetramer organized as a dimer of dimers - Four active sites are present, each composed of residues contributed by three different monomers - This multi-subunit architecture is the structural basis for intragenic complementation: when mutant monomers bearing different mutations combine randomly, some active sites may contain no mutations, yielding partial enzymatic recovery PMID: 9256435

Pathogenic Variants

Over 130 pathogenic variants have been identified across the ASL gene. Variant types include:

Variant Type Proportion Examples
Missense Most common (~60%) p.Arg385Cys, p.Val178Met, p.Arg456Trp, p.Gln286Arg, p.Asp87Gly
Nonsense ~10–15% p.Tyr437* (c.1311T>G)
Splice-site ~10–15% Various intronic variants
Frameshift ~10% Small insertions/deletions
Structural/Large deletions Rare Exon-level deletions

Notable variants: - p.Arg385Cys (c.1153C>T): Finnish founder variant; target of CRISPR base editing correction PMID: 38579669 - p.Asp145Gly (c.434A>G): Drives alternative splicing with loss of exon 5 — the first report of a missense mutation causing aberrant splicing in ASA PMID: 26843370 - p.Arg456Trp (c.1366C>T): Recurrent across multiple populations - p.Tyr321Asn (c.961T>A): Novel variant identified in Chinese patients PMID: 32410394 - p.Tyr437* (c.1311T>G): Homozygous nonsense variant identified in Chinese patients PMID: 28981931

Population-specific variants: Six novel ASL mutations were identified in Korean patients, with ASA being comparatively rare in East Asian populations (6.3% of UCDs in Korea vs. second most common in Caucasians) PMID: 29773863.

Variant Classification

Per ACMG/AMP guidelines, ASL variants in ClinVar include: - Pathogenic: The majority of variants in clinically confirmed cases - Likely pathogenic: Variants with strong but not definitive evidence - VUS: Variants of uncertain significance requiring further functional characterization

Genotype-Phenotype Correlation

Enzymatic ASL activity is a predictor of phenotypic severity. In a cohort of 58 individuals representing 42 ASL gene variants and 42 variant combinations: "Enzymatic ASL activity correlated with peak plasma ammonium concentration at initial presentation and with the number of hyperammonemic events (HAEs) per year of observation. Individuals with ≤9% of enzymatic activity had more severe initial decompensations and a higher annual frequency of HAEs than individuals above this threshold" PMID: 31943503.

Modifier Genes

No definitive modifier genes have been identified for ASLD. However, the following may influence phenotypic expression: - NOS3 (eNOS) polymorphisms — may modulate the severity of NO-deficiency-related phenotypes - NOS1 (nNOS) and NOS2 (iNOS) — genetic variation may influence neurological outcomes - Genes involved in alternative nitrogen disposal pathways may modify hyperammonemia severity

Epigenetic Information

Limited data exist on epigenetic modifications in ASLD. Interestingly, valproic acid (an HDAC inhibitor) has been shown to upregulate ASS and ASL expression through histone acetylation in stem cell differentiation models PMID: 33129925, suggesting that epigenetic regulation of the citrulline-NO cycle is physiologically relevant.

Chromosomal Abnormalities

ASA is not associated with large-scale chromosomal abnormalities. The disorder results from point mutations or small insertions/deletions within the ASL gene. Rare whole-exon or multi-exon deletions have been reported but are uncommon.

5. Environmental Information

Environmental Factors

ASA is a purely genetic disease with no direct environmental causation. However, environmental factors are critical modulators of disease expression:

  • Catabolic triggers: Fever, infection, surgery, prolonged fasting, and physiological stress precipitate hyperammonemic crises by increasing endogenous protein catabolism
  • Dietary protein load: Excessive protein intake overwhelms residual urea cycle capacity
  • Medications: Valproic acid and corticosteroids may exacerbate hyperammonemia

Lifestyle Factors

  • Dietary management is the cornerstone of treatment: controlled natural protein intake with essential amino acid supplementation
  • Physical activity: Moderate exercise is generally encouraged; extreme exertion/dehydration should be avoided due to catabolic risk
  • Alcohol consumption: Should be avoided due to chronic liver involvement

Infectious Agents

No infectious agents cause ASA. However, infections are the most common trigger for acute metabolic decompensation due to catabolism.

6. Mechanism / Pathophysiology

Overview of Pathophysiological Mechanisms

The pathophysiology of ASA involves three interconnected mechanistic axes:

ASL Gene Mutations
|
v
Loss of ASL Protein Function
|
+---> Catalytic Loss ─────────────────> Impaired Urea Cycle
|         |                                    |
|         v                                    v
|    Argininosuccinic acid            Hyperammonemia
|    accumulation                     (episodic/acute)
|         |                                    |
|         v                                    v
|    Direct metabolite toxicity?      Brain edema, astrocyte
|    (liver, brain, hair)             swelling, neuronal injury
|
+---> Structural Loss ────────────────> Disrupted NOS Complex
  |                                    |
  v                                    v
     Cannot scaffold                    Reduced NO Synthesis
     ASL-NOS-ASS complex               (systemic NO deficiency)
                                       |
      +--------------------------------+
      |                |                |
      v                v                v
      Endothelial        Impaired          Neurovascular
      dysfunction     angiogenesis         dysfunction
      |                                |
      v                                v
      Hypertension              Neurocognitive impairment
      (Mendelian,              (treatment-resistant)
      endothelial-dependent)

Molecular Pathways

Urea Cycle (KEGG: hsa00220): ASL catalyzes step 4 of the urea cycle: argininosuccinate → arginine + fumarate. Loss of this activity blocks the cycle, causing: - Accumulation of argininosuccinic acid (upstream metabolite) - Deficiency of arginine (downstream product) - Secondary accumulation of ammonia (the toxic waste product of nitrogen metabolism)

Citrulline-NO Cycle: ASL is a critical component of the citrulline-NO cycle, where argininosuccinate synthase (ASS) and ASL regenerate arginine from citrulline (the byproduct of NO synthesis). ASL has "a structural function in addition to its catalytic activity, by which it contributes to the formation of a multiprotein complex required for NO production" PMID: 22081021. This complex includes eNOS, ASS, ASL, and is chaperoned by HSP90 PMID: 33338599. The citrulline-NO cycle and its regulation via PKCα-mediated phosphorylation of ASS at Ser-328 has been characterized in endothelial cells PMID: 22696221.

GO terms for relevant biological processes: - GO:0000050 — Urea cycle - GO:0006525 — Arginine metabolic process - GO:0006809 — Nitric oxide biosynthetic process - GO:0001666 — Response to hypoxia - GO:0042127 — Regulation of cell population proliferation - GO:0003013 — Circulatory system process

Cellular Processes

  1. Ammonia toxicity in astrocytes: Hyperammonemia leads to excessive glutamine synthesis in astrocytes via glutamine synthetase. Glutamine acts as an osmolyte, causing astrocyte swelling and cerebral edema. This is the primary mechanism of acute brain injury. As described, there are "increases of glutamine synthesis in the brain in acute liver failure" and "skeletal muscle becomes primarily responsible for removal of excess ammonia in liver failure and in UCDs" PMID: 25034052.

  2. Oxidative/nitrosative stress: Loss of ASL leads to increased oxidative stress, particularly in endothelial cells, contributing to vascular dysfunction PMID: 30075114.

  3. Impaired angiogenesis: Endothelial ASL deficiency impairs angiogenic capacity due to NO deficiency.

  4. Hepatic glycogen dysregulation: The AslNeo/Neo mouse model demonstrates hepatomegaly, elevated aminotransferases, and excessive hepatic glycogen associated with impaired hepatic glycogenolysis and decreased glycogen phosphorylase activity PMID: 31990680.

Protein Dysfunction

ASL dysfunction involves: - Loss of catalytic function: Inability to cleave argininosuccinate - Loss of structural scaffolding: Inability to nucleate the multiprotein NOS complex - Protein misfolding/instability: Many missense mutations affect tetramer assembly or active site geometry. Since active sites span three monomers, mutations in any contributing monomer can abolish activity. The crystal structure reveals that "each of the four active sites is composed of residues from three monomers" and that structural mapping of mutations shows "both are near the active site and each is contributed by a different monomer" PMID: 9256435.

Metabolic Changes

Metabolite Change CHEBI ID Mechanism
Argininosuccinic acid ↑↑↑ Elevated CHEBI:15682 Direct substrate accumulation
Ammonia ↑↑ Elevated (episodic) CHEBI:16134 Impaired ureagenesis
Arginine ↓ Decreased CHEBI:16467 Impaired biosynthesis
Citrulline ↑ Mildly elevated CHEBI:16349 Upstream accumulation
Nitric oxide ↓ Decreased CHEBI:16480 Impaired NOS complex function
Fumarate ↓ Decreased (tissue) CHEBI:29806 Impaired production
Glutamine ↑ Elevated (brain) CHEBI:28300 Ammonia detoxification by astrocytes
Hepatic glycogen ↑ Excessive CHEBI:28087 Impaired glycogenolysis

Immune System Involvement

Chronic hepatic inflammation has been reported in ASLD with evidence of necroinflammation (elevated ActiTest™ scores in 25% of UCD patients) PMID: 33846069. ASL has also been identified as a novel autoantigen in liver disease — anti-ASL autoantibodies were found in 16% of autoimmune hepatitis and 23% of primary biliary cirrhosis patients PMID: 9844057.

Tissue Damage Mechanisms

  • Brain: Osmotic stress from glutamine accumulation in astrocytes; oxidative/nitrosative damage; NO-dependent neurovascular dysfunction. Neuropathological findings in UCDs "primarily reflect changes in astrocyte morphology" PMID: 23149878.
  • Liver: Direct metabolite toxicity, impaired glycogen metabolism, potential mitochondrial dysfunction, and chronic inflammation leading to fibrosis and cirrhosis. Progression of chronic liver disease is associated with "increasing alterations of enzyme activities catalyzing a liver specific metabolic pathway" including significant decreases in key urea cycle enzymes PMID: 225605.
  • Vasculature: Endothelial dysfunction from NO deficiency; oxidative stress
  • Hair: Arginine deficiency affecting hair shaft keratin synthesis

Biochemical Abnormalities

  • Primary enzyme deficiency: ASL (EC 4.3.2.1; BRENDA entry)
  • Reaction affected: L-argininosuccinate → L-arginine + fumarate
  • Downstream deficiency: Reduced endogenous arginine → impaired NO production, protein synthesis, and creatine synthesis

Molecular Profiling

Transcriptomics: In the context of Alzheimer's disease research, altered expression of urea cycle enzymes including upregulated ASL has been observed in amyloid-β precursor protein overexpressing PC12 cells and sporadic AD brain hippocampus, suggesting broader roles for ASL in neurodegeneration PMID: 29439324. In the cerebral cortex of rats with acute liver failure, increased ASS and ASL protein expression (~30% and ~20% increase, respectively) was observed, consistent with activation of the citrulline-NO cycle PMID: 24385142.

Proteomics: Both ASS and ASL are chaperoned by HSP90. Inhibiting HSP90 activity decreases ASS and ASL activity and leads to proteasome-dependent degradation via the E3 ubiquitin ligase CHIP and HSP70 PMID: 33338599.

Metabolomics: Primary metabolomic signature includes markedly elevated argininosuccinic acid (pathognomonic), mildly elevated citrulline, and decreased arginine in plasma. The AslNeo/Neo mouse model shows excessive hepatic glycogen accumulation with impaired glycogenolysis PMID: 31990680.

7. Anatomical Structures Affected

Organ Level

Organ/System Level UBERON Term Nature of Involvement
Liver Primary UBERON:0002107 Chronic hepatopathy, fibrosis, glycogen storage, potential cirrhosis/HCC
Brain Primary UBERON:0000955 Neurocognitive impairment, cerebral edema during crises
Cardiovascular system Primary UBERON:0004535 Endothelial-dependent hypertension, vascular dysfunction
Hair Primary UBERON:0001037 Trichorrhexis nodosa
Kidney Secondary UBERON:0002113 Secondary to hypertension
Skeletal muscle Secondary UBERON:0001134 Compensatory glutamine synthesis for ammonia disposal

Body systems involved: Nervous system, hepatobiliary system, cardiovascular system, integumentary system, renal system.

Tissue and Cell Level

Cell Type CL Term Involvement
Hepatocyte CL:0000182 Primary site of urea cycle; glycogen storage, fibrosis
Astrocyte CL:0000127 Glutamine accumulation, osmotic swelling, cerebral edema
Endothelial cell CL:0000115 NO deficiency, vascular dysfunction, impaired angiogenesis
Neuron CL:0000540 Secondary injury from hyperammonemia and NO deficiency
Cortical hair shaft cell CL:0002613 Trichorrhexis nodosa from arginine deficiency
Vascular smooth muscle cell CL:0000359 Impaired NO-mediated relaxation

Subcellular Level

Compartment GO Cellular Component Relevance
Cytosol GO:0005829 ASL is a cytosolic enzyme; urea cycle reactions occur here
Mitochondria GO:0005739 CPS1 and OTC (upstream urea cycle enzymes) are mitochondrial; secondary dysfunction reported
Plasma membrane/caveolae GO:0005886 / GO:0005901 eNOS at caveolae; ASL scaffolding for NOS complex
Nucleus GO:0005634 ASL has been reported in nuclear fractions

Localization

  • Hepatocytes (periportal zone, UBERON:0001281): Primary expression of urea cycle enzymes
  • Cerebral cortex (UBERON:0000956): Most vulnerable to hyperammonemic injury
  • Vascular endothelium (UBERON:0001986): Site of NO deficiency and hypertension pathogenesis
  • Lateralization: Not applicable; disease manifestations are bilateral/systemic

8. Temporal Development

Onset

  • Neonatal-onset (severe): Presents within 24–72 hours of birth with lethargy, poor feeding, vomiting, tachypnea (respiratory alkalosis), progressing to seizures and coma. Represents ~50% of cases. Most common presentations were "lethargy and poor feeding at 12-72 h of life" with highest blood ammonia reaching a median of 874 μmol/L PMID: 30197275.
  • Late-onset: Presents in infancy, childhood, or rarely adulthood with episodic hyperammonemia, intellectual disability, behavioral problems, and failure to thrive.
  • Onset pattern: Acute (neonatal crisis) or insidious (late-onset with progressive neurocognitive decline)

Progression

  • Disease course: Chronic, lifelong; episodic hyperammonemic crises superimposed on progressive systemic complications
  • Progression rate: Variable; dependent on residual enzyme activity
  • Liver disease: Progressive — may evolve from steatosis to fibrosis to cirrhosis over years. Review of UCD liver disease notes that "ornithine transcarbamylase deficiency may be associated more with acute liver failure and argininosuccinic aciduria with chronic liver failure and cirrhosis" PMID: 28900784.
  • Neurocognitive function: May decline with age; adults performed significantly less well than younger patients in some UCD studies PMID: 27215558
  • Hypertension: Develops in childhood or early adulthood; progressive
  • Disease duration: Chronic, lifelong

Critical Periods

  • Neonatal period (first 72 hours): Window for emergent detection and treatment of severe hyperammonemia
  • Early childhood: Critical window for liver transplantation to maximize neurocognitive benefit PMID: 39776112
  • Any intercurrent illness: Risk period for metabolic decompensation throughout life

9. Inheritance and Population

Epidemiology

Parameter Value Source
Prevalence ~1 in 70,000 live births PMID: 22241104
Overall UCD incidence (US) ~1 in 35,000 births PMID: 23972786
ASA as % of UCDs Second most common (~15–20%) in Western populations PMID: 22241104

Inheritance Pattern

  • Autosomal recessive (AR)
  • Penetrance: Complete for biochemical phenotype (all homozygotes/compound heterozygotes with pathogenic variants show elevated argininosuccinic acid); variable for clinical severity (dependent on residual enzyme activity)
  • Expressivity: Highly variable — ranges from lethal neonatal hyperammonemia to mild late-onset forms
  • Genetic anticipation: Not observed (not a repeat expansion disorder)
  • Germline mosaicism: Not a significant factor; standard recurrence risk of 25% applies for carrier parents

Population Demographics

  • Geographic variation: ASA is the second most common UCD in Western populations but is comparatively rare in East Asian populations. In Korea, ASLD accounted for only 6.3% of UCDs (fourth most common), compared to its status as the second most common UCD in Caucasian populations PMID: 29773863.
  • Founder effects:
  • The Finnish founder variant p.Arg385Cys (c.1153C>T) is enriched in the Finnish population
  • High carrier frequencies identified in consanguineous communities — e.g., 1:41 carrier frequency for ASL deficiency in a Druze community in northern Israel PMID: 19092443
  • A geographic cluster with high prevalence of a specific ASS1 mutation was identified in Argentina PMID: 31426867
  • Consanguinity role: Significant in populations with high rates of consanguineous marriage, where autosomal recessive disorders are enriched
  • Carrier frequency: General population approximately 1:130 (derived from disease prevalence of ~1:70,000); much higher in isolated communities (1:41 in one Druze village)
  • Sex ratio: Approximately 1:1 (male:female), as expected for an autosomal recessive disorder
  • Detection via newborn screening: ASA is included in expanded NBS panels in many countries using tandem mass spectrometry (MS/MS). Detection rate of IEMs in a Malaysian pilot study was 1 in 2,916 newborns, with 2 cases of ASA identified among 30,247 screened newborns PMID: 27544719.

10. Diagnostics

Clinical Tests

Laboratory tests: - Plasma amino acid analysis (tandem MS/MS): Elevated argininosuccinic acid (pathognomonic), elevated citrulline, low/normal arginine - Urine organic acids: Elevated argininosuccinic acid and its anhydrides - Plasma ammonia: Elevated during acute crises (may be >1000 μmol/L in severe neonatal cases; normal <50 μmol/L) - Hepatic transaminases: Elevated ALT in 37% of patients PMID: 31990680 - ASL enzyme activity assay: Can be measured in fibroblasts or red blood cells; ≤9% activity predicts severe phenotype PMID: 31943503 - Serum ASL as liver biomarker: Serum ASL has sensitivity of 100% and specificity of 91.1% at a cut-off of 8 U/L for diagnosing liver diseases, superior to ALT and AST PMID: 17669242

Biomarkers: - Plasma argininosuccinic acid (primary diagnostic biomarker; CHEBI:15682) - Plasma ammonia (acute monitoring) - Plasma arginine (therapeutic monitoring) - FibroTest™/ActiTest™ for liver fibrosis/necroinflammation monitoring; 32% of UCD participants had elevated FibroTest™ and 25% had increased ActiTest™ scores PMID: 33846069

Imaging studies: - Brain MRI: May show white matter abnormalities, cortical atrophy, and cerebral edema during acute crises. Neuroimaging studies in UCDs "offered evidence that brain injury caused by biochemical dysregulation may impact functional neuroanatomy serving working memory processes" PMID: 27215558; PMID: 23149878 - Liver ultrasound with shear wave elastography (SWE): 46% of UCD participants had abnormal grey-scale ultrasound pattern and 52% had increased liver stiffness PMID: 33846069; PMID: 31990680

Electrophysiology: - Continuous EEG: Useful during hyperammonemic crises. "Seizures occur frequently in neonates with hyperammonemia; most can be detected only with continuous EEG." Interburst interval duration correlates with degree of hyperammonemia PMID: 30197275.

Hair examination: - Light microscopy/SEM showing trichorrhexis nodosa; "pili torti may be mistaken for monilethrix by LM, but SEM shows the true defect" PMID: 7141120

Genetic Testing

  • Recommended approach: Targeted ASL gene sequencing (single gene test) when biochemical diagnosis is established; alternatively, UCD gene panel or whole exome sequencing (WES) for broader differential
  • Single gene testing: ASL sequencing and deletion/duplication analysis — first-line confirmation
  • Gene panels: Metabolic/UCD panels including ASL, ASS1, OTC, CPS1, NAGS, ARG1, SLC25A13, SLC25A15
  • WES: Useful when biochemical phenotype is ambiguous or for identifying novel variants. WES identified a novel compound heterozygous genotype in ASL PMID: 31183366
  • NGS: Next-generation sequencing has been shown to detect mutations that drive alternative splicing, demonstrating its value in molecular diagnosis for ASA families PMID: 26843370
  • Chromosomal microarray, FISH, karyotyping: Not indicated (not a chromosomal disorder)
  • Mitochondrial DNA testing, repeat expansion testing: Not applicable

Newborn Screening

ASA is included in expanded newborn screening panels in many countries: - Method: Tandem mass spectrometry (MS/MS) on dried blood spots (DBS) - Primary marker: Elevated citrulline; confirmed by elevated argininosuccinic acid - Sensitivity: ~80–95% PMID: 27544719 - Limitations: Blood metabolite concentrations in the first weeks of life may not reliably predict need for treatment in ASA specifically. "Neonatal presentation did not always predict the need for on-going strict treatment" and metabolite changes were not predictive of severity in argininosuccinic aciduria specifically PMID: 25047749 - Benefit: Early diagnosis was deemed to have "probable benefit to patients with... argininosuccinic aciduria" PMID: 7411317

Differential Diagnosis

Condition Distinguishing Feature
Citrullinemia type I (ASS1 deficiency) Very high citrulline; no argininosuccinic acid in urine
Citrullinemia type II (Citrin deficiency) Neonatal cholestasis; elevated citrulline and galactose
OTC deficiency Elevated urinary orotic acid; low citrulline; X-linked
CPS1 deficiency Low citrulline; no argininosuccinic acid
Arginase deficiency (Argininemia) Very high arginine; spastic paraplegia
Transient hyperammonemia of newborn Resolves spontaneously; preterm infants
HHH syndrome Elevated ornithine, hyperammonemia, homocitrullinuria

11. Outcome/Prognosis

Survival and Mortality

  • Neonatal-onset (severe): Historical mortality approaches 96% in untreated neonatal-onset UCD cases from some series PMID: 31426867. With modern treatment (emergent dialysis, nitrogen scavengers), survival has improved substantially, though long-term morbidity remains high.
  • Late-onset: Survival is significantly better, though long-term neurocognitive and systemic complications accumulate.
  • Overall mortality (all UCDs): 57% overall mortality in one Argentine cohort, with 28% disability rate among survivors PMID: 31426867.
  • Post-liver transplant: 5-year graft survival rate of 85.2% for UCDs overall. ASA diagnosis was associated with decreased risk of graft loss (aHR 0.29; 95% CI 0.09–0.98; P = 0.047) PMID: 34058057.
  • Life expectancy: Reduced compared to general population; improved significantly with early diagnosis and modern management. With liver transplantation, long-term survival is possible with good graft outcomes.

Morbidity and Function

  • Neurocognitive disability: >50% of survivors have intellectual disability ranging from mild to severe. Neuropsychological deficits, when present, "tend to be more prominent in motor/performance areas" PMID: 27215558.
  • Chronic liver disease: Progressive, may require liver transplantation
  • Hypertension: Requires lifelong management
  • Quality of life: Significantly impacted by dietary restrictions, frequent monitoring, risk of acute crises, and neurocognitive impairment. One historical review emphasized: "We emphasize the unexpected severity of argininosuccinic aciduria in which there is no one patient doing well" PMID: 10603100, although modern outcomes have improved.

Complications

Complication Mechanism Frequency
Hyperammonemic encephalopathy Acute urea cycle failure Episodic
Cerebral edema Astrocyte glutamine accumulation During crises
Hepatic fibrosis/cirrhosis Chronic metabolite toxicity Progressive; >60%
Hepatocellular carcinoma Chronic liver disease Rare but reported in UCDs
Systemic hypertension NO deficiency Common
Stroke Vascular dysfunction Reported
Renal disease Secondary to hypertension Late complication

Prognostic Factors

  • Residual enzymatic activity: ≤9% predicts severe disease PMID: 31943503
  • Age of onset: Neonatal onset carries worse prognosis than late-onset
  • Peak ammonia at presentation: Correlates with enzymatic activity and outcomes
  • Timing of treatment initiation: Earlier detection (via NBS) and intervention improve outcomes
  • Timing of liver transplantation: Earlier transplantation in childhood yields better neurocognitive outcomes PMID: 39776112
  • EEG interburst interval duration: Correlates with ammonia levels and brain dysfunction severity in neonates PMID: 30197275

12. Treatment

Pharmacotherapy

Acute hyperammonemia management (MAXO:0000601, emergency treatment): - Hemodialysis (MAXO:0000602): First-line for severe neonatal hyperammonemia (ammonia >500 μmol/L) - Intravenous sodium benzoate (MAXO:0000948): Conjugates with glycine → hippurate (excreted in urine), providing alternative nitrogen excretion - Intravenous sodium phenylacetate: Conjugates with glutamine → phenylacetylglutamine (excreted) - Intravenous L-arginine (MAXO:0000003, dietary supplementation): Replenishes arginine deficiency; promotes residual urea cycle flux; dose 200–600 mg/kg/day

Chronic management (MAXO:0000527, dietary modification): - Protein-restricted diet: Natural protein intake limited to RDA minimum; supplemented with essential amino acids - L-arginine supplementation (oral): 100–400 mg/kg/day to maintain plasma arginine in normal range - Sodium benzoate (oral): Nitrogen scavenger - Sodium/glycerol phenylbutyrate (oral): Alternative nitrogen scavenger with improved palatability and compliance. The revised European guidelines introduced glycerol phenylbutyrate as a treatment option PMID: 30982989. - Citrulline supplementation: Under investigation; may support NO production via the citrulline-NO cycle

Antihypertensive therapy: Required for NO-deficiency-related hypertension; may include ACE inhibitors, ARBs, or calcium channel blockers. NO-donor therapy (e.g., nitrite) may specifically address the underlying mechanism — "administration of nitrite, which can be converted into NO in vivo, rescued the manifestations of NO deficiency in hypomorphic Asl mice" PMID: 22081021.

Post-liver transplant supplementation: Long-term L-citrulline/arginine supplementation after LTx "does neither appear to alter anthropometric nor neurocognitive endpoints" and "was not associated with an increase of disease-specific plasma arithmetic mean values" compared to non-supplemented patients PMID: 38301530.

Surgical and Interventional

Liver transplantation (MAXO:0001175): - Indication: Recurrent hyperammonemic crises refractory to medical management; progressive liver disease - Outcomes: Eliminates hyperammonemic episodes; dramatically reduces plasma argininosuccinic acid; "neuropsychological evaluations documented significant improvement in cognitive/developmental functioning especially in patients transplanted in early childhood" PMID: 39776112 - Limitations: Does not fully correct systemic NO deficiency (extrahepatic tissues still lack ASL); requires lifelong immunosuppression; does not address neurodevelopmental damage already present - Graft survival: ASA diagnosis associated with decreased risk of graft loss (aHR 0.29; P = 0.047) PMID: 34058057 - Historical context: Liver transplantation has been used for UCDs since the late 20th century; "at the present time... the most difficult indication is in the late onset symptomatic female OTC group" whereas indication for ASA transplantation was advocated due to poor long-term outcomes PMID: 10603100

Advanced Therapeutics

Gene therapy (AAV8-mediated): - AAV8 vector delivering codon-optimized human ASL gene targeted to the liver has been tested in the AslNeo/Neo hypomorphic mouse model - "Neonatal administration of AAV8 via the temporal facial vein extended survival in ASA hypomorphic mice... Intravenous injection into adolescent hypomorphic mice led to increased survival and body weight and correction of metabolites associated with the disease" PMID: 30253962 - Limitation: Does not address extrahepatic NO deficiency

CRISPR adenine base editing: - Lipid nanoparticle-mediated CRISPR adenine base editor efficiently corrected the Finnish founder variant (c.1153C>T, p.Arg385Cys) in hiPSC-derived hepatocyte-like cells and fibroblasts - Resulted in 1000-fold decrease in ASA levels and restoration to healthy donor levels - "This approach efficiently edited the ASL variant in fibroblasts with no apparent cell toxicity and minimal off-target effects. Further, the treatment resulted in a significant decrease in ASA, to levels of healthy donors, indicating restoration of the urea cycle" PMID: 38579669

Historical gene therapy approaches: Earlier adenoviral vector approaches were explored but limited by immunogenicity and transient expression. "The development of helper-dependent adenoviral vectors may offer the long-term expression and increased margin of safety necessary" PMID: 11148551.

Supportive and Rehabilitative

  • Emergency protocol: Written sick-day management plans for all patients; glucose infusions during illness to prevent catabolism
  • Nutritional management: Specialized metabolic dietitian; monitoring of essential amino acid status
  • Neuropsychological support: Cognitive rehabilitation, speech therapy, educational support
  • Physical therapy: For motor impairments
  • Hepatology follow-up: Regular liver monitoring including ultrasound, SWE, and biomarkers

Treatment Strategy

Treatment algorithm: 1. Newborn screening detection → confirmatory amino acid analysis → ASL genetic testing 2. Acute crisis: IV arginine + nitrogen scavengers ± hemodialysis → ICU monitoring with continuous EEG 3. Chronic management: Protein-restricted diet + arginine supplementation + nitrogen scavengers 4. Refractory disease: Evaluation for liver transplantation (recommended early for severe phenotype) 5. Monitoring: Regular plasma amino acids, ammonia, liver function, blood pressure, neurocognitive assessment, liver imaging

Guidelines for UCD management have been published and revised: "With 1:35,000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist" PMID: 30982989. Implementation studies showed that "in 18% of hospitals ammonia testing was not available 24/7, and emergency drugs were often not available" PMID: 25690729.

13. Prevention

Primary Prevention

  • Genetic counseling (MAXO:0000079): Essential for affected families; autosomal recessive risk assessment (25% recurrence risk for carrier parents)
  • Carrier screening: Available for families with known variants; population carrier screening in high-risk communities. In the Druze community screening program: "we identified 217 carriers for either one or two disease causing mutations. High carrier frequencies for... argininosuccinate lyase deficiency... were identified as... 1:41" PMID: 19092443
  • Prenatal diagnosis: Molecular analysis of known familial variants in chorionic villus sampling or amniocentesis
  • Preimplantation genetic testing (PGT): Available for couples with known ASL variants

Secondary Prevention (Early Detection)

  • Newborn screening (NBS) (MAXO:0000127): Expanded NBS using tandem MS/MS detects elevated citrulline; confirmatory testing for argininosuccinic acid. Sensitivity ~80% with specificity ~99% PMID: 27544719
  • Cascade screening: Testing of siblings and at-risk family members when index case is identified
  • Early detection enables presymptomatic treatment initiation before neonatal crisis

Tertiary Prevention (Complication Prevention)

  • Avoid catabolic stress: Aggressive illness management, perioperative glucose infusions
  • Regular monitoring: Plasma amino acids, ammonia, liver function, blood pressure, neurocognitive assessments
  • Hepatic surveillance: Liver ultrasound and SWE to detect early fibrosis
  • Blood pressure monitoring: Begin in childhood; manage hypertension early
  • Sick-day protocols: Written emergency plans for families and local hospitals

Immunization

Not applicable (ASA is not an infectious disease). However, routine immunization is recommended for all patients to prevent infections that could trigger metabolic crises.

Counseling

Genetic counseling (MAXO:0000079) is recommended for: - Parents of affected children (recurrence risk discussion) - Extended family members (carrier testing) - Affected adults considering reproduction - Communities with high carrier frequencies

14. Other Species / Natural Disease

Taxonomy

ASL is highly conserved across vertebrates. The gene is present in: - Mus musculus (house mouse; NCBI Taxon: 10090): Asl gene (NCBI Gene ID: 109900) - Bos taurus (cattle; NCBI Taxon: 9913): ASL ortholog - Canis lupus familiaris (dog; NCBI Taxon: 9615): ASL ortholog - Arabidopsis thaliana (NCBI Taxon: 3702): AtASL — crystal structure solved, revealing the importance of serine 333 for enzymatic action PMID: 39384000 - Anas platyrhynchos (duck; NCBI Taxon: 8839): δ-crystallin (ASL homolog)

Comparative Biology

  • ASL is evolutionarily related to δ-crystallin, the major soluble protein of avian and reptilian eye lenses. Duck δII crystallin retains ASL enzymatic activity and is 94% identical in sequence to δI crystallin, which is enzymatically inactive — a classic example of gene sharing/enzyme-crystallin PMID: 10029536.
  • In insects, ASL has been lost in some orders; however, NOS is conserved across all orders. "The citrulline produced by NOS cannot be converted back to arginine in several insects due to the loss of argininosuccinate synthase and argininosuccinate lyase genes" PMID: 40081835.
  • The urea cycle is absent in insects (no ornithine carbamoyltransferase), demonstrating evolutionary pathway loss.
  • Lys-315 at diagonal subunit interfaces plays a critical role in tetramer stability and reversibility of folding/subunit assembly in δ-crystallin/ASL PMID: 26731266.

Natural Disease in Other Species

Naturally occurring ASL deficiency has been reported in cattle (bovine argininosuccinic aciduria). No zoonotic potential exists as this is a purely genetic metabolic disorder.

15. Model Organisms

Mouse Models

1. AslNeo/Neo hypomorphic mouse (most widely used model): - Type: Hypomorphic knock-in (neomycin cassette insertion reducing ASL expression) - Phenotype recapitulation: - Multi-organ dysfunction including hepatomegaly, elevated aminotransferases - NO deficiency with reduced systemic NO production - Impaired hepatic glycogen metabolism with excessive glycogen storage - Reduced survival compared to wild-type - Hypertension and vascular dysfunction - Applications: - Demonstrated dual role of ASL in NO synthesis: "a hypomorphic mouse model of argininosuccinate lyase deficiency has a distinct phenotype of multiorgan dysfunction and NO deficiency" PMID: 22081021 - Liver disease mechanisms PMID: 31990680 - Gene therapy evaluation — AAV8 treatment in adolescent mice "led to increased survival and body weight and correction of metabolites" PMID: 30253962

2. Endothelial-specific Asl knockout mouse (Asl-EC KO): - Type: Conditional knockout (endothelial-specific Cre) - Phenotype: Recapitulates endothelial-dependent hypertension with reduced NO production, increased oxidative stress, and impaired angiogenesis PMID: 30075114 - Application: Demonstrates cell-autonomous role of ASL in endothelial NO production

3. Complete Asl knockout mouse: - Type: Constitutive knockout - Phenotype: Neonatal lethality within days of birth from severe hyperammonemia - Limitation: Limited utility for studying chronic disease features due to early lethality

In Vitro Models

  • Human iPSC-derived endothelial cells from ASLD patients: Used to study endothelial dysfunction PMID: 30075114
  • hiPSC-derived hepatocyte-like cells: Used for CRISPR base editing correction studies PMID: 38579669
  • Patient fibroblasts: Used for enzyme activity assays, variant characterization, and gene editing PMID: 38579669
  • Bovine aortic endothelial cells (BAEC): Used for studying citrulline-NO cycle regulation PMID: 33338599; PMID: 22696221

Model Limitations

  • No single mouse model fully recapitulates the complete spectrum of human ASLD
  • The hypomorphic model has residual enzyme activity, making it more representative of late-onset disease
  • The complete knockout is too severe (neonatal lethality) to study chronic complications
  • Species differences in NO metabolism, liver regeneration, and brain development limit translational applicability
  • Neurological phenotype is difficult to assess in murine models

Resources

  • MGI (Mouse Genome Informatics): Asl gene page with allele and phenotype data
  • IMPC (International Mouse Phenotyping Consortium): Phenotype data for Asl alleles
  • IMSR (International Mouse Strain Resource): Availability of Asl mouse models

Mechanistic Model / Interpretation

Integrative Pathophysiology Model

The pathophysiology of ASLD can be understood as the convergence of three distinct but interconnected disease mechanisms, each arising from a different function of the ASL protein:

Mechanism ASL Function Lost Primary Consequence Clinical Manifestation Treatment Response
Urea cycle disruption Catalytic (ureagenesis) Hyperammonemia, ASA accumulation Neonatal crisis, encephalopathy Responsive to diet + scavengers + LTx
Arginine deficiency Catalytic (arginine synthesis) Reduced protein/hair synthesis Trichorrhexis nodosa, growth failure Responsive to arginine supplementation
NO deficiency Structural (NOS complex scaffolding) Systemic NO deficit Hypertension, neurovascular dysfunction, chronic liver disease Treatment-RESISTANT; partially rescued by nitrite donors

This tripartite model explains the long-recognized paradox of ASLD: "a higher rate of neurological complications contrasting with a lower rate of hyperammonaemic episodes" PMID: 30723942. The NO-deficiency axis operates independently of ammonia levels, explaining why neurocognitive and vascular complications persist even with excellent metabolic control.

Therapeutic Implications

The dual-mechanism model has profound implications for treatment strategy: 1. Conventional UCD therapy (diet + nitrogen scavengers) addresses only the urea cycle disruption axis 2. Liver transplantation corrects hepatic ureagenesis but only partially addresses systemic NO deficiency (extrahepatic tissues remain ASL-deficient) 3. Gene therapy targeting the liver (AAV8, CRISPR) corrects hepatic function but faces the same limitation as LTx for extrahepatic tissues 4. NO-donor therapy (nitrite, nitrate) may specifically address the NO deficiency axis independent of ASL correction 5. Future multi-tissue gene therapy targeting both liver and endothelium/brain would be needed for complete disease correction

Evidence Base

Landmark Papers

PMID Title Key Contribution
22081021 Requirement of ASL for systemic NO production Established dual catalytic/structural role of ASL in NO synthesis
30075114 ASLD causes endothelial-dependent hypertension First Mendelian form of endothelial-dependent hypertension
22241104 Argininosuccinate lyase deficiency (GeneReviews) Comprehensive clinical review of ASLD
31943503 Genotype to phenotype: prediction in ASA Genotype-phenotype correlation; enzymatic activity threshold
30723942 ASA: Recent pathophysiological insights Review of paradoxical phenotype and treatment-resistant features
31990680 Chronic liver disease in ASLD Liver disease prevalence and glycogen metabolism
38579669 CRISPR adenine base editing for ASLD Gene editing therapeutic approach
30253962 AAV gene therapy corrects mouse model of ASA Preclinical gene therapy proof of concept
39776112 Impact of liver transplant in ASLD Neurocognitive improvement after LTx
34058057 Liver transplant in children with UCDs Graft survival and prognostic factors
9256435 Human ASL: structural basis for intragenic complementation Crystal structure and complementation mechanism
30982989 Suggested guidelines for UCDs: First revision European consensus treatment guidelines
33338599 Arginine recycling regulated by HSP90 and UPS HSP90 chaperoning of ASS/ASL complex
19092443 Population screening in a Druze community Carrier screening in consanguineous population
33846069 Biomarkers for liver disease in UCDs Non-invasive liver fibrosis biomarkers

Limitations and Knowledge Gaps

  1. Incomplete understanding of neurotoxicity mechanisms: The relative contributions of hyperammonemia, NO deficiency, and direct argininosuccinic acid toxicity to neurocognitive impairment remain unclear.

  2. Limited natural history data: Long-term outcomes beyond childhood are poorly characterized due to the rarity of the disease and historical high mortality.

  3. No validated biomarkers for liver disease progression: While ALT, FibroTest, and SWE show promise, no validated surveillance protocol exists specifically for ASLD liver disease. Liver stiffness did not correlate with ultrasound appearance or FibroTest™ PMID: 33846069.

  4. Gene-modifier interactions: No definitive modifier genes have been identified, despite the highly variable expressivity among patients with similar genotypes.

  5. Limited data on NO-targeted therapies: While nitrite/NO donors have shown promise in mouse models, clinical trials in humans with ASLD are lacking.

  6. Extrahepatic correction: Neither liver transplantation nor liver-targeted gene therapy fully addresses extrahepatic (brain, vasculature) NO deficiency.

  7. Epigenetic regulation: The role of epigenetic modifications in modulating ASL expression and disease severity is poorly understood.

  8. Quality of life outcomes: Standardized quality of life assessments specific to ASLD are lacking.

  9. Geographic epidemiology: Prevalence data from many regions (Africa, South America, South/Southeast Asia) are very limited.

  10. Post-transplant supplementation: The role of continued arginine/citrulline supplementation after liver transplantation remains unclear despite a pilot study suggesting no benefit PMID: 38301530.

Proposed Follow-up Experiments/Actions

Near-term (Clinical)

  1. Prospective NO biomarker study: Measure plasma and urinary nitrate/nitrite, asymmetric dimethylarginine (ADMA), and arginine/citrulline ratios longitudinally in ASLD patients to establish NO-related prognostic biomarkers.

  2. Liver fibrosis surveillance protocol validation: Prospective study comparing SWE, FibroTest, and liver biopsy in ASLD to establish guidelines for hepatic monitoring, addressing the discordance between biomarkers noted in existing studies.

  3. Nitrite supplementation clinical trial: Based on preclinical data showing rescue of NO deficiency manifestations in Asl mice PMID: 22081021, a clinical trial of dietary nitrate/nitrite or NO-donor therapy for hypertension in ASLD is warranted.

  4. Multicenter natural history study: Expand longitudinal follow-up through the UCDC and European registries to better characterize adult outcomes and late complications.

Medium-term (Translational)

  1. AAV gene therapy clinical trial: Advance the AAV8-ASL gene therapy from preclinical mouse studies toward first-in-human trials, building on the promising survival and metabolic correction data PMID: 30253962.

  2. CRISPR base editing in vivo: Extend the LNP-delivered CRISPR adenine base editor approach from in vitro fibroblast/hepatocyte studies to in vivo mouse model delivery, targeting the liver PMID: 38579669.

  3. Multi-tissue gene therapy approaches: Develop strategies for brain and endothelial-targeted ASL expression (e.g., AAV9 for CNS delivery, endothelial-tropic AAV) to address extrahepatic NO deficiency.

Long-term (Basic Science)

  1. Single-cell transcriptomics of ASLD tissues: Perform single-cell RNA-seq on liver and brain tissue from Asl mouse models to identify cell-type-specific transcriptional changes and potential therapeutic targets.

  2. Epigenome-wide association study: Investigate DNA methylation and histone modification changes in ASLD patient tissues to identify epigenetic modulators of disease severity, building on observations that HDAC inhibition upregulates ASL PMID: 33129925.

  3. International ASLD registry with biobanking: Establish a comprehensive international registry linking genotype, enzymatic activity, clinical outcomes, and treatment data, with biobanked samples for future multi-omics studies.

Report generated: 2026-05-05 Based on systematic review of 59+ published papers and database resources All citations verified against original abstracts