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Subtypes

3

NICCD (Neonatal Intrahepatic Cholestasis caused by Citrin Deficiency) MONDO:0011601

Neonatal-onset presentation with intrahepatic cholestasis, conjugated hyperbilirubinemia, hepatomegaly, and transient liver dysfunction. Usually resolves by age one year with appropriate dietary management, though liver failure and transplantation are rarely required.

FTTDCD (Failure to Thrive and Dyslipidemia caused by Citrin Deficiency)

Childhood-onset presentation characterized by growth impairment, dyslipidemia, fatigue, and food preference for protein- and lipid-rich foods with aversion to carbohydrate-rich foods. Occurs after resolution of NICCD or as the first recognized clinical stage.

CTLN2 (Adult-onset Type II Citrullinemia) MONDO:0016603

Adult-onset presentation with recurrent hyperammonemic encephalopathy, elevated plasma citrulline, neuropsychiatric symptoms, and risk of hepatocellular carcinoma. Affects approximately 5% of patients with citrin deficiency, with onset ranging from 10 to 70 years of age.

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Pathophysiology

7

SLC25A13 transporter molecular function deficiency

Biallelic SLC25A13 pathogenic variants reduce mitochondrial aspartate-glutamate carrier transport activity.

hepatocyte link

SLC25A13 link

transmembrane transporter activity link

mitochondrial inner membrane link

Downstream

Malate-aspartate shuttle dysfunction and hepatocellular energy crisis Loss of AGC2 transport function disrupts hepatic MAS redox transfer and aspartate export.

Aspartate and glutamate transmembrane transport disruption Defective carrier exchange directly reduces cytosolic aspartate availability.

Show evidence (1 reference)

PMID:37254569 SUPPORT Other

"Aspartate-glutamate carrier 2 (AGC2, citrin) is a mitochondrial carrier expressed in the liver that transports aspartate from mitochondria into the cytosol in exchange for glutamate."

Supports citrin transporter molecular dysfunction as the initiating defect.

Malate-aspartate shuttle dysfunction and hepatocellular energy crisis

Loss of citrin impairs cytosolic NADH transfer into mitochondria and reduces cytosolic aspartate, NAD+, and ATP, creating a fundamental hepatocellular energy and redox deficiency.

hepatocyte link

malate-aspartate shuttle link cellular redox homeostasis link

liver link

Downstream

Impaired hepatic glycolysis and carbohydrate toxicity MAS failure impairs cytosolic NADH disposal needed for glycolytic flux.

De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment Hepatocellular redox and energy failure disrupts lipogenesis and secondarily impairs beta-oxidation.

Impaired urea cycle and ammonia detoxification Reduced aspartate export and hepatocellular ATP deficiency limit urea-cycle nitrogen disposal.

Neonatal cholestatic hepatopathy Hepatocyte energy and redox failure presents in infancy as transient cholestatic liver disease.

Failure to thrive Hepatocellular energy deficiency contributes to growth impairment and failure to thrive.

Intellectual disability Recurrent metabolic energy failure and hyperammonemic episodes create risk for irreversible brain injury.

Show evidence (1 reference)

PMID:37254569 SUPPORT Other

"Through MAS, AGC2 is necessary to maintain intracellular redox balance, mitochondrial respiration, and ATP synthesis."

Review-level mechanistic confirmation of MAS role in redox and energy homeostasis.

Impaired hepatic glycolysis and carbohydrate toxicity

Because glycolysis depends on cytosolic NAD+ regenerated via the MAS, citrin-deficient hepatocytes cannot sustain glycolysis efficiently. Under high carbohydrate load, metabolism is blocked at the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) step, leading to accumulation of glucose metabolites, depletion of inorganic phosphate, and further ATP loss. This creates an actively harmful state termed carbohydrate toxicity.

hepatocyte link

glycolytic process link

Downstream

Impaired urea cycle and ammonia detoxification High carbohydrate load worsens ATP depletion, reducing energy available for hepatic ammonia detoxification.

Abnormal food preference Protein- and lipid-rich food preference with carbohydrate aversion reflects physiologic avoidance of carbohydrate toxicity.

Hypoglycemia Impaired glycolysis, gluconeogenesis, and hepatic energy handling contribute to recurrent hypoglycemia.

Impaired urea cycle and ammonia detoxification

Citrin deficiency limits cytosolic aspartate availability, which is required by argininosuccinate synthetase 1 (ASS1) for the urea cycle. This results in citrulline accumulation and impaired ureagenesis. Additionally, hyperammonemia may be driven by failure of glutamine-synthetase-dependent perivenous ammonia detoxification due to glutamate and ATP deficiency, rather than solely by ASS1 dysfunction.

hepatocyte link

urea cycle link glutamine biosynthetic process link

liver link

Downstream

Hyperammonemia Failed hepatic ureagenesis manifests clinically as recurrent hyperammonemia, especially in CTLN2.

Encephalopathy Recurrent hyperammonemia in CTLN2 produces neuropsychiatric and neurologic manifestations captured as hyperammonemic encephalopathy.

Seizures Severe CTLN2 hyperammonemic neurologic episodes can include convulsive seizures.

Ammonia Impaired ureagenesis raises blood or plasma ammonia concentration.

Citrulline Limited cytosolic aspartate availability at ASS1 causes citrulline accumulation.

Plasma glutamine ATP and glutamate limitation can blunt glutamine-synthetase-dependent ammonia detoxification, producing absent or low glutamine elevation despite hyperammonemia.

Pancreatitis Pancreatitis is a recognized CTLN2 complication, but the intermediate causal steps are not fully resolved in the cached evidence.

Show evidence (2 references)

PMID:20301360 SUPPORT Human Clinical

"Citrin deficiency can manifest in newborns or infants as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric..."

GeneReviews entry confirms hyperammonemia with neuropsychiatric symptoms as the adult CTLN2 presentation.

PMID:37952953 SUPPORT Human Clinical

"Citrin deficiency (CD) is a hereditary disorder caused by SLC25A13 mutations that manifests as neonatal intrahepatic cholestasis caused by CD (NICCD), failure to thrive and dyslipidemia caused by CD (FTTDCD), and adult-onset type 2 citrullinemia (CTLN2)."

Supports the age-dependent clinical spectrum including CTLN2 with urea cycle perturbation.

De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment

Citrin-deficient hepatocytes have primary defects in de novo lipogenesis and exhibit secondarily downregulated PPARalpha, leading to impaired fatty acid beta-oxidation. This dual impairment contributes to dyslipidemia and hepatic steatosis.

hepatocyte link

fatty acid biosynthetic process link fatty acid beta-oxidation link

Downstream

Dyslipidemia Impaired de novo lipogenesis and beta-oxidation disrupt circulating lipid metabolism.

Hepatic steatosis Defective lipid synthesis and fatty-acid oxidation contribute to diffuse fatty liver and severe liver steatosis.

Aspartate and glutamate transmembrane transport disruption

Citrin (AGC2) normally transports aspartate from the mitochondrial matrix to the cytosol in exchange for glutamate. Loss of this transport function impairs compartmentalized amino acid metabolism, affecting ureagenesis, gluconeogenesis, protein synthesis, and nucleotide biosynthesis.

L-aspartate transmembrane transport link

mitochondrial inner membrane link

Downstream

Impaired urea cycle and ammonia detoxification Reduced mitochondrial export of aspartate limits aspartate input into the urea cycle.

Show evidence (1 reference)

PMID:37254569 SUPPORT Other

"Aspartate-glutamate carrier 2 (AGC2, citrin) is a mitochondrial carrier expressed in the liver that transports aspartate from mitochondria into the cytosol in exchange for glutamate."

Directly describes the aspartate-glutamate exchange function of citrin.

Neonatal cholestatic hepatopathy

In NICCD, citrin deficiency manifests as transient infantile intrahepatic cholestasis with low birth weight or growth restriction, hepatomegaly, fatty liver, hepatic fibrosis or cellular infiltration, variable liver dysfunction, and hypoglycemia.

hepatocyte link

bile acid metabolic process link

liver link

Downstream

Neonatal cholestasis Transient intrahepatic cholestasis is the defining neonatal presentation.

Jaundice Cholestatic liver dysfunction presents clinically with neonatal jaundice.

Hepatomegaly Infantile cholestatic hepatopathy includes liver enlargement.

Conjugated bilirubin Intrahepatic cholestasis causes conjugated bilirubin retention.

Transaminases Variable liver dysfunction in NICCD includes abnormal liver function tests.

Low birth weight Low birth weight with growth restriction is part of the infantile NICCD presentation.

Hepatic steatosis NICCD includes diffuse fatty liver, while CTLN2 can develop severe steatosis.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Children younger than age one year have a history of low birth weight with growth restriction and transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal cellular infiltration associated with hepatic fibrosis, variable liver dysfunction, hypoproteinemia,..."

GeneReviews supports the NICCD hepatic pathology cluster.

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Pathograph

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

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Phenotypes

14

Digestive 5

Neonatal cholestasis VERY_FREQUENT Neonatal cholestatic liver disease (HP:0006566)

Show evidence (2 references)

PMID:20301360 SUPPORT Human Clinical

"Citrin deficiency can manifest in newborns or infants as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric..."

GeneReviews directly identifies NICCD as the neonatal presentation.

PMID:37063661 SUPPORT Human Clinical

"Neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD) is a common clinical phenotype of citrin deficiency in infants."

Confirms NICCD as a common infant phenotype.

Hepatomegaly FREQUENT Hepatomegaly (HP:0002240)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver"

GeneReviews directly lists hepatomegaly among NICCD hepatic findings.

Hepatic steatosis FREQUENT Hepatic steatosis (HP:0001397)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Complications include severe liver steatosis and pancreatitis."

GeneReviews directly reports severe liver steatosis as a citrin deficiency complication.

Jaundice Jaundice (HP:0000952)

Show evidence (1 reference)

PMID:37063661 SUPPORT Human Clinical

"We report 4 patients with jaundice and low body weight."

Jaundice is the presenting symptom in NICCD case reports.

Pancreatitis OCCASIONAL Pancreatitis (HP:0001733)

Pancreatitis is reported as a complication of citrin deficiency, particularly associated with CTLN2, in the clinical literature.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Complications include severe liver steatosis and pancreatitis."

GeneReviews directly reports pancreatitis as a complication.

Metabolism 3

Hyperammonemia FREQUENT Hyperammonemia (HP:0001987)

Sequelae: Encephalopathy Seizures

Show evidence (2 references)

PMID:20301360 SUPPORT Human Clinical

"Citrin deficiency can manifest in newborns or infants as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric..."

Directly identifies recurrent hyperammonemia as a key feature of CTLN2.

PMID:35142380 SUPPORT Human Clinical

"Citrin deficiency is an autosomal recessive disorder caused by mutations in the SLC25A13 gene. The disease can present with age-dependent clinical manifestations: neonatal intrahepatic cholestasis by citrin deficiency (NICCD), failure to thrive, and dyslipidemia by citrin deficiency (FTTDCD),..."

Large Japanese cohort study confirming the age-dependent clinical spectrum including hyperammonemia in CTLN2.

Dyslipidemia FREQUENT Abnormal circulating lipid concentration (HP:0003119)

Show evidence (2 references)

PMID:20301360 SUPPORT Human Clinical

"in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD)"

Directly identifies dyslipidemia as part of the FTTDCD phenotype.

PMID:35142380 SUPPORT Human Clinical

"failure to thrive, and dyslipidemia by citrin deficiency (FTTDCD)"

Large cohort confirms dyslipidemia as a defining feature of FTTDCD.

Hypoglycemia OCCASIONAL Hypoglycemia (HP:0001943)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Laboratory changes are dyslipidemia, recurrent hypoglycemia, increased lactate-to-pyruvate ratio"

GeneReviews directly reports recurrent hypoglycemia as a laboratory abnormality.

Nervous System 4

Encephalopathy FREQUENT Encephalopathy (HP:0001298)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"in adults as recurrent hyperammonemia with neuropsychiatric symptoms in citrullinemia type II (CTLN2)."

Directly describes neuropsychiatric symptoms (encephalopathy) as a feature of CTLN2.

Abnormal food preference FREQUENT Abnormal eating behavior (HP:0100738)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Often citrin deficiency is characterized by strong preference for protein-rich and/or lipid-rich foods and aversion to carbohydrate-rich foods."

GeneReviews directly reports the characteristic protein/lipid-rich preference and carbohydrate aversion.

Intellectual disability Intellectual disability (HP:0001249)

Show evidence (1 reference)

PMID:37952953 PARTIAL Human Clinical

"patients with CD often exhibit growth impairment and irreversible brain and/or liver damage."

The review supports irreversible brain damage in citrin deficiency, but does not name intellectual disability specifically.

Seizures OCCASIONAL Seizure (HP:0001250)

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"memory loss, disorientation, drowsiness, convulsive seizures, coma"

GeneReviews directly lists convulsive seizures among CTLN2 neurologic manifestations.

Growth 2

Failure to thrive FREQUENT Failure to thrive (HP:0001508)

Show evidence (1 reference)

PMID:35142380 SUPPORT Human Clinical

"Patients with citrin deficiency had an increased risk for low weight and length at birth, and CTLN2 patients had an increased risk for growth impairment during adolescence."

Large cohort study documenting growth impairment across different stages of citrin deficiency.

Low birth weight FREQUENT Small for gestational age (HP:0001518)

Show evidence (1 reference)

PMID:35142380 SUPPORT Human Clinical

"Patients with citrin deficiency had an increased risk for low weight and length at birth"

Directly quantifies increased risk for low birth parameters in citrin deficiency.

🧬

Genetic Associations

1

SLC25A13 pathogenic variants

Autosomal recessive

Show evidence (2 references)

PMID:35142380 SUPPORT Human Clinical

"Citrin deficiency is an autosomal recessive disorder caused by mutations in the SLC25A13 gene."

Nationwide study confirms SLC25A13 as the causal gene.

CGGV:assertion_bc373b9e-ec5e-4471-92a1-bbdd9aa3378c-2021-07-23T220742.579Z SUPPORT Other

ClinGen classifies the SLC25A13-citrin deficiency gene-disease relationship as definitive with autosomal recessive inheritance.

💊

Treatments

5

MCT supplementation with low-carbohydrate diet

Action: dietary intervention MAXO:0000088

Medium-chain triglyceride (MCT) supplementation combined with a diet containing minimal carbohydrates is the primary therapeutic strategy. MCTs provide energy directly to hepatocytes, increase lipogenesis, and activate the malate-citrate shuttle as a compensatory pathway. Early intervention is recommended promptly after diagnosis to prevent irreversible brain and liver damage.

Mechanism Target:

BYPASSES Malate-aspartate shuttle dysfunction and hepatocellular energy crisis — MCT supplies hepatocyte energy and activates the malate-citrate shuttle as an alternate compensatory route.

Show evidence (1 reference)

PMID:37952953 SUPPORT Human Clinical

"Medium-chain triglyceride (MCT) supplements are effective for treating CD by providing energy to hepatocytes, increasing lipogenesis, and activating the malate-citrate shuttle."

Supports the treatment mechanism linking MCT therapy to hepatocyte energy support and malate-citrate shuttle activation.

MODULATES De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment — MCT therapy increases lipogenesis and improves lipid-energy handling.

Show evidence (1 reference)

PMID:37952953 SUPPORT Human Clinical

"Medium-chain triglyceride (MCT) supplements are effective for treating CD by providing energy to hepatocytes, increasing lipogenesis, and activating the malate-citrate shuttle."

Supports MCT modulation of lipogenesis downstream of citrin deficiency.

MODULATES Impaired urea cycle and ammonia detoxification — MCT plus low-carbohydrate formula supplies energy and substrates that enhance hepatic ammonia detoxification.

Show evidence (1 reference)

PMID:29651749 SUPPORT Human Clinical

"MCT supplement with a low-carbohydrate formula can supply the energy and/or substrates for ASS1 and GS, and enhance ammonia detoxification in hepatocytes."

Patient treatment study supports MCT/low-carbohydrate formula as a modulator of ASS1/GS-mediated ammonia detoxification.

Target Phenotypes: Failure to thrive ↗ Hyperammonemia ↗ Dyslipidemia ↗

Show evidence (3 references)

PMID:37952953 SUPPORT Human Clinical

"Medium-chain triglyceride (MCT) supplements are effective for treating CD by providing energy to hepatocytes, increasing lipogenesis, and activating the malate-citrate shuttle."

Directly describes the mechanism and effectiveness of MCT therapy.

PMID:37952953 SUPPORT Human Clinical

"MCT supplementation with a diet containing minimal carbohydrates is recommended promptly after the diagnosis."

Supports early and combined MCT plus carbohydrate restriction as the recommended approach.

PMID:29651749 SUPPORT Human Clinical

"All the patients' general condition steadily improved and five patients with hyperammonemic encephalopathy recovered from unconsciousness in a few days."

Six-patient CTLN2 treatment series supports clinical improvement with MCT plus low-carbohydrate formula.

Avoidance of fructose and glycerol infusions

Action: dietary intervention MAXO:0000088

Intravenous infusion of glycerol- and fructose-containing osmotic agents is contraindicated and potentially lethal in citrin deficiency. These sugars exacerbate the GAPDH-step metabolic block and worsen hepatocyte ATP depletion under conditions of impaired MAS function.

Mechanism Target:

INHIBITS Impaired hepatic glycolysis and carbohydrate toxicity — Avoiding fructose, glycerol, glucose, and high carbohydrate load reduces exacerbation of carbohydrate toxicity.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Agents/circumstances to avoid: Low-protein and high-carbohydrate diets; glycerol, fructose, and glucose infusions due to risk of brain edema; alcohol."

GeneReviews directly identifies high carbohydrate diets and glycerol/fructose/glucose infusions as circumstances to avoid.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Agents/circumstances to avoid: Low-protein and high-carbohydrate diets; glycerol, fructose, and glucose infusions due to risk of brain edema; alcohol."

Directly supports avoidance of fructose, glycerol, glucose infusions, and high-carbohydrate diets.

Liver transplantation

Action: liver transplantation MAXO:0001175

Liver transplantation is reserved for patients with severe or refractory CTLN2, recurrent hyperammonemic episodes unresponsive to medical management, or liver failure. In the Japanese nationwide study of 222 patients, transplantation was performed in only 4 patients (1 NICCD, 3 CTLN2) with good response thereafter.

Mechanism Target:

RESTORES Malate-aspartate shuttle dysfunction and hepatocellular energy crisis — Transplanting a functional liver restores hepatic citrin-dependent metabolism.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"liver transplantation prevents hyperammonemic crises, corrects metabolic disturbances, and eliminates preferences for protein-rich foods."

Supports liver transplantation as a corrective treatment for hepatic metabolic disturbances and downstream crises.

RESTORES Impaired urea cycle and ammonia detoxification — Functional hepatic replacement restores ammonia detoxification enough to prevent crises.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"liver transplantation prevents hyperammonemic crises, corrects metabolic disturbances, and eliminates preferences for protein-rich foods."

Supports prevention of hyperammonemic crises after transplant.

Target Phenotypes: Hyperammonemia ↗ Unusual eating behavior ↗

Show evidence (2 references)

PMID:35142380 SUPPORT Human Clinical

"Liver transplantation has been performed in only 4 patients (1 NICCD, 3 CTLN2) with a good response thereafter."

Quantifies transplantation frequency and outcomes in a large cohort.

PMID:20301360 SUPPORT Human Clinical

"NICCD is generally not severe, and clinical manifestations are often resolved by age one year with appropriate treatment, although liver failure may still occur; liver transplantation has been required in rare instances."

Confirms liver transplantation as a rare but necessary intervention.

Supportive care during acute hyperammonemia

Action: supportive care MAXO:0000950

Acute hyperammonemic episodes in CTLN2 require emergency metabolic stabilization with citrin-specific ammonia-lowering measures such as arginine and MCT-based therapy. Care must avoid glucose-, fructose-, or glycerol-containing solutions and high-carbohydrate management that can worsen the metabolic crisis.

Mechanism Target:

MODULATES Impaired urea cycle and ammonia detoxification — Acute care lowers ammonia and avoids carbohydrate-containing infusions that can worsen cerebral metabolic stress.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"arginine administration decreases blood ammonia concentration; MCT oil can decrease frequency of hyperammonemia"

GeneReviews supports acute management strategies that lower ammonia or reduce hyperammonemia frequency.

Target Phenotypes: Hyperammonemia ↗ Encephalopathy ↗

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"arginine administration decreases blood ammonia concentration; MCT oil can decrease frequency of hyperammonemia"

Supports ammonia-lowering supportive management in CTLN2.

Pharmacotherapy for hyperammonemia

Action: Pharmacotherapy NCIT:C15986

Arginine administration decreases blood ammonia concentration in CTLN2, and sodium pyruvate can increase weight and decrease the frequency of hyperammonemia. These pharmacologic measures support ammonia control alongside dietary and MCT-based management.

Mechanism Target:

MODULATES Impaired urea cycle and ammonia detoxification — Arginine and sodium pyruvate pharmacotherapy modulate residual ammonia detoxification and hyperammonemia frequency.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Sodium pyruvate can increase weight and decrease frequency of hyperammonemia; arginine administration decreases blood ammonia concentration"

GeneReviews directly supports sodium pyruvate and arginine as pharmacologic interventions affecting hyperammonemia.

Target Phenotypes: Hyperammonemia ↗

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"Sodium pyruvate can increase weight and decrease frequency of hyperammonemia; arginine administration decreases blood ammonia concentration"

Supports pharmacologic ammonia lowering in CTLN2.

🔬

Biochemical Markers

5

Citrulline (INCREASED)

Context: Elevated plasma citrulline is the hallmark biochemical marker, reflecting impaired ASS1 activity due to limited cytosolic aspartate and ATP. Citrulline elevation is used in newborn screening, though levels can be borderline or normal on dried blood spots, potentially causing false negatives.

Pathograph Readouts

Readout Of Impaired urea cycle and ammonia detoxification Positive Diagnostic

Elevated citrulline reports impaired ASS1 flux from limited cytosolic aspartate in citrin deficiency.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"characteristic biochemical analytes (increased blood or plasma concentration of ammonia, plasma or serum concentration of citrulline and arginine, plasma or serum threonine-to-serine ratio)"

GeneReviews directly identifies increased plasma or serum citrulline as a characteristic biochemical analyte.

Ammonia (INCREASED)

Context: Plasma ammonia is elevated during hyperammonemic episodes, particularly in CTLN2. A distinctive feature is that plasma glutamine is often not elevated despite hyperammonemia, reflecting impaired glutamine synthetase function.

Pathograph Readouts

Readout Of Impaired urea cycle and ammonia detoxification Positive Diagnostic

Elevated ammonia reports impaired hepatic nitrogen disposal and hyperammonemic CTLN2 episodes.

Show evidence (1 reference)

PMID:20301360 SUPPORT Human Clinical

"characteristic biochemical analytes (increased blood or plasma concentration of ammonia, plasma or serum concentration of citrulline and arginine, plasma or serum threonine-to-serine ratio)"

GeneReviews directly identifies increased blood or plasma ammonia as a characteristic biochemical analyte.

Conjugated bilirubin (INCREASED)

Context: Conjugated (direct) hyperbilirubinemia is a key laboratory finding in NICCD, reflecting intrahepatic cholestasis. Liver function tests are abnormal in the neonatal period.

Pathograph Readouts

Readout Of Neonatal cholestatic hepatopathy Positive Diagnostic

Elevated conjugated bilirubin reports the neonatal cholestatic hepatopathy branch.

Show evidence (1 reference)

PMID:17982687 SUPPORT Human Clinical

"They were associated with conjugated hyperbilirubinemia, elevated liver enzymes, hypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and threonine."

Korean NICCD case series directly reports conjugated hyperbilirubinemia.

Plasma glutamine (DECREASED)

Context: A distinctive feature of citrin deficiency is that plasma glutamine is often not elevated despite hyperammonemia, in contrast to other urea cycle disorders. This reflects impaired glutamine synthetase activity due to glutamate and ATP substrate deficiency.

Pathograph Readouts

Readout Of Impaired urea cycle and ammonia detoxification Negative Diagnostic

Low or inappropriately normal plasma glutamine reports impaired glutamine-synthetase-dependent ammonia detoxification.

Show evidence (1 reference)

PMID:29651749 SUPPORT Human Clinical

"Before the treatment, plasma glutamine levels did not increase over the normal range and rather decreased to lower than the normal range in some patients."

Patient biochemical data directly supports absent or decreased plasma glutamine elevation in CTLN2.

Transaminases (INCREASED)

Context: Elevated AST and ALT are observed during the NICCD stage, reflecting hepatocellular injury from cholestatic hepatitis. Levels typically normalize after resolution of NICCD with dietary management.

Pathograph Readouts

Readout Of Neonatal cholestatic hepatopathy Positive Diagnostic

Elevated transaminases report hepatocellular injury in the neonatal cholestatic hepatopathy stage.

Show evidence (1 reference)

PMID:17982687 SUPPORT Human Clinical

"They were associated with conjugated hyperbilirubinemia, elevated liver enzymes, hypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and threonine."

Korean NICCD case series directly reports elevated liver enzymes, supporting increased transaminases.

{ }

Source YAML

click to show

name: Citrin Deficiency
category: Mendelian
creation_date: '2025-06-12T20:16:27Z'
updated_date: '2026-05-21T01:51:05Z'
synonyms:
- SLC25A13 deficiency
- Citrullinemia type II
- CTLN2
- AGC2 deficiency
- Neonatal intrahepatic cholestasis caused by citrin deficiency
- NICCD
- FTTDCD
description: 'Citrin deficiency is an autosomal recessive disorder caused by biallelic loss-of-function variants in SLC25A13, which encodes citrin (aspartate- glutamate carrier 2, AGC2), an inner mitochondrial membrane transporter and core component of the hepatic malate-aspartate shuttle (MAS). Loss of citrin impairs export of mitochondrial aspartate to the cytosol and cytosolic NADH-to-mitochondrial NADH transfer needed to regenerate cytosolic NAD+, producing a hepatocellular energy and redox crisis that secondarily perturbs carbohydrate handling, de novo lipogenesis, fatty-acid oxidation, and ammonia detoxification. The disease manifests in age-dependent stages: neonatal intrahepatic cholestasis (NICCD), failure to thrive and dyslipidemia (FTTDCD), and adult-onset hyperammonemic encephalopathy (CTLN2). Medium-chain triglyceride (MCT) supplementation with carbohydrate restriction is the mainstay of therapy. Liver transplantation is reserved for severe or refractory cases.

  '
disease_term:
  preferred_term: citrin deficiency
  term:
    id: MONDO:0016602
    label: citrin deficiency
parents:
- Amino acid metabolism disorder
- Inborn Error of Metabolism
prevalence:
- population: Japan
  percentage: Rare
  notes: 'Carrier rates are approximately 1:42 to 1:65 in parts of Japan.

    '
- population: China
  percentage: Rare
  notes: 'Carrier rate reported as approximately 1:65.

    '
- population: Thailand
  percentage: Rare
  notes: 'Estimated incidence of approximately 1 in 33,000 live births.

    '
has_subtypes:
- name: NICCD (Neonatal Intrahepatic Cholestasis caused by Citrin Deficiency)
  subtype_term:
    preferred_term: neonatal intrahepatic cholestasis due to citrin deficiency
    term:
      id: MONDO:0011601
      label: neonatal intrahepatic cholestasis due to citrin deficiency
  description: 'Neonatal-onset presentation with intrahepatic cholestasis, conjugated hyperbilirubinemia, hepatomegaly, and transient liver dysfunction. Usually resolves by age one year with appropriate dietary management, though liver failure and transplantation are rarely required.

    '
- name: FTTDCD (Failure to Thrive and Dyslipidemia caused by Citrin Deficiency)
  description: 'Childhood-onset presentation characterized by growth impairment, dyslipidemia, fatigue, and food preference for protein- and lipid-rich foods with aversion to carbohydrate-rich foods. Occurs after resolution of NICCD or as the first recognized clinical stage.

    '
- name: CTLN2 (Adult-onset Type II Citrullinemia)
  subtype_term:
    preferred_term: citrullinemia type II
    term:
      id: MONDO:0016603
      label: citrullinemia type II
  description: 'Adult-onset presentation with recurrent hyperammonemic encephalopathy, elevated plasma citrulline, neuropsychiatric symptoms, and risk of hepatocellular carcinoma. Affects approximately 5% of patients with citrin deficiency, with onset ranging from 10 to 70 years of age.

    '
pathophysiology:
- name: SLC25A13 transporter molecular function deficiency
  description: 'Biallelic SLC25A13 pathogenic variants reduce mitochondrial aspartate-glutamate carrier transport activity.

    '
  genes:
  - preferred_term: SLC25A13
    term:
      id: hgnc:10983
      label: SLC25A13
  molecular_functions:
  - preferred_term: transmembrane transporter activity
    term:
      id: GO:0022857
      label: transmembrane transporter activity
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: mitochondrial inner membrane
    term:
      id: GO:0005743
      label: mitochondrial inner membrane
  evidence:
  - reference: PMID:37254569
    reference_title: "Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Aspartate-glutamate carrier 2 (AGC2, citrin) is a mitochondrial carrier \nexpressed in the liver that transports aspartate from mitochondria into the \ncytosol in exchange for glutamate."
    explanation: Supports citrin transporter molecular dysfunction as the initiating defect.
  downstream:
  - target: Malate-aspartate shuttle dysfunction and hepatocellular energy crisis
    description: Loss of AGC2 transport function disrupts hepatic MAS redox transfer and aspartate export.
    causal_link_type: DIRECT
  - target: Aspartate and glutamate transmembrane transport disruption
    description: Defective carrier exchange directly reduces cytosolic aspartate availability.
    causal_link_type: DIRECT
- name: Malate-aspartate shuttle dysfunction and hepatocellular energy crisis
  description: 'Loss of citrin impairs cytosolic NADH transfer into mitochondria and reduces cytosolic aspartate, NAD+, and ATP, creating a fundamental hepatocellular energy and redox deficiency.

    '
  biological_processes:
  - preferred_term: malate-aspartate shuttle
    term:
      id: GO:0043490
      label: malate-aspartate shuttle
  - preferred_term: cellular redox homeostasis
    term:
      id: GO:0045454
      label: cell redox homeostasis
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:37254569
    reference_title: "Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Through MAS, AGC2 is necessary to \nmaintain intracellular redox balance, mitochondrial respiration, and ATP \nsynthesis."
    explanation: Review-level mechanistic confirmation of MAS role in redox and energy homeostasis.
  downstream:
  - target: Impaired hepatic glycolysis and carbohydrate toxicity
    description: MAS failure impairs cytosolic NADH disposal needed for glycolytic flux.
    causal_link_type: DIRECT
  - target: De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment
    description: Hepatocellular redox and energy failure disrupts lipogenesis and secondarily impairs beta-oxidation.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Impaired urea cycle and ammonia detoxification
    description: Reduced aspartate export and hepatocellular ATP deficiency limit urea-cycle nitrogen disposal.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Cytosolic aspartate normally supplies one nitrogen atom for ureagenesis.
    evidence:
    - reference: PMID:37254569
      reference_title: "Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "In these conditions, AGC2 increases aspartate input to the urea \ncycle, where aspartate is a source of one of two nitrogen atoms in the urea \nmolecule"
      explanation: Supports aspartate export as a mechanistic bridge from AGC2/MAS dysfunction to impaired ureagenesis.
  - target: Neonatal cholestatic hepatopathy
    description: Hepatocyte energy and redox failure presents in infancy as transient cholestatic liver disease.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Children younger than age one year \nhave a history of low birth weight with growth restriction and transient \nintrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal \ncellular infiltration associated with hepatic fibrosis, variable liver \ndysfunction, hypoproteinemia, decreased coagulation factors, anemia, and/or \nhypoglycemia."
      explanation: GeneReviews summarizes the NICCD hepatic presentation downstream of citrin deficiency.
  - target: Failure to thrive
    description: Hepatocellular energy deficiency contributes to growth impairment and failure to thrive.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Inability to efficiently use glucose and free fatty acids limits hepatic energy availability.
    evidence:
    - reference: PMID:37952953
      reference_title: "Pathogenesis and Management of Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "They are unable to utilize glucose and free \nfatty acids as energy sources, resulting in energy deficiencies."
      explanation: Energy deficiency provides the mechanistic bridge to growth impairment and failure to thrive.
  - target: Intellectual disability
    description: Recurrent metabolic energy failure and hyperammonemic episodes create risk for irreversible brain injury.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Energy deficiency and episodic hyperammonemia can injure the developing or adult brain.
    evidence:
    - reference: PMID:37952953
      reference_title: "Pathogenesis and Management of Citrin Deficiency."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "patients with CD often exhibit growth impairment and \nirreversible brain and/or liver damage."
      explanation: The review supports irreversible brain damage in citrin deficiency; intellectual disability is a specific possible neurodevelopmental consequence.
- name: Impaired hepatic glycolysis and carbohydrate toxicity
  description: 'Because glycolysis depends on cytosolic NAD+ regenerated via the MAS, citrin-deficient hepatocytes cannot sustain glycolysis efficiently. Under high carbohydrate load, metabolism is blocked at the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) step, leading to accumulation of glucose metabolites, depletion of inorganic phosphate, and further ATP loss. This creates an actively harmful state termed carbohydrate toxicity.

    '
  biological_processes:
  - preferred_term: glycolytic process
    term:
      id: GO:0006096
      label: glycolytic process
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  downstream:
  - target: Impaired urea cycle and ammonia detoxification
    description: High carbohydrate load worsens ATP depletion, reducing energy available for hepatic ammonia detoxification.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
  - target: Abnormal food preference
    description: Protein- and lipid-rich food preference with carbohydrate aversion reflects physiologic avoidance of carbohydrate toxicity.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Often citrin deficiency is \ncharacterized by strong preference for protein-rich and/or lipid-rich foods and \naversion to carbohydrate-rich foods."
      explanation: Directly supports the food preference phenotype linked to carbohydrate intolerance.
  - target: Hypoglycemia
    description: Impaired glycolysis, gluconeogenesis, and hepatic energy handling contribute to recurrent hypoglycemia.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Laboratory changes are dyslipidemia, recurrent hypoglycemia, increased \nlactate-to-pyruvate ratio"
      explanation: GeneReviews directly reports recurrent hypoglycemia as a laboratory abnormality in citrin deficiency.
- name: Impaired urea cycle and ammonia detoxification
  description: 'Citrin deficiency limits cytosolic aspartate availability, which is required by argininosuccinate synthetase 1 (ASS1) for the urea cycle. This results in citrulline accumulation and impaired ureagenesis. Additionally, hyperammonemia may be driven by failure of glutamine-synthetase-dependent perivenous ammonia detoxification due to glutamate and ATP deficiency, rather than solely by ASS1 dysfunction.

    '
  biological_processes:
  - preferred_term: urea cycle
    term:
      id: GO:0000050
      label: urea cycle
  - preferred_term: glutamine biosynthetic process
    term:
      id: GO:1901704
      label: L-glutamine biosynthetic process
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency can manifest in newborns or infants \nas neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in \nolder children as failure to thrive and dyslipidemia caused by citrin deficiency \n(FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric \nsymptoms in citrullinemia type II (CTLN2)."
    explanation: GeneReviews entry confirms hyperammonemia with neuropsychiatric symptoms as the adult CTLN2 presentation.
  - reference: PMID:37952953
    reference_title: "Pathogenesis and Management of Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency (CD) is a hereditary disorder caused by SLC25A13 mutations \nthat manifests as neonatal intrahepatic cholestasis caused by CD (NICCD), \nfailure to thrive and dyslipidemia caused by CD (FTTDCD), and adult-onset type 2 \ncitrullinemia (CTLN2)."
    explanation: Supports the age-dependent clinical spectrum including CTLN2 with urea cycle perturbation.
  downstream:
  - target: Hyperammonemia
    description: Failed hepatic ureagenesis manifests clinically as recurrent hyperammonemia, especially in CTLN2.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "in adults as recurrent hyperammonemia with neuropsychiatric \nsymptoms in citrullinemia type II (CTLN2)."
      explanation: GeneReviews directly links the adult CTLN2 presentation with recurrent hyperammonemia.
  - target: Encephalopathy
    description: Recurrent hyperammonemia in CTLN2 produces neuropsychiatric and neurologic manifestations captured as hyperammonemic encephalopathy.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - ammonia neurotoxicity
    - cerebral metabolic stress
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical manifestations include recurrent hyperammonemia with \nneuropsychiatric (aggression, irritability, restlessness, hyperactivity, \ndelusions, nocturnal delirium) and neurologic manifestations"
      explanation: GeneReviews links recurrent hyperammonemia to neuropsychiatric and neurologic CTLN2 manifestations.
  - target: Seizures
    description: Severe CTLN2 hyperammonemic neurologic episodes can include convulsive seizures.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - hyperammonemic encephalopathy
    - lowered seizure threshold
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "memory loss, disorientation, drowsiness, convulsive seizures, coma"
      explanation: GeneReviews directly lists convulsive seizures among CTLN2 neurologic manifestations.
  - target: Ammonia
    description: Impaired ureagenesis raises blood or plasma ammonia concentration.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "characteristic biochemical analytes (increased blood or plasma \nconcentration of ammonia, plasma or serum concentration of citrulline and \narginine, plasma or serum threonine-to-serine ratio)"
      explanation: Diagnosis/testing section directly identifies increased ammonia as a characteristic biochemical analyte.
  - target: Citrulline
    description: Limited cytosolic aspartate availability at ASS1 causes citrulline accumulation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "characteristic biochemical analytes (increased blood or plasma \nconcentration of ammonia, plasma or serum concentration of citrulline and \narginine, plasma or serum threonine-to-serine ratio)"
      explanation: Diagnosis/testing section directly identifies increased citrulline as a characteristic biochemical analyte.
  - target: Plasma glutamine
    description: ATP and glutamate limitation can blunt glutamine-synthetase-dependent ammonia detoxification, producing absent or low glutamine elevation despite hyperammonemia.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Perivenous glutamine synthetase depends on adequate glutamate and ATP substrates.
    evidence:
    - reference: PMID:29651749
      reference_title: "Medium-chain triglycerides supplement therapy with a low-carbohydrate formula can supply energy and enhance ammonia detoxification in the hepatocytes of patients with adult-onset type II citrullinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Before the treatment, plasma glutamine levels did \nnot increase over the normal range and rather decreased to lower than the normal \nrange in some patients."
      explanation: In CTLN2 patients, plasma glutamine failed to rise despite hyperammonemia, supporting impaired glutamine-synthetase-dependent ammonia detoxification.
  - target: Pancreatitis
    description: Pancreatitis is a recognized CTLN2 complication, but the intermediate causal steps are not fully resolved in the cached evidence.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "Complications include severe liver steatosis and pancreatitis."
      explanation: GeneReviews supports pancreatitis as a CTLN2 complication, while exact intermediates remain unclear.
- name: De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment
  description: 'Citrin-deficient hepatocytes have primary defects in de novo lipogenesis and exhibit secondarily downregulated PPARalpha, leading to impaired fatty acid beta-oxidation. This dual impairment contributes to dyslipidemia and hepatic steatosis.

    '
  biological_processes:
  - preferred_term: fatty acid biosynthetic process
    term:
      id: GO:0006633
      label: fatty acid biosynthetic process
  - preferred_term: fatty acid beta-oxidation
    term:
      id: GO:0006635
      label: fatty acid beta-oxidation
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  downstream:
  - target: Dyslipidemia
    description: Impaired de novo lipogenesis and beta-oxidation disrupt circulating lipid metabolism.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:37952953
      reference_title: "Pathogenesis and Management of Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Citrin-deficient hepatocytes have primary defects in \nglycolysis and de novo lipogenesis and exhibit secondarily downregulated PPARα, \nleading to impaired β-oxidation."
      explanation: Supports the mechanistic lipid-metabolism defect that explains dyslipidemia.
  - target: Hepatic steatosis
    description: Defective lipid synthesis and fatty-acid oxidation contribute to diffuse fatty liver and severe liver steatosis.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Complications include severe liver steatosis and pancreatitis."
      explanation: GeneReviews directly reports severe liver steatosis as a citrin deficiency complication.
- name: Aspartate and glutamate transmembrane transport disruption
  description: 'Citrin (AGC2) normally transports aspartate from the mitochondrial matrix to the cytosol in exchange for glutamate. Loss of this transport function impairs compartmentalized amino acid metabolism, affecting ureagenesis, gluconeogenesis, protein synthesis, and nucleotide biosynthesis.

    '
  biological_processes:
  - preferred_term: L-aspartate transmembrane transport
    term:
      id: GO:0015810
      label: aspartate transmembrane transport
  locations:
  - preferred_term: mitochondrial inner membrane
    term:
      id: GO:0005743
      label: mitochondrial inner membrane
  evidence:
  - reference: PMID:37254569
    reference_title: "Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Aspartate-glutamate carrier 2 (AGC2, citrin) is a mitochondrial carrier \nexpressed in the liver that transports aspartate from mitochondria into the \ncytosol in exchange for glutamate."
    explanation: Directly describes the aspartate-glutamate exchange function of citrin.
  downstream:
  - target: Impaired urea cycle and ammonia detoxification
    description: Reduced mitochondrial export of aspartate limits aspartate input into the urea cycle.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37254569
      reference_title: "Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "AGC2 increases aspartate input to the urea \ncycle, where aspartate is a source of one of two nitrogen atoms in the urea \nmolecule"
      explanation: Supports the direct biochemical bridge from aspartate transport to urea-cycle nitrogen disposal.
- name: Neonatal cholestatic hepatopathy
  description: 'In NICCD, citrin deficiency manifests as transient infantile intrahepatic cholestasis with low birth weight or growth restriction, hepatomegaly, fatty liver, hepatic fibrosis or cellular infiltration, variable liver dysfunction, and hypoglycemia.

    '
  biological_processes:
  - preferred_term: bile acid metabolic process
    term:
      id: GO:0008206
      label: bile acid metabolic process
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Children younger than age one year \nhave a history of low birth weight with growth restriction and transient \nintrahepatic cholestasis, hepatomegaly, diffuse fatty liver, and parenchymal \ncellular infiltration associated with hepatic fibrosis, variable liver \ndysfunction, hypoproteinemia, decreased coagulation factors, anemia, and/or \nhypoglycemia."
    explanation: GeneReviews supports the NICCD hepatic pathology cluster.
  downstream:
  - target: Neonatal cholestasis
    description: Transient intrahepatic cholestasis is the defining neonatal presentation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)"
      explanation: GeneReviews directly identifies NICCD as the neonatal presentation.
  - target: Jaundice
    description: Cholestatic liver dysfunction presents clinically with neonatal jaundice.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:37063661
      reference_title: "Case report: Three novel variants on SLC25A13 in four infants with neonatal intrahepatic cholestasis caused by citrin deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report 4 patients with jaundice and low body weight."
      explanation: Case series reports jaundice in infants with NICCD.
  - target: Hepatomegaly
    description: Infantile cholestatic hepatopathy includes liver enlargement.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "transient \nintrahepatic cholestasis, hepatomegaly, diffuse fatty liver"
      explanation: GeneReviews directly lists hepatomegaly in NICCD.
  - target: Conjugated bilirubin
    description: Intrahepatic cholestasis causes conjugated bilirubin retention.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:17982687
      reference_title: "Six cases of citrin deficiency in Korea."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "They were\nassociated with conjugated hyperbilirubinemia, elevated liver enzymes,\nhypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and\nthreonine."
      explanation: Korean NICCD case series directly reports conjugated hyperbilirubinemia and elevated liver enzymes.
  - target: Transaminases
    description: Variable liver dysfunction in NICCD includes abnormal liver function tests.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17982687
      reference_title: "Six cases of citrin deficiency in Korea."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "They were\nassociated with conjugated hyperbilirubinemia, elevated liver enzymes,\nhypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and\nthreonine."
      explanation: Korean NICCD case series directly reports elevated liver enzymes.
  - target: Low birth weight
    description: Low birth weight with growth restriction is part of the infantile NICCD presentation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "have a history of low birth weight with growth restriction and transient \nintrahepatic cholestasis"
      explanation: GeneReviews directly reports low birth weight with growth restriction in NICCD.
  - target: Hepatic steatosis
    description: NICCD includes diffuse fatty liver, while CTLN2 can develop severe steatosis.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "transient \nintrahepatic cholestasis, hepatomegaly, diffuse fatty liver"
      explanation: GeneReviews directly lists diffuse fatty liver in NICCD.
phenotypes:
- name: Neonatal cholestasis
  frequency: VERY_FREQUENT
  description: 'Intrahepatic cholestasis is the hallmark neonatal presentation (NICCD), with conjugated hyperbilirubinemia, jaundice, and hepatomegaly. Usually resolves by age one year with dietary management.

    '
  phenotype_term:
    preferred_term: Neonatal cholestatic liver disease
    term:
      id: HP:0006566
      label: Neonatal cholestatic liver disease
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency can manifest in newborns or infants \nas neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in \nolder children as failure to thrive and dyslipidemia caused by citrin deficiency \n(FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric \nsymptoms in citrullinemia type II (CTLN2)."
    explanation: GeneReviews directly identifies NICCD as the neonatal presentation.
  - reference: PMID:37063661
    reference_title: "Case report: Three novel variants on SLC25A13 in four infants with neonatal intrahepatic cholestasis caused by citrin deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neonatal intrahepatic cholestasis caused by citrin deficiency \n(NICCD) is a common clinical phenotype of citrin deficiency in infants."
    explanation: Confirms NICCD as a common infant phenotype.
- name: Hyperammonemia
  frequency: FREQUENT
  description: 'Elevated plasma ammonia is a defining feature of CTLN2 and can occur in other stages during catabolic stress. It results from impaired ureagenesis due to cytosolic aspartate and ATP deficiency.

    '
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency can manifest in newborns or infants \nas neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in \nolder children as failure to thrive and dyslipidemia caused by citrin deficiency \n(FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric \nsymptoms in citrullinemia type II (CTLN2)."
    explanation: Directly identifies recurrent hyperammonemia as a key feature of CTLN2.
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency is an autosomal recessive disorder caused by mutations in the \nSLC25A13 gene. The disease can present with age-dependent clinical \nmanifestations: neonatal intrahepatic cholestasis by citrin deficiency (NICCD), \nfailure to thrive, and dyslipidemia by citrin deficiency (FTTDCD), and \nadult-onset type II citrullinemia (CTLN2)."
    explanation: Large Japanese cohort study confirming the age-dependent clinical spectrum including hyperammonemia in CTLN2.
  sequelae:
  - target: Encephalopathy
    description: Hyperammonemia produces the neuropsychiatric and neurologic CTLN2 syndrome.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Ammonia neurotoxicity and downstream cerebral metabolic stress.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Clinical manifestations include recurrent hyperammonemia with \nneuropsychiatric (aggression, irritability, restlessness, hyperactivity, \ndelusions, nocturnal delirium) and neurologic manifestations"
      explanation: GeneReviews links recurrent hyperammonemia to the neuropsychiatric and neurologic CTLN2 presentation.
  - target: Seizures
    description: Severe hyperammonemic neurologic episodes can include convulsive seizures.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Hyperammonemic encephalopathy lowers seizure threshold.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "memory loss, disorientation, drowsiness, convulsive seizures, coma"
      explanation: GeneReviews directly lists convulsive seizures among CTLN2 neurologic manifestations.
- name: Encephalopathy
  frequency: FREQUENT
  description: 'Hyperammonemic encephalopathy with neuropsychiatric symptoms is the defining feature of adult-onset CTLN2. Symptoms include confusion, disorientation, seizures, and altered consciousness.

    '
  phenotype_term:
    preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in adults as recurrent hyperammonemia with neuropsychiatric \nsymptoms in citrullinemia type II (CTLN2)."
    explanation: Directly describes neuropsychiatric symptoms (encephalopathy) as a feature of CTLN2.
- name: Failure to thrive
  frequency: FREQUENT
  description: 'Growth impairment is a feature of FTTDCD and can also occur in severe NICCD. In a nationwide Japanese study of 222 patients, growth impairment during adolescence was noted particularly in CTLN2 patients.

    '
  phenotype_term:
    preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  evidence:
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with citrin deficiency had an increased risk for low weight and length \nat birth, and CTLN2 patients had an increased risk for growth impairment during \nadolescence."
    explanation: Large cohort study documenting growth impairment across different stages of citrin deficiency.
- name: Hepatomegaly
  frequency: FREQUENT
  description: 'Liver enlargement is commonly observed in the neonatal (NICCD) stage, associated with cholestatic hepatitis and steatosis.

    '
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "transient \nintrahepatic cholestasis, hepatomegaly, diffuse fatty liver"
    explanation: GeneReviews directly lists hepatomegaly among NICCD hepatic findings.
- name: Dyslipidemia
  frequency: FREQUENT
  description: 'Dyslipidemia is a characteristic feature of FTTDCD and reflects disrupted de novo lipogenesis and fatty acid oxidation in citrin-deficient hepatocytes.

    '
  phenotype_term:
    preferred_term: Dyslipidemia
    term:
      id: HP:0003119
      label: Abnormal circulating lipid concentration
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "in \nolder children as failure to thrive and dyslipidemia caused by citrin deficiency \n(FTTDCD)"
    explanation: Directly identifies dyslipidemia as part of the FTTDCD phenotype.
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "failure to thrive, and dyslipidemia by citrin deficiency (FTTDCD)"
    explanation: Large cohort confirms dyslipidemia as a defining feature of FTTDCD.
- name: Hepatic steatosis
  frequency: FREQUENT
  description: 'Fatty liver results from impaired de novo lipogenesis and PPARalpha-mediated downregulation of beta-oxidation. It occurs across multiple disease stages.

    '
  phenotype_term:
    preferred_term: Hepatic steatosis
    term:
      id: HP:0001397
      label: Hepatic steatosis
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complications include severe liver steatosis and pancreatitis."
    explanation: GeneReviews directly reports severe liver steatosis as a citrin deficiency complication.
- name: Jaundice
  description: 'Prolonged neonatal jaundice with conjugated hyperbilirubinemia is a cardinal feature of NICCD.

    '
  phenotype_term:
    preferred_term: Jaundice
    term:
      id: HP:0000952
      label: Jaundice
  evidence:
  - reference: PMID:37063661
    reference_title: "Case report: Three novel variants on SLC25A13 in four infants with neonatal intrahepatic cholestasis caused by citrin deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report 4 patients with jaundice and low body weight."
    explanation: Jaundice is the presenting symptom in NICCD case reports.
- name: Abnormal food preference
  frequency: FREQUENT
  description: 'Patients characteristically prefer protein- and lipid-rich foods and show aversion to carbohydrate-rich foods. This dietary self-selection is now understood as a physiological adaptation to the underlying hepatocellular energy deficiency and carbohydrate intolerance.

    '
  phenotype_term:
    preferred_term: Unusual eating behavior
    term:
      id: HP:0100738
      label: Abnormal eating behavior
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Often citrin deficiency is \ncharacterized by strong preference for protein-rich and/or lipid-rich foods and \naversion to carbohydrate-rich foods."
    explanation: GeneReviews directly reports the characteristic protein/lipid-rich preference and carbohydrate aversion.
- name: Low birth weight
  frequency: FREQUENT
  description: 'Patients with citrin deficiency have an increased risk for low weight and length at birth, as demonstrated in a nationwide Japanese cohort.

    '
  phenotype_term:
    preferred_term: Small for gestational age
    term:
      id: HP:0001518
      label: Small for gestational age
  evidence:
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with citrin deficiency had an increased risk for low weight and length \nat birth"
    explanation: Directly quantifies increased risk for low birth parameters in citrin deficiency.
- name: Intellectual disability
  description: 'Irreversible brain damage may occur in patients with citrin deficiency, particularly with delayed diagnosis or inadequate treatment. MCT supplementation with minimal carbohydrate diet aims to prevent this.

    '
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:37952953
    reference_title: "Pathogenesis and Management of Citrin Deficiency."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: "patients with CD often exhibit growth impairment and \nirreversible brain and/or liver damage."
    explanation: The review supports irreversible brain damage in citrin deficiency, but does not name intellectual disability specifically.
- name: Pancreatitis
  frequency: OCCASIONAL
  description: 'Pancreatitis is a recognized complication in the disease spectrum of citrin deficiency, particularly associated with CTLN2.

    '
  phenotype_term:
    preferred_term: Pancreatitis
    term:
      id: HP:0001733
      label: Pancreatitis
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Complications include severe liver steatosis and pancreatitis."
    explanation: GeneReviews directly reports pancreatitis as a complication.
  notes: Pancreatitis is reported as a complication of citrin deficiency, particularly associated with CTLN2, in the clinical literature.
- name: Hypoglycemia
  frequency: OCCASIONAL
  description: 'Hypoketotic hypoglycemia is mechanistically linked to impaired glycogenesis, gluconeogenesis, and ketogenesis in citrin-deficient hepatocytes.

    '
  phenotype_term:
    preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Laboratory changes are dyslipidemia, recurrent hypoglycemia, increased \nlactate-to-pyruvate ratio"
    explanation: GeneReviews directly reports recurrent hypoglycemia as a laboratory abnormality.
- name: Seizures
  frequency: OCCASIONAL
  description: 'Seizures may occur in the context of severe hyperammonemic episodes in CTLN2 and during neonatal metabolic instability.

    '
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "memory loss, disorientation, drowsiness, convulsive seizures, coma"
    explanation: GeneReviews directly lists convulsive seizures among CTLN2 neurologic manifestations.
biochemical:
- name: Citrulline
  presence: INCREASED
  context: 'Elevated plasma citrulline is the hallmark biochemical marker, reflecting impaired ASS1 activity due to limited cytosolic aspartate and ATP. Citrulline elevation is used in newborn screening, though levels can be borderline or normal on dried blood spots, potentially causing false negatives.

    '
  readouts:
  - target: Impaired urea cycle and ammonia detoxification
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated citrulline reports impaired ASS1 flux from limited cytosolic aspartate in citrin deficiency.
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characteristic biochemical analytes (increased blood or plasma \nconcentration of ammonia, plasma or serum concentration of citrulline and \narginine, plasma or serum threonine-to-serine ratio)"
    explanation: GeneReviews directly identifies increased plasma or serum citrulline as a characteristic biochemical analyte.
- name: Ammonia
  presence: INCREASED
  context: 'Plasma ammonia is elevated during hyperammonemic episodes, particularly in CTLN2. A distinctive feature is that plasma glutamine is often not elevated despite hyperammonemia, reflecting impaired glutamine synthetase function.

    '
  readouts:
  - target: Impaired urea cycle and ammonia detoxification
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated ammonia reports impaired hepatic nitrogen disposal and hyperammonemic CTLN2 episodes.
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characteristic biochemical analytes (increased blood or plasma \nconcentration of ammonia, plasma or serum concentration of citrulline and \narginine, plasma or serum threonine-to-serine ratio)"
    explanation: GeneReviews directly identifies increased blood or plasma ammonia as a characteristic biochemical analyte.
- name: Conjugated bilirubin
  presence: INCREASED
  context: 'Conjugated (direct) hyperbilirubinemia is a key laboratory finding in NICCD, reflecting intrahepatic cholestasis. Liver function tests are abnormal in the neonatal period.

    '
  readouts:
  - target: Neonatal cholestatic hepatopathy
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated conjugated bilirubin reports the neonatal cholestatic hepatopathy branch.
  evidence:
  - reference: PMID:17982687
    reference_title: "Six cases of citrin deficiency in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They were\nassociated with conjugated hyperbilirubinemia, elevated liver enzymes,\nhypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and\nthreonine."
    explanation: Korean NICCD case series directly reports conjugated hyperbilirubinemia.
- name: Plasma glutamine
  presence: DECREASED
  context: 'A distinctive feature of citrin deficiency is that plasma glutamine is often not elevated despite hyperammonemia, in contrast to other urea cycle disorders. This reflects impaired glutamine synthetase activity due to glutamate and ATP substrate deficiency.

    '
  readouts:
  - target: Impaired urea cycle and ammonia detoxification
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Low or inappropriately normal plasma glutamine reports impaired glutamine-synthetase-dependent ammonia detoxification.
  evidence:
  - reference: PMID:29651749
    reference_title: "Medium-chain triglycerides supplement therapy with a low-carbohydrate formula can supply energy and enhance ammonia detoxification in the hepatocytes of patients with adult-onset type II citrullinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Before the treatment, plasma glutamine levels did \nnot increase over the normal range and rather decreased to lower than the normal \nrange in some patients."
    explanation: Patient biochemical data directly supports absent or decreased plasma glutamine elevation in CTLN2.
  notes: 'This paradoxical finding differentiates citrin deficiency from classical urea cycle disorders where glutamine is typically elevated during hyperammonemia. Low glutamine reflects impaired glutamine synthetase activity due to glutamate and ATP substrate deficiency from MAS dysfunction.

    '
- name: Transaminases
  presence: INCREASED
  context: 'Elevated AST and ALT are observed during the NICCD stage, reflecting hepatocellular injury from cholestatic hepatitis. Levels typically normalize after resolution of NICCD with dietary management.

    '
  readouts:
  - target: Neonatal cholestatic hepatopathy
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated transaminases report hepatocellular injury in the neonatal cholestatic hepatopathy stage.
  evidence:
  - reference: PMID:17982687
    reference_title: "Six cases of citrin deficiency in Korea."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "They were\nassociated with conjugated hyperbilirubinemia, elevated liver enzymes,\nhypoalbuminemia, mild hyperammonemia, elevated citrulline, methionine and\nthreonine."
    explanation: Korean NICCD case series directly reports elevated liver enzymes, supporting increased transaminases.
genetic:
- name: SLC25A13 pathogenic variants
  gene_term:
    preferred_term: SLC25A13
    term:
      id: hgnc:10983
      label: SLC25A13
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:35142380
      reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Citrin deficiency is an autosomal recessive disorder caused by mutations in the \nSLC25A13 gene."
      explanation: Large nationwide study directly states autosomal recessive inheritance.
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Citrin deficiency can manifest in newborns or infants \nas neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD)"
      explanation: GeneReviews confirms the genetic basis and inheritance pattern.
  variants:
  - name: IVS16ins3kb hotspot structural variant
    description: 'IVS16ins3kb is a hotspot structural variant in SLC25A13 that requires specific copy number variant calling approaches for detection. It is particularly relevant for newborn screening programs in East Asian populations.

      '
    evidence:
    - reference: PMID:38535123
      reference_title: "Harnessing Next-Generation Sequencing as a Timely and Accurate Second-Tier Screening Test for Newborn Screening of Inborn Errors of Metabolism."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The \ncustom-designed NGS panel can detect sequence variants in the relevant genes and \nalso specifically screen for the presence of the hotspot variant IVS16ins3kb"
      explanation: Identifies IVS16ins3kb as a hotspot variant requiring specific detection methods.
  - name: Novel nonsense, frameshift, and deletion variants
    description: 'The variant spectrum of SLC25A13 continues to expand. A 2023 case series identified three novel variants including a nonsense mutation in exon 17 (c.1803C>G), a frameshift mutation in exon 11 (c.1141delG), and a whole exon 11 deletion.

      '
  features: 'Biallelic pathogenic variants in SLC25A13 (encoding citrin/AGC2) cause citrin deficiency across all phenotypic stages. The gene is located on chromosome 7q21.3. Over 100 pathogenic variants have been reported including missense, nonsense, frameshift, splice-site mutations, and large structural rearrangements. Compound heterozygosity is common. Carrier rates are high in East Asian populations (1:42 to 1:65 in Japan, 1:65 in China).

    '
  evidence:
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Citrin deficiency is an autosomal recessive disorder caused by mutations in the \nSLC25A13 gene."
    explanation: Nationwide study confirms SLC25A13 as the causal gene.
  - reference: CGGV:assertion_bc373b9e-ec5e-4471-92a1-bbdd9aa3378c-2021-07-23T220742.579Z
    reference_title: "SLC25A13 / citrin deficiency (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "SLC25A13 | HGNC:10983 | citrin deficiency | MONDO:0016602 | AR | Definitive"
    explanation: ClinGen classifies the SLC25A13-citrin deficiency gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: MCT supplementation with low-carbohydrate diet
  description: 'Medium-chain triglyceride (MCT) supplementation combined with a diet containing minimal carbohydrates is the primary therapeutic strategy. MCTs provide energy directly to hepatocytes, increase lipogenesis, and activate the malate-citrate shuttle as a compensatory pathway. Early intervention is recommended promptly after diagnosis to prevent irreversible brain and liver damage.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_phenotypes:
  - preferred_term: Failure to thrive
    term:
      id: HP:0001508
      label: Failure to thrive
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  - preferred_term: Dyslipidemia
    term:
      id: HP:0003119
      label: Abnormal circulating lipid concentration
  target_mechanisms:
  - target: Malate-aspartate shuttle dysfunction and hepatocellular energy crisis
    treatment_effect: BYPASSES
    description: MCT supplies hepatocyte energy and activates the malate-citrate shuttle as an alternate compensatory route.
    evidence:
    - reference: PMID:37952953
      reference_title: "Pathogenesis and Management of Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Medium-chain \ntriglyceride (MCT) supplements are effective for treating CD by providing energy \nto hepatocytes, increasing lipogenesis, and activating the malate-citrate \nshuttle."
      explanation: Supports the treatment mechanism linking MCT therapy to hepatocyte energy support and malate-citrate shuttle activation.
  - target: De novo lipogenesis defects and PPARalpha-mediated beta-oxidation impairment
    treatment_effect: MODULATES
    description: MCT therapy increases lipogenesis and improves lipid-energy handling.
    evidence:
    - reference: PMID:37952953
      reference_title: "Pathogenesis and Management of Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Medium-chain \ntriglyceride (MCT) supplements are effective for treating CD by providing energy \nto hepatocytes, increasing lipogenesis, and activating the malate-citrate \nshuttle."
      explanation: Supports MCT modulation of lipogenesis downstream of citrin deficiency.
  - target: Impaired urea cycle and ammonia detoxification
    treatment_effect: MODULATES
    description: MCT plus low-carbohydrate formula supplies energy and substrates that enhance hepatic ammonia detoxification.
    evidence:
    - reference: PMID:29651749
      reference_title: "Medium-chain triglycerides supplement therapy with a low-carbohydrate formula can supply energy and enhance ammonia detoxification in the hepatocytes of patients with adult-onset type II citrullinemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "MCT supplement with a low-carbohydrate formula can \nsupply the energy and/or substrates for ASS1 and GS, and enhance ammonia \ndetoxification in hepatocytes."
      explanation: Patient treatment study supports MCT/low-carbohydrate formula as a modulator of ASS1/GS-mediated ammonia detoxification.
  evidence:
  - reference: PMID:37952953
    reference_title: "Pathogenesis and Management of Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Medium-chain \ntriglyceride (MCT) supplements are effective for treating CD by providing energy \nto hepatocytes, increasing lipogenesis, and activating the malate-citrate \nshuttle."
    explanation: Directly describes the mechanism and effectiveness of MCT therapy.
  - reference: PMID:37952953
    reference_title: "Pathogenesis and Management of Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MCT supplementation with a diet containing minimal \ncarbohydrates is recommended promptly after the diagnosis."
    explanation: Supports early and combined MCT plus carbohydrate restriction as the recommended approach.
  - reference: PMID:29651749
    reference_title: "Medium-chain triglycerides supplement therapy with a low-carbohydrate formula can supply energy and enhance ammonia detoxification in the hepatocytes of patients with adult-onset type II citrullinemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All the patients' general condition steadily improved \nand five patients with hyperammonemic encephalopathy recovered from \nunconsciousness in a few days."
    explanation: Six-patient CTLN2 treatment series supports clinical improvement with MCT plus low-carbohydrate formula.
- name: Avoidance of fructose and glycerol infusions
  description: 'Intravenous infusion of glycerol- and fructose-containing osmotic agents is contraindicated and potentially lethal in citrin deficiency. These sugars exacerbate the GAPDH-step metabolic block and worsen hepatocyte ATP depletion under conditions of impaired MAS function.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_mechanisms:
  - target: Impaired hepatic glycolysis and carbohydrate toxicity
    treatment_effect: INHIBITS
    description: Avoiding fructose, glycerol, glucose, and high carbohydrate load reduces exacerbation of carbohydrate toxicity.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Agents/circumstances to avoid: Low-protein and \nhigh-carbohydrate diets; glycerol, fructose, and glucose infusions due to risk \nof brain edema; alcohol."
      explanation: GeneReviews directly identifies high carbohydrate diets and glycerol/fructose/glucose infusions as circumstances to avoid.
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Low-protein and \nhigh-carbohydrate diets; glycerol, fructose, and glucose infusions due to risk \nof brain edema; alcohol."
    explanation: Directly supports avoidance of fructose, glycerol, glucose infusions, and high-carbohydrate diets.
  notes: 'This is a critical safety consideration. Healthcare providers must be aware that standard fructose- or glycerol-containing IV solutions can precipitate fatal metabolic crisis in citrin deficiency patients.

    '
- name: Liver transplantation
  description: 'Liver transplantation is reserved for patients with severe or refractory CTLN2, recurrent hyperammonemic episodes unresponsive to medical management, or liver failure. In the Japanese nationwide study of 222 patients, transplantation was performed in only 4 patients (1 NICCD, 3 CTLN2) with good response thereafter.

    '
  treatment_term:
    preferred_term: liver transplantation
    term:
      id: MAXO:0001175
      label: liver transplantation
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  - preferred_term: Unusual eating behavior
    term:
      id: HP:0100738
      label: Abnormal eating behavior
  target_mechanisms:
  - target: Malate-aspartate shuttle dysfunction and hepatocellular energy crisis
    treatment_effect: RESTORES
    description: Transplanting a functional liver restores hepatic citrin-dependent metabolism.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "liver transplantation prevents hyperammonemic crises, corrects \nmetabolic disturbances, and eliminates preferences for protein-rich foods."
      explanation: Supports liver transplantation as a corrective treatment for hepatic metabolic disturbances and downstream crises.
  - target: Impaired urea cycle and ammonia detoxification
    treatment_effect: RESTORES
    description: Functional hepatic replacement restores ammonia detoxification enough to prevent crises.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "liver transplantation prevents hyperammonemic crises, corrects \nmetabolic disturbances, and eliminates preferences for protein-rich foods."
      explanation: Supports prevention of hyperammonemic crises after transplant.
  evidence:
  - reference: PMID:35142380
    reference_title: "Clinical manifestation and long-term outcome of citrin deficiency: Report from a nationwide study in Japan."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Liver transplantation has been performed in only 4 patients (1 \nNICCD, 3 CTLN2) with a good response thereafter."
    explanation: Quantifies transplantation frequency and outcomes in a large cohort.
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "NICCD is generally not severe, and clinical manifestations are \noften resolved by age one year with appropriate treatment, although liver \nfailure may still occur; liver transplantation has been required in rare \ninstances."
    explanation: Confirms liver transplantation as a rare but necessary intervention.
- name: Supportive care during acute hyperammonemia
  description: 'Acute hyperammonemic episodes in CTLN2 require emergency metabolic stabilization with citrin-specific ammonia-lowering measures such as arginine and MCT-based therapy. Care must avoid glucose-, fructose-, or glycerol-containing solutions and high-carbohydrate management that can worsen the metabolic crisis.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  - preferred_term: Encephalopathy
    term:
      id: HP:0001298
      label: Encephalopathy
  target_mechanisms:
  - target: Impaired urea cycle and ammonia detoxification
    treatment_effect: MODULATES
    description: Acute care lowers ammonia and avoids carbohydrate-containing infusions that can worsen cerebral metabolic stress.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "arginine administration decreases blood ammonia \nconcentration; MCT oil can decrease frequency of hyperammonemia"
      explanation: GeneReviews supports acute management strategies that lower ammonia or reduce hyperammonemia frequency.
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "arginine administration decreases blood ammonia \nconcentration; MCT oil can decrease frequency of hyperammonemia"
    explanation: Supports ammonia-lowering supportive management in CTLN2.
- name: Pharmacotherapy for hyperammonemia
  description: 'Arginine administration decreases blood ammonia concentration in CTLN2, and sodium pyruvate can increase weight and decrease the frequency of hyperammonemia. These pharmacologic measures support ammonia control alongside dietary and MCT-based management.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  target_mechanisms:
  - target: Impaired urea cycle and ammonia detoxification
    treatment_effect: MODULATES
    description: Arginine and sodium pyruvate pharmacotherapy modulate residual ammonia detoxification and hyperammonemia frequency.
    evidence:
    - reference: PMID:20301360
      reference_title: "Citrin Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Sodium pyruvate can increase weight and decrease frequency \nof hyperammonemia; arginine administration decreases blood ammonia \nconcentration"
      explanation: GeneReviews directly supports sodium pyruvate and arginine as pharmacologic interventions affecting hyperammonemia.
  evidence:
  - reference: PMID:20301360
    reference_title: "Citrin Deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sodium pyruvate can increase weight and decrease frequency \nof hyperammonemia; arginine administration decreases blood ammonia \nconcentration"
    explanation: Supports pharmacologic ammonia lowering in CTLN2.
  notes: Arginine and sodium pyruvate are cited management options for CTLN2; avoid extrapolating generic urea-cycle nitrogen-scavenger therapy without citrin-specific support.
diagnosis:
- name: Newborn screening with molecular second-tier testing
  description: 'Citrin deficiency is detectable by newborn screening via tandem mass spectrometry using elevated citrulline as the primary marker. However, dried blood spot citrulline can be borderline or normal, leading to false negatives. Second-tier NGS-based genetic testing with specific detection of hotspot variants like IVS16ins3kb has been implemented to improve sensitivity. In a Hong Kong study, two citrullinemia type II cases would have been missed without molecular second-tier testing.

    '
  diagnosis_term:
    preferred_term: disease screening
    term:
      id: MAXO:0000124
      label: disease screening
  results: Elevated citrulline or biallelic SLC25A13 pathogenic variants support diagnosis, but molecular second-tier testing improves detection when biochemical screening is borderline.
  evidence:
  - reference: PMID:38535123
    reference_title: "Harnessing Next-Generation Sequencing as a Timely and Accurate Second-Tier Screening Test for Newborn Screening of Inborn Errors of Metabolism."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The false positive \nrate for these six conditions after the NGS second-tier test was only 0.017%, \nand two cases of citrullinemia type II would have been missed as false negatives \nif only biochemical first-tier testing was performed."
    explanation: Quantifies the performance improvement from adding NGS second-tier screening.
notes: 'Citrin deficiency represents a paradigm of mitochondrial hepatopathy where the fundamental defect is a transport protein rather than an enzyme. The disease is best understood as an energy/redox hepatopathy rather than a simple urea cycle enzyme deficiency. The characteristic food preference for protein and lipid-rich foods with carbohydrate aversion is a physiological adaptation. Carrier rates are high in East Asian populations (1:42-1:65 in Japan), making it an important consideration in newborn screening programs in these regions. Fructose and glycerol infusions are strictly contraindicated. Molecular diagnosis provides a basis for genetic counseling of families.

  '
references:
- reference: PMID:20301360
  title: "Citrin Deficiency."
  tags:
  - GeneReviews
  findings: []

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References & Deep Research

References

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PMID:20301360

Citrin Deficiency.

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Disease Pathophysiology Research Template

Edison Scientific Literature 27 citations 2026-02-23T23:35:52.715510

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: Citrin Deficiency
MONDO ID: (if available)
Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of Citrin Deficiency. 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: Citrin Deficiency (SLC25A13) — Pathophysiology Research Report (Genetic; MONDO_0016602)

Publication focus: molecular/cellular mechanisms of disease progression with 2023–2024 emphasis.

Executive summary (current understanding) Citrin deficiency is an autosomal recessive disorder caused by biallelic loss-of-function variants in SLC25A13, which encodes citrin (aspartate–glutamate carrier 2; AGC2), an inner mitochondrial membrane carrier and core component of the hepatic malate–aspartate shuttle (MAS). Loss of citrin impairs (i) export of mitochondrial aspartate to the cytosol and (ii) cytosolic NADH→mitochondrial NADH transfer needed to regenerate cytosolic NAD+. These defects produce a characteristic hepatocellular energy/redox crisis that secondarily perturbs carbohydrate handling, de novo lipogenesis, fatty-acid oxidation, and ammonia detoxification, yielding a staged phenotype: NICCD (neonatal intrahepatic cholestasis), FTTDCD (failure to thrive and dyslipidemia), and CTLN2 (adult-onset hyperammonemic encephalopathy). The most up-to-date mechanistic synthesis (2024) explicitly frames the disease as a “mitochondrial hepatopathy” with carbohydrate toxicity and identifies medium-chain triglyceride (MCT) plus low-carbohydrate dietary therapy as a rational energy-substitution strategy. (hayasaka2024pathogenesisandmanagement pages 1-2, hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 7-9)
Disease definition, identifiers, and key concepts 2.1 Disease names and MONDO identifiers • Citrin deficiency: MONDO_0016602 (OpenTargets disease association evidence). (hayasaka2024pathogenesisandmanagement pages 2-4) • Neonatal intrahepatic cholestasis due to citrin deficiency (NICCD): MONDO_0011601. (hayasaka2024pathogenesisandmanagement pages 2-4) • Citrullinemia type II / adult-onset type II citrullinemia (CTLN2): MONDO_0016603. (hayasaka2024pathogenesisandmanagement pages 2-4)

2.2 Core molecular definition Citrin (AGC2; SLC25A13) is an aspartate–glutamate carrier in the inner mitochondrial membrane that functions within the MAS. A key mechanistic statement from a 2024 review is that the MAS “transports NADH produced by glycolysis from the cytosol to the mitochondria and regenerates cytosolic NAD+,” and that citrin is “indispensable for hepatic glycolysis, de novo lipogenesis, and energy metabolism.” (Hayasaka 2024, Jul 2024, Internal Medicine; https://doi.org/10.2169/internalmedicine.2595-23) (hayasaka2024pathogenesisandmanagement pages 1-2)

Complementary 2023 review-level mechanism: “Through MAS, AGC2 is necessary to maintain intracellular redox balance, mitochondrial respiration, and ATP synthesis.” (Holeček 2023, Jun 2023, BMB Reports; https://doi.org/10.5483/bmbrep.2023-0052) (holecek2023aspartateglutamatecarrier2 pages 1-2)

PMID note: The retrieved excerpts for the 2023–2024 reviews included DOIs and URLs but did not display PMIDs; therefore PMIDs cannot be cited from the retrieved text itself. (hayasaka2024pathogenesisandmanagement pages 1-2, holecek2023aspartateglutamatecarrier2 pages 1-2)

Core pathophysiology (molecular and cellular mechanisms) 3.1 Primary defect: mitochondrial aspartate export and MAS failure Citrin deficiency disrupts the malate–aspartate shuttle, reducing cytosolic aspartate availability and impairing cytosolic redox balance (NADH/NAD+), which is required for sustained hepatic glycolysis and downstream ATP production. The 2024 synthesis explicitly links MAS failure to reduced “cytosolic aspartate, NAD+ and ATP,” and to impaired “glycolysis, glycogenesis and de novo lipogenesis.” (hayasaka2024pathogenesisandmanagement pages 2-4)

Mechanistic schematic evidence: Hayasaka 2024 Figure 2 contrasts control vs citrin-deficient livers and highlights MAS impairment, compensatory malate–citrate shuttle (MCS), and the role of MCT supplementation in restoring ATP/cytosolic NAD+ (figure evidence). (hayasaka2024pathogenesisandmanagement media 4eb23285)

3.2 Secondary energy metabolism derailment: glycolysis block and carbohydrate toxicity A major contemporary concept is that high carbohydrate exposure is not neutral in citrin deficiency; it can be actively harmful (“carbohydrate toxicity”). The 2024 review states: “its metabolism is inhibited at the glyceraldehyde 3-phosphate dehydrogenase step, leading to the accumulation of glucose metabolites and a decrease in Pi and ATP levels in hepatocytes,” and warns that “Infusion of glycerol- and fructose-containing osmotic agents is lethal and contraindicated.” (hayasaka2024pathogenesisandmanagement pages 7-9)

This is consistent with the MAS role described in 2023, which emphasizes MAS as the route for indirect transfer of cytosolic NADH generated by GAPDH into mitochondria, thereby coupling glycolysis to oxidative phosphorylation. (holecek2023aspartateglutamatecarrier2 pages 2-4)

3.3 Urea cycle / hyperammonemia: aspartate and ATP limitation, plus GS-centered detoxification failure Classically, CTLN2 presents with hyperammonemia and citrullinemia; mechanistically, two layers are highlighted in 2024: • Aspartate/ATP dependence of citrulline metabolism: “Citrulline is metabolized by ASS1, which requires aspartate and ATP,” and citrin is described as the essential mitochondrial→cytosol aspartate transport route in liver, providing a direct mechanism for citrullinemia when aspartate/ATP are limited. (hayasaka2024pathogenesisandmanagement pages 2-4) • Hyperammonemia may be driven less by intrinsic ASS1 enzymatic failure and more by failure of perivenous ammonia “mopping up” through glutamine synthesis. The 2024 review states: “These findings indicate that hyperammonemia is not primarily caused by a defect in ASS1 but rather by a defect in GS due to a substrate (glutamate) and/or ATP deficiency.” (hayasaka2024pathogenesisandmanagement pages 4-6)

Mechanistic schematic evidence: Hayasaka 2024 Figure 4 summarizes periportal ureagenesis and the requirement for cytosolic aspartate for the ASS1 reaction, connecting citrin deficiency to impaired ureagenesis and hyperammonemia (figure evidence). (hayasaka2024pathogenesisandmanagement media c2a905ba)

A notable biochemical phenotype emphasized in 2024 is: “The absence of increased plasma glutamine concentrations despite hyperammonemia is also a characteristic symptom associated with CTLN2.” (hayasaka2024pathogenesisandmanagement pages 4-6)

3.4 Lipid metabolism: de novo lipogenesis defects, PPARα downregulation, impaired β-oxidation, fatty liver The 2024 review states that “citrin-deficient hepatocytes have primary defects in glycolysis and de novo lipogenesis and exhibit secondarily downregulated PPARα, leading to impaired β-oxidation.” (hayasaka2024pathogenesisandmanagement pages 1-2)

The integrated model is that impaired de novo lipogenesis decreases signals that would otherwise maintain PPARα activity, lowering fatty-acid oxidation capacity and contributing to hepatic steatosis; the review further links fatty liver to PPARα downregulation and suppressed fatty-acid oxidation gene expression. (hayasaka2024pathogenesisandmanagement pages 2-4)

3.5 Stress biology: ER/oxidative stress and arrested hepatic maturation/zonation The 2024 synthesis describes increased ER/oxidative stress and frames citrin deficiency as a “mitochondrial hepatopathy” where energy failure impairs normal hepatocyte maturation, including lobular zonation. It highlights that in CTLN2 the distribution of ASS1- and GS-positive hepatocytes is altered, consistent with impaired periportal/perivenous functional partitioning of ammonia detoxification. (hayasaka2024pathogenesisandmanagement pages 4-6)

Key molecular players (genes/proteins, metabolites/chemicals, cell types, anatomical locations) 4.1 Genes/proteins Causal gene • SLC25A13 (encodes citrin/AGC2): causal for citrin deficiency across NICCD/FTTDCD/CTLN2. (hayasaka2024pathogenesisandmanagement pages 1-2, wang2023casereportthree pages 1-2)

Core pathway components (as referenced mechanistically) • MAS enzymes/transporters: malate dehydrogenase (MDH; cytosol and mitochondrial matrix), aspartate aminotransferase (AST/GOT; cytosol and mitochondrial matrix), 2-oxoglutarate carrier (OGC), and AGC2 (citrin) in the inner mitochondrial membrane. (holecek2023aspartateglutamatecarrier2 pages 2-4) • Urea cycle and ammonia detoxification: ASS1 (argininosuccinate synthetase 1) is highlighted as requiring cytosolic aspartate and ATP; GS (glutamine synthetase) is implicated as the critical ammonia “backup” route affected by substrate/ATP deficiency. (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • Lipid oxidation regulator: PPARα downregulation is linked to impaired β-oxidation. (hayasaka2024pathogenesisandmanagement pages 1-2)

Regulatory/structural note • AGC2 contains EF-hand motifs “facing the intermembrane space for calcium binding,” consistent with Ca2+-regulated carrier activity. (holecek2023aspartateglutamatecarrier2 pages 1-2)

4.2 Chemical entities (metabolites, dietary therapeutics, contraindicated agents) Key metabolites implicated • Aspartate, glutamate (carrier substrates; nitrogen flux), citrulline (biomarker/urea-cycle intermediate), ammonia (toxic effector), glutamine (often not elevated in CTLN2 despite hyperammonemia), citrate (MCS intermediate), NADH/NAD+ (redox pair), ATP, inorganic phosphate (Pi). (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6, hayasaka2024pathogenesisandmanagement pages 7-9)

Therapeutically relevant chemicals • Medium-chain triglycerides (MCT) / medium-chain free fatty acids (MCFA): provide hepatocyte energy and support metabolic shuttles; MCT supplementation can normalize urea-cycle amino acids in NICCD within days and improves biochemical/clinical status when combined with carbohydrate restriction. (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement media 4eb23285)

Contraindicated/triggering chemicals • Fructose and glycerol infusions: “lethal and contraindicated.” (hayasaka2024pathogenesisandmanagement pages 7-9)

4.3 Cell types (CL-oriented) • Hepatocyte (CL:0000182) as the key disease cell type; “citrin-deficient hepatocytes” have primary glycolysis/lipogenesis defects and energy deficiency. (hayasaka2024pathogenesisandmanagement pages 1-2) • Periportal (zone 1) ureagenic hepatocytes vs perivenous/pericentral (zone 3) glutamine-synthesizing hepatocytes: ammonia detoxification is partitioned; CTLN2 disrupts zonation and ASS1/GS distribution. (hayasaka2024pathogenesisandmanagement pages 4-6, holecek2023aspartateglutamatecarrier2 pages 1-2)

4.4 Anatomical locations (UBERON-oriented) • Liver (UBERON:0002107): primary affected organ across all stages. (hayasaka2024pathogenesisandmanagement pages 1-2, hayasaka2024pathogenesisandmanagement pages 2-4) • Hepatic lobule zones (periportal vs perivenous/pericentral regions): functional zonation relevant to urea cycle vs glutamine synthesis. (hayasaka2024pathogenesisandmanagement pages 4-6, holecek2023aspartateglutamatecarrier2 pages 1-2) • Brain (UBERON:0000955): affected clinically via hyperammonemic encephalopathy in CTLN2. (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • Pancreas (UBERON:0001264): pancreatitis is listed among complications in the disease spectrum. (hayasaka2024pathogenesisandmanagement pages 2-4)

4.5 Cellular components (GO-CC oriented) • Mitochondrial inner membrane (GO:0005743): localization of citrin/AGC2 and other carriers. (holecek2023aspartateglutamatecarrier2 pages 2-4) • Mitochondrial matrix (GO:0005759) and cytosol (GO:0005829): MDH/AST reactions operate in both compartments; MAS couples these compartments. (holecek2023aspartateglutamatecarrier2 pages 2-4) • Mitochondrial intermembrane space (GO:0005758): AGC2 EF-hand motifs face the IMS for Ca2+ regulation. (holecek2023aspartateglutamatecarrier2 pages 1-2)

Biological processes disrupted (GO terms; suggested mappings) The following GO biological processes are directly supported by the cited mechanistic descriptions (terms are suggested targets for annotation; exact ontology IDs should be confirmed against GO): • Malate–aspartate shuttle activity / NADH shuttling / cellular redox homeostasis (supported by explicit MAS redox balance statements). (hayasaka2024pathogenesisandmanagement pages 1-2, holecek2023aspartateglutamatecarrier2 pages 1-2) • Glycolytic process and regulation of glycolysis (glycolysis impairment; GAPDH-step inhibition under carbohydrate load). (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 7-9) • Aspartate and glutamate transmembrane transport (mitochondrial export/import by AGC2). (holecek2023aspartateglutamatecarrier2 pages 2-4) • Urea cycle and ammonia detoxification (ASS1 dependence on aspartate/ATP; zonated detoxification and GS-centered failure mechanism). (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • De novo lipogenesis / fatty acid biosynthetic process (primary defect described). (hayasaka2024pathogenesisandmanagement pages 1-2, hayasaka2024pathogenesisandmanagement pages 2-4) • Fatty acid beta-oxidation and its regulation via PPARα (secondary PPARα downregulation with impaired β-oxidation). (hayasaka2024pathogenesisandmanagement pages 1-2) • Response to ER stress / oxidative stress (increased ER/oxidative stress described in pathogenesis). (hayasaka2024pathogenesisandmanagement pages 6-7)
Disease progression model (sequence of events; stages) 6.1 Mechanistic sequence (molecular-to-clinical) 1) Trigger: congenital loss of citrin transport activity in hepatocyte mitochondria. (hayasaka2024pathogenesisandmanagement pages 1-2) 2) Early metabolic consequences: impaired MAS and aspartate export → reduced cytosolic NAD+ and ATP and cytosolic aspartate deficiency. (hayasaka2024pathogenesisandmanagement pages 2-4) 3) Pathway-level effects: • Glycolysis and glycogenesis fall; carbohydrate load can further deplete ATP due to GAPDH-step inhibition and redox imbalance. (hayasaka2024pathogenesisandmanagement pages 7-9) • De novo lipogenesis decreases; PPARα downregulates; β-oxidation becomes impaired → steatosis and dyslipidemia risk. (hayasaka2024pathogenesisandmanagement pages 1-2) • Urea-cycle flux is perturbed by limited aspartate/ATP; hyperammonemia may be driven by impaired GS-mediated detoxification due to glutamate/ATP deficiency and altered zonation. (hayasaka2024pathogenesisandmanagement pages 4-6) 4) Tissue/organ manifestations: neonatal cholestasis/steatosis (NICCD), later growth failure/hypoglycemia/hyperlipidemia (FTTDCD), and episodic hyperammonemic encephalopathy in a subset (CTLN2). (hayasaka2024pathogenesisandmanagement pages 2-4)

6.2 Clinical stages (phenotype spectrum) A 2024 synthesis explicitly describes NICCD, an interstage that may appear “apparently healthy,” possible evolution to FTTDCD, and adult-onset CTLN2 (~5% of patients; age range stated as 10–70 years) with complications including pancreatitis and HCC risk. (hayasaka2024pathogenesisandmanagement pages 2-4)

Phenotypic manifestations (HP terms; suggested mappings) Suggested phenotype mappings (HP IDs should be validated in the target ontology build): • Neonatal cholestasis / conjugated hyperbilirubinemia (NICCD). (chuenwattana2024neonatalintrahepaticcholestasis pages 1-3) • Failure to thrive / growth impairment (FTTDCD; also NICCD severe cases). (hayasaka2024pathogenesisandmanagement pages 2-4) • Dyslipidemia / hyperlipidemia (FTTDCD; CTLN2-associated metabolic phenotype). (hayasaka2024pathogenesisandmanagement pages 2-4) • Fatty liver / hepatic steatosis (common across stages). (hayasaka2024pathogenesisandmanagement pages 2-4) • Hypoketotic hypoglycemia (mechanistically linked to impaired glycogenesis/gluconeogenesis/ketogenesis). (hayasaka2024pathogenesisandmanagement pages 1-2) • Hyperammonemia and encephalopathy (CTLN2). (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • Elevated citrulline (biochemical hallmark; reflects urea-cycle perturbation). (hayasaka2024pathogenesisandmanagement pages 2-4)
Recent developments (2023–2024) and real-world implementations 8.1 Newborn screening and second-tier genetic testing A 2024 implementation study reports an operational two-tier newborn screening strategy combining first-tier MS/MS analytes with second-tier targeted NGS on dried blood spots for six IEMs including citrin deficiency. Quantitative performance/operations: • N screened: 22,883 newborns (Sept 2021–Aug 2022). (chan2024harnessingnextgenerationsequencing pages 3-5) • Second-tier genetic testing applied to 1.8% (421/22,883). (chan2024harnessingnextgenerationsequencing pages 3-5) • Recall rate: 0.031% (7/22,883). (chan2024harnessingnextgenerationsequencing pages 3-5) • False positive rate (post-NGS): 0.017% across six conditions. (chan2024harnessingnextgenerationsequencing pages 1-2, chan2024harnessingnextgenerationsequencing pages 3-5) • Turnaround time: median 3.5 days, TAT90 = 5 working days. (chan2024harnessingnextgenerationsequencing pages 3-5) • Clinical yield: true positives included citrin deficiency/citrullinemia type II (n=2); authors state two CD cases would have been missed if relying on first-tier biochemical screening alone. (chan2024harnessingnextgenerationsequencing pages 1-2) • Implementation detail: targeted detection of SLC25A13 hotspot IVS16ins3kb using a CNV-calling approach began May 2023. (chan2024harnessingnextgenerationsequencing pages 2-3) (Chan et al., Mar 2024; https://doi.org/10.3390/ijns10010019) (chan2024harnessingnextgenerationsequencing pages 1-2, chan2024harnessingnextgenerationsequencing pages 2-3)

8.2 Recognition of biochemical false negatives / borderline citrulline A 2024 Thai NICCD series emphasizes that dried blood spot citrulline can be borderline/normal and that relying only on biochemical cutoffs may miss cases; it explicitly discusses eNBS expansion (regions 7/8 from Oct 2023) and argues for ethnicity-tailored molecular second-tier testing. (Chuenwattana et al., Apr 2024; https://doi.org/10.1016/j.hmedic.2024.100051) (chuenwattana2024neonatalintrahepaticcholestasis pages 3-5, chuenwattana2024neonatalintrahepaticcholestasis pages 1-3)

8.3 Variant spectrum expansion via clinical genomics A 2023 NICCD case report of four infants reported three novel SLC25A13 variants (nonsense, frameshift, and whole-exon deletion) and reiterates that genetic testing is important for diagnosis due to atypical phenotypes. (Wang et al., Mar 2023; https://doi.org/10.3389/fped.2023.1103877) (wang2023casereportthree pages 1-2)

Epidemiology and statistics (recently reported) 9.1 Carrier rates and incidence (selected populations) • Japan: carrier rate approximately 1:42–1:65 in parts of Japan. (hayasaka2024pathogenesisandmanagement pages 1-2) • China: carrier rate reported as 1/65. (wang2023casereportthree pages 1-2) • Thailand: incidence estimated at ~1 in 33,000 live births; cited Thai carrier frequency for a variant at least 1 in 90. (chuenwattana2024neonatalintrahepaticcholestasis pages 1-3, chuenwattana2024neonatalintrahepaticcholestasis pages 3-5)

9.2 Screening yield improvement with molecular methods (Thailand; cited within 2024 report) The Thai series cites that adding molecular testing after MS/MS screening increased detection from 1/32,673 to 1/18,006. (chuenwattana2024neonatalintrahepaticcholestasis pages 3-5)

9.3 Hospitalized newborn cohort burden (China) A 2024 cohort study of 21,840 hospitalized infants (Chongqing; 2017–2022) reports IEM incidence among hospitalized newborns of 1/377 (58/21,840) and notes NICCD among prevalent disorders in premature infants (contextualizing NICCD in hospital-based diagnostic practice). (Wang et al., May 2024; https://doi.org/10.3389/fgene.2024.1395988) (hayasaka2024pathogenesisandmanagement pages 2-4)

Current applications and real-world management 10.1 Dietary therapy (MCT + carbohydrate restriction) The 2024 review frames therapy as addressing hepatocyte energy deficiency and redox/ATP limitations. It recommends MCT supplementation with a minimal-carbohydrate diet “promptly after the diagnosis” to prevent irreversible damage. (hayasaka2024pathogenesisandmanagement pages 2-4)

Operational dietary rationale and quantitative response: • The review describes an ~8 h “energy depletion period” after meals due to insulin-mediated lowering of free fatty acids, recommending MCT supplementation during this interval. (hayasaka2024pathogenesisandmanagement pages 7-9) • It provides a quantitative biochemical change: plasma glutamate increased from 51.3±18.8 to 168.3±92.0 μmol/L at 2–3 weeks after MCT (p=0.012). (hayasaka2024pathogenesisandmanagement pages 6-7)

10.2 Clinical caution points relevant to implementation • Avoid fructose/glycerol-containing infusions (contraindicated). (hayasaka2024pathogenesisandmanagement pages 7-9)

10.3 Newborn screening program design • A practical recent implementation is the addition of second-tier NGS with specific hotspot detection (IVS16ins3kb) and refined recall rules to reduce false positives while maintaining sensitivity. (chan2024harnessingnextgenerationsequencing pages 3-5, chan2024harnessingnextgenerationsequencing pages 2-3)

Expert analysis (authoritative perspectives) A key expert-level synthesis (Internal Medicine, 2024) interprets the disorder primarily as an energy/redox hepatopathy rather than a simple urea-cycle enzyme deficiency, emphasizing the MAS/MCS interplay, carbohydrate toxicity, and secondary transcriptional dysregulation (PPARα) that impairs lipid oxidation. (hayasaka2024pathogenesisandmanagement pages 1-2, hayasaka2024pathogenesisandmanagement pages 7-9)

The same synthesis argues that hyperammonemia in CTLN2 is better explained by failure of GS-dependent detoxification due to glutamate/ATP shortage (“not primarily caused by a defect in ASS1”), which reorients mechanistic thinking and provides a rationale for energy-targeted therapy. (hayasaka2024pathogenesisandmanagement pages 4-6)

Knowledge-base style annotations 12.1 Gene/protein annotations (HGNC-like) • Gene: SLC25A13 (solute carrier family 25 member 13) → Protein: citrin/AGC2; subcellular: mitochondrial inner membrane; IMS-facing Ca2+-binding EF-hand extension. (hayasaka2024pathogenesisandmanagement pages 1-2, holecek2023aspartateglutamatecarrier2 pages 1-2)

12.2 Suggested GO Biological Process annotations (evidence-cited) • Cellular redox homeostasis / NADH oxidation via MAS (holecek2023aspartateglutamatecarrier2 pages 1-2) • Malate-aspartate shuttle / mitochondrial NADH shuttling (hayasaka2024pathogenesisandmanagement pages 1-2) • Aspartate transport (mitochondrion→cytosol) (holecek2023aspartateglutamatecarrier2 pages 2-4) • Urea cycle / ammonia detoxification (ASS1 and GS-centered mechanism) (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • Fatty acid beta-oxidation regulation via PPARα (hayasaka2024pathogenesisandmanagement pages 1-2) • Glycolytic process perturbation under carbohydrate load (GAPDH-step inhibition) (hayasaka2024pathogenesisandmanagement pages 7-9)

12.3 Suggested Cellular Component annotations (evidence-cited) • Mitochondrial inner membrane (citrin location) (holecek2023aspartateglutamatecarrier2 pages 2-4) • Mitochondrial intermembrane space (EF-hand motifs face IMS) (holecek2023aspartateglutamatecarrier2 pages 1-2) • Cytosol and mitochondrial matrix (MDH/AST localizations in MAS) (holecek2023aspartateglutamatecarrier2 pages 2-4)

12.4 Phenotype associations (HP; evidence-cited) • NICCD: neonatal cholestasis resolving in infancy with diet (chuenwattana2024neonatalintrahepaticcholestasis pages 1-3) • CTLN2: hyperammonemic encephalopathy and citrullinemia (hayasaka2024pathogenesisandmanagement pages 2-4, hayasaka2024pathogenesisandmanagement pages 4-6) • Fatty liver/steatosis linked to PPARα downregulation (hayasaka2024pathogenesisandmanagement pages 2-4)

12.5 Cell type involvement (CL; evidence-cited) • Hepatocytes as principal affected cells; zonated periportal vs perivenous hepatocytes relevant to ureagenesis vs glutamine synthesis; altered ASS1/GS distributions reported in CTLN2. (hayasaka2024pathogenesisandmanagement pages 4-6)

12.6 Anatomical locations (UBERON; evidence-cited) • Liver, hepatic lobule zonation regions (periportal/perivenous), brain (encephalopathy). (hayasaka2024pathogenesisandmanagement pages 4-6, hayasaka2024pathogenesisandmanagement pages 2-4)

12.7 Chemical entities (CHEBI; evidence-cited) • Ammonia, citrulline, aspartate, glutamate, glutamine, citrate, NAD+/NADH, ATP; MCT/MCFA as therapeutic energy substrates; fructose/glycerol as hazardous infusions. (hayasaka2024pathogenesisandmanagement pages 4-6, hayasaka2024pathogenesisandmanagement pages 7-9)

Evidence items (mechanism-centric; with identifiers when available) Because the extracted 2023–2024 texts did not display PMIDs, evidence is provided with DOI/URL and the in-text direct quotes above. • Hayasaka K. “Pathogenesis and Management of Citrin Deficiency.” Internal Medicine. Jul 2024. DOI:10.2169/internalmedicine.2595-23. URL: https://doi.org/10.2169/internalmedicine.2595-23. Key mechanistic quotes include MAS role in regenerating cytosolic NAD+; GS-centered explanation of hyperammonemia; GAPDH-step carbohydrate toxicity; PPARα/β-oxidation downregulation; MCT response statistics. (hayasaka2024pathogenesisandmanagement pages 1-2, hayasaka2024pathogenesisandmanagement pages 4-6, hayasaka2024pathogenesisandmanagement pages 7-9, hayasaka2024pathogenesisandmanagement pages 6-7) • Holeček M. “Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver.” BMB Reports. Jun 2023. DOI:10.5483/bmbrep.2023-0052. URL: https://doi.org/10.5483/bmbrep.2023-0052. Key quote: MAS required for intracellular redox balance/respiration/ATP; MAS component localization; AGC2 IMS-facing EF-hands. (holecek2023aspartateglutamatecarrier2 pages 1-2, holecek2023aspartateglutamatecarrier2 pages 2-4) • Chan TCH et al. “Harnessing Next-Generation Sequencing as a Timely and Accurate Second-Tier Screening Test for Newborn Screening of Inborn Errors of Metabolism.” Int J Neonatal Screening. Mar 2024. DOI:10.3390/ijns10010019. URL: https://doi.org/10.3390/ijns10010019. Provides quantitative NBS implementation metrics for CTLN2/CD and hotspot IVS16ins3kb detection. (chan2024harnessingnextgenerationsequencing pages 1-2, chan2024harnessingnextgenerationsequencing pages 3-5, chan2024harnessingnextgenerationsequencing pages 2-3) • Chuenwattana S et al. “NICCD in Thai infants… considerations for negative newborn screening.” Medical Reports. Apr 2024. DOI:10.1016/j.hmedic.2024.100051. URL: https://doi.org/10.1016/j.hmedic.2024.100051. Provides Thailand incidence estimate (~1:33,000), variant examples, and NBS false-negative caution. (chuenwattana2024neonatalintrahepaticcholestasis pages 1-3) • Wang K et al. “Three novel variants on SLC25A13 in four infants with NICCD.” Front Pediatr. Mar 2023. DOI:10.3389/fped.2023.1103877. URL: https://doi.org/10.3389/fped.2023.1103877. Expands variant spectrum; provides China carrier estimate (1/65). (wang2023casereportthree pages 1-2)
Limitations of this report relative to the user’s requirements • PMID requirement: Several key statements are supported by peer-reviewed review articles whose PMIDs were not included in the retrieved text excerpts; therefore, this report provides DOI/URL citations and quotes but cannot supply PMIDs for those specific sources from the available evidence. (hayasaka2024pathogenesisandmanagement pages 1-2, holecek2023aspartateglutamatecarrier2 pages 1-2) • Primary mechanistic experiments: The 2024 review summarizes primary literature; however, in this retrieval run we did not fetch the underlying primary experimental papers themselves. Thus, mechanistic claims here are primarily review-supported rather than directly quoted from original experimental articles.

Figures supporting key mechanism • Hayasaka 2024 Figure 2 (MAS/MCS + MCT rationale) and Figure 4 (ammonia detoxification/urea-cycle schematic) were retrieved as cropped images and can be used as visual evidence of the pathway model. (hayasaka2024pathogenesisandmanagement media 4eb23285, hayasaka2024pathogenesisandmanagement media c2a905ba)

References

(hayasaka2024pathogenesisandmanagement pages 1-2): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(hayasaka2024pathogenesisandmanagement pages 2-4): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(hayasaka2024pathogenesisandmanagement pages 7-9): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(holecek2023aspartateglutamatecarrier2 pages 1-2): Milan Holeček. Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver. BMB Reports, 56:385-391, Jun 2023. URL: https://doi.org/10.5483/bmbrep.2023-0052, doi:10.5483/bmbrep.2023-0052. This article has 5 citations and is from a peer-reviewed journal.
(hayasaka2024pathogenesisandmanagement media 4eb23285): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(holecek2023aspartateglutamatecarrier2 pages 2-4): Milan Holeček. Aspartate-glutamate carrier 2 (citrin): a role in glucose and amino acid metabolism in the liver. BMB Reports, 56:385-391, Jun 2023. URL: https://doi.org/10.5483/bmbrep.2023-0052, doi:10.5483/bmbrep.2023-0052. This article has 5 citations and is from a peer-reviewed journal.
(hayasaka2024pathogenesisandmanagement pages 4-6): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(hayasaka2024pathogenesisandmanagement media c2a905ba): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(wang2023casereportthree pages 1-2): Kena Wang, Biao Zou, Fan Chen, Jianling Zhang, Zhihua Huang, and Sainan Shu. Case report: three novel variants on slc25a13 in four infants with neonatal intrahepatic cholestasis caused by citrin deficiency. Frontiers in Pediatrics, Mar 2023. URL: https://doi.org/10.3389/fped.2023.1103877, doi:10.3389/fped.2023.1103877. This article has 4 citations.
(hayasaka2024pathogenesisandmanagement pages 6-7): Kiyoshi Hayasaka. Pathogenesis and management of citrin deficiency. Internal Medicine, 63:1977-1986, Jul 2024. URL: https://doi.org/10.2169/internalmedicine.2595-23, doi:10.2169/internalmedicine.2595-23. This article has 13 citations and is from a peer-reviewed journal.
(chuenwattana2024neonatalintrahepaticcholestasis pages 1-3): Sirilak Chuenwattana, Kanokwan Imtawil, Kanda Sornkayasit, Aree Rattanathongkom, Busara Charoenwat, and Khunton Wichajarn. Neonatal intrahepatic cholestasis caused by citrin deficiency (niccd) in thai infants: case reports on clinical presentation, genotype analysis, and considerations for negative newborn screening. Medical Reports, 4:100051, Apr 2024. URL: https://doi.org/10.1016/j.hmedic.2024.100051, doi:10.1016/j.hmedic.2024.100051. This article has 2 citations.
(chan2024harnessingnextgenerationsequencing pages 3-5): Toby Chun Hei Chan, Chloe Miu Mak, Matthew Chun Wing Yeung, Eric Chun-Yiu Law, Jana Cheung, Tsz Ki Wong, Vincent Wing-Sang Cheng, Jacky Kwan Ho Lee, Jimmy Chi Lap Wong, Cheuk Wing Fung, Kiran Moti Belaramani, Anne Mei Kwun Kwok, and Kwok Yeung Tsang. Harnessing next-generation sequencing as a timely and accurate second-tier screening test for newborn screening of inborn errors of metabolism. International Journal of Neonatal Screening, 10:19, Mar 2024. URL: https://doi.org/10.3390/ijns10010019, doi:10.3390/ijns10010019. This article has 8 citations.
(chan2024harnessingnextgenerationsequencing pages 1-2): Toby Chun Hei Chan, Chloe Miu Mak, Matthew Chun Wing Yeung, Eric Chun-Yiu Law, Jana Cheung, Tsz Ki Wong, Vincent Wing-Sang Cheng, Jacky Kwan Ho Lee, Jimmy Chi Lap Wong, Cheuk Wing Fung, Kiran Moti Belaramani, Anne Mei Kwun Kwok, and Kwok Yeung Tsang. Harnessing next-generation sequencing as a timely and accurate second-tier screening test for newborn screening of inborn errors of metabolism. International Journal of Neonatal Screening, 10:19, Mar 2024. URL: https://doi.org/10.3390/ijns10010019, doi:10.3390/ijns10010019. This article has 8 citations.
(chan2024harnessingnextgenerationsequencing pages 2-3): Toby Chun Hei Chan, Chloe Miu Mak, Matthew Chun Wing Yeung, Eric Chun-Yiu Law, Jana Cheung, Tsz Ki Wong, Vincent Wing-Sang Cheng, Jacky Kwan Ho Lee, Jimmy Chi Lap Wong, Cheuk Wing Fung, Kiran Moti Belaramani, Anne Mei Kwun Kwok, and Kwok Yeung Tsang. Harnessing next-generation sequencing as a timely and accurate second-tier screening test for newborn screening of inborn errors of metabolism. International Journal of Neonatal Screening, 10:19, Mar 2024. URL: https://doi.org/10.3390/ijns10010019, doi:10.3390/ijns10010019. This article has 8 citations.
(chuenwattana2024neonatalintrahepaticcholestasis pages 3-5): Sirilak Chuenwattana, Kanokwan Imtawil, Kanda Sornkayasit, Aree Rattanathongkom, Busara Charoenwat, and Khunton Wichajarn. Neonatal intrahepatic cholestasis caused by citrin deficiency (niccd) in thai infants: case reports on clinical presentation, genotype analysis, and considerations for negative newborn screening. Medical Reports, 4:100051, Apr 2024. URL: https://doi.org/10.1016/j.hmedic.2024.100051, doi:10.1016/j.hmedic.2024.100051. This article has 2 citations.

Citrin Deficiency

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