👪

Inheritance

1

Autosomal recessive inheritance HP:0000007

Autosomal recessive inheritance

Show evidence (2 references)

PMID:34873722 SUPPORT Human Clinical

"MPC deficiency (OMIM#614741) due to pathogenic MPC1 variants is a rare autosomal recessive disease involving developmental delay, microcephaly, growth failure, and increased serum lactate and pyruvate."

States recessive inheritance for MPC1-related deficiency.

PMID:36417180 SUPPORT Human Clinical

"In the first family, patients presented with antenatal developmental abnormalities and harboured a homozygous c.148T>C (p.Trp50Arg) variant."

A homozygous MPC2 variant segregating with disease, consistent with recessive inheritance for the MPC2 subtype.

◆

Subtypes

2

MPC1-related mitochondrial pyruvate carrier deficiency

The original and commoner form, caused by biallelic MPC1 missense or loss-of-function variants. Variants either destabilise the MPC complex, so that MPC2 is lost as well, or ablate pyruvate uptake in an assembled complex.

Show evidence (1 reference)

PMID:22628558 SUPPORT Human Clinical

"Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes."

The first families in which the disease was mapped to MPC1.

MPC2-related mitochondrial pyruvate carrier deficiency

Described in four patients from two families, one with a homozygous p.Trp50Arg variant and antenatal developmental abnormalities and one with a start-codon variant and infantile encephalopathy. Fibroblasts show the same pyruvate-specific respiratory defect as MPC1 deficiency, rescued by wild-type MPC2.

Show evidence (1 reference)

PMID:36417180 SUPPORT Human Clinical

"The present work describes the first pathogenic variants in MPC2 associated with human disease in four patients from two unrelated families."

First report of MPC2-related disease.

⚙

Pathophysiology

6

Biallelic MPC1 or MPC2 Variants

Biallelic missense, start-codon or other loss-of-function variants in MPC1 or MPC2 are the initiating lesion. Because the two subunits stabilise each other, variants in either gene can destabilise the whole complex; patient fibroblasts with MPC1 variants show reduced MPC1 and MPC2 protein.

MPC1 hgnc:21606 MPC2 hgnc:24515

Genetic context variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

Downstream

Loss of the MPC1-MPC2 Carrier Complex

Show evidence (2 references)

PMID:34873722 SUPPORT Human Clinical

"Herein, we report three novel pathogenic MPC1 variants in six patients from three unrelated families, identified within European, Kuwaiti, and Chinese mitochondrial disease patient cohorts, one of whom presented as a Leigh-like syndrome."

Additional MPC1 variants in affected families.

PMID:37899339 SUPPORT Human Clinical

"A total of 5 MPC1 gene missense variants and 2 MPC2 gene variants were identified in 15 cases."

Summarises the allelic spectrum across both genes in 15 reported cases.

Loss of the MPC1-MPC2 Carrier Complex

MPC1 and MPC2 form a hetero-oligomeric complex of about 150 kDa in the inner mitochondrial membrane, and each subunit is needed to stabilise the other. Pathogenic variants leave either no stable complex or a complex that cannot transport pyruvate.

pyruvate transmembrane transporter activity GO:0050833 ↓ DECREASED

Downstream

Impaired Mitochondrial Pyruvate Import

Show evidence (5 references)

PMID:22628558 SUPPORT In Vitro

"Mpc1 and Mpc2 associate to form an ~150-kilodalton complex in the inner mitochondrial membrane."

Defines the carrier as a two-subunit complex.

PMID:34873722 SUPPORT In Vitro

"Functional analysis in primary fibroblasts from the patients revealed decreased expression of MPC1 and MPC2."

MPC1 variants reduce both subunits in patient cells.

PMID:31145700 SUPPORT In Vitro

"Truncated MPC1 A58G protein was intrinsically unstable and failed to form MPC complexes."

One patient allele product cannot assemble the complex.

+ 2 more references

Impaired Mitochondrial Pyruvate Import

Pyruvate cannot cross the inner mitochondrial membrane, so it is not oxidised by pyruvate dehydrogenase even though that enzyme and the respiratory chain are intact. Patient fibroblasts show reduced pyruvate-driven respiration that is restored by re-expressing the wild-type subunit, and a profile that mimics control cells treated with the carrier inhibitor alpha-cyano-4-hydroxycinnamate.

pyruvate import into mitochondria GO:0006850 ↓ DECREASED

Downstream

Reduced Mitochondrial Pyruvate Oxidation

Show evidence (3 references)

PMID:36417180 SUPPORT In Vitro

"Patient-derived skin fibroblasts exhibit decreased pyruvate-driven oxygen consumption rates with normal activities of the pyruvate dehydrogenase complex and mitochondrial respiratory chain and no defects in mitochondrial content or morphology."

Pyruvate-specific respiratory defect with intact downstream enzymes.

PMID:36417180 SUPPORT In Vitro

"Re-expression of wild-type MPC2 restored pyruvate-dependent respiration rates in patient-derived fibroblasts."

Rescue confirms the defect lies in the carrier.

PMID:12649063 SUPPORT In Vitro

"Our results are consistent with a defect of mitochondrial pyruvate transport in the patient."

The original functional description of the transport defect in permeabilised patient fibroblasts.

Reduced Mitochondrial Pyruvate Oxidation

Pyruvate-derived acetyl-CoA no longer feeds the tricarboxylic acid cycle, so oxidative energy production from glucose falls. Tissues most dependent on glucose oxidation, above all the developing brain, are most affected. Glutamine and beta-hydroxybutyrate can still sustain respiration in carrier-deficient cells because they enter the cycle by other routes.

pyruvate decarboxylation to acetyl-CoA GO:0006086 ↓ DECREASED

Animal models

Mpc1 knockout mouse Mouse recapitulates Glucose-derived pyruvate contributes less to the TCA cycle and glutaminolysis rises.

Mpc1 partial-deficiency mouse Mouse partially recapitulates A mild energy deficit compensated by fatty acid oxidation.

Downstream

Accumulation of Pyruvate and Lactate

Neuronal Energy Failure

Show evidence (2 references)

PMID:34873722 SUPPORT In Vitro

"We rescued pyruvate-driven oxygen consumption rate in patient's fibroblasts by reconstituting with wild-type MPC1."

Pyruvate-driven respiration is reduced in patient fibroblasts and restored by wild-type MPC1.

PMID:22628558 SUPPORT Model Organism

"Yeast and Drosophila mutants lacking MPC1 display impaired pyruvate metabolism, with an accumulation of upstream metabolites and a depletion of tricarboxylic acid cycle intermediates."

Loss of the carrier depletes TCA cycle intermediates in model organisms.

Accumulation of Pyruvate and Lactate

Unused pyruvate accumulates in the cytosol and is reduced to lactate, so blood and cerebrospinal fluid lactate and pyruvate rise together with a normal lactate:pyruvate ratio. The acidosis can be severe and resistant to bicarbonate.

Downstream

Lactic acidosis

Increased circulating pyruvate concentration

Show evidence (2 references)

PMID:37899339 SUPPORT Human Clinical

"All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."

Case series and literature review showing raised lactate and pyruvate with a normal ratio in every patient.

PMID:12649063 SUPPORT Human Clinical

"She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."

The first patient had marked lactic acidosis with a normal ratio.

Neuronal Energy Failure

Reduced oxidation of glucose-derived pyruvate deprives the developing brain of energy, producing developmental delay, microcephaly, hypotonia, seizures and, in severe cases, encephalopathy and early death.

Animal models

Mpc1 knockout mouse Mouse recapitulates Embryonic brains show morphological defects and energy deficit that a ketogenic diet reverses.

Downstream

Global developmental delay

Microcephaly

Hypotonia

Seizures

Periventricular cysts

Basal ganglia and thalamic signal abnormality

Growth failure

Show evidence (1 reference)

PMID:36417180 SUPPORT BACKGROUND Human Clinical

"Pathogenic variants in the MPC1 gene disrupt mitochondrial pyruvate uptake and oxidation and cause autosomal-recessive early-onset neurological dysfunction in humans."

Links loss of pyruvate uptake and oxidation to early-onset neurological dysfunction.

⬡

Pathograph

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

●

Phenotypes

10

Head and Neck 2

Microcephaly HP:0000252

Show evidence (1 reference)

PMID:37899339 SUPPORT Human Clinical

"The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."

Microcephaly is one of the commonest features.

Facial dysmorphism Abnormal facial shape HP:0001999

Show evidence (1 reference)

PMID:12649063 SUPPORT Human Clinical

"She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."

Facial dysmorphism in the index patient.

Metabolism 2

Lactic acidosis VERY_FREQUENT HP:0003128

Show evidence (2 references)

PMID:37899339 SUPPORT Human Clinical

"All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."

Raised lactate in every reported patient.

PMID:22628558 SUPPORT Human Clinical

"Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes."

Lactic acidosis in the families used to map the disease to MPC1.

Increased circulating pyruvate concentration VERY_FREQUENT HP:0003542

Show evidence (1 reference)

PMID:37899339 SUPPORT Human Clinical

"All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."

Raised pyruvate with a normal ratio in every reported patient.

Musculoskeletal 1

Hypotonia HP:0001252

Show evidence (2 references)

PMID:37899339 SUPPORT Human Clinical

"The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."

Hypotonia is one of the commonest features.

PMID:12649063 SUPPORT Human Clinical

"She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."

Neonatal hypotonia in the first described patient.

Nervous System 4

Global developmental delay VERY_FREQUENT HP:0001263

Show evidence (1 reference)

PMID:37899339 SUPPORT Human Clinical

"The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."

Developmental delay is the commonest feature across 15 reported cases.

Seizures HP:0001250

Show evidence (1 reference)

PMID:36079864 SUPPORT Human Clinical

"Subject MPC1-1 had myoclonic seizures at 2 ½ months and infantile spasms from eight months on."

Early-onset myoclonic seizures and infantile spasms in an MPC1-deficient infant.

Periventricular cysts HP:0007109

Show evidence (1 reference)

PMID:12649063 SUPPORT Human Clinical

"She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."

Periventricular cysts at birth in the first described patient.

Basal ganglia and thalamic signal abnormality Abnormal basal ganglia MRI signal intensity HP:0012751

Show evidence (1 reference)

PMID:37899339 SUPPORT Human Clinical

"Seven patients performed cranial MRI, 3 exhibited non-specific changes, 2 showed bilateral symmetrical T2 signal hyperintensity in basal ganglia and thalamus, and 3 were normal."

Basal ganglia and thalamic T2 hyperintensity in a minority of imaged patients.

Growth 1

Growth failure Growth delay HP:0001510

Show evidence (1 reference)

PMID:37899339 SUPPORT Human Clinical

"The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."

Growth failure is one of the commonest features.

💊

Medical Actions

2

Ketogenic diet

Action: ketogenic diet Ontology label: Ketogenic Diet NCIT:C173168

Platform: Behavioral / lifestyle

A high-fat, low-carbohydrate diet supplies ketone-derived acetyl-CoA that enters the tricarboxylic acid cycle without the carrier. The response is mixed: some MPC1-deficient patients improved, including seizure control, while in the first described patient the diet did not correct the lactic acidosis.

Mechanism Target:

BYPASSES Reduced Mitochondrial Pyruvate Oxidation — Ketone bodies provide acetyl-CoA downstream of the blocked pyruvate import step.

Show evidence (4 references)

PMID:36079864 SUPPORT Human Clinical

"In MPC1-deficiency, we report for the first time a beneficial clinical course on KD."

First report of clinical benefit from ketogenic diet in MPC1 deficiency.

PMID:36079864 SUPPORT Human Clinical

"Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits-mainly a striking effect against seizures."

Benefit across the pooled malate-aspartate shuttle and MPC1 group, mainly on seizures; MPC1 patients are a minority of this group.

PMID:12649063 REFUTE Human Clinical

"Hyperlactacidemia was severe (5-14 mmol/l) and not corrected with bicarbonate, thiamine (10 mg/d), 2-chloropropionate (100 mg/kg/d) and a ketogenic diet."

The index patient's lactic acidosis did not respond to the diet.

+ 1 more reference

Glutamine supplementation

Action: Pharmacotherapy NCIT:C15986

Agent: glutamine CHEBI:28300

Platform: Small molecule

Oral glutamine provides an anaplerotic substrate that can sustain mitochondrial respiration in carrier-deficient cells. Three Chinese patients improved in motor ability, cognition and endurance after two years of glutamine.

Mechanism Target:

BYPASSES Reduced Mitochondrial Pyruvate Oxidation — Glutamine enters the tricarboxylic acid cycle as alpha-ketoglutarate, independent of pyruvate import.

Show evidence (2 references)

PMID:34873722 SUPPORT In Vitro

"Furthermore, we showed that glutamine and beta-hydroxybutyrate were alternative substrates to maintain mitochondrial respiration when cells lack pyruvate."

Cellular rationale for glutamine as an alternative fuel.

PMID:37899339 SUPPORT Human Clinical

"Clinical symptoms including motor ability, cognition and activity endurance were improved in these 3 patients after taking glutamine for 2 years."

Clinical improvement in three treated patients; uncontrolled case series.

🔬

Diagnosis

1

Pyruvate oxidation studies and MPC1/MPC2 sequencing

Raised lactate and pyruvate with a normal ratio point to a pyruvate oxidation defect. Normal pyruvate dehydrogenase and respiratory chain activities with reduced pyruvate-driven respiration in intact or permeabilised cells point to the carrier, and sequencing of MPC1 and MPC2 confirms it. Import defects are missed if pyruvate oxidation is not measured in intact mitochondria.

Show evidence (2 references)

PMID:25526709 SUPPORT Human Clinical

"Cofactor and transport defects can be missed, if pyruvate oxidation is not measured in intact mitochondria routinely."

Explains why import defects escape routine enzyme testing.

PMID:36417180 SUPPORT Human Clinical

"The lactate/pyruvate (L/P) molar ratios, mitochondrial respiratory chain and pyruvate dehydrogenase (PDH) activities were normal."

The normal ratio and normal downstream enzyme activities that separate the disorder from PDH and respiratory chain defects.

🐁

Animal Models

2

Mpc1 knockout mouse

Complete Mpc1 loss is embryonic-lethal at about E13.5, with lactic acidosis, depleted TCA cycle intermediates, energy deficit and abnormal brain morphology and neurotransmitter balance. A maternal ketogenic diet reverses these changes and allows normal gestation, although pups die shortly after birth.

Species

Mouse

Genotype

Mpc1-/- (complete loss of MPC1 expression)

Publication

PMID:27176894

Pathograph links

Reduced Mitochondrial Pyruvate Oxidation recapitulates fidelity: high Glucose-derived pyruvate contributes less to the TCA cycle and glutaminolysis rises.

Show evidence (1 reference)

PMID:27176894 SUPPORT Model Organism

"Labeling experiments using 13C-labeled glucose and glutamine demonstrated that MPC deficiency causes increased glutaminolysis and reduced contribution of glucose-derived pyruvate to the TCA cycle."

Isotope tracing of the oxidation defect in knockout cells.

Neuronal Energy Failure recapitulates fidelity: moderate Embryonic brains show morphological defects and energy deficit that a ketogenic diet reverses.

Limitations: Complete knockout is embryonic-lethal, more severe than most human patients, who carry missense or partial-function alleles.

Show evidence (2 references)

PMID:27176894 SUPPORT Model Organism

"Morphological defects were observed in mutant embryonic brains, together with major alterations of their metabolome including lactic acidosis, diminished TCA cycle intermediates, energy deficit and a perturbed balance of neurotransmitters."

Brain energy failure in the knockout.

+ 1 more reference

Mpc1 partial-deficiency mouse

Viable mice with partial MPC1 loss have low body weight and reduced movement that improve on a high-fat diet, consistent with fatty acid oxidation compensating for reduced pyruvate oxidation.

Species

Mouse

Genotype

Mpc1+/- (CRISPR/Cas9)

Publication

PMID:29175325

Pathograph links

Reduced Mitochondrial Pyruvate Oxidation partially recapitulates fidelity: low A mild energy deficit compensated by fatty acid oxidation.

Limitations: Heterozygous mice model partial carrier loss; human disease is biallelic.

Show evidence (1 reference)

PMID:29175325 SUPPORT Model Organism

"The MPC1+/- mice may employ fatty acid oxidation to meet their bioenergetic demands."

Compensation by fatty acid oxidation in the partial-loss mouse.

{ }

Source YAML

click to show

name: Mitochondrial Pyruvate Carrier Deficiency
creation_date: '2026-10-12T18:40:00Z'
category: Mendelian
parents:
- Mitochondrial Disease
- Disorder of Pyruvate Metabolism
- Inborn Error of Metabolism
disease_term:
  preferred_term: mitochondrial pyruvate carrier deficiency
  term:
    id: MONDO:0013877
    label: mitochondrial pyruvate carrier deficiency
synonyms:
- MPYCD
- MPC deficiency
- MPC1 deficiency
- defect in mitochondrial pyruvate transport
description: >-
  Mitochondrial pyruvate carrier (MPC) deficiency is a rare autosomal
  recessive inborn error of pyruvate oxidation caused by biallelic variants in
  MPC1 or, less often, MPC2, which encode the two interdependent subunits of
  the carrier that imports pyruvate across the inner mitochondrial membrane.
  Without it, pyruvate made by glycolysis cannot reach pyruvate dehydrogenase
  and the tricarboxylic acid cycle, so pyruvate and lactate accumulate while
  mitochondrial respiration from pyruvate falls. Because cytosolic redox
  balance is preserved, lactate and pyruvate rise together and the
  lactate:pyruvate ratio stays normal, the same biochemical signature as
  pyruvate dehydrogenase deficiency, from which it is distinguished by normal
  pyruvate dehydrogenase and respiratory chain activities and by impaired
  pyruvate oxidation in intact or permeabilised cells. Onset is usually in the
  first six months, with global developmental delay, microcephaly, growth
  failure and hypotonia; seizures, encephalopathy, periventricular cysts and
  basal ganglia signal change occur, and some cases are lethal before birth or
  in infancy. Fewer than twenty patients are reported. Ketogenic diet and
  glutamine supplementation, which feed the tricarboxylic acid cycle by routes
  that do not need the carrier, have been followed by clinical improvement.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:34873722
    reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MPC deficiency (OMIM#614741) due to pathogenic MPC1 variants is a rare autosomal recessive disease involving developmental delay, microcephaly, growth failure, and increased serum lactate and pyruvate."
    explanation: >-
      States recessive inheritance for MPC1-related deficiency.
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In the first family, patients presented with antenatal developmental abnormalities and harboured a homozygous c.148T>C (p.Trp50Arg) variant."
    explanation: >-
      A homozygous MPC2 variant segregating with disease, consistent with
      recessive inheritance for the MPC2 subtype.
has_subtypes:
- name: MPC1
  display_name: MPC1-related mitochondrial pyruvate carrier deficiency
  description: >-
    The original and commoner form, caused by biallelic MPC1 missense or
    loss-of-function variants. Variants either destabilise the MPC complex,
    so that MPC2 is lost as well, or ablate pyruvate uptake in an assembled
    complex.
  evidence:
  - reference: PMID:22628558
    reference_title: "A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes."
    explanation: >-
      The first families in which the disease was mapped to MPC1.
- name: MPC2
  display_name: MPC2-related mitochondrial pyruvate carrier deficiency
  description: >-
    Described in four patients from two families, one with a homozygous
    p.Trp50Arg variant and antenatal developmental abnormalities and one with
    a start-codon variant and infantile encephalopathy. Fibroblasts show the
    same pyruvate-specific respiratory defect as MPC1 deficiency, rescued by
    wild-type MPC2.
  evidence:
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The present work describes the first pathogenic variants in MPC2 associated with human disease in four patients from two unrelated families."
    explanation: >-
      First report of MPC2-related disease.
pathophysiology:
- name: Biallelic MPC1 or MPC2 Variants
  biological_scale: MOLECULAR
  description: >-
    Biallelic missense, start-codon or other loss-of-function variants in
    MPC1 or MPC2 are the initiating lesion. Because the two subunits
    stabilise each other, variants in either gene can destabilise the whole
    complex; patient fibroblasts with MPC1 variants show reduced MPC1 and
    MPC2 protein.
  genetic_context:
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
  genes:
  - preferred_term: MPC1
    term:
      id: hgnc:21606
      label: MPC1
  - preferred_term: MPC2
    term:
      id: hgnc:24515
      label: MPC2
  evidence:
  - reference: PMID:34873722
    reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Herein, we report three novel pathogenic MPC1 variants in six patients from three unrelated families, identified within European, Kuwaiti, and Chinese mitochondrial disease patient cohorts, one of whom presented as a Leigh-like syndrome."
    explanation: >-
      Additional MPC1 variants in affected families.
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A total of 5 MPC1 gene missense variants and 2 MPC2 gene variants were identified in 15 cases."
    explanation: >-
      Summarises the allelic spectrum across both genes in 15 reported cases.
  downstream:
  - target: Loss of the MPC1-MPC2 Carrier Complex
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34873722
      reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Complementing homozygous MPC1 mutant cDNA with CRISPR-deleted MPC1 C2C12 cells verified the mechanism of variants: unstable MPC complex or ablated pyruvate uptake activity."
      explanation: >-
        Complementation experiments assign the variants to two mechanisms,
        complex instability or loss of transport activity.
- name: Loss of the MPC1-MPC2 Carrier Complex
  biological_scale: MOLECULAR
  description: >-
    MPC1 and MPC2 form a hetero-oligomeric complex of about 150 kDa in the
    inner mitochondrial membrane, and each subunit is needed to stabilise the
    other. Pathogenic variants leave either no stable complex or a complex
    that cannot transport pyruvate.
  molecular_functions:
  - preferred_term: pyruvate transmembrane transporter activity
    modifier: DECREASED
    term:
      id: GO:0050833
      label: pyruvate transmembrane transporter activity
  evidence:
  - reference: PMID:22628558
    reference_title: "A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Mpc1 and Mpc2 associate to form an ~150-kilodalton complex in the inner mitochondrial membrane."
    explanation: >-
      Defines the carrier as a two-subunit complex.
  - reference: PMID:34873722
    reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Functional analysis in primary fibroblasts from the patients revealed decreased expression of MPC1 and MPC2."
    explanation: >-
      MPC1 variants reduce both subunits in patient cells.
  - reference: PMID:31145700
    reference_title: "Two human patient mitochondrial pyruvate carrier mutations reveal distinct molecular mechanisms of dysfunction."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Truncated MPC1 A58G protein was intrinsically unstable and failed to form MPC complexes."
    explanation: >-
      One patient allele product cannot assemble the complex.
  - reference: PMID:31145700
    reference_title: "Two human patient mitochondrial pyruvate carrier mutations reveal distinct molecular mechanisms of dysfunction."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Conversely, MPC1 L79H protein formed stable complexes with MPC2, but these complexes failed to transport pyruvate."
    explanation: >-
      Another patient allele assembles a complex that cannot transport
      pyruvate.
  - reference: PMID:22628554
    reference_title: "Identification and functional expression of the mitochondrial pyruvate carrier."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Coexpression of mouse MPC1 and MPC2 in Lactococcus lactis promoted transport of pyruvate across the membrane."
    explanation: >-
      The two subunits together are sufficient for pyruvate transport.
  downstream:
  - target: Impaired Mitochondrial Pyruvate Import
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:22628558
      reference_title: "A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Loss of yeast Mpc1 results in defective mitochondrial pyruvate uptake, and silencing of MPC1 or MPC2 in mammalian cells impairs pyruvate oxidation."
      explanation: >-
        Loss of either subunit impairs pyruvate uptake and oxidation.
- name: Impaired Mitochondrial Pyruvate Import
  biological_scale: CELLULAR
  description: >-
    Pyruvate cannot cross the inner mitochondrial membrane, so it is not
    oxidised by pyruvate dehydrogenase even though that enzyme and the
    respiratory chain are intact. Patient fibroblasts show reduced
    pyruvate-driven respiration that is restored by re-expressing the
    wild-type subunit, and a profile that mimics control cells treated with
    the carrier inhibitor alpha-cyano-4-hydroxycinnamate.
  biological_processes:
  - preferred_term: pyruvate import into mitochondria
    modifier: DECREASED
    term:
      id: GO:0006850
      label: pyruvate import into mitochondria
  evidence:
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Patient-derived skin fibroblasts exhibit decreased pyruvate-driven oxygen consumption rates with normal activities of the pyruvate dehydrogenase complex and mitochondrial respiratory chain and no defects in mitochondrial content or morphology."
    explanation: >-
      Pyruvate-specific respiratory defect with intact downstream enzymes.
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Re-expression of wild-type MPC2 restored pyruvate-dependent respiration rates in patient-derived fibroblasts."
    explanation: >-
      Rescue confirms the defect lies in the carrier.
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Our results are consistent with a defect of mitochondrial pyruvate transport in the patient."
    explanation: >-
      The original functional description of the transport defect in
      permeabilised patient fibroblasts.
  downstream:
  - target: Reduced Mitochondrial Pyruvate Oxidation
    causal_link_type: DIRECT
- name: Reduced Mitochondrial Pyruvate Oxidation
  biological_scale: CELLULAR
  description: >-
    Pyruvate-derived acetyl-CoA no longer feeds the tricarboxylic acid cycle,
    so oxidative energy production from glucose falls. Tissues most dependent
    on glucose oxidation, above all the developing brain, are most affected.
    Glutamine and beta-hydroxybutyrate can still sustain respiration in
    carrier-deficient cells because they enter the cycle by other routes.
  biological_processes:
  - preferred_term: pyruvate decarboxylation to acetyl-CoA
    modifier: DECREASED
    term:
      id: GO:0006086
      label: pyruvate decarboxylation to acetyl-CoA
  evidence:
  - reference: PMID:34873722
    reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We rescued pyruvate-driven oxygen consumption rate in patient's fibroblasts by reconstituting with wild-type MPC1."
    explanation: >-
      Pyruvate-driven respiration is reduced in patient fibroblasts and
      restored by wild-type MPC1.
  - reference: PMID:22628558
    reference_title: "A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Yeast and Drosophila mutants lacking MPC1 display impaired pyruvate metabolism, with an accumulation of upstream metabolites and a depletion of tricarboxylic acid cycle intermediates."
    explanation: >-
      Loss of the carrier depletes TCA cycle intermediates in model
      organisms.
  downstream:
  - target: Accumulation of Pyruvate and Lactate
    causal_link_type: DIRECT
  - target: Neuronal Energy Failure
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:25526709
      reference_title: "The spectrum of pyruvate oxidation defects in the diagnosis of mitochondrial disorders."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "PDHC deficiency including regulation and import affect mainly the glucose dependent central and peripheral nervous system and skeletal muscle."
      explanation: >-
        Review of pyruvate oxidation defects placing the import defect among
        those that mainly affect glucose-dependent nervous tissue.
- name: Accumulation of Pyruvate and Lactate
  biological_scale: ORGANISM
  description: >-
    Unused pyruvate accumulates in the cytosol and is reduced to lactate, so
    blood and cerebrospinal fluid lactate and pyruvate rise together with a
    normal lactate:pyruvate ratio. The acidosis can be severe and resistant to
    bicarbonate.
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."
    explanation: >-
      Case series and literature review showing raised lactate and pyruvate
      with a normal ratio in every patient.
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."
    explanation: >-
      The first patient had marked lactic acidosis with a normal ratio.
  downstream:
  - target: Lactic acidosis
  - target: Increased circulating pyruvate concentration
- name: Neuronal Energy Failure
  biological_scale: TISSUE
  description: >-
    Reduced oxidation of glucose-derived pyruvate deprives the developing
    brain of energy, producing developmental delay, microcephaly, hypotonia,
    seizures and, in severe cases, encephalopathy and early death.
  evidence:
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "Pathogenic variants in the MPC1 gene disrupt mitochondrial pyruvate uptake and oxidation and cause autosomal-recessive early-onset neurological dysfunction in humans."
    explanation: >-
      Links loss of pyruvate uptake and oxidation to early-onset neurological
      dysfunction.
  downstream:
  - target: Global developmental delay
  - target: Microcephaly
  - target: Hypotonia
  - target: Seizures
  - target: Periventricular cysts
  - target: Basal ganglia and thalamic signal abnormality
  - target: Growth failure
phenotypes:
- name: Global developmental delay
  category: Neurologic
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."
    explanation: >-
      Developmental delay is the commonest feature across 15 reported cases.
- name: Microcephaly
  category: Neurologic
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."
    explanation: >-
      Microcephaly is one of the commonest features.
- name: Hypotonia
  category: Neurologic
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."
    explanation: >-
      Hypotonia is one of the commonest features.
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."
    explanation: >-
      Neonatal hypotonia in the first described patient.
- name: Growth failure
  category: Growth
  phenotype_term:
    preferred_term: Growth failure
    term:
      id: HP:0001510
      label: Growth delay
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most common clinical symptoms were mental and motor general developmental delay, microcephaly, growth failure and hypotonia."
    explanation: >-
      Growth failure is one of the commonest features.
- name: Seizures
  category: Neurologic
  description: >-
    Seizures including myoclonic seizures and infantile spasms are reported
    in a subset of MPC1-deficient patients.
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:36079864
    reference_title: "Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subject MPC1-1 had myoclonic seizures at 2 ½ months and infantile spasms from eight months on."
    explanation: >-
      Early-onset myoclonic seizures and infantile spasms in an MPC1-deficient
      infant.
- name: Periventricular cysts
  category: Neurologic
  phenotype_term:
    preferred_term: Periventricular cysts
    term:
      id: HP:0007109
      label: Periventricular cysts
  evidence:
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."
    explanation: >-
      Periventricular cysts at birth in the first described patient.
- name: Basal ganglia and thalamic signal abnormality
  category: Neurologic
  description: >-
    Bilateral symmetrical T2 hyperintensity of the basal ganglia and thalamus
    on MRI in some patients, including one presenting as a Leigh-like
    syndrome; MRI is normal or non-specific in others.
  phenotype_term:
    preferred_term: Abnormal basal ganglia MRI signal intensity
    term:
      id: HP:0012751
      label: Abnormal basal ganglia MRI signal intensity
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Seven patients performed cranial MRI, 3 exhibited non-specific changes, 2 showed bilateral symmetrical T2 signal hyperintensity in basal ganglia and thalamus, and 3 were normal."
    explanation: >-
      Basal ganglia and thalamic T2 hyperintensity in a minority of imaged
      patients.
- name: Facial dysmorphism
  category: Craniofacial
  description: >-
    Mild facial dysmorphism in the first described patient; not otherwise
    characterised.
  phenotype_term:
    preferred_term: Mild facial dysmorphism
    term:
      id: HP:0001999
      label: Abnormal facial shape
  evidence:
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She presented at birth with hypotonia, mild facial dysmorphism, periventricular cysts, marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia."
    explanation: >-
      Facial dysmorphism in the index patient.
- name: Lactic acidosis
  category: Metabolic
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Lactic acidosis
    term:
      id: HP:0003128
      label: Lactic acidosis
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."
    explanation: >-
      Raised lactate in every reported patient.
  - reference: PMID:22628558
    reference_title: "A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes."
    explanation: >-
      Lactic acidosis in the families used to map the disease to MPC1.
- name: Increased circulating pyruvate concentration
  category: Laboratory
  frequency: VERY_FREQUENT
  description: >-
    Raised pyruvate alongside raised lactate with a normal lactate:pyruvate
    ratio, the biochemical clue shared with pyruvate dehydrogenase
    deficiency.
  phenotype_term:
    preferred_term: Increased circulating pyruvate concentration
    term:
      id: HP:0003542
      label: Increased circulating pyruvate concentration
  evidence:
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All patients had elevated blood lactate and pyruvate, but the ratio of lactate/pyruvate was normal."
    explanation: >-
      Raised pyruvate with a normal ratio in every reported patient.
diagnosis:
- name: Pyruvate oxidation studies and MPC1/MPC2 sequencing
  description: >-
    Raised lactate and pyruvate with a normal ratio point to a pyruvate
    oxidation defect. Normal pyruvate dehydrogenase and respiratory chain
    activities with reduced pyruvate-driven respiration in intact or
    permeabilised cells point to the carrier, and sequencing of MPC1 and MPC2
    confirms it. Import defects are missed if pyruvate oxidation is not
    measured in intact mitochondria.
  evidence:
  - reference: PMID:25526709
    reference_title: "The spectrum of pyruvate oxidation defects in the diagnosis of mitochondrial disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cofactor and transport defects can be missed, if pyruvate oxidation is not measured in intact mitochondria routinely."
    explanation: >-
      Explains why import defects escape routine enzyme testing.
  - reference: PMID:36417180
    reference_title: "MPC2 variants disrupt mitochondrial pyruvate metabolism and cause an early-onset mitochondriopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The lactate/pyruvate (L/P) molar ratios, mitochondrial respiratory chain and pyruvate dehydrogenase (PDH) activities were normal."
    explanation: >-
      The normal ratio and normal downstream enzyme activities that separate
      the disorder from PDH and respiratory chain defects.
treatments:
- name: Ketogenic diet
  description: >-
    A high-fat, low-carbohydrate diet supplies ketone-derived acetyl-CoA that
    enters the tricarboxylic acid cycle without the carrier. The response is
    mixed: some MPC1-deficient patients improved, including seizure control,
    while in the first described patient the diet did not correct the lactic
    acidosis.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: ketogenic diet
    term:
      id: NCIT:C173168
      label: Ketogenic Diet
  target_mechanisms:
  - target: Reduced Mitochondrial Pyruvate Oxidation
    treatment_effect: BYPASSES
    description: >-
      Ketone bodies provide acetyl-CoA downstream of the blocked pyruvate
      import step.
  evidence:
  - reference: PMID:36079864
    reference_title: "Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In MPC1-deficiency, we report for the first time a beneficial clinical course on KD."
    explanation: >-
      First report of clinical benefit from ketogenic diet in MPC1
      deficiency.
  - reference: PMID:36079864
    reference_title: "Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of 13 MAS/MPC1-individuals with a neurological phenotype treated with KD, 11 experienced benefits-mainly a striking effect against seizures."
    explanation: >-
      Benefit across the pooled malate-aspartate shuttle and MPC1 group,
      mainly on seizures; MPC1 patients are a minority of this group.
  - reference: PMID:12649063
    reference_title: "Impaired mitochondrial pyruvate importation in a patient and a fetus at risk."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Hyperlactacidemia was severe (5-14 mmol/l) and not corrected with bicarbonate, thiamine (10 mg/d), 2-chloropropionate (100 mg/kg/d) and a ketogenic diet."
    explanation: >-
      The index patient's lactic acidosis did not respond to the diet.
  - reference: PMID:36079864
    reference_title: "Ketogenic Diet Treatment of Defects in the Mitochondrial Malate Aspartate Shuttle and Pyruvate Carrier."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: "In contrast, KD has been reported unsuccessful in one case with MPC1-deficiency"
    explanation: >-
      The same cohort paper acknowledges a previously reported non-responder.
- name: Glutamine supplementation
  description: >-
    Oral glutamine provides an anaplerotic substrate that can sustain
    mitochondrial respiration in carrier-deficient cells. Three Chinese
    patients improved in motor ability, cognition and endurance after two
    years of glutamine.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: glutamine
      term:
        id: CHEBI:28300
        label: glutamine
  target_mechanisms:
  - target: Reduced Mitochondrial Pyruvate Oxidation
    treatment_effect: BYPASSES
    description: >-
      Glutamine enters the tricarboxylic acid cycle as alpha-ketoglutarate,
      independent of pyruvate import.
  evidence:
  - reference: PMID:34873722
    reference_title: "Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Furthermore, we showed that glutamine and beta-hydroxybutyrate were alternative substrates to maintain mitochondrial respiration when cells lack pyruvate."
    explanation: >-
      Cellular rationale for glutamine as an alternative fuel.
  - reference: PMID:37899339
    reference_title: "[Mitochondrial pyruvate carrier deficiency: 3 cases report and literature review]."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Clinical symptoms including motor ability, cognition and activity endurance were improved in these 3 patients after taking glutamine for 2 years."
    explanation: >-
      Clinical improvement in three treated patients; uncontrolled case
      series.
animal_models:
- name: Mpc1 knockout mouse
  species: Mouse
  genotype: Mpc1-/- (complete loss of MPC1 expression)
  publication: PMID:27176894
  description: >-
    Complete Mpc1 loss is embryonic-lethal at about E13.5, with lactic
    acidosis, depleted TCA cycle intermediates, energy deficit and abnormal
    brain morphology and neurotransmitter balance. A maternal ketogenic diet
    reverses these changes and allows normal gestation, although pups die
    shortly after birth.
  modeled_mechanisms:
  - target: Reduced Mitochondrial Pyruvate Oxidation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Glucose-derived pyruvate contributes less to the TCA cycle and
      glutaminolysis rises.
    evidence:
    - reference: PMID:27176894
      reference_title: "Embryonic Lethality of Mitochondrial Pyruvate Carrier 1 Deficient Mouse Can Be Rescued by a Ketogenic Diet."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Labeling experiments using 13C-labeled glucose and glutamine demonstrated that MPC deficiency causes increased glutaminolysis and reduced contribution of glucose-derived pyruvate to the TCA cycle."
      explanation: >-
        Isotope tracing of the oxidation defect in knockout cells.
  - target: Neuronal Energy Failure
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Embryonic brains show morphological defects and energy deficit that a
      ketogenic diet reverses.
    limitations: >-
      Complete knockout is embryonic-lethal, more severe than most human
      patients, who carry missense or partial-function alleles.
    evidence:
    - reference: PMID:27176894
      reference_title: "Embryonic Lethality of Mitochondrial Pyruvate Carrier 1 Deficient Mouse Can Be Rescued by a Ketogenic Diet."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Morphological defects were observed in mutant embryonic brains, together with major alterations of their metabolome including lactic acidosis, diminished TCA cycle intermediates, energy deficit and a perturbed balance of neurotransmitters."
      explanation: >-
        Brain energy failure in the knockout.
    - reference: PMID:27176894
      reference_title: "Embryonic Lethality of Mitochondrial Pyruvate Carrier 1 Deficient Mouse Can Be Rescued by a Ketogenic Diet."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Strikingly, these changes were reversed when the pregnant dams were fed a ketogenic diet, which provides acetyl-CoA directly to the TCA cycle and bypasses the need for a functional MPC."
      explanation: >-
        Ketogenic diet rescues the brain phenotype, supporting the bypass
        rationale.
- name: Mpc1 partial-deficiency mouse
  species: Mouse
  genotype: Mpc1+/- (CRISPR/Cas9)
  publication: PMID:29175325
  description: >-
    Viable mice with partial MPC1 loss have low body weight and reduced
    movement that improve on a high-fat diet, consistent with fatty acid
    oxidation compensating for reduced pyruvate oxidation.
  modeled_mechanisms:
  - target: Reduced Mitochondrial Pyruvate Oxidation
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      A mild energy deficit compensated by fatty acid oxidation.
    limitations: >-
      Heterozygous mice model partial carrier loss; human disease is
      biallelic.
    evidence:
    - reference: PMID:29175325
      reference_title: "Fatty acid oxidation alleviates the energy deficiency caused by the loss of MPC1 in MPC1(+/-) mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The MPC1+/- mice may employ fatty acid oxidation to meet their bioenergetic demands."
      explanation: >-
        Compensation by fatty acid oxidation in the partial-loss mouse.
notes: >-
  No GeneReviews chapter covers this disorder. HGNC gives MPC1 as hgnc:21606
  and MPC2 as hgnc:24515.

📚

References & Deep Research

Deep Research

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

Evaluations and curation notes (1)

Create: Mitochondrial Pyruvate Carrier Deficiency · 2026-10-12T19:30:31Z · View source

New entry for mitochondrial pyruvate carrier deficiency (MONDO:0013877), MPC1 and MPC2, with MPC1 and MPC2 subtypes. Pathograph: biallelic MPC1/MPC2 variants -> loss of the MPC1-MPC2 carrier complex (unstable complex or transport-dead complex) -> impaired mitochondrial pyruvate import -> reduced pyruvate oxidation -> pyruvate and lactate accumulation (normal lactate:pyruvate ratio) and neuronal energy failure -> phenotypes (all 9 connected). Treatments: ketogenic diet and glutamine, both modelled as BYPASSES. Animal models: Mpc1 knockout mouse (embryonic lethal, rescued by maternal ketogenic diet) and Mpc1+/- mouse. One OpenScientist deep-research report: built-in validation completed (22/22 references resolved); preflight-dr PASS, with MPC2 mentions reflecting the second carrier subunit. The report swapped the HGNC identifiers of MPC1 and MPC2 and said no human MPC2 disease exists; the entry uses HGNC's own identifiers and cites PMID:36417180 for MPC2 disease. No GeneReviews chapter exists. Validated with just validate-disorders and the offline CI gates.

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Mitochondrial Pyruvate Carrier Deficiency — Comprehensive Disease Characteristics Report

openscientist-autonomous 22 citations 2026-10-12T19:16:20.531487

Mitochondrial Pyruvate Carrier Deficiency — Comprehensive Disease Characteristics Report

Disease: Mitochondrial Pyruvate Carrier Deficiency (MPC deficiency) MONDO ID: MONDO:0013877 · OMIM: 614741 · Orphanet: ORPHA:319652 Category: Mendelian (autosomal recessive inborn error of metabolism) Report date: 2026-10-12

Summary

Mitochondrial Pyruvate Carrier (MPC) Deficiency is an ultra-rare autosomal recessive inborn error of mitochondrial energy metabolism caused by biallelic loss-of-function variants in MPC1 (chromosome 6q27, HGNC:24515), the gene encoding one of the two obligate subunits of the mitochondrial pyruvate carrier. The MPC is a ~150-kDa heterocomplex of MPC1 and MPC2 embedded in the inner mitochondrial membrane, and it constitutes the sole point of entry of pyruvate into the mitochondrial matrix. When the carrier fails, glucose-derived pyruvate cannot reach pyruvate dehydrogenase (PDH) or the TCA cycle: it is shunted to lactate, producing lactic acidosis and hyperpyruvatemia, while the mitochondrion is starved of acetyl-CoA and reducing equivalents, producing a cellular energy deficit (PMID: 22628558; PMID: 22628554; PMID: 35895232).

Clinically, the disease presents in the neonatal period or infancy with developmental delay, microcephaly, hypotonia, growth failure, facial dysmorphism, and persistently elevated serum lactate and pyruvate, sometimes with a Leigh-like encephalopathy (PMID: 12649063; PMID: 34873722). The single most useful biochemical discriminator is a severe hyperlactatemia with a NORMAL lactate/pyruvate (L/P) ratio and normal PDH complex activity — a fingerprint that separates MPC deficiency from PDH complex deficiency (also normal L/P ratio but distinguished by functional pyruvate-transport assays) and from respiratory-chain defects (which raise the L/P ratio) (PMID: 12649063). Confirmation is molecular (MPC1 sequencing) supported by functional studies in digitonin-permeabilized fibroblasts and rescue of pyruvate-driven oxygen consumption by wild-type MPC1 reconstitution (PMID: 12649063; PMID: 34873722).

Fewer than ~15–20 patients have been reported worldwide, so there is no established prevalence/incidence figure and no disease-specific clinical trial. Management is supportive and mechanism-driven: metabolic bypass with a ketogenic diet and anaplerotic substrates aims to deliver acetyl-CoA to the TCA cycle downstream of the broken carrier. This approach rescues Mpc1-null mouse embryos when given to pregnant dams, but in the index human patient a ketogenic diet (and bicarbonate, thiamine, 2-chloropropionate) failed to correct severe hyperlactatemia — so treatment expectations must be tempered (PMID: 27176894; PMID: 12649063). No curative or approved targeted therapy exists; genetic counseling and (where available) prenatal diagnosis are central to care.

Key Findings

Finding 1 — Biallelic MPC1 mutations disrupt the MPC1/MPC2 heterocomplex that imports pyruvate into mitochondria

The molecular basis of the disease was established by two landmark 2012 Science papers. Bricker et al. (A mitochondrial pyruvate carrier required for pyruvate uptake in yeast, Drosophila, and humans, PMID: 22628558) identified MPC1 and MPC2 as essential components of the ~150-kDa mitochondrial pyruvate carrier conserved across yeast, Drosophila, and humans, and mapped a causal locus to MPC1 in three families whose children suffered lactic acidosis and hyperpyruvatemia: "Human genetic studies of three families with children suffering from lactic acidosis and hyperpyruvatemia revealed a causal locus that mapped to MPC1, changing single amino acids that are conserved throughout eukaryotes." In parallel, Herzig et al. (Identification and functional expression of the mitochondrial pyruvate carrier, PMID: 22628554) independently proved the carrier is a heterocomplex: "We report that MPC is a heterocomplex formed by two members of a family of previously uncharacterized membrane proteins that are conserved from yeast to mammals." Co-expression of MPC1 and MPC2 conferred pyruvate transport in Lactococcus lactis, and yeast MPC mutants showed severe defects in mitochondrial pyruvate uptake. Together these define the disrupted molecular entity (the MPC1/MPC2 heterocomplex) and establish MPC1 variants as the cause of a human disease.

Finding 2 — Clinical phenotype and an expanding variant spectrum, including Leigh-like presentations

Jiang et al. 2022 (Identification and characterization of novel MPC1 gene variants causing mitochondrial pyruvate carrier deficiency, PMID: 34873722) characterized the clinical and molecular spectrum in six patients from three unrelated families (European, Kuwaiti, Chinese), reporting three novel pathogenic MPC1 variants. They summarize the disease succinctly: "MPC deficiency (OMIM#614741) due to pathogenic MPC1 variants is a rare autosomal recessive disease involving developmental delay, microcephaly, growth failure, and increased serum lactate and pyruvate." One patient presented as a Leigh-like syndrome. Patient fibroblasts showed decreased MPC1 and MPC2 protein, and — critically — "We rescued pyruvate-driven oxygen consumption rate in patient's fibroblasts by reconstituting with wild-type MPC1," providing functional proof of causality. Mechanistically the variants act either by destabilizing the MPC complex or by abolishing pyruvate-uptake activity.

Finding 3 — Mouse genetics: complete Mpc1 loss is embryonic-lethal and rescued by maternal ketogenic diet

Vanderperre et al. 2016 (Embryonic Lethality of Mitochondrial Pyruvate Carrier 1 Deficient Mouse Can Be Rescued by a Ketogenic Diet, PMID: 27176894) showed that complete MPC1 loss in mice "resulted in embryonic lethality at around E13.5." Mutant mouse embryonic fibroblasts had defective pyruvate-driven respiration and perturbed metabolite profiles, restored by MPC1 re-expression. ¹³C-tracing revealed the key metabolic rewiring: "MPC deficiency causes increased glutaminolysis and reduced contribution of glucose-derived pyruvate to the TCA cycle." Mutant embryonic brains showed morphological defects, lactic acidosis, depleted TCA intermediates, energy deficit, and perturbed neurotransmitter balance. Strikingly, a maternal ketogenic diet rescued development: "these changes were reversed when the pregnant dams were fed a ketogenic diet, which provides acetyl-CoA directly to the TCA cycle and bypasses the need for a functional MPC." Zou et al. 2018 (PMID: 29175325) confirmed complete MPC1 deficiency is embryonic lethal and that fatty-acid oxidation alleviates the energy deficit in partial-loss models. This provides the in vivo proof-of-concept for metabolic bypass therapy.

Finding 4 — The diagnostic signature: severe hyperlactatemia with NORMAL L/P ratio, normal PDH activity, impaired pyruvate oxidation in permeabilized fibroblasts

The first biochemically defined case, Brivet et al. 2003 (Impaired mitochondrial pyruvate importation in a patient and a fetus at risk, PMID: 12649063), remains the diagnostic touchstone. A child of consanguineous parents presented at birth with hypotonia, mild facial dysmorphism, and periventricular cysts, with "marked metabolic acidosis, hyperlactacidemia with normal lactate/pyruvate molar ratios, normoglycemia, and normal ammonia." Lactate ranged 5–14 mmol/L. Crucially, "Pyruvate dehydrogenase (PDHC) activity was normal in lymphocytes and fibroblasts" — excluding the main differential. In digitonin-permeabilized fibroblasts, acetyl-carnitine/TCA-intermediate production from [2-¹⁴C]pyruvate and ¹⁴CO₂ release from [1-¹⁴C]pyruvate were severely impaired, whereas [U-¹⁴C]malate decarboxylation was normal; patient cells phenocopied control cells treated with the specific MPC inhibitor α-cyano-4-hydroxycinnamate. The authors concluded: "Our results are consistent with a defect of mitochondrial pyruvate transport in the patient." A prenatal diagnosis identified an affected fetus.

Biochemical feature	MPC deficiency	PDH complex deficiency	Respiratory-chain defect
Blood lactate	Markedly elevated	Elevated	Elevated
L/P ratio	Normal	Normal	Elevated
PDH activity	Normal	Reduced	Normal
Pyruvate transport (permeabilized fibroblasts)	Impaired	Normal	Normal
Ammonia	Normal	Normal	Variable

Finding 5 — Three distinct molecular mechanisms among patient MPC1 variants (A58G, R97W, L79H)

Oonthonpan et al. 2019 (Two human patient mitochondrial pyruvate carrier mutations reveal distinct molecular mechanisms of dysfunction, PMID: 31145700) dissected two human MPC1 alleles and revealed that disease arises through at least three separable biochemical lesions. The MPC1 c.289C>T allele yields both a mis-spliced truncation (p.A58G) and a full-length point mutant (p.R97W); MPC1 c.236T>A encodes p.L79H. Using patient fibroblasts and complementation of CRISPR MPC1-null C2C12 cells, they found: "Truncated MPC1 A58G protein was intrinsically unstable and failed to form MPC complexes. The MPC1 R97W protein was less stable but when overexpressed formed complexes with MPC2 that retained pyruvate transport activity. Conversely, MPC1 L79H protein formed stable complexes with MPC2, but these complexes failed to transport pyruvate." Thus the carrier can fail at (1) protein stability/assembly (A58G), (2) partial instability but retained transport (R97W), or (3) assembly-competent but transport-dead (L79H). These variants are tied to clinical disease: "Two reported human MPC1 mutations cause developmental abnormalities, neurological problems, metabolic deficits, and for one patient, early death."

Variant	Nomenclature	Complex assembly	Transport activity	Mechanism
A58G	c.289C>T (mis-splice)	Fails to assemble	Absent	Intrinsic instability
R97W	c.289C>T (full-length)	Assembles (when overexpressed)	Retained	Reduced stability
L79H	c.236T>A	Stable complex	Absent	Transport-dead carrier

Finding 6 — MPC is an obligate, non-redundant, druggable node; partial pharmacological inhibition is benign/beneficial, contrasting with severe complete genetic loss

The MPC is described as "the sole point of entry of pyruvate into the mitochondrial matrix" (PMID: 35895232), explaining why complete loss is catastrophic and non-bypassable at the import step. Paradoxically, partial pharmacological inhibition is therapeutically useful in other contexts: MSDC-0160 (an insulin sensitizer and MPC modulator) in 6-OHDA Parkinson's rats improved motor behavior, decreased dopaminergic denervation, reduced mTOR activity and neuroinflammation, and increased ketogenesis, β-oxidation, and glutamate oxidation (PMID: 35895232). Quansah et al. 2018 (PMID: 29793507) note the neuroprotective mechanisms "involve augmentation of autophagy via attenuation of the activity of the mammalian target of rapamycin (mTOR) in neurons, as well as the inhibition of neuroinflammation." Thiazolidinedione-class MPC modulators are in development for type 2 diabetes and NASH (PMID: 36830630; PMID: 40001526). The dose–response contrast (partial inhibition tolerable/beneficial vs. complete genetic loss lethal) is biologically informative for understanding the disease and for drug safety.

Finding 7 — Ultra-rare, autosomal recessive with consanguinity; sits in the "normal L/P ratio" congenital lactic acidosis differential

MPC deficiency is extremely rare. The literature comprises a handful of families: the consanguineous index patient (Brivet 2003, PMID: 12649063), three families in Bricker 2012 (PMID: 22628558), six patients in three families in Jiang 2022 (PMID: 34873722), and three further Chinese cases in Jiang 2023 (PMID: 37899339) — well under 20 reported individuals. Jiang 2022 states: "To date, two MPC1 variants in four cases have been reported, though only one with a detailed clinical description." No formal prevalence/incidence figure is established. Its principal differential, pyruvate dehydrogenase complex deficiency (PDCD), has an incidence of "about 1 in 42,000 live births annually in the USA" (PMID: 37688338). Other differentials sharing congenital lactic acidosis include pyruvate carboxylase deficiency (adds hyperammonemia; PMID: 32145058), ECHS1 deficiency (PMID: 31908952), and respiratory-chain complex defects (which raise the L/P ratio).

Finding 8 — Somatic MPC1 downregulation in cancer mirrors Warburg reprogramming (distinct from germline disease)

Although not the Mendelian disease itself, somatic loss of MPC1 illuminates the cellular consequences of carrier loss. Xue et al. 2021 (Mitochondrial pyruvate carrier 1: a novel prognostic biomarker, PMID: 34059057) report that "MPC1 expression is significantly decreased in cancer tissue and associated with poor prognosis." High MPC1 expression is favorable in KIRC, LUAD, PAAD, and PRAD; low MPC1 in breast-invasive carcinoma associates with shorter survival. MPC is "frequently lost or downregulated" in colorectal cancer (PMID: 42758364), while MPC2 overexpression drives OXPHOS and progression in diffuse large B-cell lymphoma (PMID: 40287899). These are acquired/somatic expression changes, not germline coding variants, but they demonstrate at the cellular level that MPC loss forces a glycolytic (Warburg-type) shift — the same metabolic rerouting seen in the inherited disease.

Finding 9 — Management is metabolic bypass and supportive care; no curative or approved targeted therapy

No disease-specific trial exists. The therapeutic rationale derives from (a) the animal proof-of-concept that a ketogenic diet bypasses the carrier by supplying acetyl-CoA directly to the TCA cycle and rescues Mpc1-null mice (PMID: 27176894), with fatty-acid oxidation alleviating partial-loss energy deficits (PMID: 29175325); and (b) extrapolation from the mechanistically analogous PDCD, where "Ketogenic diet therapy (KDT) is commonly used to bypass defective glucose metabolism" (PMID: 42341672), with earlier initiation and greater carbohydrate restriction improving longevity and mental development (PMID: 9409363). Dichloroacetate is used in PDCD (PMID: 41898592). Importantly, in the original MPC-deficient patient, these measures failed: "Hyperlactacidemia was severe (5-14 mmol/l) and not corrected with bicarbonate, thiamine (10 mg/d), 2-chloropropionate (100 mg/kg/d) and a ketogenic diet" (PMID: 12649063).

Section-by-Section Report

1. Disease Information

MPC deficiency is a Mendelian inborn error of mitochondrial energy metabolism in which pyruvate cannot be transported from the cytosol into the mitochondrial matrix, blocking its oxidation. Key identifiers: MONDO:0013877; OMIM 614741 ("Mitochondrial pyruvate carrier deficiency"); Orphanet ORPHA:319652; MeSH concept mapping to mitochondrial metabolism/lactic acidosis (no dedicated MeSH heading). No specific ICD-10 code exists; it is captured under E88.4-type mitochondrial/metabolic disorder codes. Synonyms/alternative names: MPC deficiency, mitochondrial pyruvate carrier 1 deficiency, MPYCD (OMIM phenotype symbol). Source type: Information is derived from aggregated disease-level resources and individual case reports/case series (not large EHR cohorts), reflecting extreme rarity.

2. Etiology

Causal factor: genetic — biallelic (homozygous or compound heterozygous) loss-of-function variants in MPC1 disrupting the MPC1/MPC2 heterocomplex (PMID: 22628558). Genetic risk factor: the only established risk factor is carrying two pathogenic MPC1 alleles; consanguinity increases homozygosity risk (the index patient was from a consanguineous union; PMID: 12649063). No MPC2-caused human disease has been definitively reported. Environmental risk/protective factors: none established as causal; catabolic stress (fasting, intercurrent illness) can precipitate metabolic crises generically in mitochondrial disease. Protective/modifier factors: dietary ketosis and fatty-acid oxidation partially bypass the defect in models (acetyl-CoA supplied downstream), functioning as a metabolic "protective" intervention (PMID: 27176894; PMID: 29175325). Gene–environment interaction: genotype (residual carrier function) interacts with dietary carbon source — the key actionable GxE axis.

3. Phenotypes

Phenotype	Type	HPO suggestion	Onset	Frequency
Developmental delay / intellectual disability	Neurodevelopmental	HP:0001263 / HP:0001249	Infancy	Common
Microcephaly	Physical/structural	HP:0000252	Congenital/infantile	Reported
Hypotonia	Clinical sign	HP:0001252	Neonatal	Reported
Growth failure / failure to thrive	Clinical sign	HP:0001508	Infancy	Common
Lactic acidosis (hyperlactatemia)	Laboratory	HP:0003128 / HP:0002151	Neonatal/infantile	Hallmark (all)
Hyperpyruvatemia (elevated pyruvate)	Laboratory	HP:0003542	Neonatal	Hallmark
Facial dysmorphism	Physical	HP:0001999	Congenital	Reported (index case)
Periventricular cysts / brain abnormality	Imaging/structural	HP:0002119	Congenital	Reported (index case)
Leigh-like encephalopathy	Clinical syndrome	HP:0002240 (related)	Infantile	Subset
Metabolic acidosis	Laboratory	HP:0001942	Neonatal	Common

Onset is predominantly neonatal to infantile; severity ranges from severe/lethal to milder, with variable expressivity. Progression is generally progressive/episodic with metabolic decompensations. Quality-of-life impact is substantial where neurodevelopmental impairment and recurrent acidosis occur; no disease-specific QoL instrument data exist (not available) (PMID: 12649063; PMID: 34873722).

4. Genetic / Molecular Information

Causal gene: MPC1 (HGNC:24515; NCBI Gene 51660; chromosome 6q27; UniProt Q9Y5U8; OMIM gene 614738). MPC2 (HGNC:21606; UniProt O95563) is the obligate partner subunit; no confirmed human MPC2-disease has been established. Variant classes reported: missense (p.R97W, p.L79H, novel variants in Jiang 2022/2023) and splice-altering/truncating (c.289C>T causing mis-splice → p.A58G). Classification follows ACMG/AMP; reported disease alleles are pathogenic/likely pathogenic with functional support. Allele frequencies: pathogenic alleles are absent or ultra-rare in gnomAD (consistent with recessive, ultra-rare disease). Origin: germline. Functional consequence: loss of function via (1) failed assembly/instability, (2) reduced stability, or (3) assembly-competent but transport-dead carrier (PMID: 31145700). Modifier genes: none validated; genes governing fatty-acid oxidation/ketogenesis and glutaminolysis are candidate metabolic modifiers inferred from mouse data (PMID: 27176894; PMID: 29175325). Epigenetic/chromosomal abnormalities: none described for the Mendelian disease (somatic promoter/expression changes occur in cancers; PMID: 34059057).

5. Environmental Information

No environmental toxin, infectious agent, or occupational exposure causes MPC deficiency — it is a monogenic disease. Lifestyle/dietary carbon source is the single relevant non-genetic lever (ketogenic vs. high-carbohydrate), acting as a disease-modifying rather than disease-causing factor (PMID: 27176894). Catabolic stressors (fasting, febrile illness) can trigger decompensation. Infectious agents: not applicable.

6. Mechanism / Pathophysiology

Ordered causal chain (initiating lesion → clinical manifestation):

Biallelic loss-of-function MPC1 variants are inherited → leads to reduced/absent functional MPC1 protein or an assembly-/transport-defective subunit (PMID: 22628558; PMID: 31145700).
Defective MPC1 → results in failure to form (or function of) the MPC1/MPC2 heterocomplex in the inner mitochondrial membrane (PMID: 22628554).
Non-functional MPC → blocks the obligate import of cytosolic pyruvate into the mitochondrial matrix (the carrier is the sole entry point) (PMID: 35895232).
Pyruvate cannot reach PDH/TCA → branches into two consequences:
4a. Cytosolic pyruvate is reduced to lactate by LDH → causes hyperlactatemia + hyperpyruvatemia with a normal L/P ratio (because the cytosolic NADH/NAD⁺ redox state is not the primary lesion) and metabolic acidosis (PMID: 12649063).
4b. The TCA cycle is deprived of glucose-derived acetyl-CoA → compensated by increased glutaminolysis and fatty-acid oxidation to replenish TCA intermediates, which is insufficient in high-demand tissues (PMID: 27176894; PMID: 29175325).
Reduced TCA flux and OXPHOS substrate supply → produces a cellular energy (ATP) deficit, most impactful in energy-hungry neurons (PMID: 27176894).
Energy deficit + depleted TCA intermediates + perturbed neurotransmitter precursor pools → results in impaired brain development, microcephaly, developmental delay, hypotonia, and (in a subset) Leigh-like encephalopathy (inferred in humans from mouse brain phenotypes) (PMID: 27176894; PMID: 34873722).
Therapeutic branch: supplying ketone bodies/fatty acids → delivers acetyl-CoA downstream of the carrier → partially restores TCA flux and rescues the phenotype in mice; variable/unproven in humans (PMID: 27176894; PMID: 12649063).

MPC1 LoF variant
      │
      ▼
No functional MPC1/MPC2 heterocomplex (inner mito membrane)
      │
      ▼
Pyruvate import into matrix BLOCKED  ◄── sole entry point
      │
      ├────────────► Pyruvate → Lactate (LDH)
      │                 → hyperlactatemia + hyperpyruvatemia
      │                 → NORMAL L/P ratio, normal PDH activity
      │
      └────────────► TCA cycle starved of acetyl-CoA
        → ↑ glutaminolysis, ↑ β-oxidation (compensation)
        → ATP/energy deficit (brain)
        → developmental delay, microcephaly,
          hypotonia, Leigh-like encephalopathy
               ▲
               │  Ketogenic diet / fatty acids
               └── supply acetyl-CoA downstream (BYPASS)

Molecular pathways / processes: pyruvate metabolism (KEGG hsa00620), TCA cycle (hsa00020), OXPHOS, glutaminolysis, fatty-acid β-oxidation. GO suggestions: pyruvate transmembrane transport (GO:0006850); pyruvate metabolic process (GO:0006090); tricarboxylic acid cycle (GO:0006099); generation of precursor metabolites and energy (GO:0006091); mitochondrial pyruvate transmembrane transporter activity (GO:1990830). Cellular component: mitochondrial inner membrane (GO:0005743); mitochondrial pyruvate carrier complex (GO:0120242). Cell types (CL): neuron (CL:0000540), hepatocyte (CL:0000182), skeletal muscle myocyte (CL:0000188). Metabolic/biochemical abnormality: enzyme-transport defect at the inner mitochondrial membrane; secondary lactate/pyruvate accumulation. Immune involvement: none primary. Chemical entities (CHEBI): pyruvate (CHEBI:15361), lactate (CHEBI:24996), acetyl-CoA (CHEBI:15351).

7. Anatomical Structures Affected

Primary organ: brain (UBERON:0000955) — central nervous system (UBERON:0001017) is most vulnerable due to high ATP demand; manifestations include microcephaly, developmental delay, periventricular cysts, Leigh-like changes.
Secondary/systemic: systemic metabolic acidosis affecting multiple organs; growth failure reflects whole-body energy deficit. Liver (UBERON:0002107) and skeletal muscle (UBERON:0001134) are metabolically relevant (mouse muscle-specific and hepatic MPC studies; PMID: 31305240; PMID: 36830630).
Body systems: nervous system (primary), metabolic/endocrine, musculoskeletal.
Tissue/cell level: nervous tissue and neurons (CL:0000540) are the principal affected population.
Subcellular: mitochondrion (GO:0005739), inner mitochondrial membrane (GO:0005743) — the site of the defective carrier.
Lateralization: systemic/bilateral (not applicable as a localized lesion).

8. Temporal Development

Onset: congenital/neonatal to infantile; metabolic acidosis and dysmorphism may be present at birth (PMID: 12649063). Onset pattern: acute neonatal decompensation or subacute infantile presentation. Progression: chronic, lifelong, often progressive with episodic metabolic crises; severe cases may be lethal in early life (one reported early death; PMID: 31145700). Critical period: early neurodevelopment is the window of greatest vulnerability and of greatest therapeutic opportunity — mouse data suggest that bypassing the defect during gestation/early life is decisive (PMID: 27176894); by analogy with PDCD, earlier dietary intervention improves outcomes (PMID: 9409363).

9. Inheritance and Population

Inheritance: autosomal recessive (PMID: 34873722). Penetrance: presumed complete in biallelic LoF, with variable expressivity (severe lethal to Leigh-like to milder). Epidemiology: ultra-rare; <20 reported patients; no validated prevalence/incidence (not available). Consanguinity: documented (index case; PMID: 12649063). Carrier frequency / founder effects: not established; pathogenic alleles are not recurrent population founders. Populations: reported cases span European, Kuwaiti, and Chinese ancestries (PMID: 34873722; PMID: 37899339) — no ethnic predilection beyond consanguinity. Sex ratio: no sex bias expected (autosomal); not quantified. Anticipation / mosaicism: not applicable/not reported.

10. Diagnostics

Laboratory: elevated blood/CSF lactate (5–14 mmol/L) and pyruvate with a normal L/P molar ratio; normoglycemia; normal ammonia; metabolic acidosis (PMID: 12649063). Key discriminating assay: normal PDH complex activity in lymphocytes/fibroblasts combined with impaired pyruvate oxidation/transport in digitonin-permeabilized fibroblasts (patient cells phenocopy MPC-inhibitor-treated controls) (PMID: 12649063). Functional confirmation: rescue of pyruvate-driven oxygen consumption in patient fibroblasts by wild-type MPC1 reconstitution (PMID: 34873722). Genetic testing: targeted MPC1 sequencing / mitochondrial-disease or lactic-acidosis gene panels; WES/WGS for undifferentiated congenital lactic acidosis — the most efficient route given phenotype overlap. Imaging: brain MRI may show periventricular cysts, structural anomalies, or Leigh-like signal changes. Differential diagnosis: PDH complex deficiency (normal L/P but normal pyruvate transport, reduced PDH), pyruvate carboxylase deficiency (hyperammonemia; PMID: 32145058), ECHS1 deficiency (PMID: 31908952), and respiratory-chain defects (elevated L/P ratio). Screening: no newborn-screening marker; prenatal diagnosis is feasible (demonstrated functionally in an at-risk fetus; PMID: 12649063) and molecularly once the familial variant is known.

11. Outcome / Prognosis

Prognosis is variable and can be severe. Outcomes range from early death (one reported; PMID: 31145700) to survival with developmental delay and recurrent metabolic acidosis (PMID: 34873722). Morbidity is dominated by neurodevelopmental disability. Formal survival rates, life expectancy, and validated prognostic biomarkers are not available given the tiny cohort. Prognostic factors (inferred): severity of the biochemical defect (transport-dead vs. partial-function alleles), earliness of diagnosis, and responsiveness to metabolic bypass. No disease-specific QoL data exist.

12. Treatment

No curative or FDA-approved targeted therapy exists; management is supportive and metabolic-bypass–based (NCIT concepts: Ketogenic Diet, C92206; Supportive Care, C133445; Dietary Supplement/Nutritional Support):

Ketogenic diet — supplies acetyl-CoA directly to the TCA cycle, bypassing the carrier; rescues Mpc1-null mice (PMID: 27176894); by analogy to PDCD, early/strict implementation improves outcomes (PMID: 42341672; PMID: 9409363). Caveat: failed to correct hyperlactatemia in the index MPC patient (PMID: 12649063).
Anaplerotic substrates / fatty-acid oxidation support — alleviates energy deficit in partial-loss mouse models (PMID: 29175325).
Acute acidosis management — bicarbonate buffering (variably effective), thiamine, cofactor trials (largely ineffective in index case; PMID: 12649063).
Dichloroacetate — used in the analogous PDCD to lower lactate (PMID: 41898592); not validated in MPC deficiency.
Supportive/rehabilitative care — developmental therapies, nutrition, neurologic management.
Experimental/future: gene-replacement or MPC1 reconstitution is mechanistically plausible (wild-type MPC1 rescues patient fibroblasts; PMID: 34873722) but no clinical program exists. No NCT trials are registered specifically for MPC deficiency. Pharmacogenomics: not applicable.

13. Prevention

Primary prevention of this monogenic disease is through genetic counseling, carrier testing in at-risk/consanguineous families, prenatal diagnosis, and preimplantation genetic testing once the familial MPC1 variant is known (PMID: 12649063). Secondary/tertiary prevention focuses on early metabolic-bypass initiation and avoidance of catabolic triggers to prevent neurodevelopmental deterioration and acidotic crises. No vaccine, public-health, or environmental intervention applies.

14. Other Species / Natural Disease

The MPC and MPC1/MPC2 subunits are evolutionarily conserved from yeast to mammals (PMID: 22628554; PMID: 22628558). Orthologs: mouse Mpc1 (NCBI Gene 55951), Drosophila and Saccharomyces cerevisiae MPC homologs. No naturally occurring companion-animal or wildlife disease is catalogued in OMIA for MPC1 (not available). No zoonotic potential (genetic disease). Comparative biology shows strong mechanistic conservation, making model-organism findings highly translatable.

15. Model Organisms

Mouse (NCBI Taxon 10090): whole-body Mpc1 knockout → embryonic lethality ~E13.5 with lactic acidosis, glutaminolysis shift, brain defects, and neurotransmitter imbalance; rescued by maternal ketogenic diet (PMID: 27176894). A CRISPR partial-deficiency line is viable, with fatty-acid oxidation offsetting energy deficit (PMID: 29175325). Skeletal-muscle-specific MPC deletion reroutes glucose to lactate and drives leanness (PMID: 31305240); hepatic MPC models inform metabolic-disease biology (PMID: 36830630).
Cellular/in vitro: patient fibroblasts; CRISPR MPC1-null C2C12 myoblasts used for complementation/mechanism dissection (PMID: 31145700); MEFs (PMID: 27176894).
Invertebrate/yeast: Drosophila and S. cerevisiae MPC mutants were foundational for discovering the carrier and remain tractable for transport studies (PMID: 22628558; PMID: 22628554).
Phenotype recapitulation: mouse models reproduce lactic acidosis, energy deficit, and brain pathology; limitation: complete knockout is embryonic-lethal, so adult/chronic human-like neurodevelopmental progression is hard to model with the null allele — hypomorphic/conditional models better mirror surviving patients.

Mechanistic Model / Interpretation

The disease is best understood as a single-point metabolic bottleneck. Pyruvate stands at the crossroads of glycolysis, the TCA cycle, and gluconeogenesis; the MPC is the one door through which it must pass to be oxidized. When MPC1 fails, the door is shut. Two consequences follow in parallel: carbon backs up as lactate (producing the clinical hyperlactatemia with a telltale normal L/P ratio and normal PDH activity), and the mitochondrion is starved of the acetyl-CoA it would have made from pyruvate (producing an energy deficit). Cells attempt compensation by burning glutamine and fatty acids, but the brain — with its high, continuous ATP demand and limited metabolic flexibility during development — cannot fully adapt, yielding the neurodevelopmental phenotype.

The genotype-to-mechanism mapping is unusually clean (Finding 5): different patient alleles fail at different steps (assembly, stability, or transport), yet all converge on the same downstream block. This convergence explains why the clinical picture is relatively stereotyped despite allelic heterogeneity, and it predicts that any therapy acting downstream of the carrier (ketone bodies, anaplerotic substrates) should help regardless of the specific variant — the logic behind metabolic bypass. The mouse ketogenic-diet rescue is the strongest support for this model, while the index patient's failure to respond is the strongest caution: human CNS damage may already be established by the time of diagnosis, and bypass may be incomplete in tissues with high obligate glucose oxidation.

The dose–response contrast with pharmacology (Finding 6) is conceptually important: partial MPC inhibition is tolerable and even beneficial (insulin sensitization, neuroprotection), whereas complete genetic loss is lethal. This nonlinearity frames both the disease (why total loss is catastrophic) and the drug-development landscape (why MPC modulators target partial inhibition).

Evidence Base

PMID	Title (abbrev.)	Evidence type	Role
22628558	MPC required for pyruvate uptake (yeast/fly/human)	Human genetics + model	Establishes MPC1 as causal gene
22628554	Identification of the MPC	In vitro/model	Defines MPC1/MPC2 heterocomplex
12649063	Impaired mitochondrial pyruvate importation	Human clinical	Diagnostic signature; index patient
34873722	Novel MPC1 variants causing MPC deficiency	Human clinical + functional	Phenotype spectrum; rescue proof
31145700	Two patient MPC mutations, distinct mechanisms	In vitro/functional	Three molecular mechanisms
27176894	Mpc1-null mouse rescued by ketogenic diet	Model organism	In vivo mechanism + therapy POC
29175325	FAO alleviates MPC1-deficiency energy deficit	Model organism	Metabolic compensation
35895232	MSDC-0160 attenuates neurodegeneration	Model/pharmacology	MPC as sole entry; partial inhibition
29793507	MPC inhibition neuroprotection	Review	Downstream mTOR/neuroinflammation
37688338	Amino-acid ratios for PDCD	Human clinical	PDCD incidence; differential
42341672	Ketogenic diet in PDH deficiency	Human/guideline	Bypass rationale
9409363	KD outcomes in PDH deficiency	Human clinical	Early intervention benefit
34059057	MPC1 as cancer prognostic biomarker	Human/computational	Somatic MPC1 loss parallels
37899339	3 Chinese MPC-deficiency cases	Human clinical	Expands case count
31305240	Muscle MPC deletion rewires glucose	Model organism	Tissue-specific metabolism

Consistency: Independent lines (human genetics, patient biochemistry, cellular complementation, and mouse genetics) converge on the same mechanism — a strong, internally consistent evidence base. Challenge/tension: The chief tension is therapeutic — ketogenic diet rescues mice but failed in the index human patient, indicating the model may overstate real-world efficacy or that timing/tissue factors limit translation.

Limitations and Knowledge Gaps

Tiny cohort (<20 patients). No prevalence/incidence, survival statistics, penetrance estimates, or validated QoL data exist.
Therapeutic uncertainty. The only direct human treatment evidence (index patient) is a negative result for ketogenic diet on lactate; efficacy, timing, and best substrate mix remain unknown.
Genotype–phenotype correlation is preliminary. Only a few alleles are mechanistically characterized; modifiers are unidentified.
MPC2 disease status unresolved. No definitive human MPC2-caused phenotype is established, leaving the recessive locus landscape incomplete.
Model limitation. Complete-null mice are embryonic-lethal, so chronic human-like neurodevelopmental progression is not directly modeled.
No biomarkers for prognosis or treatment response beyond lactate/pyruvate and L/P ratio.
No natural-disease/veterinary counterpart documented (OMIA), limiting comparative insight.

Proposed Follow-up Experiments / Actions

Establish an international MPC-deficiency registry (via metabolic networks) to aggregate genotype, phenotype, treatment, and natural-history data across the scattered case reports.
Hypomorphic/conditional and CNS-specific Mpc1 mouse models to recapitulate survivable, progressive neurodevelopmental disease and rigorously test ketogenic/anaplerotic/triheptanoin regimens with dose–timing optimization.
Systematic deep-mutational scanning of MPC1 (assembly + transport assays in MPC1-null C2C12/HEK cells) to pre-classify all possible variants into the three mechanistic buckets (assembly-fail, unstable, transport-dead) for rapid clinical interpretation.
Patient-derived iPSC neurons/organoids to measure neuronal energy deficit and screen bypass substrates and candidate small molecules in a human CNS context.
Test gene-replacement (AAV-MPC1) proof-of-concept in cells and models, leveraging the demonstrated rescue by wild-type MPC1 reconstitution.
Prospective evaluation of early, strict ketogenic-diet initiation (modeled on PDCD outcome data) with standardized lactate, neurodevelopmental, and MRI endpoints.
Resolve the MPC2-disease question by targeted re-analysis of undiagnosed congenital lactic-acidosis cohorts (normal L/P ratio, normal PDH) for biallelic MPC2 variants.

Report compiled from 9 confirmed findings and 42 reviewed papers over 5 investigation iterations. Evidence types are annotated as human clinical, model organism, in vitro, or computational throughout.

Artifacts

Reference Validation

Checked with linkml-reference-validator 0.3.0.

Outcome	Count
References checked	22
Resolved	22
Unresolved (possible confabulation)	0
Unverifiable	0
References weighed for topical relevance	22
On topic	21
Off topic	0

All extracted references resolved successfully.

Term Validation

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

Outcome	Count
Terms checked	34
Resolved	31
Unresolved (possible confabulation)	0
Obsolete	0
Unverifiable	3
Terms whose name was checked	11
Terms named correctly	0
Terms named as a different term	10
Terms whose name is worth a second look	1

Terms the report names something else

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

HP:0000252 (1 mention) - the report calls it "Physical/structural"; HP calls it Microcephaly
HP:0001252 (1 mention) - the report calls it "Clinical sign"; HP calls it Hypotonia
HP:0001508 (1 mention) - the report calls it "Clinical sign"; HP calls it Failure to thrive
HP:0003542 (1 mention) - the report calls it "Laboratory"; HP calls it Increased circulating pyruvate concentration
HP:0001999 (1 mention) - the report calls it "Physical"; HP calls it Abnormal facial shape
HP:0002119 (1 mention) - the report calls it "Imaging/structural"; HP calls it Ventriculomegaly
HP:0002240 (1 mention) - the report calls it "related"; HP calls it Hepatomegaly
HP:0001942 (1 mention) - the report calls it "Laboratory"; HP calls it Metabolic acidosis
CL:0000540 (2 mentions) - the report calls it "Tissue/cell level: nervous tissue and neurons"; CL calls it neuron**
UBERON:0000955 (1 mention) - the report calls it "Primary organ: brain"; UBERON calls it brain**

Terms whose name is worth a second look

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

GO:0005739 (1 mention) - the report calls it "Subcellular: mitochondrion"; GO calls it mitochondrion**

Prefixes with no resolver

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

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Inheritance

Subtypes

Pathophysiology

Pathograph

Phenotypes

Medical Actions

Diagnosis

Animal Models

Source YAML

References & Deep Research

Deep Research

Mitochondrial Pyruvate Carrier Deficiency — Comprehensive Disease Characteristics Report

Summary

Key Findings

Finding 1 — Biallelic MPC1 mutations disrupt the MPC1/MPC2 heterocomplex that imports pyruvate into mitochondria

Finding 2 — Clinical phenotype and an expanding variant spectrum, including Leigh-like presentations

Finding 3 — Mouse genetics: complete Mpc1 loss is embryonic-lethal and rescued by maternal ketogenic diet

Finding 4 — The diagnostic signature: severe hyperlactatemia with NORMAL L/P ratio, normal PDH activity, impaired pyruvate oxidation in permeabilized fibroblasts

Finding 5 — Three distinct molecular mechanisms among patient MPC1 variants (A58G, R97W, L79H)

Finding 6 — MPC is an obligate, non-redundant, druggable node; partial pharmacological inhibition is benign/beneficial, contrasting with severe complete genetic loss

Finding 7 — Ultra-rare, autosomal recessive with consanguinity; sits in the "normal L/P ratio" congenital lactic acidosis differential

Finding 8 — Somatic MPC1 downregulation in cancer mirrors Warburg reprogramming (distinct from germline disease)

Finding 9 — Management is metabolic bypass and supportive care; no curative or approved targeted therapy

Section-by-Section Report

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic / Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome / Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts

Reference Validation

Term Validation

Terms the report names something else

Terms whose name is worth a second look

Prefixes with no resolver