Neonatal Severe Encephalopathy with Lactic Acidosis and Brain Abnormalities

👪

Inheritance

1

Autosomal recessive HP:0000007

NELABA follows autosomal recessive inheritance. Affected individuals carry biallelic (homozygous or compound heterozygous) loss-of-function mutations in LIPT2. Three initial patients from two families were reported with compound heterozygous mutations.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:28757203 SUPPORT Human Clinical

"We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."

Establishes autosomal recessive inheritance pattern with biallelic mutations in two unrelated families.

⚙

Pathophysiology

6

Impaired mitochondrial lipoylation via LIPT2 deficiency

LIPT2 encodes lipoyltransferase 2, which transfers octanoyl groups from octanoyl-ACP (synthesized by the mitochondrial fatty acid synthesis system) to the glycine cleavage system H protein (GCSH). This is the first committed step in the mitochondrial lipoylation pathway. The octanoyl-GCSH is then converted to lipoyl-GCSH by lipoic acid synthetase (LIAS), and LIPT1 relays lipoyl groups from GCSH to the E2 subunits of alpha-ketoacid dehydrogenases. Loss-of-function mutations in LIPT2 abolish this initial transfer, leading to deficient lipoylation of all lipoic acid-dependent enzyme complexes and disruption of the glycine cleavage system. Unlike LIPT1 deficiency which spares glycine cleavage, LIPT2 deficiency affects all lipoylated proteins.

Neuron link

LIPT2 link

lipoate biosynthetic process link ↓ DECREASED Protein lipoylation link ↓ DECREASED

mitochondrion link

Downstream

Combined alpha-ketoacid dehydrogenase deficiency Loss of lipoylation impairs PDHc, alpha-KGDHc, and BCKDHc E2 subunits.

Glycine cleavage system dysfunction Failure to lipoylate GCSH directly impairs glycine cleavage activity.

Decreased protein lipoylation Patient fibroblast immunoblotting detects reduced protein lipoylation downstream of LIPT2 loss.

Show evidence (3 references)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Demonstrates that LIPT2 mutations cause decreased protein lipoylation and impaired function of multiple mitochondrial enzyme complexes in patient fibroblasts.

PMID:28757203 SUPPORT In Vitro

"A normalization of lipoylation was observed after expression of wild-type LIPT2, arguing for LIPT2 requirement in intramitochondrial lipoate synthesis."

Wild-type LIPT2 complementation rescues lipoylation defect, confirming LIPT2 as the causative gene.

PMID:32508887 SUPPORT Other

"LIPT2 utilizes octanoyl-ACP synthesized by the mitochondrial fatty acid synthesis system to modify GCSH."

Review defining the biochemical role of LIPT2 as the enzyme that transfers octanoyl groups to the glycine cleavage system H protein.

Combined alpha-ketoacid dehydrogenase deficiency

Defective lipoylation of the E2 subunits of pyruvate dehydrogenase (PDHc), alpha-ketoglutarate dehydrogenase (alpha-KGDHc), and branched-chain ketoacid dehydrogenase (BCKDHc) impairs oxidative metabolism of pyruvate, alpha-ketoglutarate, and branched-chain amino acids. Loss of PDHc blocks entry of glycolytic end products into the TCA cycle, causing pyruvate and lactate accumulation and energy failure. Loss of alpha-KGDHc disrupts the TCA cycle at its midpoint. The brain is particularly vulnerable due to its high dependence on oxidative metabolism.

Tricarboxylic acid cycle link ↓ DECREASED pyruvate decarboxylation to acetyl-CoA link ↓ DECREASED branched-chain amino acid catabolic process link ↓ DECREASED

Pyruvate dehydrogenase complex link

Downstream

Reduced PDHc activity Failed lipoylation of pyruvate dehydrogenase E2 reduces PDHc enzymatic activity in patient fibroblasts.

Reduced alpha-KGDHc activity Failed lipoylation of alpha-ketoglutarate dehydrogenase E2 reduces alpha-KGDHc enzymatic activity in patient fibroblasts.

Lactic acidosis Blocked oxidative metabolism diverts pyruvate to lactate, driving persistent lactic acidemia.

Elevated lactate Lactate measurement is a biochemical readout of impaired PDH flux and pyruvate reduction to lactate.

Global developmental delay Chronic cerebral energy failure impairs neurodevelopment from early infancy.

Neonatal encephalopathy from energy failure and glycine toxicity Combined energy failure and glycine accumulation converge on severe neonatal encephalopathy.

Show evidence (2 references)

PMID:32508887 SUPPORT Other

"The loss of these two dehydrogenases short-circuits the citric acid cycle, resulting in severe respiratory deficiency and extreme muscle weakness"

Review explaining how loss of PDHc and alpha-KGDHc disrupts the citric acid cycle and causes the clinical phenotype.

PMID:32508887 SUPPORT Other

"Patients that display absent or low lipoylation of all three enzymes have mutations in either of two genes LIAS or LIPT2"

Confirms that LIPT2 mutations affect all three lipoylated enzyme complexes.

Glycine cleavage system dysfunction

Unlike LIPT1 deficiency which spares the glycine cleavage system, LIPT2 deficiency impairs lipoylation of GCSH itself, leading to defective glycine cleavage and elevated glycine levels. Glycine accumulation in the brain contributes to neurological impairment including seizures and encephalopathy.

glycine catabolic process link ↓ DECREASED

Glycine cleavage complex link

Downstream

Hyperglycinemia Reduced glycine cleavage causes systemic glycine accumulation.

Elevated glycine Plasma glycine elevation is a biochemical readout of impaired glycine cleavage.

Brain glycine accumulation with NMDA receptor overactivation Glycine accumulation in the CNS increases excitatory neurotransmission through NMDA receptor co-agonism.

Show evidence (2 references)

PMID:28757203 SUPPORT Human Clinical

"Plasma glycine was mildly increased."

Demonstrates that LIPT2 deficiency impairs the glycine cleavage system, unlike LIPT1 deficiency.

PMID:32508887 SUPPORT Other

"Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"

Review explaining the neurological consequences of impaired glycine cleavage in lipoylation defects.

Brain glycine accumulation with NMDA receptor overactivation

Impaired glycine cleavage elevates CNS glycine, which can potentiate excitatory neurotransmission through NMDA receptor co-agonism and increase cortical network hyperexcitability. This provides a mechanistic bridge from glycine cleavage dysfunction to neonatal seizures.

Downstream

Seizures NMDA-mediated network hyperexcitability lowers seizure threshold and promotes epileptiform activity.

Show evidence (1 reference)

PMID:32508887 SUPPORT Other

"Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"

Supports elevated brain glycine as the proximal driver of neurologic dysfunction, including epilepsy, in lipoylation defects.

Neonatal encephalopathy from energy failure and glycine toxicity

Defective lipoylation combines two converging neurologic stresses: reduced alpha-ketoacid dehydrogenase flux, which limits cerebral energy metabolism, and impaired glycine cleavage, which raises CNS glycine and excitatory neurotransmission. Together these processes explain the severe neonatal encephalopathy, profound developmental impairment, early movement disorder, feeding impairment, and respiratory vulnerability seen in LIPT2 deficiency.

neuron link

generation of precursor metabolites and energy link ↓ DECREASED oxidative phosphorylation link ↓ DECREASED

brain link

Downstream

Neonatal hypotonia Severe neonatal encephalopathy and energy failure impair neonatal tone control.

Global developmental delay Early-onset encephalopathy and impaired energy metabolism prevent normal psychomotor development.

Dystonia Energy deficit in the developing brain is reported as the distinctive driver of early dystonia.

Feeding difficulties Neonatal encephalopathy and movement disorder impair early feeding.

Respiratory insufficiency Lipoate-dependent TCA-cycle disruption is associated with severe respiratory deficiency in LIAS/LIPT2 lipoylation defects.

Spasticity Severe neonatal encephalopathy can evolve into abnormal tone and pyramidal motor signs.

Structural brain injury and cortical malformation Severe metabolic encephalopathy and impaired developing-brain energy metabolism converge on cortical and white-matter abnormalities.

Show evidence (3 references)

PMID:28757203 SUPPORT Human Clinical

"We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."

The index case series establishes severe neonatal encephalopathy as the core LIPT2-deficiency presentation.

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Patient-cell respiratory and enzyme defects support mitochondrial energy failure as the upstream mechanism.

PMID:32508887 SUPPORT Other

"Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"

Review evidence supports the glycine-toxicity contribution to encephalopathy and epilepsy in LIAS/LIPT2 lipoylation defects.

Structural brain injury and cortical malformation

LIPT2 deficiency is associated with early structural brain abnormalities including cortical atrophy, cysts, white-matter abnormalities, and the newly reported cortical malformation spectrum of colpocephaly, polymicrogyria, and heterotopia. This node captures the structural branch downstream of neonatal metabolic encephalopathy and impaired brain development.

neuron link oligodendrocyte link

brain development link ⚠ ABNORMAL central nervous system myelination link ↓ DECREASED

brain link cerebral cortex link brain white matter link

Downstream

Cerebral atrophy Cortical atrophy is a direct MRI-observed structural feature of LIPT2 deficiency.

Abnormal cerebral white matter morphology White-matter abnormalities are directly observed on brain MRI.

Delayed myelination The white-matter abnormality branch provides a mechanistic context for delayed myelination.

Polymicrogyria Polymicrogyria is part of the cortical malformation spectrum reported in the fourth case.

Microcephaly Severe early brain-development disruption provides the mechanistic context for microcephaly in LIPT2 deficiency.

Show evidence (2 references)

PMID:28757203 SUPPORT Human Clinical

"Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."

The index case series establishes cortical atrophy, white-matter abnormalities, and cysts as MRI features.

PMID:39536593 SUPPORT Human Clinical

"Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia."

The fourth case expands the structural brain branch to cortical malformations.

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Pathograph

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Phenotypes

14

Digestive 1

Feeding difficulties Feeding difficulties in infancy (HP:0008872)

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties."

Feeding difficulties reported in the fourth case.

Head and Neck 1

Microcephaly Microcephaly (HP:0000252)

Metabolism 2

Lactic acidosis OBLIGATE Congenital lactic acidosis (HP:0004902)

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"Patient had elevations in lactate (6.1 mmol/L) and glycine."

Fourth reported case confirms lactic acidosis as a consistent feature with quantified lactate elevation.

Hyperglycinemia Hyperglycinemia (HP:0002154)

Show evidence (2 references)

PMID:28757203 SUPPORT Human Clinical

"Plasma glycine was mildly increased."

Elevated glycine reflects impaired glycine cleavage system lipoylation in LIPT2 deficiency.

PMID:39536593 SUPPORT Human Clinical

"Patient had elevations in lactate (6.1 mmol/L) and glycine."

Fourth case confirms glycine elevation as a biochemical marker of LIPT2 deficiency.

Musculoskeletal 2

Neonatal hypotonia OBLIGATE Neonatal hypotonia (HP:0001319)

Show evidence (1 reference)

PMID:28757203 SUPPORT Human Clinical

"three affected individuals from two families with severe neonatal encephalopathy"

All reported patients presented with severe neonatal encephalopathy including hypotonia.

Spasticity Spasticity (HP:0001257)

Nervous System 7

Seizures Seizure (HP:0001250)

Show evidence (1 reference)

PMID:32508887 SUPPORT Other

"Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"

Review evidence links impaired glycine cleavage to elevated brain glycine and neonatal-onset epilepsy in LIAS/LIPT2 lipoylation defects.

Cerebral atrophy Cerebral atrophy (HP:0002059)

Show evidence (1 reference)

PMID:28757203 SUPPORT Human Clinical

"Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."

Brain MRI in the index patients demonstrated cortical atrophy as a consistent feature.

Dystonia Dystonia (HP:0001332)

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"Unlike most neurometabolic disorders where dystonia develops later after metabolic stroke in basal ganglia, LIPT2-related disorder seems unique due to early onset of dystonia due to energy deficit in the developing brain."

The fourth reported case highlights early-onset dystonia as a distinctive feature of LIPT2 deficiency.

Delayed myelination Delayed myelination (HP:0012448)

Global developmental delay OBLIGATE Profound global developmental delay (HP:0012736)

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties."

Developmental delay is a universal feature across all reported LIPT2 patients.

Abnormal cerebral white matter morphology Abnormal cerebral white matter morphology (HP:0002500)

Show evidence (1 reference)

PMID:28757203 SUPPORT Human Clinical

"Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."

Brain MRI in index patients demonstrated white matter abnormalities as a consistent feature.

Polymicrogyria Polymicrogyria (HP:0002126)

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia."

Brain MRI in the fourth case revealed cortical malformations not previously described in LIPT2 deficiency.

Respiratory 1

Respiratory insufficiency Respiratory insufficiency (HP:0002093)

Show evidence (1 reference)

PMID:32508887 PARTIAL Other

"The loss of these two dehydrogenases short-circuits the citric acid cycle, resulting in severe respiratory deficiency and extreme muscle weakness"

Review evidence supports respiratory deficiency in LIAS/LIPT2 lipoylation defects through PDH/alpha-KGDH-driven TCA-cycle dysfunction.

🧬

Genetic Associations

1

LIPT2 loss-of-function variants (Causative)

Show evidence (3 references)

PMID:28757203 SUPPORT Human Clinical

"We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."

Index report identifying LIPT2 as the causative gene through exome sequencing in two families.

PMID:39536593 SUPPORT Human Clinical

"Exome sequencing showed two variants of uncertain significance in trans in the LIPT2 gene: c.346 G>T and c.418C>T."

Fourth case identifies novel LIPT2 variants confirmed by yeast complementation.

PMID:39536593 SUPPORT Model Organism

"Yeast complementation experiments indicate that both patient mutant variants result in diminished function versions of the LIPT2 protein."

Functional validation of novel LIPT2 variants in yeast model confirms pathogenicity.

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Treatments

2

Supportive care

Action: supportive care MAXO:0000950

Management is primarily supportive, including ventilatory support, anticonvulsant therapy, and nutritional supplementation. No disease-modifying therapy is currently available.

Lipoic acid supplementation (ineffective)

Action: Pharmacotherapy NCIT:C15986

Agent: alpha-lipoic acid ↗

Lipoic acid supplementation has been attempted in LIPT2 patients and in yeast models but proved ineffective, consistent with the inability of exogenous lipoate to be incorporated into the mitochondrial lipoylation pathway in mammals.

Mechanism Target:

MODULATES Impaired mitochondrial lipoylation via LIPT2 deficiency — Lipoic acid supplementation was tested as a possible pharmacologic bypass but did not improve clinical status or rescue PDHc, alpha-KGDHc, or leucine metabolism in patient fibroblasts.

Show evidence (2 references)

PMID:28757203 REFUTE In Vitro

"Lipoic acid supplementation did not improve clinical condition nor activities of PDHc, α-KGDHc, or leucine metabolism in fibroblasts and was ineffective in yeast deleted for the orthologous LIP2."

Demonstrates that lipoic acid supplementation does not rescue the enzymatic defects in LIPT2 deficiency, either in patient fibroblasts or in yeast models.

PMID:39536593 REFUTE Human Clinical

"Lipoic acid supplementation has not led to significant clinical improvement."

Fourth case confirms ineffectiveness of lipoic acid supplementation in LIPT2 deficiency.

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Biochemical Markers

5

Decreased protein lipoylation (DECREASED)

Context: Detected by anti-lipoic acid antibody immunoblotting in patient fibroblasts; directly reports failure of the mitochondrial lipoylation pathway.

Pathograph Readouts

Readout Of Impaired mitochondrial lipoylation via LIPT2 deficiency Negative Diagnostic

Lower protein lipoylation reports impaired LIPT2-dependent lipoate assembly.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Patient fibroblast assays directly connect reduced lipoylation to LIPT2 deficiency.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Western blot analysis of patient fibroblasts showed decreased lipoylation of E2 subunits, providing a functional biomarker.

Reduced PDHc activity (DECREASED)

Context: Pyruvate dehydrogenase complex activity is reduced in patient fibroblasts.

Pathograph Readouts

Readout Of Combined alpha-ketoacid dehydrogenase deficiency Negative Diagnostic

Lower PDHc activity reports the lipoate-dependent alpha-ketoacid dehydrogenase defect.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Patient fibroblast assays directly document reduced PDHc activity.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Demonstrates reduced PDHc enzymatic activity as a direct consequence of LIPT2 deficiency.

Reduced alpha-KGDHc activity (DECREASED)

Context: Alpha-ketoglutarate dehydrogenase complex activity is reduced in patient fibroblasts.

Pathograph Readouts

Readout Of Combined alpha-ketoacid dehydrogenase deficiency Negative Diagnostic

Lower alpha-KGDHc activity reports the TCA-cycle dehydrogenase branch of LIPT2 deficiency.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Patient fibroblast assays directly document reduced alpha-KGDHc activity.

Show evidence (1 reference)

PMID:28757203 SUPPORT In Vitro

"Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."

Demonstrates reduced alpha-KGDHc activity as part of the combined dehydrogenase deficiency.

Elevated lactate (INCREASED)

Context: Elevated lactate reflects impaired oxidative pyruvate metabolism and is a diagnostic biochemical marker of LIPT2 deficiency.

Pathograph Readouts

Readout Of Combined alpha-ketoacid dehydrogenase deficiency Positive Diagnostic

Higher lactate reports pyruvate diversion caused by impaired lipoate-dependent PDH activity.

Show evidence (1 reference)

PMID:39536593 SUPPORT Human Clinical

"Patient had elevations in lactate (6.1 mmol/L) and glycine."

The fourth reported case directly documents elevated lactate.

Show evidence (2 references)

PMID:39536593 SUPPORT Human Clinical

"Patient had elevations in lactate (6.1 mmol/L) and glycine."

The fourth reported case directly documents elevated lactate.

PMID:32508887 SUPPORT Other

"the presence of very high levels of lactate (resulting from reduction of the pyruvate that accumulates due to loss pyruvate dehydrogenase activity)"

Review evidence explains why impaired lipoate-dependent PDH activity raises lactate.

Elevated glycine (INCREASED)

Context: Elevated plasma glycine reflects impaired glycine cleavage system lipoylation.

Pathograph Readouts

Readout Of Glycine cleavage system dysfunction Positive Diagnostic

Higher glycine reports impaired glycine cleavage activity from defective GCSH lipoylation.

Show evidence (1 reference)

PMID:28757203 SUPPORT Human Clinical

"Plasma glycine was mildly increased."

The index patients had elevated plasma glycine.

Show evidence (2 references)

PMID:28757203 SUPPORT Human Clinical

"Plasma glycine was mildly increased."

The index patients had elevated plasma glycine.

PMID:39536593 SUPPORT Human Clinical

"Patient had elevations in lactate (6.1 mmol/L) and glycine."

The fourth case confirms glycine elevation as part of the biochemical signature.

{ }

Source YAML

click to show

name: Neonatal Severe Encephalopathy with Lactic Acidosis and Brain Abnormalities
creation_date: '2026-02-13T00:59:22Z'
updated_date: '2026-05-19T13:13:09Z'
category: Mendelian
description: >
  NELABA (Encephalopathy, Neonatal Severe, with Lactic Acidosis and Brain
  Abnormalities; OMIM 617668) is an ultra-rare autosomal recessive mitochondrial
  disorder caused by biallelic mutations in LIPT2, encoding lipoyltransferase 2.
  LIPT2 catalyzes the first committed step in the mitochondrial lipoylation
  pathway, transferring octanoyl groups from acyl carrier protein to the glycine
  cleavage system H protein (GCSH). Loss of function impairs lipoylation of all
  lipoic acid-dependent enzyme complexes: pyruvate dehydrogenase, alpha-ketoglutarate
  dehydrogenase, branched-chain ketoacid dehydrogenase, and the glycine cleavage
  system. This causes congenital lactic acidosis, hyperglycinemia, severe
  encephalopathy with minimal psychomotor development, and progressive brain
  abnormalities including cortical atrophy, cysts, white matter abnormalities, and
  cortical malformations. Onset is at birth with hypotonia and respiratory
  insufficiency. Only four cases have been reported. Prognosis is poor; lipoic acid
  supplementation is ineffective.
disease_term:
  preferred_term: NELABA
  term:
    id: MONDO:0060562
    label: encephalopathy, neonatal severe, with lactic acidosis and brain abnormalities
parents:
- Mitochondrial lipoylation defect
- Neonatal encephalopathy
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >
    NELABA follows autosomal recessive inheritance. Affected individuals carry
    biallelic (homozygous or compound heterozygous) loss-of-function mutations
    in LIPT2. Three initial patients from two families were reported with compound
    heterozygous mutations.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."
    explanation: Establishes autosomal recessive inheritance pattern with biallelic mutations in two unrelated families.
prevalence:
- population: Published literature cases worldwide
  percentage: 3 affected individuals from 2 families
  notes: >-
    PubMed-indexed epidemiology is currently limited to a handful of reported
    cases, consistent with an ultra-rare disorder without a stable population
    prevalence estimate.
  evidence:
  - reference: PMID:28757203
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."
    explanation: The initial disease-defining report provides the clearest currently citable measure of NELABA rarity in the literature.
pathophysiology:
- name: Impaired mitochondrial lipoylation via LIPT2 deficiency
  description: >
    LIPT2 encodes lipoyltransferase 2, which transfers octanoyl groups from
    octanoyl-ACP (synthesized by the mitochondrial fatty acid synthesis system) to
    the glycine cleavage system H protein (GCSH). This is the first committed step
    in the mitochondrial lipoylation pathway. The octanoyl-GCSH is then converted
    to lipoyl-GCSH by lipoic acid synthetase (LIAS), and LIPT1 relays lipoyl
    groups from GCSH to the E2 subunits of alpha-ketoacid dehydrogenases.
    Loss-of-function mutations in LIPT2 abolish this initial transfer, leading
    to deficient lipoylation of all lipoic acid-dependent enzyme complexes and
    disruption of the glycine cleavage system. Unlike LIPT1 deficiency which
    spares glycine cleavage, LIPT2 deficiency affects all lipoylated proteins.
  genes:
  - preferred_term: LIPT2
    term:
      id: hgnc:37216
      label: LIPT2
  gene:
    preferred_term: LIPT2
    description: Lipoyltransferase 2, catalyzes the first committed step in mitochondrial lipoylation by transferring octanoyl groups from octanoyl-ACP to GCSH.
    modifier: DECREASED
    term:
      id: hgnc:37216
      label: LIPT2
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: lipoate biosynthetic process
    modifier: DECREASED
    term:
      id: GO:0009107
      label: lipoate biosynthetic process
  - preferred_term: Protein lipoylation
    modifier: DECREASED
    term:
      id: GO:0009249
      label: protein lipoylation
  cellular_components:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  chemical_entities:
  - preferred_term: protein-bound lipoate
    modifier: DECREASED
    term:
      id: CHEBI:16494
      label: lipoic acid
  downstream:
  - target: Combined alpha-ketoacid dehydrogenase deficiency
    description: Loss of lipoylation impairs PDHc, alpha-KGDHc, and BCKDHc E2 subunits.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Patient fibroblast data directly link LIPT2 deficiency to reduced PDHc/alpha-KGDHc activity and reduced lipoylation.
  - target: Glycine cleavage system dysfunction
    description: Failure to lipoylate GCSH directly impairs glycine cleavage activity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:32508887
      reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "Patients that display absent or low lipoylation of all three enzymes have mutations in either of two genes LIAS or LIPT2"
      explanation: Review evidence supports that LIPT2 deficiency reduces lipoylation across the glycine cleavage and dehydrogenase enzyme set.
  - target: Decreased protein lipoylation
    description: Patient fibroblast immunoblotting detects reduced protein lipoylation downstream of LIPT2 loss.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: The same patient-cell assay provides the direct biochemical readout of reduced protein lipoylation.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
    explanation: Demonstrates that LIPT2 mutations cause decreased protein lipoylation and impaired function of multiple mitochondrial enzyme complexes in patient fibroblasts.
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "A normalization of lipoylation was observed after expression of wild-type LIPT2, arguing for LIPT2 requirement in intramitochondrial lipoate synthesis."
    explanation: Wild-type LIPT2 complementation rescues lipoylation defect, confirming LIPT2 as the causative gene.
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "LIPT2 utilizes octanoyl-ACP synthesized by the mitochondrial fatty acid synthesis system to modify GCSH."
    explanation: Review defining the biochemical role of LIPT2 as the enzyme that transfers octanoyl groups to the glycine cleavage system H protein.
- name: Combined alpha-ketoacid dehydrogenase deficiency
  description: >
    Defective lipoylation of the E2 subunits of pyruvate dehydrogenase (PDHc),
    alpha-ketoglutarate dehydrogenase (alpha-KGDHc), and branched-chain ketoacid
    dehydrogenase (BCKDHc) impairs oxidative metabolism of pyruvate, alpha-ketoglutarate,
    and branched-chain amino acids. Loss of PDHc blocks entry of glycolytic end
    products into the TCA cycle, causing pyruvate and lactate accumulation and
    energy failure. Loss of alpha-KGDHc disrupts the TCA cycle at its midpoint.
    The brain is particularly vulnerable due to its high dependence on oxidative
    metabolism.
  biological_processes:
  - preferred_term: Tricarboxylic acid cycle
    modifier: DECREASED
    term:
      id: GO:0006099
      label: tricarboxylic acid cycle
  - preferred_term: pyruvate decarboxylation to acetyl-CoA
    modifier: DECREASED
    term:
      id: GO:0006086
      label: pyruvate decarboxylation to acetyl-CoA
  - preferred_term: branched-chain amino acid catabolic process
    modifier: DECREASED
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  cellular_components:
  - preferred_term: Pyruvate dehydrogenase complex
    term:
      id: GO:0045254
      label: pyruvate dehydrogenase complex
  chemical_entities:
  - preferred_term: pyruvate
    modifier: INCREASED
    term:
      id: CHEBI:15361
      label: pyruvate
  - preferred_term: lactate
    modifier: INCREASED
    term:
      id: CHEBI:24996
      label: lactate
  downstream:
  - target: Reduced PDHc activity
    description: Failed lipoylation of pyruvate dehydrogenase E2 reduces PDHc enzymatic activity in patient fibroblasts.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Direct patient fibroblast enzymology showed reduced PDHc activity.
  - target: Reduced alpha-KGDHc activity
    description: Failed lipoylation of alpha-ketoglutarate dehydrogenase E2 reduces alpha-KGDHc enzymatic activity in patient fibroblasts.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Direct patient fibroblast enzymology showed reduced alpha-KGDHc activity.
  - target: Lactic acidosis
    description: Blocked oxidative metabolism diverts pyruvate to lactate, driving persistent lactic acidemia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:32508887
      reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "the presence of very high levels of lactate (resulting from reduction of the pyruvate that accumulates due to loss pyruvate dehydrogenase activity)"
      explanation: Review evidence connects loss of pyruvate dehydrogenase activity to pyruvate accumulation and high lactate in lipoic acid metabolism defects.
  - target: Elevated lactate
    description: Lactate measurement is a biochemical readout of impaired PDH flux and pyruvate reduction to lactate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
      explanation: The fourth reported case directly documents elevated lactate as a biochemical readout.
  - target: Global developmental delay
    description: Chronic cerebral energy failure impairs neurodevelopment from early infancy.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - cerebral energy deficit
    - impaired neuronal maturation
  - target: Neonatal encephalopathy from energy failure and glycine toxicity
    description: Combined energy failure and glycine accumulation converge on severe neonatal encephalopathy.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired oxidative pyruvate metabolism
    - citric acid cycle dysfunction
  evidence:
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "The loss of these two dehydrogenases short-circuits the citric acid cycle, resulting in severe respiratory deficiency and extreme muscle weakness"
    explanation: Review explaining how loss of PDHc and alpha-KGDHc disrupts the citric acid cycle and causes the clinical phenotype.
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Patients that display absent or low lipoylation of all three enzymes have mutations in either of two genes LIAS or LIPT2"
    explanation: Confirms that LIPT2 mutations affect all three lipoylated enzyme complexes.
- name: Glycine cleavage system dysfunction
  description: >
    Unlike LIPT1 deficiency which spares the glycine cleavage system, LIPT2
    deficiency impairs lipoylation of GCSH itself, leading to defective glycine
    cleavage and elevated glycine levels. Glycine accumulation in the brain
    contributes to neurological impairment including seizures and encephalopathy.
  biological_processes:
  - preferred_term: glycine catabolic process
    modifier: DECREASED
    term:
      id: GO:0006546
      label: glycine catabolic process
  cellular_components:
  - preferred_term: Glycine cleavage complex
    term:
      id: GO:0005960
      label: glycine cleavage complex
  chemical_entities:
  - preferred_term: glycine
    modifier: INCREASED
    term:
      id: CHEBI:15428
      label: glycine
  downstream:
  - target: Hyperglycinemia
    description: Reduced glycine cleavage causes systemic glycine accumulation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Plasma glycine was mildly increased."
      explanation: Human patient data directly support glycine accumulation downstream of LIPT2-related glycine cleavage impairment.
  - target: Elevated glycine
    description: Plasma glycine elevation is a biochemical readout of impaired glycine cleavage.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
      explanation: The fourth reported case confirms glycine elevation as a biochemical readout.
  - target: Brain glycine accumulation with NMDA receptor overactivation
    description: Glycine accumulation in the CNS increases excitatory neurotransmission through NMDA receptor co-agonism.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - elevated brain glycine
    - excitatory neurotransmission imbalance
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma glycine was mildly increased."
    explanation: Demonstrates that LIPT2 deficiency impairs the glycine cleavage system, unlike LIPT1 deficiency.
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"
    explanation: Review explaining the neurological consequences of impaired glycine cleavage in lipoylation defects.
- name: Brain glycine accumulation with NMDA receptor overactivation
  description: >
    Impaired glycine cleavage elevates CNS glycine, which can potentiate
    excitatory neurotransmission through NMDA receptor co-agonism and increase
    cortical network hyperexcitability. This provides a mechanistic bridge from
    glycine cleavage dysfunction to neonatal seizures.
  downstream:
  - target: Seizures
    description: NMDA-mediated network hyperexcitability lowers seizure threshold and promotes epileptiform activity.
    causal_link_type: DIRECT
  evidence:
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"
    explanation: Supports elevated brain glycine as the proximal driver of neurologic dysfunction, including epilepsy, in lipoylation defects.
- name: Neonatal encephalopathy from energy failure and glycine toxicity
  description: >
    Defective lipoylation combines two converging neurologic stresses: reduced
    alpha-ketoacid dehydrogenase flux, which limits cerebral energy metabolism,
    and impaired glycine cleavage, which raises CNS glycine and excitatory
    neurotransmission. Together these processes explain the severe neonatal
    encephalopathy, profound developmental impairment, early movement disorder,
    feeding impairment, and respiratory vulnerability seen in LIPT2 deficiency.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: generation of precursor metabolites and energy
    modifier: DECREASED
    term:
      id: GO:0006091
      label: generation of precursor metabolites and energy
  - preferred_term: oxidative phosphorylation
    modifier: DECREASED
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  downstream:
  - target: Neonatal hypotonia
    description: Severe neonatal encephalopathy and energy failure impair neonatal tone control.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - cerebral energy deficit
    - neonatal encephalopathy
  - target: Global developmental delay
    description: Early-onset encephalopathy and impaired energy metabolism prevent normal psychomotor development.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - neonatal encephalopathy
    - impaired neuronal maturation
  - target: Dystonia
    description: Energy deficit in the developing brain is reported as the distinctive driver of early dystonia.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - cerebral energy deficit
    - developing brain vulnerability
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "LIPT2-related disorder seems unique due to early onset of dystonia due to energy deficit in the developing brain."
      explanation: The fourth case report explicitly connects early dystonia to developing-brain energy deficit.
  - target: Feeding difficulties
    description: Neonatal encephalopathy and movement disorder impair early feeding.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties."
      explanation: The fourth case directly reports feeding difficulty with the neurologic presentation.
  - target: Respiratory insufficiency
    description: Lipoate-dependent TCA-cycle disruption is associated with severe respiratory deficiency in LIAS/LIPT2 lipoylation defects.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - citric acid cycle dysfunction
    - severe respiratory deficiency
    evidence:
    - reference: PMID:32508887
      reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "The loss of these two dehydrogenases short-circuits the citric acid cycle, resulting in severe respiratory deficiency and extreme muscle weakness"
      explanation: Review evidence supports severe respiratory deficiency downstream of PDH/alpha-KGDH loss in lipoylation disorders.
  - target: Spasticity
    description: Severe neonatal encephalopathy can evolve into abnormal tone and pyramidal motor signs.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Structural brain injury and cortical malformation
    description: Severe metabolic encephalopathy and impaired developing-brain energy metabolism converge on cortical and white-matter abnormalities.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - impaired brain development
    - white-matter vulnerability
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."
    explanation: The index case series establishes severe neonatal encephalopathy as the core LIPT2-deficiency presentation.
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
    explanation: Patient-cell respiratory and enzyme defects support mitochondrial energy failure as the upstream mechanism.
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"
    explanation: Review evidence supports the glycine-toxicity contribution to encephalopathy and epilepsy in LIAS/LIPT2 lipoylation defects.
- name: Structural brain injury and cortical malformation
  description: >
    LIPT2 deficiency is associated with early structural brain abnormalities
    including cortical atrophy, cysts, white-matter abnormalities, and the newly
    reported cortical malformation spectrum of colpocephaly, polymicrogyria, and
    heterotopia. This node captures the structural branch downstream of neonatal
    metabolic encephalopathy and impaired brain development.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  biological_processes:
  - preferred_term: brain development
    modifier: ABNORMAL
    term:
      id: GO:0007420
      label: brain development
  - preferred_term: central nervous system myelination
    modifier: DECREASED
    term:
      id: GO:0022010
      label: central nervous system myelination
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  - preferred_term: brain white matter
    term:
      id: UBERON:0003544
      label: brain white matter
  downstream:
  - target: Cerebral atrophy
    description: Cortical atrophy is a direct MRI-observed structural feature of LIPT2 deficiency.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."
      explanation: MRI evidence directly supports cerebral atrophy as a structural brain manifestation.
  - target: Abnormal cerebral white matter morphology
    description: White-matter abnormalities are directly observed on brain MRI.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."
      explanation: MRI evidence directly supports abnormal cerebral white-matter morphology.
  - target: Delayed myelination
    description: The white-matter abnormality branch provides a mechanistic context for delayed myelination.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  - target: Polymicrogyria
    description: Polymicrogyria is part of the cortical malformation spectrum reported in the fourth case.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia."
      explanation: MRI evidence directly supports polymicrogyria and broader cortical malformation.
  - target: Microcephaly
    description: Severe early brain-development disruption provides the mechanistic context for microcephaly in LIPT2 deficiency.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."
    explanation: The index case series establishes cortical atrophy, white-matter abnormalities, and cysts as MRI features.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia."
    explanation: The fourth case expands the structural brain branch to cortical malformations.
phenotypes:
- name: Neonatal hypotonia
  description: >
    Severe hypotonia present from birth, reflecting energy failure in the
    developing nervous system.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Neonatal hypotonia
    term:
      id: HP:0001319
      label: Neonatal hypotonia
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "three affected individuals from two families with severe neonatal encephalopathy"
    explanation: All reported patients presented with severe neonatal encephalopathy including hypotonia.
- name: Lactic acidosis
  description: >
    Persistent elevation of serum lactate, pyruvate, and alanine due to impaired
    oxidative metabolism from defective lipoylation of mitochondrial enzyme complexes.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Congenital lactic acidosis
    term:
      id: HP:0004902
      label: Congenital lactic acidosis
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
    explanation: Fourth reported case confirms lactic acidosis as a consistent feature with quantified lactate elevation.
- name: Seizures
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Lack of glycine cleavage activity additionally results in elevated brain glycine levels which can result in a host of neurological disorders, including neurodegeneration, encephalopathy, and neonatal-onset epilepsy"
    explanation: Review evidence links impaired glycine cleavage to elevated brain glycine and neonatal-onset epilepsy in LIAS/LIPT2 lipoylation defects.
- name: Cerebral atrophy
  description: >
    Progressive cortical and subcortical atrophy visible on brain MRI.
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."
    explanation: Brain MRI in the index patients demonstrated cortical atrophy as a consistent feature.
- name: Microcephaly
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
- name: Dystonia
  description: >
    Early-onset severe generalized dystonia is a distinctive feature of LIPT2-related
    disorder, likely due to energy deficit in the developing basal ganglia.
  phenotype_term:
    preferred_term: Dystonia
    term:
      id: HP:0001332
      label: Dystonia
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Unlike most neurometabolic disorders where dystonia develops later after metabolic stroke in basal ganglia, LIPT2-related disorder seems unique due to early onset of dystonia due to energy deficit in the developing brain."
    explanation: The fourth reported case highlights early-onset dystonia as a distinctive feature of LIPT2 deficiency.
- name: Spasticity
  phenotype_term:
    preferred_term: Spasticity
    term:
      id: HP:0001257
      label: Spasticity
- name: Delayed myelination
  phenotype_term:
    preferred_term: Delayed myelination
    term:
      id: HP:0012448
      label: Delayed myelination
- name: Global developmental delay
  description: >
    Severe to profound global developmental delay with minimal or absent
    psychomotor development.
  frequency: OBLIGATE
  phenotype_term:
    preferred_term: Profound global developmental delay
    term:
      id: HP:0012736
      label: Profound global developmental delay
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties."
    explanation: Developmental delay is a universal feature across all reported LIPT2 patients.
- name: Respiratory insufficiency
  phenotype_term:
    preferred_term: Respiratory insufficiency
    term:
      id: HP:0002093
      label: Respiratory insufficiency
  evidence:
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: PARTIAL
    evidence_source: OTHER
    snippet: "The loss of these two dehydrogenases short-circuits the citric acid cycle, resulting in severe respiratory deficiency and extreme muscle weakness"
    explanation: Review evidence supports respiratory deficiency in LIAS/LIPT2 lipoylation defects through PDH/alpha-KGDH-driven TCA-cycle dysfunction.
- name: Abnormal cerebral white matter morphology
  description: >
    White matter abnormalities and cystic changes on brain MRI, reflecting
    impaired myelination and energy failure.
  phenotype_term:
    preferred_term: Abnormal cerebral white matter morphology
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain MRI showed major cortical atrophy with white matter abnormalities and cysts."
    explanation: Brain MRI in index patients demonstrated white matter abnormalities as a consistent feature.
- name: Hyperglycinemia
  description: >
    Mildly elevated plasma glycine due to impaired glycine cleavage system
    function from defective GCSH lipoylation. Distinguishes LIPT2 deficiency
    from LIPT1 deficiency, which spares the glycine cleavage system.
  phenotype_term:
    preferred_term: Hyperglycinemia
    term:
      id: HP:0002154
      label: Hyperglycinemia
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma glycine was mildly increased."
    explanation: Elevated glycine reflects impaired glycine cleavage system lipoylation in LIPT2 deficiency.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
    explanation: Fourth case confirms glycine elevation as a biochemical marker of LIPT2 deficiency.
- name: Polymicrogyria
  description: >
    Cortical malformation reported in the fourth case, expanding the phenotypic
    spectrum of LIPT2-related disorder.
  phenotype_term:
    preferred_term: Polymicrogyria
    term:
      id: HP:0002126
      label: Polymicrogyria
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Brain magnetic resonance imaging showed cortical malformations including colpocephaly, polymicrogyria, and heterotopia."
    explanation: Brain MRI in the fourth case revealed cortical malformations not previously described in LIPT2 deficiency.
- name: Feeding difficulties
  phenotype_term:
    preferred_term: Feeding difficulties in infancy
    term:
      id: HP:0008872
      label: Feeding difficulties in infancy
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The patient was a 15-month-old female who presented at one month with dystonia, developmental delay, and feeding difficulties."
    explanation: Feeding difficulties reported in the fourth case.
biochemical:
- name: Decreased protein lipoylation
  presence: DECREASED
  context: >
    Detected by anti-lipoic acid antibody immunoblotting in patient
    fibroblasts; directly reports failure of the mitochondrial lipoylation
    pathway.
  biomarker_term:
    preferred_term: lipoic acid
    term:
      id: CHEBI:16494
      label: lipoic acid
  readouts:
  - target: Impaired mitochondrial lipoylation via LIPT2 deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Lower protein lipoylation reports impaired LIPT2-dependent lipoate assembly.
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Patient fibroblast assays directly connect reduced lipoylation to LIPT2 deficiency.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
    explanation: Western blot analysis of patient fibroblasts showed decreased lipoylation of E2 subunits, providing a functional biomarker.
- name: Reduced PDHc activity
  presence: DECREASED
  context: Pyruvate dehydrogenase complex activity is reduced in patient fibroblasts.
  readouts:
  - target: Combined alpha-ketoacid dehydrogenase deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Lower PDHc activity reports the lipoate-dependent alpha-ketoacid dehydrogenase defect.
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Patient fibroblast assays directly document reduced PDHc activity.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
    explanation: Demonstrates reduced PDHc enzymatic activity as a direct consequence of LIPT2 deficiency.
- name: Reduced alpha-KGDHc activity
  presence: DECREASED
  context: >
    Alpha-ketoglutarate dehydrogenase complex activity is reduced in patient
    fibroblasts.
  readouts:
  - target: Combined alpha-ketoacid dehydrogenase deficiency
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Lower alpha-KGDHc activity reports the TCA-cycle dehydrogenase branch of LIPT2 deficiency.
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
      explanation: Patient fibroblast assays directly document reduced alpha-KGDHc activity.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Affected individuals' fibroblasts showed reduced oxygen consumption rates, PDHc, α-KGDHc activities, leucine catabolic flux, and decreased protein lipoylation."
    explanation: Demonstrates reduced alpha-KGDHc activity as part of the combined dehydrogenase deficiency.
- name: Elevated lactate
  presence: INCREASED
  context: Elevated lactate reflects impaired oxidative pyruvate metabolism and is a diagnostic biochemical marker of LIPT2 deficiency.
  biomarker_term:
    preferred_term: lactate
    term:
      id: CHEBI:24996
      label: lactate
  readouts:
  - target: Combined alpha-ketoacid dehydrogenase deficiency
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Higher lactate reports pyruvate diversion caused by impaired lipoate-dependent PDH activity.
    evidence:
    - reference: PMID:39536593
      reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
      explanation: The fourth reported case directly documents elevated lactate.
  evidence:
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
    explanation: The fourth reported case directly documents elevated lactate.
  - reference: PMID:32508887
    reference_title: "Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "the presence of very high levels of lactate (resulting from reduction of the pyruvate that accumulates due to loss pyruvate dehydrogenase activity)"
    explanation: Review evidence explains why impaired lipoate-dependent PDH activity raises lactate.
- name: Elevated glycine
  presence: INCREASED
  context: Elevated plasma glycine reflects impaired glycine cleavage system lipoylation.
  biomarker_term:
    preferred_term: glycine
    term:
      id: CHEBI:15428
      label: glycine
  readouts:
  - target: Glycine cleavage system dysfunction
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Higher glycine reports impaired glycine cleavage activity from defective GCSH lipoylation.
    evidence:
    - reference: PMID:28757203
      reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Plasma glycine was mildly increased."
      explanation: The index patients had elevated plasma glycine.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma glycine was mildly increased."
    explanation: The index patients had elevated plasma glycine.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patient had elevations in lactate (6.1 mmol/L) and glycine."
    explanation: The fourth case confirms glycine elevation as part of the biochemical signature.
genetic:
- name: LIPT2 loss-of-function variants
  gene_term:
    preferred_term: LIPT2
    term:
      id: hgnc:37216
      label: LIPT2
  association: Causative
  notes: >
    Biallelic loss-of-function mutations in LIPT2 cause NELABA. The first reported
    mutations were compound heterozygous c.89T>C and c.377T>G. A fourth case
    carried c.346G>T and c.418C>T. Yeast complementation studies confirmed
    pathogenicity.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report on the identification of biallelic LIPT2 mutations in three affected individuals from two families with severe neonatal encephalopathy."
    explanation: Index report identifying LIPT2 as the causative gene through exome sequencing in two families.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Exome sequencing showed two variants of uncertain significance in trans in the LIPT2 gene: c.346 G>T and c.418C>T."
    explanation: Fourth case identifies novel LIPT2 variants confirmed by yeast complementation.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Yeast complementation experiments indicate that both patient mutant variants result in diminished function versions of the LIPT2 protein."
    explanation: Functional validation of novel LIPT2 variants in yeast model confirms pathogenicity.
treatments:
- name: Supportive care
  description: >
    Management is primarily supportive, including ventilatory support,
    anticonvulsant therapy, and nutritional supplementation. No disease-modifying
    therapy is currently available.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
- name: Lipoic acid supplementation (ineffective)
  description: >
    Lipoic acid supplementation has been attempted in LIPT2 patients and in
    yeast models but proved ineffective, consistent with the inability of
    exogenous lipoate to be incorporated into the mitochondrial lipoylation
    pathway in mammals.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: alpha-lipoic acid
      term:
        id: CHEBI:16494
        label: lipoic acid
  target_mechanisms:
  - target: Impaired mitochondrial lipoylation via LIPT2 deficiency
    treatment_effect: MODULATES
    description: >
      Lipoic acid supplementation was tested as a possible pharmacologic
      bypass but did not improve clinical status or rescue PDHc, alpha-KGDHc,
      or leucine metabolism in patient fibroblasts.
  evidence:
  - reference: PMID:28757203
    reference_title: "Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: "Lipoic acid supplementation did not improve clinical condition nor activities of PDHc, α-KGDHc, or leucine metabolism in fibroblasts and was ineffective in yeast deleted for the orthologous LIP2."
    explanation: Demonstrates that lipoic acid supplementation does not rescue the enzymatic defects in LIPT2 deficiency, either in patient fibroblasts or in yeast models.
  - reference: PMID:39536593
    reference_title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Lipoic acid supplementation has not led to significant clinical improvement."
    explanation: Fourth case confirms ineffectiveness of lipoic acid supplementation in LIPT2 deficiency.
datasets:
references:
- reference: PMID:28757203
  title: Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy.
  findings: []
- reference: PMID:32508887
  title: Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes.
  findings: []
- reference: PMID:39536593
  title: "Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum."
  findings: []

📚

References & Deep Research

References

3

PMID:28757203

Biallelic Mutations in LIPT2 Cause a Mitochondrial Lipoylation Defect Associated with Severe Neonatal Encephalopathy.

No top-level findings curated for this source.

PMID:32508887

Progress in the Enzymology of the Mitochondrial Diseases of Lipoic Acid Requiring Enzymes.

No top-level findings curated for this source.

PMID:39536593

Biallelic Variants in LIPT2 as a Cause of Infantile-Onset Dystonia: Expanding the Clinical and Molecular Spectrum.

No top-level findings curated for this source.

Deep Research

2

Disorder ▸

Disorder

Name: Neonatal Severe Encephalopathy with Lactic Acidosis and Brain Abnormalities
Category: Mendelian
Existing deep-research providers: falcon
Existing evidence reference count in YAML: 29

Key Pathophysiology Nodes

Impaired mitochondrial lipoylation via LIPT2 deficiency
Combined alpha-ketoacid dehydrogenase deficiency
Glycine cleavage system dysfunction
Brain glycine accumulation with NMDA receptor overactivation
Deep research literature mapping

Citation Inventory (for evidence mapping)

DOI:10.1159/000520553

Falcon ▸

Disease Pathophysiology Research Report

Edison Scientific Literature 7 citations 2026-02-10T20:21:28.351336

Disease Pathophysiology Research Report

Target disease - Disease Name: Neonatal severe encephalopathy with lactic acidosis and brain abnormalities (NELABA spectrum; mechanistic overlap with NAD(P)HX repair disorders) - MONDO ID: Not confirmed in accessible evidence during this run; likely mapped to NAXE/NAXD-related neurometabolic encephalopathies. - Category: Mendelian

1) Core pathophysiology - Concept and current understanding: In NAD(P)HX-repair deficiency (illustrated by NAXD deficiency), febrile stress and cellular metabolism generate hydrated forms of NADH/NADPH (NADHX/NAD(P)HX) that inhibit multiple dehydrogenases. NAXD (dehydratase) and NAXE (epimerase) normally reconvert these damaged cofactors to functional NAD(P)H. Loss of function leads to accumulation of inhibitory/toxic NAD(P)HX species, impairing mitochondrial respiration and cellular energy production, resulting in lactic acidosis and neuronal vulnerability with encephalopathy and seizures (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - Dysregulated pathways: Nicotinamide nucleotide metabolism/repair; mitochondrial electron transport/oxidative phosphorylation; cellular response to heat/febrile triggers; redox homeostasis (tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - Affected cellular processes: Neuronal energy metabolism, dehydrogenase-dependent pathways, maintenance of NAD(P)H pools; downstream excitability and network instability manifesting as seizures; neurodegeneration with cerebral atrophy on imaging (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4).

2) Key molecular players - Genes/Proteins: NAXD (NAD(P)HX dehydratase; HGNC symbol NAXD). Related pathway gene: NAXE (NAD(P)HX epimerase; HGNC symbol NAXE) by biological analogy, though direct NAXE/NELABA evidence was not accessible in this run (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - Chemical entities (selected): NADH (reduced nicotinamide adenine dinucleotide), NADPH (reduced nicotinamide adenine dinucleotide phosphate), hydrated derivatives NADHX/NAD(P)HX (damaged cofactors), lactate (reflecting impaired oxidative metabolism and glycolytic flux) (tuncer2022acasewith pages 2-4). - Cell types: Neurons are prominently affected; astrocytes may also be involved given brain energy coupling (inferred from clinical neurodegeneration and seizures) (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4). - Anatomical locations: Cerebrum/forebrain; corpus callosum; basal ganglia/white matter variably involved across cases; spinal cord typically spared in the single detailed case (normal spine MRI) (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4).

3) Biological processes (GO-like annotations) - Nicotinamide nucleotide metabolic process; NAD(P)H regeneration; mitochondrial electron transport chain; cellular respiration; response to heat; regulation of neuron apoptotic processes (inferred from neurodegeneration) (tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5).

4) Cellular components - Mitochondrion; cytosol; neuronal soma and processes in affected cortical/subcortical regions (tuncer2022acasewith pages 2-4).

5) Disease progression - Sequence of events (illustrated by NAXD deficiency): A trigger (often febrile illness) precedes acute deterioration with seizures and encephalopathy; inhibited dehydrogenases and mitochondrial dysfunction provoke lactic acidosis; progressive neurodegeneration manifests with developmental regression and structural brain changes (cerebral atrophy, thin corpus callosum), culminating in high infant mortality in severe cases (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - Staging: Neonatal/infantile onset with acute metabolic-neurologic crises; intermittent precipitants (fever/infection) superimposed on a chronic energy deficit; progression to severe encephalopathy (tuncer2022acasewith pages 4-5).

6) Phenotypic manifestations - Key clinical phenotypes: Neonatal/early-infantile encephalopathy, myoclonic or refractory seizures, hypotonia and loss of head control, developmental arrest/regression, elevated serum and CSF lactate (mild to moderate), possible cardiomyopathy and skin lesions in broader literature; high mortality in early life (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - Neuroimaging: Global cerebral atrophy, thin corpus callosum; other series describe basal ganglia and diffuse white/gray matter involvement; absence of diffuse restriction in the index MRI; normal spine MRI (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4). - Triggers: Febrile illness/infection commonly precipitate or exacerbate neurologic decline (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 4-5).

Ontology-grounded annotations for knowledge base use - Genes/Proteins (HGNC): NAXD (HGNC:23340). Related pathway: NAXE (HGNC:17359) [note: not evidenced in this run]. (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4) - GO Biological Processes: nicotinamide nucleotide metabolic process; cellular respiration; mitochondrial electron transport chain; response to heat (tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5). - GO Cellular Components: mitochondrion; cytosol (tuncer2022acasewith pages 2-4). - Cell types (CL): neurons; astrocytes (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4). - Anatomical structures (UBERON): brain (cerebrum), corpus callosum; basal ganglia (variable) (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4). - Chemical entities (CHEBI): NADH; NADPH; lactate; NAD(P)HX (hydrated NAD(P)H; label) (tuncer2022acasewith pages 2-4). - Phenotypes (HPO): Neonatal encephalopathy; Seizures; Lactic acidosis; Developmental regression; Generalized hypotonia; Abnormal corpus callosum morphology; Cerebral atrophy (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5).

Expert opinions and treatment attempts - Expert interpretation from the case report emphasizes that “mitochondrial cocktail” therapies (e.g., L-carnitine, CoQ10, thiamine, riboflavin, vitamin E) may be reasonable empirical interventions when NAXD deficiency is suspected; literature has suggested niacin (vitamin B3) as a potential adjunct in nicotinamide repair defects, and a longer survival in a case receiving vitamin therapy than an affected sibling was noted in prior reports cited by the authors, although definitive efficacy remains unproven (tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5).

Relevant statistics and data (from accessible source) - Biochemistry: Mildly elevated serum and CSF lactate were documented (serum ~2.7 mmol/L; CSF ~1.6 mmol/L; reference 0.4–1.4) (tuncer2022acasewith pages 1-2). - Outcomes: Despite seizure control on antiepileptics and supportive measures including a mitochondrial cocktail, the reported infant died by 18 months, underscoring severity (tuncer2022acasewith pages 1-2).

Evidence items (with URLs and dates) - Tuncer GÖ, Randa NC, Aydin S, Aksoy A. A Case with NAD(P)HX Dehydratase (NAXD) Deficiency: A Newly Defined Mutation in a Novel Neurodegenerative Disorder. Molecular Syndromology. Published online Feb 8, 2022. DOI: 10.1159/000520553. URL: https://doi.org/10.1159/000520553 (tuncer2022acasewith pages 1-2, tuncer2022acasewith pages 2-4, tuncer2022acasewith pages 4-5).

Limitations - The disease label supplied (NELABA) is classically associated with NAXE deficiency in the literature, but our tool-accessible full-text evidence here centers on NAXD deficiency, a mechanistically related NAD(P)HX-repair disorder with overlapping neonatal encephalopathy, lactic acidosis, and brain MRI abnormalities. We therefore present a mechanistic and phenotypic synthesis grounded in this accessible primary source and highlight where inferences are made. Additional 2023–2024 reviews and OMIM/MONDO entries would allow fuller NAXE-specific mapping in an updated report.

References

(tuncer2022acasewith pages 1-2): Gökçen Oz Tuncer, Nadide Cemre Randa, Seren Aydin, and Ayşe Aksoy. A case with nad(p)hx dehydratase (naxd) deficiency: a newly defined mutation in a novel neurodegenerative disorder. Molecular Syndromology, 13:1-5, Feb 2022. URL: https://doi.org/10.1159/000520553, doi:10.1159/000520553. This article has 7 citations and is from a peer-reviewed journal.
(tuncer2022acasewith pages 2-4): Gökçen Oz Tuncer, Nadide Cemre Randa, Seren Aydin, and Ayşe Aksoy. A case with nad(p)hx dehydratase (naxd) deficiency: a newly defined mutation in a novel neurodegenerative disorder. Molecular Syndromology, 13:1-5, Feb 2022. URL: https://doi.org/10.1159/000520553, doi:10.1159/000520553. This article has 7 citations and is from a peer-reviewed journal.
(tuncer2022acasewith pages 4-5): Gökçen Oz Tuncer, Nadide Cemre Randa, Seren Aydin, and Ayşe Aksoy. A case with nad(p)hx dehydratase (naxd) deficiency: a newly defined mutation in a novel neurodegenerative disorder. Molecular Syndromology, 13:1-5, Feb 2022. URL: https://doi.org/10.1159/000520553, doi:10.1159/000520553. This article has 7 citations and is from a peer-reviewed journal.

Neonatal Severe Encephalopathy with Lactic Acidosis and Brain Abnormalities

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