D-2-Hydroxyglutaric Aciduria

Mendelian MONDO:0010924 Pathograph 31 Organic Acidemia Inborn Error of Metabolism

D-2-Hydroxyglutaric aciduria (D-2-HGA) is a rare neurometabolic disorder characterized by supraphysiological accumulation of the D-enantiomer of 2-hydroxyglutarate (D-2-HG) in body fluids, and clinically by early-onset neurodevelopmental impairment with variable severity. Two genetically distinct subtypes exist: type I (D2HGA1) caused by autosomal recessive loss-of-function mutations in D2HGDH encoding mitochondrial D-2-hydroxyglutarate dehydrogenase, and type II (D2HGA2) caused by heterozygous gain-of-function mutations in IDH2 encoding isocitrate dehydrogenase 2, which confer neomorphic D-2-HG-producing activity. Type II is generally more severe, with higher D-2-HG levels, and is particularly associated with cardiomyopathy. Both subtypes share neurological features including developmental delay, epilepsy, and hypotonia.

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6
Pathophys.
10
Phenotypes
31
Pathograph
2
Genes
7
Treatments
2
Subtypes
4
References
1
Deep Research
◆

Subtypes

2
D-2-HGA type I
D2HGDH {'name': 'Autosomal recessive'}
Caused by autosomal recessive loss-of-function mutations in D2HGDH, leading to impaired mitochondrial clearance of D-2-HG. Generally milder phenotype with lower D-2-HG levels compared to type II.
D-2-HGA type II
IDH2 {'name': 'Autosomal dominant (de novo)'}
Caused by heterozygous (typically de novo) gain-of-function mutations in IDH2 at residue Arg140, conferring neomorphic D-2-HG production. Generally more severe phenotype with higher D-2-HG levels and prominent cardiomyopathy.
⚙

Pathophysiology

6
D2HGDH molecular function deficiency (type I)
In D-2-HGA type I, autosomal recessive D2HGDH loss-of-function variants reduce mitochondrial D-2-hydroxyglutarate dehydrogenase catalytic activity.
neuron link
D2HGDH
catalytic activity link
mitochondrion link
Downstream
Impaired D-2-hydroxyglutarate clearance (type I) Reduced D2HGDH activity decreases oxidation of D-2-HG to alpha-ketoglutarate.
Show evidence (1 reference)
PMID:15609246 SUPPORT In Vitro
"Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria."
Demonstrates reduction of D2HGDH catalytic function in type I disease.
Impaired D-2-hydroxyglutarate clearance (type I)
Reduced D2HGDH activity impairs oxidation of D-2-HG back to alpha-ketoglutarate, causing progressive accumulation of D-2-HG in urine, plasma, and CSF.
dicarboxylic acid metabolic process link
Downstream
Mitochondrial bioenergetic dysfunction and oxidative stress D-2-HGDH impairment causes D-2-HG accumulation, which is linked to downstream cellular and organ pathology.
Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition Accumulated D-2-HG can act as an alpha-KG antagonist and inhibit alpha-KG-dependent dioxygenases.
D-2-Hydroxyglutarate Impaired D-2-HG clearance produces the diagnostic increase in D-2-hydroxyglutarate in body fluids.
Urinary organic acids (2-hydroxyglutarate) Urinary organic acid testing is a diagnostic readout of excess D-2-HG from the type I clearance defect after chiral confirmation.
Show evidence (1 reference)
PMID:22391998 SUPPORT Human Clinical
"Accumulation of D-2-hydroxyglutarate (D-2-HG) and/or L-2-hydroxyglutarate (L-2-HG) in body fluids are the biochemical hallmarks of these disorders."
Confirms D-2-HG accumulation as the downstream biochemical hallmark.
IDH2 neomorphic molecular function gain (type II)
In D-2-HGA type II, heterozygous IDH2 gain-of-function variants (typically at Arg140) confer neomorphic catalytic activity.
cardiac muscle cell link
IDH2
catalytic activity link
mitochondrion link
Downstream
Neomorphic IDH2-driven D-2-HG overproduction (type II) Mutant IDH2 directly generates D-2-HG from 2-ketoglutarate.
Show evidence (1 reference)
PMID:20847235 SUPPORT Human Clinical
"These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
Supports neomorphic IDH2 molecular function gain in type II disease.
Neomorphic IDH2-driven D-2-HG overproduction (type II)
IDH2 neomorphic activity converts alpha-ketoglutarate to D-2-HG using NADPH, producing substantially higher D-2-HG levels than type I.
tricarboxylic acid cycle link
Downstream
Mitochondrial bioenergetic dysfunction and oxidative stress IDH2-driven 2HG overproduction causes multisystem pathology that is reversible with mutant IDH2 inhibition in a type II model.
Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition IDH2 neomorphic production of D-2-HG provides the alpha-KG antagonist that can inhibit dioxygenases.
D-2-Hydroxyglutarate Neomorphic IDH2 activity produces the diagnostic D-2-HG excess in D-2-HGA type II.
Alpha-ketoglutarate Mutant IDH2 consumes 2-ketoglutarate as substrate for neomorphic D-2-HG production, making local alpha-ketoglutarate depletion an inferred biochemical readout.
Urinary organic acids (2-hydroxyglutarate) Urinary organic acid testing also reports the type II D-2-HG overproduction mechanism after chiral and molecular confirmation.
Show evidence (1 reference)
PMID:20847235 SUPPORT Human Clinical
"We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)"
Confirms pathogenic IDH2 Arg140 variants driving type II D-2-HGA.
Mitochondrial bioenergetic dysfunction and oxidative stress
Elevated D-2-HG perturbs mitochondrial energy metabolism and redox homeostasis in both subtypes. The structural similarity of D-2-HG to alpha-ketoglutarate allows it to interfere with TCA cycle enzymes and mitochondrial respiratory chain function, leading to impaired energy production and increased oxidative stress, particularly affecting neurons and cardiomyocytes.
neuron link cardiac muscle cell link
response to oxidative stress link oxidative phosphorylation link
mitochondrion link
Downstream
Dilated cardiomyopathy Elevated 2HG-driven cellular pathology affects cardiomyocytes and can produce cardiomyopathy, especially in type II disease.
Serum phospholipids (type II) Serum phospholipid changes report downstream lipid and redox pathway effects in the type II D-2-HGA treatment context.
Epilepsy D-2-HGA-associated neurometabolic dysfunction manifests with seizures.
Global developmental delay D-2-HGA-associated neurometabolic dysfunction commonly causes developmental delay.
Muscular hypotonia D-2-HGA-associated neurometabolic dysfunction commonly manifests as hypotonia.
Cerebral white matter abnormalities D-2-HGA-associated neurometabolic pathology includes multifocal cerebral white matter abnormalities.
Intellectual disability D-2-HGA-associated neurometabolic dysfunction can manifest as psychomotor retardation and intellectual disability.
Macrocephaly D-2-HGA-associated neurodevelopmental pathology can include macrocephaly in some patients.
Subdural hygroma D-2-HGA neuroimaging abnormalities include subdural fluid collections.
Cerebral cortical atrophy Severe D-2-HGA cases can include cerebral atrophy on neuroimaging.
Visual impairment Cerebral visual failure is part of the variable neurological phenotype spectrum.
Show evidence (2 references)
PMID:27469509 SUPPORT Model Organism
"Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients."
Mouse model confirms D-2-HG accumulation causes multi-organ pathology.
PMID:22391998 SUPPORT Human Clinical
"The current review describes the knowledge gathered on 2-hydroxyglutaric acidurias (2-HGA), since the description of the first patients in 1980."
Foundational review supporting mitochondrial dysfunction as a core mechanism.
Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition
D-2-HG competitively inhibits alpha-ketoglutarate/Fe(II)-dependent dioxygenases, including histone and DNA demethylases (TET family enzymes and Jumonji-domain histone demethylases). This creates aberrant epigenetic modifications including DNA and histone hypermethylation, which may contribute to transcriptional dysregulation and the neurodevelopmental phenotype. This mechanism is shared with IDH-mutant cancers.
DNA demethylation link
histone demethylase activity link
nucleus link
Show evidence (2 references)
PMID:20847235 PARTIAL Human Clinical
"These findings provide additional impetus for investigating the role of D-2-HG in the pathophysiology of metabolic disease and cancer."
Motivates investigation of D-2-HG role in epigenetic dysregulation; the mechanism is well-established in cancer but the snippet is aspirational rather than demonstrative.
PMID:21251613 SUPPORT In Vitro
"Here we demonstrate that 2-HG is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including histone demethylases and the TET family of 5-methlycytosine (5mC) hydroxylases."
Provides direct mechanistic evidence that 2-HG inhibits the alpha-KG-dependent dioxygenases represented by this node.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for D-2-Hydroxyglutaric Aciduria Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

10
Cardiovascular 1
Dilated cardiomyopathy FREQUENT Dilated cardiomyopathy (HP:0001644)
Show evidence (2 references)
PMID:27469509 SUPPORT Model Organism
"AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice"
Demonstrates cardiomyopathy as a major feature of D-2-HGA type II in the mouse model, rescuable by IDH2 inhibition.
PMID:37248298 SUPPORT Human Clinical
"For the child with cardiomyopathy, chronic D-2-HG inhibition was associated with improved cardiac function, and for both children, therapy was associated with improved daily functioning, global motility and social interactions."
Provides direct human clinical evidence for cardiomyopathy involvement in D-2-HGA type II.
Eye 1
Visual impairment OCCASIONAL Visual impairment (HP:0000505)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires."
The comprehensive review includes visual impairment among the neurological phenotype spectrum.
Head and Neck 1
Macrocephaly OCCASIONAL Macrocephaly (HP:0000256)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires."
Questionnaire-derived clinical data in this review includes macrocephaly among reported features.
Musculoskeletal 1
Muscular hypotonia VERY_FREQUENT Hypotonia (HP:0001252)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age."
Neurological impairment at young age encompasses hypotonia as documented in questionnaire data within this review.
Nervous System 6
Epilepsy VERY_FREQUENT Seizure (HP:0001250)
Show evidence (2 references)
PMID:8981317 SUPPORT Human Clinical
"We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay."
Directly documents severe seizures as a presenting feature of D-2-HGA.
PMID:27469509 SUPPORT Model Organism
"Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span."
Confirms epilepsy as a core phenotype of D-2-HGA type II.
Global developmental delay VERY_FREQUENT Global developmental delay (HP:0001263)
Show evidence (2 references)
PMID:8981317 SUPPORT Human Clinical
"We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay."
Directly documents developmental delay as a presenting feature.
PMID:27469509 SUPPORT Model Organism
"Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span."
Confirms developmental delay as a cardinal feature in the clinical description.
Intellectual disability FREQUENT Intellectual disability (HP:0001249)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age."
Neurological impairment at young age includes intellectual disability as a core feature documented in the comprehensive review.
Subdural hygroma OCCASIONAL Subdural hygroma (HP:6001070)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires."
The comprehensive questionnaire data in this review documented subdural effusions among clinical features.
Cerebral white matter abnormalities FREQUENT Abnormal cerebral white matter morphology (HP:0002500)
Show evidence (1 reference)
PMID:22391998 PARTIAL Human Clinical
"The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age."
Neurological impairment at young age includes white matter abnormalities as documented in neuroimaging findings within this comprehensive review.
Cerebral cortical atrophy OCCASIONAL Cerebral cortical atrophy (HP:0002120)
Show evidence (1 reference)
PMID:8981317 PARTIAL Human Clinical
"Although the clinical spectrum of this inborn error of metabolism is variable, the clinical course of the D-form seems to be more severe than this of the L-form."
The more severe D-form clinical course includes progressive neurodegeneration with cortical atrophy.
🧬

Genetic Associations

2
D2HGDH deficiency (type I)
Autosomal recessive
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"Presumed pathogenic mutations were detected in 24 of 50 patients in the D-2-hydroxyglutarate dehydrogenase (D2HGDH) gene, which encodes D-2-hydroxyglutarate dehydrogenase (D-2-HGDH). Enzyme assay of D-2-HGDH confirmed that all patients with mutations had impaired enzyme activity"
Confirms D2HGDH mutations as causal with functional enzyme assay validation.
IDH2 gain-of-function mutations (type II)
Autosomal dominant (de novo)
Show evidence (2 references)
PMID:20847235 SUPPORT Human Clinical
"These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
Establishes the neomorphic mechanism of IDH2 mutations in D-2-HGA type II.
PMID:20020533 SUPPORT Human Clinical
"These results imply that multiple genetic loci may be associated with hyperexcretion of D-2-HG."
The genetic heterogeneity finding preceded the discovery of IDH2 as the second locus.
💊

Treatments

7
Enasidenib (mutant IDH2 inhibitor)
Action: targeted therapy Ontology label: Targeted Therapy NCIT:C93352
Enasidenib is a selective mutant IDH2 enzyme inhibitor originally developed for IDH2-mutant acute myeloid leukemia, now being repurposed for D-2-HGA type II. In two children with D-2-HGA type II, enasidenib normalized D-2-HG concentrations in body fluids, improved cardiac function in the child with cardiomyopathy, and was associated with improved daily functioning and social interactions.
Mechanism Target:
INHIBITS Neomorphic IDH2-driven D-2-HG overproduction (type II) — Enasidenib inhibits mutant IDH2-driven D-2-HG production in type II disease.
Show evidence (2 references)
PMID:37248298 SUPPORT Human Clinical
"In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids."
Human treatment data support enasidenib inhibition of the D-2-HG overproduction mechanism.
PMID:27469509 SUPPORT Model Organism
"AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function."
The type II mouse model supports mutant IDH2 inhibition as the mechanism for lowering 2HG.
Show evidence (3 references)
PMID:37248298 SUPPORT Human Clinical
"In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids."
Demonstrates that enasidenib normalizes D-2-HG levels in D-2-HGA type II patients.
PMID:37248298 SUPPORT Human Clinical
"For the child with cardiomyopathy, chronic D-2-HG inhibition was associated with improved cardiac function, and for both children, therapy was associated with improved daily functioning, global motility and social interactions."
Documents clinical improvement in both cardiac and neurological domains with enasidenib.
PMID:27469509 SUPPORT Model Organism
"AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function."
Preclinical evidence demonstrating IDH2 inhibitor efficacy in D-2-HGA type II mouse model.
Antiseizure medication
Action: antiepileptic drug therapy Ontology label: anticonvulsant agent therapy MAXO:0000167
Supportive antiseizure therapy is a mainstay of management for the epilepsy phenotype in D-2-HGA. Seizure management requires individualized medication selection based on seizure type and tolerability profile.
Target Phenotypes: Seizure ↗
Show evidence (1 reference)
PMID:8981317 SUPPORT Human Clinical
"We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay."
Severe seizures in D-2-HGA necessitate antiseizure medication as a core treatment.
Supportive cardiac therapy
Action: Pharmacotherapy NCIT:C15986
Standard cardiac pharmacotherapy including ACE inhibitors, beta-blockers, and diuretics for management of dilated cardiomyopathy, particularly in D-2-HGA type II patients.
Target Phenotypes: Dilated cardiomyopathy ↗
Show evidence (1 reference)
PMID:27469509 SUPPORT Model Organism
"Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span. Currently, there are no effective therapeutic interventions."
Documents cardiomyopathy as a key feature requiring cardiac management, and the unmet need that existed before IDH2 inhibitors.
Supportive care
Action: supportive care MAXO:0000950
Comprehensive supportive management including physical therapy, occupational therapy, and developmental support for neurodevelopmental impairment. Nutritional support and monitoring for metabolic complications are integral to chronic disease management.
Target Phenotypes: Global developmental delay ↗ Intellectual disability ↗
Show evidence (1 reference)
PMID:22391998 SUPPORT Human Clinical
"The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age."
Early-onset neurological impairment necessitates comprehensive supportive care.
Physical therapy
Action: physical therapy MAXO:0000011
Rehabilitation exercises and physical therapy to address hypotonia, motor delays, and functional limitations associated with the neurodevelopmental phenotype.
Target Phenotypes: Hypotonia ↗ Global developmental delay ↗
Show evidence (1 reference)
PMID:22391998 SUPPORT Human Clinical
"The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age."
Neurological impairment at young age supports the role of physical therapy in management.
Genetic counseling
Action: genetic counseling MAXO:0000079
Genetic counseling for affected families, including discussion of inheritance patterns (autosomal recessive for type I, de novo autosomal dominant for type II), recurrence risk, and the option of prenatal diagnosis. Molecular confirmation of the specific subtype is important for accurate genetic counseling.
Mechanism Target:
MODULATES D2HGDH molecular function deficiency (type I) — Counseling addresses the autosomal recessive D2HGDH etiology and recurrence risk rather than directly changing metabolism.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"D-2-HGA Type I associates with D-2-HGDH deficiency"
Molecular subtyping supports type-specific counseling for D2HGDH-related disease.
MODULATES IDH2 neomorphic molecular function gain (type II) — Counseling addresses the IDH2 gain-of-function subtype, including de novo dominant inheritance and subtype-specific recurrence risk.
Show evidence (1 reference)
PMID:20847235 SUPPORT Human Clinical
"We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)"
Identification of heterozygous germline IDH2 variants supports type II genetic counseling.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"These results imply that multiple genetic loci may be associated with hyperexcretion of D-2-HG. Accordingly, we suggest a new classification: D-2-HGA Type I associates with D-2-HGDH deficiency, whereas idiopathic D-2-HGA manifests with normal D-2-HGDH activity"
Genetic heterogeneity and distinct inheritance patterns underscore the importance of genetic counseling with molecular subtyping.
Urinary organic acid monitoring
Action: clinical laboratory procedure MAXO:0000006
Longitudinal monitoring of D-2-HG levels in urine, plasma, or CSF to assess metabolic burden and treatment response. Chiral analytical methods are essential for accurate D-2-HG quantification.
Mechanism Target:
MODULATES Impaired D-2-hydroxyglutarate clearance (type I) — Monitoring follows D-2-HG burden from the type I clearance defect and supports subtype stratification rather than directly modifying metabolism.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients."
Quantitative D-2-HG measurements distinguish mutation-positive type I from mutation-negative higher-D-2-HG cases.
MODULATES Neomorphic IDH2-driven D-2-HG overproduction (type II) — Monitoring follows the higher D-2-HG burden characteristic of the type II overproduction mechanism and can track treatment response.
Show evidence (1 reference)
PMID:37248298 SUPPORT Human Clinical
"In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids."
Human enasidenib data support serial D-2-HG monitoring as a readout of type II treatment response.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients."
Demonstrates the utility of quantitative D-2-HG measurement for subtype stratification and monitoring.
🔬

Biochemical Markers

4
D-2-Hydroxyglutarate (INCREASED)
Context: D-2-HG is the primary accumulating metabolite and diagnostic biomarker in D-2-HGA. It is markedly elevated in urine, plasma, and CSF. D-2-HG levels are substantially higher in type II compared to type I, consistent with the production-driven mechanism in type II. Chiral analytical methods are required to distinguish D-2-HG from L-2-HG.
Pathograph Readouts
Readout Of Impaired D-2-hydroxyglutarate clearance (type I) Positive Diagnostic
Elevated D-2-HG reports the type I clearance defect caused by impaired D2HGDH activity.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"Enzyme assay of D-2-HGDH confirmed that all patients with mutations had impaired enzyme activity"
The cohort links D2HGDH enzyme impairment to mutation-positive D-2-HGA, supporting D-2-HG as a readout of type I clearance failure.
Readout Of Neomorphic IDH2-driven D-2-HG overproduction (type II) Positive Diagnostic
Higher D-2-HG levels report type II neomorphic overproduction in patients without impaired D2HGDH activity.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"normal D-2-HGDH activity and higher D-2-HG levels in body fluids compared with Type I patients."
The genetic-heterogeneity study supports high D-2-HG as the biochemical signature of the non-D2HGDH subtype later attributed to IDH2.
Show evidence (2 references)
PMID:22391998 SUPPORT Human Clinical
"Accumulation of D-2-hydroxyglutarate (D-2-HG) and/or L-2-hydroxyglutarate (L-2-HG) in body fluids are the biochemical hallmarks of these disorders."
Directly confirms D-2-HG accumulation as the biochemical hallmark.
PMID:20020533 SUPPORT Human Clinical
"We performed molecular, enzyme, and metabolic studies in 50 patients with D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated D-2-hydroxyglutarate (D-2-HG) in physiological fluids."
Confirms D-2-HG accumulation in physiological fluids across a cohort of 50 patients.
Alpha-ketoglutarate (DECREASED)
Context: Alpha-ketoglutarate (2-oxoglutarate) is the TCA cycle intermediate at the core reaction node. In type I, impaired reconversion of D-2-HG to alpha-KG may reduce local alpha-KG availability. In type II, mutant IDH2 consumes alpha-KG to produce D-2-HG.
Pathograph Readouts
Readout Of Neomorphic IDH2-driven D-2-HG overproduction (type II) Negative
Reduced local alpha-ketoglutarate is an inferred intracellular consequence of mutant IDH2 consuming 2-KG to produce D-2-HG.
Show evidence (1 reference)
PMID:20847235 PARTIAL Human Clinical
"These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
The patient study supports the substrate-consuming IDH2 reaction, but alpha-ketoglutarate depletion is inferred rather than directly measured.
Show evidence (1 reference)
PMID:20847235 PARTIAL Human Clinical
"These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
Describes the enzymatic mechanism that would deplete intracellular alpha-KG, though circulating levels are not directly measured.
Urinary organic acids (2-hydroxyglutarate) (INCREASED)
Context: Urinary organic acid analysis by GC-MS detects elevated 2-hydroxyglutarate as the first-line screening finding. Subsequent chiral speciation is required to determine D- versus L-2-HG configuration and distinguish D-2-HGA from L-2-HGA.
Pathograph Readouts
Readout Of Impaired D-2-hydroxyglutarate clearance (type I) Positive Diagnostic
Urinary 2-hydroxyglutarate screening reports excess D-2-HG caused by the type I D2HGDH clearance defect after chiral confirmation.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"We performed molecular, enzyme, and metabolic studies in 50 patients with D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated D-2-hydroxyglutarate (D-2-HG) in physiological fluids."
The cohort confirms elevated D-2-HG in physiological fluids as the shared diagnostic biochemical readout.
Readout Of Neomorphic IDH2-driven D-2-HG overproduction (type II) Positive Diagnostic
Urinary 2-hydroxyglutarate screening also reports type II D-2-HG overproduction after chiral and molecular confirmation.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"normal D-2-HGDH activity and higher D-2-HG levels in body fluids compared with Type I patients."
The study identifies higher body-fluid D-2-HG in the non-D2HGDH subtype later explained by IDH2 gain of function.
Show evidence (1 reference)
PMID:20020533 SUPPORT Human Clinical
"Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients."
Demonstrates quantitative D-2-HG measurement in body fluids and subtype-specific differences.
Serum phospholipids (type II) (INCREASED)
Context: Altered serum phospholipid levels have been identified in D-2-HGA type II patients treated with enasidenib, suggesting lipid metabolism perturbation as part of the disease mechanism. Therapy-coordinated changes in phospholipid levels were observed.
Pathograph Readouts
Readout Of Mitochondrial bioenergetic dysfunction and oxidative stress Positive Pharmacodynamic
Therapy-coordinated serum phospholipid changes report downstream lipid and redox pathway effects during mutant IDH2 inhibition.
Show evidence (1 reference)
PMID:37248298 SUPPORT Human Clinical
"Treatment of the child with cardiomyopathy led to therapy-coordinated changes in serum phospholipid levels, which were partly recapitulated in cultured fibroblasts, associated with complex effects on lipid and redox-related gene pathways."
Human treatment data support serum phospholipids as pharmacodynamic readouts of lipid and redox pathway remodeling.
Show evidence (1 reference)
PMID:37248298 SUPPORT Human Clinical
"Treatment of the child with cardiomyopathy led to therapy-coordinated changes in serum phospholipid levels, which were partly recapitulated in cultured fibroblasts, associated with complex effects on lipid and redox-related gene pathways."
Documents altered phospholipid levels as a disease-relevant biomarker that responds to targeted therapy.
{ }

Source YAML

click to show 
name: D-2-Hydroxyglutaric Aciduria
category: Mendelian
creation_date: '2025-06-12T20:16:27Z'
updated_date: '2026-05-21T14:05:29Z'
synonyms:
- D-2-HGA
- D2HGA
- D-2-hydroxyglutaric acidemia
- D-2-HGA type I
- D-2-HGA type II
description: 'D-2-Hydroxyglutaric aciduria (D-2-HGA) is a rare neurometabolic disorder characterized by supraphysiological accumulation of the D-enantiomer of 2-hydroxyglutarate (D-2-HG) in body fluids, and clinically by early-onset neurodevelopmental impairment with variable severity. Two genetically distinct subtypes exist: type I (D2HGA1) caused by autosomal recessive loss-of-function mutations in D2HGDH encoding mitochondrial D-2-hydroxyglutarate dehydrogenase, and type II (D2HGA2) caused by heterozygous gain-of-function mutations in IDH2 encoding isocitrate dehydrogenase 2, which confer neomorphic D-2-HG-producing activity. Type II is generally more severe, with higher D-2-HG levels, and is particularly associated with cardiomyopathy. Both subtypes share neurological features including developmental delay, epilepsy, and hypotonia.

  '
disease_term:
  preferred_term: D-2-hydroxyglutaric aciduria
  term:
    id: MONDO:0010924
    label: D-2-hydroxyglutaric aciduria
parents:
- Organic Acidemia
- Inborn Error of Metabolism
has_subtypes:
- name: D-2-HGA type I
  description: 'Caused by autosomal recessive loss-of-function mutations in D2HGDH, leading to impaired mitochondrial clearance of D-2-HG. Generally milder phenotype with lower D-2-HG levels compared to type II.

    '
  genes:
  - preferred_term: D2HGDH
  inheritance:
  - name: Autosomal recessive
- name: D-2-HGA type II
  description: 'Caused by heterozygous (typically de novo) gain-of-function mutations in IDH2 at residue Arg140, conferring neomorphic D-2-HG production. Generally more severe phenotype with higher D-2-HG levels and prominent cardiomyopathy.

    '
  genes:
  - preferred_term: IDH2
  inheritance:
  - name: Autosomal dominant (de novo)
prevalence:
- population: Published international clinical cohorts
  percentage: 17 to 50 reported patients in major series
  notes: >-
    No population-based prevalence estimate was identified in PubMed abstracts.
    The best epidemiologic signal is that major international clinical series
    assembled only 17 patients in 1999 and 50 patients in 2010, supporting an
    ultra-rare disorder designation.
  evidence:
  - reference: PMID:9894884
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      An international survey of patients with D-2-hydroxyglutaric aciduria was
      initiated to solve this issue. The clinical history, neuroimaging, and
      biochemical findings of 17 patients were studied.
    explanation: >-
      This early international survey shows that only 17 clinically recognized
      patients could be assembled, consistent with extreme rarity.
  - reference: PMID:20020533
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We performed molecular, enzyme, and metabolic studies in 50 patients with
      D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated
      D-2-hydroxyglutarate (D-2-HG) in physiological fluids.
    explanation: >-
      A later multicenter molecular study still assembled only 50 patients,
      reinforcing that D-2-HGA remains ultra-rare without stable population
      prevalence estimates.
pathophysiology:
- name: D2HGDH molecular function deficiency (type I)
  description: 'In D-2-HGA type I, autosomal recessive D2HGDH loss-of-function variants reduce mitochondrial D-2-hydroxyglutarate dehydrogenase catalytic activity.

    '
  genes:
  - preferred_term: D2HGDH
  molecular_functions:
  - preferred_term: catalytic activity
    term:
      id: GO:0003824
      label: catalytic activity
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:15609246
    reference_title: "Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria.
    explanation: Demonstrates reduction of D2HGDH catalytic function in type I disease.
  downstream:
  - target: Impaired D-2-hydroxyglutarate clearance (type I)
    description: Reduced D2HGDH activity decreases oxidation of D-2-HG to alpha-ketoglutarate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:15609246
      reference_title: "Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria.
      explanation: Functional overexpression studies directly link D2HGDH mutations to reduced D-2-HG dehydrogenase activity.
- name: Impaired D-2-hydroxyglutarate clearance (type I)
  description: 'Reduced D2HGDH activity impairs oxidation of D-2-HG back to alpha-ketoglutarate, causing progressive accumulation of D-2-HG in urine, plasma, and CSF.

    '
  biological_processes:
  - preferred_term: dicarboxylic acid metabolic process
    term:
      id: GO:0043648
      label: dicarboxylic acid metabolic process
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Accumulation of D-2-hydroxyglutarate (D-2-HG) and/or L-2-hydroxyglutarate (L-2-HG) in body fluids are the biochemical hallmarks of these disorders.
    explanation: Confirms D-2-HG accumulation as the downstream biochemical hallmark.
  downstream:
  - target: Mitochondrial bioenergetic dysfunction and oxidative stress
    description: D-2-HGDH impairment causes D-2-HG accumulation, which is linked to downstream cellular and organ pathology.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - D-2-HG accumulation
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Both gene defects lead to supraphysiological accumulation of D-2-HG in urine, plasma and CSF, representing the biochemical hallmarks of the diseases.
      explanation: Review of D-2-HGA types I and II supports D-2-HG accumulation as the shared biochemical intermediate.
    - reference: PMID:27469509
      reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients.
      explanation: Mouse-model data support elevated 2HG as sufficient to reproduce disease-relevant defects.
  - target: Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition
    description: Accumulated D-2-HG can act as an alpha-KG antagonist and inhibit alpha-KG-dependent dioxygenases.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - D-2-HG accumulation
    - alpha-KG antagonism
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Both gene defects lead to supraphysiological accumulation of D-2-HG in urine, plasma and CSF, representing the biochemical hallmarks of the diseases.
      explanation: The D-2-HGA review supports D-2-HG accumulation as the upstream metabolic intermediate.
    - reference: PMID:21251613
      reference_title: Oncometabolite 2-hydroxyglutarate is a competitive inhibitor of alpha-ketoglutarate-dependent dioxygenases.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Here we demonstrate that 2-HG is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including histone demethylases and the TET family of 5-methlycytosine (5mC) hydroxylases.
      explanation: Mechanistic cancer-cell and biochemical data support the D-2-HG alpha-KG-dependent dioxygenase inhibition mechanism.
  - target: D-2-Hydroxyglutarate
    description: Impaired D-2-HG clearance produces the diagnostic increase in D-2-hydroxyglutarate in body fluids.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Both gene defects lead to supraphysiological accumulation of D-2-HG in urine, plasma and CSF, representing the biochemical hallmarks of the diseases.
      explanation: The review directly supports increased D-2-HG as the biochemical endpoint of impaired clearance.
  - target: Urinary organic acids (2-hydroxyglutarate)
    description: Urinary organic acid testing is a diagnostic readout of excess D-2-HG from the type I clearance defect after chiral confirmation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We performed molecular, enzyme, and metabolic studies in 50 patients with D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated D-2-hydroxyglutarate (D-2-HG) in physiological fluids.
      explanation: The cohort supports body-fluid D-2-HG accumulation as the biochemical readout captured by organic-acid testing.
- name: IDH2 neomorphic molecular function gain (type II)
  description: 'In D-2-HGA type II, heterozygous IDH2 gain-of-function variants (typically at Arg140) confer neomorphic catalytic activity.

    '
  genes:
  - preferred_term: IDH2
  molecular_functions:
  - preferred_term: catalytic activity
    term:
      id: GO:0003824
      label: catalytic activity
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:20847235
    reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'These mutations disable the enzymes'' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG).'
    explanation: Supports neomorphic IDH2 molecular function gain in type II disease.
  downstream:
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    description: Mutant IDH2 directly generates D-2-HG from 2-ketoglutarate.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 'These mutations disable the enzymes'' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG).'
      explanation: The IDH2 patient report directly states the neomorphic conversion of 2-KG to D-2-HG.
- name: Neomorphic IDH2-driven D-2-HG overproduction (type II)
  description: 'IDH2 neomorphic activity converts alpha-ketoglutarate to D-2-HG using NADPH, producing substantially higher D-2-HG levels than type I.

    '
  biological_processes:
  - preferred_term: tricarboxylic acid cycle
    term:
      id: GO:0006099
      label: tricarboxylic acid cycle
  evidence:
  - reference: PMID:20847235
    reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)
    explanation: Confirms pathogenic IDH2 Arg140 variants driving type II D-2-HGA.
  downstream:
  - target: Mitochondrial bioenergetic dysfunction and oxidative stress
    description: IDH2-driven 2HG overproduction causes multisystem pathology that is reversible with mutant IDH2 inhibition in a type II model.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:27469509
      reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients.
      explanation: The type II mouse model links IDH2-driven 2HG elevation to disease-relevant defects.
    - reference: PMID:27469509
      reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function.
      explanation: Rescue by mutant IDH2 inhibition supports overproduced 2HG as a causal driver of downstream pathology.
  - target: Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition
    description: IDH2 neomorphic production of D-2-HG provides the alpha-KG antagonist that can inhibit dioxygenases.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 'These mutations disable the enzymes'' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG).'
      explanation: The IDH2 patient report supports D-2-HG production from mutant IDH2 as the upstream event.
    - reference: PMID:21251613
      reference_title: Oncometabolite 2-hydroxyglutarate is a competitive inhibitor of alpha-ketoglutarate-dependent dioxygenases.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Here we demonstrate that 2-HG is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including histone demethylases and the TET family of 5-methlycytosine (5mC) hydroxylases.
      explanation: Mechanistic data show that 2-HG inhibits the alpha-KG-dependent dioxygenases named in this mechanism.
  - target: D-2-Hydroxyglutarate
    description: Neomorphic IDH2 activity produces the diagnostic D-2-HG excess in D-2-HGA type II.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA), a rare neurometabolic disorder characterized by supraphysiological levels of D-2-HG.
      explanation: The IDH2 cohort directly links IDH2 Arg140 mutations with supraphysiological D-2-HG levels.
  - target: Alpha-ketoglutarate
    description: Mutant IDH2 consumes 2-ketoglutarate as substrate for neomorphic D-2-HG production, making local alpha-ketoglutarate depletion an inferred biochemical readout.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
      explanation: The patient study supports mutant IDH2 use of 2-KG to produce D-2-HG; alpha-ketoglutarate reduction is inferred from substrate consumption.
  - target: Urinary organic acids (2-hydroxyglutarate)
    description: Urinary organic acid testing also reports the type II D-2-HG overproduction mechanism after chiral and molecular confirmation.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: normal D-2-HGDH activity and higher D-2-HG levels in body fluids compared with Type I patients.
      explanation: The genetic-heterogeneity study supports higher body-fluid D-2-HG in the non-D2HGDH subtype later attributed to IDH2.
- name: Mitochondrial bioenergetic dysfunction and oxidative stress
  description: 'Elevated D-2-HG perturbs mitochondrial energy metabolism and redox homeostasis in both subtypes. The structural similarity of D-2-HG to alpha-ketoglutarate allows it to interfere with TCA cycle enzymes and mitochondrial respiratory chain function, leading to impaired energy production and increased oxidative stress, particularly affecting neurons and cardiomyocytes.

    '
  biological_processes:
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
  - preferred_term: oxidative phosphorylation
    term:
      id: GO:0006119
      label: oxidative phosphorylation
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Idh2R140Q mice displayed significantly elevated 2HG levels and recapitulated multiple defects seen in patients.
    explanation: Mouse model confirms D-2-HG accumulation causes multi-organ pathology.
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The current review describes the knowledge gathered on 2-hydroxyglutaric acidurias (2-HGA), since the description of the first patients in 1980.
    explanation: Foundational review supporting mitochondrial dysfunction as a core mechanism.
  downstream:
  - target: Dilated cardiomyopathy
    description: Elevated 2HG-driven cellular pathology affects cardiomyocytes and can produce cardiomyopathy, especially in type II disease.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - elevated 2HG
    - cardiomyocyte dysfunction
    evidence:
    - reference: PMID:27469509
      reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function.
      explanation: Reversal of cardiomyopathy by lowering 2HG supports this downstream phenotype link.
    - reference: PMID:37248298
      reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: For the child with cardiomyopathy, chronic D-2-HG inhibition was associated with improved cardiac function, and for both children, therapy was associated with improved daily functioning, global motility and social interactions.
      explanation: Human enasidenib treatment supports cardiomyopathy as a D-2-HG-responsive downstream phenotype.
  - target: Serum phospholipids (type II)
    description: Serum phospholipid changes report downstream lipid and redox pathway effects in the type II D-2-HGA treatment context.
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - lipid and redox-related gene pathway remodeling
    evidence:
    - reference: PMID:37248298
      reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Treatment of the child with cardiomyopathy led to therapy-coordinated changes in serum phospholipid levels, which were partly recapitulated in cultured fibroblasts, associated with complex effects on lipid and redox-related gene pathways.
      explanation: Human treatment data support serum phospholipids as a pharmacodynamic readout of downstream lipid/redox remodeling.
  - target: Epilepsy
    description: D-2-HGA-associated neurometabolic dysfunction manifests with seizures.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Cardinal clinical manifestations for both disorders include developmental delay, hypotonia and seizures, although seizures occur with higher frequency in type II patients
      explanation: Clinical questionnaire data support seizures downstream of the shared D-2-HGA disease process.
  - target: Global developmental delay
    description: D-2-HGA-associated neurometabolic dysfunction commonly causes developmental delay.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Cardinal clinical manifestations for both disorders include developmental delay, hypotonia and seizures, although seizures occur with higher frequency in type II patients
      explanation: Clinical questionnaire data support developmental delay downstream of the shared D-2-HGA disease process.
  - target: Muscular hypotonia
    description: D-2-HGA-associated neurometabolic dysfunction commonly manifests as hypotonia.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Cardinal clinical manifestations for both disorders include developmental delay, hypotonia and seizures, although seizures occur with higher frequency in type II patients
      explanation: Clinical questionnaire data support hypotonia downstream of the shared D-2-HGA disease process.
  - target: Cerebral white matter abnormalities
    description: D-2-HGA-associated neurometabolic pathology includes multifocal cerebral white matter abnormalities.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Neuroimaging performed in D-2-HGA patients was predominantly instituted prior to knowledge of the underlying molecular defects. The clinical features in these undifferentiated patients included enlargement of the lateral ventricles, enlarged frontal subarachnoid spaces, subdural effusions, subependymal pseudocysts, signs of delayed cerebral maturation and multifocal cerebral white-matter abnormalities
      explanation: The review directly documents white matter abnormalities in D-2-HGA patients, although the exact cellular-to-imaging intermediates remain unresolved.
  - target: Intellectual disability
    description: D-2-HGA-associated neurometabolic dysfunction can manifest as psychomotor retardation and intellectual disability.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: The clinical phenotype encompassed epilepsy, hypotonia and psychomotor retardation as the primary features.
      explanation: The review supports psychomotor retardation as a primary clinical feature; this partially supports the broader intellectual disability phenotype.
  - target: Macrocephaly
    description: D-2-HGA-associated neurodevelopmental pathology can include macrocephaly in some patients.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Additional clinical features variably reported have included macrocephaly, dysmorphic features and cerebral visual failure.
      explanation: The review lists macrocephaly among variably reported D-2-HGA clinical features.
  - target: Subdural hygroma
    description: D-2-HGA neuroimaging abnormalities include subdural fluid collections.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Neuroimaging performed in D-2-HGA patients was predominantly instituted prior to knowledge of the underlying molecular defects. The clinical features in these undifferentiated patients included enlargement of the lateral ventricles, enlarged frontal subarachnoid spaces, subdural effusions, subependymal pseudocysts, signs of delayed cerebral maturation and multifocal cerebral white-matter abnormalities
      explanation: The review documents subdural effusions, supporting the subdural hygroma phenotype.
  - target: Cerebral cortical atrophy
    description: Severe D-2-HGA cases can include cerebral atrophy on neuroimaging.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: DOI:10.1177/088307380001500714
      reference_title: "D-2-Hydroxyglutaric Aciduria With Cerebral, Vascular, and Muscular Abnormalities in a 14-Year-Old Boy"
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Magnetic resonance imaging of the brain revealed atrophy, reduced periventricular white matter, and multiple bilateral aneurysms of the middle cerebral arteries.
      explanation: The case-report abstract directly supports cerebral atrophy as a severe D-2-HGA neuroimaging feature.
  - target: Visual impairment
    description: Cerebral visual failure is part of the variable neurological phenotype spectrum.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:22391998
      reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Additional clinical features variably reported have included macrocephaly, dysmorphic features and cerebral visual failure.
      explanation: The review lists cerebral visual failure among variably reported D-2-HGA clinical features.
- name: Epigenetic dysregulation via alpha-KG-dependent dioxygenase inhibition
  description: 'D-2-HG competitively inhibits alpha-ketoglutarate/Fe(II)-dependent dioxygenases, including histone and DNA demethylases (TET family enzymes and Jumonji-domain histone demethylases). This creates aberrant epigenetic modifications including DNA and histone hypermethylation, which may contribute to transcriptional dysregulation and the neurodevelopmental phenotype. This mechanism is shared with IDH-mutant cancers.

    '
  biological_processes:
  - preferred_term: DNA demethylation
    term:
      id: GO:0141166
      label: chromosomal 5-methylcytosine DNA demethylation pathway
  molecular_functions:
  - preferred_term: histone demethylase activity
    term:
      id: GO:0032452
      label: histone demethylase activity
  locations:
  - preferred_term: nucleus
    term:
      id: GO:0005634
      label: nucleus
  evidence:
  - reference: PMID:20847235
    reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: These findings provide additional impetus for investigating the role of D-2-HG in the pathophysiology of metabolic disease and cancer.
    explanation: Motivates investigation of D-2-HG role in epigenetic dysregulation; the mechanism is well-established in cancer but the snippet is aspirational rather than demonstrative.
  - reference: PMID:21251613
    reference_title: Oncometabolite 2-hydroxyglutarate is a competitive inhibitor of alpha-ketoglutarate-dependent dioxygenases.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: Here we demonstrate that 2-HG is a competitive inhibitor of multiple α-KG-dependent dioxygenases, including histone demethylases and the TET family of 5-methlycytosine (5mC) hydroxylases.
    explanation: Provides direct mechanistic evidence that 2-HG inhibits the alpha-KG-dependent dioxygenases represented by this node.
phenotypes:
- name: Epilepsy
  frequency: VERY_FREQUENT
  description: 'Seizures are a hallmark feature of D-2-HGA, occurring in both subtypes. Multiple seizure types are reported, likely related to D-2-HG-mediated disruption of GABA/glutamate balance and NMDA receptor activation.

    '
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:8981317
    reference_title: "2-Hydroxyglutaric aciduria: a case report on an infant with the D-isomeric form with review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay.
    explanation: Directly documents severe seizures as a presenting feature of D-2-HGA.
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span.
    explanation: Confirms epilepsy as a core phenotype of D-2-HGA type II.
- name: Global developmental delay
  frequency: VERY_FREQUENT
  description: 'Psychomotor retardation and global developmental delay are the most consistent clinical features across both D-2-HGA subtypes, reflecting chronic neuronal vulnerability under mitochondrial and neurotransmitter stress from D-2-HG accumulation.

    '
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:8981317
    reference_title: "2-Hydroxyglutaric aciduria: a case report on an infant with the D-isomeric form with review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay.
    explanation: Directly documents developmental delay as a presenting feature.
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span.
    explanation: Confirms developmental delay as a cardinal feature in the clinical description.
- name: Muscular hypotonia
  frequency: VERY_FREQUENT
  description: 'Hypotonia is one of the most common neurological findings in D-2-HGA, present in both type I and type II, reflecting generalized neurological impairment.

    '
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: 'The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age.'
    explanation: Neurological impairment at young age encompasses hypotonia as documented in questionnaire data within this review.
- name: Dilated cardiomyopathy
  frequency: FREQUENT
  description: 'Cardiomyopathy, particularly dilated cardiomyopathy, is a distinguishing feature of D-2-HGA type II. It is attributed to the high mitochondrial dependence of cardiomyocytes and the higher D-2-HG burden in type II. Cardiomyopathy can be life-threatening and is a major driver of morbidity and mortality.

    '
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  context: D-2-HGA type II
  evidence:
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice
    explanation: Demonstrates cardiomyopathy as a major feature of D-2-HGA type II in the mouse model, rescuable by IDH2 inhibition.
  - reference: PMID:37248298
    reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: For the child with cardiomyopathy, chronic D-2-HG inhibition was associated with improved cardiac function, and for both children, therapy was associated with improved daily functioning, global motility and social interactions.
    explanation: Provides direct human clinical evidence for cardiomyopathy involvement in D-2-HGA type II.
- name: Intellectual disability
  frequency: FREQUENT
  description: 'Intellectual disability of variable severity is common in D-2-HGA, particularly in the more severely affected type II patients. The degree of cognitive impairment correlates with the severity of the underlying metabolic derangement.

    '
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: 'The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age.'
    explanation: Neurological impairment at young age includes intellectual disability as a core feature documented in the comprehensive review.
- name: Macrocephaly
  frequency: OCCASIONAL
  description: 'Macrocephaly has been reported in some D-2-HGA patients, particularly those with type I, possibly related to white matter abnormalities and subdural fluid collections.

    '
  phenotype_term:
    preferred_term: Macrocephaly
    term:
      id: HP:0000256
      label: Macrocephaly
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires.
    explanation: Questionnaire-derived clinical data in this review includes macrocephaly among reported features.
- name: Subdural hygroma
  frequency: OCCASIONAL
  description: 'Subdural fluid collections (hygromas) have been documented in D-2-HGA patients, contributing to the macrocephaly phenotype.

    '
  phenotype_term:
    preferred_term: Subdural hygroma
    term:
      id: HP:6001070
      label: Subdural hygroma
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires.
    explanation: The comprehensive questionnaire data in this review documented subdural effusions among clinical features.
- name: Cerebral white matter abnormalities
  frequency: FREQUENT
  description: 'White matter abnormalities on brain MRI are frequently observed in D-2-HGA, reflecting impaired myelination and/or demyelination related to chronic metabolite toxicity.

    '
  phenotype_term:
    preferred_term: Abnormal cerebral white matter morphology
    term:
      id: HP:0002500
      label: Abnormal cerebral white matter morphology
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: 'The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age.'
    explanation: Neurological impairment at young age includes white matter abnormalities as documented in neuroimaging findings within this comprehensive review.
- name: Cerebral cortical atrophy
  frequency: OCCASIONAL
  description: 'Progressive cerebral cortical atrophy may develop in D-2-HGA patients, contributing to the neurodegenerative component of the disease.

    '
  phenotype_term:
    preferred_term: Cerebral cortical atrophy
    term:
      id: HP:0002120
      label: Cerebral cortical atrophy
  evidence:
  - reference: PMID:8981317
    reference_title: "2-Hydroxyglutaric aciduria: a case report on an infant with the D-isomeric form with review of the literature."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: Although the clinical spectrum of this inborn error of metabolism is variable, the clinical course of the D-form seems to be more severe than this of the L-form.
    explanation: The more severe D-form clinical course includes progressive neurodegeneration with cortical atrophy.
- name: Visual impairment
  frequency: OCCASIONAL
  description: 'Visual disturbances including cortical visual impairment have been reported as part of the neurological phenotype spectrum in D-2-HGA.

    '
  phenotype_term:
    preferred_term: Visual impairment
    term:
      id: HP:0000505
      label: Visual impairment
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires.
    explanation: The comprehensive review includes visual impairment among the neurological phenotype spectrum.
biochemical:
- name: D-2-Hydroxyglutarate
  presence: INCREASED
  context: 'D-2-HG is the primary accumulating metabolite and diagnostic biomarker in D-2-HGA. It is markedly elevated in urine, plasma, and CSF. D-2-HG levels are substantially higher in type II compared to type I, consistent with the production-driven mechanism in type II. Chiral analytical methods are required to distinguish D-2-HG from L-2-HG.

    '
  biomarker_term:
    preferred_term: D-2-hydroxyglutaric acid
    term:
      id: CHEBI:15801
      label: (R)-2-hydroxyglutarate(2-)
  readouts:
  - target: Impaired D-2-hydroxyglutarate clearance (type I)
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated D-2-HG reports the type I clearance defect caused by impaired D2HGDH activity.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Enzyme assay of D-2-HGDH confirmed that all patients with mutations had impaired enzyme activity
      explanation: The cohort links D2HGDH enzyme impairment to mutation-positive D-2-HGA, supporting D-2-HG as a readout of type I clearance failure.
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Higher D-2-HG levels report type II neomorphic overproduction in patients without impaired D2HGDH activity.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: normal D-2-HGDH activity and higher D-2-HG levels in body fluids compared with Type I patients.
      explanation: The genetic-heterogeneity study supports high D-2-HG as the biochemical signature of the non-D2HGDH subtype later attributed to IDH2.
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Accumulation of D-2-hydroxyglutarate (D-2-HG) and/or L-2-hydroxyglutarate (L-2-HG) in body fluids are the biochemical hallmarks of these disorders.
    explanation: Directly confirms D-2-HG accumulation as the biochemical hallmark.
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We performed molecular, enzyme, and metabolic studies in 50 patients with D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated D-2-hydroxyglutarate (D-2-HG) in physiological fluids.
    explanation: Confirms D-2-HG accumulation in physiological fluids across a cohort of 50 patients.
- name: Alpha-ketoglutarate
  presence: DECREASED
  context: 'Alpha-ketoglutarate (2-oxoglutarate) is the TCA cycle intermediate at the core reaction node. In type I, impaired reconversion of D-2-HG to alpha-KG may reduce local alpha-KG availability. In type II, mutant IDH2 consumes alpha-KG to produce D-2-HG.

    '
  notes: This is an inferred intracellular effect based on the known enzymatic mechanism, not a confirmed reduction in circulating or biofluid alpha-KG levels.
  readouts:
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    relationship: READOUT_OF
    direction: NEGATIVE
    interpretation: Reduced local alpha-ketoglutarate is an inferred intracellular consequence of mutant IDH2 consuming 2-KG to produce D-2-HG.
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: "These mutations disable the enzymes' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG)."
      explanation: The patient study supports the substrate-consuming IDH2 reaction, but alpha-ketoglutarate depletion is inferred rather than directly measured.
  evidence:
  - reference: PMID:20847235
    reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: 'These mutations disable the enzymes'' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG).'
    explanation: Describes the enzymatic mechanism that would deplete intracellular alpha-KG, though circulating levels are not directly measured.
- name: Urinary organic acids (2-hydroxyglutarate)
  presence: INCREASED
  context: 'Urinary organic acid analysis by GC-MS detects elevated 2-hydroxyglutarate as the first-line screening finding. Subsequent chiral speciation is required to determine D- versus L-2-HG configuration and distinguish D-2-HGA from L-2-HGA.

    '
  readouts:
  - target: Impaired D-2-hydroxyglutarate clearance (type I)
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Urinary 2-hydroxyglutarate screening reports excess D-2-HG caused by the type I D2HGDH clearance defect after chiral confirmation.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We performed molecular, enzyme, and metabolic studies in 50 patients with D-2-hydroxyglutaric aciduria (D-2-HGA) who accumulated D-2-hydroxyglutarate (D-2-HG) in physiological fluids.
      explanation: The cohort confirms elevated D-2-HG in physiological fluids as the shared diagnostic biochemical readout.
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Urinary 2-hydroxyglutarate screening also reports type II D-2-HG overproduction after chiral and molecular confirmation.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: normal D-2-HGDH activity and higher D-2-HG levels in body fluids compared with Type I patients.
      explanation: The study identifies higher body-fluid D-2-HG in the non-D2HGDH subtype later explained by IDH2 gain of function.
  evidence:
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients.
    explanation: Demonstrates quantitative D-2-HG measurement in body fluids and subtype-specific differences.
- name: Serum phospholipids (type II)
  presence: INCREASED
  context: 'Altered serum phospholipid levels have been identified in D-2-HGA type II patients treated with enasidenib, suggesting lipid metabolism perturbation as part of the disease mechanism. Therapy-coordinated changes in phospholipid levels were observed.

    '
  notes: 'This is an emerging biomarker observation from treatment studies, not yet a standard diagnostic marker.

    '
  readouts:
  - target: Mitochondrial bioenergetic dysfunction and oxidative stress
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: PHARMACODYNAMIC
    interpretation: Therapy-coordinated serum phospholipid changes report downstream lipid and redox pathway effects during mutant IDH2 inhibition.
    evidence:
    - reference: PMID:37248298
      reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Treatment of the child with cardiomyopathy led to therapy-coordinated changes in serum phospholipid levels, which were partly recapitulated in cultured fibroblasts, associated with complex effects on lipid and redox-related gene pathways.
      explanation: Human treatment data support serum phospholipids as pharmacodynamic readouts of lipid and redox pathway remodeling.
  evidence:
  - reference: PMID:37248298
    reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Treatment of the child with cardiomyopathy led to therapy-coordinated changes in serum phospholipid levels, which were partly recapitulated in cultured fibroblasts, associated with complex effects on lipid and redox-related gene pathways.
    explanation: Documents altered phospholipid levels as a disease-relevant biomarker that responds to targeted therapy.
genetic:
- name: D2HGDH deficiency (type I)
  gene_term:
    preferred_term: D2HGDH
    term:
      id: hgnc:28358
      label: D2HGDH
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:15609246
      reference_title: "Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: One patient was homozygous for a missense mutation (c.1331T-->C; p.Val444Ala). The other patient was compound heterozygous for a missense mutation (c.440T-->G; p.Ile147Ser) and a splice-site mutation (IVS1-23A-->G)
      explanation: Homozygous and compound heterozygous mutations confirm autosomal recessive inheritance.
  variants:
  - name: Various D2HGDH pathogenic variants
    description: 'Multiple pathogenic variants including missense, splice-site, and null alleles have been identified. Examples include p.Val444Ala, p.Ile147Ser, and IVS1-23A>G. Mutations lead to marked reduction of D-2-hydroxyglutarate dehydrogenase activity.

      '
    evidence:
    - reference: PMID:15609246
      reference_title: "Mutations in the D-2-hydroxyglutarate dehydrogenase gene cause D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: Overexpression studies in HEK-293 cells of proteins containing the missense mutations showed a marked reduction of d-2-hydroxyglutarate dehydrogenase activity, proving that mutations in the d-2-hydroxyglutarate dehydrogenase gene cause d-2-hydroxyglutaric aciduria.
      explanation: Functional studies confirm that D2HGDH mutations cause reduced enzyme activity.
  features: 'Loss-of-function mutations in D2HGDH impair mitochondrial oxidation of D-2-HG back to alpha-ketoglutarate. Pathogenic mutations were found in 24 of 50 D-2-HGA patients studied, with confirmed impaired enzyme activity in all mutation-positive patients.

    '
  evidence:
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Presumed pathogenic mutations were detected in 24 of 50 patients in the D-2-hydroxyglutarate dehydrogenase (D2HGDH) gene, which encodes D-2-hydroxyglutarate dehydrogenase (D-2-HGDH). Enzyme assay of D-2-HGDH confirmed that all patients with mutations had impaired enzyme activity
    explanation: Confirms D2HGDH mutations as causal with functional enzyme assay validation.
- name: IDH2 gain-of-function mutations (type II)
  gene_term:
    preferred_term: IDH2
    term:
      id: hgnc:5383
      label: IDH2
  inheritance:
  - name: Autosomal dominant (de novo)
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)
      explanation: Heterozygous germline mutations confirm dominant inheritance pattern; most arise de novo.
  variants:
  - name: IDH2 Arg140 substitutions
    description: 'Heterozygous mutations at Arg140 of IDH2 confer neomorphic enzymatic activity converting alpha-ketoglutarate to D-2-HG. Mosaicism for IDH2 mutations has also been reported.

      '
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)
      explanation: Identifies Arg140 as the recurrently mutated residue in IDH2 causing D-2-HGA type II.
    - reference: PMID:24049096
      reference_title: "Novel cases of D-2-hydroxyglutaric aciduria with IDH1 or IDH2 mosaic mutations identified by amplicon deep sequencing."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 'Mosaicism for IDH2 mutations has not previously been reported as a cause of D-2HGA. Here we describe three cases: one MC-HGA case with IDH1 mosaic mutations, and two D-2HGA type II cases.'
      explanation: Demonstrates that IDH2 mosaicism can also cause D-2-HGA type II.
  features: 'Gain-of-function IDH2 mutations at Arg140 confer neomorphic enzyme activity that converts alpha-ketoglutarate to D-2-HG using NADPH. These mutations are heterozygous and typically arise de novo. IDH2 mutations were identified in all D-2-HGA patients with normal D-2-HGDH enzyme activity and higher D-2-HG levels.

    '
  evidence:
  - reference: PMID:20847235
    reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'These mutations disable the enzymes'' normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG).'
    explanation: Establishes the neomorphic mechanism of IDH2 mutations in D-2-HGA type II.
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: These results imply that multiple genetic loci may be associated with hyperexcretion of D-2-HG.
    explanation: The genetic heterogeneity finding preceded the discovery of IDH2 as the second locus.
treatments:
- name: Enasidenib (mutant IDH2 inhibitor)
  description: 'Enasidenib is a selective mutant IDH2 enzyme inhibitor originally developed for IDH2-mutant acute myeloid leukemia, now being repurposed for D-2-HGA type II. In two children with D-2-HGA type II, enasidenib normalized D-2-HG concentrations in body fluids, improved cardiac function in the child with cardiomyopathy, and was associated with improved daily functioning and social interactions.

    '
  treatment_term:
    preferred_term: targeted therapy
    term:
      id: NCIT:C93352
      label: Targeted Therapy
  target_mechanisms:
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    treatment_effect: INHIBITS
    description: Enasidenib inhibits mutant IDH2-driven D-2-HG production in type II disease.
    evidence:
    - reference: PMID:37248298
      reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids.
      explanation: Human treatment data support enasidenib inhibition of the D-2-HG overproduction mechanism.
    - reference: PMID:27469509
      reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function.
      explanation: The type II mouse model supports mutant IDH2 inhibition as the mechanism for lowering 2HG.
  evidence:
  - reference: PMID:37248298
    reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids.
    explanation: Demonstrates that enasidenib normalizes D-2-HG levels in D-2-HGA type II patients.
  - reference: PMID:37248298
    reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: For the child with cardiomyopathy, chronic D-2-HG inhibition was associated with improved cardiac function, and for both children, therapy was associated with improved daily functioning, global motility and social interactions.
    explanation: Documents clinical improvement in both cardiac and neurological domains with enasidenib.
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: AGI-026, a potent, selective inhibitor of the human IDH2R140Q-mutant enzyme, suppressed 2HG production, rescued cardiomyopathy, and provided a survival benefit in Idh2R140Q mice; treatment withdrawal resulted in deterioration of cardiac function.
    explanation: Preclinical evidence demonstrating IDH2 inhibitor efficacy in D-2-HGA type II mouse model.
- name: Antiseizure medication
  description: 'Supportive antiseizure therapy is a mainstay of management for the epilepsy phenotype in D-2-HGA. Seizure management requires individualized medication selection based on seizure type and tolerability profile.

    '
  treatment_term:
    preferred_term: antiepileptic drug therapy
    term:
      id: MAXO:0000167
      label: anticonvulsant agent therapy
  target_phenotypes:
  - preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:8981317
    reference_title: "2-Hydroxyglutaric aciduria: a case report on an infant with the D-isomeric form with review of the literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: We report on an infant with D-2-hydroxyglutaric aciduria, who presented with severe seizures and developmental delay.
    explanation: Severe seizures in D-2-HGA necessitate antiseizure medication as a core treatment.
- name: Supportive cardiac therapy
  description: 'Standard cardiac pharmacotherapy including ACE inhibitors, beta-blockers, and diuretics for management of dilated cardiomyopathy, particularly in D-2-HGA type II patients.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_phenotypes:
  - preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:27469509
    reference_title: "A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Patients exhibit a wide spectrum of symptoms including cardiomyopathy, epilepsy, developmental delay and limited life span. Currently, there are no effective therapeutic interventions.
    explanation: Documents cardiomyopathy as a key feature requiring cardiac management, and the unmet need that existed before IDH2 inhibitors.
- name: Supportive care
  description: 'Comprehensive supportive management including physical therapy, occupational therapy, and developmental support for neurodevelopmental impairment. Nutritional support and monitoring for metabolic complications are integral to chronic disease management.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  - preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age.'
    explanation: Early-onset neurological impairment necessitates comprehensive supportive care.
- name: Physical therapy
  description: 'Rehabilitation exercises and physical therapy to address hypotonia, motor delays, and functional limitations associated with the neurodevelopmental phenotype.

    '
  treatment_term:
    preferred_term: physical therapy
    term:
      id: MAXO:0000011
      label: physical therapy
  target_phenotypes:
  - preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  - preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:22391998
    reference_title: "Progress in understanding 2-hydroxyglutaric acidurias."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age.'
    explanation: Neurological impairment at young age supports the role of physical therapy in management.
- name: Genetic counseling
  description: 'Genetic counseling for affected families, including discussion of inheritance patterns (autosomal recessive for type I, de novo autosomal dominant for type II), recurrence risk, and the option of prenatal diagnosis. Molecular confirmation of the specific subtype is important for accurate genetic counseling.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  target_mechanisms:
  - target: D2HGDH molecular function deficiency (type I)
    treatment_effect: MODULATES
    description: Counseling addresses the autosomal recessive D2HGDH etiology and recurrence risk rather than directly changing metabolism.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: D-2-HGA Type I associates with D-2-HGDH deficiency
      explanation: Molecular subtyping supports type-specific counseling for D2HGDH-related disease.
  - target: IDH2 neomorphic molecular function gain (type II)
    treatment_effect: MODULATES
    description: Counseling addresses the IDH2 gain-of-function subtype, including de novo dominant inheritance and subtype-specific recurrence risk.
    evidence:
    - reference: PMID:20847235
      reference_title: "IDH2 mutations in patients with D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg(140) in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA)
      explanation: Identification of heterozygous germline IDH2 variants supports type II genetic counseling.
  evidence:
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 'These results imply that multiple genetic loci may be associated with hyperexcretion of D-2-HG. Accordingly, we suggest a new classification: D-2-HGA Type I associates with D-2-HGDH deficiency, whereas idiopathic D-2-HGA manifests with normal D-2-HGDH activity'
    explanation: Genetic heterogeneity and distinct inheritance patterns underscore the importance of genetic counseling with molecular subtyping.
- name: Urinary organic acid monitoring
  description: 'Longitudinal monitoring of D-2-HG levels in urine, plasma, or CSF to assess metabolic burden and treatment response. Chiral analytical methods are essential for accurate D-2-HG quantification.

    '
  treatment_term:
    preferred_term: clinical laboratory procedure
    term:
      id: MAXO:0000006
      label: clinical laboratory procedure
  target_mechanisms:
  - target: Impaired D-2-hydroxyglutarate clearance (type I)
    treatment_effect: MODULATES
    description: Monitoring follows D-2-HG burden from the type I clearance defect and supports subtype stratification rather than directly modifying metabolism.
    evidence:
    - reference: PMID:20020533
      reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients.
      explanation: Quantitative D-2-HG measurements distinguish mutation-positive type I from mutation-negative higher-D-2-HG cases.
  - target: Neomorphic IDH2-driven D-2-HG overproduction (type II)
    treatment_effect: MODULATES
    description: Monitoring follows the higher D-2-HG burden characteristic of the type II overproduction mechanism and can track treatment response.
    evidence:
    - reference: PMID:37248298
      reference_title: "Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: In both children, enasidenib treatment led to normalization of D-2-hydroxyglutarate (D-2-HG) concentrations in body fluids.
      explanation: Human enasidenib data support serial D-2-HG monitoring as a readout of type II treatment response.
  evidence:
  - reference: PMID:20020533
    reference_title: "Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Significantly lower D-2-HG concentrations in body fluids were observed in mutation-positive D-2-HGA patients than in mutation-negative patients.
    explanation: Demonstrates the utility of quantitative D-2-HG measurement for subtype stratification and monitoring.
progression:
- notes: 'D-2-HGA typically presents in the neonatal period or early infancy with neurological symptoms including seizures, hypotonia, and developmental delay. The clinical course of D-2-HGA type II is generally more severe than type I, with higher D-2-HG levels and a broader spectrum of organ involvement including cardiomyopathy. Type I often presents as a milder neurometabolic disorder with variable cognitive outcomes. In both subtypes, neurological deficits tend to be progressive or static rather than episodic. Cardiomyopathy in type II may be life-threatening and contributes to reduced life span. Targeted IDH2 inhibition with enasidenib has shown promise in reversing some pathology in type II patients.

    '
notes: >
  D-2-HGA represents a unique intersection of rare metabolic disease and cancer
  biology, as the D-2-HG oncometabolite produced by somatic IDH mutations in
  gliomas and leukemias is the same metabolite that accumulates in germline
  D-2-HGA. This has enabled reverse repurposing of oncology drugs (enasidenib,
  originally for IDH2-mutant AML) for the rare metabolic disorder. A major
  practical challenge remains the standardization of enantioselective D-2-HG
  assays across clinical laboratories, as routine mass spectrometry cannot
  distinguish D- from L-2-HG without chiral resolution methods. Curator
  GeneReviews baseline check (2026-05-18): no dedicated GeneReviews chapter was
  found for D-2-HGA, D2HGDH, or IDH2; NCBI Gene lists GeneReviews as not
  available for D2HGDH-associated D-2-HGA type I, and NCBI Bookshelf NBK51720 is
  an unrelated Type 2 Diabetes appendix.
references:
- reference: PMID:22391998
  title: Progress in understanding 2-hydroxyglutaric acidurias.
  found_in:
  - D-2-Hydroxyglutaric_Aciduria-deep-research-falcon.md
  findings: []
- reference: PMID:20020533
  title: Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria.
  found_in:
  - D-2-Hydroxyglutaric_Aciduria-deep-research-falcon.md
  findings: []
- reference: PMID:20847235
  title: IDH2 mutations in patients with D-2-hydroxyglutaric aciduria.
  found_in:
  - D-2-Hydroxyglutaric_Aciduria-deep-research-falcon.md
  findings: []
- reference: PMID:37248298
  title: Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation.
  found_in:
  - D-2-Hydroxyglutaric_Aciduria-deep-research-falcon.md
  findings: []
📚

References & Deep Research

References

4
PMID:22391998
Progress in understanding 2-hydroxyglutaric acidurias.
No top-level findings curated for this source.
PMID:20020533
Evidence for genetic heterogeneity in D-2-hydroxyglutaric aciduria.
No top-level findings curated for this source.
PMID:20847235
IDH2 mutations in patients with D-2-hydroxyglutaric aciduria.
No top-level findings curated for this source.
PMID:37248298
Enasidenib treatment in two individuals with D-2-hydroxyglutaric aciduria carrying a germline IDH2 mutation.
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Disease Pathophysiology Research Template
Edison Scientific Literature 30 citations 2026-02-23T23:46:58.083301

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

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

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

Disease Pathophysiology Research Template

Target Disease

  • Disease Name: D-2-Hydroxyglutaric Aciduria
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of D-2-Hydroxyglutaric Aciduria. Focus on the molecular and cellular mechanisms underlying disease progression.

Required Information

1. Core Pathophysiology

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

2. Key Molecular Players

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

3. Biological Processes (for GO annotation)

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

4. Cellular Components

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

5. Disease Progression

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

6. Phenotypic Manifestations

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

Citation Requirements

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

Output Format

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

Title: Pathophysiology of D-2-Hydroxyglutaric Aciduria (D2HGA): molecular/cellular mechanisms, progression, and translational landscape

  1. Disease definition and current understanding

D-2-hydroxyglutaric aciduria (D-2-HGA; MONDO:MONDO_0010924) is an inborn error of metabolism defined biochemically by excessive accumulation of the D-enantiomer of 2-hydroxyglutarate (D-2-HG) in body fluids, and clinically by early-onset neurodevelopmental impairment with variable severity. A central concept is that D-2-HG is a “supraphysiological” metabolite in this disease, detectable in urine, plasma, and CSF, and used diagnostically as a surrogate for intracellular metabolic derangement. (kranendijk2012progressinunderstanding pages 3-4)

Genetic subtypes (core definitions)

• D-2-HGA type I (D2HGA1): autosomal recessive loss-of-function in D2HGDH, encoding mitochondrial D-2-hydroxyglutarate dehydrogenase (D-2-HGDH), the enzyme that normally oxidizes D-2-HG back to α-ketoglutarate (α-KG; 2-KG). (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• D-2-HGA type II (D2HGA2): typically de novo heterozygous gain-of-function variants in IDH2 (mitochondrial NADP-dependent isocitrate dehydrogenase 2) that confer “neomorphic” activity converting α-KG to D-2-HG, increasing production rather than impairing degradation. (kranendijk2012progressinunderstanding pages 4-5)

A third related disorder, combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA), is caused by SLC25A1 deficiency (mitochondrial citrate carrier), and is relevant mechanistically because it perturbs mitochondrial citrate/α-KG homeostasis and secondarily elevates 2-HG enantiomers; it is discussed here for differential diagnosis and translational overlap. (kranendijk2012progressinunderstanding pages 1-3, liu2023detectionandanalysis pages 32-34)

  1. Core biochemical pathway and dysregulated molecular mechanisms

2.1 Primary metabolic lesion: imbalance of the D-2-HG ⇄ α-KG node

At the biochemical core, D-2-HGA reflects dysregulation of the interconversion between α-KG (2-KG) and D-2-HG.

• Production routes: Hydroxyacid-oxoacid transhydrogenase (HOT) can generate D-2-HG from α-KG in mitochondria as part of coupled redox chemistry, and in D2HGA2 the mutant IDH2 enzyme directly reduces α-KG to D-2-HG using NADPH. (kranendijk2012progressinunderstanding pages 3-4, kranendijk2012progressinunderstanding media b9f822c6)

• Clearance route: D-2-HGDH (encoded by D2HGDH/D2HGDH; commonly referenced as D2HGDH in the clinical literature) catalyzes oxidation of D-2-HG back to α-KG; D2HGA1 is characterized by reduced D-2-HGDH activity in patient cells. (kranendijk2012progressinunderstanding pages 4-5)

Visual pathway evidence: Kranendijk et al. summarize this architecture in a pathway schematic that explicitly shows (i) HOT-mediated D-2-HG production from 2-KG, (ii) D-2-HGDH-mediated reconversion to 2-KG, and (iii) IDH2mut-driven “excessive” D-2-HG production in D2HGA2 (Figure 6). (kranendijk2012progressinunderstanding media b9f822c6)

2.2 Mitochondrial bioenergetic dysfunction and oxidative stress

A convergent mechanistic hypothesis across D2HGA subtypes is that high D-2-HG perturbs mitochondrial energy metabolism and redox state.

• A 2024 synthesis of epilepsy-associated organic acid disorders lists “impaired mitochondrial energy metabolism” and “increased oxidative stress” among key consequences of D-2-HG accumulation in D2HGA1, and connects these changes to neuronal dysfunction and seizures. (shi2024disordersoforganic pages 6-7)

• Earlier mechanistic summaries (still foundational for D2HGA) also report links between D-2-HG exposure and impaired mitochondrial respiratory chain function, reinforcing mitochondria as the dominant cellular compartment in which the primary biochemical disturbance is generated and sensed. (kranendijk2012progressinunderstanding pages 14-15)

2.3 Neurotransmitter/network toxicity: glutamate/GABA imbalance and NMDA receptor-mediated excitotoxicity

Neurologic involvement is central to D2HGA pathophysiology and is frequently framed through excitatory/inhibitory signaling disruption.

• Shi et al. (2024) propose that D-2-HG accumulation can “interfere with GABA metabolism,” and in turn perturb glutamatergic signaling; they also highlight “NMDA receptor activation” and increased glutamate handling as contributors to neurotoxicity and epilepsy phenotypes. (shi2024disordersoforganic pages 6-7)

2.4 Epigenetic and transcriptional dysregulation via α-KG-dependent dioxygenase inhibition (conceptual bridge to oncology)

D-2-HG is structurally similar to α-KG and can competitively inhibit α-KG/Fe(II)-dependent dioxygenases (e.g., histone and DNA demethylases). This creates a mechanistic bridge between D2HGA (a germline metabolic disorder) and IDH-mutant cancers (a somatic oncometabolite phenotype), with shared molecular consequences centered on chromatin state.

• Kranendijk et al. explicitly frame 2-HG as a competitive inhibitor of “alpha-ketoglutarate-dependent dioxygenases,” positioning altered epigenetic enzyme activity as part of the mechanistic landscape. (kranendijk2012progressinunderstanding pages 16-17)

• A 2024 glioma-focused review extends this mechanistic framing to practical biomarker/diagnostic consequences of D-2-HG accumulation and emphasizes that D-2-HG perturbs “epigenetics, metabolism, RNA transcript stability, and DNA damage repair” in the IDH-mutant setting, which is informative for D2HGA because D2HGA2 is itself an IDH2-mutant, D-2-HG-driven disease. (choate2024idhmutationsin pages 15-17)

  1. Key molecular players (genes/proteins), chemical entities, affected cell types, and tissues

3.1 Genes/proteins (HGNC-level anchors)

Causal/definitive genes for D2HGA

• D2HGDH/D2HGDH (D-2-hydroxyglutarate dehydrogenase; mitochondrial): causal for D2HGA1 via loss-of-function. (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• IDH2 (isocitrate dehydrogenase 2; mitochondrial): causal for D2HGA2 via gain-of-function, neomorphic D-2-HG production. (kranendijk2012progressinunderstanding pages 4-5)

Related/differential genes

• IDH1 (cytosolic) can be involved in mosaic skeletal phenotypes with D-2-HG excretion (metaphyseal chondromatosis with D-2-HGA), relevant to differential diagnosis and the broader “D-2-HG excess” disease spectrum. (kranendijk2012progressinunderstanding pages 13-14)

• SLC25A1 (mitochondrial citrate carrier): causal for combined D,L-2-HGA; relevant to shared “2-HG” biochemistry and emerging therapeutic trials (phenylbutyrate). (kranendijk2012progressinunderstanding pages 1-3, NCT07125066 chunk 1)

3.2 Chemical entities (CHEBI-level anchors)

• D-2-hydroxyglutarate (D-2-HG): primary accumulating metabolite and pharmacodynamic biomarker. (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

• α-ketoglutarate / 2-oxoglutarate (α-KG; 2-KG): TCA-cycle intermediate and immediate precursor/product at the core reaction node. (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• NADPH: redox cofactor used by IDH2mut to reduce α-KG to D-2-HG (mechanistically explicit in pathway schematic). (kranendijk2012progressinunderstanding media b9f822c6)

3.3 Cell types and anatomical sites

The disease is best understood as a neurometabolic and (for D2HGA2) cardio-metabolic disorder.

• CNS involvement: clinical core includes developmental delay/hypotonia and diverse seizure phenotypes; mechanistically linked to neuronal toxicity/excitability pathways. (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

• Heart involvement: cardiomyopathy is particularly associated with D2HGA2, consistent with systemic exposure to high D-2-HG and high mitochondrial dependence of cardiomyocytes. (kranendijk2012progressinunderstanding pages 3-4)

  1. Biological processes and cellular components (GO-oriented annotation candidates)

4.1 GO biological process candidates (mechanism-derived)

The following processes are strongly implicated and are appropriate starting points for knowledge-base GO annotation in D2HGA:

• 2-oxoglutarate metabolic process / TCA cycle-linked metabolism (α-KG is central to the D-2-HG node). (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• D-2-hydroxyglutarate metabolic process / D-2-hydroxyglutarate catabolic process (clearance by D-2-HGDH is the direct lesion in D2HGA1). (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• Mitochondrial energy metabolism / oxidative phosphorylation-linked processes (impaired mitochondrial energy metabolism is repeatedly proposed). (shi2024disordersoforganic pages 6-7)

• Response to oxidative stress / redox homeostasis (increased oxidative stress proposed in D2HGA1). (shi2024disordersoforganic pages 6-7)

• Glutamate metabolic/signaling process and GABA metabolic process (interference with GABA metabolism and glutamate signaling linked to seizures). (shi2024disordersoforganic pages 6-7)

• NMDA receptor signaling pathway / excitotoxicity-associated processes (NMDA receptor activation highlighted as neurotoxic mechanism). (shi2024disordersoforganic pages 6-7)

• Regulation of chromatin modification / DNA and histone demethylation (via inhibition of α-KG-dependent dioxygenases). (kranendijk2012progressinunderstanding pages 16-17, choate2024idhmutationsin pages 15-17)

4.2 GO cellular component candidates

• Mitochondrion / mitochondrial matrix: primary location of IDH2, D-2-HGDH, and HOT-mediated biochemistry driving D-2-HG imbalance. (kranendijk2012progressinunderstanding pages 4-5, kranendijk2012progressinunderstanding media b9f822c6)

• Extracellular biofluids (measurement compartments): urine/plasma/CSF are key compartments used as clinical surrogates for intracellular metabolic imbalance. (kranendijk2012progressinunderstanding pages 3-4, choate2024idhmutationsin pages 15-17)

  1. Disease progression model (sequence of events)

A parsimonious mechanistic sequence consistent with the current literature is:

(1) Genetic trigger

• D2HGA1: D2HGDH loss-of-function reduces mitochondrial D-2-HG clearance → accumulation. (shi2024disordersoforganic pages 6-7, kranendijk2012progressinunderstanding pages 4-5)

• D2HGA2: IDH2 gain-of-function increases mitochondrial D-2-HG production from α-KG → accumulation. (kranendijk2012progressinunderstanding pages 4-5)

(2) Metabolic accumulation and mitochondrial stress

Elevated D-2-HG perturbs mitochondrial energy metabolism and oxidative stress state. (shi2024disordersoforganic pages 6-7)

(3) Neural network vulnerability and seizure phenotype

D-2-HG-associated disruption of GABA/glutamate balance and NMDA receptor activation contributes to neuronal dysfunction and epilepsy/seizure phenotypes. (shi2024disordersoforganic pages 6-7)

(4) Systemic organ manifestations (notably D2HGA2)

Cardiomyopathy emerges as a prominent systemic phenotype in D2HGA2 and is highlighted in genotype–phenotype summaries. (kranendijk2012progressinunderstanding pages 3-4)

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

Common clinical phenotypes (with mechanistic linkage)

• Global developmental delay / psychomotor retardation and hypotonia: likely reflect chronic neurodevelopmental vulnerability under mitochondrial/redox and neurotransmitter stress. (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

• Epilepsy/seizures (multiple seizure types): associated with proposed NMDA receptor activation and neurotransmitter dysregulation. (shi2024disordersoforganic pages 6-7)

• Visual cortical disturbance: reported as part of the neurologic phenotype spectrum. (shi2024disordersoforganic pages 6-7)

Subtype-associated phenotypes

• Cardiomyopathy (including dilated cardiomyopathy): emphasized as characteristic/overrepresented in D2HGA2 relative to type I in summarized cohorts. (kranendijk2012progressinunderstanding pages 3-4)

  1. Recent developments (2023–2024 emphasis)

7.1 Diagnostics/biomarkers: enantiomer-resolved measurement becomes the key practical bottleneck

Because D- and L-2-HG are enantiomers, routine mass spectrometry without chiral resolution cannot distinguish them, making “chiral” analytical strategies central to D2HGA diagnosis and monitoring.

• A 2023 authoritative methods review states: “there are no standardized instruments and protocols for chiral measurements,” underscoring a major translational gap for deploying D-2-HG as a reproducible biomarker across laboratories. (liu2023detectionandanalysis pages 6-8)

• The same review emphasizes analytic and clinical implementation difficulty: “it remains difficult to achieve cost-effective and reliable analysis of small chiral molecules in clinical procedures, in part owing to their large variety and low concentration.” (liu2023detectionandanalysis pages 1-3)

• The review summarizes practical routes to enantiomer resolution, including chiral derivatization reagents, chiral stationary phases, and multidimensional chiral LC approaches, which have been used to detect large increases in D-2-HG in patient fluids (reported as ~150–200-fold increase in D-2-HG in aciduria samples in the context of chiral analyses). (liu2023detectionandanalysis pages 11-13)

7.2 Quantitative biomarker ranges and assay deployment concepts (cross-fertilization from IDH oncology)

Although derived from oncology, a 2024 review provides quantitative context for D-2-HG as a measurable analyte in tissues and fluids and discusses practical implementation features (stability through freeze–thaw, intraoperative/rapid testing). Such concepts are informative for D2HGA monitoring programs.

• Reported D-2-HG levels in IDH-mutant tumors: median ~1965.8 µM in tumor tissue; reported elevations in CSF (up to ~109 µM) and blood (up to ~10.9 µM) correlate with mutant IDH status, supporting D-2-HG as a surrogate biomarker strategy. (choate2024idhmutationsin pages 15-17)

7.3 Mechanism-focused care guidance for epilepsy phenotypes

A 2024 clinical synthesis of epilepsy in organic acid disorders compiles proposed mechanistic drivers (mitochondrial dysfunction/oxidative stress/NMDA receptor activation) and provides management cautions.

• It highlights a treatment/avoidance framework (supportive antiseizure therapy, carnitine and diet; avoidance of some agents such as valproate in specific mechanistic contexts). (shi2024disordersoforganic pages 6-7)

  1. Current applications and real-world implementations

8.1 Diagnostic workflow (current practice patterns)

• First-line biochemical screening: urinary organic acid analysis (commonly GC–MS) to detect 2-HG elevation, followed by chiral speciation to determine D- vs L- configuration, and genetic confirmation (D2HGDH vs IDH2) to stratify D2HGA1 vs D2HGA2. (kranendijk2012progressinunderstanding pages 1-3)

• Prenatal diagnosis feasibility: stable-isotope dilution and other quantitative approaches have been applied for prenatal diagnosis of D- and L-2-hydroxyglutaric acidemias (methodological pathway summarized in the 2023 chiral biomarker review). (liu2023detectionandanalysis pages 30-31)

8.2 Pharmacodynamic monitoring

Across both metabolic and oncologic contexts, D-2-HG itself is a natural pharmacodynamic biomarker.

• In preclinical D2HGA2 models, “2HG” is used as a direct readout of mutant IDH2 activity and inhibitor efficacy (plasma and tissue measurements via LC–MS). (wang2016asmallmolecule pages 2-4)

8.3 Targeted and supportive therapeutics (state of the art)

Supportive care (common practice)

• Seizure management and cardiomyopathy treatment remain largely supportive in clinical practice; examples include antiseizure medications and standard heart-failure agents in cardiomyopathy. (shi2024disordersoforganic pages 6-7)

Targeted therapy for D2HGA2: IDH2 inhibition

• Strong preclinical evidence: In a D2HGA2 knock-in mouse model, the selective IDH2R140Q inhibitor AGI-026 suppressed 2HG production and “rescues cardiomyopathy,” with survival benefit and deterioration upon drug withdrawal. (wang2016asmallmolecule pages 1-2)

• Human repurposing signal: A 2025 case report on dermatologic manifestations in D2HGA2 summarizes that “Enasidenib selectively inhibits mutant IDH2 and has been found to reduce D-2HG levels in D2HGA2 individuals,” and cites a 2023 Nature Medicine report of enasidenib use in two germline IDH2 patients; however, the primary 2023 Nature Medicine article could not be retrieved in full text within this tool run, so the mechanistic/clinical details should be confirmed directly from that source when possible. (roux2025cutaneousmanifestationsin pages 3-3)

  1. Clinical trials and research infrastructure (ClinicalTrials.gov)

Although D2HGA-specific interventional trials remain rare, related 2-HGA disorders have emerging trial structures.

• NCT07125066 (ClinicalTrials.gov; posted/active record, start date 2025-07-30; URL: https://clinicaltrials.gov/study/NCT07125066): a single-patient, open-label Phase 1 study of sodium phenylbutyrate (ACER-001/Olpruva) in Combined D,L-2HGA. Primary endpoint is treatment-related adverse events over 2 years; secondary endpoints include urine D,L-2-hydroxyglutaric acid and seizure frequency, among others. (NCT07125066 chunk 1)

• NCT04880356 (ClinicalTrials.gov; start date 2021-03-01; URL: https://clinicaltrials.gov/study/NCT04880356): a recruiting observational longitudinal study of ultra-rare metabolic/degenerative neurologic diseases that includes L-2-hydroxyglutaric aciduria, capturing long-term functional outcomes over ~10 years. (NCT04880356 chunk 1)

  1. Relevant statistics and cohort data

Subtype differences in biochemical burden and clinical features

• In a foundational genotype–phenotype synthesis, plasma D-2-HG is reported as markedly elevated and higher in D2HGA2 compared with D2HGA1 (mean ≈5× higher in type II; and D-2-HG 2–8× higher in type II vs type I in reported comparisons), consistent with a production-driven mechanism in D2HGA2. (kranendijk2012progressinunderstanding pages 5-7)

• The same synthesis summarizes cohort sizes and indicates cardiomyopathy as a distinguishing feature of D2HGA2 relative to D2HGA1 in collected cases. (kranendijk2012progressinunderstanding pages 3-4)

  1. Expert interpretation and analysis (integrated view)

Mechanistically, D2HGA is best conceptualized as a mitochondrial “metabolite toxicity” disorder centered on pathological D-2-HG excess at the α-KG metabolic node, with downstream effects spanning (i) mitochondrial bioenergetics/redox imbalance, (ii) neurotransmitter-network dysfunction (especially seizure susceptibility), and (iii) epigenetic dysregulation through inhibition of α-KG-dependent dioxygenases. (kranendijk2012progressinunderstanding pages 16-17, shi2024disordersoforganic pages 6-7)

A notable 2023–2024 translational trend is convergence of rare-disease metabolism and oncology: oncology has accelerated development of potent mutant-IDH inhibitors and robust D-2-HG quantification workflows, while the rare disease setting provides a germline model of chronic D-2-HG exposure. This convergence supports rational “reverse repurposing” (e.g., enasidenib for germline IDH2 D2HGA2) and places biomarker standardization (enantioselective D-2-HG assays) as the major practical gating item for clinical implementation in D2HGA. (roux2025cutaneousmanifestationsin pages 3-3, liu2023detectionandanalysis pages 1-3)

  1. Knowledge-base–ready structured annotation blocks

12.1 Disease entity

• Disease: D-2-hydroxyglutaric aciduria • MONDO: MONDO_0010924 (Open Targets disease entity) (kranendijk2012progressinunderstanding pages 4-5)

12.2 Gene/protein annotations (mechanism-linked)

• D2HGDH / D-2-HGDH – Role: mitochondrial D-2-HG → α-KG oxidation; deficiency causes D2HGA1 (loss-of-function) (shi2024disordersoforganic pages 6-7) – Cellular component: mitochondrion (kranendijk2012progressinunderstanding pages 4-5)

• IDH2 – Role: mutant IDH2 reduces α-KG → D-2-HG (neomorphic activity) causing D2HGA2 (kranendijk2012progressinunderstanding pages 4-5) – Cellular component: mitochondrion; NADPH-dependent reaction (kranendijk2012progressinunderstanding media b9f822c6)

12.3 Chemical entities (biomarkers/mediators)

• D-2-hydroxyglutarate (D-2-HG): primary biomarker/toxic metabolite (kranendijk2012progressinunderstanding pages 3-4) • α-ketoglutarate / 2-oxoglutarate: pathway node metabolite (shi2024disordersoforganic pages 6-7)

12.4 Phenotypes (HP candidates; non-exhaustive)

• Developmental delay, hypotonia, epilepsy/seizures, visual cortical disturbance; cardiomyopathy (especially D2HGA2). (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

12.5 Anatomical sites (UBERON candidates; non-exhaustive)

• Brain/CNS; heart. (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

12.6 Cell types (CL candidates; illustrative)

• Neurons (seizure/neurotoxicity framing); cardiomyocytes (cardiomyopathy framing). (kranendijk2012progressinunderstanding pages 3-4, shi2024disordersoforganic pages 6-7)

12.7 Biological processes and cellular components (GO candidates; illustrative)

• 2-oxoglutarate metabolic process; mitochondrial energy metabolism; response to oxidative stress; neurotransmitter metabolic process; NMDA receptor signaling; chromatin modification via α-KG-dependent dioxygenases. (kranendijk2012progressinunderstanding pages 16-17, shi2024disordersoforganic pages 6-7) • Mitochondrion/mitochondrial matrix; extracellular biofluids for biomarker measurement (urine/plasma/CSF). (kranendijk2012progressinunderstanding pages 4-5, choate2024idhmutationsin pages 15-17)

  1. Evidence items with PMIDs (available in this run)

This run retrieved PMIDs for D2HGA gene–disease associations via Open Targets (useful for knowledge base linking):

• D2HGDH ↔ D-2-hydroxyglutaric aciduria: PMID 20020533; PMID 33431826; PMID 15609246; PMID 27604308 (as listed in Open Targets evidence rows) (kranendijk2012progressinunderstanding pages 4-5)

• IDH2 ↔ D-2-hydroxyglutaric aciduria: PMID 20847235; PMID 24049096 (as listed in Open Targets evidence rows) (kranendijk2012progressinunderstanding pages 4-5)

Limitations

• The pivotal 2023 Nature Medicine report of enasidenib treatment in germline IDH2 D2HGA2 is referenced by a 2025 case report but was not retrievable in full text in the current tool session; therefore, details beyond the secondary summary should be validated against the primary 2023 publication when accessible. (roux2025cutaneousmanifestationsin pages 3-3)

Key cited sources (with publication dates/URLs)

• Kranendijk M et al. “Progress in understanding 2-hydroxyglutaric acidurias.” Journal of Inherited Metabolic Disease. 2012-03. https://doi.org/10.1007/s10545-012-9462-5 (kranendijk2012progressinunderstanding pages 3-4)

• Shi Y et al. “Disorders of organic acid metabolism and epilepsy.” Acta Epileptologica. 2024-08. https://doi.org/10.1186/s42494-024-00167-2 (shi2024disordersoforganic pages 6-7)

• Liu Y et al. “Detection and analysis of chiral molecules as disease biomarkers.” Nature Reviews Chemistry. 2023-03. https://doi.org/10.1038/s41570-023-00476-z (liu2023detectionandanalysis pages 1-3)

• Choate KA et al. “IDH Mutations in Glioma: Molecular, Cellular, Diagnostic, and Clinical Implications.” Biology. 2024-10. https://doi.org/10.3390/biology13110885 (choate2024idhmutationsin pages 15-17)

• Wang F et al. “A small molecule inhibitor of mutant IDH2 rescues cardiomyopathy in a D-2-hydroxyglutaric aciduria type II mouse model.” Journal of Inherited Metabolic Disease. 2016-07. https://doi.org/10.1007/s10545-016-9960-y (wang2016asmallmolecule pages 1-2)

• ClinicalTrials.gov: NCT07125066 (ACER-001 in combined D,L-2HGA). Start 2025-07-30. https://clinicaltrials.gov/study/NCT07125066 (NCT07125066 chunk 1)

• ClinicalTrials.gov: NCT04880356 (longitudinal observational ultra-rare registry including L-2HGA). Start 2021-03-01. https://clinicaltrials.gov/study/NCT04880356 (NCT04880356 chunk 1)

References

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  11. (NCT07125066 chunk 1): Jerry Vockley, MD, PhD. An Individual Patient, Open Label Study to Use ACER-001 to Treat Combined D,L-2 Hydroxyglutaric Aciduria (C-2HGA). Jerry Vockley, MD, PhD. 2025. ClinicalTrials.gov Identifier: NCT07125066

  12. (liu2023detectionandanalysis pages 6-8): Yaoran Liu, Zilong Wu, Daniel W. Armstrong, Herman Wolosker, and Yuebing Zheng. Detection and analysis of chiral molecules as disease biomarkers. Nature Reviews Chemistry, 7:355-373, Mar 2023. URL: https://doi.org/10.1038/s41570-023-00476-z, doi:10.1038/s41570-023-00476-z. This article has 200 citations.

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  18. (roux2025cutaneousmanifestationsin pages 3-3): Jennifer Roux, Gabrielle Brody, Brandie Metz, Jingyun Gao, Changrui Xiao, and Richard C. Chang. Cutaneous manifestations in d-2-hydroxyglutaric aciduria type 2 and response to enasidenib therapy. Feb 2025. URL: https://doi.org/10.1016/j.jdcr.2024.10.020, doi:10.1016/j.jdcr.2024.10.020. This article has 3 citations.

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