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3-Hydroxy-3-Methylglutaric Aciduria

Disease Pathophysiology Research Template

2026-02-23
Falcon MONDO:0009520 Model: Edison Scientific Literature 19 citations

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: 3-Hydroxy-3-Methylglutaric Aciduria
  • MONDO ID: (if available)
  • Category: Genetic

Research Objectives

Please provide a comprehensive research report on the pathophysiology of 3-Hydroxy-3-Methylglutaric 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 Research Report — 3‑Hydroxy‑3‑Methylglutaric Aciduria (HMG‑CoA Lyase Deficiency)

Publication window emphasized: 2023–2024 (with essential foundational mechanistic and cohort sources where needed).

  1. Disease definition, identifiers, and core biochemical defect

Disease concept. “3‑Hydroxy‑3‑methylglutaric aciduria/acidemia” in clinical practice corresponds to 3‑hydroxy‑3‑methylglutaryl‑CoA lyase deficiency (HMGCLD/HMGLD), an autosomal recessive inborn error affecting ketogenesis and leucine catabolism. The key feature is inability to generate ketone bodies during catabolic stress, coupled with accumulation of characteristic leucine‑derived metabolites (organic acids and acyl‑CoA intermediates). (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2)

OMIM/MIM. The disorder is reported as MIM/OMIM 246450 in a systematic review and in a large clinical cohort description. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2, alfadhel2022hmgcoalyasedeficiency pages 1-2)

Causal gene/protein. Biallelic pathogenic variants in HMGCL cause deficiency of mitochondrial 3‑hydroxy‑3‑methylglutaryl‑CoA lyase (EC 4.1.3.4). HMGCL catalyzes cleavage of HMG‑CoA to acetyl‑CoA and acetoacetate, “the final step of ketogenesis and leucine degradation.” (devanapalli2023useofsodium pages 1-3, devanapalli2023useofsodium pages 3-5)

Key biochemical signature (clinical definition). Typical biochemical hallmarks include: (i) absent/low ketones during crises (hypoketotic or non‑ketotic hypoglycemia) and (ii) urine organic acids showing elevated 3‑hydroxy‑3‑methylglutaric acid (HMG), 3‑methylglutaconic acid (3MGC), 3‑methylglutaric acid (3MGL), and 3‑hydroxyisovaleric acid (3‑HIVA), often with elevated acylcarnitine C5‑OH (3‑hydroxyisovalerylcarnitine) in plasma/newborn screening. (devanapalli2023useofsodium pages 1-3, devanapalli2023useofsodium pages 3-5)

  1. Core pathophysiology (molecular and cellular mechanisms)

2.1 Primary mechanism: ketogenesis failure → energy failure in brain/heart during catabolic stress

HMGCL is required for hepatic ketone production (acetoacetate and 3‑hydroxybutyrate), which supplies energy to extrahepatic tissues during fasting/illness, particularly brain. Accordingly, acute crises feature hypoglycemia with inadequate ketone availability and metabolic acidosis. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

Clinical trigger context and progression. In the compiled 211‑case systematic review, >95% had at least one metabolic decompensation; onset clustered in infancy with ~42% neonatal onset. Crises commonly include vomiting, lethargy/coma, tachypnea/apnoea, seizures, and hepatomegaly, with laboratory findings of severe hypoglycemia, metabolic acidosis, and hyperammonemia. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

2.2 Primary mechanism: leucine catabolic block → accumulation of organic acids and acyl‑CoA stress

Blockade at HMG‑CoA lyase causes upstream accumulation of leucine‑related metabolites. A 2023 longitudinal cohort emphasized illness‑driven leucine flux, stating “3‑HMG must arise from both fat and leucine oxidation,” and reporting higher leucine turnover and greater urinary excretion of 3MGC and 3‑HIVA during illness than fasting, implying leucine‑derived toxicity is prominent under inflammatory/catabolic stress. (thompson2023treatmentofhmgcoa pages 5-6)

2.3 Secondary mechanism: acyl‑CoA / free CoA disequilibrium and mitochondrial dysfunction

Acyl‑CoA disruption as a mechanistic driver. A foundational liver‑specific Hmgcl knockout mouse model demonstrated that chronic deficiency and acute crises yield “distinct abnormal liver acyl‑CoA patterns,” and that leucine metabolite loading (2‑ketoisocaproate, KIC) increases leucine‑related acyl‑CoAs while reducing acetyl‑CoA, with hepatocyte mitochondrial swelling after KIC—direct evidence of mitochondrial injury in crisis states. (gauthier2013aliverspecificdefect pages 1-2)

Hyperammonemia mechanism (acetyl‑CoA dependence of urea cycle activation). In the same mouse model, KIC‑induced hyperammonemia improved with carglumate, “which substitutes for the product of an acetyl‑CoA‑dependent reaction essential for urea cycle function,” supporting an acyl‑CoA/acetyl‑CoA–linked mechanism for hyperammonemia in HMGCLD. (gauthier2013aliverspecificdefect pages 1-2)

Clinical inference: CoA trapping and acetyl‑CoA depletion can simultaneously compromise ketogenesis, gluconeogenesis, and urea cycling, producing the characteristic triad of hypoketotic hypoglycemia + acidosis + hyperammonemia in severe crises. (gauthier2013aliverspecificdefect pages 1-2, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

2.4 2024 mechanistic advance: non‑enzymatic mitochondrial protein acylation (3MGCylation)

A 2024 mechanistic study proposed a specific chemical toxicity mechanism via trans‑3‑methylglutaconyl‑CoA (trans‑3MGC‑CoA). The study describes formation of a reactive cis‑3MGC anhydride; importantly: “The anhydride is chemically reactive… it reacts with lysine side chain amino groups to acylate nearby proteins.” (jennings2024factorsaffectingnonenzymatic pages 11-12)

In vivo relevance is supported by liver‑specific HMGCL knockout mice: “Relative protein 3MGCylation levels were much higher in liver‑specific HMGCL KO mouse liver mitochondrial samples compared with the corresponding WT mouse samples,” and “KIC loading led to increased protein 3MGCylation levels,” linking leucine flux to mitochondrial protein lysine acylation. (jennings2024factorsaffectingnonenzymatic pages 11-12)

Interpretation/expert analysis. This frames HMGCLD not only as “energy deficiency” but also as a disorder of reactive metabolite chemistry in the mitochondrial matrix, potentially altering enzyme networks by covalent modification (a hypothesis the authors identify as requiring future protein‑target identification and functional studies). (jennings2024factorsaffectingnonenzymatic pages 11-12)

2.5 2024 experimental neurotoxicity: HMG disrupts redox, bioenergetics, and mitochondrial dynamics in neonatal brain

A 2024 neonatal rat brain model directly tested toxicity of the major accumulating metabolite HMG, finding oxidative stress and bioenergetic defects, plus altered mitochondrial fission. Key statistically supported findings include:

• Citric acid cycle / respiratory chain: cortical SDH reduced (t(6)=4.899; p<0.01); cortical complexes II–III (t(6)=6.877; p<0.05) and IV (t(6)=3.329; p<0.05) reduced; striatal citrate synthase reduced (t(6)=6.460; p<0.05) and SDH reduced (t(6)=2.151; p<0.01); striatal complex IV reduced (t(6)=7.935; p<0.01). (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

• Mitochondrial dynamics: DRP1 content markedly increased (t(10)=16.88; p<0.001), consistent with increased mitochondrial fission. (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

These results connect a patient biomarker (HMG accumulation) to plausible cellular injury pathways (ETC impairment, ROS‑linked redox imbalance, and mitochondrial network fragmentation), aligning with clinical neurodevelopmental vulnerability in early life. (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

Figures providing experimental data. The study’s results are visually summarized in the main figures: antioxidant defenses (Figures 1–2), TCA enzymes and respiratory chain activities (Figures 3–4), and mitochondrial dynamics proteins (Figure 5). (silveira20243hydroxy3methylglutaricaciddisrupts media cdb163bd, silveira20243hydroxy3methylglutaricaciddisrupts media f967e15a, silveira20243hydroxy3methylglutaricaciddisrupts media cd280ab9)

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

3.1 Genes/proteins

Causal gene: HMGCL (mitochondrial HMG‑CoA lyase). (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2)

Mechanistically implicated proteins/processes: • Mitochondrial respiratory chain complexes (II–III, IV) and TCA enzymes (SDH, CS) affected by HMG exposure in brain tissue. (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • DRP1 (DNM1L protein; mitochondrial fission regulator) increased with HMG exposure. (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • AUH (3MGC‑CoA hydratase) implicated in diverting trans‑3MGC‑CoA away from reactive anhydride formation; the 2024 study shows AUH reduces (attenuates) 3MGCylation signal. (jennings2024factorsaffectingnonenzymatic pages 11-12)

Genotype–phenotype and population genetics. In the 62‑patient Saudi cohort, a founder HMGCL variant c.122G>A (p.Arg41Gln) accounted for 77.41% of affected individuals, illustrating strong population structure and potential genotype clustering of clinical risk. (alfadhel2022hmgcoalyasedeficiency pages 1-2)

3.2 Chemical entities (metabolites, drugs, small molecules)

Key metabolites/biomarkers: • 3‑hydroxy‑3‑methylglutaric acid (HMG) (major accumulating metabolite in patients; modeled as neurotoxin in 2024 rat study). (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • 3‑methylglutaconic acid (3MGC), 3‑methylglutaric acid (3MGL), 3‑hydroxyisovaleric acid (3‑HIVA). (devanapalli2023useofsodium pages 3-5, silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2) • HMG‑CoA, acetyl‑CoA, acetoacetate (reaction substrates/products). (devanapalli2023useofsodium pages 1-3) • trans‑3MGC‑CoA and reactive cis‑3MGC anhydride; protein 3MGCylation adducts. (jennings2024factorsaffectingnonenzymatic pages 11-12) • 2‑ketoisocaproate (KIC) as leucine‑catabolic stressor in mouse/mitochondrial acylation models. (gauthier2013aliverspecificdefect pages 1-2, jennings2024factorsaffectingnonenzymatic pages 11-12)

Therapeutically relevant small molecules: • Sodium D,L‑3‑hydroxybutyrate (exogenous ketone salt) used as adjunct therapy to bypass impaired ketogenesis. (devanapalli2023useofsodium pages 1-3, devanapalli2023useofsodium pages 7-10) • L‑carnitine used in long‑term management; commonly prescribed in reviewed cohorts. (devanapalli2023useofsodium pages 7-10) • Carglumate used experimentally to rescue hyperammonemia via acetyl‑CoA–dependent urea cycle activation proxy (mouse model). (gauthier2013aliverspecificdefect pages 1-2)

3.3 Cell types and tissues (CL/UBERON-style)

Dominant vulnerable organs: • Liver (ketogenesis, acyl‑CoA perturbation, hyperammonemia mechanism; hepatocyte mitochondrial swelling in crisis model). (gauthier2013aliverspecificdefect pages 1-2) • Brain (white matter/basal ganglia abnormalities clinically; cortex and striatum show redox/ETC and mitochondrial fission changes in experimental HMG exposure). (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Heart (clinically reported cardiomyopathy in systematic review; mechanistic rationale: reliance on ketone bodies in fasting/stress). (devanapalli2023useofsodium pages 7-10, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

At the cellular compartment level, the 2024 3MGCylation mechanism is explicitly mitochondrial-matrix–centric (“protein-rich environment of the mitochondrial matrix”). (jennings2024factorsaffectingnonenzymatic pages 11-12)

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

Disrupted biological processes (examples of GO-term-style concepts): • Ketone body metabolic process / ketogenesis (failure of acetoacetate and 3‑hydroxybutyrate production). (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2) • Branched‑chain amino acid catabolic process (leucine degradation). (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2) • Mitochondrial electron transport and oxidative phosphorylation (complex II–III and IV activity reductions in cortex; complex IV reduction in striatum). (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Tricarboxylic acid cycle (citrate synthase and succinate dehydrogenase decreases in striatum; SDH decrease in cortex). (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Redox homeostasis / oxidative stress response (disturbed antioxidant defenses after HMG exposure). (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Protein lysine acylation (non‑enzymatic 3MGCylation) and reactive metabolite chemistry in mitochondria. (jennings2024factorsaffectingnonenzymatic pages 11-12) • Mitochondrial fission (increased DRP1). (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

Key cellular components (examples of GO CC–style concepts): • Mitochondrial matrix (site of 3MGC anhydride formation and protein acylation). (jennings2024factorsaffectingnonenzymatic pages 11-12) • Mitochondrial respiratory chain complexes / inner mitochondrial membrane (functional outputs altered in HMG exposure model). (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

  1. Disease progression model (trigger → molecular events → cellular dysfunction → clinical manifestations)

Stage 0 (baseline/intercritical). Many patients may be clinically well between episodes; however, biochemical perturbations (abnormal metabolite excretion, acylcarnitines) persist and may contribute to chronic neurologic sequelae in a subset. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4, alfadhel2022hmgcoalyasedeficiency pages 1-2)

Stage 1 (trigger). Catabolic stress (fasting, intercurrent illness) increases reliance on ketogenesis and leucine/fat oxidation; in HMGCLD, ketone production fails and leucine‑derived intermediates accumulate. (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

Stage 2 (metabolic crisis). Combined effects manifest as hypoketotic/non‑ketotic hypoglycemia + metabolic acidosis; hyperammonemia can become severe (reports >1000–2000 µmol/L). (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

Stage 3 (cellular injury). Mechanistically supported injury pathways include acyl‑CoA/acetyl‑CoA imbalance (affecting gluconeogenesis and urea cycle activation), mitochondrial dysfunction and swelling, oxidative stress, impaired respiratory chain function, and mitochondrial network fragmentation; additionally, reactive metabolite–driven protein acylation (3MGCylation) may damage mitochondrial proteostasis/function. (gauthier2013aliverspecificdefect pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9, jennings2024factorsaffectingnonenzymatic pages 11-12)

Stage 4 (clinical outcomes). Acute encephalopathy/seizures/coma may occur, with long‑term sequelae including developmental delay, white matter abnormalities, epilepsy, and in some cases cardiomyopathy or liver failure. (devanapalli2023useofsodium pages 1-3, alfadhel2022hmgcoalyasedeficiency pages 1-2, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

  1. Phenotypic manifestations and quantitative epidemiology/statistics

6.1 Systematic review (211 reported cases; authoritative synthesis)

A 2020 Orphanet Journal of Rare Diseases systematic review compiled 211 published patients: • Acute metabolic decompensation: 95.3% (163/171 with available data) had ≥1 crisis. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4) • Neonatal onset: 42.4% (70/165 with onset data). (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4) • Mortality: 16.1% (34/211). (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4) • Neurologic outcome: 62.6% normal development among those with available outcome data. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2) • Severe hyperammonemia: reports >1000 µmol/L and one >2000 µmol/L requiring dialysis. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

6.2 Large contemporary regional cohort (Saudi Arabia; n=62)

A 2022 62‑patient Saudi cohort (molecularly confirmed) provides phenotype frequencies: • Hypoglycemia at diagnosis: 61.29% (38/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2) • Metabolic acidosis: 79.03% (49/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2) • Neonatal onset: 43.54% (27/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2) • Seizures: 27.41% (17/62); learning disability: 24.14% (15/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2) • MRI white matter hyperintensities: 25.80% (16/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2) • Genetics: founder variant c.122G>A (p.Arg41Gln) in 77.41% (48/62). (alfadhel2022hmgcoalyasedeficiency pages 1-2)

6.3 Selected recent clinical biomarker statistics (2023 case report)

In a 2023 sibling case report, representative screening/diagnostic biomarker magnitudes were provided: • Newborn screen C5‑OH 2.8 µmol/L (reference <1). (devanapalli2023useofsodium pages 3-5) • Plasma C5‑OH 2.59 µmol/L (reference <0.15). (devanapalli2023useofsodium pages 3-5) • Example metabolic crisis acid–base values: pH 7.2, HCO3 9, base excess −17. (devanapalli2023useofsodium pages 3-5)

  1. Recent developments and latest research (prioritized 2023–2024)

7.1 2023–2024 management evolution: exogenous ketone therapy and refined dietary emergency plans

Exogenous ketone (sodium D,L‑3‑hydroxybutyrate; S‑DL‑3OHB). A 2023 report of two siblings concluded: “S‑DL‑3OHB therapy is a well‑tolerated and effective therapeutic option for this disorder,” explicitly motivated by the loss of ketone supply to brain and heart during starvation. (devanapalli2023useofsodium pages 1-3)

Real‑world use in a 2023 Australian longitudinal cohort (Nutrients; 10 cases): • “Four patients have used high‑dose S‑DL‑3OHB (900 mg/kg/day) as part of their acute management plan,” and acute care emphasized carbohydrate rescue (maltodextrin-based plans) and avoidance of catabolism. (thompson2023treatmentofhmgcoa pages 4-5) • The cohort also reports long intercritical stability in some adults (no acute presentation for 11–22 years), consistent with efficacy of anticipatory management once patients reach adulthood and/or have stable care routines. (thompson2023treatmentofhmgcoa pages 4-5)

Dietary management and emergency protocols. The 2023 cohort reported emergency carbohydrate plans “based on 120% estimated energy requirement” and highlighted that illness (more than fasting alone) often precipitates severe/protracted episodes, supporting the modern emphasis on early sick‑day carbohydrate protocols. (thompson2023treatmentofhmgcoa pages 5-6)

7.2 2024 mechanistic shift: reactive metabolite chemistry in mitochondria (3MGCylation) as a candidate disease driver

The 2024 Metabolites study provides a new mechanistic concept: trans‑3MGC‑CoA instability creates a “chemical sink” that both preserves free CoA and yields toxic outputs (3MGC acid and protein 3MGCylation) in a mitochondrial matrix context. (jennings2024factorsaffectingnonenzymatic pages 11-12)

Expert interpretation. If validated in human tissues, 3MGCylation could help explain “non‑linear” phenotype severity and tissue specificity (e.g., liver vulnerability during leucine load; possible links to cardiomyopathy), and it highlights potential new therapeutic directions (e.g., reducing trans‑3MGC‑CoA formation, enhancing detoxifying hydration steps, or promoting deacylation), but the authors emphasize open questions on targeted proteins and functional consequences. (jennings2024factorsaffectingnonenzymatic pages 11-12)

7.3 2024 experimental neurobiology: identifying concrete mitochondrial targets of HMG

The 2024 Biomedicines study adds quantitative support that HMG itself can disrupt key mitochondrial nodes (SDH; complexes II–III and IV; DRP1-driven fission), aligning with the clinical predominance of neurologic manifestations early in life. (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9, silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2)

  1. Current applications and real-world implementations

8.1 Newborn screening and diagnostic workflows

Newborn screening. Tandem mass spectrometry (MS/MS) screening using elevated C5‑OH is described as a diagnostic route in the 62‑patient cohort, with confirmation by urine organic acids and molecular testing. (alfadhel2022hmgcoalyasedeficiency pages 1-2)

Confirmatory testing. Diagnosis is established by characteristic urinary organic acids plus abnormal acylcarnitines and confirmed by enzyme assays in patient cells and/or HMGCL mutation analysis. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2)

8.2 Acute crisis management (implemented clinically)

Principles reported in 2023 longitudinal and case studies include: • Rapid provision of glucose (IV dextrose and/or frequent oral carbohydrate such as maltodextrin) to suppress catabolism and prevent hypoglycemia. (thompson2023treatmentofhmgcoa pages 5-6, thompson2023treatmentofhmgcoa pages 4-5) • Avoidance of fasting, protein/leucine restriction, and frequently fat restriction in some protocols. (devanapalli2023useofsodium pages 7-10, thompson2023treatmentofhmgcoa pages 6-8) • Adjunct exogenous ketone therapy (S‑DL‑3OHB) during acute decompensation and sometimes long-term adjunct use. (thompson2023treatmentofhmgcoa pages 4-5, devanapalli2023useofsodium pages 1-3)

8.3 Long-term management and monitoring

Long-term management strategies widely used in contemporary practice (per 2023 review/case report) include: protein/leucine restriction, avoidance of fasting, carnitine supplementation (used in 78% in reviewed cases), and individualized use of exogenous ketone therapy; monitoring includes acylcarnitines/urine organic acids and clinical neurodevelopment/cardiac surveillance. (devanapalli2023useofsodium pages 7-10)

  1. Evidence items (mechanistic claims with direct quotes, URLs, and publication dates)

Key evidence quote 1 (3MGCylation mechanism; publication date: 2024‑07; URL: https://doi.org/10.3390/metabo14080421): “The anhydride is chemically reactive… it reacts with lysine side chain amino groups to acylate nearby proteins.” (jennings2024factorsaffectingnonenzymatic pages 11-12)

Key evidence quote 2 (HMGCLD definition/energy rationale; publication date: 2020‑02; URL: https://doi.org/10.1186/s13023-020-1319-7): Ketone bodies are “an important source of energy for extrahepatic organs, in particular of the brain,” and crises feature “hypoglycemia and metabolic acidosis.” (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2)

Key evidence quote 3 (acyl‑CoA mechanism for hyperammonemia; publication date: 2013‑07‑05; URL: https://doi.org/10.1371/journal.pone.0060581): “KIC‑induced hyperammonemia improved following administration of carglumate… demonstrating an acyl‑CoA‑related mechanism for this complication.” (gauthier2013aliverspecificdefect pages 1-2)

  1. Structured knowledge-base annotation (term strings; IDs not always provided in sources)

10.1 Pathophysiology description (knowledge-base ready)

HMGCLD is a mitochondrial ketogenesis/leucine-catabolism defect caused by biallelic HMGCL variants, resulting in failure to produce ketone bodies (acetoacetate, D‑3‑hydroxybutyrate) during catabolic stress and accumulation of leucine-derived organic acids and acyl‑CoA intermediates (HMG, 3MGC, 3MGL, 3‑HIVA; trans‑3MGC‑CoA). Acute illness/fasting triggers energy failure and intoxication, producing hypoketotic hypoglycemia, metabolic acidosis, and hyperammonemia; mechanistically, hepatic acyl‑CoA disturbances and acetyl‑CoA depletion can impair gluconeogenesis and urea cycle activation (carglumate responsiveness). Accumulating metabolites can also directly cause mitochondrial redox and respiratory chain dysfunction and perturb mitochondrial dynamics in the developing brain (SDH and complex II–III/IV inhibition; increased DRP1), contributing to seizures, developmental delay, and white matter disease. A 2024 mechanistic advance proposes reactive metabolite chemistry (cis‑3MGC anhydride) leading to mitochondrial protein lysine acylation (3MGCylation) as a potentially toxic process linking leucine flux to mitochondrial dysfunction. (devanapalli2023useofsodium pages 1-3, gauthier2013aliverspecificdefect pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9, jennings2024factorsaffectingnonenzymatic pages 11-12)

10.2 Gene/protein annotations

• HMGCL — 3‑hydroxy‑3‑methylglutaryl‑CoA lyase; mitochondrial enzyme; catalyzes HMG‑CoA → acetyl‑CoA + acetoacetate (ketogenesis and leucine degradation). (devanapalli2023useofsodium pages 1-3)

10.3 Candidate disrupted GO Biological Processes (term strings)

• Ketone body metabolic process / ketogenesis (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2) • Leucine catabolic process / branched-chain amino acid catabolism (devanapalli2023useofsodium pages 1-3, grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2) • Tricarboxylic acid cycle (succinate dehydrogenase; citrate synthase) (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Mitochondrial electron transport / oxidative phosphorylation (complex II–III, IV) (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Cellular redox homeostasis / oxidative stress response (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Protein lysine acylation (3MGCylation; non-enzymatic) (jennings2024factorsaffectingnonenzymatic pages 11-12) • Mitochondrial fission (DRP1 increase) (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

10.4 Cellular components (term strings)

• Mitochondrial matrix (protein-rich environment for 3MGC anhydride reactions) (jennings2024factorsaffectingnonenzymatic pages 11-12) • Mitochondrial inner membrane / respiratory chain complexes (functional impairment) (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

10.5 Phenotype associations (HP-style term strings) with evidence

• Hypoketotic/non‑ketotic hypoglycemia (devanapalli2023useofsodium pages 1-3, alfadhel2022hmgcoalyasedeficiency pages 1-2) • Metabolic acidosis (alfadhel2022hmgcoalyasedeficiency pages 1-2, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4) • Hyperammonemia (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4, gauthier2013aliverspecificdefect pages 1-2) • Seizures/status epilepticus (alfadhel2022hmgcoalyasedeficiency pages 1-2, devanapalli2023useofsodium pages 3-5) • Developmental delay / learning disability (alfadhel2022hmgcoalyasedeficiency pages 1-2) • White matter abnormalities / periventricular hyperintensities (alfadhel2022hmgcoalyasedeficiency pages 1-2) • Hepatic dysfunction / transaminase elevation; occasional liver failure (thompson2023treatmentofhmgcoa pages 5-6, grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4) • Cardiomyopathy (rare but reported; fatal cases in systematic review) (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4)

10.6 Cell type involvement (CL-style term strings)

• Hepatocytes (liver-specific KO mechanistic model; ketogenesis, acyl‑CoA patterns) (gauthier2013aliverspecificdefect pages 1-2) • Neurons and glia in cortex/striatum (modeled by region-specific brain biochemical effects; neurodevelopment impairment) (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9)

10.7 Anatomical locations (UBERON-style term strings)

• Liver (ketogenesis; acyl‑CoA disturbances; hyperammonemia mechanism) (gauthier2013aliverspecificdefect pages 1-2) • Brain: cerebral cortex; striatum; white matter; basal ganglia (clinical MRI and experimental model focus) (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9) • Heart (clinical cardiomyopathy reports; ketone reliance rationale) (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4, devanapalli2023useofsodium pages 1-3)

10.8 Chemical entities (CHEBI-style term strings)

• 3‑hydroxy‑3‑methylglutaric acid (HMG) (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2) • 3‑methylglutaconic acid (3MGC) (devanapalli2023useofsodium pages 3-5) • 3‑methylglutaric acid (3MGL) (devanapalli2023useofsodium pages 3-5) • 3‑hydroxyisovaleric acid (3‑HIVA) (devanapalli2023useofsodium pages 3-5) • 3‑hydroxyisovalerylcarnitine (C5‑OH) (devanapalli2023useofsodium pages 3-5) • HMG‑CoA; acetyl‑CoA; acetoacetate (devanapalli2023useofsodium pages 1-3) • trans‑3MGC‑CoA; cis‑3MGC anhydride; 3MGCylated proteins (jennings2024factorsaffectingnonenzymatic pages 11-12) • D,L‑3‑hydroxybutyrate (sodium salt; S‑DL‑3OHB) (devanapalli2023useofsodium pages 1-3) • 2‑ketoisocaproate (KIC) (gauthier2013aliverspecificdefect pages 1-2) • Carglumate (N‑carbamyl‑L‑glutamate) (gauthier2013aliverspecificdefect pages 1-2) • L‑carnitine (devanapalli2023useofsodium pages 7-10)

  1. Limitations and evidence gaps (important for knowledge-base curation)

• PMIDs: Several recent open-access MDPI/OAE articles and some excerpts did not contain PMIDs in the retrieved text segments; thus, citations here are DOI/URL-based for those sources. (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2, jennings2024factorsaffectingnonenzymatic pages 11-12, devanapalli2023useofsodium pages 1-3) • MONDO ID was not recoverable from the retrieved sources in this run; OMIM/MIM 246450 is explicitly supported. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2, alfadhel2022hmgcoalyasedeficiency pages 1-2) • Many mechanistic hypotheses (e.g., 3MGCylation functional consequences, best biomarkers to titrate exogenous ketone therapy) are explicitly framed by authors as requiring further study, highlighting an active research frontier rather than settled mechanisms. (jennings2024factorsaffectingnonenzymatic pages 11-12, devanapalli2023useofsodium pages 7-10)

References

  1. (devanapalli2023useofsodium pages 1-3): Beena Devanapalli, Adviye Ayper Tolun, Won-Tae Kim, Tiffany Wotton, Susan Thompson, and Shanti Balasubramaniam. Use of sodium d, l-3-hydroxybutyrate as adjunct therapy in two siblings with hmg-coa lyase deficiency. Journal of Translational Genetics and Genomics, 7:186-95, Sep 2023. URL: https://doi.org/10.20517/jtgg.2023.12, doi:10.20517/jtgg.2023.12. This article has 0 citations.

  2. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 1-2): Sarah C. Grünert and Jörn Oliver Sass. 3-hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: one disease - many faces. Orphanet Journal of Rare Diseases, Feb 2020. URL: https://doi.org/10.1186/s13023-020-1319-7, doi:10.1186/s13023-020-1319-7. This article has 41 citations and is from a peer-reviewed journal.

  3. (alfadhel2022hmgcoalyasedeficiency pages 1-2): Majid Alfadhel, Basma Abadel, Hind Almaghthawi, Muhammad Umair, Zuhair Rahbeeni, Eissa Faqeih, Mohammed Almannai, Ali Alasmari, Mohammed Saleh, Wafaa Eyaid, Ahmed Alfares, and Fuad Al Mutairi. Hmg-coa lyase deficiency: a retrospective study of 62 saudi patients. Frontiers in Genetics, May 2022. URL: https://doi.org/10.3389/fgene.2022.880464, doi:10.3389/fgene.2022.880464. This article has 19 citations and is from a peer-reviewed journal.

  4. (devanapalli2023useofsodium pages 3-5): Beena Devanapalli, Adviye Ayper Tolun, Won-Tae Kim, Tiffany Wotton, Susan Thompson, and Shanti Balasubramaniam. Use of sodium d, l-3-hydroxybutyrate as adjunct therapy in two siblings with hmg-coa lyase deficiency. Journal of Translational Genetics and Genomics, 7:186-95, Sep 2023. URL: https://doi.org/10.20517/jtgg.2023.12, doi:10.20517/jtgg.2023.12. This article has 0 citations.

  5. (grunert20203hydroxy3methylglutarylcoenzymealyase pages 2-4): Sarah C. Grünert and Jörn Oliver Sass. 3-hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: one disease - many faces. Orphanet Journal of Rare Diseases, Feb 2020. URL: https://doi.org/10.1186/s13023-020-1319-7, doi:10.1186/s13023-020-1319-7. This article has 41 citations and is from a peer-reviewed journal.

  6. (thompson2023treatmentofhmgcoa pages 5-6): Susan Thompson, Ashley Hertzog, Arthavan Selvanathan, Kiera Batten, Katherine Lewis, Janelle Nisbet, Ashleigh Mitchell, Troy Dalkeith, Kate Billmore, Francesca Moore, Adviye Ayper Tolun, Beena Devanapalli, Drago Bratkovic, Cathie Hilditch, Yusof Rahman, Michel Tchan, and Kaustuv Bhattacharya. Treatment of hmg-coa lyase deficiency—longitudinal data on clinical and nutritional management of 10 australian cases. Nutrients, 15:531, Jan 2023. URL: https://doi.org/10.3390/nu15030531, doi:10.3390/nu15030531. This article has 17 citations.

  7. (gauthier2013aliverspecificdefect pages 1-2): Nicolas Gauthier, Jiang Wei Wu, Shu Pei Wang, Pierre Allard, Orval A. Mamer, Lawrence Sweetman, Ann B. Moser, Lisa Kratz, Fernando Alvarez, Yves Robitaille, François Lépine, and Grant A. Mitchell. A liver-specific defect of acyl-coa degradation produces hyperammonemia, hypoglycemia and a distinct hepatic acyl-coa pattern. PLoS ONE, 8:e60581, Jul 2013. URL: https://doi.org/10.1371/journal.pone.0060581, doi:10.1371/journal.pone.0060581. This article has 25 citations and is from a peer-reviewed journal.

  8. (jennings2024factorsaffectingnonenzymatic pages 11-12): Elizabeth A. Jennings, Megan M. Macdonald, Irina Romenskaia, Hao Yang, Grant A. Mitchell, and Robert O. Ryan. Factors affecting non-enzymatic protein acylation by trans-3-methylglutaconyl coenzyme a. Metabolites, 14:421, Jul 2024. URL: https://doi.org/10.3390/metabo14080421, doi:10.3390/metabo14080421. This article has 2 citations.

  9. (silveira20243hydroxy3methylglutaricaciddisrupts pages 5-9): Josyane de Andrade Silveira, Manuela Bianchin Marcuzzo, Jaqueline Santana da Rosa, Nathalia Simon Kist, Chrístofer Ian Hernandez Hoffmann, Andrey Soares Carvalho, Rafael Teixeira Ribeiro, André Quincozes-Santos, Carlos Alexandre Netto, Moacir Wajner, and Guilhian Leipnitz. 3-hydroxy-3-methylglutaric acid disrupts brain bioenergetics, redox homeostasis, and mitochondrial dynamics and affects neurodevelopment in neonatal wistar rats. Biomedicines, 12:1563, Jul 2024. URL: https://doi.org/10.3390/biomedicines12071563, doi:10.3390/biomedicines12071563. This article has 4 citations.

  10. (silveira20243hydroxy3methylglutaricaciddisrupts pages 1-2): Josyane de Andrade Silveira, Manuela Bianchin Marcuzzo, Jaqueline Santana da Rosa, Nathalia Simon Kist, Chrístofer Ian Hernandez Hoffmann, Andrey Soares Carvalho, Rafael Teixeira Ribeiro, André Quincozes-Santos, Carlos Alexandre Netto, Moacir Wajner, and Guilhian Leipnitz. 3-hydroxy-3-methylglutaric acid disrupts brain bioenergetics, redox homeostasis, and mitochondrial dynamics and affects neurodevelopment in neonatal wistar rats. Biomedicines, 12:1563, Jul 2024. URL: https://doi.org/10.3390/biomedicines12071563, doi:10.3390/biomedicines12071563. This article has 4 citations.

  11. (silveira20243hydroxy3methylglutaricaciddisrupts media cdb163bd): Josyane de Andrade Silveira, Manuela Bianchin Marcuzzo, Jaqueline Santana da Rosa, Nathalia Simon Kist, Chrístofer Ian Hernandez Hoffmann, Andrey Soares Carvalho, Rafael Teixeira Ribeiro, André Quincozes-Santos, Carlos Alexandre Netto, Moacir Wajner, and Guilhian Leipnitz. 3-hydroxy-3-methylglutaric acid disrupts brain bioenergetics, redox homeostasis, and mitochondrial dynamics and affects neurodevelopment in neonatal wistar rats. Biomedicines, 12:1563, Jul 2024. URL: https://doi.org/10.3390/biomedicines12071563, doi:10.3390/biomedicines12071563. This article has 4 citations.

  12. (silveira20243hydroxy3methylglutaricaciddisrupts media f967e15a): Josyane de Andrade Silveira, Manuela Bianchin Marcuzzo, Jaqueline Santana da Rosa, Nathalia Simon Kist, Chrístofer Ian Hernandez Hoffmann, Andrey Soares Carvalho, Rafael Teixeira Ribeiro, André Quincozes-Santos, Carlos Alexandre Netto, Moacir Wajner, and Guilhian Leipnitz. 3-hydroxy-3-methylglutaric acid disrupts brain bioenergetics, redox homeostasis, and mitochondrial dynamics and affects neurodevelopment in neonatal wistar rats. Biomedicines, 12:1563, Jul 2024. URL: https://doi.org/10.3390/biomedicines12071563, doi:10.3390/biomedicines12071563. This article has 4 citations.

  13. (silveira20243hydroxy3methylglutaricaciddisrupts media cd280ab9): Josyane de Andrade Silveira, Manuela Bianchin Marcuzzo, Jaqueline Santana da Rosa, Nathalia Simon Kist, Chrístofer Ian Hernandez Hoffmann, Andrey Soares Carvalho, Rafael Teixeira Ribeiro, André Quincozes-Santos, Carlos Alexandre Netto, Moacir Wajner, and Guilhian Leipnitz. 3-hydroxy-3-methylglutaric acid disrupts brain bioenergetics, redox homeostasis, and mitochondrial dynamics and affects neurodevelopment in neonatal wistar rats. Biomedicines, 12:1563, Jul 2024. URL: https://doi.org/10.3390/biomedicines12071563, doi:10.3390/biomedicines12071563. This article has 4 citations.

  14. (devanapalli2023useofsodium pages 7-10): Beena Devanapalli, Adviye Ayper Tolun, Won-Tae Kim, Tiffany Wotton, Susan Thompson, and Shanti Balasubramaniam. Use of sodium d, l-3-hydroxybutyrate as adjunct therapy in two siblings with hmg-coa lyase deficiency. Journal of Translational Genetics and Genomics, 7:186-95, Sep 2023. URL: https://doi.org/10.20517/jtgg.2023.12, doi:10.20517/jtgg.2023.12. This article has 0 citations.

  15. (thompson2023treatmentofhmgcoa pages 4-5): Susan Thompson, Ashley Hertzog, Arthavan Selvanathan, Kiera Batten, Katherine Lewis, Janelle Nisbet, Ashleigh Mitchell, Troy Dalkeith, Kate Billmore, Francesca Moore, Adviye Ayper Tolun, Beena Devanapalli, Drago Bratkovic, Cathie Hilditch, Yusof Rahman, Michel Tchan, and Kaustuv Bhattacharya. Treatment of hmg-coa lyase deficiency—longitudinal data on clinical and nutritional management of 10 australian cases. Nutrients, 15:531, Jan 2023. URL: https://doi.org/10.3390/nu15030531, doi:10.3390/nu15030531. This article has 17 citations.

  16. (thompson2023treatmentofhmgcoa pages 6-8): Susan Thompson, Ashley Hertzog, Arthavan Selvanathan, Kiera Batten, Katherine Lewis, Janelle Nisbet, Ashleigh Mitchell, Troy Dalkeith, Kate Billmore, Francesca Moore, Adviye Ayper Tolun, Beena Devanapalli, Drago Bratkovic, Cathie Hilditch, Yusof Rahman, Michel Tchan, and Kaustuv Bhattacharya. Treatment of hmg-coa lyase deficiency—longitudinal data on clinical and nutritional management of 10 australian cases. Nutrients, 15:531, Jan 2023. URL: https://doi.org/10.3390/nu15030531, doi:10.3390/nu15030531. This article has 17 citations.