3-Hydroxy-3-Methylglutaric Aciduria

Mendelian MONDO:0009520 Pathograph 36 Organic Acidemia Inborn Error of Metabolism

3-Hydroxy-3-methylglutaric aciduria (HMGCLD) is an autosomal recessive inborn error of metabolism caused by biallelic pathogenic variants in HMGCL, encoding mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase. This enzyme catalyzes the final step of both ketogenesis and leucine degradation, cleaving HMG-CoA to acetyl-CoA and acetoacetate. Deficiency results in failure to produce ketone bodies during catabolic stress and accumulation of leucine-derived toxic organic acids. Acute metabolic crises feature hypoketotic hypoglycemia, metabolic acidosis, and hyperammonemia, with neurological sequelae including seizures, developmental delay, and white matter abnormalities. More than 95% of reported patients experience at least one metabolic decompensation episode, with approximately 42% having neonatal onset. Mortality is reported at approximately 16%, while over 60% of survivors achieve normal development with appropriate management.

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⚙

Pathophysiology

HMGCL molecular function deficiency

Biallelic pathogenic variants in HMGCL reduce mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase catalytic activity.

hepatocyte link

HMGCL link

mitochondrion link

Downstream

Ketogenesis failure and energy crisis Loss of HMGCL function blocks hepatic ketone body generation during catabolic states.

Leucine catabolic block and organic acid accumulation Loss of HMGCL function also blocks leucine degradation, causing upstream toxic organic acid accumulation.

Show evidence (1 reference)

PMID:32059735 SUPPORT Human Clinical

"3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL."

Supports HMGCL molecular deficiency as the initiating genetic and enzymatic defect.

Ketogenesis failure and energy crisis

Loss of HMGCL-mediated HMG-CoA cleavage abolishes ketogenesis, depriving brain and heart of essential energy substrates during fasting and catabolic stress. This produces hypoketotic hypoglycemia and metabolic acidosis during acute crises.

ketone body metabolic process link ↓ DECREASED fatty acid beta-oxidation link

liver link

Downstream

Ketone bodies HMGCL deficiency blocks ketone body synthesis, producing absent or inappropriately low ketones during fasting and illness.

Hypoglycemia Failure to generate ketone bodies during fasting leaves patients dependent on circulating glucose, causing hypoketotic hypoglycemia.

Metabolic acidosis Acute decompensation from ketogenesis failure and organic acid accumulation produces metabolic acidosis.

Lethargy Acute energy crisis causes reduced arousal and encephalopathic presentation.

Vomiting Vomiting occurs during acute metabolic decompensation episodes.

Cardiomyopathy Cardiac vulnerability may reflect loss of ketone-derived energy substrate during stress.

Acute liver failure Severe metabolic decompensation can present atypically with fulminant liver failure.

Hepatomegaly Hepatomegaly is reported during acute metabolic crises and hepatic metabolic stress.

Show evidence (2 references)

PMID:32059735 SUPPORT Human Clinical

"More than 95% of patients presented with acute metabolic decompensation. Most patients manifested within the first year of life, 42.4% already neonatally."

Systematic review of 211 patients demonstrates near-universal acute metabolic crises from ketogenesis failure.

PMID:32685354 SUPPORT Human Clinical

"The mitochondrial enzyme is responsible for catalyzing the cleavage of HMG‐CoA to acetyl‐CoA and acetoacetic acid. This conversion is a common last step in leucine catabolism and ketogenesis from fatty acids."

Human biomarker study background places the HMGCL-catalyzed cleavage step at the shared endpoint of ketogenesis.

Leucine catabolic block and organic acid accumulation

HMGCL is also required for leucine degradation. Blockade causes upstream accumulation of leucine-derived metabolites including 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid. Illness-driven leucine flux increases toxic metabolite excretion, implying leucine-derived toxicity is particularly prominent under inflammatory and catabolic stress.

hepatocyte link

leucine catabolic process link ↓ DECREASED branched-chain amino acid catabolic process link

mitochondrial matrix link

Downstream

Acyl-CoA disequilibrium and secondary hyperammonemia Blocked leucine degradation increases leucine-related acyl-CoAs and disrupts hepatic acyl-CoA balance.

HMG-mediated neurotoxicity via mitochondrial dysfunction Accumulation of 3-hydroxy-3-methylglutaric acid drives mitochondrial dysfunction in vulnerable brain regions.

3-Hydroxy-3-methylglutaric acid (HMG) Blocked HMG-CoA cleavage produces the characteristic accumulation of HMG.

3-Methylglutaconic acid (3-MGC) Leucine pathway blockade produces elevated urinary 3-methylglutaconic acid.

3-Methylglutaric acid (3-MGL) Leucine catabolic block produces elevated urinary 3-methylglutaric acid.

3-Hydroxyisovalerylcarnitine (C5-OH) Blocked leucine catabolism raises C5-OH acylcarnitine, the newborn screening marker.

Show evidence (2 references)

PMID:36771238 SUPPORT Human Clinical

"3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis."

Confirms the clinical presentation from toxic metabolite accumulation.

PMID:32685354 SUPPORT Human Clinical

"Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."

Human biomarker study supports the elevated leucine-derived organic acid profile downstream of the HMGCL block.

Acyl-CoA disequilibrium and secondary hyperammonemia

Chronic HMGCL deficiency and acute crises each produce distinct abnormal hepatic acyl-CoA patterns. Leucine metabolite loading increases leucine-related acyl-CoAs while depleting acetyl-CoA. Acetyl-CoA depletion impairs N-acetylglutamate synthesis, which is required for urea cycle activation via carbamoyl phosphate synthetase 1, producing secondary hyperammonemia. This mechanism was confirmed by carglumate rescue of hyperammonemia in a liver-specific HMGCL knockout mouse model.

hepatocyte link

urea cycle link ⚠ ABNORMAL

liver link mitochondrial matrix link

Downstream

Acetyl-CoA Leucine metabolite loading in HMGCL-deficient hepatocytes reduces acetyl-CoA levels.

Ammonia Increased ammonia is the biochemical readout of secondary hyperammonemia caused by impaired urea-cycle activation.

Hyperammonemia Acetyl-CoA depletion limits N-acetylglutamate-dependent urea-cycle activation, causing secondary hyperammonemia.

Hypoglycemia Acyl-CoA disequilibrium contributes to hypoglycemia during acute crises.

Show evidence (2 references)

PMID:23861731 SUPPORT Model Organism

"Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines."

Demonstrates acyl-CoA disruption as a core pathological mechanism in liver-specific HMGCL KO mice.

PMID:23861731 SUPPORT Model Organism

"KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function"

Confirms acetyl-CoA-linked mechanism for secondary hyperammonemia and carglumate responsiveness.

HMG-mediated neurotoxicity via mitochondrial dysfunction

The major accumulating metabolite 3-hydroxy-3-methylglutaric acid (HMG) directly disrupts brain mitochondrial function. In neonatal rat brain, HMG exposure reduces succinate dehydrogenase and respiratory chain complex II-III and IV activity in the cerebral cortex and striatum, impairs antioxidant defenses, and increases DRP1 levels indicating mitochondrial fission. These mechanisms connect metabolite accumulation to the neurological vulnerability observed early in life.

neuron link

electron transport chain link ↓ DECREASED response to oxidative stress link ⚠ ABNORMAL mitochondrial fission link ↑ INCREASED

cerebral cortex link striatum link

Downstream

Neurologic injury and neurodevelopmental sequelae HMG-mediated mitochondrial dysfunction contributes to neurologic injury and developmental vulnerability.

Show evidence (4 references)

PMID:39062136 SUPPORT Model Organism

"HMG decreased the activities of succinate dehydrogenase and respiratory chain complexes II-III and IV in the cortex. HMG also decreased the activities of citrate synthase and succinate dehydrogenase, as well as complex IV in the striatum."

Quantitative evidence of HMG-mediated bioenergetic disruption in brain regions.

PMID:39062136 SUPPORT Model Organism

"HMG further increased DRP1 levels in the cortex, indicating mitochondrial fission."

Demonstrates HMG drives mitochondrial network fragmentation in brain tissue.

PMID:39062136 SUPPORT Model Organism

"Our findings provide evidence that HMG causes oxidative stress, bioenergetic dysfunction, and neurodevelopmental changes in neonatal rats"

Supports oxidative-stress and bioenergetic dysfunction annotations for the HMG neurotoxicity branch.

+ 1 more reference

Neurologic injury and neurodevelopmental sequelae

Acute metabolic crises and accumulating organic acids injure vulnerable neural tissue, producing seizures, developmental and speech delay, hypotonia, and MRI abnormalities including leukoencephalopathy and rare cerebral atrophy.

neuron link

brain link

Downstream

Seizures Seizures are part of the neurologic sequelae of HMGCLD.

Global developmental delay Developmental delay is a neurodevelopmental sequela in a subset of patients.

Speech delay Speech delay reflects neurodevelopmental involvement.

Muscular hypotonia Hypotonia is reported among neurologic findings in HMGCLD cohorts.

Leukoencephalopathy White matter signal abnormalities represent leukoencephalopathy on brain MRI.

Cerebral atrophy Cerebral atrophy is a rare severe brain imaging sequela.

Show evidence (2 references)

PMID:35646072 SUPPORT Human Clinical

"Common neurological findings include seizures 17/62 (27.41%), hypotonic 3/62 (4.83%), speech delay 7/62 (11.29%), hyperactivity 4/62 (4.83%), developmental delay 6/62"

Human cohort data support neurologic and neurodevelopmental sequelae of HMGCLD.

PMID:28396157 SUPPORT Human Clinical

"Mild to extended abnormal white matter MRI signals were observed in all cases."

Brain MRI evidence supports white matter involvement in HMGCLD.

⬡

Pathograph

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

●

Phenotypes

Cardiovascular 1

Cardiomyopathy VERY_RARE Cardiomyopathy (HP:0001638)

Cardiomyopathy is a rare but potentially fatal complication of HMGCLD, reported in systematic reviews and case series. Cardiac tissue dependence on ketone bodies during stress may explain vulnerability.

Digestive 3

Vomiting FREQUENT Vomiting (HP:0002013)

Vomiting is commonly described during metabolic decompensation episodes in HMGCLD case series.

Hepatomegaly OCCASIONAL Hepatomegaly (HP:0002240)

Hepatomegaly has been reported during acute metabolic crises in HMGCLD case reports.

Acute liver failure VERY_RARE Acute hepatic failure (HP:0006554)

Show evidence (1 reference)

PMID:36771238 SUPPORT Human Clinical

"there were two patients that presented atypically-one with fulminant liver failure and the other with isolated developmental delay."

Documents fulminant liver failure as an atypical presentation of HMGCLD.

Metabolism 3

Metabolic acidosis FREQUENT Metabolic acidosis (HP:0001942)

Show evidence (2 references)

PMID:35646072 SUPPORT Human Clinical

"49 patients (79.03%) developed metabolic acidosis."

Quantifies metabolic acidosis frequency at 79% in a large molecularly confirmed cohort.

PMID:32059735 SUPPORT Human Clinical

"More than 95% of patients presented with acute metabolic decompensation."

Systematic review confirms near-universal metabolic decompensation with acidosis.

Hypoglycemia FREQUENT Hypoglycemia (HP:0001943)

Show evidence (2 references)

PMID:35646072 SUPPORT Human Clinical

"38 patients (61.29%) presented with hypoglycemia"

Quantifies hypoglycemia at diagnosis in 61% of a 62-patient cohort.

PMID:3099065 SUPPORT Human Clinical

"In the first year of life infants with HMG-CoA-LD run a high risk of developing severe hypoglycaemia which can lead to death if prompt intervention does not occur."

Foundational review emphasizing life-threatening hypoglycemia in infancy.

Hyperammonemia Hyperammonemia (HP:0001987)

Show evidence (1 reference)

PMID:23861731 SUPPORT Model Organism

"Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC."

Hyperammonemia demonstrated mechanistically in the liver-specific HMGCL KO mouse model.

Musculoskeletal 1

Muscular hypotonia OCCASIONAL Hypotonia (HP:0001252)

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"hypotonic 3/62 (4.83%)"

Quantifies hypotonia in the 62-patient cohort.

Nervous System 6

Seizures OCCASIONAL Seizure (HP:0001250)

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"Common neurological findings include seizures 17/62 (27.41%)"

Quantifies seizure frequency at 27.4% in a 62-patient cohort.

Lethargy FREQUENT Lethargy (HP:0001254)

Lethargy is a common feature during metabolic decompensation episodes in HMGCLD, progressing to encephalopathy or coma in severe crises.

Global developmental delay OCCASIONAL Global developmental delay (HP:0001263)

Show evidence (1 reference)

PMID:32059735 SUPPORT Human Clinical

"The neurologic long-term outcome was favorable with 62.6% of patients showing normal development."

Most patients develop normally, but a significant minority has long-term neurologic sequelae.

Leukoencephalopathy OCCASIONAL Leukoencephalopathy (HP:0002352)

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"An MRI of the brain exhibited nonspecific periventricular and deep white matter hyperintense signal changes in 16 patients (25.80%)"

Quantifies white matter abnormality frequency at 25.8% in the cohort.

Speech delay OCCASIONAL Delayed speech and language development (HP:0000750)

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"speech delay 7/62 (11.29%)"

Quantifies speech delay frequency in a molecularly confirmed cohort.

Cerebral atrophy VERY_RARE Cerebral atrophy (HP:0002059)

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"cerebral atrophy was found in one (1/62; 1.612%) patient."

Quantifies cerebral atrophy as a rare but documented finding.

🧬

Genetic Associations

HMGCL pathogenic variants

Autosomal recessive

Show evidence (3 references)

PMID:32059735 SUPPORT Human Clinical

"This comprehensive data analysis provides a systematic overview on all published cases with HMGCLD including a list of all known HMGCL mutations."

Provides the most comprehensive catalog of HMGCL mutations and associated phenotypes.

PMID:35646072 SUPPORT Human Clinical

"This is the largest cohort of HMGCLD patients reported from Saudi Arabia, signifying this disorder as a likely life-threatening disease, with a high prevalence in the region."

Largest regional cohort demonstrating population-specific variant enrichment.

CGGV:assertion_f4d084e5-a740-4bfd-a850-d6db900d4a4e-2018-06-26T160000.000Z SUPPORT Other

ClinGen classifies the HMGCL-3-hydroxy-3-methylglutaric aciduria gene-disease relationship as definitive with autosomal recessive inheritance.

💊

Treatments

Dietary protein and leucine restriction

Action: dietary intervention MAXO:0000088

Restriction of leucine and total protein intake is the cornerstone of long-term management. All patients in contemporary cohorts receive protein-restricted diets, with some also receiving fat restriction. Dietary management is well tolerated and helps prevent metabolic crises.

Mechanism Target:

INHIBITS Leucine catabolic block and organic acid accumulation — Restricting dietary protein and leucine lowers substrate flux into the blocked leucine degradation pathway.

Show evidence (2 references)

PMID:36771238 SUPPORT Human Clinical

"All patients have been on long-term protein restriction, and those diagnosed more recently have had additional fat restriction."

Confirms universal use of protein restriction in contemporary management.

PMID:35646072 SUPPORT Human Clinical

"Our findings suggest that diagnosis at an early stage with careful dietary management may avoid metabolic crises."

Large cohort supporting dietary management for crisis prevention.

Avoidance of fasting

Action: dietary intervention MAXO:0000088

Prevention of prolonged fasting is critical because ketogenesis failure means the patient cannot generate alternative energy substrates during fasting. Emergency carbohydrate plans are used during illness.

Mechanism Target:

MODULATES Ketogenesis failure and energy crisis — Avoiding fasting reduces the need for endogenous ketogenesis and preserves glucose availability during stress.

Show evidence (1 reference)

PMID:3099065 SUPPORT Human Clinical

"The metabolic crisis develops when the infant is first introduced to dietary protein soon after birth, or later, when a reduced intake of glucose, often during a viral infection, results in a drain on the infant's circulating glucose levels."

Identifies fasting and reduced glucose intake as key crisis triggers.

L-carnitine supplementation

Action: carnitine supplementation MAXO:0010006

Agent: carnitine ↗

L-carnitine is commonly prescribed in long-term management to support detoxification and excretion of accumulating organic acids as acylcarnitine conjugates. Used in most patients across contemporary cohorts.

Mechanism Target:

MODULATES Leucine catabolic block and organic acid accumulation — Carnitine supplementation supports acylcarnitine formation and excretion of accumulating organic acid intermediates.

Show evidence (1 reference)

PMID:36771238 SUPPORT Human Clinical

"Most patients take L-carnitine."

Confirms widespread use of carnitine supplementation in HMGCLD management.

Exogenous ketone therapy (sodium D,L-3-hydroxybutyrate)

Action: Pharmacotherapy NCIT:C15986

Agent: 3-hydroxybutyrate ↗

Exogenous ketone supplementation (sodium D,L-3-hydroxybutyrate, up to 900 mg/kg/day) bypasses impaired endogenous ketogenesis to provide alternative energy substrates for brain and heart. Used in both acute management and chronic adjunct therapy. Reported as well tolerated and effective in clinical case series.

Mechanism Target:

BYPASSES Ketogenesis failure and energy crisis — Exogenous 3-hydroxybutyrate supplies ketone substrate despite impaired endogenous ketogenesis.

Show evidence (1 reference)

PMID:36771238 SUPPORT Human Clinical

"five of nine patients have used 900 mg/kg/day of sodium D,L 3-hydroxybutyrate in combination with intravenous dextrose-containing fluids"

Documents high-dose exogenous ketone use in acute management.

Acute decompensation management

Action: supportive care MAXO:0000950

Emergency treatment includes rapid glucose provision (IV dextrose and/or frequent oral carbohydrate), cessation of protein intake, and correction of metabolic acidosis and hyperammonemia. Prompt intervention is essential to prevent death.

Mechanism Target:

BYPASSES Ketogenesis failure and energy crisis — Acute dextrose-containing support supplies glucose during crises when ketogenesis is impaired.

MODULATES Acyl-CoA disequilibrium and secondary hyperammonemia — Crisis management reduces catabolic leucine flux and treats downstream acidosis and hyperammonemia.

Target Phenotypes: Hypoglycemia ↗ Metabolic acidosis ↗ Hyperammonemia ↗

Show evidence (2 references)

PMID:3099065 SUPPORT Human Clinical

"In the first year of life infants with HMG-CoA-LD run a high risk of developing severe hypoglycaemia which can lead to death if prompt intervention does not occur."

Foundational evidence for the critical importance of prompt acute intervention.

PMID:36771238 SUPPORT Human Clinical

"Dietary management in patients with HMGCL deficiency is well tolerated, and rapid institution of acute supportive metabolic treatment is imperative to optimizing survival and improve outcomes in this disorder."

Contemporary confirmation that rapid supportive care is essential for survival.

Newborn screening

Action: disease screening MAXO:0000124

Tandem mass spectrometry screening using elevated C5-OH (3-hydroxyisovalerylcarnitine) enables presymptomatic diagnosis. Confirmation follows with urine organic acid analysis and molecular testing of HMGCL. Early detection allows initiation of dietary management before metabolic decompensation.

Target Phenotypes: Metabolic acidosis ↗ Hypoglycemia ↗ Hyperammonemia ↗

Show evidence (1 reference)

PMID:35646072 SUPPORT Human Clinical

"Our findings suggest that diagnosis at an early stage with careful dietary management may avoid metabolic crises."

Supports early detection and treatment to prevent metabolic crises.

Genetic counseling

Action: genetic counseling MAXO:0000079

Genetic counseling for affected families including discussion of autosomal recessive inheritance, 25% recurrence risk, and options for carrier testing, prenatal diagnosis, and preimplantation genetic testing.

Show evidence (1 reference)

PMID:32059735 SUPPORT Human Clinical

"3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL."

Autosomal recessive etiology supports genetic counseling for affected families.

Carglumic acid for hyperammonemia

Action: Pharmacotherapy NCIT:C15986

Agent: carglumic acid ↗

Carglumic acid (N-carbamyl-L-glutamic acid) is a synthetic analog of N-acetylglutamate that can rescue hyperammonemia by activating carbamoyl phosphate synthetase 1 in the urea cycle, bypassing the acetyl-CoA-dependent NAG synthesis that is impaired in HMGCLD. Demonstrated effective in a mouse model of HMGCLD.

Mechanism Target:

BYPASSES Acyl-CoA disequilibrium and secondary hyperammonemia — Carglumic acid substitutes for N-acetylglutamate to activate carbamoyl phosphate synthetase 1 when acetyl-CoA-dependent NAG synthesis is impaired.

Target Phenotypes: Hyperammonemia ↗

Show evidence (1 reference)

PMID:23861731 SUPPORT Model Organism

Demonstrates carglumate efficacy for hyperammonemia in the HMGCL KO mouse model.

🔬

Biochemical Markers

3-Hydroxy-3-methylglutaric acid (HMG) (INCREASED)

Context: Major accumulating urinary organic acid in HMGCLD. Also the primary metabolite tested for neurotoxicity, shown to disrupt brain mitochondrial function in neonatal rat models.

Pathograph Readouts

Readout Of Leucine catabolic block and organic acid accumulation Positive Diagnostic

Elevated HMG reports the blocked leucine-degradation endpoint shared with HMGCL-deficient ketogenesis.

Show evidence (2 references)

PMID:32685354 SUPPORT Human Clinical

Human biomarker study supports elevated HMG/3H3MG-A as part of the diagnostic organic acid pattern.

PMID:39062136 SUPPORT Model Organism

"3-Hydroxy-3-methylglutaric acidemia (HMGA) is a neurometabolic inherited disorder characterized by the predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in the brain and biological fluids of patients."

Identifies HMG as the predominant accumulating metabolite.

3-Methylglutaconic acid (3-MGC) (INCREASED)

Context: Characteristic urinary organic acid elevated in HMGCLD. Its CoA ester (trans-3MGC-CoA) is implicated as a reactive metabolite capable of non-enzymatic protein acylation (3MGCylation) in the mitochondrial matrix.

Pathograph Readouts

Readout Of Leucine catabolic block and organic acid accumulation Positive Diagnostic

Elevated 3-MGC reports diversion of upstream leucine-catabolism intermediates around the HMGCL block.

Show evidence (1 reference)

PMID:32685354 SUPPORT Human Clinical

"Using untargeted metabolomic analysis of HMGCLD patient plasma, 3MGC‐A and 3H3MG‐A were found among the most discriminating metabolites between patient and control group."

Human metabolomics identifies 3MGC-A as a discriminating elevated biomarker in HMGCLD patient plasma.

3-Hydroxyisovalerylcarnitine (C5-OH) (INCREASED)

Context: Elevated C5-OH acylcarnitine in plasma is the primary newborn screening marker for HMGCLD, detectable by tandem mass spectrometry.

Pathograph Readouts

Readout Of Leucine catabolic block and organic acid accumulation Positive Diagnostic

Elevated C5-OH/3HIV-C reports leucine-derived acyl-CoA accumulation and is used as the first-tier newborn-screening signal.

Show evidence (1 reference)

PMID:32685354 SUPPORT Human Clinical

"Plasma of these patients contains elevated levels of 3‐hydroxyisovalerylcarnitine (3HIV‐C)"

Human biomarker study supports elevated plasma 3-hydroxyisovalerylcarnitine/C5-OH in HMGCLD.

3-Methylglutaric acid (3-MGL) (INCREASED)

Context: Urinary organic acid marker elevated in HMGCLD, part of the characteristic metabolite profile used for biochemical diagnosis.

Pathograph Readouts

Readout Of Leucine catabolic block and organic acid accumulation Positive Diagnostic

Elevated 3-MGL is part of the diagnostic urinary organic acid profile for the leucine-catabolism block.

Show evidence (1 reference)

PMID:32685354 SUPPORT Human Clinical

Human biomarker study supports 3-methylglutaric acid as part of the diagnostic organic acid profile.

Ketone bodies (DECREASED)

Context: Absent or inappropriately low ketones during fasting and illness is a hallmark biochemical finding. Non-ketotic or hypoketotic hypoglycemia distinguishes HMGCLD from other organic acidemias.

Pathograph Readouts

Readout Of Ketogenesis failure and energy crisis Negative Diagnostic

Inappropriately low ketone bodies during illness report failure of endogenous ketogenesis.

Show evidence (1 reference)

PMID:36771238 SUPPORT Human Clinical

"3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia"

Confirms hypoketotic hypoglycemia as a defining feature.

Acetyl-CoA (DECREASED)

Context: Hepatic acetyl-CoA levels are reduced during leucine metabolite loading in HMGCL-deficient liver, contributing to impaired gluconeogenesis and urea cycle activation.

Pathograph Readouts

Readout Of Acyl-CoA disequilibrium and secondary hyperammonemia Negative Monitoring

Lower hepatic acetyl-CoA reports the acyl-CoA disequilibrium mechanism that impairs urea-cycle activation in the HMGCL model.

Show evidence (1 reference)

PMID:23861731 SUPPORT Model Organism

"KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels."

Direct demonstration of acetyl-CoA depletion in HMGCL-deficient hepatocytes under leucine stress.

Ammonia (INCREASED)

Context: Plasma ammonia rises during acute metabolic decompensation, reflecting secondary urea-cycle impairment from acetyl-CoA/N-acetylglutamate limitation.

Pathograph Readouts

Readout Of Acyl-CoA disequilibrium and secondary hyperammonemia Positive Monitoring

Higher ammonia reports the secondary hyperammonemia branch downstream of impaired acyl-CoA balance.

Show evidence (1 reference)

PMID:36771238 SUPPORT Human Clinical

Human clinical cohort review identifies hyperammonemia as part of acute HMGCLD decompensation.

{ }

Source YAML

click to show

name: 3-Hydroxy-3-Methylglutaric Aciduria
category: Mendelian
creation_date: '2026-02-23T00:00:00Z'
updated_date: '2026-05-21T13:49:02Z'
synonyms:
- HMG-CoA lyase deficiency
- HMGCLD
- 3-Hydroxy-3-methylglutaric acidemia
- Hydroxymethylglutaric aciduria
description: '3-Hydroxy-3-methylglutaric aciduria (HMGCLD) is an autosomal recessive inborn error of metabolism caused by biallelic pathogenic variants in HMGCL, encoding mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase. This enzyme catalyzes the final step of both ketogenesis and leucine degradation, cleaving HMG-CoA to acetyl-CoA and acetoacetate. Deficiency results in failure to produce ketone bodies during catabolic stress and accumulation of leucine-derived toxic organic acids. Acute metabolic crises feature hypoketotic hypoglycemia, metabolic acidosis, and hyperammonemia, with neurological sequelae including seizures, developmental delay, and white matter abnormalities. More than 95% of reported patients experience at least one metabolic decompensation episode, with approximately 42% having neonatal onset. Mortality is reported at approximately 16%, while over 60% of survivors achieve normal development with appropriate management.

  '
disease_term:
  preferred_term: 3-hydroxy-3-methylglutaric aciduria
  term:
    id: MONDO:0009520
    label: 3-hydroxy-3-methylglutaric aciduria
parents:
- Organic Acidemia
- Inborn Error of Metabolism
prevalence:
- population: Global
  percentage: Rare
  notes: 'Approximately 211 cases compiled in a 2020 systematic literature review. Higher prevalence in regions with high consanguinity such as Saudi Arabia, where a founder HMGCL variant c.122G>A (p.Arg41Gln) is present.

    '
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Two hundred eleven patients of whom relevant clinical data were available were included in this analysis.
    explanation: Systematic review compiling 211 published cases worldwide.
progression:
- phase: Neonatal onset
  age_range: 0-28 days
  notes: '42.4% of patients present neonatally. Crises triggered by protein introduction or catabolic stress in the first days of life.

    '
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Most patients manifested within the first year of life, 42.4% already neonatally.
    explanation: Quantifies neonatal onset frequency.
- phase: Acute metabolic decompensation
  notes: 'More than 95% of patients experience at least one metabolic crisis. Crises feature hypoketotic hypoglycemia, metabolic acidosis, and hyperammonemia. With age and dietary management, hypoglycemic attacks diminish.

    '
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: More than 95% of patients presented with acute metabolic decompensation.
    explanation: Near-universal occurrence of metabolic crises in HMGCLD.
  - reference: PMID:3099065
    reference_title: "3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: As children with HMG-CoA-LD grow older the incidence of hypoglycaemic attacks diminishes and they usually develop normally.
    explanation: Improvement with age supports staged progression.
pathophysiology:
- name: HMGCL molecular function deficiency
  description: 'Biallelic pathogenic variants in HMGCL reduce mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase catalytic activity.

    '
  genes:
  - preferred_term: HMGCL
    term:
      id: hgnc:5005
      label: HMGCL
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: mitochondrion
    term:
      id: GO:0005739
      label: mitochondrion
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL.
    explanation: Supports HMGCL molecular deficiency as the initiating genetic and enzymatic defect.
  downstream:
  - target: Ketogenesis failure and energy crisis
    causal_link_type: DIRECT
    description: Loss of HMGCL function blocks hepatic ketone body generation during catabolic states.
    evidence:
    - reference: PMID:32059735
      reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL.
      explanation: The systematic review directly links HMGCL mutations to the ketogenesis arm of the disease.
  - target: Leucine catabolic block and organic acid accumulation
    causal_link_type: DIRECT
    description: Loss of HMGCL function also blocks leucine degradation, causing upstream toxic organic acid accumulation.
    evidence:
    - reference: PMID:32059735
      reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL.
      explanation: The systematic review directly links HMGCL mutations to the leucine-degradation arm of the disease.
- name: Ketogenesis failure and energy crisis
  description: 'Loss of HMGCL-mediated HMG-CoA cleavage abolishes ketogenesis, depriving brain and heart of essential energy substrates during fasting and catabolic stress. This produces hypoketotic hypoglycemia and metabolic acidosis during acute crises.

    '
  biological_processes:
  - preferred_term: ketone body metabolic process
    term:
      id: GO:1902224
      label: ketone body metabolic process
    modifier: DECREASED
  - preferred_term: fatty acid beta-oxidation
    term:
      id: GO:0006635
      label: fatty acid beta-oxidation
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  chemical_entities:
  - preferred_term: ketone body
    term:
      id: CHEBI:73693
      label: ketone body
    modifier: DECREASED
  - preferred_term: acetoacetate
    term:
      id: CHEBI:13705
      label: acetoacetate
    modifier: DECREASED
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: More than 95% of patients presented with acute metabolic decompensation. Most patients manifested within the first year of life, 42.4% already neonatally.
    explanation: Systematic review of 211 patients demonstrates near-universal acute metabolic crises from ketogenesis failure.
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mitochondrial enzyme is responsible for catalyzing the cleavage of HMG‐CoA to acetyl‐CoA and acetoacetic acid. This conversion is a common last step in leucine catabolism and ketogenesis from fatty acids."
    explanation: Human biomarker study background places the HMGCL-catalyzed cleavage step at the shared endpoint of ketogenesis.
  downstream:
  - target: Ketone bodies
    causal_link_type: DIRECT
    description: HMGCL deficiency blocks ketone body synthesis, producing absent or inappropriately low ketones during fasting and illness.
    evidence:
    - reference: PMID:3099065
      reference_title: "3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: they cannot make ketone bodies in response to prolonged fasting.
      explanation: The clinical review directly supports impaired ketone body production during fasting.
  - target: Hypoglycemia
    causal_link_type: DIRECT
    description: Failure to generate ketone bodies during fasting leaves patients dependent on circulating glucose, causing hypoketotic hypoglycemia.
    evidence:
    - reference: PMID:36771238
      reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia
      explanation: The Australian cohort review links HMGCL deficiency decompensation with hypoketotic hypoglycemia.
  - target: Metabolic acidosis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Acute catabolism combines impaired ketone production with organic acid accumulation.
    description: Acute decompensation from ketogenesis failure and organic acid accumulation produces metabolic acidosis.
    evidence:
    - reference: PMID:36771238
      reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
      explanation: The cohort review lists metabolic acidosis among acute decompensation features.
  - target: Lethargy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Hypoglycemia and metabolic acidosis impair cerebral energy availability during crisis.
    description: Acute energy crisis causes reduced arousal and encephalopathic presentation.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients may suffer from severe attacks of metabolic decompensation with lethargy, seizures, hypotonia, vomiting and acidosis with hypoketotic hypoglycemia
      explanation: The human biomarker study background lists lethargy during severe metabolic decompensation.
  - target: Vomiting
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Vomiting occurs during acute metabolic decompensation episodes.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Patients may suffer from severe attacks of metabolic decompensation with lethargy, seizures, hypotonia, vomiting and acidosis with hypoketotic hypoglycemia
      explanation: The human biomarker study background lists vomiting during severe metabolic decompensation.
  - target: Cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Cardiac vulnerability may reflect loss of ketone-derived energy substrate during stress.
    evidence:
    - reference: PMID:7807935
      reference_title: "Fatal cardiomyopathy associated with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Fatal cardiomyopathy associated with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
      explanation: The indexed case-report title directly supports cardiomyopathy as an HMGCLD complication.
  - target: Acute liver failure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Severe metabolic decompensation can present atypically with fulminant liver failure.
    evidence:
    - reference: PMID:36771238
      reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: there were two patients that presented atypically-one with fulminant liver failure and the other with isolated developmental delay.
      explanation: The Australian cohort review documents fulminant liver failure as an atypical presentation.
  - target: Hepatomegaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Hepatomegaly is reported during acute metabolic crises and hepatic metabolic stress.
    evidence:
    - reference: PMID:34573903
      reference_title: "An Atypical Case of Head Tremor and Extensive White Matter in an Adult Female Caused by 3-Hydroxy-3-methylglutaryl-CoA Lyase Deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: this disorder is characterized by a life-threatening metabolic intoxication with a presentation including severe hypoglycemia without ketosis, metabolic acidosis, hyper-ammoniemia, hepatomegaly and a coma.
      explanation: The case report review lists hepatomegaly among life-threatening HMGCLD intoxication features.
- name: Leucine catabolic block and organic acid accumulation
  description: 'HMGCL is also required for leucine degradation. Blockade causes upstream accumulation of leucine-derived metabolites including 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid. Illness-driven leucine flux increases toxic metabolite excretion, implying leucine-derived toxicity is particularly prominent under inflammatory and catabolic stress.

    '
  biological_processes:
  - preferred_term: leucine catabolic process
    term:
      id: GO:0006552
      label: L-leucine catabolic process
    modifier: DECREASED
  - preferred_term: branched-chain amino acid catabolic process
    term:
      id: GO:0009083
      label: branched-chain amino acid catabolic process
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: mitochondrial matrix
    term:
      id: GO:0005759
      label: mitochondrial matrix
  chemical_entities:
  - preferred_term: 3-hydroxy-3-methylglutaric acid
    term:
      id: CHEBI:16831
      label: 3-hydroxy-3-methylglutaric acid
    modifier: INCREASED
  - preferred_term: 3-methylglutaconic acid
    term:
      id: CHEBI:144330
      label: 3-methylglutaconic acid
    modifier: INCREASED
  - preferred_term: 3-methylglutaric acid
    term:
      id: CHEBI:68566
      label: 3-methylglutaric acid
    modifier: INCREASED
  - preferred_term: 3-hydroxyisovalerylcarnitine
    term:
      id: CHEBI:73027
      label: 3-hydroxyisovalerylcarnitine
    modifier: INCREASED
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
    explanation: Confirms the clinical presentation from toxic metabolite accumulation.
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."
    explanation: Human biomarker study supports the elevated leucine-derived organic acid profile downstream of the HMGCL block.
  downstream:
  - target: Acyl-CoA disequilibrium and secondary hyperammonemia
    causal_link_type: DIRECT
    description: Blocked leucine degradation increases leucine-related acyl-CoAs and disrupts hepatic acyl-CoA balance.
    evidence:
    - reference: PMID:23861731
      reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels.
      explanation: Liver-specific HMGCL knockout data support leucine-stress acyl-CoA disequilibrium downstream of the block.
  - target: HMG-mediated neurotoxicity via mitochondrial dysfunction
    causal_link_type: DIRECT
    description: Accumulation of 3-hydroxy-3-methylglutaric acid drives mitochondrial dysfunction in vulnerable brain regions.
    evidence:
    - reference: PMID:39062136
      reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Our findings provide evidence that HMG causes oxidative stress, bioenergetic dysfunction, and neurodevelopmental changes in neonatal rats
      explanation: The neonatal rat model directly links accumulated HMG to mitochondrial/bioenergetic neurotoxicity.
  - target: 3-Hydroxy-3-methylglutaric acid (HMG)
    causal_link_type: DIRECT
    description: Blocked HMG-CoA cleavage produces the characteristic accumulation of HMG.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."
      explanation: The human biomarker study supports elevated HMG/3H3MG-A downstream of the leucine-catabolism block.
  - target: 3-Methylglutaconic acid (3-MGC)
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Upstream trans-3-methylglutaconyl-CoA is diverted to 3-methylglutaconic acid.
    description: Leucine pathway blockade produces elevated urinary 3-methylglutaconic acid.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Using untargeted metabolomic analysis of HMGCLD patient plasma, 3MGC‐A and 3H3MG‐A were found among the most discriminating metabolites between patient and control group."
      explanation: Human metabolomics supports elevated 3MGC-A as a discriminating downstream biomarker.
  - target: 3-Methylglutaric acid (3-MGL)
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Accumulating leucine catabolism intermediates are converted to urinary organic acids.
    description: Leucine catabolic block produces elevated urinary 3-methylglutaric acid.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."
      explanation: The human biomarker study supports elevated 3MG-A as part of the diagnostic organic-acid pattern.
  - target: 3-Hydroxyisovalerylcarnitine (C5-OH)
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Upstream leucine-derived acyl-CoA species are conjugated to carnitine.
    description: Blocked leucine catabolism raises C5-OH acylcarnitine, the newborn screening marker.
    evidence:
    - reference: PMID:32685354
      reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Plasma of these patients contains elevated levels of 3‐hydroxyisovalerylcarnitine (3HIV‐C)"
      explanation: The human biomarker study supports elevated C5-OH/3HIV-C downstream of the leucine catabolic block.
- name: Acyl-CoA disequilibrium and secondary hyperammonemia
  description: 'Chronic HMGCL deficiency and acute crises each produce distinct abnormal hepatic acyl-CoA patterns. Leucine metabolite loading increases leucine-related acyl-CoAs while depleting acetyl-CoA. Acetyl-CoA depletion impairs N-acetylglutamate synthesis, which is required for urea cycle activation via carbamoyl phosphate synthetase 1, producing secondary hyperammonemia. This mechanism was confirmed by carglumate rescue of hyperammonemia in a liver-specific HMGCL knockout mouse model.

    '
  biological_processes:
  - preferred_term: urea cycle
    term:
      id: GO:0000050
      label: urea cycle
    modifier: ABNORMAL
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  locations:
  - preferred_term: liver
    term:
      id: UBERON:0002107
      label: liver
  - preferred_term: mitochondrial matrix
    term:
      id: GO:0005759
      label: mitochondrial matrix
  chemical_entities:
  - preferred_term: acetyl-CoA
    term:
      id: CHEBI:15351
      label: acetyl-CoA
    modifier: DECREASED
  - preferred_term: ammonia
    term:
      id: CHEBI:16134
      label: ammonia
    modifier: INCREASED
  evidence:
  - reference: PMID:23861731
    reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Chronic HL deficiency and acute crises each produced distinct abnormal liver acyl-CoA patterns, which would not be predictable from levels of urine organic acids and plasma acylcarnitines.
    explanation: Demonstrates acyl-CoA disruption as a core pathological mechanism in liver-specific HMGCL KO mice.
  - reference: PMID:23861731
    reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function
    explanation: Confirms acetyl-CoA-linked mechanism for secondary hyperammonemia and carglumate responsiveness.
  downstream:
  - target: Acetyl-CoA
    causal_link_type: DIRECT
    description: Leucine metabolite loading in HMGCL-deficient hepatocytes reduces acetyl-CoA levels.
    evidence:
    - reference: PMID:23861731
      reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels.
      explanation: The HMGCL-deficient liver model directly supports acetyl-CoA depletion under leucine stress.
  - target: Ammonia
    causal_link_type: DIRECT
    description: Increased ammonia is the biochemical readout of secondary hyperammonemia caused by impaired urea-cycle activation.
    evidence:
    - reference: PMID:36771238
      reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
      explanation: Human clinical review supports hyperammonemia as a biochemical feature of acute HMGCLD decompensation.
  - target: Hyperammonemia
    causal_link_type: DIRECT
    description: Acetyl-CoA depletion limits N-acetylglutamate-dependent urea-cycle activation, causing secondary hyperammonemia.
    evidence:
    - reference: PMID:23861731
      reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function
      explanation: The liver-specific knockout model links acetyl-CoA-dependent urea-cycle activation to hyperammonemia.
  - target: Hypoglycemia
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Abnormal hepatic acyl-CoA balance impairs gluconeogenic response to pyruvate.
    description: Acyl-CoA disequilibrium contributes to hypoglycemia during acute crises.
    evidence:
    - reference: PMID:23861731
      reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC.
      explanation: The HMGCL-deficient liver model supports hypoglycemia downstream of hepatic acyl-CoA disruption.
- name: HMG-mediated neurotoxicity via mitochondrial dysfunction
  description: 'The major accumulating metabolite 3-hydroxy-3-methylglutaric acid (HMG) directly disrupts brain mitochondrial function. In neonatal rat brain, HMG exposure reduces succinate dehydrogenase and respiratory chain complex II-III and IV activity in the cerebral cortex and striatum, impairs antioxidant defenses, and increases DRP1 levels indicating mitochondrial fission. These mechanisms connect metabolite accumulation to the neurological vulnerability observed early in life.

    '
  biological_processes:
  - preferred_term: electron transport chain
    term:
      id: GO:0022900
      label: electron transport chain
    modifier: DECREASED
  - preferred_term: response to oxidative stress
    term:
      id: GO:0006979
      label: response to oxidative stress
    modifier: ABNORMAL
  - preferred_term: mitochondrial fission
    term:
      id: GO:0000266
      label: mitochondrial fission
    modifier: INCREASED
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: cerebral cortex
    term:
      id: UBERON:0000956
      label: cerebral cortex
  - preferred_term: striatum
    term:
      id: UBERON:0002435
      label: striatum
  chemical_entities:
  - preferred_term: 3-hydroxy-3-methylglutaric acid
    term:
      id: CHEBI:16831
      label: 3-hydroxy-3-methylglutaric acid
    modifier: INCREASED
  evidence:
  - reference: PMID:39062136
    reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: HMG decreased the activities of succinate dehydrogenase and respiratory chain complexes II-III and IV in the cortex. HMG also decreased the activities of citrate synthase and succinate dehydrogenase, as well as complex IV in the striatum.
    explanation: Quantitative evidence of HMG-mediated bioenergetic disruption in brain regions.
  - reference: PMID:39062136
    reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: HMG further increased DRP1 levels in the cortex, indicating mitochondrial fission.
    explanation: Demonstrates HMG drives mitochondrial network fragmentation in brain tissue.
  - reference: PMID:39062136
    reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Our findings provide evidence that HMG causes oxidative stress, bioenergetic dysfunction, and neurodevelopmental changes in neonatal rats
    explanation: Supports oxidative-stress and bioenergetic dysfunction annotations for the HMG neurotoxicity branch.
  - reference: PMID:39062136
    reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: HMG-injected animals showed impaired performance in all sensorimotor tests examined.
    explanation: Links HMG exposure directly to neurodevelopmental impairment in an animal model.
  downstream:
  - target: Neurologic injury and neurodevelopmental sequelae
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - HMG disrupts brain mitochondrial bioenergetics, redox homeostasis, and mitochondrial dynamics.
    description: HMG-mediated mitochondrial dysfunction contributes to neurologic injury and developmental vulnerability.
    evidence:
    - reference: PMID:39062136
      reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: HMG-injected animals showed impaired performance in all sensorimotor tests examined.
      explanation: The HMG exposure model supports neurodevelopmental injury downstream of mitochondrial dysfunction.
- name: Neurologic injury and neurodevelopmental sequelae
  description: 'Acute metabolic crises and accumulating organic acids injure vulnerable neural tissue, producing seizures, developmental and speech delay, hypotonia, and MRI abnormalities including leukoencephalopathy and rare cerebral atrophy.

    '
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  locations:
  - preferred_term: brain
    term:
      id: UBERON:0000955
      label: brain
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common neurological findings include seizures 17/62 (27.41%), hypotonic 3/62 (4.83%), speech delay 7/62 (11.29%), hyperactivity 4/62 (4.83%), developmental delay 6/62
    explanation: Human cohort data support neurologic and neurodevelopmental sequelae of HMGCLD.
  - reference: PMID:28396157
    reference_title: "Coupled brain and urine spectroscopy - in vivo metabolomic characterization of HMG-CoA lyase deficiency in 5 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Mild to extended abnormal white matter MRI signals were observed in all cases.
    explanation: Brain MRI evidence supports white matter involvement in HMGCLD.
  downstream:
  - target: Seizures
    causal_link_type: DIRECT
    description: Seizures are part of the neurologic sequelae of HMGCLD.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Common neurological findings include seizures 17/62 (27.41%)
      explanation: The Saudi cohort directly reports seizures among neurologic findings.
  - target: Global developmental delay
    causal_link_type: DIRECT
    description: Developmental delay is a neurodevelopmental sequela in a subset of patients.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: speech delay 7/62 (11.29%), hyperactivity 4/62 (4.83%), developmental delay 6/62
      explanation: The Saudi cohort directly reports developmental delay among long-term neurologic findings.
  - target: Speech delay
    causal_link_type: DIRECT
    description: Speech delay reflects neurodevelopmental involvement.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: speech delay 7/62 (11.29%)
      explanation: The Saudi cohort directly reports speech delay among neurologic findings.
  - target: Muscular hypotonia
    causal_link_type: DIRECT
    description: Hypotonia is reported among neurologic findings in HMGCLD cohorts.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: hypotonic 3/62 (4.83%)
      explanation: The Saudi cohort directly reports hypotonia among neurologic findings.
  - target: Leukoencephalopathy
    causal_link_type: DIRECT
    description: White matter signal abnormalities represent leukoencephalopathy on brain MRI.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: An MRI of the brain exhibited nonspecific periventricular and deep white matter hyperintense signal changes in 16 patients (25.80%)
      explanation: The Saudi cohort directly supports white matter signal abnormalities as a leukoencephalopathy readout.
  - target: Cerebral atrophy
    causal_link_type: DIRECT
    description: Cerebral atrophy is a rare severe brain imaging sequela.
    evidence:
    - reference: PMID:35646072
      reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: cerebral atrophy was found in one (1/62; 1.612%) patient.
      explanation: The Saudi cohort directly supports cerebral atrophy as a rare neurologic sequela.
phenotypes:
- name: Metabolic acidosis
  frequency: FREQUENT
  description: 'High-anion-gap metabolic acidosis during metabolic decompensation, reported in 79% of patients in a 62-patient Saudi cohort.

    '
  phenotype_term:
    preferred_term: Metabolic acidosis
    term:
      id: HP:0001942
      label: Metabolic acidosis
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 49 patients (79.03%) developed metabolic acidosis.
    explanation: Quantifies metabolic acidosis frequency at 79% in a large molecularly confirmed cohort.
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: More than 95% of patients presented with acute metabolic decompensation.
    explanation: Systematic review confirms near-universal metabolic decompensation with acidosis.
- name: Hypoglycemia
  frequency: FREQUENT
  description: 'Hypoketotic or non-ketotic hypoglycemia is a cardinal feature, resulting from failure of ketogenesis during fasting. Reported in 61% of patients at initial diagnosis in a large cohort.

    '
  phenotype_term:
    preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 38 patients (61.29%) presented with hypoglycemia
    explanation: Quantifies hypoglycemia at diagnosis in 61% of a 62-patient cohort.
  - reference: PMID:3099065
    reference_title: "3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In the first year of life infants with HMG-CoA-LD run a high risk of developing severe hypoglycaemia which can lead to death if prompt intervention does not occur.
    explanation: Foundational review emphasizing life-threatening hypoglycemia in infancy.
- name: Hyperammonemia
  description: 'Secondary hyperammonemia occurs during metabolic crises, sometimes exceeding 1000 umol/L. Mechanism involves acetyl-CoA depletion impairing N-acetylglutamate-dependent urea cycle activation.

    '
  phenotype_term:
    preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:23861731
    reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: Hyperammonemia and hypoglycemia, cardinal features of many inborn errors of acyl-CoA metabolism, occurred spontaneously in some HLLKO mice and were inducible by administering KIC.
    explanation: Hyperammonemia demonstrated mechanistically in the liver-specific HMGCL KO mouse model.
- name: Seizures
  frequency: OCCASIONAL
  description: 'Seizures occur in approximately 27% of patients, typically during metabolic decompensation or as a result of neurological injury.

    '
  phenotype_term:
    preferred_term: Seizure
    term:
      id: HP:0001250
      label: Seizure
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Common neurological findings include seizures 17/62 (27.41%)
    explanation: Quantifies seizure frequency at 27.4% in a 62-patient cohort.
- name: Lethargy
  frequency: FREQUENT
  description: 'Reduced arousal and lethargy during decompensation events, often progressing to encephalopathy or coma in severe crises.

    '
  phenotype_term:
    preferred_term: Lethargy
    term:
      id: HP:0001254
      label: Lethargy
  notes: Lethargy is a common feature during metabolic decompensation episodes in HMGCLD, progressing to encephalopathy or coma in severe crises.
- name: Global developmental delay
  frequency: OCCASIONAL
  description: 'Developmental delay occurs in a subset of patients, with 62.6% achieving normal development in a systematic review. Learning disability was reported in 24% and developmental delay in 9.7% of a Saudi cohort.

    '
  phenotype_term:
    preferred_term: Global developmental delay
    term:
      id: HP:0001263
      label: Global developmental delay
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The neurologic long-term outcome was favorable with 62.6% of patients showing normal development.
    explanation: Most patients develop normally, but a significant minority has long-term neurologic sequelae.
- name: Vomiting
  frequency: FREQUENT
  description: 'Recurrent vomiting during metabolic crises, often the presenting symptom triggering evaluation and emergency management.

    '
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
  notes: Vomiting is commonly described during metabolic decompensation episodes in HMGCLD case series.
- name: Leukoencephalopathy
  frequency: OCCASIONAL
  description: 'MRI white matter hyperintensities were observed in 25.8% of patients in a Saudi cohort, reflecting periventricular and deep white matter injury from metabolic crises.

    '
  phenotype_term:
    preferred_term: Leukoencephalopathy
    term:
      id: HP:0002352
      label: Leukoencephalopathy
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: An MRI of the brain exhibited nonspecific periventricular and deep white matter hyperintense signal changes in 16 patients (25.80%)
    explanation: Quantifies white matter abnormality frequency at 25.8% in the cohort.
- name: Hepatomegaly
  frequency: OCCASIONAL
  description: 'Hepatomegaly has been reported during acute metabolic crises, reflecting hepatic injury and metabolic stress.

    '
  phenotype_term:
    preferred_term: Hepatomegaly
    term:
      id: HP:0002240
      label: Hepatomegaly
  notes: Hepatomegaly has been reported during acute metabolic crises in HMGCLD case reports.
- name: Muscular hypotonia
  frequency: OCCASIONAL
  description: 'Hypotonia was reported in approximately 5% of a Saudi cohort as a neurological finding.

    '
  phenotype_term:
    preferred_term: Hypotonia
    term:
      id: HP:0001252
      label: Hypotonia
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: hypotonic 3/62 (4.83%)
    explanation: Quantifies hypotonia in the 62-patient cohort.
- name: Speech delay
  frequency: OCCASIONAL
  description: 'Speech delay was present in 11.3% of patients in a Saudi cohort, reflecting neurodevelopmental vulnerability.

    '
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: speech delay 7/62 (11.29%)
    explanation: Quantifies speech delay frequency in a molecularly confirmed cohort.
- name: Cerebral atrophy
  frequency: VERY_RARE
  description: 'Cerebral atrophy was found in 1/62 (1.6%) in a Saudi cohort, representing severe neurological sequelae.

    '
  phenotype_term:
    preferred_term: Cerebral atrophy
    term:
      id: HP:0002059
      label: Cerebral atrophy
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: cerebral atrophy was found in one (1/62; 1.612%) patient.
    explanation: Quantifies cerebral atrophy as a rare but documented finding.
- name: Cardiomyopathy
  frequency: VERY_RARE
  description: 'Cardiomyopathy is a rare but potentially fatal complication of HMGCLD, mechanistically related to the dependence of cardiac tissue on ketone bodies as an energy source during stress.

    '
  phenotype_term:
    preferred_term: Cardiomyopathy
    term:
      id: HP:0001638
      label: Cardiomyopathy
  notes: Cardiomyopathy is a rare but potentially fatal complication of HMGCLD, reported in systematic reviews and case series. Cardiac tissue dependence on ketone bodies during stress may explain vulnerability.
- name: Acute liver failure
  frequency: VERY_RARE
  description: 'Fulminant liver failure is an atypical but documented presentation of HMGCLD. One patient in an Australian cohort presented with isolated liver failure.

    '
  phenotype_term:
    preferred_term: Acute hepatic failure
    term:
      id: HP:0006554
      label: Acute hepatic failure
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: there were two patients that presented atypically-one with fulminant liver failure and the other with isolated developmental delay.
    explanation: Documents fulminant liver failure as an atypical presentation of HMGCLD.
biochemical:
- name: 3-Hydroxy-3-methylglutaric acid (HMG)
  presence: INCREASED
  context: 'Major accumulating urinary organic acid in HMGCLD. Also the primary metabolite tested for neurotoxicity, shown to disrupt brain mitochondrial function in neonatal rat models.

    '
  biomarker_term:
    preferred_term: 3-hydroxy-3-methylglutaric acid
    term:
      id: CHEBI:16831
      label: 3-hydroxy-3-methylglutaric acid
  readouts:
  - target: Leucine catabolic block and organic acid accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated HMG reports the blocked leucine-degradation endpoint shared with HMGCL-deficient ketogenesis.
  evidence:
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."
    explanation: Human biomarker study supports elevated HMG/3H3MG-A as part of the diagnostic organic acid pattern.
  - reference: PMID:39062136
    reference_title: "3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: 3-Hydroxy-3-methylglutaric acidemia (HMGA) is a neurometabolic inherited disorder characterized by the predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in the brain and biological fluids of patients.
    explanation: Identifies HMG as the predominant accumulating metabolite.
- name: 3-Methylglutaconic acid (3-MGC)
  presence: INCREASED
  context: 'Characteristic urinary organic acid elevated in HMGCLD. Its CoA ester (trans-3MGC-CoA) is implicated as a reactive metabolite capable of non-enzymatic protein acylation (3MGCylation) in the mitochondrial matrix.

    '
  biomarker_term:
    preferred_term: 3-methylglutaconic acid
    term:
      id: CHEBI:144330
      label: 3-methylglutaconic acid
  readouts:
  - target: Leucine catabolic block and organic acid accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated 3-MGC reports diversion of upstream leucine-catabolism intermediates around the HMGCL block.
  evidence:
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Using untargeted metabolomic analysis of HMGCLD patient plasma, 3MGC‐A and 3H3MG‐A were found among the most discriminating metabolites between patient and control group."
    explanation: Human metabolomics identifies 3MGC-A as a discriminating elevated biomarker in HMGCLD patient plasma.
- name: 3-Hydroxyisovalerylcarnitine (C5-OH)
  presence: INCREASED
  context: 'Elevated C5-OH acylcarnitine in plasma is the primary newborn screening marker for HMGCLD, detectable by tandem mass spectrometry.

    '
  biomarker_term:
    preferred_term: 3-hydroxyisovalerylcarnitine
    term:
      id: CHEBI:73027
      label: 3-hydroxyisovalerylcarnitine
  readouts:
  - target: Leucine catabolic block and organic acid accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated C5-OH/3HIV-C reports leucine-derived acyl-CoA accumulation and is used as the first-tier newborn-screening signal.
  evidence:
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Plasma of these patients contains elevated levels of 3‐hydroxyisovalerylcarnitine (3HIV‐C)"
    explanation: Human biomarker study supports elevated plasma 3-hydroxyisovalerylcarnitine/C5-OH in HMGCLD.
  notes: C5-OH acylcarnitine is the primary newborn screening marker for HMGCLD, used in tandem mass spectrometry-based screening panels.
- name: 3-Methylglutaric acid (3-MGL)
  presence: INCREASED
  context: 'Urinary organic acid marker elevated in HMGCLD, part of the characteristic metabolite profile used for biochemical diagnosis.

    '
  biomarker_term:
    preferred_term: 3-methylglutaric acid
    term:
      id: CHEBI:68566
      label: 3-methylglutaric acid
  readouts:
  - target: Leucine catabolic block and organic acid accumulation
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Elevated 3-MGL is part of the diagnostic urinary organic acid profile for the leucine-catabolism block.
  evidence:
  - reference: PMID:32685354
    reference_title: "A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with HMGCLD present with a diagnostic urinary pattern of elevated organic acids such as 3‐hydroxyisovaleric acid (3HIV‐A), 3‐methylglutaconic acid (3MGC‐A), 3‐hydroxy‐3‐methylglutaric acid (3H3MG‐A), 3‐methylglutaric acid (3MG‐A) and in some cases 3‐methylcrotonylglycine."
    explanation: Human biomarker study supports 3-methylglutaric acid as part of the diagnostic organic acid profile.
  notes: 3-Methylglutaric acid is part of the characteristic urinary organic acid profile used for biochemical diagnosis of HMGCLD.
- name: Ketone bodies
  presence: DECREASED
  context: 'Absent or inappropriately low ketones during fasting and illness is a hallmark biochemical finding. Non-ketotic or hypoketotic hypoglycemia distinguishes HMGCLD from other organic acidemias.

    '
  biomarker_term:
    preferred_term: ketone body
    term:
      id: CHEBI:73693
      label: ketone body
  readouts:
  - target: Ketogenesis failure and energy crisis
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Inappropriately low ketone bodies during illness report failure of endogenous ketogenesis.
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia
    explanation: Confirms hypoketotic hypoglycemia as a defining feature.
- name: Acetyl-CoA
  presence: DECREASED
  context: 'Hepatic acetyl-CoA levels are reduced during leucine metabolite loading in HMGCL-deficient liver, contributing to impaired gluconeogenesis and urea cycle activation.

    '
  biomarker_term:
    preferred_term: acetyl-CoA
    term:
      id: CHEBI:15351
      label: acetyl-CoA
  readouts:
  - target: Acyl-CoA disequilibrium and secondary hyperammonemia
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: MONITORING
    interpretation: Lower hepatic acetyl-CoA reports the acyl-CoA disequilibrium mechanism that impairs urea-cycle activation in the HMGCL model.
  evidence:
  - reference: PMID:23861731
    reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: KIC loading also increased levels of several leucine-related acyl-CoAs and reduced acetyl-CoA levels.
    explanation: Direct demonstration of acetyl-CoA depletion in HMGCL-deficient hepatocytes under leucine stress.
- name: Ammonia
  presence: INCREASED
  context: 'Plasma ammonia rises during acute metabolic decompensation, reflecting secondary urea-cycle impairment from acetyl-CoA/N-acetylglutamate limitation.

    '
  biomarker_term:
    preferred_term: ammonia
    term:
      id: CHEBI:16134
      label: ammonia
  readouts:
  - target: Acyl-CoA disequilibrium and secondary hyperammonemia
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: MONITORING
    interpretation: Higher ammonia reports the secondary hyperammonemia branch downstream of impaired acyl-CoA balance.
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
    explanation: Human clinical cohort review identifies hyperammonemia as part of acute HMGCLD decompensation.
genetic:
- name: HMGCL pathogenic variants
  gene_term:
    preferred_term: HMGCL
    term:
      id: hgnc:5005
      label: HMGCL
  inheritance:
  - name: Autosomal recessive
    evidence:
    - reference: PMID:32059735
      reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL.
      explanation: Directly states autosomal recessive inheritance.
  variants:
  - name: c.122G>A (p.Arg41Gln) founder variant
    description: 'A Saudi Arabian founder variant accounting for 77.4% of affected individuals in a 62-patient cohort. This illustrates strong population structure and genotype clustering.

      '
  features: 'Biallelic pathogenic variants in HMGCL cause deficiency of mitochondrial 3-hydroxy-3-methylglutaryl-CoA lyase (EC 4.1.3.4), which catalyzes cleavage of HMG-CoA to acetyl-CoA and acetoacetate. This is the final step of both ketogenesis and leucine degradation. Over 211 patients have been reported worldwide with various HMGCL mutations, with genotype-phenotype correlations influenced by residual enzyme activity and population-specific founder effects.

    '
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This comprehensive data analysis provides a systematic overview on all published cases with HMGCLD including a list of all known HMGCL mutations.
    explanation: Provides the most comprehensive catalog of HMGCL mutations and associated phenotypes.
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: This is the largest cohort of HMGCLD patients reported from Saudi Arabia, signifying this disorder as a likely life-threatening disease, with a high prevalence in the region.
    explanation: Largest regional cohort demonstrating population-specific variant enrichment.
  - reference: CGGV:assertion_f4d084e5-a740-4bfd-a850-d6db900d4a4e-2018-06-26T160000.000Z
    reference_title: "HMGCL / 3-hydroxy-3-methylglutaric aciduria (Definitive)"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HMGCL | HGNC:5005 | 3-hydroxy-3-methylglutaric aciduria | MONDO:0009520 | AR | Definitive"
    explanation: ClinGen classifies the HMGCL-3-hydroxy-3-methylglutaric aciduria gene-disease relationship as definitive with autosomal recessive inheritance.
treatments:
- name: Dietary protein and leucine restriction
  description: 'Restriction of leucine and total protein intake is the cornerstone of long-term management. All patients in contemporary cohorts receive protein-restricted diets, with some also receiving fat restriction. Dietary management is well tolerated and helps prevent metabolic crises.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_mechanisms:
  - target: Leucine catabolic block and organic acid accumulation
    treatment_effect: INHIBITS
    description: Restricting dietary protein and leucine lowers substrate flux into the blocked leucine degradation pathway.
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: All patients have been on long-term protein restriction, and those diagnosed more recently have had additional fat restriction.
    explanation: Confirms universal use of protein restriction in contemporary management.
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our findings suggest that diagnosis at an early stage with careful dietary management may avoid metabolic crises.
    explanation: Large cohort supporting dietary management for crisis prevention.
- name: Avoidance of fasting
  description: 'Prevention of prolonged fasting is critical because ketogenesis failure means the patient cannot generate alternative energy substrates during fasting. Emergency carbohydrate plans are used during illness.

    '
  treatment_term:
    preferred_term: dietary intervention
    term:
      id: MAXO:0000088
      label: dietary intervention
  target_mechanisms:
  - target: Ketogenesis failure and energy crisis
    treatment_effect: MODULATES
    description: Avoiding fasting reduces the need for endogenous ketogenesis and preserves glucose availability during stress.
  evidence:
  - reference: PMID:3099065
    reference_title: "3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: The metabolic crisis develops when the infant is first introduced to dietary protein soon after birth, or later, when a reduced intake of glucose, often during a viral infection, results in a drain on the infant's circulating glucose levels.
    explanation: Identifies fasting and reduced glucose intake as key crisis triggers.
- name: L-carnitine supplementation
  description: 'L-carnitine is commonly prescribed in long-term management to support detoxification and excretion of accumulating organic acids as acylcarnitine conjugates. Used in most patients across contemporary cohorts.

    '
  treatment_term:
    preferred_term: carnitine supplementation
    term:
      id: MAXO:0010006
      label: carnitine supplementation
    therapeutic_agent:
    - preferred_term: carnitine
      term:
        id: CHEBI:17126
        label: carnitine
  target_mechanisms:
  - target: Leucine catabolic block and organic acid accumulation
    treatment_effect: MODULATES
    description: Carnitine supplementation supports acylcarnitine formation and excretion of accumulating organic acid intermediates.
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Most patients take L-carnitine.
    explanation: Confirms widespread use of carnitine supplementation in HMGCLD management.
- name: Exogenous ketone therapy (sodium D,L-3-hydroxybutyrate)
  description: 'Exogenous ketone supplementation (sodium D,L-3-hydroxybutyrate, up to 900 mg/kg/day) bypasses impaired endogenous ketogenesis to provide alternative energy substrates for brain and heart. Used in both acute management and chronic adjunct therapy. Reported as well tolerated and effective in clinical case series.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: 3-hydroxybutyrate
      term:
        id: CHEBI:37054
        label: 3-hydroxybutyrate
  target_mechanisms:
  - target: Ketogenesis failure and energy crisis
    treatment_effect: BYPASSES
    description: Exogenous 3-hydroxybutyrate supplies ketone substrate despite impaired endogenous ketogenesis.
  evidence:
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: five of nine patients have used 900 mg/kg/day of sodium D,L 3-hydroxybutyrate in combination with intravenous dextrose-containing fluids
    explanation: Documents high-dose exogenous ketone use in acute management.
- name: Acute decompensation management
  description: 'Emergency treatment includes rapid glucose provision (IV dextrose and/or frequent oral carbohydrate), cessation of protein intake, and correction of metabolic acidosis and hyperammonemia. Prompt intervention is essential to prevent death.

    '
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  target_phenotypes:
  - preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  - preferred_term: Metabolic acidosis
    term:
      id: HP:0001942
      label: Metabolic acidosis
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  target_mechanisms:
  - target: Ketogenesis failure and energy crisis
    treatment_effect: BYPASSES
    description: Acute dextrose-containing support supplies glucose during crises when ketogenesis is impaired.
  - target: Acyl-CoA disequilibrium and secondary hyperammonemia
    treatment_effect: MODULATES
    description: Crisis management reduces catabolic leucine flux and treats downstream acidosis and hyperammonemia.
  evidence:
  - reference: PMID:3099065
    reference_title: "3-Hydroxy-3-methylglutaryl-coenzyme a lyase deficiency: a review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: In the first year of life infants with HMG-CoA-LD run a high risk of developing severe hypoglycaemia which can lead to death if prompt intervention does not occur.
    explanation: Foundational evidence for the critical importance of prompt acute intervention.
  - reference: PMID:36771238
    reference_title: "Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Dietary management in patients with HMGCL deficiency is well tolerated, and rapid institution of acute supportive metabolic treatment is imperative to optimizing survival and improve outcomes in this disorder.
    explanation: Contemporary confirmation that rapid supportive care is essential for survival.
- name: Newborn screening
  description: 'Tandem mass spectrometry screening using elevated C5-OH (3-hydroxyisovalerylcarnitine) enables presymptomatic diagnosis. Confirmation follows with urine organic acid analysis and molecular testing of HMGCL. Early detection allows initiation of dietary management before metabolic decompensation.

    '
  treatment_term:
    preferred_term: disease screening
    term:
      id: MAXO:0000124
      label: disease screening
  target_phenotypes:
  - preferred_term: Metabolic acidosis
    term:
      id: HP:0001942
      label: Metabolic acidosis
  - preferred_term: Hypoglycemia
    term:
      id: HP:0001943
      label: Hypoglycemia
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  evidence:
  - reference: PMID:35646072
    reference_title: "HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Our findings suggest that diagnosis at an early stage with careful dietary management may avoid metabolic crises.
    explanation: Supports early detection and treatment to prevent metabolic crises.
- name: Genetic counseling
  description: 'Genetic counseling for affected families including discussion of autosomal recessive inheritance, 25% recurrence risk, and options for carrier testing, prenatal diagnosis, and preimplantation genetic testing.

    '
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: MAXO:0000079
      label: genetic counseling
  evidence:
  - reference: PMID:32059735
    reference_title: "3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL.
    explanation: Autosomal recessive etiology supports genetic counseling for affected families.
- name: Carglumic acid for hyperammonemia
  description: 'Carglumic acid (N-carbamyl-L-glutamic acid) is a synthetic analog of N-acetylglutamate that can rescue hyperammonemia by activating carbamoyl phosphate synthetase 1 in the urea cycle, bypassing the acetyl-CoA-dependent NAG synthesis that is impaired in HMGCLD. Demonstrated effective in a mouse model of HMGCLD.

    '
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: carglumic acid
      term:
        id: CHEBI:71028
        label: carglumic acid
  target_phenotypes:
  - preferred_term: Hyperammonemia
    term:
      id: HP:0001987
      label: Hyperammonemia
  target_mechanisms:
  - target: Acyl-CoA disequilibrium and secondary hyperammonemia
    treatment_effect: BYPASSES
    description: Carglumic acid substitutes for N-acetylglutamate to activate carbamoyl phosphate synthetase 1 when acetyl-CoA-dependent NAG synthesis is impaired.
  evidence:
  - reference: PMID:23861731
    reference_title: "A liver-specific defect of Acyl-CoA degradation produces hyperammonemia, hypoglycemia and a distinct hepatic Acyl-CoA pattern."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: KIC-induced hyperammonemia improved following administration of carglumate (N-carbamyl-L-glutamic acid), which substitutes for the product of an acetyl-CoA-dependent reaction essential for urea cycle function
    explanation: Demonstrates carglumate efficacy for hyperammonemia in the HMGCL KO mouse model.
notes: 'The 2024 discovery of non-enzymatic mitochondrial protein acylation (3MGCylation) by reactive trans-3-methylglutaconyl-CoA intermediates (PMID:39195517) represents an active research frontier that may help explain tissue-specific injury patterns. If validated in human tissues, this mechanism could open new therapeutic directions targeting reactive metabolite chemistry. The Devanapalli et al. 2023 case report on sodium D,L-3-hydroxybutyrate therapy (doi:10.20517/jtgg.2023.12) provides additional clinical detail on exogenous ketone use but lacks a PubMed-indexed PMID.

  '
references:
- reference: PMID:7807935
  title: Fatal cardiomyopathy associated with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
- reference: PMID:34573903
  title: An Atypical Case of Head Tremor and Extensive White Matter in an Adult Female Caused by 3-Hydroxy-3-methylglutaryl-CoA Lyase Deficiency.
- reference: DOI:10.20517/jtgg.2023.12
  title: Use of sodium D, L-3-hydroxybutyrate as adjunct therapy in two siblings with HMG-CoA lyase deficiency
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: Use of sodium D, L-3-hydroxybutyrate as adjunct therapy in two siblings with HMG-CoA lyase deficiency
    supporting_text: 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase deficiency is a rare autosomal recessive mitochondrial disease characterised by recurrent life-threatening metabolic crises generally presenting in neonates or infancy during catabolic stress triggered by prolonged fasting or intercurrent illness.
- reference: DOI:10.3390/metabo14080421
  title: Factors Affecting Non-Enzymatic Protein Acylation by trans-3-Methylglutaconyl Coenzyme A
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: Factors Affecting Non-Enzymatic Protein Acylation by trans-3-Methylglutaconyl Coenzyme A
    supporting_text: The leucine catabolism pathway intermediate, trans-3-methylglutaconyl (3MGC) CoA, is considered to be the precursor of 3MGC acid, a urinary organic acid associated with specific inborn errors of metabolism (IEM). trans-3MGC CoA is an unstable molecule that can undergo a sequence of non-enzymatic chemical reactions that lead to either 3MGC acid or protein 3MGCylation.
- reference: PMID:17173698
  title: Mutations underlying 3-hydroxy-3-methylglutaryl CoA lyase deficiency in the Saudi population.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4).'
    supporting_text: '3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4).'
- reference: PMID:17391418
  title: 'The cost-effectiveness of expanding newborn screening for up to 21 inherited metabolic disorders using tandem mass spectrometry: results from a decision-analytic model.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2007 Mar-Apr;10(2):83-97. doi: 10.1111/j.1524-4733.2006.00156.x.'
    supporting_text: '2007 Mar-Apr;10(2):83-97. doi: 10.1111/j.1524-4733.2006.00156.x.'
- reference: PMID:19932602
  title: '[Late onset 3-HMG-CoA lyase deficiency: a rare but treatable disorder].'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2010 Jan;17(1):10-3. doi: 10.1016/j.arcped.2009.09.022.'
    supporting_text: '2010 Jan;17(1):10-3. doi: 10.1016/j.arcped.2009.09.022.'
- reference: PMID:24706027
  title: Ketone body metabolism and its defects.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2014 Jul;37(4):541-51. doi: 10.1007/s10545-014-9704-9.'
    supporting_text: '2014 Jul;37(4):541-51. doi: 10.1007/s10545-014-9704-9.'
- reference: PMID:26041581
  title: Disturbance of redox homeostasis as a contributing underlying pathomechanism of brain and liver alterations in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2015 Nov;38(6):1021-8. doi: 10.1007/s10545-015-9863-3.'
    supporting_text: '2015 Nov;38(6):1021-8. doi: 10.1007/s10545-015-9863-3.'
- reference: PMID:26997609
  title: The management of pregnancy and delivery in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2016 Jun;170(6):1600-2. doi: 10.1002/ajmg.a.37620.'
    supporting_text: '2016 Jun;170(6):1600-2. doi: 10.1002/ajmg.a.37620.'
- reference: PMID:28220407
  title: Favourable Outcome in Two Pregnancies in a Patient with 3-Hydroxy-3-Methylglutaryl-CoA Lyase Deficiency.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Santosa D(1), Donner MG(2)(3), Vom Dahl S(2), Fleisch M(4), Hoehn T(5), Mayatepek E(5), Heldt K(6), Niehues T(6), Häussinger D(2).
    supporting_text: Santosa D(1), Donner MG(2)(3), Vom Dahl S(2), Fleisch M(4), Hoehn T(5), Mayatepek E(5), Heldt K(6), Niehues T(6), Häussinger D(2).
- reference: PMID:28396157
  title: Coupled brain and urine spectroscopy - in vivo metabolomic characterization of HMG-CoA lyase deficiency in 5 patients.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: 3-Hydroxy-3-Methylglutaryl-Coenzyme A (HMG-CoA) lyase deficiency is a rare inborn error of leucine metabolism and ketogenesis.
    supporting_text: 3-Hydroxy-3-Methylglutaryl-Coenzyme A (HMG-CoA) lyase deficiency is a rare inborn error of leucine metabolism and ketogenesis.
- reference: PMID:28583327
  title: '3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: Clinical presentation and outcome in a series of 37 patients.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2017 Jul;121(3):206-215. doi: 10.1016/j.ymgme.2017.05.014.'
    supporting_text: '2017 Jul;121(3):206-215. doi: 10.1016/j.ymgme.2017.05.014.'
- reference: PMID:32685354
  title: A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2020 Apr 14;54(1):79-86. doi: 10.1002/jmd2.12118. eCollection 2020 Jul.'
    supporting_text: '2020 Apr 14;54(1):79-86. doi: 10.1002/jmd2.12118. eCollection 2020 Jul.'
- reference: PMID:34329521
  title: 'Inborn errors of metabolism and coronavirus disease 2019: Evaluation of the metabolic outcome.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Infectious diseases can result in a catabolic state and possibly trigger an acute metabolic decompensation in inborn errors of metabolism (IEM), which could be life threatening.
    supporting_text: Infectious diseases can result in a catabolic state and possibly trigger an acute metabolic decompensation in inborn errors of metabolism (IEM), which could be life threatening.
- reference: PMID:34573903
  title: An Atypical Case of Head Tremor and Extensive White Matter in an Adult Female Caused by 3-Hydroxy-3-methylglutaryl-CoA Lyase Deficiency.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2021 Aug 28;11(9):1561. doi: 10.3390/diagnostics11091561.'
    supporting_text: '2021 Aug 28;11(9):1561. doi: 10.3390/diagnostics11091561.'
- reference: PMID:37603033
  title: Collaborative evaluation study on 18 candidate diseases for newborn screening in 1.77 million samples.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2023 Nov;46(6):1043-1062. doi: 10.1002/jimd.12671.'
    supporting_text: '2023 Nov;46(6):1043-1062. doi: 10.1002/jimd.12671.'
- reference: PMID:38567177
  title: 'Inborn Errors of Ketogenesis: Novel Variants, Clinical Presentation, and Follow-Up in a Series of Four Patients.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2022 Jul 12;13(1):22-28. doi: 10.1055/s-0042-1749362. eCollection 2024 Mar.'
    supporting_text: '2022 Jul 12;13(1):22-28. doi: 10.1055/s-0042-1749362. eCollection 2024 Mar.'
- reference: PMID:40937535
  title: 'Evaluation of Newborn Screening for Diseases Using C5-OH as a Marker: Systematic Review of the Literature and Evaluation of 17 Years of C5-OH Screening in the Netherlands.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2025 Sep;48(5):e70088. doi: 10.1002/jimd.70088.'
    supporting_text: '2025 Sep;48(5):e70088. doi: 10.1002/jimd.70088.'
- reference: PMID:41156202
  title: 'Perioperative Anesthetic Considerations in HMG-CoA Lyase Deficiency: Case Report and Literature Review.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2025 Oct 17;14(20):7332. doi: 10.3390/jcm14207332.'
    supporting_text: '2025 Oct 17;14(20):7332. doi: 10.3390/jcm14207332.'
- reference: PMID:41323099
  title: 'Timely intervention in HMG-CoA Lyase deficiency: The role of newborn screening, metabolic management, and genomic sequencing.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2025 Nov 14;45:101278. doi: 10.1016/j.ymgmr.2025.101278. eCollection 2025 Dec.'
    supporting_text: '2025 Nov 14;45:101278. doi: 10.1016/j.ymgmr.2025.101278. eCollection 2025 Dec.'
- reference: PMID:41636194
  title: Novel FUCA1 variants in two families, including the first report of a contiguous gene deletion syndrome involving FUCA1 and HMGCL.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: Novel FUCA1 variants in two families, including the first report of a contiguous gene deletion syndrome involving FUCA1 and HMGCL
    supporting_text: Fucosidosis is a rare, autosomal recessive lysosomal storage disorder caused by deficiency of an alpha-L-fucosidase due to pathogenic variants in the FUCA1 gene, leading to the accumulation of fucoglyco-conjugates in the lysosomes of the liver, brain, skin and other organs.
- reference: PMID:41872807
  title: '3-hydroxy-3-methylglutaryl coenzyme A lyase deficiency in an adolescent male: a case report and narrative review of Chinese patients.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2026 Mar 23;26(1):390. doi: 10.1186/s12887-026-06731-8.'
    supporting_text: '2026 Mar 23;26(1):390. doi: 10.1186/s12887-026-06731-8.'
- reference: PMID:9463337
  title: 'HMG CoA lyase deficiency: identification of five causal point mutations in codons 41 and 42, including a frequent Saudi Arabian mutation, R41Q.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1998 Feb;62(2):295-300. doi: 10.1086/301730.'
    supporting_text: '1998 Feb;62(2):295-300. doi: 10.1086/301730.'
- reference: PMID:9927656
  title: Mitochondrial disease in superoxide dismutase 2 mutant mice.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '1999 Feb 2;96(3):846-51. doi: 10.1073/pnas.96.3.846.'
    supporting_text: '1999 Feb 2;96(3):846-51. doi: 10.1073/pnas.96.3.846.'
- reference: DOI:10.1186/s13023-020-1319-7
  title: '3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL .
    supporting_text: 3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL .
- reference: DOI:10.1371/journal.pone.0060581
  title: A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern
    supporting_text: A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern
- reference: DOI:10.3389/fgene.2022.880464
  title: 'HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: 3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is a rare inborn error of leucine degradation and ketone body synthesis, caused by homozygous or compound heterozygous disease-causing variants in HMGCL.
    supporting_text: 3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is a rare inborn error of leucine degradation and ketone body synthesis, caused by homozygous or compound heterozygous disease-causing variants in HMGCL.
- reference: DOI:10.3390/biomedicines12071563
  title: 3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: 3-Hydroxy-3-methylglutaric acidemia (HMGA) is a neurometabolic inherited disorder characterized by the predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in the brain and biological fluids of patients.
    supporting_text: 3-Hydroxy-3-methylglutaric acidemia (HMGA) is a neurometabolic inherited disorder characterized by the predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in the brain and biological fluids of patients.
- reference: DOI:10.3390/nu15030531
  title: Treatment of HMG-CoA Lyase Deficiency—Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-falcon.md
  findings:
  - statement: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
    supporting_text: 3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.
- reference: PMID:35646072
  title: 'HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients.'
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2022 May 13;13:880464. doi: 10.3389/fgene.2022.880464. eCollection 2022.'
    supporting_text: '2022 May 13;13:880464. doi: 10.3389/fgene.2022.880464. eCollection 2022.'
- reference: PMID:36771238
  title: Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases.
  found_in:
  - 3-Hydroxy-3-Methylglutaric_Aciduria-deep-research-openscientist.md
  findings:
  - statement: '2023 Jan 19;15(3):531. doi: 10.3390/nu15030531.'
    supporting_text: '2023 Jan 19;15(3):531. doi: 10.3390/nu15030531.'

📚

References & Deep Research

References

PMID:7807935

Fatal cardiomyopathy associated with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

No top-level findings curated for this source.

PMID:34573903

An Atypical Case of Head Tremor and Extensive White Matter in an Adult Female Caused by 3-Hydroxy-3-methylglutaryl-CoA Lyase Deficiency.

No top-level findings curated for this source.

DOI:10.20517/jtgg.2023.12

Use of sodium D, L-3-hydroxybutyrate as adjunct therapy in two siblings with HMG-CoA lyase deficiency

1 finding

Use of sodium D, L-3-hydroxybutyrate as adjunct therapy in two siblings with HMG-CoA lyase deficiency

"3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) lyase deficiency is a rare autosomal recessive mitochondrial disease characterised by recurrent life-threatening metabolic crises generally presenting in neonates or infancy during catabolic stress triggered by prolonged fasting or intercurrent illness."

DOI:10.3390/metabo14080421

Factors Affecting Non-Enzymatic Protein Acylation by trans-3-Methylglutaconyl Coenzyme A

1 finding

Factors Affecting Non-Enzymatic Protein Acylation by trans-3-Methylglutaconyl Coenzyme A

"The leucine catabolism pathway intermediate, trans-3-methylglutaconyl (3MGC) CoA, is considered to be the precursor of 3MGC acid, a urinary organic acid associated with specific inborn errors of metabolism (IEM). trans-3MGC CoA is an unstable molecule that can undergo a sequence of non-enzymatic..."

PMID:17173698

Mutations underlying 3-hydroxy-3-methylglutaryl CoA lyase deficiency in the Saudi population.

1 finding

3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4).

"3-hydroxy-3-methylglutaric aciduria (3HMG, McKusick: 246450) is an autosomal recessive branched chain organic aciduria caused by deficiency of the enzyme 3-Hydroxy-3-Methylglutaryl CoA lyase (HL, HMGCL, EC 4.1.3.4)."

PMID:17391418

The cost-effectiveness of expanding newborn screening for up to 21 inherited metabolic disorders using tandem mass spectrometry: results from a decision-analytic model.

1 finding

2007 Mar-Apr;10(2):83-97. doi: 10.1111/j.1524-4733.2006.00156.x.

"2007 Mar-Apr;10(2):83-97. doi: 10.1111/j.1524-4733.2006.00156.x."

PMID:19932602

[Late onset 3-HMG-CoA lyase deficiency: a rare but treatable disorder].

1 finding

2010 Jan;17(1):10-3. doi: 10.1016/j.arcped.2009.09.022.

"2010 Jan;17(1):10-3. doi: 10.1016/j.arcped.2009.09.022."

PMID:24706027

Ketone body metabolism and its defects.

1 finding

2014 Jul;37(4):541-51. doi: 10.1007/s10545-014-9704-9.

"2014 Jul;37(4):541-51. doi: 10.1007/s10545-014-9704-9."

PMID:26041581

Disturbance of redox homeostasis as a contributing underlying pathomechanism of brain and liver alterations in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

1 finding

2015 Nov;38(6):1021-8. doi: 10.1007/s10545-015-9863-3.

"2015 Nov;38(6):1021-8. doi: 10.1007/s10545-015-9863-3."

PMID:26997609

The management of pregnancy and delivery in 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

1 finding

2016 Jun;170(6):1600-2. doi: 10.1002/ajmg.a.37620.

"2016 Jun;170(6):1600-2. doi: 10.1002/ajmg.a.37620."

PMID:28220407

Favourable Outcome in Two Pregnancies in a Patient with 3-Hydroxy-3-Methylglutaryl-CoA Lyase Deficiency.

1 finding

Santosa D(1), Donner MG(2)(3), Vom Dahl S(2), Fleisch M(4), Hoehn T(5), Mayatepek E(5), Heldt K(6), Niehues T(6), Häussinger D(2).

"Santosa D(1), Donner MG(2)(3), Vom Dahl S(2), Fleisch M(4), Hoehn T(5), Mayatepek E(5), Heldt K(6), Niehues T(6), Häussinger D(2)."

PMID:28396157

Coupled brain and urine spectroscopy - in vivo metabolomic characterization of HMG-CoA lyase deficiency in 5 patients.

1 finding

3-Hydroxy-3-Methylglutaryl-Coenzyme A (HMG-CoA) lyase deficiency is a rare inborn error of leucine metabolism and ketogenesis.

"3-Hydroxy-3-Methylglutaryl-Coenzyme A (HMG-CoA) lyase deficiency is a rare inborn error of leucine metabolism and ketogenesis."

PMID:28583327

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: Clinical presentation and outcome in a series of 37 patients.

1 finding

2017 Jul;121(3):206-215. doi: 10.1016/j.ymgme.2017.05.014.

"2017 Jul;121(3):206-215. doi: 10.1016/j.ymgme.2017.05.014."

PMID:32685354

A newborn screening approach to diagnose 3-hydroxy-3-methylglutaryl-CoA lyase deficiency.

1 finding

2020 Apr 14;54(1):79-86. doi: 10.1002/jmd2.12118. eCollection 2020 Jul.

"2020 Apr 14;54(1):79-86. doi: 10.1002/jmd2.12118. eCollection 2020 Jul."

PMID:34329521

Inborn errors of metabolism and coronavirus disease 2019: Evaluation of the metabolic outcome.

1 finding

Infectious diseases can result in a catabolic state and possibly trigger an acute metabolic decompensation in inborn errors of metabolism (IEM), which could be life threatening.

"Infectious diseases can result in a catabolic state and possibly trigger an acute metabolic decompensation in inborn errors of metabolism (IEM), which could be life threatening."

PMID:34573903

An Atypical Case of Head Tremor and Extensive White Matter in an Adult Female Caused by 3-Hydroxy-3-methylglutaryl-CoA Lyase Deficiency.

1 finding

2021 Aug 28;11(9):1561. doi: 10.3390/diagnostics11091561.

"2021 Aug 28;11(9):1561. doi: 10.3390/diagnostics11091561."

PMID:37603033

Collaborative evaluation study on 18 candidate diseases for newborn screening in 1.77 million samples.

1 finding

2023 Nov;46(6):1043-1062. doi: 10.1002/jimd.12671.

"2023 Nov;46(6):1043-1062. doi: 10.1002/jimd.12671."

PMID:38567177

Inborn Errors of Ketogenesis: Novel Variants, Clinical Presentation, and Follow-Up in a Series of Four Patients.

1 finding

2022 Jul 12;13(1):22-28. doi: 10.1055/s-0042-1749362. eCollection 2024 Mar.

"2022 Jul 12;13(1):22-28. doi: 10.1055/s-0042-1749362. eCollection 2024 Mar."

PMID:40937535

Evaluation of Newborn Screening for Diseases Using C5-OH as a Marker: Systematic Review of the Literature and Evaluation of 17 Years of C5-OH Screening in the Netherlands.

1 finding

2025 Sep;48(5):e70088. doi: 10.1002/jimd.70088.

"2025 Sep;48(5):e70088. doi: 10.1002/jimd.70088."

PMID:41156202

Perioperative Anesthetic Considerations in HMG-CoA Lyase Deficiency: Case Report and Literature Review.

1 finding

2025 Oct 17;14(20):7332. doi: 10.3390/jcm14207332.

"2025 Oct 17;14(20):7332. doi: 10.3390/jcm14207332."

PMID:41323099

Timely intervention in HMG-CoA Lyase deficiency: The role of newborn screening, metabolic management, and genomic sequencing.

1 finding

2025 Nov 14;45:101278. doi: 10.1016/j.ymgmr.2025.101278. eCollection 2025 Dec.

"2025 Nov 14;45:101278. doi: 10.1016/j.ymgmr.2025.101278. eCollection 2025 Dec."

PMID:41636194

Novel FUCA1 variants in two families, including the first report of a contiguous gene deletion syndrome involving FUCA1 and HMGCL.

1 finding

Novel FUCA1 variants in two families, including the first report of a contiguous gene deletion syndrome involving FUCA1 and HMGCL

"Fucosidosis is a rare, autosomal recessive lysosomal storage disorder caused by deficiency of an alpha-L-fucosidase due to pathogenic variants in the FUCA1 gene, leading to the accumulation of fucoglyco-conjugates in the lysosomes of the liver, brain, skin and other organs."

PMID:41872807

3-hydroxy-3-methylglutaryl coenzyme A lyase deficiency in an adolescent male: a case report and narrative review of Chinese patients.

1 finding

2026 Mar 23;26(1):390. doi: 10.1186/s12887-026-06731-8.

"2026 Mar 23;26(1):390. doi: 10.1186/s12887-026-06731-8."

PMID:9463337

HMG CoA lyase deficiency: identification of five causal point mutations in codons 41 and 42, including a frequent Saudi Arabian mutation, R41Q.

1 finding

1998 Feb;62(2):295-300. doi: 10.1086/301730.

"1998 Feb;62(2):295-300. doi: 10.1086/301730."

PMID:9927656

Mitochondrial disease in superoxide dismutase 2 mutant mice.

1 finding

1999 Feb 2;96(3):846-51. doi: 10.1073/pnas.96.3.846.

"1999 Feb 2;96(3):846-51. doi: 10.1073/pnas.96.3.846."

DOI:10.1186/s13023-020-1319-7

3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency: one disease - many faces

1 finding

3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL .

"3-hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is an autosomal recessive disorder of ketogenesis and leucine degradation due to mutations in HMGCL ."

DOI:10.1371/journal.pone.0060581

A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern

1 finding

A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern

"A Liver-Specific Defect of Acyl-CoA Degradation Produces Hyperammonemia, Hypoglycemia and a Distinct Hepatic Acyl-CoA Pattern"

DOI:10.3389/fgene.2022.880464

HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients

1 finding

3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is a rare inborn error of leucine degradation and ketone body synthesis, caused by homozygous or compound heterozygous disease-causing variants in HMGCL.

"3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMG-CoA lyase) is a rare inborn error of leucine degradation and ketone body synthesis, caused by homozygous or compound heterozygous disease-causing variants in HMGCL."

DOI:10.3390/biomedicines12071563

3-Hydroxy-3-Methylglutaric Acid Disrupts Brain Bioenergetics, Redox Homeostasis, and Mitochondrial Dynamics and Affects Neurodevelopment in Neonatal Wistar Rats

1 finding

3-Hydroxy-3-methylglutaric acidemia (HMGA) is a neurometabolic inherited disorder characterized by the predominant accumulation of 3-hydroxy-3-methylglutaric acid (HMG) in the brain and biological fluids of patients.

DOI:10.3390/nu15030531

Treatment of HMG-CoA Lyase Deficiency—Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases

1 finding

3-Hydroxy-3-Methylglutaryl-CoA Lyase (HMGCL) deficiency can be a very severe disorder that typically presents with acute metabolic decompensation with features of hypoketotic hypoglycemia, hyperammonemia, and metabolic acidosis.

PMID:35646072

HMG-CoA Lyase Deficiency: A Retrospective Study of 62 Saudi Patients.

1 finding

2022 May 13;13:880464. doi: 10.3389/fgene.2022.880464. eCollection 2022.

"2022 May 13;13:880464. doi: 10.3389/fgene.2022.880464. eCollection 2022."

PMID:36771238

Treatment of HMG-CoA Lyase Deficiency-Longitudinal Data on Clinical and Nutritional Management of 10 Australian Cases.

1 finding

2023 Jan 19;15(3):531. doi: 10.3390/nu15030531.

"2023 Jan 19;15(3):531. doi: 10.3390/nu15030531."

Deep Research

Falcon ▸

Disease Pathophysiology Research Template

Edison Scientific Literature 19 citations 2026-02-23T23:46:59.092195

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).

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)

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)

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)

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)

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)

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)

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)

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)

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)

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)

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

(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.

OpenScientist ▸

1. Disease Information

openscientist-autonomous 23 citations 2026-05-04T22:56:41.277250

1. Disease Information

Overview

3-Hydroxy-3-methylglutaric aciduria (HMGCLD) is a rare inborn error of ketone body synthesis and leucine degradation. It was first described in the 1970s and belongs to the broader category of organic acidurias. The deficient enzyme, HMG-CoA lyase, cleaves 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) into acetoacetate and acetyl-CoA in the mitochondrial matrix. This reaction is the terminal step in leucine catabolism and the final enzymatic step in the ketogenesis pathway. Consequently, enzyme deficiency leads to both impaired leucine degradation (with accumulation of upstream metabolites) and impaired ketone body production (inability to generate the alternative fuel source during fasting).

As described by Grünert et al. (2017): "3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is a rare inborn error of ketone body synthesis and leucine degradation, caused by mutations in the HMGCL gene" (PMID: 28583327).

Key Identifiers

Database	Identifier
OMIM	246450 (phenotype); 613898 (gene)
MONDO	MONDO:0009520
Orphanet	ORPHA:20
ICD-10	E71.111
ICD-11	5C50.04
MeSH	C536914
KEGG Disease	H00179
Gene (HGNC)	HMGCL (HGNC:5005)
UniProt	P35914
EC Number	4.1.3.4

Synonyms and Alternative Names

HMG-CoA lyase deficiency
HMGCLD
3-Hydroxy-3-methylglutaryl-CoA lyase deficiency
3-HMG-CoA lyase deficiency
Hydroxymethylglutaric aciduria
HL deficiency
3-HMG aciduria
3-Hydroxy-3-methylglutaricaciduria

Information Sources

Information is derived from aggregated disease-level resources (OMIM, Orphanet, GeneReviews, HPO, ClinVar) supplemented by published case series, cohort studies, and individual patient reports in the peer-reviewed literature.

2. Etiology

Disease Causal Factors

HMGCLD is exclusively a genetic disorder. The primary cause is biallelic (homozygous or compound heterozygous) loss-of-function mutations in the HMGCL gene located on chromosome 1p36.11. The gene encodes a 325-amino acid mitochondrial protein (UniProt: P35914) that functions as a homodimer.

Genetic Risk Factors

Causal gene: HMGCL (HGNC:5005; OMIM gene: 613898)
Pathogenic variants: 147 classified pathogenic/likely pathogenic variants in ClinVar
Founder mutations:
R41Q (c.122G>A): Found in 89% of Saudi alleles. Zayed et al. (2006) reported: "We detected the common missense mutation R41Q in 89% of the tested alleles (64 alleles). 2 alleles carried the frame shift mutation F305fs (-2) and the last two alleles had a novel splice site donor IVS6+1G>A mutation" (PMID: 17173698)
Codons 41 and 42 are mutational hotspots, accounting for 26% of all mutant alleles in one large study (PMID: 9463337)
In the Chinese population, c.122G>A (R41Q) is also the most prevalent pathogenic variant (PMID: 41872807)
Consanguinity is a major risk factor, particularly in populations with high rates of consanguineous marriage (Saudi Arabia, other Middle Eastern and North African populations). A Saudi retrospective cohort of 62 patients highlights the high prevalence in consanguineous populations (PMID: 35646072)

Environmental Risk Factors

While the disease is fundamentally genetic, environmental triggers precipitate acute metabolic decompensation: - Fasting (the most critical trigger — impaired ketogenesis cannot provide alternative fuel) - Intercurrent infections with fever and catabolism - High-protein diet (excessive leucine intake) - Surgical or physiological stress (PMID: 41156202) - Pregnancy and labor (PMID: 26997609; PMID: 28220407)

COVID-19 infection has been documented as a trigger for metabolic decompensation in at least one HMGCLD patient (PMID: 34329521).

Protective Factors

Early diagnosis (especially via newborn screening) is the most significant protective factor
Dietary management with protein/leucine restriction and fat restriction
L-carnitine supplementation to enhance organic acid excretion
Avoidance of prolonged fasting
Emergency protocols during intercurrent illness (glucose infusion, sodium D,L-3-hydroxybutyrate)

Gene-Environment Interactions

The disease manifests through a gene-environment interaction model: the genetic defect creates vulnerability, but acute clinical crises are precipitated by environmental stressors (fasting, infection, catabolism). Patients can remain stable between crises with appropriate environmental management. As noted: "the therapeutical [approach] is mainly preventive and allows a very good prognosis for this disease" (PMID: 19932602). The lack of genotype-phenotype correlation further suggests that "the clinical course of HMGCLD cannot be predicted accurately from HMGCL genotype" (PMID: 28583327), implying that environmental factors and modifiers significantly influence outcome.

3. Phenotypes

Core Clinical Phenotypes

Very Frequent Phenotypes (99-80% of patients)

HPO Term	Phenotype	Frequency	Type
HP:0001942	Metabolic acidosis	~100% during crises	Laboratory abnormality
HP:0001985	Hypoketotic hypoglycemia	>90%	Laboratory abnormality
HP:0001987	Hyperammonemia	~95% during crises	Laboratory abnormality
HP:0003344	3-Methylglutaric aciduria	~100%	Laboratory abnormality

Frequent Phenotypes (79-30% of patients)

HPO Term	Phenotype	Frequency	Type
HP:0001250	Seizures	~50%	Neurological symptom
HP:0001252	Hypotonia	~32%	Physical manifestation
HP:0001254	Lethargy	Common	Clinical sign
HP:0002572	Episodic vomiting	~50%	Symptom
HP:0002240	Hepatomegaly	~38-50%	Clinical sign
HP:0002910	Elevated hepatic transaminases	~70%	Laboratory abnormality
HP:0002151	Increased circulating lactate	~58%	Laboratory abnormality
HP:0002500	Abnormal cerebral white matter morphology	~47.1%	Neuroimaging
HP:0002134	Basal ganglia abnormalities	~17.6%	Neuroimaging
HP:0001903	Anemia	Frequent	Laboratory abnormality

Occasional Phenotypes (29-5% of patients)

HPO Term	Phenotype	Frequency	Type
HP:0001259	Coma	Occasional	Neurological
HP:0001298	Encephalopathy	~15%	Neurological
HP:0001263	Psychomotor retardation	~50% (long-term outcome)	Developmental
HP:0001336	Myoclonus	~15%	Neurological
HP:0000980	Pallor	~29%	Physical sign
HP:0001944	Dehydration	~9%	Clinical sign

Very Rare Phenotypes (<5% of patients)

HPO Term	Phenotype	Type
HP:0001644	Dilated cardiomyopathy	Cardiovascular
HP:0001735	Acute pancreatitis	Gastrointestinal
HP:0002352	Leukoencephalopathy	Neuroimaging
HP:0001251	Ataxia	Neurological
HP:0001257	Spasticity	Neurological
HP:0000256	Macrocephaly	Physical finding

Phenotype Characteristics

Age of onset: Approximately 50% present in the neonatal period (first 5 days of life) and 76.5% are diagnosed during infancy. A Chinese cohort study reported: "76.5% were diagnosed during infancy, while 35.3% were identified through newborn screening protocols. Acute metabolic disturbances were reported in 88.2% of patients" (PMID: 41872807). In the largest European cohort: "In 50% of the patients, the disorder manifested neonatally, mostly within the first days of life. Only 8% of patients presented after one year of age" (PMID: 28583327). Late-onset forms exist, with presentations documented as late as adulthood, including a case of head tremor and extensive white matter changes in an adult female (PMID: 34573903), and a late-onset case in a 3-year-old (PMID: 19932602).

Symptom progression: Episodic with acute crises superimposed on a background that may be normal or show progressive neurological decline. Between episodes, patients can be asymptomatic. However, each decompensation episode risks cumulative neurological damage. White matter abnormalities may persist and progress even between crises (PMID: 28396157).

Quality of life impact: Significant. Dietary restrictions, need for emergency vigilance during illness, frequent hospitalizations, and potential developmental delays substantially affect daily functioning. Approximately 50% of patients develop some degree of psychomotor deficit.

4. Genetic/Molecular Information

Causal Gene

Gene: HMGCL (3-hydroxymethyl-3-methylglutaryl-CoA lyase, mitochondrial)
HGNC ID: HGNC:5005
NCBI Gene ID: 3155
Ensembl: ENSG00000117305
Chromosomal location: 1p36.11 (complement: 23,801,885-23,825,429 on GRCh38)
OMIM Gene: 613898
Transcript: NM_000191.3

Protein

UniProt: P35914
Length: 325 amino acids (34,360 Da)
Structure: Homodimer (disulfide-linked); can form homotetramers
Subcellular localization: Mitochondrial matrix (primary); also peroxisome
Pfam domain: HMGL-like
Crystal structures: PDB 2CW6 (2.10 Å), 3MP3, 3MP4, 3MP5
AlphaFold: AF-P35914
Catalytic reaction: (3S)-3-hydroxy-3-methylglutaryl-CoA → acetoacetate + acetyl-CoA
Tissue expression: Highest in liver; expressed in pancreas, kidney, intestine, testis, fibroblasts, lymphoblasts; very low in brain and skeletal muscle

Pathogenic Variants

Total in ClinVar: 147 pathogenic/likely pathogenic variants

Key mutations and their characteristics:

Variant	Type	Population	Frequency	Reference
c.122G>A (p.Arg41Gln, R41Q)	Missense	Saudi Arabia, China	89% of Saudi alleles	PMID: 17173698
c.124G>C (p.Asp42His, D42H)	Missense	Global	Recurrent	PMID: 9463337
c.125A>G (p.Asp42Gly, D42G)	Missense	Global	Recurrent	PMID: 9463337
c.126C>A (p.Asp42Glu, D42E)	Missense	Global	Recurrent	PMID: 9463337
c.121C>T (p.Arg41Ter, R41X)	Nonsense	Non-Saudi	Rare	PMID: 9463337
c.133C>T (p.Gln45Ter)	Nonsense	Chinese	Novel	PMID: 41872807
F305fs(-2)	Frameshift	Saudi Arabia	Minority	PMID: 17173698
IVS6+1G>A	Splice site	Saudi Arabia	Minority	PMID: 17173698
c.252+1G>A	Splice site	Chinese	Recurrent	PMID: 41872807
c.494G>A (p.Arg165Gln)	Missense	French	Novel	PMID: 19932602
c.820G>A (p.Gly274Arg)	Missense	French	Novel	PMID: 19932602
64.5 kb deletion	Structural	Turkish	Unique	PMID: 41636194

Functional consequences: All pathogenic variants cause loss of function. Recombinant enzyme studies demonstrated that "all four missense mutations in codons 41 and 42 cause a marked decrease in HL activity" (PMID: 9463337). Codons 41 and 42 are critical for catalytic function and "account for a disproportionate 21 (26%) of 82 of mutant alleles" in a large cohort.

Germline origin: All variants are germline (no somatic involvement), consistent with this being a constitutional genetic disorder.

Genotype-phenotype correlation: Absent. Grünert et al. (2017) concluded: "In agreement with previous reports, no clear genotype-phenotype correlation could be found" (PMID: 28583327). This implies environmental factors, modifier genes, and timing of metabolic stressors play significant roles in clinical outcome.

Modifier Genes

No specific modifier genes have been identified. The lack of genotype-phenotype correlation and variable phenotypic expression despite identical genotypes (especially in consanguineous populations) suggest genetic modifiers exist but remain uncharacterized.

Epigenetic Information

No disease-specific epigenetic modifications have been reported for HMGCLD.

Chromosomal Abnormalities

A 64.5 kb contiguous gene deletion at 1p36.11 encompassing HMGCL exons 1-6, FUCA1, and CNR2 has been reported, causing concurrent HMGCLD and fucosidosis (PMID: 41636194). This is the first reported case of combined fucosidosis and HMG-CoA lyase deficiency resulting from a contiguous gene deletion.

5. Environmental Information

Environmental Factors

HMGCLD is a purely genetic disorder with no environmental causative factors. However, environmental stressors are critical modulators of disease expression:

Fasting: The single most important precipitant. Impaired ketogenesis means the body cannot produce ketone bodies as alternative fuel during glucose depletion.
Febrile illness: Increases metabolic demand and catabolism, triggering leucine breakdown and accumulation of toxic metabolites.
Gastrointestinal illness: Vomiting and diarrhea cause both fasting and dehydration.
Surgical stress: Perioperative considerations are critical (PMID: 41156202).
Pregnancy/labor: Documented trigger for metabolic decompensation. "Stress of pregnancy and labor and delivery can lead to metabolic decompensation in HMG-CoA lyase deficiency" (PMID: 26997609).

Lifestyle Factors

Diet: High-protein and high-leucine diets exacerbate the metabolic defect. Fat-restricted diets reduce dependence on fatty acid oxidation and ketogenesis.
Feeding patterns: Prolonged intervals between meals are dangerous, especially in infants and young children.
Exercise: Strenuous exercise may precipitate catabolism, though this is less well documented.

Infectious Agents

No pathogen directly causes HMGCLD, but any infectious illness can precipitate metabolic decompensation. COVID-19 has been specifically documented as a trigger in an HMGCLD patient who "presented clinical and biochemical findings of an acute metabolic attack" (PMID: 34329521).

6. Mechanism / Pathophysiology

Molecular Pathways

The primary biochemical defect involves two interconnected pathways:

1. Leucine catabolism pathway (KEGG: hsa00280 — Valine, leucine and isoleucine degradation):

Leucine → α-ketoisocaproate → isovaleryl-CoA → 3-methylcrotonyl-CoA →
3-methylglutaconyl-CoA → HMG-CoA → [BLOCKED] → acetoacetate + acetyl-CoA

2. Ketogenesis pathway (KEGG: hsa00072 — Synthesis and degradation of ketone bodies):

Acetyl-CoA → acetoacetyl-CoA → HMG-CoA → [BLOCKED] → acetoacetate → 3-hydroxybutyrate

Causal Chain (Upstream → Downstream)

HMGCL gene mutation (upstream)
       ↓
HMG-CoA lyase enzyme deficiency (EC 4.1.3.4)
       ↓
   ┌───┴───────────────────┐
   ↓                       ↓
Blocked leucine         Blocked ketogenesis
catabolism              (no ketone body production)
   ↓                       ↓
Accumulation of         Hypoketotic hypoglycemia
toxic organic acids     during fasting
   ↓                       ↓
┌──┴──────────┐         Energy failure in brain
↓             ↓         and other organs
Oxidative     Direct        ↓
stress        toxicity   Neurological damage
   ↓             ↓      (seizures, coma)
Mitochondrial  Hepato-
dysfunction    toxicity
   ↓
White matter damage
Basal ganglia injury

Oxidative Stress Mechanism

The accumulated organic acids — particularly 3-hydroxy-3-methylglutarate, 3-methylglutarate, 3-methylglutaconate, and 3-hydroxyisovalerate — disrupt cellular redox homeostasis. Ribeiro et al. (2015) established that "recent animal and human in vitro and in vivo studies have suggested that oxidative stress caused by the major accumulating organic acids may represent a pathomechanism of brain and liver damage in HL deficiency" (PMID: 26041581).

Brain Metabolite Accumulation

Brain MR spectroscopy has directly demonstrated accumulation of toxic metabolites in the central nervous system. Couce et al. (2017) showed that "brain abnormal peaks in patients were formally identified to be those of 3-hydroxyisovaleric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxy-3-methylglutaric acids" (PMID: 28396157). The same study noted that "Mild to extended abnormal white matter MRI signals were observed in all cases".

Metabolic Changes

Accumulating metabolites:

Metabolite	CHEBI	Change	Compartment
3-Hydroxy-3-methylglutaric acid	CHEBI:37631	Markedly elevated	Urine, plasma, CSF, brain
3-Methylglutaconic acid	CHEBI:73738	Elevated	Urine, brain
3-Methylglutaric acid	CHEBI:68553	Elevated	Urine, brain
3-Hydroxyisovaleric acid	CHEBI:15751	Elevated	Urine, brain
3-Hydroxyisovalerylcarnitine (C5-OH)	—	Elevated	Blood (NBS marker)

Deficient metabolites:

Metabolite	CHEBI	Change	Consequence
Acetoacetate	CHEBI:15351	Decreased/absent during crisis	Ketogenesis failure
3-Hydroxybutyrate	CHEBI:37054	Decreased/absent during crisis	Brain energy failure
Glucose	CHEBI:17234	Low during crisis	Hypoglycemia

Secondary metabolic disturbances: Lactic acidosis, hyperammonemia (impaired urea cycle during crisis), secondary carnitine deficiency.

Protein Dysfunction

HMGCL protein dysfunction is primarily loss of function: - Missense mutations at the catalytic site (codons 41-42) directly abolish enzymatic activity - Nonsense and frameshift mutations produce truncated, non-functional proteins - Splice site mutations lead to aberrant mRNA processing - The enzyme normally functions as a homodimer in the mitochondrial matrix

Cellular Processes Involved

GO:0006552 — Leucine catabolic process (directly impaired)
GO:0016573 — Ketone body biosynthetic process (directly impaired)
GO:0006979 — Response to oxidative stress (secondarily activated)
GO:0006915 — Apoptosis (downstream consequence in neurons)
GO:0007005 — Mitochondrial organization (disrupted)
GO:0006631 — Fatty acid metabolic process (secondarily affected)

Cell Types Involved

CL:0000182 — Hepatocyte (primary metabolic site, liver damage, ketogenesis site)
CL:0000540 — Neuron (energy failure target)
CL:0000128 — Oligodendrocyte (white matter damage)
CL:0002063 — Astrocyte (supportive metabolic role)
CL:0002306 — Kidney epithelial cell (organic acid excretion)

Tissue Damage Mechanisms

Oxidative stress: Organic acid-induced disruption of redox balance, particularly affecting mitochondrial function
Energy failure: Hypoketotic hypoglycemia deprives the brain of its primary alternative fuel source
Excitotoxicity: Secondary to energy failure in neurons
Demyelination: White matter damage from both direct toxicity and energy failure in oligodendrocytes
Hepatic steatosis: Lipid accumulation in hepatocytes from impaired fat metabolism
Reye syndrome-like episodes: Acute hepatic failure with encephalopathy during severe crises

Immune System Involvement

No primary immune dysfunction. However, intercurrent infections are the most common triggers for metabolic crises, and the catabolic state induced by infection precipitates the metabolic block's clinical consequences.

Molecular Profiling

No comprehensive transcriptomic, proteomic, or multi-omics studies have been specifically published for HMGCLD patient tissues. Metabolomic profiling has been performed primarily in the context of newborn screening optimization, identifying "3-methylglutaconic acid and 3-hydroxy-3-methylglutaric acid, together with 3-hydroxyisovalerylcarnitine as the most discriminating metabolites" between patients and controls (PMID: 32685354).

Connection to Mitochondrial Oxidative Stress

The Sod2 mutant mouse (mitochondrial superoxide dismutase knockout) provides a key mechanistic link: "The Sod2 mutant mice exhibit a tissue-specific inhibition of the respiratory chain enzymes... inactivation of the tricarboxylic acid cycle enzyme aconitase, development of a urine organic aciduria in conjunction with a partial defect in 3-hydroxy-3-methylglutaryl-CoA lyase" with "features reminiscent of... 3-hydroxy-3-methylglutaryl-CoA lyase deficiency" (PMID: 9927656). This suggests a potential positive feedback loop between HMG-CoA lyase deficiency, organic acid accumulation, oxidative stress, and further mitochondrial dysfunction.

7. Anatomical Structures Affected

Organ Level

Organ/System	UBERON Term	Involvement	Mechanism
Brain	UBERON:0000955	Primary	Energy failure, oxidative stress, metabolite accumulation
Liver	UBERON:0002107	Primary	Oxidative stress, metabolic disruption, steatosis
Heart	UBERON:0000948	Secondary (rare)	Dilated cardiomyopathy
Pancreas	UBERON:0001264	Secondary (rare)	Pancreatitis
Kidney	UBERON:0002113	Secondary	Organic acid excretion

Body systems involved: Nervous system (primary), digestive/hepatic system (primary), metabolic/endocrine system (primary), cardiovascular system (rare).

Tissue and Cell Level

Cerebral white matter (UBERON:0002316): Abnormalities in 47.1% of patients. "Imaging revealed white matter abnormalities in 47.1% of patients and basal ganglia alterations in 17.6%" (PMID: 41872807)
Basal ganglia (UBERON:0002420): Alterations in 17.6% of patients
Hepatic parenchyma (UBERON:0001280): Hepatomegaly, steatosis, hepatic dysfunction
Cerebral cortex (UBERON:0000956): Cortical atrophy in some patients

Subcellular Level

Mitochondrial matrix (GO:0005759): Primary site of the enzymatic defect; HMG-CoA lyase is a mitochondrial matrix enzyme
Peroxisome (GO:0005777): HMGCL also localizes to peroxisomes; potential role in peroxisomal fatty acid metabolism
Cytoplasm (GO:0005737): Accumulation of organic acid intermediates

Localization

Central nervous system: Bilateral, diffuse white matter involvement; basal ganglia may be affected
Liver: Diffuse involvement
Disease effects are bilateral and systemic during metabolic crises

8. Temporal Development

Onset

Typical age of onset: Neonatal (50%) to infantile (76.5% diagnosed during infancy)
HPO onset term: HP:0003593 (Infantile onset)
Onset pattern: Acute metabolic crisis, often triggered by the physiological fasting that occurs during the first days of life
Late-onset forms: Documented up to adulthood — a case at 3 years (PMID: 19932602), at 5 years (PMID: 38567177), and an adult female with head tremor and white matter changes (PMID: 34573903)

Progression

Disease course: Episodic acute crises superimposed on a chronic condition
Between episodes: Patients may be clinically stable with appropriate dietary management
Cumulative damage: Each metabolic decompensation episode risks progressive neurological injury
Duration: Chronic, lifelong condition requiring ongoing management
Progression rate: Variable; depends on frequency and severity of metabolic crises and quality of chronic management
With treatment: Many patients stabilize and frequency of crises decreases with age

Critical Periods

Neonatal period (first 5 days): Highest risk for initial presentation due to physiological fasting and catabolism
Infancy/early childhood: Frequent intercurrent illnesses create repeated risk of decompensation
Pregnancy/labor: Documented metabolic stress period requiring careful monitoring. "Stress of pregnancy and labor and delivery can lead to metabolic decompensation in HMG-CoA lyase deficiency" (PMID: 26997609)
Adolescence/adulthood: Risk persists; decompensation documented in adolescents and adults. "Patients with HL deficiency can develop hypoglycemic crises and neurological symptoms even in adolescents and adults" (PMID: 24706027)

9. Inheritance and Population

Inheritance Pattern

Mode: Autosomal recessive (HP:0000007)
Penetrance: Complete for biochemical phenotype (all biallelic mutation carriers show enzymatic deficiency); clinical expressivity is highly variable
Expressivity: Highly variable — no genotype-phenotype correlation
Genetic anticipation: Not applicable
Germline mosaicism: Not specifically reported but theoretically possible

Epidemiology

Worldwide prevalence: <1 per 100,000; classified as ultra-rare
Orphanet classification: Prevalence <1/1,000,000 in most populations
Estimated prevalence at birth: Portugal ~1:1,250,000; United States and China <1:1,000,000
Saudi Arabia: Significantly higher due to R41Q founder mutation and consanguinity
Netherlands NBS data (2007-2023): Screening detected multiple cases over 17 years (PMID: 40937535)
Fewer than 200 cases reported globally in the literature

Population Demographics

Founder effects: - Saudi Arabia: R41Q accounts for 89% of pathogenic alleles. "All mutations were present in a homozygous state, reflecting extensive consanguinity" (PMID: 17173698) - China: c.122G>A is also the most prevalent variant (PMID: 41872807)

Consanguinity role: Significant, especially in Saudi Arabia and other Middle Eastern populations where the disease is most frequently observed.

Sex ratio: No sex predilection (autosomal recessive).

Geographic distribution: Worldwide, but higher prevalence in Saudi Arabia and the Arabian Peninsula, Mediterranean populations, Turkey, and South Asia — all areas with elevated consanguinity rates.

10. Diagnostics

Clinical Tests

Laboratory Tests

Urine organic acids (gold standard for biochemical diagnosis): - Elevated: 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, 3-hydroxyisovaleric acid, 3-methylcrotonylglycine - HP:0410051 (Increased level of 3-hydroxy-3-methylglutaric acid in urine)

Blood acylcarnitines (tandem mass spectrometry): - Elevated C5-OH (3-hydroxyisovalerylcarnitine) — primary NBS marker - Elevated C6DC (adipoylcarnitine/3-methylglutarylcarnitine)

Blood chemistry during crisis: - Hypoglycemia with absent/low ketone bodies (hypoketotic hypoglycemia) - Metabolic acidosis with elevated anion gap - Hyperammonemia - Elevated lactate (variable) - Elevated hepatic transaminases

Enzyme assay: - HMG-CoA lyase activity in cultured fibroblasts or leukocytes - HP:6000216 (Reduced HMG-CoA lyase activity in cultured fibroblasts) — found in 13/13 tested patients (PMID: 28583327)

Biomarkers

Primary diagnostic: C5-OH acylcarnitine (blood), 3-hydroxy-3-methylglutaric acid (urine)
Discriminating metabolites: "3-methylglutaconic acid and 3-hydroxy-3-methylglutaric acid, together with 3-hydroxyisovalerylcarnitine as the most discriminating metabolites" (PMID: 32685354)
Monitoring: Plasma amino acids (leucine), urine organic acids, carnitine levels

Imaging Studies

Brain MRI: White matter signal abnormalities (47.1%), basal ganglia alterations (17.6%), leukoencephalopathy (PMID: 41872807)
Brain MR spectroscopy: Abnormal peaks corresponding to accumulating organic acids — directly confirmed in 5 patients (PMID: 28396157)
Liver ultrasound: Hepatomegaly, steatosis

Electrophysiology

EEG: Abnormalities including hypsarrhythmia in some patients

Newborn Screening

HMGCLD is included on the Recommended Uniform Screening Panel (RUSP) in the United States as a core condition (PMID: 41323099). Screening uses C5-OH as a marker in dried blood spots collected between 24-48 hours of life.

Dutch NBS performance (2007-2023): "Of the 126 neonates referred on the basis of elevated C5-OH concentrations in the Netherlands, 46 were true positive cases... resulting in a positive predictive value of 38.3% and a negative predictive value of 100%" (PMID: 40937535).

HMGCLD has notably high PPV among NBS-screened conditions: "The positive predictive value ranged from 0.07 (carnitine transporter defect) to 0.67 (HMG-CoA lyase deficiency)" (PMID: 37603033).

Limitation: C5-OH is not specific — it is also elevated in 3-methylcrotonyl-CoA carboxylase deficiency and holocarboxylase synthetase deficiency. "C5-OH concentrations of patients with different IEMs reported in the literature were insufficiently distinctive to differentiate between these diseases" (PMID: 40937535).

Second-tier testing using UHPLC-MS/MS for 3-hydroxy-3-methylglutaric acid and 3-methylglutaconic acid in dried blood spots can unequivocally confirm diagnosis (PMID: 32685354).

Genetic Testing

Single gene testing: Sanger sequencing of HMGCL (9 exons) — first-line molecular confirmatory test
Gene panels: Organic acidemia panels, metabolic disease panels
Whole exome sequencing (WES): Effective for identifying novel variants (PMID: 38567177)
Chromosomal microarray / exon array: Useful for detecting large deletions at 1p36.11 (PMID: 41636194)
Prenatal diagnosis: Available via molecular testing in CVS or amniocentesis

Differential Diagnosis

Condition	Distinguishing Feature
3-Methylcrotonyl-CoA carboxylase deficiency (3-MCCD)	Elevated C5-OH but different organic acid profile; elevated 3-methylcrotonylglycine
Holocarboxylase synthetase deficiency (HLCSD)	Multiple carboxylase deficiency; different organic acid pattern; responds to biotin
Biotinidase deficiency	Responds to biotin; skin rash, alopecia
Mitochondrial HMG-CoA synthase deficiency	Normal organic acids between crises; no characteristic organic acid elevations
MCADD	Different acylcarnitine profile (elevated C8)
Reye syndrome	No characteristic organic aciduria

11. Outcome / Prognosis

Survival and Mortality

Mortality in largest European cohort: 6/37 patients (16.2%) died (PMID: 28583327)
With comprehensive treatment (Australian cohort): "there is 100% survival in the remainder of the cases despite several having experienced life-threatening episodes" (PMID: 36771238)
Life expectancy: Variable; with optimal management, survival into adulthood is expected, including successful pregnancies (PMID: 28220407; PMID: 26997609)

Cognitive Outcomes

Grünert et al. (2017) reported: "Half of the patients had a normal cognitive development while the remainder showed psychomotor deficits. We identified seven novel HMGCL mutations. In agreement with previous reports, no clear genotype-phenotype correlation could be found" (PMID: 28583327).

Normal cognition: ~50% with treatment
Global developmental delay: ~49% (17/35 patients)
Neurological sequelae: Seizures, spasticity, ataxia in severe cases

Prognostic Factors

Factor	Direction	Evidence
Early diagnosis (NBS)	Favorable	Enables pre-symptomatic treatment
Timely crisis treatment	Favorable	Prevents cumulative neurological damage
Dietary compliance	Favorable	Reduces metabolic stress
Late diagnosis	Unfavorable	Risk of irreversible brain damage
Recurrent/prolonged crises	Unfavorable	Cumulative neurological injury
HMGCL genotype	Not predictive	No genotype-phenotype correlation

Complications

Metabolic encephalopathy
Permanent intellectual disability from severe/recurrent metabolic crises
Epilepsy and movement disorders
Hepatic steatosis / acute liver failure (rare)
Dilated cardiomyopathy (rare)
Acute pancreatitis (rare)

12. Treatment

Acute Crisis Management (MAXO:0000127 — Emergency treatment)

Intravenous glucose: 10% dextrose at twice-maintenance rate to suppress catabolism
Sodium D,L-3-hydroxybutyrate: Exogenous ketone body supplementation (900 mg/kg/day). "Five of nine patients have used 900 mg/kg/day of sodium D,L 3-hydroxybutyrate in combination with intravenous dextrose-containing fluids" (PMID: 36771238)
Bicarbonate correction: For severe metabolic acidosis
Ammonia-lowering therapy: Sodium benzoate/phenylbutyrate if needed

Long-term Dietary Management (MAXO:0000087 — Dietary modification)

Protein restriction (MAXO:0000098): Low-protein diet to reduce leucine intake (typically 1.0-1.5 g/kg/day). "All patients have been on long-term protein restriction, and those diagnosed more recently have had additional fat restriction" (PMID: 36771238)
Fat restriction: Reduces dependence on fatty acid oxidation/ketogenesis
L-carnitine supplementation (CHEBI:16347): 50-100 mg/kg/day. "Long-term treatment consists in limited fasting time, continuous low protein diet and l-carnitine supplementation" (PMID: 19932602)
Nocturnal uncooked cornstarch: Used in some pediatric patients to prevent overnight fasting hypoglycemia
Avoidance of fasting (MAXO:0001344): Critical preventive measure with age-specific maximum fasting times
Frequent feeding: Carbohydrate-enriched diet to provide alternative energy

Special Situations

Perioperative management: Minimization of fasting period, perioperative glucose infusion, monitoring for metabolic decompensation (PMID: 41156202).

Pregnancy management: Gradual increase in protein and carnitine supplementation; close monitoring by metabolic specialist, dietitian, and high-risk obstetrician; IV glucose during labor; avoidance of fasting (PMID: 26997609; PMID: 28220407).

Cost-Effectiveness of Screening

NBS for HMGCLD is among the most cost-effective of all screened conditions: "The incremental costs of screening ranged from $222,000 (HMG-CoA lyase deficiency) to $142,500,000 (glutaric acidemia type II) per LY gained" (PMID: 17391418).

Advanced Therapeutics

Gene therapy: No approved gene therapy available. The well-defined single-gene etiology and mitochondrial target make HMGCLD a potential candidate for future liver-directed gene therapy approaches.
Liver transplantation: Considered for severe cases (liver is primary ketogenesis site), but not established as standard treatment.
No RNA-based therapies, cell therapies, or targeted molecular therapies are currently available or in clinical trials.

Supportive and Rehabilitative Care

Developmental support and early intervention for neurodevelopmental delays
Physical therapy, occupational therapy, speech therapy as needed (MAXO:0000451)
Nutritional counseling and dietary management
Genetic counseling for families (MAXO:0000079)
Emergency protocols (emergency letters/cards) for metabolic crises
Psychological support for chronic disease management

Treatment Strategy Summary

Newborn screening → early identification
Immediate dietary modification → protein and fat restriction
L-carnitine supplementation → improve organic acid excretion
Fasting avoidance → frequent meals, cornstarch at night
Emergency protocol during illness → aggressive IV glucose, exogenous ketone bodies
Long-term monitoring → urine organic acids, amino acids, carnitine levels, neurodevelopmental assessment

13. Prevention

Primary Prevention

Genetic counseling (MAXO:0000079): For at-risk families, especially in populations with high consanguinity. 25% recurrence risk per pregnancy in carrier parents.
Carrier screening: Especially relevant in Saudi Arabia. "Our findings have direct implications on rapid molecular diagnosis, prenatal and pre-implantation diagnosis and population based prevention programs" (PMID: 17173698)
Prenatal diagnosis: Available via molecular testing in CVS or amniocentesis
Pre-implantation genetic diagnosis (PGD): Available for families with known mutations

Secondary Prevention (Early Detection)

Newborn screening (MAXO:0000118): HMGCLD is on the RUSP in the United States and included in NBS programs in the Netherlands, China, Australia, and many other countries
Marker: Elevated C5-OH on acylcarnitine profile
Second-tier testing improves specificity (PMID: 32685354)
Enables pre-symptomatic treatment initiation
Cascade testing: Testing siblings and extended family of affected individuals

Tertiary Prevention

Fasting avoidance: Strict adherence to maximum fasting times by age
Sick-day protocols: Emergency plans for intercurrent illness
Emergency letters/cards: Carried by patients/families for acute care settings
Regular metabolic follow-up: Monitoring of growth, development, metabolite levels
Pregnancy management: Close monitoring by metabolic specialist team (PMID: 26997609)
COVID-19 vigilance: IEM patients are vulnerable to metabolic decompensation during infection (PMID: 34329521)

14. Other Species / Natural Disease

Orthologous Genes

Species	Gene	NCBI Gene ID
Human (Homo sapiens)	HMGCL	3155
Mouse (Mus musculus)	Hmgcl	15356
Rat (Rattus norvegicus)	Hmgcl	79238
Zebrafish (Danio rerio)	hmgcl	378727

Natural Disease in Other Species

HMGCLD has not been widely reported as a naturally occurring disease in companion animals or livestock. The leucine catabolism and ketogenesis pathways are fundamental to mammalian metabolism, and the enzyme is highly conserved across vertebrates.

OMIA (Online Mendelian Inheritance in Animals): No specific entry confirmed for naturally occurring HMG-CoA lyase deficiency.

Comparative Biology

The Sod2 knockout mouse provides indirect evidence of evolutionary conservation: oxidative stress alone can impair HMG-CoA lyase function in mice, producing "features reminiscent of... 3-hydroxy-3-methylglutaryl-CoA lyase deficiency" (PMID: 9927656). A contiguous gene deletion at 1p36.11 involving HMGCL, FUCA1, and CNR2 demonstrates the genomic architecture is conserved, and large deletions can produce combined phenotypes (PMID: 41636194).

Zoonotic Potential

Not applicable — HMGCLD is a non-infectious genetic disorder.

15. Model Organisms

Available Models

Model	Type	Key Features	Limitations
Sod2-/- mouse	Knockout (indirect)	Develops HMG-CoA lyase dysfunction via oxidative stress; organic aciduria (PMID: 9927656)	Not a direct HMGCL knockout; mixed phenotype with respiratory chain defects
Patient-derived fibroblasts	In vitro	Enzyme activity assays and variant characterization; 13/13 showed reduced activity (PMID: 28583327)	Limited tissue-specific information
Recombinant enzyme systems	In vitro	Functional characterization of mutations at codons 41-42 (PMID: 9463337)	No systemic phenotype
Rat brain/liver studies	Chemical model (in vivo/in vitro)	Evaluation of organic acid toxicity on redox homeostasis (PMID: 26041581)	Lack genetic basis of disease

Genetic Models

No dedicated Hmgcl knockout mouse has been widely characterized in the published literature. This represents a significant gap for preclinical research.

Model Characteristics

Sod2-/- mouse: Partially recapitulates organic aciduria and mitochondrial dysfunction but through an oxidative stress mechanism rather than direct enzyme deficiency
Patient fibroblasts: Can measure enzyme activity and confirm pathogenicity of variants but cannot model systemic crises
Recombinant protein studies: Essential for structure-function analysis but limited to enzymatic characterization

Research Applications

Fibroblast enzyme assays for diagnostic confirmation
Recombinant protein studies for functional characterization of novel variants
Rat brain/liver studies for understanding pathomechanisms of metabolite toxicity
Development and validation of improved NBS strategies

Key Findings (Expanded)

Finding 1: HMGCL Gene Mutations Cause Dual Metabolic Block in Ketogenesis and Leucine Catabolism

HMGCLD results from biallelic loss-of-function mutations in the HMGCL gene (1p36.11), encoding a 325-amino acid mitochondrial enzyme (UniProt P35914). The enzyme sits at a critical metabolic junction — the terminal step of both leucine catabolism and ketogenesis. This dual role explains the disease's characteristic biochemical signature: accumulation of leucine degradation intermediates combined with an inability to produce ketone bodies during fasting. With 147 catalogued pathogenic variants spanning missense, nonsense, frameshift, splice-site, and large deletion types, the disease shows substantial allelic heterogeneity. The R41Q founder mutation predominates in Saudi Arabia (89% of alleles), while codons 41-42 collectively account for 26% of all known mutant alleles globally, indicating a catalytic hotspot critical for enzymatic function. In the Chinese population, R41Q is also the most prevalent variant. Despite this genetic diversity, no genotype-phenotype correlation exists, meaning that clinical severity cannot be predicted from the specific mutation.

Supporting evidence: - "3-Hydroxy-3-methylglutaryl-coenzyme A lyase deficiency (HMGCLD) is a rare inborn error of ketone body synthesis and leucine degradation, caused by mutations in the HMGCL gene" (PMID: 28583327) - "We detected the common missense mutation R41Q in 89% of the tested alleles (64 alleles)" (PMID: 17173698) - "76.5% were diagnosed during infancy, while 35.3% were identified through newborn screening protocols. Acute metabolic disturbances were reported in 88.2% of patients" (PMID: 41872807)

Finding 2: Oxidative Stress from Accumulated Organic Acids Drives Brain and Liver Pathology

The toxic organic acids that accumulate upstream of the enzymatic block — 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid — are not merely biomarkers but active pathogenic mediators. In vitro and in vivo studies demonstrate that these metabolites disrupt cellular redox homeostasis, causing oxidative stress in brain and liver tissues. Brain MR spectroscopy has directly confirmed the presence of these metabolites within brain parenchyma, demonstrating that the blood-brain barrier does not fully protect the CNS from these toxic intermediates. Neuroimaging reveals white matter abnormalities in 47.1% and basal ganglia alterations in 17.6% of patients, consistent with a model of progressive neurotoxicity. The Sod2-/- mouse model provides independent evidence that oxidative stress impairs HMG-CoA lyase function, suggesting a potential positive feedback loop where enzyme deficiency leads to metabolite accumulation, which causes oxidative stress, which further impairs mitochondrial function.

Supporting evidence: - "recent animal and human in vitro and in vivo studies have suggested that oxidative stress caused by the major accumulating organic acids may represent a pathomechanism of brain and liver damage in HL deficiency" (PMID: 26041581) - "brain abnormal peaks in patients were formally identified to be those of 3-hydroxyisovaleric, 3-methylglutaconic, 3-methylglutaric and 3-hydroxy-3-methylglutaric acids" (PMID: 28396157) - "Imaging revealed white matter abnormalities in 47.1% of patients and basal ganglia alterations in 17.6%" (PMID: 41872807)

Finding 3: Variable Outcomes with ~50% Achieving Normal Cognition Under Treatment

The largest published cohort (37 patients) demonstrated that approximately half of patients achieve normal cognitive development with appropriate management, while the remaining half develop psychomotor deficits of varying severity. Mortality was 16.2% (6/37). Importantly, the Australian cohort of 10 patients achieved 100% survival with comprehensive dietary management, L-carnitine supplementation, and acute crisis protocols including sodium D,L-3-hydroxybutyrate. No genotype-phenotype correlation exists, meaning clinical outcomes are primarily determined by the quality and timeliness of medical management rather than the specific mutation. Newborn screening has emerged as a critical prognostic modifier: HMGCLD has the highest positive predictive value (0.67) among all conditions screened by C5-OH-based NBS, and early detection enables pre-symptomatic treatment initiation.

Supporting evidence: - "Half of the patients had a normal cognitive development while the remainder showed psychomotor deficits. We identified seven novel HMGCL mutations. In agreement with previous reports, no clear genotype-phenotype correlation could be found" (PMID: 28583327) - "there is 100% survival in the remainder of the cases despite several having experienced life-threatening episodes" (PMID: 36771238) - "The positive predictive value ranged from 0.07 (carnitine transporter defect) to 0.67 (HMG-CoA lyase deficiency)" (PMID: 37603033)

Mechanistic Model / Interpretation

Integrated Pathophysiological Model

HMGCLD can be understood through a two-hit model:

Hit 1 — Chronic metabolic vulnerability: The constitutional enzyme deficiency creates a baseline state of impaired leucine handling and absent ketogenic capacity. Even between crises, patients accumulate low levels of toxic organic acids and are unable to produce ketone bodies. This baseline vulnerability manifests as restricted dietary tolerance, limited fasting capacity, and subtle ongoing metabolite-mediated tissue damage.

Hit 2 — Acute metabolic decompensation: Physiological stress (fasting, infection, catabolism) tips the metabolic balance into crisis. Three pathogenic mechanisms converge: 1. Energy failure — Without ketone bodies, the brain loses its primary alternative fuel during hypoglycemia 2. Acute metabolite toxicity — Rapid accumulation of leucine-derived organic acids during catabolism 3. Oxidative damage — Metabolite-driven redox disruption in mitochondria, particularly affecting neurons and hepatocytes

This model explains several clinical observations: - Variable expressivity without genotype-phenotype correlation: Outcomes depend on the frequency and management of acute crises, not the specific mutation - White matter predilection: Oligodendrocytes are particularly vulnerable to both energy failure and oxidative stress - Effectiveness of dietary management: Reducing leucine intake and preventing fasting addresses both hits - Value of exogenous ketone body therapy: Sodium D,L-3-hydroxybutyrate directly compensates for the ketogenic defect - Lifelong vulnerability: Even adults can decompensate during metabolic stress (pregnancy, infection, surgery)

Evidence Base

Key Supporting Literature

Study	PMID	Contribution
Grünert et al. (2017) — Largest European cohort (n=37)	28583327	Defined clinical spectrum, outcomes (50% normal cognition), lack of genotype-phenotype correlation
Zayed et al. (2006) — Saudi mutation spectrum	17173698	Identified R41Q founder effect (89% of Saudi alleles)
Wang et al. (2025) — Chinese cohort	41872807	76.5% infantile diagnosis, 47.1% white matter abnormalities, 88.2% acute metabolic disturbances
Ribeiro et al. (2015) — Oxidative stress review	26041581	Established oxidative stress as key pathomechanism of brain/liver damage
Couce et al. (2017) — Brain spectroscopy	28396157	Direct evidence of brain metabolite accumulation via coupled brain/urine MR spectroscopy
Thompson et al. (2023) — Australian cohort (n=10)	36771238	100% survival with comprehensive management including sodium D,L-3-hydroxybutyrate
Li et al. (2023) — NBS collaborative study	37603033	HMGCLD has highest PPV (0.67) among screened conditions
Mitchell et al. (1998) — Codon 41/42 hotspot	9463337	Functional characterization of catalytic hotspot mutations; 26% of all mutant alleles
Groeneveld et al. (2025) — Dutch NBS evaluation	40937535	17-year NBS performance data (PPV 38.3%, NPV 100%)
Barić et al. (2020) — NBS approach	32685354	Second-tier NBS testing methodology; new diagnostic biomarkers
Melov et al. (1999) — Sod2 mouse model	9927656	Oxidative stress-HMG-CoA lyase connection in vivo
Ly et al. (2016) — Pregnancy management	26997609	Obstetric management protocols and complications
Alfadhel et al. (2022) — Saudi cohort (n=62)	35646072	Largest Saudi cohort, consanguinity patterns
Fukao et al. (2014) — Ketone body metabolism review	24706027	Comprehensive review of ketogenesis defects including HMGCLD
Cipriano et al. (2007) — NBS cost-effectiveness	17391418	HMGCLD screening at $222,000/LY gained — most cost-effective of screened conditions
Zubarioglu et al. (2022) — IEM and COVID-19	34329521	COVID-19 as trigger for metabolic decompensation in IEM patients
Sait et al. (2024) — Ketogenesis errors series	38567177	Novel variants, clinical profiles, and dietary intervention outcomes
Kilic et al. (2025) — Contiguous gene deletion	41636194	First case of concurrent HMGCLD and fucosidosis from contiguous gene deletion

Ontology Summary

Key Terms for Knowledge Base Population

Category	Term	ID
Disease	3-hydroxy-3-methylglutaric aciduria	MONDO:0009520
Gene	HMGCL	HGNC:5005
Phenotype	Hypoketotic hypoglycemia	HP:0001985
Phenotype	Metabolic acidosis	HP:0001942
Phenotype	Hyperammonemia	HP:0001987
Phenotype	Hepatomegaly	HP:0002240
Phenotype	Seizures	HP:0001250
Phenotype	Psychomotor retardation	HP:0001263
Phenotype	Abnormality cerebral white matter	HP:0002500
Phenotype	3-Methylglutaric aciduria	HP:0003344
Phenotype	Autosomal recessive inheritance	HP:0000007
Biological Process	Leucine catabolic process	GO:0006552
Biological Process	Ketone body biosynthetic process	GO:0016573
Biological Process	Response to oxidative stress	GO:0006979
Cellular Component	Mitochondrial matrix	GO:0005759
Cellular Component	Peroxisome	GO:0005777
Cell Type	Hepatocyte	CL:0000182
Cell Type	Neuron	CL:0000540
Cell Type	Oligodendrocyte	CL:0000128
Anatomy	Brain	UBERON:0000955
Anatomy	Liver	UBERON:0002107
Anatomy	Cerebral white matter	UBERON:0002316
Anatomy	Basal ganglia	UBERON:0002420
Chemical	3-Hydroxy-3-methylglutaric acid	CHEBI:37631
Chemical	3-Methylglutaconic acid	CHEBI:73738
Chemical	Acetoacetate	CHEBI:15351
Chemical	L-Carnitine	CHEBI:16347
Treatment	Dietary modification	MAXO:0000087
Treatment	Protein restriction	MAXO:0000098
Treatment	Emergency treatment	MAXO:0000127
Treatment	Genetic counseling	MAXO:0000079
Treatment	Newborn screening	MAXO:0000118

Limitations and Knowledge Gaps

Limited cohort sizes: Even the largest published series includes only 37-62 patients, limiting statistical power for subgroup analyses and genotype-phenotype correlation studies.
Absence of genotype-phenotype correlation: Despite over 147 known variants, no reliable predictors of disease severity or outcome have been identified, making prognostic counseling challenging.
Incomplete understanding of long-term outcomes: Most published data focus on pediatric outcomes. Adult natural history data are sparse, and long-term neurocognitive trajectories are insufficiently characterized.
Oxidative stress mechanism needs further elucidation: While the role of oxidative stress is established, the specific molecular targets, signaling pathways, and potential therapeutic interventions targeting this mechanism remain incompletely defined.
No specific animal model: A dedicated Hmgcl knockout mouse model with full phenotypic characterization has not been extensively published, limiting preclinical research.
Therapeutic limitations: Current treatment is purely supportive/preventive. No enzyme replacement therapy, gene therapy, or substrate reduction therapy has been developed.
NBS specificity challenges: The C5-OH marker has significant overlap between true and false positives, and between different C5-OH-related disorders, necessitating second-tier testing.
Lack of molecular profiling data: No transcriptomic, proteomic, or comprehensive metabolomic studies from patient tissues have been published, limiting systems-level understanding.
Pregnancy management data limited: Only a handful of pregnancies have been reported, with variable outcomes.
No formal quality of life studies: Disease-specific QoL instruments and formal QoL assessments have not been published for HMGCLD patients.

Proposed Follow-up Experiments / Actions

High Priority

International patient registry: Establish a centralized, prospective HMGCLD registry to collect standardized longitudinal data on genotype, treatment protocols, neurocognitive outcomes, and quality of life across the lifespan. This is the single most impactful action for improving knowledge of this ultra-rare disease.
Hmgcl knockout mouse model: Generate and fully characterize a conditional Hmgcl knockout mouse (liver-specific and global) to study tissue-specific pathophysiology, test therapeutic interventions, and identify biomarkers of disease progression.
Multi-omics profiling: Conduct transcriptomic, proteomic, and metabolomic analyses on patient-derived fibroblasts, iPSC-derived hepatocytes, and available biobank samples to identify novel therapeutic targets and prognostic biomarkers.

Medium Priority

Antioxidant therapy trials: Based on the established role of oxidative stress, investigate whether mitochondria-targeted antioxidants (idebenone, MitoQ, N-acetylcysteine) can reduce metabolite-mediated tissue damage — initially in cell models, then in animal models.
Improved NBS algorithms: Develop and validate multi-analyte NBS algorithms incorporating second-tier metabolites (3-HMG acid, 3-MGA) to improve screening specificity and reduce false-positive rates across diverse populations.
Gene therapy feasibility study: Evaluate AAV-mediated liver-directed gene therapy in animal models, leveraging the liver as the primary ketogenic organ. HMGCLD is an attractive gene therapy target due to its monogenic nature and the possibility that restoring liver expression alone may correct the most dangerous aspect (ketogenesis failure).
Adult outcome and pregnancy study: Retrospective/prospective study of adult HMGCLD patients to characterize long-term neurocognitive outcomes, reproductive health, and management during pregnancy.

Lower Priority

Modifier gene identification: Whole-genome sequencing in phenotypically discordant sibling pairs or large cohorts to identify genetic modifiers of disease severity that explain the variable expressivity.
iPSC-derived models: Generate patient-specific iPSCs, differentiate into hepatocytes and neurons, and use these for drug screening, mechanistic studies, and potential personalized therapy development.
Quality of life assessment: Develop and validate a disease-specific quality of life instrument for organic acidurias, including HMGCLD, to better quantify the burden of disease and evaluate treatment effectiveness.

Report generated 2026-05-05 | Based on comprehensive analysis of 29 published studies and multiple database resources (OMIM, Orphanet, ClinVar, HPO, KEGG, UniProt, PDB)

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