Home / Deep Research / 3-Hydroxy-3-Methylglutaryl-CoA Synthase Deficiency

3-Hydroxy-3-Methylglutaryl-CoA Synthase Deficiency

1. Disease Information

2026-05-29
Falcon MONDO:0011614 Model: Edison Scientific Literature 20 citations

1. Disease Information

1.1 Overview / definition

Mitochondrial 3‑hydroxy‑3‑methylglutaryl‑CoA synthase deficiency (HMGCS2D) is a rare inborn error of ketone body synthesis (ketogenesis) caused by loss of function of mitochondrial HMG‑CoA synthase (encoded by HMGCS2), leading to inability to appropriately generate ketone bodies during fasting or illness and resulting in episodic metabolic decompensation. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23)

Direct abstract quote (2025 Vietnamese case series): “Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency (HMGCS2D) is a rare metabolic disorder that impairs the body’s ability to produce ketone bodies and regulate energy metabolism.” (Nguyen et al., 2025; https://doi.org/10.3390/ijms26041644; published Feb 2025) (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

1.2 Key identifiers

1.3 Synonyms / alternative names

Common names in the literature include: - “Mitochondrial HMG‑CoA synthase deficiency” - “mHS deficiency” (mitochondrial HMG‑CoA synthase deficiency) - “HMGCS2 deficiency” - “Mitochondrial 3‑hydroxy‑3‑methylglutaryl‑CoA synthase deficiency” (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23)

1.4 Evidence source type

Evidence in this report is primarily derived from aggregated disease-level clinical resources in peer‑reviewed case series and case reports (human clinical evidence), plus mechanistic interpretation from reviews. The quantitative phenotype and laboratory frequencies below come mainly from two retrospective patient series: a Vietnamese cohort (n=19) and a Chinese cohort (n=10). (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3)

2. Etiology

2.1 Disease causal factors

Genetic cause (primary): biallelic pathogenic variants in HMGCS2 cause autosomal recessive mitochondrial HMG‑CoA synthase deficiency. (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23, dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3)

Direct abstract quote (2020 JIMD Reports): “Mitochondrial 3‐hydroxy‐3‐methylglutaryl‐CoA (HMG Co‐A) synthase (mHS) deficiency is an autosomal recessive disorder of ketone body synthesis…” (Conlon et al., 2020; https://doi.org/10.1002/jmd2.12146; published Jun 2020) (conlon2020hypoglycemiaisnot pages 1-3)

Mechanistic cause: deficiency of the mitochondrial ketogenesis enzyme leads to inadequate ketone availability under catabolic stress and downstream biochemical derangements (see Section 6). (suresh2025notjustan pages 22-23, kılıc2020expandingtheclinical pages 6-7)

2.2 Risk factors

In the Vietnamese series, the most common triggers for the initial crisis were poor feeding/fasting (93.8%), vomiting (56.3%), diarrhea (25.0%), and fever (18.8%). (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

2.3 Protective factors

No validated genetic protective variants or environmental protective exposures were identified in the retrieved evidence. Clinically, prevention of prolonged fasting and proactive carbohydrate administration during illness function as protective management strategies against acute decompensation (Section 12/13), but these are not “protective factors” for disease occurrence. (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

2.4 Gene–environment interaction

The dominant gene–environment interaction is that HMGCS2 loss of function may be clinically silent until a catabolic state (fasting/illness) increases reliance on ketogenesis, precipitating crisis. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, suresh2025notjustan pages 22-23)

3. Phenotypes

3.1 Core phenotype pattern

HMGCS2 deficiency typically manifests as episodic metabolic decompensation in infancy/early childhood, often with encephalopathy (lethargy, coma), respiratory compensation for acidosis, and hepatic involvement (hepatomegaly, transaminitis). (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3)

A key clinical point is that hypoglycemia is common but not universal; cases with normal glucose at presentation are documented. (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2)

3.2 Age of onset, severity, and course

3.3 Symptom/sign frequencies (recent patient series)

Vietnamese cohort (n=16 symptomatic of 19 total): - Lethargy/coma 81.3% - Rapid breathing 68.8% - Hepatomegaly 56.3% - Shock 37.5% - Seizures 18.8% (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

Chinese cohort (n=10): - Anorexia 10/10 - Dyspnea 10/10 - Disturbance of consciousness 10/10 - Vomiting 8/10 - Fever 7/10 - Cough 4/10 - Diarrhea 3/10 - Seizures 3/10 - Hepatomegaly 10/10 (wu2022clinicalbiochemicalmolecular pages 2-3, wu2022clinicalbiochemicalmolecular pages 1-2)

3.4 Laboratory abnormalities (phenotype‑linked)

Common acute‑episode laboratory findings include metabolic acidosis, hypoglycemia (variable), elevated aminotransferases, and sometimes hyperammonemia and hypertriglyceridemia. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 1-2)

Notably, Conlon et al. emphasize that hypoglycemia is not mandatory for crisis presentation. (conlon2020hypoglycemiaisnot pages 1-3)

3.5 Neuroimaging findings

In the Chinese series, brain MRI abnormalities were variably present, including widened sulci/subarachnoid spaces, basal ganglia signal abnormalities, and delayed myelination in subsets of imaged patients. (wu2022clinicalbiochemicalmolecular pages 2-3)

3.6 Suggested HPO terms (non-exhaustive)

Based on the reported clinical features and labs: - Hypoglycemia (HP:0001943) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 1-2) - Metabolic acidosis (HP:0001942) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) - Encephalopathy / altered mental status (HP:0001298) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) - Lethargy (HP:0001254) / Coma (HP:0001259) (nguyen2025mitochondrialhmgcoasynthase pages 1-2) - Hepatomegaly (HP:0002240) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) - Elevated hepatic transaminases (HP:0002910) (nguyen2025mitochondrialhmgcoasynthase pages 1-2) - Hyperammonemia (HP:0001987) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 1-2) - Seizures (HP:0001250) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) - Shock (HP:0030148) (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

(Exact HPO IDs are provided as standard ontology mappings; the clinical evidence for each term is as cited.)

4. Genetic / Molecular Information

4.1 Causal gene

4.2 Pathogenic variants and variant classes

Across clinical series and reviews, pathogenic variants include missense, nonsense, frameshift, and splice‑site changes. (suresh2025notjustan pages 22-23, wu2022clinicalbiochemicalmolecular pages 1-2)

Examples from recent cohorts/case reports: - Vietnamese series identified a novel c.407A>T (p.D136V) and recurrent variants c.559+1G>A and c.1090T>A (p.F364I), each present in >50% of the 19 cases (57.9% and 55.5%, respectively). (nguyen2025mitochondrialhmgcoasynthase pages 1-2) - Chinese cohort identified 15 variants (10 novel) including missense, frameshift, nonsense, and splice variants; and highlighted c.1201G>T (p.E401*) as a possible hotspot in Chinese patients (6/40 mutated alleles, 15.0% in their combined dataset of Chinese patients). (wu2022clinicalbiochemicalmolecular pages 1-2)

4.3 Genotype–phenotype correlation (severity)

An aggregated analysis (Wu et al., combining their cases with literature) reported that severity correlates with truncating alleles; mortality was highest in the group with biallelic truncating variants (25% in their grouped analysis). (wu2022clinicalbiochemicalmolecular pages 8-9, wu2022clinicalbiochemicalmolecular media ec3f9f64)

4.4 Population genetics / epidemiology (limited)

4.5 Somatic vs germline

All cited disease-causing variants are inherited germline variants in HMGCS2 causing an autosomal recessive metabolic disease. (suresh2025notjustan pages 22-23, dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3)

4.6 Modifier genes / epigenetics / chromosomal abnormalities

No validated modifier genes, epigenetic signatures, or chromosomal abnormalities specific to HMGCS2 deficiency were identified in the retrieved evidence.

5. Environmental Information

This is a Mendelian disorder; environmental factors primarily influence crisis occurrence rather than disease causation.

5.1 Key environmental/physiologic precipitants

5.2 Infectious triggers

Fever/illness is repeatedly reported as a precipitant of metabolic crises. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, conlon2020hypoglycemiaisnot pages 1-3)

6. Mechanism / Pathophysiology

6.1 Key pathway and biochemical defect

HMGCS2 is the mitochondrial HMG‑CoA synthase, a rate‑limiting ketogenesis enzyme. Loss-of-function variants block ketone body synthesis, particularly critical during fasting/illness when ketones act as alternative fuels. (suresh2025notjustan pages 22-23, kılıc2020expandingtheclinical pages 6-7)

6.2 Causal chain (clinical mechanism narrative)

  1. Trigger: fasting/reduced intake or intercurrent illness increases catabolic demand and lipolysis. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, conlon2020hypoglycemiaisnot pages 1-3)
  2. Primary defect: impaired mitochondrial ketogenesis due to HMGCS2 deficiency limits ketone production. (suresh2025notjustan pages 22-23)
  3. Biochemical consequences: inadequate ketone availability leads to metabolic crisis characterized by severe metabolic acidosis and “hypoketotic” patterns; urine organic acids may show dicarboxylic aciduria and proposed markers such as 4HMP and 3‑hydroxyglutarate in some cases. (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2)
  4. Clinical manifestations: encephalopathy (lethargy/coma), respiratory compensation (tachypnea), hepatic stress (hepatomegaly/transaminitis), and in severe cases shock, seizures, and multi‑organ dysfunction. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3)

6.3 Proposed diagnostic biomarkers (expert interpretation)

A recurring expert opinion across case-based literature is that biochemical markers can be inconsistent and therefore diagnosis is frequently delayed unless samples are captured during crisis. - Conlon et al. propose additional acute clues including elevated acetylcarnitine, triglycerides, and 3‑hydroxyglutarate. (conlon2020hypoglycemiaisnot pages 1-3) - Wu et al. propose an elevated acetylcarnitine/free carnitine ratio as an additional signature. (wu2022clinicalbiochemicalmolecular pages 1-2) - Nguyen et al. note 4‑hydroxy‑6‑methyl‑2‑pyrone (4HMP) as a recently reported biomarker but not routine. (nguyen2025mitochondrialhmgcoasynthase pages 2-3)

6.4 Suggested ontology mappings

  • Pathway: ketone body synthesis / ketogenesis (supported conceptually by disease definition and review) (suresh2025notjustan pages 22-23)
  • GO biological processes (suggested): “ketone body biosynthetic process”, “fatty acid beta-oxidation” (secondary metabolic interplay), “response to starvation”. Evidence for ketogenesis impairment is explicit; downstream processes are inferred as standard biology of fasting dependence on ketones. (suresh2025notjustan pages 22-23, kılıc2020expandingtheclinical pages 6-7)
  • Cell types (CL, suggested): hepatocyte (primary site of hepatic ketogenesis and prominent liver phenotype), supported by clinical liver involvement and ketogenesis biology described in reviews. (suresh2025notjustan pages 22-23, wu2022clinicalbiochemicalmolecular pages 2-3)

7. Anatomical Structures Affected

7.1 Primary organs/systems

7.2 Suggested UBERON terms (examples)

7.3 Subcellular localization

The affected enzyme is mitochondrial; the disorder is a mitochondrial ketogenesis defect. (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23)

8. Temporal Development

8.1 Onset and pattern

8.2 Progression/course

9. Inheritance and Population

9.1 Inheritance

Autosomal recessive inheritance is consistently reported. (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23)

9.2 Epidemiology

  • A Vietnamese series/review reports estimated incidence <1/1,000,000. (nguyen2025mitochondrialhmgcoasynthase pages 1-2)
  • Robust population prevalence, incidence, and carrier frequency estimates were not identified in the retrieved evidence.

9.3 Population-specific variants

10. Diagnostics

10.1 Clinical and biochemical testing

During acute crisis, testing commonly includes: - Blood gas (metabolic acidosis), plasma glucose, ammonia - Liver enzymes (ALT/AST), coagulation markers (e.g., fibrinogen) - Plasma acylcarnitines (may show elevated acetylcarnitine and/or low free carnitine; and proposed elevated C2/C0 ratio) - Urine organic acids (dicarboxylic aciduria; potential presence of 4HMP, elevated glutarate/3HG in some cases) (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2)

Quantitative series examples: - Vietnamese cohort: elevated transaminases 100%, metabolic acidosis 75%, hypoglycemia 56.3%, elevated ammonia 31.3%. (nguyen2025mitochondrialhmgcoasynthase pages 1-2) - Chinese cohort: severe metabolic acidosis 10/10; hypoglycemia 9/10; hyperammonemia 5/10; hypertriglyceridemia 3/10; hypofibrinogenemia 10/10. (wu2022clinicalbiochemicalmolecular pages 2-3, wu2022clinicalbiochemicalmolecular pages 1-2)

10.2 Genetic testing (definitive diagnosis)

Multiple sources emphasize that due to the lack of reliable biochemical markers and limitations of enzyme assays, genetic testing is considered definitive.

Direct abstract quote (2025 Vietnamese case series): “Due to the absence of reliable biochemical markers, genetic testing has become the definitive method for diagnosing HMGCS2D.” (Nguyen et al., 2025; https://doi.org/10.3390/ijms26041644; published Feb 2025) (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

10.3 Enzyme assay limitations (expert opinion)

Enzyme assays are described as limited by challenges in distinguishing mitochondrial vs cytosolic HMG‑CoA synthase in practice, reinforcing reliance on molecular diagnosis. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3)

10.4 Differential diagnosis

Clinical presentations overlap with fatty acid oxidation disorders (FAODs) due to fasting intolerance and hypoketotic crisis patterns. (kılıc2020expandingtheclinical pages 6-7)

11. Outcome / Prognosis

11.1 Overall prognosis with diagnosis and prevention

With timely diagnosis and preventive management (fasting avoidance, sick-day carbohydrate plans), outcomes can be favorable. - Vietnamese cohort: “Currently, all 19 patients are alive… and exhibit normal physical development.” (Nguyen et al., 2025; https://doi.org/10.3390/ijms26041644; published Feb 2025) (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

11.2 Risk of severe outcomes

Severe metabolic crises can require intensive care measures (mechanical ventilation, CRRT) and deaths have occurred in reported cohorts; aggregated genotype–phenotype analysis suggests higher mortality with biallelic truncating variants. (wu2022clinicalbiochemicalmolecular pages 3-4, wu2022clinicalbiochemicalmolecular pages 8-9, wu2022clinicalbiochemicalmolecular media 0a979ec7)

12. Treatment

12.1 Acute management (real-world implementation)

Management is largely supportive and aims to reverse catabolism: - High glucose/dextrose infusion is emphasized as a key acute therapy in series and reports. (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) - Correction of metabolic acidosis (e.g., bicarbonate) and supportive critical care when required. (wu2022clinicalbiochemicalmolecular pages 2-3) - Adjuncts used in some reports/series include carnitine supplementation and organ-support therapies (mechanical ventilation, CRRT/hemodialysis for severe crises). (wu2022clinicalbiochemicalmolecular pages 3-4, wu2022clinicalbiochemicalmolecular pages 2-3)

12.2 Long-term management

The Vietnamese cohort specifically reports that “high glucose infusion” combined with proactive strategies (prevent prolonged fasting; enteral carbohydrate/glucose infusion during illness) reduced acute relapse rates. (nguyen2025mitochondrialhmgcoasynthase pages 1-2)

12.3 Experimental/advanced therapeutics

No gene therapy, RNA therapy, or targeted molecular therapy trials specific to HMGCS2 deficiency were identified in the retrieved evidence for this run.

12.4 Suggested MAXO terms (examples)

13. Prevention

13.1 Primary prevention

Not applicable in the classical public-health sense (genetic disease), but risk reduction for crises includes: - Avoid prolonged fasting - Provide early carbohydrate during intercurrent illness - Care pathways for vomiting/poor intake (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3)

13.2 Secondary prevention

13.3 Newborn screening

HMGCS2 deficiency is described as not detectable via standard newborn screening dried blood spot approaches in at least one literature review excerpt; the condition lacks a consistently reliable routine biochemical marker. (kılıc2020expandingtheclinical pages 6-7)

14. Other Species / Natural Disease

No naturally occurring veterinary disease analogs were identified in the retrieved evidence.

15. Model Organisms

No model organism specifically established to recapitulate human HMGCS2 deficiency was identified in the retrieved evidence for this run. (Note: retrieved papers included HMGCS2 biology in mice and other disease contexts, but not a dedicated HMGCS2-deficiency Mendelian disease model relevant to the human inborn error.) (suresh2025notjustan pages 22-23)

Recent developments and latest research emphasis (2023–2025)

  1. Larger contemporary cohorts with systematic frequencies and variant spectra: The 2025 Vietnamese case series (n=19, Oct 2018–Oct 2024) provides detailed trigger frequencies, clinical presentation frequencies, and recurrent variants in that population, and reports favorable outcomes with proactive management. (Nguyen et al., Feb 2025; https://doi.org/10.3390/ijms26041644) (nguyen2025mitochondrialhmgcoasynthase pages 1-2)
  2. Ongoing refinement of diagnostic biomarkers beyond “hypoketotic hypoglycemia”: Case-based evidence emphasizes that hypoglycemia may be absent, and proposes additional acute-phase biomarkers (e.g., 4HMP, 3HG, hypertriglyceridemia, acetylcarnitine patterns and C2/C0 ratio). (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3)
  3. Genotype–phenotype correlation analyses: Aggregated analysis suggests truncating variant burden influences severity and mortality risk, supporting more genotype-informed counseling and risk stratification. (wu2022clinicalbiochemicalmolecular pages 8-9, wu2022clinicalbiochemicalmolecular media ec3f9f64)

Key statistics (selected)

Summary table (knowledge-base ready)

The following table consolidates identifiers, phenotype frequencies, diagnostic markers, and management.

Table (click to expand)
Domain Summary Key details / frequencies
Identifiers Disease: mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency / HMGCS2 deficiency; OMIM disease #605911; causal gene HMGCS2 (OMIM gene #600234) (nguyen2025mitochondrialhmgcoasynthase pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3, conlon2020hypoglycemiaisnot pages 1-3) Rare ketogenesis disorder with estimated incidence <1/1,000,000 in the 2025 Vietnamese series/review (nguyen2025mitochondrialhmgcoasynthase pages 1-2)
Synonyms Mitochondrial HMG-CoA synthase deficiency; mHS deficiency; HMGCS2 deficiency; mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23) Defect of hepatic ketone-body synthesis due to loss of mitochondrial HMG-CoA synthase activity (nguyen2025mitochondrialhmgcoasynthase pages 1-2, suresh2025notjustan pages 22-23)
Inheritance Autosomal recessive; caused by biallelic pathogenic variants in HMGCS2 (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23, dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3) Missense, nonsense, splice, and frameshift variants reported; biallelic truncating variants are associated with more severe disease/higher mortality in aggregated analyses (suresh2025notjustan pages 22-23, wu2022clinicalbiochemicalmolecular pages 8-9, nguyen2025mitochondrialhmgcoasynthase pages 2-3)
Typical onset / triggers Usually infancy to early childhood; first crisis often in the first year of life and may occur from 10 days to 28 months (nguyen2025mitochondrialhmgcoasynthase pages 1-2, suresh2025notjustan pages 22-23, wu2022clinicalbiochemicalmolecular pages 2-3) Vietnamese series: poor feeding 93.8%, vomiting 56.3%, diarrhea 25.0%, fever 18.8% as triggers (nguyen2025mitochondrialhmgcoasynthase pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3); crises typically follow fasting or intercurrent illness (conlon2020hypoglycemiaisnot pages 1-3, suresh2025notjustan pages 22-23, sait2024inbornerrorsof pages 1-2)
Key clinical features Acute metabolic decompensation with encephalopathy and liver involvement (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) Nguyen 2025: lethargy/coma 81.3%, rapid breathing 68.8%, hepatomegaly 56.3%, shock 37.5%, seizures 18.8% (nguyen2025mitochondrialhmgcoasynthase pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3); Wu 2022: anorexia 10/10, dyspnea 10/10, disturbance of consciousness 10/10, vomiting 8/10, fever 7/10, cough 4/10, diarrhea 3/10, seizures 3/10, hepatomegaly 10/10 (wu2022clinicalbiochemicalmolecular pages 2-3, wu2022clinicalbiochemicalmolecular pages 1-2)
Key lab findings Hallmark pattern is impaired ketogenesis with severe metabolic crisis; findings may be nonspecific and can normalize between episodes (nguyen2025mitochondrialhmgcoasynthase pages 2-3, wu2022clinicalbiochemicalmolecular pages 1-2) Metabolic acidosis: 75% in Nguyen 2025; 10/10 in Wu 2022 (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3). Hypoglycemia: 56.3% in Nguyen 2025; 9/10 in Wu 2022, but absence of hypoglycemia does not exclude disease (nguyen2025mitochondrialhmgcoasynthase pages 1-2, conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2). Elevated transaminases: 100% in Nguyen 2025 and 10/10 in Wu 2022 (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3). Hyperammonemia: 31.3% in Nguyen 2025 and 5/10 in Wu 2022 (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 1-2). Hypofibrinogenemia: 10/10 in Wu 2022 (wu2022clinicalbiochemicalmolecular pages 2-3, wu2022clinicalbiochemicalmolecular pages 1-2). Urinary dicarboxylic acids: reported during crises, often prominent, with only mild/absent ketones (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 3-4, wu2022clinicalbiochemicalmolecular pages 1-2). Acetylcarnitine/free carnitine signal: elevated C2/C0 ratio proposed by Wu 2022; low free carnitine and/or elevated acetylcarnitine variably observed across patients (wu2022clinicalbiochemicalmolecular pages 3-4, wu2022clinicalbiochemicalmolecular pages 1-2)
Proposed biomarkers No single routine biomarker is fully reliable; several candidate acute-phase markers have been proposed (nguyen2025mitochondrialhmgcoasynthase pages 2-3, conlon2020hypoglycemiaisnot pages 1-3, kılıc2020expandingtheclinical pages 6-7) 4-hydroxy-6-methyl-2-pyrone (4HMP) proposed as a novel marker (conlon2020hypoglycemiaisnot pages 1-3, nguyen2025mitochondrialhmgcoasynthase pages 2-3); 3-hydroxyglutarate (3HG) and markedly elevated glutarate may support diagnosis (conlon2020hypoglycemiaisnot pages 1-3); hypertriglyceridemia proposed as an additional acute clue (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2); raised acetylcarnitine (C2) and elevated acetylcarnitine/free carnitine ratio proposed as signatures in some patients (conlon2020hypoglycemiaisnot pages 1-3, wu2022clinicalbiochemicalmolecular pages 1-2)
Diagnostic approach Diagnosis requires integration of acute biochemical testing with molecular confirmation; genetic testing is now considered definitive because enzyme assay and routine biochemical markers can be unreliable (nguyen2025mitochondrialhmgcoasynthase pages 1-2, nguyen2025mitochondrialhmgcoasynthase pages 2-3) Suggested workup during crisis: blood gas, glucose, ammonia, liver enzymes, free fatty acids/ketones if available, plasma acylcarnitines, and urine organic acids/GC-MS (conlon2020hypoglycemiaisnot pages 1-3, kılıc2020expandingtheclinical pages 6-7, wu2022clinicalbiochemicalmolecular pages 2-3). Typical clues: hypoketotic or relatively low-ketone crisis, dicarboxylic aciduria, raised C2 or C2/C0 ratio, normal/nonspecific TMS, and sometimes 4HMP/3HG (conlon2020hypoglycemiaisnot pages 1-3, sait2024inbornerrorsof pages 1-2, wu2022clinicalbiochemicalmolecular pages 1-2). Confirm by Sanger, targeted NGS, WES or similar sequencing of HMGCS2 (nguyen2025mitochondrialhmgcoasynthase pages 2-3, dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3)
Management / treatment Acute care centers on reversal of catabolism with high-glucose/dextrose infusion, correction of acidosis, and supportive intensive care as needed; long-term care focuses on fasting avoidance and sick-day carbohydrate plans (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3) Reported acute measures: IV glucose/dextrose, sodium bicarbonate, carnitine, liver-protective/supportive therapy, mechanical ventilation, and CRRT/hemodialysis for severe crises (sait2024inbornerrorsof pages 1-2, wu2022clinicalbiochemicalmolecular pages 3-4, wu2022clinicalbiochemicalmolecular pages 2-3). Vietnamese series noted that high-glucose infusion plus prevention of prolonged fasting and enteral carbohydrate/glucose during illness reduced relapses (nguyen2025mitochondrialhmgcoasynthase pages 1-2). Long-term diet: avoidance of prolonged fasting and often low/moderate-fat intake (sait2024inbornerrorsof pages 1-2, wu2022clinicalbiochemicalmolecular pages 2-3)
Prognosis / outcomes Prognosis is often good after diagnosis with preventive management, but acute episodes can be life-threatening and fatalities are reported (nguyen2025mitochondrialhmgcoasynthase pages 1-2, wu2022clinicalbiochemicalmolecular pages 8-9) Nguyen 2025: all 19 patients alive at follow-up (ages 5 months-14 years) with normal physical development after proactive management (nguyen2025mitochondrialhmgcoasynthase pages 1-2). Wu 2022/literature aggregation: most recover fully and maintain normal growth; only limited neurologic sequelae reported, but genotype severity matters; mortality highest in the biallelic truncating group (25%) (wu2022clinicalbiochemicalmolecular pages 8-9). Individual severe cases can progress to multiorgan failure and death (dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3, wu2022clinicalbiochemicalmolecular pages 3-4)

Table: This table condenses identifiers, phenotype frequencies, biochemical clues, diagnostic strategy, management, and prognosis for mitochondrial HMG-CoA synthase deficiency. It is designed as a disease knowledge base quick-reference using recent case-series evidence plus key prior reports.

Visual evidence from tables (original sources)

The extracted tables below contain the underlying cohort-level clinical and genotype–phenotype correlation information discussed in this report.

  • Patient clinical/laboratory/outcome summary table crop (Wu et al., 2022). (wu2022clinicalbiochemicalmolecular media 0a979ec7)
  • Genotype–phenotype correlation table crop (Wu et al., 2022). (wu2022clinicalbiochemicalmolecular media ec3f9f64)

References

  1. (nguyen2025mitochondrialhmgcoasynthase pages 1-2): Khanh Ngoc Nguyen, Tran Minh Dien, Thi Bich Ngoc Can, Bui Phuong Thao, Thi Kim Giang Dang, Ngoc Lan Nguyen, Van Khanh Tran, Thuy Thu Nguyen, Tran Thi Quynh Trang, Le Thi Phuong, Phan Long Nguyen, Thinh Huy Tran, Nguyen Huu Tu, and Chi Dung Vu. Mitochondrial hmg-coa synthase deficiency in vietnamese patients. International Journal of Molecular Sciences, Feb 2025. URL: https://doi.org/10.3390/ijms26041644, doi:10.3390/ijms26041644. This article has 2 citations.

  2. (conlon2020hypoglycemiaisnot pages 1-3): Tracey A. Conlon, Patricia E. Fitzsimons, Ingrid Borovickova, Fidelma Kirby, Sinéad Murphy, Ina Knerr, and Ellen Crushell. Hypoglycemia is not a defining feature of metabolic crisis in mitochondrial 3‐hydroxy‐3‐methylglutaryl‐coa synthase deficiency: further evidence of specific biochemical markers which may aid diagnosis. JIMD Reports, 55:26-31, Jun 2020. URL: https://doi.org/10.1002/jmd2.12146, doi:10.1002/jmd2.12146. This article has 11 citations and is from a peer-reviewed journal.

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  4. (nguyen2025mitochondrialhmgcoasynthase pages 2-3): Khanh Ngoc Nguyen, Tran Minh Dien, Thi Bich Ngoc Can, Bui Phuong Thao, Thi Kim Giang Dang, Ngoc Lan Nguyen, Van Khanh Tran, Thuy Thu Nguyen, Tran Thi Quynh Trang, Le Thi Phuong, Phan Long Nguyen, Thinh Huy Tran, Nguyen Huu Tu, and Chi Dung Vu. Mitochondrial hmg-coa synthase deficiency in vietnamese patients. International Journal of Molecular Sciences, Feb 2025. URL: https://doi.org/10.3390/ijms26041644, doi:10.3390/ijms26041644. This article has 2 citations.

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  6. (dong2025mitochondrial3hydroxy3methylglutarylcoenzymea pages 1-3): Chang Dong, Tiantian Lu, Yazhou Jiang, Zihao Yan, and Suyue Zhu. Mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme a synthase 2 deficiency with severe hyperglycemia in a child: a rare case report. Sep 2025. URL: https://doi.org/10.1177/03000605251375537, doi:10.1177/03000605251375537. This article has 0 citations and is from a peer-reviewed journal.

  7. (kılıc2020expandingtheclinical pages 6-7): Mustafa Kılıç, Sevil Dorum, Ali Topak, Mutlu U. Yazıcı, Fatih S. Ezgu, and Turgay Coskun. Expanding the clinical spectrum of mitochondrial 3‐hydroxy‐3‐methylglutaryl‐coa synthase deficiency with turkish cases harboring novel hmgcs2 gene mutations and literature review. American Journal of Medical Genetics Part A, 182:1608-1614, Apr 2020. URL: https://doi.org/10.1002/ajmg.a.61590, doi:10.1002/ajmg.a.61590. This article has 15 citations.

  8. (wu2022clinicalbiochemicalmolecular pages 8-9): Shengnan Wu, Linghua Shen, Qiong Chen, Chunxiu Gong, Yanling Yang, Haiyan Wei, Bingyan Cao, and Yongxing Chen. Clinical, biochemical, molecular, and outcome features of mitochondrial 3-hydroxy-3-methylglutaryl-coa synthase deficiency in 10 chinese patients. Frontiers in Genetics, Mar 2022. URL: https://doi.org/10.3389/fgene.2021.816779, doi:10.3389/fgene.2021.816779. This article has 13 citations and is from a peer-reviewed journal.

  9. (wu2022clinicalbiochemicalmolecular media 0a979ec7): Shengnan Wu, Linghua Shen, Qiong Chen, Chunxiu Gong, Yanling Yang, Haiyan Wei, Bingyan Cao, and Yongxing Chen. Clinical, biochemical, molecular, and outcome features of mitochondrial 3-hydroxy-3-methylglutaryl-coa synthase deficiency in 10 chinese patients. Frontiers in Genetics, Mar 2022. URL: https://doi.org/10.3389/fgene.2021.816779, doi:10.3389/fgene.2021.816779. This article has 13 citations and is from a peer-reviewed journal.

  10. (wu2022clinicalbiochemicalmolecular pages 1-2): Shengnan Wu, Linghua Shen, Qiong Chen, Chunxiu Gong, Yanling Yang, Haiyan Wei, Bingyan Cao, and Yongxing Chen. Clinical, biochemical, molecular, and outcome features of mitochondrial 3-hydroxy-3-methylglutaryl-coa synthase deficiency in 10 chinese patients. Frontiers in Genetics, Mar 2022. URL: https://doi.org/10.3389/fgene.2021.816779, doi:10.3389/fgene.2021.816779. This article has 13 citations and is from a peer-reviewed journal.

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