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HMGCS2
3-hydroxy-3-methylglutaryl-CoA synthase 2
HMGCS2 is located on the short (p) arm of chromosome 1, at band 1p12. Arm ratio per GRCh38 - banding schematic.
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Overview
HMGCS2 is located on chromosome 1 and encodes the mitochondrial isoform of HMG-CoA synthase, distinguishing it from the cytoplasmic isoform (HMGCS1) involved in cholesterol synthesis. The protein catalyses the condensation of acetyl-CoA and acetoacetyl-CoA to form HMG-CoA, the committed step in ketone body formation.
Ketogenesis occurs primarily in liver mitochondria and becomes particularly important during prolonged fasting, low-carbohydrate diets, or periods of increased energy demand. The enzyme's activity is tightly regulated to match the body's metabolic state, ensuring appropriate fuel availability for organs that can utilise ketone bodies.
What the gene does
The HMGCS2 protein operates within the mitochondrial matrix, where it catalyses the second step of the ketogenic pathway. The enzyme combines acetyl-CoA, derived from fatty acid oxidation, with acetoacetyl-CoA to produce 3-hydroxy-3-methylglutaryl-CoA. This product is subsequently cleaved by HMG-CoA lyase to yield acetoacetate, one of the primary ketone bodies.
Enzyme activity is regulated at multiple levels, including transcriptional control by metabolic signals and post-translational modifications. During fasting states, hormonal changes increase HMGCS2 expression in hepatocytes, enhancing the liver's capacity to generate ketone bodies. These molecules are then exported to peripheral tissues, where they can be converted back to acetyl-CoA and oxidised for energy production. The brain is particularly dependent on ketone bodies during glucose scarcity, as these compounds can cross the blood-brain barrier and provide an alternative energy substrate.
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Chromosome location
HMGCS2 is positioned on the short arm of chromosome 1 at band p12, specifically within the cytogenetic location 1p12. The gene spans a region that includes multiple exons encoding the mitochondrial targeting sequence and catalytic domains of the enzyme. Structural features of the genomic region have not been extensively characterised in public databases.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The HMGCS2 enzyme shares structural similarity with other members of the thiolase superfamily, featuring a catalytic core that facilitates the condensation reaction. The protein includes an N-terminal mitochondrial targeting sequence that directs the nascent polypeptide to the mitochondrial matrix, where it undergoes proteolytic processing to yield the mature, active enzyme.
Key variants
Genetic variants in HMGCS2 have been identified through population sequencing studies, though the clinical significance of most remains uncertain. Loss-of-function variants would be expected to impair ketone body synthesis, potentially affecting metabolic adaptation during fasting or illness. However, documented cases of HMGCS2-related metabolic disorders are rare, and the gene's variant landscape has not been comprehensively catalogued in clinical genetics databases.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1016+1G>A | - | Pathogenic | ★★☆☆ | HMGCS2-related disorders |
c.1090T>A | p.Phe364Ile | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.1162G>A | p.Gly388Arg | Pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.1394del | p.Asn465fs | Pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.1499G>A | p.Arg500His | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.1502G>C | p.Arg501Pro | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.181_182insCCAATATGGCCCTGGAGGCCAA | p.Val61fs | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.634G>A | p.Gly212Arg | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.726C>G | p.Tyr242Ter | Pathogenic/Likely pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
c.862C>T | p.Arg288Ter | Pathogenic | ★★☆☆ | 3-hydroxy-3-methylglutaryl-CoA synthase deficiency |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Clinical conditions directly attributed to HMGCS2 variants have not been well established in the medical literature. Theoretical considerations suggest that severe deficiency could lead to hypoketotic hypoglycaemia during metabolic stress, similar to defects in other ketogenic enzymes. Individuals with impaired ketogenesis may experience difficulty maintaining blood glucose levels during fasting, though compensatory mechanisms and the rarity of complete enzyme absence mean such presentations remain poorly documented.
No disease links recorded for this gene in our reference set.
UK clinical status
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the difference between HMGCS1 and HMGCS2?
HMGCS1 encodes the cytoplasmic isoform of HMG-CoA synthase, which participates in cholesterol biosynthesis, whilst HMGCS2 encodes the mitochondrial isoform dedicated to ketone body production. The two proteins function in separate cellular compartments and serve distinct metabolic purposes.
Can diet influence HMGCS2 activity?
Dietary composition affects HMGCS2 expression levels. Low-carbohydrate, high-fat diets and fasting states increase the gene's transcription in the liver, enhancing ketogenic capacity. However, these are general metabolic responses rather than effects on the gene itself.
Are HMGCS2 variants common in the general population?
Population frequency data for HMGCS2 variants are limited. The gene has not been extensively studied in large-scale sequencing projects focused on disease-associated variation, and most identified variants have not been classified for clinical significance.