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ACAT1 gene

acetyl-CoA acetyltransferase 1

Normal Function

The ACAT1 gene provides instructions for making an enzyme that is found in the energy-producing centers within cells (mitochondria). This enzyme plays an essential role in breaking down proteins and fats from the diet. Specifically, it helps process isoleucine, an amino acid that is a building block of many proteins. This enzyme is also involved in processing ketones, which are molecules that are produced when fats are broken down in the body.

During the breakdown of proteins, the ACAT1 enzyme is responsible for a step in processing isoleucine. It converts a molecule called 2-methyl-acetoacetyl-CoA into two smaller molecules, propionyl-CoA and acetyl-CoA, that can be used to produce energy.

The ACAT1 enzyme carries out the last step in ketone breakdown (ketolysis) during the processing of fats. The enzyme converts a molecule called acetoacetyl-CoA into two molecules of acetyl-CoA, which can be used to produce energy. In the liver, the enzyme also carries out this chemical reaction in reverse, which is a step in building new ketones (ketogenesis).

Health Conditions Related to Genetic Changes

Beta-ketothiolase deficiency

More than 100 mutations in the ACAT1 gene have been identified in people with beta-ketothiolase deficiency. The condition usually appears before age 2 and causes episodes (called ketoacidotic attacks) of vomiting, dehydration and other health problems, which can lead to coma. Some of the genetic changes that cause beta-ketothiolase deficiency disrupt the normal function of the enzyme, while other mutations prevent cells from producing any functional enzyme.

A shortage of the ACAT1 enzyme prevents the body from processing proteins and fats properly. As a result, chemical byproducts called organic acids can build up to toxic levels in the blood. These substances may cause the blood to become too acidic (ketoacidosis) and can damage the body's tissues and organs, particularly in the nervous system. This damage likely underlies the episodes associated with beta-ketothiolase deficiency.

More About This Health Condition

Other Names for This Gene

  • ACAT
  • acetoacetyl Coenzyme A thiolase
  • acetyl-Coenzyme A acetyltransferase 1
  • acetyl-Coenzyme A acetyltransferase 1 (acetoacetyl Coenzyme A thiolase)
  • MAT
  • methylacetoacetyl-Coenzyme A thiolase
  • T2
  • THIL

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Abdelkreem E, Harijan RK, Yamaguchi S, Wierenga RK, Fukao T. Mutation update on ACAT1 variants associated with mitochondrial acetoacetyl-CoA thiolase (T2) deficiency. Hum Mutat. 2019 Oct;40(10):1641-1663. doi: 10.1002/humu.23831. Epub 2019 Jul 3. Citation on PubMed or Free article on PubMed Central
  • Fukao T, Yamaguchi S, Orii T, Hashimoto T. Molecular basis of beta-ketothiolase deficiency: mutations and polymorphisms in the human mitochondrial acetoacetyl-coenzyme A thiolase gene. Hum Mutat. 1995;5(2):113-20. doi: 10.1002/humu.1380050203. Citation on PubMed
  • Grunert SC, Sass JO. 2-methylacetoacetyl-coenzyme A thiolase (beta-ketothiolase) deficiency: one disease - two pathways. Orphanet J Rare Dis. 2020 Apr 28;15(1):106. doi: 10.1186/s13023-020-01357-0. Citation on PubMed or Free article on PubMed Central
  • Kano M, Fukao T, Yamaguchi S, Orii T, Osumi T, Hashimoto T. Structure and expression of the human mitochondrial acetoacetyl-CoA thiolase-encoding gene. Gene. 1991 Dec 30;109(2):285-90. doi: 10.1016/0378-1119(91)90623-j. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.