Plays a major role in ketone body metabolism. Defects in ACAT1 are a cause of 3-ketothiolase deficiency (3KTD); also known as alpha- methylacetoaceticaciduria. 3KTD is an inborn error of isoleucine catabolism characterized by intermittent ketoacidotic attacks associated with unconsciousness. Some patients die during an attack or are mentally retarded. Urinary excretion of 2-methyl-3- hydroxybutyric acid, 2-methylacetoacetic acid, triglylglycine, butanone is increased. It seems likely that the severity of this disease correlates better with the environmental or acquired factors than with the ACAT1 genotype. Belongs to the thiolase family. Note: This description may include information from UniProtKB.