ACAT1 and hyperinsulinemic hypoglycemia, familial, 4: Beta-ketothiolase (T2, mitochondrial acetoacetyl-CoA thiolase) deficiency is an autosomal recessive disorder of isoleucine catabolism and ketone body metabolism that is characterized by increased urinary excretion of 2-methylacetoacetate, 2-methyl-3-hydroxybutyrate, and tiglylglycine.