ACAT1 and hyperinsulinemic hypoglycemia, familial, 4: β‐Ketothiolase deficiency (OMIM #203750, *607809), a defect of mitochondrial acetoacetyl‐CoA thiolase (T2, EC 2.3.1.9, gene symbol ACAT1, RefSeq NM_000019.3), is an autosomal recessive disorder, affecting isoleucine and ketone body metabolism (Fukao et al.