ACAT1 and beta-ketothiolase deficiency: Beta-ketothiolase deficiency (MIM 203750) occurs due to a mitochondrial acetoacetyl-CoA thiolase (T2; EC2.3.1.9) defect caused by mutation of ACAT1 (NG_009888, NM_000019.3), leading to the abnormal metabolism of isoleucine and ketone.