Ketone bodies are major vectors of energy transfer from the liver to extrahepatic tissues and are the main source of lipid-derived energy for the brain. Mitchell et al. (1995) reviewed medical aspects of ketone body metabolism, including the differential diagnosis of abnormalities. As the first step of ketone body utilization, succinyl-CoA:3-oxoacid CoA transferase (SCOT, or OXCT1; EC 2.8.3.5) catalyzes the reversible transfer of CoA from succinyl-CoA to acetoacetate.

Mitochondrial HMG-CoA synthase deficiency (HMGCS2D) is an inherited metabolic disorder caused by a defect in the enzyme that regulates the formation of ketone bodies. Patients present with hypoketotic hypoglycemia, encephalopathy, and hepatomegaly, usually precipitated by an intercurrent infection or prolonged fasting (summary by Aledo et al., 2006).

Methylmalonate semialdehyde dehydrogenase deficiency is a rare autosomal recessive inborn error of metabolism with a highly variable phenotype. Some patients may be asymptomatic, whereas others show global developmental delay, nonspecific dysmorphic features, and delayed myelination on brain imaging. Laboratory studies typically show increased urinary 3-hydroxyisobutyric acid, although additional metabolic abnormalities may also be observed (summary by Marcadier et al., 2013).

Most children with carbonic anhydrase VA (CA-VA) deficiency reported to date have presented between day 2 of life and early childhood (up to age 20 months) with hyperammonemic encephalopathy (i.e., lethargy, feeding intolerance, weight loss, tachypnea, seizures, and coma). Given that fewer than 20 affected individuals have been reported to date, the ranges of initial presentations and long-term prognoses are not completely understood. As of 2021 the oldest known affected individual is an adolescent. Almost all affected individuals reported to date have shown normal psychomotor development and no further episodes of metabolic crisis; however, a few have shown mild learning difficulties or delayed motor skills.