Pathophysiology of acute fatty liver of pregnancy. Impaired mitochondrial β-oxidation of fatty acids caused by enzyme deficiencies has been implicated in the pathogenesis of acute fatty liver of pregnancy. Homozygous fetal enzymatic deficiencies result in increased levels of free fatty acid metabolites that cross into the maternal circulation. Pregnant women who are heterozygous for fatty acid oxidation enzyme defects may be more susceptible to the increased metabolic demands of pregnancy and more susceptible to liver injury from lipotoxic metabolites, inflammatory pathway activation, reactive oxygen species, and apoptosis. The fetal fatty acid oxidation defects that have been associated with acute fatty liver of pregnancy are deficiencies in long-chain acyl-coenzyme A (CoA) dehydrogenases (LCHAD) and mitochondrial trifunctional protein (most common), as well as deficiencies in short-chain acyl-coenzyme A dehydrogenases (SCAD) and medium-chain acyl-coenzyme A dehydrogenases (MCAD).^1,33  CPT, carnitine palmitoyltransferase; LCAD, long-chain acyl-coenzyme A dehydrogenase; LKAT, long-chain 3-ketoacyl-coenzyme A thiolase; SCHAD, short-chain 3-hydroxyacyl-coenzyme A dehydrogenase; SKAT, short-chain 3-ketoacyl-coenzyme A thiolase. Figure adapted from Liu J, Ghaziani TT, Wolf JL: Acute fatty liver disease of pregnancy: Updates in pathogenesis, diagnosis, and management. Am J Gastroenterol 2017; 112:838–46 and Treem WR, Rinaldo P, Hale DE, Stanley CA, Millington DS, Hyams JS, Jackson S, Turnbull DM: Acute fatty liver of pregnancy and long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency. Hepatology 1994; 19:339–45.