Fasting is accompanied by a decrease in the availability of glucose for energy use in peripheral tissues and, consequently, an increased reliance of these tissues on the availability of ketone bodies and fatty acids for energy. The availability of ketone bodies depends almost exclusively on hepatic ketogenesis. Failure of ketogenesis may occur in patients with any defect of the enzymes associated with the mitochondrial oxidation of fatty acids.¹ These defects are typically manifested by hypoglycemia, which results from the inadequate supply of alternative substrate (ketones). Other clinical features are more variable and may include myopathy, cardiomyopathy, hepatocellular damage, and neuropathies. . . .