Medium‐chain and long‐chain acyl CoA dehydrogenase deficiency: Clinical, pathologic and ultrastructural differentiation from Reye's syndrome

The clinical and pathologic findings in 12 patients with medium‐chain acyl CoA dehydrogenase deficiency and three patients with long‐chain acyl CoA dehydrogenase deficiency are summarized. Although these inborn errors of intramitochondrial β‐oxidation of fatty acids present with similar findings to Reye's syndrome, there are clinical, laboratory and hepatic histologic differences. Younger age at presentation, history of unexplained sibling death, a previous episode of lethargy, hypoglycemia or acidosis precipitated by fasting stress and only mildly elevated serum transaminases with normal or only mildly prolonged prothrombin time may all suggest an acyl CoA dehydrogenase deficiency. Long‐chain acyl CoA dehydrogenase deficiency is differentiated from medium‐chain acyl CoA dehydrogenase deficiency by younger age at presentation, more profound cardiorespiratory depression, evidence of cardiomyopathy, and sequelae of muscle weakness, hypotonia and developmental delay. Definitive diagnosis is made by assay of medium‐chain or long‐chain enzyme activity in cultured skin fibroblasts or in leukocytes. Hepatic light microscopic alterations are essentially limited to steatosis, which may be either macro‐ or microvesicular. The cases with microvesicular steatosis can be differentiated morphologically from Reye's syndrome by electron microscopy, showing the absence of the mitochondrial changes characteristic of Reye's. Four of seven cases of acyl CoA dehydrogenase deficiency showed some variations from normal in the appearance of the hepatocyte mitochondria. The relationship of these variations to the basic metabolic defect(s) remains to be determined.