Gas-chromatographic/mass spectrometric detection of 3-hydroxy-3-methylglutaryl-CoA lyase deficiency in double first cousins.

Gas chromatography/mass spectrometry was used for the detection of 3-hydroxy-3-methylglutaryl-CoA lyase (EC 4.1.3.4) deficiency in double first cousins. This enzyme is in the last step of leucine catabolism and is also involved in ketogenesis. Quantitation of urinary organic acids as their cyclohexyl esters demonstrated increased concentrations of 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid. The procedure is more rapid, sensitive, and specific than previously reported gas-chromatographic methods for acid quantitation. The affected children initially presented with symptoms similar to Reye's syndrome; the acids were quantitated during periods of altered intake of protein and fat. Both leucine and fat intake contributed to increased acid excretion. These studies suggest that life-threatening episodes of hypoglycemia are best prevented with a low-protein, low-fat diet.