3-Hydroxy-3-Methylglutaric Aciduria

3-Hydroxy-3-methylglutaric aciduria was found in a newborn infant whose parents are first cousins. The patient presented at 5 days of life with hyperammonemia, hypoglecemia, and metabolic acidosis. There was no ketonuria. Diagnosis was made by analysis of the pattern of organic acids excreted in the urine. A profound deficiency in activity of 3-hydroxy-3-methylglutaryl-coenzyme A lyase was found in cultured skin fibroblasts. The parents had intermediate levels of enzyme activity.