3-Hydroxy-3-methylglutaric aciduria in an Italian patient is caused by a new nonsense mutation in the HMGCL gene.

3-Hydroxy-3-methylglutaric aciduria is a rare autosomal recessive inborn error of metabolism caused by deficiency of the mitochondrial enzyme 3-hydroxy-3-methylglutaryl-CoA lyase (HMGCL). Up to now only a few mutations have been reported in the HMGCL gene. We report the first Italian patient, a female who presented metabolic acidosis at 3 days of age and then 3 months later. Analysis of urinary organic acids showed the excretion of 3-hydroxy-3-methylglutaric acid, 3-methylglutaconic acid, 3-methylglutaric acid, and 3-hydroxyisovaleric acid. A defect of HMGCL activity was suspected and then confirmed on cultured skin fibroblasts. Brain RM showed a diffuse mild abnormality of cerebral white matter in the periventricular regions, and the single voxel proton MRI spectroscopy showed abnormal peaks. In the patient's full-length HMGCL-cDNA a new c286C > T transition that leads to the stop codon Q96X was detected at the homozygous level. This mutation, that gives rise to a truncated protein, was confirmed in the patient's and also her parents' genomic DNA. The severe genetic lesion identified in the patient, which is in contrast with the mild clinical phenotype, stresses the importance of early diagnosis and therapy in HMGCL deficiency.