Quantitative LC/MS-MS Analysis of Urinary Acylglycines: Application to theDiagnosis of Inborn Errors of Metabolism

The analysis of urinary acylglycines is an important biochemical tool for the diagnosis of many organic acidemias and mitochondrial fatty acid ???-oxidation defects. A new rapid analytical method has been developed for quantification of acylglycines in urine by liquid chromatography coupled with tandem mass spectrometry (LC/MS-MS). The method requires a simple sample preparation avoiding derivatization. It has high sensitivity, specificity and throughput capability; it requires minimal instrument maintenance. The use of chromatographic separation allows us to identify and quantify isomeric compounds that cannot be solved by appropriate MRM transitions. Urinary concentrations of the different acylglycines were determined using deuterated internal standards. Reference interval for the various metabolites was established using 120 healthy controls. The diagnostic usefulness of the method was demonstrated in 3 patients with propionic acidemia (PA), 1 patients with isovaleric acidemia (IVA), 2 patients with beta ketothiolase deficiency (???KTD), 1 patient with short branched chain amino acid deficiency (SBCADD), 4 patients with medium-chain acyl-CoA dehydrogenase deficiency (MCADD), 1 patient with isobutyryl-CoA dehydrogenase deficiency (IBDHD) and 1 patient with multiple acyl-CoA dehydrogenase deficiency (MADD).