Quantitative liquid chromatography coupled with tandem mass spectrometry analysis of urinary acylglycines: Application to the diagnosis 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 β-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, and it requires minimal instrument maintenance. The use of chromatographic separation allows us to identify and quantify isomeric compounds that cannot be solved by appropriate multiple reaction monitoring (MRM) transitions. Urinary concentrations of the different acylglycines were determined using deuterated internal standards. The reference interval for the various metabolites was established using 120 healthy controls. The diagnostic usefulness of the method was demonstrated in three patients with propionic acidemia (PA), one patient with isovaleric acidemia (IVA), two patients with beta ketothiolase deficiency (BKTD), one patient with short branched chain amino acid deficiency (SBCAD), four patients with medium chain acyl-coenzyme A dehydrogenase deficiency (MCADD), one patient with isobutyryl-coenzyme A dehydrogenase deficiency (IBDHD), and one patient with multiple acyl-coenzyme A dehydrogenase deficiency (MADD).