Enhanced differentiation between 3‐hydroxyglutaric and 2‐hydroxyglutaric acids facilitates diagnostic testing for glutaric aciduria type 1

Glutaric aciduria type 1 (GA1) is an inherited neurometabolic disorder, in which deficiency of glutaryl-CoA dehydrogenase leads to accumulation of glutaric acid (GA) and 3-hydroxyglutaric acid (3-HG). Some low excretors may exhibit only slight elevation of urinary 3-HG, with normal urinary GA, yet are at significant risk of severe clinical disease. Accurate quantitation of urinary 3-HG is crucial in diagnostic workup for GA1, but in this context, current gas chromatography-mass spectrometry (GC-MS) methods have inherent analytical challenges. Co-elution and spectral similarities of the 3-HG and 2-HG structural isomers can cause difficulties in quantitation of slightly elevated 3-HG. Our laboratory recently acquired a gas chromatography system coupled to a triple quadrupole mass spectrometer (GC-MS/MS), and we took advantage of its increased sensitivity and specificity to improve our existing GC-MS method. A stable isotope dilution process is used, with sample treatment consisting of a double liquid-liquid extraction followed by a trimethylsilyl derivatization. The transitions