title: Quantitation of orotic acid in urine using isotope dilution-selected ion gas chromatography-mass spectrometry.
abstract: The measurement of urinary orotic acid excretion is an important test for establishing a diagnosis of hereditary orotic aciduria, a genetic defect of pyrimidine biosynthesis. Measurement of secondary urinary orotic acid elevation is also an important clinical test for the differential diagnosis of hyperammonemia due to some of the primary disorders of the urea cycle including ornithine transcarbamylase (OTC) deficiency, and the hyperornithinemia-hyperammonemia-homocitrullinemia (HHH) syndrome. Low levels of orotic acid are observed in carbamylphosphate synthetase (CPS) defects. This method utilizes a stable-isotope labeled internal standard (1, 3-(15)N-orotic acid), which is added to the standards, controls, and patient samples prior to extraction. Interference from urea is removed by incubation of samples with urease and the orotic acid is derivatized by trimethylsilylation. Quantitation is made against an eight-point standard curve using specific selected ions from both the labeled and unlabeled orotic acid.
authors.affiliation: Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Bennett
mesh_terms: D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D009963:Orotic Acid / Q000737:chemistry / Q000652:urine*; D015203:Reproducibility of Results; D014297:Trimethylsilyl Compounds / Q000737:chemistry; D056806:Urea Cycle Disorders, Inborn / Q000652:urine
chemical_list: D014297:Trimethylsilyl Compounds; C047270:N,N-bis(trimethylsilyl)-2,2,2-trifluoroacetamide; D009963:Orotic Acid; C039293:trimethylchlorosilane