Chen Jie, Bennett Michael J
Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
Methods Mol Biol. 2010;603:445-51. doi: 10.1007/978-1-60761-459-3_43.
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.
尿乳清酸排泄量的测定是诊断遗传性乳清酸尿症（一种嘧啶生物合成的遗传缺陷）的重要检测方法。继发性尿乳清酸升高的测定也是鉴别诊断某些尿素循环原发性疾病所致高氨血症的重要临床检测方法，这些原发性疾病包括鸟氨酸转氨甲酰酶（OTC）缺乏症以及高鸟氨酸血症-高氨血症-高瓜氨酸血症（HHH）综合征。在氨基甲酰磷酸合成酶（CPS）缺陷中观察到乳清酸水平较低。该方法使用稳定同位素标记的内标（1, 3-(15)N-乳清酸），在提取前将其添加到标准品、对照品和患者样品中。通过将样品与脲酶孵育去除尿素的干扰，乳清酸通过三甲基硅烷化进行衍生化处理。使用来自标记和未标记乳清酸的特定选择离子，根据八点标准曲线进行定量分析。
