Simple gas chromatographic-mass spectrometric procedure for diagnosing pyrimidine degradation defects for prevention of severe anticancer side effects

Inborn errors of pyrimidine degradation, dihydropyrimidine dehydrogenase de ficiency and dihydropyrimidinase deficiency, are less rare than has general ly been assumed. Many asymptomatic cases have been reported, and in patient s with symptoms, the clinical abnormalities are variable and nonspecific. W ithdrawal of pyrimidine analogues such as 5-fluorouracil (5FU), a commonly used anticancer drug, from the cancer chemotherapy regimens of patients wit h pyrimidine degradation deficiencies, however, is critical because 5FU is degraded in vivo by pyrimidine-degradative enzymes. Patients with these def iciencies suffer from severe neurotoxicity, sometimes leading to death, fol lowing administration of 5FU, and even otherwise asymptomatic homozygotes o r heterozygotes may develop severe clinical symptoms upon administration of such medication. Therefore, a rapid and specific method for identifying ca ncer patients with these enzyme deficiencies prior to treatment with 5FU is critical. To address this problem, we established methods for highly sensi tive yet specific determinations of thymine, uracil, dihydrothymine, dihydr ouracil, orotate and creatinine simultaneously in 0.1-ml liquid urine or fi lter-paper urine. This method involves stable isotope dilution, a simplifie d urease treatment previously described and gas chromatography-mass spectro metry without prior fractionation. The high recovery and low C.V. values we re obtained and healthy control values were also determined for these metab olites. Using artificially prepared urine specimens simulating these disord ers, the chemical diagnosis can be made clearly, and no further analysis ap pears to be required for differential chemical diagnosis. (C) 2001 Elsevier Science B.V. All rights reserved.