Dihydropyrimidine dehydrogenase deficiency leading to thymine-uraciluria. An inborn error of pyrimidine metabolism.

Three unrelated patients with excessive thymine-uraciluria due to dihydropyrimidine dehydrogenase deficiency are described. Excretory values (mmol/g creatinine) were: uracil 2.0-10.5, thymine 2.3-7.5, 5-hydroxymethyluracil 0.2-0.9. Orally administered (index patient) uracil and thymine were excreted for the greater part whilst dihydrouracil and S-dihydrothymine were mainly metabolised. Dihydropyrimidine dehydrogenase activities (nmol X h-1 X mg-1 protein) in leucocytes were 0.04, 0.01 and less than 0.01 in the patients, 0.31-1.66 in their parents, and 1.01-4.46 in controls (n = 4). The patients presented with a non-specific clinical picture of cerebral dysfunction.