This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
b-hydroxybutyric aciduria is associated with deficiency of 
Select and explain. 
A. Orotidylic acid decarboxylase, B. Orotate phosphoribosyl transferase, C. PRPP Synthase, D. Dihydropyrimidine dehydrogenase
D: Dihydropyrimidine dehydrogenase
Answer: D: Dihydropyrimidine dehydrogenase 
Explanation: b-hydroxybutyric aciduria, a pyrimidine catabolism disorder due to total or paial deficiency of the enzyme dihydropyrimidine dehydrogenase. This disorder can develop toxicity to 5-fluorouracil, also a substrate for this dehydrogenase enzyme. Reference: Harpers illustrated biochemistry 30th edition