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
Increase in xanthine and hyposanthine occurs in which deficiency? 
Select and explain. 
A. Xanthine oxidase, B. HGP synthase, C. Urate oxidase, D. Adenosine deaminase
A: Xanthine oxidase
Answer: A: Xanthine oxidase 
Explanation: Xanthine oxidase (xanthine dehydrogenase) deficiency, type I, is an uncommon autosomal recessive disorder characterized by the excretion of urinary xanthine and hypoxanthine as the chief end products of purine metabolism, and by low serum and urinary uric acid levels. Xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and xanthine to uric acid, hence the biochemical abnormalities which define the syndrome. The disorder may be asymptomatic and diagnosed only after the fouitous finding of a low serum urate, usually less than 2 mg/dl. Ref-Sathyanarayana 4/e p407