This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
A patient with increased Hypoxanthine and Xanthine in blood with hypouricemia which enzyme is deficient? 
Select and explain. 
A. HGPase, B. Xanthine oxidase, C. Adenosine deaminase, D. APRtase
B: Xanthine oxidase
Answer: B: Xanthine oxidase 
Explanation: Hypouricemia- Hypouricemia and increased excretion of hypoxanthine and xanthine are associated with xanthine oxidase deficiency.Lesch-Nyhan Syndrome- The Lesch-Nyhan syndrome, an overproduction hyperuricemia characterized by frequent episodes of uric acid lithiasis and a bizarre syndrome of selfmutilation reflects a defect in hypoxanthine-guanine phosphoribosyltransferase, an enzyme of purine salvage.Adenosine Deaminase Deficiency- Adenosine deaminase deficiency is associated with an immunodeficiency disease in which both thymus-derived lymphocytes (T cells) and bone marrow-derived lymphocytes (B cells) are sparse and dysfunctional. Patients suffer from severe immunodeficiency.Purine Nucleoside Phosphorylase Deficiency- Purine nucleoside phosphorylase deficiency is associated with a severe deficiency of T cells but apparently normal B cell function