This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Genetics, Subject name: Biochemistry
Lesch-Nyhan syndrome, the sex linked recessive disorder is due to the lack of the enzyme: 
Select and explain. 
A. Hypoxanthine-guanine phosphoribosyl transferase, B. Xanthine oxidase, C. Adenine phosphoribosyl transferase, D. Adenosine deaminase
A: Hypoxanthine-guanine phosphoribosyl transferase
Answer: A: Hypoxanthine-guanine phosphoribosyl transferase 
Explanation: Ans. A. Hypoxanthine-guanine phosphoribosyl transferasePurine biosynthesis takes place by de novo and salvage pathway. Erythrocytes, Neutrophils and the brain cells lack the enzyme "PRPP-amido transferase" so salvage pathway is operative there. It is one step synthesis.HGPRT ase (Hypoxanthine guanine phosphoribosyl transferase)Deficiency of HGPRT (Hypoxanthine-guanine phosphoribosyl transferase) leads to an inherited X-linked disorder, Lesch- Nyhan syndrome, which affects only males. In this salvage pathway is not operative, purines can't be converted into nucleotides and degraded to uric acid. The symptoms area. Hyperuricemiab. Goutc. Urinary tract stonesd. Neurological symptoms of mental retardatione. Self-mutilation (painful, destructive biting of fingers and lips).