Question

The enzyme that is deficient in Lesch-Nyhan patients is hypoxanthine-guanine phosphoribosyltransferase (HGPRTase).This deficiency results in:

	A.	an increase in production of Figure D:
	B.	a decrease in purine salvage and an increase in de novo synthesis of purine nucleotides.
	C.	a decrease in the urinary excretion of uric acid.
	D.	an increase in feedback inhibition of the de novo synthetic pathways.
	E.	a decrease in phosphoribosylpyrophosphate (PRPP) concentrations.
	F.	an increase in purine salvage and a decrease in de novo synthesis of purine nucleotides.

Answer 1

B. A decrease in purine salvage and an increase in de novo synthesis of purine nucleotides.

Hypoxanthine-guanine phosphoribosyl transferase (HGPRTase) is an enzyme of the purine salvage pathway. It helps in recycling of purines (Salvage pathway), which ensures that the cell has adequate supply of purines for DNA synthesis. When purines cannot be recycled, there is a lack of feedback inhibition of their synthesis, resulting in catabolism of these excess bases to uric acid. Thus, Uric acid concentrations in the blood and urine are elevated leading to symptoms related to Lesch-Nyhan syndrome.