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Old 07-10-2010
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Default Lesch Nyhan Syndrome and Allopurino

Correct option is,

A. Decrease de novo purine synthesis

Allopurinol is structural isomer of hypoxanthine and acts by two mechanisms:

(1) it inhibits xanthine oxidase, which catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid

(2) it also inhibits the purine synthesis by inhibiting the rate limiting enzyme PRPP amidotransferase. As it is a purine analogue, allopurinol must be converted to its respective nucleotide by HGPRT to inhibit this enzyme.

So it needs an intact HGPRT. As in Lesch Nyhan Syndrome there is complete deficiency of this enzyme so it cannot inhibit purine synthesis & which continues unchecked.
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