Demonstration of a combined deficiency of xanthine oxidase and aldehyde oxidase in xanthinuric patients not forming oxipurinol.

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Genetic heterogeneity has been suggested in xanthinuria from the hitherto unexplained ability of some patients with this hereditary disorder to convert allopurinol to its active metabolite oxipurinol--an activity generally attributed to xanthine oxidase . This study provides evidence that the enzyme aldehyde oxidase is also deficient in xanthinuric patients not converting allopurinol to oxipurinol , whereas a xanthinuric patient with normal formation of oxipurinol had normal aldehyde oxidase activity . It is concluded that the enzyme aldehyde oxidase is the principal enzyme responsible for the formation of oxipurinol in man .