Increase in xanthine and hyposanthine occurs in which deficiency?

Xanthine oxidase (xanthine dehydrogenase) deficiency, type I, is an uncommon autosomal recessive disorder characterized by the excretion of urinary xanthine and hypoxanthine as the chief end products of purine metabolism, and by low serum and urinary uric acid levels. Xanthine oxidase catalyses the oxidation of hypoxanthine to xanthine and xanthine to uric acid, hence the biochemical abnormalities which define the syndrome. The disorder may be asymptomatic and diagnosed only after the fouitous finding of a low serum urate, usually less than 2 mg/dl. Ref-Sathyanarayana 4/e p407