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Abstract
Two brothers with hereditary xanthinuria (xanthine oxidase deficiency) and several
members of their family were studied. In both subjects, plasma and urinary concentrations
of uric acid were low whereas xanthine and hypoxanthine concentrations were markedly
elevated. Xanthine oxidase activity was virtually absent in the patients' duodenal
mucosa, a finding that established the diagnosis of hereditary xanthinuria. In their
parents (obligate heterozygotes), the duodenal xanthine oxidase activity was about
50% of that in control subjects (father 9.3 and mother 12.8 mU/g tissue compared with
21.3 +/- 5.0 mU/g tissue, mean +/- SD). The residual xanthine oxidase from the parents
exhibited normal kinetics with respect to hypoxanthine. The parents' urinary xanthine
and hypoxanthine concentrations were significantly greater than those of control subjects,
while their plasma concentrations of oxypurines were normal. Similar findings were
observed in at least 6 other relatives, a finding that suggested that they were heterozygotes.
This study suggests that obligate hereditary xanthinuria heterozygotes have only 50%
of the xanthine oxidase activity of controls; this deficiency results in a partial
metabolic blockage at this enzymatic step in heterozygotes.