Three cases of xanthinuria identified by gas chromatography/mass spectrometry‐based urine metabolomics

INTRODUCTION: Early diagnosis of patients with urolithiasis or hypouricemia owing to inborn errors of hypoxanthine metabolism is important in preventing renal failure or drug‐induced toxicity. CASE PRESENTATION: We identified three patients with xanthinuria using gas chromatography/mass spectrometry‐based urine metabolomics: a 72‐year‐old male with bladder stone, a severe hypouricemic 59‐year‐old female with type 2 diabetes mellitus, and an 8‐year and 9‐month‐old female who was first discovered to harbor a mutation in the xanthine dehydrogenase gene using whole‐exome sequencing, but had a normal molybdenum cofactor sulfurase gene. Hydantoin‐5‐propionate was detected in the first and third patients but not in the second, suggesting that the first and second patients had type I and II xanthinuria, respectively. CONCLUSION: Gas chromatography/mass spectrometry‐based metabolomics can be used for undiagnosed patients with xanthinuria, identification of the type of xanthinuria without allopurinol loading, and the quick functional evaluation of mutations in the xanthinuria‐related genes.