An even more rapid progression of the disorder leading to nephrectomy in a 3 years old boy was recently reported from Tunisia.36 Another important health aspect of classical xanthinuria, irrespective of its clinical manifestation is the risk of drug toxicity/inefficiency due to the fact that both XDH and AO are drug‐metabolizing enzymes.4 Two cases of severe thiopurine‐induced toxicity in xanthinuria patients were recently reported.37, 38. Here, AOX1 is linked to xanthinuria.