Hypouricemia can be caused by hyperexcretion of UA, renal hypouricemia, and Fanconi syndrome, or by lower uric acid production, including that associated with xanthinuria, molybdenum cofactor deficiency, purine nucleoside phosphorylase deficiency, phosphoribosyl pyrophosphate synthetase hypoactivity, severe hepatic injury, and emaciation10. The gene discussed is PNP; the disease is xanthinuria.