Twenty percent of patients are asymptomatic. Symptoms
are not specific. Irritability, vomiting, and failure to thrive may be the
presenting symptoms. The patient may present at any age with hematuria,
pyuria, renal colic, dysuria, urinary frequency, urine incontinence,
polyuria, abdominal pain, or symptoms of a urinary tract infection.
Laboratory findings include low or absent uric acid replaced by xanthine in
concentrations from 10 to 40 μmol/L. Hypoxanthine concentrations are
lower than 5 μmol/L. Xanthine and hypoxanthine can be find in the
urine, xanthine calculi in the urinary tract, and crystalline deposits in
skeletal muscles.