Hypouricaemia in a patient with hereditary xanthinuria type I

A 67-year-old woman was referred to our department for investigation of a 3-year history of declining renal function—serum creatinine concentration was 1·2 mg/dL (typical range 0·51–0·95) and the estimated glomerular filtration rate was 47 mL/min per 1·73 m2 (typical range >60). The patient had also been found to have persistent painless microscopic haematuria and a urinary albumin-to-creatinine ratio of up to 235 mg/g (typical range <30). She also reported mild muscle pains in her arms and legs.