Hypouricemia with recurrent nephrolithiasis: an overlooked entity: Answers

Excerpt

This patient with nephrolithiasis presents with both hypouricemia and reduced urinary uric acid excretion. Uric acid is the final product of the metabolic pathway for purine nucleotides. This metabolic pathway involves purine degradation to inosinic acid and hypoxanthine. The enzyme xanthine oxidase (XO) is an isoform of xanthine oxidoreductase that catalyzes the oxidation of hypoxanthine to xanthine and uric acid (Fig. 1) [1, 2]. Uric acid is eliminated by the kidneys and gastrointestinal pathways [3]. Hypouricemia is a level of uric acid in the blood that is less than 2.0 mg/dl [4]. Hypouricemia deserves the same attention as hyperuricemia. It may be the only marker of different underlying diseases. The decreased blood uric acid level is characterized by increased uric acid clearance or decreased uric acid production [4]. The differential diagnosis is made based on urine uric acid level. Hypouricemia with a reduced urine uric acid level is associated with uric acid production defects [4]. Three hereditary diseases may cause nephrolithiasis with uric acid production defects. These are Lesch Nyhan syndrome, molybdenum cofactor deficiency, and hereditary xanthinuria, respectively [5‐7]. …