[Definition and classification of hyperuricemia].

Hyperuricemia (serum urate level >7 mg/dL) is caused by accelerated generation of uric acid and/or impaired excretion in the kidney. It is classified into three types (overproduction, underexcretion and mixed types). The typical cases with the type of uric acid overproduction are hypoxanthine guanine phosphoribosyl transferase deficiency due to HPRT gene abnormality, excessive consumption of purine-rich diet, and cytolysis induced by chemotherapy for blood neoplasm, those with the type of underexcretion are familial juvenile hyperuricemic nephropathy due to uromodulin gene abnormality and abrupt body weight loss due to low calorie diet, and those with the mixed type are glucose 6-phosphatase deficiency due to glucose 6-phosphatase gene abnormality and excessive consumption of alcohol beverages.