Response to: Hypouricaemia and acute kidney injury: a hereditary condition should be considered.

Abstract

First, we would like to thank Dr Martin for his insightful comments. We agree that we should evaluate the mutations in the gene that caused renal hypouricemia (RHUC) in the patient in this report.1 The patient was of Japanese ethnicity with no family history of nephrolithiasis or exercise-induced acute kidney injury (EIAKI), and this was the first instance that they noticed symptoms suggesting EIAKI. At discharge, we recommended sufficient hydration during exercise and avoiding strenuous activity. After kidney function recovery, the patient’s uric acid (UA) level was as low as it was at hospitalization, but the fractional excretion of UA remained high. Although we did not mention it in our report, we diagnosed this case as RHUC and excluded diseases that could cause hypouricemia with increased UA excretion, such as the syndrome of inappropriate secretion of antidiuretic hormone and Fanconi syndrome.1 UA is excreted from the renal glomerulus into the renal tubules and reabsorbed via UA transporters, such as urate transporter 1 (encoded by the URAT1/SLC22A12 gene) and glucose transporter 9 (encoded by the GLUT9/SLC2A9 gene), expressed in the proximal tubular epithelium. Dysfunction of these transporters causes RHUC, and nephrolithiasis or EIAKI are known complications of RHUC; however, the exact frequencies of these complications remain unknown. It is postulated that there are genes other than URAT1/SLC22A12 and GLUT9/SLC2A9 that cause RHUC.2,3 The genetic test could have been performed to discover the causative gene. Although allopurinol might prevent EIAKI in patients with RHUC, its administration remains controversial, and the dosage and dosing period are unclear.2,4 Therefore, we did not administer allopurinol.