Low-dose or high-dose hydrochlorothiazide in idiopathic hypercalciuria among children? Re: role of high-dose hydrochlorothiazide in idiopathic hypercalciuric urolithiasis of childhood.

Dear Editor, We read with interest the article “Role of high-dose hydrochlorothiazide in idiopathic hypercalciuric urolithiasis of childhood” by Naseri and Sadeghi.1 They used high-dose hydrochlorothiazide (1 mg/ kg/d to 2 mg/kg/d) in hypercalciuric children and described that no study has addressed whether low doses of thiazides have a hypocalciuric effect, especially in children.1 We recently reported that a low dose (0.5 mg/kg/d) of hydrochlorothiazide may be safe and effective in controlling renal hypercalciuria in children and found that hematuria and urolithiasis gradually resolved in accordance with the improvement of hypercalciuria.2 Although Naseri and Sadeghi did not mention the mechanisms action of hydrochlorothiazide,1 extracellular volume contraction resulting in a compensatory increase in renal proximal sodium reabsorption with passive paracellular calcium reabsorption3 and transient receptor potential vanil loid 5 (TRPV5)4, 5 might be important in understanding the hypocalciuric effect of hydrochlorothiazide. Hoenderop and colleagues4 showed active calcium reabsorption in the distal convoluted tubule was completely abolished in TRPV5 knockout mice, and Jang and colleagues5 recently demonstrated that the hypocalciuric effect of hydrochlorothiazide might be associated with increased protein abundance of TRPV5 in highsalt or calcium-diet-induced hypercalciuric rats. Therefore, we speculate that the degree of response to hydrochlorothiazide might be different in relation to not only dietary factors such as sodium intake, but also TRPV5-related mechanisms. Further studies are necessary to evaluate the role of TRPV5 in children with idiopathic hypercalciuria and elucidate whether there is a relationship between the dose of hydrochlorothiazide and abundance of TRPV5.