Urine with stones: nephrocalcinosis and vitamin D

Background Nephrocalcinosis (NC) refers to diffuse, fine, renal parenchymal calcification, as assessed by radiology or ultrasonography. In medullary NC, the calcification tends to occur in the area of the renal pyramids. It is typically associated with elevated urinary calcium, phosphate, and oxalate, or it can occur with alkaline urine. Any disorder that can lead to hypercalcemia or hypercalciuria may be implicated. Instead of stone formation, smaller parenchymal calcifications are deposited in the medulla, usually bilateral and symmetric. Vitamin D hormones play a central role in calcium homeostasis. Tight control of the vitamin D system requires inactivation of its active compound 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) through 24-hydroxylation by means of the enzyme 24-hydroxylase (CYP24A1) and degradation to calcitroic acid [1]. Recently loss-of-function mutations of vitamin D-24 hydroxylase (gene CYP24A1) have been recognized as a cause of hypercalcaemia and NC/nephrolithiasis in infants and adults suffering from Idiopathic Infantile Hypercalcaemia (IIH) [2]. Prevalence and natural history of this condition are still to be defined also in pediatric patients. We investigated the prevalence of CYP24A1 mutations in a cohort of pediatric patients with NC referred to our outpatient service from January 2012 to December 2013.