Recently, infants [19, 20, 27] and adults [19, 28] with elevated serum 1,25(OH)2D concentrations, hypercalcemia, hypercalciuria and nephrolithiasis have been found to have inactivating mutations of the 24-hydroxylase cytochrome P450 (CYP24A1) gene, the product of which degrades 25(OH)D and 1,25(OH)2D to less active metabolites, 24,25(OH)2D and 1,24,25-trihydroxyvitamin D, respectively, in target organs such as the intestine and kidney [12, 29]. Here, CYP24A1 is linked to Hypercalciuria.