CYP24A1 and nephrocalcinosis: Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)2D, suppressed parathyroid hormone (PTH) concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density [5].