CYP24A1 encodes 1, 25(OH)2-D-24-hydroxylase, a key enzyme of vitamin D metabolism. CYP24A1 deficiency due to bi-allelic mutations causes idiopathic infantile hypercalcemia (IIH), particularly in the setting of vitamin D supplementation. IIH is characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, fever, nephrocalcinosis, and hypercalciuria. CYP24A1 deficiency has also been reported to cause nephrolithiasis (kidney stone) and nephrocalcinosis in children and adults, which is a frequent clinical condition in both general and patient populations. Heterozygous carriers of CYP24A1 mutations may have an increased risk of hypercalciuria. This laboratory performs sequencing of the CYP24A1 gene.