Vitamin D plays a central role in calcium homeostasis. Impaired degradation of 1,25-dihydroxyvitamin D due to loss-of-function mutations in CYP24A1 leads to significant hypercalcemia, hypercalciuria, suppressed level of parathyroid hormone (PTH), nephrocalcinosis and nephrolithiasis. This condition has been called Idiopathic infantile hypercalcemia. Treatment includes low calcium diet, rehydration, furosemid, avoidance of vitamin D supplements and sun protection. In severe cases

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... ketoconazole, bisphosphonates and hemodiafiltration may be used. Early diagnosis of the disease allows to develop an individual plan for managing these patients to prevent the formation of kidney disease, to conduct a genetic family counseling. Here, we describe the cohort of patients (3 children, 2 adults) with significant hypercalcemia due to homo- and compound heterozygous mutations in CYP24A1, describe the main clinical and laboratory characteristics, diagnosis, principles and foundations of the management of patients with this pathology.