Background. Hypercalcemia is a manifestation of a wide range of hereditary and acquired conditions encountered in pediatric practice. There are two main groups of diseases occurring with hypercalcemia: parathyroid hormone (PTH)-dependent and PTH-independent. The most common causes of PTH-independent hypercalcemia are hypervitaminosis D, granulomatous and oncological diseases, idiopathic infantile hypercalcemia, and Williams syndrome.
Description of the clinical case. The article presents two clinical cases of PTH-independent hypercalcemia in siblings, most likely associated with impaired vitamin D inactivation due to CYP24A1 gene mutation.
Conclusion. In the presence of symptoms characteristic of hypercalcemia, it is important to suspect it in a timely manner, because early diagnosis and timely treatment of patients with hypercalcemia prevent the development of nephrolithiasis and urolithiasis. It must be remembered that against the background of taking prophylactic doses of vitamin D, in rare cases, hypercalcemia may occur as a result of a mutation in the CYP24A1 gene.

Keywords: secondary hypoparathyroidism, hypervitaminosis D, CYP24A1 mutation, idiopathic infantile hypercalcemia, hypercalcemia, nephrocalcinosis