CYP24A1 Mutation in a Girl Infant with Idiopathic Infantile Hypercalcemia

Idiopathic infantile hypercalcemia (IIH) was associated with vitamin-D supplementation in the 1950's. Fifty years later, mutations in the CYP241A gene, involved in the degradation of vitamin-D, have been identified as being a part of the etiology. We report a case of a 21-month old girl, initially hospitalized due to excessive consumption of water and behavioral difficulties. Blood tests showed hypercalcemia and borderline high vitamin-D levels. Renal ultrasound revealed medullary nephrocalcinosis. An abnormality in vitamin-D metabolism was suspected and genetic testing was performed. This revealed the patient to be compound heterozygous for a common (p.E143del) and a novel (likely) disease-causing mutation (p.H83D) in the CYP24A1 gene. The hypercalcemia normalized following a calcium depleted diet and discontinuation of vitamin-D supplementation. Increased awareness of the typical symptoms of hypercalcemia, such as anorexia, polydipsia, vomiting and failure to thrive, is of utmost importance in diagnosing IHH early and preventing long-term complications such as nephrocalcinosis. Further identification of as many disease-causing mutations in the CYP24A1 gene as possible can help identification of predisposed individuals in whom vitamin-D supplementation should be reconsidered.