Phenotype of Idiopathic Infantile Hypercalcemia Associated with the Heterozygous Pathogenic Variant of SLC34A1 and CYP24A1

Idiopathic infantile hypercalcemia (IIH) is a rare genetic disease, also called hypersensitivity to vitamin D3. The molecular heterogeneity allows for the differentiation between the two forms; IIH type 1 caused by CYP24A1 genetic variants and IIH type 2 associated with SLC34A1 mutations. The affected individuals express a variety of symptoms: hypercalcemia, hypercalciuria, suppressed intact parathormone levels (PTH), nephrocalcinosis, elevated levels of serum 1,25 (OH)2-vitamin D3 or inappropriately normal levels, and kidney phosphate wasting. The present paper describes three cases of IIH with heterozygous mutations in SLC34A1 and CYP24A1 genes, respectively. The genetic diagnosis is of paramount importance for proper treatment and the prediction of long-term outcomes.