CYP24A1 and Hypercalcemia: We have also reported a patient, presenting with idiopathic infantile hypercalcaemia (IIH), who was diagnosed with biallelic CYP24A1 mutations resulting in the inability to produce 24,25(OH)2D from 25(OH)D, and had an elevated serum 1,25(OH)2D and a persistent state of hypercalcaemia.