While primary hyperparathyroidism is one of the most frequent causes, loss-of-function mutations in the CYP24A1 gene, which encodes for the 24-hydroxylase enzyme responsible for the catabolism of 25(OH)D3 and 1,25(OH)2D3, have been described as a rare cause of hypercalcemia associated with nephrocalcinosis and nephrolithiasis due to the reduced degradation of vitamin D metabolites. The gene discussed is CYP24A1; the disease is nephrocalcinosis.