Although controversial, it is possible that intermittent increases in prolactin during lactation may contribute to hypercalcemia by stimulating CYP27B1, which drives 25(OH)D to 1,25(OH)2D.38Further, it should not be surprising that hypercalcemia can worsen during lactation in patients with CYP24A1 variants. The gene discussed is CYP24A1; the disease is Hypercalcemia.