Maternal Hypercalcemia Due to Failure of 1,25-Dihydroxyvitamin-D3 Catabolism in a Patient With CYP24A1 Mutations

Context: Calcium metabolism changes in pregnancy and lactation to meet fetal needs, with increases in 1,25-dihydroxyvitamin D [1,25-(OH)(2)D] during pregnancy playing an important role. However, these changes rarely cause maternal hypercalcemia. When maternal hypercalcemia occurs, further investigation is essential, and disorders of 1,25-(OH)(2)D catabolism should be carefully considered in the differential diagnosis. Case: A patient with a childhood history of recurrent renal stone disease and hypercalciuria presented with recurrent hypercalcemia and elevated 1,25-(OH)(2)D levels during pregnancy. Laboratory tests in the fourth pregnancy showed suppressed PTH, elevated 1,25-(OH)(2)D, and high-normal 25-hydroxyvitamin D levels, suggesting disordered vitamin D metabolism. Analysis revealed low 24,25-dihydroxyvitamin D-3 and high 25-hydroxyvitamin D-3 levels, suggesting loss of function of CYP24A1 (25-hydroxyvitamin-D-3-24-hydroxylase). Gene sequencing confirmed that she was a compound heterozygote with the E143del and R396W mutations in CYP24A1. Conclusions: This case broadens presentations of CYP24A1 mutations and hypercalcemia in pregnancy. Furthermore, it illustrates that patients with CYP24A1 mutations can maintain normal calcium levels during the steady state but can develop hypercalcemia when challenged, such as in pregnancy when 1,25-(OH)(2)D levels are physiologically elevated.