Therapy-Resistant Hypercalcemia in a Patient with Inactivating CYP24A1 Mutation and Recurrent Nephrolithiasis: Beware of Concomitant Hyperparathyroidism.

We describe a case harboring a homozygous CYP24A1 mutation with mild loss of function, first presenting with recurrent nephrolithiasis from the age of 22 onward, initially associated with hypercalcemia and low PTH concentrations. Over the years, hyperparathyroidism developed, resulting in more severe hypercalcemia. Also, kidney function deteriorated, most probably as a consequence of biopsy-proven nephrocalcinosis. Conventional treatment options for CYP24A1 mutation were not effective and/or tolerated (avoidance of sun exposure, diet, pamidronate, itraconazole). A total parathyroidectomy was performed resulting in a normocalcemic hypoparathyroidism without need for treatment with vitamin D analogs, a positive bone mineral balance and an improved kidney function.