SUN-774 - Recurrent Vitamin D-Mediated Hypercalcemia in Pregnancy Due to CYP24A1 Deficiency

Introduction: CYP24A1 deficiency is a rare cause of non-PTH mediated hypercalcemia due to impaired degradation of active vitamin D metabolites. Pregnancy can exacerbate hypercalcemia through physiologic increases in 1,25-dihydroxyvitamin D posing significant maternal and fetal risks. Data on management during pregnancy remains limited.

Case Presentation: A 33-year old woman with a history of hypertension and nephrolithiasis presented for follow up of recurrent gestational hypercalcemia during her second pregnancy. Her initial presentation occurred in 2020 during her first pregnancy, complicated by severe hypercalcemia (serum calcium 12.4mg/dL), markedly elevated 1,25-dihydroxyvitamin D (556 pg/ml), suppressed intact PTH ( < 3 pg/mL), normal 25-hydroxyvitamin , and normal ACE levels. She received pamidronate, calcitonin and magnesium infusion which was then complicated by hypocalcemia. That pregnancy ended in neonatal loss at 22.3 weeks, attributed to severe early-onset preeclampsia.

Calcium and vitamin D metabolite levels normalized postpartum and remained stable until her second pregnancy. At 18 weeks gestation, she developed recurrent hypercalcemia with elevated 1,25-dihydroxyvitamin D, prompting genetic testing that revealed a pathogenic CYP24A1 mutation consistent with partial enzyme deficiency. She was initiated on low-dose prednisone with stabilization of serum calcium. Attempts to taper prednisone to 2.5mg daily resulted in recurrent calcium elevation. She remained on prednisone 5mg for the remainder of the pregnancy and was able to deliver without any complications.

Conclusion: This case highlights the role of CYP24A1 deficiency as a cause of recurrent, pregnancy associated vitamin D-mediated hypercalcemia and demonstrates that low dose glucocorticoid therapy can be effective in maintaining normocalcemia throughout gestation. Early recognition and multidisciplinary management are essential to optimize maternal and fetal outcomes in this rare disorder.

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