LBSAT130 Hypercalcemia In Pregnancy Due To CYP24A1 Mutation

BACKGROUND: The active form of vitamin D (1,25 OH2 vitamin D) is catabolized by a key enzyme 1,25 OH vitamin D-24 hydroxylase, which is encoded by the CYP24A1 gene. Loss of function mutation in the CYP24A1 leads to elevated levels of active vitamin D, causing PTH independent hypercalcemia with nephrolithiasis and nephrocalcinosis. Two phenotypic variants have been identified: idiopathic infantile hypercalcemia, which is a more severe form presenting in infancy, and a milder form with onset in adulthood as is this case. Pregnancy is known to initiate or worsen the hypercalcemia. CLINICAL CASE: A 27-year-old woman presented at 11 weeks gestation with hyperemesis, noted to have hypercalcemia calcium 15.7mg/dl (8.2 to 10.1 pg/ml), low PTH 2pg/ml (24 -85 pg/ml) with high serum 1,25 OHD 309pg/ml (nl 19.9-79.3 pg/ml). She had low PTHrp, normal ACE level, and negative TB testing. Pre-pregnancy calcium was normal (9.8mg/dl). She had a history of hypercalcemia in previous pregnancy (Calcium 13mg/dl) that ended in IUFD. Family history revealed nephrolithiasis in her sister, mother, and paternal aunt as well as a consanguineous marriage in our patient and her parents. Vitamin D metabolites evaluated via liquid chromatography showed low serum 24,25(OH)2D (0.29ng/ml nl N/A) and elevated 25OHD 138 ng/mL (20-80 ng/ml). Ratio of 25 (OH) Vit D to 24,25(OH)2D was 475.86 (values >80 indicate probable bi-allelic CYP24A1 deletion or mutation. Genetic test pending. CONCLUSION: This case highlights the fact that patients with 24 hydroxylase deficiency may be normocalcemic with hypercalcemia unveiled during pregnancy due to increased 1alpha hydroxylase production by the placenta and kidneys as well as intake of prenatal vitamins containing calciferol. An index of suspicion for CYP24A1 mutation is needed in patients with high active vitamin D metabolites, high or normal calcium, low PTH, family history of kidney stones or worsening hypercalcemia in pregnancy. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.