CYP24A1 Mutations in a Cohort of Hypercalcemic Patients: Evidence for a Recessive Trait

J Clin Endocrinol Metab. 2015 Oct;100(10):E1343-52. doi: 10.1210/jc.2014-4387. Epub 2015 Jul 27.


Context: Loss-of-function mutations of CYP24A1 (which encodes the 25-OH-D3-24-hydroxylase) have recently been reported to cause hypercalcemia.

Objectives: The aims of this study were: 1) to evaluate the frequency of CYP24A1 mutations in patients with medical history of hypercalcemia; 2) to show the clinical utility of a simultaneous assay of serum 25-hydroxyvitamin D3 (25-OH-D3) and 24,25-dihydroxyvitamin D3 (24,25-[OH]2D3) by liquid chromatography tandem mass spectrometry (LC-MS/MS); and 3) to investigate biochemical parameters in heterozygous gene carriers with CYP24A1 mutations.

Patients and methods: We screened for CYP24A1 mutations in 72 patients with serum calcium levels > 2.6 mmol/L and PTH levels < 20 pg/mL and recruited 24 relatives after genetic counseling for subsequent investigations. Vitamin D metabolite concentrations were assessed in a subset of patients by LC-MS/MS and results expressed as a ratio (R) of 25-OH-D3:24,25-(OH)2D3.

Results: Twenty-five patients with hypercalcemia (35%) harbored CYP24A1 variations. Twenty (28%) had biallelic variations, mostly found in subjects with nephrocalcinosis or renal stones (19/20). Five patients, all neonates, were heterozygous, without renal disease. We describe 15 new variations leading to loss-of-function according to pathogenicity prediction programs, and we functionally characterized 5 of them in vitro. A dramatic increase of R, usually >80, was found in patients harboring biallelic mutations providing evidence in vivo for the loss of CYP24A1 activity. In contrast, R value remains <25 in patients without CYP24A1 mutations. Subjects carrying one mutant allele, hypercalcemic individuals, as well as gene-carrier relatives, had a detectable 24,25-(OH)2D3 level and R < 25, indicating normal 24-hydroxylase activity.

Conclusion: CYP24A1 biallelic mutations are frequently found in patients presenting with hypercalcemia, low PTH, and renal disease. We confirm the accuracy and effectiveness of a novel blood test estimating the ratio between relevant vitamin D metabolites as a useful screening tool for CYP24A1 mutations. Haploinsufficiency is not associated with CYP24A1 deficiency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 24,25-Dihydroxyvitamin D 3 / blood
  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Calcium / blood
  • Child
  • Child, Preschool
  • Chromatography, Liquid
  • Female
  • Humans
  • Hypercalcemia / blood
  • Hypercalcemia / genetics*
  • Infant
  • Infant, Newborn
  • Male
  • Middle Aged
  • Mutation*
  • Parathyroid Hormone / blood
  • Tandem Mass Spectrometry
  • Vitamin D / analogs & derivatives
  • Vitamin D / blood
  • Vitamin D3 24-Hydroxylase / genetics*
  • Young Adult


  • Parathyroid Hormone
  • dihydroxy-vitamin D3
  • Vitamin D
  • 24,25-Dihydroxyvitamin D 3
  • Vitamin D3 24-Hydroxylase
  • Calcium