OR45-2 CYP24A1 Molecular Analysis and Simultaneous Assay of Multiple Vitamin D Metabolites By LC-MS/MS in Patients with Hypercalcemia and Suppressed PTH : a Cohort Study

Program: Abstracts - Orals, Poster Previews, and Posters
Session: OR45-What Is New in Vitamin D?
Sunday, March 8, 2015: 9:30 AM-11:00 AM
Presentation Start Time: 9:45 AM
Room 29 (San Diego Convention Center)
Marie-Laure Kottler, MD, PHD1, Arnaud Molin2, Martin Kaufmann, PhD3, Anatoly Tiulpakov, MD, PhD4 and Glenville Jones3
1CHU of Caen, Caen, France, 2Caen University Hospital, Caen, France, 3Queen's University, Kingston, ON, Canada, 4Endocrinology Research Centre, Moscow, Russia
Background: Homozygous or compound heterozygous mutations of CYP24A1(which encodes the catabolic 25-hydroxyvitamin D3-24-hydroxylase) have recently been reported to cause hypercalcemia with suppressed PTH due to increased intestinal absorption of calcium.

Objective : 1) Evaluation of the frequency of CYP24A1 mutation in a cohort of patients; 2) Evaluation of the clinical utility of simultaneous assay of multiple vitamin D metabolites by liquid chromatography tandem mass spectrometry (LC-MS/MS); 3) Investigation of patients harboring CYP24A1 mutation in a heterozygous state to better understand the role of CYP24A1 haploinsufficiency in the occurrence of hypercalcemia.

Patients and Methods: We studied 72 index cases (38 males (53%) and 34 females (47%)), presenting with hypercalcemia (>2.6 mmol/L) and low PTH levels (<20 pg/mL). We also included 22 relatives. Biochemical data and CYP24A1 sequencing were obtained with routine methods. Serum 25-hydroxyvitamin D3 (25-OH-D3) and 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3) were assessed by LC-MS/MS using 100 µL of serum (1); results were expressed as a ratio (R) of 25-OH-D3:24,25-(OH)2D3. Values under 25 were considered as normal.

Results: We identified 25 patients (35%) harboring mutations in the coding sequence of CYP24A1. Twenty patients (28%) have bi-allelic mutations that were found more frequently in patients with renal disease (67%) (nephrocalcinosis or renal stones) than in patients without renal symptoms (23%). Patients with bi-allelic CYP24A1 mutations have very low 24,25-(OH)2 D3 levels and exhibit a dramatic increase in R (mean [range] :105 [48.8-173.4] n = 7) providing evidence “in vivo” for the loss of 24-hydroxylase activity. We found 5 patients (7%), all neonates, harboring CYP24A1 mutations in a heterozygous state raising the question of a dominant trait. In contrast with children harboring bi-allelic mutations, none presented with renal pathology. Probands (n=3) as well as relatives (n=14) harboring heterozygous mutations, have measurable amounts of 24,25-(OH)2D3 and R below 25, suggesting functional CYP24A1 activity. Last, probands without CYP24A1 mutations have measurable amounts of 24,25-(OH)2D3 and normal R.

Conclusion: CYP24A1 mutation are frequently found in patients presenting hypercalcemia with low or suppressed PTH especially in patients with nephrocalcinosis or renal stones. We confirm the accuracy and effectiveness of a novel blood test estimating the ratio between relevant vitamin D metabolites 25-OH-D3 and 24,25-(OH)2D3 as a useful screening tool for CYP24A1 mutation. Even so most of heterozygous patients with CYP24A1 mutation remain asymptomatic, this study leads to recommend preventive measures including restriction of vitamin D supplementation that could protect affected relatives particularly during the neonatal period.

1. Kaufmann M et al. J Clin Endocrinol Metab 99: 2567–2574, 2014

Nothing to Disclose: MLK, AM, MK, AT, GJ

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