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Plasma 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and PTH in familial hypocalciuric hypercalcaemia (FHH) and primary hyperparathyroidism (PHPT).

S Christensen, Denmark
P Nissen, Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus C., Denmark
P Vestergaard, Department of Endocrinology and Metabolism C, Aarhus University Hospital, Aarhus C., Denmark
L Heickendorff, Department of Clinical Biochemistry, Aarhus University Hospital, Aarhus C., Denmark
L Rejnmark, Dept of Endocrinology and Metabolism C, Aarhus University Hospital, Aarhus, Denmark
K Brixen, Department of Endocrinology, Odense University Hospital, Odense, Denmark
L Mosekilde, Dept of Endocrinology and Metabolism C, Aarhus University Hospital, Aarhus, Denmark

Correspondence: Signe Christensen, Email: rlg06sec{at}as.aaa.dk

Abstract

Abstract:

Introduction: Familial hypocalciuric hypercalcaemia (FHH) is a lifelong, benign, inherited condition caused by inactivating mutations in the Calcium Sensing Receptor (CASR) gene. Both FHH and primary hyperparathyroidism (PHPT) are characterized by elevated P-calcium, normal or elevated P-parathyroid hormone (P-PTH), and typically normal renal function. In PHPT, Vitamin D metabolism is typically characterized by low plasma levels of 25-hydroxyvitamin D (25OHD), and high plasma levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). In FHH, the vitamin D metabolism is not very well known.

Objective: To compare and evaluate plasma 25OHD, 1,25(OH)2D and PTH in FHH and PHPT.

Design: Cross-sectional study.

Materials: 66 FHH-patients with mutations in the CASR gene, 147 patients with surgically verified PHPT, and 46 controls matched to FHH patients according to age (±5 years), sex and season. All patients had a P-creatinine < 140 µmol/l.

Methods: We measured P-calcium, P-Ca2+, P-albumin, P-creatinine, P-phosphate, P-magnesium, and P-PTH by standard laboratory methods. P-25OHD and P-1,25(OH)2D were measured by radioimmunoassay or enzymeimmunoassay. In FHH, all protein coding exons in the CASR were sequenced and aligned to GenBank reference sequence NM_000388 [GenBank] .2.

Results: PHPT patients had higher BMI (2p<0.01), together with higher P-PTH (2p<0.01) and P-1,25(OH)2D (2p<0.01) compared to FHH patients. The groups had similar levels of P- Ca2+ and of P-25OHD. The phenotypic expression of the CASR mutations (as determined by the degree of hypercalcaemia) did not influence the levels of P-1,25(OH)2D.

Conclusion: Even though P-calcium and P-25OHD were comparable, P-1,25(OH)2D and P-PTH differed between FHH and PHPT.