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Calcium and vitamin D metabolism in hypocalcemic vitamin D-resistant rickets carriers
Polyxeni Nicolaidou1, Anna Papadopoulou, Helen Georgouli
1Third Department of Pediatrics, Athens University Medical School, University General Hospital Attikon, Chaidari, Greece. pedatt@med.uoa.gr
Background/Aims:
Hypocalcemic vitamin D-resistant rickets (HVDRR) is a rare monogenic autosomal recessive disorder associated with mutations in the gene of the vitamin D receptor (VDR), the mediator of 1,25(OH)2D3 action. Although many investigations have discussed the clinical manifestations and molecular etiology of this disease, only a few have investigated the biochemical and hormonal status of heterozygous HVDRR. The aim of the current work was to investigate the profile of selected biochemical and hormonal parameters related to the vitamin D endocrine system in a large number of HVDRR heterozygotes.
Methods:
67 relatives of 2 HVDRR patients, all members of an extended Greek kindred of five generations with a common ancestor, were included in the study. Direct sequencing was used to identify VDR gene mutations. Serum Ca, P, 25(OH)D, iPTH, and 1,25(OH)2D levels were determined in all members of the kindred.
Results:
DNA analysis of the participants led to the design of two study groups: the HVDRR carriers (24) and the control subjects (43). Our results showed elevated circulating serum levels of 1,25(OH)2D3 and lower levels of PTH than their age- and sex-matched controls. No hypocalcemia or hypophosphatemia were detected in HVDRR carriers.
Conclusions:
Our findings suggest that HVDRR carriers may have compensatory elevated serum levels of 1,25(OH)2D3 through which they restrain PTH secretion. The study of HVDRR carriers could be a useful tool for the investigation of the vitamin D endocrine system.
Insights
Hypocalcemic vitamin D-resistant rickets (HVDRR) carriers exhibit elevated 1,25(OH)2D3 and reduced PTH levels. This suggests a compensatory mechanism in the vitamin D endocrine system within these individuals.
Area of Science:
- Endocrinology
- Genetics
- Metabolic Bone Disease
Background:
- Hypocalcemic vitamin D-resistant rickets (HVDRR) is a rare genetic disorder caused by mutations in the vitamin D receptor (VDR) gene.
- While the molecular basis of HVDRR is known, the biochemical and hormonal status of heterozygotes remains understudied.
Purpose of the Study:
- To investigate the biochemical and hormonal profile of HVDRR heterozygotes within a large kindred.
- To explore the role of the vitamin D endocrine system in carriers of VDR mutations.
Main Methods:
- Studied 67 relatives from an extended Greek kindred with a common ancestor.
- Identified VDR gene mutations using direct sequencing.
- Measured serum calcium, phosphorus, 25(OH)D, iPTH, and 1,25(OH)2D levels in all participants.
Main Results:
- Classified participants into HVDRR carriers (n=24) and control subjects (n=43).
- HVDRR carriers showed significantly elevated serum 1,25(OH)2D3 levels.
- Carriers had lower parathyroid hormone (PTH) levels and no evidence of hypocalcemia or hypophosphatemia.
Conclusions:
- HVDRR carriers may possess compensatory elevated 1,25(OH)2D3 levels, which suppress PTH secretion.
- Studying HVDRR carriers provides valuable insights into the regulation of the vitamin D endocrine system.
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