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Bone mineral density in patients with familial hypocalciuric hypercalcaemia (FHH)
S Abugassa1, J Nordenström, J Järhult
1Department of Surgery, Huddinge University Hospital, Sweden.
Insights
Familial hypocalciuric hypercalcaemia (FHH) patients with high parathyroid hormone (PTH) levels do not experience skeletal demineralization. Their normal bone mass suggests relative insensitivity to PTH
Area of Science:
- Endocrinology
- Bone Metabolism
- Genetics
Background:
- Familial hypocalciuric hypercalcaemia (FHH) is a genetic disorder characterized by hypercalcaemia and inappropriately normal or elevated parathyroid hormone (PTH) levels.
- The association between chronic hypercalcaemia, elevated PTH, and skeletal integrity in FHH remains incompletely understood.
Purpose of the Study:
- To investigate whether chronic hypercalcaemia and excessive PTH secretion in FHH are linked to skeletal demineralization.
- To assess bone mineral density and content in individuals with FHH compared to controls.
Main Methods:
- An open study involving nine affected and three unaffected members from two FHH kindreds, alongside 12 age- and sex-matched controls.
- Bone mineral density (BMD) and bone mineral content (BMC) were measured using dual and single photon absorptiometry.
- Serum levels of PTH, calcium, phosphate, magnesium, alkaline phosphatase, and 24-hour urinary calcium excretion were analyzed.
Main Results:
- Members with FHH exhibited significantly higher bone mineral density in Wards' triangle of the femur compared to controls.
- Other femur regions and lumbar vertebrae showed slightly, though not significantly, higher BMD, as did BMC in the distal and midradius.
- Affected individuals had elevated serum calcium and low urinary calcium excretion, consistent with FHH, with one case developing hypoparathyroidism.
Conclusions:
- Chronic hypercalcaemia in FHH does not result in increased bone mineralization rates, as evidenced by normal bone mass.
- Individuals with FHH appear relatively resistant to the bone-resorptive effects of PTH, as elevated PTH levels were not associated with reduced bone mass.
Objective:
To find out whether chronic hypercalcaemia and excessive secretion of parathyroid hormone (PTH) is associated with skeletal demineralisation in familial hypocalciuric hypercalcaemia (FHH).
Design:
Open study.
Setting:
Huddinge University Hospital, Sweden.
Subjects:
Nine affected and three unaffected members of two kindreds with FHH, and 12 age- and sex-matched controls.
Interventions:
Measurement of bone mineral density (g/cm2) in the proximal femur and lumbar spine by dual photon absorptiometry, and of bone mineral content in the distal radius and midradius (g/cm) by single photon absorptiometry. Measurement of serum concentrations of PTH, total and ionised calcium, phosphate, and magnesium, and alkaline phosphatase activity, and 24 hour urinary calcium excretion were also made.
Results:
Bone mineral density was significantly higher in Wards's triangle of the femur (p < 0.05) in the members of families with FHH than in control subjects. In the other parts of the femur and in the lumbar vertebrae it was slightly but not significantly higher, as was the bone mineral content of the distal radius and midradius. Family members with FHH all had increased total and ionised serum calcium concentrations, except for the index case in one of the families who developed hypoparathyroidism postoperatively. Twenty-four urinary calcium excretion was less than 5 mmol (the upper limit of the reference range for FHH) in all the affected patients.
Conclusion:
Chronic hypercalcaemia in affected members of families with FHH is not the result of an increase rate of bone mineralisation, because they have normal bone mass. They seem to be relatively insensitive to the deleterious effects of PTH on bone mineral state, because raised concentrations of PTH were not associated with reduced bone mass.