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.