Increased
1,25-dihydroxyvitamin D levels and decreased basal and
calcium-stimulated
calcitonin serum levels have been found in children with
Williams-Beuren syndrome (WBS). To determine whether isolated or combined disturbances of secretion or action of the
calcium-regulating hormones may cause the tendency to
hypercalcemia in WBS, we investigated several aspects of
calcium metabolism in 27 normocalcemic children and adults, aged 2 to 47 years, with WBS. With the exception of slightly decreased
25-hydroxyvitamin D and slightly increased
calcitonin in serum, all measured basal indexes of
calcium and bone metabolism, including the serum levels of intact
parathyroid hormone and
1,25-dihydroxyvitamin D, were comparable to control values. Total and extractable
calcitonin, the latter representing the monomeric and biologically important form of the
hormone, showed the same relative increase after a low-dose
calcium infusion in patients and control subjects, indicating a normal capacity of the
calcitonin-producing C cells of the thyroid gland in WBS. Furthermore, exogenous
parathyroid hormone induced a normal response of
1,25-dihydroxyvitamin D, cyclic
adenosine monophosphate, and
phosphate excretion, indicating a normal response of the renal 25-hydroxyvitamin D-1 alpha-
hydroxylase and the renal receptor-
adenylate cyclase system to
parathyroid hormone. These findings suggest that neither deficient
calcitonin secretion nor increased renal sensitivity to
parathyroid hormone is a feature of WBS in normocalcemic patients.