| Research Abstract |
Vitamin D-dependent rickets type II (VDDR II) is a hereditary disease of target organ resistance to 1,25(OH)_2D_3. Five patients with this disease were diagnosed in our laboratory. Three patients with clinically different severities of this disease, with alopecia, were treated with large doses of 1 (OH)D_3. Except for the alopecia, all of the abnormalities of patients 1 and 2 were reversed by treatment with 3 g/kg/d of 1 (OH)D3, and those of patient 3, who had the severest manifestations, were reversed by treatment with 6 g/kg/d. The serum 24,25(OH)_2D concentrations of the three patients were low before treatment and those of patients 1 and 2 increased during treatment. These findings suggest that in patients 1 and 2, 25(OH)D-24-hydroxylase was stimulated via a 1,25(OH)_2D-receptormediated system by treatment with 1 (OH)D_3. In two adult siblings with this disease, rickets did not recur after cessation of therapy for 14 years. But the serum concentrations of 1,25(OH)_2D and 24,25(OH)_
… More
2D of these patients were high and low, respectively.Since 1,25(OH)_2D_3 stimulates 24,25(OH)_2D synthesis mediated by the receptor for 1,25(OH)_2D, serum concentration is a useful indication of the treatment.
The interaction of 1,25(OH)_2D_3 with cultured skin fibroblasts from these patients with VDDR II were investigated. Impaired nuclear uptake and normal cytosol binding of ^3H 1,25(OH)_2D_3 were observed with skin fibroblasts. Then, ^3H 1,25(OH)_2D_3 receptor complex incorporated into nucleus of fibroblasts was eluted with various concentrations of HCL. Receptor complex of cells from control subjects eluted as a single peak at 210mM KCl. With cells from a patient, Soluble extracts produced single peak eluting at 210 mM KCl. This finding suggested that a receptor domain not assessed by hormone binding or DNA binding assays might be defective in this patient. Soluble extracts from cells of two patients yielded single peaks eluting at 90 mM KCl. This suggested mutation(s) that affected a DNA-binding domain of the receptor in these two patients. Stimulation of 24-hydroxylase activity by 1,25(OH)_2D_3 was investigated to evaluate the overall pathway of hormone action in fibroblasts. Maximal activity of 24-hydroxylase was observed after exposure to 10^<-8> and 10^<-7>M 1,25(OH)_2D_3 In fibroblasts from control subjects. In contrast, no 24-hydroxylase activity was detected after exposure to 10^<-8> M, 10^<-7> M and 10^<-6> M 1,25(OH)_2D_3 in cells from patients with VDDR II.
From this project, heterogenity of VDDR II and the role of intracellular receptor effector system in vitamin D action was clarified. Less
|
