A Cellular Defect in Hereditary Vitamin-D-Dependent Rickets Type II: Defective Nuclear Uptake of 1,25-Dihydroxyvitamin D in Cultured Skin Fibroblasts

VITAMIN-D-dependent (or pseudo-vitamin-D-deficient) rickets is characterized by clinical and biochemical features of vitamin-D-deficient rickets and by remission of these features during treatment with supraphysiologic doses of vitamin D or of 25-hydroxyvitamin D (25-(OH)D).^{1 , 2} It is often hereditary, with patterns suggestive of autosomal-recessive transmission. In members of several kindreds who are classified as having vitamin-D-dependent rickets Type I, concentrations of 1,25-dihydroxyvitamin D (1,25(OH)₂D) in serum have been low^{3 , 4}; these patients can be treated with doses of 1,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) that are estimated to maintain a normal average serum concentration and turnover of this metabolite.³ Presumably, . . .