A novel inborn error in the ligand-binding domain of the vitamin D receptor causes hereditary vitamin D-resistant rickets

Mutations in the vitamin D receptor (VDR) cause hereditary vitamin D-resist ant rickets (HVDRR), an autosomal recessive disease resulting in target org an resistance to 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3]. In this report , we describe the clinical case and molecular basis of HVDRR in an Asian bo y exhibiting the typical clinical features of the disease including alopeci a. Using cultured dermal fibroblasts from the patient, 1,25(OH)(2)D-3 resis tance was demonstrated by a shift in the dose response required for 25-hydr oxyvitamin D-24-hydroxylase (24-hydroxylase) mRNA induction, Western blot s howed that the cells express a normal size VDR but contained reduced levels of receptor compared to normal cells. At 24 degreesC, the affinity of the patient's VDR for [H-3]1,25(OH)(2)D-3 was 50-fold lower than the VDR in nor mal fibroblasts. Sequence analysis identified a unique T to G missense muta tion in exon 6 that changed phenylalanine to cysteine at amino acid 251 (F2 51C). The recreated F251C mutant VDR showed reduced transactivation activit y using a 24-hydroxylase promoter-luciferase reporter. Maximal transactivat ion activity exhibited by the WT VDR was not achieved by the mutant VDR eve n when the cells were treated with up to 10(-6) M 1,25(OH)(2)D-3. However, the transactivation activity was partially rescued by addition of RXR alpha . In the yeast two-hybrid system and GST-pull-down assays, high concentrati ons of 1,25(OH)(2)D-3 were needed to promote F251C mutant VDR binding to RX R alpha, indicating defective heterodimerization. In conclusion, a novel mu tation was identified in the VDR LBD that reduces VDR abundance and its aff inity for 1,25(OH)(2)D-3 and interferes with RXR alpha heterodimerization r esulting in the syndrome of HVDRR. (C) 2001 Academic Press.