A unique point mutation in the human vitamin D receptor chromosomal gene confers hereditary resistance to 1,25-dihydroxyvitamin D3.
The syndrome of hereditary resistance to 1,25-dihydroxyvitamin D3 is due to defective function of the vitamin D receptor (VDR). The recent cloning and nucleotide sequence determination of the human VDR chromosomal gene have enabled a direct evaluation of the genetic basis for this disease in affected patients. In this report we employed polymerase chain reaction techniques to amplify the gene exons that encode the DNA-binding domain of the VDR from two 1,25-dihydroxyvitamin D3-resistant patients whose receptors displayed defective binding to nonspecific DNA. Although their families were apparently unrelated, each patient displayed an identical homozygous point mutation within the third exon, a mutation that causes substitution of a glutamine for an arginine residue highly conserved within the entire steroid receptor superfamily. We introduced this base change into the normal VDR cDNA via site-directed mutagenesis, transfected an expression vector containing this cDNA into cells, and examined the functional properties of the resultant VDR expression product. The produced mutant receptor bound 1,25-dihydroxyvitamin D3 with normal affinity, but displayed weak affinity for the nuclear fraction and for heterologous DNA. More importantly, the protein was inactive in promoting transcription in a cotransfection assay employing a chloramphenicol acetyltransferase gene reporter fused down-stream of the VDR-inducible osteocalcin gene promoter-enhancer. These results provide the genetic and functional basis for the phenotype of rickets in this inherited disease.
Sone
T
T
Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030.
Marx
S J
SJ
Liberman
U A
UA
Pike
J W
JW
D000595:Amino Acid Sequence; D001483:Base Sequence; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics*; D005796:Genes; D006801:Humans; D007015:Hypophosphatemia, Familial / Q000235:genetics*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015675:Osteocalcin / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000172:deficiency / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D015675:Osteocalcin; D004247:DNA; D002117:Calcitriol