DNA tip analysis for the polymorphisms of osteoporosis

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To analyze the gene polymorphism for osteroprosis, we developed FRET based polymerase chain reaction for multiple region of the polymorphism. In addition, we identified the polymorphism of the human vitamin D receptor gene promoter. The major physiological activity of 1,25-hydroxyvitamin D3 (1,25(OH)2D3) is the regulation of calcium absorption in the small intestine, and the level of vitamin D receptor (VDR) is an important factor in this regulation. We demonstrated that the caudal-related homeodomain Cdx-2 played an important role in the intestine-specific transcription of the human VDR gene. In the present project, the polymorphism was identified in the core sequence in the Cdx-2 binding site in the VDR gene promoter. In 261 Japanese women with genotyped VDR polymorphisms, 48 were genotype Cdx-A (adenine at -3731 nt relative to the transcription start site of human VDR gene), 82 were genotype Cdx-G (guanine at -3731 nt), 131 were genotype Cdx-A/G (heterozygote). In postmenopausal Japanese women, the bone mineral density (BMD) in the lumbar spine (L2-4) with the Cdx-G homozygote was 12% lower than that with the Cdx-A homozygote (P<0.05). In electrophoretic gel mobility shift assay, the oligonucleotide with Cdx-G allele markedly decreased the binding to Cdx-2 compared with that in the Cdx-A allele. The transcriptional activity of the VDR promoter with Cdx-G allele was decreased to 70% of the Cdx-A allele. In addition, in the herpes simplex virus thymidine kinase promoter, the Cdx-2 binding element with the G allele showed significantly lower transcriptional activity than that of the A allele. Thus, the polymorphism in the Cdx-2 binding site of the VDR gene (Cdx-polymorphism) would affect the expression of VDR in the small intestine. In addition, this polymorphism may modulate BMD in postmenopausal Japanese women.