The vitamin D receptor start codon polymorphism (Fok1) and bone mineral density in premenopausal women in Taiwan

The Vitamin D receptor gene (VDRG) polymorphism as a factor of bone turnover rate or bone mineral density (BMD) is a controversial issue, especially in different ethnic populations. In addition to intron 8 (Bsm1, Taq1) and exon 9 (Apa1), VDRG polymorphism is present at its translation initiation site on exon 2. The VDRG has two translation initiation sites. The first shows a thymine/cytosine polymorphism and can be detected by restriction fragment length polymorphism (RFLP) using the endonuclease Fok1. This start codon polymorphism (SCP) of the VDRG was detected by polymerase chain reaction and then by RFLP with Fok1. While the f allele was assigned for the presence of the restriction site, the F allele was assigned for the absence of the restriction site, and the encoded vitamin D receptor is shorter by three amino acids. We examined the association between this SCP of the VDRG and bone turnover as well as BMD in 101 premenopausal Taiwanese women aged 40-53 years. Total body bone mineral content and BMD of proximal femur and lumbar spine were measured by dual-energy X-ray absorptiometry. We found a prevalence of 39.6% for the f allele of the VDRG. The frequencies of FF, Ff and ff genotypes were 35.6%, 49.5% and 14.9%, respectively. There was no statistically significant difference in BMD at any site or bone turnover markers among the three Fok1 genotypes (FF, Ff and ff). The SCP is independent of Bsm1, Apa1 or Taq1 polymorphisms of the VDRG at intron 8 and exon 9. In conclusion, the SCP polymorphism detected by endonuclease Fok1 does not significantly influence BMD or bone turnover in premenopausal women in Taiwan.