Tissue-specific effect of VDR gene polymorphisms on the response to calcitriol.

In the last decade, the likely role of vitamin D receptor (VDR) polymorphisms in different diseases has been extensively discussed. In this paper we review several studies carried out in this field to investigate the possible influence of VDR polymorphisms on different aspects of bone and parathyroid gland metabolism. On one hand, most of the epidemiological studies showed that the BAt haplotype, from BsmI, ApaI and TaqI polymorphisms in VDR, is associated with a lower bone mineral density (BMD) in women and a higher risk of osteoporotic fractures. On the other hand, experimental studies carried out in both human primary osteoblasts and human parathyroid glands showed that while in osteoblasts the BAt haplotype showed a worse response to calcitriol, in parathyroid glands the results were the opposite, and BAt was the haplotype associated with better responses. Overall, the results reinforce the suggestion that VDR polymorphisms play an important role in bone and parathyroid gland behavior, leading to different response patterns due to a likely tissue-specific effect of the VDR response to calcitriol.