Vitamin D receptor (VDR) TaqI polymorphism, vitamin D and bone mineral density in patients with inflammatory bowel diseases.

BACKGROUND

A common feature in the etiology of inflammatory bowel disease (IBD) and osteoporosis is a complex genetic background. Moreover, it has been shown that some of the susceptibility loci overlap for both diseases. One of the genes that may be involved in the pathogenesis of IBD as well as decreased bone mass is the vitamin D receptor (VDR) gene.

OBJECTIVES

The aim of this study was to investigate the association of the TaqI polymorphism (rs731236, c.1056T >C) in the VDR gene with serum vitamin D concentration and bone mineral density (BMD) in patients with IBD.

MATERIAL AND METHODS

A total of 172 IBD patients (85 with Crohn's disease (CD) and 87 with ulcerative colitis (UC)) and 39 healthy controls were enrolled in the study. Polymorphism was determined with polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). Bone mineral density was measured at the lumbar spine (L2-L4) and the femoral neck (FN) using dual-energy x-ray absorptiometry (DEXA). Serum concentrations of 25-hydroxyvitamin D were determined using electrochemiluminescence binding assay (ECLIA).

RESULTS

Our studies revealed that serum vitamin D concentration in IBD patients was not lowered in comparison with healthy controls. Patients with CD presented more advanced osteopenia and osteoporosis. Individuals with UC carrying the TaqI tt genotype of VDR gene showed significantly higher FN BMD than carriers of TT and Tt genotypes (p = 0.02). Moreover, tt genotype was present with higher frequency in UC patients than in controls and CD patients (23% vs 7.7% and 16.5%, respectively).

CONCLUSIONS

The tt genotype may have a protective effect on BMD in UC patients.