Vitamin-D receptor gene polymorphisms (TaqI and ApaI) and circulating osteocalcin in patients with type 2 diabetes and healthy subjects

Abstract

Introduction: Vitamin D receptor (VDR) is encoded by the VDR gene. Several studies have supported that this gene is associated with diabetes. Heterodimer VDR/RXR functions as an enhancer of the BGLAP gene and increases the basal transcription rate of osteocalcin (OC) during osteoblast differentiation. OC is a regulator of glucose metabolism in mice. Moreover, OC level is decreased in patients with type 2 diabetes (T2D). Although inversely correlated with serum glucose insulin and glycated haemoglobin, it is unclear whether OC reduction is caused by diabetes or plays a role in the pathogenesis and/or progression of the disease. In this study we analysed the association between TaqI and ApaI VDR gene polymorphisms and OC serum concentration in T2D subjects. Material and methods: Patients underwent clinical and nutritional assessment. Genomic DNA was extracted from leucocytes using a standard salting-out procedure. The polymorphisms were genotyped by PCR-RFLP method. ELISA was used to measure OC and insulin concentrations. Results: Association between TT genotype of TaqI polymorphism and low levels of OC was observed only in the population with overweight and obesity. No association between TaqI and ApaI polymorphisms and T2D was observed (p > 0.05). Furthermore, in T2D subjects, no correlation between ApaI and TaqI genotypes and age, sex, Body Mass Index (BMI), glucose, or OC was observed. Conclusions: The TT genotype of TaqI VDR gene polymorphism was correlated with low levels of OC in overweight and obese subjects. However, TaqI and ApaI VDR gene polymorphisms were not associated with T2D.