Vitamin D receptor and vitamin D binding protein gene polymorphisms in patients with asthma

Abstract Background. Vitamin D and its metabolites are transported to tissues and cells bound to a specific vitamin D binding protein (VDBP also known as GC-globulin). Most biological actions of this vitamin are exerted through the vitamin D receptor (VDR). Polymorphisms in VDR or VDBP genes may affect vitamin D level, influencing the pathogenesis of asthma. The aim of this study was to investigate the possible association of VDR and VDBP gene single-nucleotide polymorphisms (SNP), serum 25-hydroxyvitamin D, blood eosinophils and total IgE level in subject with asthma in comparison with healthy individuals. Methods. In total 63 subjects with asthma (45 allergic and 18 non-allergic) and 32 healthy subjects were involved in the study. Sensitization of subjects to inhaled allergens was determined by skin prick test, lung function was evaluated by spirometry. Serum 25-hydroxyvitamin D, total IgE levels were evaluated by ELISA. Eosinophils evaluation were performed on an automated hematology analyzer (Sysmex, Japan). DNA was isolated using the QIAamp DNA blood mini kit. Polymorphisms in the VDR and VDBP gene on the 12q13.11 chromosomal region were analyzed using TaqMan SNP Genotyping Assay probes. Results. We observed lower serum 25-hydroxyvitamin D level in patients with allergic asthma and non-allergic asthma compared to healthy subjects (13.96 ± 0.79 ng/ml and 15.35 ± 0.99 ng/ml vs 22.55 ± 1.23 ng/ml, p < 0.01). In asthma patients with vitamin D deficient (< 20 ng/ml) the allele G of Rs11168293 on VDR was more common than in those having insufficiency (20–30 ng/ml) of vitamin D (62.9% and 31.3%, p < 0.05). Moreover, asthmatic subject with Rs11168293 G allele has significant higher blood eosinophil count (% of leukocytes) compared to asthmatic without the Rs11168293 G allele (8.45 ± 12.27% vs 5.14 ± 1.52%, p < 0.05). Significantly higher IgE level was found in subjects with allergic asthma with the allele A of Rs7041 on VDBP gene than in those without this allele (536.4 ± 106.1 and 239.0 ± 75.8 IU/ml, p < 0.05). Conclusions. The association of polymorphisms in VDBP and VDR gene, the rs11168293 G allele and the rs7041 A allele, with serum 25-hydroxyvitamin D, blood eosinophil and total IgE level in asthma, let us suggest that vitamin D, VDR and VDBP gene polymorphisms are important in pathogenesis of asthma despite its form in relation to atopy.