Evaluation of Vitamin D binding protein gene polymorphism and serum free and bioavailable levels among tuberculosis patients: A cross sectional study

Abstract

Background Genetic variants influence the distribution of vitamin D in circulation leading to vitamin D deficiency. The two extensively studied non-synonymous DBP single nucleotide polymorphisms (SNPs) rs7041 and rs4588 are found in different populations. The aim of this study was to determine the frequency distribution of DBPgene polymorphism andcompare the free and bioavailable vitamin D levels among active tuberculosis patients, latent tuberculosis infection individuals,and those without tuberculosis infection. This was across-sectional study with 53 active tuberculosis patients,23 latent tuberculosis individuals, and27 individuals without tuberculosis infection.Free and bioavailable vitamin D levels were measured using ELISA method.DNA extraction and PCR were performed and a product of 498 bp was obtained. We genotyped the DBP gene by Sanger sequencing and the single nucleotide polymorphisms were identified using the BioEdit tool. Results The study frequency distributions of the DBP genotypes were reported as97% Gc1F, 2% Gc2 and 1% Gc1S.Significantly low vitamin D levels were found among the TB patients, p=,0.001.The median (IQR) vitamin D levels of the predominant genotype, Gc1F were 3.8(1.1–10.5) ng/ml,Gc1S individuals, 2.2ng/ml, and Gc2 individuals were 1.9 ng/ml. A non significant association was found between the vitamin D binding protein genes and free and bioavailable vitamin D levels, p = > 0.05. Conclusion The Gc1F genotype was predominantly found in the study population with the minor alleles associated with active and latent TB states. Significantly low free and bioavailable vitamin D levels were found among TB patients compared to other TB states. However a non- significant association was found between the DBP gene polymorphismsand the free and bioavailable vitamin D levels.