Coding and non-coding polymorphisms in VDR gene and susceptibility to pulmonary tuberculosis in tribes, castes and Muslims of Central India
Highlights
► We studied VDR gene polymorphisms in TB patients showing different clinical outcomes ► Multiethnic samples were recruited to study ethnic variations in genetic predisposition ► We found significant association between VDR gene polymorphisms and clinical subtypes ► Study hints at ethnic differences in genetic susceptibility through VDR genotypes ► Data on genotype-phenotype correlation may help in diagnosis, screening and counselling
Introduction
Tuberculosis (TB), caused by the human pathogen Mycobacterium tuberculosis has remained the major cause of morbidity and mortality in the human populations worldwide. Recent investigations have implicated the role of certain human genes and their polymorphisms in clinical outcome as well as severity of the disease (disease phenotype). The candidate genes of immune pathways, such as Toll like receptor (TLR) and VDR, are generally activated to recognize and kill the bacteria inside the macrophage cells. Polymorphisms in these genes may result in the altered immune response and, thus, help progression of the disease in an immuno-compromised host. VDR is a ligand activated transcription factor, which upon binding to vitamin D3, interacts with Vitamin D response elements and signals other target genes (Malloy and Feldman, 1999). Studies in mouse models have reported that vitamin D-deficient mice show increased sensitivity to autoimmune diseases and loss of VDR results in chemo-carcinogen-induced tumours (Bouillon et al., 2008). Four common polymorphisms (BsmI, ApaI, Taq1 and FokI) of VDR gene are reported, which, in their different genotypic combinations, are believed to alter the immune response. Significantly, a few studies have also demonstrated vitamin D-mediated innate immunity, suggesting VDR as a good target for therapeutic implications in future (Liu et al., 2006, Liu et al., 2007). This makes it pertinent that different genotypic combinations of VDR gene polymorphisms be studied simultaneously in a group of cases (susceptible) and healthy controls (at the time of sampling) in order to identify susceptible and resistant genotypes of these genes in populations under study. Present study has investigated the possible association of VDR gene polymorphisms (ApaI, TaqI, FokI and BsmI) with different clinical categories of pulmonary tuberculosis patients from tribes, general populations (castes) and Muslims.
Section snippets
Sample collection
The present study was carried out in tribals, general population and Muslim TB patients from North-Central India, recruited through field and hospital-based sampling programmes. Each sample was characterized as patient or control after initial disease diagnosis by an expert TB/chest specialist (MBBS, Doctor), followed by acid fast bacilli (AFB) staining of sputum smears and radiological (X-ray) investigations as per standard Revised National Tuberculosis Control Programme (RNTCP) guidelines.
VDR gene polymorphisms in tribes
The details about studied population groups and number of participants enrolled from each group along with their socio-economic and health status are given in Table 2. Genotypic and allelic frequencies of studied VDR gene polymorphisms are also given for each group (Table 2).
Discussion
Many studies have shown involvement of VDR gene in tuberculosis susceptibility. Liu et al. (2006) demonstrated that VDR is involved in a crucial signalling pathway through human macrophage TLR1/2 toll-like receptors. These receptors, upon bacterial stimulation, induce the VDR gene expression, which further triggers innate immunity against infection. It is therefore likely that any genetic change i.e. single nucleotide polymorphism/s in VDR gene might predict final clinical outcome of the
Conclusion
We conclude that bb (BsmI) and ff (FokI) genotypes are associated with susceptibility to smear positive tuberculosis. Individuals with tt (TaqI) genotype are more likely to develop smear positive, MDR and TAD form of tuberculosis, especially in general populations. It seems that aa (ApaI) genotype in Muslims and Aa (ApaI) genotype in general population, are at high risk of smear positive disease. Overall, study demonstrates that VDR gene polymorphisms, alone or in combinations (haplotypes),
Acknowledgement
This work was supported by a BT/PR/6982/MED/12/266/2005/24.11.2006 Grant from Department of Biotechnology (DBT), Ministry of Science & Technology, Government of India, New Delhi.
References (12)
- et al.
Therapeutic implications of the TLR and VDR partnership
Trends Mol. Med.
(2007) - et al.
Vitamin D resistance
Am. J. Med.
(1999) - et al.
5′ regulatory and 3′ untranslated region polymorphisms of vitamin D receptor gene in South Indian HIV and HIV–TB patients
J. Clin. Immunol.
(2008) - et al.
Vitamin D receptor gene polymorphisms and sputum conversion time in pulmonary tuberculosis patients
Tuberculosis
(2009) - et al.
Vitamin D and Human Health: Lessons from Vitamin D Receptor Null Mice
Endocrine Reviews
(2008) - et al.
Factors affecting susceptibility and resistance to tuberculosis
Thorax
(2001)
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These authors contributed equally to this work.