ethnicity was not controlled for in more than a half of included studies, which makes the interpretation of the results and stratified analyses difficult. Second, because not all necessary information could be obtained from all included studies, more detailed sub-grouping analysis (e.g. by HIV status or type of TB) could not be performed. Third, the crude division of ethnics groups into ‘Asian’, ‘African’, and ‘Western’ makes the analyses be prone to bias. Further studies from different populations are warranted to verify current findings. Fourth, included studies were restricted to those published in English or Chinese in our study which might introduce potential bias into data analysis as well. Fifth, only 17 included studies mentioned whether their study population was in HWE for the investigated variants [11,14,16,17,23–30,33–35,39,43]. Based on the data provided by the articles and own calculations, significant deviations from HWE (p,0.05) in controls were observed for three studies for any of their studied polymorphisms [12,38,42]. Their results should be interpreted with more caution. We therefore repeated the meta-analyses after exclusion of these studies. However, this exclusion did not materially affect the results (see Table S4). In conclusion, this systematic review summarized the associa- tions between SLC11A1 polymorphisms and TB susceptibility. Our results suggested a consistent association between SLC11A1 polymorphisms and TB in different populations, which supports the hypothesis that NRAMP1 might play an important role in the host defense to the development of TB. However, due to the moderate strength of the associations, their values to be used for risk prediction should be considered cautiously. Materials and Methods Literature search Studies addressing the association between SLC11A1 polymor- phisms and TB were identified by searching for articles in the PubMed, EMBASE and Chinese BioMedical Literature (CBM) Database until 15 September 2010 [5]. Various combinations of the terms ‘‘tuberculosis’’, ‘‘NRAMP1’’, ‘‘SLC11A1’’, ‘‘polymor- phism’’ and ‘‘susceptibility’’ were used to screen for potentially relevant studies. Additional studies were also identified by means of cross-referencing. Inclusion and exclusion criteria Case-control or cohort studies presenting original data on the associations between SLC11A1 polymorphisms and TB were included. Only the most widely studied polymorphisms were considered: 39 UTR (1729+55del4) (rs17235416), D543N (As- p543Asn) (rs17235409), INT4 (469+14G/C) (rs3731865), and 59 promoter (GT)n (rs34448891). Exclusion criteria were: 1) review articles; 2) studies in languages other than English or Chinese; 2) studies on other polymorphisms other than the target four polymorphisms; 3) previous articles addressing meta-analysis of the associations between SLC11A1 polymorphisms and TB. If the eligible study was reported in duplication, the article published in English or published earlier was included in this review. References 1. Burgner D, Jamieson SE, Blackwell JM (2006) Genetic susceptibility to infectious diseases: big is beautiful, but will bigger be even better? Lancet Infect Dis 6: 653–663. 2. Motsinger AA, Haas DW, Hulgan T, Ritchie MD (2007) Human genomic association studies: a primer for the infectious diseases specialist. J Infect Dis 195: 1737–1744. 3. Canonne-Hergaux F, Gruenheid S, Govoni G, Gros P (1999) The Nramp1 protein and its role in resistance to infection and macrophage function. Proc Assoc Am Physicians 111: 283–289. 4. Dye C, Williams BG (2010) The population dynamics and control of tuberculosis. Science 328: 856–861. SLC11A1 Polymorphisms and TB Data extraction For all studies, we extracted the following data from original publications: first author and year of publication; distribution of genotypes for each polymorphism among cases and controls; characteristics of the study design and the study population (study base, numbers and mean age of cases and controls, TB diagnosis, HIV status, source of controls, matching criteria and host ethnicity). Statistical analysis Hardy-Weinberg Equilibrium (HWE) was examined in controls by asymptotic Pearson’s chi-square test for each polymorphism in each study. The association between polymorphism and TB was estimated by means of odds ratios (OR) and corresponding 95% confidence intervals (CI) comparing cases to controls. Co- dominant model was used for 39 UTR, D543N, and INT4. The effect of allele 3 carriage was assessed for 59 (GT)n. Meta-analyses were carried out using Comprehensive Meta-Analysis (V2.0, Biostat, Englewood, NJ, USA). Random effects models were used for meta-analysis, taking into account the possibility of heteroge- neity between studies which was tested by the Q test and I2 test. Stratified analyses were conducted with respect to study base (hospital or population based) and host ethnicity. The latter was categorized into Africans, Asians and Westerns (Europeans and Americans). Because of the limited number of publications in Americans, they were sub-grouped to Westerns combined with studies from Europeans. Begg rank correlation method and Egger weighted regression method were used to statistically assess publication bias (p,0.05 was considered indicative of statistically significant publication bias). Sensitivity analyses were performed after excluding studies specifically on extra-pulmonary TB, or restricting the analysis specifically on pulmonary TB. Supporting Information List of excluded studies and corresponding exclusion Characteristics of the included studies (Part 1/2). Characteristics of the included studies (Part 2/2). Sensitivity analyses of meta-analyses. Table S1 criteria. (DOC) Table S2 (DOC) Table S3 (DOC) Table S4 (DOC) Author Contributions Conceived and designed the experiments: XWL LG QJ. Analyzed the data: XWL YY YZZ FZ. Contributed reagents/materials/analysis tools: HZL QJ. Wrote the paper: XEL LG. 5. Gao L, Tao Y, Zhang L, Jin Q (2010) Vitamin D receptor genetic polymorphisms and tuberculosis: updated systematic review and meta-analysis. Int J Tuberc Lung Dis 14: 15–23. 6. Pacheco AG, Moraes MO (2009) Genetic polymorphisms of infectious diseases in case-control studies. Dis Markers 27: 173–186. 7. Bellamy R, Ruwende C, Corrah T, McAdam KP, Whittle HC, et al. (1998) Variations in the NRAMP1 gene and susceptibility to tuberculosis in West Africans. N Engl J Med 338: 640–644. 8. Li HT, Zhang TT, Zhou YQ, Huang QH, Huang J (2006) SLC11A1 (formerly NRAMP1) gene polymorphisms and tuberculosis susceptibility: a meta-analysis. Int J Tuberc Lung Dis 10: 3–12. PLoS ONE | www.plosone.org 7 January 2011 | Volume 6 | Issue 1 | e15831