Associations between NRAMP1 Polymorphisms and Susceptibility to Ulcerative Colitis/Crohn's Disease: A Meta-Analysis

Objective: Multiple environmental and genetic factors contribute to the risks of ulcerative colitis (UC) and Crohn's disease (CD). Several allelic variants have been identified in natural resistance associated macrophage protein 1 (NRAMP1) gene; however, their association with UC/CD remains conflicting. The purpose of this study was to evaluate whether NRAMP1 polymorphisms are associated with the susceptibility to UC/CD. Methods: A meta-analysis on the association between the NRAMP1 polymorphisms and susceptibility to UC/CD was performed. Relevant studies were retrieved from the databases. After eligible data were extracted, Mantel-Haenszel statistics and random/fixed effects model were applied to calculate the pooled odds radio (OR) and 95% confidence interval (95% CI). Results: Seven articles containing 536 UC cases, 997 CD cases, and 1361 controls were collected. No significant association between allele 2 frequency of NRAMP1 and susceptibility to UC/CD was detected in overall population (all p > 0.05). However, increased UC/CD risk for allele 3 was observed in Caucasian population (OR = 1.27, 95% CI = 1.08~1.50, p = 0.04), whereas decreased UC/CD risk was detected in non-Caucasian population (OR = 0.72, 95% CI = 0.60~0.87, p < 0.001), under allele 3 vs. other alleles model. Moreover, a significant increase in CD risk for T carrier frequency of -237 C/T (OR = 0.44, 95% CI, 0.26~0.75, p = 0.003) was detected, but not 274 C/T and 1729+55del4 (TGTG) +/del. Conclusions: The polymorphism of -237 C/T is related to the risk of CD; and the association of allele 3 with UC/CD risk differs in Caucasian and non-Caucasian population, which might be the potential biomarkers for clinical diagnosis of UC/CD.