Associations of TNF-Α -308 and -238 Polymorphisms with Inflammatory Bowel Disease: A Case-Control Study and Meta-Analysis of Published Data

Background: Inflammatory bowel disease (IBD) is a chronic relapsing-remitting inflammatory disease of the intestinal tract. Tumor necrosis factor-alpha (TNF-α) signaling plays a major role in the pathogenesis of IBD and is commonly targeted for therapeutic purposes. Results on the contribution of TNF-α -308 and -238 single nucleotide polymorphisms (SNP) to the susceptibility to IBD have been contradictory in differ- ent populations. Methods: Allele frequency and genotype status of TNF-α -308 and -238 SNPs were investigated in 75 un- related patients with IBD [40 Crohn’s disease (CD) and 35 ulcerative colitis (UC)] and 140 healthy controls by polymerase chain reaction with sequence-specific primers (PCR-SSP). We also conducted a systematic review and meta-analysis of the published reports. Results: TNF-α -238 GG was detected at a higher frequency in CD and UC. TNF-α -308 GG was more frequently detected in UC compared to control. There was no significant association between TNF-α -238 or -308 gene polymorphisms and patients’ demography (i.e., gender and age) or disease phenotype (i.e., extraintestinal manifestations, treatment, activity index, age at onset, and duration of the disease). In the meta-analysis, TNF-α -238 (AA/AG) genotype tended to be less frequent in patients with UC compared to healthy controls. There was no association between TNF-α -238 gene polymorphisms (AA/AG or GG genotypes) and either form of IBD. Conclusion: TNF-α -308 and -238 SNPs are associated with IBD in Iranian patients. TNF-α -308 AA gen- otype is positively correlated with UC in this meta-analysis.