The role of TNF-alpha gene (-238G/A and -308G/A) polymorphisms in the etiology and pathogenesis of inflammatory bowel diseases in various ethnic groups

Abstract

This literature review deals with specifics of the natural course of inflammatory bowel disease (IBD) in patients from various ethnic groups and -308G/A and -238G/A promoter polymorphisms in tumor necrosis factor-alpha (TNF-α) gene. The search in PubMed, Medline, Еlibrary.ru databases has led to identify in total 20 studies, including 2 meta-analyses, on the role of TNF-α-308G/A and -238G/A gene polymorphism in the etiology and pathophysiology of IBD. The TNF-α-308G/A polymorphism is associated with increased secretion of this proinflammatory cytokine, whereas the TNF-α-238G/A genotype is characterized by reduced TNF-α secretion. A number of studies have shown an association between TNF-α-308G/A gene polymorphism and severe course of IBD, requiring more active treatment of patients (cytostatics, corticosteroids, biological agents). Some investigators have found that the patients carriers of TNF-α-308G/A had a higher probability of surgical interventions. The association between TNF-α-308G/A and the phenotypic characteristics of IBD has been identified in studies performed in Europe, Asia, and Russia. The association of this polymorphism with the prevalence of ulcerative colitis has been proven in some studies, in particular, in the Asian population. Similar associations have been noted in few publications originating from Europe and North America, while some studies have found no links between TNF-α-308G/A, -238G/A, and the course of IBD. TNF-α-238G/A gene polymorphism has not shown any significance for the prevalence and course of ulcerative colitis and Crohn's disease. One can assume that the differences in the study results arising from one and the same geographical area are related to genetic heterogeneity of the study groups, phenotypic variances between the study subjects, as well as relatively small sample sizes. Currently, the search for genetic, biochemical and other prognostic criteria for IBD course is in progress. There are studies in progress to investigate the mechanisms of transformation of the genetic information into the particulars of ulcerative colitis and Crohn's disease manifestations, with consideration of ethnicity.