MTHFR C677T and colorectal cancer risk: A meta-analysis of 25 populations.

The common functional methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism may influence the risk of colorectal cancer (CRC), but data from published studies with individually low statistical power are conflicting. To clarify the role of MTHFR C677T genotype in CRC, we considered all available studies in a meta-analysis. Studies reporting on MTHFR C677T genotype and CRC were searched in PubMed up to April 2006. The principle prior hypothesis was that homozygosity for MTHFR 677TT would be associated with reduced risk of CRC. Data were available for 29,931 subjects, including 12,243 with CRC, from 25 independent populations. Compared to the homozygous CC genotype, the MTHFR 677TT genotype was associated with a reduced risk of CRC (odds ratio (OR): 0.83; 95% confidence interval (CI): 0.75-0.93; p = 0.001). There was some heterogeneity among the results of individual studies, but this was not statistically significant (heterogeneity p = 0.12; I2 = 25.8%). Heterozygosity for MTHFR 677 did not influence CRC risk (OR: 0.99; 95% CI: 0.94-1.04). These findings indicate that individuals homozygous for the MTHFR 677TT genotype are at moderately reduced risk of CRC, and support the proposal that common genetic variation in the MTHFR gene contributes to CRC susceptibility, probably accounting for at least 9% of the total incidence. Copyright 2006 Wiley-Liss, Inc.