Interaction between the MTHFR C677T polymorphism and alcohol--impact on oral cancer risk and multiple DNA methylation of tumor-related genes.

Several studies have reported Oral Squamous Cell Carcinoma (OSCC) association with etiological factors, such as smoking and alcohol. The aim of the present study was to establish whether the methylenetetrahydrofolate reductase (MTHFR) C677T genotype and a high alcohol intake, solely or in interaction, have an impact on the oral cancer risk, DNA methylation, or multiple methylation of tumor-related genes. MTHFR C677T genetic polymorphism was determined by the PCR/RFLP method, and DNA methylation was assessed by nested methylation-specific PCR. The risk for multiple methylation was significantly increased in heavy-drinking patients with the TT genotype, compared with CC and CT patients (OR = 10.873; 95% CI, 1.134-104.24). Multiple methylation was significantly associated with tumor stage (p = 0.018), and showed a trend of association with the presence of nodal metastases (p = 0.058). A significant association was found between TT genotype and methylation status of the RASSF1A gene in OSCC patients (p = 0.012). Heavy-drinking individuals with the TT genotype showed increased oral cancer risk compared with the CC genotype (OR = 3.601; 95% CI, 1.036-12.513), and compared with the CC and CT genotypes (OR = 4.288; 95% CI, 1.325-13.877). Our study suggested gene-environment interactions between high alcohol intake and the MTHFR 677TT genotype for elevated oral cancer risk, with a significant impact on multiple methylation of cancer-related genes.