MTHFR and breast cancer: We did not detect an association between genetic variants directly or indirectly involved in epigenetic processes such as C677T in MTHFR, rs4665777 in DNMT3A, rs406193 in DNMT3B, rs16942, rs1799950, rs8176092, rs8176193in BRCA1, and global DNA methylation levels in the breast cancer study (p > 0.05 for all, Additional file 6: Table S3).