Stratification analyses by body mass index, exercise, and dietary fat intake with combined phenotypes showed that genetically elevated IR was associated with greater breast cancer risk in overall obesity and inactive subgroups (single contributor: MTRR/LOC729506 rs13188458; HR = 2.21, 95% CI: 1.03-4.75).
Cross-talk was observed between one-carbon and xenobiotic pathways in breast cancer (RFC 80 G>A, COMT H108L and TYMS 5'-UTR 28 bp tandem repeat) and SLE (CYP1A1 m1, MTRR 66 A>G and GSTT1).
We found three single-nucleotide polymorphisms in those genes associated with LINE-1 methylation: SLC19A1 (rs1051266); MTRR (rs10380) and MTHFR (rs1537514), one of which was also associated with breast cancer risk: MTHFR (rs1537514).
A large number of studies investigated the role of methylenetetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) polymorphisms in breast cancer with inconsistent results.
The aim of our study was to investigate the association of three single-nucleotide polymorphisms (SNPs) in the folate-metabolizing genes - A2756G MTR, A66GMTRR, and 844ins68 CBS - which have putative functional significance in breast cancer risk.
We hypothesized that heritable methylation potential might be a risk factor for breast cancer and evaluated possible association with breast cancer for single nucleotide polymorphisms (SNPs) either involving CpG sequences in extended 5'-regulatory regions of candidate genes (ESR1, ESR2, PGR, and SHBG) or CpG and missense coding SNPs in genes involved in methylation (MBD1, MECP2, DNMT1, MGMT, MTHFR, MTR, MTRR, MTHFD1, MTHFD2, BHMT, DCTD, and SLC19A1).
A stratified analysis by menopausal status indicated the association between the NAT2 SNP (rs1799930) and breast cancer was mainly evident in premenopausal women (OR 2.70, 95% CI 1.20-6.07), while the MTRR SNP (rs162049) was significant in postmenopausal women (OR 1.61, 95% CI 1.07-2.44).
In conclusion, this meta-analysis strongly suggests that MTRRA66G polymorphism is not associated with breast cancer risk, especially in Caucasians and Asians.
In addition, interaction between the MTRRA66G polymorphism and folate intake for risk of postmenopausal breast cancer was observed (interaction P = 0.008).
Viable cell growth, MDI, and polymorphism frequency in MTRR (A66G and C524T) and MTHFR (A1298C and A1793G) did not differ among the study groups; however, MDI tended to be higher in BRCA carriers with breast cancer than those without and was significantly increased in MTHFR 677T allele carriers relative to wild-type carriers (P=0.017).