When BC patients were grouped into two categories with regard to age at the diagnosis (age ≤ 40 and age > 40 years) (Table 3), MTHFR rs1801133 revealed a positive correlation with early age at diagnosis (under 40 years); this polymorphism was found to be a BC risk factor among young patients in 4 genetic models (heterozygote: OR: 2.84, 95% CI: 1.35–6.0, p = 0.006; dominant: OR: 2.56, 95% CI: 1.29–5.09, p = 0.0061; over-dominant: OR: 2.34, 95% CI: 1.18–4.67, p = 0.015 and log-additive: OR: 1.62, 95% CI: 1.03–2.55, p = 0.036). Here, MTHFR is linked to breast cancer.