MTHFR and cervical squamous intraepithelial neoplasia: The purpose of the current study was therefore to investigate the following in a population exposed to FA fortification: 1) The association between MTHFR C677T polymorphism and risk of CIN 2+; 2) The modifying effects of plasma folate concentrations on this association; and 3) The modifying effects of plasma folate on the association between MTHFR C677T polymorphism and the degree of PBMC L1 methylation, a documented biomarker of CIN risk.