MTHFR and cervical squamous intraepithelial neoplasia: We aimed to investigate the roles and interaction effects of high-risk human papillomavirus (HR-HPV) infection, methyltetrahydrofolate reductase (MTHFR) polymorphism, and paired box gene 1 (PAX1) methylation in cervical intraepithelial neoplasia (CIN) and cervical cancer.