In this study, we investigated plasma vitamin B12, folate, homocysteine concentrations, and MTHFR C677T polymorphism in SCD patients and identified the TT genotype of MTHFR C677T as a pivotal risk factor for SCD, thus revealing an important association between MTHFR C677T polymorphism and SCD. The gene discussed is MTHFR; the disease is Schnyder corneal dystrophy.