To date, no significant association has been shown between cognitive impairment in PD and the MTHFR C677T, MTHFR A1298C, TCN2 G776C, SLC19A1 G80A, COMT G472A, MTR A2756G, and CBS 844ins68 polymorphisms. The gene discussed is SLC19A1; the disease is Parkinson disease.