Abstract:Objective To determine the relationship of the plasma homocysteine (Hcy) level with Parkinson’s disease (PD) with or without L-dopa treatment. Methods According to the UK Parkinson’s Disease Society Brain Bank Clinical Diagnostic Criteria, 161 identified PD in- and out-patients admitted in the Fifth Hospital of Peking University from May 2011 to March 2013 were enrolled in this study. They were 88 males and 73 females, at age of (64.36±11.06) years, and suffered from PD for 0.5?22 (6.3±5.4) years. Another 80 age- and sex-matched healthy volunteers taking physical examination during the same period served as normal controls. The plasma levels of Hcy, Vit B12 and folic acid were measured and compared between the 2 groups. Univariate linear regression analysis was carried out for the correlation of the plasma levels of Hcy, Vit B12 and folic acid with the duration and dosage of L-dopa treatment, motor complications, anxiety, depression and dementia incidence. The causing factors of hyperhomocysteinemia (HHcy) in PD patients was also analyzed. The polymorphisms of MTHFR and COMT genes were detected in the 161 PD patients and 240 normal individuals. Results The plasma Hcy level was (17.65±9.36)μmol/L for the 161 PD patients, which was significantly higher than that in the normal controls [(10.12±3.20)μmol/L, P<0.001]. Among the 6 factors (sex, age, duration and dosage of L-dopa treatment, plasma levels of folic acid and Vit B12), univariate linear regression analysis showed that L-dopa treatment caused the incidence of HHcy (P<0.01). The causes of HHcy were mainly normal folate and Vit B12 levels in PD patients (more than 84%), which indirectly suggesting that there were some mutations in the relative enzymes regulating the metabolism of Hcy. There was no obvious difference in the distribution of COMT and MTHFR polymorphism between PD group and control group (P>0.05). Based on Hcy level, PD patients were subdivided into HHcy and mormal Hcy group, the frequency distributions of C677T alleles and genotypes were significantly different between HHcy group and normal Hcy group. There were 77 PD patients out of 161 with HHcy. Excluding 22 cases without L-dopa treatment, there were 35 from the left 55 cases having motor fluctuations (63.6%), 3 having dyskenisia (5.5%), 30 having anxiety and depression (54.5%), and 12 having dementia (21.8%). Conclusion PD patients with L-dopa treatment are prone to having HHcy, and HHcy exacerbates the severities or increases the incidences of motor complications, anxiety, depression and dementia in PD patients with L-dopa treatment.