The overall aim of this observational study is to investigate the impact of COMT inhibition on homocysteine metabolism, vascular physiology and correlates of neurodegeneration in PD patients with certain COMT genotype. It is designed to evaluate effect size of Hcy lowering to secondary outcome parameters. Assessment of outcome parameters will be rater-blinded or computer-based.

Inclusion Criteria:

• Age 60 - 75 years,
• Caucasian ethnicity,
• diagnosed PD by UK brain bank criteria,
• Hoehn & Yahr scale 2 - 3,
• fertile females have to use contraception
• Group 1: medication with Stalevo® (L-DOPA/DDI + Entacapone)
• Group 2: medication with Madopar® or Sinemet® (L-DOPA/DDI)

Exclusion Criteria:

• methotrexate therapy during the last 12 months,
• treatment with Tolcapone
• vitamin B6, B12 and/or folic acid supplementation during last 6 months,
• pregnancy,
• intention to become pregnant during the course of the study,
• breast feeding,
• other clinically relevant concomitant disease states by discretion of the investigator
• known or suspected non-compliance, drug or alcohol abuse,
• inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia or confusional state of the subject,
• participation in another study with investigational drug within the 30 days preceding and during the present study,
• enrolment of the investigator, his/her family members, employees and other dependent persons.

Tertiary movement disorder clinic