There are two main purposes of this study.
The first purpose is to determine whether people who have characteristics that may be risk factors for Parkinson disease (PD) have objective evidence—“biomarkers”—that the disease process is actually going on. The evidence we are looking for is loss of nerves and nerve cells that use particular chemicals, called catecholamines. PD patients typically have a loss of nerves and nerve cells that use the catecholamines dopamine and norepinephrine as chemical messengers.
The second purpose is to determine whether people who have abnormal “biomarkers” actually develop PD during several years of follow-up.