To date there is no readily accessible laboratory test available for the diagnosis of Parkinson disease. The diagnosis of probable PD is generally made over time by a neurologist who serially examines the patient, observes his/her response to treatment and who rules out other possible diseases. During microscopic examination of the brain of patients with PD and related disorders, a neuropathologist observes both selective cell loss and abnormal aggregates of a brain protein called alpha-synuclein. These findings are essential for the definitive diagnosis. Our research plan for a possible biomarker of PD is to measure the levels of alpha-synuclein protein in the cerebrospinal fluid (CSF) during a routine procedure called lumbar puncture by a sensitive and specific test. Our laboratory will examine the CSF levels of alpha-synuclein from age-matched patients with different disease categories that include PD, dementia with Lewy bodies, multiple system atrophy, stroke, meningitis, encephalitis and others. We plan to enroll at least 30 patients that have PD or related disorders during our pilot study. Following the comparison with non PD-related proteins and careful statistical analyses, our data will provide us with information as to the suitability of subsequent studies in a larger group of patients.