Participants: 535   Link to Case-Control Study

Cases: All cases were evaluated by a neurologist. Each participant underwent a detailed evaluation for Parkinson's disease, and met either the Gelb criteria or the UK Brain Bank Criteria (both below). All were white and from the USA, ranking in age of onset from 55 to 84 years. Disease onset was defined as the time when symptoms of the disease were first noted, including at least one of the following: resting tremor, rigidity bradykinesia, gait disorder, postural instability. Those with and without a family history of Parkinson's disease were included, but those who had three or more relatives with parkinsonism, or apparent Mendelian inheritance of neurodegenerative disease were excluded.

Controls: Blood samples were drawn from neurologically normal, unrelated, white individuals at many different sites in the USA. Each participant underwent a detailed medical history interview and had no family history on specific query of Alzheimer's disease, amyotrophic lateral sclerosis, ataxia, autism, bipolar disorder, brain aneurysm, dementia, dystonia, or Parkinson's disease. Folstein Mini-mental state examination scores ranged from 26-30. All participants were interviewed for family history in detail and specifically had no first degree relative with any of the following: amyotrophic lateral sclerosis, ataxia, autism, brain aneurysm, dystonia, Parkinson's disease, and schizophrenia. The mean age of participants at sample collection was 68 (range 55-88 years).