This study wants to focus on mitochondrial defects associated with Parkinson's disease (PD) and how they relate to alpha-synuclein (SNCA) expression and function. Individuals from families with inherited Parkinson's disease (affected and at risk members), as well as normal individuals, will be enrolled. All subjects will be asked to provide blood samples in order to study bioenergetic function in mitochondria from their platelets. These studies will include genotyping and determination of polymorphisms in the subjects' mitochondrial DNA (mtDNA) in order to delineate any significant abnormality that may be associated with a particular group. Cardiolipin levels will be obtained fee for service at Lipomics. Basic respirometry, enzyme activity, and somatic cell hybridization will be performed in the PI's lab. Protein analysis will be performed in the proteomics facility at NIMH.