alpha Synuclein is a member of a family of small, highly conserved proteins, including synuclein-alpha, -beta, and -gamma, and synoretin. These proteins are localized predominantly in the brain, concentrated in presynaptic nerve terminals. Synuclein-alpha is normally a soluble protein. Abnormal synuclein-alpha forms filamentous inclusions (Lewy bodies and Lewy neurites) in several neurodegenerative diseases, including Parkinson's disease (PD), dementia with Lewy bodies, and Alzheimer's disease. It is a major component of intracellular inclusions in sporadic PD. Mutations in the synuclein-alpha gene (A53T and A30P) have been reported in several families with autosomal dominant Parkinsonism.