A shared neuropathological feature of idiopathic Parkinson's disease, dementia 
with Lewy bodies, and multiple system atrophy is the development of 
intracellular aggregates of α-synuclein that gradually engage increasing parts 
of the nervous system. The pathogenetic mechanisms underlying these 
neurodegenerative disorders, however, are unknown. Several studies have 
highlighted similarities between classic prion diseases and these neurological 
proteinopathies. Specifically, identification of Lewy bodies in fetal 
mesencephalic neurons transplanted in patients with Parkinson's disease raised 
the hypothesis that α-synuclein, the main component of Lewy bodies, could be 
transmitted from the host brain to a graft of healthy neurons. These results and 
others have led to the hypothesis that a prion-like mechanism might underlie 
progression of synucleinopathy within the nervous system. We review experimental 
findings showing that misfolded α-synuclein can transfer between cells and, once 
transferred into a new cell, can act as a seed that recruits endogenous 
α-synuclein, leading to formation of larger aggregates. This model suggests that 
strategies aimed at prevention of cell-to-cell transfer of α-synuclein could 
retard progression of symptoms in Parkinson's disease and other 
synucleinopathies.