A mutation in the alpha-synuclein gene has recently been linked to some cases of 
familial Parkinson's disease (PD). We characterized the expression of this 
presynaptic protein in the midbrain, striatum, and temporal cortex of control, 
PD, and dementia with Lewy bodies (DLB) brain. Control brain showed punctate 
pericellular immunostaining. PD brain demonstrated alpha-synuclein 
immunoreactivity in nigral Lewy bodies, pale bodies and abnormal neurites. Rare 
neuronal soma in PD brain were immunoreactive for alpha-synuclein. DLB cases 
demonstrated these findings as well as alpha-synuclein immunoreactivity in 
cortical Lewy bodies and CA2-3 neurites. These results suggest that, even in 
sporadic cases, there is an early and direct role for alpha-synuclein in the 
pathogenesis of PD and the neuropathologically related disorder DLB.