Enteric alpha‐synuclein expression is increased in P arkinson's disease but not A lzheimer's disease

BACKGROUND AND OBJECTIVE: Alpha-synuclein (α-Syn) is immunohistochemically detectable in enteric neurons in some subjects. We determined its age distribution in the general autopsy population and in an age-matched subset investigated differences with Parkinson's (PD) and Alzheimer's diseases (AD). METHODS: Archival autopsy samples of colon from 95 cases (77 general population, 10 PD, and 8 AD) were immunostained with monoclonal antibody KM51. α-Syn detectability was semiquantitatively graded 1 to 3. RESULTS: α-Syn was detectable in 52% of the general population, and its level of expression did not change between ages 40 and 91. All PD subjects were α-Syn positive, with higher prevalence (P = 0.001) and grade (P = 0.003) than age-matched controls. AD subjects were no more likely to be α-Syn positive or have a higher grade than controls. CONCLUSIONS: Either PD develops selectively in the enterically α-Syn-positive population subset or PD induces this expression. Absence of increased α-Syn expression in AD points to differences in pathogenesis.