Alpha-synuclein lesions in normal aging, Parkinson disease, and Alzheimer disease: Evidence from the Baltimore Longitudinal Study of Aging (BLSA)

Alpha-synuclein (α-synuclein) lesions are characteristic of idiopathic Parkinson disease (PD) and other α-synucleinopathies. To study the frequency of α-synuclein lesions in normal aging and how frequently they coexist with lesions of Alzheimer disease (AD), we examined the autopsy brains from normal and demented subjects in the Baltimore Longitudinal Study of Aging (BLSA) (n = 117). We found that the overall frequency of α-synuclein lesions was 25%, with 100% in 7 cases of PD, 31.5% in 56 cases with AD lesions, and 8.3% among 36 older control brains. Among brains with AD lesions, the frequency of α-synuclein pathology was higher in those with higher scores for neuritic plaques, but not in those with higher scores for neurofibrillary tangles. Our observations indicate that α-synuclein lesions are uncommon in aged control subjects. Finally, the coexistence of Aβ amyloid and α-synuclein pathology in AD brains suggests that the pathogenic mechanism/s leading to the accumulation of Aβ and α-synuclein may be similar.