Alpha-synuclein (α-syn) is abundantly expressed in neurons and is the major constituent of Lewy bodies, which are the hallmarks of neurodegenerative diseases called synucleinopathies, which like PD, results in multiple system atrophy, Lewy body dementia, Alzheimer’s disease, and frontotemporal dementia. Here, SNCA is linked to early-onset autosomal dominant Alzheimer disease.