The progression of many human neurodegenerative disorders is associated with an accumulation of alpha-synuclein (α-Syn), including Alzheimer's disease (AD) and Parkinson's diseases (PD), dementia associated with Lewy body disease (DLB), diffuse Lewy body disease (DLBD) and multiple system atrophy (MSA). This evidence concerns the gene SNCA and Alzheimer disease.