These include Parkinson’s disease (PD) and dementia with Lewy bodies (DLB) characterized by the presence of intraneuronal Lewy bodies (LB) and belonging together to the group of LB diseases, and multiple system atrophy (MSA), where α-synuclein accumulates in glial cytoplasmic inclusions (GCI). This evidence concerns the gene SNCA and Lewy body dementia.