Parkinson’s disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are named α-synucleinopathies, because of the accumulation of misfolded α-synuclein (α-syn) in fibrillary intracellular inclusions, providing a diagnostic signature of these disorders. The gene discussed is SNCA; the disease is Lewy body dementia.