It is difficult to diagnose dementia with Lewy bodies (DLB) because it exhibits clinical and neuropathological overlap with both Alzheimer's disease and Parkinson's disease. The α-synuclein protein is a major component of Lewy bodies, and accumulation of α-synuclein aggregates causes synaptic dysfunction in DLB. Epigenetic changes at the synuclein alpha ( SNCA ) gene may be involved in DLB pathogenesis.