SNCB and early-onset autosomal dominant Alzheimer disease: The synuclein family is composed of three members, two of which, α- and β-synuclein, play a major role in the development of synucleinopathies, including Parkinson’s disease (PD) as most important movement disorder, dementia with Lewy bodies (DLB) as the second most frequent cause of dementia after Alzheimer’s disease and multiple system atrophy.