SNCA and Alzheimer disease: Lewy body pathology consisting of alpha-synuclein (αSyn) aggregates, i.e. the hallmark pathology of Parkinson’s disease and Lewy body dementia [11], is one of the most common co-pathologies found in ~ 50% of AD cases at autopsy [6, 7, 9] and concomitant αSyn has been shown to exacerbate cerebral glucose hypometabolism, cognitive impairment and rate of decline in AD patients [7, 12–14].