Alzheimer families with mutations in APP, PSEN1 and PSEN2 have been described with phenotypes of mixed parkinsonism and dementia suggestive of DLB [91–93], and extensive Lewy body pathology has also been found in Alzheimer’s families with these mutations [94, 95], suggestive of a possible mechanistic link. Here, PSEN2 is linked to Lewy body dementia.