Although low/intermediate or indeed severe/high levels of concomitant pathology are present across numerous diseases, they are particularly evident across Lewy body diseases (LBDs) including dementia with Lewy bodies, Parkinson’s disease (PD), and Parkinson’s disease dementia (PDD), where in addition to hallmark inclusions of α-synuclein, concomitant AD related pathology (intracellular tau-immunoreactive neurofibrillary tangles and extracellular amyloid β (Aβ) plaques) is a prominent feature [17, 35, 39, 61, 62]. This evidence concerns the gene MAPT and Parkinson disease.