MAPT and Alzheimer disease: Thus, the combination of Lewy pathology and Alzheimer’s disease (AD) pathology (fibrillary β-amyloid and intraneuronal tangles consisting of hyperhosphorylated tau) predicts dementia in PD better than the severity of any single pathology18; and in clinical studies in patients with newly diagnosed PD, cerebrospinal fluid (CSF) biomarker evidence for β-amyloid pathology (for example, low concentrations of Aβ1-42) is a significant predictor of subsequent cognitive impairment19.