MAPT and early-onset autosomal dominant Alzheimer disease: Most individuals who have DS develop the neuropathological features of Alzheimer's disease (AD); amyloid-β (Aβ) plaques and tau neurofibrillary tangles by the age of 50 (Davidson et al., 2018), and 80% of individuals will have developed dementia by age 65 (McCarron et al., 2017).