APP and early-onset autosomal dominant Alzheimer disease: In the case of Alzheimer’s disease (AD), the pathology is characterized by the intracellular accumulation of hyperphosphorylated tau protein aggregates and by the altered processing of amyloid precursor protein (APP) into amyloid β peptide (Aβ), which accumulates intracellularly and extracellularly into amyloid plaques [54].