MAPT and Alzheimer disease: Even though the key hallmarks of the disease are the extracellular accumulation of β-Amyloid peptides (Aβ-42) and intracellular accumulation of hyperphosphorylated Tau neurofibrillary tangles, evidence showed that AD pathogenesis has a significant molecular complexity that also affects peripheral tissues and suggests that there are key molecular events that still need to be elucidated [209].