APP and proteostasis deficiencies: This protein misfolding disorder is caused by the misfolding and aggregation of amyloid β peptides and tau, which give rise to amyloid plaques and neurofibrillary tangles, respectively.91 Aβ is a 42-residue product resulting from two sequential cleavages of the amyloid precursor protein (APP), a transmembrane protein with no clearly defined function.