APP and Alzheimer disease: While in inherited cases of AD, genetic mutations in amyloid precursor protein (APP) and presenilins (PS1 and PS2) lead to the pathological features of extracellular Aβ plaques and intracellular neurofibrillary tangles [2], mutations in the α-synuclein gene (Snca) confer familial PD, and its protein product is a component of the pathological hallmark, the intracellular Lewy bodies [3,4].