APP and early-onset autosomal dominant Alzheimer disease: The amyloid precursor protein (APP), a membrane protein with the ability to regulate synapse formation and repair (Priller et al., 2006; Nalivaeva and Turner, 2013; Octave et al., 2013) has been widely studied for its role in Alzheimer's disease, but its role in other neurodegenerative diseases such as ALS continue to be discovered (Muresan et al., 2014).