APP and juvenile Huntington disease: Pathologically, most neurodegenerative diseases are associated with accumulation of protein aggregates, including mutant α‐synuclein in Parkinson disease (PD), Aβ and C‐terminal fragments of the amyloid precursor protein (APP) in Alzheimer disease (AD), pathogenic mutant huntingtin (mHtt) in Huntington disease (HD), and mutant SOD1 (superoxide dismutase 1) as well as TDP‐43/TARDBP (TAR DNA binding protein) in amyotrophic lateral sclerosis (ALS).172, 174