HTT and Alzheimer disease: Most neurodegenerative diseases exhibit pathological abnormal protein aggregates, developing neurofibrillary tangles; for example, Aβ and C-terminal fragments (CTF) of the amyloid precursor protein (APP) in Alzheimer’s disease (AD), mutant α-synuclein in Parkinson’s disease (PD), polyglutamine (polyQ)-expanded huntingtin (mHtt) in Huntington’s disease (HD), and mutant superoxide dismutase 1 (SOD1) and TAR DNA-binding protein 43 (TDP-43) in amyotrophic lateral sclerosis (ALS) [57,101,102].