HTT and early-onset autosomal dominant Alzheimer disease: Neurodegenerative disease processes have been shown to involve dysregulation of several relevant proteins, such as α-synuclein (Parkinson’s and Lewy body diseases), tau, and amyloid beta (Aβ) (Alzheimer’s disease) huntingtin (Huntington’s disease), and TDP-43 (Frontotemporal dementia).