Distinct NDDs are coupled to the accumulation of different misfolded amyloid proteins: AD to β-amyloid (Aβ), hyperphosphorylated tau (pTau) and other proteins, Parkinson’s disease (PD) to α-synuclein (α-syn), Huntington’s disease (HD) to huntingtin, amyotrophic lateral sclerosis (ALS) to SOD-1 or TDP-43, and prion diseases to prion proteins. The gene discussed is HTT; the disease is Huntington disease.