The primary insoluble constituent is often a disease-specific protein, such as amyloid-β (Aβ) and tau in AD, α-synuclein (α-syn) in PD, Zn-Cu superoxidase dismutase (SOD1)/Fused in Sarcoma RNA Binding Protein (FUS) in ALS, Huntingtin (Htt) in HD, and prions in CJD. The gene discussed is HTT; the disease is Alzheimer disease.