HTT and neurodegenerative disease: Aggregated proteins are characteristic of neurodegenerative disease, hence they are sometimes known as “proteinopathies” owing to the deposition of aggregates of tau, α-synuclein, huntingtin, superoxide dismutase-1, or TDP-43, which characterize such human neurodegenerative disorders as frontotemporal degeneration, Parkinson’s disease, Lewy body disease, Huntington’s disease, and ALS.