HTT and Parkinson disease: Many neurodegenerative diseases, such as AD, Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS) are characterized by abnormal aggregation of misfolded proteins, i.e., amyloid β (Aβ) and tau in AD; α-synuclein in PD; huntingtin in HD, and TAR DNA-binding protein (TDP-43, also known as TARDBP) in ALS (Knowles et al., 2014).