HTT and Parkinson disease: Majority of the neurodegenerative diseases are characterized by the aggregation of intracellular proteins or their extracellular depositions (plaques) such as α-synuclein in Parkinson’s disease (PD), amyloid beta (Aβ)/tau aggregates in Alzheimer’s disease (AD), superoxide dismutase 1 (SOD 1) in amyotrophic lateral sclerosis (ALS), or huntingtin protein with tandem glutamine repeats in Huntington’s disease (HD) [2].