HTT and Parkinson disease: Failure in eliminating toxic misfolded proteins has been observed in several neurological disorders, with mutant huntingtin in Huntington’s disease, α-synuclein in PD, mutant SOD1 in familial amyotrophic lateral sclerosis, and β-amyloid in Alzheimer’s disease representing optimal examples of the relationship between proteasome malfunction and neurodegeneration [75].