HTT and Huntington disease: Protein inclusions, in particular, are relevant hallmarks of neurodegenerative diseases and are specific for each pathology; for example, amyloid-β (Aβ) and tau are hallmarks in Alzheimer’s disease (AD), α-synuclein in Parkinson’s disease (PD), mutant huntingtin (mHTT) in Huntington’s disease (HD), and mutant ataxin-3 in Spinocerebellar Ataxia type 3/Machado–Joseph disease (SCA3/MJD) [17,18,21].