HTT and Huntington disease: Notably, different neurodegenerative conditions exhibit disease-specific protein aggregates: α-synuclein in Parkinson’s disease forms Lewy bodies, amyloid beta and tau in Alzheimer’s disease produce extracellular plaques and intracellular neurofibrillary tangles, respectively, while the huntingtin protein with expanded polyglutamine repeats aggregates in Huntington’s disease.