SNCA and Parkinson disease: Protein aggregates comprise structures composed of pathological unfolded or misfolded proteins such as α-synuclein (α-syn) in PD, amyloid β (Aβ) or tau protein in AD, mutant huntingtin protein (mHtt) in HD, as well as prion protein (PrP) in transmissible prion encephalopathies [7,8].