SNCA and Parkinson disease: In a few percentage of cases, PD behaves as a monogenic condition, with mutations in one of the genes involved in the accumulation of α-synuclein and coding for components of the ubiquitin-proteasome system: α-synuclein (SNCA/PARK1), leucine-rich repeat kinase 2 (LRRK2/PARK8), ubiquitin carboxyl-terminal esterase L1 (UCHL1), Parkinson protein 2 (Parkin/PARK2), PTEN-induced kinase 1 (PINK1/PARK6), PD 7 (DJ-1/PARK7) and PD 9 (ATP13A2/PARK9) [152,164].