SNCA and Parkinson disease: Early-onset PD is often associated with familial inheritance caused by gene mutations in 18 specific chromosomal regions/PD-related loci (i.e. PARK1-18), such as the SNCA gene (α-synuclein; PARK1 and 4), Parkin (ubiquitin protein ligase; PARK2), DJ-1 (PARK7) or LRRK2 (PARK8) [16].