Although familial types of PD account for less than 10% of all cases, the identification of multiple genes (e.g., parkin, DJ1[a parkin-associated protein involved with oxidative stress], α-synuclein, UCHL1 [ubiquitin carboxy-terminal hydrolase L1], and PINK1 [putative serine-threonine kinase]) that cause early onset PD has provided vital information about possible pathological pathways [40]. Here, UCHL1 is linked to Parkinson disease.