About 5–10% of PD patients have familial patterns of inheritance [320]. Several genes have been identified in Mendelian forms of PD. Gene mutations with autosomal dominant or autosomal recessive inheritance patterns have been identified in familial forms of PD (Table 3). PD-linked mutations occur in the genes encoding α-Syn, Parkin, ubiquitin carboxy-terminal hydrolyase-L1 (UCH-L1), phosphatase and tensin homolog (PTEN)-induced putative kinase-1 (PINK1), DJ-1, and leucine-rich repeat kinase-2 (LRRK2). In rare autosomal dominant inherited forms of PD, missense mutations in the α-syn gene (PARK1) result in amino acid substitutions Ala-53→Thr, Ala-30→Pro, Glu-46→Lys; in addition, duplication and triplication mutations in the α-syn gene (PARK4) have been found [322,323,324]. A missense mutation in the UCH-L1 gene (PARK5), resulting in the amino acid substitution Ile-93→Met, can also cause very rare autosomal dominant PD [325]. Loss-of-function mutations due to large deletions and truncations and also missense or nonsense mutations in parkin (PARK2), PINK1 (PARK 6), and DJ-1 (PARK7) are the cause of autosomal-recessive inheritance of PD [326,327,328,329]. Several missense mutations in the LRRK2 gene (PARK8) have been found, resulting in amino acid substitutions Tyr-1654→Cys, Arg-1396→Gly, Tyr-1699→Cys, Arg-1441→Cys, Ile-1122→Val, Ile-2020→Thr, that cause more commonly occurring autosomal dominant PD and possibly ‘sporadic’ PD [330,331]. PARK9 has been ascribed to a deletion mutation (cytosine at nucleotide position 3057) or guanine-to-adenine transition at a splice site of exon 13 in the ATP13A2 gene that encodes a predominantly neuronal P-type lysosomal ATPase [332]. Potential lysosomal dysfunction related to ATP13A2 mutant proteins might tie into PD etiology through abnormalities in autophagy. Mutations of genes at other PD loci are more controversial (Table 3).