Over the past decade, genetic causes of parkinsonism have been elucidated but in less than 10 % of the cases. Since the discovery of the fi rst gene responsible for Parkinson's disease (PD), SCNA encoding α-synuclein, linkage mapping, and positional cloning have identifi ed autosomal dominantly or recessively inherited PD-causing mutations in the genes encoding Parkin , PTEN-induced kinase 1 ( PINK1 ), DJ -1 , leucine-rich repeat kinase 2 ( LRRK2 ), and ATP13A2 , indicating that PD has a highly heterogeneous etiology. With the introduction of next-generation sequencing, rare mutations in DNAJC6 , SYNJ1 , VPS35 , and DNAJC13 were then discovered to cause inherited parkinsonism. In addition, polymorphic variants in SNCA and LRRK2 and heterozygous mutations in the genes encoding β-glucocerebrosidase ( GBA ) and guanosine triphosphate cyclohydrolase 1 ( GCH1 ) appear to contribute to sporadic PD in several populations. These mutations have been linked to mitochondrial dysfunction, accumulation of abnormal and misfolded proteins, impaired protein clearance, defective recycling of synaptic vesicles, and oxidative stress. Identifi cation of other Mendelian forms of PD will be the main challenge for the next decade.