Kindreds with Mendelian inheritance of Parkinson disease (PD) have been known since a long time ago. Nine loci have been mapped in familial PD by linkage study and four causative genes have been cloned. This paper discusses Park 1 and Park 2, the identification of which has brought about many advances in the studies on pathomechanism of PD. Investigations of these genes in familial PD have expanded their clinical and pathological phenotypes. However, to clarify the effect of mutations on these phenotypes, additional post-mortem neuropathological studies are required.