Mutations in several other genes (PARK2 (Parkin), PARK6 (phosphatase and tensin homolog (PTEN)-induced kinase 1—PINK1), PARK7 (DJ-1), PARK8 (leucine rich repeat kinase 2—LRRK2), PARK9 (ATP13A2)) are implicated as a causal factor in familial PD, although most cases of PD are sporadic. Here, LRRK2 is linked to Parkinson disease.