RAB6A and Parkinson disease: Moreover, the protein kinase PINK1 (PTEN-induced putative kinase 1; PARK6) and the ubiquitin E3 ligase Parkin (PARK2) are also linked to PD signalling upstream of Rab GTPases [28], and the Rab (Ras-related proteins in brain) GTPase-related protein RAB7L1 (PARK16) functions in a vesicular trafficking pathway downstream of LRRK2 [29].