RAB6A and Parkinson disease: Although a subset of Rab GTPases has been identified as authentic LRRK2 substrates (Dodson et al., 2012; Steger et al., 2016), a continuing search for additional LRRK2 substrates and associated upstream and downstream effectors is of critical importance to understand LRRK2 PD-mediated mechanisms, to identify specific and sensitive disease biomarkers and to develop targeted therapies.