In Parkinson disease, the most common mutation in the multidomain Leucine-rich repeat kinase 2 (LRRK2) protein leads to a hyper-activation of the kinase domain, resulting in hyper-phosphorylation of a number of Rab GTPase substrates including Rab5 (Steger et al., 2017; Steger et al., 2016). The gene discussed is LRRK2; the disease is Parkinson disease.