LRRK2 and Parkinson disease: With emerging reports that LRRK2 functionally interacts with α-syn and other PD-linked proteins in axons and at the synapse (Lin et al., 2009; Inoshita et al., 2017; Mir et al., 2018; Novello et al., 2018; MacIsaac et al., 2020), therapeutic advancements may well depend on understanding how mutations in LRRK2 disrupt synaptic activity within the complex neural circuitry underlying PD.