LRRK2 and Parkinson disease: Here, we extend this evidence in an unexpected direction by showing that two pathogenic mutations of LRRK2, G2019S, and R1441C – among the more common genetic alterations to emerge from what was previously considered to be ‘sporadic’ PD – can consistently and significantly decrease the T:M ratio of WT αSyn at normal levels of endogenous expression in human neurons.