LRRK2 and Parkinson disease: While the cause of most Parkinson’s disease (PD) cases is unknown, perhaps as many as 15% of PD cases are due to genetic variation.1–4 Of these, around 3% are due to activating variants in the leucine-rich repeat kinase 2 (LRRK2) gene,3–5 making it one of the most clinically relevant PD genes.