At inhibitor concentrations that caused maximal reduction of phosphorylation of both biomarkers in samples from PD patients homozygous for the G2019S LRRK2 mutation, only intermediate reduction was observed in samples from PD patients heterozygous for the G2019S LRRK2 mutation, and little or no loss of phosphorylation was observed in the control subject and PD patients without the G2019S mutation. This evidence concerns the gene LRRK2 and Parkinson disease.