In this cohort study combining data for 1193 participants with PD from multiple studies, individuals with dual LRRK2 G2019S and GBA variation PD had a slower rate of cognitive decline than those with GBA PD alone, and this was not different from individuals with LRRK2 G2019S PD alone, supporting the notion that there is a dominant association of the LRRK2 gene in individuals with both variations. The gene discussed is LRRK2; the disease is Mental deterioration.