LRRK2 and Parkinson disease: However, limitations in enrolling appropriate numbers of suitable LRRK2 mutation carriers will likely provide a significant hurdle in Phase 2 and Phase 3 trials; as the prevalence of LRRK2 mutations, which are estimated at approximately 5% of all PD cases, vary significantly depending on the geographic location, and the relative frequency of specific mutations, which also varies greatly (Monfrini and Di Fonzo, 2017).