LRRK2 and Parkinson disease: Their frequency varies markedly depending on the population founder effects of the G2019S-LRRK2 mutation, reaching 30–42% of PD patients in North African Arabic populations as well as 6–30% in Ashkenazi Jewish populations, probably resulting from a mutation arising at least 5,000 years ago (for review of the genetics of LRRK2, please see Monfrini and Di Fonzo, 2017).