To the Editor: Most cases of Parkinson's disease are considered sporadic and idiopathic, although there is evidence of familial aggregation, and several monogenic forms have been identified.¹ Recently, several pathogenic mutations in the highly conserved leucine-rich repeat kinase 2 gene (LRRK2) have been associated with autosomal dominant, late-onset Parkinson's disease.¹ Of these, the G2019S substitution is the most frequently reported.² It occurs in about 1 percent of unselected cases and 3 to 6 percent of familial cases of Parkinson's disease in persons primarily of European ancestry² but in 7 of 17 cases of familial disease in persons from . . .