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Mutations in the Leucine-Rich Repeat Kinase 2 gene (LRRK2) are mainly responsible for idiopathic Parkinson's disease (PD) with either a dominant pattern of transmission or a sporadic occurrence due to the reduced penetrance. A majority of LRRK2 kindreds demonstrate an extremely variable age-at-onset in affected members of the same family. The G2019S is the most common LRRK2 mutation, which accounts for 1-5% PD patients in North America, and up to 40% of patients from an isolated Arab population. We assessed the frequency of the G2019S mutation in 83 Brazilian PD patients originally preselected for having an early age-at-onset (<50 years) and/or a positive family history. The mutation was detected in three probands (3.5%). Our clinical findings in these kindreds include the first description of the phenotype in identical twins discordant for handedness (a general phenomenon found in approximately 25% monozygotic twins). However, both twins developed right asymmetric PD. The clinical presentation of twins was strikingly similar including an identical PD onset at age 60. This observation may suggest that genetic factors predominantly determine age-at-onset., (2007 Movement Disorder Society)