Wile et al. (93) did two cross-sectional PET studies showing that LRRK2 mutation carriers without manifest Parkinson's disease had greater 18F-fluorodopa uptake and dopamine transporter binding than did individuals with sporadic Parkinson's disease increased serotonin transporter binding in the striatum, brainstem, and hypothalamus, possibly reflecting compensatory changes in serotonergic innervation preceding the motor onset of Parkinson's disease. This evidence concerns the gene SLC6A3 and Parkinson disease.