LRRK2 and Parkinson disease: Recent brain imaging studies demonstrate that clinically manifest LRRK2 mutation carriers develop deterioration of the dopamine and serotonin systems, similarly to sporadic PD patients (Sossi et al., 2010; Wile et al., 2017); however, non-manifest mutation carriers exhibit increased striatal dopamine turnover (Sossi et al., 2010) and early increases in serotonin transporter binding (Wile et al., 2017).