DRD2 and multiple system atrophy: A partial correlation analysis between dopamine transporter and dopamine D2 receptor availability, controlling for the effects of striatal subregional differences, revealed a positive correlation in the patient with multiple system atrophy (r = 0.893, P = 0.0002), but no significant correlation in the patient with Parkinson’s disease (r = −0.036, P = 0.89).