Although we showed a relationship between nigrostriatal innervation and motor score in PD patients without probable RBD, investigating motor features while “ON” and “OFF” medication and changes with VMAT2 levels may provide more insight about the true relationship observed between PD with and without probable RBD and motor severity in relation to the left caudate VMAT2 availability. The gene discussed is SLC18A2; the disease is Parkinson disease.