SLC6A3 and Parkinson disease: The observed heterogeneity in DAT levels may reflect ET clinical and kinematic heterogeneity (Tarakad and Jankovic, 2019, Thenganatt and Jankovic, 2016), also confirming the pathophysiological link between ET and PD (Minen and Louis, 2008, Rajput et al., 2019, Pietracupa et al., 2021, Espay and Fasano, 2023).