SLC6A3 and tic disorder: Pharmacological studies.Maia & Conceição (2018) elaborate on their theory of how dopamine may relate to tics in TS.Hienertet al. (2018) provide a meta-analysis of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) studies in TS measuring the dopamine transporter (DAT) or D2-like dopamine receptors; neither showed conclusive differences in patients, but sample sizes and methodological limitations may explain the negative results.