A meta-analysis of 9 PET and 10 SPECT studies revealed that patients with ADHD had 14% greater striatal DAT density than in TD, but this was influenced by previous exposure to ADHD medication with lower DAT density in medication naïve ADHD subjects (Fusar-Poli et al., 2012). Here, SLC6A3 is linked to attention deficit-hyperactivity disorder.