Gene deficiency or reduction of dopamine transporter (DAT) gene is a valuable model for investigating DAT dysfunction, which is usually involved in transmitter imbalances in psychiatric and neurodegenerative diseases, (e.g., addictive disorders, attention-deficit/hyperactivity disorder, schizophrenia, Parkinson’s disease), frequently associated to gastrointestinal disorders [1,2]. This evidence concerns the gene SLC6A3 and attention deficit-hyperactivity disorder.