Basically, serotonin transporter knock-out mice (5-HTT KO) demonstrate a range of behavioral abnormalities that resemble symptoms of anxiety disorders, like increased fear- and anxiety-related behaviors and reduced exploratory locomotion in behavioral standard tests [1], [33], [51]–[53]; mice with an overexpression of the 5-HTT gene display the opposite phenotype; i.e. reduced anxiety-like behavior [33], [54]. This evidence concerns the gene SLC6A4 and Anxiety.