SLC6A4 and Anxiety: The depletion of serotonin (5-HT) concentration and defects of the 5-HT synthesizing enzyme (tph2) in the brain, hyperserotonemia, the time course of 5-HT release and variants of the different types of 5-HT receptors (htr1a, htr1d, htr2a, htr5a) and solute transporters (slc6a4) have been linked to anxiety or ASD-like behaviors [4–8].