In all facts, even though TPH2 is the rate limiting enzyme for the synthesis of serotonin in central nervous system [32], a molecular role that candidates it as a central regulator of psychiatric disorders such as major depressive disorder [33–35] and bipolar disorder [35–37], recent reports rejected the hypothesis that variations located in the TPH2 gene could modulate alcohol dependence [17–19]. Here, TPH2 is linked to bipolar disorder.