Most molecular genetic studies of neuroticism have focused on polymorphisms of genes thought to be good candidates for neuroticism because they are associated with neural systems related to emotion. For example, the serotonergic system is known to be involved in emotion processing (Leonardo & Hen, 2006). The association between a polymorphism (5-HTTLPR) of the serotonin transporter gene and neuroticism has been investigated many times. This is because the serotonin transporter is involved in the reuptake of serotonin from the synapse and variations in transporter functioning can influence serotonergic transmission. The 5-HTTLPR polymorphism is of particular interest because (a) it is a functional polymorphism that influences gene products that influence activity of the serotonin transporter on neurons (Haddley et al., 2008), and (b) because the serotonin transporter is the target of some medications that are effective in treating anxiety and depression (Leonardo & Hen, 2006).
