Serotonin is one of several chemical messengers in the brain, or neurotransmitters, which help brain cells communicate with one another. Among many other functions, serotonin is involved in regulating mood. Problems with making or using the right amount of serotonin have been linked to many mental disorders, including depression, bipolar disorder, anxiety disorder, autism, and schizophrenia.
There are many genes that code for serotonin. Some of these genes guide serotonin production and other are involved in its activity. The serotonin transporter gene makes a protein that directs serotonin from the space between brain cells — where most neurotransmitters are relayed from one cell to another — back into cells, where it can be reused. Since the most widely prescribed class of medications for treating major depression acts by blocking this transporter protein, the gene has been a prime suspect in mood and anxiety disorders.
The serotonin transporter gene has many versions. Since everyone inherits a copy of this gene from each parent, a person may have two copies of the same version or one copy each of two different versions. One version of the serotonin transporter gene makes less protein, resulting in decreased transport of serotonin back into cells. This version has also long been the focus of depression research due to its suggested effect on risk.