SLC6A4, also known as a serotonin transporter (SERT), belongs to the Na+- and Cl–　-dependent neurotransmitter transporter family and transports the neurotransmitter serotonin from synaptic spaces into presynaptic neurons. This activity of SLC6A4 terminates the synaptic actions of serotonin, and the presynaptic neurons release it once again into the neurotransmitter pool. A repeat length polymorphism in the SLC6A4 gene promoter has been shown to affect the rate of serotonin uptake and may thus be associated with the sudden infant death syndrome, aggressive behavior in Alzheimer disease patients, and the susceptibility of people experiencing emotional trauma to depression.