SLC6A4 and psychiatric disorder: A consensus finding from association studies seems to hold that the low-expressing variants of these genes are risk factors for vulnerability to develop psychiatric disorders, conditions associated with reduced serotonergic activity, despite the fact that the low-expressing variants of 5HTTLPR and MAOA-LPR should intuitively promote increased serotonergic activity by keeping extracellular levels of serotonin high.