This resembles the results of two different studies performed by the group of Wellman [5] and Carroll [91] who showed that 5-HTT-/- mice exhibit significantly increased depression-related behavior compared to 5-HTT+/- and 5-HTT+/+ mice exclusively in response to repeated forced swimming, but not to a single exposure to the forced swim test. The gene discussed is SLC6A4; the disease is depressive disorder.