The SLC6A4 gene that encodes the serotonin transporter has a repeat promoter polymorphism, 5-HTTLPR. The “L” long allele is associated with increased gene activity and therefore increased reuptake of serotonin from the synaptic cleft compared with the “S” short allele. In the Mannheim Children at Risk Study, male (but not female) LL homozygotes with significant adversity consumed more drinks and had more heavy drinking days than S allele carriers and individuals unaffected by adversity. This G×E interaction was present for both early family adversity and recent SLEs (separate analyses), but the effects were stronger for recent SLEs [76]. In contrast, in a small study from the United States, the S allele predicted early alcohol use in maltreated children entering out-of-home care [77]. Likewise, the S allele predicted the use of illicit drugs in Italian adolescents who had experienced poor maternal care [78]. The S allele has also been associated with increased drinking and drug use in US college students who had experienced multiple past year SLEs [79]. Sex-specific effects also have been detected in rhesus macaque monkeys, but in contrast
