Previous research has demonstrated that a polymorphism in the serotonin transporter gene (5-HTTLPR) and adverse psychosocial circumstances interact to predict depression. The purpose of the present study was to explore the extent to which sex modulates these effects. Eighty-one boys and 119 girls (16-19 years old) were interviewed about psychosocial background variables and genotyped for the 5-HTT promoter polymorphism. There were two main results. First, boys and girls carrying the short 5-HTTLPR allele react to different kinds of environmental factors. Whereas males were affected by living in public housing rather than in own owned homes and by living with separated parents, females were affected by traumatic conflicts within the family. Second, the responses of males and females carrying the short 5-HTTLPR allele to environmental stress factors go in opposite directions. Thus, whereas females tend to develop depressive symptoms, males seem to be protected from depression. The results suggest that both the molecular and the psychosocial mechanisms underlying depression may differ between boys and girls.

Rheumatoid arthritis (RA) is a chronic and genetically complex inflammatory disorder that leads to erosive destruction of peripheral joints. The use of animal models mimicking RA, such as pristane-induced arthritis (PIA) in rats, should facilitate its genetic analysis. Pristane is a non-immunogenic synthetic oil that, after a single subcutaneous injection into DA rats, induces arthritis restricted to peripheral joints with a chronic relapsing disease course. To identify genes involved in the control of chronic arthritis, we made crosses between susceptible DA rats and resistant E3 rats and analysed the progeny with microsatellite markers covering the entire rat genome. Our results show that different arthritis phenotypes are associated with different chromosomal loci. Loci on chromosomes 4 and 6 (Pia2 and Pia3) influence arthritis onset, whereas a locus on chromosome 12 (Pia4) is associated with severity and joint erosion. We found that chronicity is associated with a different set of loci, one on chromosome 4 and the other on chromosome 14 (Pia5, Pia6). These findings demonstrate for the first time that different phases of a chronic self-perpetuative disease which mimics RA are associated with distinct sets of genes.

Brain monoamines, and serotonin in particular, have repeatedly been shown to be linked to different psychiatric conditions such as depression, anxiety, antisocial behaviour, and dependence. Many studies have implicated genetic variability in the genes encoding monoamine oxidase A (MAOA) and the serotonin transporter (5HTT) in modulating susceptibility to these conditions. Paradoxically, the risk variants of these genes have been shown, in vitro, to increase levels of serotonin, although many of the conditions are associated with decreased levels of serotonin. Furthermore, in adult humans, and monkeys with orthologous genetic polymorphisms, there is no observable correlation between these functional genetic variants and the amount or activity of the corresponding proteins in the brain. These seemingly contradictory data might be explained if the association between serotonin and these behavioural and psychiatric conditions were mainly a consequence of events taking place during foetal and neonatal brain development. In this review we explore, based on recent research, the hypothesis that the dual role of serotonin as a neurotransmitter and a neurotrophic factor has a significant impact on behaviour and risk for neuropsychiatric disorders through altered development of limbic neurocircuitry involved in emotional processing, and development of the serotonergic neurons, during early brain development.

The present study investigated a possible interaction between a functional polymorphism in the MAOA gene promoter (MAOA-VNTR) and childhood maltreatment in the prediction of adolescent male and female delinquency. A cohort of 1,825 high school students, 17-18 years old, completed an anonymous questionnaire during class hours which included questions on childhood maltreatment, sexual abuse, and delinquency. Saliva samples were collected for DNA isolation, and analyzed for the MAOA-VNTR polymorphism. Self-reported maltreatment was a strong risk factor for adolescent delinquent behavior. The MAOA genotype also showed a significant main effect when controlled for maltreatment. Boys with a short variant and girls with one or two long variants of the polymorphism showed a higher risk for delinquency when exposed to maltreatment. Our results confirm previous findings of an interaction between the MAOA-VNTR polymorphism and self-reported maltreatment. Results for boys and girls differ according to MAOA-VNTR genotype and direction of phenotypic expression.

Serotonin plays a central role in mood regulation and the development of depressive disorders. The present study investigated whether a functional polymorphism (5HTTLPR) of the serotonin transporter gene interacts with maltreatment in the prediction of depression. A cohort of 17-18 years old students (n = 1,482) anonymously completed the Survey of Adolescent Life and Health in Vestmanland 2006 and gave a saliva sample for DNA extraction. An association between maltreatment and adolescent depression was found independent of sex. When the whole population was analyzed, no main effect of 5HTTLPR in association with depression was found. When separated by sex, a significant main effect and a G x E interaction effect of the SS allele was found among girls. No gene main effect or G x E interaction effect was found among boys. The present study confirms previous findings of sex differences in interaction effects between the 5HTTLPR polymorphism and maltreatment in the prediction of adolescent depression.