Abstract
Appetitive aggression is a sub-category of instrumental aggression, characterised by the primary intrinsic enjoyment of aggressive activity. Aggression is heritable, and serotonergic and monoaminergic neurotransmitter systems have been found to contribute to the underlying molecular mechanisms. The aim of this study was to investigate the role that genetic variants in the serotonin transporter (SLC6A4) and monoamine oxidase A (MAOA) genes play in the aetiology of appetitive aggression in South African Xhosa males (n = 290). SLC6A4 5-HTTLPR, rs25531, and STin2 variants, as well as MAOA-uVNTR were investigated for their association with levels of appetitive aggression using Poisson regression analysis. The STin2 VNTR12 allele was found to be associated with increased levels of appetitive aggression (p = 0.003), but with decreased levels of reactive aggression (p = 7 × 10−5). This study is the first to investigate genetic underpinnings of appetitive aggression in a South African population, with preliminary evidence suggesting that SCL6A4 STin2 variants play a role in its aetiology, and may also be important in differentiating between appetitive and reactive aggression. Although the results require replication, they shed some preliminary light on the molecular dichotomy that may underlie the two forms of aggression.
Highlights
Aggression can occur in two main forms: appetitive and reactive aggression, which are broadly characterised by the motivation to perpetrate aggression[1]
Many researchers have indicated that it is functionally more sound to group subjects who carry the L-G haplotype with those carrying S-alleles[24,26]. This is important in populations with African ancestry, as the frequency of the L-G haplotype has been found to be much higher than in other populations[27]. Another SLC6A4 variant that has been investigated for its role in aggression is a variable number of tandem repeats (VNTR) polymorphism located in intron 2, referred to as STin[2]
When reactive aggression was investigated, we found that the STin[2] VNTR was significantly associated with Buss-Perry Aggression Questionnaire (BPAQ) score; this association was in the opposite direction to that observed for Appetitive Aggression Scale (AAS) score
Summary
Aggression can occur in two main forms: appetitive and reactive aggression, which are broadly characterised by the motivation to perpetrate aggression[1]. Hu et al.[24] identified a single nucleotide polymorphism (SNP), rs25531, situated within the 5-HTTLPR variant This SNP has been found to modulate the functionality of the L-allele, such that the L-G haplotype results in reduced SLC6A4 expression (comparable to that of the S-allele), whilst the L-A haplotype is associated with increased SLC6A4 expression, and increased SLC6A4 binding potential in the putamen[25]. This is important in populations with African ancestry, as the frequency of the L-G haplotype has been found to be much higher than in other populations[27] Another SLC6A4 variant that has been investigated for its role in aggression is a variable number of tandem repeats (VNTR) polymorphism located in intron 2, referred to as STin[2]. Recent evidence suggests that the 5-HTTLPR and STin[2] VNTR polymorphisms may be controlled by the same regulatory pathway[36], with the S-STin2.12 allele combination resulting in increased SLC6A4 expression compared to the L-STin2.10 allele combination
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