The Tale of Warrior Gene: The MAOA-upstream Variable Number Tandem Repeat (MAOA-uVNTR) Polymorphism and Its Role in Shaping Aggressive and Violent Behaviour

The Monoamine Oxidase A (MAOA) gene has acquired significant attention across the field of behavioral genetics over time due to its association with different adverse impacts it has had on altering human behavior. Research suggests that specific genetic variations of the MAOA gene, particularly the MAOA low allelic variants (MAOA-L alleles), are linked to increased susceptibility to aggression. Due to this association, the low-activity variations of the MAOA gene's upstream Variable Number Tandem Repeat (uVNTR) promoter region have conferred the name "warrior gene." A plethora of neurobiological investigations have revealed that the MAOA gene plays a significant role in the metabolism of neurotransmitters, such as dopamine, serotonin, and norepinephrine, that are implicated in regulating mood, impulse control, and emotional processing. Further, a wealth of research highlights that any form of dysregulation of these neurotransmitter systems, stemming from the genetic variants of the MAOA gene, can contribute to aberrant behavior and lead to aggressive tendencies. However, a negative association between the MAOA low allelic variant (MAOA-L) and aggressive behavior has recently been presented. Hence, a critical evaluation of available literature is important to retreat the relationship between the MAOA variants and human aggression and violence. A comprehensive review was conducted by utilizing Google Scholar, PubMed, and Scopus databases to explore the association of MAOA gene polymorphism with aggressive and violent behaviours. This review will be centered on peer-reviewed literature, evaluating the caliber of the studies and highlighting their profound outcomes. Therefore, this narrative review primarily focuses on the MAOA-uVNTR polymorphism and its influence on antisocial spectrum behaviors like aggression and violence. It also emphasizes the moral, legal, and societal issues that genetically influence human behavior. This comprehensive review conducted by utilizing 33 studies, where 19 studies revealed that the MAOA-L allelic variants are consistently associated with aggression. A total number of 14 studies supported the notion that MAOA-L allelic variants to show a positive correlation with violence and criminal violence. It was also disclosed that the MAOA-L variants are influenced by both genetic and environmental factors, underscoring the intricacy of its role in behavioral outcomes. Nevertheless, it is anticipated that the literature compiled herein would provide a critical justification for MAOA-L as a genetic risk factor for humans' aggressive and violent behavioral traits.