Understanding the connection between childhood maltreatment and the subsequent development of behavior problems is complicated by the fact that behavior problems are also known to be genetically influenced. Meta-analyses suggest heritability estimates of ~40–50% for conduct disorder and ASPD (Rhee & Waldman, 2002; Rose, Dick, Viken, Pulkkinen, & Kaprio, 2004). One gene that has received much attention for its effect on pathological or otherwise problematic externalizing outcomes (ASPD, CD, violent arrests, etc.) is monoamine oxidase A (MAOA). MAOA is located on the X chromosome and is involved in the catabolism of monoamines such as dopamine, serotonin, and noradrenaline. Many animal studies demonstrate that increased functioning of dopaminergic and noradrenergic pathways is associated with increases in aggression (Volavka et al. 2004). These catecholamines can affect aggressive behavior in a variety of ways, from their influence on energy and metabolism to their involvement in the central nervous system on arousal, attention, and the neural mechanisms that make possible the manifestation of physical or social aggression (Haller et al. 1998). Further support for the role of monoamines in aggression comes from evidence that pharmacological treatment with drugs acting on these systems attenuates aggressive behavior (de Almeida et al. 2005).
