|Classification and external resources|
Brunner syndrome is a rare genetic disorder associated with a mutation in the MAOA gene. It is characterized by lower than average IQ (typically about 85), problematic impulsive behavior (such as arson, hypersexuality and violence), sleep disorders and mood swings. It was identified in fourteen males from one family in 1993. It has since been discovered in two additional families.
Brunner syndrome is caused by a monoamine oxidase A (MAOA) deficiency, which leads to an excess of monoamines in the brain, such as serotonin, dopamine, and norepinephrine (noradrenaline). In both mice and humans, a mutation was located on the eighth exon of the MAO-A gene, which created a dysfunctional MAO-A gene. The regular function of MAO-A, breaking down monoamines, is disrupted, and monoamines build up within the brain. Mice that lacked a functional MAO-A gene displayed higher levels of aggression, in comparison to mice with a functional MAO-A gene.
Brunner Syndrome was described in 1993 by H.G. Brunner et al upon the discovery of a particular genetic defect in male members of a large Dutch family. Brunner found that all of the male family members with this defect reacted aggressively when angry, fearful, or frustrated. The defect discovered was later found to be a mutation in the gene that codes for monoamine oxidase A (MAOA gene). Brunner said that an "MAO-A deficiency is associated with a recognizable behavioural phenotype that included disturbed regulation of impulsive aggression".
A letter published by Hebebrand and Klug (1995) criticized Brunner's findings for not using strict DSM criteria.
Society and culture
Brunner's findings have been used to argue that genetics, rather than decision-making processes, can cause criminal activity. Evidence supporting the genetic defense stems from both Brunner's findings and a series of studies on mice. To prove the correlation between MAO-A deficiency and aggression in courts, it is often contended that individuals cannot be held accountable for their genes, and as a result, should not be held responsible for their dispositions and resulting actions.
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- Online 'Mendelian Inheritance in Man' (OMIM) 300615
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