Brunner syndrome

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 pyromania, hypersexuality and violence), sleep disorders and mood swings.[1][2] It was identified in fourteen males from one family in 1993.[1][3] It has since been discovered in two additional families.[4]

Brunner syndrome
Other namesMonoamine oxidase A deficiency
This condition is inherited via X-linked recessive manner


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.[5][6] 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.[6]



Progesterone & Rauwolfia Serpentina (containing Reserpine) are a possible treatment as they both increase MAO-A activity.


Brunner Syndrome was described in 1993 by H.G. Brunner and his colleagues upon the discovery of a particular genetic defect in male members of a large Dutch family.[5] 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).[5] Brunner said that an "MAO-A deficiency is associated with a recognizable behavioural phenotype that included disturbed regulation of impulsive aggression".[5]

A letter published by Hebebrand and Klug (1995)[7] 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.[8] Evidence supporting the genetic defense stems from both Brunner's findings and a series of studies on mice.[9] 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.[8][9]


  1. Hunter P (September 2010). "The psycho gene". EMBO Rep. 11 (9): 667–9. doi:10.1038/embor.2010.122. PMC 2933872. PMID 20805840.
  2. Online Mendelian Inheritance in Man (OMIM) 300615
  3. Brunner HG; Nelen MR; van Zandvoort P; Abeling NGGM; van Gennip AH; Wolters EC; Kuiper MA; Ropers HH; van Oost BA (June 1993). "X-linked borderline mental retardation with prominent behavioral disturbance: phenotype, genetic localization, and evidence for disturbed monoamine metabolism". Am. J. Hum. Genet. 52 (6): 1032–9. PMC 1682278. PMID 8503438.
  4. Piton A, Redin C, Mandel JL (August 2013). "XLID-causing mutations and associated genes challenged in light of data from large-scale human exome sequencing". Am. J. Hum. Genet. 93 (2): 368–83. doi:10.1016/j.ajhg.2013.06.013. PMC 3738825. PMID 23871722.
  5. Brunner HG, Nelen M, Breakefield XO, Ropers HH, van Oost BA (October 1993). "Abnormal behavior associated with a point mutation in the structural gene for monoamine oxidase A". Science. 262 (5133): 578–80. Bibcode:1993Sci...262..578B. doi:10.1126/science.8211186. PMID 8211186.
  6. Scott, AL; Bortolato, M; Chen, K; Shih, JC (2008-05-07). "Novel monoamine oxidase A knock out mice with human-like spontaneous mutation". NeuroReport. 19 (7): 739–43. doi:10.1097/WNR.0b013e3282fd6e88. PMC 3435113. PMID 18418249.
  7. Hebebrand J, Klug B (September 1995). "Specification of the phenotype required for men with monoamine oxidase type A deficiency". Hum. Genet. 96 (3): 372–6. doi:10.1007/BF00210430. PMID 7649563.
  8. Halwani S, Krupp DB (2004). "The genetic defence: the impact of genetics on the concept of criminal responsibility". Health Law J. 12: 35–70. PMID 16539076.
  9. Baker LA, Bezdjian S, Raine A (2006). "Behavioral genetics: the science of antisocial behavior". Law Contemp Probl. 69 (1–2): 7–46. PMC 2174903. PMID 18176636.
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