1972年にスタートして26年間かけて、442名の男性を誕生から成人まで追跡した研究がある。このデータから"MAO A genotype"の効果を調べたのが、Capsi et al.[2002]である。
Avshalom Caspi et al: "Role of Genotype in the Cycle of Violence in Maltreated Children", Science 2 August 2002: Vol. 297. no. 5582, pp. 851 - 854, DOI: 10.1126/science.1072290

We studied a large sample of male children from birth to adulthood to determine why some children who are maltreated grow up to develop antisocial behavior, whereas others do not. A functional polymorphism in the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA) was found to moderate the effect of maltreatment. Maltreated children with a genotype conferring high levels of MAOA expression were less likely to develop antisocial problems. These findings may partly explain why not all victims of maltreatment grow up to victimize others, and they provide epidemiological evidence that genotypes can moderate children's sensitivity to environmental insults.

[Emiliano Feresin: "Lighter sentence for murderer with 'bad genes'" (2009/10/30) Nature | doi:10.1038/news.2009.1050]

An Italian court has cut the sentence given to a convicted murderer by a year because he has genes linked to violent behaviour — the first time that behavioural genetics has affected a sentence passed by a European court. But researchers contacted by Nature have questioned whether the decision was based on sound science.



During the trial, Bayout's lawyer, Tania Cattarossi, asked the court to take into account that her client may have been mentally ill at the time of the murder. After considering three psychiatric reports, the judge, Paolo Alessio Vernì, partially agreed that Bayout's psychiatric illness was a mitigating factor and sentenced him to 9 years and 2 months in prison — around three years less than Bayout would have received had he been deemed to be of sound mind.

裁判で、被告Bayoutの弁護人Tania Cattarossiは法廷に対して、被告が殺人を犯したときに精神障害があったことを考慮するように求めた。3つの精神鑑定を考慮して、Paolo Alessio Vernì裁判官は部分的にBayoutの精神障害を減刑要因と認め、精神状態が正常である場合より3年短い、懲役9年2か月を言い渡した。

But at an appeal hearing in May this year, Pier Valerio Reinotti, a judge of the Court of Appeal in Trieste, asked forensic scientists for a new independent psychiatric report to decide whether he should commute the sentence further.

しかし、今年5月の上告審で、Trieste控訴裁判所のPier Valerio Reinotti裁判官は、さらに判決を修正すべきか判断するために、新たな独立の精神鑑定を法医学者に依頼した。

For the new report, Pietro Pietrini, a molecular neuroscientist at Italy's University of Pisa, and Giuseppe Sartori, a cognitive neuroscientist at the University of Padova, conducted a series of tests and found abnormalities in brain-imaging scans and in five genes that have been linked to violent behaviour — including the gene encoding the neurotransmitter-metabolizing enzyme monoamine oxidase A (MAOA). A 2002 study led by Terrie Moffitt, a geneticist at the Institute of Psychiatry, King's College, London, had found low levels of MAOA expression to be associated with aggressiveness and criminal conduct of young boys raised in abusive environments1.

新たな精神鑑定のために、イタリアのUniversity of Pisaの分子神経学者 Pietro Pietriniと、University of Padovaの認知神経学者Giuseppe Sartoriが、一連の検査を行い、脳イメージスキャンに異常を発見し、暴力的行動に関連した5つの遺伝子を発見した。この遺伝子には、神経伝達物質を新陳代謝させている酵素モノアミンオキシダーゼA(MAOA)をコーディングしている遺伝子も含まれる。 LondonのKing's CollegeのInstitute of Psychiatryの遺伝学者Terrie Moffittが率いた2002年の研究で、MAOA表現形が低水準だと、虐待的環境で育った男の子は、アグレッシブな行動や犯罪を犯すことに関連していることが見つかっている。
"We don't know how the whole genome functions and the [possible] protective effects of other genes," says Giuseppe Novelli, a forensic scientist and geneticist at the University Tor Vergata in Rome. Tests for single genes such as MAOA are "useless and expensive", he adds.

ローマのUniversity Tor Vergataの法医学者であり遺伝学者であるGiuseppe Novelliは「我々はゲノムの機能をすべて知っているわけではなく、他の遺伝子の防御効果もわかっていない。MAOAのような一つの遺伝子を検査するだけでは、役に立たないし、高くつくだけだ」と述べた。

One problem is that the effects of the MAOA gene are known to vary between different ethnic groups, Moffit says. A 2006 study in the United States found that former victims of child abuse with high levels of MAOA were less likely to commit violent crimes — but only if they were white. The effect was not evident in non-white children[2].



Other genes, such as those that encode the serotonin transporter, have also been linked to different reactions to stress. But these also show a large degree of dependence on environmental factors. "The point is that behavioural genetics is not there yet, we cannot explain individual behaviour, only large population statistics," says Nita Farahany of Vanderbilt University in Nashville, Tennessee, who specializes in the legal and ethical issues arising from behavioural genetics and neuroscience.

セロトニン輸送体をコーディングしている遺伝子なども、ストレスに対する反応の違いと関連している。しかし、これらも環境に大きく依存している。「行動に関連する遺伝子では、個々人の行動は説明できない。できるのは大きな集団の統計的挙動だけだ。」と、行動に関連した遺伝子および神経科学から起きる法律および倫理問題の専門家であるテネシー州NashvilleのVanderbilt UniversityのVanderbilt Universityは述べた。

"90% of all murders are committed by people with a Y chromosome — males. Should we always give males a shorter sentence?" says Steve Jones, a geneticist at University College London. "I have low MAOA activity but I don't go around attacking people."

University College Londonの遺伝学者Steve Jonesは「殺人の90%はY染色体を持つ者によるものだ。すなわち男性だ。では、我々は男性の刑を軽くすべきか? 私はMAOAの活動度が低いが、周囲の人々を攻撃するわけではない」と述べた。...

1.Caspi, A. et al. Science 297, 851-854 (2002).
2.Widom, C. S. & Brzustowicz, L. M. Biol. Psychiatry 60, 684-689 (2006).

[Emiliano Feresin: "Lighter sentence for murderer with 'bad genes'" (2009/10/30) Nature | doi:10.1038/news.2009.1050]


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