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Richard TremblayNaît-on bon ou mauvais ? Le psychologue Canadien Richard Tremblay a su y apporter une réponse scientifique claire, basée sur l'observation systématique du développement de milliers d'enfants... (source ©.gouv.qc)

Abstract :

Suite à une invitation des Prs Manuel Bouvard et Grégory Michel, le mardi 20 Octobre, Richard Tremblay présentera un documentaire dont il est le producteur avec Jean Gervais : Aux origines de l'agression "La violence de l'agneau". L'agressivité humaine est-elle innée ou prend-elle sa source dans l'éducation? Dans ce film des interviews avec des chercheurs de différents domaines font la lumière sur cette question... A l'Athénée municipal de Bordeaux 18 h , ouvert à tous . Ci dessous pour l'INB il répond à notre question : De quelle manière la perspective épigénétique apportera t'elle des réponses sur la prévention de la violence ?



INB

Richard Tremblay "How does the epigenic perspective provide us with insight or answers regarding the prevention of violence? "

Pr.Richard Tremblay
Four years after Darwin published “On the Origin of Species”, the French naturalist Quatrefages wrote: “nowadays I admit, with everybody, the doctrine of epigenesis. Every normal egg which gives birth to an abnormal individual is influenced by external agents whatever they are; this is what I call action of the milieu”. Epigenetics re-emerged recently with the study of the mechanisms involved in gene expression.

The term “epigenetic” now refers to the mechanisms which program genes and can change gene function without changing its sequence (mainly changes in DNA methylation and chromatine structure). This programming is responsive to environmental effects, especially during fetal and early post natal development. Thus, environments can impact phenotypes through their chemical impact on programming of gene function. Epigenetic effects are well known in cancer research and have recently been shown to possibly play an important role in the obesity epidemic we are facing and in behaviour regulation.

To grasp the potential contribution of epigenetics to the mechanisms involved in early development and prevention of chronic aggression it is important to understand the difference between the traditional gene-environment interaction story and the epigenetic story. To explain key differences I will use two studies which attempt to explain the effects of a neglectful environment on development. Let’s start by the gene-environment statistical interaction story of MAOA.

Males brought up in a neglectful environment have been shown to be more at risk of violent behaviour if they have a short rather than a long allele on the promoter region of the MAOA gene. It is presumed that individuals with short and long alleles react differently to the abusive environment because their neural system functions differently and such differences are due to the MAOA activity. Epigenetic studies have a different approach, they focus specifically on the physical effects the environment has on gene expression.

The classic example for effects of neglectful environments comes from an experimental study of maternal behaviour in rats which showed that rat pups insufficiently licked by they mothers (i.e. neglected) have more methylated genes, i.e. genes that are not expressed. The study further showed that this gene methylation effect had downstream effects on the hypothalamic–pituitary–adrenal axis which regulates stress.
Epigenetic mechanisms are especially important because they provide a powerful explanation for maternal transmission of disorders above and beyong the traditional genetic explanation. Chronic forms of violent behaviour are specifically related to maternal characteristics: maternal age at first pregnancy, history of behaviour problems, education, smoking, depression, coercive parenting, etc. This can easily be understood from the traditional environmental perspective: a poor early environment has an impact on the developing foetus and infant.

Mother characteristics turn out to be more important risk factors than father characteristics because the former carry the child in their womb during foetal life and are more involved in the care giving during early childhood. However, the exact bio-psycho-social mechanisms linking poor quality environment to disorganised behaviour remain unclear, to say the least.


The epigenetic story provides a basic mechanism that met much disbelief (and still does) but has the advantage of being parsimonious, testable and promising for prevention.
The most fascinating aspect of this mechanism is that it provides an environmentally based explanation of intergenerational transmission for physical and mental disorders which involves genes but is not genetically transmitted. These mechanisms are far from being clearly demonstrated, but they provide a challenging alternative perspective to the traditional gene vs environment and gene-environment interaction hypotheses.

Interesting examples are now available from the obesity literature but the best example for DB is the link between quality of early environment and development of the HPA axis first shown with the rat experiments discussed above and recently applied to humans.

In a recent study of brains from individuals who committed suicide, epigenetic differences were observed in a neuron-specific glucocorticoid receptor promoter when three groups were compared: those who committed suicide and had been abused during childhood were more methylated compared to those who were not, and compared to a group that had died in a car accident. Another study is showing differences in methylation profiles from blood samples of males on chronic and normal trajectories of physical aggression.



In conclusion, if the early environment has an impact on behaviour development through it’s impact on DNA methylation, then prevention of the ensuing social behaviour problems must start by supporting that early environment.



Propos recueillis par Yves Deris le 10 Octobre 2009



Le dogme de l’âge génétique est en train de connaître une révolution silencieuse. On commence à penser moins en termes de séquences de gènes et plus en termes du comportement des gènes dans leur contexte environnemental. Au cours du développement, certaines parties du génome passent à des volumes différents, en réaction à des stimuli environnementaux. (Source : Réseau d’Excellence (NoE) Epigénome CE)

On considére que Richard Tremblay a littéralement renversé la façon d'envisager l'agressivité humaine. Le chercheur est à l'origine d'une véritable école du développement social de l'enfant, aujourd’hui reconnue à l'échelle internationale.

Selected publications

Brezo, J., Bureau, A., Mérette, C., Jomphe, V., Barker, T., Vitaro, F., Hébert, M., Carbonneau, R., Tremblay, R. E. & Turecki, G. (Sous presse). Differences and similarities in the serotonergic diathesis for suicide attempts & mood disorders: A 22-year longitudinal gene-environment study. Molecular Psychiatry.

Fontaine, N., Carbonneau, R., Vitaro, F., Barker, E. D. & Tremblay, R. E. (Sous presse). A critical review of studies on the developmental trajectories of antisocial
behavior in females. Journal of Child Psychology and Psychiatry.