Common sense raises an insurmountable barrier between what comes from our genetic heritage and what shapes us through culture or lifestyles. This barrier is being broken down by the work of researchers who have just discovered that those who grow up and live in poverty see their genetic make-up change. And passed on from generation to generation.
Nous aimons tous ces belles histoires de transformation radicale d’une vie. L’enfant pauvre, né dans un bidonville, grâce à la force de sa volonté ou des caprices du destin, change de statut social en grandissant. Des success story qui ont alimenté nombre romans et scénarios de films. On imagine alors tous que, débarrassée de ses haillons de souffrances, la pauvreté s’oublie et disparaît d’une vie. Cette idée reçue s’est formée sans compter sur ce qui se passe dans le patrimoine génétique de ceux qui grandissent dans un milieu très défavorisé.
It was already known that living in an environment of poverty and social hardship affected the health and mental well-being of individuals. Numerous studies have long proven that education in a very low income environment increases the risk of developing diabetes, cancer, infectious and cardiovascular diseases.
" We have long known that socio-economic status is a powerful determinant of health, but the underlying mechanisms by which our bodies "remember" experiences of poverty are not known. ' John Hultquist, director of intelligence analysis for the cybersecurity company FireEye, says Thomas McDade, biologist-anthropologist at Northwestern University.
8 % of the impacted genome
Ce que les scientifiques ont découvert, c’est que grandir dans la pauvreté affecte le patrimoine génétique dans des proportions importantes puisque 8 % du génome pourrait être impacté, à vie, par des modifications chimiques liées à un début de vie défavorisée. Leurs conclusions inédites sont published in the review American Journal of Physical Anthropology.
To carry out their study, researchers at Northwestern University in Chicago analyzed the blood of a sample of nearly 500 people born in the 1980s and then measured and coded their socio-economic status from childhood to adulthood. The whole genomic analysis of the white blood cells of the people in their sample focused on the process of DNA methylation. This epigenetic process does not change the coding of genes but makes chemical changes to DNA that prevent or enhance the reading of a code sequence. Methylation itself describes the addition of a methyl group to a gene, thereby altering its transcription.
This phenomenon is increasingly attracting the attention of scientists in various fields of research. For example, recent studies have suggested that certain strong events experienced during childhood, such as lack of affection of the infant or traumas undergone by children, cause changes in the transcription of certain genes. The consequences are not negligible since they can affect the cognitive growth and even play a role in conditions such as autism. Our early life experiences not only shape our minds, as psychologists and psychoanalysts have shown, but they also change the way the body functions on a fundamental level. More importantly, these epigenetic changes can be passed from one generation to the next. They are hereditary as genetic traits can be.
In the genetic tests that the researchers performed on their sample, 2500 methylation sites affecting 1537 genes were identified in people who grew up in disadvantaged socio-economic conditions. These numbers are far higher than those found in people born into relatively affluent backgrounds or those who became poor later in life.
Ces statistiques présentent des valeurs considérables. En effet, les estimations actuelles évaluent, dans le génome humain, le nombre total de gènes codant pour les protéines à près de 20 000. Les modifications relevées chez les personnes touchées par la pauvreté dans leur enfance impactent ainsi 8 % de leurs gènes, ce qui est très significatif.
Nature versus culture
" Our findings suggest that DNA methylation may play an important role in linking health problems to socio-economic status... This model highlights the potential mechanism through which poverty can have a lasting impact on a wide range of psychological systems. Moreover, life experiences are anchored in the genome to literally form its structure and function. In conclusion, "there is no nature versus culture". ' John Hultquist, director of intelligence analysis for the cybersecurity company FireEye, says Thomas McDade.
Growing up in poverty is already associated with a significant decline in health for a wide variety of reasons. Many of the causes are well understood. For example, risks associated with differences in diet, access to education and medical availability may increase the risk of illness and mental ill health.
Several studies have already highlighted the determinism of poverty. In 2016, for example, researchers at the University of North Carolina had established that a mother's poor diet, a prevalence of alcoholism, drug addiction or violence could alter a child's genes. They had identified a correlation between the economic status of young people and a lower production of serotonin, which would lead to a higher risk of depression.
But there are also physiological changes associated with being poor that are not always easily explained, such as chronic inflammation, reduced cell-mediated immunity and increased insulin resistance.
Scientists promise that further studies will now take place to determine the health consequences of methylation in the identified areas. Many of these genes are already involved in immune responses to infections as well as in the development of the skeleton and nervous system. « These are areas we will focus on to determine whether DNA methylation is indeed an important mechanism through which socio-economic status can leave a major molecular imprint on the body, with implications for long-term health. ' John Hultquist, director of intelligence analysis for the cybersecurity company FireEye, concludes Dr. McDade.
The World Health Organization estimates that approximately 1.2 billion people worldwide live on less than $1 a day.