Emotional deprivation of parents, vaccines against measles, and now pollutants or drugs… To explain the appearance of autism spectrum disorders, the “environment” in the broad sense has always been put forward, especially in France. The psychoanalytical theories of Sigmund Freud and Bruno Bettelheim, which have long made mothers feel guilty, have been invalidated. As for the supposed involvement of vaccines, it has been shown to be a fraud. At present, the interest is therefore directed towards the “exposome”: on the occasion of the international day of autism, the government has indeed announced an investment of 6 million euros to dissect environmental exposures patients affected by these disorders.
Increase in incidence
Some 1,700 children will be followed from the fetal period until they are six years old (1,200 more at risk because of an affected brother or sister, and 500 in the general population). At the origin of this approach, the increase in the incidence of autism in recent years: a point that remains much debated in the scientific community, between better detection, evolution of diagnostic criteria and real environmental effect. The study of the interactions between their genes and the living environment of children is of course also part of the research program.
But the emphasis placed on pesticides, atmospheric pollution or endocrine disruptors can only be surprising given the weight of genetics in the appearance of these disorders. “Heritability studies show that genes weigh around 80%”, recalls the biologist and geneticist Thomas Bourgeron, who has just published Genes, synapses and autisms (Odile Jacob). Head of the “Human Genetics and Cognitive Functions” laboratory at the Institut Pasteur, this scientist was the first to discover, in the early 2000s, a gene involved in these disorders. Since then, more than 200 others have been unearthed by different teams. However, talking about genetics and autism remains complicated in France. Thomas Bourgeron, for example, assures that he will not be able to have his work financed by French research organizations.
Deleterious Mutations
“No matter how much we insist on the role of the genome in these disorders, we are still considered, in a very surprising way, as charlatans in certain circles”, regrets Professor Arnold Münnich, pediatric geneticist and president of Imagine, the Institute of genetic diseases, at Necker Hospital (AP-HP). This ignorance is not without consequences for the care of children, who are often deprived of access to an analysis of their genome. To overcome this, this doctor created a mobile clinical genetics team in 1998, whose specialists go to meet patients in the host institutions in Ile-de-France. In an article published in 2019 on this experience, he reports that out of 500 children examined, 72 were indeed carriers of a deleterious mutation causing their autism.
Obtaining a diagnosis is often invaluable for the families concerned. But there is still much to discover: geneticists have observed that the mutations identified so far correspond to at most 50% of cases of autism. To go further, Thomas Bourgeron’s team went from looking for rare mutations to analyzing frequent variants in the population which, depending on their combination, increase the risk of developing autism spectrum disorders. Still too imprecise, this method cannot be used at the individual level to diagnose patients. It could, however, make it possible to discover new biological mechanisms involved.
Permanent interactions between genes and environment
Geneticists are not ignorant of environmental effects, however. On the contrary, since between our genes and our environment, the interactions are permanent. With potentially negative consequences, but also favorable ones. This is the meaning of a project launched by Thomas Bourgeron, funded to the tune of ten million euros by the European Union: “We want to focus on resilience factors. It may be that certain individuals carrying genetic characteristics have a priori deleterious do not develop disorders, and we want to understand why”, he explains.
For his part, Professor Münnich immersed himself in the medical records of children for whom no genetic factor had been identified to date. “As if by chance, disturbing events marked the conception and the pregnancy”, notes the doctor. For example, medically assisted procreation multiplies the risk of autistic disorders by four, and taking antiretroviral drugs or cocaine by ten. Here, it is indeed the fact of having previously eliminated the genetic causes which made it possible to better identify environmental signals a priori weak…