much more extensive brain changes than expected

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It is a new vision of the molecular differences involved in autism that a study, published on November 2 in the journal Nature. Analysis of the brains of people with autism, after their death, shows that the activity of certain genes is altered in almost all regions of the cortex. In other words, these disturbances are not limited to the regions of the brain called “higher associations” – those that govern reasoning, language, social behavior and the ability to adapt to new situations. The primary sensory regions – those involved in vision, touch, pain – are also affected by these changes.

The authors, from the University of California at Los Angeles (UCLA), analyzed 725 brain tissue samples taken after the death of 112 people of both sexes, aged 2 to 68 years. Among these individuals, 49 had a diagnosis of autism and 54 subjects were free of these (neurotypical) disorders. They then quantified the activity of genes in eleven regions of the cortex. To do this, they sequenced the RNA molecules produced in the cells of these various regions. Then, they compared the two groups (autistic and neurotypical), matched according to age and sex.

So far, two types of changes in gene activity in autistic brains have been known. On the one hand, an increase in the activity of certain genes involved in cells which are not neurons (cells not electrically excitable, forming glia) and in cells mobilized in the immune response. On the other hand, a decrease in the activity of the genes involved in the modulation of the nervous signal – at the level of the synapses, these areas through which the neurons communicate with each other.

Understanding the Molecular Basis of Disorders

This new work confirms these discoveries, but reveals, in addition, that these modifications concern the whole of the cortex. Moreover, the most marked drops in gene activity are seen in the visual cortex and in the parietal cortex, which processes information such as touch, pain or temperature. This deficit would explain the sensory disorders, very common in autistic people: hypersensitivity, or sometimes hyposensitivity. All the senses can be involved: sight, hearing, smell, touch, but also the proprioceptive and vestibular senses (involved in the perception of movements and the position of our body in space).

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