Scientists from the University of California, San Diego School of Medicine and the Allen Institute for Brain Science have connected the development of autism spectrum disorders (ASD) to changes that take place during fetal brain development. An analysis of children with autism revealed abnormalities in the cortex, a part of the brain that develops while a baby is in the womb. The findings have implications for understanding the development and treatment of autism.
Data for the study came from the Allen Brain Atlas and the BrainSpan Atlas of the Developing Human Brain. The researchers analyzed genes found in the cortex. As the brain develops, the cortex is assembled in six layers. Each layer is characterized by its own type of cell and a unique pattern of connectivity. As brain cells settle into their roles in the cortex, they acquire their own markers, which are observable by scientists.
The researchers assembled a panel of 25 genes that function as biomarkers of certain cell types in the multiple layers of the cortex, genes associated with ASD, and several control genes. They examined genes found in the post-mortem brain tissue of 22 children who died between the ages of two and 15 years. Half of the children were diagnosed with autism before they died while the other half served as the control. Although the sample of children was small, the gene panel was extremely large, numbering over 12,000 slides.
In a typical brain, the layers of the cortex develop evenly, one on top of another, but the researchers found that for 10 of the 11 children with autism (and one not diagnosed with autism) the development of the cortex was patchy. Multiple layers of their cortices were missing key genetic markers, which “indicates that the crucial early developmental step of creating six distinct layers with specific types of brain cells—something that begins in prenatal life—had been disrupted,” explains Eric Courchense, PhD, professor of neurosciences and director of the Autism Center of Excellence at UC San Diego.
These disruptions in cortical development were similar in all autistic brains, despite the fact that autism is considered a diverse disorder. The defects were present in focal patches, which suggests that the aberrations were not distributed uniformly throughout the cortex. The frontal cortex (responsible for higher-order brain functions like understanding social cues) and the temporal cortex (related to language) were the most affected. This could explain the characteristic autistic problems in social and linguistic development.
The next phase of this research will be identifying how these disruptions to cortical development occur and what, if anything, can be done to prevent or correct it.
This research is published in the online edition of the New England Journal of Medicine.
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