Last year we reported on the work of researcher Eric Courchesne, PhD, director of the Autism Center of Excellence at the Universityof California, San Diego School of Medicine. He had found children with autism to have about 67% more nerve cells in a part of the brain known as the prefrontal cortex than children without autism. The prefrontal cortex is responsible for communication, cognitive functions, decision making and moderating correct social behavior – areas which autistic children have difficulty with.
“Our next step was to see whether there might be abnormalities of genetic functioning in that same region that might give us insight into why there are too many cells and why that specific region does not develop normally in autism,” said Courchesne.
Dr. Courchesne continued his researched and for the first time, identified in young autism patients the genetic mechanisms involved in this abnormal early brain development.
The recent study published in PLoS Genetics March 22nd uncovered differences between young (2-14 years) and adult individuals with autism in the way their genes are expressed. This has provided important clues as to why brain growth and development are abnormal in this disorder.
The researchers showed that genetic mechanisms that normally regulate the number of cortical neurons are abnormal. “The genes that control the number of brain cells did not have the normal functional expression, and the level of gene expression that governs the pattern of neural organization across the prefrontal cortex is turned down. There are abnormal numbers and patterns of brain cells, and subsequently the pattern is disturbed,” Courchesne said. “This probably leads to too many brain cells in some locations, such as prefrontal cortex, but perhaps too few in other regions of cortex as well.”
The scientists have also discovered a turning down of the mechanisms that usually detecting DNA defects and correcting or removing affected cells during periods of rapid prenatal development.
Autism is a highly heritable neurodevelopmental disorder, yet the genetic causes in the brain at young ages have remained largely unknown. Until now, few studies have been able to investigate whole-genome gene expression and genotype variation in the brains of young patients with autism, especially in regions such as the prefrontal cortex that display the greatest growth abnormality.
Scientists — including co-first authors Maggie Chow, PhD, and Tiziano Pramparo, PhD, at UC San Diego — found evidence of dysregulation in the pathways that govern cell number, cortical patterning and cell differentiation in the young autistic prefrontal cortex. In contrast, in adult patients with autism, the study found that this area of the brain shows dysregulation of signaling and repair pathways.
“Our results indicate that gene expression abnormalities change across the lifespan in autism, and that dysregulated processes in the developing brain of autistic patients differ from those detected at adult ages,” said Courchesne. “The dysregulated genetic pathways we found at young ages in autism may underlie the excess of neurons — and early brain overgrowth — associated with this disorder.”
These new findings could lead to discoveries as well as new prevention strategies and treatment for autism.