Age-Dependent Brain Gene Expression and Copy Number Anomalies in Autism Suggest Distinct Pathological Processes at Young Versus Mature Ages

Department of Neuroscience, NIH-UCSD Autism Center of Excellence, School of Medicine, University of California San Diego, La Jolla, California, United States of America.
PLoS Genetics (Impact Factor: 8.17). 03/2012; 8(3):e1002592. DOI: 10.1371/journal.pgen.1002592
Source: PubMed

ABSTRACT Autism is a highly heritable neurodevelopmental disorder, yet the genetic underpinnings of the disorder are largely unknown. Aberrant brain overgrowth is a well-replicated observation in the autism literature; but association, linkage, and expression studies have not identified genetic factors that explain this trajectory. Few studies have had sufficient statistical power to investigate whole-genome gene expression and genotypic variation in the autistic brain, especially in regions that display the greatest growth abnormality. Previous functional genomic studies have identified possible alterations in transcript levels of genes related to neurodevelopment and immune function. Thus, there is a need for genetic studies involving key brain regions to replicate these findings and solidify the role of particular functional pathways in autism pathogenesis. We therefore sought to identify abnormal brain gene expression patterns via whole-genome analysis of mRNA levels and copy number variations (CNVs) in autistic and control postmortem brain samples. We focused on prefrontal cortex tissue where excess neuron numbers and cortical overgrowth are pronounced in the majority of autism cases. We found evidence for dysregulation in pathways governing cell number, cortical patterning, and differentiation in young autistic prefrontal cortex. In contrast, adult autistic prefrontal cortex showed dysregulation of signaling and repair pathways. Genes regulating cell cycle also exhibited autism-specific CNVs in DNA derived from prefrontal cortex, and these genes were significantly associated with autism in genome-wide association study datasets. Our results suggest that CNVs and age-dependent gene expression changes in autism may reflect distinct pathological processes in the developing versus the mature autistic prefrontal cortex. Our results raise the hypothesis that genetic dysregulation in the developing brain leads to abnormal regional patterning, excess prefrontal neurons, cortical overgrowth, and neural dysfunction in autism.

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Available from: Lauren A Weiss, Aug 24, 2015
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    • "We chose to investigate the DLPFC as dysfunction or lack of normal maturation of the DLPFC is heavily implicated in ASD and is thought to underpin many ASD symptoms, including behavioural deficits (Bachevalier and Loveland, 2006), with neuroimaging studies also supporting this hypothesis (Schmitz et al., 2007; Sun et al., 2012). This part of our investigation was carried out utilising recently published microarray gene expression data patients with ASD and controls (Chow et al., 2012). We then investigated whether mGluR5 protein levels were altered in the DLPFC of individuals with ASD utilising post-mortem stereological quantitation and investigating the number of mGluR5-positive neurons and glia within the DLPFC of individuals with ASD versus normal controls. "
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    • "Imaging studies of the brains of autistic individuals have demonstrated abnormalities in the PFC (Herbert et al., 2003), which is a key area involved in social cognition. For example, toddlers and children with autism often exhibit early brain enlargement and excessive numbers of neurons in the PFC (Chow et al., 2012). According to Rinaldi et al. (2008) the social deficit in autism could be re-interpreted in the light of a hyperfunctional PFC. "
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    • "On a cellular level these neurobiological abnormalities are associated with changes in cytoarchitectural and neuronal organization that may be determined by genetic, environmental, immunological and toxic factors (Courchesne et al. 2005). At the microscopic level, due to genetic dysregulation, neuroinflammotory reactions involving glial activation, migration deficits and excess cerebral neurogenesis and/or defective apoptosis might generate cortical neural pathology early in development (Chow et al. 2012 ). "
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