Objectives: We aimed to identify genome-wide expression signatures, copy number variation (CNV), and cortical microstructure in autistic and control tissue from prefrontal cortex where growth abnormality is pronounced. We then sought to expand upon the genetic analyses using publicly available genotypic datasets.
Methods: Genome-wide expression analyses were performed in 33 autistic and control postmortem frozen tissue cases (ages 2-56 years). mRNA was processed with the DASL protocol and hybridized on Illumina microarray. Differential expression was assessed using 2-way ANOVA with diagnosis and categorical age as variables of interest and validated by RT-PCR. Enrichment analyses were performed using Metacore. Nissl staining and in situ hybridization (ISH) of laminar specific genes were performed to identify microstructural correlates of aberrant expression in a subset of young autistic males. Nissl sections were examined by a blinded neuropathologist and through blinded stereological measurement of neuron density. Subjective impressions of ISH abnormalities in autistic cases were systematically recorded.
Results: Pathways and processes mediating cell cycle, DNA damage, apoptotic, cellular specification and neural patterning functions were aberrantly expressed in the young autistic prefrontal cortex. CNVs were highly enriched in cell cycle and cytoskeleton processes. In AGRE/BROAD/JHI datasets, genes mediating cell cycle processes were significantly associated with autism, but not genes regulating inflammation, apoptosis, or synaptogenesis. Histological examination of sections from young cases correctly identified 6/7 autistic cases as having areas of pathologically disorganized cortex. Regions neighboring or overlapping with these disorganized areas showed deficits of ISH laminar marker labeling. Examination of neuron density showed a 17% increase in regions showing disorganization or ISH deficits compared to controls.
Conclusions: Dysregulation of proliferative processes, particularly cell cycle and DNA-damage pathways during neurodevelopment, could give rise to increased cell density and susceptibility to incorporation of DNA-damaged cells in the autistic cortex. Aberrant expression of neural patterning genes may lead to gross morphological and functional lateralization and anterior/posterior abnormality patterns identified by MRI and fMRI in individuals with autism. Finally, these expression deficits may be related to common and rare genotypic variation, playing a mechanistic role in the pathogenesis of autism. Other implications will be discussed.
See more of: Genetics
See more of: Biological Mechanisms