ASDs (autism spectrum disorders) are a group of complex disorders with different origins and causes. The authors explained that neuronal abnormality in the cerebral cortex and other brain regions may impact on the behavioral and cognitive defects present in autism.
A neuron is a nerve cell. Neurons send and receive electrical signals over long distances inside our bodies.
Hennady P. Shulha, Ph.D. and team examined postmortem brain tissue of 16 people aged between 2 and 60 years; average age 17.4 years. They all had an ASD. They compared their findings with postmortem brain tissue of 16 controls (people with no ASD) aged between less than 12 months to 70 years. They received the tissue from the Autism Tissue Program.
They searched throughout the genome for histone methylation. Histone methylation is evidence of an abnormal epigenetic signature. Histones are tiny proteins that attach themselves to DNA and control gene activity and expression. Genetic data is encoded by the genome's DNA sequences. Methylation and other kinds of histone alterations control gene expression as well as regulating how the genome is organized.
Hundreds of loci across the whole genome were found to be affected by modified histone methylation in the brain tissue of people with ASDs. Loci are where genes are located on chromosomes.
Less than 10% of the affected genes were affected by DNA mutations, however. The scientists do not yet know whether genetic abnormalities in other parts of the genome might have contributed to the epigenetic changes they observed. They do not know either whether the ASD process affects individuals through non-genetic factors.
The scientists wrote:
"Prefrontal cortex neurons from subjects with autism show changes in chromatin (the substance of chromosomes) structures at hundreds of loci genome-wide, revealing considerable overlap between genetic and epigenetic risk maps of developmental brain disorders."