Deep DNA Sequencing Study Almost Quadruples Number Of Genes Linked To Autism

Chuck Bednar for redOrbit.com – Your Universe Online
By using deep DNA sequencing, an international team of researchers led by the Autism Sequencing Consortium (ASC) has increased the number of genes identified with autism spectrum disorder (ASD) from nine to 33.
The research, published Wednesday in the journal Nature, analyzed data on several types of rare genetic differences in over 14,000 DNA samples from parents, autistic children and unrelated individuals, according to the study authors. In addition to quadrupling the number of definitive autism genes discovered to date, the researchers also found more than 70 other likely ASD genes.
Working at three different universities throughout the country, researchers from over three dozen institutions found seven genes that have mutations in three or more children with autism, implicating those genes with the disorder with a level of near-certainty. Another 20 genes with mutations were found in two children, giving each of them a better than 90 percent chance of being a true autism gene, the authors reported in their paper.
The majority of the newly identified mutations are de novo mutations, meaning that they are not present in unaffected parents’ genomes, but appear spontaneously in a single sperm or egg cell just prior to conception of a child, the research team explained. The DNA implicated fall into three broad classes: those involved in the formation and function of synapses, those that regulate transcription, and those involved in the cellular packaging of DNA.
The first group helps with the creation and operation of sites of nerve-cell communication in the brain, while the second regulates how the instructions in other genes are relayed to the protein-making machinery in cells, and the third impacts how genetic information is wound up and packed into cells in a structure known as chromatin. Mutations that alter chromatin and affect transcription are believed to affect the activity of many genes, the researchers noted.
“We have a set of genes for which now, if people see a likely gene-disrupting mutation when sequencing a young child, there’s a high risk of the child developing autism, and that, to my mind, is pretty powerful stuff,” the University of Washington’s Evan Eichler, who leads one of the laboratories involved in the study, said in a statement. “Recognizing this early on may allow for earlier interventions, such as behavioral therapies, improving outcomes in children.”
“Our findings lend new weight to the hypothesis that there are specific functional categories of genes – likely conserved by evolution in development of the human neurological system and brain – that strongly contribute to autism’s causation, such as genes expressed during embryonic development and genes that encode proteins that remodel chromatin, the bundles in which our DNA is stored,” added Michael Ronemus of Cold Spring Harbor Laboratory.
This marks the first time that the scientists were able to assess the impact of both inherited genetic differences and the spontaneous de novo ones. While slight, rare genetic differences in over 100 top genes were found to increase a person’s risk by a relatively sizable amount, the research team said that looking at the prevalence of those variations allowed them to predict slight differences in up to 1,000 others that could eventually be found to increase ASD risk.
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