CHOP, Penn research points to genetic link in autism
By analyzing DNA from more than 2,000 autistic children, researchers have uncovered the best evidence yet for genetic links to the disorder - all tied to the way brain cells form and dissolve connections.
The research effort, led by Hakon Hakonarson at Children's Hospital of Philadelphia, used much larger samples than had been analyzed before to identify genetic differences between autistic subjects and controls.
The CHOP group collaborated with Penn, UCLA, and other institutions, announcing their findings in two papers in today's issue of the journal Nature.
One paper revealed the first common genetic variation found to occur more often among autistic people. The other paper announced 13 rarer genetic mistakes that are strongly associated with autism.
Both papers back the consensus that there is no single autism gene, but perhaps 100 ways to develop the disorder.
As a side note, kudos to the writer of this article, Faye Flam, for not reducing the autistic population to only children.
The most intriguing finding of these studies for me is this,
Scientists have known for years that this code differed between people at several hundred thousand points, referred to as single nucleotide polymorphisms (SNPs). At such sites, one person may have a C, another a T, for example.
The more prominent autism paper released today described the results of scanning 550,000 known SNPs. That revealed just one stretch of DNA, on chromosome 5, where people with autism were more likely to have one of several SNPs.
It took a huge study to bring this out because these autism-related spellings also show up in half the general population. They are somewhat more frequent in autistic children - occurring in about 65 percent of cases.
The fact that this genetic variation occurs in half the general population has some interesting implications. It suggests that autism may be more common than we realise with the true rate of occurrence masked by a narrow focus on autism in children. It may also suggest under or misdiagnosis of autism. Another implication may be that the things we now call autism are not as much of a deviation from the norm of human behaviour as is currently thought.
The following article makes the mistake of focusing on autism as a childhood, rather than life long, issue but does do a good job of putting the study results into layman terms.
Autistic Kids Have Altered Genes Controlling Brain Development
Autistic children have variations on genes that help neurons route themselves in the brain of a developing fetus, according to a new set of studies that provide evidence how the autistic mind’s structure may go awry.
One of the gene variants occurs 20 percent more often in autistic children and may play a role in 12 percent to 18 percent of cases of autism, according to a study published online today in the journal Nature. The altered DNA is found near a gene that is active in the development of the frontal cortex, a brain region necessary for language and judgment.
The gene variants found in the new research occurs in a region of a cell’s chromosome 5 near the gene CDH10, the researchers reported in the study. Because CDH10 influences development, it provides a link between the way the brain is wired and a child’s development, the researchers said. The gene variant occurs in the normal population, so autistic children may have other high-risk variants as well, Schellenberg said.
The CDH10 pathway provides instructions for so-called neuronal cell adhesion molecules. These molecules affect how nerve cells communicate, and help shape the structure of the developing brain, the study authors said.
A second study from Hakonarson and others, also published in Nature, examined two gene pathways that help eliminate connections between nerve cells. They help produce ubiquitins, which are enzymes that help degrade connections made by the neuronal adhesion molecules. This seems to link the two discoveries together, said Hakonarson, who is also a professor at the University of Pennsylvania.
“Both studies implicated genes involved in synaptic generation and neuronal connectivity,” Hakonarson said. “This is highly consistent with previously published research.”
It also boosts a theory that autism is caused by abnormal connections between nerves in the brain, Hakonarson said.
Researchers wisely caution that this new information won't immediately lead to clinical treatments for autism but it does add to our understanding of the condition.
Autism genes discovered; help shape connections among brain cells
"Although we cannot immediately apply this research to clinical treatments, these findings increase our understanding of how autism spectrum disorders arise, and may in time foster the development of strategies for prevention and early treatment," said developmental pediatrician Susan E. Levy, M.D., a co-author of both studies who is the medical director of the Regional Autism Center and a member of the Center for Autism Research (CAR), both at Children's Hospital
Any mention of preventing a genetic condition such as autism reasonably raises the specter of wide spread selective abortions of otherwise healthy fetuses that carry any of the genetic changes now known to be associated with autism. It is currently the case with Down Syndrome where it is estimated that as many as 90% of fetuses that test positive are terminated. I take solace in the fact that the genetic variations found in autistic individuals are also found in the general population.
You can search for information on these studies, titles are listed below, at nature.com (registration required) and pubmed.gov.