Study: Dozens of new genes influencing autism discovered, more complicated than imagined.

Liz Szabo


Scientists have found dozens of new autism-related genes, according to a new study that may eventually help doctors develop better ways to diagnose and treat the condition.

Yet the study, published online today in Nature, also suggests that the genetic roots of autism are far more complicated than many imagined.

Unlike children with cystic fibrosis, whose disease is caused by defects in a single gene, people with autism may share relatively little in common genetically, even though their symptoms are similar, says study coauthor Stephen Scherer, who compared the DNA of nearly 1,000 children with autism with nearly 1,300 children without the disease.

But even the most common genetic changes in his study were found in only 1% or less of patients, Scherer says.

That suggests that "most individuals with autism are probably genetically quite unique, each having their own genetic form of autism," says Scherer, of the Hospital for Sick Children in Toronto, one of 120 scientists from 11 countries working on the study, called the Autism Genome Project.

As co-author Stanley Nelson of the University of California-Los Angeles describes it, "If you had 100 kids with autism, you could have 100 different genetic causes."

Taken together, these many genetic changes could explain up to 20% of cases of autism, says Hakon Hakonarson, director of Children's Hospital of Philadelphia's Center for Applied Genomics, a co-author of the study, which was funded by Autism Speaks and the National Institutes of Health.

Researchers focused on a particular type of genetic change, called "copy number variations," places where DNA has been either inserted or deleted. Because genes include instructions for making proteins, that can lead to an overdose of a protein, an underdose, a total absence of protein, or a malfunctioning one, Hakonarson says.

Interesting, some of these genetic changes appeared to be new, appearing in children but not in their parents, Hakonarson says. It's possible that these genetic errors occurred during the formation of their parents' sperm and eggs.

But much about autism remains a mystery, including the cause of the other 80% of cases, says Bryan King, an autism expert at Seattle Children's Hospital, who was not involved in the new study.

The study reinforces the growing consensus is not really a single disease, but a set of similar symptoms with many different causes, King says.

Study authors say they need to study the genes of many more children — perhaps 10,000 — to get more precise answers about autism's genetic roots.

But in the near future, doctors may be able to use these findings to offer parents an early genetic test to help predict children's risk of development autism, says coauthor Louise Gallagher of Trinity College Dubin. That could be very help for children at high risk, such as the younger siblings of children already diagnosed with autism. The results may also one day help doctors to counsel parents about their risks of conceiving another child with the condition, she says.

"With earlier detection, these children could get earlier intervention, which could limit the severity of the disease," says Gallagher, noting that some kids aren't diagnosed until age 5.

Full article from USA Today here

Press release from Autism Speaks on this study's findings

NEW YORK, N.Y. (June 9, 2010) – Autism Speaks, the world’s largest autism science and advocacy organization, and an international consortium of researchers, along with participating families, joined together to announce new autism genetic discoveries from the second phase of its collaborative study: the Autism Genome Project. The results were published today in the journal Nature, one of the world’s most respected peer-reviewed scientific publications.

The Autism Genome Project (AGP) is an international autism genetics research consortium co-funded by Autism Speaks, the Medical Research Council, Canadian Institutes of Health Research, Health Research Board (Ireland), Genome Canada, the Hilibrand Foundation and Autistica. Based on analysis of high-density genotyping data collected from 1,000 individuals with autism spectrum disorder (ASD) and 1,300 without ASD, the AGP reported that individuals with autism tend to carry more submicroscopic insertions and deletions called copy number variants (CNV) in their genome than controls. Some of these CNV appeared to be inherited, while others are considered de novo, or new, because they are found only in affected offspring and not in the parents. Taken together, more of the CNVs disrupt genes, previously reported to be implicated in intellectual disability without autism or in autism, than expected by chance.

The new AGP study also identified new autism susceptibility genes including SHANK2, SYNGAP1, DLGAP2 and the X-linked DDX53–PTCHD1 locus. Some of these genes belong to synapse-related pathways, while others are involved in cellular proliferation, projection and motility, and intracellular signaling, functional targets that may lead to the development of new treatment approaches.

These findings further support an emerging consensus within the scientific community that autism is caused in part by many “rare variants” or genetic changes found in less than one percent of the population. While each of these variants may only account for a small fraction of the cases, collectively they are starting to account for a greater percentage of individuals in the autism community, as well as providing insights into possible common pathogenic mechanisms. The overlap between autism susceptibility genes and genes previously implicated in intellectual disabilities further supports the hypothesis that at least some genetic risk factors are shared by different psychiatric developmental disabilities. Finally, identification of these biological pathways points to new avenues of scientific investigation, as well as potential targets for the development of novel treatments.

“Piece by piece, we are discovering genetic mutations that can cause autism. These findings will provide answers for families about what contributed to their autism,” said Andy Shih, Ph.D., Autism Speaks vice president for scientific affairs. “Furthermore, as we have learned from examples involving other genetic risk factors of autism (e.g., Fragile X, Rett, TSC), these genetic findings help us understand the underlying biology of autism, which can lead to the development of novel treatments.”

The AGP consists of 120 scientists from more than 60 institutions representing 11 countries who formed a first-of-its-kind autism genetics consortium. The AGP began in 2002 when researchers from around the world decided to come together and share their samples, data, and expertise to facilitate the identification of autism susceptibility genes. This continuing collaboration and its unique scientific assets (e.g., large sample set and multidisciplinary expertise) created scientific opportunities that otherwise would not exist. The AGP is well positioned to build on these extraordinary assets as the field of autism genetics further investigates rare variants, requiring larger sample sets to identify more CNV. Additional support for Phase 2 of the AGP was provided by the National Institutes of Health. The first phase of the AGP, the assembly of the largest-ever autism DNA collection and whole genome linkage scan, was funded by Autism Speaks and the National Institutes of Health and completed in 2007. For more information about the AGP please visit http://www.autismgenome.org/


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