Researchers have published the largest-existing study on the genetic causes of autism, comparing 996 autistic individuals to 1,287 people without the condition. Their results, which appear today in Nature, may provide unexplored avenues for treatment research, but also show in new detail the disorder’s sheer genetic complexity. For example, they have found “private mutations” not shared between people with autism and not inherited from their parents.

According to The Centers for Disease Control and Prevention, one in 110 children in the United States has autism spectrum disorder, and that the prevalence of autism among eight-year-olds has increased 57 percent from 2002 to 2006. There is no known cure, although intensive behavioral therapy helps some kids.

Hilary Coon, Ph.D., a lead author on the study and research professor of psychiatry at the University of Utah School of Medicine, said while research shows scientists are making progress in understanding the causes of autism, it is increasingly clear that autism is a multifaceted disorder with both genetic and environmental causes. “We are whittling away at it,” Coon said. “But a brain-related disorder, such as autism, is amazingly complex. It’s not really one entity.” [University of Utah press release]

For this study, researchers at the international Autism Genome Project wanted a closer, more detailed picture of the over 100 genes commonly linked to autism. They looked for rare variants–small deletions or additions to the DNA sequences that make up these genes. They found that people with autism had a higher number of these variants than those without the disorder, and that some of these DNA differences were not inherited. That means these DNA changes occurred either in the egg cell, sperm, or in the developing embryo.

“Most individuals that [sic] have autism will have their own rare form,” genetically speaking, concludes senior author Stephen Scherer, a geneticist at the Hospital for Sick Children in Toronto, Canada. That said, the team found that genes deleted in autistic patients tended to perform similar tasks. Many were involved in aspects of cell proliferation, such as organ formation. A number participated in development of the central nervous system and others in maintaining the cytoskeleton, which protects the cell and helps it move. “These are not random hits in the genome” and clearly have some connection to autism, says Jonathan Sebat, a geneticist at Cold Spring Harbor Laboratory in New York state. [Science Now]

Some believe that looking more closely at these variants may eventually lead to novel treatments.

Two categories of genes were affected more frequently than others: those coding for the neural cell development, and those involved in the signalling or “communication” between cells. Many of these same genes are thought to play a role in other neuro-development disorders. There may even be some overlap with conditions such as epilepsy and schizophrenia, the researchers said. “These and other recent findings have very real potential to lead to the development of novel interventions and treatments for these disorder,” said Louse Gallagher, a professor at Trinity College Dublin, one of the universities in the consortium. [AFP]

So what’s the next step towards such treatments? For now, it’s more big genetics studies. The Autism Genome Project has enrolled another 1,500 families and hopes for their next testing phase to look at people’s complete genomes and exomes (the part of the genome that codes for RNA or protein), reports Nature’s blog The Great Beyond.

The study has been hailed as a positive step by researchers, though one can imagine the parents of autistic children still feeling frustrated by the slow pace of progress. Perhaps to avoid giving false hopes, Dr Gina Gomez de la Cuesta of The National Autistic Society was cautious in her assessment of the study, saying:

“This study furthers our understanding of genetic variation in autism, however there is a great deal more research to be done. Research into autism is constantly evolving but the exact causes are as yet still unknown. The difficulty of establishing gene involvement is compounded by the interaction of genes with the environment. Genetic testing for autism is still a long way off, given that autism is so complex.” [BBC]

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Image: flickr / net efekt