Major Gene Study Points to Causes of Autism

"We found several regions of the genome -- sometimes the same region popping up in unrelated individuals -- with 3 or more copies," Scherer said. "We didn't see these in the individuals' parents, so that implies that these regions are harboring susceptibility genes for autism."

One gene in particular, calledneurexin 1, appeared in some cases in just one copy. "In one family, both of the children who were autistic actually had that piece missing," Scherer said. "That's kind of a smoking gun that the gene is implicated."

It makes intuitive sense that dysfunctionalneurexin 1might play some role in autistic disorders, another expert said.

Theneurexin 1protein and its kin, "are very important in determining how properly the brain is wired up from one nerve cell to another, and in the chemical transmission of information from one nerve cell to another," said Dr. Bradley Peterson, a professor of child psychiatry at Columbia University Medical Center and the New York State Psychiatric Institute, in New York City.

Peterson, who was not involved in the project, said genes that effect early neural growth could be key to autistic disorders, since "the genetic and the non-genetic contributions to autism, by definition, have to exert their effect very early in brain development, eitherin uteroor in the first months or couple of years of life."

Still, he and Scherer both stressed that the new study only points to potential leads for future research. Because of the study's particular methodology, no one finding reached statistical significance, Peterson said. "This is all very strong evidence, and a very good set of leads, but we can't yet say that we haveprovedthe involvement of these regions in autism," he said.

Scherer said that, except in very rare instances, there isn't likely to be a single gene responsible for autism. Instead, a variety of genetic abnormalities may work on each other during development to create some level of autism. And experts don't discount the potential role of environmental stresses on that mix, either.

"Remember, autism is actually a grab bag of different developmental disorders. And what we show here is that many genes can be involved, and also these copy number variants," Scherer said. "And could it be that environment is contributing? Absolutely."

One thing is for sure, however: Autism research holds more promise now than ever before, the experts said.

"Anybody that's working out here can use this information now, and it really provides a great path forward as to how we need to do our experiments over the next five years or so," Scherer said. "We've now got all these new candidate genes --- the neurexins, the various copy number variants -- and we can tackle the problem in a much more focused and organized way."

More information

Find out more about the fight against autism at Autism Speaks.

SOURCES: Stephen Scherer, M.D., director, Center for Applied Genomics, The Hospital for Sick Children, Toronto, and professor, medicine, the University of Toronto; Bradley Peterson, M.D., Murphy professor of child psychiatry, Columbia University Medical Center and the New York State Psychiatric Institute, New York City; Feb. 18, 2007,Nature Geneticsonline