Scientists always knew it was devilishly complex.
Autism, is found in one of about every 150 people around the world, according to a recent Centers for Disease Control study. That figure has been disputed, but clearly autisim has many degrees and types, and piles of evidence hinting that genes -- not one but many genes -- are to blame.
But how to find them? It's like trying to find a few dozen innocent looking criminals in a crowd of millions.
Now, scientists have probable cause implicating dozens of prime suspects all corralled in one place -- the collection of 23 X-shaped chromosomes that hold our DNA and are found in every cell in the body.
The Autism Genome Project (AGP), by far the largest autism study ever, has tamed the immense complexity by using new computer technology that can read billions of DNA signals in a few minutes.
AGP Researchers at 50 study centers in 19 countries brought the new technology to bear on the genomes of 1,168 families that each had at least two autistic children.
"We had a few isolated suspect genes before," principal AGP investigator Steven Scherer of the University of Toronto told ABC News. "But now, for the first time, we can finally see the forest for the trees."
The massive new study pinpoints the probable culprits -- not just one but many genes and abnormalities -- on every one of the 23 chromosomes.
The findings also strongly suggest that different combinations of genes may cause the different degrees and kinds of autism found in different people -- ranging from mild to severe.
"Autism has such a wide spectrum. Every child presents differently," Theresa Wadell of Arlington, Va., told ABC.
She and her husband, Chris, have had three boys. The first two -- now aged 7 and 5 -- have mild autism.
"We always have to watch them," she says. "Each child is in their own world. Paul, he's all over the room. Will, who is older, is the quieter one."
"The message here," says another principle investigator in the study, Joseph Buxbaum, "is that there is great hope now."
Hope, explains Buxbaum, because so many "probable causes" of autism have at least been located where researchers can find them -- in the genes -- and where they can now start checking out the particular role each implicated gene and genetic abnormality plays in the disease.
They found one prime suspect on chromosome number 11.
"A smoking gun," says Buxbaum, "that implicates a series of genes that all work together, and may together cause autism."
In the 1950's, a widely believed theory promoted by Chicago psychologist Bruno Betelheim held that autism was caused by cold and distant parenting in infancy.
It was coined the "refrigerator mom" theory, and made many mothers feel guilty until the 1980's, when studies of identical twins found that if one twin suffers from autism, the other almost always does, too -- strong evidence of genetic cause.
Both AGP researchers Scherer and Buxbaum say their new study also shows environmental toxins are not, as some argue, a major cause of autism.
"The evidence suggests autism is over 90 percent caused by genes," says Buxbaum.
"As we find more and more genes for autism," he says, "I think it will begin to reduce some of the clamor that there's environmental causes for autism."
Next, the AGP scientists will spend three years focusing on the many genes they've implicated in the autism families in their study, narrowing in on the exact roles of each gene or abnormality and trying to understand how they interact.
"We have the beginnings of the beginning, I would call it," says Buxbaum.
They hope that within 5 to 10 years, it will lead to drugs to prevent, fight and possibly even reverse autism.