ATLANTA — More than $1 billion has been spent over the past decade researching autism. In some ways, the search for its causes looks like a long-running fishing expedition, with a focus on everything from genetics to the age of the father, the weight of the mother, and how close a child lives to a freeway.
That perception may soon change. Some in the field say they are seeing the beginning of a wave of scientific reports that should strengthen some theories, jettison others and perhaps even herald new drugs.
"I do think over the next three to five years we'll be able to paint a much clearer picture of how genes and environmental factors combine" to cause autism, said Geraldine Dawson, a psychologist who is chief science officer for the advocacy group Autism Speaks.
The effort has been infused with new urgency by a recent federal report that found autism disorders are far more common than was previously understood, affecting 1 in 88 U.S. children. Better diagnosis is largely responsible for the new estimate, but health officials said there may actually be more cases of autism, too.
If autism's causes remain a mystery, "you're not going to be able to stop this increase," said Irva Hertz-Picciotto, a researcher at the University of California, Davis who is leading a closely watched study into what sparks autism disorders.
In the past week, a spate of studies released during National Autism Awareness Month has offered tantalizing new information about potential causes. Research published in the journal Nature widened the understanding of the genetic roots of some cases and confirmed the elevated risks for children with older fathers. Another study, released online Monday in Pediatrics, suggested maternal obesity may play a role.
To be sure, finding the causes of autism — an umbrella term for a variety of disorders that delay children socially or intellectually — remains daunting. The causes are believed to be complicated, and not necessarily the same for each child. Some liken autism to cancer — a small word for a wide range of illnesses. Autism can be blamed on both genetic problems that load the gun and other factors that pull the trigger.
It has been a growing public concern for two decades, as studies have found it to be more and more prevalent. The U.S. government dramatically increased funding for autism research in the last decade, and now budgets about $170 million a year through the National Institutes of Health. That's only about a quarter of what NIH will spend on breast cancer research and $50 million less than what it will spend on asthma.
But more than a half-dozen foundations and autism advocacy groups have been adding to the pot, putting annual research spending in recent years at more than $300 million. About a third of that has been devoted to finding autism's causes.
The lion's share of money for finding a cause has been spent on genetics, which so far experts believe can account for roughly 20 percent of cases. The earliest success was in the early 1990s and involved the discovery of the genetic underpinnings of Fragile X syndrome, a rare condition that accounts for just 2 to 4 percent of autism cases but is the most common form of inherited intellectual disability in boys.
The focus on genetics has been bolstered by dramatic improvements in gene mapping as well as the bioengineering of mice with autism symptoms. Dozens of risk genes have been identified, and a half-dozen drug companies are said to be working on developing new treatments.
But even genetics enthusiasts acknowledge that genes are only part of the answer. Studies of identical twins have shown that autism can occur in one and not the other, meaning something outside a child's DNA is triggering the disorder in many cases. Some cases may be entirely due to other causes, Dawson said.
That broad "other" category means "environmental" influences — not necessarily chemicals, but a grab bag of outside factors that include things like the age of the father at conception and illnesses and medications the mother had while pregnant.
For years, the best-known environmental theory involved childhood vaccines, prompted by a flawed 1998 British study that has been thoroughly discredited. Dozens of later studies have found no link between vaccines and autism.