It is time to focus on environmental causes for the rapid rise in autism, a leading researcher said Thursday, after her study concluded that such factors as earlier diagnosis and families moving to California cannot fully explain a dramatic seven- to eightfold increase in the state since the early 1990s.

"With no evidence of a leveling off, the possibility of a true increase in incidence deserves serious consideration," states the study, published in the January issue of the journal Epidemiology.

For years, experts have debated whether the autism increase is real. Skeptics argue that it is a result of better diagnosis, a change in definitions and the inclusion of children with milder forms of the disorder.

Irva Hertz-Picciotto and her colleagues at the UC Davis M.I.N.D. Institute and Department of Public Health Sciences set out to explore such hypotheses.

They concluded that while those factors explain some of the increase, they do not account for most of it.

The findings prompted Hertz-Picciotto, a leading autism researcher and a professor of environmental and occupational health and epidemiology, to urge policy makers to devote more research money to looking for an environmental trigger.

"Right now, about 10 to 20 times more research dollars are spent on studies of the genetic causes of autism than on environmental ones," she said. "We need to even out the funding."

Rick Rollens, the father of an autistic child and a co-founder of the M.I.N.D. Institute, agreed.

"This is a definitive study that should once and for all put the proverbial nail in the coffin of those who have been denying the existence of an autism epidemic," he said.

"The sooner that people recognize the significance of this crisis, the sooner we'll be on our way in trying to address the needs of the children and families," Rollens said.

Autism is a developmental disorder marked by poor verbal and communication skills, repetitive behaviors and an inability to form social connections.

Once considered a rare disorder, it is now prevalent in industrialized countries around the world.

The search for answers has taken on added urgency because children who have autism often need expensive educational services and may require a lifetime of care. As they reach adulthood and no longer have parents who can care for them, the burden on taxpayers will escalate.

"Unless some really miraculous treatments come along, there are some big financial questions ahead," Hertz-Picciotto said.

Her study found that the incidence of children diagnosed with autism by age 6 in California has risen dramatically. Fewer than nine out of 10,000 children born in 1990 were diagnosed with the disorder. But for those born in 2000, the rate had jumped to 44 per 10,000.

"The rise is still happening," Hertz-Picciotto said. "It's really important to realize it's not leveling off and it's definitely not declining."

To determine whether people moving to the state could explain this increase, the researchers compared autism diagnoses with birth records and excluded children who were not born in California. They concluded that migration to the state has had little impact on the large increase in autism.

They also looked at whether including people with milder forms of the disorder could explain the increase.

In 1993-94, the standard definition of autism was broadened, enabling more people to receive the diagnosis. But the study determined that including milder cases accounted for less than one-tenth of the 600 percent to 700 percent increase in autism since 1990.

Diagnosing children at an earlier age, which could make it seem as if more people have the disorder, also accounted for only a small portion of the increase, the study found. That left most of it unexplained.

The study did not directly address another factor that could play a role in the increase in diagnoses — greater public awareness. But if that is a major cause, at some point the numbers should start leveling off. Hertz-Picciotto notes that this is not happening.

She and her colleagues at the M.I.N.D. Institute are conducting two large studies to explore whether some combination of environmental factors may be triggering autism in genetically susceptible children.

"We're looking at the possible effects of metals, pesticides and infectious agents on neurodevelopment," she said. "If we're going to stop the rise in autism in California, we need to keep these studies going and expand them to the extent possible."

Rollens, like many other parents of autistic children, also believes vaccines should be investigated, although much of the medical community disagrees.

"We've put way too much time and effort in trying to find the elusive autism gene," Rollens said. "We've got a big problem here and we need to be addressing it."

In addition to focusing on possible environmental causes, Hertz-Picciotto urged her fellow scientists to continue focusing on improving therapies and developing new ones.

"These children are now moving toward adulthood," she said, "and a sizable percentage of them have not developed the life skills that would allow them to live independently."

Reach Sandy Kleffman at 925-943-8249 or skleffman@bayareanewsgroup.com.