Siding with parents over insurance companies, Gov. Janet Napolitano signed legislation Friday that eventually will require insurance companies to provide coverage for autism.

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But there will be limits.

Napolitano's decision caps months of intensive lobbying by parents of children who have been diagnosed with autism and varying related conditions to finally get some financial help from insurers.

The move came despite lobbying from not only insurance companies, but business interests. Marc Osborn, who represents the Arizona Chamber of Commerce and Industry, predicted the new mandate will lead to higher insurance costs for businesses - and even the possibility that the additional charges will result in some firms deciding they can no longer afford to provide coverage.

But Osborn found a hostile audience, even among otherwise business-friendly lawmakers who said they wouldn't be enacting legislation if insurers worked with parents.

Gretchen Jacobs, the mother of a 4-year-old girl with autism, rejected the notion that the law, which takes effect in mid-2009, amounts to a new mandate.

She said insurers refused to provide coverage for children with autism or even its milder form, known as Asperger's syndrome, on the basis that it was not treatable.

Statistics from the Centers for Disease Control and Prevention show one out of every 150 children is affected with some form of autism that can manifest itself as an impairment in thinking, feeling, language and the ability to relate to others. The CDC said it appears to be far more common in boys than girls.

The state Department of Developmental Disabilities provides coverage for about 3,160 children with the most severe form of autism. Other forms are not covered.

Jacobs, who used to lobby on behalf of insurance companies, said evidence now shows that children do respond to certain types of treatment. But it can be costly, which is why the parents want coverage.

Osborn, in testifying against the bill before the Senate Health Committee, said that it is shifting the cost from the developmental disabilities department to insurers - and, ultimately, to the companies that pick up the tab. That brought an angry response from Sen. Barbara Leff, R-Paradise Valley.

"If you have insurance, your employer pays for insurance. Your baby has a heart condition, you're going to pay for that surgery," she said. Leff said autism "is still an illness."

Lawmakers did agree to some limits.

First, the mandate applies only to employer-purchased insurance for companies with at least 50 workers under the premise that these firms, with a larger base, are better able to absorb the cost.

Second, benefits would be limited to $50,000 a year for children through age 8; those 9 through 16 would have benefits capped at $25,000 a year.

Jacobs said the higher figure for younger children makes sense as there is evidence that early and intense intervention can make a difference.

Less clear is what causes autism.

There have been some claims that mercury-based preservatives used in some children's vaccines have an effect. Jacobs said even though most vaccines no longer have that chemical, other environmental factors are suspected.

But she said the increased number of children diagnosed with autism could also be due to a "greater awareness" by doctors and others of the condition - and the willingness to make that diagnosis.

Sen. Tom O'Halleran, R-Sedona, who voted for the measure, said the issue of autism goes beyond the families and the insurance company.

"It is the problems of America and the problems we are having with our health care system," he said.