Missouri's health insurance costs rose just one-tenth of 1 percent due to a requirement that some Missouri health insurers pay to treat autism, the state Department of Insurance reported Tuesday.

The state said Missourians filed 3,805 claims for coverage and they cost insurers $4.3 million. One out of every 350 people with coverage received autism therapy.

After a long campaign, parents of autistic children convinced the legislature to mandate coverage in 2010, and the mandate began to take efect in January 2011. The insurance industry opposed the bill, as it does most coverage mandates, claiming they raise insurance premiums.

"This report shows good news on two fronts," said John M. Huff, state director of insurance. "First, it shows that the new law has already helped thousands of Missourians. Second, it shows the autism mandate should have minimal impact on health care costs and insurance premiums."

The mandate covers only about a quarter of Missourians with health insurance, mainly those who get coverage from small and mid-sized companies. It doesn't affect large employers who self-insure. Federal law exempts them from many state requirements.

For health insurance policies sold to indivicuals, insurers are required to offer autism coverage as an option and can charge extra for it. About a third of people with individual policies now have autism coverage.

Until the mandate, Missouri health insurers rarely covered autism.

The state rule required covered insurers to pay up to $40,000 per year for each autism patient last year, and that will rise to $41,263 for 2012. The actual cost averaged $143 per month for each autism patient last year, the Insurance Department reported.

Autism, a neurological disorder, affects about one in 110 children, impairing their ability to socially interact and communicate with others. Proponents say intensive one-on-one therapy can bring significant improvement.

Michael Wasmer, lobbyist for the advocacy group Autism Speaks, said the costs reported in Missouri are consistent with those from five other states where the group studied the effect on health insurance plans for state workers. The cost of autism treatment in those states equaled 15 cents per covered person per month in the first year of coverage and 31 cents in the second year.

Autism coverage gradually rolled out last year as insurance plans hit their annual renewal dates and autism therapists were licensed. The Insurance Department expects use of the coverage will increase this year.