By Maggie Fox, Health and Science Correspondent

WASHINGTON, Nov 19 (Reuters) - Government agencies and autism advocacy groups announced a new alliance on Wednesday to shed some light on autism -- a disorder surrounded by angry parents, frightening rumors and little solid fact.

The advocates, once fierce critics of the government, said they were teaming up to encourage and actively participate in research to battle the brain disorder and find out out not only what causes it but precisely how many people have it.

They announced four new programs to find the genetic causes, screen children earlier, identify treatments and pool information. They account for $5.2 million, about half from the groups and half from the National Institutes of Health.

"This really is a different way of doing business," Dr. Duane Alexander, head of the National Institute of Child Health and Human Development, told a conference on autism.

"This public-private partnership should make it possible to move much more quickly to find answers to the genetic puzzle that autism presents," added Dr. Story Landis, Director of the National Institute of Neurological Disorders and Stroke.

Autism is a spectrum disorder, meaning it varies from person to person.

Usually diagnosed around the time children learn to talk well -- at age 2 or 3 -- autism affects communication and social skills. "About 40 percent of children with autism spectrum disorders do not talk at all," the Centers for Disease Control and Prevention said in a statement.

Many refuse to be held or cuddled and may engage in repetitive behaviors.

"We don't know what causes this. There is no cure. There is no treatment. We want to change this," Prisca Chen Marvin of the National Alliance for Autism Research, and the mother of a child with autism, told the conference.

COUNTERING RUMORS

The researchers also hinted that the new research may counter what they consider to be misleading ideas about autism, including fears that vaccines could cause the disorder. Several studies have found no link between vaccines and autism.

"It will defuse some of these other issues," said one researcher, who asked not to be named.

Another common but unproven theory is that there is a new epidemic of autism.

"We know that autism is much more common than previously thought," said Dr. Jose Cordero, head of the new birth defects branch at the CDC. It may be as common as 1 in every 250 births, he said.

"We don't have enough rigorous, long-term data to know if the actual incidence of autism is increasing," Steve Foote, director of neuroscience at NIMH, said in an interview.

What the groups have to offer are the families to be studied, and expertise in gathering information.

One alliance will help researchers get more DNA samples from families affected by autism so they can find the genes that may underlie the disorder. "You have to have the numbers or you are just looking for a needle in a haystack," said NIMH Director Dr. Thomas Insel.

Cure Autism Now trained people to take blood samples from all members of families with autistic children. The goal is a more complete genetic database.

Another alliance, between the CDC and the Autism Society of America, aims to create an awareness campaign and a standardized screening program so parents, teachers and doctors can find children with autism as early as possible.

While there is no cure, some therapies may help autistic children interact better with others.