News that a nearly 300 percent increase in autism cases in California appears to be a real phenomenon is lending urgency to the search for a cause -- and a cure -- for this mysterious disease.

California now has 18,460 reported cases of autism, mostly in children. An alarming spike in the state's caseload starting in the late 1980s cannot be explained simply by better diagnoses, increased awareness of the disease or families moving to the state for treatment, University of California-Davis scientists reported last week.

But their research didn't answer the urgent questions of every parent who has an autistic child: How did this happen? And how can we treat it?

Answers can't come fast enough for Jill Rege, whose 4-year-old son, Kieran, is autistic. Rege, of Palo Alto, described her son as fairly high-functioning. Yet Kieran cannot attend a regular classroom and receives intensive therapy to improve his social skills.

``I'd love to see more funding go to the cause of this, of why this happens,'' Rege said. ``You have to have people realize this is an epidemic. These kids aren't going away. ''

Despite decades of genetic, epidemiological and brain imaging research, scientists still don't know what causes autism. They have only limited treatments for some of its symptoms.

First described by an American psychiatrist in 1943, autism is a complex neurological disorder that makes communication and normal social interaction difficult, if not impossible, for autistic children and adults. Typical symptoms include lack of eye contact, repetitive behaviors and intolerance of change.

Autism was once thought to be a psychiatric disorder, perhaps caused by an unloving mother. Today, scientists believe the disease is genetic in origin and might be ``triggered'' by environmental factors. Autism is 50 to 100 times more common among siblings of autistic people than in the general population, according to the National Alliance of Autism Research.

Researchers also are exploring other possibilities: Could a mother's immune system attack the brain of a child who is genetically vulnerable to autism during pregnancy, triggering the disease? Could problems with a child's metabolism or gastrointestinal system be to blame? Might childhood or prenatal infections play a role? What about vaccines?

Studies are ongoing in many areas, but genetic research has generated particular excitement in recent years, said Andy Shih, research director of the National Alliance for Autism Research.

Scientists believe several genes might interact to cause autism, and they have begun to pin down some regions where those genes might be located, said Dr. Joachim Hallmayer, a psychiatric geneticist at Stanford University.

Studies of families with autism have shown that two chromosomes, numbered 2 and 7, might be ``hot spots'' for autism genes. Other studies have pinpointed the serotonin receptor gene as a possible culprit: Many autistic children have abnormally high levels of serotonin, a chemical involved in transmitting nerve impulses.

Another gene that initially seemed promising produces a protein called reelin that is associated with development of neuron connections in the brain. But while research in this area continues, ``the trail is cold at this point,'' Shih said.

Researchers are also combining genetic inquiries with brain imaging to look for differences between autistic brains and normal brains, Hallmayer said.

Researchers have investigated whether components of vaccines, such as thimerosal, could trigger autism but have found little connection. Hallmayer said he is skeptical of that link, espoused by some parents of autistic children.

A major challenge for scientists, Hallmayer said, is that people with autism do not have easy-to-find ``markers'' for the disease in the same way that diabetics have abnormal blood sugar levels. And more than one gene -- indeed, as many as 15 -- are believed to be involved in autism, adding to the complexity.

``You have to know where to look,'' Hallmayer said. ``It is very difficult to distinguish the `noise' from the `signal.' ''

Unlike other diseases such as cancer or AIDS, there are no animal models to help scientists in their research. There is no suggestion of autism or similar disorders in primates, Hallmayer said, noting that ``we would not know how to measure it'' even if it existed.

Scientists are still waiting for their big break in autism research, a break that might come with increased federal funding: The government's $5 million-a-year spending on autism research is expected to expand tenfold, Shih said.

``There's nothing that's been truly revolutionary,'' Shih said. ``This research is still in its infancy and a big issue is the availability of resources.''