The number of kids in California being treated for autism doubled between 1998 and 2002, and there is still no end in sight to the growing trend, state officials reported. The report ... found that 10,360 autistic children sought services in 1998. By the end of last year the number had jumped to 20,377, a 97 percent increase, far outstripping the growth rate in population or births. Concern over rising autism rates has been growing since the late 1990s as parents, educators and pediatricians began reporting increasing numbers of affected children across the country. As many as 20 different genes are known to play a role, but it also is believed that environmental factors are at work. Steep increases have also been documented in other industrialized countries such as Japan and Israel. California is absolutely not special," Huff said. "In fact, we're middle of the road in terms of our rates." Scientists continue to search for a cause. Theories abound, including the possibility that childhood immunizations may be involved. However, recent studies into the measles, mumps and rubella (MMR) vaccine have not shown a link. Others have suggested that environmental toxins or food additives might be the cause. Some research has focused on possible causes in the womb, including a mother's immune response to common infections that could affect the developing fetus. Researchers connected to the MIND Institute found in an initial study that high levels of certain proteins in the blood of newborns could predict which ones went on to develop autism and mental retardation.