Parents of 1,000 California children enrolled in the state's developmental-disabilities system are receiving letters in the mail asking them to participate in a study examining an unprecedented increase in autism in the state.

The M.I.N.D. Institute at UC Davis is conducting the study to help explain the reasons behind a 273 percent increase in the number of autistic children entering the state's 21 regional centers between 1987 to 1998. The upsurge was highlighted in a 1999 report by the California Department of Developmental Services (DDS), which operates the centers. As a result of that report, the state Legislature and Gov. Gray Davis directed DDS and the M.I.N.D. Institute to identify factors that may be responsible for the increase, funding the effort with a $1 million appropriation.

The latest DDS figures available show that 2,331 persons entered the regional center system with a diagnosis of autism during 2001. That amounts to an average of six new individuals a day.

Autism is a complex and severe developmental disorder that affects brain function, interfering with reasoning ability, imagination, communication and social interaction. Children with autism start talking later than other children, and when they do speak, their communication skills are extremely limited. They often avoid looking at other people and do not learn to read others' faces for signs of emotion or other cues. These children typically are unable to play creatively, and some engage in repetitive, sometimes self-destructive behavior, such as rocking, hand-flapping or head-banging.

Opinions vary among researchers and parents as to the reasons behind the increase, said UC Davis pediatric epidemiologist Robert S. Byrd, who is the principal investigator on the study. Byrd is asking parents to describe what they think caused their child's disorder as part of the study.

"In this study, we are examining a number of possibilities, including whether there is an actual increase, whether the criteria used to diagnose autism has changed over time or if by applying today's diagnostic standards, children have been misclassified," Byrd said. "We also are determining whether the number of families with autistic children moving into California accounts for some of the observed increase in autism cases."

Byrd said his team is enrolling 1,000 children and their families -- 500 children diagnosed with autism and 500 diagnosed with other developmental disabilities who have been randomly selected from the DDS regional centers -- to participate in the study. The two groups of children are divided into two age groups, based on year of birth. The first group was born between 1983 to 1985 (15 to 17 years old) and the second between 1993 to 1995 (5 to 7 years old).

As part of the study, researchers are recording if and how the characteristics of children reported with autism in California have changed over time. They also are asking about specific medical or developmental problems, such as mental retardation, allergies, gastrointestinal disorders, pregnancy and birth complications.

"We are also asking about regression, that is whether children seemed normal at birth and had relatively normal development to a certain point, then lost the ability to do things that other children who are developing normally might be expected to do," Byrd said. "Parents and caregivers frequently report these problems, which have not been systematically studied. Our research should be able to estimate how much these occur and whether they have changed over the years between the two age groups we are evaluating."

As part of the study, the researchers are reviewing the children's regional center records. All participating families are completing a questionnaire while families of autistic children are taking part in an autism diagnostic interview at their regional center.

Results of the statewide study will be compiled and presented to the California Legislature in early summer.

Established in 1998 through the efforts of four Sacramento families whose children have autism, the M.I.N.D. Institute at UC Davis is a unique multidisciplinary research institute devoted to the study of autism and other neurodevelopmental disorders.