Researchers have found that mothers of some autistic children may have made antibodies against their fetuses' brain tissue during pregnancy.

Autism is an extremely complex condition and one that is still poorly understood. It has been estimated that the cause of the condition in over 90% of cases is unknown. It is now widely thought to stem from interactions between genetics, the immune system, and environmental triggers.

New research suggests that antibodies produced by a mother's immune system that target her developing baby's brain tissue can be now be added to the list of potential triggers for the developmental disorder which now affects around 1 in 150 children.

Previous research has revealed abnormalities in the immune systems of those with autism. In 2005 researchers at the University of Calfornia Davis' Mind Institute found that autistic children had 20% more B-lymphocytes (the cells that produce antibodies) and 40% more natural killer cells than healthy children. Other research has shown immune abnormalities in certain areas of the brains of those with autism when examined postmortem.

The latest study was led by a team from Johns Hopkins Children's Center. They noted that despite these immune system abnormalities most children with autism don't produce antibodies against their own tissues, including the brain. This led them to look elsewhere and hypothesise that antibodies produced by mothers during pregnancy may cross the placenta and damage their child's brain before birth.

To test this hypothesis researchers led by Harvey Singer, M.D., director of pediatric neurology at Hopkins Children's used a technique called the Western blot (or immunoblotting) to examine the antibody-brain interaction in 100 mothers of autistic children and 100 mothers of healthy children. The technique involved exposing samples of both adult and fetal brain tissue to antibodies obtained from the 200 women in the study.

Dr. Singer and colleagues found that around 40 per cent of samples from mothers of autistic children showed either a stronger reaction or more areas of reactivity between antibodies and brain proteins compared to samples taken from mothers of healthy children.

The researchers also found that the presence of maternal antibodies was associated with the increasingly immature behaviours, referred to as developmental regression, that are one of the fundamental signs of autism.

The results certainly suggest a link between autism and antibodies produced by mothers during pregnancy but the researchers caution that the results are not definitive. They say that further studies are needed to confirm that specific antibodies are actually able to cross the placenta and cause damage to the baby's brain as it develops in the womb.

"The mere fact that a pregnant woman has antibodies against the fetal brain doesn't mean she will have an autistic child," Singer says. "Autism is a complex condition and one that is likely caused by the interplay of immune, genetic and environmental factors."

The research team were also quick to assure women that they should not be alarmed by these findings and they should be viewed as another step forward in the understanding of autism.

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