A new study has found a group of genes which control vital immune cells are more active in children with autism, providing more evidence of immune system involvement in the disorder.

Researchers from the University of California Davis discovered 11 genes, which are all involved in the control of "natural killer" immune cells, that are more active in autistic children than in healthy youngsters.

Natural killer cells are part of the body's first line of defence against attack from pathogens such as bacteria and viruses, as well as tumour cells.

The study which is published in the January edition of the journal Genomics was only a small preliminary investigation, involving 61 children, but it provides important clues as to where larger studies should look in the future.

It was long thought that autism was purely genetic but research in recent years has shifted the focus to include environmental factors as important triggers. It is now thought that an interaction between certain genetic characteristics and triggers in the environment is what leads to children developing the condition.

Dr Jeffrey Gregg, director of molecular diagnostics for the UC Davis Medical Centre, and 10 of his colleagues involved in the study feel that the findings provide some validation for theories that suggest an infectious agent encountered some time in early childhood, or even in the womb, may trigger immune reactions that contribute to the development of autism.

Previous research carried out at UC Davis's MIND Institute in 2005 also found immune system abnormalities in children with autism. Compared to healthy children those with autism were found to have 20 per cent more B cells, which produce antibodies, as well as 40 per cent more natural killer cells.

What is usually called simply 'autism' is actually a spectrum of developmental disorders collectively known as autism spectrum disorders (ASDs). This latest research found that children throughout the spectrum of disorders all strongly expressed the 11 genes responsible for the increased natural killer cell activity.

Dr. Gregg and colleagues did uncover differences between different groups of autistic children however, particularly between those who show signs of the disorder early and those who have a late onset.

In some cases of autism the symptoms are apparent from a very early age but in other cases children seem to develop perfectly normally for 18 months or more, then begin to slip backwards.

The researchers found that children with that "regressive" form of autism had nearly 500 genes that were activated differently than children with "early onset" autism.

They concluded that this indicates the two groups may be distinct in how they are caused which means different approaches to prevention and treatment may be needed.

In terms of the main findings, the researchers said that considering they set out to examine how ever gene was expressed in autistic children, to have the 11 genes responsible for natural killer cells stand out so clearly indicates that this is a key finding and something requiring further investigation.

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