(Xinhua)
Updated: 2008-05-16 07:25

LONDON - Insecticides in pet shampoos trigger autism spectrum disorder (ASD), according to survey results presented Thursday at the International Meeting for Autism Research in London.

According to one of the first large-scale population-based studies to look how environmental factors and their interactions with genes contribute to the condition, mothers of children with an ASD were twice as likely to have reported using pet shampoos containing a class of insecticide called pyrethrins as those of healthy children.

The risk was greatest if the shampoo was used during the second trimester of pregnancy, the study showed.

Previous studies in insects and rodents have suggested that pyrethrins could damage the blood-brain barrier during early life, and cause neuronal damage. They may also interfere with the transmission of signals along nerve fibres.

Autism is associated with an imbalance between excitatory and inhibitory neurotransmitters within the brain.

While many chemicals have previously been blamed for triggering autism, there have been very few rigorous studies designed to investigate the link.

To remedy this, researchers led by Irva Hertz-Picciotto at the University of California in Davis, United States, studied 333 children with ASD and 198 healthy children, and their families.

The researchers made the findings after collecting blood and urine samples, conducting in-depth questionnaires on medical history and any possible exposure to medications, household products or metals that could have occurred around the time of conception, during pregnancy, or after birth, as well as collecting information on lifestyle.

However, lead researcher Irva Hertz-Picciotto and other experts caution that pyrethrins were unlikely to be the only cause of autism, which is increasingly recognized as being caused by a complex interplay of both genetic and environmental factors.

Another study suggested that exposure to organophosphate insecticides double the risk of developmental disorders, including autism.