The results of a national birth cohort study published today provide the first biomarker evidence that the insecticide, DDT, increases the risk of autism for the first time in history.
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Autism is the term generally used to describe a spectrum of related disorders that affect an individual's capacity for social interaction and communication.
It typically begins in early childhood and presents as lack of interest and difficult behaviour.
Although in many cases the symptoms may be mild and not prevent the affected individual from living independently, some sufferers have severe disabilities that necessitate life-long care and support.
Autism commonly has a negative impact on educational and social attainments, which can limit employment opportunities.
Globally 1 in 160 children has a disorder on the autism spectrum and epidemiological studies conducted over the past 50 years indicate that the prevalence of autism is increasing.
Scientific evidence has implicated a range of environmental and genetic factors in the risk of a child developing autism.
A recent study conducted in Finland is the first to connect the banned insecticide DDT with increased risk for autism.
The team followed more than a million pregnant women and their offspring from 1987 to 2005. They identified 778 cases of childhood autism. Each child with autism along with the mother was matched with a control mother-child pair that was not affected by autism.
Mothers with high levels of a DDT metabolite in their blood were more than twice as likely to have a child with autism including intellectual disability compared with controls.
The odds for the offspring developing any type of autism were nearly one-third higher among offspring exposed to elevated maternal levels of the DDT metabolite. No association between maternal PCB insecticide exposure and autism was observed.
Although the use of DDT and PCBs was widely banned in Finland, and many other countries, over 30 years ago, they still persist in the environment due to the slow rate at which they are broken down.
Along with genetic and other environmental factors, our findings suggest that prenatal exposure to the DDT toxin may be a trigger for autism.”
Professor Alan S Brown, Lead Author
The researchers hypothesise that maternal exposure to DDT, but not PCBs, increases the risk of autism due to its inhibitory affects on birth weight and androgen receptor binding.
Studies have shown that both of these are risk factors for autism.