August 16, 2018

expert reaction to pesticide exposure during pregnancy and autism

A study published in the American Journal of Psychiatry looked at levels of DDE (a breakdown product of the pesticide DDT) and PCBs during pregnancy, and risk of autism in children.

Ian Dale, Head of Research at the National Autistic Society, said:

“We’d urge people not to jump to conclusions about the implications of this study.  It’s based on good data and analysis, but for a range of reasons, it would be wrong to draw conclusions about DDE’s link to autism.  At most, it can add to the range of possible contributory factors to autism, and should in no sense be seen as identifying ‘the’ cause.

“Firstly, the findings aren’t particularly consistent with other smaller pieces of research – although this isn’t surprising, given that there aren’t many studies of this nature.

“Secondly, although there’s an increase in the ‘risk’ factor, as this is an increase on a small risk, this can only suggest a link.  And, the ‘increased risk’ is being driven mainly by people who are autistic and have an accompanying intellectual disability.  As the authors say in the paper, the way they designed their comparison group does not allow them to judge whether it’s actually a finding of a DDE link to intellectual disability or a link to autism, because autism and intellectual disability are highly comorbid, which makes it look like there’s a link.

“Finally, the authors also recognise that if they had adjusted for multiple tests, their main finding would not be considered statistically significant.”

Prof Uta Frith, Emeritus Professor of Cognitive Development, UCL, said:

“The evidence that autism has genetic causes is overwhelming. But the search for environmental causes is indefatigable, despite a conspicuous lack of success. There is an endless list of toxins in our environment. It may well be that man-made hazards harbour dangers that we don’t yet know about, and insecticides in particular are worrying for many reasons. Unfortunately, it is not possible to draw practical implications from the present study. An increased risk of autism in the presence of high levels of maternal pesticides does not necessarily mean that pesticides are a cause, nor even a contributory cause. As the authors themselves acknowledge, this is because correlation is not causation. It would be different if there was a testable idea of what mechanism could be at play.”

* ‘Association of Maternal Insecticide Levels With Autism in Offspring From a National Birth Cohort’ by Brown et al. was published in the American Journal of Psychiatry on Thursday 16 August 2018. 

Declared interests

Prof Uta Frith: “I have no conflict of interest to declare.”

None others received.