Fish, Antidepressants, Autism and a Problematic Research Premise

This week saw publication of a PLOS One paper on a potential environmental cause of autism that caught the attention of the media. The Daily Mail, a newspaper that has a track record of sensationalist health scares announced “Autism ‘could be triggered by very low doses of anti-depressants or other chemicals found in water supply’”. On the same day, three excellent critiques of the study appeared on the blogosphere, by Tom Chivers, writing in the Daily Telegraph, by Dianthus Medical, and by Neuroskeptic.

As it happened, I had blogged about autism earlier this week, reconsidering the enduring question of whether there really is an autism epidemic in need of explanation. I was therefore interested to see that the PLOS One paper confidently asserted: “Idiopathic ASD, caused by genetic susceptibility factors interacting with unknown environmental triggers has increased dramatically in the past 25 years.”  Well, everyone agrees there has been a remarkable increase in autism diagnosis across the world in the past 25 years, but in my blogpost, I questioned whether this meant an increase in autism. So here are the arguments that I put forward that might give one pause.

Three very different kinds of explanation exist for the growth in diagnoses:

  • Explanation #1 maintains that something in our modern environment has come along to increase the risk of autism. There are numerous candidates, as indicated in this blogpost by Emily Willingham.
  • Explanation #2 sees the risks as largely biological or genetic, with changing patterns of reproduction altering prevalence rates, either because of assortative mating (not much evidence, in my view) or because of an increase in older parents (more plausible).
  • Explanation #3 is very different: it says the increase is not a real increase – it’s just a change in what we count as autism. This has been termed ‘diagnostic substitution’ – the basic idea is that children who would previously have received another diagnosis or no diagnosis are now being identified with autism spectrum disorder (ASD). This could be in part because of new conceptualisations of autism, but may also be fuelled by strategic considerations: resources for children with ASD tend to be much better than those for children with other related conditions, such as language impairment or intellectual handicaps, so this diagnosis may be preferred.

via Fish, Antidepressants, Autism and a Problematic Research Premise | PLoS Blogs Network.

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