Conceptual and methodological flaws undermine claims of a link between the gut microbiome and autism
By Kevin J. Mitchell, Darren L. Dahly, and Dorothy V.M. Bishop
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The second, and more radical, position is to argue that research on autism and the microbiome has turned out to be a cul-de-sac and that it is not warranted to spend further time and funding on this topic. In practice, we doubt that this advice would be followed, but we would recommend that if researchers do want to persevere in this area, then they should first ask themselves what evidence would convince them that this is an unproductive line of research. Too often, research topics have no sense of a “stop rule,” with null results being greeted with ever more specific and complex speculations about the nature of associations. Our impression is that autism-microbiome research is an example of a field that has generated its own momentum, without necessarily going anywhere.
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By Kevin J. Mitchell, Darren L. Dahly, and Dorothy V.M. Bishop
Summary
The idea that the gut microbiome causally contributes to autism has gained currency in the scientific literature and popular press. Support for this hypothesis comes from three lines of evidence: human observational studies, preclinical experiments in mice, and human clinical trials. We critically assessed this literature and found that it is beset by conceptual and methodological flaws and limitations that undermine claims that the gut microbiome is causally involved in the etiology or pathophysiology of autism....
What now?
There are two positions one can take regarding future research. First, for those who think this topic is worth taking further, it would make sense to adopt some ground rules. In many ways, these would be similar to those adopted by geneticists after the first frenzy of candidate gene associations was found to be a waste of time and money because the area was overwhelmed by nonreplicable false positive results. The solution was an increase in experimental rigor, with requirements for adequate statistical power, standardized protocols, and a clear distinction drawn between exploratory and confirmatory studies. Four practical steps to improve matters would be (1) to conclude an exploratory study with a clear statement of a hypothesis to be tested in a follow-up study, including a specification of the specific association being tested and details of methods and analytic strategy; (2) encouragement for researchers to work in consortia to achieve adequate sample sizes to look for small effects in what are likely to be heterogeneous samples; (3) a requirement of replication of results obtained in exploratory studies prior to publication; and (4) genuine triangulation: i.e., looking for converging evidence from methods that make different assumptions yet demonstrably tap into the same phenomenon.The second, and more radical, position is to argue that research on autism and the microbiome has turned out to be a cul-de-sac and that it is not warranted to spend further time and funding on this topic. In practice, we doubt that this advice would be followed, but we would recommend that if researchers do want to persevere in this area, then they should first ask themselves what evidence would convince them that this is an unproductive line of research. Too often, research topics have no sense of a “stop rule,” with null results being greeted with ever more specific and complex speculations about the nature of associations. Our impression is that autism-microbiome research is an example of a field that has generated its own momentum, without necessarily going anywhere.
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