The Microbiome in Posttraumatic Stress Disorder and Trauma-Exposed Controls: An Exploratory Study

[Andy]

Objective: Inadequate immunoregulation and elevated inflammation may be risk factors for posttraumatic stress disorder (PTSD), and microbial inputs are important determinants of immunoregulation; however, the association between the gut microbiota and PTSD is unknown. This study investigated the gut microbiome in a South African sample of PTSD-affected individuals and trauma-exposed (TE) controls to identify potential differences in microbial diversity or microbial community structure.

Methods: The Clinician-Administered PTSD Scale for DSM-5 was used to diagnose PTSD according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition criteria. Microbial DNA was extracted from stool samples obtained from 18 individuals with PTSD and 12 TE control participants. Bacterial 16S ribosomal RNA gene V3/V4 amplicons were generated and sequenced. Microbial community structure, α-diversity, and β-diversity were analyzed; random forest analysis was used to identify associations between bacterial taxa and PTSD.

Results: There were no differences between PTSD and TE control groups in α- or β-diversity measures (e.g., α-diversity: Shannon index, t = 0.386, p = .70; β-diversity, on the basis of analysis of similarities: Bray-Curtis test statistic = –0.033, p = .70); however, random forest analysis highlighted three phyla as important to distinguish PTSD status: Actinobacteria, Lentisphaerae, and Verrucomicrobia. Decreased total abundance of these taxa was associated with higher Clinician-Administered PTSD Scale scores (r = –0.387, p = .035).

Conclusions: In this exploratory study, measures of overall microbial diversity were similar among individuals with PTSD and TE controls; however, decreased total abundance of Actinobacteria, Lentisphaerae, and Verrucomicrobia was associated with PTSD status.

Paywalled at http://journals.lww.com/psychosomat...iome_in_Posttraumatic_Stress_Disorder.14.aspx

Article on paper - https://www.sciencedaily.com/releases/2017/10/171025103140.htm

 

[Trish]

As we know, correlation does not imply causation. Does trauma cause stress that leads to upset in gut flora, or does imbalance in gut flora predispose to suffering PTSD following trauma? Or is some other factor influencing both.

Or is it such weak evidence that it could be chance variation. p = 0.035, PTSD sample size 18, 12 control. Several different associations tested, only one was significant at 5%level.

We are none the wiser.

 

[JCB]

random forest analysis? WTF? Is this some form of p-hacking or is there something more to it?

 

[Woolie]

full text at scihub: https://sci-hub.cc/10.1097/PSY.0000000000000512

Let me share with you the author list for this study:

Hemmings, Sian M.J. PhD; Malan-Müller, Stefanie PhD; van den Heuvel, Leigh L. MMed (Psych); Demmitt, Brittany A. PhD; Stanislawski, Maggie A. PhD; Smith, David G. BS; Bohr, Adam D. PhD; Stamper, Christopher E. MS; Hyde, Embriette R. PhD; Morton, James T. BS; Marotz, Clarisse A. MS; Siebler, Philip H. BS; Braspenning, Maarten Ir; Van Criekinge, Wim PhD, Ir; Hoisington, Andrew J. PhD; Brenner, Lisa A. PhD; Postolache, Teodor T. MD; McQueen, Matthew B. ScD; Krauter, Kenneth S. PhD; Knight, Rob PhD; Seedat, Soraya MD, PhD; Lowry, Christopher A. PhD

That lightbulb sure must have been tough to change, eh?

The primary result is that there were no significant differences between groups in microbiome diversity, contrary to their predictions.

The forest thing they did (Variable Selection using Random Forests), trawls through a large dataset to find variables that reliably distinguish your two groups. If you have a large enough set of variables, you are pretty much guaranteed to find something with this approach. So you can't really conclude anything from it. All you can use it for is to generate a hypothesis to test on your next set of participants. They also tried to do various confirmatory analysis of the variables after they had dug them out, but they've used correlation, which doesn't seem to me to be the right approach when you have two groups that are strictly delineated.

Still, at least they were honest about their predictions not being confirmed. They could have done what a lot of their colleagues done, and re-written the intro to make their predictions fit with the findings.

 

[Adrian]

random forest analysis? WTF? Is this some form of p-hacking or is there something more to it?

Random forest techniques are quite a popular classification technique in machine learning.