Review for 10.1186/1471-230X-14-23 (2014)

Reviewer's report
Title:The Serotonin Transporter Gene Polymorphism (5-HTTLPR) and Irritable
Bowel Syndrome: A Meta-Analysis of 25 Studies
Version:3Date:29 December 2013
Reviewer: Mohammad Bashashati
Reviewer's report:
Dear Authors,
It is my pleasure that I have the opportunity of reading your article, and I
understand how much effort you have put on this work. Please find my
comments below:
1- Recently, C. Dai and colleagues have published a meta-analysis on the same
topic (Aliment Pharmacol Ther. 2013 Mar;37(6):657-8. doi: 10.1111/apt.12222).
Their included studies based on their reported Forest Plot are from 2002 to 2012.
Although, the current study has searched up to 2013, I am not seeing any
significant addition rather than some non-English included studies. Dai an
colleagues concluded there is an association between the genetic polymorphism
in the SERT-P gene (L/L) and C-IBS. The current study, also showed the LL
genotype is a risk factor for IBS-C. What does this meta-analysis add to the
literature? Why do you think this manuscript is timely?
2- In the conclusion of your abstract, you have mentioned your founding are
contrary to the results of the earlier meta-analyses. As you know, Dai and
colleagues had the same conclusion. Why your findings are contrary?
3- The recent study published in PLoS One. 2013 Sep 19;8(9):e75567. doi:
10.1371/journal.pone.0075567, has not included some of the studies which are
included in the current meta-analysis. I am not talking about the quality of that
study; however, I understand some of the included studies in your meta-analysis
are in Korean or Chinese. Please mention if you have read the full-text of those
articles and clarify it in the methods section. Besides, there are also English
articles (e.g. Whitehead) which are included here and not in the former article.
Have all these original studies included the same polymorphism?
4- The value of meta-analysis is providing raw data as well as OR (95% CI) for
gene polymorphisms. It is important, because others can continue this work and
also the readers can judge on the quality of work. A better approach in
meta-analysis for gene polymorphisms is reporting (number of positive
cases/total number of cases) as well as (number of positive controls/total number
of controls) for L allele, LL genotype, LS genotype, and SS genotype (alleles and
genotypes in different forest plots) plus OR, 95% CI and weight of the study. In
other words instead of comparing LL vs. SS, you should compare LL in cases vs.
controls. You can also do LL+ LS (cases/controls) or LS+SS (cases/controls).
Just reporting Forest Plot for Asian/C-IBS is not enough. All analyses should
come in the supplementary results if the journal volume does not allow.
5- Why did not you include 5-HTTLPR in the search terms?
6- You also searched a Chinese database. Did it add to your study?
7- In Figure 2, units should be similar to the text. In the text you have used %.
8- In the author contribution section, please mention who have searched,
selected, analyzed the data and wrote the paper.
9- Why Shiotani's study has not been included in your Forest Plot? Hasn't it
evaluated C-IBS?
10- Study of Farjadian is on Iranians. Please correct this.
11-What is the rational behind confirming the results with DNA sequencing?
Thank you.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Needs some language corrections before being
published
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I declare that I have no competing interests.