Review for 10.1186/1471-230X-11-124 (2011)

Reviewer's report
Title:Lactase non-persistent genotype influences on dairy product consumption
and gastrointestinal symptoms in Northern Russians
Version: 1Date:1 May 2011
Reviewer: Andrew Szilagyi
Reviewer's report:
Editor BMC Gastroenterology May 1.2011
Dear Sir
Khabarova et al report a study which examines the relationship between dairy
food intake, symptoms from milk intake and the north European genetic
polymorphism for lactase in a northern region of Russia. A large number of
participants are included.
Symptoms and intake of various foods are recorded using a previously published
questionnaire. Genetic testing was carried out using PCR assay. Their findings
confirm the approximate 35% frequency of CC genotype in the population under
study. Although, the milk intake of the entire group is modest participants with CC
genotype take in statistically significantly less milk by 10% than lactose digesters.
Gastroenterological symptoms are similar in maldigesters and digesters but
symptoms in response to milk are statistically significantly higher than in
digesters.
This study is of interest because it is one of the few attempts to link self reported
symptoms with genetic analysis. The strengths are that it is based on a relatively
large cohort population and the questionnaire was not specifically directed
(therefore biasing) toward establishing milk intolerance. The target population of
the study is relevant. The methods used by the authors are appropriate and
mostly well defined (see minor comment below). The title and abstract convey
the gist of the article. The discussion and English syntax and typographics should
be more inclusive and corrected, respectively.
Comments (Minor Essential Revisions)
I have no major criticisms as such. I have some conception related disagreement
with the statement in the introduction that “nowadays genotyping is the most
appropriate method for diagnostics….”. The genotype is not a physiologic test.
The genotype is an excellent test for epidemiology. It is also dependent on the
population under study and the kit used likely needs to be tailored to contain the
dominant polymorphism responsible for lactase persistent status.
The other comment which follows from the first is that the use of milk was very
low in all subjects in the study and the reporting of lactose intolerance even in the
CC genotype was only 13%. The low rate of symptoms may be partly related to
the low total intake.
Did the authors think that the low intake is due to cultural preference or other
reasons? According to a recent NIH report an important consequence of self
reported lactose intolerance, is related to decreased intake of dairy foods and
calcium from these (Suchy FJ et al. Ann Int Med 2010; 152: 792-796). Universal
testing of genetics only, may actually increase the risk of avoiding dairy foods by
a larger number, if they are told they cannot digest lactose due to an inherited
trait. In the case of physiological tests sometimes low dose lactose load (which
may induce less symptoms) may convince the person that lactose is tolerable
even if they are maldigesters.
Other Comments (Discretionary Revisions)
I think the paper could use an overview from someone proficient in English for
several syntax spelling and typographical related sentences.
In the Materials and Methods section it states students were selected randomly.
This could be further specified as to the actual method.
There is no distinction made in outcome between males and females. This may
or may not be relevant but could be included.
A previous study from Austria using only men and a smaller group did not find a
statistically significant difference in reporting lactose intolerance between CC, CT
or TT (Gugatschka et al. QJ Med, 2005).
Sincerely
Andrew Szilagyi
I consent to publication of the review on the stated manuscript.
Level of interest: An article of importance in its field
Quality of written English: Needs some language corrections before being
published
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
'I declare that I have no competing interests' below