Review for 10.1186/1471-230X-14-8 (2014)

Reviewer's report
Title:Telomere shortening correlates to dysplasia but not to DNA aneuploidy in
longstanding ulcerative colitis
Version: 4Date:16 October 2013
Reviewer: Rosana Risques
Reviewer's report:
This is an interesting manuscript that reports the first study of ultra-short
telomeres in ulcerative colitis (UC) tumorigenesis. As hypothesized, ultra-short
telomeres show a stronger association with cancer progression than mean
telomere length. However, there is no association with aneuploidy. The
manuscript is well written, the research is sound, and the results are relevant.
However, there are some review points to consider.
Minor Essential Revisions
1. The authors discuss the somewhat surprising result that ultra-short telomeres
do not associate with aneuploidy and offer the reasonable explanation that the
lack of association could be due to the admixture of diploid and aneuploid cells in
the biopsies. However, the discussion section ends on a rather negative note,
indicating that the lack of association of ultra-short telomeres with aneuploidy
does not support the hypothesis of a carcinogenic pathway based on short
telomeres. This appears to contradict their own findings, since they report that
both ultra-short telomeres as well as mean telomere length are associated with
UC cancer progression, in agreement with previous literature. The postulated
mechanism is through cycles of breakage-fusion-bridge and subsequent
chromosomal instability and evidence for these events has been previously
described in UC (O’Sullivan et al, Nature Genetics 2002). Thus, the lack of
association between aneuploidy and short telomeres in this given study should
not be view as a disproof of this mechanism, especially when there are specific
methodological and biological reasons that might account for the lack of
association. The authors mention the admixture of diploid and aneuploidy cells in
biopsies. Aneuploidy ranged from 5 to 50%. Does the percentage of aneuploidy
associate with the number of ultra-short telomeres? Another reason could be the
threshold for short telomeres, which was set at 900bp, but there is no explanation
for that. A lower threshold could potentially improve the association with
aneuploidy. A third consideration is the small number of biopsies. Finally, recent
literature suggests that UC Progressors might develop cancer by two different
mechanisms (see Discretionary revisions). By separating these two types of
Progressors, the associations might improve.
2. In Abstract, the Methods section should include the type and number of
samples analyzed. If space is limited, the Abstract Background could be
shortened.
3. In Background, the authors state: “Oxidative stress (ROS)”. It should say
“Reactive Oxygen Species (ROS)”.
4. In Background, the description of the limitation of FISH methods for the
detection of shorter telomeres is not clear. Flow FISH is cited, but this technique
does not detect shorter telomeres.
5. In Background, the definition of Progressor is not clear. Progressors are
typically defined as patients with dysplasia or cancer. Non Progressors are
patients dysplasia-free.
6. In Material and Methods, what was the average coefficient of variation for
Q-PCR telomere length measurements?
7. In Material and Methods, “scg” should be defined.
8. In Material and Methods, please indicate that RNAse P was the scg of choice
for the results presented in figure 2 and in results section.
9. Results section would benefit from a table that summarizes the main models
performed as well as a figure similar to the current figure 2, but splitting biopsies
into diploid and aneuploidy and indicating the corresponding p-values for
comparisons.
10. Table 1 should include age, age of onset of disease, and disease duration for
all the patients. Also, it would be very useful if the aneuploid biopsies could be
indicated in the corresponding dysplasia box, maybe in brackets?
11. Supplementary Table 1 is hard to read. Reformatting would be helpful.
Discretionary Revisions
12. Recent literature has reported two potential groups of UC Progressors. One
with early onset of disease (<50 years) and non-dysplastic epithelium that
harbors shorter telomeres and clonal expansions, and a second group with late
onset of disease, no clonal expansions and longer telomeres (Salk et al. in
Inflammatory Bowel Disease 2013). Previously, two groups of UC Progressors
were described based on the presence of widespread vs. localized neoplasia
(Brackmann et al. Inflammatory Bowel Diseases 2009). Patients with widespread
neoplasia tended to have early onset of disease. Thus, it appears that UC
patients with early onset of disease might progress to cancer through a process
that involves telomere shortening and clonal expansions throughout the colon,
resulting in widespread neoplasia. In contrast, UC patients with late onset of
disease might develop cancer by a different mechanism and in a localized
fashion. This consideration is highly relevant in this study, which might benefit
from a separate analysis excluding UC Progressors with late age of onset and/or
localized neoplasia.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
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.