Chromosomal Microarray Study in Prader-Willi Syndrome

Round 1

Reviewer 1 Report

It has been a pleasure to read this exhaustive work, which analyzes the results of the high-resolution chromosome microarray analysis performed on 154 consecutive individuals enrolled in the DESTINY PWS clinical trial for Prader-Willi syndrome (PWS). Certainly in those caused by maternal disomies we should expand the genetic study and better assess the family history in search of other underlying pathologies.

Unfortunately, not all hospitals have the possibility of carrying out this type of advanced genetic study, so I suggest to the authors some tips that can help to suspect these newly described genetic alterations.

Author Response

Thank you so much for the review and comments. 

Reviewer 2 Report

The manuscript «Chromosomal microarray study in Prader-Willi syndrome » by Merlin G. Butler, Waheeda A. Hossain, Neil Cowen and Anish Bhatnagar is devoted to the systematic description of 154 Prader-Willi syndrome individual cases. It demonstrates the diversity of the molecular genetic background leading to the development of symptoms and demonstrates the practical value of using the high-resolution chromosome microarray analysis. The practical value of the manuscript and its importance for publication lies in the detailed description of the various disorders that lead to the development of symptoms. It will certainly be of interest to the readers of the «International Journal of Molecular Sciences» and deserves publication after minor revisions. 

Comments 

1. The work done and its description in itself demonstrates the resolution of the method. In this regard, we would like to warn the authors against using an incorrect comparison of the use of the FISH method (Line 41-44). The resolution of the method is determined by the use of a particular probe, so if it is not used for its intended purpose, it will be difficult to expect a result. I believe that in this case one should appeal to a significant increase in the number of analyzed loci due to a significantly larger number of probes. This is precisely what justifies the increase in the cost of diagnostics for such patients and the use of a more expensive method. Avoiding incorrect comparison of methods will improve the quality of the article and demonstrate the professional level of its authors.

 2. I cannot agree that isodisomy is the result of a meiotic error in gametogenesis (Line 235-237). To date, there is no evidence for this. Moreover, the presence of centromeric interference, which prevents recombination near centromers, has been absolutely proven. On the other hand, there is growing evidence in favor of a high frequency of mitotic recombination during the early divisions of the embryonic cleavage, which can lead to the formation of an abnormal clone that can enter the germline cells. In this case, the article does not have the opportunity to discuss the nature of the occurrence of chromosome 15 isodisomy, therefore, the nature of its occurrence should be more correctly described, as an error in female germline cell. 

3. It may be worth mentioning somewhere that uniparental disomy on the paternal chromosome 15 leads to the development of another disease (Angelman syndrome), so that the reader does not have the assumption that such pathologies are only of maternal origin (DOI: 10.1002/ana.410320406), but this question can be left to the discretion of the authors. 

4. The disadvantage of the manuscript is the lack of cytogenetic karyotyping data, which does not allow understanding the real structure of the karyotype and assessing the presence of marker and rearranged chromosomes.

5. Also, this manuscript lacks information about the karyotypes of parents, which is of great prognostic value for the possibility of having healthy children in couples in the future.

Comments for author File: Comments.pdf

Author Response

We rewrote the Introduction section including the first and now second paragraph to further describe the differences between FISH and CGH. They are different methods with different applications, that is, FISH is based on finding single chromosome defects focused on certain regions of specific chromosomes such as 15q11-q13 in PWS while CGH expands this technology to examine for genetic defects (deletions or duplications) for all chromosomes at once using thousands of DNA probes.  Information on centromeric interference of recombination, mitotic recombination during early embryo development and mosacism with a role in segmental isodisomy was now included in the Discussion section to strengthen the manuscript (noted in red). We added information on cytogenetic karyotyping and Angelman syndrome overlap genetically with PWS as requested.  Thank you for the suggestions.

Reviewer 3 Report

I found a few spelling error but otherwise we’ll written

Author Response

Thank you so much for your review and comments.

Reviewer 4 Report

This is a comprehensive investigation into copy number variation and loss of heterozygosity in chromosome 15q region involved in Prader Willi Syndrome, in a large cohort of patients with this condition. The work is thorough and documents in details the findings, as well as incorporating important implications for clinical practice.

Author Response

Thank you for the review and comments.