Cardiovascular Involvement in SYNE Variants: A Case Series and Narrative Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article by Ravera et al. investigates the cardiovascular effects of SYNE gene variants, presenting four case studies of unrelated patients alongside a review of relevant literature. The authors emphasize the critical role of nesprin-1 and nesprin-2 in cardiomyocytes and propose that SYNE genes be included in routine genetic panels for diagnosing cardiomyopathies and conduction disorders. The review is commendable for addressing a relatively underexplored area, providing real-world clinical evidence that supports the potential pathogenic role of these variants in cardiac conduction diseases and cardiomyopathy. The paper also presents a strong case for the inclusion of SYNE genes in genetic testing, particularly for idiopathic cardiac conduction disorders and dilated cardiomyopathies, which could influence clinical practice, especially in pediatric and early-onset cases. Additionally, the authors offer valuable mechanistic insights by explaining how SYNE variants may disrupt nuclear-cytoskeletal coupling, leading to conduction blocks, arrhythmias, and impaired cardiac function. This opens potential avenues for therapeutic development. Importantly, the paper maintains a balanced discussion by acknowledging the complexity of interpreting SYNE variants, most of which are classified as variants of uncertain significance (VUS), thus highlighting the need for further research without overstating conclusions. However, the study is limited by the small cohort size of only four patients, which may not fully represent the broader population with SYNE-related cardiac issues. Moreover, while the paper focuses on the diagnostic value of identifying SYNE variants, it lacks a detailed discussion of therapeutic interventions or management strategies. The absence of family members for genetic testing in these cases also limits the ability to explore genotype-phenotype correlations more comprehensively.

Specific comments: The introduction provides a clear and concise background on nuclear envelope proteins and their involvement in cardiac disease, effectively setting up the discussion on SYNE variants. However, the authors could have further elaborated on how SYNE variants differ from more commonly studied genes like LMNA. The case series is detailed and informative, although some sections are overly technical and may benefit from simplification to increase accessibility for clinicians who are not specialists in electrophysiology. Each case presents a unique manifestation of SYNE variants, but the lack of familial genetic analysis is acknowledged as a limitation. Nonetheless, the longitudinal follow-up offers valuable insights into disease progression. The discussion of nesprin’s role in the LINC complex and cardiomyocytes is comprehensive, though it would have been beneficial to expand on potential therapeutic interventions, especially regarding the LINC complex in SYNE-related cardiomyopathies. The conclusion reinforces the importance of considering SYNE variants in genetic panels but would be strengthened by a clearer outline of future directions, particularly regarding therapeutic strategies and the utility of SYNE variants in risk stratification for arrhythmias and sudden cardiac death.

Author Response

Reviewer 1

The article by Ravera et al. investigates the cardiovascular effects of SYNE gene variants, presenting four case studies of unrelated patients alongside a review of relevant literature. The authors emphasize the critical role of nesprin-1 and nesprin-2 in cardiomyocytes and propose that SYNE genes be included in routine genetic panels for diagnosing cardiomyopathies and conduction disorders. The review is commendable for addressing a relatively underexplored area, providing real-world clinical evidence that supports the potential pathogenic role of these variants in cardiac conduction diseases and cardiomyopathy. The paper also presents a strong case for the inclusion of SYNE genes in genetic testing, particularly for idiopathic cardiac conduction disorders and dilated cardiomyopathies, which could influence clinical practice, especially in pediatric and early-onset cases. Additionally, the authors offer valuable mechanistic insights by explaining how SYNE variants may disrupt nuclear-cytoskeletal coupling, leading to conduction blocks, arrhythmias, and impaired cardiac function. This opens potential avenues for therapeutic development. Importantly, the paper maintains a balanced discussion by acknowledging the complexity of interpreting SYNE variants, most of which are classified as variants of uncertain significance (VUS), thus highlighting the need for further research without overstating conclusions. However, the study is limited by the small cohort size of only four patients, which may not fully represent the broader population with SYNE-related cardiac issues. Moreover, while the paper focuses on the diagnostic value of identifying SYNE variants, it lacks a detailed discussion of therapeutic interventions or management strategies. The absence of family members for genetic testing in these cases also limits the ability to explore genotype-phenotype correlations more comprehensively.

We thank the reviewer for the overall appreciation of our work. A specific session in the discussion was added concerning the potential therapeutic interventions or management strategies associated with the discovery of nuclear envelope associated proteins variants.

Specific comments: The introduction provides a clear and concise background on nuclear envelope proteins and their involvement in cardiac disease, effectively setting up the discussion on SYNE variants. However, the authors could have further elaborated on how SYNE variants differ from more commonly studied genes like LMNA. The case series is detailed and informative, although some sections are overly technical and may benefit from simplification to increase accessibility for clinicians who are not specialists in electrophysiology.

Thanks for the note, a simplification was made.

Each case presents a unique manifestation of SYNE variants, but the lack of familial genetic analysis is acknowledged as a limitation. Nonetheless, the longitudinal follow-up offers valuable insights into disease progression. The discussion of nesprin’s role in the LINC complex and cardiomyocytes is comprehensive, though it would have been beneficial to expand on potential therapeutic interventions, especially regarding the LINC complex in SYNE-related cardiomyopathies.

The conclusion reinforces the importance of considering SYNE variants in genetic panels but would be strengthened by a clearer outline of future directions, particularly regarding therapeutic strategies and the utility of SYNE variants in risk stratification for arrhythmias and sudden cardiac death.

Thanks for the note, as already mentioned, a specific paragraph was added (Potential therapeutic implications of cardiomyopathy due to nuclear envelope related proteins) concerning the potential therapeutic interventions or management strategies associated with the discovery of nuclear envelope related proteins variants. The importance of these variants for arrhythmic risk stratification was also added to paragraph 3.7.

“Notably, independently from the presence of an associated CCD, when the clinical presentation is a CMP with only a mildly depressed LVEF, there are few recognized genotypes associated with a high risk of sudden cardiac death, that should prompt a tailored arrhythmic risk stratification and eventually ICD implantation. According to the 2023 CMP guidelines, the list currently includes 6 genes, namely LMNA, FLNC (truncating variants), TMEM43, PLN, DSP, RBM20. Therefore, 2 over 6 codify for nuclear envelope related proteins.”

Also, a newly identified patient harboring a C4 SYNE-2 variant was added.

Reviewer 2 Report

Comments and Suggestions for Authors

The topic of the review article ‘Cardiovascular involvement in SYNE variants: a case-series and narrative review’ submitted by Francesco Ravera et al. to Cardiogenetics is interesting. However, this manuscript has several limitations:

1.)   The genetic cases are really not supportive. All variants are currently classified as VUS or benign variants. A co-segregation analysis is missing. Functional data are not presented and the genetic investigations (whole exome sequencing done?, List of variants in other cardiomyopathy genes) are also only partially presented. I have severe doubts if these limitations can be corrected in a revised manuscript.

2.)   However, the review part of this manuscript is partially interesting and provides a good overview but is also missing relevant literature.

3.)   For example, the genetic background of cardiomyopathies needs further explanations. See the following book chapter as a starting point ‘The Genetic Landscape of Cardiomyopathies’.

4.)   It is clear that also mutations in the intermediate filament protein desmin cause cardiomyopathies by impacting the filament assembly process. See: ‘The N-Terminal Part of the 1A Domain of Desmin Is a Hot Spot Region for Putative Pathogenic DES Mutations Affecting Filament Assembly’. Therefore, I would describe how the desmin filaments are  linked to the LINC complex?

5.)    Could you add also the nuclear envelope proteins TMEM43 and LEMD2 to your discussion? For TMEM43, it was recently described generating a zebrafish model that a mutation cause structural defects to the heart. See ‘Altered Expression of TMEM43 Causes Abnormal Cardiac Structure and Function in Zebrafish’ (2022). For LEMD2 it is also clear that is a nuclear envelope protein leading to cardiomyopathies. See ‘Mechanistic Insights of the LEMD2 p.L13R Mutation and Its Role in Cardiomyopathy’. Therefore, I would explain also the affects of mutations in these two nuclear envelope proteins/genes.

In summary, I suggest to rewrite this article and concentrate to submit a clear review article without presenting unclear genetic cases with limited functional, genetic data on specific variants in the SYNE gene. For the review part of this article. I see potential to get a revised manuscript. For the presented genetic data, I see no potential and I am highly wondering, if these cases support the conclusion of the authors.

Author Response

Reviewer 2

The topic of the review article ‘Cardiovascular involvement in SYNE variants: a case-series and narrative review’ submitted by Francesco Ravera et al. to Cardiogenetics is interesting. However, this manuscript has several limitations:

 

1.)   The genetic cases are really not supportive. All variants are currently classified as VUS or benign variants. A co-segregation analysis is missing. Functional data are not presented and the genetic investigations (whole exome sequencing done?, List of variants in other cardiomyopathy genes) are also only partially presented. I have severe doubts if these limitations can be corrected in a revised manuscript.

Overall, we agree with the Reviewer that genetics is not conclusive for most of our patients at this stage. We would however like to point out that all 5 patients were tested using the True Sight One Clinical Exome Sequencing kit by Illumina, as indicated in the text, with analysis centered on pertinent in silico panels. Additionally, deletions of LMNA gene were ruled out by MLPA analysis, as indicated in the text. Family segregation studies are not possible for these families, since potentially informative relatives are lacking.

So, while we agree on the inconclusiveness of genetic data, we would like to stress that SYNE genes were not present in the Illumina Cardio Panel that was extensively used worldwide to test mutations in heart genes. Therefore, knowledge on the prevalence and relevance of genetic variants of these genes remains very limited and the report of single patient cases bearing variants including those that are currently classified as of unknown significance may be useful in acquiring critical information. For this reason, we would like to keep the patient case descriptions on the paper and not limit it to a review article.  Furthermore, a newly identified patient harboring a C4 SYNE-2 variant was added (patient 5).

 

2.)   However, the review part of this manuscript is partially interesting and provides a good overview but is also missing relevant literature.

3.)   For example, the genetic background of cardiomyopathies needs further explanations. See the following book chapter as a starting point ‘The Genetic Landscape of Cardiomyopathies’.

Thanks for the note. All the suggestions reported below concerning nuclear envelope related proteins have been followed, leading to a considerable expansion and improvement of the text.  On the other hand, we believe that a comprehensive discussion on the overall genetic landscape of cardiomyopathies is beyond the scope of the present review. We therefore would favor keeping the current structure, but are available, if the Reviewer and the Editor consider this more detailed discussion compulsory, to comply with their indication.  

 

4.)   It is clear that also mutations in the intermediate filament protein desmin cause cardiomyopathies by impacting the filament assembly process. See: ‘The N-Terminal Part of the 1A Domain of Desmin Is a Hot Spot Region for Putative Pathogenic DES Mutations Affecting Filament Assembly’. Therefore, I would describe how the desmin filaments are  linked to the LINC complex?

We appreciate the comment, dedicated parts have been added interspersed to the text.  A new updated figure 2 has been created including SYNE-3, luma and lemd2.

 

5.)    Could you add also the nuclear envelope proteins TMEM43 and LEMD2 to your discussion? For TMEM43, it was recently described generating a zebrafish model that a mutation cause structural defects to the heart. See ‘Altered Expression of TMEM43 Causes Abnormal Cardiac Structure and Function in Zebrafish’ (2022).

We appreciate the comment, dedicated parts have been added interspersed to the text. A new updated figure 2 has been created including SYNE-3, luma and lemd2.

For LEMD2 it is also clear that it is a nuclear envelope protein leading to cardiomyopathies. See ‘Mechanistic Insights of the LEMD2 p.L13R Mutation and Its Role in Cardiomyopathy’. Therefore, I would explain also the effects of mutations in these two nuclear envelope proteins/genes.

We appreciate the comment, dedicated parts have been added interspersed to the text. A new updated figure 2 has been created including SYNE-3, luma and lemd2.

In summary, I suggest to rewrite this article and concentrate to submit a clear review article without presenting unclear genetic cases with limited functional, genetic data on specific variants in the SYNE gene. For the review part of this article. I see potential to get a revised manuscript. For the presented genetic data, I see no potential and I am highly wondering, if these cases support the conclusion of the authors.

We thank the reviewer for the constructive comments. As previously expressed, we still believe that our findings, now including 4 VUS and one C4 SYNE variant, are worth reporting with the scope of not missing a potentially very significant genotype-phenotype association. Furthermore, the fact that 33% of the genes currently associated with a high risk of sudden cardiac death despite an only mildly depressed LVEF, codify for nuclear envelope related proteins mandates extreme caution before dismissing variants potentially associated with dysfunction of these proteins, as now added also to the text.

We hope the Reviewer might find the current, revised version of the manuscript acceptable for publication.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

THe authors have improved their manuscript significantly. I really like their novel figure! Congratulation. In summary I suggest to accept this manuscript for publication.