Mutation in the STXBP1 Gene Associated with Early Onset West Syndrome: A Case Report and Literature Review

Round 1

Reviewer 1 Report

The article entitled “ STBX1 gene associated with symptomatic West syndrome” describes a case diagnosed with West syndrome and later received the genetic diagnosis of STXB1 gene missense mutation.

 

The article describes the underlying genetic etiology of early infantile epileptic encephalopathy in infants, to be considered one of the etiologic factors. The authors also reviewed the function of this gene and the potential mechanism for epileptogenesis. 

 

1.      Article is overall well written, however, the specific aim for this case report was lost in the details. The authors may consider reorganizing the manuscript around the discussion of STXB1 mutation leading to early onset infantile spasm in young infants. In this case report, the early EEG demonstrated non-specific EEG findings although the figure was not provided. Later at around 2.5 months of age, the child was diagnosed with infantile spasm. Unfortunately, the genetic diagnosis was made much later when the child reached the age of 1.5 years. The causes of early onset infantile spasms following newborn seizures are worth reviewing in light of this case.  The introduction could be centered around the etiologies listed for early onset infantile spasms and potential causes.

2.      Please review the earlier course of the case, particularly the newborn period and following the seizure diagnosis, and the other clinical features including the neurodevelopmental course. Lack of response to ACTH and the other treatments, and multiple seizure types are the potential clues leading to STXB1 gene mutation in this case report.

3.      Please provide additional figures for early EEG findings for the newborn period.

4.      Discussion could focus on the earlier reports of STXB1 genetic mutation associated with suppression burst EEG pattern and EEIE, published in 2010. The article by Saitsu et al, published in Epilepsia should be added to the citation list. This case does not have burst suppression EEG and therefore the diagnosis of this genetic condition despite seizure onset in the newborn period may be missed. This is worth mentioning for the reviewers.

5.      I would consider changing the title of the manuscript to “ Mutation in the STXB1 gene associated with early onset West syndrome and literature review” as such.

 

6.      I would avoid using symptomatic WEST syndrome as classification which is no longer recommended. The best to describe this epileptic syndrome is to use West syndrome associated with genetic etiology. 

Author Response

Response to Reviewer 1 Comments

Thank you for your review of our paper. We have answered each of your points below.

 

1. Article is overall well written, however, the specific aim for this case report was lost in the details. The authors may consider reorganizing the manuscript around the discussion of STXB1 mutation leading to early onset infantile spasm in young infants. In this case report, the early EEG demonstrated non-specific EEG findings although the figure was not provided. Later at around 2.5 months of age, the child was diagnosed with infantile spasm. Unfortunately, the genetic diagnosis was made much later when the child reached the age of 1.5 years. The causes of early onset infantile spasms following newborn seizures are worth reviewing in light of this case. The introduction could be centered around the etiologies listed for early onset infantile spasms and potential causes.

 

I appreciate your suggestion. In line with your comment, our introduction has been remarkably changed to include information on the causes of neonatal-onset epilepsy, with regard to developmental epileptic encephalopathy (DEE) occurring in the neonatal period, STXBP1 gene mutations as a cause and infantile spasm as a phenotype of the same mutation. The genes responsible for IS were also discussed.

 

2. Please review the earlier course of the case, particularly the newborn period and following the seizure diagnosis, and the other clinical features including the neurodevelopmental course. Lack of response to ACTH and the other treatments, and multiple seizure types are the potential clues leading to STXB1 gene mutation in this case report.

 

I appreciate your advice. We added the following to the discussion: the symptom details and our consideration about the seizure diagnosis (in lines 182-188), and the other clinical features including the neurodevelopmental course (in lines 208-223), response to ACTH and the other treatments (in lines 224-247), and multiple seizure types (in lines 202-207).

 

3. Please provide additional figures for early EEG findings for the newborn period.

 

Thank you for your suggestion. Our patient was originally transferred to our hospital at 2 months of age and the original EEG data was returned to the previous hospital. Therefore, it would be impossible to add the data in time and would require approval from the ethics committee of the previous hospital. For this reason, I added more detailed EEG findings in the neonatal period to this paper because I checked the neonatal EEG findings by myself that the patient brings with them at the time of introduction(in lines 80-82).

 

4. Discussion could focus on the earlier reports of STXB1 genetic mutation associated with suppression burst EEG pattern and EEIE, published in 2010. The article by Saitsu et al, published in Epilepsia should be added to the citation list. This case does not have burst suppression EEG and therefore the diagnosis of this genetic condition despite seizure onset in the newborn period may be missed. This is worth mentioning for the reviewers.

 

Thank you for your suggestion. We have added the paper you mentioned and dicussed the course of this case. The patient did not have a suppression-burst pattern in the early stages and an epileptic spasm was not the first symptom. Although many reports described that the clinical spectrum of STXBP1 mutations may be broader and there are differences between reports on the early features of onset, the presence of EEG suppression burst patterns and epileptic spasms may better characterise STXBP1 encephalopathy; however, even when there is not a noticeable early EEG suppression burst pattern, as our case, the likelihood of STXBP1 mutation should be considered. We added these comments in lines 188-199.

 

5. I would consider changing the title of the manuscript to “ Mutation in the STXB1 gene associated with early onset West syndrome and literature review” as such.

 

I appreciate your suggestion. We also believe that the title you have suggested is appropriate, and thus, we have modified the title of this article to “Mutation in the STXB1 gene associated with early onset West syndrome: A case report and literature review”

 

6. I would avoid using symptomatic WEST syndrome as classification which is no longer recommended. The best to describe this epileptic syndrome is to use West syndrome associated with genetic etiology.

 

Thank you for your suggestion. I corrected the title of this article and the expression in lines 103, 171–172 of the text.

Reviewer 2 Report

This manuscript is clinical case report of a single patient presenting recurrent episodes of severe epilepsy and seizures. The patient was found to have a mutation in STXBP1 gene (R292H) which was previously reported in ClinVar (rs796053361) as a pathogenic variant. Overall the manuscript provides a detailed description of the clinical presentation and therapeutic strategies utilized to treat this patient that could be of interest to the reader and benefit future patients. However, the manuscript would need some improvements to better describe some clinical  and genetics findings as listed below:

1- From the text it is not clear whether the STXBP1 variant found in this patient is mono- or ballelic?

2- How was the STXBP1 variant identified? Full Exome / Whole genome/ targeted sequencing? If full Exome / Whole genome sequencing was used, did they found any additional variant, it would be important to disclosed a list of all potential variant that may directly or indirectly contribute to disease. IF target sequencing was performed, it would need to be stated that it remains to be investigated whether other unknown variant beside STXBP1-R292H may have contributed to clincal phenotype.

3- It would important that authors mention whether the patient manifested with any other symptoms beside the neurological phenotype extensively describe. For example, there is information in the literature that suggest that STXBP1  is also involved in immune cell function (CD8 cytotoxic activity) , does this patient present any immune dysregulation, repetitive infection or hyper inflammatory condition? How about metabolic disorder (diabetes, etc).

 

Author Response

Response to Reviewer 2 Comments

Thank you for your review of our paper. We have answered each of your points below.

 

Point 1: From the text, it is not clear whether the STXBP1 variant found in this patient is mono- or bi-allelic?

 

Response 1:

I appreciate your suggestion. A monoallelic STXBP1 variant is present in this patient, and we noted this in the figure legend (Lines 161-162).

 

Point 2: How was the STXBP1 variant identified? Full Exome / Whole genome/ targeted sequencing? If full Exome/ Whole genome sequencing was used, did they found any additional variant, it would be important to disclosed a list of all potential variant that may directly or indirectly contribute to disease. IF target sequencing was performed, it would need to be stated that it remains to be investigated whether other unknown variant beside STXBP1-R292H may have contributed to clincal phenotype.

 

Response 2:

Thank you for your suggestion. As I wrote in lines 136-138, target capture sequencing was performed to screen 114 epilepsy-related genes in the proband of the Department of Pediatrics at Fukuoka. Other unidentified variants in addition to STXBP1-R292H may have contributed to her clinical phenotype because she did not undergo whole genome or whole exome sequencing as you pointed out. Accordingly, we have added this statement in the text in lines 145-147.

 

Point 3: It would important that authors mention whether the patient manifested with any other symptoms beside the neurological phenotype extensively describe. For example, there is information in the literature that suggest that STXBP1  is also involved in immune cell function (CD8 cytotoxic activity), does this patient present any immune dysregulation, repetitive infection or hyper inflammatory condition? How about metabolic disorder (diabetes, etc).

 

Response 3:

I appreciate your advice. As a result, up to the preparation of this report, the patient had no symptoms other than the neurological phenotype. First, she is anatomically normal. Second, she did not have a metabolic condition since when we tested her blood and urine for amino acids and organic acids, respectively, there were no pathogenic findings. Last, she did not have a reduced glucose tolerance despite receiving ACTH therapy.

 

The patient had a history of infection from the immune system's perspective. She experienced urinary tract infections at 11 months and aspiration pneumonia at 6 months and 1.3 years of age. There were no aberrant results from her routine blood tests for the immune system, including the level of immunoglobulins and the differential count of leukocytes. During these infectious times, she did not have a hyperinflammatory state. Given the burden on the patient, no additional research was conducted because the aspiration and the existence of a neurogenic bladder made it evident what caused the infection, and the course of therapy was successful.

As you suggested, we discovered papers about the functional role of STXBP1 in NK and cytotoxic T-cell cytotoxicity [1,2]. Accordingly, we tried to verify her immune system detail connected to NK and cytotoxic T-cell cytotoxicity if she had a recurring viral infection and a high level of inflammation. We have added the statement you pointed out to us in the text in lines 165-167 of the text.

 

References:

1. Lopez, J.A.; Noori, T.; Minson, A.; Jovanoska, L.L.; Thia, K.; Hildebrand, M.S.; Akhlaghi, H.; Darcy, P.K.; Kershaw, M.H.; Brown, N.J.; et al. Bi-Allelic Mutations in STXBP2 Reveal a Complementary Role for STXBP1 in Cytotoxic Lymphocyte Killing. Front Immunol 2018, 9, doi:10.3389/fimmu.2018.00529.
2. Gipson, K.F.J.K.T.B.; Author, A.; Massachusetts; General Hospital, B.U.S.; Correspondence, A.; K. Gipson, M.G.H.B.U.S.E.; kgipson@mgh.harvard.edu; Full Record Entry, D. Syntaxin Binding Protein 1 Mutation in a 3-Year-Old Female with Recurrent Viral Pneumonia. In Am J Respir Crit Care Med; American Thoracic Society International Conference Abstracts; American Thoracic Society, 2017; Vol. 195., pp. A6168–A6168.

Reviewer 3 Report

We thank for submitting this valuable case report to our MDPI journal of pediatric reports. I read a case report of symptomatic West syndrome with genetic abnormalities of STBPX1.This case report is described in the formal style. I see no reason to reject this report. However, there are several major modification requests to have this report for accept. Please answer all items faithfully. If you do not have an appropriate response due to my insufficient knowledge of pediatric neurology field, please reply with the authors' opinions.

The title is appropriate. However, the key words need improvement. The reason is that the terms in the title are already searched in PubMed. Therefore, listing important terms other than the title as keywords will increase the hit rate of PubMed searches. Authors should change the two terms in the keywords.

The introduction is brief and clear. However, if this paper were submitted for publication in Pediatric Neurology, Journal of Child Neurology, Brain and Development, the comment would be. This journal to which the author submitted the article is a journal of general pediatrics. Therefore, it would be desirable to add a more detailed definition of the disease, e.g., West syndrome is..., which would be easier for the general pediatrician to understand.

Several antiepileptic drug (AED) medications were tried in sequence in the case description. While there is nothing wrong with the choice of drug, we would like to see additions to the dosage or whether it is changed with sufficient blood concentration. This is because the treatment of symptomatic West syndrome is a difficult process experienced by many pediatric neurologists. Therefore, it would be desirable to add the dosage and blood concentration of AEDs (or add a Table of the course of treatment). In particular, vitamin B6 therapy and ACTH therapy should be added, as dosage and methods vary from country to country.

This is a point that many neurologists wonder, does this case really fit the definition of symptomatic West syndrome? Are the early epileptic seizures myoclonic? Were series-forming seizures present? Were there any developmental problems from birth rather than psycho-intellectual regression? Has an electroencephalogram (EEG) demonstrated hypersalmia? ...The basis for these diagnoses is key and should be clearly stated (as described in the introductory remarks).

How would you rule out this condition when it is indicated as Otawara syndrome, early infantile epileptic encephalopathy, or early infantile microneurosis? Please add a reason for the differential diagnosis.

What is the next treatment of choice for epilepsy syndromes associated with such genetic abnormalities?
What is the next treatment of choice for epilepsy syndrome with such a genetic abnormality? Have a ketone diet or epilepsy surgery been considered? Are cannabioids indicated? If you have any comments, please add them to the case or discussion.

What other genetic abnormalities were tested for, such as ARX?

Was an MRI taken after ACTH, and is the atrophy in the frontal dominance on the MRI due to ACTH? Or is it associated with developmental delay?

I think the table is of very good quality.

Please reconsider the discussion if necessary after making corrections according to the previous several comments.

Overall this report is very good. Please re-submit it with an arrangement that is easier for many pediatricians to understand and with evidence that clarifies the basis for the authors' diagnosis of symptomatic West syndrome. The reviewers look forward to re-reviewing this report, which has improved to the best quality.

 

Author Response

Response to Reviewer 3 Comments

Thank you for your review of our paper. We have answered each of your points below.

 

Point 1: The title is appropriate. However, the key words need improvement. The reason is that the terms in the title are already searched in PubMed. Therefore, listing important terms other than the title as keywords will increase the hit rate of PubMed searches. Authors should change the two terms in the keywords.

 

Response 1:

I appreciate your suggestion. I changed the two keywords (West syndrome and the STXBP1 gene) to ACTH therapy and severe intellectual disability according to your advice.

 

Point 2: The introduction is brief and clear. However, if this paper were submitted for publication in Pediatric Neurology, Journal of Child Neurology, Brain and Development, the comment would be. This journal to which the author submitted the article is a journal of general pediatrics. Therefore, it would be desirable to add a more detailed definition of the disease, e.g., West syndrome is..., which would be easier for the general pediatrician to understand.

 

Response 2:

I appreciate your advice. I added lines (42–63) with references to the epileptic syndromes that can develop in STXBP1 encephalopathy and the features of West syndrome as per your suggestion.

 

Point 3: Several antiepileptic drug (AED) medications were tried in sequence in the case description. While there is nothing wrong with the choice of drug, we would like to see additions to the dosage or whether it is changed with sufficient blood concentration. This is because the treatment of symptomatic West syndrome is a difficult process experienced by many pediatric neurologists. Therefore, it would be desirable to add the dosage and blood concentration of AEDs (or add a Table of the course of treatment). In particular, vitamin B6 therapy and ACTH therapy should be added, as dosage and methods vary from country to country.

 

Response 3:

Thank you for your comments. We agree with your opinion that the treatment of symptomatic West syndrome is difficult and needs to be described better. In line with your comment, we have added a diagram of the patient's treatment progress. In this diagram, the dosage of ASMs is given and, within the notes, the blood levels are listed. Pyridoxal phosphate hydrate 30 mg/kg/day as vitamin B6 therapy and tetracosactide acetate 0.0125 mg/kg/day as ACTH therapy. The numbers in the subsequent figures have been corrected due to the addition of more figures.

 

Point 4: This is a point that many neurologists wonder, does this case really fit the definition of symptomatic West syndrome? Are the early epileptic seizures myoclonic? Were series-forming seizures present? Were there any developmental problems from birth rather than psycho-intellectual regression? Has an electroencephalogram (EEG) demonstrated hypersalmia? ...The basis for these diagnoses is key and should be clearly stated (as described in the introductory remarks).

 

Response 4:

Thank you for your suggestion. We answered your question and also added an additional note in the text.

1. Does this case really fit the definition of symptomatic West syndrome?

The patient experienced bilateral tonic-clonic seizures and had multifocal focal abnor-malities on the EEG from the beginning of her epilepsy, but not a suppression-burst pattern. Consequently, neither the conventional EIEE nor the EME diagnosis was established, and the patient was first considered to be in a condition of DEE with no specific syndrome diagnosis and was followed up. Subsequently, the seizure type and EEG findings changed to hypsarhythmia, developmental regression was observed and the condition was diagnosed as West syndrome within the concept of DEE. I added these in lines 182-187 of the text.

 

2. Are the early epileptic seizures myoclonic? Were series-forming seizures present?

At age 15 days, she presented with bilateral tonic-clonic seizures that lasted for a few minutes, which started in the left upper extremity. When the patient was transferred to our hospital, the seizures were similar, but the onset was both left and right (added to lines 85-86) and these were not myoclonic and series-forming seizures.

 

3. Were there any developmental problems from birth rather than psycho-intellectual regression?

There were no developmental problems from birth. Eye-tracking and smiling when someone touched or hold her were appropriate for infant age the first time the patient came to our hospital.

 

4. Has an electroencephalogram (EEG) demonstrated hypsarrisumia?

Interictal EEGs of IS are characterized by hypsarrhythmia with chaotic, nonrhythmic, asynchronous, disorganized, high-voltage spike and slow-wave activity and we observed these states in this case. Although a small amount of increased interhemispheric synchronisation was sometimes observed, multiple careful recordings and discussions led to the conclusion that the above features persisted as basic findings, and therefore a hypsalysmia was concluded. We wrote in lines 119–120.

 

Point 5: How would you rule out this condition when it is indicated as Otawara syndrome, early infantile epileptic encephalopathy, or early infantile microneurosis? Please add a reason for the differential diagnosis.

 

Response 5:

Thank you for your suggestion. We added the the reasons for the diagnosis of this case as West syndrome have been added to the Discussion in lines 182–187.

 

Point 6: What is the next treatment of choice for epilepsy syndromes associated with such genetic abnormalities? What is the next treatment of choice for epilepsy syndrome with such a genetic abnormality? Have a ketone diet or epilepsy surgery been considered? Are cannabioids indicated? If you have any comments, please add them to the case or discussion.

 

Response 6:

I appreciate your suggestion. Treatment options should be determined by the type of genetic abnormality, and thus my answer is on STXBP1 encephalopathy. According to previous studies, about 25% of those with STXBP1 encephalopathy were resistant to ASM therapy, and more than 20% of those with the condition required the use of two or more ASMs together [1]. The ketogenic diet was tried to treat a seizure in about 1% of patients with STXBP1 encephalopathy, and response to the diet was either minimal or nonexistent [2,3]. The chosen course of treatment for epilepsy was surgery, such as corpus callosotomy [4] and resection of the patient's affected cortex if they have focal cortical dysplasia [2]. I added these states in lines 224–230.

 

There was a case report of cannabinoids being effective in reducing seizures in an adult patient with Dravet syndrome with STXBP1 gene mutation [5]; however, our case does not apply to the clinical form of EIEE and the drug is not approved in Japan, so we did not consider this case. If the seizures worsen in the future, we will review the choice of drug according to the seizure type and consider palliative epilepsy surgical treatment to reduce seizure frequency. I added this comment to the case in lines 167–169.

 

Point 7: What other genetic abnormalities were tested for, such as ARX?

 

Response 7:

Thank you for your comment. Target capture sequencing was used to examine 114 genes associated with epilepsy in the proband of the Department of Pediatrics in Fukuoka, as I noted in lines 136-138. These genes included ARX, SCN1A, CDKL5, and many others.

 

Point 8: Was an MRI taken after ACTH, and is the atrophy in the frontal dominance on the MRI due to ACTH? Or is it associated with developmental delay?

 

Response 8:

I appreciate your comments. We believe that ACTH therapy may have had an influence, as there is a history of conspicuous frontal atrophy on head MRI after ACTH therapy. However, as diffuse cerebral atrophy has been noted in STXBP1 encephalopathy itself [6], we believe that there is a definite possibility of an effect of the original genetic abnormality.

 

References:

1. Deprez, L.; Weckhuysen, S.; Holmgren, P.; Suls, A.; van Dyck, T.; Goossens, D.; Del-Favero, J.; Jansen, A.; Verhaert, K.; Lagae, L.; et al. Clinical Spectrum of Early-Onset Epileptic Encephalopathies Associated with STXBP1 Mutations. Neurology 2010, 75, 1159–1165, doi:10.1212/WNL.0b013e3181f4d7bf.
2. Weckhuysen, S.; Holmgren, P.; Hendrickx, R.; Jansen, A.C.; Hasaerts, D.; Dielman, C.; de Bellescize, J.; Boutry-Kryza, N.; Lesca, G.; Spiczak, S. von; et al. Reduction of Seizure Frequency after Epilepsy Surgery in a Patient with STXBP1 Encephalopathy and Clinical Description of Six Novel Mutation Carriers. Epilepsia 2013, 54, 74–80, doi:10.1111/epi.12124.
3. Saitsu, H.; Hoshino, H.; Kato, M.; Nishiyama, K.; Okada, I.; Yoneda, Y.; Tsurusaki, Y.; Doi, H.; Miyake, N.; Kubota, M.; et al. Paternal Mosaicism of an STXBP1 Mutation in OS. Clin Genet 2011, 80, 484–488, doi:10.1111/j.1399-0004.2010.01575.x.
4. Otsuka, M.; Oguni, H.; Liang, J.S.; Ikeda, H.; Imai, K.; Hirasawa, K.; Imai, K.; Tachikawa, E.; Shimojima, K.; Osawa, M.; et al. STXBP1 Mutations Cause Not Only Ohtahara Syndrome but Also West Syndrome-Result of Japanese Cohort Study. Epilepsia 2010, 51, 2449–2452, doi:10.1111/j.1528-1167.2010.02767.x.
5. Álvarez Bravo, G.; Yusta Izquierdo, A. The Adult Motor Phenotype of Dravet Syndrome Is Associated with Mutation of the STXBP1 Gene and Responds Well to Cannabidiol Treatment. Seizure 2018, 60, 68–70, doi:10.1016/j.seizure.2018.06.010.
6. Stamberger, H.; Nikanorova, M.; Willemsen, M.H.; Accorsi, P.; Angriman, M.; Baier, H.; Benkel-Herrenbrueck, I.; Benoit, V.; Budetta, M.; Caliebe, A.; et al. STXBP1 Encephalopathy: A Neurodevelopmental Disorder Including Epilepsy. Neurology 2016, 86, 954–962, doi:10.1212/WNL.0000000000002457.

Round 2

Reviewer 3 Report

The reviewers have seen the revised resubmitted paper by the authors.

Thank you for the satisfactory revision of the title, keywords, and introduction. I also checked the description of other differential diagnoses such as Oawara syndrome and early myoclonic encephalopathy. Thank you also for the addition about the epilepsy gene panel test performed at Fukuoka University. Overall, the case reports, including the discussion, were of a very high level.

As a reviewer, I also learned a lot from this paper. I hope you will continue your efforts in the treatment of neurological intractable diseases and epilepsy. I look forward to the publication of your paper.

 

Best regards,

Dr. Reviewer