Disrupted epigenetic regulation causes
syndromes of overgrowth
- A systematic review
Version 2
Author: Nadine Norlin,
Bachelor of Medicine
Supervisor: Ola Nilsson, MD, PhD
Örebro University School of Medicine Degree project, 30 ECTS January 12th, 2018
Table of content
Abstract ... 3
Introduction ... 4
Aim ... 5
Material and methods ... 5
Data collection ... 5 Qualitative analysis ... 8 Ethics ... 8 Results ... 8 Discussion ... 11 Conclusion ... 13 Acknowledgement ... 13 References ... 14 Appendices ... 17 Appendix 1. ... 17 Appendix 2. ... 18 Appendix 3. ... 20 Appendix 4. ... 24 Populärvetenskaplig sammanfattning ... 25 Cover letter ... 26 Ethical considerations ... 27
Abstract
Introduction: Mutations in genes involved in regulating epigenetic marks, e.g. DNA and histone methylation, are major causes for syndromes of overgrowth and intellectual disability. Affected individuals share phenotypic traits with similar facial appearance, tall stature,
macrocephaly and intellectual disability.
Aim: To conduct a thorough investigation of available, scientific studies explaining how a mutation in a gene responsible for epigenetic regulation can result in a syndrome of
overgrowth. A secondary aim was to illustrate similarities and differences between distinct syndromes of overgrowth.
Material and methods: Systematic review, search conducted in PubMed database using broad search terms. Only articles in English and published after year 2000. Twenty-six
observational studies included. Quality assessment using SBU:s system, based on the GRADE system.
Results: Mutations in nine different genes involved in creation and maintenance of epigenetic marks have been found and so far all identified mutations are loss-of-function mutations. Mutations in the NSD1 gene were most frequently found, associated with Sotos syndrome. Several syndromes are similar, especially when it comes to phenotype. Common traits are tall stature, macrocephaly, intellectual disability and advanced bone age. The strength of evidence to address the primary aim was graded to be moderately strong (+++0).
Conclusion: Phenotypic and molecular overlap between different syndromes of overgrowth was observed. Several of the causative mutations were loss-of-function in genes that produce epigenetic marks that regulate gene transcription, thus causing abnormal expression of growth genes. Further research is required to fully assess the molecular mechanisms underlying syndromes of overgrowth.
Key words: epigenetic regulation, loss-of-function, overgrowth, macrocephaly, intellectual disability
Introduction
Linear growth of children is the result of chondrogenesis at growth plates [1], thin layers of cartilage located at the ends of long bones and vertebrae [1]. Chondrogenesis is the process where new cartilage is made, remodelled and eventually turned in to bone [2]. The net result is bone elongation and therefore an increase in height.
Growth plate chondrogenesis is continuous and under the influence of multiple systemic and local factors [3]. Among the systemic factors influencing linear growth are nutritional intake, hormones and inflammatory cytokines [3]. For example, growth hormone (GH), produced from the pituitary gland induce insulin-like growth-factor-1 (IGF-1), in the liver, which in turn acts on the growth plate to increase chondrogenesis and therefore growth [4]. Several other hormones also regulate linear growth, including thyroid hormone, glucocorticoids, oestrogens and androgens [1]. In addition, many local factors and molecules are necessary for normal growth plate chondrogenesis, including paracrine factors, intracellular regulatory mechanisms in the chondrocytes and cartilage ECM components. What all these systemic and local factors have in common is the fact that they affect the growth plate [3]. Consequently, all forms of short stature are due to decreased growth plate chondrogenesis and all forms of tall stature are due to increased growth plate chondrogenesis.
Identifying genetic causes of short and tall stature syndromes have greatly contributed to our understanding of growth regulation. The development of new genetic testing methods,
including massive parallel sequencing, have lead to increasing possibilities to identify genetic causes underlying previously unknown monogenic syndromes, including those syndromes affecting growth [1]. One recent discovery is that several cases of extreme tall stature are caused by mutations in genes that have an impact on epigenetic gene regulation. Epigenetics has been defined as “the study of changes in gene function that are mitotically and/or
meiotically heritable and that do not entail a change in DNA sequence” [5]. Epigenetic marks are inherited and can be modified during development in different ways, for example through methylation of nucleotides and alteration of chromatin structure [5]. A mutation in a gene responsible for epigenetic gene regulation can result in a syndrome of overgrowth if the mutation occurs in a gene involved in regulation of linear growth. A few syndromes of overgrowth are today relatively well known, for example Sotos syndrome, which is most commonly caused by mutations in the NSD1 gene[6]. There is an apparent overlap between several of the syndromes of overgrowth, both clinically and genetically. For instance, there is
a considerable phenotypic overlap between Sotos syndrome and Weaver syndrome [7]. Weaver syndrome is a syndrome that most often arises form a mutation in the EZH2 gene[6]. Also, in the literature, many individuals have been described to have a Sotos-like phenotype, but have not tested positive for a mutation in the NSD1 gene, leading to the assumption that other genes can cause a similar phenotype, beside Weaver syndrome [8]. In an article by Dong H-Y et al, from 2016, mutations in the NFIX gene can result in a syndrome of overgrowth, (Malan syndrome), with a Sotos-like phenotype [8]. Common traits for most individuals affected by different syndromes of overgrowth have been illustrated to be tall stature, macrocephaly, and intellectual disability, varying in severity [6]. Many of the known epigenetic genes causing syndromes of overgrowth have also been shown to be quite similar when it comes to their molecular mechanisms, where for example both NSD1 and EZH2 encode methyl transferases involved in the regulation of transcription [7].
The understanding of the phenotypic spectrum and the pathogenic mechanisms of these newly found syndromes of overgrowth is limited, but rapidly improving.
Aim
The primary aim of this systematic review is to conduct a thorough investigation of available, scientific studies explaining how a mutation in a gene responsible for epigenetic gene
regulation can result in syndromes of overgrowth. A secondary aim, with the aid of scientific literature, is to illustrate similarities and differences between distinct syndromes of
overgrowth.
Material and methods
Data collectionArticles were searched for in PubMed database and to ensure that the whole field of research was completely covered, and that the research question was properly answered, broad search terms were set up and the search was conducted using both MeSH-terms and words in free text. The search terms were then divided into two categories; “Exposure” or “Outcome”, where words included under “Exposure” were meant to cover different factors, mutations or alterations that could lead to the “Outcome”, which in turn meant different terms for
overgrowth and/or overgrowth syndromes. The search terms are presented in Figure 1. After searching “Exposure” and “Outcome” separately a combined search of the two categories was
conducted. Inclusion criteria were set up, where only articles in English that had been published after year 2000 were considered for inclusion. A number of 93 items were found and scanned to determine whether they addressed the primary or secondary aim. The entire search process and selection of articles is presented in Figure 2. During the reduction process, 68 articles were excluded because they did not address aim one or two. Some examples why articles were excluded:
•! Articles covering symptoms, management, and/or diagnostic tests without addressing the underlying pathogenic mechanism
•! Articles describing mutations in genes regulating the epigenome, without mentioning the connection with tall stature
•! Articles about tall stature that is not caused by mutations in epigenetic genes
Again, the overriding cause of why articles were excluded was that they did not answer either of the aims set up for this systematic review. A full list of reasons for exclusion is presented in Appendix 1.
Exposure MeSH-terms:
! Epigenesis, genetic ! DNA methylation
! EZH2 (Enhancer of Zeste Homolog 2) Free text searches:
! Epigenetic mutations ! Epigenetic regulation ! Chromatin formation ! Overgrowth genes
! DNMT3A (DNA methyltransferase 3A) ! NSD1 (NSD1 protein, human)
! CHD8 (CHD8 protein, human) ! EED (EED protein, human) ! HISTH1E
Outcome MeSH-terms:
! Sotos syndrome Free text searches:
! Body overgrowth
! Epigenetic overgrowth syndromes ! Overgrowth with intellectual disability ! Tall stature
! Syndromes of tall stature ! Weaver syndrome
Finally, 25 articles were considered for inclusion. However, two of these were review articles. To ensure a high quality of this study the two review articles were excluded from the material, but their respective reference lists were searched to see if any of the original articles included in the reviews fitted our aim and could be included in this study. After repeating a selection process equal to the one in Figure 2, three additional articles were included in the material resulting in a total number of 26 articles included in this systematic review.
PubMed search (exposure) 132 774 items PubMed search (outcome) 783 items PubMed search (exposure + outcome) 93 items 63 items excluded 30 items included 25 items included 23 items included (observational studies) 26 items included (final inclusion) 2 items excluded (review articles) 3 items included 5 items excluded Reading abstracts
Reading in full text
Reading references
Qualitative analysis
Once included, all 26 articles were thoroughly read and assessed by the author of this review, and independently reviewed by the supervisor of this project. To analyse the quality of the included articles in a well recognized order, SBU:s system for grading scientific evidence was used [9]. SBU uses different systems depending on which study design the article has. All of the included articles in this systematic review are observational studies, and for this SBU uses a system partly based on the international GRADE system [10]. The strength of evidence in the studies is classified as; strong (++++), moderately strong (+++0), limited (++00) or insufficient (+000) [9]. Depending on which study design an article has, it is given a
preliminary strength of evidence, where observational studies are considered to have limited (++00) strength. The preliminary strength can then be graded up or down depending on the overall quality of the study, which is judged according to five different variables:
•! Study quality
•! Consistency/ Coherence •! Relevance/ Generalizability •! Data precision
•! Risk of publication bias
A conclusive assessment of the individual strength of evidence for all included studies is presented in Appendix 2.
Ethics
Since this study is a systematic review, an ethical approval is not required. We have however reviewed all included articles regarding application for ethical approval and if the patients had given informed consent. How and if the authors presented these factors was taken into
consideration when assessing the articles individual strength of evidence.
Results
A total of 26 articles were included in this systematic review and strength of evidence was graded (Appendix 2). One graded to have strong (++++) [6], ten to have moderately strong (+++0) [11-20], nine to have limited (++00) [21-29] and six to have insufficient (+000) [30-35] strength of evidence. The majority of the articles were considered to be of moderately
strong strength of evidence, but since many articles also were of limited or insufficient strength of evidence and only one was assessed to be strong, the overall strength was graded to limited strength of evidence.
A total of nine different genes affecting epigenetic regulation were found from the material included in this systematic review. Twenty-five of the included 26 articles addressed one, two or three different genes and the associated phenotype. In Appendix 3, a summarized picture of these articles is presented. However, there was one article that was particularly well executed, covering six different epigenetic regulatory genes and their relationship to syndromes of overgrowth [6]. This article is summarized and presented in Appendix 4. In this study, 710 individuals with overgrowth and intellectual disability were tested with targeted gene
analysis. The targeted genes were genes already known to cause overgrowth and intellectual disability. If no mutation was found using this technique, an unbiased search for causative genetic variants was performed using exome sequencing. Using strict criteria, 49.7 % (353 of 710 individuals) of the participants were found to have a pathogenic mutation in one of 14 genes (Fig 3). Six of these 14 genes ie. NSD1, EZH2, DNMT3A, CHD8, HISTH1E and EED, are known to have an effect on epigenetic regulatory mechanisms and accounted for as many as 43.8 % (311/710) of the individuals. The distribution of the number of mutations over the six genes is presented in Figure 3. The most commonly mutated gene was the NSD1 gene, accounting for 77.2 % of all cases with mutations in epigenetic genes (Fig. 3) [6].
Figure 3. Distribution of mutations over the different epigenetic regulatory genes, based on data from article by K. Tatton-Brown et al. from 2017.
77.2% 10.9% 5.8% 3.9% 1.6% 0.6% NSD1 EZH2 DNMT3A CHD8 HIST1H1E EED
Interestingly, for all the known epigenetic overgrowth syndromes illustrated in the 26 articles combined, the molecular defect is somewhat similar, in that all identified mutations appear to be loss of function [6, 36]. The nine genes in this study are presented in Table 1, with their pathogenic mechanism of mutation. Moreover, most of the mutations impair DNA
methylation in some way. One example is seen in a study made by Camille Tlemsani et al; where a targeted next-generation sequencing screening was performed in 210 individuals with Sotos-like phenotype and no NSD1-mutation [13]. Six previously unreported mutations in the DNMT3A gene and one unreported mutation in the SETD2 gene was discovered. Both of these genes have an impact on the methylation of histone 3 lysine 36 (H3K36), and when mutated, may give rise to a Sotos-like phenotype [13].
Gene Gene function Pathogenic mechanism of mutation
(gain/ loss of function)
Syndrome NSD1 Methylation of H4K20 and H3K36,
associated with transcriptional repression
Loss of function Sotos syndrome EZH2 Histone MT included in PRC2 as a
catalytic agent, suppressing gene transcription by methylation of H3K27
Loss of function Weaver syndrome
EED Key component in the PRC2, which catalyses methylation of H3K27, leading to transcriptional repression
Loss of function Weaver syndrome
DNMT3A Important for de novo DNA methylation during early embryogenesis
Loss of function Tatton- Brown- Rahman syndrome NFIX DNA-binding protein involved in gene
expression regulation, promoter of transcription
Loss of function Malan syndrome
SETD2 Histone MT responsible for trimethylation of H3K36
Loss of function Unknown (Sotos-like phenotype)
SUZ12 Key component in the PRC2, which catalyses methylation of H3K27, leading to transcriptional repression
Loss of function Atypical Weaver syndrome CHD8 ATP-dependent chromatin remodeler Loss of function CHD8 syndrome HIST1H1E Linker histone that mediate formation of
chromatin by neutralizing negatively charged linker DNA
Loss of function Unknown
Table 1. Illustration of nine different epigenetic genes associated with syndromes of overgrowth.
In most of the included articles, the overlap between distinct syndromes of overgrowth was taken up for discussion. For example, a comparison between Sotos and Malan syndrome is presented in an article by Merel Klaassens et al; from 2015 [16]. Common features are macrocephaly, advanced bone age and a moderate intellectual disability. Differences are seen in the degree and onset of overgrowth, patients with Malan syndrome suffer from a milder degree of overgrowth, observed mainly after birth, than those suffering from SoS that show more severe pre- and postnatal overgrowth [16]. However, the most commonly compared syndromes are Sotos and Weaver syndrome. In an observational study by Armelle Luscan et al from 2014 one of the differences between these two syndromes is said to be in bone age. For both syndromes, advanced bone age is seen, but for Weaver syndrome carpal bone development is advanced over the rest of the hand, whereas carpal bone development is at or behind that of the rest of the hand for Sotos syndrome [23]. Common traits for both
syndromes are tall stature, increased head circumference, frontal bossing and a variable degree of intellectual disability, reported by K. Tatton-Brown et al; from 2014 [17].
Discussion
The main findings from this systematic review are that loss-of-function mutations in genes involved in epigenetic regulation are one of the major causes of syndromes of overgrowth (Table 1). Nine different epigenetically associated genes and the linked mutational pattern, which cause syndromes of overgrowth, are illustrated in our results, based on 26
observational studies (Appendix 3-4). In the study from 2017 by K. Tatton-Brown et al, included in this review, six different genes are described, and is to our knowledge the greatest study performed this far [6]. Given this, a new study with an analysis of all nine genes we hereby illustrate, would be even greater, providing further knowledge and an increased possibility to diagnose more individuals with syndromes of overgrowth.
Also, the most commonly found epigenetic mutation was in the NSD1 gene, associated with Sotos syndrome, this in accordance with multiple previously published studies [1, 2]. Sotos syndrome was first described in 1964, and mutations in the NSD1 gene were found causative in 2002 and has therefore been investigated and researched for a longer time than other epigenetic syndromes of overgrowth, something that might contribute to these findings [37]. The second most common mutation is in the EZH2 gene, associated with Weaver syndrome, first discovered in 2011 [18]. When comparing these two syndromes, there are some evidence
to the fact that individuals with Weaver syndrome are more often mildly affected than those with Sotos syndrome [7, 17]. The late discovery of the molecular basis and the often mild phenotype might influence in the small number of diagnosed individuals with Weaver
syndrome. A comparison between Sotos and Weaver syndrome is often being made since they share several phenotypic and molecular traits and before the EZH2 gene was found
researchers reported that the two syndromes were allelic conditions [29]. According to our results pre- and postnatal overgrowth, macrocephaly, advanced bone age, similar facial features and a variable degree of intellectual disability affect individuals of both syndromes. This has previously been described in other studies [4-6].
The greatest limitation of this study is that the joint strength of evidence for the entire content of this review is assessed to be limited (++00). However, eleven of the included studies were graded to strong (++++) or moderately strong (+++0) strength of evidence, a total of 42.3 %, displaying a great dissemination in the quality of the studies. Even if the joint assessment of the material is of limited (++00) strength, the result could have a clinical implication. This according to SBU, which states that the results can be implicated in clinical praxis if it fulfils other criteria, such as cost- efficiency and being ethically correct [38]. Furthermore, all the included articles show a consistent, united result when it comes to mutated epigenetic genes and their involvement in the development of syndromes of overgrowth. This united result, and the fact that 42.3 % of the studies were of strong or moderately strong strength of evidence is an implication for a higher strength of evidence for the entire material, why it should be assessed to be moderately strong. Also, 26 articles is a big material, and even though the articles individually does not fully answer the primary aim, they combined provide sufficient data to answer the primary aim with a moderate strength. One other limitation regarding this study concerns the fact that several of the authors of the included articles have written or co-written more than one article. For example, K. Tatton-Brown is the first author of four different articles and has co-written additionally one. Furthermore, K. Tatton-Brown, N. Rahman and J. Douglas all work at the same institute and are often listed as co-writers on each other’s articles. Although this may be a concern, their results are consistent with the results from other research, conducted by other authors, strengthening the credibility. Moreover, K. Tatton-Brown is one of the leading researchers in this field of expertise, why her multiple articles is not unexpected, and all four of her articles included in this systematic review have been graded to be of strong or moderately strong strength of evidence, supporting
Finally, previous studies on the subject of epigenetic syndromes of overgrowth have been made, but since it is a relatively new and fresh area of research there is still a considerable amount of knowledge yet to be known. Many of these syndromes are still widely unknown, and in combination with the fact that the phenotype is most distinct in young children, many individuals evade diagnosis. The results from our study will hopefully make syndromes of overgrowth more familiar and contribute to increasing numbers of individuals with a correct diagnosis. A correct diagnosis means increasing possibilities to monitor for, and treat,
symptoms and associated complaints, offering the patient´s and their families a higher quality of life. This systematic review would also pose additional possibilities for researchers to get a more extensive illustration of the subject, since it provides a summarized picture of the current level of knowledge. Studies about syndromes of overgrowth further more offers an extended understanding of normal growth patterns since it has been illustrated that several of the genes involved in the syndromes, are also involved in the regulation of linear growth within normal limits [6].
Conclusion
In this systematic review, phenotypic and molecular overlap between several different types of syndromes of overgrowth were observed. Several of the causative mutations were loss-of-function in genes that produce epigenetic marks that, in turn, regulate gene transcription, thus causing abnormal expression of growth genes, resulting in tall stature. Further research is required to clarify the exact molecular mechanisms underlying syndromes of overgrowth.
Acknowledgement
I would like to express my deepest gratitude to prof. Ola Nilsson, my research supervisor, for his patient guidance, encouragement and useful critiques. Without his encouragement and support this project would not have been possible.
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Appendices
Appendix 1.Table 2. Reasons for exclusion of articles.
Reason Nr.
Only covering the symptoms associated with a syndrome and that should be monitored for (including malignancies) 37 Describing a specific testing method of value 9 Describing epigenetic mutations, however not in relation to syndromes of
overgrowth 5
Full text article not available 3 Explaining the relationship between a mutation and short stature 3 Describing syndromes of overgrowth not caused by epigenetic mutations 8 No specific mutation mentioned in relation to a specific phenotype 3
Review article 2
Appendix 2.
Table 3. Strength of evidence for included articles, based on the GRADE system applied by SBU (part 1 of 2). Study Population Study design
(preliminary strength of evidence)
Quality of study
Consistency Relevance Data precision Publication bias Final scientific evidence Ethical approval mentioned T. Suri et al. 2017 1 Observational study
(Limited (++00)) 0 + + 0 / - 0 Insufficient (+000) No K. Tatton-Brown et al. 2017 710 Observational study (Limited (++00)) + + + + 0 Strong (++++) Yes
G. Lemire et al. 2016 3 Observational study (Limited (++00))
0 / + + + - 0 Insufficient (+000)
No
E. Imagawa et al. 2016 8 Observational study (Limited (++00))
+ + + 0 / - 0 Moderately
strong (+++0) Yes
E. Cooney et al. 2016 1 Observational study (Limited (++00))
0 / + + + - 0 Insufficient
(+000)
Yes
B. Xin et al. 2017 6 Observational study (Limited (++00))
0 / + + + 0 / - 0 Moderately strong (+++0)
Yes
C. Tlemsani et al. 2017 210 Observational study (Limited (++00))
+ + + 0 0 Moderately
strong (+++0) Yes
A. Berardi et al. 2016 6 Observational study
(Limited (++00)) + + - 0 0 Moderately strong (+++0) No
A. S.A. Cohen, D. B.
Yap. 2015 1 Observational study (Limited (++00)) + + + + 0 Moderately strong (+++0) Yes
F. Gurrieri et al. 2015 3 Observational study (Limited (++00))
0 + + - 0 Limited (++00) No
A. S.A. Cohen, B.
Tuysuz et al. 2015 1 Observational study (Limited (++00)) 0 / + + + - 0 Limited (++00) No
M. Klaassens et al. 2015 20 (6 new cases) Observational study (Limited (++00)) 0 / + + + 0 0 Moderately strong (+++0) Yes
A. Luscan et al. 2014 16 Observational study (Limited (++00)) + + + - 0 Limited (++00) Yes K. Tatton-Brown et al. 2013 48 Observational study (Limited (++00)) 0 / + + + + - Moderately strong (+++0) Yes
Table 3. Strength of evidence for included articles, based on the GRADE system applied by SBU (part 2 of 2). Study Population Study design (preliminary
strength of evidence)
Quality of study
Consistency Relevance Data precision Publication bias Final scientific evidence Ethical approval mentioned R. Visser et al.
2012 18 Observational study (Limited (++00)) 0 + - - 0 Insufficient (+000) Yes
Y. Yoneda et al. 2012 48 Observational study (Limited (++00)) 0 + + - 0 Limited (++00) Yes K. Tatton-Brown et al. 2011 304 Observational study (Limited (++00)) + + + 0 / + 0 Moderately strong (+++0) Yes W. T. Gibson et
al. 2012 3 Observational study (Limited (++00)) + + + 0 0 Limited (++00) Yes
M. P. Pasillas et al. 2010 13 Observational study (Limited (++00)) + + + 0 / + 0 Moderately strong (+++0) No M. Cecconi et al.
2005 59 Observational study (Limited (++00)) + + + 0 0 Limited (++00) No
S. Türkmen et al. 2003
38 Observational study (Limited (++00))
0 + + + - Limited (++00) No
M. Rio et al. 2003 39 Observational study
(Limited (++00)) 0 / + + + 0 / + - Limited (++00) No J. Douglas et al. 2003 75 Observational study (Limited (++00)) 0 / + + + 0 0 Limited (++00) Yes P. Hoglund et al. 2003 3 Observational study (Limited (++00)) 0 + + - 0 Insufficient (+000) No K. Tatton-Brown, J. Douglas et al. 2005 530 Observational study (Limited (++00)) 0 / + + + + 0 Moderately strong (+++0) Yes D. J. Waggoner et al. 2005 435 Observational study (Limited (++00)) - + + - 0 Insufficient (+000) Yes
Appendix 3.
Table 4. Summary of 25 out of 26 articles, describing mutated epigenetic gene, molecular mechanisms and associated syndromes (part 4 of 4).
EZH2 = Enhancer of Zeste Homolog 2, DNMT3A = DNA methyltransferase 3A, EED = Embryonic ectoderm development protein, SUZ12 = polycomb protein SUZ12, SETD2 = SET domain containing, NSD1 = nuclear receptor binding SET domain protein 1, PRC2 = polycomb repression complex 2, 2H3K27 = lysine 27 of histone 3, MT = methyltransferase, H3K36 = lysine 36 of histone 3, WS = Weaver syndrome, TBRS = Tatton- Brown- Rahman syndrome, SoS = Sotos syndrome, NFIX = Nuclear factor I-X, MaS = Malan syndrome, H4K20 = lysine 20 of histone 4, CHD8 = chromodomain helicase DNA binding protein 8
Appendix 4.
Table 5. Summary of article 26 out of 26 included. K. Tatton-Brown et al. 2017. Strength of evidence: Strong (++++). Population:
710
NSD1 gene EZH2 gene DNMT3A gene CHD8 gene HIST1H1E gene EED Protein
products
NSD1 protein EZH2 protein DNMT3A CHD8 protein Histone H1.4 EED protein
Normal function of protein Histone MT that catalyses methylation of H3K36, leading to transcriptional activation
Key component in the PRC2, which catalyses methylation of H3K27, leading to transcriptional repression Important for de novo DNA methylation during early embryogenesis ATP-dependent chromatin remodeler
Functions as a linker histone that mediate formation of chromatin by neutralizing negatively charged linker DNA
Key component in the PRC2, which catalyses methylation of H3K27, leading to transcriptional repression Type of mutation(s) in study Most commonly microdeletions Frameshift mutations Inheritance Heterozygous mutations, 114 de novo, 7 maternal inheritance, 119 unknown inheritance Heterozygous mutations, 21 de novo, 3 paternal inheritance, 2 maternal inheritance, 8 unknown inheritance Heterozygous mutations, de novo Heterozygous mutations, 5 de novo, 3 maternal inheritance, 4 unknown inheritance Heterozygous mutations, 4 de novo, 1 unknown inheritance Heterozygous mutations, de novo Gain/ loss of function Loss of function Defect caused by mutation
Less effective in neutralizing the linker DNA and
impairing DNA-binding
Associated syndrome
SoS WS
NSD1 = nuclear receptor binding SET domain protein 1, EZH2 = Enhancer of Zeste Homolog 2, DNMT3A = DNA methyltransferase 3A, CHD8 = chromodomain helicase DNA binding protein 8, HIST1H1E = histone H1.4, EED = Embryonic ectoderm development protein, MT = methyltransferase, H3K36 = lysine 36 of histone 3, PRC2 = polycomb repression complex 2, 2H3K27 = lysine 27 of histone 3, SoS = Sotos syndrome, WS = Weaver syndrome
Populärvetenskaplig sammanfattning
- Mutationer i epigenetiska reglerare är en vanlig orsak till långvuxenhetssyndrom
Extrem långvuxenhet kan orsakas av flera olika saker, till exempel för hög produktion av
tillväxthormon. Sedan länge vet man också att förändringar i och runt arvsmassan spelar roll för hur lång en individ blir. I takt med att den tekniska utvecklingen går framåt har det blivit lättare att diagnostisera sjukdomar och syndrom som beror på denna typ av förändringar. Epigenetik handlar om arvsmassans “kläder”; de strukturer som omger arvsmassan och bidrar till hur den uttrycks. Epigenetiska gener ärvs från våra föräldrar och om det blir fel i dessa gener kan det leda till en rad sjukdomar och syndrom, bland annat s.k. epigenetiska långvuxenhetssyndrom. Gemensamt för individer drabbade av denna typ av syndrom är att de alla är längre än normalt, har större huvudomfång och intellektuell funktionsnedsättning av varierande grad.
Denna studie är en systematisk litteraturstudie, vilket innebär att vetenskaplig litteratur har
insamlats på ett strukturerat sätt för att sedan kvalitetsgranskas. Syftet med studien är att visa hur ett fel i en gen som är ansvarig för epigenetisk genreglering kan leda till ett långvuxenhetssyndrom. Dessutom jämförs olika epigenetiska långvuxenhetssyndrom med varandra, speciellt avseende utseende hos påverkade individer. I studien kunde vi påvisa nio olika epigenetiska gener som leder till långvuxenhetssyndrom. Det vanligast förekommande syndromet tycks vara Sotos syndrom, som orsakas av fel i en gen som heter NSD1. I studien bekräftades också att det finns en viss
överlappning i individernas ansiktsdrag mellan de olika syndromen samt att de alla är drabbade av någon form av överväxt och en varierande grad av intellektuell funktionsnedsättning.
Cover letter
December 5th, 2017.
Corresponding author: Nadine Norlin, Bachelor of Medicine, Örebro University Dear Editor,
Please consider the enclosed manuscript entitled “Disrupted epigenetic regulation causes syndromes of overgrowth- A systematic review” for publication.
Epigenetic syndromes of overgrowth are a relatively new and fresh area of research and
considerable amounts of knowledge is still to be known. The development of new testing methods has led to increasing possibilities to diagnose genetic and epigenetic syndromes such as these, why many previously unknown syndromes and the associated gene mutations has been brought to light. In our systematic review we have included 26 observational studies and illustrated a total of nine different genes involved in epigenetic gene regulation that, when mutated can lead to syndromes of overgrowth. This is, to our knowledge, the most comprehensive review of the subject. The
publication of this systematic review would provide researchers with a more extensive overview of the subject, thus making it easier to form a more focused research question for future research. It would also help increase public awareness of these syndromes, which is of greatest importance since a lot of affected individuals remain undiagnosed. Our results also indicated that these
syndromes overlap, especially when it comes to phenotype. Common traits, observed in a majority of affected individuals, included tall stature, macrocephaly, intellectual disability and advanced bone age.
Both authors of this systematic review have approved of the content in the study and given consent to following publication. The manuscript has not been published before and is not considered for publication elsewhere.
Best regards, Nadine Norlin
Ethical considerations
Most studies included in the systematic review include genome sequencing of patients and their relatives. Therefore, healthy individuals, with no actual benefit from the result, are being exposed to somewhat painful blood draws. More importantly, genome sequencing may result in accidental findings of other mutations than those being targeted in the analysis. This gives rise to several ethical dilemmas such as;
!! Should accidental findings be reported and if so, which findings?
!! Is it ethically justified to expose a healthy relative to the knowledge of previously unknown genetic risks?
However, there are also positive aspects on genome sequencing. For example, the finding of a mutation means the ability to give the patient a molecular diagnosis. This results in increasing possibilities to treat and monitor the disease accurately. It can also be used for prenatal diagnosis, allowing an earlier discovery of the disease. Also, accidental findings may have benefits as they may allow for screening and preventive measure.
In addition, the case report (not attached to this version due to future publication), is part of another project “Genetic causes of short and tall stature syndromes” enrolled at the Karolinska Institute, which has been approved by the ethical review board in Stockholm and is lead by supervisor Dr Ola Nilsson. Informed consent was obtained from patients and/ or parents before inclusion into the study, prior to the outset. I have gained access to the depersonalized medical records of the patient and only know him by gender, year of birth and geographical entity, protecting the patient’s integrity.
