Genome-wide methylation profiling of Beckwith-Wiedemann syndrome patients without molecular confirmation after routine diagnostics

Multi-locus imprinting disturbance (MLID): interim joint statement for clinical and molecular diagnosis

BACKGROUND

Imprinting disorders are rare diseases resulting from altered expression of imprinted genes, which exhibit parent-of-origin-specific expression patterns regulated through differential DNA methylation. A subgroup of patients with imprinting disorders have DNA methylation changes at multiple imprinted loci, a condition referred to as multi-locus imprinting disturbance (MLID). MLID is recognised in most but not all imprinting disorders and is also found in individuals with atypical clinical features; the presence of MLID often alters the management or prognosis of the affected person. Some cases of MLID are caused by trans-acting genetic variants, frequently not in the patients but their mothers, which have counselling implications. There is currently no consensus on the definition of MLID, clinical indications prompting testing, molecular procedures and methods for epigenetic and genetic diagnosis, recommendations for laboratory reporting, considerations for counselling, and implications for prognosis and management. The purpose of this study is thus to cover this unmet need.

METHODS

A comprehensive literature search was conducted resulting in identification of more than 100 articles which formed the basis of discussions by two working groups focusing on clinical diagnosis (n = 12 members) and molecular testing (n = 19 members). Following eight months of preparations and regular online discussions, the experts from 11 countries compiled the preliminary documentation and determined the questions to be addressed during a face-to-face meeting which was held with the attendance of the experts together with four representatives of patient advocacy organisations.

RESULTS

In light of available evidence and expert consensus, we formulated 16 propositions and 8 recommendations as interim guidance for the clinical and molecular diagnosis of MLID.

CONCLUSIONS

MLID is a molecular designation, and for patients with MLID and atypical phenotypes, we propose the alternative term multi-locus imprinting syndrome. Due to the intrinsic variability of MLID, the guidelines underscore the importance of involving experts from various fields to ensure a confident approach to diagnosis, counselling, and care. The authors advocate for global, collaborative efforts in both basic and translational research to tackle numerous crucial questions that currently lack answers, and suggest reconvening within the next 3-5 years to evaluate the research advancements and update this guidance as needed.

The counterpart congenital overgrowth syndromes Beckwith-Wiedemann Syndrome in human and large offspring syndrome in bovine involve alterations in DNA methylation, transcription, and chromatin configuration

Beckwith-Wiedemann Syndrome (BWS, OMIM #130650) is a congenital epigenetic disorder in humans which affects approximately 1 in 10,340 children. The incidence is likely an underestimation as the condition is usually recognized based on observable phenotypes at birth. BWS children have up to a 28% risk of developing tumors and currently, only 80% of patients can be corroborated molecularly (epimutations/variants). It is unknown how the subtypes of this condition are molecularly similar/dissimilar globally, therefore there is a need to deeply characterize the syndrome at the molecular level. Here we characterize the methylome, transcriptome and chromatin configuration of 18 BWS individuals together with the animal model of the condition, the bovine large offspring syndrome (LOS). Sex specific comparisons are performed for a subset of the BWS patients and LOS. Given that this epigenetic overgrowth syndrome has been characterized as a loss-of-imprinting condition, parental allele-specific comparisons were performed using the bovine animal model. In general, the differentially methylated regions (DMRs) detected in BWS and LOS showed significant enrichment for CTCF binding sites. Altered chromosome compartments in BWS and LOS were positively correlated with gene expression changes, and the promoters of differentially expressed genes showed significant enrichment for DMRs, differential topologically associating domains, and differential A/B compartments in some comparisons of BWS subtypes and LOS. We show shared regions of dysregulation between BWS and LOS, including several HOX gene clusters, and also demonstrate that altered DNA methylation differs between the clinically epigenetically identified BWS patients and those identified as having DNA variants (i.e. CDKN1C microdeletion). Lastly, we highlight additional genes and genomic regions that have the potential to serve as targets for biomarker development to improve current molecular methodologies. In summary, our results suggest that genome-wide alternation of chromosome architecture, which is partially caused by DNA methylation changes, also contribute to the development of BWS and LOS.

Uncovering the phenotypic consequences of multi-locus imprinting disturbances using genome-wide methylation analysis in genomic imprinting disorders

Imprinted genes are regulated by DNA methylation of imprinted differentially methylated regions (iDMRs). An increasing number of patients with congenital imprinting disorders (IDs) exhibit aberrant methylation at multiple imprinted loci, multi-locus imprinting disturbance (MLID). We examined MLID and its possible impact on clinical features in patients with IDs. Genome-wide DNA methylation analysis (GWMA) using blood leukocyte DNA was performed on 13 patients with Beckwith-Wiedemann syndrome (BWS), two patients with Silver-Russell syndrome (SRS), and four controls. HumanMethylation850 BeadChip analysis for 77 iDMRs (809 CpG sites) identified three patients with BWS and one patient with SRS showing additional hypomethylation, other than the disease-related iDMRs, suggestive of MLID. Two regions were aberrantly methylated in at least two patients with BWS showing MLID: PPIEL locus (chromosome 1: 39559298 to 39559744), and FAM50B locus (chromosome 6: 3849096 to 3849469). All patients with BWS- and SRS-MLID did not show any other clinical characteristics associated with additional involved iDMRs. Exome analysis in three patients with BWS who exhibited multiple hypomethylation did not identify any causative variant related to MLID. This study indicates that a genome-wide approach can unravel MLID in patients with an apparently isolated ID. Patients with MLID showed only clinical features related to the original IDs. Long-term follow-up studies in larger cohorts are warranted to evaluate any possible phenotypic consequences of other disturbed imprinted loci.

Molecular characterisation of 36 multilocus imprinting disturbance (MLID) patients: a comprehensive approach

BACKGROUND

Imprinting disorders (ImpDis) comprise diseases which are caused by aberrant regulation of monoallelically and parent-of-origin-dependent expressed genes. A characteristic molecular change in ImpDis patients is aberrant methylation signatures at disease-specific loci, without an obvious DNA change at the specific differentially methylated region (DMR). However, there is a growing number of reports on multilocus imprinting disturbances (MLIDs), i.e. aberrant methylation at different DMRs in the same patient. These MLIDs account for a significant number of patients with specific ImpDis, and several reports indicate a central role of pathogenic maternal effect variants in their aetiology by affecting the maturation of the oocyte and the early embryo. Though several studies on the prevalence and the molecular causes of MLID have been conducted, homogeneous datasets comprising both genomic and methylation data are still lacking.

RESULTS

Based on a cohort of 36 MLID patients, we here present both methylation data obtained from next-generation sequencing (NGS, ImprintSeq) approaches and whole-exome sequencing (WES). The compilation of methylation data did not reveal a disease-specific MLID episignature, and a predisposition for the phenotypic modification was not obvious as well. In fact, this lack of epigenotype-phenotype correlation might be related to the mosaic distribution of imprinting defects and their functional relevance in specific tissues.

CONCLUSIONS

Due to the higher sensitivity of NGS-based approaches, we suggest that ImprintSeq might be offered at reference centres in case of ImpDis patients with unusual phenotypes but MLID negative by conventional tests. By WES, additional MLID causes than the already known maternal effect variants could not be identified, neither in the patients nor in the maternal exomes. In cases with negative WES results, it is currently unclear to what extent either environmental factors or undetected genetic variants contribute to MLID.

Further Introduction of DNA Methylation (DNAm) Arrays in Regular Diagnostics

Methylation tests have been used for decades in regular DNA diagnostics focusing primarily on Imprinting disorders or specific loci annotated to specific disease associated gene promotors. With the introduction of DNA methylation (DNAm) arrays such as the Illumina Infinium HumanMethylation450 Beadchip array or the Illumina Infinium Methylation EPIC Beadchip array (850 k), it has become feasible to study the epigenome in a timely and cost-effective way. This has led to new insights regarding the complexity of well-studied imprinting disorders such as the Beckwith Wiedemann syndrome, but it has also led to the introduction of tests such as EpiSign, implemented as a diagnostic test in which a single array experiment can be compared to databases with known episignatures of multiple genetic disorders, especially neurodevelopmental disorders. The successful use of such DNAm tests is rapidly expanding. More and more disorders are found to be associated with discrete episignatures which enables fast and definite diagnoses, as we have shown. The first examples of environmentally induced clinical disorders characterized by discrete aberrant DNAm are discussed underlining the broad application of DNAm testing in regular diagnostics. Here we discuss exemplary findings in our laboratory covering this broad range of applications and we discuss further use of DNAm tests in the near future.

Spontaneous and ART-induced large offspring syndrome: similarities and differences in DNA methylome

Large/abnormal offspring syndrome (LOS/AOS) is a congenital overgrowth syndrome reported in ruminants produced by assisted reproduction (ART-LOS) which exhibit global disruption of the epigenome and transcriptome. LOS/AOS shares phenotypes and epigenotypes with the human congenital overgrowth condition Beckwith-Wiedemann syndrome. We have reported that LOS occurs spontaneously (SLOS); however, to date, no study has been conducted to determine if SLOS has the same methylome epimutations as ART-LOS. In this study, we performed whole-genome bisulphite sequencing to examine global DNA methylation in bovine SLOS and ART-LOS tissues. We observed unique patterns of global distribution of differentially methylated regions (DMRs) over different genomic contexts, such as promoters, CpG Islands, shores and shelves, as well as at repetitive sequences. In addition, we included data from two previous LOS studies to identify shared vulnerable genomic loci in LOS. Overall, we identified 320 genomic loci in LOS that have alterations in DNA methylation when compared to controls. Specifically, there are 25 highly vulnerable loci that could potentially serve as molecular markers for the diagnosis of LOS, including at the promoters of DMRT2 and TBX18, at the imprinted gene bodies of IGF2R, PRDM8, and BLCAP/NNAT, and at multiple CpG Islands. We also observed tissue-specific DNA methylation patterns between muscle and blood, and conservation of ART-induced DNA methylation changes between muscle and blood. We conclude that as ART-LOS, SLOS is an epigenetic condition. In addition, SLOS and ART-LOS share similarities in methylome epimutations.

Epigenetics in the Uterine Environment: How Maternal Diet and ART May Influence the Epigenome in the Offspring with Long-Term Health Consequences

The societal burden of non-communicable disease is closely linked with environmental exposures and lifestyle behaviours, including the adherence to a poor maternal diet from the earliest preimplantation period of the life course onwards. Epigenetic variations caused by a compromised maternal nutritional status can affect embryonic development. This review summarises the main epigenetic modifications in mammals, especially DNA methylation, histone modifications, and ncRNA. These epigenetic changes can compromise the health of the offspring later in life. We discuss different types of nutritional stressors in human and animal models, such as maternal undernutrition, seasonal diets, low-protein diet, high-fat diet, and synthetic folic acid supplement use, and how these nutritional exposures epigenetically affect target genes and their outcomes. In addition, we review the concept of thrifty genes during the preimplantation period, and some examples that relate to epigenetic change and diet. Finally, we discuss different examples of maternal diets, their effect on outcomes, and their relationship with assisted reproductive technology (ART), including their implications on epigenetic modifications.

Case Studies of Two Classical Imprinting Growth Disorders: Silver–Russell and Beckwith–Wiedemann Syndromes

The genetic influences on human growth are being increasingly deciphered. Silver–Russell and Beckwith–Wiedemann syndromes (SRS; BWS) are two relatively common genetic syndromes with under- and overgrowth-related issues being the reason for referral. Aberration in genomic imprinting is the underlying genetic pathomechanism behind these syndromes. Herein, we described a series of children with these two growth disorders and give an orientation to the reader of the concept of imprinting as well as the genetic testing strategy and counseling to be offered in these syndromes.

Multi-locus imprinting disturbances of Beckwith-Wiedemann and Large offspring syndrome/Abnormal offspring syndrome: A brief review

In vitro fertilization and somatic cell nuclear transfer are assisted reproduction technologies commonly used in humans and cattle, respectively. Despite advances in these technologies, molecular failures can occur, increasing the chance of the onset of imprinting disorders in the offspring. Large offspring syndrome/abnormal offspring syndrome (LOS/AOS) has been described in cattle and has features such as hypergrowth, malformation of organs, and skeletal and placental defects. In humans, Beckwith-Wiedemann syndrome (BWS) has phenotypic characteristics similar to those found in LOS/AOS. In both syndromes, disruption of genomic imprinting associated with loss of parental-specific expression and parental-specific epigenetic marks is involved in the molecular etiology. Changes in the imprinting pattern of these genes lead to loss of imprinting (LOI) due to gain or loss of methylation, inducing the emergence of these syndromes. Several studies have reported locus-specific alterations in these syndromes, such as hypomethylation in imprinting control region 2 (KvDMR1) in BWS and LOS/AOS. These LOI events can occur at multiple imprinted loci in the same affected individual, which are called multi-locus methylation defect (MLMD) events. Although the bovine species has been proposed as a developmental model for human imprinting disorders, there is little information on bovine imprinted genes in the literature, even the correlation of epimutation data with clinical characteristics. In this study, we performed a systematic review of all the multi-locus LOI events described in human BWS and LOS/AOS, in order to determine in which imprinted genes the largest changes in the pattern of DNA methylation and expression occur, helping to fill gaps for a better understanding of the etiology of both syndromes.

A case of unilateral sectoral iris heterochromia in an infant with Beckwith-Wiedemann syndrome

Purpose

To report a case of unilateral sectoral iris heterochromia in an infant with Beckwith-Wiedemann syndrome (BWS).

Observations

An 8-month-old girl known case of BWS, due to hypomethylation of the DMR2 (KCNQ1OT1) on chromosome 11p15.5, with features of macroglossia, neonatal hypoglycaemia and an unusual finding of partial iris hypopegmentaion in her left eye.

Conclusions

This is the first reported case of iris heterochromia in a BWS patient. Further studies are needed to support the association between eye findings and BWS related genetic defects.

Clinical and Molecular Diagnosis of Beckwith-Wiedemann Syndrome with Single- or Multi-Locus Imprinting Disturbance

Beckwith-Wiedemann syndrome (BWS) is a clinically and genetically heterogeneous overgrowth disease. BWS is caused by (epi)genetic defects at the 11p15 chromosomal region, which harbors two clusters of imprinted genes, IGF2/H19 and CDKN1C/KCNQ1OT1, regulated by differential methylation of imprinting control regions, H19/IGF2:IG DMR and KCNQ1OT1:TSS DMR, respectively. A subset of BWS patients show multi-locus imprinting disturbances (MLID), with methylation defects extended to other imprinted genes in addition to the disease-specific locus. Specific (epi)genotype-phenotype correlations have been defined in order to help clinicians in the classification of patients and referring them to a timely diagnosis and a tailored follow-up. However, specific phenotypic correlations have not been identified among MLID patients, thus causing a debate on the usefulness of multi-locus testing in clinical diagnosis. Finally, the high incidence of BWS monozygotic twins with discordant phenotypes, the high frequency of BWS among babies conceived by assisted reproductive technologies, and the female prevalence among BWS-MLID cases provide new insights into the timing of imprint establishment during embryo development. In this review, we provide an overview on the clinical and molecular diagnosis of single- and multi-locus BWS in pre- and post-natal settings, and a comprehensive analysis of the literature in order to define possible (epi)genotype-phenotype correlations in MLID patients.

Case Report: A Novel Deletion in the 11p15 Region Causing a Familial Beckwith-Wiedemann Syndrome

Beckwith–Wiedemann syndrome (BWS; OMIM 130650) is a human overgrowth and cancer susceptibility disorder with a wide clinical spectrum, which cannot be predicted based on genomic variants alone. Most reports on BWS cases focus on childhood patients. Studies on adult BWS patients are scarce. Our study reports a BWS family in which the disorder appears to be caused by deletion of H19 and its upstream regulatory elements. Genetic analysis showed a heterozygous microdeletion (~chr11:2009895-2070570 (GRCh37)) in the patients. Maternal deletion in H19 can result in loss of function of the IGF2-H19 imprinting control element, which leads to BWS. The male proband in this family was affected by the testicular anomaly and cryptorchidism. Early orchidopexy did not rescue his azoospermia, which might be not the consequence of cryptorchidism, but due to genetic defects associated with H19 deletion. In summary, our study gives some insights on the presentation of BWS in adulthood.

Preclinical and Clinical Epigenetic-Based Reconsideration of Beckwith-Wiedemann Syndrome

Epigenetics has achieved a profound impact in the biomedical field, providing new experimental opportunities and innovative therapeutic strategies to face a plethora of diseases. In the rare diseases scenario, Beckwith-Wiedemann syndrome (BWS) is a pediatric pathological condition characterized by a complex molecular basis, showing alterations in the expression of different growth-regulating genes. The molecular origin of BWS is associated with impairments in the genomic imprinting of two domains at the 11p15.5 chromosomal region. The first domain contains three different regions: insulin growth like factor gene (IGF2), H19, and abnormally methylated DMR1 region. The second domain consists of cell proliferation and regulating-genes such as CDKN1C gene encoding for cyclin kinase inhibitor its role is to block cell proliferation. Although most cases are sporadic, about 5-10% of BWS patients have inheritance characteristics. In the 11p15.5 region, some of the patients have maternal chromosomal rearrangements while others have Uniparental Paternal Disomy UPD(11)pat. Defects in DNA methylation cause alteration of genes and the genomic structure equilibrium leading uncontrolled cell proliferation, which is a typical tumorigenesis event. Indeed, in BWS patients an increased childhood tumor predisposition is observed. Here, we summarize the latest knowledge on BWS and focus on the impact of epigenetic alterations to an increased cancer risk development and to metabolic disorders. Moreover, we highlight the correlation between assisted reproductive technologies and this rare disease. We also discuss intriguing aspects of BWS in twinning. Epigenetic therapies in clinical trials have already demonstrated effectiveness in oncological and non-oncological diseases. In this review, we propose a potential "epigenetic-based" approaches may unveil new therapeutic options for BWS patients. Although the complexity of the syndrome is high, patients can be able to lead a normal life but tumor predispositions might impair life expectancy. In this sense epigenetic therapies should have a supporting role in order to guarantee a good prognosis.

A genome-wide DNA methylation signature for SETD1B-related syndrome

SETD1B is a component of a histone methyltransferase complex that specifically methylates Lys-4 of histone H3 (H3K4) and is responsible for the epigenetic control of chromatin structure and gene expression. De novo microdeletions encompassing this gene as well as de novo missense mutations were previously linked to syndromic intellectual disability (ID). Here, we identify a specific hypermethylation signature associated with loss of function mutations in the SETD1B gene which may be used as an epigenetic marker supporting the diagnosis of syndromic SETD1B-related diseases. We demonstrate the clinical utility of this unique epi-signature by reclassifying previously identified SETD1B VUS (variant of uncertain significance) in two patients.

The Bright and Dark Side of DNA Methylation: A Matter of Balance

DNA methylation controls several cellular processes, from early development to old age, including biological responses to endogenous or exogenous stimuli contributing to disease transition. As a result, minimal DNA methylation changes during developmental stages drive severe phenotypes, as observed in germ-line imprinting disorders, while genome-wide alterations occurring in somatic cells are linked to cancer onset and progression. By summarizing the molecular events governing DNA methylation, we focus on the methods that have facilitated mapping and understanding of this epigenetic mark in healthy conditions and diseases. Overall, we review the bright (health-related) and dark (disease-related) side of DNA methylation changes, outlining how bulk and single-cell genomic analyses are moving toward the identification of new molecular targets and driving the development of more specific and less toxic demethylating agents.