Comprehensive and quantitative multilocus methylation analysis reveals the susceptibility of specific imprinted differentially methylated regions to aberrant methylation in Beckwith-Wiedemann syndrome with epimutations

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.

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.

DNA Methylation Analysis of Imprinted Genes in the Cortex and Hippocampus of Cross-Fostered Mice Selectively Bred for Increased Voluntary Wheel-Running

We have previously shown that high runner (HR) mice (from a line genetically selected for increased wheel-running behavior) have distinct, genetically based, neurobiological phenotypes as compared with non-selected control (C) mice. However, developmental programming effects during early life, including maternal care and parent-of-origin-dependent expression of imprinted genes, can also contribute to variation in physical activity. Here, we used cross-fostering to address two questions. First, do HR mice have altered DNA methylation profiles of imprinted genes in the brain compared to C mice? Second, does maternal upbringing further modify the DNA methylation status of these imprinted genes? To address these questions, we cross-fostered all offspring at birth to create four experimental groups: C pups to other C dams, HR pups to other HR dams, C pups to HR dams, and HR pups to C dams. Bisulfite sequencing of 16 imprinted genes in the cortex and hippocampus revealed that the HR line had altered DNA methylation patterns of the paternally imprinted genes, Rasgrf1 and Zdbf2, as compared with the C line. Both fostering between the HR and C lines and sex modified the DNA methylation profiles for the paternally expressed genes Mest, Peg3, Igf2, Snrpn, and Impact. Ig-DMR, a gene with multiple paternal and maternal imprinted clusters, was also affected by maternal upbringing and sex. Our results suggest that differential methylation patterns of imprinted genes in the brain could contribute to evolutionary increases in wheel-running behavior and are also dependent on maternal upbringing and sex.

First report of a successful pregnancy by preimplantation genetic testing for Beckwith-Wiedemann syndrome

OBJECTIVE

Beckwith-Wiedemann syndrome (BWS) is a rare imprinting gene disorder. Maternal CDKN1C mutation comprises 5% of etiologies of BWS. There is no successful report of preventing BWS by preimplantation genetic testing for monogenic disease (PGT-M) in the literature. Is PGT-M applicable for preventing BWS ?

CASE REPORT

This 39-year-old woman conceived naturally and delivered a boy who was diagnosed of BWS. The genetic testing of her son revealed CDKN1C gene mutation, and of the mother showed a carrier of the same mutation. She underwent controlled ovarian stimulation, oocyte pickup, and intracytoplasmic sperm injection. Trophectoderm biopsies were performed and samples were checked for PGT. Two wild-type and euploid embryos were thawed and transferred. One intrauterine pregnancy was achieved. The patient delivered a healthy female baby at 37 weeks of gestation.

CONCLUSION

In this case, we first report a successful pregnancy with a wild-type CDKN1C gene baby achieved by PGT-M.

Cohesin Mutations Induce Chromatin Conformation Perturbation of the H19/IGF2 Imprinted Region and Gene Expression Dysregulation in Cornelia de Lange Syndrome Cell Lines

Traditionally, Cornelia de Lange Syndrome (CdLS) is considered a cohesinopathy caused by constitutive mutations in cohesin complex genes. Cohesin is a major regulator of chromatin architecture, including the formation of chromatin loops at the imprinted IGF2/H19 domain. We used 3C analysis on lymphoblastoid cells from CdLS patients carrying mutations in NIPBL and SMC1A genes to explore 3D chromatin structure of the IGF2/H19 locus and evaluate the influence of cohesin alterations in chromatin architecture. We also assessed quantitative expression of imprinted loci and WNT pathway genes, together with DMR methylation status of the imprinted genes. A general impairment of chromatin architecture and the emergence of new interactions were found. Moreover, imprinting alterations also involved the expression and methylation levels of imprinted genes, suggesting an association among cohesin genetic defects, chromatin architecture impairment, and imprinting network alteration. The WNT pathway resulted dysregulated: canonical WNT, cell cycle, and WNT signal negative regulation were the most significantly affected subpathways. Among the deregulated pathway nodes, the key node of the frizzled receptors was repressed. Our study provides new evidence that mutations in genes of the cohesin complex have effects on the chromatin architecture and epigenetic stability of genes commonly regulated by high order chromatin structure.

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.

Phenotypically concordant but epigenetically discordant monozygotic dichorionic diamniotic twins with Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder caused by (epi)genetic alterations. The incidence of monozygotic (MZ) twins in BWS is higher than in the general population. Most MZ twins with BWS are female and have phenotypical discordance: one twin is clinically diagnosed with BWS, while the other shows a mild or normal phenotype. The most frequent (epi)genetic alteration in MZ twins is loss of methylation of imprinting control region 2 (ICR2-LOM) at 11p15.5. Intriguingly, ICR2-LOM is usually found in the peripheral blood leukocytes (PBL) of both twins, even if they are clinically discordant. Here, we present a rare pair of MZ dichorionic diamniotic female twins with BWS and concordant phenotypes (a Beckwith-Wiedemann spectrum score of 5 in each twin). Molecular analysis of genomic DNA from PBL revealed ICR2-LOM in one twin but not the other. Our analyses suggest that ICR2-LOM occurred between days 1 and 3 after fertilization, followed by twinning. We speculate that during embryogenesis, ICR2-LOM cells were distributed to the hematopoietic stem cells in different ratios in the two fetuses, and also to commonly affected tissues, such as the tongue, in similar ratios, although we were unable to analyze any tissues other than PBL.

Suppression of choroidal neovascularization by silencing of long non-coding RNA IPW

Long noncoding RNAs (lncRNAs) have emerged as the key regulators in the pathogenesis of human disorders. This study aimed to investigate the role of lncRNA-IPW in the progression of choroidal neovascularization (CNV) and the underlying molecular mechanism. IPW was significantly up-regulated in the choroidal tissues of laser-induced CNV mice and in the endothelial cells in response to hypoxic stress. IPW silencing led to reduced formation of CNV in laser-induced CNV model and ex vivo choroidal sprouting model, which could achieve similar therapeutic effects of anti-VEGF on CNV formation. Silencing or transgenic overexpression of IPW could alter endothelial cell viability, proliferation, migration, and tube formation ability in vitro. Mechanistically, IPW silencing led to increased expression of miR-370. Increased miR-370 could mimic the effects of IPW silencing on CNV formation and endothelial angiogenic phenotypes in vivo and in vitro. This study suggests that IPW silencing is a promising strategy for the treatment of neovascular ocular diseases.

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.

Paternal Uniparental Disomy of the Entire Chromosome 20 in a Child with Beckwith-Wiedemann Syndrome

Epigenetic alterations at imprinted genes on different chromosomes have been linked to several imprinting disorders (IDs) such as Beckwith-Wiedemann syndrome (BWS) and pseudohypoparathyroidism type 1b (PHP1b). Here, we present a male patient with these two distinct IDs caused by two independent mechanisms-loss of methylation (LOM) at chromosome 11p15.5 associated with multi-locus imprinting disturbances (MLID and paternal uniparental disomy of chromosome 20 (patUPD20). A clinical diagnosis of BWS was made based on the clinical features of macrosomia, macroglossia, and umbilical hernia. The diagnosis of PHP1b was supported by the presence of reduced growth velocity and mild learning disability as well as hypocalcemia and hyperphosphatemia at 14 years of age. Molecular analyses, including genome-wide DNA methylation (Illumina 450k array), bisulfite pyrosequencing, single nucleotide polymorphism (SNP) array and microsatellite analysis, demonstrated loss of methylation (LOM) at IC2 on chromosome 11p15.5, and paternal isodisomy of the entire chromosome 20. In addition, imprinting disturbances were noted at the differentially methylated regions (DMRs) associated with DIRAS3 on chromosome 1 and PLAGL1 on chromosome 6. This is the first case report of PHP1b due to patUPD20 diagnosed in a BWS patient with LOM at IC2 demonstrating etiologic heterogeneity for multiple imprinting disorders in a single individual.

Molecular characterization of temple syndrome families with 14q32 epimutations

Temple Syndrome (TS14) is an imprinting disorder caused by molecular disruptions of the imprinted region in 14q32 (MEG3:TSS-DMR). The frequency of the three known TS14 subtypes (deletions, maternal uniparental disomy (upd(14)mat), loss of methylation (LOM)) is currently in discussion, and within the LOM group, the occurrence of Multilocus Imprinting Disturbances (MLID) has been identified. We present 16 TS14 patients with molecular alterations affecting the MEG3:TSS-DMR, comprising seven patients (43.8%) with LOM, six carriers with upd(14)mat (37.5%), and three cases (18.8%) with a deletion affecting the paternal MEG3:TSS-DMR. We did not find any evidence for MLID in the LOM group, including two cases in which different tissues were available. Whole exome sequencing (WES) in the MEG3:TSS-DMR LOM patients and their parents (Trio WES) did not reveal an obvious pathogenic variant which might cause aberrant methylation at imprinted loci. By summarizing our data with those from the literature, we could show that MLID affecting clinically relevant imprinted loci is rare in TS14 and therefore differs markedly from other imprinting disorders associated with MLID, e.g. Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS). However, consistent with the clinical overlap with TS14, in SRS patients carrying MLID the MEG3:TSS-DMR is frequently affected. Variants in the known candidate genes for maternal effect variants causing MLID and fetal MLID determinants could not be identified in TS14 patients. Thus, 14q32 epimutations probably have other molecular causes than epimutations in BWS or SRS patients.

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.

Need for a precise molecular diagnosis in Beckwith-Wiedemann and Silver-Russell syndrome: what has to be considered and why it is important

Abstract

Molecular diagnostic testing of the 11p15.5-associated imprinting disorders Silver-Russell and Beckwith-Wiedemann syndrome (SRS, BWS) is challenging due to the broad spectrum of molecular defects and their mosaic occurrence. Additionally, the decision on the molecular testing algorithm is hindered by their clinical heterogeneity. However, the precise identification of the type of defect is often a prerequisite for the clinical management and genetic counselling. Four major molecular alterations (epimutations, uniparental disomies, copy number variants, single nucleotide variants) have been identified, but their frequencies vary between SRS and BWS. Due to their molecular aetiology, epimutations in both disorders as well as upd(11)pat in BWS are particular prone to mosaicism which might additionally complicate the interpretation of testing results. We report on our experience of molecular analysis in a total cohort of 1448 patients referred for diagnostic testing of BWS and SRS, comprising a dataset from 737 new patients and from 711 cases from a recent study. Though the majority of positively tested patients showed the expected molecular results, we identified a considerable number of clinically unexpected molecular alterations as well as not yet reported changes and discrepant mosaic distributions. Additionally, the rate of multilocus imprinting disturbances among the patients with epimutations and uniparental diploidies could be further specified. Altogether, these cases show that comprehensive testing strategies have to be applied in diagnostic testing of SRS and BWS. The precise molecular diagnosis is required as the basis for a targeted management (e.g. ECG (electrocardiogram) and tumour surveillance in BWS, growth treatment in SRS). The molecular diagnosis furthermore provides the basis for genetic counselling. However, it has to be considered that recurrence risk calculation is determined by the phenotypic consequences of each molecular alteration and mechanism by which the alteration arose.

Key messages

The detection rates for the typical molecular defects of Beckwith-Wiedemann syndrome or Silver-Russell syndrome (BWS, SRS) are lower in routine cohorts than in clinically well-characterised ones.

A broad spectrum of (unexpected) molecular alterations in both disorders can be identified.

Multilocus imprinting disturbances (MLID) are less frequent in SRS than expected.

The frequency of MLID and uniparental diploidy in BWS is confirmed.

Mosaicism is a diagnostic challenge in BWS and SRS.

The precise determination of the molecular defects affecting is the basis for a targeted clinical management and genetic counselling.

(Epi)genetic profiling of extraembryonic and postnatal tissues from female monozygotic twins discordant for Beckwith-Wiedemann syndrome

Background

Beckwith–Wiedemann syndrome (BWS) is an overgrowth disorder caused by defects at the 11p15.5 imprinted region. Many cases of female monozygotic (MZ) twins discordant for BWS have been reported, but no definitive conclusions have been drawn regarding the link between epigenetic defects, twinning process, and gender. Here, we report a comprehensive characterization and follow‐up of female MZ twins discordant for BWS.

Methods

Methylation pattern at 11p15.5 and multilocus methylation disturbance (MLID) profiling were performed by pyrosequencing and MassARRAY in placental/umbilical cord samples and postnatal tissues. Whole‐exome sequencing was carried out to identify MLID causative mutations. X‐chromosome inactivation (XCI) was determined by HUMARA test.

Results

Both twins share KCNQ1OT1:TSS‐DMR loss of methylation (LOM) and MLID in blood and the epigenetic defect remained stable in the healthy twin over time. KCNQ1OT1:TSS‐DMRLOM was nonhomogeneously distributed in placental samples and the twins showed the same severely skewed XCI pattern. No MLID‐causative mutations were identified.

Conclusion

This is the first report on BWS‐discordant twins with methylation analyses extended to extraembryonic tissues. The results suggest that caution is required when attempting prenatal diagnosis in similar cases. Although the causative mechanism underlying LOM remains undiscovered, the XCI pattern and mosaic LOM suggest that both twinning and LOM/MLID occurred after XCI commitment.

DNA Methylation in the Diagnosis of Monogenic Diseases

DNA methylation in the human genome is largely programmed and shaped by transcription factor binding and interaction between DNA methyltransferases and histone marks during gamete and embryo development. Normal methylation profiles can be modified at single or multiple loci, more frequently as consequences of genetic variants acting in cis or in trans, or in some cases stochastically or through interaction with environmental factors. For many developmental disorders, specific methylation patterns or signatures can be detected in blood DNA. The recent use of high-throughput assays investigating the whole genome has largely increased the number of diseases for which DNA methylation analysis provides information for their diagnosis. Here, we review the methylation abnormalities that have been associated with mono/oligogenic diseases, their relationship with genotype and phenotype and relevance for diagnosis, as well as the limitations in their use and interpretation of results.

DNA methylation analysis of multiple imprinted DMRs in Sotos syndrome reveals IGF2-DMR0 as a DNA methylation-dependent, P0 promoter-specific enhancer

Haploinsufficiency of NSD1, which dimethylates histone H3 lysine 36 (H3K36), causes Sotos syndrome (SoS), an overgrowth syndrome. DNMT3A and DNMT3B recognizes H3K36 trimethylation (H3K36me3) through PWWP domain to exert de novo DNA methyltransferase activity and establish imprinted differentially methylated regions (DMRs). Since decrease of H3K36me3 and genome‐wide DNA hypomethylation in SoS were observed, hypomethylation of imprinted DMRs in SoS was suggested. We explored DNA methylation status of 28 imprinted DMRs in 31 SoS patients with NSD1 defect and found that hypomethylation of IGF2‐DMR0 and IG‐DMR in a substantial proportion of SoS patients. Luciferase assay revealed that IGF2‐DMR0 enhanced transcription from the IGF2 P0 promoter but not the P3 and P4 promoters. Chromatin immunoprecipitation‐quantitative PCR (ChIP‐qPCR) revealed active enhancer histone modifications at IGF2‐DMR0, with high enrichment of H3K4me1 and H3 lysine 27 acetylation (H3K27ac). CRISPR‐Cas9 epigenome editing revealed that specifically induced hypomethylation at IGF2‐DMR0 increased transcription from the P0 promoter but not the P3 and P4 promoters. NSD1 knockdown suggested that NSD1 targeted IGF2‐DMR0; however, IGF2‐DMR0 DNA methylation and IGF2 expression were unaltered. This study could elucidate the function of IGF2‐DMR0 as a DNA methylation dependent, P0 promoter‐specific enhancer. NSD1 may play a role in the establishment or maintenance of IGF2‐DMR0 methylation during the postimplantation period.

A Bayesian hidden Markov model for detecting differentially methylated regions

Alterations in DNA methylation have been linked to the development and progression of many diseases. The bisulfite sequencing technique presents methylation profiles at base resolution. Count data on methylated and unmethylated reads provide information on the methylation level at each CpG site. As more bisulfite sequencing data become available, these data are increasingly needed to infer methylation aberrations in diseases. Automated and powerful algorithms also need to be developed to accurately identify differentially methylated regions between treatment groups. This study adopts a Bayesian approach using the hidden Markov model to account for inherent dependence in read count data. Given the expense of sequencing experiments, few replicates are available for each treatment group. A Bayesian approach that borrows information across an entire chromosome improves the reliability of statistical inferences. The proposed hidden Markov model considers location dependence among genomic loci by incorporating correlation structures as a function of genomic distance. An iterative algorithm based on expectation-maximization is designed for parameter estimation. Methylation states are inferred by identifying the optimal sequence of latent states from observations. Real datasets and simulation studies that mimic the real datasets are used to illustrate the reliability and success of the proposed method.

Temple syndrome in a patient with variably methylated CpGs at the primary MEG3/DLK1:IG-DMR and severely hypomethylated CpGs at the secondary MEG3:TSS-DMR

Background

The human chromosome 14q32.2 imprinted region harbors the primary MEG3/DLK1:IG-differentially methylated region (DMR) and secondary MEG3:TSS-DMR. The MEG3:TSS-DMR can remain unmethylated only in the presence of unmethylated MEG3/DLK1:IG-DMR in somatic tissues, but not in the placenta, because of a hierarchical regulation of the methylation pattern between the two DMRs.

Methods

We performed molecular studies in a 4-year-old Japanese girl with Temple syndrome (TS14).

Results

Pyrosequencing analysis showed extremely low methylation levels of five CpGs at the MEG3:TSS-DMR and grossly normal methylation levels of four CpGs at the MEG3/DLK1:IG-DMR in leukocytes. HumanMethylation450 BeadChip confirmed marked hypomethylation of the MEG3:TSS-DMR and revealed multilocus imprinting disturbance (MLID) including mild hypomethylation of the H19/IGF2:IG-DMR and mild hypermethylation of the GNAS A/B:TSS-DMR in leukocytes. Bisulfite sequencing showed markedly hypomethylated CpGs at the MEG3:TSS-DMR and irregularly and non-differentially methylated CpGs at the MEG3/DLK1:IG-DMR in leukocytes and apparently normal methylation patterns of the two DMRs in the placenta. Maternal uniparental disomy 14 and a deletion involving this imprinted region were excluded.

Conclusions

Such a methylation pattern of the MEG3/DLK1:IG-DMR has not been reported in patients with TS14. It may be possible that a certain degree of irregular hypomethylation at the MEG3/DLK1:IG-DMR has prevented methylation of the MEG3:TSS-DMR in somatic tissues and that a hypermethylation type MLID has occurred at the MEG3/DLK1:IG-DMR to yield the apparently normal methylation pattern in the placenta.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0640-2) contains supplementary material, which is available to authorized users.

Cerebral Cortex Generated from Pluripotent Stem Cells to Model Corticogenesis and Rebuild Cortical Circuits: In Vitro Veritas?

Organoids and cells generated in vitro from pluripotent stem cells (PSCs) are considered to be robust models of development and a conceivable source of transplants for putative cell therapy. However, a fundamental question about organoids and cells generated from PSCs is as follows: do they faithfully reproduce the in vivo tissue they are supposed to mimic and replace? This question is particularly relevant to complex tissues such as the cerebral cortex. In this review, we have tackled this issue by comparing cerebral cortices generated in vitro from PSCs to the in vivo cortex, with a particular focus on their respective cellular composition, molecular and epigenetic signatures, and brain connectivity. In short, in vitro cortex generated from PSCs reproduces most of the cardinal features of the in vivo cortex, including temporal corticogenesis and connectivity when PSC-derived cortical cells are grafted in recipient mouse cortex. However, compared to in vivo cortex, in vitro cortex lacks microglia and blood vessels and is less mature. Recent experiments show that the brain of the transplanted host provides these missing cell types together with an environment that promotes the synaptic maturation of the cortical transplant. Taken together, these data suggest that corticogenesis is largely intrinsic and well recapitulated in vitro, while the full maturation of cortical cells requires additional environmental clues. Finally, we propose some lines of work to improve corticogenesis from PSCs as a tool to model corticogenesis and rebuild cortical circuits.

Characterization of multi-locus imprinting disturbances and underlying genetic defects in patients with chromosome 11p15.5 related imprinting disorders

The identification of multilocus imprinting disturbances (MLID) appears fundamental to uncover molecular pathways underlying imprinting disorders (IDs) and to complete clinical diagnosis of patients. However, MLID genetic associated mechanisms remain largely unknown. To characterize MLID in Beckwith-Wiedemann (BWS) and Silver-Russell (SRS) syndromes, we profiled by MassARRAY the methylation of 12 imprinted differentially methylated regions (iDMRs) in 21 BWS and 7 SRS patients with chromosome 11p15.5 epimutations. MLID was identified in 50% of BWS and 29% of SRS patients as a maternal hypomethylation syndrome. By next-generation sequencing, we searched for putative MLID-causative mutations in genes involved in methylation establishment/maintenance and found two novel missense mutations possibly causative of MLID: one in NLRP2, affecting ADP binding and protein activity, and one in ZFP42, likely leading to loss of DNA binding specificity. Both variants were paternally inherited. In silico protein modelling allowed to define the functional effect of these mutations. We found that MLID is very frequent in BWS/SRS. In addition, since MLID-BWS patients in our cohort show a peculiar pattern of BWS-associated clinical signs, MLID test could be important for a comprehensive clinical assessment. Finally, we highlighted the possible involvement of ZFP42 variants in MLID development and confirmed NLRP2 as causative locus in BWS-MLID.

Expert consensus document: Clinical and molecular diagnosis, screening and management of Beckwith-Wiedemann syndrome: an international consensus statement

Beckwith-Wiedemann syndrome (BWS), a human genomic imprinting disorder, is characterized by phenotypic variability that might include overgrowth, macroglossia, abdominal wall defects, neonatal hypoglycaemia, lateralized overgrowth and predisposition to embryonal tumours. Delineation of the molecular defects within the imprinted 11p15.5 region can predict familial recurrence risks and the risk (and type) of embryonal tumour. Despite recent advances in knowledge, there is marked heterogeneity in clinical diagnostic criteria and care. As detailed in this Consensus Statement, an international consensus group agreed upon 72 recommendations for the clinical and molecular diagnosis and management of BWS, including comprehensive protocols for the molecular investigation, care and treatment of patients from the prenatal period to adulthood. The consensus recommendations apply to patients with Beckwith-Wiedemann spectrum (BWSp), covering classical BWS without a molecular diagnosis and BWS-related phenotypes with an 11p15.5 molecular anomaly. Although the consensus group recommends a tumour surveillance programme targeted by molecular subgroups, surveillance might differ according to the local health-care system (for example, in the United States), and the results of targeted and universal surveillance should be evaluated prospectively. International collaboration, including a prospective audit of the results of implementing these consensus recommendations, is required to expand the evidence base for the design of optimum care pathways.

Maternal 5mCpG Imprints at the PARD6G-AS1 and GCSAML Differentially Methylated Regions Are Decoupled From Parent-of-Origin Expression Effects in Multiple Human Tissues

A hallmark of imprinted genes in mammals is the occurrence of parent-of-origin-dependent asymmetry of DNA cytosine methylation (5^mC) of alleles at CpG islands (CGIs) in their promoter regions. This 5^mCpG asymmetry between the parental alleles creates allele-specific imprinted differentially methylated regions (iDMRs). iDMRs are often coupled to the transcriptional repression of the methylated allele and the activation of the unmethylated allele in a tissue-specific, developmental-stage-specific and/or isoform-specific fashion. iDMRs function as regulatory platforms, built through the recruitment of chemical modifications to histones to achieve differential, parent-of-origin-dependent chromatin segmentation states. Here, we used a comparative computational data mining approach to identify 125 novel constitutive candidate iDMRs that integrate the maximal number of allele-specific methylation region records overlapping CGIs in human methylomes. Twenty-nine candidate iDMRs display gametic 5^mCpG asymmetry, and another 96 are candidate secondary iDMRs. We established the maternal origin of the 5^mCpG imprints of one gametic (PARD6G-AS1) and one secondary (GCSAML) iDMRs. We also found a constitutively hemimethylated, nonimprinted domain at the PWWP2AP1 promoter CGI with oocyte-derived methylation asymmetry. Given that the 5^mCpG level at the iDMRs is not a sufficient criterion to predict active or silent locus states and that iDMRs can regulate genes from a distance of more than 1 Mb, we used RNA-Seq experiments from the Genotype-Tissue Expression project and public archives to assess the transcriptional expression profiles of SNPs across 4.6 Mb spans around the novel maternal iDMRs. We showed that PARD6G-AS1 and GCSAML are expressed biallelically in multiple tissues. We found evidence of tissue-specific monoallelic expression of ZNF124 and OR2L13, located 363 kb upstream and 419 kb downstream, respectively, of the GCSAML iDMR. We hypothesize that the GCSAML iDMR regulates the tissue-specific, monoallelic expression of ZNF124 but not of OR2L13. We annotated the non-coding epigenomic marks in the two maternal iDMRs using data from the Roadmap Epigenomics project and showed that the PARD6G-AS1 and GCSAML iDMRs achieve contrasting activation and repression chromatin segmentations. Lastly, we found that the maternal 5^mCpG imprints are perturbed in several hematopoietic cancers. We conclude that the maternal 5^mCpG imprints at PARD6G-AS1 and GCSAML iDMRs are decoupled from parent-of-origin transcriptional expression effects in multiple tissues.

In Vitro Corticogenesis from Embryonic Stem Cells Recapitulates the In Vivo Epigenetic Control of Imprinted Gene Expression

In vitro corticogenesis from embryonic stem cells (ESCs) is an attractive model of cortical development and a promising tool for cortical therapy. It is unknown to which extent epigenetic mechanisms crucial for cortex development and function, such as parental genomic imprinting, are recapitulated by in vitro corticogenesis. Here, using genome-wide transcriptomic and methylation analyses on hybrid mouse tissues and cells, we find a high concordance of imprinting status between in vivo and ESC-derived cortices. Notably, in vitro corticogenesis strictly reproduced the in vivo parent-of-origin-dependent expression of 41 imprinted genes (IGs), including Mest and Cdkn1c known to control corticogenesis. Parent-of-origin-dependent DNA methylation was also conserved at 14 of 18 imprinted differentially methylated regions. The least concordant imprinted locus was Gpr1-Zdbf2, where the aberrant bi-allelic expression of Zdbf2 and Adam23 was concomitant with a gain of methylation on the maternal allele in vitro. Combined, our data argue for a broad conservation of the epigenetic mechanisms at imprinted loci in cortical cells derived from ESCs. We propose that in vitro corticogenesis helps to define the still poorly understood mechanisms that regulate imprinting in the brain and the roles of IGs in cortical development.

Beckwith-Wiedemann syndrome and pseudohypoparathyroidism type Ib in a patient with multilocus imprinting disturbance: a female-dominant phenomenon?

Although recent studies have often revealed the presence of multilocus imprinting disturbance (MLID) at differentially methylated regions (DMRs) in patients with imprinting disorders (IDs), most patients exhibit clinical features of the original ID only. Here we report a Japanese female patient with Beckwith-Wiedemann syndrome and pseudohypoparathyroidism type Ib. Molecular studies revealed marked methylation defects (MDs) at the Kv-DMR and the GNAS-DMRs and variable MDs at four additional DMRs, in the absence of a mutation in ZFP57, NLRP2, NLRP7, KHDC3L and NLRP5. It is likely that the MDs at the Kv-DMR and the GNAS-DMRs were sufficient to cause clinically recognizable IDs, whereas the remaining MDs were insufficient to result in clinical consequences or took place at DMRs with no disease-causing imprinted gene(s). The development of MLID and the two IDs of this patient may be due to a mutation in a hitherto unknown gene for MLID, or to a reduced amount of DNA methyltransferase-1 (DNMT1) available for the methylation maintenance of DMRs because of the consumption of DNMT1 by the maintenance of X-inactivation. In support of the latter possibility, such co-existence of two IDs has primarily been identified in female patients, and MLID has predominantly been identified as loss of methylations.

Phenotypic spectrum and extent of DNA methylation defects associated with multilocus imprinting disturbances

AIM

To characterize the genotypic and phenotypic extent of multilocus imprinting disturbances (MLID).

MATERIALS & METHODS

We analyzed 37 patients with imprinting disorders (explorative cohort) for DNA methylation changes using the Infinium HumanMethylation450 BeadChip. For validation, three independent cohorts with imprinting disorders or cardinal features thereof were analyzed (84 patients with imprinting disorders, 52 with growth disorder, 81 with developmental delay).

RESULTS

In the explorative cohort 21 individuals showed array-based MLID with each one displaying an Angelman or Temple syndrome phenotype, respectively. Epimutations in ZDBF2 and FAM50B were associated with severe MLID regarding number of affected regions. By targeted analysis we identified methylation changes of ZDBF2 and FAM50B also in the three validation cohorts.

CONCLUSION

We corroborate epimutations in ZDBF2 and FAM50B as frequent changes in MLID whereas these rarely occur in other patients with cardinal features of imprinting disorders. Moreover, we show cell lineage specific differences in the genomic extent of FAM50B epimutation.

Causes and Consequences of Multi-Locus Imprinting Disturbances in Humans

Eight syndromes are associated with the loss of methylation at specific imprinted loci. There has been increasing evidence that these methylation defects in patients are not isolated events occurring at a given disease-associated locus but that some of these patients may have multi-locus imprinting disturbances (MLID) affecting additional imprinted regions. With the recent advances in technology, methylation profiling has revealed that imprinted loci represent only a small fraction of the methylation differences observed between the gametes. To figure out how imprinting anomalies occur at multiple imprinted domains, we have to understand the interplay between DNA methylation and histone modifications in the process of selective imprint protection during pre-implantation reprogramming, which, if disrupted, leads to these complex imprinting disorders (IDs).

Beckwith-Wiedemann syndrome prenatal diagnosis by methylation analysis in chorionic villi

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder that can be prenatally suspected or diagnosed based on established clinical guidelines. Molecular confirmation is commonly performed on amniocytes. The possibility to use fresh (CVF) and cultured (CVC) chorionic villi has never been investigated. To verify whether CVF and CVC are reliable sources of DNA to study fetal methylation, we used pyrosequencing to test the methylation level of a number of differentially methylated regions (DMRs) at several imprinted loci (ICR1, ICR2, H19, PWS/AS-ICR, GNASXL, GNAS1A, ZAC/PLAGL1, and MEST) and at non-imprinted MGMT and RASSF1A promoters. We analyzed these regions in 19 healthy pregnancies and highlighted stable methylation levels between CVF and CVC at ICR1, ICR2, GNASXL, PWS/AS-ICR, and MEST. Conversely, the methylation levels at H19 promoter, GNAS1A and ZAC/PLAGL1 were different in CVC compared to fresh CV. We also investigated ICR1 and ICR2 methylation level of CVF/CVC of 2 BWS-suspected fetuses (P1 and P2). P1 showed ICR2 hypomethylation, P2 showed normal methylation at both ICR1 and ICR2. Our findings, although limited to one case of BWS fetus with an imprinting defect, can suggest that ICR1 and ICR2, but not H19, could be reliable targets for prenatal BWS diagnosis by methylation test in CVF and CVC. In addition, PWS/AS-ICR, GNASXL, and MEST, but not GNAS1A and ZAC/PLAGL1, are steadily hemimethylated in CV from healthy pregnancies, independently from culture. Thus, prenatal investigation of genomic imprinting in CV needs to be validated in a locus-specific manner.

(Epi)genotype-phenotype correlations in Beckwith-Wiedemann syndrome: a paradigm for genomic medicine

Beckwith-Wiedemann syndrome (BWS) is the commonest overgrowth cancer predisposition disorder and represents a model for human imprinting dysregulation and tumorigenesis. BWS features can variably combine and present a widely variable range of severity in the phenotypic expression. This wide spectrum is paralleled at molecular level by complex (epi)genetic defects on chromosome 11p15.5 leading to disrupted expression of imprinted genes controlling growth and cellular proliferation. In this review, we outline the spectrum of clinical manifestations of BWS analyzing their (epi)genotype-phenotype correlations. The differences observed in the phenotypic profiles of BWS molecular subtypes allow a composite view of this syndrome with implications on clinical care, diagnosis, follow-up, and management, and provide directions for future disease monitoring.

Characterization of global loss of imprinting in fetal overgrowth syndrome induced by assisted reproduction

Embryos generated with the use of assisted reproductive technologies (ART) can develop overgrowth syndromes. In ruminants, the condition is referred to as large offspring syndrome (LOS) and exhibits variable phenotypic abnormalities including overgrowth, enlarged tongue, and abdominal wall defects. These characteristics recapitulate those observed in the human loss-of-imprinting (LOI) overgrowth syndrome Beckwith-Wiedemann (BWS). We have recently shown LOI at the KCNQ1 locus in LOS, the most common epimutation in BWS. Although the first case of ART-induced LOS was reported in 1995, studies have not yet determined the extent of LOI in this condition. Here, we determined allele-specific expression of imprinted genes previously identified in human and/or mouse in day ∼105 Bos taurus indicus × Bos taurus taurus F1 hybrid control and LOS fetuses using RNAseq. Our analysis allowed us to determine the monoallelic expression of 20 genes in tissues of control fetuses. LOS fetuses displayed variable LOI compared with controls. Biallelic expression of imprinted genes in LOS was associated with tissue-specific hypomethylation of the normally methylated parental allele. In addition, a positive correlation was observed between body weight and the number of biallelically expressed imprinted genes in LOS fetuses. Furthermore, not only was there loss of allele-specific expression of imprinted genes in LOS, but also differential transcript amounts of these genes between control and overgrown fetuses. In summary, we characterized previously unidentified imprinted genes in bovines and identified misregulation of imprinting at multiple loci in LOS. We concluded that LOS is a multilocus LOI syndrome, as is BWS.