The extent of DNA methylation anticipation due to a genetic defect in ICR1 in Beckwith-Wiedemann syndrome

Thirteen cases support the clinical significance of imprinting center 1 (IC1) microdeletions in Beckwith-Wiedemann syndrome

Most Beckwith-Wiedemann syndrome (BWS) cases are sporadic; nonetheless, imprinting center 1 (IC1) microdeletions have been suggested as a rare cause of familial BWS, with ~ 20 reported cases. We report 13 cases from nine families with IC1 microdeletions. Recurrent 1.4-kb, 1.8-kb, and 2.2-kb deletions were observed. IC1 hypermethylation was identified in all families, and we established a statistically significant relationship between IC1 microdeletions and hypermethylation (OR: 108.17, p = 2.76e-13). This study confirms IC1 microdeletions as a cause of familial BWS, expands the understanding of their molecular mechanisms, and supports a Likely Pathogenic clinical classification for IC1 microdeletions.

Identification of responsible sequences which mutations cause maternal H19-ICR hypermethylation with Beckwith-Wiedemann syndrome-like overgrowth

Beckwith-Wiedemann syndrome (BWS) is caused by a gain of methylation (GOM) at the imprinting control region within the Igf2-H19 domain on the maternal allele (H19-ICR GOM). Mutations in the binding sites of several transcription factors are involved in H19-ICR GOM and BWS. However, the responsible sequence(s) for H19-ICR GOM with BWS-like overgrowth has not been identified in mice. Here, we report that a mutation in the SOX-OCT binding site (SOBS) causes partial H19-ICR GOM, which does not extend beyond CTCF binding site 3 (CTS3). Moreover, simultaneously mutating both SOBS and CTS3 causes complete GOM of the entire H19-ICR, leading to the misexpression of the imprinted genes, and frequent BWS-like overgrowth. In addition, CTS3 is critical for CTCF/cohesin-mediated chromatin conformation. These results indicate that SOBS and CTS3 are the sequences in which mutations cause H19-ICR GOM leading to BWS-like overgrowth and are essential for maintaining the unmethylated state of maternal H19-ICR.

Whole-exome sequencing reveals causative genetic variants for several overgrowth syndromes in molecularly negative Beckwith-Wiedemann spectrum

Background Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder caused by (epi)genetic alterations at 11p15. Because approximately 20% of patients test negative via molecular testing of peripheral blood leukocytes, the concept of Beckwith-Wiedemann spectrum (BWSp) was established to encompass a broader cohort with diverse and overlapping phenotypes. The prevalence of other overgrowth syndromes concealed within molecularly negative BWSp remains unexplored. Methods We conducted whole-exome sequencing (WES) on 69 singleton patients exhibiting molecularly negative BWSp. Variants were confirmed by Sanger sequencing or quantitative genomic PCR. We compared BWSp scores and clinical features between groups with classical BWS (cBWS), atypical BWS or isolated lateralised overgrowth (aBWS+ILO) and overgrowth syndromes identified via WES. Results Ten patients, one classified as aBWS and nine as cBWS, showed causative gene variants for Simpson-Golabi-Behmel syndrome (five patients), Sotos syndrome (two), Imagawa-Matsumoto syndrome (one), glycosylphosphatidylinositol biosynthesis defect 11 (one) or 8q duplication/9p deletion (one). BWSp scores did not distinguish between cBWS and other overgrowth syndromes. Birth weight and height in other overgrowth syndromes were significantly larger than in aBWS+ILO and cBWS, with varying intergroup frequencies of clinical features. Conclusion Molecularly negative BWSp encapsulates other syndromes, and considering both WES and clinical features may facilitate accurate diagnosis.

Placental Mesenchymal Dysplasia and Beckwith-Wiedemann Syndrome

Placental mesenchymal dysplasia (PMD) is characterized by placentomegaly, aneurysmally dilated chorionic plate vessels, thrombosis of the dilated vessels, and large grapelike vesicles, and is often mistaken for partial or complete hydatidiform mole with a coexisting normal fetus. Androgenetic/biparental mosaicism (ABM) has been found in many PMD cases. Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder with complex and diverse phenotypes and an increased risk of developing embryonal tumors. There are five major causative alterations: loss of methylation of imprinting control region 2 (KCNQ1OT1:TSS-DMR) (ICR2-LOM), gain of methylation at ICR1 (H19/IGF2:IG-DMR) (ICR1-GOM), paternal uniparental disomy of 11 (pUPD11), loss-of-function variants of the CDKN1C gene, and paternal duplication of 11p15. Additional minor alterations include genetic variants within ICR1, paternal uniparental diploidy/biparental diploidy mosaicism (PUDM, also called ABM), and genetic variants of KCNQ1. ABM (PUDM) is found in both conditions, and approximately 20% of fetuses from PMD cases are BWS and vice versa, suggesting a molecular link. PMD and BWS share some molecular characteristics in some cases, but not in others. These findings raise questions concerning the timing of the occurrence of the molecularly abnormal cells during the postfertilization period and the effects of these abnormalities on cell fates after implantation.

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.

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.

Hypomethylation of a centromeric block of ICR1 is sufficient to cause Silver-Russell syndrome

Silver-Russell syndrome (SRS) is a representative imprinting disorder. A major cause is the loss of methylation (LOM) of imprinting control region 1 (ICR1) within the IGF2/H19 domain. ICR1 is a gametic differentially methylated region (DMR) consisting of two repeat blocks, with each block including three CTCF target sites (CTSs). ICR1-LOM on the paternal allele allows CTCF to bind to CTSs, resulting in IGF2 repression on the paternal allele and biallelic expression of H19. We analysed 10 differentially methylated sites (DMSs) (ie, seven CTSs and three somatic DMRs within the IGF2/H19 domain, including two IGF2-DMRs and the H19-promoter) in five SRS patients with ICR1-LOM. Four patients showed consistent hypomethylation at all DMSs; however, one exhibited a peculiar LOM pattern, showing LOM at the centromeric region of the IGF2/H19 domain but normal methylation at the telomeric region. This raised important points: there may be a separate regulation of DNA methylation for the two repeat blocks within ICR1; there is independent control of somatic DMRs under each repeat block; sufficient IGF2 repression to cause SRS phenotypes occurs by LOM only in the centromeric block; and the need for simultaneous methylation analysis of several DMSs in both blocks for a correct molecular diagnosis.

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.