Beckwith-Wiedemann Syndrome (BWS) is an overgrowth syndrome caused by various genetic or epigenetic abnormalities in a cluster of imprinted genes on chromosome 11p15. Congenital hyperinsulinism (HI) is one of the cardinal features of BWS, but the pathophysiology of HI in BWS has not been clearly defined. We describe the islet phenotype of a series of infants with severe HI and comorbid BWS who required pancreatectomy for intractable hypoglycemia. The cases are a subset of HI patients who required pancreatectomy and had Beckwith-Wiedemann Syndrome. Molecular testing for BWS was performed by SNP array and chromosome 11p15 methylation analysis. Functional analysis of insulin secretion in pancreatic islets isolated from pancreatectomy samples was completed with perifusion experiments and cytosolic Ca2+ measurements. Similar to what we had previously described in islets isolated from the pancreas of infants with HI due to inactivating mutations in the KATP channel, BWS-HI islets have elevated concentrations of cytosolic calcium and secrete insulin in response to stimulation with a physiologic mixture of amino acids. However, unlike KATPHI islets, most BWS-HI islets retain responsiveness to stimulation with glucose and the KATP channel inhibitor glyburide. Through RNAseq analysis, we observed that expression of KCNQ1, encoding the pore-forming subunit of a voltage-gated K+ channel (Kv7.1), is reduced in BWS-HI islets compared to normal human islets (3-fold; p = 4.5 x 10-7). Our expression analysis and functional evaluation of islets isolated from BWS-HI patients reveal the spectrum of insulin secretion responses found across BWS etiologies and suggest a potential role for loss of KCNQ1 expression in the complex pathophysiology responsible for the hyperinsulinism in BWS.

Imprinted genes, characterized by monoallelic expressions (either maternal or paternal), they are crucial for normal growth and development. Disruption of their monoallelic expressions leads to imprinting disorders (ImpDis). The aim of this study is to achieve proper diagnosis of ImpDis in Egyptian patients through clinical evaluation and genetic testing, emphasizing certain clinical manifestations that may indicate ImpDis to provide accurate diagnosis and genetic counseling. Fifty-three patients, either clinically evaluated for Impaired Disposition (ImpDis) or suspected to have it, were referred from the outpatient genetic clinics at the National Research Center, Egypt. Nineteen patients displayed clinical manifestations of ImpDis syndromes, while 34 showed signs affecting growth, which suggested ImpDis. These growth-related symptoms included growth retardation, feeding problems, failure to thrive, hypoglycemia, obesity, hemihypertrophy, asymmetry, and overgrowth. Of the 19 patients with syndromic ImpDis, 8 were clinically diagnosed with Silver-Russell syndrome (SRS), 7 with Prader-Willi syndrome (PWS), and 4 with Beckwith-Wiedemann syndrome (BWS). We employed methylation-specific multiple ligation-dependent probe amplification (MS-MLPA) for all patients, SNP-array testing for 12 patients, and whole exome sequencing (WES) for one patient. In patients with Silver-Russell syndrome (SRS), one patient exhibited hypermethylation of the GRB10 and MEST genes, along with segmental uniparental disomy (UPD) on chromosome 7 (patient 1). Another patient had a variant in the HMGA2 gene (NM_001300918.1:c.310dup), which, according to the American College of Medical Genetics (ACMG) criteria, was classified as PM2 VUS (patient 2). In patients with Prader-Willi syndrome (PWS), one patient showed hypermethylation of the SNPRN gene (patient 3). In patients with Beckwith-Wiedemann syndrome (BWS), two displayed hypomethylation of the KCNQ-CR region (patients 4 and 5). Among the group of patients with symptoms suggestive of ImpDis, no methylation defects were detected through MS-MLPA. It is crucial to diagnose ImpDis accurately, as understanding the exact cause of ImpDis is important for genetic counseling and personalized medicine. Early diagnosis enables timely interventions, which can improve developmental outcomes. Precision in diagnosis helps differentiate between conditions with overlapping clinical features. HMGA2 mutation should be verified in SRs patients with negative 11p15 methylation defect and matUPD7.

The expression of imprinted genes, which depends on their gamete of origin, is regulated by DNA sequences characterized by differential methylation between the maternal and paternal alleles (also known as germline differentially methylated regions or gDMRs). The most common molecular defect associated with Beckwith-Wiedemann syndrome (BWS), a condition linked to overgrowth and tumours, is the loss of methylation of the KCNQ1OT1-TSS gDMR located on chromosome 11p15.5 (also known as IC2 LoM). Approximately one-third of BWS patients with IC2 LoM exhibit multi-locus imprinting disturbances (MLID). While maternal-effect variants in proteins of the oocyte subcortical maternal complex (SCMC) have been linked to MLID, the underlying mechanisms and health impact of this epigenetic disturbance remain unclear. We used the Infinium EPIC methylation array to investigate whole-genome CpG methylation in 64 BWS patients with IC2 LoM and 37 control subjects. We distinguished two patient groups, one with a variable methylation level of 24 gDMRs and the other with single-locus IC2 LoM. We observed that the mothers of the former patient group carried more variants in maternal-effect genes than those of the latter group, and 50% of them, but none of the latter group had variants in the SCMC genes. Additionally, in the former group, the mothers were older at the time of pregnancy, and the patients showed higher variation in methylation levels of thousands of CpGs located in non-imprinted loci, including protochaderins and cancer-associated genes. We found no differences in clinical features or in the incidence of assisted reproductive technology between the two patient groups. However, multiple affected siblings and recurrent miscarriages were observed only among cases with biallelic maternal-effect SCMC gene variants. This study demonstrates that the BWS patients with MLID exhibit highly variable methylation changes that affect both imprinted and non-imprinted loci in a seemingly stochastic manner throughout the genome. These findings support the hypothesis that MLID results from the interaction of maternal-effect genes and environmental factors in aged oocytes, leading to disordered DNA methylation in the whole genome. Future research should investigate whether and how these epimutations impact the health of affected individuals, particularly in adulthood.

Beckwith-Wiedemann syndrome (BWS) is a congenital imprinting disorder (ID) caused by molecular defects in the 11p15.5 imprinted region, such as hypomethylation of the KCNQ1OT1:TSS-differentially methylated region (KCNQ1OT1-DMR) and hypermethylation of the H19/IGF2:IG-DMR, and maternal CDKN1C pathogenic variants, with various clinical characteristics, including overgrowth and macroglossia. Recently, the concept of Beckwith-Wiedemann spectrum (BWSp) and a clinical scoring system for BWS have been proposed, and cases with four or more points are diagnosed with classic BWS, and 20% of cases with BWS have no molecular defects in the 11p15.5 imprinted region. Pseudohypoparathyroidism type 1B (PHP1B, alias inactivating parathyroid hormone (PTH)/PTH-related protein signaling disorder 3) has characteristics of hormone resistance, particularly PTH, caused by methylation defects in DMRs at the GNAS locus (GNAS-DMRs). Some cases with PHP1B show postnatal overgrowth, which overlaps the BWS-phenotype. However, no studies have conducted a multi-locus methylation analysis for the ID-responsible DMRs other than the DMRs in 11p15.5 in cases with the BWS-phenotype and without molecular defects in the 11p15.5 imprinted region. We conducted methylation analysis using pyrosequencing in 77 patients showing the BWS-phenotype without molecular defects in the 11p15.5 imprinted region. Consequently, we identified three patients with methylation defects in the GNAS-DMRs. Patients 1, 2, and 3 had 9, 5, and 4 points in a BWSp score, respectively. All three patients had macroglossia and postnatal overgrowth. Further analyses, methylation-specific multiple ligation-dependent probe amplification for multiple DMRs, array-based methylation analysis, exome sequencing, array comparative genome hybridization analysis, and microsatellite marker analysis showed 9p deletion in Patient 1 and paternal uniparental isodisomy of chromosome 20 in Patient 2 together with multiple methylation defects in DMRs other than the GNAS-DMRs. Patient 3 had methylation defects in only the GNAS-DMRs. Methylation defects in the GNAS-DMRs can cause the BWS-phenotype. For cases with the BWS-phenotype but no molecular defects in the 11p15.5 imprinted region, methylation analysis for the DMRs at the GNAS locus should be considered.

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder caused by various genetic or epigenetic alterations involving growth regulatory genes located on chromosome 11p15.5 region. Conventionally, most cases of BWS are diagnosed during the neonatal period or early childhood. Early prenatal diagnosis is very important because it provides information regarding the prognosis, guidance of delivery preparation, and postnatal care plan. We report two cases of BWS diagnosed in utero using exome sequencing (ES) after the early identification of fetal omphalocele and normal findings of microarray and methylation analyses. Case 1 carried a de novo CDKN1C c.694C>T (p.Gln232*) variant. Case 2 carried a familial CDKN1C c.827_828delinsAA (p.Phe276*) variant; another member in the family presented with features of BWS. In both cases, no macrosomia and visceromegaly were demonstrated. Although fetal omphalocele was identified in the first trimester, invasive testing was delayed to the early second trimester for methylation in the two cases. Fetal omphalocele should not be regarded as just an abdominal wall defect. When a fetal omphalocele was identified, a detailed family history, especially with searching for the signs of BWS in familial members, should be undertaken. For an omphalocele, ES is an option for patients after normal microarray and methylation analyses.