Cancer predisposition signaling in Beckwith-Wiedemann Syndrome drives Wilms tumor development.

BACKGROUND: Wilms tumor (WT) exhibits structural and epigenetic changes at chromosome 11p15, which also cause Beckwith-Wiedemann Syndrome (BWS). Children diagnosed with BWS have increased risk for WT. The aim of this study is to identify the molecular signaling signatures in BWS driving these tumors. METHODS: We performed whole exome sequencing, methylation array analysis, and gene expression analysis on BWS-WT samples. Our data were compared to publicly available nonBWS data. We categorized WT from BWS and nonBWS patients by assessment of 11p15 methylation status and defined 5 groups- control kidney, BWS-nontumor kidney, BWS-WT, normal-11p15 nonBWS-WT, altered-11p15 nonBWS-WT. RESULTS: BWS-WT samples showed single nucleotide variants in BCORL1, ASXL1, ATM and AXL but absence of recurrent gene mutations associated with sporadic WT. We defined a narrow methylation range stratifying nonBWS-WT samples. BWS-WT and altered-11p15 nonBWS-WT showed enrichment of common and unique molecular signatures based on global differential methylation and gene expression analysis. CTNNB1 overexpression and broad range of interactions were seen in the BWS-WT interactome study. CONCLUSION: While WT predisposition in BWS is well-established, as are 11p15 alterations in nonBWS-WT, this study focused on stratifying tumor genomics by 11p15 status. Further investigation of our findings may identify novel therapeutic targets in WT oncogenesis.

A dyadic approach to the delineation of diagnostic entities in clinical genomics.

The delineation of disease entities is complex, yet recent advances in the molecular characterization of diseases provide opportunities to designate diseases in a biologically valid manner. Here, we have formalized an approach to the delineation of Mendelian genetic disorders that encompasses two distinct but inter-related concepts: (1) the gene that is mutated and (2) the phenotypic descriptor, preferably a recognizably distinct phenotype. We assert that only by a combinatorial or dyadic approach taking both of these attributes into account can a unitary, distinct genetic disorder be designated. We propose that all Mendelian disorders should be designated as "GENE-related phenotype descriptor" (e.g., "CFTR-related cystic fibrosis"). This approach to delineating and naming disorders reconciles the complexity of gene-to-phenotype relationships in a simple and clear manner yet communicates the complexity and nuance of these relationships.

A Novel Macroglossia Severity Index for Beckwith-Wiedemann Syndrome.

OBJECTIVE/ SUMMARY BACKGROUND DATA: We propose the first classification scheme for macroglossia in patients with Beckwith-Wiedemann Syndrome (BWS), the BWS Index of macroGlossia (BIG). METHODS: Patients with molecularly confirmed BWS seen from 2004-2023 were included to develop this system. Relationships among BIG scores, tongue reduction surgery, BWS clinical score, percent mosaicism, and polysomnography findings were examined. RESULTS: Patients were classified from BIG0 to BIG3. BIG0 includes those without macroglossia; BIG1 includes those with macroglossia not protruding beyond the teeth/alveolus; BIG2 includes those with tongue protrusion past the teeth/alveolus to the lips but that can be contained within the mouth; and BIG3 includes those with tongues that protrude beyond the teeth/alveolus and lips but that cannot be closed within the mouth. Of the 459 patients with molecularly confirmed BWS, 266 (58.0%) patients were scored. One hundred and eleven (41.7%) were BIG0, 44 (16.5%) were BIG1, 90 (33.8%) were BIG2, and 21 (7.9%) were BIG3. As scores increased, patients had an increased incidence of tongue reduction surgery (BIG0: 0% versus BIG1: 20.5% versus BIG2: 51.1% versus BIG3: 100%; r=0.66, P <0.01). Higher BIG scores were associated with elevated BWS clinical scores (r=0.68, P <0.01) and increased tissue mosaicism (r=0.50, P <0.01) as well as trends towards worse obstructive apnea-hypopnea indices (r=0.29, P =0.02) and lower SpO 2 nadirs (r=-0.29, P =0.02). CONCLUSION: In this large series of patients with Beckwith-Wiedemann Syndrome, increased BIG score correlates with undergoing tongue reduction surgery and increased phenotypic severity. Adoption of the BIG scoring system may facilitate communication and risk stratification across institutions.

Expanded phenotype and cancer risk in patients with Beckwith-Wiedemann spectrum caused by CDKN1C variants.

Beckwith-Wiedemann spectrum (BWSp) is caused by genetic and epigenetic alterations on chromosome 11 that regulate cell growth and division. Considering the diverse phenotypic landscape in BWSp, the characterization of the CDKN1C molecular subtype remains relatively limited. Here, we investigate the role of CDKN1C in the broader BWSp phenotype. Notably, patients with CDKN1C variants appear to exhibit a different tumor risk than other BWSp molecular subtypes. We performed a comprehensive literature review using the search term "CDKN1C Beckwith" to identify 113 cases of patients with molecularly confirmed CDKN1C-BWSp. We then assessed the genotype and phenotype in a novel cohort of patients with CDKN1C-BWSp enrolled in the BWS Research Registry. Cardinal and suggestive features were evaluated for all patients reported, and tumor risk was established based on available reports. The most common phenotypes included macroglossia, omphalocele, and ear creases/pits. Tumor types reported from the literature included neuroblastoma, acute lymphocytic leukemia, superficial spreading melanoma, and intratubular germ cell neoplasia. Overall, this study identifies unique features associated with CDKN1C variants in BWSp, enabling more accurate clinical management. The absence of Wilms tumor and hepatoblastoma suggests that screening for these tumors may not be necessary, while the neuroblastoma risk warrants appropriate screening recommendations.

Visualizing allele-specific expression in single cells reveals epigenetic mosaicism in an H19 loss-of-imprinting mutant.

Imprinting is a classic mammalian epigenetic phenomenon that results in expression from a single parental allele. Imprinting defects can lead to inappropriate expression from the normally silenced allele, but it remains unclear whether every cell in a mutant organism follows the population average, which would have profound implications for human imprinting disorders. Here, we apply a new fluorescence in situ hybridization method that measures allele-specific expression in single cells to address this question in mutants exhibiting aberrant H19/Igf2 (insulin-like growth factor 2) imprinting. We show that mutant primary embryonic mouse fibroblasts are comprised of two subpopulations: one expressing both H19 alleles and another expressing only the maternal copy. Only in the latter cell population is Igf2 expression detected. Furthermore, the two subpopulations are stable in that cells do not interconvert between the two expression patterns. Combined small input methylation analysis and transcriptional imaging revealed that these two mutant subpopulations exhibit distinct methylation patterns at their imprinting control regions. Consistently, pharmacological inhibition of DNA methylation reduced the proportion of monoallelic cells. Importantly, we observed that the same two subpopulations are also present in vivo within murine cardiac tissue. Our results establish that imprinting disorders can display striking single-cell heterogeneity in their molecular phenotypes and suggest that such heterogeneity may underlie epigenetic mosaicism in human imprinting disorders.

Adult experiences in Beckwith-Wiedemann syndrome.

Beckwith-Wiedemann syndrome (BWS) is an overgrowth and epigenetic disorder caused by changes on chromosome 11p15. The primary features requiring management in childhood include macroglossia, omphalocele, lateralized overgrowth, hyperinsulinism, and embryonal tumors. Management guidelines have not been developed for adults with BWS and there have been few studies to assess the clinical needs of these patients. Furthermore, there have been few studies on the psychosocial implications of BWS in children or adults. Here, we present a descriptive summary of data gathered from two separate adult BWS cohorts. The first, a patient-based survey cohort, includes self-reported health information and recollections about BWS experiences, while the second provides results of a medical record-based assessment from patients in an overgrowth registry. Results highlight the clinical features and medical issues affecting two large independent cohorts of adults with BWS while noting similarities. Open-ended questions asked of the survey cohort yielded themes to guide future qualitative studies. Finally, the study demonstrated the reliability of patient-reported data and the utility of international partnerships in this context.

Investigation of a pervasive immune, cardiac, and behavioral phenotype in Beckwith-Wiedemann syndrome: A case report.

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder caused by genetic and epigenetic changes in the chromosome 11p15 region. The syndrome is characterized by a wide range of features including macrosomia, lateralized overgrowth, abdominal wall defects, and hypoglycemia. BWS presentation is variable across the entire patient population, but certain areas including immunology, cardiology, and behavioral differences are not well characterized. We present a case of a male patient with BWS due to the most common cause of BWS, loss of methylation at imprinting center 2 with a variable phenotype, including classical features (macrosomia, macroglossia, omphalocele, placentomegaly and mild lateralized overgrowth) in addition to uncommon features (immune deficiency, developmental delays, and pulmonary stenosis) not typically seen in BWS. This study defines a patient's clinical presentation and course and highlights the need to consider atypical organ systems in BWS as either an expansion of the phenotype or co-existing conditions to develop personalized care models.

Familial Beckwith-Wiedemann syndrome in a multigenerational family: Forty years of careful phenotyping.

Beckwith-Wiedemann Spectrum (BWSp) is an overgrowth and cancer predisposition disorder characterized by a wide spectrum of phenotypic manifestations including macroglossia, abdominal wall defects, neonatal hypoglycemia, and predisposition to embryonal tumors. In 1981, Best and Hoekstra reported four patients with BWSp in a single family which suggested autosomal dominant inheritance, but standard clinical testing for BWSp was not available during this time. Meticulous phenotyping of this family has occurred over the past 40 years of follow-up with additional family members being identified and samples collected for genetic testing. Genetic testing revealed a pathogenic mutation in CDKN1C, consistent with the most common cause of familial BWSp. CDKN1C mutations account for just 5% of sporadic cases of BWSp. Here, we report the variable presentation of BWSp across the individuals affected by the CDKN1C mutation and other extended family members spanning multiple generations, all examined by the same physician. Additional phenotypes thought to be atypical in patients with BWSp were reported which included cardiac abnormalities. The incidence of tumors was documented in extended family members and included rhabdomyosarcoma, astrocytoma, and thyroid carcinoma, which have previously been reported in patients with BWSp. These observations suggest that in addition to the inheritance of the CDKN1C variant, there are modifying factors in this family driving the phenotypic spectrum observed. Alternative theories are suggested to explain the etiology of clinical variability including diffused mosaicism, anticipation, and the presence of additional variants tracking in the family. This study highlights the necessity of long-term follow-up in patients with BWSp and consideration of individual familial characteristics in the context of phenotype and/or (epi)genotype associations.

Overgrowth syndromes, diagnosis and management.

PURPOSE OF REVIEW: This review will focus on the current knowledge of the diagnosis and management of overgrowth syndromes with specific focus on mosaic conditions and treatment strategies. RECENT FINDINGS: With the implementation of massively parallel sequencing, the genetic etiology of many classically described overgrowth syndromes have been identified. More recently, the role of mosaic genetic changes has been well described in numerous syndromes. Furthermore, the role of imprinting and methylation, especially of the 11p15 region, has been shown to be instrumental for growth. Perhaps most importantly, many overgrowth syndromes carry an increased risk of neoplasm formation especially in the first 10 years of life and possibly beyond. The systematic approach to the child with overgrowth will aide in timely diagnosis and efficiently align them with appropriate screening strategies. In some cases, precision medical interventions are available to target the perturbed growth signaling pathways. SUMMARY: The systematic approach to the child with overgrowth aids in the standardization of the diagnostic pathway for these young patients, thereby expediting the diagnostic timeline, enabling rigorous monitoring, and delivering tailored therapeutic interventions.

The role of CTCF in the organization of the centromeric 11p15 imprinted domain interactome.

DNA methylation, chromatin-binding proteins, and DNA looping are common components regulating genomic imprinting which leads to parent-specific monoallelic gene expression. Loss of methylation (LOM) at the human imprinting center 2 (IC2) on chromosome 11p15 is the most common cause of the imprinting overgrowth disorder Beckwith-Wiedemann Syndrome (BWS). Here, we report a familial transmission of a 7.6 kB deletion that ablates the core promoter of KCNQ1. This structural alteration leads to IC2 LOM and causes recurrent BWS. We find that occupancy of the chromatin organizer CTCF is disrupted proximal to the deletion, which causes chromatin architecture changes both in cis and in trans. We also profile the chromatin architecture of IC2 in patients with sporadic BWS caused by isolated LOM to identify conserved features of IC2 regulatory disruption. A strong interaction between CTCF sites around KCNQ1 and CDKN1C likely drive their expression on the maternal allele, while a weaker interaction involving the imprinting control region element may impede this connection and mediate gene silencing on the paternal allele. We present an imprinting model in which KCNQ1 transcription is necessary for appropriate CTCF binding and a novel chromatin conformation to drive allele-specific gene expression.

Improved molecular detection of mosaicism in Beckwith-Wiedemann Syndrome.

BACKGROUND: Beckwith-Wiedemann Syndrome (BWS) is characterised by overgrowth and tumour predisposition. While multiple epigenetic and genetic mechanisms cause BWS, the majority are caused by methylation defects in imprinting control regions on chromosome 11p15.5. Disease-causing methylation defects are often mosaic within affected individuals. Phenotypic variability among individuals with chromosome 11p15.5 defects and tissue mosaicism led to the definition of the Beckwith-Wiedemann Spectrum (BWSp). Molecular diagnosis of BWSp requires use of multiple sensitive diagnostic techniques to reliably detect low-level aberrations. METHODS: Multimodal BWS diagnostic testing was performed on samples from 1057 individuals. Testing included use of a sensitive qRT-PCR-based quantitation method enabling identification of low-level mosaic disease, identification of CNVs within 11p15.5 via array comparative genomic hybridisation or qRT-PCR, and Sanger sequencing of CDKN1C. RESULTS: A molecular diagnosis was confirmed for 27.4% of individuals tested, of whom 43.4% had mosaic disease. The presence of a single cardinal feature was associated with a molecular diagnosis of BWSp in 20% of cases. Additionally, significant differences in the prevalence of mosaic disease among BWS molecular subtypes were identified. Finally, the diagnostic yield obtained by testing solid tissue samples from individuals with negative blood testing results shows improved molecular diagnosis. CONCLUSION: This study highlights the prevalence of mosaic disease among individuals with BWSp and the increases in diagnostic yield obtained via testing both blood and solid tissue samples from affected individuals. Additionally, the results establish the presence of a molecular diagnosis in individuals with very subtle features of BWSp.

Allele-specific RNA imaging shows that allelic imbalances can arise in tissues through transcriptional bursting.

Extensive cell-to-cell variation exists even among putatively identical cells, and there is great interest in understanding how the properties of transcription relate to this heterogeneity. Differential expression from the two gene copies in diploid cells could potentially contribute, yet our ability to measure from which gene copy individual RNAs originated remains limited, particularly in the context of tissues. Here, we demonstrate quantitative, single molecule allele-specific RNA FISH adapted for use on tissue sections, allowing us to determine the chromosome of origin of individual RNA molecules in formaldehyde-fixed tissues. We used this method to visualize the allele-specific expression of Xist and multiple autosomal genes in mouse kidney. By combining these data with mathematical modeling, we evaluated models for allele-specific heterogeneity, in particular demonstrating that apparent expression from only one of the alleles in single cells can arise as a consequence of low-level mRNA abundance and transcriptional bursting.

Expanding the genetic landscape of oral-facial-digital syndrome with two novel genes.

Oral-facial-digital syndromes (OFDS) are a heterogeneous and rare group of Mendelian disorders characterized by developmental abnormalities of the oral cavity, face, and digits caused by dysfunction of the primary cilium, a mechanosensory organelle that exists atop most cell types that facilitates organ patterning and growth. OFDS is inherited both in an X-linked dominant, X-linked recessive, and autosomal recessive manner. Importantly, though many of the causal genes for OFDS have been identified, up to 40% of OFD syndromes are of unknown genetic basis. Here we describe three children with classical presentations of OFDS including lingual hamartomas, polydactyly, and characteristic facial features found by exome sequencing to harbor variants in causal genes not previously associated with OFDS. We describe a female with hypothalamic hamartoma, urogenital sinus, polysyndactyly, and multiple lingual hamartomas consistent with OFDVI with biallelic pathogenic variants in CEP164, a gene associated with ciliopathy-spectrum disease, but never before with OFDS. We additionally describe two unrelated probands with postaxial polydactyly, multiple lingual hamartomas, and dysmorphic features both found to be homozygous for an identical TOPORS missense variant, c.29 C>A; (p.Pro10Gln). Heterozygous TOPORS pathogenic gene variants are associated with autosomal dominant retinitis pigmentosa, but never before with syndromic ciliopathy. Of note, both probands are of Dominican ancestry, suggesting a possible founder allele.

The Prevalence of Difficult Airway in Children With Beckwith-Wiedemann Syndrome: A Retrospective Cohort Study.

BACKGROUND: Beckwith-Wiedemann syndrome (BWS) is the most common congenital overgrowth disorder with an incidence of approximately 1 in 10,000 live births. The condition is characterized by lateralized overgrowth, abdominal wall defects, macroglossia, and predisposition to malignancy. Historically, children with BWS have been presumed to have difficult airways; however, most of the evidence to support this has been anecdotal and derived from case reports. Our study aimed to determine the prevalence of difficult airway in patients with BWS. We hypothesized that most patients with BWS would not have difficult airways. METHODS: We retrospectively reviewed the electronic medical records of patients enrolled in our institution's BWS registry. Patients with a molecular diagnosis of BWS who were anesthetized between January 2012 and July 2019 were included for analysis. The primary outcome was the presence of difficult airway, defined as difficult facemask ventilation, difficult intubation, or both. We defined difficult intubation as the need for 3 or more tracheal intubation attempts and the need for advanced airway techniques (nondirect laryngoscopy) to perform tracheal intubation or a Cormack and Lehane grade ≥3 during direct laryngoscopy. Secondary objectives were to define predictors of difficult intubation and difficult facemask ventilation, and the prevalence of adverse airway events. Generalized linear mixed-effect models were used to account for multiple anesthesia events per patient. RESULTS: Of 201 BWS patients enrolled in the registry, 60% (n = 122) had one or more documented anesthetics, for a total of 310 anesthetics. A preexisting airway was present in 22 anesthetics. The prevalence of difficult airway was 5.3% (95% confidence interval [CI], 3.0-9.3; 18 of 288) of the cases. The prevalence of difficult intubation was 5.2% (95% CI, 2.9-9.4; 12 of 226). The prevalence of difficult facemask ventilation was 2.9% (95% CI, 1.4-6.2; 12 of 277), and facemask ventilation was not attempted in 42 anesthetics. Age <1 year, macroglossia, lower weight, endocrine comorbidities, plastics/craniofacial surgery, tongue reduction surgery, and obstructive sleep apnea were associated with difficult airways in cases without a preexisting airway. About 83.8% (95% CI, 77.6-88.5) of the cases were intubated with a single attempt. Hypoxemia was the most common adverse event. CONCLUSIONS: The prevalence of difficult tracheal intubation and difficult facemask ventilation in children with BWS was 5.2% and 2.9%, respectively. We identified factors associated with difficult airway, which included age <1 year, macroglossia, endocrine abnormalities, plastics/craniofacial surgery, tongue reduction surgery, and obstructive sleep apnea. Clinicians should anticipate difficult airways in patients with these factors.

Prenatal molecular testing and diagnosis of Beckwith-Wiedemann syndrome.

OBJECTIVE: The objective of this study was to describe molecular findings and phenotypic features among individuals referred for prenatal Beckwith-Wiedemann syndrome (BWS) testing. METHODS: Molecular diagnostic testing was performed using a sensitive quantitative real-time PCR-based assay capable of detecting mosaic methylation to the level of 3% at IC1 and IC2. Sanger sequencing of CDKN1C was performed in cases with normal methylation. RESULTS: Of the 94 patients tested, a molecular diagnosis was identified for 25.5% of cases; 70.9% of diagnosed cases had loss of methylation at IC2, 4.2% had gain of methylation at IC1, 12.5% had paternal uniparental isodisomy, and 12.5% had CDKN1C loss-of-function variants. Methylation level changes in prenatal cases were significantly greater than changes identified in cases tested after birth. Cases with a prenatal molecular diagnosis had a significantly greater number of BWS-associated phenotypic features. The presence of either macroglossia or placentomegaly was most predictive of a BWS diagnosis. CONCLUSION: Our results support the consensus statement advocating BWS molecular testing for all patients with one or more BWS-associated prenatal features and suggest that low-level mosaic methylation changes may be uncommon among prenatal BWS diagnoses.

11p15.5 epimutations in children with Wilms tumor and hepatoblastoma detected in peripheral blood.

BACKGROUND: Constitutional or somatic mosaic epimutations are increasingly recognized as a mechanism of gene dysregulation resulting in cancer susceptibility. Beckwith-Wiedemann syndrome is the cancer predisposition syndrome most commonly associated with epimutation and is extremely variable in its phenotypic presentation, which can include isolated tumors. Because to the authors' knowledge large-scale germline DNA sequencing studies have not included methylation analysis, the percentage of pediatric cancer predisposition that is due to epimutations is unknown. METHODS: Germline methylation testing at the 11p15.5 locus was performed in blood for 24 consecutive patients presenting with hepatoblastoma (3 patients) or Wilms tumor (21 patients). RESULTS: Six individuals with Wilms tumor and 1 patient with hepatoblastoma were found to have low-level gain of methylation at imprinting control 1, and a child with hepatoblastoma was found to have loss of methylation at imprinting control 2. The loss of methylation at imprinting control 2 was found to be maternally inherited, despite not being associated with any detectable genomic alteration. CONCLUSIONS: Overall, 33% of patients (8 of 24 patients) with Wilms tumor or hepatoblastoma were found to have an epigenetic susceptibility that was detectable in the blood. It is interesting to note that low-level gain of methylation at imprinting control 1 predominantly was detected in females with bilateral Wilms tumors. Further studies in larger cohorts are needed to determine the efficacy of testing all patients with Wilms tumor or hepatoblastoma for 11p15.5 epimutations in the blood as part of DNA analysis because this hallmark of predisposition will not be detected by sequencing-based approaches and detecting a cancer predisposition may modify treatment.

Novel variants in CDH2 are associated with a new syndrome including Peters anomaly.

Peters anomaly (PA) is a congenital corneal opacity associated with corneo-lenticular attachments. PA can be isolated or part of a syndrome with most cases remaining genetically unsolved. Exome sequencing of a trio with syndromic PA and 145 additional unexplained probands with developmental ocular conditions identified a de novo splicing and three novel missense heterozygous CDH2 variants affecting the extracellular cadherin domains in four individuals with PA. Syndromic anomalies were seen in three individuals and included left-sided cardiac lesions, dysmorphic facial features, and decreasing height percentiles; brain magnetic resonance imaging identified agenesis of the corpus callosum and hypoplasia of the inferior cerebellar vermis. CDH2 encodes for N-cadherin, a transmembrane protein that mediates cell-cell adhesion in multiple tissues. Immunostaining in mouse embryonic eyes confirmed N-cadherin is present in the lens stalk at the time of separation from the future cornea and in the developing lens and corneal endothelium at later stages, supporting a possible role in PA. Previous studies in animal models have noted the importance of Cdh2/cdh2 in the development of the eye, heart, brain, and skeletal structures, also consistent with the patient features presented here. Examination of CDH2 in additional patients with PA is indicated to confirm this association.

Tatton-Brown-Rahman syndrome: Six individuals with novel features.

Tatton-Brown Rahman syndrome (TBRS) is an overgrowth-intellectual disability syndrome caused by heterozygous variants in DNMT3A. Seventy-eight individuals have been reported with a consistent phenotype of somatic overgrowth, mild to moderate intellectual disability, and similar dysmorphisms. We present six individuals with TBRS, including the youngest individual thus far reported, first individual to be diagnosed with tumor testing and two individuals with variants at the Arg882 domain, bringing the total number of reported cases to 82. Patients reported herein have additional clinical features not previously reported in TBRS. One patient had congenital diaphragmatic hernia. One patient carrying the recurrent p.Arg882His DNMT3A variant, who was previously reported as having a phenotype due to a truncating variant in the CLTC gene, developed a ganglioneuroblastoma at 18 months and T-cell lymphoblastic lymphoma at 6 years of age. Four patients manifested symptoms suggestive of autonomic dysfunction, including central sleep apnea, postural orthostatic hypotension, and episodic vasomotor instability in the extremities. We discuss the molecular and clinical findings in our patients with TBRS in context of existing literature.

Characterization of the Beckwith-Wiedemann spectrum: Diagnosis and management.

Beckwith-Wiedemann syndrome (BWS) is the most common epigenetic overgrowth and cancer predisposition disorder. Due to both varying molecular defects involving chromosome 11p15 and tissue mosaicism, patients can present with a variety of clinical features, leading to the newly defined Beckwith-Wiedemann spectrum (BWSp). The BWSp can be further divided into three subsets of patients: those presenting with classic features, those presenting with isolated lateralized overgrowth (ILO) and those not fitting into the previous two categories, termed atypical BWSp. Previous reports of patients with BWS have focused on those with the more recognizable, classic features, and limited information is available on those who fit into the atypical and ILO categories. Here, we present the first cohort of patients recruited across the entire BWSp, describe clinical features and molecular diagnostic characteristics, and provide insight into practical diagnosis and management recommendations that we have gained from this cohort.