The clinical phenotype of mosaicism for genome-wide paternal uniparental disomy: Two new reports

An expert opinion on rescuing atypically pronucleated human zygotes by molecular genetic fertilization checks in IVF

IVF laboratories routinely adopt morphological pronuclear assessment at the zygote stage to identify abnormally fertilized embryos deemed unsuitable for clinical use. In essence, this is a pseudo-genetic test for ploidy motivated by the notion that biparental diploidy is required for normal human life and abnormal ploidy will lead to either failed implantation, miscarriage, or significant pregnancy complications, including molar pregnancy and chorionic carcinoma. Here, we review the literature associated with ploidy assessment of human embryos derived from zygotes displaying a pronuclear configuration other than the canonical two, and the related pregnancy outcome following transfer. We highlight that pronuclear assessment, although associated with aberrant ploidy outcomes, has a low specificity in the prediction of abnormal ploidy status in the developing embryo, while embryos deemed abnormally fertilized can yield healthy pregnancies. Therefore, this universal strategy of pronuclear assessment invariably leads to incorrect classification of over 50% of blastocysts derived from atypically pronucleated zygotes, and the systematic disposal of potentially viable embryos in IVF. To overcome this limitation of current practice, we discuss the new preimplantation genetic testing technologies that enable accurate identification of the ploidy status of preimplantation embryos and suggest a progress from morphology-based checks to molecular fertilization check as the new gold standard. This alternative molecular fertilization checking represents a possible non-incremental and controversy-free improvement to live birth rates in IVF as it adds to the pool of viable embryos available for transfer. This is especially important for the purposes of 'family building' or for poor-prognosis IVF patients where embryo numbers are often limited.

[Sperm Mosaic Variants and Their Influence on the Offspring]

Genomic mosaicism arising from mosaic variants is a phenomenon that describes the presence of a cell or cell populations with different genome compositions from the germline cells of an individual. It comprises all types of genetic variants. A large proportion of childhood genetic disorders are defined as being de novo, meaning that the disease-causing mutations are only detected in the proband, not in any of the parents. Population studies show that 80% of the de novo mutations arise from the paternal haplotype, that is, from paternal sperm mosaicism. This review provides a summary of the types and detection strategies of sperm mosaicism. In addition, it provides discussions on how recent studies demonstrated that genomic mosaic mutations in parents, especially those in the paternal sperms, could be inherited by the offspring and cause childhood disorders. According to the previous findings of the author's research team, sperm mosaicism derived from early embryogenesis and primordial germ cell stages can explain 5% to 20% of the de novo mutations related to clinical phenotypes and can serve as an important predictor of both rare and complex disorders. Sperm mosaicism shows great potential for clinical genetic diagnosis and consultations. Based on the published literature, the author suggests that, large-scale screening for de novo sperm mosaic mutations and population-based genetic screening should be conducted in future studies, which will greatly enhance the risk assessment in the offspring and effectively improve the genetic health at the population level. Implementation of direct sperm detection for de novo mutations will significantly increase the efficiency of the stratification of patient cohorts and improve recurrence risk assessment for future births. Future research in the field should be focused on the impact of environmental and lifestyle factors on the health of the offspring through sperms and their modeling of mutation signatures. In addition, targeted in vitro modeling of sperm mutations will also be a promising direction.

Prenatal detection of mosaicism for a genome wide uniparental disomy cell line in a cohort of patients: Implications and outcomes

OBJECTIVES

To investigate the prenatal detection rate of mosaicism by SNP microarray analysis, in which an individual has not one, but two, complete genomes (sets of DNA) in their body, a normal biparental line with a Genome Wide Uniparental Disomy (GWUPD) cell line was used.

METHODS

This study retrospectively examines the prenatal detection of GWUPD in a cohort of ∼90,000 prenatal specimens and ∼20,000 products of conceptions (POCs) that were studied by SNP microarray.

RESULTS

In total, 25 cases of GWUPD were detected; 16 cases were detected prenatally with GWUPD (∼0.018%) and 9 POCs revealed GWUPD (0.045%). The nine POC specimens presented with placental abnormalities. The 12 amniotic fluid specimens were ascertained because of abnormal ultrasound findings. Nine of 12 pregnancies had findings consistent with Beckwith-Wiedemann syndrome or because of abnormal placentas. However, three pregnancies were detected with GWUPD of maternal origin, with less common findings and demonstrated maternal origin. Four other pregnancies showed GWUPD in a chorionic villus sample, but normal findings in amniotic fluid and apparently normal fetal development.

CONCLUSIONS

This cohort with GWUPD mosaicism expands our understanding of GWUPD and has implications for prenatal care and counseling. Additional studies are necessary to understand the rarer maternal GWUPD.

SNP chromosome microarray genotyping for detection of uniparental disomy in the clinical diagnostic laboratory

Single nucleotide polymorphism (SNP) chromosome microarray is well established for investigation of children with intellectual deficit/development delay and prenatal diagnosis of fetal malformation but has also emerged for uniparental disomy (UPD) genotyping. Despite published guidelines on clinical indications for testing there are no laboratory guidelines published for performing SNP microarray UPD genotyping. We evaluated SNP microarray UPD genotyping using Illumina beadchips on family trios/duos within a clinical cohort (n=98) and then explored our findings in a post-study audit (n=123). UPD occurred in 18.6% and 19.5% cases, respectively, with chromosome 15 most frequent (62.5% and 25.0%). UPD was predominantly maternal in origin (87.5% and 79.2%), highest in suspected genomic imprinting disorder cases (56.3% and 41.7%) but absent amongst children of translocation carriers. We assessed regions of homozygosity among UPD cases. The smallest interstitial and terminal regions were 2.5 Mb and 9.3 Mb, respectively. We found regions of homozygosity confounded genotyping in a consanguineous case with UPD15 and another with segmental UPD due to non-informative probes. In a unique case with chromosome 15q UPD mosaicism, we established the detection limit of mosaicism as ∼5%. From the benefits and pitfalls identified in this study, we propose a testing model and recommendations for UPD genotyping by SNP microarray.

Mosaic genome-wide paternal uniparental disomy after discordant results from primary fetal samples and cultured cells

Mosaic genome-wide paternal uniparental disomy (GWpUPD) is a rare condition in which two euploid cell lines coexist in the same individual, one with biparental content and one with genome-wide paternal isodisomy. We report a complex prenatal diagnosis with discordant results from cultured and uncultured samples. A pregnant woman was referred for placental mesenchymal dysplasia and fetal omphalocele. Karyotype, array-CGH and Beckwith-Wiedemann Syndrome (BWS) testing (methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) of 11p15) performed on amniocytes were negative. After intrauterine fetal demise, the clinical suspicion persisted and BWS MS-MLPA was repeated on cultured cells from umbilical cord and amniotic fluid, revealing a mosaicism for KvH19 hypermethylation/KCNQ1OT1:TSS:DMR hypomethylation. These results, along with microsatellite analysis of the BWS region, were consistent with mosaic paternal 11p15 isodisomy. A concurrent maternal contamination exclusion test, analyzing polymorphic microsatellite markers on multiple chromosomes, showed an imbalance in favor of paternal alleles at all examined loci on cultured amniocytes and umbilical cord samples. This led to suspicion of mosaic GWpUPD, later confirmed by SNP-array, identifying a mosaic genome-wide paternal isodisomy affecting 60% of fetal cells. The assessment of mosaic GWpUPD requires multiple approaches beyond the current established diagnostic processes, also entertaining possible low-rate mosaicism. Clinical acumen and an integrated testing approach are the key to a successful diagnosis.

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

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

Prenatal presentation in two fetuses with features of Beckwith Wiedemann syndrome-An unexpected diagnosis of androgenetic chimera and its clinical implications

Beckwith Wiedemann Syndrome (BWS, OMIM 130650) is an imprinting disorder that may present antenatally with a constellation of sonographic features namely polyhydramnios, macrosomia, macroglossia, omphalocele, placental mesenchymal dysplasia, cardiomegaly, nephromegaly, fetal hydrops, and other rare anomalies. Paternal uniparental disomy in chromosome 11p15 imprinting region accounts for 20% of all BWS, and 8% among those were due to genome-wide paternal uniparental disomy (GWpUPD). GWpUPD is a rare condition and usually results in prenatal lethality. The 31 liveborns reported in the literature demonstrate female predominance in surviving GWpUPD. Here, we reported two prenatal cases which initially presented with features suggestive of BWS, which subsequently were confirmed to have GWpUPD. Further trio SNP genotyping analysis using SNP-based chromosomal microarray revealed androgenetic biparental chimera as the underlying cause. Finally, we highlighted the importance of recognizing GWpUPD as a possible cause in a fetus presenting with BWS phenotype, as it carried a different disease prognosis, tumor predisposition, manifestations of other imprinting disorders, and possibility in unmasking autosomal recessive disorders from the paternal alleles.

Sperm mosaicism: implications for genomic diversity and disease

While sperm mosaicism has few consequences for men, the offspring and future generations are unwitting recipients of gonadal cell mutations, often yielding severe disease. Recent studies, fueled by emergent technologies, show that sperm mosaicism is a common source of de novo mutations (DNMs) that underlie severe pediatric disease as well as human genetic diversity. Sperm mosaicism can be divided into three types: Type I arises during sperm meiosis and is non-age dependent; Type II arises in spermatogonia and increases as men age; and Type III arises during paternal embryogenesis, spreads throughout the body, and contributes stably to sperm throughout life. Where Types I and II confer little risk of recurrence, Type III may confer identifiable risk to future offspring. These mutations are likely to be the single largest contributor to human genetic diversity. New sequencing approaches may leverage this framework to evaluate and reduce disease risk for future generations.

Multiple tumors due to mosaic genome-wide paternal uniparental disomy

Mosaic genome-wide paternal uniparental disomy is an infrequently described disorder in which affected individuals have signs and symptoms that may resemble Beckwith-Wiedemann syndrome. In addition, they can develop multiple benign and malignant tumors throughout life. Routine molecular diagnostics may not detect the (characteristic) low level of mosaicism, and the diagnosis is likely to be missed. Genetic counseling and a life-long alertness for the development of tumors is indicated. We describe the long diagnostic process of a patient who already had a tumor at birth and developed multiple tumors in childhood and adulthood. Furthermore, we offer clues to recognize the entity.

Placental mesenchymal dysplasia: An underdiagnosed placental pathology with various clinical outcomes

BACKGROUND

Placental mesenchymal dysplasia (PMD) is a rare vascular and connective placental anomaly, which is often associated with severe fetal and/or maternal complications. The diversity of presentation of PMD challenges diagnosis and effective pregnancy management.

OBJECTIVE

We aimed to review cases presenting at 7 tertiary centers worldwide over the last decade and to study the occurrence of obstetric and neonatal complications.

STUDY DESIGN

Pathology databases from 7 tertiary hospitals were screened for cases of PMD (between 2007-2017). Pregnancy history, outcomes and ultrasound images were then reviewed for each case.

RESULTS

Twenty-two cases of PMD were identified. Mean gestational age at diagnosis was 23 weeks (16-39 weeks). Prenatal biochemical screening was abnormal in 8 cases (36%). Of the 12 cases that underwent invasive genetic testing, 4 were abnormal. Six patients (27%) developed maternal complications (preeclampsia/gestational hypertension). Fetal growth restriction was identified in 11 cases (50%) and fetal death in 4 (18%). Four (18%) pregnancies were terminated, 9/14 (64%) delivered preterm and only three (14%) progressed normally. Fourteen babies were born alive; 5 (35%) died in the first sixty-one days after birth, 5 (35%) had transient thrombopenia and 1 (7%) had developmental delay at last follow-up. Our series identified four potential new associations with PMD: placental triploidy mosaicism, CHARGE syndrome, fetal pleuropulmonary blastoma and fetal skeletal dysplasia.

CONCLUSIONS

PMD was substantially under-diagnosed before delivery in this cohort. Sonographers, fetal medicine specialists, obstetricians and pathologists should all suspect PMD in cases of an enlarged placenta and should look for fetal abnormalities. Diagnostic genetic testing should be discussed to exclude partial molar pregnancy. Close pregnancy follow-up is indicated due to the high risk of associated fetal or maternal adverse outcomes.

Diagnosis and Management of Beckwith-Wiedemann Syndrome

Beckwith-Wiedemann syndrome (BWS) is a human genomic imprinting disorder that presents with a wide spectrum of clinical features including overgrowth, abdominal wall defects, macroglossia, neonatal hypoglycemia, and predisposition to embryonal tumors. It is associated with genetic and epigenetic changes on the chromosome 11p15 region, which includes two imprinting control regions. Here we review strategies for diagnosing and managing BWS and delineate commonly used genetic tests to establish a molecular diagnosis of BWS. Recommended first-line testing assesses DNA methylation and copy number variation of the BWS region. Tissue mosaicism can occur in patients with BWS, posing a challenge for genetic testing, and a negative test result does not exclude a diagnosis of BWS. Further testing should analyze additional tissue samples or employ techniques with higher diagnostic yield. Identifying the BWS molecular subtype is valuable for coordinating patient care because of the (epi)genotype-phenotype correlations, including different risks and types of embryonal tumors.

Biparental/androgenetic mosaicism in a male with features of overgrowth and placental mesenchymal dysplasia

Biparental/androgenetic mosaicism is a rarely diagnosed condition in humans. It is typically ascertained prenatally on the basis of placental mesenchymal dysplasia. Fetal outcome can range from demise due to intrauterine growth retardation to term delivery. Most of the published cases of liveborns represent females that are either completely normal or have features of Beckwith-Wiedemann syndrome. Only two healthy liveborn males with mosaicism detected in the placenta have been described to date. Here, we report another liveborn male with hepatic mesenchymal hamartoma, soft tissue overgrowth on his right fifth toe, hemangiomas over his chest, right buttock and foot, anemia, thrombocytopenia and congenital hypothyroidism with biparental/androgenetic mosaicism detected in the toe mass in addition to the placenta. This new case adds to the existing literature of individuals with biparental/androgenetic mosaicism and expands the range of clinical presentations that may be seen in male patients with this condition. This study also illustrates the important use of single-nucleotide polymorphism microarray in conjunction with short-tandem repeat analysis on affected tissue to provide a diagnosis for patients with features of overgrowth and prior, non-diagnostic, genetic analyses of their peripheral blood.

Genetic variation affecting DNA methylation and the human imprinting disorder, Beckwith-Wiedemann syndrome

Background

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder with a population frequency of approximately 1 in 10,000. The most common epigenetic defect in BWS is a loss of methylation (LOM) at the 11p15.5 imprinting centre, KCNQ1OT1 TSS-DMR, and affects 50% of cases. We hypothesised that genetic factors linked to folate metabolism may play a role in BWS predisposition via effects on methylation maintenance at KCNQ1OT1 TSS-DMR.

Results

Single nucleotide variants (SNVs) in the folate pathway affecting methylenetetrahydrofolate reductase (MTHFR), methionine synthase reductase (MTRR), 5-methyltetrahydrofolate-homocysteine S-methyltransferase (MTR), cystathionine beta-synthase (CBS) and methionine adenosyltransferase (MAT1A) were examined in 55 BWS patients with KCNQ1OT1 TSS-DMR LOM and in 100 unaffected cases. MTHFR rs1801133: C>T was more prevalent in BWS with KCNQ1OT1 TSS-DMR LOM (p < 0.017); however, the relationship was not significant when the Bonferroni correction for multiple testing was applied (significance, p = 0.0036). None of the remaining 13 SNVs were significantly different in the two populations tested. The DNMT1 locus was screened in 53 BWS cases, and three rare missense variants were identified in each of three patients: rs138841970: C>T, rs150331990: A>G and rs757460628: G>A encoding NP_001124295 p.Arg136Cys, p.His1118Arg and p.Arg1223His, respectively. These variants have population frequencies of less than 1 in 1000 and were absent from 100 control cases. Functional characterization using a hemimethylated DNA trapping assay revealed a reduced methyltransferase activity relative to wild-type DNMT1 for each variant ranging from 40 to 70% reduction in activity.

Conclusions

This study is the first to examine folate pathway genetics in BWS and to identify rare DNMT1 missense variants in affected individuals. Our data suggests that reduced DNMT1 activity could affect maintenance of methylation at KCNQ1OT1 TSS-DMR in some cases of BWS, possibly via a maternal effect in the early embryo. Larger cohort studies are warranted to further interrogate the relationship between impaired MTHFR enzymatic activity attributable to MTHFR rs1801133: C>T, dietary folate intake and BWS.

Electronic supplementary material

The online version of this article (10.1186/s13148-018-0546-4) contains supplementary material, which is available to authorized users.

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.

Mosaic genome-wide maternal isodiploidy: an extreme form of imprinting disorder presenting as prenatal diagnostic challenge

Background

Uniparental disomy of certain chromosomes are associated with a group of well-known genetic syndromes referred to as imprinting disorders. However, the extreme form of uniparental disomy affecting the whole genome is usually not compatible with life, with the exception of very rare cases of patients with mosaic genome-wide uniparental disomy reported in the literature.

Results

We here report on a fetus with intrauterine growth retardation and malformations observed on prenatal ultrasound leading to invasive prenatal testing. By cytogenetic (conventional karyotyping), molecular cytogenetic (QF-PCR, FISH, array), and methylation (MS-MLPA) analyses of amniotic fluid, we detected mosaicism for one cell line with genome-wide maternal uniparental disomy and a second diploid cell line of biparental inheritance with trisomy X due to paternal isodisomy X. As expected for this constellation, we observed DNA methylation changes at all imprinted loci investigated.

Conclusions

This report adds new information on phenotypic outcome of mosaic genome-wide maternal uniparental disomy leading to an extreme form of multilocus imprinting disturbance. Moreover, the findings highlight the technical challenges of detecting these rare chromosome disorders prenatally.

Electronic supplementary material

The online version of this article (10.1186/s13148-017-0410-y) contains supplementary material, which is available to authorized users.

Management of adrenal masses in patients with Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a genetic overgrowth and cancer predisposition syndrome, associated with both benign and malignant adrenal findings. Literature review and an institutional case series elucidate the wide spectrum of adrenal findings in BWS patients. The altered expression of the 11p15 region is likely related to adrenal gland hyperplasia and growth dysregulation. Given the absence of guidelines for managing adrenal findings in BWS, we propose a systematic approach to adrenal findings in BWS patients, to allow for maximum detection of potentially malignant pathology without posing additional risk to patients.

Identification of consensus motifs associated with mitotic recombination and clinical characteristics in patients with paternal uniparental isodisomy of chromosome 11

Uniparental disomy (UPD) is defined as the inheritance of both homologs of a given genomic region from only one parent. The majority of UPD includes an entire chromosome. However, the extent of UPD is sometimes limited to a subchromosomal region (segmental UPD). Mosaic paternal UPD (pUPD) of chromosome 11 is found in approximately 20% of patients with Beckwith-Wiedemann syndrome (BWS) and almost all pUPDs are segmental isodisomic pUPDs resulting from mitotic recombination at an early embryonic stage. A mechanism initiating a DNA double strand break (DSB) within 11p has been predicted to lead to segmental pUPD. However, no consensus motif has yet been found. Here, we analyzed 32 BWS patients with pUPD by SNP array and searched for consensus motifs. We identified four consensus motifs frequently appearing within breakpoint regions of segmental pUPD. These motifs were found in another nine BWS patients with pUPD. In addition, the seven motifs found in meiotic recombination hot spots could not be found within pUPD breakpoint regions. Histone H3 lysine 4 trimethylation, a marker of DSB initiation, could not be found either. These findings suggest that the mechanism(s) of mitotic recombination leading to segmental pUPD are different from that of meiotic recombination. Furthermore, we found seven patients with paternal uniparental diploidy (PUD) mosaicism. Comparison of clinical features between segmental pUPDs and PUDs showed that developmental disability and cardiac abnormalities were additional characteristic features of PUD mosaicism, along with high risk of tumor development. We also found that macroglossia was characteristic of segmental pUPD mosaicism.

Paternal Hemizygosity in 11p15 in Mole-like Conceptuses: Two Case Reports

Hydatidiform mole is an abnormal human pregnancy characterized by the fetus being absent or nonviable, and the chorionic villi being vesicular and with trophoblastic hyperplasia. Most often, the mole phenotype is seen in conceptuses with an excess of paternally inherited genome set(s) relative to maternally inherited genome set(s), suggesting that the phenotype is caused by an excess of genome with a paternal imprinting pattern. However, it is unknown if correct parental origin of every imprinted gene is crucial for normal early differentiation or if abnormal parental imprinting of only one, or some, gene(s) can cause the mole phenotype.Two conceptuses included in the Danish Mole Project stood out since they presented with vesicular chorionic villi and without signs of fetal differentiation, and had apparently biparental diploid genomes, and no mutations in NLRP7 or KHDC3L were detected in the mothers. These conceptuses were subjected to a centralized histopathological revision and their genetic complements were scrutinized using fluorescence in situ hybridization, and DNA-marker and array comparative genomic hybridization analyses. Both conceptuses showed dysmorphic chorionic villi with some similarities to hydatidiform moles; however, no definite florid trophoblast hyperplasia was observed. Both conceptuses showed paternal hemizygosity of 11pter-11p15.4, most likely in nonmosaic state.Our findings suggest that the product of one (or a few) maternally expressed gene(s) on the tip of chromosome 11 is necessary for normal early embryonic differentiation. However, since the present two cases did not exhibit all features of hydatidiform moles, it is likely that abnormal parental imprinting of genes in other regions contribute to the phenotype of a hydatidiform mole.

Mosaic paternal genome-wide uniparental isodisomy with down syndrome

We report on a 6-month-old girl with two apparent cell lines; one with trisomy 21, and the other with paternal genome-wide uniparental isodisomy (GWUPiD), identified using single nucleotide polymorphism (SNP) based microarray and microsatellite analysis of polymorphic loci. The patient has Beckwith-Wiedemann syndrome (BWS) due to paternal uniparental disomy (UPD) at chromosome location 11p15 (UPD 11p15), which was confirmed through methylation analysis. Hyperinsulinemic hypoglycemia is present, which is associated with paternal UPD 11p15.5; and she likely has medullary nephrocalcinosis, which is associated with paternal UPD 20, although this was not biochemically confirmed. Angelman syndrome (AS) analysis was negative but this testing is not completely informative; she has no specific features of AS. Clinical features of this patient include: dysmorphic features consistent with trisomy 21, tetralogy of Fallot, hemihypertrophy, swirled skin hyperpigmentation, hepatoblastoma, and Wilms tumor. Her karyotype is 47,XX,+21[19]/46,XX[4], and microarray results suggest that the cell line with trisomy 21 is biparentally inherited and represents 40-50% of the genomic material in the tested specimen. The difference in the level of cytogenetically detected mosaicism versus the level of mosaicism observed via microarray analysis is likely caused by differences in the test methodologies. While a handful of cases of mosaic paternal GWUPiD have been reported, this patient is the only reported case that also involves trisomy 21. Other GWUPiD patients have presented with features associated with multiple imprinted regions, as does our patient.

The clinical course of an overgrowth syndrome, from diagnosis in infancy through adulthood: the case of Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is the most common genetic overgrowth syndrome, and it is frequently clinically recognizable because of characteristic features. These features include macrosomia, hemihypertrophy, macroglossia, facial nevus flammeus, earlobe creases and pits, omphalocele, and organomegaly. The most common molecular cause is hypomethylation of the maternal imprinting control region 2 (ICR2) in 11p15. Other molecular causes include hypermethylation of the maternal ICR1 in 11p15, mutations in CDKN1C, mosaic uniparental disomy 11p15, and chromosomal abnormalities involving 11p15. Some of these abnormalities are testable, and DNA methylation tests of 11p15 confirm about 60% of cases with BWS. The main management issues in pediatrics are hypoglycemia at birth, macroglossia, and surveillance for embryonal tumors, especially Wilms and hepatoblastoma.

Novel fetal and maternal sonographic findings in confirmed cases of Beckwith-Wiedemann syndrome

OBJECTIVE

The objective of the study was to examine the prenatal anomalies in fetuses with Beckwith-Wiedemann syndrome (BWS).

METHODS

The study included a retrospective assessment of 12 pregnancies that were seen at three tertiary referral centres (Universities of Tübingen, Bonn, and Cologne/Germany). The genetic mutation, the results of the second trimester ultrasound examination, and the outcome of the pregnancies are shown. Biometric data were transformed into z-values.

RESULTS

Median gestational age at the time of examination was 22.6 (range 19.0-29.7) weeks of gestation. In all cases, the head circumference (HC) and the femur length (FL) were within the normal range, but the HC-FL ratio was above the 95th centile in 75% of the cases. An exomphalos, macroglossia, and visceromegaly were observed in 67%, 50%, and 83% of the cases, and in 58% and 83%, there were polyhydramnios and placentamegaly respectively. The fetal pancreas was identified in three quarters of the cases. A third of the women had large, overstimulation-like ovaries, although each pregnancy was conceived naturally. In four cases, beta-human chorionic gonadotropin (hCG) levels were measured and mean hCG levels were 498 106 IU/L.

DISCUSSION

Besides exomphalos, BWS should be considered if there is macroglossia, a distinct growth pattern, pancreatic hyperplasia, placentamegaly, and substantially increased levels of beta-hCG. © 2015 John Wiley & Sons, Ltd.

Beckwith-Wiedemann and IMAGe syndromes: two very different diseases caused by mutations on the same gene

Genomic imprinting is an epigenetically regulated mechanism leading to parental-origin allele-specific expression. Beckwith-Wiedemann syndrome (BWS) is an imprinting disease related to 11p15.5 genetic and epigenetic alterations, among them loss-of-function CDKN1C mutations. Intriguing is that CDKN1C gain-of-function variations were recently found in patients with IMAGe syndrome (intrauterine growth restriction, metaphyseal dysplasia, congenital adrenal hypoplasia, and genital anomalies). BWS and IMAGe share an imprinted mode of inheritance; familial analysis demonstrated the presence of the phenotype exclusively when the mutant CDKN1C allele is inherited from the mother. Interestingly, both IMAGe and BWS are characterized by growth disturbances, although with opposite clinical phenotypes; IMAGe patients display growth restriction whereas BWS patients display overgrowth. CDKN1C codifies for CDKN1C/KIP2, a nuclear protein and potent tight-binding inhibitor of several cyclin/Cdk complexes, playing a role in maintenance of the nonproliferative state of cells. The mirror phenotype of BWS and IMAGe can be, at least in part, explained by the effect of mutations on protein functions. All the IMAGe-associated mutations are clustered in the proliferating cell nuclear antigen-binding domain of CDKN1C and cause a dramatic increase in the stability of the protein, which probably results in a functional gain of growth inhibition properties. In contrast, BWS mutations are not clustered within a single domain, are loss-of-function, and promote cell proliferation. CDKN1C is an example of allelic heterogeneity associated with opposite syndromes.

Autosomal recessive cystinuria caused by genome-wide paternal uniparental isodisomy in a patient with Beckwith-Wiedemann syndrome

Approximately 20% of Beckwith-Wiedemann syndrome (BWS) cases are caused by mosaic paternal uniparental disomy of chromosome 11 (pUPD11). Although pUPD11 is usually limited to the short arm of chromosome 11, a small minority of BWS cases show genome-wide mosaic pUPD (GWpUPD). These patients show variable clinical features depending on mosaic ratio, imprinting status of other chromosomes, and paternally inherited recessive mutations. To date, there have been no reports of a mosaic GWpUPD patient with an autosomal recessive disease caused by a paternally inherited recessive mutation. Here, we describe a patient concurrently showing the clinical features of BWS and autosomal recessive cystinuria. Genetic analyses revealed that the patient has mosaic GWpUPD and an inherited paternal homozygous mutation in SLC7A9. This is the first report indicating that a paternally inherited recessive mutation can cause an autosomal recessive disease in cases of GWpUPD mosaicism. Investigation into recessive mutations and the dysregulation of imprinting domains is critical in understanding precise clinical conditions of patients with mosaic GWpUPD.

Recurrent benign adrenal pheochromocytomas associated with hemihypertrophy

We report a case of a female with hemihypertrophy, who developed five recurrences of pheochromocytomas until the age of 35. Timely follow-up of the patient's blood pressure assisted in early diagnosis and treatment of recurrent tumors.

Activation of the chromosome 19q microRNA cluster in sporadic and androgenetic-biparental mosaicism-associated hepatic mesenchymal hamartoma

Recurrent genetic alterations found in hepatic mesenchymal hamartoma include either androgenetic-biparental mosaicism or chromosomal rearrangements involving chromosome 19q13.4, in the vicinity of the chromosome 19q microRNA cluster (C19MC). Abnormal activation of C19MC, which is subject to paternal imprinting and is normally expressed only in placenta, could account for both genetic associations because androgenetic cells carry only paternal chromosomes. In this study, a 4.2-Mb deletion involving the 5'-end of C19MC was detected in a sporadic mesenchymal hamartoma by chromosomal microarray. Fluorescence in situ hybridization studies showed that the deletion localized to mesenchymal cells in the stroma of the hamartoma. Quantitative real-time polymerase chain reaction analysis of this tumor, 9 other sporadic hepatic mesenchymal hamartomas, and 3 hamartomas associated with androgenetic-biparental mosaicism demonstrated C19MC microRNA expression in all but 2 sporadic cases, with no significant expression in control liver. The findings support a pathogenetic model for mesenchymal hamartoma as a consequence of "ectopic" activation of C19MC in hepatic stroma, due to either chromosomal rearrangements or paternal uniparental disomy.

Chromosome microarrays in diagnostic testing: interpreting the genomic data

DNA-based Chromosome MicroArrays (CMAs) are now well established as diagnostic tools in clinical genetics laboratories. Over the last decade, the primary application of CMAs has been the genome-wide detection of a particular class of mutation known as copy number variants (CNVs). Since 2010, CMA testing has been recommended as a first-tier test for detection of CNVs associated with intellectual disability, autism spectrum disorders, and/or multiple congenital anomalies…in the post-natal setting. CNVs are now regarded as pathogenic in 14-18 % of patients referred for these (and related) disorders.Through consideration of clinical examples, and several microarray platforms, we attempt to provide an appreciation of microarray diagnostics, from the initial inspection of the microarray data, to the composing of the patient report. In CMA data interpretation, a major challenge comes from the high frequency of clinically irrelevant CNVs observed within "patient" and "normal" populations. As might be predicted, the more common and clinically insignificant CNVs tend to be the smaller ones <100 kb in length, involving few or no known genes. However, this relationship is not at all straightforward: CNV length and gene content are only very imperfect indicators of CNV pathogenicity. Presently, there are no reliable means of separating, a priori, the benign from the pathological CNV classes.This chapter also considers sources of technical "noise" within CMA data sets. Some level of noise is inevitable in diagnostic genomics, given the very large number of data points generated in any one test. Noise further limits CMA resolution, and some miscalling of CNVs is unavoidable. In this, there is no ideal solution, but various strategies for handling noise are available. Even without solutions, consideration of these diagnostic problems per se is informative, as they afford critical insights into the biological and technical underpinnings of CNV discovery. These are indispensable to any clinician or scientist practising within the field of genome diagnostics.

Clinical features of three girls with mosaic genome-wide paternal uniparental isodisomy

Here we describe three subjects with mosaic genome-wide paternal uniparental isodisomy (GWpUPD) each of whom presented initially with overgrowth, hemihyperplasia (HH), and hyperinsulinism (HI). Due to the severity of findings and the presence of additional features, SNP array testing was performed, which demonstrated mosaic GWpUPD. Comparing these individuals to 10 other live-born subjects reported in the literature, the predominant phenotype is that of pUPD11 and notable for a very high incidence of tumor development. Our subjects developed non-metastatic tumors of the adrenal gland, kidney, and/or liver. All three subjects had pancreatic hyperplasia resulting in HI. Notably, our subjects to date display minimal features of other diseases associated with paternal UPD loci. Both children who survived the neonatal period have displayed near-normal cognitive development, likely due to a favorable tissue distribution of the mosaicism. To understand the range of UPD mosaicism levels, we studied multiple tissues using SNP array analysis and detected levels of 5-95%, roughly correlating with the extent of tissue involvement. Given the rapidity of tumor growth and the difficulty distinguishing malignant and benign tumors in these GWpUPD subjects, we have utilized increased frequency of ultrasound (US) and alpha-fetoprotein (AFP) screening in the first years of life. Because of a later age of onset of additional tumors, continued tumor surveillance into adolescence may need to be considered in these rare patients.

Genome-wide androgenetic mosaicism

Individuals with mosaic paternal uniparental disomy (UPD) of apparently all chromosomes have recently been described. They show a 46,XX karyotype, but with a mixture of normal biparental cells and cells entirely of paternal isodisomic origin. We describe an infant who primarily showed signs of Beckwith-Wiedemann syndrome (BWS), but also had other severe and eventually lethal medical problems, notably refractory hypoglycemia. We performed methylation studies for BWS, but incidentally for Angelman syndrome (AS) on leukocytes and in a skin FFPE sample. We also performed chromosome microarray [CNV and single-nucleotide polymorphism (SNP) array] on leukocytes. We found that the patient had hypomethylation consistent with both BWS and AS. Remarkably, this was due to mosaic paternal UPD for chromosomes 11 and 15, respectively. The SNP microarray showed mosaic paternal UPD for all chromosomes. Patients with unusual phenotypes for a typical imprinting disorder should be studied further with assays for imprinted loci on other chromosomes. Chromosomal SNP microarrays are useful in identifying patients with multiple UPDs, sometimes of the whole genome.

Systematic review of sonographic findings of placental mesenchymal dysplasia and subsequent pregnancy outcome

OBJECTIVE

To describe the sonographic features and pregnancy outcomes of placental mesenchymal dysplasia (PMD), an entity often misdiagnosed as molar pregnancy.

METHODS

We reviewed PMD cases from our institution and performed a systematic review of the existing literature. Inclusion criteria for the review were diagnosis of PMD as defined by placental pathology, description of placental morphology on antenatal ultrasound and reporting of pregnancy outcomes.

RESULTS

We found three cases of PMD at our institution. Patient 1 had elevated human chorionic gonadotropin (hCG) and an enlarged, hydropic placenta at 13 weeks, suggestive of a molar pregnancy. Patient 2 also had elevated hCG with large, vascular placental lakes on ultrasound suggesting placenta accreta or molar pregnancy. Case 3 involved placentomegaly and fetal anomalies suggestive of Beckwith-Wiedemann syndrome. From the literature review, 61 cases met the inclusion criteria. The most common sonographic features included enlarged (50%) and cystic (80%) placenta with dilated chorionic vessels. Biochemical aneuploidy screening abnormalities were relatively common as were fetal anomalies, Beckwith-Wiedemann syndrome and other genetic abnormalities. Pregnancy complications included intrauterine growth restriction (IUGR; 33%), intrauterine fetal death (IUFD; 13%), and preterm labor (33%). Pregnancies without fetal anomalies, IUGR, IUFD or preterm labor had normal neonatal outcomes despite PMD (9%).

CONCLUSIONS

The differential diagnosis of PMD includes molar pregnancy and other placental vascular anomalies. PMD is associated with adverse pregnancy outcome, so heightened surveillance with genetic evaluation, serial growth scans and third-trimester assessment of wellbeing should be considered. PMD must be differentiated from gestational trophoblastic disease because management and outcomes differ.

Bilateral pheochromocytomas, hemihyperplasia, and subtle somatic mosaicism: the importance of detecting low-level uniparental disomy

We report on a patient with early onset pediatric bilateral pheochromocytomas caused by mosaic chromosome 11p15 paternal uniparental isodisomy (UPD). Hemihyperplasia of the arm was diagnosed in a 4-month-old female and clinical methylation testing for 11p15 in the blood was normal, with a reported detection threshold for mosaicism of 20%. She was subsequently diagnosed at 18 months with bilateral pheochromocytomas. Single-nucleotide polymorphism (SNP) array analysis of pheochromocytoma tissue demonstrated mosaic deletions of 8p12pter, 21q21.1qter, 22q11.23qter; commonly seen in pheochromocytomas. In addition, mosaic 11p15.3pter homozygosity was noted. Molecular testing for other causes of pheochromocytomas was normal, suggesting that 11p15 homozygosity was the primary event. Subsequent SNP array analysis of skin fibroblasts from the hyperplastic side demonstrated 5% mosaic paternal UPD for 11p15. We have subsequently used SNP array analysis to identify four patients with subtle hemihyperplasia with low-level mosaic UPD that was not detected by methylation analysis. Given the increased sensitivity of SNP array analysis to detect UPD along with the increased incidence of tumorigenesis in these UPD patients, we suggest that it has high utility in the clinical work-up of hemihyperplasia. The present case also suggests that 11p15 paternal UPD may be an under-detected mechanism of sporadic pheochromocytoma in the pediatric population. Furthermore, a review of the literature suggests that patients with 11p15 paternal UPD may present after 8 years of age with pheochromocytoma and raises the possibility that ultrasound screening could be considered beyond 8 years of age in this subset of hemihyperplasia and Beckwith-Wiedemann syndrome patients.

Mosaicism for genome-wide paternal uniparental disomy with features of multiple imprinting disorders: diagnostic and management issues

Mosaicism for genome-wide paternal uniparental disomy (UPD) has been reported in only seven live born individuals to date. Clinical presentation includes manifestations of multiple paternal UPD syndromes with high variability, likely due to the variable levels of mosaicism in different somatic tissues. We report an eighth case in a female patient with mosaicism for genome-wide paternal UPD which highlights the complex clinical presentation. Our patient had features of Beckwith-Wiedemann syndrome (BWS), Angelman syndrome, and congenital hyperinsulinism. The clinical findings included prematurity, organomegaly, hemihyperplasia, developmental delay, benign tumors, and cystic lesions. The diagnosis in our patient was established utilizing microarray-based genome-wide DNA methylation analysis performed on leukocyte DNA. Targeted multiplex ligation-dependent probe amplification (MLPA) analysis of chromosome regions 11p15 and 15q13 confirmed mosaicism for paternal UPD at these genomic regions. This case represents the first report of microarray-based genome-wide DNA methylation analysis in the diagnosis of genome-wide paternal UPD. The application of microarray-based genome-wide DNA methylation analysis on selected individuals with complex clinical presentations could be a valuable diagnostic tool to improve the detection rate of mosaic genome-wide paternal UPD. This approach, which screens many loci simultaneously, is more cost-effective and less labor-intensive than performing multiple targeted DNA methylation-based assays. Identification of individuals with mosaicism for genome-wide paternal UPD is an important goal as it confers a low recurrence risk for the family and identifies individuals who require surveillance due to increased tumor risk.

Genome-wide paternal uniparental disomy mosaicism in a woman with Beckwith-Wiedemann syndrome and ovarian steroid cell tumour

Uniparental disomy (UPD) of single chromosomes is a well-known molecular aberration in a group of congenital diseases commonly known as imprinting disorders (IDs). Whereas maternal and/or paternal UPD of chromosomes 6, 7, 11, 14 and 15 are associated with specific IDs (Transient neonatal diabetes mellitus, Silver-Russell syndrome, Beckwith-Wiedemann syndrome (BWS), upd(14)-syndromes, Prader-Willi syndrome, Angelman Syndrome), the other autosomes are not. UPD of the whole genome is not consistent with life, in case of non-mosaic genome-wide paternal UPD (patUPD) it leads to hydatidiform mole. In contrast, mosaic genome-wide patUPD might be compatible with life. Here we present a 19-year-old woman with BWS features and initially diagnosed to be carrier of a mosaic patUPD of chromosome 11p15. However, the patient presented further clinical findings not typically associated with BWS, including nesidioblastosis, fibroadenoma, hamartoma of the liver, hypoglycaemia and ovarian steroid cell tumour. Additional molecular investigations revealed a mosaic genome-wide patUPD. So far, only nine cases with mosaic genome-wide patUPD and similar clinical findings have been reported, but these patients were nearly almost diagnosed in early childhood. Summarising the data from the literature and those from our patient, it can be concluded that the mosaic genome-wide patUPD (also known as androgenic/biparental mosaicism) might explain unusual BWS phenotypes. Thus, these findings emphasise the need for multilocus testing in IDs to efficiently detect cases with disturbances affecting more than one chromosome.

Use of multilocus methylation-specific single nucleotide primer extension (MS-SNuPE) technology in diagnostic testing for human imprinted loci

A number of diseases have been found to be linked to aberrant methylation of specific genes. However, most of the routine diagnostic techniques to detect epigenetic disturbances are restricted to single loci. Additionally, a precise quantification of the methylation status is often hampered. A considerable fraction of patients with Silver-Russell syndrome, Beckwith-Wiedemann syndrome and transient neonatal diabetes mellitus exhibit loss of methylation at further imprinted loci in addition to the disease specific ones (multilocus methylation defects, MLMD). As the currently available tests are mainly focused on single imprinted loci on different chromosomes and thereby make the detection of multilocus methylation defects time-consuming and expensive, we established methylation-specific single nucleotide primer extension (MS-SNuPE) assays for a simultaneous quantification of methylation at multiple methylated loci. We chose loci generally affected in patients with MLMD. The method was validated by screening 66 individuals with known (epi)genetic disturbances. In comparison to other methylation-specific techniques, multilocus methylation-specific single nucleotide primer extension allows the quantitative analysis of numerous CpG islands of different loci in one assay and is, therefore, suitable for the simultaneous diagnostic testing for different congenital imprinting disorders in parallel, as well as for MLMD.

Structural genetic variation in the context of somatic mosaicism

Somatic mosaicism is the result of postzygotic de novo mutation occurring in a portion of the cells making up an organism. Structural genetic variation is a very heterogeneous group of changes, in terms of numerous types of aberrations that are included in this category, involvement of many mechanisms behind the generation of structural variants, and because structural variation can encompass genomic regions highly variable in size. Structural variation rapidly evolved as the dominating type of changes behind human genetic diversity, and the importance of this variation in biology and medicine is continuously increasing. In this review, we combine the evidence of structural variation in the context of somatic cells. We discuss the normal and disease-related somatic structural variation. We review the recent advances in the field of monozygotic twins and other models that have been studied for somatic mutations, including other vertebrates. We also discuss chromosomal mosaicism in a few prime examples of disease genes that contributed to understanding of the importance of somatic heterogeneity. We further highlight challenges and opportunities related to this field, including methodological and practical aspects of detection of somatic mosaicism. The literature devoted to interindividual variation versus papers reporting on somatic variation suggests that the latter is understudied and underestimated. It is important to increase our awareness about somatic mosaicism, in particular, related to structural variation. We believe that further research of somatic mosaicism will prove beneficial for better understanding of common sporadic disorders.

Occult androgenetic-biparental mosaicism and sporadic hepatic mesenchymal hamartoma

The incidence of hepatic mesenchymal hamartoma (HMH) is increased in patients with placental mesenchymal dysplasia (PMD), which appears to be caused by androgenetic-biparental mosaicism (ABM). We hypothesized that occult ABM might underlie cases of HMH with no known history of PMD. Formalin-fixed, paraffin-embedded HMH specimens from 10 such patients and liver specimens from 6 non-HMH controls were identified retrospectively from the surgical pathology records of a pediatric hospital. The relative abundance of maternal and paternal alleles was assessed by quantitative polymerase chain reaction amplification of polymorphic short tandem repeats and single nucleotide polymorphisms located on 15 different chromosomes. Androgenetic-biparental mosaicism was diagnosed in one patient based on global allelic imbalances at all informative loci. In that patient, the greatest imbalances were observed in stroma-rich portions of the hamartoma, with no significant imbalance in histologically normal liver or epithelium-rich portions of the hamartoma. A retrospective, unbiased review of the histology and clinical records from all 10 patients revealed no morphologic or clinical correlates to distinguish the affected patient, except that she had multiple cutaneous hemangiomas, which like HMH, appear to be more common in patients with PMD. Our findings suggest that other patients with apparently sporadic HMH, hemangioma, or other lesions seen more frequently with PMD may harbor occult ABM. Recognition of ABM may be important because its long-term consequences are unknown but may be significant.

Mosaics and moles

Hydatidiform mole (HM) is an abnormal human pregnancy, where the placenta presents with vesicular swelling of the chorionic villi. A fetus is either not present, or malformed and not viable. Most moles are diploid androgenetic as if one spermatozoon fertilized an empty oocyte, or triploid with one maternal and two paternal chromosome sets as if two spermatozoa fertilized a normal oocyte. However, diploid moles with both paternal and maternal markers of the nuclear genome have been reported. Among 162 consecutively collected diploid moles, we have earlier found indications of both maternal and paternal genomes in 11. In the present study, we have performed detailed analysis of DNA-markers in tissue and single cells from these 11 HMs. In 3/11, we identified one biparental cell population only, whereas in 8/11, we demonstrated mosaicism: one biparental cell population and one androgenetic cell population. One mosaic mole was followed by persistent trophoblastic disease (PTD). In seven of the mosaics, one spermatozoon appeared to have contributed to the genomes of both cell types. Our observations make it likely that mosaic conceptuses, encompassing an androgenetic cell population, result from various postzygotic abnormalities, including paternal pronuclear duplication, asymmetric cytokinesis, and postzygotic diploidization. This corroborates the suggestion that fertilization of an empty egg is not mandatory for the creation of an androgenetic cell population. Future studies of mosaic conceptuses may disclose details about fertilization, early cell divisions and differentiation. Apparently, only a minority of diploid moles with both paternal and maternal markers are 'genuine' diploid biparental moles (DiBiparHMs).

Uniparental disomy and human disease: an overview

Uniparental disomy (UPD) refers to the situation in which both homologues of a chromosomal region/segment have originated from only one parent. This can involve the entire chromosome or only a small segment. As a consequence of UPD, or uniparental duplication/deficiency of part of a chromosome, there are two types of developmental risk: aberrant dosage of genes regulated by genomic imprinting and homozygosity of a recessive mutation. UPD models generated by reciprocal and Robertsonian translocation heterozygote intercrosses have been a powerful tool to investigate genomic imprinting in mice, whereas novel UPD patients such as those with cystic fibrosis and Prader-Willi syndrome, triggered the clarification of recessive diseases and genomic imprinting disorders in human. Newly developed genomic technologies as well as conventional microsatellite marker methods have been contributing to the functional and mechanistic investigation of UPD, leading to not only the acquisition of clinically valuable information, but also the further clarification of diverse genetic processes and disease pathogenesis.

Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by overgrowth, tumor predisposition, and congenital malformations. Approximately 85% of reported BWS cases are sporadic, while the remaining 15% are familial. BWS is caused by epigenetic or genomic alterations which disrupt genes in one or both of the two imprinted domains on chromosome 11p15.5. In each domain, an imprinting center regulates the expression of imprinted genes in cis. Normally in domain 1, insulin-like growth factor 2 (IGF2) and the untranslated mRNA H19 are monoallelically expressed. In BWS, increased expression of IGF2 occurs via several mechanisms. In domain 2, CDKN1C, a growth repressor, and an untranslated RNA, KCNQ1OT1, are normally expressed monoallelically. In cases of BWS, several mechanisms result in reduced expression of CDKN1C. Recent reports of BWS cases have identified mutations outside the chromosome 11p15.5 critical region, thereby broadening the challenges in the diagnosis and genetic counseling of individuals and families with BWS.