Epigenetic modification and uniparental inheritance of H19 in Beckwith-Wiedemann syndrome

Prenatal diagnosis of 7 cases with uniparental disomy by utilization of single nucleotide polymorphism array

Background

The phenotypes of uniparental disomy (UPD) are variable, which may either have no clinical impact, lead to clinical signs and symptoms. Molecular analysis is essential for making a correct diagnosis. This study involved a retrospective analysis of 4512 prenatal diagnosis samples and explored the molecular characteristics and prenatal phenotypes of UPD using a single nucleotide polymorphism (SNP) array.

Results

Out of the 4512 samples, a total of seven cases of UPD were detected with an overall frequency of 0.16%. Among the seven cases of UPD, two cases are associated with chromosomal aberrations (2/7), four cases (4/7) had abnormal ultrasonographic findings. One case presented with iso-UPD (14), and two case presented with mixed hetero/iso-UPD (15), which were confirmed by Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) as maternal UPD (15) associated with Prader-Willi syndrome (PWS). Four cases had iso-UPD for chromosome 1, 3, 14, and 16, respectively; this is consistent with the monosomy rescue mechanism. Another three cases presented with mixed hetero/isodisomy were consistent with a trisomy rescue mechanism.

Conclusion

The prenatal phenotypes of UPD are variable and molecular analysis is essential for making a correct diagnosis and genetic counselling of UPD. The SNP array is a useful genetic test in prenatal diagnosis cases with UPD.

How Does Reprogramming to Pluripotency Affect Genomic Imprinting?

Human induced Pluripotent Stem Cells (hiPSCs) have the capacity to generate a wide range of somatic cells, thus representing an ideal tool for regenerative medicine. Patient-derived hiPSCs are also used for in vitro disease modeling and drug screenings. Several studies focused on the identification of DNA mutations generated, or selected, during the derivation of hiPSCs, some of which are known to drive cancer formation. Avoiding such stable genomic aberrations is paramount for successful use of hiPSCs, but it is equally important to ensure that their epigenetic information is correct, given the critical role of epigenetics in transcriptional regulation and its involvement in a plethora of pathologic conditions. In this review we will focus on genomic imprinting, a prototypical epigenetic mechanism whereby a gene is expressed in a parent-of-origin specific manner, thanks to the differential methylation of specific DNA sequences. Conventional hiPSCs are thought to be in a pluripotent state primed for differentiation. They display a hypermethylated genome with an unexpected loss of DNA methylation at imprinted loci. Several groups recently reported the generation of hiPSCs in a more primitive developmental stage, called naïve pluripotency. Naïve hiPSCs share several features with early human embryos, such as a global genome hypomethylation, which is also accompanied by a widespread loss of DNA methylation at imprinted loci. Given that loss of imprinting has been observed in genetic developmental disorders as well as in a wide range of cancers, it is fundamental to make sure that hiPSCs do not show such epigenetic aberrations. We will discuss what specific imprinted genes, associated with human pathologies, have been found commonly misregulated in hiPSCs and suggest strategies to effectively detect and avoid such undesirable epigenetic abnormalities.

Prognostic significance of INF-induced transmembrane protein 1 in colorectal cancer

Interferon-induced transmembrane protein 1 (IFITM1) has recently been implicated in tumorigenesis. However, the prognostic value of IFITM1 in colorectal cancer remains unknown. The present study aimed to examine the expression and prognostic significance of IFITM1 in human colorectal cancer. IFITM1 expression was analyzed in 144 archived, paraffin-embedded colorectal cancer tissues and corresponding normal colorectal mucosa by immunohistochemistry. The correlation of IFITM1 with clinic-pathological features and overall survival of colorectal cancer patients was evaluated. IFITM1 was overexpressed in colonic cancer tissues but not in rectal cancer tissues, compared to control normal tissues. The expression of IFITM1 was significantly higher in patients with poor differentiation (P=0.031). The patients with higher IFITM1 expression had worse overall survival outcomes than those with lower IFITM1 expression in rectal cancer (P=0.037). Univariate Cox regression suggested that older age and poorly differentiation status predict shorter overall survival in colorectal cancer (P<0.05). However, IFITM1 expression was not a significant prognostic factor for survival by univariate or multivariate analyses. In conclusion, high expression of IFITM1 is associated with poor prognosis of rectal cancer. IFITM1 may serve as an independent prognostic biomarker for colorectal cancer.

Similar frequency of paternal uniparental disomy involving chromosome 20q (patUPD20q) in Japanese and Caucasian patients affected by sporadic pseudohypoparathyroidism type Ib (sporPHP1B)

Pseudohypoparathyroidism type Ib (PHP1B) is caused by proximal tubular resistance to parathyroid hormone that occurs in most cases in the absence of Albright's Hereditary Osteodystrophy (AHO). Familial forms of PHP1B are caused by maternally inherited microdeletions within STX16, the gene encoding syntaxin 16, or within GNAS, a complex genetic locus on chromosome 20q13.3 encoding Gsα and several splice variants thereof. These deletions lead either to a loss-of-methylation affecting GNAS exon A/B alone or to epigenetic changes involving multiple differentially methylated regions (DMRs) within GNAS. Broad GNAS methylation abnormalities are also observed in most sporadic PHP1B (sporPHP1B) cases. However, with the exception of paternal uniparental disomy involving chromosome 20q (patUPD20q), the molecular mechanism leading to this disease variant remains unknown. We now investigated 23 Japanese sporPHP1B cases, who presented with hypocalcemia, hyperphosphatemia, elevated PTH levels, and occasionally with TSH elevations and mild AHO features. Age at diagnosis was 10.6 ± 1.45 years. Calcium, phosphate, and PTH were 6.3 ± 0.23 mg/dL, 7.7 ± 0.33 mg/dL, and 305 ± 34.5 pg/mL, respectively, i.e. laboratory findings that are indistinguishable from those previously observed for Caucasian sporPHP1B cases. All investigated patients showed broad GNAS methylation changes. Eleven individuals were homozygous for SNPs within exon NESP and a pentanucleotide repeat in exon A/B. Two of these patients furthermore revealed homozygosity for numerous microsatellite markers on chromosome 20q raising the possibility of patUPD20q, which was confirmed through the analysis of parental DNA. Based on this and our previous reports, paternal duplication of the chromosomal region comprising the GNAS locus appears to be a fairly common cause of sporPHP1B that is likely to occur with equal frequency in Caucasians and Asians.

Exploring the spectrum of 3-M syndrome, a primordial short stature disorder of disrupted ubiquitination

3-M syndrome is an autosomal recessive primordial growth disorder characterized by small birth size and post-natal growth restriction associated with a spectrum of minor anomalies (including a triangular-shaped face, flat cheeks, full lips, short chest and prominent fleshy heels). Unlike many other primordial short stature syndromes, intelligence is normal and there is no other major system involvement, indicating that 3-M is predominantly a growth-related condition. From an endocrine perspective, serum GH levels are usually normal and IGF-I normal or low, while growth response to rhGH therapy is variable but typically poor. All these features suggest a degree of resistance in the GH-IGF axis. To date, mutations in three genes CUL7, OBSL1 and CCDC8 have been shown to cause 3-M. CUL7 acts an ubiquitin ligase and is known to interact with p53, cyclin D-1 and the growth factor signalling molecule IRS-1, the link with the latter may contribute to the GH-IGF resistance. OBSL1 is a putative cytoskeletal adaptor that interacts with and stabilizes CUL7. CCDC8 is the newest member of the pathway and interacts with OBSL1 and, like CUL7, associates with p53, acting as a co-factor in p53-medicated apoptosis. 3-M patients without a mutation have also been identified, indicating the involvement of additional genes in the pathway. Potentially damaging sequence variants in CUL7 and OBSL1 have been identified in idiopathic short stature (ISS), including those born small with failure of catch-up growth, signifying that the 3-M pathway could play a wider role in disordered growth.

The role of imprinted genes in humans

Genomic imprinting, a process of epigenetic modification which allows the gene to be expressed in a parent-of-origin specific manner, has an essential role in normal growth and development. Imprinting is found predominantly in placental mammals, and has potentially evolved as a mechanism to balance parental resource allocation to the offspring. Therefore, genetic and epigenetic disruptions which alter the specific dosage of imprinted genes can lead to various developmental abnormalities often associated with fetal growth and neurological behaviour. Over the past 20 years since the first imprinted gene was discovered, many different mechanisms have been implicated in this special regulatory mode of gene expression. This review includes a brief summary of the current understanding of the key molecular events taking place during imprint establishment and maintenance in early embryos, and their relationship to epigenetic disruptions seen in imprinting disorders. Genetic and epigenetic causes of eight recognised imprinting disorders including Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS), and also their association with Assisted reproductive technology (ART) will be discussed. Finally, the role of imprinted genes in fetal growth will be explored by investigating their relationship to a common growth disorder, intrauterine growth restriction (IUGR) and also their potential role in regulating normal growth variation.

DNA methylation studies on imprinted loci in a male monozygotic twin pair discordant for Beckwith-Wiedemann syndrome

Beckwith–Wiedemann syndrome (BWS) is one of the most prevalent congenital disorders predominantly caused by epigenetic alterations. Here we present an extensive case study of a monozygotic monochorionic male twin pair discordant for BWS. Our analysis allows to correlate BWS symptoms, like a protruding tongue, indented ears and transient neonatal hypoglycaemia, to an abnormal methylation at the KvDMR1. DNAs extracted from peripheral blood, skin fibroblasts, saliva and buccal swab of both twins, their sister and parents were analysed at 11 differentially methylated regions (DMRs) including all four relevant DMRs of the BWS region. The KvDMR1 was exclusively found to be hypomethylated in all cell types of the affected BWS twin, while the unaffected twin and the relatives showed normal methylation in fibroblasts, buccal swab and saliva DNA. Interestingly, the twins share a common blood-specific hypomethylation phenotype most probably caused by a feto-fetal transfusion between both twins. Because microsatellite analysis furthermore revealed a normal biparental karyotype for chromosome 11, our results point to an exclusive correlation of the observed BWS symptoms to locally restricted epimutations at the KvDMR1 of the maternal chromosome.

Beckwith-Wiedemann syndrome and uniparental disomy 11p: fine mapping of the recombination breakpoints and evaluation of several techniques

Beckwith-Wiedemann syndrome (BWS) is a phenotypically and genotypically heterogeneous overgrowth syndrome characterized by somatic overgrowth, macroglossia and abdominal wall defects. Other usual findings are hemihyperplasia, embryonal tumours, adrenocortical cytomegaly, ear anomalies, visceromegaly, renal abnormalities, neonatal hypoglycaemia, cleft palate, polydactyly and a positive family history. BWS is a complex, multigenic disorder associated, in up to 90% of patients, with alteration in the expression or function of one or more genes in the 11p15.5 imprinted gene cluster. There are several molecular anomalies associated with BWS and the large proportion of cases, about 85%, is sporadic and karyotypically normal. One of the major categories of BWS molecular alteration (10-20% of cases) is represented by mosaic paternal uniparental disomy (pUPD), namely patients with two paternally derived copies of chromosome 11p15 and no maternal contribution for that. In these patients, in addition to the effects of IGF2 overexpression, a decreased level of the maternally expressed gene CDKN1C may contribute to the BWS phenotype. In this paper, we reviewed a series of nine patients with BWS because of pUPD using several methods with the aim to evaluate the percentage of mosaicism, the methylation status at both loci, the extension of the pUPD at the short arm and the breakpoints of recombination. Fine mapping of mitotic recombination breakpoints by single-nucleotide polymorphism-array in individuals with UPD and fine estimation of epigenetic defects will provide a basis for understanding the aetiology of BWS, allowing more accurate prognostic predictions and facilitating management and surveillance of individuals with this disorder.

Aging induces a distinct gene expression program in mouse islets

The role of aging in the pathogenesis of type 2 diabetes remains poorly understood. In the past adult β-cells were assumed to undergo frequent turnover. However, we find that β-cell turnover declines to very low levels in middle-aged mice. We therefore hypothesized that aged islets could exhibit a distinct gene expression program. We compared gene expression in islets from young mice to islets from aged mice under basal conditions. Aging was associated with differential expression of many genes in islets, including mRNAs encoding for chromatin remodeling components, RNA binding proteins, and pancreatic endocrine transcription factors. We previously observed that cell cycle entry of β-cells is severely restricted by middle age, with minimal of β-cell proliferation in response to regenerative stimuli such as 50% partial pancreatectomy. To characterize the effect of age in adaptive β-cell proliferation, we measured gene expression in islets from young mice after pancreatectomy. As expected, partial pancreatectomy induced differential expression of many genes, including those encoding Reg (regenerating) proteins. Surprisingly, partial pancreatectomy also induced expression of Reg genes in islets from aged mice, which have greatly reduced capacity for adaptive β-cell proliferation. However, there was little overlap (besides the Reg genes) in between the partial pancreatectomy induced islet genes in young mice versus old mice. Thus, partial pancreatectomy does not induce the same gene expression program in young mice vs old mice. Taken together, our results reveal that aged islets exhibit a unique gene expression signature that could contribute to the limited regenerative capacity of mature β-cells.

Addition of H19 'loss of methylation testing' for Beckwith-Wiedemann syndrome (BWS) increases the diagnostic yield

Beckwith-Wiedemann syndrome (BWS) is a clinical diagnosis; however, molecular confirmation via abnormal methylation of DMR2(LIT1) and/or DMR1(H19) has clinical utility due to epigenotype-tumor association. Despite the strong link between H19 hypermethylation and tumor risk, several diagnostic laboratories only test for hypomethylation of LIT1. We assessed the added diagnostic value of combined LIT1 and H19 testing in a large series of referred samples from 1298 patients, including 53 well-characterized patients from the St. Louis Children's Hospital BWS-Registry (validation samples) and 1245 consecutive nationwide referrals (practice samples). Methylation-sensitive enzymatic digestion with Southern hybridization assessed loss of normal imprinting. In the validation group, abnormal LIT1 hypomethylation was detected in 60% (32/52) of patients but LIT1/H19-combined testing was abnormal in 68% (36/53); sensitivity in the practice setting demonstrated 27% (342/1245) abnormal LIT1 and 32% (404/1245) abnormal LIT1/H19-combined. In addition, H19 methylation was abnormal in 7% of LIT1-normal patients. We observed absence of uniparental disomy (UPD) in 27% of combined LIT1/H19-abnormal samples, diagnostic of multilocus methylation abnormalities; in contrast to studies implicating that combined LIT1/H19 abnormalities are diagnostic of UPD. The overall low detection rate, even in validated patient samples and despite characterization of both loci and UPD status, emphasizes the importance of clinical diagnosis in BWS.

Human intelligence and polymorphisms in the DNA methyltransferase genes involved in epigenetic marking

Epigenetic mechanisms have been implicated in syndromes associated with mental impairment but little is known about the role of epigenetics in determining the normal variation in human intelligence. We measured polymorphisms in four DNA methyltransferases (DNMT1, DNMT3A, DNMT3B and DNMT3L) involved in epigenetic marking and related these to childhood and adult general intelligence in a population (n = 1542) consisting of two Scottish cohorts born in 1936 and residing in Lothian (n = 1075) or Aberdeen (n = 467). All subjects had taken the same test of intelligence at age 11yrs. The Lothian cohort took the test again at age 70yrs. The minor T allele of DNMT3L SNP 11330C>T (rs7354779) allele was associated with a higher standardised childhood intelligence score; greatest effect in the dominant analysis but also significant in the additive model (coefficient = 1.40_additive; 95%CI 0.22,2.59; p = 0.020 and 1.99_dominant; 95%CI 0.55,3.43; p = 0.007). The DNMT3L C allele was associated with an increased risk of being below average intelligence (OR 1.25_additive; 95%CI 1.05,1.51; p = 0.011 and OR 1.37_dominant; 95%CI 1.11,1.68; p = 0.003), and being in the lowest 40^th (p_additive = 0.009; p_dominant = 0.002) and lowest 30^th (p_additive = 0.004; p_dominant = 0.002) centiles for intelligence. After Bonferroni correction for the number variants tested the link between DNMT3L 11330C>T and childhood intelligence remained significant by linear regression and centile analysis; only the additive regression model was borderline significant. Adult intelligence was similarly linked to the DNMT3L variant but this analysis was limited by the numbers studied and nature of the test and the association was not significant after Bonferroni correction. We believe that the role of epigenetics in the normal variation in human intelligence merits further study and that this novel finding should be tested in other cohorts.

The human 1-8D gene (IFITM2) is a novel p53 independent pro-apoptotic gene

The human 1-8 interferon inducible gene family consists of at least 3 functional genes; 9-27, 1-8D and 1-8U, which are all linked on an 18-kb fragment of chromosome 11 and are highly homologous. It has recently been shown by us and others that the 1-8D gene is overexpressed in colon carcinoma. Here, we show, by sequence comparison of the 1-8D in pairs of tumor/normal colon tissues, the existence of 6 different alleles, containing single-nucleotide polymorphisms with no mutations. Transformation assays revealed a possible role for the 1-8D gene as a transformation inhibitor. Further, transient expression of the human 1-8D gene in multiple mammalian cell lines showed accumulation of cells in the G1 phase followed by elevation in the subG1 phase. SubG1 elevation was confirmed as apoptosis by Annexin-V binding assays and transferase-mediated dUTP nick end labeling assays. Moreover, knock-down of 1-8D provided partial protection from Etoposide and UV-induced apoptosis. The induction of apoptosis by 1-8D is dependent on caspase activities but not on p53 expression. Although 1-8D induces apoptosis independently of p53, p53 expression downregulates 1-8D protein expression. Our data suggest a role for the 1-8D gene as a novel pro-apoptotic gene that will provide new insights into the regulated cellular pathways to death.

p57KIP2: "Kip"ing the cell under control

p57(KIP2) is an imprinted gene located at the chromosomal locus 11p15.5. It is a cyclin-dependent kinase inhibitor belonging to the CIP/KIP family, which includes additionally p21(CIP1/WAF1) and p27(KIP1). It is the least studied CIP/KIP member and has a unique role in embryogenesis. p57(KIP2) regulates the cell cycle, although novel functions have been attributed to this protein including cytoskeletal organization. Molecular analysis of animal models and patients with Beckwith-Wiedemann Syndrome have shown its nodal implication in the pathogenesis of this syndrome. p57(KIP2) is frequently down-regulated in many common human malignancies through several mechanisms, denoting its anti-oncogenic function. This review is a thorough analysis of data available on p57(KIP2), in relation to p21(CIP1/WAF1) and p27(KIP1), on gene and protein structure, its transcriptional and translational regulation, and its role in human physiology and pathology, focusing on cancer development.

Mitotic recombination and uniparental disomy in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a model human imprinting disorder resulting from altered activity of one or more genes in the 11p15.5 imprinted gene cluster. Approximately 20% of BWS cases have uniparental disomy (UPD) of chromosome 11. Such cases appear to result from mitotic recombination occurring in early embryogenesis and offer a rare opportunity to study mitotic recombination in nonneoplastic cells. We analyzed a cohort of 52 children with BWS and UPD using a panel of microsatellite markers for chromosome 11. All cases demonstrated mosaic paternal isodisomy, and IGF2 and H19 were included in the segment of UPD in all cases. However, the extent of segmental disomy was variable, with no evidence of clustering of the proximal UPD breakpoint. In most cases (92% of those informative) UPD did not involve 11q, but 4 patients demonstrated UPD for the whole of chromosome 11. In contrast to meiotic recombination, the mitotic recombination frequency did not decline near the centromere.

Paternally Inherited Submicroscopic Duplication at 11p15.5 Implicates Insulin-like Growth Factor II in Overgrowth and Wilms' Tumorigenesis

Loss of imprinting at insulin-like growth factor II (IGFII), in association with H19 silencing, has been described previously in a subgroup of Beckwith-Wiedemann syndrome (BWS) patients who have an elevated risk for Wilms' tumor. An equivalent somatic mutation occurs in sporadic Wilms' tumor. We describe a family with overgrowth in three generations and Wilms' tumor in two generations, with paternal inheritance of a cis-duplication at 11p15.5 spanning the BWS IC1 region and including H19, IGFII, INS, and TH. The duplicated region was below the limit of detection by high-resolution karyotyping and fluorescence in situ hybridization, has a predicted minimum size of 400 kb, and was confirmed by genotyping and gene-dosage analysis on a CytoChip comparative genomic hybridization bacterial artificial chromosome array. IGFII is the only known paternally expressed oncogene mapping within the duplicated region and our findings directly implicate IGFII in Wilms' tumorigenesis and add to the mutation spectrum that increases the effective dose of IGFII. Furthermore, this study raises the possibility that sporadic cases of overgrowth and Wilms' tumor, presenting with apparent gain of methylation at IC1, may be explained by submicroscopic paternal duplications. This finding has important implications for determining the transmission risk in these disorders.

Chromosome 11 segmental paternal isodisomy in amniocytes from two fetuses with omphalocoele: new highlights on phenotype-genotype correlations in Beckwith-Wiedemann syndrome

BACKGROUND

The phenotypic variability in Beckwith-Wiedemann syndrome (BWS) reflects the genetic heterogeneity of the mechanism which by default leads to the deregulation of genes located at 11p15.5. Genotype-phenotype correlation studies have demonstrated an association between omphalocoele and CDKN1C/p57 mutations or hypermethylation. Paternal uniparental disomy 11 (pUPD11) has been described only in the mosaic condition with both uniparental and biparental cell lines, and no association with omphalocoele has been pointed out.

METHODS

Two cases are presented here, in which a paternal segmental UPD11 was detected by molecular investigation of amniotic fluid cell cultures after the presence of apparently isolated omphalocoele was revealed in the fetuses by ultrasound scan. Further studies were performed on additional autoptic feto-placental tissues to characterise the distribution of the uniparental cell line and to unmask any biparental lineage in order to document in more detail the as yet unreported association between omphalocoele and pUPD11.

RESULTS

Results on the UPD distribution profile showed that the abdominal organs have a predominant uniparental constitution. This condition could mimic the effect of CDKN1C/p57 inactivation, causing the omphalocoele.

CONCLUSION

New genotype-phenotype correlations emerge from the investigated cases, suggesting that molecular analysis be extended to all cases with fetal omphalocoele in order to establish the incidence of pUPD11 in complete BWS and in monosymptomatic/mild forms.

Molecular and genomic characterisation of cryptic chromosomal alterations leading to paternal duplication of the 11p15.5 Beckwith-Wiedemann region

BACKGROUND

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder with increased risk of paediatric tumours. The aetiology involves epigenetic and genetic alterations affecting the 11p15 region, methylation of the differentially methylated DMR2 region being the most common defect, while less frequent aetiologies include mosaic paternal 11p uniparental disomy (11patUPD), maternally inherited mutations of the CDKN1C gene, and hypermethylation of DMR1. A few patients have cytogenetic abnormalities involving 11p15.5.

METHODS

Screening of 70 trios of BWS probands for 11p mosaic paternal UPD and for cryptic cytogenetic rearrangements using microsatellite segregation analysis identified a profile compatible with paternal 11p15 duplication in two patients.

RESULTS

Fluorescence in situ hybridisation analysis revealed in one case the unbalanced translocation der(21)t(11;21)(p15.4;q22.3) originated from missegregation of a cryptic paternal balanced translocation. The second patient, trisomic for D11S1318, carried a small de novo dup(11)(p15.5p15.5), resulting from unequal recombination at paternal meiosis I. The duplicated region involves only IC1 and spares IC2/LIT1, as shown by fluorescent in situ hybridisation (FISH) mapping of the proximal duplication breakpoint within the amino-terminal part of KvLQT1.

CONCLUSIONS

An additional patient with Wolf-Hirschorn syndrome was shown by FISH studies to carry a der(4)t(4;11)(p16.3;p15.4), contributed by a balanced translocation father. Interestingly, refined breakpoint mapping on 11p and the critical regions on the partner 21q and 4p chromosomal regions suggested that both translocations affecting 11p15.4 are mediated by segmental duplications. These findings of chromosomal rearrangements affecting 11p15.5-15.4 provide a tool to further dissect the genomics of the BWS region and the pathogenesis of this imprinting disorder.

IFITM1 plays an essential role in the antiproliferative action of interferon-gamma

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine involved in antiproliferative and anti-virus responses, immune surveillance and tumor suppression. These biological responses to IFN-gamma are mainly mediated by the regulation of gene expression. It has been reported that growth-inhibitory role of IFN-gamma is dependent on activation of signal transducers and activators of transcription 1 (STAT1); however, the molecular basis downstream of STAT1 remains unclear. Here, we report that an IFN-gamma-induced gene, interferon-induced transmembrane protein 1 (IFITM1), plays a key role in the antiproliferative action of IFN-gamma. Overexpression of IFITM1 negatively regulated cell growth, whereas suppression of IFITM1 blocked the antiproliferative effect of IFN-gamma, accelerated the cell growth rate and conferred tumorigenicity to a non-malignant hepatocyte in nude mice. Further, IFITM1 could inhibit the activity of extracellular signal-regulated kinase, enhance the transcriptional activity of p53 and stabilize the p53 protein by inhibiting p53 phosphorylation on Thr55. Suppression of p53 reduced the growth-inhibitory capacity of both IFITM1 and IFN-gamma. Therefore, these findings indicated that the antiproliferative action of IFN-gamma requires the induction of IFITM1, and provided a crosstalk between two well-known signaling mediators, STAT1 and p53, both of which play critical roles in tumor suppression.

Epigenetic deregulation of imprinting in congenital diseases of aberrant growth

Human chromosome 11p15 comprises two imprinted domains important in the control of fetal and postnatal growth. Novel studies establish that imprinting at one of these, the IGF2-H19 domain, is epigenetically deregulated (with loss of DNA methylation) in Silver-Russell Syndrome (SRS), a congenital disease of growth retardation and asymmetry. Previously, the exact opposite epigenetic alteration (gain of DNA methylation) had been detected at the domain's 'imprinting control region' (ICR) in patients with Beckwith-Wiedemann Syndrome (BWS), a complex disorder of fetal overgrowth. However, more frequently, BWS is caused by loss of DNA methylation at the ICR that regulates the second imprinted domain at 11p15. Interestingly, a similar epigenetic alteration (with loss of methylation) at a putative ICR on human chromosome 6q24, is involved in transient neonatal diabetes mellitus (TNDM), a congenital disease with intrauterine growth retardation and a transient lack of insulin. Thus, fetal and postnatal growth is epigenetically controlled by different ICRs, at 11p15 and other chromosomal regions.

Mechanisms predisposing to childhood overgrowth and cancer

Several overgrowth conditions are believed to be associated with elevated risks of cancer, particularly in childhood. Beckwith-Wiedemann syndrome and Sotos syndrome are the most common overgrowth conditions, and both carry increased risks of certain tumors. In recent years, the identification of both the gene causing Sotos syndrome and the epigenetic subgroups underlying Beckwith-Wiedemann syndrome have enabled clarification of the cancer types and risks associated with these conditions. This has revealed striking differences in the cancer phenotypes associated with different molecular abnormalities. Elucidation of the mechanisms underlying cancer in overgrowth syndromes might yield important insights into the molecular basis of childhood tumors.

Molecular subtypes and phenotypic expression of Beckwith-Wiedemann syndrome

Beckwith-Wiedemann Syndrome (BWS) results from mutations or epigenetic events involving imprinted genes at 11p15.5. Most BWS cases are sporadic and uniparental disomy (UPD) or putative imprinting errors predominate in this group. Sporadic cases with putative imprinting defects may be subdivided into (a) those with loss of imprinting (LOI) of IGF2 and H19 hypermethylation and silencing due to a defect in a distal 11p15.5 imprinting control element (IC1) and (b) those with loss of methylation at KvDMR1, LOI of KCNQ1OT1 (LIT1) and variable LOI of IGF2 in whom there is a defect at a more proximal imprinting control element (IC2). We investigated genotype/epigenotype-phenotype correlations in 200 cases with a confirmed molecular genetic diagnosis of BWS (16 with CDKN1C mutations, 116 with imprinting centre 2 defects, 14 with imprinting centre 1 defects and 54 with UPD). Hemihypertrophy was strongly associated with UPD (P<0.0001) and exomphalos was associated with an IC2 defect or CDKN1C mutation but not UPD or IC1 defect (P<0.0001). When comparing birth weight centile, IC1 defect cases were significantly heavier than the patients with CDKN1C mutations or IC2 defect (P=0.018). The risk of neoplasia was significantly higher in UPD and IC1 defect cases than in IC2 defect and CDKN1C mutation cases. Kaplan-Meier analysis revealed a risk of neoplasia for all patients of 9% at age 5 years, but 24% in the UPD subgroup. The risk of Wilms' tumour in the IC2 defect subgroup appears to be minimal and intensive screening for Wilms' tumour appears not to be indicated. In UPD patients, UPD extending to WT1 was associated with renal neoplasia (P=0.054). These findings demonstrate that BWS represents a spectrum of disorders. Identification of the molecular subtype allows more accurate prognostic predictions and enhances the management and surveillance of BWS children such that screening for Wilms' tumour and hepatoblastoma can be focused on those at highest risk.

Risk of tumorigenesis in overgrowth syndromes: a comprehensive review

Overgrowth syndromes (OGS) comprise a heterogeneous group of disorders in which the main characteristic is that either weight, height, or head circumference is 2-3 standard deviations (SD) above the mean for sex and age. A striking feature of OGS is the risk of neoplasms. Here, the relative frequency of specific tumors in each OGS, topographic location, and age of appearance is determined by reviewing published cases. In some OGS (Perlman, Beckwith-Wiedemann, and Simpson-Golabi-Behmel syndromes and hemihyperplasia) more than 94% of tumors appeared in the abdomen usually before 10 years of age, mainly embryonal in type. In Perlman syndrome, only Wilms tumor has been recorded, whereas in Sotos syndrome, lympho-hematologic tumors are most frequent. Based on literature review, a specific schedule protocol for tumor screening is suggested for each OGS. A schedule with different intervals and specific tests is proposed for a more rational cost/benefit program for these disorders.

Beckwith-Wiedemann syndrome: historical, clinicopathological, and etiopathogenetic perspectives

Macroglossia, prenatal or postnatal overgrowth, and abdominal wall defects (omphalocele, umbilical hernia, or diastasis recti) permit early recognition of Beckwith-Wiedemann syndrome. Complications include neonatal hypoglycemia and an increased risk for Wilms tumor, adrenal cortical carcinoma, hepatoblastoma, rhabdomyosarcoma, and neuroblastoma, among others. Perinatal mortality can result from complications of prematurity, pronounced macroglossia, and rarely cardiomyopathy. The molecular basis of Beckwith-Wiedemann syndrome is complex, involving deregulation of imprinted genes found in 2 domains within the 11p15 region: telomeric Domain 1 (IGF2 and H19) and centromeric Domain 2 (KCNQ1, KCNQ1OT1, and CDKN1C). Topics discussed in this article are organized as a series of perspectives: general, historical, epidemiologic, clinical, pathologic, genetic/molecular, diagnostic, and differential diagnostic.

The influence of non-coding RNAs on allele-specific gene expression in mammals

Current research has revealed that the influence of RNA molecules on gene expression reaches beyond the realm of protein synthesis back into the nucleus, where it not only dictates the transcriptional activity of genes, but also shapes the chromatin architecture of extensive regions of DNA. Non-coding RNA, in the context of this review, refers to transcripts expressed and processed in the nucleus much like any protein coding gene, but lacking an open reading frame and often transcribed antisense to bona fide protein coding genes. In mammals, these types of transcripts are highly coincident with allele-specific silencing of imprinted genes and have a proven role in dosage compensation via X-inactivation. The biochemistry of how non-coding RNAs regulate transcription is the subject of intense research in both prokaryotic and eukaryotic models. Mechanisms such as RNA interference may have deep phylogenetic roots, but their relevance to imprinting and X-inactivation in mammals has not been proven. The remarkable diversity of non-coding transcription associated with parent-of-origin directed gene silencing hints at an equally diverse assortment of mechanisms.

CDKN1C mutation in Wiedemann-Beckwith syndrome patients reduces RNA splicing efficiency and identifies a splicing enhancer

Wiedemann-Beckwith syndrome (WBS) is a human overgrowth disorder that is accompanied by an increased risk of embryonal tumors and is associated with dsyregulation of the imprinting of genes in chromosome 11p15.5. Maternally inherited mutations in the imprinted CDKN1C gene are known to be associated with WBS. We have identified a novel mutation in several members of a large family affected by WBS. The mutation is a G --> T change in a run of seven G's near the 5' splice site of intron 3. All obligate carriers and affected individuals carry the mutation, and in each affected case, the allele was inherited maternally, strongly suggesting a role in causing WBS. The mutation is located in a poly-G tract in the intron; intronic G-rich sequences in other genes have been shown to have a role in promoting splicing. In transfected 293HEK cells, we found that the G --> T mutation reduced splicing efficiency. Mutation of all seven G's in the poly-G tract further reduced splicing efficiency, supporting a role for the G-tract as a splicing enhancer. The fibroblasts of one affected patient showed a similar reduction in splicing efficiency. Maternal monoallelic expression of CDKN1C was verified in this patient cell line. However, the total amount of spliced message was not reduced by the mutation in spite of the reduced efficiency of splicing. We discuss the possible role of the splicing defect in the pathogenesis of WBS in this pedigree.

Tumor risk in Beckwith-Wiedemann syndrome: A review and meta-analysis

Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with macroglossia, abdominal wall defects, ear anomalies, and an increased risk for embryonic tumors. Reported tumor risk estimates vary between 4% and 21%. It has been hypothesized that tumor predisposition in BWS is related to the imprinting status of the H19 and LIT1 genes on chromosome 11p15. A loss of imprinting (LOI) of H19 implies a higher tumor risk. However, a systematic analysis of available data is lacking. Therefore, we performed a review and meta-analysis of reported associations between the imprinting status of the LIT1 and H19 genes and the risk for tumor development in BWS. Five publications suitable for meta-analysis were identified by electronic database searches. Sufficient data were available for 402 out of 520 patients. Patients were divided into four groups based on the imprinting status of H19 and LIT1: group I with LOI of LIT1 (45%); group II with LOI of H19 (9%); group III with LOI of LIT1 and LOI of H19 (21%); and group IV with normal imprinting patterns (26%). Differences in tumor risk between groups were studied with random effects meta-analysis. Tumors occurred in 55 patients. The odds of tumor development was significantly lower in group I when compared to group II (OR=0.06; 95% CI: 0.02-0.21) and group III (OR=0.12; 95% CI: 0.04-0.37). Tumor risk did not differ significantly between groups II and III (OR=1.40; 95% CI: 0.56-3.50). Compared to group IV, tumor risk was significantly lower in group I (OR=0.33; 95% CI: 0.12-0.87) and higher in groups II (OR=4.0; 95% CI: 1.5-10.4) and III (OR=2.6; 95% CI: 1.2-5.7). Tumor incidence rate for group IV was 10.6% (95% CI: 3.6-17.7). Calculated absolute risks were 3% for group I, 43% for group II, and 28% for group III, respectively. No Wilms tumor was seen in group I. In total, other tumors were seen with comparable frequencies in groups I-III. The results show a strong association between a LOI of H19 and especially Wilms tumor development in BWS.

A fluorescent method for detecting low-grade 11patUPD mosaicism in Beckwith–Wiedemann syndrome

The quantitative evaluation of mosaicism for uniparental disomy (UPD) involving a restricted chromosomal region requires the availability of a sensitive and reproducible method that is capable of detecting even a small percentage of disomic cells and avoiding false positive and false negative results. The occurrence of UPD is usually monitored by means of the parent-proband segregation analysis of microsatellites mapping to the target region. We here describe the quantitative blood cell evaluation of segmental mosaic UPD11, a marker of Beckwith-Wiedemann syndrome, by means of the segregation analysis of 11p15 microsatellites using both radioactive and fluorescence-based techniques. As the greater amplification efficiency of the shorter allele in heterozygous subjects may bias the correct evaluation of disomy, the mean short/long allele ratio was established at three loci of each of 30 normal heterozygous subjects, as well as the peak As/Al area in the presence of 50% of each allele. The interval was defined using a 5% level of significance. The results show that the fluorescence-based technique is superior to radioactivity in detecting the subtle allelic imbalances present in low-grade mosaicism conditions.

Physiological functions of imprinted genes

Genomic imprinting in gametogenesis marks a subset of mammalian genes for parent-of-origin-dependent monoallelic expression in the offspring. Embryological and classical genetic experiments in mice that uncovered the existence of genomic imprinting nearly two decades ago produced abnormalities of growth or behavior, without severe developmental malformations. Since then, the identification and manipulation of individual imprinted genes has continued to suggest that the diverse products of these genes are largely devoted to controlling pre- and post-natal growth, as well as brain function and behavior. Here, we review this evidence, and link our discussion to a website (http://www.otago.ac.nz/IGC) containing a comprehensive database of imprinted genes. Ultimately, these data will answer the long-debated question of whether there is a coherent biological rationale for imprinting.

Loss of methylation at chromosome 11p15.5 is common in human adult tumors

Chromosome 11p15 deletion is frequent in human tumors, suggesting the presence of at least one tumor suppressor gene within this region. While mutation analyses of local genes revealed only rare mutations, we have previously described a mechanism, gain of imprinting, that leads to loss of expression of genes located on the maternal 11p15 chromosome in human hepatocarcinomas. Loss of expression was often associated with loss of maternal-specific methylation at the KvDMR1 locus. Here, we show that loss of the maternal KvDMR1 methylation is common, ranging from 30 to 50%, to a variety of adult neoplasms, including liver, breast, cervical and gastric carcinomas. We found that other 11p15.5 loci were concomitantly hypomethylated, indicating that loss of KvDMR1 methylation occurred in the context of a common mechanism affecting the methylation of a large 11p15 subchromosomal domain. These epigenetic abnormalities were not detected in any normal somatic tissue. Therefore, it seems possible that, contrary to the repression of promoter activity caused by hypermethylation, loss of gene expression at 11p15.5 may result from the activation, by hypomethylation, of one or more negative regulatory elements.

Successful laparoscopic operation of bilateral pheochromocytoma in a patient with Beckwith-Wiedemann syndrome

We report the case of a 20-year-old female patient with Beckwith-Wiedemann syndrome presenting with high blood pressure and bilateral adrenal pheochromocytoma successfully removed with laparoscopy in the same time. To our knowledge, the present case is the first observation of a bilateral pheochromocytoma occurring in the Beckwith-Wiedemann syndrome. It provides further support for a genetic anomaly in this condition. Our case also indicates the interest of laparoscopy for the surgical treatment of adrenal pheochromocytoma, even in bilateral tumors.

Wiedemann-Beckwith syndrome: further prenatal characterization of the condition

We describe three unrelated cases of Wiedemann-Beckwith syndrome (WBS). Two of them were diagnosed postnatally while the third was detected during pregnancy that resulted in elective termination. Amniotic karyotypes were normal in all. PCR amplification of polymorphic loci mapping to 11p15.5 region documented partial trisomy of 11p15.5 due to paternal translocation in one, and segmental and mosaic segmental unipaternal disomy (UPD) in the second and third cases, respectively. Based on findings documented in these cases and the literature, we tabulated the anomalies that might be detected prenatally by ultrasound and that may suggest the syndrome. Constant findings included fetal overgrowth, polyhydramios, enlarged placenta, and specifically a distended abdomen. As most described signs developed after 22 weeks of gestation, a careful follow-up should be carried on until late stages of pregnancy. An amniotic karyotype might not detect subtle chromosomal rearrangements. We therefore recommend utilizing PCR of polymorphic loci on 11p15.5, in addition to conventional cytogenetic analysis of the fetus and both parents to detect possible maternal deletions or inversions, paternal duplications, and UPD that may account for the largest subset of sporadic WBS reaching 25% of cases. An early diagnosis of WBS is important for counseling the parents concerning potential risk for developing embryonic tumors, selection of the mode of delivery due to potential adrenal cysts that might bleed during labor, and prevention of neonatal hypoglycemia.

Imprinting defects in mouse embryos: stochastic errors or polymorphic phenotype?

Defects in expression of imprinted genes are believed to cause developmental abnormalities and play a role in carcinogenesis. To determine whether spontaneous imprinting defects may occur in mouse embryos, we studied the expression of two imprinted genes H19 and Igf2 in individual postimplantation 7.5 d.p.c. and 8.5 d.p.c. embryos. Biallelic expression of H19 was found in 1.6% of the embryos, whereas biallelic expression of Igf2 was found in 0.5% of the embryos. The loss of H19 imprinting (LOI) observed in a small fraction of early postimplantation embryos may be purely stochastic. Alternatively, since we never observed it in an inbred background, it may depend on genetic factors acting in trans. Either mechanism could explain the occurrence of polymorphic imprinting as well as the genesis of sporadic imprinting defects, including cancer. The frequency of LOI of H19 was higher than the incidence of sporadic imprinting disorders in humans (about 1 in 20,000). This contradiction may be explained by different incidence of imprinting errors in different imprinted regions of the genome, in different species, or by loss of the majority of nonmosaic embryos with imprinting defects before birth.

Imprinting status of 11p15 genes in Beckwith-Wiedemann syndrome patients with CDKN1C mutations

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by somatic overgrowth, congenital malformations, and predisposition to childhood tumors. Aberrant expression of multiple imprinted genes, including H19, IGF2, KCNQ1OT1, and CDKN1C, has been observed in BWS patients. It has been estimated that mutations in CDKN1C occur in 12-17% of BWS patients. We have screened 10 autosomal dominant pedigrees and 65 sporadic BWS cases by PCR/heteroduplex analysis and DNA sequencing and have identified four mutations, two of which were associated with biallelic IGF2 expression and normal H19 and KCNQ1OT1 imprinting. One patient demonstrated phenotypic expression of paternally transmitted mutation in this maternally expressed gene, a second proband is the child of one of a pair of monozygotic twin females who carry the mutation de novo, and a third patient exhibited unusual skeletal changes more commonly found in other overgrowth syndromes. When considered with other studies published to date, this work reveals the frequency of CDKN1C mutations in BWS to be only 4.9%. This is the first report of an analysis of the imprinting status of genes in the 11p15 region where CDKN1C mutations were associated with loss of IGF2 imprinting and maintenance of H19 and KCNQ1OT1 imprinting.

Imprinting and deviation from Mendelian transmission ratios

Deviations from a Mendelian 1:1 transmission ratio have been observed in human and mouse chromosomes. With few exceptions, the underlying mechanism of the transmission-ratio distortion remains obscure. We tested a hypothesis that grandparental-origin dependent transmission-ratio distortion is related to imprinting and possibly results from the loss of embryos which carry imprinted genes with imprinting marks that have been incorrectly reset. We analyzed transmission of alleles in four regions of the human genome that carry imprinted genes presumably critical for normal embryonic growth and development: 11p15.5 (H19, IGF2, HASH2, etc.), 11p13 (WT1), 7p11-12 (GRB10), and 6q25-q27 (IGF2R), among the offspring of 31 three-generation Centre d'Etude de polymorphism Humain (CEPH) families. Deviations from expected 1:1 ratios were found in the maternal chromosomes for regions 11p15.5, 11p13, and 6q25-27 and in the paternal chromosomes for regions 11p15 and 7p11-p12. The likelihood of the results was assessed empirically to be statistically significant (p = 0.0008), suggesting that the transmission ratios in the imprinted regions significantly deviated from 1:1. We did not find deviations from a 1:1 transmission ratio in imprinted regions that are not crucial for embryo viability (13q14 and 15q11-q13). The analysis of a larger set of 51 families for the 11p15.5 region suggests that there is heterogeneity among the families with regard to the transmission of 11p15.5 alleles. The results of this study are consistent with the hypothesis that grandparental-origin dependent transmission-ratio distortion is related to imprinting and embryo loss.

Genomic imprinting and cancer; new paradigms in the genetics of neoplasia

The role of epigenetic modification of gene expression is becoming increasingly important in how we understand the loss of tumour suppressor gene function in a variety of tumours and tumour predisposing syndromes. This review explores the importance of epimutation in Beckwith-Wiedemann syndrome and Wilms' tumour and focuses on genomic methylation in both imprinted and non-imprinted genes as a key mechanism in the development of cancer.

Partial paternal uniparental disomy of chromosome 6 in an infant with neonatal diabetes, macroglossia, and craniofacial abnormalities

Neonatal diabetes, which can be transient or permanent, is defined as hyperglycemia that presents within the first month of life and requires insulin therapy. Transient neonatal diabetes mellitus has been associated with abnormalities of the paternally inherited copy of chromosome 6, including duplications of a portion of the long arm of chromosome 6 and uniparental disomy, implicating overexpression of an imprinted gene in this disorder. To date, all patients with transient neonatal diabetes mellitus and uniparental disomy have had complete paternal isodisomy. We describe a patient with neonatal diabetes, macroglossia, and craniofacial abnormalities, with partial paternal uniparental disomy of chromosome 6 involving the distal portion of 6q, from 6q24-qter. This observation demonstrates that mitotic recombination of chromosome 6 can also give rise to uniparental disomy and neonatal diabetes, a situation similar to that observed in Beckwith-Wiedemann syndrome, another imprinted disorder. This finding has clinical implications, since somatic mosaicism for uniparental disomy of chromosome 6 should also be considered in patients with transient neonatal diabetes mellitus.

Epigenotype-phenotype correlations in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a model imprinting disorder resulting from mutations or epigenetic events involving imprinted genes at chromosome 11p15.5. Thus, germline mutations in CDKN1C, uniparental disomy (UPD), and loss of imprinting of IGF2 and other imprinted genes have been implicated. Many familial BWS cases have germline CDKN1C mutations. However, most BWS cases are sporadic and UPD or putative imprinting errors predominate in this group. We have identified previously a subgroup of sporadic cases with loss of imprinting (LOI) of IGF2 and epigenetic silencing of H19 proposed to be caused by a defect in a distal 11p15.5 imprinting control element (designated BWSIC1). However, many sporadic BWS patients show biallelic IGF2 expression in the presence of normal H19 methylation and expression patterns. This and other evidence suggested the existence of a further imprinting control element (BWSIC2) at 11p15. 5. Recently, we showed that a subgroup of BWS patients have loss of methylation (LOM) at a differentially methylated region (KvDMR1) within the KCNQ1 gene centromeric to the IGF2 and H19 genes. We have now analysed a large series of sporadic cases to define the frequency and phenotypic correlates of epigenetic abnormalities in BWS. LOM at KvDMR1 was detected by Southern analysis or a novel PCR based method in 35 of 69 (51%) sporadic BWS without UPD. LOM at KvDMR1 was often, but not invariably associated with LOI of IGF2. KvDMR1 LOM was not detected in BWS patients with putative BWSIC1 defects and cases with KvDMR1 LOM (that is, putative BWSIC2 defects) invariably had a normal H19 methylation pattern. The incidence of exomphalos in putative BWSIC2 defect patients was not significantly different from that in patients with germline CDKN1C mutations (20/29 and 13/15 respectively), but was significantly greater than that in patients with putative BWSIC1 defects (0/5, p=0.007) and UPD (0/22, p<0.0001). These findings are consistent with the hypothesis that LOM of KvDMR1 (BWSIC2 defect) results in epigenetic silencing of CDKN1C and variable LOI of IGF2. BWS patients with embryonal tumours have UPD or a BWSIC1 defect but not LOM of KvDMR1. This study has further shown how (1) variations in phenotypic expression of BWS may be linked to specific molecular subgroups and (2) molecular analysis of BWS can provide insights into mechanisms of imprinting regulation.

Mechanisms of genomic imprinting

Imprinted genes represent a curious defiance of normal Mendelian genetics. Mammals inherit two complete sets of chromosomes, one from the mother and one from the father, and most autosomal genes will be expressed from both the maternal and the paternal alleles. Imprinted genes, however, are expressed from only one chromosome, in a parent-of-origin-dependent manner. Because silent and active promoters are present in a single nucleus, the differences in activity cannot be explained by transcription-factor abundance. Thus, transcription of imprinted genes represents a clear situation in which epigenetic mechanisms restrict gene expression and, therefore, offers a model for understanding the role of DNA modifications and chromatin structure in maintaining appropriate patterns of expression. Furthermore, because of their parent-of-origin-restricted expression, phenotypes determined by imprinted genes are susceptible not only to genetic alterations in the genes but also to disruptions in the epigenetic programs controlling regulation. Imprinted genes are often associated with human diseases, including disorders affecting cell growth, development, and behavior.

[Genes and intra-uterine growth retardation]

Genetic analysis of growth from birth to adulthood shows the existence of a strong genetic component in the variance of size at particular milestones in the growth process, such as height at take-off, at peak velocity and at adulthood. While it is well known that postnatal growth is strongly genetically determined, the importance of genes in normal variations of prenatal growth is less known. Genetic analysis of prenatal growth in human is not an easy problem and weighing the genetic and non-genetic component in intra-uterine growth retardation an almost impossible task. It is now well known that adults who had a low birthweight or who were thin at birth, with a low ponderal index, tend to be insulin resistant and have an increased risk of developing non-insulin-dependent diabetes mellitus later in life. According to the thrifty genotype hypothesis, genes predisposing to type 2 diabetes mellitus are very likely to have been survival genes for our ancestors, helping them to store energy during long periods of starvation. Both epidemiological surveys of adults born after prenatal exposure to exposure to famine and biochemical investigations of insulin resistance in low birthweight children show that the association between a low birthweight and an increased risk of developing type 2 diabetes mellitus later in life has a genetic basis. While low birthweight infants have a decreased survival probability in infancy, having a small baby may have been a selective advantage during long periods of starvation. This could explain why the same genetic variants cause low birthweight phenotype and insulin resistance predisposing to non-insulin-dependent diabetes.

Genetics of Beckwith-Wiedemann syndrome-associated tumors: common genetic pathways

A specific subset of solid childhood tumors-Wilms' tumor, adrenocortical carcinoma, rhabdomyosarcoma, and hepatoblastoma-is characterized by its association with Beckwith-Wiedemann syndrome. Genetic abnormalities found in these tumors affect the same chromosome region (11p15), which has been implicated in the etiology of Beckwith-Wiedemann syndrome. This suggests that the development of these tumors occurs along a common genetic pathway involving chromosome 11. To search for additional common genetic pathways, this article reviews the genetic data published for these tumors. It was found that, up until now, the only genetic abnormalities detected in all four tumors affect chromosome band 11p15 and the TP53 gene. In addition, there are several aberrations that occur in two or three of the neoplasms. It is concluded that, of the four tumors, the genetic relationship is most evident between Wilms' tumor and rhabdomyosarcoma.

Alterations of H19 imprinting and IGF2 replication timing are infrequent in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder resulting from dysregulation of multiple imprinted genes through a variety of distinct mechanisms. A frequent alteration in BWS involves changes in the imprinting status of the coordinately regulated IGF2 and H19 genes on 11p15. Patients have been categorized according to alterations in the imprinted expression, allele-specific methylation, and regional replication timing of these genes. In this work, IGF2/H19 expression, H19 DNA methylation, and IGF2 regional replication timing were studied in nine karyotypically normal BWS fibroblasts and two BWS patients with maternally inherited 11p15 chromosomal rearrangements. Informative patients (9/9) maintained normal monoallelic H19 expression/methylation, despite biallelic IGF2 expression in 6/9. Replication timing studies revealed no changes in the pattern of asynchronous replication timing for both a patient with biallelic IGF2 expression and a patient carrying an 11p15 inversion. In contrast, a patient with a chromosome 11;22 translocation and normal H19 expression/methylation exhibited partial loss of asynchrony and a shift toward earlier replication times. These results indicate that in BWS, (1) H19 imprinting alterations are less frequent than previously estimated, (2) IGF2 imprinting and H19 imprinting are not necessarily coordinated, and (3) alterations in regional replication timing are generally not correlated with either chromosomal rearrangements or the imprinting status of IGF2 and H19.

Imprinted genes as potential genetic and epigenetic toxicologic targets

Genomic imprinting is an epigenetic phenomenon in eutherian mammals that results in the differential expression of the paternally and maternally inherited alleles of a gene. Imprinted genes are necessary for normal mammalian development. This requirement has been proposed to have evolved because of an interparental genetic battle for the utilization of maternal resources during gestation and postnatally. The nonrandom requisite for monoallelic expression of a subset of genes has also resulted in the formation of susceptibility loci for neurobehavioral disorders, developmental disorders, and cancer. Since imprinting involves both cytosine methylation within CpG islands and changes in chromatin structure, imprinted genes are potential targets for dysregulation by epigenetic toxicants that modify DNA methylation and histone acetylation.

Methylation sequencing analysis refines the region of H19 epimutation in Wilms tumor

Differential DNA methylation of the parental alleles has been implicated in the establishment and maintenance of the monoallelic expression of imprinted genes. H19 and IGF2 are oppositely imprinted with only the maternal and the paternal alleles expressed, respectively. In Wilms tumor, a childhood renal neoplasm, loss of the H19/IGF2 imprinted expression pattern results in silencing of H19 and biallelic expression of IGF2. This was shown to be associated with biallelic methylation of the H19 promoter in the tumor and the adjacent kidney tissue suggesting that epigenetic H19 silencing is an early event in Wilms tumorigenesis. An imprinting mark region characterized by paternal allele-specific methylation has been suggested to reside in a GC-rich region of 400-base pair direct repeats starting at -2 kilobase pairs (kb) relative to the H19 transcription start and extending upstream. The upstream boundary of the potential paternal methylation imprint of the H19 gene has yet to be defined. We sought to define this upstream imprint boundary and investigate whether Wilms tumors with loss of imprinting are biallelically methylated in this imprinting mark region. The analysis of 6.6 kb of new upstream H19 sequence determined in this study identified a series of the direct 400-base pair repeats that extends to approximately -5.3 kb relative to the transcription start. DNA methylation analyses indicated that the upstream boundary of the potential imprint may coincide with the 5' end of the direct repeats. We found that Wilms tumors with loss of imprinting are biallelically methylated in the H19 upstream repeat region, and we suggest that pathological methylation in this region is the epigenetic error that initiates H19 silencing.