Epigenotype-phenotype correlations in Beckwith-Wiedemann syndrome

Abstract

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 diVerentially 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 diVerent 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. (J Med Genet 2000;37:921-926)

Analysis of the methylation status of the KCNQ1OT and H19 genes in leukocyte DNA for the diagnosis and prognosis of Beckwith–Wiedemann syndrome

“…Both abnormalities are responsible for reduced H19 expression. An association between reduced H19 expression in BWS and susceptibility to Wilms tumour has been suggested 7,9,24,30 and our data are consistent with this hypothesis. However, due to the small sample size and the low frequency of events (tumours in 12 patients of our study and three patients of Engel's study), these results require confirmation in larger series of patients.…”

“…We also observed that demethylation of the KCNQ1OT gene was never associated with abnormal methylation of the H19 gene except in patients with 11p15 UPD, suggesting that at least two imprinting centres exist on 11p15.5. 7, 24 We also observed that exomphalos was associated with demethylation of the KCNQ1OT gene and these data are consistent with the recent study by Engel et al 24 Mosaicism for 11p15 UPD was more frequent in complete forms than in incomplete forms of BWS, suggesting that both the tissue distribution of mosaicism and the proportion of mosaic cells may account for the various phenotypes, as recently shown by Itoh et al 25 In addition, 11p15 UPD was significantly more frequent in patients with hemihyperplasia than in patients without hemihyperplasia.…”

Genomic Profiling Maps Loss of Heterozygosity and Defines the Timing and Stage Dependence of Epigenetic and Genetic Events in Wilms' Tumors

“…First, gain of methylation in H19 upstream DNA sequences (as well as in the transcribed region of the H19 gene), which is the DNA counterpart of LOI that is scored in this and many other studies, can be seen in the nonneoplastic kidney parenchyma of a substantial group of sporadic Wilms' tumor patients (36,45). Second, IGF2 LOI associated with gain of methylation at the H19 5V DMR in various somatic tissues is the defining feature of the class of Beckwith-Wiedemann syndrome that is associated with a predisposition to Wilms' tumor (12,46,47). Recently, it has been suggested that rare cases of sporadic Wilms' tumor might have LOI secondary to LOH affecting the chromosome 16q CTCF gene (48).…”

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

“…26 Clinically, a clear association between mosaic UPD and hemihyperplasia exists. 15,19,22,27 In addition, it was noted that neoplasias and Wilms' tumours are more frequent in BWS patients with pUPD or H19DMR hypermethylation than in BWS patients with other molecular defect. [27][28][29] Moreover, it has been hypothesized that extremely high levels of UPD might drive severe phenotypic expression of BWS; 30 but it is often difficult to determine if levels of UPD correlate with severity of the phenotype especially when the tissues/organs involved are not usually directly tested.…”

“…13,14 The other alteration is loss of maternal methylation of KvDMR (observed in B50% of BWS patients), usually accompanied by biallelic expression of the KCNQ1OT1 transcript and downregulation of CDKN1C. [15][16][17] Finally, another large category of BWS molecular alteration, 10-20% of cases, is represented by paternal uniparental disomy (pUPD), namely patients with two paternally derived copies of chromosome 11p15 and no maternal contribution for that region. 18,19 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.…”