Different mechanisms cause imprinting defects at the IGF2/H19 locus in Beckwith-Wiedemann syndrome and Wilms' tumour

Abstract

The parent of origin-dependent expression of the IGF2 and H19 genes is controlled by the imprinting centre 1 (IC1) consisting in a methylation-sensitive chromatin insulator. Deletions removing part of IC1 have been found in patients affected by the overgrowth- and tumour-associated Beckwith-Wiedemann syndrome (BWS). These mutations result in the hypermethylation of the remaining IC1 region, loss of IGF2/H19 imprinting and fully penetrant BWS phenotype when maternally transmitted. We now report that 12 additional cases with IC1 hypermethylation have a similar clinical phenotype but showed neither a detectable deletion nor other mutation in the local vicinity. Likewise, no IC1 deletion was detected in 40 sporadic non-syndromic Wilms' tumours. A detailed analysis of the BWS patients showed that the hypermethylation variably affected the IC1 region and was generally mosaic. We observed that all these cases were sporadic and in at least two families affected and unaffected members shared the same maternal IC1 allele but not the abnormal maternal chromosome epigenotype. Furthermore, the chromosome with the imprinting defect derived from either the maternal grandfather or maternal grandmother. Overall, these results indicate that methylation-imprinting defects at the IGF2-H19 locus can result from inherited mutations of the IC and have high recurrence risk or arise independently from the sequence context and generally not transmitted to the progeny. Despite these differences, the epigenetic abnormalities are usually present in the patients in the mosaic form and probably acquired by post-zygotic de novo methylation. Distinguishing between these two groups of cases is important for genetic counselling.

(Epi)genotype–phenotype correlations in Beckwith–Wiedemann syndrome

“…The following molecular anomalies were identified: 190 IC2-LoM (184 epigenetic anomalies, 5 already published cases with familial IC2 duplications 21 and 1 IC2 deletion), 87 UPD carriers, 31 IC1-GoM (21 already published cases 22,23 including one IC1 duplication, one translocation, 11 familial microdeletions [24][25][26] ), 10 CDKN1C variants (all unrelated cases, 9 maternally inherited). None of the patients tested was positive for genome-wide UPD.…”

Different incidences of epigenetic but not genetic abnormalities between Wilms tumors in Japanese and Caucasian children

“…Five to 10% of patients with BWS have methylation of H19 DMR on both parental chromosomes, resulting in IGF2 LOI. (29) Interestingly, Japanese patients with BWS were shown to have a significantly lower frequency of H19-DMR hypermethylation than North American and European patients, suggesting that susceptibility to epigenetic alterations differs between populations. (30) The same decreased susceptibility to epigenetic change may have also caused the decreased incidence of WTs with IGF2 LOI.…”

Beckwith–Wiedemann syndrome caused by maternally inherited mutation of an OCT-binding motif in the IGF2/H19-imprinting control region, ICR1

“…Although recombinative deletions of B-type repeats in ICR1 have been identified in several BWS pedigrees, [3][4][5][6] and in apparently sporadic Wilms' tumours, 9 the group of Gicquel were the first to describe a mutation in a pluripotency factor-binding site. 6 Interestingly, the point mutation in our pedigree, like that described by Demars et al, 6 disrupted a conserved OCT-binding motif within repeat A2 of ICR1.…”

“…8 Long-range PCR of H19 was performed as described. 5 The H19 ICR and proximal promoter (HG18:chr11:1976978-1981258) were sequenced by standard methods from a single amplicon of 4281 bp; further details are available on request. For some experiments, 200 ng genomic DNA was cleaved using restriction enzyme BstUI (New England Biolabs, Ipswich, MA, USA) following the manufacturer's instructions; then DNA was desalted and concentrated using Amicon 30 K microconcentrator columns (Millipore, Billerica, MA, USA) before amplification and sequencing.…”

“…[3][4][5][6] We recently described BWS pedigrees with novel deletions/mutations involving binding sites other than CTCF-binding sites, and in particular binding sites for the OCT4 and SOX2 pluripotency factors, including a point mutation in an OCT4-binding site. 6 In this study, we report another BWS family with a point mutation affecting an OCT-binding DNA sequence.…”