title: Mechanisms causing imprinting defects in familial Beckwith-Wiedemann syndrome with Wilms' tumour.
abstract: The imprinted expression of the IGF2 and H19 genes is controlled by the Imprinting Centre 1 (IC1) at chromosome 11p15.5. This is a methylation-sensitive chromatin insulator that works by binding the zinc-finger protein CTCF in a parent-specific manner. Microdeletions abolishing some of the CTCF target sites (CTSs) of IC1 have been associated with the Beckwith-Wiedemann syndrome (BWS). However, the link between these mutations and the molecular and clinical phenotypes was debated. We have identified two novel families with IC1 deletions, in which individuals with the clinical features of the BWS are present in multiple generations. By analysing the methylation pattern at the IGF2-H19 locus together with the clinical phenotypes in the individuals with maternal and those with paternal transmission of five different deletions, we demonstrate that maternal transmission of 1.4-1.8 kb deletions in the IC1 region co-segregates with the hypermethylation of the residual CTSs and BWS phenotype with complete penetrance, whereas normal phenotype is observed upon paternal transmission. Although gene expression could not be assayed in all cases, the methylation detected at the IGF2 DMR2 and H19 promoter suggests that IC1 hypermethylation is consistently associated with biallelic activation of IGF2 and biallelic silencing of H19. Comparison of these deletions with a 2.2 kb one previously reported by another group indicates that the spacing of the CTSs on the deleted allele is critical for the gain of the abnormal methylation and penetrance of the clinical phenotype. Furthermore, we observe that the hypermethylation resulting from the deletions is always mosaic, suggesting that the epigenetic defect at the IGF2-H19 locus is established post-zygotically and may cause body asymmetry and heterogeneity of the clinical phenotype. Finally, the IC1 microdeletions are associated with a high incidence of Wilms' tumour, making their molecular diagnosis particularly important for genetic counselling and tumour surveillance at follow-up.
authors.affiliation: Dipartimento di Scienze Ambientali, Seconda Università di Napoli, via Vivaldi 43, 81100 Caserta, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Sparago
authors.forename: Silvia
authors.initials: S
authors.lastname: Russo
authors.forename: Flavia
authors.initials: F
authors.lastname: Cerrato
authors.forename: Serena
authors.initials: S
authors.lastname: Ferraiuolo
authors.forename: Pierangela
authors.initials: P
authors.lastname: Castorina
authors.forename: Angelo
authors.initials: A
authors.lastname: Selicorni
authors.forename: Christine
authors.initials: C
authors.lastname: Schwienbacher
authors.forename: Massimo
authors.initials: M
authors.lastname: Negrini
authors.forename: Giovanni Battista
authors.initials: GB
authors.lastname: Ferrero
authors.forename: Margherita Cirillo
authors.initials: MC
authors.lastname: Silengo
authors.forename: Cecilia
authors.initials: C
authors.lastname: Anichini
authors.forename: Lidia
authors.initials: L
authors.lastname: Larizza
authors.forename: Andrea
authors.initials: A
authors.lastname: Riccio
mesh_terms: D001506:Beckwith-Wiedemann Syndrome / Q000150:complications / Q000235:genetics*; D002648:Child; D002675:Child, Preschool; D002872:Chromosome Deletion; D002880:Chromosomes, Human, Pair 11; D019175:DNA Methylation; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007335:Insulin-Like Growth Factor II; D007680:Kidney Neoplasms / Q000150:complications / Q000235:genetics*; D008297:Male; D010375:Pedigree; D011506:Proteins / Q000235:genetics; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics; D009396:Wilms Tumor / Q000150:complications / Q000235:genetics*
chemical_list: C094335:H19 long non-coding RNA; C035170:IGF2 protein, human; D011506:Proteins; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D007335:Insulin-Like Growth Factor II