Different mechanisms cause imprinting defects at the IGF2/H19 locus in Beckwith-Wiedemann syndrome and Wilms' tumour.
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.
Cerrato
Flavia
F
Dipartimento di Scienze Ambientali, Seconda Università di Napoli, via Vivaldi 43, 81100 Caserta, Italy.
Sparago
Angela
A
Verde
Gaetano
G
De Crescenzo
Agostina
A
Citro
Valentina
V
Cubellis
Maria Vittoria
MV
Rinaldi
Maria Michela
MM
Boccuto
Luigi
L
Neri
Giovanni
G
Magnani
Cinzia
C
D'Angelo
Paolo
P
Collini
Paola
P
Perotti
Daniela
D
Sebastio
Gianfranco
G
Maher
Eamonn R
ER
Riccio
Andrea
A
D000483:Alleles; D001506:Beckwith-Wiedemann Syndrome / Q000175:diagnosis / Q000235:genetics*; D000076246:CCCTC-Binding Factor; D020090:Chromosome Segregation; D002880:Chromosomes, Human, Pair 11; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics; D005260:Female; D017353:Gene Deletion; D018392:Genomic Imprinting; D006239:Haplotypes; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D007558:Italy; D008297:Male; D009154:Mutation; D010375:Pedigree; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics; D009396:Wilms Tumor / Q000235:genetics*
D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; D004268:DNA-Binding Proteins; C094335:H19 long non-coding RNA; C035170:IGF2 protein, human; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D012097:Repressor Proteins; D007335:Insulin-Like Growth Factor II