Evidence for anticipation in Beckwith–Wiedemann syndrome

Siren Berland,I Karen Temple,Deborah J G Mackay,Ove Bruland,Mia Appelbäck,Karin Buiting,Gunnar Houge,Jasmin Beygo

doi:10.1038/ejhg.2013.71

Abstract

Classical Beckwith–Wiedemann syndrome (BWS) was diagnosed in two sisters and their male cousin. The children's mothers and a third sister were tall statured (178, 185 and 187 cm) and one had mild BWS features as a child. Their parents had average heights of 173 cm (mother) and 180 cm (father). This second generation tall stature and third generation BWS correlated with increased methylation of the maternal H19/IGF2-locus. The results were obtained by bisulphite treatment and subclone Sanger sequencing or next generation sequencing to quantitate the degree of CpG-methylation on three locations: the H19 promoter region and two CTCF binding sites in the H19 imprinting control region (ICR1), specifically in ICR1 repeats B1 and B7. Upon ICR1 copy number analysis and sequencing, the same maternal point variant NCBI36:11:g.1979595T>C that had been described previously as a cause of BWS in three brothers, was found. As expected, this point variant was on the paternal allele in the non-affected grandmother. This nucleotide variant has been shown to affect OCTamer-binding transcription factor-4 (OCT4) binding, which may be necessary for maintaining the unmethylated state of the maternal allele. Our data extend these findings by showing that the OCT4 binding site mutation caused incomplete switching from paternal to maternal ICR1 methylation imprint, and that upon further maternal transmission, methylation of the incompletely demethylated variant ICR1 allele was further increased. This suggests that maternal and paternal ICR1 alleles are treated differentially in the female germline, and only the paternal allele appears to be capable of demethylation.

Highlights

Beckwith–Wiedemann syndrome (BWS, OMIM no. 130650) is an overgrowth condition caused by epigenetic or genetic alterations in the imprinted H19/IGF2-KCNQ1/CDKN1C locus, spanning nearly 1 Mb in 11p15.5.1 The two major causes of BWS are increased IGF2 expression or decreased CDKN1C expression
This impression was in line with the results of the routine MS-multiplex ligation-dependent probe amplification (MLPA) methylation testing of the BWS locus, which showed an increase in imprinting centre region 1 (ICR1) methylation from normal level (0.49) in the grandmother to B0.71 in the second generation with tall stature and B0.84 in the third generation (Table 1, Supplementary Table 1), in the three children with classical BWS (Figure 1)
To investigate whether the same tendency could be found in the CTCF binding sites of the ICR1 repeats (Figure 2), the degree of methylation of two such sites was investigated by highly quantitative generation bisulphite sequencing: CTS6 in B-type repeat B1, on the H19-side of ICR1, and CTS1 in B-type repeat B7, on the IGF2-side of ICR1 (Figure 2)

Summary

Introduction

Beckwith–Wiedemann syndrome (BWS, OMIM no. 130650) is an overgrowth condition caused by epigenetic or genetic alterations in the imprinted H19/IGF2-KCNQ1/CDKN1C locus, spanning nearly 1 Mb in 11p15.5.1 The two major causes of BWS are increased IGF2 expression or decreased CDKN1C expression. We describe a family with a previously reported ICR1 single nucleotide variant (NCBI36:11:g.1979595T4C) in an OCTamerbinding transcription factor-4 (OCT4) binding site and a gradual increase in ICR1 methylation over the two generations, the first generation being tall statured, the second generation having full-BWS phenotype with Wilms tumours.

Results

Conclusion