Epimutation profiling in Beckwith-Wiedemann syndrome: relationship with assisted reproductive technology

Louise Tee,Tom Hancocks,Eamonn R Maher,Marie-Odile Baudement,Renuka P Dias,Fiona Macdonald,Derek Hk Lim,Amy A Slater,Carol Hardy,Gail Kirby,Helen Stewart

doi:10.1186/1868-7083-5-23

Abstract

BackgroundBeckwith-Wiedemann syndrome (BWS) is a congenital overgrowth disorder associated with abnormalities in 11p15.5 imprinted genes. The most common cause is loss of methylation (epimutation) at the imprinting control centre 2 (IC2/KvDMR1). Most IC2 epimutations occur sporadically but an association with conception after assisted reproductive technologies (ART) has been reported. A subgroup of IC2 epimutation cases also harbour epimutations at other imprinting centres (ICs) outside of 11p15.5. We have investigated the relationship between these multiple epimutation cases (ME+), history of ART and clinical phenotype in a cohort of 187 BWS IC2 epimutation patients.ResultsMethylation analysis at PLAGL1, MEST and IGF2R ICs demonstrated an over-representation of patients with abnormally low methylation (8.5%, 12% and 6% respectively). At IGF2R some patients (2%) had gain of methylation but this was also detected in controls. Though there were no significant correlations between the methylation index (MIs) at the three ICs tested, a subset of patients appeared to be susceptible to multiple epimutations (ME+) and 21.2% of ME + patients had been conceived by ART compared to 4.5% (P = 0.0033) without additional epimutations. Methylation array profiling (Illumina Goldengate®) of patients and controls (excluding 11p15.5 loci) demonstrated significant differences between patients and controls. No significant associations were found between aspects of the BWS phenotype and individual epimutations but we describe a case presenting with a post-ART BWS-like phenotype in which molecular analysis demonstrated loss of paternal allele methylation at the 11p15.5 IC1 locus (IC1 regulates imprinting of IGF2 and H19). Loss of paternal allele methylation at the IC1 is the molecular finding associated with Silver-Russell syndrome whereas BWS is associated with gain of maternal allele methylation at IC1. Further analysis demonstrated epimutations at PLAGL1 and MEST consistent with the hypothesis that the presence of multiple epimutations may be of clinical relevance.ConclusionsThese findings suggest that the ME + subgroup of BWS patients are preferentially, but not exclusively, associated with a history of ART and that, though at present, there are no clear epigenotype-phenotype correlations for ME + BWS patients, non-11p15.5 IC epimutations can influence clinical phenotype.

Highlights

Beckwith-Wiedemann syndrome (BWS) is a congenital overgrowth disorder associated with abnormalities in 11p15.5 imprinted genes
In comparison to normal controls (n = 20), there was an over-representation of low methylation index (MI) in patient samples (Figure 1A) and the distribution of PLAGL1 Differentially methylated region (DMR) MIs did not conform to a normal distribution (D’Agostino-Pearson test for normal distribution rejected at P
We investigated whether the loss of maternal allele KvDMR1 methylation in BWS IC2 epimutation cases was associated with the grandparental origin of the allele

Summary

Introduction

Beckwith-Wiedemann syndrome (BWS) is a congenital overgrowth disorder associated with abnormalities in 11p15.5 imprinted genes. Genomic imprinting is a form of epigenetic control of gene expression in which one allele of a gene is preferentially expressed according to the parent-of-origin of the allele [1]. A number of different mechanisms (for example, DNA methylation, chromatin modification and expression of large noncoding RNAs) have been implicated in the establishment and maintenance of genomic imprinting and a key role is played by imprinting control centres (ICs), which may regulate the imprinting of several genes [1]. Gain of methylation (GOM) at the normally unmethylated maternal allele of the chromosome 11p15.5 IC1 DMR is associated with bi-allelic expression of the paternally expressed growth promoter IGF2 and is associated with the Beckwith-Wiedemann congenital overgrowth syndrome (BWS) [4]. Loss of methylation (LOM) of the paternal allele at the same IC is associated with loss of paternal allele IGF2 expression and the phenotype of Silver-Russell syndrome (SRS), which is characterised by pre- and postnatal growth restriction [5]

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