• Beckwith-Wiedemann syndrome
• ICSI
• IVF
• imprinting
• methylation

Beckwith-Wiedemann syndrome (BWS) is a model imprinting disorder resulting from mutations or epimutations affecting imprinted genes on chromosome 11p15.5.¹ The classical clinical features of BWS are macroglossia, pre- and/or postnatal overgrowth, and anterior abdominal wall defects (umbilical hernia or exomphalos). Additional more variable features include hemihypertrophy, neonatal hypoglycaemia, facial naevus flammeus, ear pits and creases, renal anomalies, and an increased risk of embryonal tumours.² Most cases of BWS are sporadic and ∼20% of these have uniparental disomy (paternal isodisomy) for a variable region of chromosome 11 which always includes the 11p15.5 imprinted gene cluster.^3–5 Up to 60% of sporadic BWS patients have epigenetic changes at differentially methylated regions within 11p15.5 that are associated with alterations in the imprinting or expression of paternally expressed genes, such as IGF2 and KCNQ1OT, or maternally expressed genes, such as H19 and CDKN1C.¹ Thus, 5–10% have epigenetic alterations at the IGF2/H19 loci (the maternal H19 and IGF2 alleles display paternal allele methylation and expression patterns with biallelic IGF2 expression and silencing of H19 expression),⁶ and 40–50% have loss of maternal allele methylation at a differentially methylated region (KvDMR1) within an intron of KCNQ1. KvDMR1 loss of methylation is associated with biallelic expression of KCNQ1OT.^7–9 The epigenetic alterations at H19/IGF2 or KvDMR1 are thought to result from defects at two putative imprinting control centres (BWSIC1 and BWSIC2, respectively).¹ The precise nature of the putative BWSIC2 is unknown and therefore the origin of these putative BWSIC2 defects is unknown. Weksberg et al¹⁰ showed a clear association between monozygotic twinning and BWS with KvDMR1 loss of methylation and suggested two possible explanations: (1) that discordance for BWS in monozygotic twins is caused by unequal splitting of the inner cell mass …