Multilocus methylation analysis in a large cohort of 11p15-related foetal growth disorders (Russell Silver and Beckwith Wiedemann syndromes) reveals simultaneous loss of methylation at paternal and maternal imprinted loci

Abstract

Genomic imprinting plays an important role in mammalian development. Loss of imprinting (LOI) through loss (LOM) or gain (GOM) of methylation is involved in many human disorders and cancers. The imprinted 11p15 region is crucial for the control of foetal growth and LOI at this locus is implicated in two clinically opposite disorders: Beckwith Wiedemann syndrome (BWS) with foetal overgrowth associated with an enhanced tumour risk and Russell-Silver syndrome (RSS) with intrauterine and postnatal growth restriction. So far, only a few studies have assessed multilocus LOM in human imprinting diseases. To investigate multilocus LOI syndrome, we studied the methylation status of five maternally and two paternally methylated loci in a large series (n = 167) of patients with 11p15-related foetal growth disorders. We found that 9.5% of RSS and 24% of BWS patients showed multilocus LOM at regions other than ICR1 and ICR2 11p15, respectively. Moreover, over two third of multilocus LOM RSS patients also had LOM at a second paternally methylated locus, DLK1/GTL2 IG-DMR. No additional clinical features due to LOM of other loci were found suggesting an (epi)dominant effect of the 11p15 LOM on the clinical phenotype for this series of patients. Surprisingly, four patients displayed LOM at both ICR1 and ICR2 11p15. Three of them had a RSS and one a BWS phenotype. Our results show for the first time that multilocus LOM can also concern RSS patients. Moreover, LOM can involve both paternally and maternally methylated loci in the same patient.

Characterization of multi-locus imprinting disturbances and underlying genetic defects in patients with chromosome 11p15.5 related imprinting disorders

“…No significant differences between the clinical features of patients with mono-locus and multi-locus BWS were observed, as previously reported [19]. Nevertheless, it is intriguing that a number of clinical features appeared to be more frequent in patients with MLID (Figure 4), such as facial nevus flammeus (5/6 MLID vs. 3/10 non-MLID), and, in contrast with previous reports [7], macroglossia (6/6 MLID vs. 6/10 non-MLID) and outer ears anomalies (3/6 MLID vs. 1/10 non-MLID).…”

“…In this study, we set up a panel of 12 iDMRs by MassARRAY technology and applied it to a cohort of patients with BWS, presenting with primary GOM at ICR1 or LOM at ICR2, and with SRS, showing LOM at ICR1. We found a higher frequency of MLID in both BWS (50%) and SRS (29%) patients, compared with previous reports [6–8,15,19], probably because we selected the iDMRs most frequently associated with BWS/SRS. Our data confirm that the iDMRs involved in both BWS- and SRS-MLID can vary among patients, supporting that the defect is non-recurrent.…”

“…This hypothesis is also supported by the following evidences: i) both BWS epimutations (ICR1 GOM or ICR2 LOM) result from defective methylation of the maternal allele, and ii) no [7,19], or very few [15] cases with MLID have been identified among ICR1 hypermethylated patients.…”

“…The frequency of MLID appears to vary depending on the sensitivity of the technology used for analyses and the iDMRs investigated [6–8,15,19]. In this study, we set up a panel of 12 iDMRs by MassARRAY technology and applied it to a cohort of patients with BWS, presenting with primary GOM at ICR1 or LOM at ICR2, and with SRS, showing LOM at ICR1.…”

“…The phenotypic consequences of MLID in BWS and SRS patients are disputed, since not all patients with MLID show peculiar phenotypic features, probably as a consequence of the (epi)dominance of one locus above the others [19] or as a result of mosaicism. However, some exceptions have been reported.…”