New insights into the imprinted MEG8-DMR in 14q32 and clinical and molecular description of novel patients with Temple syndrome

Abstract

The chromosomal region 14q32 contains several imprinted genes, which are expressed either from the paternal (DLK1 and RTL1) or the maternal (MEG3, RTL1as and MEG8) allele only. Imprinted expression of these genes is regulated by two differentially methylated regions (DMRs), the germline DLK1/MEG3 intergenic (IG)-DMR (MEG3/DLK1:IG-DMR) and the somatic MEG3-DMR (MEG3:TSS-DMR), which are methylated on the paternal and unmethylated on the maternal allele. Disruption of imprinting in the 14q32 region results in two clinically distinct imprinting disorders, Temple syndrome (TS14) and Kagami-Ogata syndrome (KOS14). Another DMR with a yet unknown function is located in intron 2 of MEG8 (MEG8-DMR, MEG8:Int2-DMR). In contrast to the IG-DMR and the MEG3-DMR, this somatic DMR is methylated on the maternal chromosome and unmethylated on the paternal chromosome. We have performed extensive methylation analyses by deep bisulfite sequencing of the IG-DMR, MEG3-DMR and MEG8-DMR in different prenatal tissues including amniotic fluid cells and chorionic villi. In addition, we have studied the methylation pattern of the MEG8-DMR in different postnatal tissues. We show that the MEG8-DMR is hypermethylated in each of 13 non-deletion TS14 patients (seven newly identified and six previously published patients), irrespective of the underlying molecular cause, and is always hypomethylated in the four patients with KOS14, who have different deletions not encompassing the MEG8-DMR itself. The size and the extent of the deletions and the resulting methylation pattern suggest that transcription starting from the MEG3 promoter may be necessary to establish the methylation imprint at the MEG8-DMR.

Molecular and clinical studies in 8 patients with Temple syndrome

“…The table summarises the clinical features in the 8 TS14 patients described in this study. Although all 6 patients with an ID are female, the reported frequency of males and females with TS14 so far is equal (Reference , summarised in Reference ).…”

“…A third DMR is present in intron 2 of the MEG8 gene ( MEG8 :Int2‐DMR). It is also a secondary‐derived, somatic DMR and is, in contrast to the 2 others, methylated on the maternal allele . Methylation analyses are performed using methylation‐specific multiplex ligation‐dependent probe amplification (MS‐MLPA; SALSA MS‐MLPA kit ME032, MRC Holland) which includes several probes within the MEG3 :TSS‐DMR (see section 3).…”

“…Since then approximately 120 TS14 patients have been described, the majority with a UPD(14)mat and merely 22 patients with a primary imprinting defect (ID).…”

“…7 Beside maternal UPDs of chromosome 14 with and without Robertsonian translocations, paternal deletions and imprinting defects have been identified as the molecular causes of TS14. 5,8,9 Since then approximately 120 TS14 patients have been described, the majority with a UPD (14)mat and merely 22 patients with a primary imprinting defect (ID 1,5,10,11 ).…”

Kagami‐Ogata syndrome: an important differential diagnosis to Beckwith‐Wiedemann syndrome

“…The coat‐hanger sign was introduced by Offiah et al, who detected these short, abnormally shaped ribs on postnatal chest X‐ray . Since many skeletal dysplasias may present with a small thorax, coat‐hanger ribs serve as a distinct feature of KOS facilitating the differentiation between KOS and other skeletal dysplasias . We report the case of a fetus with KOS whose ultrasound (US) characteristics were initially diagnosed as Beckwith‐Wiedemann syndrome (BWS).…”