Molecular characterization of temple syndrome families with 14q32 epimutations.

Temple Syndrome (TS14) is an imprinting disorder caused by molecular disruptions of the imprinted region in 14q32 (MEG3:TSS-DMR). The frequency of the three known TS14 subtypes (deletions, maternal uniparental disomy (upd(14)mat), loss of methylation (LOM)) is currently in discussion, and within the LOM group, the occurrence of Multilocus Imprinting Disturbances (MLID) has been identified. We present 16 TS14 patients with molecular alterations affecting the MEG3:TSS-DMR, comprising seven patients (43.8%) with LOM, six carriers with upd(14)mat (37.5%), and three cases (18.8%) with a deletion affecting the paternal MEG3:TSS-DMR. We did not find any evidence for MLID in the LOM group, including two cases in which different tissues were available. Whole exome sequencing (WES) in the MEG3:TSS-DMR LOM patients and their parents (Trio WES) did not reveal an obvious pathogenic variant which might cause aberrant methylation at imprinted loci. By summarizing our data with those from the literature, we could show that MLID affecting clinically relevant imprinted loci is rare in TS14 and therefore differs markedly from other imprinting disorders associated with MLID, e.g. Silver-Russell syndrome (SRS) and Beckwith-Wiedemann syndrome (BWS). However, consistent with the clinical overlap with TS14, in SRS patients carrying MLID the MEG3:TSS-DMR is frequently affected. Variants in the known candidate genes for maternal effect variants causing MLID and fetal MLID determinants could not be identified in TS14 patients. Thus, 14q32 epimutations probably have other molecular causes than epimutations in BWS or SRS patients.

Need for a precise molecular diagnosis in Beckwith-Wiedemann and Silver-Russell syndrome: what has to be considered and why it is important.

Molecular diagnostic testing of the 11p15.5-associated imprinting disorders Silver-Russell and Beckwith-Wiedemann syndrome (SRS, BWS) is challenging due to the broad spectrum of molecular defects and their mosaic occurrence. Additionally, the decision on the molecular testing algorithm is hindered by their clinical heterogeneity. However, the precise identification of the type of defect is often a prerequisite for the clinical management and genetic counselling. Four major molecular alterations (epimutations, uniparental disomies, copy number variants, single nucleotide variants) have been identified, but their frequencies vary between SRS and BWS. Due to their molecular aetiology, epimutations in both disorders as well as upd(11)pat in BWS are particular prone to mosaicism which might additionally complicate the interpretation of testing results. We report on our experience of molecular analysis in a total cohort of 1448 patients referred for diagnostic testing of BWS and SRS, comprising a dataset from 737 new patients and from 711 cases from a recent study. Though the majority of positively tested patients showed the expected molecular results, we identified a considerable number of clinically unexpected molecular alterations as well as not yet reported changes and discrepant mosaic distributions. Additionally, the rate of multilocus imprinting disturbances among the patients with epimutations and uniparental diploidies could be further specified. Altogether, these cases show that comprehensive testing strategies have to be applied in diagnostic testing of SRS and BWS. The precise molecular diagnosis is required as the basis for a targeted management (e.g. ECG (electrocardiogram) and tumour surveillance in BWS, growth treatment in SRS). The molecular diagnosis furthermore provides the basis for genetic counselling. However, it has to be considered that recurrence risk calculation is determined by the phenotypic consequences of each molecular alteration and mechanism by which the alteration arose. KEY MESSAGES: The detection rates for the typical molecular defects of Beckwith-Wiedemann syndrome or Silver-Russell syndrome (BWS, SRS) are lower in routine cohorts than in clinically well-characterised ones. A broad spectrum of (unexpected) molecular alterations in both disorders can be identified. Multilocus imprinting disturbances (MLID) are less frequent in SRS than expected. The frequency of MLID and uniparental diploidy in BWS is confirmed. Mosaicism is a diagnostic challenge in BWS and SRS. The precise determination of the molecular defects affecting is the basis for a targeted clinical management and genetic counselling.