Abstract
BackgroundA subset of individuals affected by imprinting disorders displays multi-locus imprinting disturbances (MLID). MLID has been associated with maternal-effect variants that alter the maintenance of methylation at germline-derived differentially methylated regions (gDMRs) in early embryogenesis. Pedigrees of individuals with MLID also include siblings with healthy phenotype. However, it is unknown if these healthy individuals have MLID themselves or if their methylation patterns differ from those associated with imprinting disorders, and in general, if MLID affects the clinical phenotype.MethodsWe have investigated gDMR methylation by locus-specific and whole-genome analyses in a family with multiple pregnancy losses, a child with Beckwith-Wiedemann syndrome (BWS) and a further child with no clinical diagnosis of imprinting disorder or other pathologies.ResultsWe detected MLID with different methylation profiles in the BWS-affected and healthy siblings. Whole-exome sequencing demonstrated the presence of novel loss-of-function variants of NLRP5 in compound heterozygosity in the mother. The methylation profiles of the two siblings were compared with those of other cases with MLID and control groups by principal component analysis and unsupervised hierarchical clustering, but while their patterns were clearly separated from those of controls, we were unable to cluster those associated with specific clinical phenotypes among the MLID cases.ConclusionThe identification of two novel maternal-effect variants of NLRP5 associated with poly-abortivity and MLID adds further evidence to the role of this gene in the maintenance of genomic imprinting in early embryos. Furthermore, our results demonstrate that within these pedigrees, MLID can also be present in the progeny with healthy phenotype, indicating that some sort of compensation occurs between altered imprinted loci in these individuals. The analysis of larger cohorts of patients with MLID is needed to formulate more accurate epigenotype-phenotype correlations.
Highlights
Imprinting disorders are a clinically heterogeneous group of diseases characterized by defective expression associated with genetic or epigenetic abnormalities of imprinted genes [1]
The identification of two novel maternal-effect variants of NLRP5 associated with poly-abortivity and multi-locus imprinting disturbances (MLID) adds further evidence to the role of this gene in the maintenance of genomic imprinting in early embryos
Our results demonstrate that within these pedigrees, MLID can be present in the progeny with healthy phenotype, indicating that some sort of compensation occurs between altered imprinted loci in these individuals
Summary
Imprinting disorders are a clinically heterogeneous group of diseases characterized by defective expression associated with genetic or epigenetic abnormalities of imprinted genes [1]. DNA methylation abnormalities in imprinting disorders typically affect a germline-derived differentially methylated region (gDMR) that regulates the gamete-of-origin-specific expression of a cluster of imprinted genes [1]. A subgroup of patients, exhibits multi-locus imprinting disturbances (MLID) that potentially alter the expression of multiple imprinted gene clusters [3, 4]. Individuals with MLID usually present with clinical features characteristic of one imprinting disorder, most frequently BWS, Silver-Russell syndrome (SRS), and transient neonatal diabetes mellitus (TNDM), but some cases show complex or atypical phenotypes, possibly reflecting the loci and tissues affected with the mosaic epigenetic abnormalities [5, 6]. Pedigrees of individuals with MLID include siblings with healthy phenotype It is unknown if these healthy individuals have MLID themselves or if their methylation patterns differ from those associated with imprinting disorders, and in general, if MLID affects the clinical phenotype
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