A maternal-effect Padi6 variant causes nuclear and cytoplasmic abnormalities in oocytes, as well as failure of epigenetic reprogramming and zygotic genome activation in embryos

Maternal inactivation of genes encoding components of the subcortical maternal complex (SCMC) and its associated member, PADI6, generally results in early embryo lethality. In humans, SCMC gene variants were found in the healthy mothers of children affected by multilocus imprinting disturbances (MLID). However, how the SCMC controls the DNA methylation required to regulate imprinting remains poorly defined. We generated a mouse line carrying a Padi6 missense variant that was identified in a family with Beckwith-Wiedemann syndrome and MLID. If homozygous in female mice, this variant resulted in interruption of embryo development at the two-cell stage. Single-cell multiomic analyses demonstrated defective maturation of Padi6 mutant oocytes and incomplete DNA demethylation, down-regulation of zygotic genome activation (ZGA) genes, up-regulation of maternal decay genes, and developmental delay in two-cell embryos developing from Padi6 mutant oocytes but little effect on genomic imprinting. Western blotting and immunofluorescence analyses showed reduced levels of UHRF1 in oocytes and abnormal localization of DNMT1 and UHRF1 in both oocytes and zygotes. Treatment with 5-azacytidine reverted DNA hypermethylation but did not rescue the developmental arrest of mutant embryos. Taken together, this study demonstrates that PADI6 controls both nuclear and cytoplasmic oocyte processes that are necessary for preimplantation epigenetic reprogramming and ZGA.

Co-occurrence of Beckwith-Wiedemann syndrome and pseudohypoparathyroidism type 1B: coincidence or common molecular mechanism?

Imprinting disorders are congenital diseases caused by dysregulation of genomic imprinting, affecting growth, neurocognitive development, metabolism and cancer predisposition. Overlapping clinical features are often observed among this group of diseases. In rare cases, two fully expressed imprinting disorders may coexist in the same patient. A dozen cases of this type have been reported so far. Most of them are represented by individuals affected by Beckwith-Wiedemann spectrum (BWSp) and Transient Neonatal Diabetes Mellitus (TNDM) or BWSp and Pseudo-hypoparathyroidism type 1B (PHP1B). All these patients displayed Multilocus imprinting disturbances (MLID). Here, we report the first case of co-occurrence of BWS and PHP1B in the same individual in absence of MLID. Genome-wide methylation and SNP-array analyses demonstrated loss of methylation of the KCNQ1OT1:TSS-DMR on chromosome 11p15.5 as molecular cause of BWSp, and upd(20)pat as cause of PHP1B. The absence of MLID and the heterodisomy of chromosome 20 suggests that BWSp and PHP1B arose through distinct and independent mechanism in our patient. However, we cannot exclude that the rare combination of the epigenetic defect on chromosome 11 and the UPD on chromosome 20 may originate from a common so far undetermined predisposing molecular lesion. A better comprehension of the molecular mechanisms underlying the co-occurrence of two imprinting disorders will improve genetic counselling and estimate of familial recurrence risk of these rare cases. Furthermore, our study also supports the importance of multilocus molecular testing for revealing MLID as well as complex cases of imprinting disorders.

A patient with multilocus imprinting disturbance involving hypomethylation at 11p15 and 14q32, and phenotypic features of Beckwith-Wiedemann and Temple syndromes

Beckwith‐Wiedemann syndrome (BWS) and Temple syndrome (TS) are classical imprinting disorders (IDs) with nonconfluent clinical features. We report here on a patient with clinical features of both syndromes, in whom epimutations were found at the BWS and TS imprinted regions, consistent with multilocus imprinting disturbance (MLID). This is the first case report of a patient with clinical features of both conditions who was found to have loss of methylation (LOM) of KCNQ1OT1: TSS‐DMR (ICR2) in the 11p15 imprinted region associated with BWS and LOM of MEG3: TSS‐DMR in the 14q32 imprinted region associated with TS. The report draws attention to the importance of testing for MLID as a cause of atypical clinical presentations of patients with IDs.

Maternal Effect Mutations: A Novel Cause for Human Reproductive Failure

Genetic alterations significantly contribute to the aetiology of reproductive failure and comprise monogenic, chromosomal and epigenetic disturbances. The implementation of next-generation sequencing (NGS) based approaches in research and diagnostics allows the comprehensive analysis of these genetic causes, and the increasing detection rates of genetic mutations causing reproductive complications confirm the potential of the new techniques. Whereas mutations affecting the fetal genome are well known to affect pregnancies and their outcome, the contribution of alterations of the maternal genome was widely unclear. With the recent mainly NGS-based identification of maternal effect variants, a new cause of human reproductive failure has been identified. Maternal effect mutations affect the expression of subcortical maternal complex (SCMC) proteins from the maternal genome, and thereby disturb oocyte maturation and progression of the early embryo. They cause a broad range of reproductive failures and pregnancy complications, including infertility, miscarriages, hydatidiform moles, aneuploidies and imprinting disturbances in the fetus. The identification of women carrying these molecular alterations in SCMC encoding genes is therefore essential for a personalised reproductive and genetic counselling. The diagnostic application of new NGS-based assays allows the comprehensive analysis of these factors, and helps to further decipher these functional links between the factors and their disturbances. A close interdisciplinary collaboration between different disciplines is definitely required to further decipher the complex regulation of early embryo development, and to translate the basic research results into clinical practice.

Clinical and Molecular Diagnosis of Beckwith-Wiedemann Syndrome with Single- or Multi-Locus Imprinting Disturbance

Beckwith-Wiedemann syndrome (BWS) is a clinically and genetically heterogeneous overgrowth disease. BWS is caused by (epi)genetic defects at the 11p15 chromosomal region, which harbors two clusters of imprinted genes, IGF2/H19 and CDKN1C/KCNQ1OT1, regulated by differential methylation of imprinting control regions, H19/IGF2:IG DMR and KCNQ1OT1:TSS DMR, respectively. A subset of BWS patients show multi-locus imprinting disturbances (MLID), with methylation defects extended to other imprinted genes in addition to the disease-specific locus. Specific (epi)genotype-phenotype correlations have been defined in order to help clinicians in the classification of patients and referring them to a timely diagnosis and a tailored follow-up. However, specific phenotypic correlations have not been identified among MLID patients, thus causing a debate on the usefulness of multi-locus testing in clinical diagnosis. Finally, the high incidence of BWS monozygotic twins with discordant phenotypes, the high frequency of BWS among babies conceived by assisted reproductive technologies, and the female prevalence among BWS-MLID cases provide new insights into the timing of imprint establishment during embryo development. In this review, we provide an overview on the clinical and molecular diagnosis of single- and multi-locus BWS in pre- and post-natal settings, and a comprehensive analysis of the literature in order to define possible (epi)genotype-phenotype correlations in MLID patients.

New developments in Silver-Russell syndrome and implications for clinical practice

Silver-Russell syndrome is a clinically and genetically heterogeneous disorder, characterized by prenatal and postnatal growth restriction, relative macrocephaly, body asymmetry and characteristic facial features. It is one of the imprinting disorders, which results as a consequence of aberrant imprinted gene expressions. Currently, maternal uniparental disomy of chromosome 7 accounts for approximately 10% of Silver-Russell syndrome cases, while ~50% of patients have hypomethylation at imprinting control region 1 at chromosome 11p15.5 locus, leaving ~40% of cases with unknown etiologies. This review aims to provide a comprehensive list of molecular defects in Silver-Russell syndrome reported to date and to highlight the importance of multiple-loci/tissue testing and trio (both parents and proband) screening. The epigenetic and phenotypic overlaps with other imprinting disorders will also be discussed.