First report on concordant monozygotic twins with Silver-Russell syndrome and ICR1 hypomethylation

Imprinting disorders

Imprinting disorders (ImpDis) are congenital conditions that are characterized by disturbances of genomic imprinting. The most common individual ImpDis are Prader-Willi syndrome, Angelman syndrome and Beckwith-Wiedemann syndrome. Individual ImpDis have similar clinical features, such as growth disturbances and developmental delay, but the disorders are heterogeneous and the key clinical manifestations are often non-specific, rendering diagnosis difficult. Four types of genomic and imprinting defect (ImpDef) affecting differentially methylated regions (DMRs) can cause ImpDis. These defects affect the monoallelic and parent-of-origin-specific expression of imprinted genes. The regulation within DMRs as well as their functional consequences are mainly unknown, but functional cross-talk between imprinted genes and functional pathways has been identified, giving insight into the pathophysiology of ImpDefs. Treatment of ImpDis is symptomatic. Targeted therapies are lacking owing to the rarity of these disorders; however, personalized treatments are in development. Understanding the underlying mechanisms of ImpDis, and improving diagnosis and treatment of these disorders, requires a multidisciplinary approach with input from patient representatives.

Monozygotic twin rate among ART centers: a multicenter analysis of data from 18 Italian units

PURPOSE

The risk of monozygotic twins (MZTs) is increased in couples undergoing assisted reproductive technology (ART) treatments. Several systematic reviews have investigated the possible determinants linked to ART, but results obtained have not been conclusive. The study aims to investigate whether the incidence of MZT differed among ART centers.

METHODS

This is a multicenter retrospective cohort study using the Italian ART National Registry database and involving the centers reporting data from individual ART cycles from 2015 to 2019. To investigate the incidence of MZT, only single embryo transfer cycles were considered. Women who had sex-discordant deliveries were excluded. MZT rate was calculated as the number of multiple pregnancies (more than one gestational sac at first ultrasound) out of the total number of clinical pregnancies. A binomial distribution model was used to determine the 95% CI of the frequency of MZT.

RESULTS

Eighteen centers were included, and they provided data on 10,433 pregnancies. The total number of MZT was 162, corresponding to an incidence of 1.5% (95% CI: 1.3-1.8%). The rate of MZT among centers varied between 0% (95% CI: 0.0-25.9%) and 3.2% (95% CI: 1.3-8.1%). All the 95% CIs included 1.5%, rejecting the hypothesis that the MZT rate may significantly differ among centers.

CONCLUSIONS

The rate of MZT did not significantly vary among ART centers. Local factors are unlikely to explain the increased rate of MZT in ART pregnancies.

Components of IGF-axis in growth disorders: a systematic review and patent landscape report

PURPOSE

In this review, epi/genetic mutations of IGF-axis components associated with growth disorders have been summarized alongwith assessment of relevant diagnostic and therapeutic technology through patent literature.

METHODOLOGY

PROSPERO protocol registration CRD42021279468. For scientific literature search Literature databases (PubMed, EMBASE, ScienceDirect, and Google Scholar) were queried using the appropriate syntax. Various filters were applied based on inclusion and exclusion criteria. Search results were further refined by two authors for finalizing studies to be included in this synthesis. For patent documents search Patent databases (Patentscope and Espacenet) were queried using keywords: IGF or IGFBP. Filters were applied according to International Patent Classification (IPC) and Cooperative Patent Classification (CPC). Search results were reviewed by two authors for inclusion in the patent landscape report.

RESULTS

For scientific literature analysis, out of 545 search results, 196 were selected for review based on the inclusion criteria. For Patent literature search, out of 485 results, 37 were selected for this synthesis.

CONCLUSION

Dysregulation of IGF-axis components leads to various abnormalities and their key role in growth and development suggests epi/mutations or structural defects among IGF-axis genes can be associated with growth disorders and may explain some of the idiopathic short stature cases. Trend of patent filings indicate advent of recombinant technology for therapeutics.

Sporadic Pseudohypoparathyroidism Type 1B in Monozygotic Twins: Insights Into the Pathogenesis of Methylation Defects

CONTEXT

Sporadic pseudohypoparathyroidism type 1B (sporPHP1B) is an imprinting disease without a defined genetic cause, characterized by broad methylation changes in differentially methylated regions (DMRs) of the GNAS gene.

OBJECTIVE

This work aims to provide insights into the causative event leading to the GNAS methylation defects through comprehensive molecular genetic analyses of a pair of female monozygotic twins concordant for sporPHP1B who were conceived naturally, that is, without assisted reproductive techniques.

METHODS

Using the leukocyte genome of the twins and family members, we performed targeted bisulfite sequencing, methylation-sensitive restriction enzyme (MSRE)-quantitative polymerase chain reaction (qPCR), whole-genome sequencing (WGS), high-density single-nucleotide polymorphism (SNP) array, and Sanger sequencing.

RESULTS

Methylation analyses by targeted bisulfite sequencing and MSRE-qPCR revealed almost complete losses of methylation at the GNAS AS, XL, and A/B DMRs and a gain of methylation at the NESP55 DMR in the twins, but not in other family members. Except for the GNAS locus, we did not find apparent methylation defects at other imprinted genome loci of the twins. WGS, SNP array, and Sanger sequencing did not detect the previously described genetic defects associated with familial PHP1B. Sanger sequencing also ruled out any novel genetic alterations in the entire NESP55/AS region. However, the analysis of 28 consecutive SNPs could not exclude the possibility of paternal heterodisomy in a span of 22 kb comprising exon NESP55 and AS exon 5.

CONCLUSION

Our comprehensive analysis of a pair of monozygotic twins with sporPHP1B ruled out all previously described genetic causes. Twin concordance indicates that the causative event was an imprinting error earlier than the timing of monozygotic twinning.

Twin Registries Moving Forward and Meeting the Future: A Review

Twin registries have developed as a valuable resource for the study of many aspects of disease and society over the years in many different countries. A number of these registries include large numbers of twins with data collected at varying information levels for twin cohorts over the past several decades. More recent expansion of twin datasets has allowed for the collection of genetic data, together with many other levels of 'omic' information along with multiple demographic, physiological, health outcomes and other measures typically used in epidemiologic research. Other twin data sources outside these registries reflect research interests in particular aspects of disease or specific phenotypic assessment. Twin registries have the potential to play a key role in many aspects of the artificial intelligence/machine learning-driven projects of the future and will continue to keep adapting to the changing research landscape.

Genomic imprinting disorders: lessons on how genome, epigenome and environment interact

Genomic imprinting, the monoallelic and parent-of-origin-dependent expression of a subset of genes, is required for normal development, and its disruption leads to human disease. Imprinting defects can involve isolated or multilocus epigenetic changes that may have no evident genetic cause, or imprinting disruption can be traced back to alterations of cis-acting elements or trans-acting factors that control the establishment, maintenance and erasure of germline epigenetic imprints. Recent insights into the dynamics of the epigenome, including the effect of environmental factors, suggest that the developmental outcomes and heritability of imprinting disorders are influenced by interactions between the genome, the epigenome and the environment in germ cells and early embryos.

Diagnosis and management of the phenotypic spectrum of twins with Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an overgrowth disorder with a heterogeneous phenotypic spectrum. There is an increased prevalence of monozygotic twinning in BWS. Given the epigenetic nature and phenotypic spectrum that defines BWS, twins are often discordant for clinical features, and clinicians are faced with the challenge of diagnosing and managing these twins. We present a cohort of multiple pregnancies in which one or more child from each pregnancy was diagnosed with BWS. We conducted a chart review of monochorionic and dichorionic gestations. Clinical scores for monochorionic twins demonstrated phenotypic discordance between the proband and twin. Based on linear regression analysis, a higher clinical score in the proband correlated with larger phenotypic discordance between twin siblings. Despite phenotypic discordance, however, we observed a consistent additive clinical score for a pregnancy (proband's plus twin's scores from a pregnancy). This idea of a finite degree of affectedness for a pregnancy implies a finite number of epigenetically affected cells. This further corroborates the idea that timing of monozygotic monochorionic twinning correlates with the disruption of establishment and/or maintenance of imprinting. The difference in clinical score between a proband and their twin may be due to diffused mosaicism, whereby there is an asymmetric distribution of affected cells among the multiple fetuses in a monozygotic monochorionic pregnancy, leading to a spectrum of variably affected phenotypes. Based on these findings, we recommend an algorithm for a conservative approach to clinically evaluate all children in a monozygotic multiple gestation affected by BWS.

DNA methylation signatures of monozygotic twins clinically discordant for multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system with a modest concordance rate in monozygotic twins, which strongly argues for involvement of epigenetic factors. We observe highly similar peripheral blood mononuclear cell-based methylomes in 45 MS-discordant monozygotic twins. Nevertheless, we identify seven MS-associated differentially methylated positions (DMPs) of which we validate two, including a region in the TMEM232 promoter and ZBTB16 enhancer. In CD4 + T cells we find an MS-associated differentially methylated region in FIRRE. Additionally, 45 regions show large methylation differences in individual pairs, but they do not clearly associate with MS. Furthermore, we present epigenetic biomarkers for current interferon-beta treatment, and extensive validation shows that the ZBTB16 DMP is a signature for prior glucocorticoid treatment. Taken together, this study represents an important reference for epigenomic MS studies, identifies new candidate epigenetic markers, and highlights treatment effects and genetic background as major confounders.

Monozygotic (MZ) twins are ideal to study the influence of non-genetic factors on complex phenotypes. Here, Souren et al. perform an EWAS in peripheral blood mononuclear cells from 45 MZ twins discordant for multiple sclerosis and identify disease and treatment-associated epigenetic markers.

Dwarfism and insulin resistance in male offspring caused by α1-adrenergic antagonism during pregnancy

OBJECTIVE

Maternal and environmental factors control the epigenetic fetal programming of the embryo, thereby defining the susceptibility for metabolic or endocrine disorders in the offspring. Pharmacological interventions required as a consequence of gestational problems, e.g. hypertension, can potentially interfere with correct fetal programming. As epigenetic alterations are usually only revealed later in life and not detected in studies focusing on early perinatal outcomes, little is known about the long-term epigenetic effects of gestational drug treatments. We sought to test the consequences of maternal α1-adrenergic antagonism during pregnancy, which can occur e.g. during hypertension treatment, for the endocrine and metabolic phenotype of the offspring.

METHODS

We treated C57BL/6NCrl female mice with the α1-adrenergic antagonist prazosin during pregnancy and analyzed the male and female offspring for endocrine and metabolic abnormalities.

RESULTS

Our data revealed that maternal α1-adrenergic blockade caused dwarfism, elevated body temperature, and insulin resistance in male offspring, accompanied by reduced IGF-1 serum concentrations as the result of reduced hepatic growth hormone receptor (Ghr) expression. We subsequently identified increased CpG DNA methylation at the transcriptional start site of the alternative Ghr promotor caused by the maternal treatment, which showed a strong inverse correlation to hepatic Ghr expression.

CONCLUSIONS

Our results demonstrate that maternal α1-adrenergic blockade can constitute an epigenetic cause for dwarfism and insulin resistance. The findings are of immediate clinical relevance as combined α/β-adrenergic blockers are first-line treatment of maternal hypertension.