DNA Methylation Variation Is Identified in Monozygotic Twins Discordant for Congenital Heart Diseases

Aims:Multiple genes and environmental factors are known to be involved in congenital heart disease(CHD),but epigenetic variation has received little attention.Monozygotic(MZ)twins with CHD provide a unique model for exploring this phenomenon.In order to investigate the potential role of Deoxyribonucleic Acid(DNA)methyla-tion in CHD pathogenesis,the present study examined DNA methylation variation in MZ twins discordant for CHD,especially ventricular septal defect(VSD).Methods and Results:Using genome-wide DNA methylation profiles,we identified 4004 differentially methylated regions(DMRs)in 18 MZ twin pairs discordant for CHD,and 2826 genes were identified.Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)analysis revealed a list of CHD-associated pathways.To further investigate the role of DNA methylation in VSD,data from 7 pairs of MZ twins with VSD were analyzed.We identified 1614 DMRs corresponding to 1443 genes associated with arrhythmogenic right ventricular cardiomyopathy,cyclic guanosine monopho-sphate-protein kinase G(cGMP-PKG)signaling pathway by KEGG analysis,and cell-cell adhesion,calcium ion transmembrane transport by GO analysis.A proportion of DMR-associated genes were involved in calcium signaling pathways.The methylation changes of calcium signaling genes might be related to VSD pathogenesis.Conclusion:CHD is associated with differential DNA methylation in MZ twins.CHD may be etiologically linked to DNA methylation,and methylation of calcium signaling genes may be involved in the development of VSD.

Identifying a novel frameshift pathogenic variant in a Chinese family with neurofibromatosis type 1 and review of literature

AIM:To detect the pathogenic gene variant in a family with neurofibromatosis type 1(NF1).METHODS:This patient with NF1 was sequenced using target sequence capture and high-throughput sequencing technology.After detecting the suspicious pathogenic variant type,the pathogenic variant sites of the patient and the patient’s family members were verified by multiple ligation dependent probe amplification and Sanger sequencing.Sift,polyphen-2,Mutation Taster and GERP++software were used to predict the pathogenicity of the unknown loci.The clinical data,diagnosis and treatment process of the patients were reviewed.Using the keyword“NF1;frameshift pathogenic variant”,relevant literature was gathered for analysis from Chinese and international databases,with articles dating from the establishment of each database to April 2022.RESULTS:A heterozygous frameshift pathogenic variant of NF1 in exon 33 was detected in the patient.The insertion of adenine in coding region 4486 resulted in the replacement of isoleucine with asparagine in protein 1497.Sanger sequencing validation and segregation analysis were performed,which demonstrated that the NF1 gene was cosegregated with the disease phenotype in this family.This study identified a novel NF1 heterozygous frameshift mutation c.4486dupA(p.I1497Nfs*12).Relevant literature retrieval found 7 Chinese articles and 12 foreign articles.With NF1 gene mutation,mutation types are diverse,including point mutation,frameshift mutation,splice site mutation,exon mutation,chimeric mutation and de novo mutation.Foreign reports are based on autosomal dominant inheritance.CONCLUSION:This study’s results demonstrate that a novel deletion in exon 33 caused NF1 in this Chinese family,expanding the mutational spectrum of the NF1 gene.

Incidence and Potential Causes affecting Monozygotic Twin Formation Following in vitro Fertilization and Embryo Transfer

Objectives To study the incidence and potential causes of monozygotic twins after in vitro fertilization and embryo transfer （IVF-ET）. Methods A retrospective study was performed on women carrying monozygotic twins （MZTs） after conventional IVF-ET treatment at the Third Affiliated Hospital of Guangzhou Medical College in China from January 2003 to May 2009. The incidence and the miscarriage rate for MZTs following IVF-ET were examined iin relation to maternal age, duration of infertility, type and dose of hormone treatment, conventional IVF-ET cycles versus intracytoplasmic sperm injection （ICSI） cycles, the use of fresh or frozen-thawed embryos, and day （post-fertilization） of embryo transfer. Results Sixteen MZT pregnancies occurred in 2 161 patients （incidence of 0.74%）, of which 5 miscarried （31.25%）. No significant difference was found between MZT and non-MZT groups in terms of maternal age, duration of infertilit）, duration of gonadotropin （Gn） administration, dosage of Gn, number of oocytes retrieved, number of oocytes fertilized, or number of embryos transferred （P〉O.05）. The incidence of MZT was not statistically different between conventional IVF-ET cycles and ICSI cycles, between fresh embryos transfer cycles and frozen-thawed embryo cycles, or between different transfer days （P〉0.05）. Conclusion The incidence of MZTs following IVF-ET treatment greatly exceeds that observed following spontaneous conception. Intracytoplasmic sperm injection, frozenthawed procedures, and embryo transfer on different days were not correlated with an increased incidence of MZT pregnancies.

Whole-genome sequencing of monozygotic twins discordant for schizophrenia indicates multiple genetic risk factors for schizophrenia

Schizophrenia is a common disorder with a high heritability, but its genetic architecture is still elusive.We implemented whole-genome sequencing(WGS) analysis of 8 families with monozygotic(MZ) twin pairs discordant for schizophrenia to assess potential association of de novo mutations(DNMs) or inherited variants with susceptibility to schizophrenia. Eight non-synonymous DNMs(including one splicing site) were identified and shared by twins, which were either located in previously reported schizophrenia risk genes(p.V24689 I mutation in TTN, p.S2506 T mutation in GCN1L1, IVS3+1G > T in DOCK1) or had a benign to damaging effect according to in silico prediction analysis. By searching the inherited rare damaging or loss-of-function(LOF) variants and common susceptible alleles from three classes of schizophrenia candidate genes, we were able to distill genetic alterations in several schizophrenia risk genes, including GAD1, PLXNA2, RELN and FEZ1. Four inherited copy number variations(CNVs; including a large deletion at 16p13.11) implicated for schizophrenia were identified in four families, respectively. Most of families carried both missense DNMs and inherited risk variants, which might suggest that DNMs, inherited rare damaging variants and common risk alleles together conferred to schizophrenia susceptibility. Our results support that schizophrenia is caused by a combination of multiple genetic factors, with each DNM/variant showing a relatively small effect size.

Transcriptome Analysis of Monozygotic Twin Brothers with Childhood Primary Myelofibrosis

Primary myelofibrosis （PMF） is a chronic myeloproliferative disorder in human bone marrow. Over 50% of patients with myelofibrosis have mutations in JAK2, MPL, or CALR. However, these mutations are rarely detected in children, suggesting a difference in the pathogenesis of childhood PMF. In this study, we investigated the response to drug treatment of a monozygotic twin pair with typical childhood PMF. The twin exhibited different clinical outcomes despite following

Failure to Identify Somatic Mutations in Monozygotic Twins Discordant for Schizophrenia by Whole Exome Sequencing

Background： Schizophrenia （SCZ） is a severe, debilitating, and complex psychiatric disorder with multiple causative factors. An increasing number of studies have determined that rare variations play an important role in its etiology. A somatic mutation is a rare form of genetic variation that occurs at an early stage of embryonic development and is thought to contribute substantially to the development of SCZ. The aim of the study was to explore the novel pathogenic somatic single nucleotide variations （SNVs） and somatic insertions and deletions （indels） of SCZ. Methods： One Chinese family with a monozygotic （MZ） twin pair discordant for SCZ was included. Whole exome sequencing was performed in the co-twin and their parents. Rigorous filtering processes were conducted to prioritize pathogenic somatic variations, and all identified SNVs and indels were further confirmed by Sanger sequencing. Results： One somatic SNV and two somatic indels were identified after rigorous selection processes. However, none was validated by Sanger sequencing. Conclusions： This study is not alone in the failure to identify pathogenic somatic variations in MZ twins, suggesting that exonic somatic variations are extremely rare. Further efforts are warranted to explore the potential genetic mechanism of SCZ.