Novel insertion mutation (Arg1822_Glu1823dup) in MYH6 coiled-coil domain causing familial atrial septal defect

Exploring the role of non-coding RNAs in atrial septal defect pathogenesis: A systematic review

BACKGROUND

Extensive research has recognized the significant roles of non-coding RNAs (ncRNAs) in various cellular pathophysiological processes and their association with diverse diseases, including atrial septal defect (ASD), one of the most prevalent congenital heart diseases. This systematic review aims to explore the intricate involvement and significance of ncRNAs in the pathogenesis and progression of ASD.

METHODS

Four databases (PubMed, Embase, Scopus, and the Web of Science) were searched systematically up to June 19, 2023, with no year restriction. The risk of bias assessment was evaluated using the Newcastle-Ottawa scale.

RESULTS

The present systematic review included thirteen studies with a collective study population of 874 individuals diagnosed with ASD, 21 parents of ASD patients, and 22 pregnant women carrying ASD fetuses. Our analysis revealed evidence linking five long ncRNAs (STX18-AS1, HOTAIR, AA709223, BX478947, and Moshe) and several microRNAs (hsa-miR-19a, hsa-miR-19b, hsa-miR-375, hsa-miR-29c, miR-29, miR-143/145, miR-17-92, miR-106b-25, and miR-503/424, miR-9, miR-30a, miR-196a2, miR-139-5p, hsa-let-7a, hsa-let-7b, and hsa-miR-486) to ASD progression, corresponding to previous studies.

CONCLUSIONS

NcRNAs play a crucial role in unraveling the underlying mechanisms of ASD, contributing to both biomarker discovery and therapeutic advancements. This systematic review sheds light on the mechanisms of action of key ncRNAs involved in ASD progression, providing valuable insights for future research in this field.

Motor proteins, spermatogenesis and testis function

The role of motor proteins in supporting intracellular transports of vesicles and organelles in mammalian cells has been known for decades. On the other hand, the function of motor proteins that support spermatogenesis is also well established since the deletion of motor protein genes leads to subfertility and/or infertility. Furthermore, mutations and genetic variations of motor protein genes affect fertility in men, but also a wide range of developmental defects in humans including multiple organs besides the testis. In this review, we seek to provide a summary of microtubule and actin-dependent motor proteins based on earlier and recent findings in the field. Since these two cytoskeletons are polarized structures, different motor proteins are being used to transport cargoes to different ends of these cytoskeletons. However, their involvement in germ cell transport across the blood-testis barrier (BTB) and the epithelium of the seminiferous tubules remains relatively unknown. It is based on recent findings in the field, we have provided a hypothetical model by which motor proteins are being used to support germ cell transport across the BTB and the seminiferous epithelium during the epithelial cycle of spermatogenesis. In our discussion, we have highlighted the areas of research that deserve attention to bridge the gap of research in relating the function of motor proteins to spermatogenesis.

Human Genetics of Atrial Septal Defect

Although atrial septal defects (ASD) can be subdivided based on their anatomical location, an essential aspect of human genetics and genetic counseling is distinguishing between isolated and familiar cases without extracardiac features and syndromic cases with the co-occurrence of extracardiac abnormalities, such as developmental delay. Isolated or familial cases tend to show genetic alterations in genes related to important cardiac transcription factors and genes encoding for sarcomeric proteins. By contrast, the spectrum of genes with genetic alterations observed in syndromic cases is diverse. Currently, it points to different pathways and gene networks relevant to the dysregulation of cardiomyogenesis and ASD pathogenesis. Therefore, this chapter reflects the current knowledge and highlights stable associations observed in human genetics studies. It gives an overview of the different types of genetic alterations in these subtypes, including common associations based on genome-wide association studies (GWAS), and it highlights the most frequently observed syndromes associated with ASD pathogenesis.

SMAD4 loss-of-function mutation predisposes to congenital heart disease

Congenital heart disease (CHD) represents the most frequent developmental deformity in human beings and accounts for substantial morbidity and mortality worldwide. Accumulating investigations underscore the strong inherited basis of CHD, and pathogenic variations in >100 genes have been related to CHD. Nevertheless, the heritable defects underpinning CHD remain elusive in most cases, mainly because of the pronounced genetic heterogeneity. In this investigation, a four-generation family with CHD was recruited and clinically investigated. Via whole-exome sequencing and Sanger sequencing assays in selected family members, a heterozygous variation in the SMAD4 gene (coding for a transcription factor essential for cardiovascular morphogenesis), NM_005359.6: c.285T > A; p.(Tyr95*), was identified to be in co-segregation with autosomal-dominant CHD in the entire family. The truncating variation was not observed in 460 unrelated non-CHD volunteers employed as control subjects. Functional exploration by dual-reporter gene analysis demonstrated that Tyr95*-mutant SMAD4 lost transactivation of its two key downstream target genes NKX2.5 and ID2, which were both implicated with CHD. Additionally, the variation nullified the synergistic transcriptional activation between SMAD4 and GATA4, another transcription factor involved in CHD. These data strongly indicate SMAD4 may be associated with CHD and shed more light on the molecular pathogenesis underlying CHD, implying potential implications for antenatal precise prevention and prognostic risk stratification of the patients affected with CHD.

Identification and functional analysis of variants of MYH6 gene promoter in isolated ventricular septal defects

BACKGROUND

Ventricular septal defect is the most common form of congenital heart diseases. MYH6 gene has a critical effect on the growth and development of the heart but the variants in the promoter of MYH6 is unknown.

PATIENTS AND METHODS

In 604 of the subjects (311 isolated and sporadic ventricular septal defect patients and 293 healthy controls), DNA was extracted from blood samples and MYH6 gene promoter region variants were analyzed by sequencing. Further functional verification was performed by cellular experiments using dual luciferase reporter gene analysis, electrophoretic mobility shift assays, and bioinformatics analysis.

RESULTS

Nine variants were identified in the MYH6 gene promoter and two of those variants [g.4085G>C(rs1222539675) and g.4716G>A(rs377648095)] were only found in the ventricular septal defect patients. Cellular function experiments showed that these two variants reduced the transcriptional activity of the MYH6 gene promoter (p < 0.001). Further analysis with online JASPAR database suggests that these variants may alter a set of putative transcription factor binding sites that possibly lead to changes in myosin subunit expression and ventricular septal defect formation.

CONCLUSIONS

Our study for the first time identifies variants in the promoter region of the MYH6 gene in Chinese patients with isolated and sporadic ventricular septal defect. These variants significantly reduced MYH6 gene expression and affected transcription factor binding sites and therefore are pathogenic. The present study provides new insights in the role of the MYH6 gene promoter region to better understand the genetic basis of VSD formation.

A Novel Splicing Mutation c.335-1 G > A in the Cardiac Transcription Factor NKX2-5 Leads to Familial Atrial Septal Defect Through miR-19 and PYK2

Mutations of NKX2-5 largely contribute to congenital heart diseases (CHDs), especially atrial septal defect (ASD). We identified a novel heterozygous splicing mutation c.335-1G > A in NKX2-5 gene in an ASD family via whole exome sequencing (WES) and linkage analysis. Utilizing the human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) as a disease model, we showed that haploinsufficiency of NKX2-5 contributed to aberrant orchestration of apoptosis and proliferation in ASD patient-derived hiPSC-CMs. RNA-seq profiling and dual-luciferase reporter assay revealed that NKX2-5 acts upstream of PYK2 via miR-19a and miR-19b (miR-19a/b) to regulate cardiomyocyte apoptosis. Meanwhile, miR-19a/b are also downstream mediators of NKX2-5 during cardiomyocyte proliferation. The novel splicing mutation c.335-1G > A in NKX2-5 and its potential pathogenic roles in ASD were demonstrated. Our work provides clues not only for deep understanding of NKX2-5 in cardia development, but also for better knowledge in the molecular mechanisms of CHDs.

Significance of α-Myosin Heavy Chain (MYH6) Variants in Hypoplastic Left Heart Syndrome and Related Cardiovascular Diseases

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart disease (CHD) with complex genetic inheritance. HLHS segregates with other left ventricular outflow tract (LVOT) malformations in families, and can present as either an isolated phenotype or as a feature of a larger genetic disorder. The multifactorial etiology of HLHS makes it difficult to interpret the clinical significance of genetic variants. Specific genes have been implicated in HLHS, including rare, predicted damaging MYH6 variants that are present in >10% of HLHS patients, and which have been shown to be associated with decreased transplant-free survival in our previous studies. MYH6 (α-myosin heavy chain, α-MHC) variants have been reported in HLHS and numerous other CHDs, including LVOT malformations, and may provide a genetic link to these disorders. In this paper, we outline the MYH6 variants that have been identified, discuss how bioinformatic and functional studies can inform clinical decision making, and highlight the importance of genetic testing in HLHS.