A 1.1 Mb deletion in distal 13q deletion syndrome region with congenital heart defect and postaxial polydactyly: Additional support for a CHD locus at distal 13q34 region

13q deletion syndrome is a rare genetic disorder, especially for group 3 deletion (13q33–q34 deletion). Previously we described a patient with congenital heart defect and mental retardation and proposed that a distal 6 Mb region might contain the causative gene of congenital heart defect. Here we present a new patient with congenital heart defects (CHD), hand and foot anomalies and mild mental retardation. We identified a 1.1 Mb deletion at chromosome 13q34 with high resolution SNP-array BeadChips (HumanOmni1-Quad, Illumina, USA). This chromosome region contains ten annotated genes, including GRK1, TFDP1, RASA3 and GAS6. To our knowledge, this represents the smallest 13q34 deletion identified to date. Our study provides additional support that distal 13q34 deletion region might contain key gene(s) responsible for cardiac development.     

Effects of Regulator of G Protein Signaling 19 (RGS19) on Heart Development and Function

Wnt/Wg genes play a critical role in the development of various organisms. For example, the Wnt/β-catenin signal promotes heart formation and cardiomyocyte differentiation in mice. Previous studies have shown that RGS19 (regulator of G protein signaling 19), which has Gα subunits with GTPase activity, inhibits the Wnt/β-catenin signal through inactivation of Gα_o. In the present study, the effects of RGS19 on mouse cardiac development were observed. In P19 teratocarcinoma cells with RGS19 overexpression, RGS19 inhibited cardiomyocyte differentiation by blocking the Wnt signal. Additionally, several genes targeted by Wnt were down-regulated. For the in vivo study, we generated RGS19-overexpressing transgenic (RGS19 TG) mice. In these transgenic mice, septal defects and thin-walled ventricles were observed during the embryonic phase of development, and the expression of cardiogenesis-related genes, BMP4 and Mef2C, was reduced significantly. RGS19 TG mice showed increased expression levels of brain natriuretic peptide and β-MHC, which are markers of heart failure, increase of cell proliferation, and electrocardiogram analysis shows abnormal ventricle repolarization. These data provide in vitro and in vivo evidence that RGS19 influenced cardiac development and had negative effects on heart function.     

Myocardial deletion of Smad4 using a novel α skeletal muscle actin Cre recombinase transgenic mouse causes misalignment of the cardiac outflow tract

SMAD4 acts as the converging point for TGFβ and BMP signaling in heart development. Here, we investigated the role of SMAD4 in heart development using a novel α skeletal muscle actin Cre recombinase (MuCre) transgenic mouse strain. Lineage tracing using MuCre/ROSA26^LacZ reporter mice indicated strong Cre-recombinase expression in developing and adult heart and skeletal muscles. In heart development, significant MuCre expression was noted at E11.5 in the atrial, ventricular, outflow tract and atrioventricular canal myocardium, but not in the endocardial cushions. MuCre-driven conditional deletion of Smad4 in mice caused double outlet right ventricle (DORV), ventricular septal defect (VSD), impaired trabeculation and thinning of ventricular myocardium, and mid-gestational embryonic lethality. In conclusion, MuCre mice effectively delete genes in both heart and skeletal muscles, thus enabling the discovery that myocardial Smad4 deletion causes misalignment of the outflow tract and DORV.     

576 kb deletion in 1p36.33–p36.32 containing SKI is associated with limb malformation,congenital heart disease and epilepsy

1p36 deletion (monosomy 1p36) is one of the most common terminal deletions observed in humans, characterized by special facial features, mental retardation, heart defects, development delay and epilepsy. Previously, we reported molecular findings in patients with limb, congenital heart disease (CHD) and other malformations with SNP-array. In a syndromic patient of the same cohort, we detected a small deletion of 1p36.33–p36.32 containing SKI (Sloan–Kettering Institute protooncoprotein). Recently, dominant mutations in SKI were identified to be correlated with Shprintzen–Goldberg syndrome. Retrospective examination revealed this patient with limb malformations, CHD, epilepsy and mild development delay. Together with previous reports, our study suggests that the 1p36.33–1p36.32 deletion encompassing SKI may represents a previous undescribed microdeletion disorder.     

Suppression of Rap1 Impairs Cardiac Myofibrils and Conduction System in Zebrafish

Numerous studies have revealed that Rap1 (Ras-proximate-1 or Ras-related protein 1), a small GTPase protein, plays a crucial role in mediating cAMP signaling in isolated cardiac tissues and cell lines. However, the involvement of Rap1 in the cardiac development in vivo is largely unknown. By injecting anti-sense morpholino oligonucleotides to knock down Rap1a and Rap1b in zebrafish embryos, and in combination with time-lapsed imaging, in situ hybridization, immunohistochemistry and transmission electron microscope techniques, we seek to understand the role of Rap1 in cardiac development and functions. At an optimized low dose of mixed rap1a and rap1b morpholino oligonucleotides, the heart developed essentially normally until cardiac contraction occurred. Morphant hearts showed the myocardium defect phenotypes, most likely due to disrupted myofibril assembly and alignment. In vivo heart electrocardiography revealed prolonged P-R interval and QRS duration, consistent with an adherens junction defect and reduced Connexons in cardiac myocytes of morphants. We conclude that a proper level of Rap1 is crucial for heart morphogenesis and function, and suggest that Rap1 and/or their downstream factor genes are potential candidates for genetic screening for human heart diseases.     

Identification of differentially expressed genes in human heart with ventricular septal defect using suppression subtractive hybridization

Ventricular septal defect (VSD) accounts for the largest number of birth congenital heart defects in human, but the genetic programs that control ventricular septation are poorly understood. To identify differentially expressed genes between ventricular septal defect and normal ventricular septum myocardium, we have undertaken suppression subtractive hybridization (SSH) and generated reciprocal cDNA collections of representative mRNAs specific to human heart with ventricular septal defect versus normal control. Following SSH, 1378 clones were sequenced and found to derive from 551 different genes. These predominately expressed genes included genes involved in energy metabolism, cell cycle and growth, cytoskeleton and cell adhesion, LIM protein, zinc finger protein, and development. It is anticipated that further study of genes identified will provide insights into their specific roles in the etiology of VSD, even in cardiac development, aging, and disease.     

Missense mutation G296S in GATA4 is not responsible for cardiac septal defects

BACKGROUND:

The most common type of congenital heart disease is the cardiac septal defects, which has reported to be caused by a missense mutation (G296S) in exon 3 of the GATA4 gene.

AIMS:

The present study was undertaken to find out whether GATA4 gene is the prime cause of the septal defects in Mysore population.

MATERIALS AND METHODS:

GATA4 gene analyses were undertaken on 21 confirmed CHD cases by PCR and DNA sequencing.

RESULTS AND CONCLUSION:

Analysis of this particular mutation in 21 septal defect patients revealed that none of the patients had the mutation, indicating that this mutation is population specific or septal defect in Mysore population is caused due to mutations in other regions of the GATA4 gene.     

Haploinsufficiency of TAB2 Causes Congenital Heart Defects in Humans

Congenital heart defects (CHDs) are the most common major developmental anomalies and the most frequent cause for perinatal mortality, but their etiology remains often obscure. We identified a locus for CHDs on 6q24-q25. Genotype-phenotype correlations in 12 patients carrying a chromosomal deletion on 6q delineated a critical 850 kb region on 6q25.1 harboring five genes. Bioinformatics prioritization of candidate genes in this locus for a role in CHDs identified the TGF-β-activated kinase 1/MAP3K7 binding protein 2 gene (TAB2) as the top-ranking candidate gene. A role for this candidate gene in cardiac development was further supported by its conserved expression in the developing human and zebrafish heart. Moreover, a critical, dosage-sensitive role during development was demonstrated by the cardiac defects observed upon titrated knockdown of tab2 expression in zebrafish embryos. To definitively confirm the role of this candidate gene in CHDs, we performed mutation analysis of TAB2 in 402 patients with a CHD, which revealed two evolutionarily conserved missense mutations. Finally, a balanced translocation was identified, cosegregating with familial CHD. Mapping of the breakpoints demonstrated that this translocation disrupts TAB2. Taken together, these data clearly demonstrate a role for TAB2 in human cardiac development.     

Heart-specific Deletion of CnB1 Reveals Multiple Mechanisms Whereby Calcineurin Regulates Cardiac Growth and Function

Calcineurin is a protein phosphatase that is uniquely regulated by sustained increases in intracellular Ca²⁺ following signal transduction events. Calcineurin controls cellular proliferation, differentiation, apoptosis, and inducible gene expression following stress and neuroendocrine stimulation. In the adult heart, calcineurin regulates hypertrophic growth of cardiomyocytes in response to pathologic insults that are associated with altered Ca²⁺ handling. Here we determined that calcineurin signaling is directly linked to the proper control of cardiac contractility, rhythm, and the expression of Ca²⁺-handling genes in the heart. Our approach involved a cardiomyocyte-specific deletion using a CnB1-LoxP-targeted allele in mice and three different cardiac-expressing Cre alleles/transgenes. Deletion of calcineurin with the Nkx2.5-Cre knock-in allele resulted in lethality at 1 day after birth due to altered right ventricular morphogenesis, reduced ventricular trabeculation, septal defects, and valvular overgrowth. Slightly later deletion of calcineurin with the α-myosin heavy chain Cre transgene resulted in lethality in early mid adulthood that was characterized by substantial reductions in cardiac contractility, severe arrhythmia, and reduced myocyte content in the heart. Young calcineurin heart-deleted mice died suddenly after pressure overload stimulation or neuroendocrine agonist infusion, and telemetric monitoring of older mice showed arrhythmia leading to sudden death. Mechanistically, loss of calcineurin reduced expression of key Ca²⁺-handling genes that likely lead to arrhythmia and reduced contractility. Loss of calcineurin also directly impacted cellular proliferation in the postnatal developing heart. These results reveal multiple mechanisms whereby calcineurin regulates cardiac development and myocyte contractility.     

An Excess of Deleterious Variants in VEGF-A Pathway Genes in Down-Syndrome-Associated Atrioventricular Septal Defects

About half of people with trisomy 21 have a congenital heart defect (CHD), whereas the remainder have a structurally normal heart, demonstrating that trisomy 21 is a significant risk factor but is not causal for abnormal heart development. Atrioventricular septal defects (AVSD) are the most commonly occurring heart defects in Down syndrome (DS), and ∼65% of all AVSD is associated with DS. We used a candidate-gene approach among individuals with DS and complete AVSD (cases = 141) and DS with no CHD (controls = 141) to determine whether rare genetic variants in genes involved in atrioventricular valvuloseptal morphogenesis contribute to AVSD in this sensitized population. We found a significant excess (p < 0.0001) of variants predicted to be deleterious in cases compared to controls. At the most stringent level of filtering, we found potentially damaging variants in nearly 20% of cases but fewer than 3% of controls. The variants with the highest probability of being damaging in cases only were found in six genes: COL6A1, COL6A2, CRELD1, FBLN2, FRZB, and GATA5. Several of the case-specific variants were recurrent in unrelated individuals, occurring in 10% of cases studied. No variants with an equal probability of being damaging were found in controls, demonstrating a highly specific association with AVSD. Of note, all of these genes are in the VEGF-A pathway, even though the candidate genes analyzed in this study represented numerous biochemical and developmental pathways, suggesting that rare variants in the VEGF-A pathway might contribute to the genetic underpinnings of AVSD in humans.     

Additional sex combs‐like family genes are required for normal cardiovascular development

Congenital heart disease (CHD) is the most common birth defect. However, the majority of CHD cases have unknown etiology. Here we report the identification of ASXL2 and ASXL1, two homologous chromatin factors, as novel regulators of heart development. Asxl2^?/? fetuses have reduced body weight and display congenital heart malformations including thickened compact myocardium in the left ventricle, membranous ventricular septal defect, and atrioventricular valval stenosis. Although most Asxl2^?/? animals survive to term, the neonates have patent ductus arteriosus and consequent lung hemorrhage and die soon after birth. Asxl1^?/? fetuses have reduced body weight and display cleft palate, anophthalmia as well as ventricular septal defects and a failure in lung maturation. From these results, we conclude that normal heart development requires both ASXL proteins. In particular, ASXL2 plays an important role in heart morphogenesis and the transition from fetal to postnatal circulation. genesis 52:671–686, 2014. © 2014 Wiley Periodicals, Inc.