Complete transposition of the great arteries: patterns of congenital heart disease in familial precurrence

Pathogenesis and Surgical Treatment of Dextro-Transposition of the Great Arteries (D-TGA): Part II

Dextro-transposition of the great arteries (D-TGA) is the second most common cyanotic heart disease, accounting for 5-7% of all congenital heart defects (CHDs). It is characterized by ventriculoarterial (VA) connection discordance, atrioventricular (AV) concordance, and a parallel relationship with D-TGA. As a result, the pulmonary and systemic circulations are separated [the morphological right ventricle (RV) is connected to the aorta and the morphological left ventricle (LV) is connected to the pulmonary artery]. This anomaly is included in the group of developmental disorders of embryonic heart conotruncal irregularities, and their pathogenesis is multifactorial. The anomaly's development is influenced by genetic, epigenetic, and environmental factors. It can occur either as an isolated anomaly, or in association with other cardiac defects. The typical concomitant cardiac anomalies that may occur in patients with D-TGA include ventriculoseptal defects, patent ductus arteriosus, left ventricular outflow tract obstruction (LVOTO), mitral and tricuspid valve abnormalities, and coronary artery variations. Correction of the defect during infancy is the preferred treatment for D-TGA. Balloon atrial septostomy (BAS) is necessary prior to the operation. The recommended surgical correction methods include arterial switch operation (ASO) and atrial switch operation (AtrSR), as well as the Rastelli and Nikaidoh procedures. The most common postoperative complications include coronary artery stenosis, neoaortic root dilation, neoaortic insufficiency and neopulmonic stenosis, right ventricular (RV) outflow tract obstruction (RVOTO), left ventricular (LV) dysfunction, arrhythmias, and heart failure. Early diagnosis and treatment of D-TGA is paramount to the prognosis of the patient. Improved surgical techniques have made it possible for patients with D-TGA to survive into adulthood.

Hybrid Stenting of Pulmonary Venous Baffle Stenosis: Subxiphoid Approach in Transposition of the Great Arteries

A 31-year-old woman with transposition of the great arteries status post-Senning operation presents with severe pulmonary venous baffle obstruction. Both standards of care (percutaneous stenting or open repair) were deemed suboptimal and/or high risk. A multidisciplinary, hybrid approach via subxiphoid incision, guided by 3-dimensional modeling, provided a lower risk and minimally invasive intervention.

Human Genetics of d-Transposition of Great Arteries

Although several genes underlying occurrence of transposition of the great arteries have been found in the mouse, human genetics of the most frequent cyanotic congenital heart defect diagnosed in neonates is still largely unknown. Development of the outflow tract is a complex process which involves the major genes of cardiac development, acting on myocardial cells from the anterior second heart field, and on mesenchymal cells from endocardial cushions. These genes, coding for transcription factors, interact with each other, and their differential expression conditions the severity of the phenotype. A precise description of the anatomic phenotypes is mandatory to achieve a better comprehension of the complex mechanisms responsible for transposition of the great arteries.

Triple repeated fetal congenital heart disease linked to PLD1 mutation: a case report

BACKGROUND

Congenital heart disease occurs in approximately 1 in 100 cases. Although sibling occurrence is high (3-9%), the causative genes for this disease are still being elucidated. PLD1 (Phospholipase D1) is a recently discovered gene; however, few case reports have been published on it. In this report, we describe a case of triplicate fetal congenital heart disease that was diagnosed as a PDL1 mutation. Our objective is to explore the clinical manifestations of PLD1 mutations in this particular case.

CASE PRESENTATION

A 32-year-old Japanese woman (gravida, para 0) was introduced since fetus four chamber view was not clear and was diagnosed with ductus arteriosus-dependent left ventricular single ventricle and pulmonary atresia at 21 weeks and 1 day of gestation during her first pregnancy. Artificial abortion using Gemeprost was performed at 21 weeks and 5 days of gestation. The second pregnancy was diagnosed as pulmonary atresia with intact ventricular septum with cardiomegaly, a cardiothoracic area ratio of more than 35%, and a circulatory shunt at 13 weeks and 3 days of gestation. Subsequently, intrauterine fetal death was confirmed at 14 weeks and 3 days of gestation. Regarding the third pregnancy, fetal ultrasonography at 11 weeks and 5 days of gestation showed mild fetal hydrops and moderate tricuspid valve regurgitation. At 16 weeks and 5 days of gestation, the fetus was suspected to have a left ventricular-type single ventricle, trace right ventricle, pulmonary atresia with intact ventricular septum, or cardiomyopathy. Cardiac function gradually declined at 26 weeks of gestation, and intrauterine fetal death was confirmed at 27 weeks and 5 days of gestation. The fourth pregnancy resulted in a normal heart with good progression and no abnormal baby. We submitted the first and second fetuses' umbilical cord, third fetus' placenta, and the fourth fetus' blood to genetic testing using whole exome analysis with next generation sequencing. Genetic analysis identified hemizygous PLD1 mutations in the first, second, and third fetuses. The fourth fetus was heterozygous. In addition, the parents were heterozygous for PLD1. This case is based on three consecutive cases of homozygosity for the PLD1 gene in the sibling cases and the fetuses with recurrent right ventricular valve dysplasia. This will elucidate the cause of recurrent congenital heart disease and intrauterine fetal death and may serve as an indicator for screening the next fetus. To date, homozygous mutations in PLD1 that repeat three times in a row are not reported, only up to two times. The novelty of this report is that it was repeated three times, followed by a heterozygous live birth.

CONCLUSIONS

This report is consistent with previous reports that mutations in PLD1 cause right ventricular valve dysplasia. However, there have been few case reports of PLD1 mutations, and we hope that this report will contribute to elucidate the causes of congenital heart disease, especially right ventricular valve dysplasia, and that the accumulation of such information will provide more detailed information on PLD1 mutations in heart disease.

Outcome of Pregnancy in Women With D-Transposition of the Great Arteries: A Systematic Review

Background Information on maternal and fetal outcomes of pregnancy in women with D-transposition of the great arteries is limited. We conducted a systematic literature review on pregnancies in women with transposition of the great arteries after atrial and arterial switch operations to better define maternal and fetal risk. Methods and Results A systematic review was performed on studies between 2000 and 2021 that identified 676 pregnancies in 444 women with transposition of the great arteries. A total of 556 pregnancies in women with atrial switch operation were tolerated by most cases with low mortality (0.6%). Most common maternal complications, however, were arrhythmias (9%) and heart failure (8%) associated with serious morbidity in some patients. Worsening functional capacity, right ventricular function, and tricuspid regurgitation occurred in ≈20% of the cases. Rate of fetal and neonatal mortality was 1.4% and 0.8%, respectively, and rate of prematurity was 32%. A total of 120 pregnancies in women with arterial switch operation were associated with no maternal mortality, numerically lower rates of arrhythmias and heart failure (6% and 5%, respectively), significantly lower rate of prematurity (11%; P<0.001), and only 1 fetal loss. Conclusions Pregnancy is tolerated by most women with transposition of the great arteries and atrial switch operation with low mortality but important morbidity. Most common maternal complications were arrhythmias, heart failure, worsening of right ventricular function, and tricuspid regurgitation. There was also a high incidence of prematurity and increased rate of fetal loss and neonatal mortality. Outcome of pregnancy in women after arterial switch operations is more favorable, with reduced incidence of maternal complications and fetal outcomes similar to women without underlying cardiac disease.

Clustering of Genetic Anomalies of Cilia Outer Dynein Arm and Central Apparatus in Patients with Transposition of the Great Arteries

Transposition of the great arteries (TGA) is a congenital heart defect with a complex pathogenesis that has not been fully elucidated. In this study, we performed whole-exome sequencing (WES) in isolated TGA-diagnosed patients and analyzed genes of motile and non-motile cilia ciliogenesis and ciliary trafficking, as well as genes previously associated with this heart malformation. Deleterious missense and splicing variants of genes DNAH9, DNAH11, and ODAD4 of cilia outer dynein arm and central apparatus, HYDIN, were found in our TGA patients. Remarkable, there is a clustering of deleterious genetic variants in cilia genes, suggesting it could be an oligogenic disease. Our data evidence the genetic diversity and etiological complexity of TGA and point out that population allele determination and genetic aggregation studies are required to improve genetic counseling.

Dextro-transposition of the great arteries in one twin: case reports and literature review

BACKGROUND

Dextro-transposition of the great arteries (D-TGA) is a rare congenital heart disease, as it affects only 0.02-0.05% of live births. It is the second most common cyanotic heart disease following Tetralogy of Fallot. It has a male predominance. Fetal echocardiography is an optimal method for prenatal diagnosis of fetal D-TGA. In twin pregnancies, fetal D-TGA in one twin is very rare, especially in monochorionic-diamniotic twin pregnancies. Herein, we report a case of D-TGA in one twin in two dichorionic-diamniotic twin pregnancies and one monochorionic-diamniotic twin pregnancy from January 2018 to June 2021.

CASE DESCRIPTION

One twin with D-TGA was diagnosed by fetal echocardiography in the second trimester, and the co-twin was normal in all three cases. A multidisciplinary team provided extensive counseling regarding the D-TGA twin and the co-twin, and adequate perinatal management was provided. In cases 1, 2, and 3, the mothers underwent cesarean sections at 37 weeks + 2 days, 34 weeks + 5 days, and 36 weeks + 1 day, respectively. In case 1, which involved a female D-TGA neonate with birth weight 2,410 g, an emergent atrial septostomy was performed at 20 h after birth, and the neonate underwent atrial switch operation (ASO) 24 days after birth. In case 2, involving a male D-TGA neonate with a birth weight of 2,380 g, ASO was performed 24 days after birth. In case 3, involving a female D-TGA neonate with birth weight 2,240 g, ASO was performed 19 days after birth and delayed sternal closure was performed 4 days later. All six infants showed normal development during follow-up.

CONCLUSIONS

Early antenatal diagnosis of D-TGA in one fetus of a twin pregnancy is significantly important. A multidisciplinary team should carry individual evaluation and integrated management of the D-TGA twin and co-twin during the pregnancy and perinatal period. After birth, delayed ductus arteriosus closure in the D-TGA twins should be performed when necessary and individualized timings for arterial switch operation should be considered.

Common Genetic Variants Contribute to Risk of Transposition of the Great Arteries

RATIONALE

Dextro-transposition of the great arteries (D-TGA) is a severe congenital heart defect which affects approximately 1 in 4,000 live births. While there are several reports of D-TGA patients with rare variants in individual genes, the majority of D-TGA cases remain genetically elusive. Familial recurrence patterns and the observation that most cases with D-TGA are sporadic suggest a polygenic inheritance for the disorder, yet this remains unexplored.

OBJECTIVE

We sought to study the role of common single nucleotide polymorphisms (SNPs) in risk for D-TGA.

METHODS AND RESULTS

We conducted a genome-wide association study in an international set of 1,237 patients with D-TGA and identified a genome-wide significant susceptibility locus on chromosome 3p14.3, which was subsequently replicated in an independent case-control set (rs56219800, meta-analysis P=8.6x10-10, OR=0.69 per C allele). SNP-based heritability analysis showed that 25% of variance in susceptibility to D-TGA may be explained by common variants. A genome-wide polygenic risk score derived from the discovery set was significantly associated to D-TGA in the replication set (P=4x10-5). The genome-wide significant locus (3p14.3) co-localizes with a putative regulatory element that interacts with the promoter of WNT5A, which encodes the Wnt Family Member 5A protein known for its role in cardiac development in mice. We show that this element drives reporter gene activity in the developing heart of mice and zebrafish and is bound by the developmental transcription factor TBX20. We further demonstrate that TBX20 attenuates Wnt5a expression levels in the developing mouse heart.

CONCLUSIONS

This work provides support for a polygenic architecture in D-TGA and identifies a susceptibility locus on chromosome 3p14.3 near WNT5A. Genomic and functional data support a causal role of WNT5A at the locus.

Deep Phenotypic Analysis for Transposition of the Great Arteries and Prognosis Implication

Background

Transposition of the great arteries (TGA) consists of about 3% of all congenital heart diseases and 20% of cyanotic congenital heart diseases. It is always accompanied by a series of other cardiac malformations that affect the surgical intervention strategy as well as prognosis. In this study, we comprehensively analyzed the phenotypes of the patients who had TGA with concordant atrioventricular and discordant ventriculoarterial connections and explored their association with prognosis.

Methods and Results

We retrospectively reviewed 666 patients with a diagnosis of TGA with concordant atrioventricular and discordant ventriculoarterial connections in Fuwai Hospital from 1997 to 2019. Under the guidance of the Human Phenotype Ontology database, patients were classified into 3 clusters. The Kaplan‐Meier method was used to analyze the prognosis, and the Cox proportional regression model was used to investigate the risk factors. In this 666‐patient TGA cohort, the overall 5‐year survival rate was 94.70% (92.95%–96.49%). Three clusters with distinct phenotypes were obtained by the Human Phenotype Ontology database. Kaplan‐Meier analysis revealed a significant difference in freedom from reintervention among 3 clusters (P<0.001). To eliminate the effect of surgeries, we analyzed patients who only received an arterial switch operation and still found a significant difference in reintervention (P=0.019).

Conclusions

We delineated a big cardiovascular phenotypic profile of an unprecedentedly large TGA cohort and successfully risk stratified them to reveal prognostic significance. Also, we reported the outcomes of a large TGA population in China.

Chromosomal microarray detects genetic risks of neurodevelopmental disorders in newborns with congenital heart disease

OBJECTIVE

To compare the genetic testing results of neonates with CHD by chromosomal microarray to karyotyping and fluorescence in situ hybridisation analysis.

METHODS

This was a single-centre retrospective comparative study of patients with CHD and available genetic testing results admitted to the cardiac ICU between January, 2004 and December, 2017. Patients from 2004 to 2010 were tested by karyotyping and fluorescence in situ hybridisation analysis, while patients from 2012 to 2017 were analysed by chromosomal microarray.

RESULTS

Eight-hundred and forty-nine neonates with CHD underwent genetic testing, 482 by karyotyping and fluorescence in situ hybridization, and 367 by chromosomal microarray. In the karyotyping and fluorescence in situ hybridisation analysis group, 86/482 (17.8%) had genetic abnormalities detected, while in the chromosomal microarray group, 135/367 (36.8%) had genetic abnormalities detected (p < 0.00001). Of patients with abnormal chromosomal microarray results, 41/135 (30.4%) had genetic abnormality associated with neurodevelopmental disorders that were exclusively identified by chromosomal microarray. Conotruncal abnormalities were the most common diagnosis in both groups, with karyotyping and fluorescence in situ hybridisation analysis detecting genetic abnormalities in 26/160 (16.3%) patients and chromosomal microarray detecting abnormalities in 41/135 (30.4%) patients (p = 0.004). In patients with d-transposition of the great arteries, 0/68 (0%) were found to have genetic abnormalities by karyotyping and fluorescence in situ hybridisation compared to 7/54 (13.0%) by chromosomal microarray.

CONCLUSIONS

Chromosomal microarray identified patients with CHD at genetic risk of neurodevelopmental disorders, allowing earlier intervention with multidisciplinary care and more accurate pre-surgical prognostic counselling.

Risk factors for transposition of the great arteries in Saudi population

Objectives:

To assess potential risk factors and their effect on the development of transposition of the great arteries (TGA).

Methods:

A retrospective case-control study of all patients diagnosed with TGA between 1999 to 2016 at King Abdulaziz Medical City, Riyadh, Saudi Arabia. Age and gender-matched controls were selected. Risk factors, including consanguinity, gestational diabetes, family history of congenital heart disease, parental age, and maternal parity, were collected. Regression modeling was used to analyze the effects of risk factors on the development of TGA.

Results:

A total of 206 patients with transposition of the great arteries were enrolled in the study. Transposition of the great arteries cases were divided into simple and complex TGA. Selected healthy controls were 446. In the studied cases, consanguinity was found in 95 (46%) of cases, gestational diabetes was diagnosed in 36 (17.5%) mothers, and 35 (17%) had a confirmed family history of congenital heart disease. When risk factors of the cases were compared to the controls, consanguinity, gestational diabetes, maternal age, and parity were found to significantly increase the incidence of TGA.

Conclusion:

Our study revealed significant risk factors for the development of transposition of great arteries including first degree consanguineous marriages, gestational diabetes, family history of congenital cardiac anomalies, and increasing maternal age and parity. These factors increased the risk by at least 2 folds.

Double-Outlet Right Ventricle in a Chianina Calf

Congenital heart defects have been occasionally reported in cattle and ventricular septal defect represents the most frequently encountered anomaly. The double-outlet right ventricle is a rare congenital ventriculoarterial malformation reported only in certain cattle breeds. We describe this rare and complex congenital cardiac malformation observed in a 10-day-old male Chianina calf. Clinical examination showed tachycardia, tachypnea, jugular pulses, cyanotic mucous membranes and a right apical systolic murmur. Transthoracic echocardiography revealed severe dilation of the right-sided cardiac chambers with a markedly hypoplastic left ventricle. Both aorta and pulmonary artery leaving the right ventricle in parallel alignment with the tricuspid valve were suggestive of a dual-outlet right ventricle. Interventricular and interatrial septal defects were also visualized. Post-mortem examination confirmed the echocardiographic findings. To the authors' knowledge, a similar complex congenital cardiac malformation has not been reported in calves of the Chianina breed to date.

Familial co-occurrence of congenital heart defects follows distinct patterns

Aims

Congenital heart defects (CHD) affect almost 1% of all live born children and the number of adults with CHD is increasing. In families where CHD has occurred previously, estimates of recurrence risk, and the type of recurring malformation are important for counselling and clinical decision-making, but the recurrence patterns in families are poorly understood. We aimed to determine recurrence patterns, by investigating the co-occurrences of CHD in 1163 families with known malformations, comprising 3080 individuals with clinically confirmed diagnosis.

Methods and results

We calculated rates of concordance and discordance for 41 specific types of malformations, observing a high variability in the rates of concordance and discordance. By calculating odds ratios for each of 1640 pairs of discordant lesions observed between affected family members, we were able to identify 178 pairs of malformations that co-occurred significantly more or less often than expected in families. The data show that distinct groups of cardiac malformations co-occur in families, suggesting influence from underlying developmental mechanisms. Analysis of human and mouse susceptibility genes showed that they were shared in 19% and 20% of pairs of co-occurring discordant malformations, respectively, but none of malformations that rarely co-occur, suggesting that a significant proportion of co-occurring lesions in families is caused by overlapping susceptibility genes.

Conclusion

Familial CHD follow specific patterns of recurrence, suggesting a strong influence from genetically regulated developmental mechanisms. Co-occurrence of malformations in families is caused by shared susceptibility genes.

Left-right asymmetry in heart development and disease: forming the right loop

Extensive studies have shown how bilateral symmetry of the vertebrate embryo is broken during early development, resulting in a molecular left-right bias in the mesoderm. However, how this early asymmetry drives the asymmetric morphogenesis of visceral organs remains poorly understood. The heart provides a striking model of left-right asymmetric morphogenesis, undergoing rightward looping to shape an initially linear heart tube and align cardiac chambers. Importantly, abnormal left-right patterning is associated with severe congenital heart defects, as exemplified in heterotaxy syndrome. Here, we compare the mechanisms underlying the rightward looping of the heart tube in fish, chick and mouse embryos. We propose that heart looping is not only a question of direction, but also one of fine-tuning shape. This is discussed in the context of evolutionary and clinical perspectives.

Two Brothers With Dextro-Transposition of the Great Arteries

Dextro-transposition of the great arteries (d-TGA) is a common cause of cyanotic heart disease in neonates. Current thought is d-TGA is a sporadic occurrence in families with an unclear etiology. We describe a case of brothers with d-TGA. Genetic testing revealed that both are heterozygous for two gene variations that are associated with congenital heart disease.

Some Isolated Cardiac Malformations Can Be Related to Laterality Defects

Human beings are characterized by a left–right asymmetric arrangement of their internal organs, and the heart is the first organ to break symmetry in the developing embryo. Aberrations in normal left–right axis determination during embryogenesis lead to a wide spectrum of abnormal internal laterality phenotypes, including situs inversus and heterotaxy. In more than 90% of instances, the latter condition is accompanied by complex and severe cardiovascular malformations. Atrioventricular canal defect and transposition of the great arteries—which are particularly frequent in the setting of heterotaxy—are commonly found in situs solitus with or without genetic syndromes. Here, we review current data on morphogenesis of the heart in human beings and animal models, familial recurrence, and upstream genetic pathways of left–right determination in order to highlight how some isolated congenital heart diseases, very common in heterotaxy, even in the setting of situs solitus, may actually be considered in the pathogenetic field of laterality defects.

Situs Inversus Totalis: Single-Stage Anatomic Repair of Complex Congenital Heart Disease

Transposition of the great arteries occurs rarely in patients with mirror image dextrocardia and situs inversus, while the combination with severe coarctation of the descending aorta (CoA) makes the anatomy even more unusual. Therefore, it is not surprising that a case with such unusual and complicated anatomy presents unique problems when a primary definitive correction is attempted. We report a patient with situs inversus totalis and complex congenital heart disease including transposition of the great arteries and severe CoA who underwent successful complete, single-stage, anatomic correction.

Complete transposition of the great arteries with double outlet right ventricle in a dog

A 2-year old intact male Collie dog presented to the cardiology service at Oregon State University for evaluation of cyanosis and suspected congenital cardiac disease. Echocardiography revealed a constellation of cardiac abnormalities including a single large vessel exiting the right ventricle with a diminutive left ventricular outflow tract, a ventricular septal defect, and marked concentric right ventricular hypertrophy with moderate right atrial dilation. Cardiac-gated computed tomography confirmed the previous anomalies in addition to supporting a diagnosis of complete transposition of the great arteries, double outlet right ventricle, and pulmonic hypoplasia with a single coronary ostium. Prominent bronchoesophageal collateral vessels were concurrently identified. Clinically, the dog was stable despite mild cyanosis that worsened with exercise; no intervention was elected at the time. This case report describes a rare combination of congenital cardiac defects and the usefulness of cardiac-gated cross-sectional imaging in the anatomic diagnosis.

Genetic testing in congenital heart disease: A clinical approach

Congenital heart disease (CHD) is the most common type of birth defect. Traditionally, a polygenic model defined by the interaction of multiple genes and environmental factors was hypothesized to account for different forms of CHD. It is now understood that the contribution of genetics to CHD extends beyond a single unified paradigm. For example, monogenic models and chromosomal abnormalities have been associated with various syndromic and non-syndromic forms of CHD. In such instances, genetic investigation and testing may potentially play an important role in clinical care. A family tree with a detailed phenotypic description serves as the initial screening tool to identify potentially inherited defects and to guide further genetic investigation. The selection of a genetic test is contingent upon the particular diagnostic hypothesis generated by clinical examination. Genetic investigation in CHD may carry the potential to improve prognosis by yielding valuable information with regards to personalized medical care, confidence in the clinical diagnosis, and/or targeted patient follow-up. Moreover, genetic assessment may serve as a tool to predict recurrence risk, define the pattern of inheritance within a family, and evaluate the need for further family screening. In some circumstances, prenatal or preimplantation genetic screening could identify fetuses or embryos at high risk for CHD. Although genetics may appear to constitute a highly specialized sector of cardiology, basic knowledge regarding inheritance patterns, recurrence risks, and available screening and diagnostic tools, including their strengths and limitations, could assist the treating physician in providing sound counsel.

Primary Prevention of Sudden Cardiac Death in Adults with Transposition of the Great Arteries: A Review of Implantable Cardioverter-Defibrillator Placement

Transposition of the great arteries encompasses a set of structural congenital cardiac lesions that has in common ventriculoarterial discordance. Primarily because of advances in medical and surgical care, an increasing number of children born with this anomaly are surviving into adulthood. Depending upon the subtype of lesion or the particular corrective surgery that the patient might have undergone, this group of adult congenital heart disease patients constitutes a relatively new population with unique medical sequelae. Among the more common and difficult to manage are cardiac arrhythmias and other sequelae that can lead to sudden cardiac death. To date, the question of whether implantable cardioverter-defibrillators should be placed in this cohort as a preventive measure to abort sudden death has largely gone unanswered. Therefore, we review the available literature surrounding this issue.

D-transposition of the great arteries: the current era of the arterial switch operation

This paper aims to update clinicians on "hot topics" in the management of patients with D-loop transposition of the great arteries (D-TGA) in the current surgical era. The arterial switch operation (ASO) has replaced atrial switch procedures for D-TGA, and 90% of patients now reach adulthood. The Adult Congenital and Pediatric Cardiology Council of the American College of Cardiology assembled a team of experts to summarize current knowledge on genetics, pre-natal diagnosis, surgical timing, balloon atrial septostomy, prostaglandin E1 therapy, intraoperative techniques, imaging, coronary obstruction, arrhythmias, sudden death, neoaortic regurgitation and dilation, neurodevelopmental (ND) issues, and lifelong care of D-TGA patients. In simple D-TGA: 1) familial recurrence risk is low; 2) children diagnosed pre-natally have improved cognitive skills compared with those diagnosed post-natally; 3) echocardiography helps to identify risk factors; 4) routine use of BAS and prostaglandin E1 may not be indicated in all cases; 5) early ASO improves outcomes and reduces costs with a low mortality; 6) single or intramural coronary arteries remain risk factors; 7) post-ASO arrhythmias and cardiac dysfunction should raise suspicion of coronary insufficiency; 8) coronary insufficiency and arrhythmias are rare but are associated with sudden death; 9) early- and late-onset ND abnormalities are common; 10) aortic regurgitation and aortic root dilation are well tolerated; and 11) the aging ASO patient may benefit from "exercise-prescription" rather than restriction. Significant strides have been made in understanding risk factors for cardiac, ND, and other important clinical outcomes after ASO.

Genetic basis of congenital cardiovascular malformations

Cardiovascular malformations are a singularly important class of birth defects and due to dramatic improvements in medical and surgical care, there are now large numbers of adult survivors. The etiologies are complex, but there is strong evidence that genetic factors play a crucial role. Over the last 15 years there has been enormous progress in the discovery of causative genes for syndromic heart malformations and in rare families with Mendelian forms. The rapid characterization of genomic disorders as major contributors to congenital heart defects is also notable. The genes identified encode many transcription factors, chromatin regulators, growth factors and signal transduction proteins- all unified by their required roles in normal cardiac development. Genome-wide sequencing of the coding regions promises to elucidate genetic causation in several disorders affecting cardiac development. Such comprehensive studies evaluating both common and rare variants would be essential in characterizing gene-gene interactions, as well as in understanding the gene-environment interactions that increase susceptibility to congenital heart defects.

Risk of congenital heart disease in relatives of probands with conotruncal cardiac defects: an evaluation of 1,620 families

Current recurrence risk counseling for conotruncal cardiac defects (CTD) is based on empiric estimates from multiple studies. We examined the risk of congenital heart disease (CHD) in relatives of probands with CTDs to assist in counseling practices in the current era. One thousand six-twenty probands with CTDs and no reported chromosomal or genetic abnormalities were recruited sequentially. A three-generation pedigree was obtained for each proband by a genetic counselor detailing the presence and type of CHD in each family member. Risks and 95% confidence intervals (CI) were calculated for sub-groups of relatives based on degree of relationship for all probands and by individual lesion of the proband. For pairs of affected relatives, concordance rates were calculated. Severity of CHD in the affected relative was assessed. The risk of CHD was higher in siblings (4.4%, 95% CI 3.4-5.4) than in parents (1.5%, 95% CI 1.1-1.9). Risk varied by the cardiac lesion of the proband with the highest risk in first-degree relatives of probands with tetralogy of Fallot and the lowest in D-transposition of the great arteries. 39% of affected parents and 69% of affected siblings had a concordant lesion (i.e., CTD). Most affected siblings of probands with severe CTDs had complex defects (58%), whereas very few affected parents had complex defects (20%). These data suggest that recurrence risk varies by lesion and relationship, with substantial concordance observed by cardiac lesion and complexity of disease, particularly among siblings. These findings contribute to risk counseling in the current era.

Transposition of great arteries: new insights into the pathogenesis

Transposition of great arteries (TGA) is one of the most common and severe congenital heart diseases (CHD). It is also one of the most mysterious CHD because it has no precedent in phylogenetic and ontogenetic development, it does not represent an alternative physiological model of blood circulation and its etiology and morphogenesis are still largely unknown. However, recent epidemiologic, experimental, and genetic data suggest new insights into the pathogenesis. TGA is very rarely associated with the most frequent genetic syndromes, such as Turner, Noonan, Williams or Marfan syndromes, and in Down syndrome, it is virtually absent. The only genetic syndrome with a strong relation with TGA is Heterotaxy. In lateralization defects TGA is frequently associated with asplenia syndrome. Moreover, TGA is rather frequent in cases of isolated dextrocardia with situs solitus, showing link with defect of visceral situs. Nowadays, the most reliable method to induce TGA consists in treating pregnant mice with retinoic acid or with retinoic acid inhibitors. Following such treatment not only cases of TGA with d-ventricular loop have been registered, but also some cases of congenitally corrected transposition of great arteries (CCTGA). In another experiment, the embryos of mice treated with retinoic acid in day 6.5 presented Heterotaxy, suggesting a relationship among these morphologically different CHD. In humans, some families, beside TGA cases, present first-degree relatives with CCTGA. This data suggest that monogenic inheritance with a variable phenotypic expression could explain the familial aggregation of TGA and CCTGA. In some of these families we previously found multiple mutations in laterality genes including Nodal and ZIC3, confirming a pathogenetic relation between TGA and Heterotaxy. These overall data suggest to include TGA in the pathogenetic group of laterality defects instead of conotruncal abnormalities due to ectomesenchymal tissue migration.

[Congenital heart defects of the septa, endocardial cushions and the conotruncus]

During embryological development the heart develops from a simple tube into a complex fully developed heart with four chambers. Hence all congenital heart defects develop before the ninth week of gestation. Currently a steadily increasing number of genetic mutations have been found to be responsible for congenital heart defects. Nevertheless, up to now it has been impossible to diagnose a heart defect just on the basis of molecular pathology. Despite the current excellent prenatal and postnatal ultrasound diagnostics, the post-mortem examination is still the gold standard for the diagnosis of complex heart malformations. However, this requires knowledge of the pathomorphology of the heart malformation in question. Therefore, characteristic and distinguishing features of septal defects including atrioventricular septal defects are presented, especially as the latter are part of complex heart defects, such as conotruncal heart malformations.

Familial recurrence of congenital heart diseases

Familial recurrence of congenital heart disease (CHD), in particular, d-transposition of great arteries (d-TGA) is rare. However, there have been several reports in the literature of sibling recurrence of total anomalous pulmonary venous return (TAPVR). This is the first case report in the literature, describing mother to offspring recurrence of d-TGA. We describe two cases of non-syndromic CHD with mother to offspring and sibling recurrence. The first case is an antenatally diagnosed d-TGA on fetal echocardiogram at 25 weeks of gestational age in the offspring of a 30-year-old mother with d-TGA. The second case is a sibling reoccurrence of TAPVR diagnosed antenatally at 30 weeks of gestational age, with supradiaphragmatic TAPVR on fetal echocardiogram in a mother, whose first child was diagnosed with infradiaphragmatic TAPVR in infancy.

Recurrence of congenital heart disease in cases with familial risk screened prenatally by echocardiography

Objectives. To evaluate the recurrence of congenital heart disease (CHD) in pregnant women with familial risk who had been referred for fetal echocardiography. Material and Methods. 1634 pregnancies from 1483 women with familial history of CHD in one or more relatives were studied. Fetal cardiologic diagnosis was compared with postnatal findings at 6 months or at autopsy. Results. Total recurrence rate of CHD was 3.98%, 4.06% in single familial risk, 2.9% in double, and 5% in multiple risk. It was 3.5% in case of one previously affected child; 4.5% with 2 children; 5.2% with the mother alone affected and 7,5% with father alone affected and 3.5% with a single distant relative. Exact concordance of CHD was found in 21.5% and a partial concordance in 20% of cases. Conclusions. Our data show a higher recurrence rate of CHD than previously published data and high relative risk ratios compared to normal population.

Complete transposition of the aorta and pulmonary artery in a Belgian Blue crossbreed calf: a case report

BACKGROUND

Complete transposition of the great arteries is a congenital cardiac malformation occasionally encountered in cattle and other species. The objective of the present report was to provide a detailed clinical, echocardiographic and post mortem description of a calf presenting with this condition.

CASE PRESENTATION

A 6-week old male Belgian Blue cross-breed calf was examined for respiratory distress and exercise intolerance. The patient was bright, alert and responsive without any neurologic abnormalities but was exercise intolerant, had marked cyanosis, tachycardia, tachypnea, a pansystolic heart murmur as well as a bilaterally palpable thrill over the heart. Arterial blood gas analysis revealed marked hypoxemia (PaO(2)=23 mmHg, O(2)sat=41.1%), mild hypercapnia and compensated respiratory acidosis. Echocardiographic examination revealed a complete transposition of the great arteries in combination with a ventricular septal defect through which blood shunted bidirectionally. Cardiac catheterization confirmed that arterialization of blood of the systemic circulation solely occurred in the right ventricle through blood shunting from the left into the right ventricle. Results of post mortem examination are presented.

CONCLUSION

Complete transposition of the great arteries is a cyanotic congenital anomaly repeatedly reported in calves that should be considered as differential diagnosis in patients presenting with hypoxemia more severe than commonly encountered with other congenital cyanotic heart conditions. We give a comprehensive summary of the clinical presentation, diagnostic work-up and post mortem examination of a Belgian Blue cross-breed calf with complete transposition of the great arteries.

Shells and heart: are human laterality and chirality of snails controlled by the same maternal genes?

The body of most animals display left-right asymmetry of internal organs. Alteration of such asymmetry results in severe congenital defects particularly affecting the cardiovascular system. The earliest known genes involved in asymmetry, the Nodal signalling cascade, are expressed asymmetrically during embryonic development. Nodal was discovered in the mouse, but orthologs (also involved in left-right specification) were reported in ascidians, sea-urchins, and snails. Mutations in Nodal-pathway genes cause alteration of several aspects of chirality, but not entirely mirror phenotypes of the body. Other factors upstream of nodal must be involved in the generation of left-right asymmetry. In snails, breeding experiments have demonstrated that chirality is controlled by a nuclear gene with maternal effect. Given the available evidence, we propose that an evolutionarily conserved genetic basis of chirality (the same that controls left-right asymmetry in snails) is a major synapomorphy of the Bilateria. This hypothesis fits with the observation that: (a) the proportion of patients with heterotaxy and a detected mutation in a gene of the Nodal cascade is actually low, and (b) horizontal recurrence of laterality defects is remarkably more frequent than vertical recurrence, and includes a notable number of affected sibs and/or repeated abortions from unaffected mothers. Identification of the maternal gene(s) involved will allow for the identification of homozygous females at risk of having affected children and spontaneous abortions, and would provide a general medical framework for understanding the genetics of most alterations of chirality.

Hif1α down-regulation is associated with transposition of great arteries in mice treated with a retinoic acid antagonist

BACKGROUND

Congenital heart defect (CHD) account for 25% of all human congenital abnormalities. However, very few CHD-causing genes have been identified so far. A promising approach for the identification of essential cardiac regulators whose mutations may be linked to human CHD, is the molecular and genetic analysis of heart development. With the use of a triple retinoic acid competitive antagonist (BMS189453) we previously developed a mouse model of congenital heart defects (81%), thymic abnormalities (98%) and neural tube defects (20%). D-TGA (D-transposition of great arteries) was the most prevalent cardiac defect observed (61%). Recently we were able to partially rescue this abnormal phenotype (CHD were reduced to 64.8%, p = 0.05), by oral administration of folic acid (FA). Now we have performed a microarray analysis in our mouse models to discover genes/transcripts potentially implicated in the pathogenesis of this CHD.

RESULTS

We analysed mouse embryos (8.5 dpc) treated with BMS189453 alone and with BMS189453 plus folic acid (FA) by microarray and qRT-PCR. By selecting a fold change (FC) ≥ ± 1.5, we detected 447 genes that were differentially expressed in BMS-treated embryos vs. untreated control embryos, while 239 genes were differentially expressed in BMS-treated embryos whose mothers had also received FA supplementation vs. BMS-treated embryos. On the basis of microarray and qRT-PCR results, we further analysed the Hif1α gene. In fact Hif1α is down-regulated in BMS-treated embryos vs. untreated controls (FCmicro = -1.79; FCqRT-PCR = -1.76; p = 0.005) and its expression level is increased in BMS+FA-treated embryos compared to BMS-treated embryos (FCmicro = +1.17; FCqRT-PCR = +1.28: p = 0.005). Immunofluorescence experiments confirmed the under-expression of Hif1α protein in BMS-treated embryos compared to untreated and BMS+FA-treated embryos and, moreover, we demonstrated that at 8.5 dpc, Hif1α is mainly expressed in the embryo heart region.

CONCLUSIONS

We propose that Hif1α down-regulation in response to blocking retinoic acid binding may contribute to the development of cardiac defects in mouse newborns. In line with our hypothesis, when Hif1α expression level is restored (by supplementation of folic acid), a decrement of CHD is found. To the best of our knowledge, this is the first report that links retinoic acid metabolism to Hif1α regulation and the development of D-TGA.

New mutations in ZFPM2/FOG2 gene in tetralogy of Fallot and double outlet right ventricle

Conotruncal defects (CTDs) represent 15-20% of all congenital heart defects. Mutations in a number of genes have been associated with CTD in humans and animal models. We investigated the occurrence and the prevalence of GATA4, NKX2.5, ZFPM2/FOG2, GDF1, and ISLET1 gene mutations in a large cohort of individuals with CTD, including tetralogy of Fallot with or without pulmonary atresia (TOF, 178 patients), double outlet right ventricle (DORV, 13 patients), and truncus arteriosus (11 patients). Denaturing high-performance liquid chromatography (DHPLC) analysis followed by bidirectional sequencing disclosed no putative pathogenic mutation in GATA4, ISLET1, and GDF1 genes. Two novel (Ile227Val, Met544Ile) and one previously reported (Glu30Gly) possibly pathogenic missense variants were identified in the ZFPM2/FOG2 gene in 3 sporadic patients of 202 (1.5%) with CTD, including 1 of 178 (0.6%) with TOF and 2 of 13 (15.4%) with DORV. Mutation analysis also detected one known missense change (Arg25Cys) in NKX2.5 gene in two (1.1%) sporadic patients with TOF. These sequence alterations were found to be absent in 500 population-matched controls. In conclusion, the present results (i) indicate and confirm that mutations in the GATA4, GDF1, and ISLET1 genes are not major determinants in the pathogenesis of TOF, (ii) provide supportive evidence of an association between ZFPM2/FOG2 gene and TOF/DORV, and (iii) provide additional examples of the possible contribution of the Arg25Cys change in the NKX2.5 to a small number of TOF cases.

Genetic factors in non-syndromic congenital heart malformations

The genetic defect in most patients with non-syndromic congenital heart malformations (CHM) is unknown, although more than 40 different genes have already been implicated. Only a minority of CHM seems to be due to monogenetic mutations, and the majority occurs sporadically. The multifactorial inheritance hypothesis of common diseases suggesting that the cumulative effect of multiple genetic and environmental risk factors leads to disease, might also apply for CHM. We review here the monogenic disease genes with high-penetrance mutations, susceptibility genes with reduced-penetrance mutations, and somatic mutations implicated in non-syndromic CHM.

Increased prevalence of cardiovascular defects among 56,709 California twin pairs

This study compared the prevalence of cardiovascular defects in twin and singleton births and explored the influences of zygosity (monozygotic and dizygotic) and maternal age (<35 and >or=35 years of age) on concordance. Data on twin and singleton infants with (n = 628 twin pairs and n = 14,078 singletons) and without (n = 53,974 twin pairs and n = 4,858,255 singletons) cardiovascular defects were obtained from the California Birth Defects Monitoring Program and the California vital statistics birth and fetal death records during the period 1983-2003. Prevalence ratios (PR) (prevalence of twin/singleton) and approximate 95% confidence intervals were calculated for 16 congenital cardiovascular categories. Poisson regression techniques using log-linear models were employed to assess whether the probability of concordance of defects within each cardiovascular category varied by zygosity or maternal age. An increased prevalence was observed in twins compared to singletons in all 16 cardiovascular categories. Seven of the cardiovascular categories had at least double the prevalence in twins compared to singletons. Like-sex twins, as a proxy of monozygosity, had an increased prevalence of cardiovascular defects compared to unlike sex twins. Probabilities of concordance for flow lesions were higher among monozygotic than dizygotic twins. Our study provides evidence that twinning is associated with more cardiovascular defects than singletons. Increased concordance for flow lesions in monozygotic twins was observed, an observation that is in agreement with findings from familial recurrence studies of cardiovascular defects.

An infant with transposition and cystic fibrosis

We report an infant with transposition, with the circumflex artery arising from the right coronary artery, who was diagnosed with cystic fibrosis following the occurrence of meconium ileus in the postoperative period.

Improving Detection of Transposition of the Great Arteries in Routine Obstetric Sonographic Screening

Transposition of the great arteries (TGA) is a congenital malformation in which the pulmonary artery arises from the left ventricle and the aorta arises from the right ventricle. At birth, when the ductus arteriosus and foramen ovale close, severe hypoxemia results, and intervention is necessary. Prenatal diagnosis of TGA is associated with a significant decrease in mortality and morbidity. Currently, detection of TGA is low. This literature review explores techniques for detecting TGA, the importance of prenatal diagnosis, scanning techniques, new technologies, and possible maternal risk factors.

Congenital cardiac disease and inbreeding: specific defects escape higher risk due to parental consanguinity

AIMS

To test on a large cohort whether parental consanguinity varies among different types of congenitally malformed hearts.

METHODS AND RESULTS

Between 1 May, 1999, and 28 February, 2006, a large cohort of 1585 newly diagnosed cases with non-syndromic congenitally malformed heart was enrolled at the National Register of Paediatric and Congenital Heart Disease, Lebanese Society of Cardiology, Beirut. Another group, made up of 1979 cases referred to the National Register of Paediatric and Congenital Heart Disease, but free of any malformation, and with a rate of consanguinity similar to a recent survey made by UNICEF in Lebanon, was used for the purposes of control. We used the Chi-squared test, and ratio of risk, to compare the groups. Subgroups with first degree cousins, first plus second degree cousins, and any degree of consanguinity, are significantly larger in the cohort with congenitally malformed hearts than in the control cohort, with proportions of 19.4%, 25.7%, and 27.4% versus 14.4%, 20.3%, and 23.9%, respectively. Those with tetralogy of Fallot, valvar aortic stenosis, and atrial septal defect have a significantly higher percentage of consanguineous parents than do the controls. By contrast, this is not the case for those with atrioventricular septal defect and common atrioventricular junction ("atrioventricular canal"), or discordant ventriculo-arterial connections ("transposition"). These differences persist when the types of congenital cardiac defect types are pooled according to presumed embryological processes. Those with hypoplasia of the left heart have increased parental consanguinity, but not the group of various types of discordant ventriculo-arterial connections.

CONCLUSION

Only some types of congenitally malformed hearts have an increased percentage of parental consanguinity, suggesting that those types with no increased risk due to parental consanguinity are determined by genetic factors that are X-linked or exclusively autosomal dominant.

Elucidation of penetrance variability of aZIC3mutation in a family with complex heart defects and functional analysis ofZIC3mutations in the first zinc finger domain

We studied a series of 42 cases of transposition of the great arteries (TGA), a complex heart defect (CHD) that is two times more prevalent in males than in females. A mutation in the X chromosome at the ZIC3 gene was found in two affected siblings (one male, one female) and their unaffected mother. A second factor, skewed X-inactivation pattern explained the discrepancy between the daughter/mother phenotype. In this family, the missense mutation (p.W255G) was found in the first zinc finger of ZIC3, a domain that is relatively specific to each of the five human ZIC genes. It was tested further along with two other mutations of this domain (p.C253S and p.H286R). In transfected 3T3 cells, mutants p.W255G and p.H286R expressed lower protein levels, and an increased protein degradation (p.W255G only). Moreover, mutants p.C253S and p.W255G had a decreased transcription activation of the TK-luciferase reporter gene. Nuclear translocation of the three ZIC3 mutants varied considerably depending on the experimental models. Finally, p.W255G and p.H286R showed diminished activities for both left-right axis disturbance and neural crest induction in Xenopus embryos. These results suggest that mutations in the first zinc finger of ZIC3 mildly affect several functions of the protein.

Persistent Pulmonary Hypertension of the Newborn With Transposition of the Great Arteries

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) in patients with transposition of the great arteries (TGA) is reported to be a high-risk and often therapy-resistant condition, associated with a high mortality. However, data on its incidence and prognosis are scarce and originate mostly from the era before introduction of inhaled nitric oxide (iNO) therapy for PPHN.

METHODS

This is a retrospective study of consecutive newborns with TGA, admitted to a tertiary cardiac and neonatal intensive unit over a 10-year period. In this period, iNO therapy was available.

RESULTS

Fourteen out of 112 patients with TGA (12.5%) presented with associated PPHN. The PPHN occurred more frequently in patients with TGA and intact ventricular septum (IVS) compared with those with TGA and ventricular septal defect (13 out of 83 patients versus one out of 29 patients, respectively; p = 0.06, Fisher exact test). Of those newborns, six presented with severe PPHN, whereas eight presented with mild-to-moderate PPHN. Despite currently available treatment modalities, including iNO, four out of 14 patients died before corrective surgical procedures were considered to be an option (TGA/PPHN preoperative mortality 28.6%). These included three out of six patients (50%) with severe PPHN and one out of eight (12.5%) with mild-to-moderate PPHN.

CONCLUSIONS

The combination of TGA with PPHN is a serious and often fatal condition. It may jeopardize the usually favorable outcome of newborns with TGA. Despite the introduction of iNO therapy, the combination of TGA and PPHN remains a condition with unacceptable high mortality (in our series). Additional treatment strategies need to be investigated.