Transposition of the great arteries in asplenia and polysplenia phenotypes

Transpositions of the great arteries versus aortic dextropositions. A review of some embryogenetic and morphological aspects

This review examines and discusses the morphology and embryology of two main groups of conotruncal cardiac malformations: (a) transposition of the great arteries (complete transposition and incomplete/partial transposition namely double outlet right ventricle), and (b) aortic dextroposition defects (tetralogy of Fallot and Eisenmenger malformation). In both groups, persistent truncus arteriosus was included because maldevelopment of the neural crest cell supply to the outflow tract, contributing to the production of the persistent truncus arteriosus, is shared by both groups of malformations. The potentially important role of the proximal conal cushions in the rotatory sequence of the conotruncus is emphasized. Most importantly, this study emphasizes the differentiation between the double-outlet right ventricle, which is a partial or incomplete transposition of the great arteries, and the Eisenmenger malformation, which is an aortic dextroposition. Special emphasis is also given to the leftward shift of the conoventricular junction, which covers an important morphogenetic role in both aortic dextropositions and transposition defects as well as in normal development, and whose molecular genetic regulation seems to remain unclear at present. Emphasis is placed on the distinct and overlapping roles of Tbx1 and Pitx2 transcription factors in modulating the development of the cardiac outflow tract.

The Secrets of the Frogs Heart

The heart of the African clawed frog has a double-inlet and single-outlet ventricle supporting systemic and pulmonary circulations via a truncus, and a lifespan of 25-30 years. We sought to understand the unique cardiac anatomic and physiologic characteristics, with balanced circulation and low metabolic rate, by comparing the basic anatomy structures with focused echocardiography and cardiac magnetic resonance imaging. Twenty-four adult female African clawed frogs were randomly subjected to anatomic dissection (n = 4), echocardiography (n = 10), and cardiac magnetic resonance (n = 10). All anatomical features were confirmed and compared with echocardiography and cardiac magnetic resonance imaging. The main characteristics of the cardiovascular circulation in frogs are the following: Intact interatrial septum, with two separate atrio-ventricular valves, preventing atrial mixing of oxygenated and desaturated blood. Single spongiform ventricular cavity, non-conducive for homogeneous mixing. Single outlet with a valve-like mobile spiral structure, actively streaming into systemic and pulmonary arteries. Intact interatrial septum, spongiform ventricle, and valve-like spiral in the conus arteriosus are likely responsible for balanced systemic and pulmonary circulation in frogs, in spite of double-inlet and single-outlet ventricle.

High Familial Recurrence of Congenital Heart Defects in Laterality Defects Patients: An Evaluation of 184 Families

As a rare disease with genetic pathogenesis, observational study about familial CHD recurrence risk on CHD patients with laterality defects is lacking. This study aimed to investigate familial recurrence among families of patients with CHD and laterality defects, and compare them with CHD patients without laterality defects. A total of 184 patients with CHD and laterality defects treated in Cardiovascular Center, Children's Hospital of Fudan University were observed from 2008 to 2019. A detailed family history was documented by trained staff using questionnaires, and information about the subtypes of CHD and laterality defects was also collected. In addition, positive family history information, including all three degrees relatives and all affected family members, was reconfirmed by trained medical staff through face-to-face interviews, telephone interviews, and letter return visits. Of the 184 included patients, 30 had at least one family member (from among three linear generations and distant relatives) with CHD. The familial recurrence rate of CHD in our cohort was 16.3% (30/184), which was higher than the 3.3% (67/2024) of patients with CHD without laterality defects. This result shows that the recurrence rate among the first-, second-, and third-degree relatives was 11.7% (11/94), 1.5% (3/204), and 3.1% (6/91) and that the recurrence rate among siblings (21.4%, 9/42) was higher than that among parents (3.8%, 2/52). The familial recurrence risk of CHD among patients with CHD and laterality defects is high, which is consistent with the previous study that reported a high familial recurrence of heterotaxy of 10%. First-degree relatives have a higher recurrence rate than second- and third-degree relatives, especially siblings. These findings have important significance for prenatal screening, intervention, and genetic counseling in the Chinese population, but may not be generalizable to other populations that may have different rates of familial and sporadic cases.

Transposition of the great arteries: A laterality defect in the group of heterotaxy syndromes or an outflow tract malformation?

BACKGROUND/AIM

Transposition of the great arteries (TGA) is traditionally classified as a "conotruncal heart defect", implying that TGA evolves from abnormal development of the outflow tract (OFT) of the embryonic heart. However, recently published genetic data suggest that TGA may be linked to laterality gene defects rather than OFT gene defects. The aim of our study was to clarify whether there is any statistically significant link between TGA and clinically diagnosed laterality defects (heterotaxy).

METHODS

Retrospective cross-sectional analysis of 533 patients diagnosed with TGA at our cardiac center over a period of 13 years (2002-2015). Hospital informatics and digital data recording systems were used for collecting patients' data and all patients were reviewed to check the echocardiograms for verification of the diagnosis, type (TGA, congenitally corrected TGA (ccTGA), and levo-position of the great arteries (LGA)), complexity of TGA, and all other variables (e.g., abdominal organ arrangement, cardiac position, presence or absence of other cardiac defects).

RESULTS

Of 533 TGA patients, 495 (92.9%) had the usual arrangement of the internal organs, 21 (3.9%) had mirror-imagery, 7 (1.3%) had left and 10 (1.8%) had right isomerism. 444 (83.3%) patients had TGA. The number of patients who had usual visceral arrangement in each TGA type was: 418 (94.1%) in TGA, 49 (92.4%) in ccTGA, and 28 (77.7%) in LGA. 6 (1.4%) TGA patients, 4 (11.1%) patients with LGA were found to have right isomerism, while no ccTGA patient presented with this asymmetry. 4 (0.9%) TGA patients, 1 (1.9%) ccTGA patient and 2 (5.6%) patients with LGA had left isomerism. Heterotaxy (mirror-imagery, left and right isomerism) was more associated with LGA than TGA or ccTGA with a statistically significant difference (P value of 0.001).

CONCLUSION

In contrast to recently published genetic data, our morphological data do not disclose a significant link between TGA and heterotaxy.

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.

Transposition of the great arteries - a phenotype associated with 16p11.2 duplications?

Genetic analyses of patients with transposition of the great arteries have identified rare copy number variations, suggesting that they may be significant to the aetiology of the disease. This paper reports the identification of a 16p11.2 microduplication, a variation that has yet to be reported in association with transposition of the great arteries. The 16p11.2 microduplication is associated with autism spectrum disorder and developmental delay, but with highly variable phenotypic effects. Autism and attention deficit disorders are observed more frequently in children with congenital heart disease than in the general population. Neonatal surgery is proposed as a risk factor, but as yet unidentified genetic abnormalities should also be taken into account. Thus, congenital heart abnormalities may constitute a part of the phenotypic spectrum associated with duplications at 16p11.2. We suggest chromosomal microarray be considered part of the diagnostic work-up in patients with transposition of the great arteries.

DNA methyltransferase 1 rs16999593 genetic polymorphism decreases risk in patients with transposition of great arteries

Complete transposition of the great arteries (TGA) is the most frequent cyanotic heart defect diagnosed in neonates. However, the exact etiology of TGA is unknown. The aim of the present study was to assess the association of TGA pathogenesis with single nucleotide polymorphisms (SNPs) in DNA methyltransferases (DNMTs)-1 and 3a- in Chinese children. We genotyped 5 SNPs (rs16999593, rs16999358, and rs2228611 in DNMT1; and rs2276599 and rs2276598 in DNMT3A) in 206 patients with complete TGA and 252 healthy children. Statistical analysis was performed to explore the association of the 5 SNPs with complete TGA susceptibility. Compared with the T/T and C/C genotypes, the heterozygous genotype C/T of rs16999593 correlated with a decreased risk for complete TGA under codominant (OR=0.46; 95% CI=0.29-0.72), dominant (OR=0.58; 95% CI=0.38-0.88), and overdominant (OR=0.44; 95% CI=0.28-0.68) models. In contrast, the genotype C/C of rs16999593 correlated with a higher risk for TGA under a recessive model (OR=3.15; 95% CI=1.14-8.68) compared with the T/T and C/T genotypes. Furthermore, the TGC, TGT, CGC, and CGT haplotypes of DNMT1 did not differ significantly between the two groups, whereas the frequency of the TAC haplotype was lower in the case group (OR<1; P=0.002). No significant differences in the frequencies of the TC, CC, TT, and CT haplotypes of DNMT3A were found between the two groups. Furthermore, logistic regression showed that sex and the rs16999358 SNP were two independent risk factors for complete TGA. Overall, the C/T genotype of the rs16999593 SNP in DNMT1 might decrease the risk of complete TGA pathogenesis in the Southern Chinese population.

Mechanism responsible for D-transposition of the great arteries: Is this part of the spectrum of right isomerism?

D-transposition of the great arteries (TGA) is one of the most common conotruncal heart defects at birth and is characterized by a discordant ventriculoarterial connection with a concordant atrioventricular connection. The morphological etiology of TGA is an inverted or arrested rotation of the heart outflow tract (OFT, conotruncus), by which the aorta is transposed in the right ventral direction to the pulmonary trunk. The rotational defect of the OFT is thought to be attributed to hypoplasia of the subpulmonic conus, which originates from the left anterior heart field (AHF) residing in the mesodermal core of the first and second pharyngeal arches. AHF, especially on the left, at the early looped heart stage (corresponding to Carnegie stage 10-11 in the human embryo) is one of the regions responsible for the impediment that causes TGA morphology. In human or experimentally produced right isomerism, malposition of the great arteries including D-TGA is frequently associated. Mutations in genes involving left-right (L-R) asymmetry, such as NODAL, ACTRIIB and downstream target FOXH1, have been found in patients with right isomerism as well as in isolated TGA. The downstream pathways of Nodal-Foxh1 play a critical role not only in L-R determination in the lateral plate mesoderm but also in myocardial specification and differentiation in the AHF, suggesting that TGA is a phenotype in heterotaxia as well as the primary developmental defect of the AHF.

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.

Double outlet right ventricle versus aortic dextroposition: morphologically distinct defects

This study concerns the morphological differentiation between double outlet right ventricle (DORV) and aortic dextroposition (AD) defects, namely tetralogy of Fallot and Eisenmenger anomaly. Indeed, despite the similar condition in terms of sequential ventriculo-arterial connections, DORV and AD are two distinct morphological entities. It is proposed that the borderline between these two groups of malformations is represented by the specific insertion of the infundibular septum into the left anterior cranial division of the septomarginal trabeculation (or septal band) occurring in ADs and lacking in DORV. Furthermore, the spiraliform versus straight parallel arrangement of the great arteries in the two groups of anomalies is emphasized as an additional and distinctive morphological feature. Emphasis is also given to the association of straight parallel great arteries conotruncal malformations, DORV and transposition of the great arteries, with the asplenia type of heterotaxy laterality defects. Within this context, the absence of subaortic ventricular septal defect and concomitantly of spiraliform great arteries in the asplenia group of heterotaxy anomalies, as detected by this study, further substantiates our belief of not mixing collectively the ADs with the DORV in clinico-pathological diagnosis.

Biliary atresia with associated structural malformations in Canadian infants

BACKGROUND

Biliary atresia (BA) is associated with extrahepatic congenital malformations in a minority of affected infants. The term commonly applied to this subgroup is 'BASM' for biliary atresia splenic malformation syndrome, as spleen abnormalities are prominent.

AIMS AND METHODS

To examine clinical outcome in Canadian BA patients with extrahepatic congenital malformations in the Canada-wide BA database of patients born between 1985 and 2002, and additionally, to recharacterized the syndrome. Patients had ≥1 of the following: a/polysplenia, abnormal abdominal situs, intestinal malrotation, abdominal vascular anomaly or congenital heart disease.

RESULTS

Among 328 BA patients, 44 (13%) had associated congenital abnormalities. Intra-abdominal anomalies included polysplenia (n=25), abnormal abdominal situs (n=9), intestinal malrotation (n=19), portal vein anomaly (n=12), hepatic artery anomaly (n=3) and inferior vena cava interruption (n=20). Twenty-six patients had cardiac malformations including pulmonary stenosis (n=11), ventricular septal defect (n=10), atrial septal defect (n=7), total anomalous pulmonary venous return (n=3), double outlet right ventricle (n=3), tetralogy of Fallot (n=2), atrioventricular canal (n=2), dextrocardia (n=2), bicuspid aortic valve (n=2), hypoplastic left heart (n=1) and partial anomalous pulmonary venous return (n=1). Age at Kasai operation, performance of liver transplant, overall survival, post-Kasai native liver survival and transplant survival were comparable to isolated BA. Presence of polysplenia or complex cardiac disease did not reduce post-Kasai native liver survival. Three patients had ≥2 typical abnormalities without polysplenia: thus, splenic malformations are not essential to this BA subgroup. Hierarchical cluster analysis demonstrated characteristic abnormalities grouped in a multiplicity of combinations, consistent with a spectrum of defective lateralization.

CONCLUSION

We suggest that the acronym 'BASM' be redefined as 'biliary atresia structural malformation'.

Transposition of the great arteries

PURPOSE OF REVIEW

Transposition of the great arteries (TGA) is a complex congenital heart defect usually defined within the group of conotruncal defects. Some astonishing similarities between the spiral pattern of great arteries and the spiral pattern of snail shells and a possible common genetic mechanism of normal and abnormal anatomical aspects of the heart and shells are examined.

RECENT FINDINGS

The pulmonary vascular resistances in TGA and ventricular septal defect (VSD) need to be assessed before surgery, as they are the key factors for the success of the surgical procedure. A noninvasive method has been proposed to assess this key factor. A first series of the pregnancy outcomes in young women after arterial switch operation (ASO) is promising and encouraging for even better results. The systemic failing right ventricle (RV) is treated empirically using the same drugs and devices as for the failing left ventricle. The rationale for the treatment of ventricular failure, similar or different for predominantly right or left ventricle, is debated. The results of Rastelli operation are compared with those of the other surgical procedures for the treatment of TGA, VSD and pulmonary stenosis, namely reparation a l'ètage ventriculaire and Nikaidoh interventions.

SUMMARY

This review outlines some new aspects of the embryologic cardiac development and reveals astonishing similarities between heart and shells. A new diagnostic noninvasive method for measuring pulmonary vascular resistances, the pregnancy outcome of a first series of women operated by ASO, and the pharmacological and cardiac devices used in the failing systemic RV are presented. Finally, the review comments on the Rastelli operation as the 'gold standard' for TGA, VSD, and pulmonary stenosis.

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.

Familial recurrence of nonsyndromic congenital heart defects in first degree relatives of patients with deletion 22q11.2

The majority of nonsyndromic congenital heart defects (CHDs) are considered to follow a multifactorial model of inheritance. Multiple family members affected by CHD can occasionally be detected, and the involvement of several genetic loci interacting with environmental factors is suspected to be implicated. The DiGeorge/velo-cardio-facial syndrome related to microdeletion 22q11.2 (del22) is a genetic condition associated with CHD in most of the cases. We report here on five pedigrees of patients with del22, showing occurrence of nonsyndromic CHD in a first-degree relative of the proband case. Familial aggregation of syndromic and nonsyndromic CHD as observed in our series is to be considered as an unusual pattern of recurrence. The interaction between several different genes and environmental factors, a familial susceptibility predisposing to a specific cardiac malformation, or chance association can all be hypothesized searching an explanation for these particular observations.