Human Genetics of Defects of Situs.

Defects of situs are associated with complex sets of congenital heart defects in which the normal concordance of asymmetric thoracic and abdominal organs is disturbed. The cellular and molecular mechanisms underlying the formation of the embryonic left-right axis have been investigated extensively in the past decade. This has led to the identification of mutations in at least 33 different genes in humans with heterotaxy and situs defects. Those mutations affect a broad range of molecular components, from transcription factors, signaling molecules, and chromatin modifiers to ciliary proteins. A substantial overlap of these genes is observed with genes associated with other congenital heart diseases such as tetralogy of Fallot and double-outlet right ventricle, d-transposition of the great arteries, and atrioventricular septal defects. In this chapter, we present the broad genetic heterogeneity of situs defects including recent human genomics efforts.

Clinical Presentation and Therapy of Anomalies of the Situs.

Situs abnormalities may occur in many and most often more complex congenital cardiac malformations. These conditions are collectively referred to as heterotaxy syndromes, derived from the Greek words "heteros" meaning different and "taxos" meaning orientation or arrangement. Clinically, heterotaxy spectrum encompasses defects in the left-right laterality and arrangement of visceral organs. "Situs" is derived from Latin and is the place where something exists or originates. In human anatomy, situs can be solitus (derived from Latin, meaning "normal"), inversus, or ambiguus. Heterotaxy syndrome represents an intermediate arrangement of internal organs between situs solitus and situs inversus, also known as "situs ambiguous." Situs ambiguus describes an abnormal distribution of major visceral organs within the chest and abdomen. The determination of situs as normal, inversus, or ambiguus is primarily based on the location of unpaired organs such as the spleen, liver, stomach, and intestines. Diagnosis is made by clinical examination, echocardiography, a chest X-ray (position of the heart, stomach, and liver), and ultrasound of the abdominal organs. Situs is considered solitus if the left atrium, spleen, stomach, and the trilobed lung are on the left side and the liver and bilobed lung are on the right side. Situs ambiguus is present if the location of unpaired structures is random or indeterminate even after detailed and appropriate imaging. Situs inversus results when the arrangement of the thoracic and abdominal organs is mirrored. Individuals with situs inversus or situs solitus do not experience fatal dysfunction of their organ systems, as general anatomy and morphology of the abdominothoracic organ-vessel systems are conserved.

Total Anomalous Pulmonary Venous Connections, Human Genetics.

Partial anomalous pulmonary venous connections (PAVC) have been found after abnormal gene expressions involving several syndromes. Total anomalous pulmonary venous connection (TAPVC) is found in conjunction with heterotaxia syndrome as well as several other syndromes. It has been reported with an autosomal dominance with variable expression and incomplete penetrance. The occurrence is also related to environmental factors which may superimpose on a familial susceptibility for TAPVC. Many pathways are involved in the normal development of the pulmonary venous connections and as a consequence disturbance of many genetic and epigenetic pathways lead to partial or total pulmonary venous misconnections. In this chapter, an overview of current knowledge regarding human genetics of anomalous venous connections is provided.

Outcomes of heart transplants in children with heterotaxy syndrome.

OBJECTIVES: End-stage congenital heart disease (CHD) in children with heterotaxy syndrome might necessitate a heart transplant (HTx). An HTx in heterotaxy patients can be associated with several technical (e.g. redo, systemic/pulmonary-venous/situs anomalies, pulmonary artery reconstruction) and extra-cardiac (e.g. ciliary dyskinesia, infections, gastrointestinal) challenges. Our goal was to determine if heterotaxy syndrome is associated with increased early or late transplant risks. METHODS: The United Network for Organ Sharing transplant database was merged with the Paediatric Health Information System administrative database to identify children with heterotaxy who received an HTx. Characteristics and outcomes were compared between children with heterotaxy and contemporaneous non-heterotaxy congenital and non-congenital cardiomyopathy control groups. RESULTS: After we merged the databases, we divided our cohort of 1122 patients into 3 groups: the heterotaxy (n = 143), group the non-heterotaxy congenital (n = 428) group and the cardiomyopathy (n = 551) group. There were differences in the characteristics between the 3 groups, with the heterotaxy group being comparable to the non-heterotaxy congenital group. The waiting list duration was longer for the heterotaxy than for the non-heterotaxy congenital and cardiomyopathy groups (91 vs 63 vs 56 days, P < 0.001). Early post-transplant complications were similar for all groups except for operative mortality, which was 1% for the cardiomyopathy and 4% for the heterotaxy and non-heterotaxy congenital groups (P < 0.001). The post-transplant hospital stay was shorter for the cardiomyopathy (57 days) compared to the non-heterotaxy congenital (99 days) and heterotaxy (89 days) groups (P < 0.001). Whereas rejection prior to discharge was comparable between the heterotaxy and the CHD groups, it was higher at 1 year for the heterotaxy (22%) than for the non-heterotaxy congenital (19%) and cardiomyopathy (13%) groups (P < 0.001). Survival at 5 years was superior for the cardiomyopathy (87%) compared to the heterotaxy (69%) and non-heterotaxy congenital groups (78%) (P < 0.001). For the heterotaxy group, no risk factors affecting survival were identified on multivariable analysis. CONCLUSIONS: Regardless of the complexity, an HTx in selected children with heterotaxy is associated with good mid-term outcomes. Despite early results that are comparable to those of other patients with CHD, the increasing rejection rate at 1 year and the relatively accelerated attrition at mid-term warrant further follow-up. Due to database limitations in defining morphologic and surgical details, further work is warranted to delineate anatomical and surgical variables that could affect survival.

NODAL variants are associated with a continuum of laterality defects from simple D-transposition of the great arteries to heterotaxy.

BACKGROUND: NODAL signaling plays a critical role in embryonic patterning and heart development in vertebrates. Genetic variants resulting in perturbations of the TGF-ß/NODAL signaling pathway have reproducibly been shown to cause laterality defects in humans. To further explore this association and improve genetic diagnosis, the study aims to identify and characterize a broader range of NODAL variants in a large number of individuals with laterality defects. METHODS: We re-analyzed a cohort of 321 proband-only exomes of individuals with clinically diagnosed laterality congenital heart disease (CHD) using family-based, rare variant genomic analyses. To this cohort we added 12 affected subjects with known NODAL variants and CHD from institutional research and clinical cohorts to investigate an allelic series. For those with candidate contributory variants, variant allele confirmation and segregation analysis were studied by Sanger sequencing in available family members. Array comparative genomic hybridization and droplet digital PCR were utilized for copy number variants (CNV) validation and characterization. We performed Human Phenotype Ontology (HPO)-based quantitative phenotypic analyses to dissect allele-specific phenotypic differences. RESULTS: Missense, nonsense, splice site, indels, and/or structural variants of NODAL were identified as potential causes of heterotaxy and other laterality defects in 33 CHD cases. We describe a recurrent complex indel variant for which the nucleic acid secondary structure predictions implicate secondary structure mutagenesis as a possible mechanism for formation. We identified two CNV deletion alleles spanning NODAL in two unrelated CHD cases. Furthermore, 17 CHD individuals were found (16/17 with known Hispanic ancestry) to have the c.778G > A:p.G260R NODAL missense variant which we propose reclassification from variant of uncertain significance (VUS) to likely pathogenic. Quantitative HPO-based analyses of the observed clinical phenotype for all cases with p.G260R variation, including heterozygous, homozygous, and compound heterozygous cases, reveal clustering of individuals with biallelic variation. This finding provides evidence for a genotypic-phenotypic correlation and an allele-specific gene dosage model. CONCLUSION: Our data further support a role for rare deleterious variants in NODAL as a cause for sporadic human laterality defects, expand the repertoire of observed anatomical complexity of potential cardiovascular anomalies, and implicate an allele specific gene dosage model.

A novel NODAL variant in a young embolic stroke patient with visceral heterotaxy.

BACKGROUND: Ischemic stroke in young adults can be caused by a variety of etiologies including the monogenic disorders. Visceral heterotaxy is a condition caused by abnormal left-right determinations during embryonic development. We aimed to determine the cause of a young ischemic stroke patient with visceral heterotaxy. CASE PRESENTATION: We performed neurological, radiological, and genetic evaluations in a 17-year-old male patient presenting ischemic stroke and visceral heterotaxy to determine the underlying cause of this rare disease combination. Brain magnetic resonance imaging (MRI) showed evidence of embolic stroke, abdominal computed tomography (CT) showed visceral heterotaxy, and echocardiogram showed cardiac anomaly with right-to-left-shunt (RLS). Whole genome sequencing (WGS) revealed a heterozygous missense variant (NM_018055.5: c.1016 T > C, p.(Met339Val)) in the NODAL gene, which is essential to the determination of the left-right body axis. CONCLUSIONS: Our study highlights the importance of evaluating genetic etiology in young ischemic stroke and the need for stroke risk management in visceral heterotaxy patients with RLS. To the best of our knowledge, we report the first genetically-confirmed case of visceral heterotaxy with young embolic stroke reported to date.

Interventions on residual lesions in patients with heterotaxy syndrome following orthotropic heart transplantation: A single-center experience.

BACKGROUND: Heterotaxy syndrome (HS) is a defect in lateralization which often results in complex intra and extracardiac abnormalities. Orthotropic heart transplantation (OHT) in HS involves intricate and individualized modifications to surgical technique. Post-OHT outcomes are worse in patients with HS, however, the impact of post-OHT residual lesions has not yet been characterized. METHODS: Patients with HS who underwent OHT at Ann & Robert H. Lurie Children's Hospital of Chicago between January 2012 and June 2023 were identified. Patients were excluded if follow-up data was not available due to follow up at a different institution of early mortality. Pre-OHT clinical data, surgical data, and post-OHT surgical and catheterization data were collected. RESULTS: Two early mortalities were excluded from analysis, leaving 15 patients in the study cohort. Median age at OHT was 3.7 years (range: 0.7-15.4). Nine out of 15 patients were diagnosed with residual lesions requiring intervention at a median of 188 days post transplantation. All interventions on residual lesions occurred via catheterization. Overall mortality rate was 27% (4/15) with all deaths occurring in patients with residual lesions (4/9 patients, 44%). 83% (10/12) of lesions were diagnosed via catheterization, and 83% (10/12) of lesions of occurred in the first year after transplant. CONCLUSIONS: Patients with HS are at high risk for residual lesions after OHT, which may contribute to increased mortality. Comprehensive invasive diagnostics were required to diagnose residual lesions, which were all addressed percutaneously.

Use of Interactive Visualization and 3D Printing in the Repair of Complex Congenital Heart Disease Presenting in Adult Life.

We report a case of a 25-year-old male with a heterotaxy-like constellation of congenital heart defects consisting of complete atrioventricular septal defect, transposition of the great arteries, subpulmonary stenosis, L-looped ventricles, hypoplastic right ventricle, and a distant aorta arising from the right ventricle. This case demonstrates how 3D printing and interactive 3D visualization may facilitate a unique surgical repair.

Impact of Optimal Fenestration Size on Outcomes of High-Risk Fontan Patients.

BACKGROUND: We aimed to analyze mid-term outcomes of the fenestrated Fontan procedure, focusing on the fenestration size. METHODS: We retrospectively reviewed the outcomes of the fenestrated Fontan procedure. Among 165 patients who underwent the Fontan procedure from 2011 to 2021, fenestration was created in 27 patients with the highest risks, including those with hypoplastic left heart syndrome, hypoplastic pulmonary arteries, heterotaxy syndrome with high pulmonary vascular resistance, and pulmonary arterial pressure >15 mm Hg. The patients underwent the procedure at a median age of three years (body weight, 11.4 kg; body surface area, 0.54 m2). Fenestration sizes were 3.5 to 5 mm. RESULTS: Spontaneous fenestration closure occurred within one year postoperatively in nine patients. Among them, three experienced Fontan failure, necessitating refenestration. Although fenestration size did not differ, the size corrected by body surface area at the time of surgery was smaller in patients with fenestration closure (6.4 mm/m2 vs 8.3 mm/m2, P < .05). Patients with a fenestration <7 mm/m2 were more likely to have fenestration closure within one year postoperatively, and those with a fenestration >9 mm/m2 were more likely to have severe desaturation and require home oxygen therapy following discharge. CONCLUSIONS: Spontaneous fenestration closure affected the frequency of Fontan complications. A very small fenestration size corrected by body surface area was a significant risk factor for spontaneous closure. Conversely, a very large fenestration size corrected by body surface area resulted in severe desaturation. The optimal fenestration size to prevent early spontaneous closure and severe desaturation is approximately 8 mm/m2.

A rare combination: a single common pulmonary vein with polysplenia syndrome.

A single common pulmonary vein is a rare anomaly, mostly occurring with asplenia. We wanted to report our case because it co-exists with polysplenia and ciliary dyskinesia.A baby girl about 2 months old with respiratory arrest was admitted to the emergency room of our hospital. She responded to pulmonary resuscitation. We ascertained from her medical history that she had been hospitalised twice because of recurrent lung infections. After the initial check and treatment, we applied imaging modalities to detect underlying problems of recurrent lung infection. Echocardiographic evaluation was suboptimal because of the widespread pulmonary infiltration. Still, we noticed a single common pulmonary vein without obstruction at the junction of the left atrium. Subsequently, a chest CT scan with contrast was performed. It revealed a single common pulmonary vein entering the left atrium with a single orifice, atrial septal defect, two lobes in both lungs, hepatic veins draining directly into the right atrium, and polysplenia. When the flow of a single common pulmonary vein goes directly to the right atrium through the defect, it may cause right heart dilatation as it did in our case. Therefore, patients may need to undergo surgery at an earlier age.

Persistant Left Superior Vena Cava with and Without Right Superior Vena Cava: Significance of Prenatal Diagnosis.

This study aims to define the associated anomalies with PLSVC, and to compare single PLSVC and bilateral superior vena cava in terms of accompanying anomalies and pregnancy outcomes. This was a retrospective study of the fetuses diagnosed with single and/or bilateral SVC at a tertiary fetal medicine center during 8 years. We detected 16 cases of single PLSVC and 84 cases of bilateral SVC. We found an association between the PLSVC and cardiac and extracardiac anomalies. Comparison between single PLSVC and BSVC cases revealed significant differences in the occurrence of heterotaxy and right isomerism. The study highlights the importance of prenatal diagnosis in PLSVC cases. Isolated PLSVC with situs solitus may be considered a benign finding, but larger studies are needed to understand the clinical implications of PLSVC in relation to chromosomal anomalies. Routine screening protocols should include three-vessel and trachea views to detect PLSVC.

Functions of cilia in cardiac development and disease.

Errors in embryonic cardiac development are a leading cause of congenital heart defects (CHDs), including morphological abnormalities of the heart that are often detected after birth. In the past few decades, an emerging role for cilia in the pathogenesis of CHD has been identified, but this topic still largely remains an unexplored area. Mouse forward genetic screens and whole exome sequencing analysis of CHD patients have identified enrichment for de novo mutations in ciliary genes or non-ciliary genes, which regulate cilia-related pathways, linking cilia function to aberrant cardiac development. Key events in cardiac morphogenesis, including left-right asymmetric development of the heart, are dependent upon cilia function. Cilia dysfunction during left-right axis formation contributes to CHD as evidenced by the substantial proportion of heterotaxy patients displaying complex CHD. Cilia-transduced signaling also regulates later events during heart development such as cardiac valve formation, outflow tract septation, ventricle development, and atrioventricular septa formation. In this review, we summarize the role of motile and non-motile (primary cilia) in cardiac asymmetry establishment and later events during heart development.

Anomalous hepatic drainage and platypnea-orthodeoxia in cyanotic children.

The aetiology of cyanosis could be unclear in children, even for specialised paediatricians. Two cases were reported: first, a 6-year-old child with features of left isomerism and Fallot was fortuitously diagnosed with anomalous hepatic venous drainage before complete repair. Second, a newborn with an antenatal diagnosis of ductus venosus agenesis had an isolated intermittent right-to-left atrial shunt when upright, with favourable outcome, in contrast to the association with significant heart malformations including inferior caval vein interruption. Multimodality imaging and 3D printing helped to rule out extracardiac causes of persistent cyanosis and plan surgical repair.

Long-term outcomes of functional single ventricles associated with heterotaxy syndrome†.

OBJECTIVES: The goal of this study was to determine the long-term surgical outcomes of patients with functional single ventricles associated with heterotaxy syndrome, risk factors for mortality and factors associated with Fontan stage completion. METHODS: Overall, 279 patients with a functional single ventricle associated with heterotaxy syndrome who underwent an initial surgical procedure at our institute between 1978 and 2021 were grouped into 4 "eras" based on the surgical year during which the initial procedure was performed: era 1 (1978-1989, n = 71), era 2 (1990-1999, n = 98), era 3 (2000-2009, n = 64) and era 4 (2010-2021, n = 46). Neonatal surgery was more frequent in eras 3 and 4 than in eras 1 and 2. RESULTS: Overall, 228 patients had right atrial isomerism; 120 patients (43.0%) had a total anomalous pulmonary venous connection; and 58 patients (20.8%) underwent an initial procedure as neonates. Overall survival rates at 10, 20 and 30 years after the initial procedure were 47.1%, 40.6% and 36.1%, respectively. Neonatal surgery (P < 0.001), total anomalous pulmonary venous connection repair at the initial procedure (P < 0.001) and early era (P < 0.001) were identified as risk factors for mortality, with the last 2 variables being negatively associated with Fontan stage completion (P < 0.001 for both). CONCLUSIONS: Although era had a favourable effect on survival, total anomalous pulmonary venous connection with intrinsic pulmonary vein obstruction was associated with both mortality and Fontan stage completion. CLINICAL REGISTRATION NUMBER: R19092.

Intracardiac total anomalous pulmonary venous return or septum primum malposition? Complete repair in left atrial isomerism.

Total anomalous pulmonary venous return due to septum primum malposition is a poorly understood condition despite being very common in left atrial isomerism or polysplenia syndrome. Due to the leftward displacement of the septum primum, either the two right pulmonary veins or all four pulmonary veins can drain abnormally into the right atrium, despite their correct position. In other words, the four pulmonary veins (or the two right pulmonary veins), looking from outside the heart, return at the back of the atrium in the normal position. Nevertheless, from the inside of the heart, two or all four pulmonary veins drain into the right atrium due to the leftward displacement of the septum primum. As an example, we report a 5-month-old patient with severe malposition of the septum primum and consequent total anomalous pulmonary venous drainage into the right atrium. The patient underwent surgical correction with resection of the malpositioned septum primum and reconstruction of a normal interatrial septation with a pericardial patch.