Hypoplastic Left Heart Syndrome: Signaling & Molecular Perspectives, and the Road Ahead.

Hypoplastic left heart syndrome (HLHS) is a lethal congenital heart disease (CHD) affecting 8-25 per 100,000 neonates globally. Clinical interventions, primarily surgical, have improved the life expectancy of the affected subjects substantially over the years. However, the etiological basis of HLHS remains fundamentally unclear to this day. Based upon the existing paradigm of studies, HLHS exhibits a multifactorial mode of etiology mediated by a complicated course of genetic and signaling cascade. This review presents a detailed outline of the HLHS phenotype, the prenatal and postnatal risks, and the signaling and molecular mechanisms driving HLHS pathogenesis. The review discusses the potential limitations and future perspectives of studies that can be undertaken to address the existing scientific gap. Mechanistic studies to explain HLHS etiology will potentially elucidate novel druggable targets and empower the development of therapeutic regimens against HLHS in the future.

Intrinsic myocardial defects underlie an Rbfox-deficient zebrafish model of hypoplastic left heart syndrome.

Hypoplastic left heart syndrome (HLHS) is characterized by underdevelopment of left sided structures including the ventricle, valves, and aorta. Prevailing paradigm suggests that HLHS is a multigenic disease of co-occurring phenotypes. Here, we report that zebrafish lacking two orthologs of the RNA binding protein RBFOX2, a gene linked to HLHS in humans, display cardiovascular defects overlapping those in HLHS patients including ventricular, valve, and aortic deficiencies. In contrast to current models, we demonstrate that these structural deficits arise secondary to impaired pump function as these phenotypes are rescued when Rbfox is specifically expressed in the myocardium. Mechanistically, we find diminished expression and alternative splicing of sarcomere and mitochondrial components that compromise sarcomere assembly and mitochondrial respiration, respectively. Injection of human RBFOX2 mRNA restores cardiovascular development in rbfox mutant zebrafish, while HLHS-linked RBFOX2 variants fail to rescue. This work supports an emerging paradigm for HLHS pathogenesis that centers on myocardial intrinsic defects.

Integrated multi-omic characterization of congenital heart disease.

The heart, the first organ to develop in the embryo, undergoes complex morphogenesis that when defective results in congenital heart disease (CHD). With current therapies, more than 90% of patients with CHD survive into adulthood, but many suffer premature death from heart failure and non-cardiac causes1. Here, to gain insight into this disease progression, we performed single-nucleus RNA sequencing on 157,273 nuclei from control hearts and hearts from patients with CHD, including those with hypoplastic left heart syndrome (HLHS) and tetralogy of Fallot, two common forms of cyanotic CHD lesions, as well as dilated and hypertrophic cardiomyopathies. We observed CHD-specific cell states in cardiomyocytes, which showed evidence of insulin resistance and increased expression of genes associated with FOXO signalling and CRIM1. Cardiac fibroblasts in HLHS were enriched in a low-Hippo and high-YAP cell state characteristic of activated cardiac fibroblasts. Imaging mass cytometry uncovered a spatially resolved perivascular microenvironment consistent with an immunodeficient state in CHD. Peripheral immune cell profiling suggested deficient monocytic immunity in CHD, in agreement with the predilection in CHD to infection and cancer2. Our comprehensive phenotyping of CHD provides a roadmap towards future personalized treatments for CHD.

Probing single ventricle heart defects with patient-derived induced pluripotent stem cells and emerging technologies.

Single ventricle heart defects (SVHDs) are a severe type of congenital heart disease with poorly understood pathogenic mechanisms. New research using patient-specific induced pluripotent stem cells (iPSCs) as a cellular model is beginning to uncover genetic and cellular etiologies of SVHDs. Hypoplastic left heart syndrome (HLHS) is a type of SVHD that is characterized by an underdeveloped left ventricle and other malformations in the left side of the heart. Hypoplastic right heart syndrome (HRHS), the second type of SVHD, is characterized by an underdeveloped right heart, including malformed tricuspid and pulmonary valves. Despite a noticeable lack of research on SVHD, emerging technologies offer a promising future to further probe the genetic and cellular mechanisms of these diseases. Pediatric cardiovascular research is at the dawn of a new era in terms of what can be discovered with patient-specific iPSCs in conjunction with other technologies (e.g., organoids, single-cell genomics, CRISPR/Cas9 genome editing). In this review, we present recent approaches and findings utilizing patient-specific iPSCs to identify cellular mechanisms responsible for improper cardiac organogenesis in HLHS and HRHS.

Placental and fetal characteristics of the Ohia mouse line recapitulate outcomes in human hypoplastic left heart syndrome.

Congenital heart defects (CHDs) are the most common birth defect worldwide. The morbidity and mortality associated with these defects is compounded by increased frequency of fetal growth abnormalities. In the Ohia mouse model of hypoplastic left heart syndrome (HLHS), the double homozygous genotype is embryonically lethal at mid-pregnancy; a time in which optimal establishment of the placenta is crucial to fetal survival. We aimed to characterize placental and fetal growth and development in the double heterozygous genotype (Sap130m/+Pcdha9m/+). There was a shift in frequency of fetuses with reduced weight near term in the Sap130m/+Pcdha9m/+ fetuses compared to wildtype, driven by lower fetal weight in male fetuses compared to female. This shift in fetal weight distribution in the Sap130m/+Pcdha9m/+ fetuses was associated with reduced labyrinth region area (P < 0.001) and reduced fetal capillary density (P < 0.001) in the placentas, the latter being significantly lower in male Sap130m/+Pcdha9m/+ placentas compared to female. mRNA expression of several nutrient transporters was also lower in placentas from males compared to placentas from females, irrespective of genotype. Overall, this data shows that whilst the double heterozygous fetuses do not carry heart defects, placental development and function is impaired, particularly in males. Such differences are similar to findings in studies of human placentas and highlights the importance of this mouse model in continuing to understand the developmental links and disruptions to the heart-placenta axis.

Genetic Association Between Hypoplastic Left Heart Syndrome and Cardiomyopathies.

BACKGROUND: Hypoplastic left heart syndrome (HLHS) with risk of poor outcome has been linked to MYH6 variants, implicating overlap in genetic etiologies of structural and myopathic heart disease. METHODS: Whole genome sequencing was performed in 197 probands with HLHS, 43 family members, and 813 controls. Data were filtered for rare, segregating variants in 3 index families comprised of an HLHS proband and relative(s) with cardiomyopathy. Whole genome sequencing data from cases and controls were compared for rare variant burden across 56 cardiomyopathy genes utilizing a weighted burden test approach, accounting for multiple testing using a Bonferroni correction. RESULTS: A pathogenic MYBPC3 nonsense variant was identified in the first proband who underwent cardiac transplantation for diastolic heart failure, her father with left ventricular noncompaction, and 2 fourth-degree relatives with hypertrophic cardiomyopathy. A likely pathogenic RYR2 missense variant was identified in the second proband, a second-degree relative with aortic dilation, and a fourth-degree relative with dilated cardiomyopathy. A pathogenic RYR2 exon 3 in-frame deletion was identified in the third proband diagnosed with catecholaminergic polymorphic ventricular tachycardia and his father with left ventricular noncompaction and catecholaminergic polymorphic ventricular tachycardia. To further investigate HLHS-cardiomyopathy gene associations in cases versus controls, rare variant burden testing of 56 genes revealed enrichment in MYH6 (P=0.000068). Rare, predicted-damaging MYH6 variants were identified in 10% of probands in our cohort-4 with familial congenital heart disease, 4 with compound heterozygosity (3 with systolic ventricular dysfunction), and 4 with MYH6-FLNC synergistic heterozygosity. CONCLUSIONS: Whole genome sequencing in multiplex families, proband-parent trios, and case-control cohorts revealed defects in cardiomyopathy-associated genes in patients with HLHS, which may portend impaired functional reserve of the single-ventricle circulation.

Abnormalities of placental development and function are associated with the different fetal growth patterns of hypoplastic left heart syndrome and transposition of the great arteries.

BACKGROUND: Birthweight is a critical predictor of congenital heart disease (CHD) surgical outcomes. Hypoplastic left heart syndrome (HLHS) is cyanotic CHD with known fetal growth restriction and placental abnormalities. Transposition of the great arteries (TGA) is cyanotic CHD with normal fetal growth. Comparison of the placenta in these diagnoses may provide insights on the fetal growth abnormality of CHD. METHODS: Clinical data and placental histology from placentas associated with Transposition of the Great Arteries (TGA) were analyzed for gross pathology, morphology, maturity and vascularity and compared to both control and previously analyzed HLHS placentas [1]. RNA was isolated from HLHS, TGA and control placentas and sequenced by Illumina HiSeq.Transcriptome analysis was performed using AltAnalyze. Immunohistochemistry was utilized to assess placental nutrient transporter expression in all three groups. RESULTS: Placental weight was reduced in TGA cases, and demonstrated reduced villous vasculature, immature terminal villi in the parenchyma compared to controls and reflected our previous data from HLHS placentas. However, birth weight was not reduced in TGA cases compared to controls in contrast to the HLHS cohort and birthweight:placental weight ratio was significantly increased in TGA cases but not HLHS compared to control. Transcriptomic and histologic analysis demonstrates reduced cell activity and nutrient transport capability in HLHS but not TGA placentas which appear to increase/maintain these mechanisms. CONCLUSIONS: Despite common vascular disturbances in placentas from HLHAs and TGA, these do not account for the disparities in birthweights frequently seen between these CHD subtypes, in contrast our transcriptomic and histologic analyses reveal differentially regulated mechanisms between the subtypes that may explain these disparities.

[HYPOPLASTIC LEFT HEART SYNDROME: MORPHOGENESIS OF PATOMORPHOLOGICAL TYPES OF THE LEFT VENTRICLE].

The purpose of the study was to investigate the morphogenesis of the left ventricle in the hypoplastic left heart syndrome (HLHS). There are five types of hypoplastic left ventricles were identified: with a slit-like shape and hypoplasia of LV wall, with a slit-like cavity shape and wall hypertrophy and types with endocardial fibroelastosis (with a cylindrical cavity shape, with lacunar cavities and lacunar-cylindrical cavity of the left ventricle), as a result of differences in the wall structure, cavity shape, presence or absence of endocardial fibroelastosis. The analysis of morphometric data of pathomorphological types of the left ventricle in the HLHS revealed the possible ways of their morphogenesis. Left displacement of interventricular septum in embryogenesis at 4-5 weeks of intrauterine development is associated with the occurrence of atresia of the left atrioventricular orifice and aortic valve and the appearance of a slit-like shape and hypoplasia of LV wall in the HLHS. The displacement of only the conotruncus septum leads to the appearance of a slit-like shape of cavity and hypertrophy of LV wall in the HLHS. The pathomorphological types with endocardial fibroelastosis in the HLHS depends on the stage of embryogenesis of myocardium at which fibroelastosis appears: before the myocardial compaction (up to 4th week of gestation) - the lacunar shape of LV cavity with thin compact layer of myocardium; during the compaction of myocardium (5-6th week of gestation) - the lacunar-cylindrical shape of LV cavity and after compaction (after 7-8th week of fetal development) - a cylindrical shape of LV cavity.

Grandparental genotyping enhances exome variant interpretation.

Trio exome sequencing is a powerful tool in the molecular investigation of monogenic disorders and provides an incremental diagnostic yield over proband-only sequencing, mainly due to the rapid identification of de novo disease-causing variants. However, heterozygous variants inherited from unaffected parents may be inadvertently dismissed, although multiple explanations are available for such scenarios including mosaicism in the parent, incomplete penetrance, imprinting, or skewed X-inactivation. We report three probands, in which a pathogenic or likely pathogenic variant was identified upon exome sequencing, yet was inherited from an unaffected parent. Segregation of the variants (in NOTCH1, PHF6, and SOX10) in the grandparent generation revealed that the variant was de novo in each case. Additionally, one proband had skewed X-inactivation. We discuss the possible genetic mechanism in each case, and urge caution in data interpretation of exome sequencing data. We illustrate the utility of expanding segregation studies to the grandparent generation and demonstrate the impact on exome interpretation strategies, by showing that objective genotype data can overcome subjective parental report of lack of symptoms.

Coronary Arterial Abnormalities in Hypoplastic Left Heart Syndrome: Pathologic Characteristics of Archived Specimens.

Palliation of patients with hypoplastic left heart syndrome remains challenging. Although coronary ischemia can be catastrophic, the prevalence and pathologies of anomalies of the coronary arteries remains unknown. We reviewed 119 specimens with the features of hypoplastic left heart syndrome, focusing our attention on the aortic root and the coronary arteries. We found 36 (30%) specimens with the combination of mitral and aortic atresia, 26 (22%) with mitral and aortic stenosis, and 57 (48%) with mitral stenosis combined with aortic atresia. In 29 specimens (24%), the coronary arteries were not located in the center of any sinuses, while in 24 specimens (21%) at least 1 coronary artery was located very proximal to a raphe or commissure, with potential for obstruction. The specimens with combined stenosis were more likely to have eccentric positions of the coronary arteries (11 specimens, 42%), compared to the 3 specimens with combined atresia (9%, P = 0.009). The specimens with combined stenosis were also more likely to have positioning at risk for obstruction (9 specimens, 35%), compared to those with combined atresia (3 specimens, 9%, P = 0.05). Coronary arterial fistulous communications were found in 11 specimens (9%), significantly more frequently in specimens with mitral stenosis and aortic atresia (9 specimens, 16%, P = 0.041). The origins of the coronary arteries in patients with hypoplastic left heart syndrome place them at potential risk for ischemia, with fistulous communications being a particular risk in those with mitral stenosis combined with aortic atresia.

Expression of connexin-43 in the cardiac muscle of children diagnosed with hypoplastic left heart syndrome: a Western blot and confocal laser scanning microscopy study.

Hypoplastic left heart syndrome consists of several structural abnormalities in the left side of the heart and may be associated with a hereditary genetic cause, possibly related to the connexin gene GJA1; however, only a few studies have investigated it. The present study aimed to analyse the expression of connexin-43 in the cardiac muscle of hypoplastic left heart syndrome children by Western blot method and confocal laser scanning microscopy. For that, tissue samples were taken during corrective surgery to treat heart defects. Patients of control group (8) presented any type of heart defect not related to hypoplastic left heart syndrome, connexin-43, or its gene and those of hypoplastic left heart syndrome group (9) presented this disease singly, without any other associated congenital diseases. By means of confocal laser scanning microscopy, it was noticed no connexin-43 qualitative differences in positioning and location pattern between both groups. From Western blot analysis, the connexin-43 expression did not show a statistically significant difference (p = 0.0571) as well. Within the limits of this study, it is suggested that cardiomyocytes of hypoplastic left heart syndrome children are similar in connexin-43 location, distribution, and structural and conformational patterns to those of children with heart defects not related to this protein and its genes.

miR-486 is modulated by stretch and increases ventricular growth.

Perturbations in biomechanical stimuli during cardiac development contribute to congenital cardiac defects such as hypoplastic left heart syndrome (HLHS). This study sought to identify stretch-responsive pathways involved in cardiac development. miRNA-Seq identified miR-486 as being increased in cardiomyocytes exposed to cyclic stretch in vitro. The right ventricles (RVs) of patients with HLHS experienced increased stretch and had a trend toward higher miR-486 levels. Sheep RVs dilated from excessive pulmonary blood flow had 60% more miR-486 compared with control RVs. The left ventricles of newborn mice treated with miR-486 mimic were 16.9%-24.6% larger and displayed a 2.48-fold increase in cardiomyocyte proliferation. miR-486 treatment decreased FoxO1 and Smad signaling while increasing the protein levels of Stat1. Stat1 associated with Gata-4 and serum response factor (Srf), 2 key cardiac transcription factors with protein levels that increase in response to miR-486. This is the first report to our knowledge of a stretch-responsive miRNA that increases the growth of the ventricle in vivo.

Hypoplastic left heart syndrome: From bedside to bench and back.

Hypoplastic Left Heart Syndrome (HLHS) is a complex Congenital Heart Disease (CHD) that was almost universally fatal until the advent of the Norwood operation in 1981. Children with HLHS who largely succumbed to the disease within the first year of life, are now surviving to adulthood. However, this survival is associated with multiple comorbidities and HLHS infants have a higher mortality rate as compared to other non-HLHS single ventricle patients. In this review we (a) discuss current clinical challenges associated in the care of HLHS patients, (b) explore the use of systems biology in understanding the molecular framework of this disease, (c) evaluate induced pluripotent stem cells as a translational model to understand molecular mechanisms and manipulate them to improve outcomes, and (d) investigate cell therapy, gene therapy, and tissue engineering as a potential tool to regenerate hypoplastic cardiac structures and improve outcomes.

Sindrome de corazón izquierdo hipoplásico: análisis de las características de una población en un hospital público / Hipoplastic left heart syndrome: analysis of the characteristics of a population in a public hospital

The authors present a study on prenatal diagnosis of hipoplastic left heart syndrome, and an analysis of the characteristics of a population in a public hospital. The hypoplastic left heart syndrome, and an analysis of the characteristics of a population in a public hospital. The hypoplastic left heart syndrome (HLHS) is a rare congenital heart deficit consisting in the hypodevelopment of the left ventricle, aortic valve, mitral valve and the ascendent aorta. Its incidence is 0,016% to 0.034% of the total of newborns alive. It represents between 1 - 3% of the whole congenital cardiopaties (cc). Its natural evolution is severe and it represents the greater cause of death by CC during the neonatal period. There is a predominance in males between the 55 to 67%. The etiology is multifactorial. Presents risk of recurrency between brothers, and because of that circumstance it could have genetical basis. The ais of this report were to analyze the clinical variables, electrocardiographis, echocardiographic and therapeutical, of a population with diagnosis fo HLHS. The incidence of HLHS in the population studied was 0.06% of life births. The results obtained are detailed (AU)

Intravascular Papillary Endothelial Hyperplasia in the Coronary Artery: An Unusual Cause of Massive Myocardial Infarction in Hypoplastic Left Heart Syndrome.

Background: Intravascular papillary endothelial hyperplasia (IPEH) is a benign vascular lesion that usually involves the head and neck or extremities. Involvement of the coronary arterial system is unreported. Case: A 1-month-old patient born with hypoplastic left heart syndrome died from a massive myocardial infarction shortly after first stage palliation with Norwood/Sano. Autopsy demonstrated a massive univentricular hemorrhagic infarction with complete occlusion of the left main coronary artery and its intramural branches by intraluminal papillary endothelial hyperplasia (IPEH). Immunostaining with CD34 and CD31 confirmed the diagnosis. The inferior and superior mesenteric artery branches also had IPEH. Conclusion: IPEH can involve the coronary vasculature, can be multifocal and can occur in the newborn.

The impact of morphological characteristics on late outcomes in patients born with hypoplastic left heart syndrome†.

OBJECTIVES: Patients with hypoplastic left heart syndrome are at high risk of late adverse events after Fontan completion, but it is unclear whether their morphological characteristics influence these outcomes. METHODS: Retrospective review of the data from the Australian and New Zealand Fontan Registry identified 185 patients with hypoplastic left heart syndrome who survived to hospital discharge after Fontan completion. Their outcomes were reviewed to identify predictors of adverse events with a particular focus on the impact of morphological characteristics. All available echocardiographic parameters were collected, and the hypoplasia of the left ventricle was subjectively considered to be mild, moderate or severe. RESULTS: The mean follow-up after the Fontan procedure was 6.4 ± 4.7 years. The median age at Fontan procedure was 4.41 years, 95% (176/185) of patients underwent an extracardiac conduit Fontan procedure and 71% (132/185) of those were fenestrated. At 15 years after Fontan, freedom from death and cardiac transplantation was 90% [95% confidence interval (CI) 85-97], freedom from Fontan failure was 78% (95% CI 70-87) and freedom from adverse events was 32% (95% CI 22-46). Morphological parameters did not influence transplant-free survival or Fontan failure. Independent risk factors predicting higher incidence of adverse events included aortic atresia (P = 0.003). CONCLUSIONS: The long-term survival of Fontan survivors with hypoplastic left heart syndrome is excellent and appears comparable to that of the general Fontan population. However, intrinsic morphological characteristics may continue to burden patients with late morbidity.

Tricuspid Valve Hemangioma Associated with Hypoplastic Left Heart Syndrome Presenting as Sudden Infant Death Syndrome.

Primary cardiac tumors are rare in children with a low incidence varying from 0.0017 to 0.28% in autopsy studies. Approximately 90% of the reported primary cardiac tumors in the pediatric population are benign and the most common subtype is rhabdomyomas accounting for approximately 60%, while hemangiomas are rare primary tumors with a 5% incidence. Hypoplastic left heart syndrome is abnormal development of the left-sided cardiac structures, leading to obstruction of blood flow from the left ventricle out-flow tract. Here we report a case of tricuspid hemangioma in association with hypoplastic left heart syndrome, a rare association not previously reported in the literature.

Regenerative Therapy for Patients with Congenital Heart Disease.

Congenital heart disease (CHD) is the most common birth defect, affecting 1 in 100 babies. Among CHDs, single ventricle (SV) physiologies, such as hypoplastic left heart syndrome and tricuspid atresia, are particularly severe conditions that require multiple palliative surgeries, including the Fontan procedure. Although the management strategies for SV patients have markedly improved, the prevalence of ventricular dysfunction continues to increase over time, especially after the Fontan procedure. At present, the final treatment for SV patients who develop heart failure is heart transplantation; however, transplantation is difficult to achieve because of severe donor shortages. Recently, various regenerative therapies for heart failure have been developed that increase cardiomyocytes and restore cardiac function, with promising results in adults. The clinical application of various forms of regenerative medicine for CHD patients with heart failure is highly anticipated, and the latest research in this field is reviewed here. In addition, regenerative therapy is important for children with CHD because of their natural growth. The ideal pediatric cardiovascular device would have the potential to adapt to a child's growth. Therefore, if a device that increases in size in accordance with the patient's growth could be developed using regenerative medicine, it would be highly beneficial. This review provides an overview of the available regenerative technologies for CHD patients.

Anomalous Origin of Left Coronary Artery From Aortic Arch Associated With Hypoplastic Left Heart Syndrome.

Anomalous origin of the coronary artery from the aortic arch associated with hypoplastic left heart syndrome is an extremely rare anomaly. Coronary anomalies can significantly deteriorate the clinical outcomes of hypoplastic left heart syndrome. We describe the case of a newborn with concomitant hypoplastic left heart syndrome and abnormal origin of the left coronary artery arising from the distal aortic arch.

The "double dunk" technique for a right ventricle to pulmonary artery conduit implantation during the Norwood procedure reduces unintended shunt-related events.

BACKGROUND: The introduction of a right ventricle to pulmonary artery conduit (RVPAc) during the Norwood procedure (NP) for hypoplastic left heart syndrome (HLHS) resulted in a higher survival rate, but also in an increased number of unintended pulmonary and shunt-related interventions. AIM: To analyse how several modifications employed in RVPAc implantation during NP may influence the interstage course, unintended surgical or catheter-based interventions, and pulmonary artery development in a cohort of patients with HLHS. METHODS: We retrospectively analysed three groups of non-selected, consecutive neonates who underwent the NP between 2011 and 2014, with different RVPAc surgical techniques employed: Group I (n = 32) - left RVPAc with distal homograft cuff, Group II (n = 28) - right RVPAc with distal homograft cuff, and Group III (n = 41) - "double dunk," right reinforced RVPAc (n = 41). RESULTS: There were no intergroup differences in terms of age, weight, prevalence of aortic atresia, diameter of the ascending aorta, deep hypothermic circulatory arrest time, and hospital mortality rate (9.3% vs. 14.2% vs. 7.3%, respectively). There was a significant difference between the groups in the number of catheter-based interventions during the interstage period (34% vs. 25% vs. 0%, respectively, p < 0.05) and/or concomitant surgical interventions (17.2% vs. 4.1% vs. 2.6%, respectively). The diameter of the pulmonary arteries was most homogenous in the third group. CONCLUSIONS: The modified strategy of using the "double dunk," right reinforced RVPAc during the NP for HLHS significantly reduces the number of unintended catheter-based and surgical shunt-related reinterventions during the interstage period. This technique allows a more homogenous development of pulmonary arteries before the second, surgical stage.