RARE DISEASE
Hypoplastic left heart syndrome
Hypoplastic left heart syndrome
Hypoplastic left heart syndrome
Synonyms: HLHS
Synonyms: HLHS
Synonyms: HLHS
Drug discovery
4
drugs
With orphan designations
Overview
Hypoplastic left heart syndrome (HLHS) is a lethal congenital heart defect characterized by underdeveloped left-sided cardiac structures, including the left ventricle, mitral/aortic valves, and aorta. Postnatal survival depends on prostaglandin E1 to maintain ductus arteriosus patency and staged palliative surgeries (Norwood, Glenn, Fontan) to reroute systemic circulation through the right ventricle. Despite advancements, patients face lifelong risks of heart failure, arrhythmias, and Fontan-associated complications [6][10].
Burden
Survival: 63.5% at 1 year, 54.6% at 10 years, and 32.6% at 15 years [2]
Complications: Ventricular dysfunction, protein-losing enteropathy, plastic bronchitis, and neurodevelopmental delays [7][11][14]
Psychosocial/financial strain on families due to complex care needs and frequent hospitalizations [16]
Therapies
Staged palliation: Norwood (neonatal), Glenn (4-6 months), and Fontan (18-36 months) procedures to reconfigure single-ventricle physiology [3][5][12]
Alternative approaches: Hybrid procedures combining catheter-based and surgical interventions [8][14]
Heart transplantation (limited by donor availability) and lifelong cardiac monitoring [3][20]
Categories: rare cardiac malformations, rare developmental anomalies during embryogenesis
Research Papers
1,907 drug discovery papers about Hypoplastic left heart syndrome, with 1 first-in-class and 1 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
1,907 drug discovery papers about Hypoplastic left heart syndrome, with 1 first-in-class and 1 next-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
proteins
2026-08-04 | Sex-stratified trends in hypoplastic left heart syndrome-related mortality among children and young adults in the United States, 1999–2024: a pre- and post-COVID-19 analysis
Background Hypoplastic left heart syndrome (HLHS) is a congenital heart disease that accounts for approximately 3% of congenital heart defects, making it a leading cause of mortality in this population. Timely staged palliation, such as Norwood, Glenn, and Fontan, are required to reduce the incidence of adverse outcomes. Data over the long term suggest that only about 31% of patients with HLHS are alive at age 35 years after Fontan completion. However, national mortality trend data stratified by sex, extending through 2024 and spanning the COVID-19 era, have not been characterised. Methods Data for this study were obtained from the CDC WONDER (Centres for Disease Control and Prevention Wide-ranging Online Data for Epidemiologic Research) Multiple Cause of Death database using ICD-10 code Q23.4 from 1999 through 2024 in individuals aged 0–24 years. Joinpoint regression was used to analyse trends. Analyses were conducted using a Poisson variation model with Monte Carlo permutation testing. Statistical significance was defined as p < 0.05 based on two-tailed testing and was stratified by sex. Results A total of 10,138 deaths were identified in the United States during the study period. Among these, 4,285 were females, and 5,853 were males. Joinpoint regression identified a declining trend from 1999 to 2021 (APC: −2.22%; 95% CI: −3.08 to −1.89; p = 0.006), with a non-significant increase from 2021 to 2024 (APC: +4.97%; p = 0.156). In 2020, total HLHS-related deaths reached their lowest point ( n = 287) before rising consecutively to 358 in 2024. Female mortality trends declined throughout the study period (APC: −1.96%; 95% CI: −2.61 to −1.33; p < 0.001) compared with males, who remained consistently high. Conclusion HLHS mortality has declined following surgical advances and perioperative care management. Persistent higher mortality rates were noted among males than females throughout both pre- and post-COVID eras. The rise in post-pandemic mortality is a new and concerning trend that warrants close national monitoring. These trends emphasise the need for uninterrupted staged palliation and continued population-level surveillance of HLHS outcomes.
2026-04-15 | Single Nuclei Transcriptome of a Hypoplastic Left Heart Syndrome Patient Post Myocardial Infarction
Single-nucleus RNA sequencing (snRNA-seq) was performed on right ventricular (RV) myocardial tissue obtained at transplantation from a patient with HLHS complicated by myocardial infarction (HLHS-MI). After quality control and doublet removal, 4,134 nuclei were retained. Cell types were identified by graph-based clustering and canonical marker expression.
2026-04-06 | Risk factors for complications of necrotizing enterocolitis in term neonates with congenital heart disease at a referral hospital in Colombia: A retrospective cohort study.
Necrotizing enterocolitis (NEC) is one of the most severe complications in neonates and infants. However, term infants with congenital heart disease (CHD) represent a scenario of multiple complications due to pathophysiological mechanisms that differ from the classic pathogenesis. The objective of the study was to determine factors associated with complications of NEC in term infants hospitalized for CHD in a pediatric intensive care unit of a referral hospital in Colombia between 2010 and 2023. A retrospective cohort study was conducted, including 148 term infants with CHD who developed NEC during their hospitalization. Demographic and clinical characteristics were analyzed. Descriptive and bivariate analyses were performed using the Chi-square and Mann-Whitney U-tests. A multivariate analysis was conducted using robust Poisson regression with Stata 18.0® software. The most frequent CHD were hypoplastic left heart syndrome (HLHS), pulmonary atresia, and persistent ductus arteriosus. The most common NEC stages were IIa (38.5%) and IIb (23.7%), which were associated with complications such as short bowel syndrome (18.8%) and post-surgical sepsis (37.5%). Among factors related to complications from NEC, medical-surgical management increased the risk (adjusted relative risk: 10.14 and 95% confidence interval: 1.95-48.72), while cardiac surgery reduced the likelihood of complications. NEC in infants with CHD is associated with multiple factors currently under investigation, which may explain a pathophysiological mechanism distinct from that of classic NEC.
2025-11-05 | Histologic changes in systemically loaded right ventricles at time of transplantation.
In a subset of complex congenital heart disease patients, the right ventricle (RV) is connected to the higher-resistance systemic circulation, often leading to RV dysfunction. This study characterizes the systemic RV histology at time of heart transplantation in two groups - patients with hypoplastic left heart syndrome with Fontan palliation (HLHS-F) and those with dextro-transposition of the great arteries post atrial switch operation (d-TGA-AS). We sought to better understand histological differences between the systemic RV in the single ventricle vs. biventricular circulations. We procured RV tissue samples at the mid-cavity free walls from nine explanted recipient hearts: six HLHS-F and three d-TGA-AS. RV and LV muscle samples from two organ donors whose hearts were unused for non-cardiac reasons served as controls. Tissue sections were stained with Masson's Trichrome and Hematoxylin and Eosin. Given the small cohort size and heterogeneity, analyses were descriptive. Continuous variables are reported as median (range). The d-TGA-AS population was older than the HLHS-F population (median: 42 years; range: 38-44 vs. median: 24 years; range: 12-32, respectively). RV fibrosis in the d-TGA-AS population was greater at 28% (7-35) vs. the HLHS-F population which was 4% (2-24) and donor controls (median: 2% range: 0-4). In contrast, RV wall thickness was greater in HLHS-F (median: 12,303 µm; range: 9,976-15,745) than in d-TGA-AS (median: 9,063 µm; range: 8,316-10,322) and donors (median 7,984 µm; range: 2,582-13,386). Donor LV thickness (median: 17,056 µm; range: 16,688-17,423) exceeded all RV groups. The primary histologic finding for the d-TGA-AS group was fibrosis, while the HLHS-F group showed predominantly hypertrophy. The temporal presentation of the patients was different, with the HLHS-F patients presenting earlier for transplant than the d-TGA-AS. These observations suggest that different histologic changes may occur in response to longstanding systemic pressures in these two anatomic subgroups of patients with systemic RV.
2025-09-25 | Effectiveness of therapy with recombinant human growth hormone (rhGH) in patients with hypoplastic left heart syndrome (HLHS) and short stature.
Hypoplastic left heart syndrome (HLHS) is among the most severe and complex forms of congenital heart disease. Despite advances in medical and surgical management, patients with HLHS remain at risk for numerous short- and long-term complications, including growth impairment. The aim of this study is to evaluate the effectiveness and safety of recombinant human growth hormone (rhGH) therapy in patients with HLHS and either growth hormone deficiency (GHD) or small for gestational age (SGA) status, treated at a single tertiary pediatric endocrinology center. We retrospectively studied eight male patients with HLHS and short stature. Patients were qualified for rhGH therapy in accordance with the guidelines of the Polish rhGH treatment program dedicated to children with short stature and GHD or SGA. Five patients with GHD were qualified for rhGH therapy. The median age of the patients was 14.4 years, and the median height standard deviation score (SDS) was -5.82. Patients who did not initiate rhGH therapy had a median age of 13.8 years and a median height SDS of -3.97. To evaluate the effectiveness of rhGH therapy, we assessed patients' height SDS, bone age, and serum insulin-like growth factor 1 (IGF-1) concentrations at baseline (prior to treatment initiation), approximately one year after the start of therapy, and annually thereafter. During rhGH therapy, the mean height SDS improved from -5.82 to -5.38 at the first follow-up after a mean duration of 1.1 years. Ultimately, the mean height SDS further improved to -4.92 after an average of 2.5 years of treatment. In contrast, patients who did not receive rhGH therapy showed no improvement; their mean height SDS declined from -3.79 to -4.15 over an observation period of 8 to 16 months. Growth failure in patients with HLHS is likely multifactorial in origin, extending beyond the cardiac defect and its treatment. Short stature in this population warrants thorough evaluation, and in cases of confirmed GHD, rhGH therapy should be considered when feasible. Treatment decisions must be individualized, considering the patient's overall clinical condition and coexisting comorbidities.
cell therapies
2026-07-31 | Cell-Derived Therapies for Hypoplastic Left Heart Syndrome: A Meta- Analysis
Background: Hypoplastic left heart syndrome is a severe single-ventricle congenital heart disease in which the right ventricle sustains systemic circulation after staged palliation. Cell-derived therapies have been investigated as adjunctive strategies to preserve ventricular function. This meta-analysis evaluated the safety and efficacy of cell-derived therapy in patients with hypoplastic left heart syndrome. Methods: PubMed, ScienceDirect, Wiley, and Cochrane were searched from inception to January 31, 2026. Database-specific search strings combined MeSH terms and free- text keywords for hypoplastic left heart syndrome, stem cells, cell-derived therapy, cardiosphere-derived cells, umbilical cord blood mononuclear cells, and mesenchymal precursor cells. Comparative human studies in HLHS or HLHS variants were included. Pooled odds ratios or mean differences with 95% confidence intervals were calculated using fixed-effect or random-effects models according to heterogeneity. Results: Six studies involving 218 patients were included. Cell-derived therapy improved right ventricular ejection fraction (mean difference, 4.61; 95% CI 0.28 to 8.94) and weight- for-age z score (MD 1.80; 95% CI 1.72 to 1.88). Mortality and hospital length of stay did not differ significantly between groups. Cardiopulmonary bypass time appeared shorter, but this finding was based on only two heterogeneous studies and should be interpreted cautiously. Conclusion: Adjunctive cell-derived therapy may improve ventricular function and somatic growth without a detectable early mortality signal, but the current evidence remains limited by small sample sizes, heterogeneity, and early-phase study designs.
2026-06-12 | Valved Sano Conduit During the Norwood Procedure: A Contemporary Review of Early Outcomes, Reintervention Burden, and Pulmonary Artery Growth.
The valved Sano (VS) right ventricle-to-pulmonary artery (RV-PA) shunt was developed to eliminate conduit regurgitation and thereby decrease volume load on the single right ventricle (RV) after the Norwood procedure. By reducing diastolic backflow, VS may limit tricuspid regurgitation and preserve RV function. Additional theoretical advantages include facilitated postoperative recovery and improved pulmonary artery (PA) growth. Despite compelling physiology, available evidence remains limited and largely retrospective. We describe the postoperative course of a low-weight neonate with hypoplastic left heart syndrome who underwent a Norwood procedure using a VS, and we review published literature addressing early outcomes, reintervention burden, late survival, and PA growth. Use of a VS can be associated with improved early physiologic recovery, lower postoperative lactate, faster diuresis and enteral advancement, and better early RV function. Short-term survival appears equivalent to the non-valved Sano. Interstage reinterventions remain frequent (40%-60% before stage II). Late survival beyond stage II is comparable to non-valved Sano. Femoral vein homograft-based conduits may promote greater PA growth and reduce the need for PA augmentation, but findings vary across centers. Valve competence commonly decays within 3-6 months, resulting in conduit regurgitation. VS conduits may facilitate early recovery and potentially favor PA growth when constructed with competent Femoral vein homograft segments, yet they have not demonstrated superior late survival or reduced reintervention burden. Larger multicenter studies are required to clarify optimal patient selection and long-term impact.
2026-05-05 | Progress in cell therapies for neonatal conditions: Proceedings of the Third Neonatal Cell Therapies Symposium (2025).
This special article synthesizes transformative insights from a recent international neonatal cell therapy symposium (held in Noosa, Australia) where leading experts convened to explore regenerative solutions for serious perinatal and neonatal conditions. The discussions highlighted pioneering cell-based therapies targeting preterm brain injury, bronchopulmonary dysplasia, fetal growth restriction, hypoplastic left heart syndrome and congenital diaphragmatic hernia; neonatal conditions that present both neonatal challenges and long-term morbidities, demanding innovation beyond conventional medical, surgical and supportive care. Advances in regenerative medicine, particularly those leveraging umbilical cord blood-derived cells, mesenchymal stromal cells from various sources, amniotic fluid and human amnion epithelial derived cells and extracellular vesicles, are redefining therapeutic possibilities through paracrine signaling, immunomodulation, and tissue repair to counteract shared mechanisms of inflammation, oxidative stress, apoptosis, and impaired regeneration. This article integrates the symposium's key clinical and translational perspectives, emphasizing system-specific developments across cardiovascular, pulmonary, neurological, and systemic domains, with a particular focus on scalable production strategies, and the importance of multidisciplinary collaboration. IMPACT: Synthesizes global evidence from preclinical and clinical studies to define the current translational trajectory of cell therapies across major neonatal conditions. Highlights integrative frameworks combining advanced preclinical modeling, clinical trials, scalable manufacturing and stakeholder collaboration to accelerate translation in neonatal regenerative medicine.
2026-04-21 | From Fetal Aortic Valvuloplasty to Ross Operation: An Exciting Journey
Fetuses with critical left ventricular outflow tract obstruction (LVOTO) without ventricular septal defect are at risk of developing signs of an evolving hypoplastic left heart syndrome. Besides reduced flow across the left ventricular outflow tract and impaired left ventricular function, abnormal size of the left ventricle (either hypoplastic or severely dilated), abnormal left-to-right shunt across the atrial septum, and retrograde flow in the aortic arch can be observed. Other left heart structures may also be affected, including the mitral valve, subaortic region, and aortic arch. Fetal aortic valvuloplasty (FAV) can relieve left ventricular outflow obstruction, improve left ventricular haemodynamics, and promote left ventricular growth.1,2 In selected patients, single ventricle palliation can be avoided and a biventricular circulation achieved. Nevertheless, most patients after FAV will need postnatal surgery to enable functional improvement. In cases of severe LVOTO and duct-dependent systemic circulation postnatally, an early Ross–Konno procedure is a radical and sustainable solution with growth potential to decompress the stressed left ventricle.3–5
2025-12-08 | Stem cell therapy for hypoplastic left heart syndrome: a systematic review of efficacy, safety, and future directions
Abstract Background Hypoplastic Left Heart Syndrome (HLHS) is a severe congenital heart disease characterized by underdevelopment of the left heart structures, often requiring staged surgical palliation. Despite improvements in surgical management, HLHS is associated with high mortality and long-term morbidity. Stem cell-based therapies have emerged as a promising adjunct to improve cardiac function and outcomes in these patients. Objectives This systematic review evaluates the long-term safety and efficacy of stem cell therapy, particularly cardiosphere-derived cells (CDCs) and umbilical cord blood-derived mononuclear cells (UCB-MNCs), in the treatment of HLHS. Methods Following PRISMA guidelines, a comprehensive search was conducted across major databases. Seven studies met the inclusion criteria, comprising randomized controlled trials, observational cohorts, and in vitro analyses. Quality appraisal was performed using RoB2, Newcastle–Ottawa, and SYRCLE tools. Results Stem cell therapy was associated with improvements in right ventricular ejection fraction, somatic growth, heart failure status, and psychosocial quality of life. CDCs showed favorable outcomes in both early and long-term follow-up, with reductions in scar burden, ventricular volume, and adverse events. Importantly, no major adverse effects such as arrhythmias, systemic infections, or tumor formation were reported. The use of allogeneic cells could extend beyond HLHS to other forms of congenital heart disease with right ventricular dysfunction, including tetralogy of Fallot, pulmonary atresia, and other single-ventricle variants. In vitro studies confirmed the regenerative capacity of pediatric-derived stem cells, with the highest potential in the first year of life. Conclusion Stem cell therapy demonstrates safety, feasibility, and potential efficacy in improving cardiac outcomes in HLHS. Larger, multicenter trials such as the APOLLON trial are warranted to validate these findings and support integration into standard clinical care.
small molecules
2026-07-22 | In Situ Alteplase for Rescue Recanalization After Glenn Thrombosis.
Superior vena cava (SVC) thrombosis after Glenn palliation constitutes acute cavopulmonary circuit failure. A 6-month-old boy with hypoplastic left heart syndrome developed SVC syndrome on postoperative day 13 after bidirectional Glenn, secondary to catheter-associated SVC-Glenn thrombosis with distal pulmonary embolisms. Alteplase infused in situ through the existing catheter (0.2 mg/kg/h, 72 hours) achieved complete recanalization without bleeding. Mediastinal hemorrhage and 4-day veno-arterial extracorporeal membrane oxygenation precluded thrombolysis and surgery, and mechanical disruption risked embolization into the compromised pulmonary bed. When an indwelling catheter traverses the thrombus, catheter-directed alteplase achieves complete recanalization, even after hemorrhage and extracorporeal support.
2026-07-14 | Functional improvement of heart failure in infants and children following the neonatal Norwood procedure.
Heart failure induced by systemic ventricular dysfunction after the Norwood procedure may improve with medications. This study aimed to evaluate the incidence of heart failure, medication use, and subsequent improvement after the Norwood procedure. Among the patients undergoing the Norwood procedure between 2001 and 2024, those who demonstrated heart failure (systemic ventricular dysfunction lasting > 30 days) were identified. Medical therapy and clinical outcomes were evaluated in relation to the recovery of systemic ventricular dysfunction. Among 380 patients after the Norwood procedure, heart failure was observed in 55 patients. Recovery of systemic ventricular function occurred in 21 patients with a median duration of 187 (interquartile range: 77-354) days. The cumulative incidence of recovery was 60.9% at 5 years. Recovery was more frequently observed in patients whose onset was between stage II and III palliation than in other periods (58% vs. 28%, p = .029). Survival after the onset of heart failure was better in patients who showed recovery than in those who did not (88.8% vs. 26.7% at 5 years, p < .001). At the onset of heart failure, zlog-N-terminal prohormone of brain natriuretic peptide (4.2 ± 1.3 vs. 4.5 ± 1.3, p = .55) was similar but differed at the last follow-up (2.2 ± 1.3 vs. 5.1 ± 1.5, p = .01) in patients with and without recovery. A phosphodiesterase type 5 inhibitor was identified as a factor that promoted the recovery (hazard ratio: 5.89, p < .01). In patients who developed heart failure after the Norwood procedure, survival was better in those with recovered function than in those with sustained dysfunction. Phosphodiesterase type 5 inhibitors were identified as a factor promoting the recovery.
2026-07-03 | Association of Digoxin Use at Norwood Discharge with Fontan Completion: A Study from the Pediatric Heart Network Public Dataset.
Digoxin use after the Norwood procedure has been associated with improved interstage survival in hypoplastic left heart syndrome and related conditions. Whether this benefit translates into improved longer-term outcomes through staged palliation remains unknown. We aimed to determine the association of digoxin use at Norwood discharge with transplant-free survival and Fontan completion. We conducted a retrospective cohort study using the Pediatric Heart Network (PHN) Single Ventricle Reconstruction trial public dataset, including 549 infants enrolled at 15 North American centers between 2005 and 2008. Competing risk analysis was used to evaluate Fontan completion and Cox regression to assess death or transplantation within 6 years after the Norwood procedure. Mixed-effects models compared pre-Fontan hemodynamic and echocardiographic right ventricular indices between patients treated with and without digoxin after accounting for center clustering and adjustment for sex, shunt type, heart failure medications at Norwood discharge, and census block poverty level. The 6-year cumulative incidence of Fontan completion was higher among patients discharged on digoxin than among those not receiving digoxin (82% vs 71%; p = 0.013). Competing-risk analysis accounting for death and transplant demonstrated a greater likelihood of Fontan completion among digoxin users (aHR 1.31; 95%CI 1.09-1.58; p = 0.005), without significant difference in the hazard of death or transplant (aHR 0.78; 95%CI 0.53-1.15; p = 0.208). No significant differences in pre-Fontan hemodynamic or echocardiographic indices were observed between groups. Initiation of digoxin post Stage II procedure was not associated with improved survival or likelihood to complete Fontan. Digoxin use at the time of Norwood discharge was associated with a 30% greater likelihood of Fontan completion by 6 years, without accompanying improvement in transplant-free survival. These findings extend prior observations of improved interstage outcomes associated with digoxin use and suggest that treatment may facilitate progression through staged palliation. What is new?: 1)Digoxin use during the interstage was associated with a greater likelihood of reaching Fontan completion within 6 years after Norwood discharge. However, this association was not accompanied by differences in right ventricular hemodynamic or echocardiographic indices at the time of Fontan evaluation.What are the clinical implications?: 2)These findings extend prior observations of improved interstage outcomes associated with digoxin use and provide important information for clinicians caring for patients with single-ventricle heart disease. Further studies are needed to clarify the mechanisms underlying this association and to identify patients most likely to benefit.
2026-05-13 | Fetal Intervention Using an Everolimus-Eluting Stent in HLHS With Intact Atrial Septum.
In utero stenting of the atrial septum has been introduced for fetuses with hypoplastic left heart syndrome (HLHS) and intact atrial septum (IAS) to prevent secondary pulmonary vascular damage caused by left atrial hypertension. Previous reports revealed a high risk of significant or complete in-stent obstruction after successful intervention due to endothelial proliferation. We report a fetus with HLHS and IAS complicated by nutmeg lung who underwent successful fetal atrial septal stenting using an everolimus-eluting stent (Xience Sierra; Abbott). The procedure resulted in immediate left atrial decompression and maintained an unrestrictive interatrial communication until delivery. The use of a drug-eluting stent resulted in sustained stent patency without evidence of endothelial overgrowth and without detectable systemic adverse effects in the fetus. In utero use of an everolimus-eluting stent appears safe and may reduce the risk of in-stent obstruction in fetuses with HLHS and IAS.
2026-04-24 | Successful Fontan Completion in a Patient With Ellis-van Creveld Syndrome and a Hypoplastic Left Heart Syndrome Variant.
Ellis-van Creveld (EVC) syndrome is a rare genetic disorder often associated with skeletal abnormalities and congenital heart defects. Hypoplastic left heart syndrome (HLHS) in EVC is extremely rare and typically has a poor prognosis. We report a case of a 2-year and 7-month-old girl with EVC and HLHS who successfully underwent staged single-ventricle palliation, including the Norwood, Glenn, and Fontan procedures. Pre-Fontan evaluation showed acceptable pulmonary vascular resistance, and a fenestrated extracardiac Fontan procedure was performed without complications. This case underscores the importance of early pulmonary vascular protection and careful perioperative planning in achieving favorable outcomes in complex EVC-related congenital heart disease.
gene therapies
2026-03-04 | Animal models of hypoplastic left heart syndrome: genetic and anatomical approaches.
Hypoplastic Left Heart Syndrome (HLHS) is a life-threatening congenital heart disease characterized by underdevelopment of the left heart and aorta. Animal models of HLHS are used to study mechanisms of disease onset and progression and generally fall into two in vivo categories: genetic and mechanical. Genetic models primarily employ zebrafish and mice, whereas mechanically induced models are developed in chick embryos, fetal lambs, and rodents. Together, genetic and mechanical models provide insight into developmental and hemodynamic mechanisms of HLHS but differ in their ability to reproduce key anatomical and physiological features. Genetic models have identified genes and pathways involved in structural abnormalities and disrupted cell lineage. Mechanical models commonly restrict left-heart inflow using surgical or catheter-based techniques to induce hypoplasia of the left ventricle, valves, and aorta. Findings across chick embryos, fetal lambs, and mouse models support the "no flow, no grow" theory. This review synthesizes current HLHS animal models, evaluates their advantages and limitations, and considers their translational relevance from genetic and hemodynamic perspectives, while emphasizing species-specific limitations. IMPACT: Systematically evaluate genetically and mechanically induced HLHS models across zebrafish, mice, rats, chick embryos, and fetal lambs. Discuss how these models elucidate developmental and hemodynamic mechanisms of HLHS, highlight innovations such as CRISPR-based gene editing and staged in utero flow restriction, and assess their translational relevance, particularly for fetal intervention research. Provide practical criteria for model selection and interpretation, weighing strengths, limitations, and fidelity to human HLHS for mechanistic and translational aims.
2025-11-07 | Fetal magnetic resonance imaging diagnosis of pulmonary lymphangiectasia in hypoplastic left heart syndrome: Association with fetal echocardiography and postnatal outcome.
Secondary pulmonary lymphangiectasia (PL) is a recognised complication of hypoplastic left heart syndrome (HLHS) with an intact or restrictive atrial septum, associated with poor postnatal outcomes. Fetal MRI has been increasingly used to assess pulmonary abnormalities in HLHS, but the prognostic significance of subtle PL-like changes remains unclear. In this study, we evaluate the relationship between fetal MRI lung findings, echocardiographic markers of pulmonary venous obstruction, and postnatal outcomes. A retrospective analysis of all fetuses with HLHS who underwent fetal MRI between July 2019 and December 2022 was performed. MRI images were reviewed for features of PL and categorised as "normal," "suspicious," or "diagnostic" of PL. Pulmonary venous Doppler velocity-time integral (VTI) ratios from the most recent fetal echocardiogram were then compared to MRI findings. Postnatal outcomes, including early ventilation, need for intervention, and survival at 28 days and 1 year, were assessed. Of 20 fetuses with HLHS who underwent MRI, 6/20 (30%) showed features suspicious or diagnostic of PL (5 "suspicious" and 1 "diagnostic"), and 6/20 (30%) showed some evidence of pulmonary venous obstruction (PVO) on echo. While echo markers of PVO were significantly associated with some degree of PL on MRI (p=0.006), neither PL nor PVO predicted the need for early support/intervention or survival in fetuses who underwent active postnatal management. Fetuses with HLHS may exhibit a spectrum of lung changes on fetal MRI related to pulmonary venous obstruction. Whilst technical factors may also play a role, a degree of caution is advisable when interpreting more subtle forms of PL in fetal life, particularly in the absence of echocardiographic markers of severe atrial restriction. Larger, multi-centre prospective studies are needed to refine diagnostic criteria for PL in HLHS and better understand its prognostic significance in terms of both early and long-term outcome.
2025-06-19 | Long-Term Survival and Patient-Reported Outcomes After Staged Reconstructive Surgery for Hypoplastic Left Heart Syndrome.
Survival for hypoplastic left heart syndrome (HLHS) and variants has improved over the past 4 decades; however, survival remains low compared with other forms of congenital heart disease. There is a paucity of data concerning long-term outcomes. This study aims to: 1) examine long-term survival and the impact of patient factors on survival for newborns with HLHS; and 2) examine functional and health outcomes, including quality-of-life (QOL) in adulthood. The study cohort included patients with HLHS and variants undergoing the Norwood or hybrid procedure between January 1984 and December 2023. Data on patient characteristics and management were abstracted from medical records. Vital status was ascertained by direct subject and family contact, review of the medical record, and publicly available data. Functional outcomes and QOL in adults (≥18 years of age) were assessed by patient reports. The primary outcome was death or cardiac transplantation at last follow-up. In the study period, 2,012 neonates underwent staged reconstructive surgery for HLHS (Norwood, n = 1,921 and hybrid, n = 91). Transplant-free survival was 31.0% at 35 years. Transplant-free survival improved over time but is not different across recent eras. Most responders reported good to excellent general health. In this cohort of newborns undergoing staged reconstructive surgery for HLHS, fewer than one-third are alive without a transplant at 35 years of age. Survival has not improved in recent years. However, there is a group of survivors who report good to excellent outcomes and QOL, consistent with a "high-performing" Fontan phenotype.
2025-05-22 | eLife Assessment: Functional analysis across model systems implicates ribosomal proteins in growth and proliferation defects associated with hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) is the most lethal congenital heart disease (CHD). The pathogenesis of HLHS is poorly understood, and due to the likely oligogenic complexity of the disease, definitive HLHS-causing genes have not yet been identified. Postulating impaired cardiomyocyte proliferation as a likely important contributing mechanism to HLHS pathogenesis, and we conducted a genome-wide siRNA screen to identify genes affecting proliferation of human iPSC-derived cardiomyocytes (hPSC-CMs). This yielded ribosomal protein (RP) genes as the most prominent class of effectors of CM proliferation. In parallel, whole genome sequencing and rare variant filtering of a cohort of 25 HLHS proband-parent trios with poor clinical outcome revealed enrichment of rare variants of RP genes. In addition, in a familial CHD case we identified a rare, predicted-damaging promoter variant affecting RPS15A that was shared between the HLHS proband and a distant relative with CHD. Functional testing with an integrated multi-model system approach reinforced the idea that RP genes are major regulators of cardiac growth and proliferation, thus potentially contributing to the hypoplastic phenotype observed in HLHS patients. Cardiac knockdown (KD) of RP genes with promoter or coding variants (RPS15A, RPS17, RPL26L1, RPL39, RPS15) reduced proliferation in generic hPSC-CMs and caused malformed hearts, heart-loss or even lethality in Drosophila. In zebrafish, diminished rps15a function caused reduced CM numbers, heart looping defects, or weakened contractility, while reduced rps17 or rpl39 function caused reduced ventricular size or systolic atrial dysfunction of the atrium, respectively. Importantly, genetic interactions between RPS15A and core cardiac transcription factors TBX5 in CMs, Drosocross, pannier and tinman in flies, and tbx5 and nkx2-7 (nkx2-5 paralog) in fish, support a specific role for RP genes in heart development. Furthermore, RPS15A KD-induced heart/CM proliferation defects were significantly attenuated by p53 KD in both hPSC- CMs and zebrafish, and by Hippo activation (YAP/yorkie overexpression) in developing fly hearts. Based on these findings, we conclude that RP genes play novel critical roles in cardiogenesis and constitute an emerging class of gene candidates likely involved in HLHS and other CHDs.
2025-01-31 | EBV encephalitis in an immunocompetent adult with hypoplastic left heart syndrome A case report
EBV is a rare cause of encephalitis which can present with a broad spectrum of focal and diffuse neurological symptoms. In immunocompetent patients, prompt diagnosis can be difficult, especially in the context of comorbid conditions with similar symptomatology.
other
2026-04-17 | Single-cell omics uncovers novel pathological mechanisms and therapeutic targets for congenital heart diseases: insights from integrated intercellular communication analysis.
Congenital heart disease (CHD) affects approximately 1% of live births worldwide and remains the leading cause of infant mortality from congenital anomalies. Despite advances in diagnosis and therapeutics, the molecular mechanisms underlying CHD pathogenesis remain incompletely understood, limiting the development of efficient targeted therapies. Single-cell omics approaches including single-cell RNA sequencing (scRNA-seq) have revolutionized our understanding of cardiac cellular heterogeneity and intercellular signalling. This review synthesizes recent single-cell omics studies in cardiogenesis and CHD, and presents novel insights from an integrated reanalysis to identify potential therapeutic targets. We systematically reviewed single-cell omics studies in human cardiogenesis and CHD (2019-2025), then reanalysed the Hill et al. dataset comprising 157,273 nuclei from paediatric patients across five diagnostic categories, including neonatal and infant hypoplastic left heart syndrome (HLHS), tetralogy of Fallot (TOF), dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) with healthy donor controls. We quantified cardiac-specific ligand-receptor interactions to characterize disease-specific intercellular communication networks through pathway enrichment and network topology analysis. Reanalysis revealed extensive remodelling of cell-cell communication networks across CHD subtypes, each displaying distinct signalling architectures. Neonatal HLHS and TOF demonstrated hyperactivation of metabolic and growth factor pathways with highly centralized endothelial cell (EC) to cardiomyocyte (CM) and cardiac fibroblast (CF) to CM networks. DCM showed selective metabolic enhancement with preserved integration. In contrast, HCM exhibited broad pathway suppression, particularly morphogen signalling, and fragmented connectivity with weakened CF-CM and EC-CM coupling. Infant HLHS represented an intermediate phenotype with suppressed Notch and extracellular matrix signalling. Single-cell omics studies have revealed cellular heterogeneity and disease-specific mechanisms across CHD subtypes. Our network-based reanalysis demonstrates that CHD involves not only transcriptional defects but also profound disruptions in multicellular communication, with each subtype exhibiting distinct signalling architectures. These findings provide a foundation for precision therapeutic strategies tailored to individual CHD subtypes, with future multimodal approaches accelerating clinical translation.
2025-11-03 | Abstract 4367268: Regulatory LncRNA H19 and mitophagy in hypoplastic left heart syndrome and in immature ischemic/reperfused rodent hearts
Introduction: Hypoplastic left heart syndrome (HLHS) is one of the most clinically challenging congenital heart diseases. The long non-coding RNA (lncRNA) H19 has been identified as a key regulator of mitochondrial function and myocardial ischemia/reperfusion injury (MIRI) in adult human and animal hearts. However, the regulation and role of H19 in immature human and animal hearts remain unknown. Hypothesis: Upregulated H19 in HLHS and in immature ischemic/reperfused animal hearts suppresses mitophagy through the PINK1/Parkin pathway. Methods: Myocardial tissues were collected from HLHS patients at the time of heart transplantation, and control tissues were obtained from donor hearts. HLHS-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes were subjected to hypoxia for 3 hours followed by 24 hours of reoxygenation. MIRI was induced in 14–15-day-old Wistar rats by ligating coronary artery for 60 min, followed by 24-hour reperfusion (Fig. 1), H19 expression was measured by quantitative PCR. Myocardial tissues were examined by electron microscopy to identify autophagosomes/autolysosomes containing mitochondria. Mitochondrial PINK1 and Parkin protein levels were assessed by Western blot analysis. In separate experiments, 2–3-day-old Wistar rats were injected with lentiviral vectors carrying siRNA targeting H19 or control vectors. Additionally, PINK1 knockout and C57BL/6 control mice were subjected to MIRI on a Langendorff apparatus. Results: H19 expression was upregulated and mitophagy was decreased in cardiac tissues from HLHS patients compared to controls, accompanied by reduced mitochondrial PINK1 and Parkin expression (Fig. 2). In iPSC-derived cardiomyocytes, hypoxia/reoxygenation induced lactate dehydrogenase release and H19 expression and decreased PINK1 and Parkin expression. In rats, MIRI resulted in an infarct size of 40 ± 2% of the area-at-risk (n = 10), accompanied by elevated H19 expression, reduced mitochondrial PINK1 and Parkin levels, and suppressed mitophagy (Fig.3). H19 knockdown reduced infarct size (decreased lactate dehydrogenase release in iPSC-derived cardiomyocytes), increased mitochondrial PINK1 and Parkin levels, and enhanced mitophagy in ischemic/reperfused hearts. Compared to C57BL/6 controls, PINK1 knockout mice exhibited significantly reduced ±dP/dt and decreased mitophagy two hours after reperfusion. Conclusions: Upregulated H19 exacerbates MIRI by suppressing PINK1/Parkin-mediated mitophagy in immature hearts.
2025-08-01 | Abstract Thu063: Functional siRNA Screen Reveals Core Regulators of Hypoplastic Left Heart Syndrome Cardiomyocyte Defects
Hypoplastic Left Heart Syndrome (HLHS) is a congenital heart disease with high mortality, but its molecular underpinnings remain poorly understood. Previous findings in patient-derived induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) revealed conserved defects (reduced proliferation, disrupted sarcomere organization). We hypothesize these phenotypes result from shared transcriptional and epigenetic regulators. We performed a functional siRNA screen with high-content morphological profiling to identify these regulators. From single-cell RNA-seq data, we selected 112 transcriptional/epigenetic regulators enriched in hiPSC-CMs for a custom siRNA library. Day 25 hiPSC-CMs from an unaffected father were treated and compared to control siRNA-treated father- and HLHS proband-derived hiPSC-CMs (4 replicate wells/siRNA, ~137 cells/well). Morphological profiling used high-content microscopy of ACTN2, DAPI, phalloidin, and MitoTracker-stained cells, measuring ~150 features (sarcomere organization, nuclear morphology, cell size, cytoskeleton integrity…). This workflow will be applied to additional HLHS trios to validate conserved regulators. Using 85 unbiased morphological features, we developed a k-nearest neighbors classifier, trained on untreated father- and proband-derived cells, that achieved 85% accuracy (AUC = 0.92) in distinguishing healthy from disease cells. Applied to siRNA-treated cells, it identified eight candidate genes whose knockdown caused ≥2-fold shift from healthy to disease-like phenotypes including known cardiac transcription factors (GATA6, PRDM16, PBX1) and additional regulators (TEAD4, NR6A1, PPP1R13B, NR4A3, ASB3) implicated in proliferation, cell structure, and extracellular matrix regulation—processes linked to HLHS. By integrating siRNA screening, morphological profiling, and machine learning, our study reveals a core regulatory network driving HLHS-associated cardiomyocyte defects. These findings advance our understanding of HLHS pathology and could inform therapeutic strategies. Our classification model may also generalize to other HLHS variants and congenital heart diseases, enabling broader applications in personalized disease modeling and drug discovery.
2022-10-07 | 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.
2022-07-08 | Epicardial HDAC3 Promotes Myocardial Growth Through a Novel MicroRNA Pathway
Background: Establishment of the myocardial wall requires proper growth cues from nonmyocardial tissues. During heart development, the epicardium and epicardium-derived cells instruct myocardial growth by secreting essential factors including FGF (fibroblast growth factor) 9 and IGF (insulin-like growth factor) 2. However, it is poorly understood how the epicardial secreted factors are regulated, in particular by chromatin modifications for myocardial formation. The current study is to investigate whether and how HDAC (histone deacetylase) 3 in the developing epicardium regulates myocardial growth. Methods: Various cellular and mouse models in conjunction with biochemical and molecular tools were employed to study the role of HDAC3 in the developing epicardium. Results: We deleted Hdac3 in the developing murine epicardium, and mutant hearts showed ventricular myocardial wall hypoplasia with reduction of epicardium-derived cells. The cultured embryonic cardiomyocytes with supernatants from Hdac3 knockout (KO) mouse epicardial cells also showed decreased proliferation. Genome-wide transcriptomic analysis revealed that Fgf9 and Igf2 were significantly downregulated in Hdac3 KO mouse epicardial cells. We further found that Fgf9 and Igf2 expression is dependent on HDAC3 deacetylase activity. The supplementation of FGF9 or IGF2 can rescue the myocardial proliferation defects treated by Hdac3 KO supernatant. Mechanistically, we identified that microRNA (miR)-322 and miR-503 were upregulated in Hdac3 KO mouse epicardial cells and Hdac3 epicardial KO hearts. Overexpression of miR-322 or miR-503 repressed FGF9 and IGF2 expression, while knockdown of miR-322 or miR-503 restored FGF9 and IGF2 expression in Hdac3 KO mouse epicardial cells. Conclusions: Our findings reveal a critical signaling pathway in which epicardial HDAC3 promotes compact myocardial growth by stimulating FGF9 and IGF2 through repressing miR-322 or miR-503, providing novel insights in elucidating the etiology of congenital heart defects and conceptual strategies to promote myocardial regeneration.
proteins
2026-08-04 | Sex-stratified trends in hypoplastic left heart syndrome-related mortality among children and young adults in the United States, 1999–2024: a pre- and post-COVID-19 analysis
Background Hypoplastic left heart syndrome (HLHS) is a congenital heart disease that accounts for approximately 3% of congenital heart defects, making it a leading cause of mortality in this population. Timely staged palliation, such as Norwood, Glenn, and Fontan, are required to reduce the incidence of adverse outcomes. Data over the long term suggest that only about 31% of patients with HLHS are alive at age 35 years after Fontan completion. However, national mortality trend data stratified by sex, extending through 2024 and spanning the COVID-19 era, have not been characterised. Methods Data for this study were obtained from the CDC WONDER (Centres for Disease Control and Prevention Wide-ranging Online Data for Epidemiologic Research) Multiple Cause of Death database using ICD-10 code Q23.4 from 1999 through 2024 in individuals aged 0–24 years. Joinpoint regression was used to analyse trends. Analyses were conducted using a Poisson variation model with Monte Carlo permutation testing. Statistical significance was defined as p < 0.05 based on two-tailed testing and was stratified by sex. Results A total of 10,138 deaths were identified in the United States during the study period. Among these, 4,285 were females, and 5,853 were males. Joinpoint regression identified a declining trend from 1999 to 2021 (APC: −2.22%; 95% CI: −3.08 to −1.89; p = 0.006), with a non-significant increase from 2021 to 2024 (APC: +4.97%; p = 0.156). In 2020, total HLHS-related deaths reached their lowest point ( n = 287) before rising consecutively to 358 in 2024. Female mortality trends declined throughout the study period (APC: −1.96%; 95% CI: −2.61 to −1.33; p < 0.001) compared with males, who remained consistently high. Conclusion HLHS mortality has declined following surgical advances and perioperative care management. Persistent higher mortality rates were noted among males than females throughout both pre- and post-COVID eras. The rise in post-pandemic mortality is a new and concerning trend that warrants close national monitoring. These trends emphasise the need for uninterrupted staged palliation and continued population-level surveillance of HLHS outcomes.
2026-04-15 | Single Nuclei Transcriptome of a Hypoplastic Left Heart Syndrome Patient Post Myocardial Infarction
Single-nucleus RNA sequencing (snRNA-seq) was performed on right ventricular (RV) myocardial tissue obtained at transplantation from a patient with HLHS complicated by myocardial infarction (HLHS-MI). After quality control and doublet removal, 4,134 nuclei were retained. Cell types were identified by graph-based clustering and canonical marker expression.
2026-04-06 | Risk factors for complications of necrotizing enterocolitis in term neonates with congenital heart disease at a referral hospital in Colombia: A retrospective cohort study.
Necrotizing enterocolitis (NEC) is one of the most severe complications in neonates and infants. However, term infants with congenital heart disease (CHD) represent a scenario of multiple complications due to pathophysiological mechanisms that differ from the classic pathogenesis. The objective of the study was to determine factors associated with complications of NEC in term infants hospitalized for CHD in a pediatric intensive care unit of a referral hospital in Colombia between 2010 and 2023. A retrospective cohort study was conducted, including 148 term infants with CHD who developed NEC during their hospitalization. Demographic and clinical characteristics were analyzed. Descriptive and bivariate analyses were performed using the Chi-square and Mann-Whitney U-tests. A multivariate analysis was conducted using robust Poisson regression with Stata 18.0® software. The most frequent CHD were hypoplastic left heart syndrome (HLHS), pulmonary atresia, and persistent ductus arteriosus. The most common NEC stages were IIa (38.5%) and IIb (23.7%), which were associated with complications such as short bowel syndrome (18.8%) and post-surgical sepsis (37.5%). Among factors related to complications from NEC, medical-surgical management increased the risk (adjusted relative risk: 10.14 and 95% confidence interval: 1.95-48.72), while cardiac surgery reduced the likelihood of complications. NEC in infants with CHD is associated with multiple factors currently under investigation, which may explain a pathophysiological mechanism distinct from that of classic NEC.
2025-11-05 | Histologic changes in systemically loaded right ventricles at time of transplantation.
In a subset of complex congenital heart disease patients, the right ventricle (RV) is connected to the higher-resistance systemic circulation, often leading to RV dysfunction. This study characterizes the systemic RV histology at time of heart transplantation in two groups - patients with hypoplastic left heart syndrome with Fontan palliation (HLHS-F) and those with dextro-transposition of the great arteries post atrial switch operation (d-TGA-AS). We sought to better understand histological differences between the systemic RV in the single ventricle vs. biventricular circulations. We procured RV tissue samples at the mid-cavity free walls from nine explanted recipient hearts: six HLHS-F and three d-TGA-AS. RV and LV muscle samples from two organ donors whose hearts were unused for non-cardiac reasons served as controls. Tissue sections were stained with Masson's Trichrome and Hematoxylin and Eosin. Given the small cohort size and heterogeneity, analyses were descriptive. Continuous variables are reported as median (range). The d-TGA-AS population was older than the HLHS-F population (median: 42 years; range: 38-44 vs. median: 24 years; range: 12-32, respectively). RV fibrosis in the d-TGA-AS population was greater at 28% (7-35) vs. the HLHS-F population which was 4% (2-24) and donor controls (median: 2% range: 0-4). In contrast, RV wall thickness was greater in HLHS-F (median: 12,303 µm; range: 9,976-15,745) than in d-TGA-AS (median: 9,063 µm; range: 8,316-10,322) and donors (median 7,984 µm; range: 2,582-13,386). Donor LV thickness (median: 17,056 µm; range: 16,688-17,423) exceeded all RV groups. The primary histologic finding for the d-TGA-AS group was fibrosis, while the HLHS-F group showed predominantly hypertrophy. The temporal presentation of the patients was different, with the HLHS-F patients presenting earlier for transplant than the d-TGA-AS. These observations suggest that different histologic changes may occur in response to longstanding systemic pressures in these two anatomic subgroups of patients with systemic RV.
2025-09-25 | Effectiveness of therapy with recombinant human growth hormone (rhGH) in patients with hypoplastic left heart syndrome (HLHS) and short stature.
Hypoplastic left heart syndrome (HLHS) is among the most severe and complex forms of congenital heart disease. Despite advances in medical and surgical management, patients with HLHS remain at risk for numerous short- and long-term complications, including growth impairment. The aim of this study is to evaluate the effectiveness and safety of recombinant human growth hormone (rhGH) therapy in patients with HLHS and either growth hormone deficiency (GHD) or small for gestational age (SGA) status, treated at a single tertiary pediatric endocrinology center. We retrospectively studied eight male patients with HLHS and short stature. Patients were qualified for rhGH therapy in accordance with the guidelines of the Polish rhGH treatment program dedicated to children with short stature and GHD or SGA. Five patients with GHD were qualified for rhGH therapy. The median age of the patients was 14.4 years, and the median height standard deviation score (SDS) was -5.82. Patients who did not initiate rhGH therapy had a median age of 13.8 years and a median height SDS of -3.97. To evaluate the effectiveness of rhGH therapy, we assessed patients' height SDS, bone age, and serum insulin-like growth factor 1 (IGF-1) concentrations at baseline (prior to treatment initiation), approximately one year after the start of therapy, and annually thereafter. During rhGH therapy, the mean height SDS improved from -5.82 to -5.38 at the first follow-up after a mean duration of 1.1 years. Ultimately, the mean height SDS further improved to -4.92 after an average of 2.5 years of treatment. In contrast, patients who did not receive rhGH therapy showed no improvement; their mean height SDS declined from -3.79 to -4.15 over an observation period of 8 to 16 months. Growth failure in patients with HLHS is likely multifactorial in origin, extending beyond the cardiac defect and its treatment. Short stature in this population warrants thorough evaluation, and in cases of confirmed GHD, rhGH therapy should be considered when feasible. Treatment decisions must be individualized, considering the patient's overall clinical condition and coexisting comorbidities.
cell therapies
2026-07-31 | Cell-Derived Therapies for Hypoplastic Left Heart Syndrome: A Meta- Analysis
Background: Hypoplastic left heart syndrome is a severe single-ventricle congenital heart disease in which the right ventricle sustains systemic circulation after staged palliation. Cell-derived therapies have been investigated as adjunctive strategies to preserve ventricular function. This meta-analysis evaluated the safety and efficacy of cell-derived therapy in patients with hypoplastic left heart syndrome. Methods: PubMed, ScienceDirect, Wiley, and Cochrane were searched from inception to January 31, 2026. Database-specific search strings combined MeSH terms and free- text keywords for hypoplastic left heart syndrome, stem cells, cell-derived therapy, cardiosphere-derived cells, umbilical cord blood mononuclear cells, and mesenchymal precursor cells. Comparative human studies in HLHS or HLHS variants were included. Pooled odds ratios or mean differences with 95% confidence intervals were calculated using fixed-effect or random-effects models according to heterogeneity. Results: Six studies involving 218 patients were included. Cell-derived therapy improved right ventricular ejection fraction (mean difference, 4.61; 95% CI 0.28 to 8.94) and weight- for-age z score (MD 1.80; 95% CI 1.72 to 1.88). Mortality and hospital length of stay did not differ significantly between groups. Cardiopulmonary bypass time appeared shorter, but this finding was based on only two heterogeneous studies and should be interpreted cautiously. Conclusion: Adjunctive cell-derived therapy may improve ventricular function and somatic growth without a detectable early mortality signal, but the current evidence remains limited by small sample sizes, heterogeneity, and early-phase study designs.
2026-06-12 | Valved Sano Conduit During the Norwood Procedure: A Contemporary Review of Early Outcomes, Reintervention Burden, and Pulmonary Artery Growth.
The valved Sano (VS) right ventricle-to-pulmonary artery (RV-PA) shunt was developed to eliminate conduit regurgitation and thereby decrease volume load on the single right ventricle (RV) after the Norwood procedure. By reducing diastolic backflow, VS may limit tricuspid regurgitation and preserve RV function. Additional theoretical advantages include facilitated postoperative recovery and improved pulmonary artery (PA) growth. Despite compelling physiology, available evidence remains limited and largely retrospective. We describe the postoperative course of a low-weight neonate with hypoplastic left heart syndrome who underwent a Norwood procedure using a VS, and we review published literature addressing early outcomes, reintervention burden, late survival, and PA growth. Use of a VS can be associated with improved early physiologic recovery, lower postoperative lactate, faster diuresis and enteral advancement, and better early RV function. Short-term survival appears equivalent to the non-valved Sano. Interstage reinterventions remain frequent (40%-60% before stage II). Late survival beyond stage II is comparable to non-valved Sano. Femoral vein homograft-based conduits may promote greater PA growth and reduce the need for PA augmentation, but findings vary across centers. Valve competence commonly decays within 3-6 months, resulting in conduit regurgitation. VS conduits may facilitate early recovery and potentially favor PA growth when constructed with competent Femoral vein homograft segments, yet they have not demonstrated superior late survival or reduced reintervention burden. Larger multicenter studies are required to clarify optimal patient selection and long-term impact.
2026-05-05 | Progress in cell therapies for neonatal conditions: Proceedings of the Third Neonatal Cell Therapies Symposium (2025).
This special article synthesizes transformative insights from a recent international neonatal cell therapy symposium (held in Noosa, Australia) where leading experts convened to explore regenerative solutions for serious perinatal and neonatal conditions. The discussions highlighted pioneering cell-based therapies targeting preterm brain injury, bronchopulmonary dysplasia, fetal growth restriction, hypoplastic left heart syndrome and congenital diaphragmatic hernia; neonatal conditions that present both neonatal challenges and long-term morbidities, demanding innovation beyond conventional medical, surgical and supportive care. Advances in regenerative medicine, particularly those leveraging umbilical cord blood-derived cells, mesenchymal stromal cells from various sources, amniotic fluid and human amnion epithelial derived cells and extracellular vesicles, are redefining therapeutic possibilities through paracrine signaling, immunomodulation, and tissue repair to counteract shared mechanisms of inflammation, oxidative stress, apoptosis, and impaired regeneration. This article integrates the symposium's key clinical and translational perspectives, emphasizing system-specific developments across cardiovascular, pulmonary, neurological, and systemic domains, with a particular focus on scalable production strategies, and the importance of multidisciplinary collaboration. IMPACT: Synthesizes global evidence from preclinical and clinical studies to define the current translational trajectory of cell therapies across major neonatal conditions. Highlights integrative frameworks combining advanced preclinical modeling, clinical trials, scalable manufacturing and stakeholder collaboration to accelerate translation in neonatal regenerative medicine.
2026-04-21 | From Fetal Aortic Valvuloplasty to Ross Operation: An Exciting Journey
Fetuses with critical left ventricular outflow tract obstruction (LVOTO) without ventricular septal defect are at risk of developing signs of an evolving hypoplastic left heart syndrome. Besides reduced flow across the left ventricular outflow tract and impaired left ventricular function, abnormal size of the left ventricle (either hypoplastic or severely dilated), abnormal left-to-right shunt across the atrial septum, and retrograde flow in the aortic arch can be observed. Other left heart structures may also be affected, including the mitral valve, subaortic region, and aortic arch. Fetal aortic valvuloplasty (FAV) can relieve left ventricular outflow obstruction, improve left ventricular haemodynamics, and promote left ventricular growth.1,2 In selected patients, single ventricle palliation can be avoided and a biventricular circulation achieved. Nevertheless, most patients after FAV will need postnatal surgery to enable functional improvement. In cases of severe LVOTO and duct-dependent systemic circulation postnatally, an early Ross–Konno procedure is a radical and sustainable solution with growth potential to decompress the stressed left ventricle.3–5
2025-12-08 | Stem cell therapy for hypoplastic left heart syndrome: a systematic review of efficacy, safety, and future directions
Abstract Background Hypoplastic Left Heart Syndrome (HLHS) is a severe congenital heart disease characterized by underdevelopment of the left heart structures, often requiring staged surgical palliation. Despite improvements in surgical management, HLHS is associated with high mortality and long-term morbidity. Stem cell-based therapies have emerged as a promising adjunct to improve cardiac function and outcomes in these patients. Objectives This systematic review evaluates the long-term safety and efficacy of stem cell therapy, particularly cardiosphere-derived cells (CDCs) and umbilical cord blood-derived mononuclear cells (UCB-MNCs), in the treatment of HLHS. Methods Following PRISMA guidelines, a comprehensive search was conducted across major databases. Seven studies met the inclusion criteria, comprising randomized controlled trials, observational cohorts, and in vitro analyses. Quality appraisal was performed using RoB2, Newcastle–Ottawa, and SYRCLE tools. Results Stem cell therapy was associated with improvements in right ventricular ejection fraction, somatic growth, heart failure status, and psychosocial quality of life. CDCs showed favorable outcomes in both early and long-term follow-up, with reductions in scar burden, ventricular volume, and adverse events. Importantly, no major adverse effects such as arrhythmias, systemic infections, or tumor formation were reported. The use of allogeneic cells could extend beyond HLHS to other forms of congenital heart disease with right ventricular dysfunction, including tetralogy of Fallot, pulmonary atresia, and other single-ventricle variants. In vitro studies confirmed the regenerative capacity of pediatric-derived stem cells, with the highest potential in the first year of life. Conclusion Stem cell therapy demonstrates safety, feasibility, and potential efficacy in improving cardiac outcomes in HLHS. Larger, multicenter trials such as the APOLLON trial are warranted to validate these findings and support integration into standard clinical care.
small molecules
2026-07-22 | In Situ Alteplase for Rescue Recanalization After Glenn Thrombosis.
Superior vena cava (SVC) thrombosis after Glenn palliation constitutes acute cavopulmonary circuit failure. A 6-month-old boy with hypoplastic left heart syndrome developed SVC syndrome on postoperative day 13 after bidirectional Glenn, secondary to catheter-associated SVC-Glenn thrombosis with distal pulmonary embolisms. Alteplase infused in situ through the existing catheter (0.2 mg/kg/h, 72 hours) achieved complete recanalization without bleeding. Mediastinal hemorrhage and 4-day veno-arterial extracorporeal membrane oxygenation precluded thrombolysis and surgery, and mechanical disruption risked embolization into the compromised pulmonary bed. When an indwelling catheter traverses the thrombus, catheter-directed alteplase achieves complete recanalization, even after hemorrhage and extracorporeal support.
2026-07-14 | Functional improvement of heart failure in infants and children following the neonatal Norwood procedure.
Heart failure induced by systemic ventricular dysfunction after the Norwood procedure may improve with medications. This study aimed to evaluate the incidence of heart failure, medication use, and subsequent improvement after the Norwood procedure. Among the patients undergoing the Norwood procedure between 2001 and 2024, those who demonstrated heart failure (systemic ventricular dysfunction lasting > 30 days) were identified. Medical therapy and clinical outcomes were evaluated in relation to the recovery of systemic ventricular dysfunction. Among 380 patients after the Norwood procedure, heart failure was observed in 55 patients. Recovery of systemic ventricular function occurred in 21 patients with a median duration of 187 (interquartile range: 77-354) days. The cumulative incidence of recovery was 60.9% at 5 years. Recovery was more frequently observed in patients whose onset was between stage II and III palliation than in other periods (58% vs. 28%, p = .029). Survival after the onset of heart failure was better in patients who showed recovery than in those who did not (88.8% vs. 26.7% at 5 years, p < .001). At the onset of heart failure, zlog-N-terminal prohormone of brain natriuretic peptide (4.2 ± 1.3 vs. 4.5 ± 1.3, p = .55) was similar but differed at the last follow-up (2.2 ± 1.3 vs. 5.1 ± 1.5, p = .01) in patients with and without recovery. A phosphodiesterase type 5 inhibitor was identified as a factor that promoted the recovery (hazard ratio: 5.89, p < .01). In patients who developed heart failure after the Norwood procedure, survival was better in those with recovered function than in those with sustained dysfunction. Phosphodiesterase type 5 inhibitors were identified as a factor promoting the recovery.
2026-07-03 | Association of Digoxin Use at Norwood Discharge with Fontan Completion: A Study from the Pediatric Heart Network Public Dataset.
Digoxin use after the Norwood procedure has been associated with improved interstage survival in hypoplastic left heart syndrome and related conditions. Whether this benefit translates into improved longer-term outcomes through staged palliation remains unknown. We aimed to determine the association of digoxin use at Norwood discharge with transplant-free survival and Fontan completion. We conducted a retrospective cohort study using the Pediatric Heart Network (PHN) Single Ventricle Reconstruction trial public dataset, including 549 infants enrolled at 15 North American centers between 2005 and 2008. Competing risk analysis was used to evaluate Fontan completion and Cox regression to assess death or transplantation within 6 years after the Norwood procedure. Mixed-effects models compared pre-Fontan hemodynamic and echocardiographic right ventricular indices between patients treated with and without digoxin after accounting for center clustering and adjustment for sex, shunt type, heart failure medications at Norwood discharge, and census block poverty level. The 6-year cumulative incidence of Fontan completion was higher among patients discharged on digoxin than among those not receiving digoxin (82% vs 71%; p = 0.013). Competing-risk analysis accounting for death and transplant demonstrated a greater likelihood of Fontan completion among digoxin users (aHR 1.31; 95%CI 1.09-1.58; p = 0.005), without significant difference in the hazard of death or transplant (aHR 0.78; 95%CI 0.53-1.15; p = 0.208). No significant differences in pre-Fontan hemodynamic or echocardiographic indices were observed between groups. Initiation of digoxin post Stage II procedure was not associated with improved survival or likelihood to complete Fontan. Digoxin use at the time of Norwood discharge was associated with a 30% greater likelihood of Fontan completion by 6 years, without accompanying improvement in transplant-free survival. These findings extend prior observations of improved interstage outcomes associated with digoxin use and suggest that treatment may facilitate progression through staged palliation. What is new?: 1)Digoxin use during the interstage was associated with a greater likelihood of reaching Fontan completion within 6 years after Norwood discharge. However, this association was not accompanied by differences in right ventricular hemodynamic or echocardiographic indices at the time of Fontan evaluation.What are the clinical implications?: 2)These findings extend prior observations of improved interstage outcomes associated with digoxin use and provide important information for clinicians caring for patients with single-ventricle heart disease. Further studies are needed to clarify the mechanisms underlying this association and to identify patients most likely to benefit.
2026-05-13 | Fetal Intervention Using an Everolimus-Eluting Stent in HLHS With Intact Atrial Septum.
In utero stenting of the atrial septum has been introduced for fetuses with hypoplastic left heart syndrome (HLHS) and intact atrial septum (IAS) to prevent secondary pulmonary vascular damage caused by left atrial hypertension. Previous reports revealed a high risk of significant or complete in-stent obstruction after successful intervention due to endothelial proliferation. We report a fetus with HLHS and IAS complicated by nutmeg lung who underwent successful fetal atrial septal stenting using an everolimus-eluting stent (Xience Sierra; Abbott). The procedure resulted in immediate left atrial decompression and maintained an unrestrictive interatrial communication until delivery. The use of a drug-eluting stent resulted in sustained stent patency without evidence of endothelial overgrowth and without detectable systemic adverse effects in the fetus. In utero use of an everolimus-eluting stent appears safe and may reduce the risk of in-stent obstruction in fetuses with HLHS and IAS.
2026-04-24 | Successful Fontan Completion in a Patient With Ellis-van Creveld Syndrome and a Hypoplastic Left Heart Syndrome Variant.
Ellis-van Creveld (EVC) syndrome is a rare genetic disorder often associated with skeletal abnormalities and congenital heart defects. Hypoplastic left heart syndrome (HLHS) in EVC is extremely rare and typically has a poor prognosis. We report a case of a 2-year and 7-month-old girl with EVC and HLHS who successfully underwent staged single-ventricle palliation, including the Norwood, Glenn, and Fontan procedures. Pre-Fontan evaluation showed acceptable pulmonary vascular resistance, and a fenestrated extracardiac Fontan procedure was performed without complications. This case underscores the importance of early pulmonary vascular protection and careful perioperative planning in achieving favorable outcomes in complex EVC-related congenital heart disease.
gene therapies
2026-03-04 | Animal models of hypoplastic left heart syndrome: genetic and anatomical approaches.
Hypoplastic Left Heart Syndrome (HLHS) is a life-threatening congenital heart disease characterized by underdevelopment of the left heart and aorta. Animal models of HLHS are used to study mechanisms of disease onset and progression and generally fall into two in vivo categories: genetic and mechanical. Genetic models primarily employ zebrafish and mice, whereas mechanically induced models are developed in chick embryos, fetal lambs, and rodents. Together, genetic and mechanical models provide insight into developmental and hemodynamic mechanisms of HLHS but differ in their ability to reproduce key anatomical and physiological features. Genetic models have identified genes and pathways involved in structural abnormalities and disrupted cell lineage. Mechanical models commonly restrict left-heart inflow using surgical or catheter-based techniques to induce hypoplasia of the left ventricle, valves, and aorta. Findings across chick embryos, fetal lambs, and mouse models support the "no flow, no grow" theory. This review synthesizes current HLHS animal models, evaluates their advantages and limitations, and considers their translational relevance from genetic and hemodynamic perspectives, while emphasizing species-specific limitations. IMPACT: Systematically evaluate genetically and mechanically induced HLHS models across zebrafish, mice, rats, chick embryos, and fetal lambs. Discuss how these models elucidate developmental and hemodynamic mechanisms of HLHS, highlight innovations such as CRISPR-based gene editing and staged in utero flow restriction, and assess their translational relevance, particularly for fetal intervention research. Provide practical criteria for model selection and interpretation, weighing strengths, limitations, and fidelity to human HLHS for mechanistic and translational aims.
2025-11-07 | Fetal magnetic resonance imaging diagnosis of pulmonary lymphangiectasia in hypoplastic left heart syndrome: Association with fetal echocardiography and postnatal outcome.
Secondary pulmonary lymphangiectasia (PL) is a recognised complication of hypoplastic left heart syndrome (HLHS) with an intact or restrictive atrial septum, associated with poor postnatal outcomes. Fetal MRI has been increasingly used to assess pulmonary abnormalities in HLHS, but the prognostic significance of subtle PL-like changes remains unclear. In this study, we evaluate the relationship between fetal MRI lung findings, echocardiographic markers of pulmonary venous obstruction, and postnatal outcomes. A retrospective analysis of all fetuses with HLHS who underwent fetal MRI between July 2019 and December 2022 was performed. MRI images were reviewed for features of PL and categorised as "normal," "suspicious," or "diagnostic" of PL. Pulmonary venous Doppler velocity-time integral (VTI) ratios from the most recent fetal echocardiogram were then compared to MRI findings. Postnatal outcomes, including early ventilation, need for intervention, and survival at 28 days and 1 year, were assessed. Of 20 fetuses with HLHS who underwent MRI, 6/20 (30%) showed features suspicious or diagnostic of PL (5 "suspicious" and 1 "diagnostic"), and 6/20 (30%) showed some evidence of pulmonary venous obstruction (PVO) on echo. While echo markers of PVO were significantly associated with some degree of PL on MRI (p=0.006), neither PL nor PVO predicted the need for early support/intervention or survival in fetuses who underwent active postnatal management. Fetuses with HLHS may exhibit a spectrum of lung changes on fetal MRI related to pulmonary venous obstruction. Whilst technical factors may also play a role, a degree of caution is advisable when interpreting more subtle forms of PL in fetal life, particularly in the absence of echocardiographic markers of severe atrial restriction. Larger, multi-centre prospective studies are needed to refine diagnostic criteria for PL in HLHS and better understand its prognostic significance in terms of both early and long-term outcome.
2025-06-19 | Long-Term Survival and Patient-Reported Outcomes After Staged Reconstructive Surgery for Hypoplastic Left Heart Syndrome.
Survival for hypoplastic left heart syndrome (HLHS) and variants has improved over the past 4 decades; however, survival remains low compared with other forms of congenital heart disease. There is a paucity of data concerning long-term outcomes. This study aims to: 1) examine long-term survival and the impact of patient factors on survival for newborns with HLHS; and 2) examine functional and health outcomes, including quality-of-life (QOL) in adulthood. The study cohort included patients with HLHS and variants undergoing the Norwood or hybrid procedure between January 1984 and December 2023. Data on patient characteristics and management were abstracted from medical records. Vital status was ascertained by direct subject and family contact, review of the medical record, and publicly available data. Functional outcomes and QOL in adults (≥18 years of age) were assessed by patient reports. The primary outcome was death or cardiac transplantation at last follow-up. In the study period, 2,012 neonates underwent staged reconstructive surgery for HLHS (Norwood, n = 1,921 and hybrid, n = 91). Transplant-free survival was 31.0% at 35 years. Transplant-free survival improved over time but is not different across recent eras. Most responders reported good to excellent general health. In this cohort of newborns undergoing staged reconstructive surgery for HLHS, fewer than one-third are alive without a transplant at 35 years of age. Survival has not improved in recent years. However, there is a group of survivors who report good to excellent outcomes and QOL, consistent with a "high-performing" Fontan phenotype.
2025-05-22 | eLife Assessment: Functional analysis across model systems implicates ribosomal proteins in growth and proliferation defects associated with hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) is the most lethal congenital heart disease (CHD). The pathogenesis of HLHS is poorly understood, and due to the likely oligogenic complexity of the disease, definitive HLHS-causing genes have not yet been identified. Postulating impaired cardiomyocyte proliferation as a likely important contributing mechanism to HLHS pathogenesis, and we conducted a genome-wide siRNA screen to identify genes affecting proliferation of human iPSC-derived cardiomyocytes (hPSC-CMs). This yielded ribosomal protein (RP) genes as the most prominent class of effectors of CM proliferation. In parallel, whole genome sequencing and rare variant filtering of a cohort of 25 HLHS proband-parent trios with poor clinical outcome revealed enrichment of rare variants of RP genes. In addition, in a familial CHD case we identified a rare, predicted-damaging promoter variant affecting RPS15A that was shared between the HLHS proband and a distant relative with CHD. Functional testing with an integrated multi-model system approach reinforced the idea that RP genes are major regulators of cardiac growth and proliferation, thus potentially contributing to the hypoplastic phenotype observed in HLHS patients. Cardiac knockdown (KD) of RP genes with promoter or coding variants (RPS15A, RPS17, RPL26L1, RPL39, RPS15) reduced proliferation in generic hPSC-CMs and caused malformed hearts, heart-loss or even lethality in Drosophila. In zebrafish, diminished rps15a function caused reduced CM numbers, heart looping defects, or weakened contractility, while reduced rps17 or rpl39 function caused reduced ventricular size or systolic atrial dysfunction of the atrium, respectively. Importantly, genetic interactions between RPS15A and core cardiac transcription factors TBX5 in CMs, Drosocross, pannier and tinman in flies, and tbx5 and nkx2-7 (nkx2-5 paralog) in fish, support a specific role for RP genes in heart development. Furthermore, RPS15A KD-induced heart/CM proliferation defects were significantly attenuated by p53 KD in both hPSC- CMs and zebrafish, and by Hippo activation (YAP/yorkie overexpression) in developing fly hearts. Based on these findings, we conclude that RP genes play novel critical roles in cardiogenesis and constitute an emerging class of gene candidates likely involved in HLHS and other CHDs.
2025-01-31 | EBV encephalitis in an immunocompetent adult with hypoplastic left heart syndrome A case report
EBV is a rare cause of encephalitis which can present with a broad spectrum of focal and diffuse neurological symptoms. In immunocompetent patients, prompt diagnosis can be difficult, especially in the context of comorbid conditions with similar symptomatology.
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2026-04-17 | Single-cell omics uncovers novel pathological mechanisms and therapeutic targets for congenital heart diseases: insights from integrated intercellular communication analysis.
Congenital heart disease (CHD) affects approximately 1% of live births worldwide and remains the leading cause of infant mortality from congenital anomalies. Despite advances in diagnosis and therapeutics, the molecular mechanisms underlying CHD pathogenesis remain incompletely understood, limiting the development of efficient targeted therapies. Single-cell omics approaches including single-cell RNA sequencing (scRNA-seq) have revolutionized our understanding of cardiac cellular heterogeneity and intercellular signalling. This review synthesizes recent single-cell omics studies in cardiogenesis and CHD, and presents novel insights from an integrated reanalysis to identify potential therapeutic targets. We systematically reviewed single-cell omics studies in human cardiogenesis and CHD (2019-2025), then reanalysed the Hill et al. dataset comprising 157,273 nuclei from paediatric patients across five diagnostic categories, including neonatal and infant hypoplastic left heart syndrome (HLHS), tetralogy of Fallot (TOF), dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) with healthy donor controls. We quantified cardiac-specific ligand-receptor interactions to characterize disease-specific intercellular communication networks through pathway enrichment and network topology analysis. Reanalysis revealed extensive remodelling of cell-cell communication networks across CHD subtypes, each displaying distinct signalling architectures. Neonatal HLHS and TOF demonstrated hyperactivation of metabolic and growth factor pathways with highly centralized endothelial cell (EC) to cardiomyocyte (CM) and cardiac fibroblast (CF) to CM networks. DCM showed selective metabolic enhancement with preserved integration. In contrast, HCM exhibited broad pathway suppression, particularly morphogen signalling, and fragmented connectivity with weakened CF-CM and EC-CM coupling. Infant HLHS represented an intermediate phenotype with suppressed Notch and extracellular matrix signalling. Single-cell omics studies have revealed cellular heterogeneity and disease-specific mechanisms across CHD subtypes. Our network-based reanalysis demonstrates that CHD involves not only transcriptional defects but also profound disruptions in multicellular communication, with each subtype exhibiting distinct signalling architectures. These findings provide a foundation for precision therapeutic strategies tailored to individual CHD subtypes, with future multimodal approaches accelerating clinical translation.
2025-11-03 | Abstract 4367268: Regulatory LncRNA H19 and mitophagy in hypoplastic left heart syndrome and in immature ischemic/reperfused rodent hearts
Introduction: Hypoplastic left heart syndrome (HLHS) is one of the most clinically challenging congenital heart diseases. The long non-coding RNA (lncRNA) H19 has been identified as a key regulator of mitochondrial function and myocardial ischemia/reperfusion injury (MIRI) in adult human and animal hearts. However, the regulation and role of H19 in immature human and animal hearts remain unknown. Hypothesis: Upregulated H19 in HLHS and in immature ischemic/reperfused animal hearts suppresses mitophagy through the PINK1/Parkin pathway. Methods: Myocardial tissues were collected from HLHS patients at the time of heart transplantation, and control tissues were obtained from donor hearts. HLHS-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes were subjected to hypoxia for 3 hours followed by 24 hours of reoxygenation. MIRI was induced in 14–15-day-old Wistar rats by ligating coronary artery for 60 min, followed by 24-hour reperfusion (Fig. 1), H19 expression was measured by quantitative PCR. Myocardial tissues were examined by electron microscopy to identify autophagosomes/autolysosomes containing mitochondria. Mitochondrial PINK1 and Parkin protein levels were assessed by Western blot analysis. In separate experiments, 2–3-day-old Wistar rats were injected with lentiviral vectors carrying siRNA targeting H19 or control vectors. Additionally, PINK1 knockout and C57BL/6 control mice were subjected to MIRI on a Langendorff apparatus. Results: H19 expression was upregulated and mitophagy was decreased in cardiac tissues from HLHS patients compared to controls, accompanied by reduced mitochondrial PINK1 and Parkin expression (Fig. 2). In iPSC-derived cardiomyocytes, hypoxia/reoxygenation induced lactate dehydrogenase release and H19 expression and decreased PINK1 and Parkin expression. In rats, MIRI resulted in an infarct size of 40 ± 2% of the area-at-risk (n = 10), accompanied by elevated H19 expression, reduced mitochondrial PINK1 and Parkin levels, and suppressed mitophagy (Fig.3). H19 knockdown reduced infarct size (decreased lactate dehydrogenase release in iPSC-derived cardiomyocytes), increased mitochondrial PINK1 and Parkin levels, and enhanced mitophagy in ischemic/reperfused hearts. Compared to C57BL/6 controls, PINK1 knockout mice exhibited significantly reduced ±dP/dt and decreased mitophagy two hours after reperfusion. Conclusions: Upregulated H19 exacerbates MIRI by suppressing PINK1/Parkin-mediated mitophagy in immature hearts.
2025-08-01 | Abstract Thu063: Functional siRNA Screen Reveals Core Regulators of Hypoplastic Left Heart Syndrome Cardiomyocyte Defects
Hypoplastic Left Heart Syndrome (HLHS) is a congenital heart disease with high mortality, but its molecular underpinnings remain poorly understood. Previous findings in patient-derived induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) revealed conserved defects (reduced proliferation, disrupted sarcomere organization). We hypothesize these phenotypes result from shared transcriptional and epigenetic regulators. We performed a functional siRNA screen with high-content morphological profiling to identify these regulators. From single-cell RNA-seq data, we selected 112 transcriptional/epigenetic regulators enriched in hiPSC-CMs for a custom siRNA library. Day 25 hiPSC-CMs from an unaffected father were treated and compared to control siRNA-treated father- and HLHS proband-derived hiPSC-CMs (4 replicate wells/siRNA, ~137 cells/well). Morphological profiling used high-content microscopy of ACTN2, DAPI, phalloidin, and MitoTracker-stained cells, measuring ~150 features (sarcomere organization, nuclear morphology, cell size, cytoskeleton integrity…). This workflow will be applied to additional HLHS trios to validate conserved regulators. Using 85 unbiased morphological features, we developed a k-nearest neighbors classifier, trained on untreated father- and proband-derived cells, that achieved 85% accuracy (AUC = 0.92) in distinguishing healthy from disease cells. Applied to siRNA-treated cells, it identified eight candidate genes whose knockdown caused ≥2-fold shift from healthy to disease-like phenotypes including known cardiac transcription factors (GATA6, PRDM16, PBX1) and additional regulators (TEAD4, NR6A1, PPP1R13B, NR4A3, ASB3) implicated in proliferation, cell structure, and extracellular matrix regulation—processes linked to HLHS. By integrating siRNA screening, morphological profiling, and machine learning, our study reveals a core regulatory network driving HLHS-associated cardiomyocyte defects. These findings advance our understanding of HLHS pathology and could inform therapeutic strategies. Our classification model may also generalize to other HLHS variants and congenital heart diseases, enabling broader applications in personalized disease modeling and drug discovery.
2022-10-07 | 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.
2022-07-08 | Epicardial HDAC3 Promotes Myocardial Growth Through a Novel MicroRNA Pathway
Background: Establishment of the myocardial wall requires proper growth cues from nonmyocardial tissues. During heart development, the epicardium and epicardium-derived cells instruct myocardial growth by secreting essential factors including FGF (fibroblast growth factor) 9 and IGF (insulin-like growth factor) 2. However, it is poorly understood how the epicardial secreted factors are regulated, in particular by chromatin modifications for myocardial formation. The current study is to investigate whether and how HDAC (histone deacetylase) 3 in the developing epicardium regulates myocardial growth. Methods: Various cellular and mouse models in conjunction with biochemical and molecular tools were employed to study the role of HDAC3 in the developing epicardium. Results: We deleted Hdac3 in the developing murine epicardium, and mutant hearts showed ventricular myocardial wall hypoplasia with reduction of epicardium-derived cells. The cultured embryonic cardiomyocytes with supernatants from Hdac3 knockout (KO) mouse epicardial cells also showed decreased proliferation. Genome-wide transcriptomic analysis revealed that Fgf9 and Igf2 were significantly downregulated in Hdac3 KO mouse epicardial cells. We further found that Fgf9 and Igf2 expression is dependent on HDAC3 deacetylase activity. The supplementation of FGF9 or IGF2 can rescue the myocardial proliferation defects treated by Hdac3 KO supernatant. Mechanistically, we identified that microRNA (miR)-322 and miR-503 were upregulated in Hdac3 KO mouse epicardial cells and Hdac3 epicardial KO hearts. Overexpression of miR-322 or miR-503 repressed FGF9 and IGF2 expression, while knockdown of miR-322 or miR-503 restored FGF9 and IGF2 expression in Hdac3 KO mouse epicardial cells. Conclusions: Our findings reveal a critical signaling pathway in which epicardial HDAC3 promotes compact myocardial growth by stimulating FGF9 and IGF2 through repressing miR-322 or miR-503, providing novel insights in elucidating the etiology of congenital heart defects and conceptual strategies to promote myocardial regeneration.
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Drug Discovery Landscape
4 orphan drug designations for Hypoplastic left heart syndrome.
4 orphan drug designations for Hypoplastic left heart syndrome.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
rexlemestrocel-L | cell therapies | FDA | 2024-02-14 | — | Mesoblast, Inc. |
Allogeneic bone marrow-derived mesenchymal stromal cells (MSCs) | cell therapies | FDA | 2021-12-02 | — | Longeveron, Inc. |
riociguat | small molecules | FDA | 2019-06-26 | — | Bayer U.S. LLC |
macitentan | small molecules | FDA | 2017-06-06 | — | Janssen Research & Development, LLC |
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