Loss of Nexilin function leads to a recessive lethal fetal cardiomyopathy characterized by cardiomegaly and endocardial fibroelastosis.

The Nexilin F-Actin Binding Protein (Nexilin) encoded by NEXN is a cardiac Z-disc protein important for cardiac function and development in humans, zebrafish, and mice. Heterozygote variants in the human NEXN gene have been reported to cause dilated and hypertrophic cardiomyopathy. Homozygous variants in NEXN cause a lethal form of human fetal cardiomyopathy, only described in two patients before. In a Swedish, four-generation, non-consanguineous family comprising 42 individuals, one female had three consecutive pregnancies with intrauterine fetal deaths caused by a lethal form of dilated cardiomyopathy. Whole-exome sequencing and variant analysis revealed that the affected fetuses were homozygous for a NEXN variant (NM_144573:c.1302del;p.(Ile435Serfs*3)). Moreover, autopsy and histology staining declared that they presented with cardiomegaly and endocardial fibroelastosis. Immunohistochemistry staining for Nexilin in the affected fetuses revealed reduced antibody staining and loss of striation in the heart, supporting loss of Nexilin function. Clinical examination of seven heterozygote carriers confirmed dilated cardiomyopathy (two individuals), other cardiac findings (three individuals), or no cardiac deviations (two individuals), indicating incomplete penetrance or age-dependent expression of dilated cardiomyopathy. RNA sequencing spanning the variant in cDNA blood of heterozygote individuals revealed nonsense-mediated mRNA decay of the mutated transcripts. In the current study, we present the first natural course of the recessively inherited lethal form of human fetal cardiomyopathy caused by loss of Nexilin function. The affected family had uneventful pregnancies until week 23-24, followed by fetal death at week 24-30, characterized by cardiomegaly and endocardial fibroelastosis.

A rare cause of sudden unexpected death syndrome (SUDS) in the first year of life: endomyocardial fibroelastosis (EFE) due to two compound heterozygous MYBPC3 mutations.

BACKGROUND: Autopsies regularly aim to clarify the cause of death; however, relatives may directly benefit from autopsy results in the setting of heritable traits ("mortui vivos docent"). CASE PRESENTATION: A case of a sudden unexpected cardiac death of a 5.5-months-old child is presented. Autopsy and thorough postmortem cardiac examinations revealed a massively enlarged heart with endomyocardial fibroelastosis. Postmortem molecular testing (molecular autopsy) revealed an unusual combination of two biparental MYBPC3 gene mutations likely to underlie the cardiac abnormalities. Thus, the molecular autoptic findings also had consequences for the relatives of the deceased child and impact on further family planning. CONCLUSIONS: The presented case highlights the need for clinical autopsies including cardiac examinations and postmortem molecular testing; it also paves the way for further cascade screening of family members for cardiac disease, if a distinct genetic disorder is suspected.

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

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

Endocardial fibroelastosis is caused by aberrant endothelial to mesenchymal transition.

RATIONALE: Endocardial fibroelastosis (EFE) is a unique form of fibrosis, which forms a de novo subendocardial tissue layer encapsulating the myocardium and stunting its growth, and which is typically associated with congenital heart diseases of heterogeneous origin, such as hypoplastic left heart syndrome. Relevance of EFE was only recently highlighted through the establishment of staged biventricular repair surgery in infant patients with hypoplastic left heart syndrome, where surgical removal of EFE tissue has resulted in improvement in the restrictive physiology leading to the growth of the left ventricle in parallel with somatic growth. However, pathomechanisms underlying EFE formation are still scarce, and specific therapeutic targets are not yet known. OBJECTIVE: Here, we aimed to investigate the cellular origins of EFE tissue and to gain insights into the underlying molecular mechanisms to ultimately develop novel therapeutic strategies. METHODS AND RESULTS: By utilizing a novel EFE model of heterotopic transplantation of hearts from newborn reporter mice and by analyzing human EFE tissue, we demonstrate for the first time that fibrogenic cells within EFE tissue originate from endocardial endothelial cells via aberrant endothelial to mesenchymal transition. We further demonstrate that such aberrant endothelial to mesenchymal transition involving endocardial endothelial cells is caused by dysregulated transforming growth factor beta/bone morphogenetic proteins signaling and that this imbalance is at least in part caused by aberrant promoter methylation and subsequent transcriptional suppression of bone morphogenetic proteins 5 and 7. Finally, we provide evidence that supplementation of exogenous recombinant bone morphogenetic proteins 7 effectively ameliorates endothelial to mesenchymal transition and experimental EFE in rats. CONCLUSIONS: In summary, our data point to aberrant endothelial to mesenchymal transition as a common denominator of infant EFE development in heterogeneous, congenital heart diseases, and to bone morphogenetic proteins 7 as an effective treatment for EFE and its restriction of heart growth.

Knock-out of nexilin in mice leads to dilated cardiomyopathy and endomyocardial fibroelastosis.

Cardiomyopathy is one of the most common causes of chronic heart failure worldwide. Mutations in the gene encoding nexilin (NEXN) occur in patients with both hypertrophic and dilated cardiomyopathy (DCM); however, little is known about the pathophysiological mechanisms and relevance of NEXN to these disorders. Here, we evaluated the functional role of NEXN using a constitutive Nexn knock-out (KO) mouse model. Heterozygous (Het) mice were inter-crossed to produce wild-type (WT), Het, and homozygous KO mice. At birth, 32, 46, and 22 % of the mice were WT, Het, and KO, respectively, which is close to the expected Mendelian ratio. After postnatal day 6, the survival of the Nexn KO mice decreased dramatically and all of the animals died by day 8. Phenotypic characterizations of the WT and KO mice were performed at postnatal days 1, 2, 4, and 6. At birth, the relative heart weights of the WT and KO mice were similar; however, at day 4, the relative heart weight of the KO group was 2.3-fold higher than of the WT group. In addition, the KO mice developed rapidly progressive cardiomyopathy with left ventricular dilation and wall thinning and decreased cardiac function. At day 6, the KO mice developed a fulminant DCM phenotype characterized by dilated ventricular chambers and systolic dysfunction. At this stage, collagen deposits and some elastin deposits were observed within the left ventricle cavity, which resembles the features of endomyocardial fibroelastosis (EFE). Overall, these results further emphasize the role of NEXN in DCM and suggest a novel role in EFE.

Primary endocardial fibroelastosis and nonimmune hydrops fetalis: case report with autopsy.

Endocardial fibroelastosis is an important cause of congestive heart failure and death in infancy and early childhood. When present, it is commonly associated with non immune hydrops fetalis. The aim of this study is to draw attention for possible cardiac abnormalities in cases of fetal hydrops, and report a case of premature death by primary endocardial fibroelastosis with autopsy.

An animal model of endocardial fibroelastosis.

BACKGROUND: Hypoplastic left heart syndrome (HLHS) is one of the most common severe congenital cardiac anomalies, characterized by a marked hypoplasia of left-sided structures of the heart, which is commonly accompanied by a thick layer of fibroelastic tissue, termed endocardial fibroelastosis (EFE). Because human EFE develops only in fetal or neonatal hearts, and often in association with reduced blood flow, we sought to mimic these conditions by subjecting neonatal and 2-wk-old rat hearts to variations of the heterotopically transplanted heart model with either no intracavitary or normal flow and compare endocardium with human EFE tissue. MATERIALS AND METHODS: Hearts obtained from neonatal and 2-wk-old rats were heterotopically transplanted in young adult Lewis rats in a working (loaded) or nonworking (unloaded) mode. After 2-wk survival, hearts were explanted for histologic analysis by staining for collagen, elastin, and cellular elements. These sections were compared with human EFE tissue from HLHS. RESULTS: EFE, consisting of collagen and elastin with scarce cellular and vascular components, developed only in neonatal unloaded transplanted hearts and displayed the same histopathologic findings as EFE from patients with HLHS. Loaded hearts and 2-wk-old hearts did not show these alterations. CONCLUSIONS: This animal model for EFE will serve as a tool to study the mechanisms of EFE formation, such as fluid forces, in HLHS in a systematic manner. A better understanding of the underlying cause of the EFE formation in HLHS will help to develop novel treatment strategies to better preserve growth of the hypoplastic left ventricle.

Cardiac mass in Behçet's disease.

Cardiac mass is a rare manifestation of Behçet's disease (BD). Intracardiac thrombosis, endomyocardiofibrosis, endocardial fibroelastosis, inflammatory mass and cystic change have been reported as different entities of cardiac mass in BD. Here we presented 6 cases of this rare manifestation of BD. The clinical and pathological features were reviewed.

Ross-Konno and endocardial fibroelastosis resection after hybrid stage I palliation in infancy: successful staged left-ventricular rehabilitation and conversion to biventricular circulation after fetal diagnosis of aortic stenosis.

We report a patient who presented during fetal life with severe aortic stenosis, left-ventricular dysfunction, and endocardial fibroelastosis (evolving hypoplastic left heart syndrome). Management involved in utero and postnatal balloon aortic valvuloplasty for partial relief of obstruction and early postnatal hybrid stage I palliation until recovery of left-ventricular systolic function had occurred. The infant subsequently had successful conversion to a biventricular circulation by combining resection of endocardial fibroelastosis with single-stage Ross-Konno, aortic arch reconstruction, hybrid takedown, and pulmonary artery reconstruction.

Recessive ciliopathy mutations in primary endocardial fibroelastosis: a rare neonatal cardiomyopathy in a case of Alstrom syndrome.

Among neonatal cardiomyopathies, primary endocardial fibroelastosis (pEFE) remains a mysterious disease of the endomyocardium that is poorly genetically characterized, affecting 1/5000 live births and accounting for 25% of the entire pediatric dilated cardiomyopathy (DCM) with a devastating course and grave prognosis. To investigate the potential genetic contribution to pEFE, we performed integrative genomic analysis, using whole exome sequencing (WES) and RNA-seq in a female infant with confirmed pathological diagnosis of pEFE. Within regions of homozygosity in the proband genome, WES analysis revealed novel parent-transmitted homozygous mutations affecting three genes with known roles in cilia assembly or function. Among them, a novel homozygous variant [c.1943delA] of uncertain significance in ALMS1 was prioritized for functional genomic and mechanistic analysis. Loss of function mutations of ALMS1 have been implicated in Alstrom syndrome (AS) [OMIM 203800], a rare recessive ciliopathy that has been associated with cardiomyopathy. The variant of interest results in a frameshift introducing a premature stop codon. RNA-seq of the proband's dermal fibroblasts confirmed the impact of the novel ALMS1 variant on RNA-seq reads and revealed dysregulated cellular signaling and function, including the induction of epithelial mesenchymal transition (EMT) and activation of TGFß signaling. ALMS1 loss enhanced cellular migration in patient fibroblasts as well as neonatal cardiac fibroblasts, while ALMS1-depleted cardiomyocytes exhibited enhanced proliferation activity. Herein, we present the unique pathological features of pEFE compared to DCM and utilize integrated genomic analysis to elucidate the molecular impact of a novel mutation in ALMS1 gene in an AS case. Our report provides insights into pEFE etiology and suggests, for the first time to our knowledge, ciliopathy as a potential underlying mechanism for this poorly understood and incurable form of neonatal cardiomyopathy. KEY MESSAGE: Primary endocardial fibroelastosis (pEFE) is a rare form of neonatal cardiomyopathy that occurs in 1/5000 live births with significant consequences but unknown etiology. Integrated genomics analysis (whole exome sequencing and RNA sequencing) elucidates novel genetic contribution to pEFE etiology. In this case, the cardiac manifestation in Alstrom syndrome is pEFE. To our knowledge, this report provides the first evidence linking ciliopathy to pEFE etiology. Infants with pEFE should be examined for syndromic features of Alstrom syndrome. Our findings lead to a better understanding of the molecular mechanisms of pEFE, paving the way to potential diagnostic and therapeutic applications.

Barth syndrome: an X-linked cause of fetal cardiomyopathy and stillbirth.

OBJECTIVE: Barth Syndrome (BTHS) is an X-linked multisystem disorder (OMIM 302060) usually diagnosed in infancy and characterized by cardiac problems [dilated cardiomyopathy (DCM) ± endocardial fibroelastosis (EFE) ± left ventricular non-compaction (LVNC)], proximal myopathy, feeding problems, growth retardation, neutropenia, organic aciduria and variable respiratory chain abnormalities. We wished to determine whether BTHS had a significant impact on fetal and perinatal health in a large cohort of family groups originating from a defined region. METHOD: Case note review on 19 families originating from the UK and known to the Barth Syndrome Service of the Bristol Royal Hospital for Children. RESULTS: Details are presented on six kindreds (32%) with genetically and biochemically proven BTHS that demonstrate a wider phenotype including male fetal loss, stillbirth and severe neonatal illness or death. In these families, 9 males were stillborn and 14 died as neonates or infants but there were no losses of females. BTHS was definitively proven in five males with fetal onset of DCM ± hydrops/EFE/LVNC. CONCLUSION: These findings stress the importance of considering BTHS in the differential diagnosis of unexplained male hydrops, DCM, EFE, LVNC or pregnancy loss, as well as in neonates with hypoglycemia, lactic acidosis and idiopathic mitochondrial disease.

Endocardial fibroelastosis of the right ventricle and tricuspid valve in a young adult with Behcet's disease.

Endocardial fibroelastosis is characterized by massive proliferation of collagenous and elastic tissue, in which the pathological process is restricted to the endocardium. In this report, we present the case of a 20-year-old man with Behcet's disease and endocardial fibroelastosis of the right ventricle involving tricuspid valve resulting in a tumor mass that was resected along with tricuspid valve replacement. The clinical and pathological features of this rare entity are reviewed.

Changing concepts of endocardial fibroelastosis.

Endocardial fibroelastosis is not a disease but a reaction of the endocardium. I review the history of the term with emphasis on the gradual understanding of the many causes of this reaction. I include a comprehensive list of diseases or other cardiac stresses that authors have reported in association, and I try to explain the mechanism of the reaction. Although endocardial fibroelastosis is rare today, I issue a warning of a possible epidemic recrudescence of some of the associated diseases. My hope is for nosologic purity, therefore that outworn but surviving concepts will be firmly rejected.

Sudden unexpected death due to left ventricular noncompaction of myocardium: case report and review of the literature.

Left ventricular noncompaction of the myocardium is a rare genetic cardiac disease characterized by a prominent meshwork and deep intertrabecular recesses of the left ventricle. The condition has frequently been misdiagnosed as other cardiomyopathies. Sudden deaths due to the disease are rarely reported in the literature of forensic sciences. We report 2 cases of sudden death due to undiagnosed left ventricular noncompaction. One was a 30-year-old man who suddenly collapsed while eating breakfast. He was pronounced dead on arrival at the hospital. The other 24-year-old man had a witness collapse at home. Despite immediate resuscitation, he expired 11 hours after hospitalization. Postmortem examination revealed that both patients died of left ventricular noncompaction. The key pathologic findings are described. Additionally, the literature is reviewed, and the incidence, clinical and pathophysiologic presentation, pathogenesis, and diagnostic criteria for the left ventricular noncompaction are discussed.

Echocardiographic evaluation of fetal cardiac function: clinical and anatomical correlations in two cases of endocardial fibroelastosis.

BACKGROUND: Two fetuses with endocardial fibroelastosis, one with critical aortic stenosis and one with high-output cardiac failure due to chorioangiomatosis, are presented to evaluate the correlation between Doppler echocardiographic findings, the fetal clinical condition and the anatomical substrate found at postmortem. METHODS: Doppler measurements of cardiac function (systolic, diastolic and global) and a cardiovascular score incorporating five parameters of fetal well-being were recorded. RESULTS: In the fetus with critical aortic stenosis, the cardiovascular score was diminished, there was no hydrops, the systolic and global cardiac function indices were within normal limits but the diastolic function indices were abnormal. The fetus with high-output cardiac failure was hydropic, the cardiovascular score was diminished and abnormal Doppler indices of systolic, diastolic and global cardiac function were found. In both fetuses, abnormalities in the measured Doppler parameters were found consistent with clinical cardiac dysfunction and the postmortem findings. CONCLUSION: Recognition of abnormal diastolic function Doppler indices may assist in earlier identification of fetal cardiac compromise.

Flow disturbances and the development of endocardial fibroelastosis.

OBJECTIVES: Endothelial-to-mesenchymal transition (EndMT) has been identified as the underlying mechanism of endocardial fibroelastosis (EFE) formation. The purpose of this study was to determine whether hemodynamic alterations due to valvar defects promote EndMT and whether age-specific structural changes affect ventricular diastolic compliance despite extensive surgical resection of EFE tissue. MATERIAL AND METHODS: We analyzed EFE tissue from 24 patients with hypoplastic left heart syndrome (HLHS) who underwent left ventricular (LV) rehabilitation surgery at Boston Children's Hospital between December 2011 and March 2018. Six patients with flow disturbances across the aortic valve and/or mitral valve but no HLHS diagnosis and macroscopic appearance of "EFE-like tissue" in the LV were included for comparison. All samples were examined for amount of collagen/elastin production and degradation, and presence of active EndMT by histologic analysis. RESULTS: EFE tissue from patients with and without HLHS consisted predominantly of elastin and collagen fibers. There was no alteration in degradation activity for collagen or elastin as shown by in situ zymography. Active EndMT was found in all patients with and without HLHS with flow disturbances ("EFE-like"). In patients with HLHS, EFE infiltrated into the underlying myocardium with increasing age. CONCLUSIONS: Patients with and without HLHS with flow disturbances due to stenotic or incompetent valves develop EndMT-derived fibrotic tissue covering the LV. When EFE recurs, it is directly associated with flow disturbances and switches to an infiltrative growth pattern with increasing age, leading to increased diastolic stiffness of the LV.

Flow disturbances and progression of endocardial fibroelastosis - a case report.

Endocardial fibroelastosis (EFE) is described as thickening of the endocardium and is associated with hypoplastic left heart syndrome (HLHS). The stimulus for EFE and the mechanism for recurrence and/or progression need to be investigated. In this report, we describe the case of a 4-year-old HLHS patient who underwent several surgeries with EFE resections due to recurrence of EFE. EFE recurrence was associated with flow disturbances due to valvar defects. At her latest follow-up 7 months after the last surgery, competent valves and no EFE were identified on all imaging study.

Papillary fibroelastoma arising from the pulmonary valve associated with pulmonary embolization.

Cardiac papillary fibroelastomas are rare, usuallybenign tumors that can be detected at autopsy, during open-heart surgery, or with echocardiography. They usually arise from the cardiac valves and more commonly are found on the left side of the heart. Embolization of left-sided and tricuspid valve tumors has been well documented. This is the 1st reported case of pulmonary embolization of a papillary fibroelastoma arising from the pulmonary valve.