Genetics of neonatal cardiomyopathy

Imaging Features of Pediatric Left Ventricular Noncompaction Cardiomyopathy in Echocardiography and Cardiovascular Magnetic Resonance

Background: Left ventricular noncompaction (LVNC) is a distinct cardiomyopathy characterized by the presence of a two-layer myocardium with prominent trabeculation and deep intertrabecular recesses. The diagnosis of LVNC can be challenging because the diagnostic criteria are not uniform. The aim of our study was to evaluate echocardiographic and CMR findings in a group of children with isolated LVNC. Methods: From February 2008 to July 2021, pediatric patients under 18 years of age at the time of diagnosis with echocardiographic evidence of isolated LVNC were prospectively enrolled. The patients underwent echocardiography and contrast-enhanced cardiovascular magnetic resonance (CMR) with late gadolinium enhancement to assess myocardial noncompaction, ventricular size, and function. Results: A total of 34 patients, with a median age of 11.9 years, were recruited. The patients were followed prospectively for a median of 5.1 years. Of the 31 patients who met Jenni’s criteria in echocardiography, CMR was performed on 27 (79%). Further comprehensive analysis was performed in the group of 25 patients who met the echocardiographic and CMR criteria for LVNC. In echocardiography, the median NC/C ratio in systole was 2.60 and in diastole 3.40. In 25 out of 27 children (93%), LVNC was confirmed by CMR, according to Petersen’s criteria, with a median NC/C ratio of 3.27. Conclusions: (1) Echocardiography precisely identifies patients with LVNC. (2) Echocardiography is a good method for monitoring LV systolic function, but CMR is indicated for the precise assessment of LV remodeling and RV size and function, as well as for the detection of myocardial fibrosis.

Next-generation sequencing (NGS) as a molecular diagnostic tool for hypertrophic cardiomyopathy in a Chinese boy due to novel compound heterozygous mutations in the MYBPC3 gene: A case report

RATIONALE

Hypertrophic cardiomyopathy (HCM) is mainly caused by mutations in genes encoding sarcomeric proteins. One of the most commonly mutated HCM genes is the MYBPC3 gene. Mutations in this gene lead mainly to truncation of the protein, which gives rise to a relatively severe phenotype. Analyses of gene mutations associated with HCM are valuable for molecular diagnosis, genetic counseling, and management of familial HCM.

PATIENT CONCERNS

A 12-year-old boy presented with palpitations and dyspnea after exercise for 1 year. Echocardiography showed myocardial asymmetric hypertrophy of the ventricular septum, the anterior wall, and the lateral wall of the left ventricle. The thickness of the interventricular septum was estimated to be 33 mm. ECG showed left ventricular high voltage and ST-T changes. He had been diagnosed with HCM 3 months previously.

DIAGNOSES

Due to his clinical presentation, he was determined to have HCM via a molecular analysis, revealing compound heterozygotes (p.R597W and p.Q1012Sfs*8) in the MYBPC3 gene.

INTERVENTIONS

The patient was prescribed metoprolol to slow the heart rate and increase diastolic filling time.

OUTCOMES

The boy was treated with metoprolol 6.75 mg b.i.d. Approximately 3 months later, review of the echocardiography showed that the peak velocity across the LVOT dropped to 2.3 m/seconds and that the pressure gradient dropped to 21 mm Hg.

LESSONS

A custom next-generation sequencing (NGS) technology for the HCM panel allowed us to identify compound heterozygous mutations in the MYBPC3 gene, confirming NGS as a molecular diagnostic tool.

Androgen receptor (AR) in cardiovascular diseases

Cardiovascular diseases (CVDs) are still the highest leading cause of death worldwide. Several risk factors have been linked to CVDs, including smoking, diabetes, hyperlipidemia, and gender among others. Sex hormones, especially the androgen and its receptor, androgen receptor (AR), have been linked to many diseases with a clear gender difference. Here, we summarize the effects of androgen/AR on CVDs, including hypertension, stroke, atherosclerosis, abdominal aortic aneurysm (AAA), myocardial hypertrophy, and heart failure, as well as the metabolic syndrome/diabetes and their impacts on CVDs. Androgen/AR signaling exacerbates hypertension, and anti-androgens may suppress hypertension. Androgen/AR signaling plays dual roles in strokes, depending on different kinds of factors; however, generally males have a higher incidence of strokes than females. Androgen and AR differentially modulate atherosclerosis. Androgen deficiency causes elevated lipid accumulation to enhance atherosclerosis; however, targeting AR in selective cells without altering serum androgen levels would suppress atherosclerosis progression. Androgen/AR signaling is crucial in AAA development and progression, and targeting androgen/AR profoundly restricts AAA progression. Men have increased cardiac hypertrophy compared with age-matched women that may be due to androgens. Finally, androgen/AR plays important roles in contributing to obesity and insulin/leptin resistance to increase the metabolic syndrome.

Left ventricular noncompaction: A rare indication for pediatric heart transplantation

Isolated left ventricular noncompaction is a rare congenital cardiomyopathy, characterized morphologically by a dilated left ventricle, prominent trabeculations and deep intertrabecular recesses in the ventricular myocardium, with no other structural heart disease. It is thought to be secondary to an arrest of normal myocardial compaction during fetal life. Clinically, the disease presents with heart failure, embolic events, arrhythmias or sudden death. Current diagnostic criteria are based on clinical and imaging data and two-dimensional and color Doppler echocardiography is the first-line exam. There is no specific therapy and treatment is aimed at associated comorbidities. Cases refractory to medical therapy may require heart transplantation. The authors describe a case of severe and refractory heart failure, which was the initial presentation of isolated left ventricular noncompaction in a previously healthy male child, who underwent successful heart transplantation.

Loss of Function Mutations in NNT Are Associated With Left Ventricular Noncompaction

BACKGROUND

Left ventricular noncompaction (LVNC) is an autosomal-dominant, genetically heterogeneous cardiomyopathy with variable severity, which may co-occur with cardiac hypertrophy.

METHODS AND RESULTS

Here, we generated whole exome sequence data from multiple members from 5 families with LVNC. In 4 of 5 families, the candidate causative mutation segregates with disease in known LVNC genes MYH7 and TPM1. Subsequent sequencing of MYH7 in a larger LVNC cohort identified 7 novel likely disease causing variants. In the fifth family, we identified a frameshift mutation in NNT, a nuclear-encoded mitochondrial protein, not implicated previously in human cardiomyopathies. Resequencing of NNT in additional LVNC families identified a second likely pathogenic missense allele. Suppression of nnt in zebrafish caused early ventricular malformation and contractility defects, probably driven by altered cardiomyocyte proliferation. In vivo complementation studies showed that mutant human NNT failed to rescue nnt morpholino-induced heart dysfunction, indicating a probable haploinsufficiency mechanism.

CONCLUSIONS

Together, our data expand the genetic spectrum of LVNC and demonstrate how the intersection of whole exome sequence with in vivo functional studies can accelerate the identification of genes that drive human genetic disorders.

Genetics of inherited cardiomyopathies

Cardiomyopathies are the most common disorders resulting in heart failure, with dilated cardiomyopathy being responsible for the majority of cases. Other forms of cardiomyopathy, especially hypertrophic forms, are also important causes of heart failure. The mortality rate due to cardiomyopathy in the USA is over 10,000 deaths per year, and the costs associated with heart failure are approximately 200 million US dollars per year in the USA alone. Over the past few years, breakthroughs have occurred in understanding the basic mechanisms of these disorders, potentially enabling clinicians to devise improved diagnostic strategies and therapies. As at least 30 to 40% of cases are inherited, it is now imperative that the genetic basis for these disorders is clearly recognized by caregivers and scientists. However, it has also become clear that these diseases are genetically highly heterogeneous, with multiple genes identified for each of the major forms of cardiomyopathy, and most patients having private mutations. These data suggest that the genetic diagnosis of most patients with cardiomyopathy will be impractical with current technologies. However, there are a few exceptions, such as patients with X-linked cardiomyopathies, with or without the concomitant abnormalities of cyclic neutropenia and 3-methylglutaconic aciduria, or patients with cardiomyopathy associated with conduction disease: these appear to be associated with mutations in a small subset of genes, and can be investigated by certified diagnostic laboratories. This review will summarize current knowledge of the genetics of inherited cardiomyopathies and how findings from research laboratories may be translated into the diagnostic laboratory.

Noncompaction syndrome of the myocardium: pathophysiology and imaging pearls

Patients with noncompaction syndrome of the myocardium may present with cardiac arrhythmia, thromboembolic events, or left ventricular failure. Associations with other diseases, including neurologic or other cardiac syndromes, have been noted. Noncompaction syndrome of the myocardium is primarily diagnosed by echocardiography; however, CT scanning and magnetic resonance imaging are useful tools for determining severity and the patient's prognosis. With these methods, high-resolution images of the myocardium are obtained that enable better recognition of the areas over which the trabeculae are distributed. Early diagnosis can improve the patient's survival by premature heart transplantation or implantation of a defibrillator. Also, as there are many reports of occurrence of this syndrome in several members of the same family (mainly X-linked inheritance), upon accurate and early diagnosis, the patient's family can be further screened.

ANKRD1, the gene encoding cardiac ankyrin repeat protein, is a novel dilated cardiomyopathy gene

OBJECTIVES

We evaluated ankyrin repeat domain 1 (ANKRD1), the gene encoding cardiac ankyrin repeat protein (CARP), as a novel candidate gene for dilated cardiomyopathy (DCM) through mutation analysis of a cohort of familial or idiopathic DCM patients, based on the hypothesis that inherited dysfunction of mechanical stretch-based signaling is present in a subset of DCM patients.

BACKGROUND

CARP, a transcription coinhibitor, is a member of the titin-N2A mechanosensory complex and translocates to the nucleus in response to stretch. It is up-regulated in cardiac failure and hypertrophy and represses expression of sarcomeric proteins. Its overexpression results in contractile dysfunction.

METHODS

In all, 208 DCM patients were screened for mutations/variants in the coding region of ANKRD1 using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct deoxyribonucleic acid sequencing. In vitro functional analyses of the mutation were performed using yeast 2-hybrid assays and investigating the effect on stretch-mediated gene expression in myoblastoid cell lines using quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

Three missense heterozygous ANKRD1 mutations (P105S, V107L, and M184I) were identified in 4 DCM patients. The M184I mutation results in loss of CARP binding with Talin 1 and FHL2, and the P105S mutation in loss of Talin 1 binding. Intracellular localization of mutant CARP proteins is not altered. The mutations result in differential stretch-induced gene expression compared with wild-type CARP.

CONCLUSIONS

ANKRD1 is a novel DCM gene, with mutations present in 1.9% of DCM patients. The ANKRD1 mutations may cause DCM as a result of disruption of the normal cardiac stretch-based signaling.

Cardiomyopathy in newborns and infants: a broad spectrum of aetiologies and poor prognosis

AIM

This study set out to describe the initial clinical findings, morbidity, mortality and aetiology of infant cardiomyopathy focusing on potential risk factors for an adverse outcome.

METHODS

We retrospectively analysed clinical and laboratory findings of all patients diagnosed at our institution from 1995 to 2004 with cardiomyopathy within their first year of life.

RESULTS

Of the 35 patients, cardiomyopathy was classified as dilated in 18, hypertrophic in 14 and unclassified in 3. The aetiologies were genetic syndromes (8), metabolic diseases (5), familial isolated cardiomyopathy (3) and myopathy (1). During a median follow-up of 1.5 years (range 0-9 years), 13 patients died from progressive heart failure and two underwent heart transplants. Estimated survival and freedom from transplant was 69, 66, 58 and 50% after 0.5, 1, 2 and 6 years, respectively. Patients with severe heart failure symptoms within the first month of life had significantly worse outcomes than patients without heart failure symptoms.

CONCLUSION

High morbidity and poor prognosis result through progressive heart failure. Aetiology and clinical course are especially heterogeneous in infants. The most commonly identified aetiologies are genetic syndromes and metabolic diseases. A multidisciplinary approach is recommended for defining the aetiology and developing individual treatment strategies.

Fetal and Neonatal Presentation of Noncompacted Ventricular Myocardium: Expanding the Clinical Spectrum

BACKGROUND

Noncompaction of the ventricular myocardium (NCVM) is a rare cardiomyopathy characterized by varying degrees of ventricular dysfunction and numerous, prominent trabeculations with deep intertrabecular recesses caused by arrest in myocardial embryogenesis. NCVM is rarely described in fetal and neonatal patients, and only isolated reports exist to date.

METHODS

We conducted a review of clinical and echocardiographic data from 6 neonates found to have NCVM to elucidate aspects of prenatal manifestations, initial presentations, and clinical course/outcome.

RESULTS

Six neonates met criteria for diagnosis of NCVM. Five were initially evaluated during fetal life, whereas one patient presented for initial cardiology examination as a neonate. Three of the 5 fetuses had NCVM recognized at the initial examination. Both unrecognized fetuses also had severe prenatal left ventricular dilation and dysfunction. Left ventricular enlargement or increased wall thickness with decreased ejection fraction was evident in all patients at presentation. Mean ejection fraction at presentation was 36% and improved to 57% during an average follow-up of 2 years. Associated congenital cardiac anomalies were noted in 3 patients. After initial improvement, two patients had transient, late decreases in ejection fraction, which improved with medication adjustment. There have been no deaths.

CONCLUSION

Fetuses with enlarged and poorly functioning left ventricles should be evaluated for NCVM, which may not be easily recognized on initial fetal studies. Unlike previous reports of neonatal NCVM, all 6 neonates, including the 3 requiring inotropic support, showed significant early recovery of cardiac function with aggressive therapy.

Factors associated with establishing a causal diagnosis for children with cardiomyopathy

OBJECTIVE

The goal was to identify the clinical variables associated with establishing a cause of cardiomyopathy in children.

METHODS

The Pediatric Cardiomyopathy Registry contains clinical and causal testing information for 916 children who were diagnosed as having cardiomyopathy in North America between 1990 and 1995. Children with a causal diagnosis were compared with those without with respect to several demographic, clinical, and causal testing variables.

RESULTS

Cardiomyopathy was 1 of 4 types, hypertrophic (34.2%), dilated (53.8%), restrictive (3.2%), or other or mixed (8.9%). Only one third of cases had a known cause. Children with a known cause for hypertrophic cardiomyopathy were more likely to be female, to be relatively smaller, to present with congestive heart failure, and to have increased left ventricular posterior wall thickness without outflow tract obstruction. For dilated cardiomyopathy, a known cause was associated with older age, lower heart rate, smaller left ventricular dimensions, and greater shortening fraction. Family history of cardiomyopathy predicted a significantly higher rate of causal diagnoses for all cardiomyopathy types, whereas family histories of genetic syndromes and sudden death were also predictive of a cause for hypertrophic and dilated cardiomyopathies. For hypertrophic cardiomyopathy, only blood and urine testing was associated with a causal diagnosis, whereas both viral serologic testing or culture and endomyocardial biopsy were independent predictors of a causal diagnosis in dilated cardiomyopathy.

CONCLUSIONS

Certain patient characteristics, family history, echocardiographic findings, laboratory testing, and biopsy were associated significantly with establishing a cause of pediatric cardiomyopathy. Early endomyocardial biopsy should be considered strongly for children with dilated cardiomyopathy, for definitive diagnosis of viral myocarditis. Although not widely used, skeletal muscle biopsy may yield a cause for some patients with hypertrophic cardiomyopathy and for patients suspected of having a mitochondrial disorder.

Two cases of severe neonatal hypertrophic cardiomyopathy caused by compound heterozygous mutations in the MYBPC3 gene

BACKGROUND

Idiopathic (primary) hypertrophic cardiomyopathy (HCM) is mainly caused by mutations in genes encoding sarcomeric proteins. One of the most commonly mutated HCM genes is the myosin binding protein C (MYBPC3) gene. Mutations in this gene lead mainly to truncation of the protein which gives rise to a relatively mild phenotype. Pure HCM in neonates is rare and most of the time childhood HCM occurs in association with another underlying condition.

OBJECTIVE

To study the presence of mutations in the MYBPC3 gene in idiopathic childhood HCM.

METHODS

MYBPC3 coding region and splice junction variation were analysed by denaturing high performance liquid chromatography (DHPLC) and sequencing in DNA isolated from two neonates with severe unexplained HCM, who died within the first weeks of life.

RESULTS

Truncating mutations were found in both alleles of the MYBPC3 gene in both patients, suggesting there was no functional copy of the MYBPC3 protein. Patient 1 carried the maternally inherited c.2373_2374insG mutation and the paternally inherited splice-donor site mutation c.1624+1G-->A. Patient 2 carried the maternally inherited frameshift mutation c.3288delA (p.Glu1096fsX92) and the paternally inherited non-sense mutation c.2827C-->T (p.Arg943X).

CONCLUSIONS

The findings indicate the need for mutation analysis of genes encoding sarcomeric proteins in childhood HCM and the possibility of compound heterozygosity.

The unique expression profile of the androgen receptor gene in a rat model of neonatal cardiac hypertrophy

Gender can influence many cardiovascular events, including cardiac hypertrophy. The presence of and dynamic changes involving androgen receptor (AR) gene expression are important confirmatory findings for androgen modulation in the pathogenesis of cardiac hypertrophy.

AIMS

To determine AR expression profile during neonatal hypertrophy and its regression process using a rat model.

METHODS

Relative mRNA levels of the AR gene were quantified at postnatal days 1, 7, 14, 21 and 28 using real time PCR.

RESULTS

A significant 10.6-fold decrease in AR transcription levels was observed at birth in neonates with cardiac hypertrophy (p < 0.05). Our analysis also showed a significant increase in AR mRNA levels at day 28, corresponding with regression of cardiac hypertrophy.

DISCUSSION

The AR gene demonstrated a noteworthy trend in its expression pattern. The initial down-regulation was most likely the result of increased testosterone levels induced by hyperinsulinaemia and hypoglycaemia, which were present in neonates from diabetic mothers during pregnancy. The paradoxical increase in AR at day 28 suggested a potential long term-effect of the in utero diabetic environment.

Cardiotropic viruses in the myocardium of children with end-stage heart disease

BACKGROUND

Transplantation has become a lifesaving procedure for children with end-stage heart failure. The long-term outcome for children who undergo transplantation has been of considerable interest, but the causes of graft failure and death are largely unknown, and the role of pre-transplant viral infection is unclear.

METHODS

Myocardial samples from 80 explanted hearts from children with end-stage heart disease caused by congenital heart disease (CHD), cardiomyopathy, or chronic rejection were analyzed using polymerase chain reaction and reverse-transcriptase polymerase chain reaction for cardiotropic viruses using virus-specific primers. We used immunohistochemical analysis of cytoskeletal proteins to evaluate myocyte architecture.

RESULTS

We identified parvoviral genomes in 6 patients (3 with CHD and 3 with cardiomyopathy). We detected no other viruses. Immunohistochemistry showed normal staining for key components of the cytoskeleton/sarcolemma, sarcomere, and nuclear membrane in the 6 virus-positive samples. The clinical outcome of these children was worse (4 long-term survivors, but 2 deaths) than for individuals without the genome.

CONCLUSIONS

Detecting viruses within the myocardium at the point of end-stage heart failure is not common, regardless of the primary pathology. However, the presence of viruses may result in poor outcome for the patient.

Molecular characterisation of neonatal cardiac hypertrophy and its regression

Neonatal cardiac hypertrophy associated with diabetic pregnancy is transient and regresses naturally, but is associated with increased morbidity and mortality. This study was undertaken to analyse the changes in expression of 5 cardiac genes, including atrial natriuretic peptide, alpha- and beta-myosin heavy chain, and cardiac and skeletal alpha-actin genes, using a rat neonatal model, in which cardiac hypertrophy was induced via maternal diabetes. In the hypertrophied left ventricle of neonates from diabetic mothers, the levels of mRNA from all the above genes except skeletal alpha-actin were increased by between 1.8- and 12-fold compared with the controls at birth (p < 0.05). In the first 28 days, the level of mRNA for alpha-myosin heavy chain increased slightly, while that for atrial natriuretic peptide and beta-myosin heavy chain decreased continuously similar to the controls, but at a significantly faster rate. No significant difference between the two groups of neonates was observed in all 5 genes after 1 month, indicating complete regression. Expression of 5 cardiac genes in the neonatal cardiac hypertrophy was characterised in both hypertrophic and regressive phases. Hypertrophic regression provides a unique model for the testing of new drugs or genetic modifying factors in cardiac hypertrophy.

Clinical spectrum, morbidity, and mortality in 113 pediatric patients with mitochondrial disease

OBJECTIVES

The aim of this study was to elucidate the frequency of major clinical manifestations in children with mitochondrial disease and establish their clinical course, prognosis, and rates of survival depending on their clinical features.

METHODS

We performed a retrospective review of the medical records of 400 patients who were referred for evaluation of mitochondrial disease. By use of the modified Walker criteria, only patients who were assigned a definite diagnosis were included in the study.

RESULTS

A total of 113 pediatric patients with mitochondrial disease were identified. A total of 102 (90%) patients underwent a muscle biopsy as part of the diagnostic workup. A significant respiratory chain (RC) defect, according to the diagnostic criteria, was found in 71% of the patients who were evaluated. In this cohort, complex I deficiency (32%) and combined complex I, III, and IV deficiencies (26%) were the most common causes of RC defects, followed by complex IV (19%), complex III (16%), and complex II deficiencies (7%). Pathogenic mitochondrial DNA abnormalities were found in 11.5% of the patients. A substantial fraction (40%) of patients with mitochondrial disorders exhibited cardiac disease, diagnosed by Doppler echocardiography; however, the majority (60%) of patients had predominant neuromuscular manifestations. No correlation between the type of RC defect and the clinical presentation was observed. Overall, the mean age at presentation was 40 months. However, the mean age at presentation was 33 months in the cardiac group and 44 months in the noncardiac group. Twenty-six (58%) patients in the cardiac group exhibited hypertrophic cardiomyopathy, 29% had dilated cardiomyopathy, and the remainder (13%) had left ventricular noncompaction. Patients with cardiomyopathy had an 18% survival rate at 16 years of age. Patients with neuromuscular features but no cardiomyopathy had a 95% survival at the same age.

CONCLUSIONS

This study gives strong support to the view that in patients with RC defects, cardiomyopathy is more common than previously thought and tends to follow a different and more severe clinical course. Although with a greater frequency than previously reported, mitochondrial DNA mutations were found in a minority of patients, emphasizing that most mitochondrial disorders of childhood follow a Mendelian pattern of inheritance.

Improved outcomes of pediatric dilated cardiomyopathy with utilization of heart transplantation

OBJECTIVES

We studied the outcomes of pediatric patients diagnosed with dilated cardiomyopathy (DCM) and their relation to epidemiologic and echocardiographic variables at the time of presentation.

BACKGROUND

The outcome of pediatric DCM patients ranges from recovery to a 50% to 60% chance of death within five years of diagnosis. The impact of heart transplantation and other emerging therapies on the outcomes of pediatric DCM patients is uncertain.

METHODS

We performed a retrospective study of the outcomes in 91 pediatric patients diagnosed with DCM from 1990 to 1999. Routine therapy included use of digoxin, diuretics, angiotensin-converting enzyme inhibitors, and heart transplantation.

RESULTS

At the time of last follow-up, 11 patients (12%) had died without transplantation; 20 (22%) underwent transplantation; 27 (30%) had persistent cardiomyopathy; and 33 (36%) had recovery of left ventricular systolic function. Overall actuarial one-year survival was 90%, and five-year survival was 83%. However, actuarial freedom from "heart death" (death or transplantation) was only 70% at one year and 58% at five years. Multivariate analysis found age <1 year (hazard ratio 7.1), age >12 years (hazard ratio 4.5), and female gender (hazard ratio 3.0) to be significantly associated with a greater risk of death or transplantation and a higher left ventricular shortening fraction at presentation (hazard ratio 0.92), with a slightly decreased risk of death or transplantation.

CONCLUSIONS

Pediatric DCM patients continue to have multiple outcomes, with recovery of left ventricular systolic function occurring most frequently. Utilization of heart transplantation has led to improved survival after the diagnosis of pediatric DCM.

Sequelae of storage in Fabry disease--pathology and comparison with other lysosomal storage diseases

AIM

To evaluate the sequelae of the lysosomal storage of globotriaosylceramide (Gb3) in a series of patients with Fabry disease.

METHODS

Biopsy and post-mortem samples from 12 patients with Fabry disease were examined microscopically, including, in some cases, immunohistochemistry and electron microscopy. Where possible, comparisons were made with other lysosomal storage disorders.

RESULTS

Storage of Gb3 in cardiocytes leads commonly to progressive hypertrophy, which is a non-specific phenomenon also observed in other lysosomal storage disorders. Capillary endothelial storage was associated with a tendency for capillary basement membrane multiplication. In the single angiokeratoma studied, the basement membrane was rudimentary. Sinusoids in the adrenal cortex and liver displayed either a slight degree of storage or were unaffected. The glomeruli of the kidney exhibited focal hyalinization starting in the mesangial region. Proximal tubular cells were essentially free of lysosomal accumulation, including protein absorption droplets, despite the presence of proteinuria. In only one case, an autopsied Fabry heterozygote, were the proximal tubular cells loaded with protein absorption droplets. The arterial wall in large muscular arteries (coronary, renal and intrarenal) displayed arteriopathy with pronounced involvement of the smooth muscle cells in the media. Arteriopathy started with storage, followed by cell degeneration and breakdown, extracellular matrix deposition and, often, calcification (confined to the muscular layer). Smooth muscle cells occasionally exhibited shrinkage-type necrosis, with dispersion of the stored lipid into the dense cytoplasmic mass. Intimal and mitral valve fibroblasts exhibited variable storage, which was associated with cell loss and necrosis. Intensive storage was found in Leydig cells and in the epididymal epithelium.

CONCLUSION

These long-term sequelae of Gb3 storage are mostly irreversible. Some may interfere with enzyme replacement therapy. It is important, therefore, to consider starting enzyme replacement therapy as early as possible.

Clinical characterization of left ventricular noncompaction in children: a relatively common form of cardiomyopathy

BACKGROUND

Left ventricular noncompaction (LVNC) is a reportedly uncommon genetic disorder of endocardial morphogenesis with a reportedly high mortality rate. The purpose of this study was to identify the clinical characteristics of children with LVNC.

METHODS AND RESULTS

We retrospectively reviewed 36 children with LVNC evaluated at Texas Children's Hospital (TCH) from January 1997 to December 2002. Five children had associated cardiac lesions. There were 16 girls and 20 boys. The median age at presentation was 90 days (range, 1 day to 17 years). The median duration of follow-up was 3.2 years (range, 0.5 to 12 years). Twenty-seven patients (75%) had ECG abnormalities, most commonly biventricular hypertrophy (10 patients, 28%). Both ventricles were involved in 8 patients (22%) and only the left ventricle in 28 patients (78%). Left ventricular systolic function was depressed in 30 patients (83%), with a median ejection fraction of 30% (range, 15% to 66%) at diagnosis. Nine patients presenting in the first year of life with depressed left ventricular contractility had a transient recovery of function; however, ejection fraction deteriorated later in life, at a median interval of 6.3years (range, 3 to 12 years). Two patients had an "undulating" phenotype from dilated to hypertrophic cardiomyopathy. Two patients (6%) were identified with an underlying G4.5 gene mutation. Five patients (14%) died during the study.

CONCLUSIONS

LVNC does not have an invariably fatal course when diagnosed in the neonatal period. A significant number of patients have transient recovery of function followed by later deterioration, which may account for many patients presenting as adults, some manifesting an "undulating" phenotype.

The incidence of pediatric cardiomyopathy in two regions of the United States

BACKGROUND

Population-based data on the incidence of pediatric cardiomyopathy are rare because of the lack of large, prospective studies.

METHODS

Since 1996 the Pediatric Cardiomyopathy Registry sponsored by the National Heart, Lung, and Blood Institute has collected data on all children with newly diagnosed cardiomyopathy in New England and the Central Southwest region (Texas, Oklahoma, and Arkansas) of the United States. We report on all children in these regions who received this diagnosis between 1996 and 1999.

RESULTS

We identified 467 cases of cardiomyopathy, for an overall annual incidence of 1.13 per 100,000 children (95 percent confidence interval, 1.03 to 1.23). The incidence was significantly higher among infants younger than 1 year old than among children and adolescents who were 1 to 18 years old (8.34 vs. 0.70 per 100,000, P<0.001). The annual incidence of cardiomyopathy was lower among white children (upper-bound estimate, 1.06 cases per 100,000) than among black children (lower-bound estimate, 1.47 per 100,000; P=0.02) and higher among boys than among girls (1.32 vs. 0.92 per 100,000, P<0.001). The incidence also varied significantly by region: 1.44 cases per 100,000 in New England and 0.98 per 100,000 in the Central Southwest region (P<0.001). When categorized according to type, dilated cardiomyopathy made up 51 percent of the cases, hypertrophic cardiomyopathy 42 percent, and restrictive or other types 3 percent; 4 percent were unspecified. There was no significant difference in the incidence rates according to the year.

CONCLUSIONS

The estimated incidence of pediatric cardiomyopathy in two large regions of the United States is 1.13 cases per 100,000 children. Most cases are identified at an early age, and the incidence varies according to sex, region, and racial or ethnic origin.

Mitochondrial deficiency and cardiac sudden death in mice lacking the MEF2A transcription factor

The four MEF2 transcription factors (MEF2A, -B, -C, and -D) regulate differentiation and calcium-dependent gene expression in muscle cells. We generated mice deficient in MEF2A, the predominant Mef2 gene product expressed in post-natal cardiac muscle. Most mice lacking Mef2a died suddenly within the first week of life and exhibited pronounced dilation of the right ventricle, myofibrillar fragmentation, mitochondrial disorganization and activation of a fetal cardiac gene program. The few Mef2a(-/-) mice that survived to adulthood also showed a deficiency of cardiac mitochondria and susceptibility to sudden death. Paradoxically, MEF2 transcriptional activity, revealed by the expression of a MEF2-dependent transgene, was enhanced in the hearts of Mef2a-mutant mice, reflecting the transcriptional activation of residual MEF2D. These findings reveal specific roles for MEF2A in maintaining appropriate mitochondrial content and cyto-architectural integrity in the post-natal heart and show that other MEF2 isoforms cannot support these activities.

Children are not small adults: some differences between pediatric and adult cardiac transplantation

Cardiac transplantation is a viable therapy for end-stage heart disease in both adults and children. Overall posttransplant survival in the pediatric age group (birth up to 18 years of age) is excellent (greater than 65% at 5 years for all age groups), comparable with the overall survival in the adult transplant recipients. Important differences exist regarding indications, evaluation, surgical technique, and posttransplant management. Indications for transplant in pediatric patients include metabolic and genetic forms of cardiomyopathy and structural congenital heart disease. Evaluation should include a metabolic workup, because potential etiologic factors include mitochondrial disorders, and genetic studies if indicated by phenotypic appearance or family pedigree. Children referred for transplantation with congenital heart disease have often had multiple attempts at palliative surgery, which increase peritransplant surgical risks. Key pediatric issues after transplantation include psychosocial support for the patient and family with regard to school, growth, development, and future expectations.

Mitochondria and the heart

Since the identification of the first pathogenic mutations of mitochondrial DNA in 1988, a plethora of information about human mitochondrial diseases has been brought to light. Not surprisingly, many of these disorders affect the myocardium, because this tissue relies heavily upon oxidative metabolism. This review focuses on disorders of the respiratory chain, the only area of mammalian cellular metabolism under the control of two genomes, nuclear and mitochondrial. Consequently, defects of aerobic synthesis of adenosine triphosphate (ATP) can be due to mutations of either genome. We describe genetic mitochondrial cardiomyopathies and briefly review mouse models and the mitochondrial theory of presbycardia.

Ventricular dysfunction clinical research in infants, children and adolescents

These two issues of Progress in Pediatric Cardiology comprehensively illustrate the wealth of currently available information on the pathophysiology of heart failure, age-related myocardial responsiveness, energy metabolism, cardiopulmonary interactions, the pressure-volume relationship, the systemic inflammatory response, the management of heart failure, pediatric pharmacology, the use of heart failure therapies including digoxin, ACE inhibitors, beta-adrenergic blockers, inotropic agents, diuretics, vasodilators, calcium sensitizers, angiotensin and aldosterone receptor blockers, growth hormone, and future gene therapy. The etiology and course of ventricular dysfunction in children is poorly characterized. Furthermore, many changing developmental properties of the pediatric myocardium and differences in the etiologies of ventricular dysfunction in children compared with adults are illustrated in these articles, invalidating the concept that children can safely be considered small adults for the purpose of understanding heart failure pathophysiology and treatment. However, these articles reveal that strikingly little research in children with ventricular dysfunction exists in terms of well-designed large-scale studies of the epidemiology or multicenter controlled clinical therapeutic trials. A future research agenda is proposed to improve understanding etiologies, course and treatment of ventricular dysfunction in children that is based on organized and funded cooperative groups since no one pediatric cardiac center treats enough children with a particular etiology of ventricular dysfunction. In conclusion, significant understanding of basic mechanisms of pediatric ventricular dysfunction and effective therapies for adults with ventricular dysfunction exist. A multicenter pediatric cardiac ventricular dysfunction network would allow improved understanding of diseases and treatments, and result in evidence-based medicine for pediatric patients with ventricular dysfunction.

Genetic abnormalities responsible for dilated cardiomyopathy

Dilated cardiomyopathy (DCM), a disorder in which left ventricular dilation and dysfunction leads to congestive heart failure, is inherited in over 30% of cases. The underlying genetic mechanisms are slowly being unraveled, with multiple genes recently identified as causing DCM in some patients. The genes identified to date appear to encode proteins that either support the cytoskeleton or interact with the cytoskeleton. When mutated, these proteins destabilize the cardiomyocyte membrane or cytoskeleton via mechanical instability or force transduction causing poor cardiac systolic function and compensatory dilation. Once the entire group of genes causing DCM (genetic heterogeneity) are identified, improvements in diagnosis and treatment are expected.

Molecular genetics of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM), a serious and often tragic disorder, is characterized by hypertrophy of the interventricular septum and left ventricular wall, hypercontractile systolic function with diastolic dysfunction, and in some cases, left ventricular outflow tract obstruction. On histopathologic examination, myofiber disarray is common. The genes for familial cases of hypertrophic cardiomyopathy are known to encode members of the sarcomere and to date nine genes have been identified (beta-myosin heavy chain, alpha-tropomyosin, cardiac troponin T, troponin I, myosin binding protein-C, regulatory myosin light chain, essential myosin light chain, cardiac actin, and titin) for this genetically and clinically heterogeneous disease. In this review the genetic basis of HCM is discussed.