Danon disease: clinical features, evaluation, and management

Risk Stratification in Patients With Nonisquemic Dilated Cardiomyopathy. The Role of Genetic Testing

Dilated cardiomyopathy is inherited in nearly 50% of cases. More than 90 genes have been associated with this disease, which is one of the main causes of heart transplant and has been associated with an increased risk of sudden cardiac death. Risk stratification in these patients continues to be challenging. The identification of the specific etiology of the disease is very useful for the early detection of mutation carriers. Genetic study often provides prognostic information and can determine the therapeutic approach. Wide phenotypic variability is observed depending on the mutated gene, the type of mutation, and the presence of additional genetic and environmental factors.

Danon disease: Gender differences in presentation and outcomes

BACKGROUND

Danon disease (DD) is a rare X-linked autophagic vacuolar myopathy, characterized by high penetrance and severe cardiomyopathy. Because of its rarity, the natural history (NH) is uncertain.

OBJECTIVES

We aimed to describe disease variability and outcomes through a systematic review of all published DD cases.

METHODS

Among 83 manuscripts in MEDLINE and EMBASE on DD cases published until October 2017, we identified 146 patients with positive genetic testing for DD or positive muscle biopsy in a relative of a genetically diagnosed proband.

RESULTS

56 females and 90 males were identified. 92.5% of patients had cardiac abnormalities. Females presented with either hypertrophic cardiomyopathy (HCM, 70.3%) or dilated cardiomyopathy (DCM, 29.3%) whereas males presented with HCM 96.2% of the time. The composite outcome of death, heart transplant or ventricular assist devices occurred equally in both sexes (32% of females and 37% of males, p = 0.60) but later in females (median age 38 years) than in males (median age 21 years, p < 0.001). Whereas women present with isolated cardiac disease 73% of the time, in males DD was frequently multisystemic and presented as a triad of cognitive impairment, skeletal myopathy, and HCM in 42% of patients.

CONCLUSIONS

In this first systematic review of DD, we confirmed the severe morbidity and mortality associated with disease in both sexes. Women presented with both HCM and DCM and generally with isolated cardiac disease, whereas in men DD usually presented as HCM and was frequently multi-systemic. Further prospective NH studies will be required to confirm these findings.

A family with Danon disease caused by a splice site mutation in LAMP2 that generates a truncated protein

Background

Danon disease is an X‐linked dominant hereditary condition caused by mutations in the gene encoding lysosomal‐associated membrane protein 2 (LAMP2), leading to failure of lysosome binding to autophagosomes, accumulation of glycogen in the heart, and abnormal cardiac function.

Methods

We describe identification of a mutation in LAMP2, c.741+1G>T, in a family with Danon disease by whole exome sequencing.

Results

Pathology examination of patient skeletal muscle biopsy showed myogenic damage and autophagic vacuoles with sarcolemmal features (AVSF). Numerous autophagic vacuoles accumulated in muscle cells were detected by electron microscopy, indicating abnormal autophagy function.

Conclusion

The mutation did not result in loss of mRNA exons; rather, a 6‐nucleotide (two‐codon) insertion, where the latter was a stop codon, leading to early termination of LAMP2 protein translation. The resulting truncated protein lacks an important transmembrane domain, which will impair lysosome/autophagosome fusion, damage autophagy function, and result in the clinical manifestations of Danon disease.

Neuropsychological functioning following cardiac transplant in Danon disease

PURPOSE

To present a unique case involving a 31-year-old male with Danon disease (diagnosed at 14) who received cardiac transplant and subsequent cardiac re-transplant.

RESEARCH DESIGN

Brief report/case study.

METHODS

Serial neuropsychological assessment across a 23-year span along with a review of school records and prior psychoeducational assessment.

RESULTS

A consistent pattern of higher level cognitive impairment from childhood through adulthood was found. This pattern is interpreted in light of the sparse literature regarding cognitive and adaptive functioning related to Danon disease.

CONCLUSIONS

The noteworthy aspects of this case include the preservation of some academic abilities and an unexpected level of functional independence given cognitive concerns. This case study further explores the nature of the deficits related to Danon disease and highlights the benefits of neuropsychological evaluation to guide functional interventions and maximize level of independence across the life span.

LAMP-2B regulates human cardiomyocyte function by mediating autophagosome-lysosome fusion

Mutations in lysosomal-associated membrane protein 2 (LAMP-2) gene are associated with Danon disease, which often leads to cardiomyopathy/heart failure through poorly defined mechanisms. Here, we identify the LAMP-2 isoform B (LAMP-2B) as required for autophagosome-lysosome fusion in human cardiomyocytes (CMs). Remarkably, LAMP-2B functions independently of syntaxin 17 (STX17), a protein that is essential for autophagosome-lysosome fusion in non-CMs. Instead, LAMP-2B interacts with autophagy related 14 (ATG14) and vesicle-associated membrane protein 8 (VAMP8) through its C-terminal coiled coil domain (CCD) to promote autophagic fusion. CMs derived from induced pluripotent stem cells (hiPSC-CMs) from Danon patients exhibit decreased colocalization between ATG14 and VAMP8, profound defects in autophagic fusion, as well as mitochondrial and contractile abnormalities. This phenotype was recapitulated by LAMP-2B knockout in non-Danon hiPSC-CMs. Finally, gene correction of LAMP-2 mutation rescues the Danon phenotype. These findings reveal a STX17-independent autophagic fusion mechanism in human CMs, providing an explanation for cardiomyopathy in Danon patients and a foundation for targeting defective LAMP-2B-mediated autophagy to treat this patient population.

Mitochondrial breakdown in skeletal muscle and the emerging role of the lysosomes

Skeletal muscle mitochondria are essential in providing the energy required for locomotion. In response to contractile activity, the production of mitochondria is upregulated to meet the energy demands placed upon muscle cells. In a coordinated fashion, exercise also promotes the breakdown of dysfunctional mitochondria via mitophagy. Mitophagy is characterized by the selection of poorly functioning organelles, engulfment in an autophagosome and transport to lysosomes for degradation. In addition to the activation of mitophagy, exercise also elevates lysosome biogenesis. This coordinated increase in mitophagy targeting and lysosomal biogenesis serves to enhance the capacity for autophagosomal degradation, thereby aiding in the maintenance of mitochondrial quality. Lysosome dysfunction, as observed in lysosomal storage disorders (LSDs), negatively impacts mitochondrial function likely through the suppression of mitophagy. Since exercise is capable of activating mitophagy and lysosome biogenesis, researchers have begun to investigate physical activity as an effective therapy for LSDs. This review summarizes the current understanding of how mitophagy and lysosomal biogenesis are regulated in exercising skeletal, with potential therapeutic implications.

LAMP2 exon-copy number variations in Danon disease heterozygote female probands: Infrequent or underdetected?

Danon disease (DD) is an X-linked disorder caused by mutations in the lysosomal-associated membrane protein 2 (LAMP2) gene (Xq24). DD is characterized by cognitive deficit, myopathy, and cardiomyopathy in male patients. The phenotype is variable and mitigated in females. The timely identification of de-novo LAMP2 mutated family members, many of whom are heterozygous females, remains critical for their treatment and family counseling. DD laboratory testing builds on minimally invasive quantification of the LAMP2 protein in white blood cells and characterization of the specific mutation. This integrative approach is particularly helpful when assessing suspect female heterozygotes. LAMP2 exon-copy number variations (eCNVs) were so far reported only in X-hemizygous male DD probands. In heterozygous female DD probands, the wild-type allele may hamper the identification of an eCNV even if it results in the complete abolition of LAMP2 transcription and/or translation. To document the likely underappreciated rate of occurrence and point out numerous potential pitfalls of detection of the LAMP2 eCNVs, we present the first two DD heterozygote female probands who harbor novel multi-exon LAMP2 deletions. Critical for counseling and recurrence prediction, we also highlight the need to search for somatic-germinal mosaicism in DD families.

Storage diseases with hypertrophic cardiomyopathy phenotype

Never judge a book by its cover, nor assume hypertrophic cardiomyopathy (HCM) as sarcomeric, as appearances can deceive. HCM phenocopies account for a 5–10% of the cases, mainly represented by storage diseases, flagged by the increasing prevalence of senile cardiac amyloid in developing countries. Multisystemic and heterogeneous presentation of these entities is a challenge for clinicians, and time delay in diagnosis is a major concern. Promising drugs and gene-specific tailored therapies are under development, therefore, more than ever, appropriate understanding of these conditions is mandatory for adequate early treatment and counselling.

In this review, storage disorders will be classified as extracellular and intracellular deposit storage diseases, focusing our attention on the most prevalent conditions from the cardiologist’s perspective.

Clinical Findings and Prognosis of Danon Disease. An Analysis of the Spanish Multicenter Danon Registry

INTRODUCTION AND OBJECTIVES

Danon disease (DD) is caused by mutations in the LAMP2 gene. It is considered a multisystemic disease characterized by hypertrophic cardiomyopathy with pre-excitation and extreme hypertrophy, intellectual disability, myopathy, childhood presentation, and worse prognosis in men. There are scarce data on the clinical characteristics and prognosis of DD.

METHODS

We analyzed the clinical records of patients with DD from 10 Spanish hospitals.

RESULTS

Twenty-seven patients were included (mean age, 31 ± 19 years; 78% women). Male patients showed a high prevalence of extracardiac manifestations: myopathy (80%), learning disorders (83%), and visual alterations (60%), which were uncommon findings in women (5%, 0%, and 27%, respectively). Although hypertrophic cardiomyopathy was the most common form of heart disease (61%), the mean maximum wall thickness was 15 ± 7 mm and dilated cardiomyopathy was present in 12 patients (10 women). Pre-excitation was found in only 11 patients (49%). Age at presentation was older than 20 years in 16 patients (65%). After a median follow-up of 4 years (interquartile range, 2-9), 4 men (67%) and 9 women (43%) died or required a transplant. Cardiac disease and adverse events occurred later in women (37 ± 9 vs 23 ± 16 and 36 ± 20 vs 20 ± 11 years, respectively).

CONCLUSIONS

The clinical characteristics of DD differ substantially from traditional descriptions: age at presentation of DD is older, the disease is not multisystemic in women, and pre-excitation is infrequent.

Multimodality Imaging in Restrictive Cardiomyopathies: An EACVI expert consensus document In collaboration with the "Working Group on myocardial and pericardial diseases" of the European Society of Cardiology Endorsed by The Indian Academy of Echocardiography

Restrictive cardiomyopathies (RCMs) are a diverse group of myocardial diseases with a wide range of aetiologies, including familial, genetic and acquired diseases and ranging from very rare to relatively frequent cardiac disorders. In all these diseases, imaging techniques play a central role. Advanced imaging techniques provide important novel data on the diagnostic and prognostic assessment of RCMs. This EACVI consensus document provides comprehensive information for the appropriateness of all non-invasive imaging techniques for the diagnosis, prognostic evaluation, and management of patients with RCM.

Cardiac arrhythmias in patients with Danon disease

Aims

Different cardiac arrhythmias have been suggested to be associated with Danon disease, e.g. Wolff-Parkinson-White syndrome. However, a systematic electrophysiological investigation of patients with Danon disease is lacking thus far.

Methods and results

Seven patients with Danon disease (4 males, 35.8 ± 10.8 years; 3 females, 51.3 ± 19.9 years) from 3 different families were studied. In all patients, the presence of Danon disease was confirmed by western blot of biopsy material or genetic testing. The patients were characterized by 12-lead electrocardiogram (ECG), Holter ECG, echocardiography, and serial implantable cardioverter defibrillator (ICD) interrogations (in ICD recipients). All male patients underwent electrophysiological investigation (EP study). Asymptomatic ventricular tachyarrhythmias were documented in six of the seven patients. Moreover, 5 of the 7 patients suffered from atrial fibrillation (AF), with 1 of them experiencing thromboembolic stroke at the age of 30 years. In male patients, the initial QRS complex was characterized by a slurring upstroke and shortened PQ interval mimicking ventricular pre-excitation. One male patient showed initial QRS complex slurring with prolonged PR interval. However, the presence of an accessory pathway was excluded by an EP study in all patients. In female patients, initial QRS complex slurring was significantly less distinct. In four patients, ICD implantation was performed for primary prevention of sudden cardiac death. However, sustained ventricular arrhythmias were not documented in any of the patients.

Conclusions

The present study indicates that the distinct surface ECG pattern in Danon disease is not associated with ventricular pre-excitation. Atrial fibrillation is frequently observed in these patients and may be associated with thromboembolic events in the young, while sustained ventricular arrhythmias occur less frequently than previously reported.

A new phenotype of severe dilated cardiomyopathy associated with a mutation in the LAMP2 gene previously known to cause hypertrophic cardiomyopathy in the context of Danon disease

Danon disease is a rare X-linked cardiac and skeletal muscle disorder with multisystem clinical manifestations. Genetic defects at the lysosome-associated membrane 2 protein (LAMP2) are the cause of the disorder. Due to the rarity of the disease, there is limited progress in understanding the correlation between genotype and phenotype, and explaining the large variability of the clinical features of the disease. In this study, we report two patients, twin sisters, referred to our hospital for end stage heart failure due to dilated cardiomyopathy, requiring heart transplant evaluation. Genetic analysis, using targeted next generation sequencing, showed that the proband carried a LAMP2 missense variant, c.928G > A. The mutation was also detected in her twin sister by sanger sequencing. This variant has already been reported by other investigators and was correlated with the clinical triad of Danon disease i.e. hypertrophic cardiomyopathy, mental retardation and peripheral myopathy. The new phenotype of dilated cardiomyopathy associated with this mutation, confirms the phenotypic heterogeneity of the particular mutation, as well as of Danon disease.

Genetic Infiltrative Cardiomyopathies

Infiltrative cardiomyopathies are characterized by abnormal accumulation or deposition of substances in cardiac tissue leading to cardiac dysfunction. These can be inherited, resulting from mutations in specific genes, which engender a diverse array of extracardiac features but overlapping cardiac phenotypes. This article provides an overview of each inherited infiltrative cardiomyopathy, describing the causative genes, the pathologic mechanisms involved, the resulting cardiac manifestations, and the therapies currently offered or being developed.

Characterisation of Lamp2-deficient rats for potential new animal model of Danon disease

Danon disease (DD) is caused by the absence or malfunction of lysosomal-associated membrane protein 2 (LAMP2). Although Lamp2-deficient mice and DD patients have similar characteristics, these mice have clear limitations and are clinically inconsistent. The aim of our paper is to outline the characteristics of Lamp2-deficient rats and to contrast this model with currently available DD mouse models. The baseline levels of some serum enzymes were elevated in Lamp2y/- rats along with hypercholesterolemia and hyperglycaemia at 8 weeks. Echocardiography showed that IVSd (1.500 ± 0.071 vs. 2.200 ± 1.147, P < 0.01) and LVPWd (1.575 ± 0.063 vs. 1.850 ± 0.029, P < 0.01) were significantly increased, and GCS (-13.20 ± 0.4814 vs. -6.954 ± 0.665) and GRS (21.42 ± 1.807 vs. 7.788 ± 1.140) were sharply decreased. Meanwhile, substantial myocyte disruption, hypertrophic muscle fibres, interstitial fibrosis and microvascular hyperplasia could be observed in the heart tissue. Lamp2y/- rats also displayed abnormal behaviours in the open field and fear conditioning tests. Notably, Lamp2y/- rats manifested other system dysfunctions, such as retinopathy, chronic kidney injury and sterility. Based on these results, Lamp2-deficient rats exhibited greater similarity to DD patients in terms of onset and multisystem lesions than did mouse models, and these rats could be used as a valuable animal model for DD.

Cardiac Arrhythmias and Antiarrhythmic Drugs: An Autophagic Perspective

Degradation of cellular material by lysosomes is known as autophagy, and its main function is to maintain cellular homeostasis for growth, proliferation and survival of the cell. In recent years, research has focused on the characterization of autophagy pathways. Targeting of autophagy mediators has been described predominantly in cancer treatment, but also in neurological and cardiovascular diseases. Although the number of studies is still limited, there are indications that activity of autophagy pathways increases under arrhythmic conditions. Moreover, an increasing number of antiarrhythmic and non-cardiac drugs are found to affect autophagy pathways. We, therefore, suggest that future work should recognize the largely unaddressed effects of antiarrhythmic agents and other classes of drugs on autophagy pathway activation and inhibition.

Heterogeneity in a large pedigree with Danon disease: Implications for pathogenesis and management

BACKGROUND

Danon disease is an X-linked disturbance of autophagy manifesting with cognitive impairment and disordered heart and skeletal muscle. After a period of relative stability, patients deteriorate rapidly and may quickly become ineligible for elective heart transplantation - the only life-saving therapy.

METHODS

We report a large pedigree with diverse manifestations of Danon disease in hemizygotes and female heterozygotes.

RESULTS

Malignant cardiac arrhythmias requiring amiodarone treatment induced thyroid disease in two patients; intractable thyrotoxicosis, which enhances autophagy, caused the death of a 21year-old man. Our patients also had striking elevation of serum troponin I during the accelerated phase of their illness (p<0.01) and rising concentrations heralded cardiac decompensation. We argue for changes to cardiac transplantation eligibility criteria.

CONCLUSION

Danon disease causes hypertrophic cardiomyopathy - here we propose a common pathophysiological basis for the metabolic and structural effects of this descriptive class of heart disorders. We also contend that troponin I may have prognostic value and merits exploration for clinical decision-making including health warning bracelets. Rapamycin (Sirolimus®), an approved immunosuppressant which also influences autophagy, may prove beneficial. In the interim, while new treatments are developed, a revaluation of cardiac transplantation eligibility criteria is warranted.

Macroautophagy and Chaperone-Mediated Autophagy in Heart Failure: The Known and the Unknown

Cardiac diseases including hypertrophic and ischemic cardiomyopathies are increasingly being reported to accumulate misfolded proteins and damaged organelles. These findings have led to an increasing interest in protein degradation pathways, like autophagy, which are essential not only for normal protein turnover but also in the removal of misfolded and damaged proteins. Emerging evidence suggests a previously unprecedented role for autophagic processes in cardiac physiology and pathology. This review focuses on the major types of autophagic processes, the genes and protein complexes involved, and their regulation. It discusses the key similarities and differences between macroautophagy, chaperone-mediated autophagy, and selective mitophagy structures and functions. The genetic models available to study loss and gain of macroautophagy, mitophagy, and CMA are discussed. It defines the markers of autophagic processes, methods for measuring autophagic activities, and their interpretations. This review then summarizes the major studies of autophagy in the heart and their contribution to cardiac pathology. Some reports suggest macroautophagy imparts cardioprotection from heart failure pathology. Meanwhile, other studies find macroautophagy activation may be detrimental in cardiac pathology. An improved understanding of autophagic processes and their regulation may lead to a new genre of treatments for cardiac diseases.

Human-Induced Pluripotent Stem Cell-Based Modeling of Cardiac Storage Disorders

PURPOSE OF REVIEW

The aim of this study is to review the published human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) models of cardiac storage disorders and to evaluate the limitations and future applications of this technology.

RECENT FINDINGS

Several cardiac storage disorders (CSDs) have been modeled using patient-specific hiPSC-CMs, including Anderson-Fabry disease, Danon disease, and Pompe disease. These models have shown that patient-specific hiPSC-CMs faithfully recapitulate key phenotypic features of CSDs and respond predictably to pharmacologic manipulation. hiPSC-CMs generated from patients with CSDs are representative models of the patient disease state and can be used as an in vitro system for the study of human cardiomyocytes. While these models suffer from several limitations, they are likely to play an important role in future mechanistic studies of cardiac storage disorders and the development of targeted therapeutics for these diseases.

Transient Ischemic Attack and Ischemic Stroke in Danon Disease with Formation of Left Ventricular Apical Thrombus despite Normal Systolic Function

Danon disease is a rare X-linked dominant skeletal and cardiac muscle disorder presenting with hypertrophic cardiomyopathy, Wolf-Parkinson-White syndrome, skeletal myopathy, and mild intellectual disability. Early morbidity and mortality due to heart failure or sudden death are known in Danon disease, more in males than in females. Here, we present a 17-year-old female adolescent with Danon disease and severe concentric hypertrophy with normal left ventricular (LV) systolic function, who has been complaining of intermittent headache and weakness for about 3 years, initially diagnosed with hemiplegic migraine. Subsequently, her neurological manifestation progressed to transient ischemic attack (TIA) and eventually to ischemic stroke confirmed by CT scan with 1-day history of expressive aphasia followed by persistent left side weakness and numbness. Detailed echocardiogram for the first time revealed a small LV apical thrombus with unchanged severe biventricular hypertrophy and normal systolic function. This unexpected LV apical thrombus may be associated with a wide spectrum of neurological deficits ranging from TIA to ischemic stroke in Danon disease. Possibility of cerebral ischemic events should be suspected in Danon disease when presenting with neurological deficits even with normal systolic function. Careful assessment for LV apical thrombus is warranted in such cases.

Cardiomyopathies Due to Left Ventricular Noncompaction, Mitochondrial and Storage Diseases, and Inborn Errors of Metabolism

The normal function of the human myocardium requires the proper generation and utilization of energy and relies on a series of complex metabolic processes to achieve this normal function. When metabolic processes fail to work properly or effectively, heart muscle dysfunction can occur with or without accompanying functional abnormalities of other organ systems, particularly skeletal muscle. These metabolic derangements can result in structural, functional, and infiltrative deficiencies of the heart muscle. Mitochondrial and enzyme defects predominate as disease-related etiologies. In this review, left ventricular noncompaction cardiomyopathy, which is often caused by mutations in sarcomere and cytoskeletal proteins and is also associated with metabolic abnormalities, is discussed. In addition, cardiomyopathies resulting from mitochondrial dysfunction, metabolic abnormalities, storage diseases, and inborn errors of metabolism are described.

Danon disease for the cardiologist: case report and review of the literature

Danon disease is a rare, X-linked dominant genetic disorder that is caused by defects in the lysosome-associated membrane protein 2 (LAMP2) gene. It manifests predominantly in young males with a classic triad of cardiomyopathy, skeletal myopathy, and intellectual disability. Death from cardiac disease is the ultimate cause of demise in many patients if left untreated. Given the rarity of the condition, the natural history is poorly understood. Here, we present a case report on a 14-year-old Hispanic boy with Danon disease, highlighting major clinical events and diagnostic study findings over a six-year period from age of symptom onset to age of death. He had significant hypertrophic cardiomyopathy (ventricular septal thickness 65 mm) and experienced various arrhythmias during his clinical course including Wolf-Parkinson-White syndrome, non-sustained ventricular tachycardia, and pre-excited atrial fibrillation with a fasciculoventricular anomalous accessory pathway. He had sudden cardiac death from ventricular fibrillation at age 14 and his heart had a weight of 1425 grams at autopsy. We also provide a review of the cardiac Danon disease literature related to diagnostic and management approaches to aid cardiologists in evaluating and treating cardiac manifestations in Danon disease patients.

Disorders of lysosomal acidification-The emerging role of v-ATPase in aging and neurodegenerative disease

Autophagy and endocytosis deliver unneeded cellular materials to lysosomes for degradation. Beyond processing cellular waste, lysosomes release metabolites and ions that serve signaling and nutrient sensing roles, linking the functions of the lysosome to various pathways for intracellular metabolism and nutrient homeostasis. Each of these lysosomal behaviors is influenced by the intraluminal pH of the lysosome, which is maintained in the low acidic range by a proton pump, the vacuolar ATPase (v-ATPase). New reports implicate altered v-ATPase activity and lysosomal pH dysregulation in cellular aging, longevity, and adult-onset neurodegenerative diseases, including forms of Parkinson disease and Alzheimer disease. Genetic defects of subunits composing the v-ATPase or v-ATPase-related proteins occur in an increasingly recognized group of familial neurodegenerative diseases. Here, we review the expanding roles of the v-ATPase complex as a platform regulating lysosomal hydrolysis and cellular homeostasis. We discuss the unique vulnerability of neurons to persistent low level lysosomal dysfunction and review recent clinical and experimental studies that link dysfunction of the v-ATPase complex to neurodegenerative diseases across the age spectrum.

Identification of LAMP2 Mutations in Early-Onset Danon Disease With Hypertrophic Cardiomyopathy by Targeted Next-Generation Sequencing

Danon disease is an X-linked disorder with the clinical triad of cardiomyopathy, skeletal myopathy, and mental retardation. Early diagnosis of this disease remains a challenge, especially in the pediatric population. In this study, we developed a targeted panel-based next generation sequencing pipeline to identify mutations by sequencing of selected candidate genes in 136 pediatric patients with either hypertrophic cardiomyopathy (HC) or idiopathic dilated cardiomyopathy (IDC). This led to the identification of lysosome-associated membrane protein 2 (LAMP2) mutations in 4 of the 64 (6%) probands with HC, including 3 novel nonsense mutations (p.Q240X, p.S250X, and p.G22X). No LAMP2 mutation was detected in the other 72 probands with IDC. All 4 probands and one additional affected family member (2 men and 3 women) had an early-onset age and presented either HC alone or combined with Wolff-Parkinson-White syndrome and skeletal myopathy. Immunofluorescence staining and Western blot analysis revealed absent LAMP2 expression in both cardiac and skeletal muscle samples of the first proband and severely decreased LAMP2 expression in the skeletal muscle samples of the second proband. In conclusion, cardiomyopathy in the patients with Danon disease may occur during early childhood and tend to be HC rather than IDC in both affected men and women. Therefore, Danon disease should be considered as one of the leading causes of unexplained ventricular hypertrophy in pediatric patients. The inclusion of LAMP2 gene in cardiomyopathy genetic screening panels may contribute to early diagnosis of Danon disease.

A 12-year-old boy with chest pain and dyspnoea

CLINICAL INTRODUCTION

A previously healthy 12-year-old boy presented with chest pain and dyspnoea. ECG (figure 1), echocardiogram (figure 2) and myocardial MRI (figure 3) were performed.Electromyography revealed mild proximal weakness. Blood tests showed creatine kinase 997 UI/L, aspartate transaminase 398 UI/L, alanine transaminase 293 UI/L and lactate deshidrogenase 1730 UI/L. Ophthalmology test showed diffuse loss of pigment in the retinal pigment epithelium. Myocardial biopsy was performed (figure 4). A cardiomyopathy was suspected. LAMP2 gene was sequenced, and a stop mutation was identified.

QUESTION

What is the most likely diagnosis suggested based on the patient's tests and history? Danon's disease.Fabry's disease.Hypertrophic cardiomyopathy.Noonan's syndrome.Pompe's disease.

Accuracy and clinical value of maternal incidental findings during noninvasive prenatal testing for fetal aneuploidies

PURPOSE

Genome-wide sequencing of cell-free (cf)DNA of pregnant women aims to detect fetal chromosomal imbalances. Because the largest fraction of cfDNA consists of maternal rather than fetal DNA fragments, maternally derived copy-number variants (CNVs) are also measured. Despite their potential clinical relevance, current analyses do not interpret maternal CNVs. Here, we explore the accuracy and clinical value of maternal CNV analysis.

METHODS

Noninvasive prenatal testing was performed by whole-genome shotgun sequencing on plasma samples. Following mapping of the sequencing reads, the landscape of maternal CNVs was charted for 9,882 women using SeqCBS analysis. Recurrent CNVs were validated retrospectively by comparing their incidence with published reports. Nonrecurrent CNVs were prospectively confirmed by array comparative genomic hybridization or fluorescent in situ hybridization analysis on maternal lymphocytes.

RESULTS

Consistent with population estimates, 10% nonrecurrent and 0.4% susceptibility CNVs for low-penetrant genomic disorders were identified. Five clinically actionable variants were reported to the pregnant women, including haploinsufficiency of RUNX1, a mosaicism for segmental chromosome 13 deletion, an unbalanced translocation, and two interstitial chromosome X deletions.

CONCLUSION

Shotgun sequencing of cfDNA not only enables the detection of fetal aneuploidies but also reveals the presence of maternal CNVs. Some of those variants are clinically actionable or could potentially be harmful for the fetus. Interrogating the maternal CNV landscape can improve overall pregnancy management, and we propose reporting those variants if clinically relevant. The identification and reporting of such CNVs pose novel counseling dilemmas that warrant further discussions and development of societal guidelines.Genet Med 19 3, 306-313.

A novel LAMP2 mutation associated with severe cardiac hypertrophy and microvascular remodeling in a female with Danon disease: a case report and literature review

BACKGROUND

Danon disease (DD) is a rare disorder characterized by cardiomyopathy, intellectual disability, and proximal myopathy. It is caused by mutations in the LAMP2 gene on X chromosome. Female patients most often present with late-onset cardiomyopathy and slow disease progression, but early-onset cases with unfavorable prognosis have been reported.

CASE REPORT

We describe the clinical, pathological, and molecular features of a novel LAMP2 c.453delT mutation in a female patient with severe hypertrophic cardiomyopathy, Wolff Parkinson White (WPW) syndrome and rapid progression to heart failure, requiring heart transplant. Immunohistochemical analysis of LAMP2 in the explanted heart revealed a mosaic pattern of distribution, with discrete clusters of either stained or unstained cardiac myocytes, the latter being more frequent in the septum. These findings paralleled X chromosome inactivation within the myocardium. Interestingly, multiple foci of microscarring were found on histology in the Left Ventricle (LV) free wall and septum, in a close spatial relationship with remodeling and severe stenosis of intramural coronary arterioles.

CONCLUSIONS

Our findings suggest that several features may contribute to the early and severe cardiac phenotype in female DD patients. The type of mutation may account for the early disease onset, while both the inhomogeneous distribution of LAMP2 loss and the presence of microvascular remodeling may be determinant in the rapid progression to heart failure.

Lymphoma in Danon disease with chronic rhabdomyolysis treated with EPOCH-R: A case report

Rare disorders often represent a challenge for clinicians and require close collaboration of an interdisciplinary team.We present the complex case of a 22-year-old male with Danon disease and late-onset of posttransplant lymphoproliferative disorder after heart transplantation. The critical aspects of his condition were: pre-existing rhabdomyolysis; infiltration of muscle and gut with lymphoma; advanced clinical stage with bulky disease; nonresponsiveness to the reduction of immunosuppression and rituximab monotherapy; expected cardiotoxicity of anthracyclines. Therefore, the patient was treated with the EPOCH-R protocol, which includes continuous administration of doxorubicin over 4 days, instead of R-CHOP, in which the anthracycline is given in a short single infusion. Complete remission was achieved after the third cycle; rhabdomyolysis did not increase and heart function was not affected. The patient received a total of 6 cycles and is still in metabolic complete remission.We conclude that patients with Danon disease can be treated with anthracycline-containing chemotherapy and that continuous infusion of EPOCH-R does not exacerbate pre-existing rhabdomyolysis.

Danon disease - dysregulation of autophagy in a multisystem disorder with cardiomyopathy

Danon disease is a rare, severe X-linked form of cardiomyopathy caused by deficiency of lysosome-associated membrane protein 2 (LAMP-2). Other clinical manifestations include skeletal myopathy, cognitive defects and visual problems. Although individuals with Danon disease have been clinically described since the early 1980s, the underlying molecular mechanisms involved in pathological progression remain poorly understood. LAMP-2 is known to be involved in autophagy, and a characteristic accumulation of autophagic vacuoles in the affected tissues further supports the idea that autophagy is disrupted in this disease. The LAMP2 gene is alternatively spliced to form three splice isoforms, which are thought to play different autophagy-related cellular roles. This Commentary explores findings from genetic, histological, functional and tissue expression studies that suggest that the specific loss of the LAMP-2B isoform, which is likely to be involved in macroautophagy, plays a crucial role in causing the Danon phenotype. We also compare findings from mouse and cellular models, which have allowed for further molecular characterization but have also shown phenotypic differences that warrant attention. Overall, there is a need to better functionally characterize the LAMP-2B isoform in order to rationally explore more effective therapeutic options for individuals with Danon disease.

Crosstalk between Autophagy and Apoptosis: Potential and Emerging Therapeutic Targets for Cardiac Diseases

Autophagy is a cell survival process which is related to breaking down and reusing cytoplasm components. Moreover, autophagy regulates cell death under certain conditions. Apoptosis has the characteristics of chromatin agglutination and the shrinking of nuclear and apoptosis body form. Even if the mechanisms of autophagy and apoptosis have differences, some proteins modulate both autophagy and apoptosis. Crosstalk between them exists. This review highlights recent advances in the interaction of autophagy and apoptosis and its importance in the development of cardiovascular diseases.

Therapeutic targeting of autophagy in cardiovascular disease

Autophagy is an evolutionarily ancient process of intracellular catabolism necessary to preserve cellular homeostasis in response to a wide variety of stresses. In the case of post-mitotic cells, where cell replacement is not an option, finely tuned quality control of cytoplasmic constituents and organelles is especially critical. And due to the ubiquitous and critical role of autophagic flux in the maintenance of cell health, it comes as little surprise that perturbation of the autophagic process is observed in multiple disease processes. A large body of preclinical evidence suggests that autophagy is a double-edged sword in cardiovascular disease, acting in either beneficial or maladaptive ways, depending on the context. In light of this, the autophagic machinery in cardiomyocytes and other cardiovascular cell types has been proposed as a potential therapeutic target. Here, we summarize current knowledge regarding the dual functions of autophagy in cardiovascular disease. We go on to analyze recent evidence suggesting that titration of autophagic flux holds potential as a novel treatment strategy.

Inherited cardiomyopathies--Novel therapies

Cardiomyopathies arising due to a single gene defect represent various pathways that evoke adverse remodeling and cardiac dysfunction. While the gene therapy approach is slowly evolving and has not yet reached clinical "prime time" and gene correction approaches are applicable at the bench but not at the bedside, major advances are being made with molecular and drug therapies. This review summarizes the contemporary drugs introduced or being tested to help manage these unique disorders bearing a major impact on the quality of life and survival of the affected individuals. The restoration of the RNA reading frame facilitates the expression of partly functional protein to salvage or alleviate the disease phenotype. Chaperones are used to prevent the degradation of abnormal but still functional proteins, while other molecules are given for pathogen silencing, to prevent aggregation or to enhance clearance of protein deposits. The absence of protein may be managed by viral gene delivery or protein therapy. Enzyme replacement therapy is already a clinical reality for a series of metabolic diseases. The progress in molecular biology, based on the knowledge of the gene defect, helps generate small molecules and pharmaceuticals targeting the key events occurring in the malfunctioning element of the sick organ. Cumulatively, these tools augment the existing armamentarium of phenotype oriented symptomatic and evidence-based therapies for patients with inherited cardiomyopathies.

Brief Report: Oxidative Stress Mediates Cardiomyocyte Apoptosis in a Human Model of Danon Disease and Heart Failure

Danon disease is a familial cardiomyopathy associated with impaired autophagy due to mutations in the gene encoding lysosomal-associated membrane protein type 2 (LAMP-2). Emerging evidence has highlighted the importance of autophagy in regulating cardiomyocyte bioenergetics, function, and survival. However, the mechanisms responsible for cellular dysfunction and death in cardiomyocytes with impaired autophagic flux remain unclear. To investigate the molecular mechanisms responsible for Danon disease, we created induced pluripotent stem cells (iPSCs) from two patients with different LAMP-2 mutations. Danon iPSC-derived cardiomyocytes (iPSC-CMs) exhibited impaired autophagic flux and key features of heart failure such as increased cell size, increased expression of natriuretic peptides, and abnormal calcium handling compared to control iPSC-CMs. Additionally, Danon iPSC-CMs demonstrated excessive amounts of mitochondrial oxidative stress and apoptosis. Using the sulfhydryl antioxidant N-acetylcysteine to scavenge free radicals resulted in a significant reduction in apoptotic cell death in Danon iPSC-CMs. In summary, we have modeled Danon disease using human iPSC-CMs from patients with mutations in LAMP-2, allowing us to gain mechanistic insight into the pathogenesis of this disease. We demonstrate that LAMP-2 deficiency leads to an impairment in autophagic flux, which results in excessive oxidative stress, and subsequent cardiomyocyte apoptosis. Scavenging excessive free radicals with antioxidants may be beneficial for patients with Danon disease. In vivo studies will be necessary to validate this new treatment strategy.