Danon disease: clinical features, evaluation, and management

Rat models of musculoskeletal lysosomal storage disorders and their role in pre-clinical evaluation of gene therapy approaches

Mice have been a cornerstone of biomedical research for decades for studying a wide range of biological processes, disease mechanisms, and the assessment of therapies. Moreover, mice present several practical advantages such as small size, low cost and ease of genetic manipulation. While mice offer numerous benefits, for certain disease areas, rat models provide a closer representation of human disease progression, offering better insights for translational research and therapeutic development. This closer resemblance is particularly important for research focusing on diseases involving the cardiovascular and musculoskeletal system. In rats, the pathophysiology of these diseases mirrors the clinical alterations observed in humans. This review focuses on the key phenotypic differences between mouse and rat models of lysosomal storage disorders that specifically manifest with cardiac, skeletal muscle, and bone and joint involvement (Pompe and Danon diseases, and Maroteaux-Lamy and Morquio A syndromes). Furthermore, we discuss the therapeutic potential of various adeno-associated viral vector-mediated gene therapies that have been evaluated in these rat models, highlighting their contributions to advancing treatment options for these debilitating conditions.

Danon Disease Presenting with Slowly Progressive Cardiomyopathy and Harboring a Novel Missense Variant in the Lysosome-associated Membrane Protein Type 2 (LAMP-2) Gene

Danon disease (DD) is a rare lysosomal storage disorder resulting from pathogenic variants of the lysosome-associated membrane protein type 2 (LAMP-2) gene. The disease is characterized by severe cardiomyopathy, which rapidly progresses to end-stage heart failure. This case, with DD caused by a missense variant, exhibited slow progressive cardiomyopathy and survived for an extended period despite being a male. A pathological analysis revealed that only a minority of the samples exhibited autophagic vacuoles with unique sarcolemmal features, which are typical of DD. Importantly, LAMP-2 expression was absent and the myocardial tissue contained a substantial amount of p62-positive aggregates.

Phase 1 Study of AAV9.LAMP2B Gene Therapy in Danon Disease

BACKGROUND

Danon disease is a rare, X-linked, monogenic cardiomyopathy caused by mutations in the lysosomal-associated membrane 2 gene (LAMP2), which encodes the LAMP2 protein. In male patients, the predominant phenotype is progressive cardiac hypertrophy, cardiac dysfunction, and early death. There are no directed therapies for the disease.

METHODS

In this phase 1 study, we evaluated the safety and efficacy of a single infusion of RP-A501, a recombinant adeno-associated virus serotype 9 containing the transgene LAMP2B, which encodes an isoform of LAMP2. The primary outcomes were the safety and toxic effects of RP-A501, myocardial LAMP2 transduction and protein expression, stabilization of or reduction in heart-failure symptoms, and stabilization of or improvement in cardiac structure and function. Key secondary outcomes were sustained reduction in or stabilization of symptoms, immunologic response to RP-A501, end-stage heart failure, and overall survival. Exploratory outcomes included improvement in serologic markers of cardiac disease, patient-reported outcomes, and quality-of-life assessments.

RESULTS

RP-A501 infusion was administered to seven male patients with Danon disease: five who were 15 years of age or older and two who were between 11 and 14 years of age. All the patients received a transient immunomodulatory regimen of prednisone, tacrolimus or sirolimus, and rituximab. Phase 1 data over 24 to 54 months, including interim data from a long-term follow-up study, are reported here. One patient had complement-mediated thrombotic microangiopathy (grade 4) with thrombocytopenia and acute kidney injury. Three patients had glucocorticoid-related exacerbation (grade 3) of Danon disease-related skeletal myopathy. One patient with left ventricular systolic dysfunction at baseline had progressive heart failure and underwent transplantation 5 months after infusion. In the six patients with normal left ventricular ejection fraction at baseline, we observed cardiac LAMP2 protein expression and a reduction from baseline in or stabilization of the left ventricular mass index, preservation of left ventricular ejection fraction, and reduction in or stabilization of the levels of cardiac troponin I and N-terminal pro-B-type natriuretic peptide. At 24 to 54 months, all the patients were alive, with complete resolution of side effects.

CONCLUSIONS

A single infusion of RP-A501 appeared to be safe and was associated with cardiac LAMP2 expression and evidence of clinical improvement over a period of 24 to 54 months. (Funded by Rocket Pharmaceuticals; ClinicalTrials.gov number, NCT03882437.).

Thrombotic Microangiopathy Associated with Systemic Adeno-Associated Virus Gene Transfer: Review of Reported Cases

Complement-mediated thrombotic microangiopathy (TMA) in the form of atypical hemolytic uremic syndrome (aHUS) has emerged as an immune complication of systemic adeno-associated virus (AAV) gene transfer that was unforeseen based on nonclinical studies. Understanding this phenomenon in the clinical setting has been limited by incomplete data and a lack of uniform diagnostic and reporting criteria. While apparently rare based on available information, AAV-associated TMA/aHUS can pose a substantial risk to patients including one published fatality. Reported cases were originally limited to pediatric Duchenne muscular dystrophy patients receiving micro- or mini-dystrophin transgenes via AAV9 but have subsequently been reported in both pediatric and adult patients across a range of disorders, transgenes, promoters, and AAV capsid types. This article provides an introduction to the complement system, TMA and aHUS, and anticomplement therapies, then presents clinical reviews of AAV-associated TMA/aHUS cases that have been reported publicly. Finally, exploration of risk factors and current and future mitigation approaches are discussed.

Clinical and Genetic Profile of Chinese Children With Danon Disease: A Single-Center Retrospective Cohort Study

BACKGROUND

Danon disease (DD) is a rare X-linked dominant lysosomal storage disorder. Studies on DD pediatric patients are limited owing to the small number of cases and challenges in early detection.

METHODS

We retrospectively analysed clinical and genetic data of 29 pediatric patients who visited our hospital for treatment or genetic counselling for DD from July 2014 to December 2023.

RESULTS

The mean age at diagnosis was 7.2 ± 5.9 years for boys (n = 21) and 9.4 ± 5.0 years for girls (n = 8). Asymptomatic elevated liver transaminase or creatine kinase (CK) levels were initial manifestations detected in 10 male patients (48%) and absent in female patients. Hypertrophic cardiomyopathy (HCM) was observed in 20 male patients (95%) and 7 female patients (88%), whereas dilated cardiomyopathy (DCM) was not detected. Ventricular preexcitation (VP) was observed initially in 10 patients (36%) and in 15 (54%) at latest evaluation. Patients with VP had higher left ventricular posterior wall thickness in end-diastole z-scores than those without VP (5.6 ± 2.2 vs 3.5 ± 2.1; P = 0.029). During a median 2.7 years of follow-up, 2 male patients received heart transplants. One boy and 1 girl died of heart failure and sudden cardiac arrest, respectively. Twenty-three pathogenic LAMP2 variants were identified, including 7 novel variants.

CONCLUSIONS

A retrospective review of 29 DD cases suggests an underrecognised asymptomatic period in male DD patients, characterised by elevations in serum CK and transaminases. HCM appears to be the only cardiac manifestation in pediatric female patients, unlike a high incidence of DCM in adult female patients. The incidence of VP may increase with disease progression.

Ring-like late gadolinium enhancement: differential diagnosis and mimics

Advances in cardiac magnetic resonance have promoted tissue characterization with high spatial and contrast resolution, and late gadolinium enhancement (LGE) sequences have improved the detection of myocardial fibrosis. The distribution pattern of LGE facilitates differentiation between ischemic and nonischemic etiologies and aids in refining diagnoses within nonischemic cardiomyopathies, suggesting specific etiological factors. A distinctive nonischemic LGE pattern that has recently gained prominence is the ring-like pattern, defined as a subepicardial or mid-wall circumferential or semi-circumferential enhancement, which involves at least three contiguous segments within the same short-axis slice. Initially identified as a diagnostic marker for desmoplakin and filamin C-related cardiomyopathies, the pattern has been reported in nongenetic conditions; nevertheless, it remains an uncommon finding in these diseases. In this article, we aim to present the differential diagnoses of ring-like LGE and its mimics. The combination of epidemiological, clinical, electrocardiographic, and additional features enables a focused refinement of the differential diagnosis associated with ring-like LGE.

Precision Genetic Therapies: Balancing Risk and Benefit in Patients with Heart Failure

PURPOSE OF REVIEW

Precision genetic medicine is evolving at a rapid pace and bears significant implications for clinical cardiology. Herein, we discuss the latest advancements and emerging strategies in gene therapy for cardiomyopathy and heart failure.

RECENT FINDINGS

Elucidating the genetic architecture of heart failure has paved the way for precision therapies in cardiovascular medicine. Recent preclinical studies and early-phase clinical trials have demonstrated encouraging results that support the development of gene therapies for heart failure arising from a variety of etiologies. In addition to the discovery of new therapeutic targets, innovative delivery platforms are being leveraged to improve the safety and efficacy of cardiac gene therapies. Precision genetic therapy represents a potentially safe and effective approach for improving outcomes in patients with heart failure. It holds promise for radically transforming the treatment paradigm for heart failure by directly targeting the underlying etiology. As this new generation of cardiovascular medicines progress to the clinic, it is especially important to carefully evaluate the benefits and risks for patients.

Application of Calcium Kinetics Characterization in Cardiac Disease Modeling and Drug Discovery

Calcium regulation is essential in virtually any cell due to its critical role as a second messenger in multiple signaling pathways [...].

Chimeric Cell Therapies as a Novel Approach for Duchenne Muscular Dystrophy (DMD) and Muscle Regeneration

Chimerism-based strategies represent a pioneering concept which has led to groundbreaking advancements in regenerative medicine and transplantation. This new approach offers therapeutic potential for the treatment of various diseases, including inherited disorders. The ongoing studies on chimeric cells prompted the development of Dystrophin-Expressing Chimeric (DEC) cells which were introduced as a potential therapy for Duchenne Muscular Dystrophy (DMD). DMD is a genetic condition that leads to premature death in adolescent boys and remains incurable with current methods. DEC therapy, created via the fusion of human myoblasts derived from normal and DMD-affected donors, has proven to be safe and efficacious when tested in experimental models of DMD after systemic-intraosseous administration. These studies confirmed increased dystrophin expression, which correlated with functional and morphological improvements in DMD-affected muscles, including cardiac, respiratory, and skeletal muscles. Furthermore, the application of DEC therapy in a clinical study confirmed its long-term safety and efficacy in DMD patients. This review summarizes the development of chimeric cell technology tested in preclinical models and clinical studies, highlighting the potential of DEC therapy in muscle regeneration and repair, and introduces chimeric cell-based therapies as a promising, novel approach for muscle regeneration and the treatment of DMD and other neuromuscular disorders.

Cardiomyopathies and Psychiatric Disorders: An Overview and General Clinical Recommendations

The association between cardiomyopathies (CMPs) and psychiatric disorders is a complex and bidirectional phenomenon that involves multiple mechanisms and factors. CMPs may raise the risk of psychiatric disorders due to the psychological stress, physical limitations, social isolation, or poor prognosis associated with the underlying disease. Psychiatric disorders, on the other hand, can increase the possibility of developing or worsening CMPs due to the behavioral, neuroendocrine, inflammatory, or pharmacological effects of mental illness or its treatment. Moreover, some common genetic or environmental factors may have a relevant influence on both conditions. With this comprehensive review, we sought to provide an overview of the current evidence on the strict and intriguing interconnection between CMPs and psychiatric disorders, focusing on the epidemiology, pathophysiology, clinical implications, and management strategies.

Case Report: Multiple types of arrhythmias in a late-confirmed Danon disease

Introduction

Danon disease is an X-linked disorder caused by pathogenic variants in lysosome-associated membrane protein 2 (LAMP2) gene, typically characterized by the triad of hypertrophic cardiomyopathy, myopathy, and intellectual disability. However, many patients may not present the typical presentation, especially in the early stage. Electrocardiogram (ECG) abnormalities can be found in almost all patients, with Wolff-Parkinson-White (WPW) syndrome being the most common. We reported the case of a 51-year-old woman who experienced multiple types of arrhythmias over three decades and was diagnosed with Danon disease late by genetic testing.

Case summary

A 51-year-old woman with a 36-year history of intermittent palpitations was admitted due to hemodynamically stable ventricular tachycardia (VT). Her past medical history revealed multiple arrhythmias and ECG abnormalities in her 30s and 40s, including WPW syndrome with paroxysmal supraventricular tachycardia, paroxysmal atrial flutter, atrial fibrillation, ventricular tachycardia, and complete left bundle branch block. She denied any family history of cardiovascular disease or sudden death. Upon arrival, her vital signs were unremarkable. Cardiovascular magnetic resonance (CMR) imaging revealed left ventricular enlargement and late gadolinium enhancement (LGE) in the anterior, inferior, and lateral walls. Subsequent, whole-exome sequencing (WES) gene testing revealed a pathogenic heterozygous variant in LAMP2 gene (c.696T>A; p.Cys232Ter), which confirmed the diagnosis of Danon disease.

Conclusion

Genetic testing should be considered in patients who display multiple arrhythmias with LV structural abnormalities of unknown etiology for a possible Danon disease.

Genetic Testing in Hypertrophic Cardiomyopathy

Genetic testing is an important tool in the diagnosis and management of patients and families with hypertrophic cardiomyopathy (HCM). Modern testing can identify causative variants in 30 to >60% of patients, with probability of a positive test varying with baseline characteristics such as known family history of HCM. Patients diagnosed with HCM should be offered genetic counseling and genetic testing as appropriate. Standard multigene panels evaluate sarcomeric genes known to cause HCM as well as genetic conditions that can mimic HCM but require different management. Positive genetic testing (finding a pathogenic or likely pathogenic variant) helps to clarify diagnosis and assists in family screening. If there is high confidence that an identified variant is the cause of HCM, at-risk family members can pursue predictive testing to determine if they are truly at risk or if they can be dismissed from serial screening based on whether they inherited the family's causative variant. Interpreting test results can be complex, and providers should make use of multidisciplinary teams as well as evidence-based resources to obtain the best possible understanding of pathogenicity.

Altered Splicing of LAMP2 in a Multigenerational Family from Latvia Affected by Danon Disease

Background and Objectives: Danon disease is a multisystemic disorder associated with variants in the LAMP2 gene, mainly affecting the cardiac muscle. Here, we report a multigenerational family from Latvia with two male patients, hemizygous for a novel splice-affecting variant c.928+3A>G. Affected patients exhibit a cardiac phenotype, moderate mental disability, and mild retinal changes. Materials and Methods: Both patients underwent either exome or hypertrophic cardiomyopathy gene panel next-generation sequencing. The pathogenic variant effect was determined using reverse transcription, Sanger sequencing, and high-resolution electrophoresis. Results: Evaluation of the splicing process revealed that approximately 80% of the transcripts exhibited a lack of the entire exon 7. This alteration was predicted to cause a shift of the reading frame, consequently introducing a premature stop codon downstream in the sequence. Conclusions: Based on our data, we propose that c.928+3A>G is a pathogenic variant associated with Danon disease.

Lysosomal glucose sensing and glycophagy in metabolism

Lysosomes are cellular organelles that function to catabolize both extra- and intracellular cargo, act as a platform for nutrient sensing, and represent a core signaling node integrating bioenergetic cues to changes in cellular metabolism. Although lysosomal amino acid and lipid sensing in metabolism has been well characterized, lysosomal glucose sensing and the role of lysosomes in glucose metabolism is unrefined. This review will highlight the role of the lysosome in glucose metabolism with a focus on lysosomal glucose and glycogen sensing, glycophagy, and lysosomal glucose transport and how these processes impact autophagy and energy metabolism. Additionally, the role of lysosomal glucose metabolism in genetic and metabolic diseases will be briefly discussed.

State-of-the-Art Imaging of Infiltrative Cardiomyopathies: A Scientific Statement From the American Heart Association

Infiltrative cardiomyopathies comprise a broad spectrum of inherited or acquired conditions caused by deposition of abnormal substances within the myocardium. Increased wall thickness, inflammation, microvascular dysfunction, and fibrosis are the common pathological processes that lead to abnormal myocardial filling, chamber dilation, and disruption of conduction system. Advanced disease presents as heart failure and cardiac arrhythmias conferring poor prognosis. Infiltrative cardiomyopathies are often diagnosed late or misclassified as other more common conditions, such as hypertrophic cardiomyopathy, hypertensive heart disease, ischemic or other forms of nonischemic cardiomyopathies. Accurate diagnosis is also critical because clinical features, testing methodologies, and approach to treatment vary significantly even within the different types of infiltrative cardiomyopathies on the basis of the type of substance deposited. Substantial advances in noninvasive cardiac imaging have enabled accurate and early diagnosis. thereby eliminating the need for endomyocardial biopsy in most cases. This scientific statement discusses the role of contemporary multimodality imaging of infiltrative cardiomyopathies, including echocardiography, nuclear and cardiac magnetic resonance imaging in the diagnosis, prognostication, and assessment of response to treatment.

International Consensus on Differential Diagnosis and Management of Patients With Danon Disease: JACC State-of-the-Art Review

Danon disease is a rare X-linked autophagic vacuolar cardioskeletal myopathy associated with severe heart failure that can be accompanied with extracardiac neurologic, skeletal, and ophthalmologic manifestations. It is caused by loss of function variants in the LAMP2 gene and is among the most severe and penetrant of the genetic cardiomyopathies. Most patients with Danon disease will experience symptomatic heart failure. Male individuals generally present earlier than women and die of either heart failure or arrhythmia or receive a heart transplant by the third decade of life. Herein, the authors review the differential diagnosis of Danon disease, diagnostic criteria, natural history, management recommendations, and recent advances in treatment of this increasingly recognized and extremely morbid cardiomyopathy.

Clinical features of pediatric Danon disease and the importance of early diagnosis

Successful therapy in a cohort with early onset Danon disease (DD) highlights the potential importance of earlier disease recognition. We present experience from the largest National Pediatric Center in Russia for cardiomyopathy patients. This report focuses on identification of early clinical features of DD in the pediatric population by detailed pedigree analysis and review of medical records. RESULTS: Nine patients (3 females) were identified with DD at the Russian National Medical Research Center of Children's Health ("National Pediatric Center") aged birth to 16 years. At presentation/evaluation: all patients had left ventricular hypertrophy (LVH), ECG features of Wolff-Parkinson-White (WPW), and an increase in hepatic enzymes (particularly lactate dehydrogenase (LDH)); three had marked increase in NT-proBNP; two had HCM with impaired LV function; one had LVH with LV noncompaction; five had arrhythmia with paroxysmal supraventricular and/or ventricular tachycardia. Two teenagers died at ages 16-17 from refractory heart failure and two underwent heart transplantation. All patients were found to have a pathogenic/likely pathogenic variant in the LAMP2 gene, six patients had no family history and a de novo evolvement was documented in 4/6 of those available for genetic tested. Retrospective review related to family background and earlier clinical evaluations revealed a definitive or highly suspicious family history of DD in 3, early clinical presentation with cardiac abnormalities (ECG, echo) in 3, and cerebral, hepatic and/or neuromuscular symptoms in 5. Abnormalities were detected 9,5 months to 5,8 years, median 3,5 years prior to referral to the National Pediatric Center. CONCLUSION: The earliest clinical manifestations of Danon disease occur in the first 12 years of life with symptoms of skeletal muscle and cerebral disease, raised hepatic enzymes, and evidence of cardiac disease on ECG/echo.

Identification and functional analysis of a novel de novo missense mutation located in the initiation codon of LAMP2 associated with early onset female Danon disease

BACKGROUND

Danon disease is characterized by the failure of lysosomal biogenesis, maturation, and function due to a deficiency of lysosomal membrane structural protein (LAMP2).

METHODS

The current report describes a female patient with a sudden syncope and hypertrophic cardiomyopathy phenotype. We identified the pathogenic mutations in patients by whole-exon sequencing, followed by a series of molecular biology and genetic approaches to identify and functional analysis of the mutations.

RESULTS

Suggestive findings by cardiac magnetic resonance (CMR), electrocardiogram (ECG), and laboratory examination suggested Danon disease which was confirmed by genetic testing. The patient carried a novel de novo mutation, LAMP2 c.2T>C located at the initiation codon. The quantitative polymerase chain reaction (qPCR) and Western blot (WB) analysis of peripheral blood leukocytes from the patients revealed evidence of LAMP2 haploinsufficiency. Labeling of the new initiation codon predicted by the software with green fluorescent protein followed by fluorescence microscopy and Western blotting showed that the first ATG downstream from the original initiation codon became the new translational initiation codon. The three-dimensional structure of the mutated protein predicted by alphafold2 revealed that it consisted of only six amino acids and failed to form a functional polypeptide or protein. Overexpression of the mutated LAMP2 c.2T>C showed a loss of function of the protein, as assessed by the dual-fluorescence autophagy indicator system. The mutation was confirmed to be null, AR experiments and sequencing results confirmed that 28% of the mutant X chromosome remained active.

CONCLUSION

We propose possible mechanisms of mutations associated with haploinsufficiency of LAMP2: (1) The inactivation X chromosome carrying the mutation was not significantly skewed. However, it decreased in the mRNA level and the expression ratio of the mutant transcripts; (2) The identified mutation is null, and the active mutant transcript fails to translate into the normal LAMP2 proteins. The presence of haploinsufficiency in LAMP2 and the X chromosome inactivation pattern were crucial factors contributing to the early onset of Danon disease in this female patient.

Hypertrophic Cardiomyopathy versus Storage Diseases with Myocardial Involvement

One of the main causes of heart failure is cardiomyopathies. Among them, the most common is hypertrophic cardiomyopathy (HCM), characterized by thickening of the left ventricular muscle. This article focuses on HCM and other cardiomyopathies with myocardial hypertrophy, including Fabry disease, Pompe disease, and Danon disease. The genetics and pathogenesis of these diseases are described, as well as current and experimental treatment options, such as pharmacological intervention and the potential of gene therapies. Although genetic approaches are promising and have the potential to become the best treatments for these diseases, further research is needed to evaluate their efficacy and safety. This article describes current knowledge and advances in the treatment of the aforementioned cardiomyopathies.

A Case Study and Literature Review of the Diagnosis of Danon Disease in Patients Presenting Only with Severe Cardiac Symptoms

The clinical manifestations of Danon disease, which result from the primary deficiency of the lysosome-associated membrane protein 2 gene, include cardiomyopathy, skeletal myopathy, and different degrees of intellectual disability that vary greatly among patients. The present study reports on two cases of Danon disease in two patients who only presented cardiac symptoms. Cardiac symptoms usually occur in adolescence and during a patient's twenties, and most patients die from heart failure. However, the lab results from these cases suggested that other systems were involved, despite no other clinical symptoms. Significantly, the two patients had elevated serum cardiac troponin I, which often manifests in the acute cardiac phase, especially in severely affected patients with rapidly fatal outcomes. Danon disease is a multi-system involvement disease. Therefore, clinicians must be aware of its complexity when evaluating newly diagnosed patients due to its vastly different clinical course and prognosis and the importance of multidisciplinary management.

Genetic Abnormalities of the Sinoatrial Node and Atrioventricular Conduction

The peculiar electrophysiological properties of the sinoatrial node and the cardiac conduction system are key components of the normal physiology of cardiac impulse generation and propagation. Multiple genes and transcription factors and metabolic proteins are involved in their development and regulation. In this review, we have summarized the genetic underlying causes, key clinical findings, and the latest available clinical evidence. We will discuss clinical diagnosis and management of the genetic conditions associated with conduction disorders that are more prevalent in clinical practice, for this reason, very rare genetic diseases presenting sinus node or cardiac conduction system abnormalities are not discussed.

Identification of a novel splicing-altering LAMP2 variant in a Chinese family with Danon disease

AIMS

This study aimed to identify a novel splicing-altering LAMP2 variant associated with Danon disease.

METHODS AND RESULTS

To identify the potential genetic mutation in a Chinese pedigree, whole-exome sequencing was conducted in the proband, and Sanger sequencing was performed on the proband's parents. To verify the impact of the splice-site variant, a minigene splicing assay was applied. The AlphaFold2 analysis was used to analyse the mutant protein structure. A splice-site variant (NM_013995.2:c.864+5G>A) located at intron 6 of the LAMP2 gene was identified as a potential pathogenic variant. The minigene splicing revealed that this variant causes exon 6 to be skipped, resulting in a truncated protein. The AlphaFold2 analysis showed that the mutation caused a protein twist direction change, leading to conformational abnormality.

CONCLUSIONS

A novel splice-site variant (NM_013995.2:c.864+5G>A) located at intron 6 of the LAMP2 gene was identified. This discovery may enlarge the LAMP2 variant spectrum, promote accurate genetic counselling, and contribute to the diagnosis of Danon disease.

Danon Disease: Entire LAMP2 Gene Deletion with Unusual Clinical Presentation-Case Report and Review of the Literature

Danon disease is a rare x-linked dominant multisystemic disorder with a clinical triad of severe cardiomyopathy, skeletal myopathy, and intellectual disability. It is caused by defects in the lysosome-associated membrane protein-2 (LAMP2) gene. Numerous different mutations in the LAMP2 protein have been described. Danon disease is typically lethal by the mid-twenties in male patients due to cardiomyopathy and heart failure. Female patients usually present with milder and variable symptoms. This report describes a 42-year-old father and his 3-year-old daughter presenting with mild manifestations of the disease. The father has normal intellectual development and normal physical activity. At the age of 13, he was diagnosed with mild ventricular pre-excitation known as Wolf-Parkinson-White syndrome (WPWs), very mild and mostly asymptomatic cardiomyopathy and left ventricular hypertrophy, and at about the age of 25 presented with visual impairment due to cone-rod dystrophy. His daughter showed normal development and very mild asymptomatic electrocardiographic WPWs abnormalities with left mild ventricular hypertrophy. Genetic testing revealed an Xq24 microdeletion encompassing the entire LAMP2 gene. Relevant literature was reviewed as a reference for the etiology, diagnosis, treatment and case management.

The pivotal role of ECG in cardiomyopathies

Cardiomyopathies are a heterogeneous group of pathologies characterized by structural and functional alterations of the heart. Recent technological advances in cardiovascular imaging offer an opportunity for deep phenotypic and etiological definition. Electrocardiogram (ECG) is the first-line diagnostic tool in the evaluation of both asymptomatic and symptomatic individuals. Some electrocardiographic signs are pathognomonic or fall within validated diagnostic criteria of individual cardiomyopathy such as the inverted T waves in right precordial leads (V1-V3) or beyond in individuals with complete pubertal development in the absence of complete right bundle branch block for the diagnosis of arrhythmogenic cardiomyopathy of the right ventricle (ARVC) or the presence of low voltages typically seen in more than 60% of patients with amyloidosis. Most other electrocardiographic findings such as the presence of depolarization changes including QRS fragmentation, the presence of epsilon wave, the presence of reduced or increased voltages as well as alterations in the repolarization phase including the negative T waves in the lateral leads, or the profound inversion of the T waves or downsloping of the ST tract are more non-specific signs which can however raise the clinical suspicion of cardiomyopathy in order to initiate a diagnostic procedure especially using imaging techniques for diagnostic confirmation. Such electrocardiographic alterations not only have a counterpart in imaging investigations such as evidence of late gadolinium enhancement on magnetic resonance imaging, but may also have an important prognostic value once a definite diagnosis has been made. In addition, the presence of electrical stimulus conduction disturbances or advanced atrioventricular blocks that can be seen especially in conditions such as cardiac amyloidosis or sarcoidosis, or the presence of left bundle branch block or posterior fascicular block in dilated or arrhythmogenic left ventricular cardiomyopathies are recognized as a possible expression of advanced pathology. Similarly, the presence of ventricular arrhythmias with typical patterns such as non-sustained or sustained ventricular tachycardia of LBBB morphology in ARVC or non-sustained or sustained ventricular tachycardia with an RBBB morphology (excluding the "fascicular pattern") in arrhythmogenic left ventricle cardiomyopathy could have a significant impact on the course of each disease. It is therefore clear that a learned and careful interpretation of ECG features can raise suspicion of the presence of a cardiomyopathy, identify diagnostic "red flags" useful for orienting the diagnosis toward specific forms, and provide useful tools for risk stratification. The purpose of this review is to emphasize the important role of the ECG in the diagnostic workup, describing the main ECG findings of different cardiomyopathies.

Dropped Head Syndrome Secondary to Danon Disease: A Case Report

Dropped head syndrome (DHS) is characterized by neck extensor muscle weakness, which may be isolated or secondary to another neurologic diagnosis. DHS, due to lysosomal storage disorders, has not been reported in the literature. We present a 21-year-old male who had complaints of slowly worsening difficulty swallowing for the past eight years, along with difficulty keeping his head erect. His past medical history was significant for apical hypertrophic cardiomyopathy (HCM), and he had a history of sudden cardiac death in his immediate family. Clinical examination was significant only for neck extensor muscle weakness. His laboratory investigations were unremarkable, save for a significantly elevated creatine kinase (CK). Finally, whole exome sequencing identified a hemizygous stop gain variant in the lysosome-associated membrane protein 2 (LAMP-2) gene, pointing to a diagnosis of Danon disease (DD). DD is a rare, X-linked, inherited disease, due to a defect in the LAMP-2 gene that disrupts lysosomal autophagy. It is characterized by a triad of HCM, skeletal myopathy, and intellectual disability. Males typically suffer a more severe phenotype, and the cardiac disease drives its prognosis. Management involves regular cardiac monitoring, with appropriate physical therapy for myopathy and multidisciplinary treatment for intellectual disability. We suggest that DD be considered in the differential diagnosis for patients with HCM and elevated CK.

Danon disease in a Sardinian family: different aspects of the same mutation-a case report

Background

Danon disease (DD) is a rare X-linked disorder due to mutations in the lysosome-associated membrane protein 2 gene. It is characterized by a clinical triad of hypertrophic cardiomyopathy, skeletal myopathy, and a variable degree of intellectual disability.

Case summary

In this case series, we describe a mother and her son affected by DD, highlighting consistent clinical severity despite the expected variability related to gender. The mother (Case 1) presented isolated cardiac involvement, with an arrhythmogenic phenotype that evolved into severe heart failure requiring heart transplantation (HT). Danon disease was diagnosed 1 year after this event. Her son (Case 2) showed an earlier age onset of symptoms with complete atrioventricular block and fast progression of cardiac disease. Diagnosis was established 2 years after clinical presentation. He is currently listed for HT.

Discussion

In both of our patients, diagnostic delay was extremely long and could have been avoided by emphasizing the relevant clinical red flags. Patients affected by DD may present clinical heterogeneity in terms of natural history, age of onset, and cardiac and extracardiac involvement, even in the same family. Early diagnosis that phenotypic sex differences may impact is a crucial factor in managing patients with DD. Considering the rapid progression of cardiac disease and the poor prognosis, early diagnosis is important and close surveillance should be mandatory during follow-up.

Danon Disease Presenting as Eosinophilic Myocarditis

A 21-year-old woman with a history of atopy, peripheral eosinophilia, Wolf-Parkinson-White syndrome, and 5 episodes of myocarditis was diagnosed with eosinophilic myocarditis. Despite adequate immunosuppressive treatment and resolution of the myocarditis episode, the patient developed dilated cardiomyopathy and presented with worsening of her functional class. Finally, genetic testing unveiled an additional diagnosis: Danon disease. (Level of Difficulty: Advanced.).

Sudden cardiac death in childhood hypertrophic cardiomyopathy

The most prevalent cause of mortality in children with hypertrophic cardiomyopathy (HCM) is sudden cardiac death (SCD), which happens more frequently than in adult patients. Risk stratification tactics have generally been drawn from adult practice, however emerging data has revealed significant disparities between children and adult cohorts, implying the need for pediatric-specific risk stratification methodologies. We conducted an all-language literature search on Medline, Cochrane, Embase, and Google Scholar until October 2021. The following search strings and Medical Subject Heading (MeSH) terms were used: "HCM," "SCD," "Sudden Cardiac Death," and "Childhood Onset HCM." We explored the literature on the risk of SCD in HCM for its epidemiology, pathophysiology, the role of various genes and their influence, associated complications leading to SCD and preventive and treatment modalities. Childhood-onset HCM is linked to significant life-long morbidity and mortality, including a higher SCD rate in children than in adults. The present focus is on symptom relief and avoiding illness-related consequences, but the prospect of future disease-modifying medicines offers an intriguing opportunity to alter disease expression and outcomes in these young individuals. Current preventive recommendations promote implantable cardioverter defibrillator placement based on cumulative risk factor thresholds, although they have been demonstrated to have weak discriminating capacity. This article addresses questions and discusses the etiology, risk factors, and method to risk stratification for SCD in children with HCM.

Clinical features of Danon disease and insights gained from LAMP-2 deficiency models

Danon disease (DD) is an X-linked multisystem disorder with clinical features characterized by the triad of hypertrophic cardiomyopathy, skeletal muscle weakness, and mental retardation. Cardiac involvement can be fatal in the absence of an effective treatment option such as heart transplantation. Molecular studies have proved that LAMP-2 protein deficiency, mainly LAMP-2B isoform, resulting from LAMP2 gene mutation, is the culprit for DD. Autophagy impairment due to LAMP-2 deficiency mediated the accumulation of abnormal autophagic vacuoles in cells. While it is not ideal for mimicking DD phenotypes in humans, the emergence of LAMP-2-deficient animal models and induced pluripotent stem cells from DD patients provided powerful tools for exploring DD mechanism. In both in vitro and in vivo studies, much evidence has demonstrated that mitochondria dysfunction and fragmentation can result in DD pathology. Fundamental research contributes to the therapeutic transformation. By targeting the molecular core, several potential therapies have demonstrated promising results in partial phenotypes improvement. Among them, gene therapies anticipate inaugurate a class of symptom control and prevention drugs as their in vivo effects are promising, and one clinical trial is currently underway.

Metabolic Maturation Exaggerates Abnormal Calcium Handling in a Lamp2 Knockout Human Pluripotent Stem Cell-Derived Cardiomyocyte Model of Danon Disease

Danon disease (DD) is caused by mutations of the gene encoding lysosomal-associated membrane protein type 2 (LAMP2), which lead to impaired autophagy, glycogen accumulation, and cardiac hypertrophy. However, it is not well understood why a large portion of DD patients develop arrhythmia and sudden cardiac death. In the current study, we generated LAMP2 knockout (KO) human iPSC-derived cardiomyocytes (CM), which mimic the LAMP2 dysfunction in DD heart. Morphologic analysis demonstrated the sarcomere disarrangement in LAMP2 KO CMs. In functional studies, LAMP2 KO CMs showed near-normal calcium handling at base level. However, treatment of pro-maturation medium (MM) exaggerated the disease phenotype in the KO cells as they exhibited impaired calcium recycling and increased irregular beating events, which recapitulates the pro-arrhythmia phenotypes of DD patients. Further mechanistic study confirmed that MM treatment significantly enhanced the autophagic stress in the LAMP2 KO CMs, which was accompanied by an increase of both cellular and mitochondrial reactive oxygen species (ROS) levels. Excess ROS accumulation in LAMP2 KO CMs resulted in the over-activation of calcium/calmodulin dependent protein kinase IIδ (CaMKIIδ) and arrhythmogenesis, which was partially rescued by the treatment of ROS scavenger. In summary, our study has revealed ROS induced CaMKIIδ overactivation as a key mechanism that promotes cardiac arrhythmia in DD patients.

Models to study basic and applied aspects of lysosomal storage disorders

The lack of available treatments and fatal outcome in most lysosomal storage disorders (LSDs) have spurred research on pathological mechanisms and novel therapies in recent years. In this effort, experimental methodology in cellular and animal models have been developed, with aims to address major challenges in many LSDs such as patient-to-patient variability and brain condition. These techniques and models have advanced knowledge not only of LSDs but also for other lysosomal disorders and have provided fundamental insights into the biological roles of lysosomes. They can also serve to assess the efficacy of classical therapies and modern drug delivery systems. Here, we summarize the techniques and models used in LSD research, which include both established and recently developed in vitro methods, with general utility or specifically addressing lysosomal features. We also review animal models of LSDs together with cutting-edge technology that may reduce the need for animals in the study of these devastating diseases.

Dilated Cardiomyopathy and Systolic Heart Failure in a Female Patient With Danon Disease

Danon disease commonly manifests as isolated hypertrophic cardiomyopathy in female patients. The diagnosis is easily missed as it is rare and its pathophysiology is poorly understood. Without early diagnosis and treatment with heart transplantation, cardiomyopathy may progress to heart failure. We present the case of an adolescent female with Danon disease who presented with heart failure with reduced ejection fraction secondary to dilated cardiomyopathy. Her original presentation included a six-month history of shortness of breath, vomiting, and abdominal pain. Further workup revealed pelvic ascites and dilated cardiomyopathy with signs of heart failure. Genetic testing confirmed the diagnosis, revealing a previously undocumented amino acid substitution in the lysosomal-associated membrane protein-2 (LAMP2) gene. The patient received a heart transplant which led to an improvement in her symptoms. The patient's unique symptomatology illustrates the importance of early cardiac monitoring and transplantation if Danon disease is suspected. This uncommon presentation of dilated cardiomyopathy followed by psychiatric impairment, developmental disability, and unique LAMP2 genetic substitution provides a rare phenotype of Danon disease.

De novo LAMP2 insertion mutation causes cardiac-only Danon disease: A case report

Danon disease is a rare disease caused by glycogen storage lysosomal disorder. It is related to the pathogenic mutation of the LAMP2 gene. In this case report, we present a patient with a novel pathogenic mutation (c.764_765insGA) with cardiac-only symptoms. Her family members do not carry the same mutation she does, suggesting this is a de novo mutation. Further tests revealed vacuoles and glycogen disposition in the patient's heart tissue and a significant decrease in LAMP2 protein expression. Protein structure remodeling of LAMP2 predicted that the mutant protein has conformational change lacking an important transmembrane domain, subsequently causing protein destabilization.

Case Report: Danon Disease: Six Family Members and Literature Review

Danon disease is a rare X-linked dominant genetic disorder that manifests with a clinical triad of cardiomyopathy, skeletal myopathy, and intellectual disability. It is caused by mutations in the lysosome-associated membrane 2 (LAMP2) gene. We report one case of Danon disease and his family members, characterized by ventricular pre-excitation, ventricular hypertrophy, abnormal muscle enzymes, and aberrant liver function. All the patients were confirmed to have Danon disease through genetic screening. Relevant literature was reviewed as a reference for the diagnosis and treatment of the disease.

Cardiomyopathies in Children and Systemic Disorders When Is It Useful to Look beyond the Heart?

Cardiomyopathy (CMP) is a rare disease in the pediatric population, with a high risk of morbidity and mortality. The genetic etiology of CMPs in children is extremely heterogenous. These two factors play a major role in the difficulties of establishing standard diagnostic and therapeutic protocols. Isolated CMP in children is a frequent finding, mainly caused by sarcomeric gene variants with a detection rate that can reach up to 50% of analyzed cohorts. Complex multisystemic forms of pediatric CMP are even more heterogenous. Few studies in literature take into consideration this topic as the main core since it represents a rarity (systemic CMP) within a rarity (pediatric population CMP). Identifying etiology in this cohort is essential for understanding prognosis, risk stratification, eligibility to heart transplantation and/or mechanical-assisted procedures, preventing multiorgan complications, and relatives' recurrence risk calculation. The previous points represent a cornerstone in patients' empowerment and personalized medical care approach. The aim of this work is to propose a new approach for an algorithm in the setting of the diagnostic framework of systemic pediatric CMP. On the other hand, during the literature review, we noticed a relatively common etiologic pattern in some forms of complex/multisystem CMP. In other words, certain syndromes such as Danon, Vici, Alström, Barth, and Myhre syndrome share a common pathway of directly or indirectly defective "autophagy" process, which appears to be a possible initiating/triggering factor for CMPs. This conjoint aspect could be important for possible prognostic/therapeutic implications in this category of patients. However, multicentric studies detailed functional and experimental models are needed prior to deriving conclusions.

A Frequent Observation of Wolff-Parkinson-White Syndrome and Fasciculoventricular Pathways in Patients With Danon Disease

BACKGROUND

Danon disease is typically associated with cardiomyopathy and ventricular pre-excitation. The study aimed to characterize the clinical profile of Danon disease, analyze electrocardiographic (ECG) and electrophysiologic features, and investigate their association with Wolff-Parkinson-White (WPW) syndrome and fasciculoventricular pathways (FVPs).

METHODS AND RESULTS

Clinical course, family history, ECG and electrophysiological data were collected from 16 patients with Danon disease. Over 0.4-8 years of follow up, 1 female patient died suddenly, and 5 male patients died of progressive heart failure by age 13-20 years. Family history analysis revealed that 3 mothers experienced hospitalization or death for heart failure at age 28-41 years. There was 100% penetrance for ECG abnormalities in 13 patients with original ECGs. Short PR intervals and delta waves were present in 9 and 8 patients, respectively. There were significant age-associated increases in the QRS complex width (r=0.556, P=0.048) and the number of leads with notched QRS (r=0.575, P=0.04). Four patients who underwent electrophysiological studies all had FVPs, and 2 of them still had left-side atrioventricular pathways.

CONCLUSIONS

Danon disease causes a malignant clinical course characterized by early death caused by heart failure in both genders and progressive ECG changes as patients age. The pre-excited ECG pattern is related to FVPs and WPW, which is suggestive of extensive cardiac involvement.

Case Report: A Novel LAMP2 Splice-Altering Mutation Causes Cardiac-Only Danon Disease

Danon disease (DD) is a rare glycogen storage lysosomal disorder caused by mutations in the LAMP2 gene. Patients with DD are usually characterized clinically by severe multisystem syndromes. We describe a specific family with a novel pathogenic splice-altering mutation in the LAMP2 gene (c.741+2T>C) with cardiac-only symptoms (frequent ventricular tachycardia, intraventricular block, and hypertrophic cardiomyopathy). Minigene assays were used to evaluate the consequence of the splice-site mutation in the LAMP2 gene. The results showed that the c.741+2T>C mutation led to extra 6-bp preservation of intron 5 at the junction between exons 5 and 6 during transcriptional processing of the mRNA, which creates a stop codon and truncated the LAMP2 protein to 248-amino-acid residues. The mutant LAMP2 protein was predicted to have a conformational change, lacks the important transmembrane domain, and subsequent protein destabilization.

Myocardial Strain and Association With Clinical Outcomes in Danon Disease: A Model for Monitoring Progression of Genetic Cardiomyopathies

Background

Myocardial strain can identify subclinical left ventricular dysfunction in various cardiac diseases, but its association with clinical outcomes in genetic cardiomyopathies remains unknown. Herein, we assessed myocardial strain in patients with Danon disease (DD), a rare X‐linked autophagic disorder that causes severe cardiac manifestations.

Methods and Results

Echocardiographic images were reviewed and used to calculate myocardial strain from a retrospective, international registry of patients with DD. Regression analyses were performed to evaluate for an association of global longitudinal strain (GLS) and ejection fraction with the composite outcome (death, ventricular assist device, heart transplantation, and implantable cardioverter defibrillator for secondary prevention). A total of 22 patients with DD (male 14 [63.6%], median age 16.5 years) had sufficient echocardiograms for analysis. Absolute GLS was reduced with a mean of 12.2% with an apical‐sparing pattern observed. Univariable regression for GLS and composite outcome showed an odds ratio of 1.32 (95% CI, 1.02–1.71) with P=0.03. For receiver operating characteristic analysis, the areas under the curve for GLS and ejection fraction were 0.810 (P=0.02) and 0.605 (P=0.44), respectively. An absolute GLS cutoff of 10.0% yielded a true positive rate of 85.7% and false positive rate of 13.3%.

Conclusions

In this cohort of patients with DD, GLS may be a useful assessment of myocardial function and may predict clinical outcomes. This study highlights the potential use of myocardial strain phenotyping to monitor disease progression and potentially to predict clinical outcomes in DD and other genetic cardiomyopathies.

Four-dimensional echocardiography and left ventricular systolic strain measured via two-dimensional speckle-tracking for Danon disease: a case series

BACKGROUND

Danon disease is an X-linked multisystemic disorder characterized by skeletal myopathy, cardiomyopathy, and intellectual disability.

CASE SUMMARY

Herein, we describe two patients affected by Danon disease from the same family, a father (Patient 1) and his daughter (Patient 2). In Patient 1, a short PR interval with pre-excitation was evident. In Patient 2, over a 24-h period 2369 atrial premature beats and rare isolated ventricular ectopics were detected. Both patients exhibited left ventricular hypertrophy with non-compaction myocardium, and the left ventricular ejection fraction was impaired in Patient 1 and normal in Patient 2. In Patient 2, the total left ventricular strain value was reduced, and layer-specific strain revealed that subepicardial strain impaired more than in other layers. Late gadolinium enhancement was detected both in left and right ventricles in Patient 2, and cardiac fibrosis was more apparent in the subepicardium of left ventricular free wall. Four-dimensional (4D) echocardiography revealed that left atrial reservoir strain and left ventricular total longitudinal strain were induced.

DISCUSSION

Novel 4D echocardiography and left ventricular systolic strain may play important role in diagnosis and myocardial functional evaluation in Danon disease.

Genetic Abnormalities of the Sinoatrial Node and Atrioventricular Conduction

The peculiar electrophysiological properties of the sinoatrial node and the cardiac conduction system are key components of the normal physiology of cardiac impulse generation and propagation. Multiple genes and transcription factors and metabolic proteins are involved in their development and regulation. In this review, we have summarized the genetic underlying causes, key clinical findings, and the latest available clinical evidence. We will discuss clinical diagnosis and management of the genetic conditions associated with conduction disorders that are more prevalent in clinical practice, for this reason, very rare genetic diseases presenting sinus node or cardiac conduction system abnormalities are not discussed.

Application of Patient-Specific iPSCs for Modelling and Treatment of X-Linked Cardiomyopathies

Inherited cardiomyopathies are among the major causes of heart failure and associated with significant mortality and morbidity. Currently, over 70 genes have been linked to the etiology of various forms of cardiomyopathy, some of which are X-linked. Due to the lack of appropriate cell and animal models, it has been difficult to model these X-linked cardiomyopathies. With the advancement of induced pluripotent stem cell (iPSC) technology, the ability to generate iPSC lines from patients with X-linked cardiomyopathy has facilitated in vitro modelling and drug testing for the condition. Nonetheless, due to the mosaicism of the X-chromosome inactivation, disease phenotypes of X-linked cardiomyopathy in heterozygous females are also usually more heterogeneous, with a broad spectrum of presentation. Recent advancements in iPSC procedures have enabled the isolation of cells with different lyonisation to generate isogenic disease and control cell lines. In this review, we will summarise the current strategies and examples of using an iPSC-based model to study different types of X-linked cardiomyopathy. The potential application of isogenic iPSC lines derived from a female patient with heterozygous Danon disease and drug screening will be demonstrated by our preliminary data. The limitations of an iPSC-derived cardiomyocyte-based platform will also be addressed.