Effect of pharmacological heart failure drugs and gene therapy on Danon's cardiomyopathy.

Danon disease is a rare X-linked genetic disease resulting from LAMP2 mutations leading to defective lysosomal function. Heart failure is the main causes of morbidity and mortality. Mice with an LAMP2-exon-6-deletion (L2Δ6), develop cardiac hypertrophy followed by dilated cardiomyopathy, in association with accumulation of autophagosomes, fibrosis and oxidative stress. We investigated the effect of drugs used to treat heart failure and of LAMP2 gene therapy on the phenotype, molecular markers and ROS in LAMP2 cardiomyopathy. L2Δ6 mice were treated with Angiotensin II, Ramipril, Metoprolol or Spironolactone. Gene therapy was delivered by IP injection of Adeno-associated-virus (AAV9) -LAMP2 vector to neonates ("AAVLAMP2-Prevention"), or at 15 weeks of age ("AAVLAMP2-Treatment"). Angiotensin II markedly aggravated the cardiac phenotype. Ramipril and Spironolactone were effective in attenuating left ventricular hypertrophy and preserving the systolic function. Cardiac protection was associated with decreased autophagosome accumulation, reduced fibrosis and oxidative stress. Gene therapy effectively attenuated autophagosome accumulation and ROS in L2Δ6 hearts, lowering troponin release to nearly normal levels. AAVLAMP2-Prevention protected against systolic dysfunction and decreased hypertrophy. AAVLAMP2-Treatment prevented ventricular dilatation and dysfunction but had no effect on wall thickness. We conclude that RAAS inhibitors are highly effective against cardiomyopathy progression in an experimental mouse model of Danon's and shall be considered in human patients for this purpose until novel therapies become clinically available.

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.

Autophagy guided interventions to modify the cardiac phenotype of Danon disease.

Danon disease is a lethal X-linked genetic syndrome resulting from radical mutations in the LAMP2 gene. LAMP2 protein deficiency results in defective lysosomal function, autophagy arrest and a multisystem disorder primarily involving the heart, skeletal muscle and the central nervous system. Cardiomyopathy is the main cause of morbidity and mortality. To investigate the mechanisms of and develop therapies for cardiac Danon disease we engineered a mouse model carrying an exon 6 deletion human mutation in LAMP2, which recapitulates the human cardiac disease phenotype. Mice develop cardiac hypertrophy followed by left ventricular dilatation and systolic dysfunction, in association with progressive fibrosis, oxidative stress, accumulation of autophagosomes and activation of proteasome. Stimulation of autophagy in Danon mice (by exercise training, caloric restriction, and rapamycin) aggravate the disease phenotype, promoting dilated cardiomyopathy. Inhibiting autophagy (by high fat diet or hydroxychloroquine) is better tolerated by Danon mice compared to wild type but is not curative. Inhibiting proteasome by Velcade was found to be highly toxic to Danon mice, suggesting that proteasome is activated to compensate for defective autophagy. In conclusion, activation of autophagy should be avoided in Danon patients. Since Danon's is a lifelong disease, we suggest that lifestyle interventions to decrease cardiac stress may be useful to slow progression of Danon's cardiomyopathy. While Danon mice better tolerate high fat diet and sedentary lifestyle, the benefit regarding cardiomyopathy in humans needs to be balanced against other health consequences of such interventions.

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.

A case report of delayed diagnosis of danon disease: Caused by a newly recognized mutation in the lysosome-associated membrane protein-2 gene.

INTRODUCTION: Danon disease is a rare X-linked dominant genetic disorder caused by defects in the lysosome-associated membrane protein 2 (LAMP2) gene. Unless treated, cardiogenic death is the main cause of mortality. This case report describes a 19-year-old man who was diagnosed with Danon disease and survived for 3 years from symptom onset to death. The mutation in his LAMP2 gene (p.Gly221Ilefs*19) had not been previously reported. PATIENT CONCERNS: A 19-year-old man patient was hospitalized for intermittent palpitations. He had no family history of cardiomyopathy, arrhythmia, or sudden cardiac death, but his sister had died of cirrhosis at age 12 years, but the exact cause of cirrhosis was unknown. DIAGNOSIS: Exome sequencing and Sanger sequencing identified a novel missense mutation (p.Gly221Ilefs*19) in the LAMP2 gene of the proband. This mutation was also detected in his mother, confirming the diagnosis of Danon disease. INTERVENTIONS: The patient experienced various types of arrhythmia throughout the clinical process, including Wolff-Parkinson-White syndrome, non-sustained atrial tachycardia, atrial flutter, and third-degree atrioventricular block. He was therefore treated with cardiac ablation procedures and cardiac resynchronization therapy. OUTCOMES: The period from the onset of symptoms to the onset of heart failure was 2 years. The patient died of cardiogenic death during the third year, at age 22 years. LESSONS: Danon disease is a rare disease that is difficult to recognize because of its hidden early manifestations. Early identification of its clinical symptoms can lead to early diagnosis and treatment.

Arrhythmias and fasciculoventricular pathways in patients with Danon disease: A single center experience.

BACKGROUND: Danon disease is a rare X-linked storage disorder characterized by hypertrophic cardiomyopathy leading to arrhythmias and heart failure. A preexcitation pattern on electrocardiogram (ECG) has been described in these patients, however, invasive studies to distinguish between Wolff-Parkinson-White syndrome syndrome and fasciculoventricular pathways (FVP) are limited. OBJECTIVES: The purpose of this study was to delineate the electrophysiological cardiac abnormalities in patients with Danon disease and to describe the presence of FVP in this population. METHODS: We performed a retrospective study of all patients with a confirmed diagnosis of Danon disease presenting to a single center from May 2005 to May 2018. Baseline demographics, clinical characteristics, ECG findings, and electrophysiology study (EPS) results were collected. RESULTS: Ten patients with Danon disease (30% male, average age 17.4 years) were identified. Seven patients (70%) had tachyarrhythmias including five with atrial arrhythmias and six with nonsustained ventricular tachycardia. Preexcitation pattern on ECG was found in four (40%) patients. Of these, two underwent an EPS which confirmed the presence of an FVP. One patient underwent an adenosine challenge which supported a FVP. Implantable cardioverter defibrillator was placed in five patients for primary prevention with no patients receiving an appropriate discharge. Over a follow-up of 5.3 years, five underwent heart transplantation. CONCLUSIONS: This study reports a high incidence of FVP in patients with Danon disease and preexcitation. It underscores an alternate etiology of preexcitation in this population which can potentially be diagnosed without invasive EPS testing. Future multicenter studies are needed to expand this experience.

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.

Asymptomatic young man with Danon disease.

Danon disease is a rare, codominant X-linked genetic disorder characterized by the triad of left ventricular hypertrophy, mental retardation, and peripheral myopathy. This disease is caused by mutations in the gene that encodes lysosomal associated membrane protein 2 (LAMP2), a deficiency of which results in the accumulation of autophagic granular débris within the vacuoles of muscle cells. This is a report of an asymptomatic 19-year-old man with Danon disease in the absence of mental retardation or clinically significant skeletal myopathy. This case underscores the importance of accurate diagnosis of unexplained left ventricular hypertrophy, in order to establish an appropriate treatment plan and to advise genetic counseling.

Advantages of a subcutaneous implantable cardioverter-defibrillator in LAMP2 hypertrophic cardiomyopathy.

Danon disease is a rare X-linked lysosomal disease causing severe hypertrophic cardiomyopathy (LAMP2 cardiomyopathy) and an extremely poor prognosis in males, with several reported cases of sudden cardiac death despite the use of transvenous implantable cardioverter defibrillators (TV-ICD). We describe a case in which a TV-ICD was unable to defibrillate induced ventricular fibrillation (VF), but a wholly subcutaneous system (S-ICD) was successful in terminating induced VF and spontaneous ventricular tachycardia. These findings have relevance to the selection of device therapy in the management of these individuals and a wider group of young patients with severe hypertrophic cardiomyopathy.

Exercise training does not correct abnormal cardiac glycogen accumulation in the db/db mouse model of type 2 diabetes.

Substrate imbalance is a well-recognized feature of diabetic cardiomyopathy. Insulin resistance effectively limits carbohydrate oxidation, resulting in abnormal cardiac glycogen accumulation. Aims of the present study were to 1) characterize the role of glycogen-associated proteins involved in excessive glycogen accumulation in type 2 diabetic hearts and 2) determine if exercise training can attenuate abnormal cardiac glycogen accumulation. Control (db(+)) and genetically diabetic (db/db) C57BL/KsJ-lepr(db)/lepr(db) mice were subjected to sedentary or treadmill exercise regimens. Exercise training consisted of high-intensity/short-duration (10 days) and low-intensity/long-duration (6 wk) protocols. Glycogen levels were elevated by 35-50% in db/db hearts. Exercise training further increased (2- to 3-fold) glycogen levels in db/db hearts. Analysis of soluble and insoluble glycogen pools revealed no differential accumulation of one glycogen subspecies. Phosphorylation (Ser(640)) of glycogen synthase, an indicator of enzymatic fractional activity, was greater in db/db mice subjected to sedentary and exercise regimens. Elevated glycogen levels were accompanied by decreased phosphorylation (Thr(172)) of 5'-AMP-activated kinase and phosphorylation (Ser(79)) of its downstream substrate acetyl-CoA carboxylase. Glycogen concentration was not associated with increases in other glycogen-associated proteins, including malin and laforin. Novel observations show that exercise training does not correct diabetes-induced elevations in cardiac glycogen but, rather, precipitates further accumulation.

A young patient with Danon disease receives two ICD shocks: why?

We report the case of an 18-year-old man with Danon disease, a genetic disorder inclunding a severe hypertrophic cardiomyopathy with very broad QRS, who had an implantable cardioverter defibrillator for primary prevention. Nine months after implantation, he received two inappropriate shocks due to R-wave double counting during sinus tachycardia. We discuss how to avoid such inappropriate therapy.

Pacemaker malfunctions in Danon's disease.

We describe a case of a 30-year-old man with Danon's disease, an X-linked genetic disorder due to deficiency of lysosomal-associated membrane protein 2 with secondary intracytoplasmatic glycogen and autophagic material storage. This disease is characterized by skeletal muscle involvement, mental retardation, ophthalmic abnormalities, and cardiac disease. In this patient, cardiac involvement was characterized by hypertrophic cardiomyopathy in young age, preexcitation, and parossistic atrioventricular block. The patient underwent to an implantable cardioverter defibrillator implantation for conduction disorders and for primary prevention of sudden death, a frequent event in Danon's disease. This case report describes cardiac involvement with conduction disorders and multiple pacemaker malfunctions in Danon's disease.

Reversibility of PRKAG2 glycogen-storage cardiomyopathy and electrophysiological manifestations.

BACKGROUND: PRKAG2 mutations cause glycogen-storage cardiomyopathy, ventricular preexcitation, and conduction system degeneration. A genetic approach that utilizes a binary inducible transgenic system was used to investigate the disease mechanism and to assess preventability and reversibility of disease features in a mouse model of glycogen-storage cardiomyopathy. METHODS AND RESULTS: Transgenic (Tg) mice expressing a human N488I PRKAG2 cDNA under control of the tetracycline-repressible alpha-myosin heavy chain promoter underwent echocardiography, ECG, and in vivo electrophysiology studies. Transgene suppression by tetracycline administration caused a reduction in cardiac glycogen content and was initiated either prenatally (Tg(OFF(E-8 weeks))) or at different time points during life (Tg(OFF(4-16 weeks)), Tg(OFF(8-20 weeks)), and Tg(OFF(>20 weeks))). One group never received tetracycline, expressing transgene throughout life (Tg(ON)). Tg(ON) mice developed cardiac hypertrophy followed by dilatation, ventricular preexcitation involving multiple accessory pathways, and conduction system disease, including sinus and atrioventricular node dysfunction. CONCLUSIONS: Using an externally modifiable transgenic system, cardiomyopathy, cardiac dysfunction, and electrophysiological disorders were demonstrated to be reversible processes in PRKAG2 disease. Transgene suppression during early postnatal development prevented the development of accessory electrical pathways but not cardiomyopathy or conduction system degeneration. Taken together, these data provide insight into mechanisms of cardiac PRKAG2 disease and suggest that glycogen-storage cardiomyopathy can be modulated by lowering glycogen content in the heart.

Benign course of glycogen storage disease type IIb in two brothers: nature or nurture?

Two brothers with the childhood variant of type II glycogenosis (GSD-IIb) treated with nutrition and exercise therapy (NET) from a young age showed an unusually benign course. Muscle biopsy from the older brother, which showed characteristic vacuolar glycogen accumulation at age 2, had reverted to normal by age 16. A muscle biopsy from the younger brother was normal at 5 years. It is uncertain whether this anomalous evolution was spontaneous (nature) or due to the symptomatic therapy (nurture), but NET should be considered in patients with GSD-IIb until enzyme replacement or gene therapy become generally available.