Functional performance and muscle strength phenotypes in men and women with Danon disease

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.

Role of autophagy in muscle disease

Beside inherited muscle diseases many catabolic conditions such as insulin resistance, malnutrition, cancer growth, aging, infections, chronic inflammatory status, inactivity, obesity are characterized by loss of muscle mass, strength and function. The decrease of muscle quality and quantity increases morbidity, mortality and has a major impact on the quality of life. One of the pathogenetic mechanisms of muscle wasting is the dysregulation of the main protein and organelles quality control system of the cell: the autophagy-lysosome. This review will focus on the role of the autophagy-lysosome system in the different conditions of muscle loss. We will also dissect the signalling pathways that are involved in excessive or defective autophagy regulation. Finally, the state of the art of autophagy modulators that have been used in preclinical or clinical studies to ameliorate muscle mass will be also described.

Danon disease: a case report and literature review

BACKGROUND

Danon disease (DD) is a rare x-linked dominant multisystemic disorder with a clinical triad of severe cardiomyopathy, skeletal myopathy, and mental retardation. It is caused by a defect in the lysosomal-associated membrane protein-2 (LAMP2) gene, which leads to the formation of autophagic vacuoles containing glycogen granule deposits in skeletal and cardiac muscle fibers. So far, more than 50 different mutations in LAMP2 have been identified.

CASE PRESENTATION

Here, we report an 18-year-old male patient who was hospitalized for heart failure. Biopsy of the left lateral femoral muscle revealed scattered autophagic vacuoles in the muscle fibers with increased glycogen. Next generation sequencing (NGS) was used to detect gene mutations of the proband sample and a novel frameshift mutation (c.1052delG) has been identified in exon 8 of LAMP2, which leads to truncation of the protein.

CONCLUSION

We found a novel frameshift mutation, a hemizygous mutation (c.1052delG) in exon 8 of LAMP2, identified as presenting the hypertrophic cardiomyopathy (HCM) phenotype. Genetic analysis is the gold standard for the diagnosis of DD and is essential to determine appropriate treatment strategies and to confirm the genetic risk of family members.

Manifestations of Age on Autophagy, Mitophagy and Lysosomes in Skeletal Muscle

Sarcopenia is the loss of both muscle mass and function with age. Although the molecular underpinnings of sarcopenia are not fully understood, numerous pathways are implicated, including autophagy, in which defective cargo is selectively identified and degraded at the lysosome. The specific tagging and degradation of mitochondria is termed mitophagy, a process important for the maintenance of an organelle pool that functions efficiently in energy production and with relatively low reactive oxygen species production. Emerging data, yet insufficient, have implicated various steps in this pathway as potential contributors to the aging muscle atrophy phenotype. Included in this is the lysosome, the end-stage organelle possessing a host of proteolytic and degradative enzymes, and a function devoted to the hydrolysis and breakdown of defective molecular complexes and organelles. This review provides a summary of our current understanding of how the autophagy-lysosome system is regulated in aging muscle, highlighting specific areas where knowledge gaps exist. Characterization of the autophagy pathway with a particular focus on the lysosome will undoubtedly pave the way for the development of novel therapeutic strategies to combat age-related muscle loss.

Hypertrophic Cardiomyopathy in Children: Pathophysiology, Diagnosis, and Treatment of Non-sarcomeric Causes

Hypertrophic cardiomyopathy (HCM) is a myocardial disease characterized by left ventricular hypertrophy not solely explained by abnormal loading conditions. Despite its rare prevalence in pediatric age, HCM carries a relevant risk of mortality and morbidity in both infants and children. Pediatric HCM is a large heterogeneous group of disorders. Other than mutations in sarcomeric genes, which represent the most important cause of HCM in adults, childhood HCM includes a high prevalence of non-sarcomeric causes, including inherited errors of metabolism (i.e., glycogen storage diseases, lysosomal storage diseases, and fatty acid oxidation disorders), malformation syndromes, neuromuscular diseases, and mitochondrial disease, which globally represent up to 35% of children with HCM. The age of presentation and the underlying etiology significantly impact the prognosis of children with HCM. Moreover, in recent years, different targeted approaches for non-sarcomeric etiologies of HCM have emerged. Therefore, the etiological diagnosis is a fundamental step in designing specific management and therapy in these subjects. The present review aims to provide an overview of the non-sarcomeric causes of HCM in children, focusing on the pathophysiology, clinical features, diagnosis, and treatment of these rare disorders.

Danon Disease-Associated LAMP-2 Deficiency Drives Metabolic Signature Indicative of Mitochondrial Aging and Fibrosis in Cardiac Tissue and hiPSC-Derived Cardiomyocytes

Danon disease is a severe X-linked disorder caused by deficiency of the lysosome-associated membrane protein-2 (LAMP-2). Clinical manifestations are phenotypically diverse and consist of hypertrophic and dilated cardiomyopathies, skeletal myopathy, retinopathy, and intellectual dysfunction. Here, we investigated the metabolic landscape of Danon disease by applying a multi-omics approach and combined structural and functional readouts provided by Raman and atomic force microscopy. Using these tools, Danon patient-derived cardiac tissue, primary fibroblasts, and human induced pluripotent stem cells differentiated into cardiomyocytes (hiPSC-CMs) were analyzed. Metabolic profiling indicated LAMP-2 deficiency promoted a switch toward glycolysis accompanied by rerouting of tryptophan metabolism. Cardiomyocytes' energetic balance and NAD+/NADH ratio appeared to be maintained despite mitochondrial aging. In turn, metabolic adaption was accompanied by a senescence-associated signature. Similarly, Danon fibroblasts appeared more stress prone and less biomechanically compliant. Overall, shaping of both morphology and metabolism contributed to the loss of cardiac biomechanical competence that characterizes the clinical progression of Danon disease.

Cardiomyopathy with Restrictive-Hypertrophic Phenotype and Initial Morphological Diagnosis “Amyloidosis” as a Manifestation of Danon Disease in a Woman

Aim. To analyze the difficulties of diagnosis and the clinical features of the Danon disease in women.

Results. An observation of Danon disease in a woman aged 18 years with an uncomplicated family history is presented. The early development of atrial fibrillation (at the age of not more than 15 years) in combination with atrioventricular blockade against the background of regular sports was not attracted due attention for 3 years. The examination revealed: a moderate degree of left ventricular hypertrophy (up to 17 mm), its diffuse nature and simultaneous involvement of the right ventricle, signs of heart failure due to severe restrictive disorders with preserved ejection fraction. Cardiac magnetic resonance imaging data (non-specific late gadolinium enhancement) became the basis for the assumption of amyloidosis and the implementation of a myocardial biopsy. An erroneous diagnosis of cardiac amyloidosis according to myocardial biopsy was refuted during a second study, the PAS reaction revealed signs of storage disease. The diagnosis of Danon disease was verified using DNA diagnostics (c.731delG mutation was detected). Due to the presence of unsustained paroxysmal ventricular tachycardia and a high calculated risk of sudden death, cardioverter-defibrillator was implanted. The analysis of literature data on the frequency and the manifestation of Danon disease in women, the place of this disease in the structure of the causes of myocardial hypertrophy is given.

Conclusion. Atrial fibrillation at a young age and left ventricular hypertrophy syndrome can develop due to primary myocardial diseases not well known in the practice of a cardiologist. They require an in-depth diagnostic search; their identification is critical for determining treatment tactics and prognosis.

Reliability, responsiveness, and validity of handheld dynamometry for assessing quadriceps strength in total knee arthroplasty

PURPOSE

To determine the reliability, responsiveness, validity, and agreement of handheld dynamometry, relative to electromechanical dynamometry, for assessing quadriceps strength surrounding total knee arthroplasty.

METHODS

Fifty-six patients (48% female) undergoing total knee arthroplasty were assessed prior to surgery and at 2 and 6 weeks following surgery. Maximum isometric quadriceps force was assessed at each time point by handheld dynamometry and electromechanical dynamometry. Within-session test-retest reliability was determined by intraclass correlation coefficient (ICC). Standard error of measurement and relative standard error (RSE) values were calculated. Standardized response means were used to describe responsiveness. Pearson's correlations examined construct validity. Agreement was assessed by the Bland-Altman method.

RESULTS

Both handheld dynamometry and electromechanical dynamometry demonstrated excellent test-retest reliability (ICC >0.90) and RSE (<15%). Both methods were responsive, with large postoperative standardized response means of 1.57 (handheld dynamometry) and 1.37 (electromechanical dynamometry). Pearson's correlations were moderate to strong. The Bland-Altman analysis revealed underestimation of force by handheld dynamometry, although this effect was diminished in the early postoperative period.

CONCLUSIONS

Our results suggest handheld dynamometry is a promising tool for monitoring quadriceps strength in patients pre- and post-total knee arthroplasty.IMPLICATIONS FOR REHABILITATIONThis study provides evidence of high reliability and responsiveness of handheld dynamometry for assessing quadriceps strength throughout a clinically relevant time frame for patients with total knee arthroplasty.There is construct validity of handheld dynamometry for measuring quadriceps strength, with moderate to high correlations between handheld dynamometry and electromechanical dynamometry, both pre- and post-total knee arthroplasty.Rehabilitation professionals should be aware that handheld dynamometry and electromechanical dynamometry do not agree in terms of the force measurement itself; particularly at higher force values, handheld dynamometry underestimates force output relative to electromechanical dynamometry.Overall, this study supports the use of handheld dynamometry for monitoring quadriceps strength in clinical settings for patient with total knee arthroplasty.

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.

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.