Lysosome-associated Membrane Protein-2 Gene Research Articles

198 ROLE OF CARDIAC MAGNETIC RESONANCE IMAGING IN ARRHYTMICH RISK STRATIFICATION

Abstract Introduction Danon disease (DD) is a rare multi-systemic disorder firstly described by Danon et al. in 1981 and characterized by a triad consisting with hypertrophic cardiomyopathy, skeletal myopathy, and intellectual disability. It is an inherited dominant X-linked condition, due to mutations in the lysosome-associated membrane protein 2 (LAMP2) gene. Typically, males present a more severe phenotype with earlier onset and rapid heart failure progression with extracardiac manifestations; female patients manifest a milder phenotype with later onset and isolated cardiac involvement. Female carriers may develop dilated cardiomyopathy (DCM). In recent years, it has been described a severe arrhythmogenic phenotype, particularly in women, with a high risk of sudden cardiac death (SCD). Case presentation Case 1 is a 16 y.o. woman referred to our outpatient cardiomyopathies clinic, diagnosed with left ventricle (LV) hypertrophy on the basis of ECG and echocardiography, performed in 2016, in view of cutaneous nevus surgical exeresis. At echocardiographic evaluation we found an asymmetric LV hypertrophy with preserved LV ejection fraction (LVEF 65%). A cMRI was performed, showing mild LV thickening and left ventricular hypertrabeculation morphology, mainly in the LV lateral wall, but not all criteria for LV noncompaction (NC) were satisfied. There was no late gadolinium enhancement (LGE) accumulation. She underwent a genetic screening with inconclusive results, so we started a clinical outpatient follow-up showing no significant arrhythmias at ECG Holter and no limitation of physical activities. In 2021, when she was 21 yo, her father died suddenly and no autoptic examination was performed. A genetic exam was repeated, highlighting a LAMP2 gene mutation. In 2016 her 3 years older sister, Case 2, underwent a familiar screening. She had a long history of mild dyspnea occurring during exertion. Echocardiography showed asymmetric hypertrophy with marked thickening of infero-lateral wall (25 mm,) with normal systolic function (EF 70%). She underwent a cMRI, highlighting diffuse asymmetric hypertrophy (max 24 mm) with LGE in lateral wall and lower septum. First genetic test was nonconclusive but after her father's death another test was performed, demonstrating LAMP2 gene mutation. In 2021 a follow-up cMRI showed markedly reduced myocardial thickness of the apex, with a pattern of noncompaction myocardial. We found a LVEF at lower limits, depressed longitudinal function (MAPSE 8 mm) and manly severe progression of fibrotic degeneration. ECG Holter revealed premature ventricular complex, in absence of nonsustained ventricular tachycardia. Following the evolution of fibrosis, cardioverter defibrillator (ICD) implantation was performed. Case 1 was clinically stable during strict follow-up. Conclusion Cardiac magnetic resonance imaging (cMRI) may be useful in arrhythmic risk stratification, accurate systolic dysfunction evaluation, and proper timing and indication for ICD implantation.

LAMP2 Cardiomyopathy: Consequences of Impaired Autophagy in the Heart.

BackgroundHuman mutations in the X‐linked lysosome‐associated membrane protein‐2 (LAMP2) gene can cause a multisystem Danon disease or a primary cardiomyopathy characterized by massive hypertrophy, conduction system abnormalities, and malignant ventricular arrhythmias. We introduced an in‐frame LAMP2 gene exon 6 deletion mutation (denoted L2Δ6) causing human cardiomyopathy, into mouse LAMP2 gene, to elucidate its consequences on cardiomyocyte biology. This mutation results in in‐frame deletion of 41 amino acids, compatible with presence of some defective LAMP2 protein.Methods and ResultsLeft ventricular tissues from L2Δ6 and wild‐type mice had equivalent amounts of LAMP2 RNA, but a significantly lower level of LAMP2 protein. By 20 weeks of age male mutant mice developed left ventricular hypertrophy which was followed by left ventricular dilatation and reduced systolic function. Cardiac electrophysiology and isolated cardiomyocyte studies demonstrated ventricular arrhythmia, conduction disturbances, abnormal calcium transients and increased sensitivity to catecholamines. Myocardial fibrosis was strikingly increased in 40‐week‐old L2Δ6 mice, recapitulating findings of human LAMP2 cardiomyopathy. Immunofluorescence and transmission electron microscopy identified mislocalization of lysosomes and accumulation of autophagosomes between sarcomeres, causing profound morphological changes disrupting the cellular ultrastructure. Transcription profile and protein expression analyses of L2Δ6 hearts showed significantly increased expression of genes encoding activators and protein components of autophagy, hypertrophy, and apoptosis.ConclusionsWe suggest that impaired autophagy results in cardiac hypertrophy and profound transcriptional reactions that impacted metabolism, calcium homeostasis, and cell survival. These responses define the molecular pathways that underlie the pathology and aberrant electrophysiology in cardiomyopathy of Danon disease.

Pathological diagnosis of Danon disease by endomyocardial biopsy

Objective To investigate the clinicopathological features and differential diagnosis of Danon disease. Methods: Two cases of Danon disease were selected from Beijing Anzhen Hospital Affiliated to Capital Medical University from January 2019 to December 2019. The clinical history, histological, immunohistochemical, ultrastructural and gene mutation analysis were collected. Results: Both of the patients were male, aged 21 and 19 years old, respectively. They were diagnosed with hypertrophic cardiomyopathy by clinicians. The histologic features of endocardial biopsies were hypertrophy and vacuolar degeneration of cardiomyocytes. Part of cardiomyocytes appeared as intracellular clear areas lacking myofibers. The nuclei were large, irregular and hyperchromatic. And lipofuscin was occasionally observed in the nuclei of cardiomyocytes. Ultrastructural feature of electron microscopic was glycogen accumulation. Genetic analysis identified two lysosome-associated membrane protein-2 (LAMP2) gene mutations. A 1-bp deletion in exon 8 (c.973delC) was found in patient 1, leading to a frame-shift mutation. A 3-bp duplication in exon 5 (c.719_721dupAGC) was found in patient 2, leading to an insertion mutation. Conclusions: Danon disease is a rare disease characterized by hypertrophic cardiomyopathy. It is caused by mutations in the LAMP2 gene. Vacuolar degeneration of cardiomyocytes, glycogen accumulation under electron microscope and the mutation of LAMP2 gene are the critical features of Danon disease. Familiar with its clinicopathological characteristics would be helpful to avoid the misdiagnosis of Danon disease.

Heart transplantation in Danon disease: Long term single centre experience and review of the literature

Danon disease is characterized by hypertrophic cardiomyopathy, skeletal myopathy, and intellectual disability due to deficiency of the lysosome-associated membrane protein-2 (LAMP-2). Although heart transplantation is considered an option for end stage Danon cardiomyopathy, scarce information is available about long term follow up. We report on long term follow up (14.7 years, IQ range 9–21 years) of 4 patients, transplanted for Danon disease cardiomyopathy, showing two LAMP-2 gene variants, the novel c.815T > C and the previously reported c.294G > A. We have also analysed previous published paper on this topic comparing available data from different follow up. Being a skeletal and cardiac muscle disease, with systemic effects, long term results about HTx are indispensable to justify any treatments in this subset of patients.

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

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

THE PHYSIOLOGY OF THE RETINAL PIGMENT EPITHELIUM IN DANON DISEASE.

Danon disease is caused by mutations in the lysosome-associated membrane protein-2 gene (LAMP2). In the eye, LAMP2 is expressed only in the retinal pigment epithelium. This study aimed to investigate the previously unreported impact of LAMP2 mutations on the electrooculogram generated by the retinal pigment epithelium. Four members of a family with Danon disease were examined. All have mutations in c294G > A, of the LAMP2 gene on Xq24, by which no, or aberrant, protein will be formed. Electrooculograms to International Society for the Clinical Electrophysiology of Vision (ISCEV) standards were recorded with full-field electroretinography, Goldmann kinetic visual fields, and spectral optical coherence tomography with fundus autofluorescence imaging. Electrooculogram amplitude ratios of light rise:dark trough, the Arden index, fell at low-normal limits (range: 1.68-3.94) but misrepresent retinal pigment epithelium health, because the absolute dark trough voltages were abnormally low (median: 140 μV, range: 72-192 μV) as were the light rise amplitudes (median: 297 μV, range: 198-366 μV), and full-field electroretinograms were normal. Hyperfundus autofluorescence and hypofundus autofluorescence changes became more confluent and florid with increasing age of female patients. Goldmann visual field testing showed constriction of the central field. Low electrooculogram voltages indicate that the retinal pigment epithelium is unable to maintain its tight junctions in Danon disease.

Early onset cardiomyopathy in females with Danon disease

Danon disease is caused by mutations in the lysosome-associated membrane protein-2 gene, LAMP2, located on the X chromosome. Female carriers with LAMP2 mutations most often present with late onset cardiomyopathy and slow disease progress; however, there are unusual cases that emerge early and show a more severe disease course. We investigated the explanted heart and skeletal muscle biopsies in two girls, aged ten and thirteen years, who underwent cardiac transplantation because of hypertrophic cardiomyopathy secondary to LAMP2 mutations and a 41-year old female with late-onset familial LAMP2 cardiomyopathy with more typical clinical phenotype. The two girls in contrast had clinical features that mimicked severe primary hypertrophic cardiomyopathy caused by mutations in genes encoding sarcomeric proteins. Immunohistochemistry in cardiac muscles showed a remarkable pattern with lack of LAMP2 protein in large regions including thousands of cardiomyocytes that also showed myocyte hypertrophy, lysosomal enlargement and disarray. In other equally large regions there were preserved LAMP2 expression and nearly normal histology. The skeletal muscle biopsy revealed no pathological changes. An uneven distribution of LAMP2 protein may cause deleterious effects depending on which regions of the myocardium are lacking LAMP2 protein in spite of an overall moderate reduction of LAMP2 protein. This may be a more common mechanism behind early aggressive disease in females than an overall skewed X-chromosome inactivation in the tissue.

A.P.15: Severe early onset cardiomyopathy in females with Danon disease is not caused by skewed X-chromosome inactivation

Danon disease is caused by mutations in the lysosome-associated membrane protein-2 gene, LAMP2, which is located on the X chromosome. Female carriers may occasionally present already in childhood with cardiomyopathy and a very severe disease course. It has been proposed that this is a result of unfavorable skewing of X-chromosome inactivation. We have investigated two young girls aged ten and thirteen years who underwent cardiac transplantation because of cardiomyopathy due to de novo heterozygous LAMP2 mutations. We also investigated one adult female with a more typical clinical phenotype. We found no evidence of skewed X-chromosome inactivation in the two young girls. In accordance with this finding skeletal muscle biopsy revealed no pathological changes. Expression of LAMP2 mRNA in cardiac muscle in the youngest patient revealed equal expression of both alleles also supporting the concept that there was no skewed X-chromosome inactivation. Immunohistochemistry in cardiac muscles of all three patients showed an unexpected and remarkable pattern with lack of LAMP2 protein large regions that also showed myocyte hypertrophy, disarray and lysosomal enlargement. In other large regions there was preserved LAMP2 expression and nearly normal histology. Our results demonstrate that skewed X-chromosome inactivation may not be a common cause of the severe cardiac phenotype seen in occasional female carriers of pathogenic LAMP2 mutations. Instead an uneven distribution of LAMP2 protein may cause deleterious effects depending on which regions of the myocardium that are lacking LAMP2 protein in spite of an overall moderate reduction of LAMP2 protein.

Morphologic and Clinical Aspects of Danon Disease in a Patient with a Mutation c.137G > A in the LAMP-2 Gene

Danon disease is caused by a primary deficiency of lysosome-associated membrane protein-2 (LAMP-2). Our study describes a 19-year-old man with isolated hypertrophic cardiomyopathy, in whom we performed DNA analysis and compared results of microscopic analysis of skeletal and cardiac muscles. Sequencing of the LAMP-2 gene revealed a novel point mutation c.137G > A in exon 2, leading to premature stop codon. Ultrastructural analysis of cardiac and skeletal muscles revealed the presence of unusual autophagic vacuoles in both. Although some vacuoles in skeletal muscle reacted strongly with dystrophin, β-sarcoglycan, and laminin, those in cardiomyocytes showed no immunoreactivity. Our immunohistochemical and ultrastructural findings reinforce the claim that in Danon disease the pathomechanism of chaperone-mediated autophagy in cardiomyocytes differs from that in skeletal muscle.

Danon disease caused by two novel mutations of the LAMP2 gene: implications for two ends of the clinical spectrum

Danon disease is caused by mutations of the lysosome-associated membrane protein-2 (LAMP2) gene at Xq24. Male patients usually manifested as severe cardiomyopathy, mild myopathy and mental retardation. We describe two patients: the first patient presented with severe hypertrophic cardiomyopathy, Wolff-Parkinson-White syndrome, proximal muscle weakness, and chronic painless diarrhea; the second patient manifested as limb-girdle muscle weakness, mild left ventricular diastolic dysfunction, sub-clinical neuropathy. Muscle biopsies indicated autophagic vacuolar myopathy. Immunologic analysis demonstrated absence of the LAMP2 protein in the first patient, while a smear of expression was detected in the second patient. Two nonsense mutations (p.E298X and p. K402X) were identified in the two cases, respectively located in exon 7 and exon 9B of the LAMP2 gene. Our findings indicated that patients with Danon disease caused by mutations in exon 1 – 8 manifested as a typically severe phenotype, while patients with mutations in exon 9 of the LAMP2B isoform presented with a relatively benign phenotype.

Danon disease: Case report and detection of new mutation

Danon disease is an X-linked disorder resulting from mutations in the lysosome-associated membrane protein-2 (LAMP2) gene. We report a male patient with skeletal myopathy, mental retardation, and massive hypertrophic obstructive cardiomyopathy necessitating heart transplantation. Immunohistochemistry of skeletal muscle and leukocytes, western blot analysis of leukocytes and cardiac muscle, flow cytometry, and DNA sequencing were performed. Muscle biopsy revealed autophagic vacuolar myopathy and lack of immunohistochemically detectable LAMP-2. Diagnosis of Danon disease was confirmed by western blot analysis of myocardial tissue and peripheral blood sample of the patient showing deficiency of LAMP-2 in myocardium and leukocytes. Moreover, absence of LAMP-2 in lymphocytes, monocytes and granulocytes was shown by flow cytometric analysis. Genetic analysis of the LAMP2 gene revealed a novel 1-bp deletion at position 179 (c.179delC) at the 3' end of exon 2, resulting in a frameshift with a premature stop codon.

Danon Disease: An Unusual Presentation of Autism

Danon disease is an X-linked cardioskeletal myopathy, originally reported as "lysosomal glycogen storage disease with normal acid maltase," resulting from a primary deficiency of lysosome-associated membrane protein-2 because of mutations in the lysosome-associated membrane protein-2 gene. Classic clinical features in males include cardiomyopathy (100%, eventually), myopathy (90%), and mental retardation (70%), but mostly of a mild degree. We report on an unusual presentation in a patient with autism, motor delay, and a normal cardiac evaluation. The presence of multiorgan involvement, including elevated liver enzymes, abnormal cranial magnetic resonance imaging, and diffuse hypotonia with swallowing difficulties, prompted a muscle biopsy. A quadriceps muscle biopsy was performed, and the findings were most suspicious for a glycogen storage-type disease. Subsequently, a pathogenic lysosome-associated membrane protein-2 mutation was found. To our knowledge, there are no previous clinical reports of autism in children with Danon disease.

Generalized Lysosome-Associated Membrane Protein-2 Defect Explains Multisystem Clinical Involvement and Allows Leukocyte Diagnostic Screening in Danon Disease

Danon disease, an X-linked dominant disorder, results from mutations in the lysosome-associated membrane protein-2 (LAMP2) gene and presents with hypertrophic cardiomyopathy, skeletal myopathy, and mental retardation. To investigate the effects of LAMP2 gene mutations on protein expression in different tissues, we screened LAMP2 gene mutations and LAMP-2 protein deficiency in the skeletal muscle of nine unrelated patients with hypertrophic cardiomyopathy and vacuolar myopathy. We identified three novel families (including one affected mother) with unreported LAMP2 gene null mutations and LAMP-2 protein deficiency in skeletal and myocardial muscle, leukocytes, and fibroblasts. LAMP-2 protein deficiency was detectable in various tissues, including leukocytes, explaining the multisystem clinical involvement. Skeletal muscle immunopathology showed that mutant protein was not localized in the Golgi complex, vacuolar membranes expressed sarcolemmal-specific proteins, and the degree of muscle fiber vacuolization correlated with clinical muscle involvement. In our female patient, muscle histopathology and LAMP-2 protein analysis was inconclusive, indicating that diagnosis in females requires mutation identification. The random X-chromosome inactivation found in muscle and leukocytes excluded the possibility that selective involvement of some tissues in females is due to skewed X-chromosome inactivation. Therefore, biochemical analysis of leukocytes might be used for screening in male patients, but genetic screening is required in females.

Phenotypic Heterogeneity in Two Unrelated Danon Patients Associated with the SameLAMP‐2Gene Mutation

Danon disease, an X-linked cardioskeletal myopathy caused by primary deficiency of lysosome-associated membrane protein-2 (LAMP-2), is clinically characterized by cardiomyopathy, myopathy, and variable mental retardation. The pathological hallmark of the disease is the absence of LAMP-2 immunohistochemical staining in muscle. The LAMP-2 gene mutations reported thus far are generally private mutations. We describe two cases of Danon disease with different clinical presentation, in whom we identified the same exon skipping mutation c.928G>A in the LAMP-2 gene. The first patient was affected by an early onset myopathy and hypertrophic cardiomyopathy (HCM) that partially improved with drug treatment. A first muscle biopsy at age 4 months showed markedly increased glycogen, and acid maltase deficiency was ruled out biochemically. A second muscle biopsy, performed at age 3(1/2) years, showed very mild abnormalities. The second child at age 15 years had mild, diffuse muscle weakness and wasting, moderate mental deficiency, and HCM. Two serial biopsies performed at age 8 and 15 years showed similar findings of multiple esterase-positive vacuoles in type I myofibers. In both patients the immunohistochemical study demonstrated the absence of LAMP-2 in skeletal muscle.

An Alternatively Spliced Form of the Human Lysosome-Associated Membrane Protein-2 Gene Is Expressed in a Tissue-Specific Manner

We report the isolation of an alternatively spliced human lysosome-associated membrane protein-2 (h-lamp-2) transcript which is overexpressed in human muscle. The cloning of this transcript is an indication for the tissue-specific expression of lysosomal membrane proteins and implicates the possibility of multiple functions for the protein products of the h-lamp-2 gene, as well as other lysosome-associated membrane proteins. The new transcript, designated h-lamp-2b, results from the alternative splicing of the last exon, exon 9, the alternative form of which is approximately 2800 bp in length. The resulting protein is identical in length to the previously reported h-lamp-2 protein, 410 amino acids including the leader peptide. This final exon, which encodes the last eleven amino acids of the luminal domain, the 24 amino acid transmembrane spanning region, and an eleven amino acid cytoplasmic tail, shows complete conservation of the Gly·Tyr·X·X lysosomal targeting signal with regard to its position relative to the transmembrane spanning region and the carboxy terminus of the protein. Immune electron microscopy studies verified localization of this alternative gene product to the lysosomal membrane.