Generalized lysosome-associated membrane protein-2 defect explains multisystem clinical involvement and allows leukocyte diagnostic screening in 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.

Metabolic Cardiomyopathies and Cardiac Defects in Inherited Disorders of Carbohydrate Metabolism: A Systematic Review

Heart failure (HF) is a progressive chronic disease that remains a primary cause of death worldwide, affecting over 64 million patients. HF can be caused by cardiomyopathies and congenital cardiac defects with monogenic etiology. The number of genes and monogenic disorders linked to development of cardiac defects is constantly growing and includes inherited metabolic disorders (IMDs). Several IMDs affecting various metabolic pathways have been reported presenting cardiomyopathies and cardiac defects. Considering the pivotal role of sugar metabolism in cardiac tissue, including energy production, nucleic acid synthesis and glycosylation, it is not surprising that an increasing number of IMDs linked to carbohydrate metabolism are described with cardiac manifestations. In this systematic review, we offer a comprehensive overview of IMDs linked to carbohydrate metabolism presenting that present with cardiomyopathies, arrhythmogenic disorders and/or structural cardiac defects. We identified 58 IMDs presenting with cardiac complications: 3 defects of sugar/sugar-linked transporters (GLUT3, GLUT10, THTR1); 2 disorders of the pentose phosphate pathway (G6PDH, TALDO); 9 diseases of glycogen metabolism (GAA, GBE1, GDE, GYG1, GYS1, LAMP2, RBCK1, PRKAG2, G6PT1); 29 congenital disorders of glycosylation (ALG3, ALG6, ALG9, ALG12, ATP6V1A, ATP6V1E1, B3GALTL, B3GAT3, COG1, COG7, DOLK, DPM3, FKRP, FKTN, GMPPB, MPDU1, NPL, PGM1, PIGA, PIGL, PIGN, PIGO, PIGT, PIGV, PMM2, POMT1, POMT2, SRD5A3, XYLT2); 15 carbohydrate-linked lysosomal storage diseases (CTSA, GBA1, GLA, GLB1, HEXB, IDUA, IDS, SGSH, NAGLU, HGSNAT, GNS, GALNS, ARSB, GUSB, ARSK). With this systematic review we aim to raise awareness about the cardiac presentations in carbohydrate-linked IMDs and draw attention to carbohydrate-linked pathogenic mechanisms that may underlie cardiac complications.

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.

New deletion in LAMP2 causing familial Danon disease. Effect of the X-chromosome inactivation

Danon disease (DD), a rare X-linked genetic illness with a poor prognosis, is caused by a mutation in the lysosome-associated membrane protein 2 gene (LAMP2). Three main clinical features of this pathology are cardiomyopathy, skeletal myopathy, and mental retardation. Most Danon disease mutations create premature stop codons resulting in the decrease or absence of LAMP2 protein.

Clinical and biochemical footprints of inherited metabolic disorders: X. Metabolic myopathies

Metabolic myopathies are characterized by the deficiency or dysfunction of essential metabolites or fuels to generate energy for muscle contraction; they most commonly manifest with neuromuscular symptoms due to impaired muscle development or functioning. We have summarized associations of signs and symptoms in 358 inherited metabolic diseases presenting with myopathies. This represents the tenth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

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.

Dosage Compensation in Females with X-Linked Metabolic Disorders

Through the use of new genomic and metabolomic technologies, our comprehension of the molecular and biochemical etiologies of genetic disorders is rapidly expanding, and so are insights into their varying phenotypes. Dosage compensation (lyonization) is an epigenetic mechanism that balances the expression of genes on heteromorphic sex chromosomes. Many studies in the literature have suggested a profound influence of this phenomenon on the manifestation of X-linked disorders in females. In this review, we summarize the clinical and genetic findings in female heterozygotic carriers of a pathogenic variant in one of ten selected X-linked genes whose defects result in metabolic disorders.

Clinical Profile of Cardiac Involvement in Danon Disease: A Multicenter European Registry

BACKGROUND

The X-linked Danon disease manifests by severe cardiomyopathy, myopathy, and neuropsychiatric problems. We designed this registry to generate a comprehensive picture of clinical presentations and outcome of patients with Danon disease in cardiomyopathy centers throughout Europe.

METHODS

Clinical and genetic data were collected in 16 cardiology centers from 8 European countries.

RESULTS

The cohort comprised 30 male and 27 female patients. The age at diagnosis was birth to 42 years in men and 2 to 65 in women. Cardiac involvement was observed in 96%. Extracardiac manifestations were prominent in men but not in women. Left ventricular (LV) hypertrophy was reported in 73% of male and 74% of female patients. LV systolic dysfunction was reported in 40% of men (who had LV ejection fraction, 34±11%) and 59% of women (LV ejection fraction, 28±13%). The risk of arrhythmia and heart failure was comparable among sexes. The age of first heart failure hospitalization was lower in men (18±6 versus 28±17 years; P<0.003). Heart failure was the leading cause of death (10 of 17; 59%), and LV systolic dysfunction predicted an adverse outcome. Eight men and 8 women (28%) underwent heart transplantation or received an LV assist device. Our cohort suggests better prognosis of female compared with male heart transplant recipients.

CONCLUSIONS

Danon disease presents earlier in men than in women and runs a malignant course in both sexes, due to cardiac complications. Cardiomyopathy features, heart failure and arrhythmia, are similar among the sexes. Clinical diagnosis and management is extremely challenging in women due to phenotypic diversity and the absence of extracardiac manifestations.

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.

Danon disease is an underdiagnosed cause of advanced heart failure in young female patients: a LAMP2 flow cytometric study

Aims

Danon disease (DD) is a rare X‐linked disorder caused by mutations in the lysosomal‐associated membrane protein type 2 gene (LAMP2). DD is difficult to distinguish from other causes of dilated or hypertrophic cardiomyopathy (HCM) in female patients. As DD female patients regularly progress into advanced heart failure (AHF) aged 20–40 years, their early identification is critical to improve patient survival and facilitate genetic counselling. In this study, we evaluated the prevalence of DD among female patients with non‐ischemic cardiomyopathy, who reached AHF and were younger than 40 years.

Methods and results

The study cohort comprised 60 female patients: 47 (78%) heart transplant recipients, 2 (3%) patients treated with ventricular assist device, and 11 (18%) patients undergoing pre‐transplant assessment. Aetiology of the cardiomyopathy was known in 15 patients (including two DD patients). LAMP2 expression in peripheral white blood cells (WBC) was tested by flow cytometry (FC) in the remaining 45 female patients. Whole exome sequencing was used as an alternative independent testing method to FC. Five additional female DD patients (two with different novel LAMP2 mutations) were identified by FC. The total prevalence of DD in this cohort was 12%. HCM phenotype (57% vs. 9%, ^*P = 0.022) and delta waves identified by electrocardiography (43% vs. 0%, ^**P = 0.002) were significantly more frequent in DD female patients.

Conclusions

Danon disease is an underdiagnosed cause of AHF in young female patients. LAMP2 expression testing in peripheral WBCs by FC can be used as an effective screening/diagnostic tool to identify DD in this patient population.

Danon disease presenting with early onset of hypertrophic cardiomyopathy and peripheral pigmentary retinal dystrophy in a female with a de novo novel mosaic mutation in the LAMP2 gene

Purpose: To describe the phenotype and genotype in a young woman with Danon disease. Methods: The patient underwent an ophthalmic examination including best corrected visual acuity (BCVA), fundus photography and fundus autofluorescence (FAF), full-field electroretinography (full-field ERG), multifocal ERG, optical coherence tomography (OCT) and SAP-Humphrey 30-2 at the ages of 20 and 25. Electrooculography, fluorescein angiography (FA), indocyanine angiography and OCT angiography were performed only once. Genetic testing using a Next-Generation Sequencing panel and immunohistochemical analysis of LAMP2 protein expression were performed in the patient's explanted heart, and the patient's cardiologic and ophthalmologic records were retrospectively reviewed. Results: A de novo, novel, mosaic mutation, c.135dupA; p.(Trp46Metfs*10) was identified in exon 2 of the LAMP2 gene. Immunohistochemical investigation of the myocardium in the explanted heart revealed pronounced deficiency of LAMP2 protein in cardiomyocytes. The color photographs, FAF images and FA revealed more extensive peripheral pigmentary retinal dystrophy (PPRD) at the 5-year follow-up examination. No changes were observed in BCVA, OCT, SAP-Humphrey 30-2 or multifocal ERG findings at follow-up. Full-field ERG showed an asymmetric interocular reduction in ERG response at follow-up: the b-wave amplitude of the rod response had decreased by 29% in the right eye, but by only 6 % in the left eye. The a-wave amplitude of single-flash response had decreased by 9 % in the left eye, while it had increased by 3% in the right eye. Conclusions: Although PPRD progressed slowly, it was an important clue in the diagnosis of the life-threatening condition of Danon disease.

Prevalence and clinical characteristics of Danon disease among patients with left ventricular hypertrophy and concomitant electrocardiographic preexcitation

BACKGROUND

Cardiac involvement in Danon disease typically manifests as left ventricular hypertrophy (LVH) and ventricular preexcitation. This study aimed to identify patients with Danon disease among patients with LVH and concurrent electrocardiographic preexcitation.

METHODS

Electrocardiographic preexcitation was identified in 10 of 197 patients with unexplained LVH in whom genetic testing was performed using next-generation sequencing.

RESULTS

Three (3/10, 30%) patients with Danon disease were found in association with different mutations in the gene of lysosome-associated membrane protein 2 (LAMP2). Compared to seven patients without Danon disease, these three patients presented with distinctive clinical phenotypes, including onset at an earlier age (20 ± 2 years vs. 53 ± 9 years, p < 0.001), more neurological involvements (100% vs. 0, p = 0.008), higher electrocardiographic voltages (10 ± 1 mV vs. 5 ± 1 mV, p < 0.001), wider QRS complexes (163 ± 5 ms vs. 115 ± 20 ms, p = 0.006), less common asymmetric hypertrophy (0% vs. 86%, p = 0.033), and more frequent elevation of three serum enzymes (creatine kinase, aspartate aminotransferase, and lactate dehydrogenase). Intracellular vacuoles accumulation with deficiencies of LAMP2 protein was found in both cardiac and skeletal myocytes of patients with Danon disease.

CONCLUSION

In patients with coexistent LVH and ventricular preexcitation, Danon disease is common with distinctive clinical presentations. Comprehensive assessment of these resemble patients can provide valuable findings for early identification and clinical decision making of patients with Danon disease.

Heart transplantation in two adolescents with Danon disease

Danon disease (DD) is an X-linked dominant disorder caused by a mutation in the lysosomal-associated membrane protein-2 (LAMP-2) gene coding for the LAMP-2 protein. We report two cases of successful heart transplantation (HT) in adolescent brothers with DD, including one who was bridged to HT for 34 days with a HeartWare left ventricular assist device. In both patients, the post-transplant course was complicated by profound skeletal muscle weakness that resolved with corticosteroid withdrawal. These cases highlight that both HT and ventricular assist device support are feasible in patients with DD. Corticosteroid use may exacerbate skeletal myopathy, and therefore, steroid minimization may be warranted whenever possible.

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

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

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

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

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 Lamp2^y/− 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. Lamp2^y/− rats also displayed abnormal behaviours in the open field and fear conditioning tests. Notably, Lamp2^y/− 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.

A Critical Evaluation of Liver Pathology in Humans with Danon Disease and Experimental Correlates in a Rat Model of LAMP-2 Deficiency

Danon disease is a genetic deficiency in lysosome-associated membrane protein 2 (LAMP-2), a highly glycosylated constituent of the lysosomal membrane and characterized by a cardiomyopathy, skeletal muscle myopathy, and cognitive impairment. Patients, however, often manifest hepatic abnormalities, but liver function has not been well evaluated and the syndrome is relatively uncommon. Hence, we have taken advantage of a rat that has been deleted of LAMP-2 to study the relative role of LAMP-2 on liver function. Interestingly, rats deficient in LAMP-2 develop a striking increase in serum alkaline phosphatase (ALP) and a decrease in bile flow compared with wild-type littermates. Importantly and by ultrastructural analysis, deficient rats manifest dilated canaliculi that lack microvilli with evidence of bile-containing bodies. Moreover, following bile duct ligation, LAMP-2-deficient rats develop rapid and severe evidence of advanced cholestasis, with an increase in serum bilirubin, as early as 6 h later. In wild-type control rats, multidrug resistance-associated protein 2 (Mrp2) normally concentrates at the bile canalicular membranes to secrete conjugated bilirubin into bile. However, in LAMP-2^y/- rats, Mrp2 was detected in hepatocytes compared with other canalicular proteins including P-glycoproteins, dipeptidyl peptidase IV (CD26), and aminopeptidase (CD13). Our data further suggest that LAMP-2 interacts with the membrane cytoskeletal proteins radixin and F-actin in determining the localization of integral membrane proteins.

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

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

The renal Fanconi syndrome in cystinosis: pathogenic insights and therapeutic perspectives

Cystinosis is an autosomal recessive metabolic disease that belongs to the family of lysosomal storage disorders. It is caused by a defect in the lysosomal cystine transporter, cystinosin, which results in an accumulation of cystine in all organs. Despite the ubiquitous expression of cystinosin, a renal Fanconi syndrome is often the first manifestation of cystinosis, usually presenting within the first year of life and characterized by the early and severe dysfunction of proximal tubule cells, highlighting the unique vulnerability of this cell type. The current therapy for cystinosis, cysteamine, facilitates lysosomal cystine clearance and greatly delays progression to kidney failure but is unable to correct the Fanconi syndrome. This Review summarizes decades of studies that have fostered a better understanding of the pathogenesis of the renal Fanconi syndrome associated with cystinosis. These studies have unraveled some of the early molecular changes that occur before the onset of tubular atrophy and identified a role for cystinosin beyond cystine transport, in endolysosomal trafficking and proteolysis, lysosomal clearance, autophagy and the regulation of energy balance. These studies have also led to the identification of new potential therapeutic targets and here, we outline the potential role of stem cell therapy for cystinosis and provide insights into the mechanism of haematopoietic stem cell-mediated kidney protection.

THE PHYSIOLOGY OF THE RETINAL PIGMENT EPITHELIUM IN DANON DISEASE

PURPOSE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

Low electrooculogram voltages indicate that the retinal pigment epithelium is unable to maintain its tight junctions in Danon disease.

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

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

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

BACKGROUND

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

CASE REPORT

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

CONCLUSIONS

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

Lysosomal membrane permeabilization is involved in oxidative stress-induced apoptotic cell death in LAMP2-deficient iPSCs-derived cerebral cortical neurons

Patients with Danon disease may suffer from severe cardiomyopathy, skeletal muscle dysfunction as well as varying degrees of mental retardation, in which the primary deficiency of lysosomal membrane-associated protein-2 (LAMP2) is considerably associated. Owing to the scarcity of human neurons, the pathological role of LAMP2 deficiency in neural injury of humans remains largely elusive. However, the application of induced pluripotent stem cells (iPSCs) may shed light on overcoming such scarcity.

In this study, we obtained iPSCs derived from a patient carrying a mutated LAMP2 gene that is associated with Danon disease. By differentiating such LAMP2-deficient iPSCs into cerebral cortical neurons and with the aid of various biochemical assays, we demonstrated that the LAMP2-deficient neurons are more susceptible to mild oxidative stress-induced injury.

The data from MTT assay and apoptotic analysis demonstrated that there was no notable difference in cellular viability between the normal and LAMP2-deficient neurons under non-stressed condition. When exposed to mild oxidative stress (10 μM H₂O₂), the LAMP2-deficient neurons exhibited a significant increase in apoptosis. Surprisingly, we did not observe any aberrant accumulation of autophagic materials in the LAMP2-deficient neurons under such stress condition.

Our results from cellular fractionation and inhibitor blockade experiments further revealed that oxidative stress-induced apoptosis in the LAMP2-deficient cortical neurons was caused by increased abundance of cytosolic cathepsin L. These results suggest the involvement of lysosomal membrane permeabilization in the LAMP2 deficiency associated neural injury.

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We generated iPSCs from patients with LAMP2-c.183_184insA mutation.

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We differentiated the patient specific iPSCs into LAMP2-deficient cortical neurons.

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The LAMP2-deficient neurons are more susceptible to oxidative stress induced cell death.

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Cathepsin L inhibitor rescued oxidative stress induced cell death in LAMP2-deficient neurons.

Next generation sequencing-based copy number analysis reveals low prevalence of deletions and duplications in 46 genes associated with genetic cardiomyopathies

Background

Diagnostic testing for genetic cardiomyopathies has undergone dramatic changes in the last decade with next generation sequencing (NGS) expanding the number of genes that can be interrogated simultaneously. Exon resolution copy number analysis is increasingly incorporated into routine diagnostic testing via cytogenomic arrays and more recently via NGS. While NGS is an attractive option for laboratories that have no access to array platforms, its higher false positive rate requires weighing the added cost incurred by orthogonal confirmation against the magnitude of the increase in diagnostic yield. Although copy number variants (CNVs) have been reported in various cardiomyopathy genes, their contribution has not been systematically studied.

Methods

We performed single exon resolution NGS‐based deletion/duplication analysis for up to 46 cardiomyopathy genes in >1400 individuals with cardiomyopathies including HCM, DCM, ARVC, RCM, and LVNC.

Results and Conclusion

Clinically significant deletions and duplications were identified in only 9 of 1425 (0.63%) individuals. The majority of those (6/9) represented intragenic events. We conclude that the added benefit of exon level deletion/duplication analysis is low for currently known cardiomyopathy genes and may not outweigh the increased cost and complexity of incorporating it into routine diagnostic testing for these disorders.

Early diagnosis of Danon disease: Flow cytometric detection of lysosome-associated membrane protein-2-negative leukocytes

INTRODUCTION

Danon disease is an extremely rare X-linked dominant disorder characterized by progressive cardiomyopathy, muscle weakness, and mild mental retardation. Most cases harbor nonsense, frameshift, or splice-site mutations in LAMP2 that result in lysosome-associated membrane protein-2 (LAMP-2) deficiency and lysosomal defects. The identification of LAMP2 mutations makes it possible to detect female carriers with significant cardiomyopathy. Therefore, it is of paramount importance to develop useful carrier detection methods.

METHODS

To screen for diminished LAMP-2 expression among female patients with progressive cardiomyopathy, we developed a flow cytometric method to detect LAMP-2-deficient leukocytes.

RESULTS

In healthy controls, all circulating leukocyte populations, including granulocytes, monocytes, and lymphocytes, expressed significant levels of LAMP-2. In contrast, cells from a male patient with Danon disease lacked detectable LAMP-2. His younger twin sisters showed reduced levels of LAMP-2 expression with characteristic bimodal fluorescence intensity patterns. The percentage of LAMP-2-negative cells in the asymptomatic sibling was nearly the same as that in the symptomatic sibling.

CONCLUSION

We developed a flow cytometric assay for LAMP-2 expression that can serve as a rapid primary screening method to detect carriers of LAMP-2 deficiencies. This assay will narrow the target population before subjecting patients to more laborious and expensive gene mutation analysis.

Mosaic tissue distribution of the tandem duplication of LAMP2 exons 4 and 5 demonstrates the limits of Danon disease cellular and molecular diagnostics

Alu-mediated tandem duplication of exons 4 and 5 (g.15815_22218dup6404) is a novel mutation that has been detected in the LAMP2 gene (Xq24). This exon copy number variation was found in two brothers with the typical phenotype of Danon disease, including characteristic myocardial changes on magnetic resonance imaging. The 6.4 kb duplication was identified in both boys by a combination of exon dosage qPCR analyses and duplication breakpoint/junction mapping. The rearrangement results in a plethora of abnormal LAMP2 splicing variants and also in use of likely cryptic splice sites in the 3' terminus of LAMP2 gene. Although we found minute amounts of normal LAMP2B and LAMP2A mRNAs, no protein was detectable in peripheral blood leukocytes by flow cytometry in both brothers. Uniquely, the fraction of LAMP2-deficient granulocytes (0.06%) assessed by flow cytometry in the patients' asymptomatic mother substantially differed from the random distribution of X-chromosome inactivation in her leukocytes. This discrepancy was later explained by molecular genetic methods as a consequence of mosaic distribution of the mutation in her somatic tissues. Altogether, we report a novel and mosaically distributed exon copy number rearrangement in the LAMP2 gene and comment on obstacles this genetic setup presents to the overall cellular and molecular diagnostic algorithm of Danon disease. Our observations of the mosaicism in the asymptomatic mother suggest that similarly affected females could be a potentially under-diagnosed Danon disease carrier group and that LAMP2 flow cytometry, because of its supreme sensitivity, can be an efficient method for pedigree screening.

Danon Disease Due to a Novel LAMP2 Microduplication

Danon disease is a rare X-linked disorder comprising hypertrophic cardiomyopathy, skeletal myopathy, intellectual disability, and retinopathy; mutations of the lysosome-associated membrane protein gene LAMP2 are responsible. Most affected persons exhibit "private" point mutations; small locus rearrangements have recently been reported in four cases. Here, we describe the clinical, pathologic, and molecular features of a male proband and his affected mother with Danon disease and a small LAMP2 microduplication. The proband presented at age 12 years with exercise intolerance, hypertrophic cardiomyopathy, and increased creatine kinase. Endomyocardial biopsy findings were nonspecific, showing myocyte hypertrophy and reactive mitochondrial changes. Quadriceps muscle biopsy demonstrated the characteristic autophagic vacuoles with sarcolemma-like features. LAMP2 tissue immunostaining was absent; however, LAMP2 sequencing was normal. Deletion/duplication testing by multiplex ligation-dependent probe amplification (MLPA) assay revealed a 1.5kb microduplication containing LAMP2 exons 4 and 5. RT-PCR studies were consistent with the inclusion of these two duplicated exons in the final spliced transcript, resulting in a frameshift. The proband's mother, who had died following cardiac transplantation due to suspected myocarditis at age 35, was reviewed and was shown to be affected upon immunostaining of banked myocardial tissue. This case constitutes the second report of a pathogenic microduplication in Danon disease, and illustrates a number of potential diagnostic pitfalls. Firstly, given the imperfect sensitivity of LAMP2 sequencing, tissue immunostaining and/or MLPA should be considered as a diagnostic adjunct in the workup for this disorder. Secondly, the pathological findings in myocardium may be falsely indicative of relatively common conditions such as myocarditis.

Genetic analysis of the LAMP-2 gene promoter in patients with sporadic Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease in the people of over 65. Majority of PD is sporadic, which is caused by interaction of genetic and environmental factors. To date, genetic causes and underlying molecular mechanisms for sporadic PD remain largely unknown. Autophagy is a conserved cellular degradative process, consisting of macroautophagy, microautophagy and chaperone-mediated autophagy (CMA). Macroautophagy (hereafter referred to as autophagy) and CMA are involved in the degradation of alpha-synuclein, a critical protein in the PD pathogenesis. Previous studies with brain tissues and leukocytes have shown that the expression levels of lysosome-associated membrane-2 (LAMP-2) gene are significantly decreased in PD patients. In this study, we genetically and functionally analyze the promoter region of LAMP-2 gene in sporadic PD patients. Two novel sequence variants and two single nucleotide polymorphisms (SNPs) were identified. The heterozygous variant, g.4127A>C, which was only found in one female PD patient, significantly reduced the transcriptional activities of LAMP-2 gene promoter. The hemizygous variant, g.5038G>A, which was only found in one male control, enhanced the transcriptional activities of LAMP-2 gene promoter. No significant difference in frequencies of the SNPs, rs42900 (g.4569A>C) and rs28603270 (g.4760T>G), was observed between PD patients and controls. Collectively, the sequence variants within the LAMP-2 gene promoter may be linked to the PD onset by changing LAMP-2 protein levels and impairing autophagy and CMA activities.

Danon disease: focusing on heart

Danon disease is a rare X-linked dominant lysosomal disease due to the primary deficiency of lysosome-associated membrane protein 2 (LAMP2) gene. Cardiomyopathy, skeletal myopathy and mental retardation are the typical triad of Danon disease. More than 60 LAMP2 mutations have been reported. The molecular mechanism is defects in LAMP2 protein (due to LAMP2 mutation) which causes insidious glycogen accumulation in cardiac muscle cells and resulting in cardiac hypertrophy and electrophysiological abnormalities. However, there are significant differences between the male and female Danon disease patients with regard to clinical features and cardiac manifestations. The clinical symptoms are variable, from asymptomatic to sudden cardiac death. Wolff-Parkinson-White syndrome is more common in male than female patients. Hypertrophic cardiomyopathy is predominant in male patients, whereas the similar prevalence of hypertrophic and dilated cardiomyopathy in female patients. Male patients are diagnosed usually at teenage, whereas the diagnosis and events occurred approximately 15 years later in female than male patients. Heart transplantation is the reliable treatment once the occurrence of heart failure and should be considered as early as possible due to its rapid progression.

Danon disease: a focus on processing of the novel LAMP2 mutation and comments on the beneficial use of peripheral white blood cells in the diagnosis of LAMP2 deficiency

Danon disease (DD) is a monogenic X-linked disorder characterized by cardiomyopathy, skeletal myopathy and variable degrees of intellectual disability. DD develops due to mutations in the gene encoding lysosomal-associated membrane protein 2 (LAMP2). We report on a family exhibiting the clinical phenotype comprising of hypertrophic cardiomyopathy and ventricular pre-excitation, myopia and mild myopathy in two male patients and cardiomyopathy and myopia in a female patient. The diagnosis of DD in this family was based on the assessment of the clinical phenotypes and the absence of LAMP2 in skeletal and/or cardiac muscle biopsy specimens. Sequence analysis of the LAMP2 gene and its mRNA revealed a novel LAMP2 mutation (c.940delG) in all three patients. Approximately 25% of the female patient's cardiomyocytes were LAMP2 positive apparently due to the unfavorable skewing of X chromosome inactivation. We further performed qualitative LAMP2 immunohistochemistry on peripheral white blood cells using the smear technique and revealed the absence of LAMP2 in the male patients. LAMP2 expression was further assessed in granulocytes, CD4+ and CD8+ T lymphocytes, CD20+ B lymphocytes, CD14+ monocytes and CD56+ natural killer cells by quantitative polychromatic flow cytometry. Whereas the male DD patients lacked LAMP2 in all WBC populations, the female patient expressed LAMP2 in 15.1% and 12.8% of monocytes and granulocytes, respectively. LAMP2 expression ratiometrics of highly vs. weakly expressing WBC populations discriminated the DD patients from the healthy controls. WBCs are thus suitable for initial LAMP2 expression testing when DD is a differential diagnostic option. Moreover, flow cytometry represents a quantitative method to assess the skewing of LAMP2 expression in female heterozygotes. Because LAMP2 is a major protein constituent of the membranes of a number of lysosome-related organelles, we also tested the exocytic capacity of the lytic granules from CD8+ T lymphocytes in the patient samples. The degranulation triggered by a specific stimulus (anti-CD3 antibody) was normal. Therefore, this process can be considered LAMP2 independent in human T cells. The c.940delG mutation results in a putatively truncated protein (p.A314QfsX32), which lacks the transmembrane domain and the cytosolic tail of the wild-type LAMP2. We tested whether this variant becomes exocytosed because of a failure in targeting to late endosomes/lysosomes. Western blotting of cardiac muscle, WBCs and cultured skin fibroblasts (and their culture media) showed no intra- or extracellular truncated LAMP2. By comparing the expression pattern and intracellular targeting in cultured skin fibroblasts of normal LAMP2 isoforms (A, B and C) tagged with green fluorescent protein (GFP) and the A314Qfs32-GFP fusion, we found that the A314Qfs32-GFP protein is not even expressed. These observations suggest that the truncated protein is unstable and is co-translationally or early post-translationally degraded.

Sudden death associated with danon disease in women

Danon disease is an X-linked systemic disorder characterized by left ventricular hypertrophy, mental retardation, and skeletal myopathy affecting young men. Electrocardiogram usually displays a Wolff-Parkinson-White preexcitation pattern. Less has been reported about the phenotype in women, although later-onset cardiac symptoms have been described. The aim of this study was to expand the knowledge of the phenotype of Danon disease in women. We clinically followed and evaluated with echocardiography, cardiac magnetic resonance imaging (cMRI), and genetic testing a family affected by Danon disease in which 2 men and 6 women showed a severe arrhythmogenic phenotype. Affected family members carried a nucleotide substitution at position 294 in exon 3 (c.294 G → A) that changed a tryptophan residue to a stop codon at position W98X in the lysosome-associated membrane protein 2 (LAMP2) gene. Four women died suddenly (1 aborted) at 37 to 54 years of age. Wolff-Parkinson-White pattern with atrioventricular block was detected in 2 of 6 women. Four had successful pregnancies without symptoms of heart failure. cMRI showed late gadolinium enhancement areas in a clinically healthy woman who was a mutation carrier. Two patients underwent heart transplantation; histology of explanted hearts demonstrated severe interstitial fibrosis, hypertrophic cardiomyocytes with cytoplasmic vacuoles, and myofibrillar disarray. In conclusion, LAMP2 mutation can cause a severe arrhythmogenic phenotype in women that includes a high risk of sudden death. cMRI may be useful in women harboring LAMP2 mutations to permit early detection of cardiac involvement and guide timely considerations of implantable cardioverter-defibrillator therapy. Heart transplantation should be considered at onset of heart failure symptoms owing to rapid progression of the disease.

Increase in endoplasmic reticulum-associated tissue transglutaminase and enzymatic activation in a cellular model of Parkinson's disease

Parkinson's disease (PD) is characterized by accumulation of α-synuclein aggregates and degeneration of melanized, catecholaminergic neurons. The tissue transglutaminase (tTG) enzyme catalyzes molecular protein cross-linking. In PD, tTG levels are increased and cross-linking has been identified as an important factor in α-synuclein aggregation. In our quest to link tTGs distribution in the human brain to the hallmarks of PD pathology, we recently reported that catecholaminergic neurons in PD disease-affected brain areas display typical endoplasmic reticulum (ER) granules showing tTG immunoreactivity. In the present study, we set out to elucidate the nature of the interaction between tTG and the ER in PD pathogenesis, using retinoic-acid differentiated SH-SY5Y cells exposed to the PD-mimetic 1-methyl-4-phenylpyridinium (MPP(+)). Alike our observations in PD brain, MPP(+)-treated cells displayed typical TG-positive granules, that were also induced by other PD mimetics and by ER-stress inducing toxins. Additional immunocytochemical and biochemical investigation revealed that tTG is indeed associated to the ER, in particular at the cytoplasmic face of the ER. Upon MPP(+) exposure, additional recruitment of tTG toward the ER was found. In addition, we observed that MPP(+)-induced tTG activity results in transamidation of ER membrane proteins, like calnexin. Our data provide strong evidence for a, so far unrecognized, localization of tTG at the ER, at least in catecholaminergic neurons, and suggests that in PD activation of tTG may have a direct impact on ER function, in particular via post-translational modification of ER membrane proteins.

Natural history of Danon disease

BACKGROUND

Danon disease is a rare but serious cardiac and skeletal myopathy leading to substantial morbidity and early mortality due to arrhythmia and cardiomyopathy. The X-linked nature of inheritance accounts for reported differences in phenotypic severity between men and women. The rarity of Danon disease has limited understanding of the complete phenotype. Clinical estimates of ages of disease onset and survival based on gender have not been published.

METHODS AND RESULTS

We present data on 82 patients with Danon disease from 36 families, the largest series to date. Men were severely affected with cognitive disabilities (100%), hypertrophic cardiomyopathy (88%), and muscle weakness (80%). Men had a high morbidity and were unlikely to reach the age of 25 years without a cardiac transplantation. Women were less severely affected but reported higher than expected levels of cognitive (47%) and skeletal muscle complaints (50%) and manifesting an equal prevalence of dilated cardiomyopathy and hypertrophic cardiomyopathy. Combining our data with that of 63 other Danon disease case reports in the literature, the average ages of first symptom, cardiac transplantation, and death were 12.1, 17.9, and 19.0 years in men and 27.9, 33.7, and 34.6 years in women, respectively.

CONCLUSION

These data more broadly illuminate the Danon disease phenotype and should prove useful to physicians working with and providing genetic counseling to families with Danon disease. Women with Danon disease present with clinical symptoms and events approximately 15 years after men and report a higher proportion of cognitive and skeletal muscle problems than previously recognized.

Danon disease: intrafamilial phenotypic variability related to a novel LAMP-2 mutation

Danon disease is an X-linked lysosomal disorder, characterized by hypertrophic cardiomyopathy, skeletal myopathy and mental retardation. We report a family with a novel mutation, in which the mother and her three sons were affected with various clinical presentations. A massive hypertrophy of the left ventricle was the predominant feature in the three male patients, with different degrees of severity of cardiac symptoms, from isolated palpitations to cardiac failure and sudden death. Muscle pain and weakness were also variable, but constantly associated with increased plasma CK levels. Finally, the male patients had variable degree of a mental retardation. The mother had an attenuated phenotype, limited to a mild hypertrophic cardiomyopathy with premature ventricular contractions diagnosed during her 40's. Microscopy examination of skeletal muscle biopsy, performed in the youngest patient, demonstrated atrophic myofibers with intracytoplasmic vacuoles suggesting lysosomal glycogen storage disease. Immunohistochemistry analyses in muscle specimen showed no detectable Lysosomal-Associated Membrane Protein-2 (LAMP-2), in keeping with the diagnosis of Danon disease. However, a very low expression of a shortened LAMP-2 protein could be evidenced by Western-blot in the patient's fibroblasts. Molecular investigations identified a novel splicing mutation (IVS6 + 1delG) in the LAMP-2 gene. This case report highlights the intrafamilial variability of Danon disease phenotype. In this case, morphological examination of muscle biopsy, showing lysosomal storage myopathy, and immunohistochemistry analyses can provide key elements for orienting etiologic investigations.

Electron microscopic findings in skin biopsies from patients with Danon disease

Danon disease is a rare lysosomal disorder. It is due to deficiency of lysosomal-associated protein-2. In human LAMP-2 gene is located at chromosome region Xq24. Danon disease is characterized by hypertrophic cardiomyopathy, skeletal myopathy, mental retardation and retinopathy. To date, the morphological characterization of Danon disease has been limited to endomyocardial and skeletal muscle biopsies. In the current study we demonstrated that electron microscopy of a more accessible tissue, skin biopsies, is a useful method in the diagnosis of Danon disease.

A 13-year-old girl with proximal weakness and hypertrophic cardiomyopathy with Danon disease

Danon disease is caused by deficiency of lysosome-associated membrane protein-2 (LAMP-2). It is characterized clinically by cardiomyopathy, myopathy, and mental retardation in boys. Herein we report a 13-year-old female patient with Danon disease who presented with early-onset skeletal myopathy and cardiomyopathy. She had a de novo novel mutation in the LAMP2 gene, and her muscles showed many autophagic vacuoles with sarcolemmal features and complete absence of LAMP-2 expression. To the best of our knowledge, this girl is one of the earliest-onset manifesting carriers of Danon disease with typical muscle pathology.

LAMP2 microdeletions in patients with Danon disease

BACKGROUND

Danon disease is an X-linked dominant disorder characterized by the clinical triad of hypertrophic cardiomyopathy, skeletal myopathy, and variable mental retardation. Pathologically, autophagic vacuoles are noted in both skeletal and cardiac muscle. It exhibits an X-linked dominant mode of inheritance, and male carriers are severely affected, whereas female carriers develop milder and later-onset cardiac symptoms. Danon disease has been associated with mutations in the lysosome-associated membrane glycoprotein 2 (LAMP2) gene located at Xq24, typically resulting in splicing defects or protein truncation affecting the LAMP2. Because of its rarity, the full spectrum of genetic mutation resulting in Danon disease has not been elucidated.

METHODS AND RESULTS

We analyzed 3 male cases with clinical and pathological findings consistent with Danon disease. Comprehensive mutational analysis failed to yield detectable products for selected LAMP2 exons, and genomic DNA deletion was suspected. Genomic junction fragment polymerase chain reaction analysis in case 1 identified a novel Alu-mediated 34-kb microdeletion encompassing the entire 5'-untranslated region and exon 1 of LAMP2. In case 2 and 3, junctional polymerase chain reaction and Southern blot analyses mapped the breakpoint to an MIRb and (TA)(n) simple repeats present in intron 3, which determined a 64-kb and a 58-kb deletion, respectively, thereby ablating exons 4 to 10. Western blot analysis confirmed the absence of LAMP2 in protein extract from lymphocytes of index case 2.

CONCLUSIONS

This article is the first report of Danon disease caused by microdeletions at Xq24, which functionally ablate LAMP2. The microdeletion mechanism appears to involve 1 Alu-mediated unequal recombination and 2 chromosomal breakage points involving TA-rich repeat sequences.

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: further clinical and molecular heterogeneity

Two families of Greek patients with subclinical to severe cardiomyopathy are presented. The diagnosis of Danon disease was supported by a total lack of LAMP2 immunostaining in cultured skin fibroblasts and muscle biopsies. The LAMP2 mutation carried by one patient (c.928G>A) has already been reported but with different symptoms. The second patient had a novel point deletion. This has not been described previously, but it could be detected easily by restriction analysis. This mutation was also found in the patient's brother, and it was associated with severe cardiomyopathy leading to heart failure. Surprisingly, the proband also had partial reduction of alpha-galactosidase A activity, despite the absence of characteristic clinical features of Fabry disease. A substitution in the GLA gene (c.937G>T) was found, and its involvement in the cardiac disease is discussed.