Search

Introduction: Postoperative muscle weakness is a serious complication in surgical intensive care patients. It is mostly described as critical illness polyneuromyopathy. Risk factors include intensive care length of stay, sepsis, poor glycemic control, and combined use of corticosteroids and neuromuscular blocking agents, malnutrition, and electrolyte imbalance. Methods: We report a case of late-progressive, profound weakness after heart transplantation for noncompaction cardiomyopathy which required prolonged mechanical ventilation. The patient's muscle strength recovered completely after prolonged rehabilitation. Results: Electromyographic assessment showed myopathy. Muscle biopsy revealed Danon disease, a genetic disorder affecting the lysosomal-associated membrane protein 2 gene (LAMP2). Conclusions: The finding of this genetic disorder was unexpected, because the preoperative echocardiographic diagnosis of noncompaction cardiomyopathy has not been reported in Danon disease. This report underlines the need for early availability of pathology results from the explanted heart, which showed the same disorder. Muscle Nerve, 2013

Danon disease (DD) is a rare lysosomal glycogen storage disease with normal acid maltase activity, which is characterised clinically by cardiomyopathy and myopathy, and a variable degree of mental retardation. The causative gene, LAMP2, has been mapped to chromosome Xq24-q25. LAMP2 encodes a lysosome-associated membrane glycoprotein. We identified a novel LAMP2 mutation of the exon 8 splice acceptor site (IVS7-1G --> A) in an affected male and female, which predicts abnormal splicing. Both affected individuals presented solely with hypertrophic cardiomyopathy. Muscle weakness and mental impairment were absent. Diagnosis of Danon disease was established by muscle biopsy, when the male index patient developed transient severe muscle weakness following heart transplantation. Typical biopsy findings were also found in a heart muscle specimen. Demonstration of the LAMP2 mutation in affected male and female siblings is compatible with X-linked dominant inheritance. Danon disease should be actively looked for in cardiomyopathy patients.

It has recently become clear that lysosomes have more complex functions than simply being the end-point on a degradative pathway. Similarly, it is now emerging that there are interesting functions for the limiting membranes around these organelles and their associated proteins. Although it has been known for several decades that the lysosomal membrane contains several highly N-glycosylated proteins, including the lysosome-associated membrane proteins LAMP-1 and LAMP-2 and lysosomal integral membrane protein-2/lysosomal membrane glycoprotein-85 (LIMP-2/LGP85), specific functions of these proteins have only recently begun to be recognized. Although the normal functions of LAMP-1 can be substituted by the structurally related LAMP-2, LAMP-2 itself has more specific tasks. Knockout of LAMP-2 in mice has revealed roles for LAMP-2 in lysosomal enzyme targeting, autophagy and lysosomal biogenesis. LAMP-2 deficiency in humans leads to Danon disease, a fatal cardiomyopathy and myopathy. Furthermore, there is evidence that LAMP-2 functions in chaperone-mediated autophagy. LIMP-2/LGP85 also seems to have specific functions in maintaining endosomal transport and lysosomal biogenesis. The pivotal function of lysosomal membrane proteins is also highlighted by the recent identification of disease-causing mutations in cystine and sialic acid transporter proteins, leading to nephropathic cystinosis and Salla disease.

Hereditary myopathies characterized by the development of autophagic vacuoles can be categorized into three groups: rimmed vacuolar myopathies, acid maltase deficiency (glycogen storage disease type II), and myopathies characterized by the autophagic vacuoles with unique vacuolar membranes. Rimmed vacuolar myopathies are most likely secondary lysosomal myopathies because all of the identified causative genes encode extralysosomal proteins. Deficiency of acid maltase, a lysosomal enzyme, has been well characterized clinically, pathologically, biochemically, and genetically, and may become treatable in the near future. The diseases in the last category are relatively rare, but appear to be genetically heterogeneous and the list of these diseases is expanding. Danon disease, the best-characterized disorder in this group, is caused by primary deficiency of a lysosomal membrane protein, LAMP-2. Therefore, diseases in this category are expected to be primary lysosomal disease.

This editorial refers to ‘Danon disease as a cause of concentric left ventricular hypertrophy in patients who underwent endomyocardial biopsy’, by Z. Cheng et al. , doi:10.1093/eurheartj/ehr420 Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disease characterized by otherwise unexplained left ventricular (LV) hypertrophy, and caused by a multitude of mutations in genes encoding proteins of the cardiac sarcomere.1–3 Notably, HCM is heterogeneous in terms of phenotypic expression, clinical presentation and course, as well as management strategies, i.e. with severe disease consequences in some patients but a benign course and normal life expectancy in many others.2,3 Recently, there has been increasing recognition that other uncommon inherited diseases may mimic the phenotypic and clinical features of sarcomeric HCM, but are caused by distinctly different gene mutations.4–7 These conditions include most prominently Fabry disease (X-linked α-galactosidase deficiency with glycosphingolipid deposition), PRKAG2 (regulatory subunit of adenosine monophosphate-activated protein kinase), and LAMP2 (a lysosomal storage disease, also known as Danon disease) ( Figure 1 ).4–7 Figure 1 Sarcomere and non-sarcomere mutations responsible for hypertrophic cardiomyopathy and its phenocopies. LVH, left ventricular hypertrophy. LAMP2 cardiomyopathy is an X-linked primary deficiency in lyosome-associated membrane protein-2 caused by several ‘private’ (i.e. reported in only a single patient or family) radical mutations in the LAMP2 gene, including frameshifts, splicing sites, deletions, and insertions.5–7 Although apparently rare, the geographic distribution of LAMP2 mutations is wide, i.e. reported from the USA, Italy, Australia, Sweden, the UK, and Japan,5–9 and now recognized in China.10 Most of the current knowledge of LAMP2 is based on case reports …

Danon disease is a rare entity associated with the clinical triad of mental retardation, skeletal myopathy, and severe hypertrophic cardiomyopathy. We report two cases of Danon disease and describe the results of the cardiac magnetic resonance imaging studies that were conducted to assess the pattern of cardiac hypertrophy.

Danon disease is an X-linked dominant skeletal and cardiac muscle disorder with multisystem clinical manifestations. It was first described in boys presenting with cardiomyopathy, skeletal myopathy, and varying degrees of intellectual disability.1 As histological findings of glycogen buildup in muscle tissue similar to those seen in Pompe disease were noted, the condition was originally considered to be a lysosomal storage disease and was termed glycogen storage disease type IIb. In 2000, Nishino et al2 identified the genetic defects in the lysosome-associated membrane protein 2 ( LAMP2 ) gene, encoding the LAMP2 protein. Most Danon disease mutations lead to an absence of LAMP2 protein expression,2 a situation more problematic in men who are hemizygous for LAMP2 . For reasons not yet fully understood, reduction in LAMP2 disrupts intracytoplasmic trafficking and leads to accumulation of autophagic material and often glycogen in skeletal muscle and cardiac muscle cells (Figure 1).2 Major clinical features include skeletal and cardiac myopathy, cardiac conduction abnormalities, mild intellectual difficulties, and retinal disease. Men are typically affected earlier and more severely than women. The disease is unfamiliar to many practitioners, and the majority of published data stem from case reports with a brief clinical review published in 2002.4 Our aim was to perform a systematic review of Danon disease, provide a comprehensive clinical and molecular update, and propose diagnostic and management guidelines for clinicians and researchers working with patients with Danon disease. Figure 1. Histological images from skeletal muscle biopsy and endomyocardial biopsy.3 Electron microscopy shows intracytoplasmic vacuoles (arrows) containing autophagic material and glycogen in both ( A ) skeletal muscle (bar 1 μm) and ( B ) endomyocardial tissue biopsy (bar 1 μm). Reprinted from Taylor et al3 with permission of the publisher. Copyright © 2007, Nature Publishing Group. Authorization for this adaptation has been obtained both from …

Aims Danon disease is an Xlinked dominant lysosomal glycogen storage disorder characterized by cardiomyopathy, skeletal myopathy, and mental retardation. This study described two Chinese cases of Danon disease in order to broaden the phenotypic and genetic spectrum. Methods Clinical data were collected and LAMP2 mutations were analyzed. Results Patient A had fluctuating limb weakness during 6 months follow-up and was diagnosed with drug-induced myopathy due to anti-hepatitis B therapy with lamivudine. However, the first muscle biopsy with large cytoplasmic vacuoles confused the diagnosis and led to the second biopsy that allowed for the final diagnosis. Patient B had severe cardiac disturbances leading to sudden death. Molecularly, patient A harbored a synonymous mutation adjacent to the exon 6-intron 6 junction; mRNA analysis provided evidence that totally abolished the donor site and caused skipping of exon 6. Patient B harbored a frame-shift deletion mutation in exon 3 (c.396delA) leading to a truncated protein. Discussion To our knowledge, this is the first report of Danon disease caused by a synonymous exon mutation that affected mRNA splicing, which indicates that a synonymous substitution may not be silent when it is in the exon sequences close to the splice sites. It is also the first description of Danon disease clinically presenting as druginduced myopathy at onset; the pathological changes might be the key point for making a differential diagnosis. *These two authors contributed equally to this work.

Background Danon disease is a rare X-linked inherited disorder characterized by massive left ventricular hypertrophy, skeletal muscle dystrophy, and mental retardation. The disease is caused by mutations in the LAMP2 gene encoding for lysosome-associated membrane protein-2. Methods Two young male patients with hypertrophic cardiomyopathy, characterized by marked, concentric left ventricular hypertrophy, elevated levels of creatine kinase, and manifest limb-girdle muscular dystrophy in 1 case, were investigated. Genetic screening included direct sequencing of the whole coding sequence of the LAMP2 gene. Results Genetic analysis identified 2 novel LAMP2 gene mutations. In Family A, a G-A transition (c.962G > A) leading to a nonsense mutation at codon 321 (p.Trp321Ter), and in Family B, a one-nucleotide insertion (c.973insC) leading to a full frame-shift (p.Pro324+24X) was detected in exon 8 of the LAMP2 gene. Family screening identified 8 mutation carriers, with 4 nonpenetrant cases and 3 additional, probably affected family members without DNA diagnosis. The cardiac phenotype was hypertrophic cardiomyopathy in all cases, including female mutation carriers. Five disease-related deaths occurred in the families, at an average age of 33 ± 16 years, which was clearly lower in male than in female patients (28 ± 7 vs 42 ± 25 years). A high prevalence of arrhythmias or conduction abnormalities was also observed. Conclusions The reported 2 novel LAMP2 gene mutation carrier families, one of them being one of the largest reported to date, highlight the malignant clinical course of Danon disease, characterized by a high rate of disease-related death at an early age and a high prevalence of arrhythmias or conduction abnormalities.

To the Editor: Male patients with Danon disease usually present in adolescence with left ventricular hypertrophy (LVH) and a Wolff-Parkinson-White (WPW) pre-excitation pattern on electrocardiogram (ECG). The typical course involves deterioration to severe ventricular dysfunction with end-stage

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.

In a male infant who had cardiomyopathy, generalized muscle weakness and increased serum creatine kinase levels, his muscle biopsy revealed myopathic changes with tiny intracytoplasmic vacuoles containing PAS-positive material and high acid phosphatase activity, but had normal acid maltase activity biochemically. These findings were consistent with those seen in lysosomal glycogen storage disease with normal acid maltase (Danon disease). Sarcolemmal indentations commonly seen in this disease were missing, but a complement membrane attack complex, C5b-9 was positive along the surface membrane of the muscle fibers as seen in X-linked vacuolar myopathy. The patient was on a respirator and died at 27 months of age from pneumonia and hypertrophic cardiomyopathy. Lysosomal glycogen storage disease with normal acid maltase may be manifested at birth with marked skeletal and cardiac involvement leading to death in early infancy.

Primary lysosome-associated membrane protein-2 (LAMP-2) deficiency is an X-linked disease, characterized by the clinical triad of cardiomyopathy, vacuolar myopathy and mental retardation, previously known as Danon disease. Mutations of lamp-2 gene have been reported so far in about 20 patients, one of whom was Italian. We describe a new Italian case with persistent hyperCKemia, exercise intolerance and hypertrophic cardiomyopathy but with no muscle weakness or mental impairment. Muscle biopsy revealed a vacuolar myopathy with mild glycogen storage, and immunohistochemical studies detected LAMP-2 deficiency. A new nucleotide substitution (T961C) on exon 8 of lamp-2 gene was identified as responsible for the protein deficiency. This is the first missense mutation so far described. LAMP-2 deficiency should be considered as a cause of recurrent hyperCKemia and hypertrophic cardiomyopathy.

The link between heart and skeletal muscle disorders is based on similar molecular, anatomical and clinical features, which are shared by the 'primary' cardiomyopathies and 'primary' neuromuscular disorders. There are, however, some peculiarities that are typical of cardiac and skeletal muscle disorders. Skeletal muscle weakness presenting at any age may indicate a primary neuromuscular disorder (associated with creatine kinase elevation as in dystrophinopathies), a mitochondrial disease (particularly if encephalopathy, ocular myopathy, retinitis, neurosensorineural deafness, lactic acidosis are present), a storage disorder (progressive exercise intolerance, cognitive impairment and retinitis pigmentosa, as in Danon disease), or metabolic disorders (hypoglycaemia, metabolic acidosis, hyperammonaemia or other specific biochemical abnormalities). In such patients, skeletal muscle weakness usually precedes the cardiomyopathy and dominates the clinical picture. Nevertheless, skeletal involvement may be subtle, and the first clinical manifestation of a neuromuscular disorder may be the occurrence of heart failure, conduction disorders or ventricular arrhythmias due to cardiomyopathy. ECG and echocardiogram, and eventually, a more detailed cardiovascular evaluation may be required to identify early cardiac involvement. Paediatric and adult cardiologists should be proactive in screening for neuromuscular and related disorders to enable diagnosis in probands and evaluation of families with a focus on the identification of those at risk of cardiac arrhythmia and emboli who may require specific prophylactic treatments, for example, pacemaker, implantable cardioverter-defibrillator and anticoagulation.

The concept of lysosomal storage disorders (LSDs) has existed for over 50 years, but our understanding of the causes and pathobiology of these diseases have come to light only recently, following advances in genetic technology. In this Review, Rose-Mary Boustany summarizes current understanding of known LSDs, highlighting existing treatment approaches for patients with these often devastating disorders, and outlining the barriers to development of novel therapies. Since the discovery of the lysosome in 1955, advances have been made in understanding the key roles and functions of this organelle. The concept of lysosomal storage diseases (LSDs)—disorders characterized by aberrant, excessive storage of cellular material in lysosomes—developed following the discovery of α-glucosidase deficiency as the cause of Pompe disease in 1963. Great strides have since been made in understanding the pathobiology of LSDs and the neuronal ceroid lipofuscinoses (NCLs). The NCLs are neurodegenerative disorders that display symptoms of cognitive and motor decline, seizures, blindness, early death, and accumulation of lipofuscin in various cell types, and also show some similarities to 'classic' LSDs. Defective lysosomal storage can occur in many cell types, but the CNS and PNS are particularly vulnerable to LSDs and NCLs, being affected in two-thirds of these disorders. Most LSDs are inherited in an autosomal recessive manner, with the exception of X-linked Hunter disease, Fabry disease and Danon disease, and a variant type of adult NCL (Kuf disease). This Review provides a summary of known LSDs, and the pathways affected in these disorders. Existing therapies and barriers to development of novel and improved treatments for LSDs and NCLs are also discussed.

Emerging evidence has highlighted the importance of autophagy, an intracellular recycling pathway, in regulating cardiomyocyte bioenergetics, function, and survival. However, the mechanisms responsible for cellular dysfunction and death in cardiomyocytes with impaired autophagic flux remain unclear. Danon disease is a familial cardiomyopathy associated with impaired autophagy due to mutations in the gene encoding lysosomal associated membrane protein type 2 (LAMP-2). To investigate the pathogenesis of Danon disease, we created iPS cells from a patient with a mutation in LAMP-2 who expired from heart failure. Danon iPS-derived cardiomyocytes recapitulated key features of the disease in vitro, including impaired autophagic flux, increased cell size, abnormal calcium handling, and increased expression of natriuretic peptides. Danon cells were noted to have significant amounts of mitochondrial oxidative stress and apoptosis, both of which could be abrogated by treatment with the antioxidant N-acetylcysteine. These results implicate mitochondrial oxidative stress and apoptosis in the pathogenesis of Danon disease. They also provide the basis for the use of antioxidants for Danon disease and other autophagy-related human diseases such as heart failure, diabetes, cancer, and neurodegenerative disorders.

A 58-year-old woman with long-standing mixed connective tissue disorder had proximal leg weakness for 4 months. She had been treated with 400 mg/day of hydroxychloroquine and varying doses of prednisone over 15 years. Creatine kinase was 600 U/mL. MRI of quadriceps showed edema and its biopsy revealed myriad acid-phosphatase–positive autophagic vacuoles indicating increased lysosomal activity (figure). Hydroxychloroquine induces autophagy by reducing lysosomal acidity.1 Autophagic vacuolar myopathy can be seen with chloroquine or colchicine therapy or in inherited disorders (α-glucosidase deficiency, Danon disease, and X-linked myopathy with excessive autophagy).1 Hydroxychloroquine myopathy usually presents with mild to moderate proximal weakness and rarely causes severe weakness and respiratory failure.2 Our patient's weakness improved after discontinuing hydroxychloroquine.

Background Danon disease is caused by a primary deficiency of lysosome-associated membrane protein-2 (LAMP-2). Materials and Methods 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. Results 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. Conclusion 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.

This chapter summarizes our current knowledge of lysosomes and lysosomal proteins referring to recent reviews, general schemes for degradation of substrates, and various causes of lysosomal storage diseases (LSDs). It then discusses the main principles for laboratory diagnosis. Initial screening by study of accumulated substrates in urine is helpful for mucopolysaccharidoses and oligosaccharidoses. A majority of LSDs result from the deficient activity of one acid hydrolase (in some diseases, several). Establishment of the diagnosis in this group of disorders is based on the measurement of the particular enzymic activity. Pseudodeficiencies are a possible source of error. For defects in lysosomal membrane transporters such as cystinosin or sialin, study of substrate accumulation in readily available cells/fluids is still the method of choice. Demonstration of a metabolic block in living cells is rarely used today, except for Niemann-Pick C disease. For primary diagnosis of patients, molecular genetic testing is necessary when no functional tests exist (e.g., many ceroid lipofuscinoses, Danon disease) and it is the preferred strategy when functional tests are too elaborate. Genotyping patients already diagnosed by biochemical methods is, however, essential for genetic counseling in the family; it may also be useful for optimal management.

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.

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.

A 43-year-old woman with a familial history of Danon disease and early sudden death was clinically followed because of carrier of LAMP-2 mutation. She was symptomatic for palpitations. Clinical evaluation and electrocardiogram were normal ( Panel A ), while Holter monitoring revealed non-sustained ventricular tachycardia (VT; Panel B ). Conventional two- and three-dimensional echocardiograms were unremarkable (see Supplementary …

Danon disease is a rare X-linked lysosomal storage disease characterized by hypertrophic cardiomyopathy, myopathy and mental retardation, and is due to a primary defect in lysosome-associated membrane protein-2 (LAMP 2). More than 26 mutations in the LAMP2 gene have been described, including a small number of de novo mutations, some of which are suspected to be caused by germline mosaicism. Here, we describe the first molecularly documented evidence of somatic mosaicism for a LAMP2 mutation, identified in the asymptomatic mother of a boy with Danon disease caused by the frameshift mutation c.808dupG (p.A270Gfx3) within exon 6. In addition, in order to gain insight into the possible explanation for the mother's lack of phenotype, the level of somatic mosaicism and the X-chromosome inactivation pattern were investigated. This study provides new insight into the causes of phenotypic variability in female mutation-carriers and underlines the importance of parental molecular testing for accurate genetic counseling for Danon disease.

In this issue, Thiadens and colleagues report ophthalmoscopic findings of macular disruption and physiologic findings of cone-rod dystrophy in two of four cousins from a family with Danon disease, a rare X-linked disorder characterized by muscle weakness, cardiomyopathy, and mental impairment, which has been mapped to mutations in the lysosomeassociated membrane protein gene, LAMP2 (OMIM #300257) [1]. Though descriptions of this disorder date from 1940 [2], there are only a handful of reports in the literature of ocular abnormalities [3–6]. The spectrum of the ocular findings remains unclear: the published reports are incomplete and the findings appear to differ markedly between families. For example, the report of LacosteCollin et al. [3] mentions “a diffuse chorio-capillary ocular atrophy,” but presents no details or fundus images. Prall et al. [5] report a “peripheral pigmentary retinopathy,” with “near-complete loss of pigment in the retinal pigment epithelium, ” and show images of peppered pigmentary mottling in affected females and an asymptomatic carrier, and complete loss of RPE pigmentation in an affected male, but provide no images of the posterior pole. They report prolongation of ERG latencies, but mention no reductions in amplitude. Schorderet et al. [6] show much milder pigmentary disturbance in two affected males, and asymmetric reduction in multifocal ERG amplitudes in one patient. In contrast, Thiadens et al. report predominantly central fundus abnormalities (a “bull’s-eye maculopathy”), severe color vision disturbances, and a cone-rod pattern of amplitude reduction in the full-field ERG. Their report is also of interest in expanding the spectrum of mutations linked to cone-rod dystrophies. OMIM lists at least 15 such disorders, of which three are X-linked. Of equal interest is the apparent variable expressivity in the present report, in which only two of four male cousins carrying the same LAMP2 mutation developed retinal symptoms. Much remains to be learned about both cone-rod dystrophies and about Danon disease and the pathogenetic implications of LAMP2 mutations.

Danon disease is a rare X-linked dominant metabolic disorder caused by a primary deficiency in lysosome-associated membrane protein 2. It is characterized by the development of cardiac disease, skeletal myopathy and cognitive disorder. Due to the rarity of Danon disease, physicians may be unfamiliar with the phenotype, confusing it with hypertrophic cardiomyopathy or other causes of left ventricular hypertrophy. The present report demonstrates the clinical value of cardiac magnetic resonance imaging for the diagnostic work-up of Danon disease.