Evicenter
P&T meetings

RP-A501 (AAV9.LAMP2B)

Danon disease

Regulatory submission
BLA planned for late 2028
Last updated
300 sources

Product information and disease descriptionPlace of product in therapyDisease description

Pathophysiology

19 evidence topics · 29 sources

LAMP-2 protein: location and structure

“Danon disease is caused by loss-of-function mutations in the LAMP2 gene, which encodes lysosome-associated membrane protein 2 (LAMP-2), a single-spanned transmembrane protein localized in the limiting membranes of lysosomes and late endosomes.” (opens the source at this quote in a new tab)

“Most mutations lead to splicing defects or protein truncation, resulting in a loss of transmembrane and/or cytoplasmic domains, leading to LAMP-2 protein deficiency.” (opens the source at this quote in a new tab)

“The LAMP2 protein is a type 1 membrane protein predominantly located in the lysosomal compartment and its structure consists of a large luminal domain that is heavily glycosylated, a transmembrane region, and a short carboxy-terminal cytoplasmic tail.” (opens the source at this quote in a new tab)

Isoform functions: LAMP-2A in chaperone-mediated autophagy and LAMP-2B in heart, skeletal muscle, and brain

“The short LAMP-2A cytoplasmic tail is thought to serve as a receptor for uptake of certain proteins into the lysosome for degradation, a process termed chaperone-mediated autophagy.” (opens the source at this quote in a new tab)

“While LAMP-2A is more ubiquitously expressed, there are indications that LAMP-2B is expressed at a higher level in the heart, skeletal muscle and brain.” (opens the source at this quote in a new tab)

“Further supporting this notion is the observation that the tissues most affected in Danon disease (myocardium, skeletal muscle, and brain) manifest higher LAMP-2B isoform expression.” (opens the source at this quote in a new tab)

“Clinical features of Danon disease are thought to be mediated by loss of the LAMP-2B isoform which is the major isoform expressed in muscle.” (opens the source at this quote in a new tab)

“It is also known that LAMP-2 plays a role in chaperone-mediated autophagy and RNA- and DNA-targeting autophagy.” (opens the source at this quote in a new tab)

“LAMP2B is the predominant isoform expressed in cardiomyocytes.” (opens the source at this quote in a new tab)

Impaired macroautophagy and failure of autophagosome and lysosome fusion

“LAMP-2 is required for the maturation of autophagosomes by fusion with lysosomes; therefore, LAMP-2 deficiency leads to a failure in macroautophagy.” (opens the source at this quote in a new tab)

“Deficient production of LAMP-2B results in impaired macroautophagy.” (opens the source at this quote in a new tab)

“Intracellular vacuoles containing glycogen and other cytoplasmic components accumulate, instead of being degraded and recycled for reuse by the cell, resulting in cardiomyocyte hypertrophy.” (opens the source at this quote in a new tab)

“In Danon disease, autophagy, which occurs constantly in these regions, is thought to cease at the final stage of fusion between autophagosomes and lysosomes” (opens the source at this quote in a new tab)

LAMP-2B in human cardiomyocytes: fusion mechanism in patient-derived cells

“Here, we identify the LAMP-2 isoform B (LAMP-2B) as required for autophagosome–lysosome fusion in human cardiomyocytes (CMs).” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

“This phenotype was recapitulated by LAMP-2B knockout in non-Danon hiPSC-CMs. Finally, gene correction of LAMP-2 mutation rescues the Danon phenotype.” (opens the source at this quote in a new tab)

Autophagic vacuoles with sarcolemmal features in muscle

“The pathological hallmark of the disease is intracytoplasmic vacuoles containing autophagic material and glycogen in skeletal and cardiac muscle cells.” (opens the source at this quote in a new tab)

“The most striking finding in muscle biopsy samples is small basophilic granules scattered in myofibers, which are in fact small autophagic vacuoles surrounded by membranes with sarcolemmal features characterized by the recruitment of sarcolemmal proteins and acetylcholine esterase and by the presence of basal lamina on its luminal side.” (opens the source at this quote in a new tab)

“The mechanism underlying the formation of these autophagic vacuoles with unique sarcolemmal features (AVSF) still remains a mystery and its origin is unknown.” (opens the source at this quote in a new tab)

“In heart, cardiomyocytes show dramatically increased vacuolation and degenerative features, including myofibrillar disruption and lipofuscin accumulation.” (opens the source at this quote in a new tab)

“In Danon disease, the number of fibers with AVSF increased linearly with age while the number with autolysosomal accumulations decreased slightly, suggesting that AVSF are produced secondarily in response to autolysosomes.” (opens the source at this quote in a new tab)

Glycogen accumulation

“When Danon disease was first described in 1981, ultrastructural analysis of muscle biopsies from two boys with the disease showed that their cells contained abundant glycogen particles, primarily within lysosomal vacuoles” (opens the source at this quote in a new tab)

“Because of these observations, the disease was originally postulated to be due to a glycogen storage defect.” (opens the source at this quote in a new tab)

“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” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

Mitochondrial dysfunction and impaired mitophagy

“Danon hiPSC-CMs demonstrated an accumulation of damaged mitochondria, disrupted mitophagic flux, depressed mitochondrial respiratory capacity, and abnormal gene expression of key mitochondrial pathways.” (opens the source at this quote in a new tab)

“Restoring the expression of LAMP-2B, the most abundant LAMP-2 isoform in the heart, rescued mitophagic flux as well as mitochondrial health and bioenergetics.” (opens the source at this quote in a new tab)

“Incomplete mitophagic flux and mitochondrial dysfunction are noted in both in vitro and in vivo models of Danon disease, and proceed overt cardiac contractile dysfunction.” (opens the source at this quote in a new tab)

“Dysfunction of mitophagy may be an early pathological hallmark of Danon disease with important upstream effects such as impaired mitochondrial metabolism.” (opens the source at this quote in a new tab)

Oxidative stress and cardiomyocyte apoptosis

“Danon iPSC-derived cardiomyocytes (iPSC-CMs) exhibited impaired autophagic flux and key features of heart failure such as increased cell size, increased expression of natriuretic peptides, and abnormal calcium handling compared to control iPSC-CMs.” (opens the source at this quote in a new tab)

“Additionally, Danon iPSC-CMs demonstrated excessive amounts of mitochondrial oxidative stress and apoptosis.” (opens the source at this quote in a new tab)

“Using the sulfhydryl antioxidant N-acetylcysteine to scavenge free radicals resulted in a significant reduction in apoptotic cell death in Danon iPSC-CMs.” (opens the source at this quote in a new tab)

Metabolic profile of cardiac tissue and patient-derived cells

“Metabolic profiling indicated LAMP-2 deficiency promoted a switch toward glycolysis accompanied by rerouting of tryptophan metabolism.” (opens the source at this quote in a new tab)

“In turn, metabolic adaption was accompanied by a senescence-associated signature.” (opens the source at this quote in a new tab)

“Overall, shaping of both morphology and metabolism contributed to the loss of cardiac biomechanical competence that characterizes the clinical progression of Danon disease.” (opens the source at this quote in a new tab)

From hypertrophy to fibrosis, hypokinesis, and dilation

“Defective autophagy results in a mismatch between the supply and demand of energy and resources within cells and oxidative stress, causing cell death and diffuse fibrosis, which affects conduction and increases susceptibility to arrhythmias.” (opens the source at this quote in a new tab)

“Typically, owing to cardiomyocyte death and progressive fibrosis, the hypertrophic heart becomes hypokinetic, followed by wall thinning and possible dilation.” (opens the source at this quote in a new tab)

“It remains unclear whether the dilated cardiomyopathy in female individuals is part of the continuum of disease that begins as cardiac hypertrophy or whether it represents an independent disease phenotype.” (opens the source at this quote in a new tab)

“Autopsy findings included a combination of histopathologic features consistent with a storage disease (i.e., clusters of vacuolated myocytes), but also typical of HCM due to sarcomere protein mutations (i.e., myocyte disarray, small vessel disease, myocardial scarring).” (opens the source at this quote in a new tab)

Conduction system involvement and pre-excitation: proposed mechanism

“Although the mechanism for pre-excitation in Danon disease is unknown, disruption of the annulus fibrosus that surrounds the atrioventricular node by glycogen-filled myocytes is speculated to be a mechanism for accessory conduction pathways in PRKAG2 mutations, another disorder associated with glycogen storage and dysfunctional autophagy.” (opens the source at this quote in a new tab)

“The mechanism of pre-excitation anomalies is not known but could be due to myocardial hypertrophy” (opens the source at this quote in a new tab)

Pre-excitation: fasciculoventricular and extranodal pathways found at electrophysiological study

“EPS performed in 9 of 13 patients (69%) demonstrated FVP only in 2 (22.2%), extranodal pathway without exclusion of FVP in 2 (22.2%), and both FVP and extranodal pathway in 5 (55.6%).” (opens the source at this quote in a new tab)

“Four patients who underwent electrophysiological studies all had FVPs, and 2 of them still had left-side atrioventricular pathways.” (opens the source at this quote in a new tab)

Pre-excitation: no accessory pathway at electrophysiological study in a 7-participant series

“In male patients, the initial QRS complex was characterized by a slurring upstroke and shortened PQ interval mimicking ventricular pre-excitation.” (opens the source at this quote in a new tab)

“However, the presence of an accessory pathway was excluded by an EP study in all patients.” (opens the source at this quote in a new tab)

X-chromosome inactivation and variable expression in females

“The clinical presentation and specific cardiac features demonstrate large variability in female individuals, presumably because of different patterns of X chromosome inactivation.” (opens the source at this quote in a new tab)

“Heterogenous penetrance and expressivity in female individuals is thought to be due to skewed X-chromosome inactivation and functional mosaicism of LAMP-2 expression.” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

“In contrast, female patients showed decreased LAMP-2 expression, which is suggested to reflect LAMP-2 haploinsufficiency due to a heterozygous null mutation.” (opens the source at this quote in a new tab)

Mosaic distribution of LAMP-2 in the myocardium of females

“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.” (opens the source at this quote in a new tab)

“These findings paralleled X chromosome inactivation within the myocardium.” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

“In other equally large regions there were preserved LAMP2 expression and nearly normal histology.” (opens the source at this quote in a new tab)

“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.” (opens the source at this quote in a new tab)

“This may be a more common mechanism behind early aggressive disease in females than an overall skewed X-chromosome inactivation in the tissue.” (opens the source at this quote in a new tab)

Animal model: Lamp2 knockout mouse

“Here we show that LAMP-2 deficiency in mice increases mortality between 20 and 40 days of age.” (opens the source at this quote in a new tab)

“Ultrastructurally, there is extensive accumulation of autophagic vacuoles in many tissues including liver, pancreas, spleen, kidney and skeletal and heart muscle.” (opens the source at this quote in a new tab)

“Cardiac myocytes are ultrastructurally abnormal and heart contractility is severely reduced.” (opens the source at this quote in a new tab)

“LAMP-2 deficient mice displayed reduced ejection fraction (EF) (58.9+/-3.4 vs. 80.7+/-5.1%, P<0.05) and reduced cardiac output (8.3+/-3.1 vs. 14.7+/-3.6 ml/min, P<0.05) as compared to wild-type controls.” (opens the source at this quote in a new tab)

“Physiologically, Lamp-2 KO mice demonstrated early features of contractile dysfunction without overt heart failure, indicating that the metabolic abnormalities associated with Danon disease precede the development of end-stage disease and are not merely part of the secondary changes associated with heart failure.” (opens the source at this quote in a new tab)

Animal model: mouse carrying a human LAMP2 exon 6 deletion

“By 20 weeks of age male mutant mice developed left ventricular hypertrophy which was followed by left ventricular dilatation and reduced systolic function.” (opens the source at this quote in a new tab)

“Cardiac electrophysiology and isolated cardiomyocyte studies demonstrated ventricular arrhythmia, conduction disturbances, abnormal calcium transients and increased sensitivity to catecholamines.” (opens the source at this quote in a new tab)

“Immunofluorescence and transmission electron microscopy identified mislocalization of lysosomes and accumulation of autophagosomes between sarcomeres, causing profound morphological changes disrupting the cellular ultrastructure.” (opens the source at this quote in a new tab)

“We suggest that impaired autophagy results in cardiac hypertrophy and profound transcriptional reactions that impacted metabolism, calcium homeostasis, and cell survival.” (opens the source at this quote in a new tab)

“Stimulation of autophagy in Danon mice (by exercise training, caloric restriction, and rapamycin) aggravate the disease phenotype, promoting dilated cardiomyopathy.” (opens the source at this quote in a new tab)

Animal models: rat and zebrafish

“Meanwhile, substantial myocyte disruption, hypertrophic muscle fibres, interstitial fibrosis and microvascular hyperplasia could be observed in the heart tissue.” (opens the source at this quote in a new tab)

“We found that haploinsufficiency of mtor was able to normalize some characteristics of the lamp2 KO, including ejection fraction, β-adrenergic response, and the actomyosin activation kinetics.” (opens the source at this quote in a new tab)

Limits of animal and cell models and of current mechanistic understanding

“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.” (opens the source at this quote in a new tab)

“We also compare findings from mouse and cellular models, which have allowed for further molecular characterization but have also shown phenotypic differences that warrant attention.” (opens the source at this quote in a new tab)

“However, the precise pathophysiological mechanism through which LAMP-2 deficiency causes Danon disease is still not fully understood and its elucidation would promote the development of new therapies.” (opens the source at this quote in a new tab)