This is a mechanism module, not a disease; do NOT create a "sarcolemmal fragility" or "myofiber necrosis" Disease entry from it. It is deliberately skeletal-muscle focused: the dystrophic cardiomyopathy arm belongs to cardiomyopathy_maladaptive_remodeling, and the generic bioenergetic arm to mitochondrial_dysfunction, so conforming disorders should route their cardiac nodes there rather than here. It is not an Xogenesis (pathological structure-formation) module. Scope and boundary decisions: (1) The membrane mechanical-fragility arm (Dystrophin-Glycoprotein Complex Mechanical Link Loss to Contraction-Induced Sarcolemmal Lesions) is solid for dystrophin, sarcoglycan, and alpha-dystroglycan hypoglycosylation; for laminin-alpha2 (LAMA2 / MDC1A) documented membrane rupture is contested, so those entries conform at Sarcolemmal Mechanical Fragility (vulnerability to contraction stress, which fits fibre detachment) rather than at Contraction-Induced Sarcolemmal Lesions, which asserts frank tracer-proven membrane tears. The curated MDC1A conformer (Contraction-Induced Myofibre Detachment and Mechanical Injury) does exactly this; its own evidence records that detached fibres retain membrane integrity. (2) A membrane-repair arm (Sarcolemmal Membrane Repair Failure) is where dysferlinopathy (DYSF) and anoctaminopathy (ANO5) enter: the DGC is intact but tears fail to reseal, so these conform at the repair node and the calcium node, bypassing the mechanical-link trigger. (3) Calpain-3 deficiency (CAPN3, LGMDR1) is OUT of scope as a conformer: calpain-3 is a titin-bound sarcomeric protease whose loss (not calcium-driven overactivation of ubiquitous mu/m-calpain) causes disease. (4) Modulator genes such as TRPC, ORAI1/STIM1 and PPIF are not disease genes here; they are represented through the calcium node and the drug-target treatments, not as genes on pathophysiology nodes. Modules bind GO and CL terms only (plus UBERON locations / GO cellular components) and do not use chemical (CHEBI) or disease (MONDO) term bindings in nodes; drug chemistry is carried in the treatments block's therapeutic_agent per the treatment schema. Worked conformers: Duchenne and Becker muscular dystrophy (dystrophinopathy), autosomal recessive limb-girdle muscular dystrophy (sarcoglycanopathy / dysferlinopathy), dystroglycanopathy, and congenital merosin-deficient muscular dystrophy 1A (LAMA2).
Dystrophin-Glycoprotein Complex Mechanical Link Loss
trigger
The shared upstream lesion of the DGC muscular dystrophies. Dystrophin binds cytoskeletal F-actin at its N-terminus and the dystrophin-glycoprotein complex at its C-terminus; within that complex, glycosylated alpha-dystroglycan binds laminin-211 in the basal lamina. Loss of dystrophin, of a sarcoglycan, of alpha-dystroglycan O-mannosyl glycosylation, or of laminin-211 itself therefore breaks the continuous mechanical link between the contractile cytoskeleton and the extracellular matrix. The specific protein lost differs by disorder, but the loss of the cytoskeleton to matrix mechanical coupling is the conserved trigger.
Downstream
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Sarcolemmal Mechanical Fragility
Show evidence (2 references)
"Our results support a role for the striated muscle dystrophin-glycoprotein complex in linking the actin-based cytoskeleton with the extracellular matrix."
Biochemical binding and cosedimentation assays establish the DGC as the transmembrane link between cytoskeletal actin and extracellular laminin, the structure whose loss is this module's trigger. Evidence source is IN_VITRO because the interactions were measured in protein overlay and precipitation assays.
"part of the dystrophin-glycoprotein complex (DGC) present in muscle sarcolemma, which acts as a linker between the cytoskeleton of the muscle fiber and the extracellular matrix, providing mechanical support to the sarcolemma during myofiber contraction"
A sarcoglycanopathy review states that the DGC links the muscle-fiber cytoskeleton to the extracellular matrix and gives the sarcolemma mechanical support during contraction, framing the trigger node. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review restating the established structural role.
Sarcolemmal Membrane Repair Failure
trigger
An alternative upstream arm, independent of the DGC mechanical link. In healthy fibers, dysferlin-dependent vesicle fusion reseals sarcolemmal tears in a calcium-dependent membrane-repair response. Where the repair machinery is defective (dysferlinopathy, anoctaminopathy), the DGC is structurally intact but tears that normally reseal instead persist, so even ordinary contraction-induced lesions remain open conduits for calcium entry. This arm enters the shared chain at the calcium node, bypassing the mechanical-link trigger.
Downstream
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Myofiber Cytosolic Calcium Overload
Show evidence (2 references)
"dysferlin-null mice maintain a functional dystrophin-glycoprotein complex but nevertheless develop a progressive muscular dystrophy"
Dysferlin-null mice show that muscular dystrophy can arise from a membrane-repair defect with an intact DGC, establishing this arm as independent of the mechanical-link trigger. Evidence source is MODEL_ORGANISM because the finding is from knockout mice.
"dysferlin-deficient muscle fibres are defective in Ca2+-dependent sarcolemma resealing"
Two-photon membrane-wounding assays show dysferlin-deficient fibers fail to reseal the sarcolemma, the molecular lesion of this repair-failure node. Evidence source is MODEL_ORGANISM because the assay was performed on mouse muscle fibers.
Sarcolemmal Mechanical Fragility
amplifier
With the cytoskeleton-to-matrix link gone, the sarcolemma loses the mechanical reinforcement the DGC normally provides and becomes abnormally vulnerable to the stresses developed during contraction. This is a change in the membrane's physical robustness that precedes any actual tear.
Downstream
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Contraction-Induced Sarcolemmal Lesions
Show evidence (1 reference)
"These findings strongly support the proposition that the primary function of dystrophin is to provide mechanical reinforcement to the sarcolemma and thereby protect it from the membrane stresses developed during muscle contraction."
The mdx mouse study concludes that dystrophin's primary role is mechanical reinforcement of the sarcolemma against contraction stress, so its loss produces the membrane fragility of this node. Evidence source is MODEL_ORGANISM because the work was done in mdx mouse muscle.
Contraction-Induced Sarcolemmal Lesions
effector
Eccentric (lengthening) contractions impose the largest mechanical stress on the membrane, and in the fragile dystrophic sarcolemma they produce frank membrane lesions. These breaches are demonstrable because low-molecular-weight tracers that are excluded from healthy fibers (Evans blue dye, procion orange) now enter the cytoplasm, and the amount of damage scales with the magnitude of the mechanical stress rather than with the number of contractions.
Downstream
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Myofiber Cytosolic Calcium Overload
Show evidence (2 references)
"The level of sarcolemmal damage is directly correlated with the magnitude of mechanical stress placed upon the membrane during contraction rather than the number of activations of the muscle."
Shows that sarcolemmal damage in mdx muscle scales with contraction-induced mechanical stress, establishing eccentric contraction as the source of the lesions. Evidence source is MODEL_ORGANISM because it is an mdx mouse contraction protocol.
"mdx mice, a dystrophin-deficient animal model for Duchenne muscular dystrophy, showed significant Evans blue accumulation in skeletal muscle fibers"
Evans blue dye enters dystrophin-deficient fibers but not healthy ones, directly demonstrating sarcolemmal breaches. Evidence source is MODEL_ORGANISM because the tracer study was done in mice (the same paper notes dy/dy laminin-alpha2 mice accumulate little dye, the basis of the LAMA2 caveat in notes).
Myofiber Cytosolic Calcium Overload
central effector
The rate-limiting central effector and the module's key conformance target. Calcium enters the fiber both through the membrane lesions and through stretch-activated and store-operated channels (TRPC and the Orai1-STIM1 complex) whose activity is increased in dystrophic muscle, raising cytosolic calcium above its normal tightly regulated level. This is where the mechanical-fragility arm and the membrane-repair-failure arm converge, and it is sufficient on its own: artificially raising calcium influx reproduces muscular dystrophy independent of membrane fragility, while enhancing calcium clearance is protective. Every conforming disorder funnels through this node.
Downstream
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Calpain Activation
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Mitochondrial Permeability Transition
Show evidence (4 references)
"Here we demonstrate that calcium itself is sufficient to cause a dystrophic phenotype in skeletal muscle independent of membrane fragility."
TRPC3 overexpression raises calcium influx and reproduces muscular dystrophy with no primary membrane defect, establishing cytosolic calcium overload as the sufficient central effector and justifying it as the key conformance target. Evidence source is MODEL_ORGANISM because it is a transgenic mouse experiment.
"These results demonstrate that calcium itself is sufficient to induce muscular dystrophy in vivo, and that TRPC channels are key disease initiators downstream of the unstable membrane that characterizes many types of muscular dystrophy."
Identifies TRPC channels as a calcium-entry route downstream of the unstable membrane across many dystrophies, supporting the channel arm of this node. Evidence source is MODEL_ORGANISM because it is an in vivo mouse study.
"Enhanced store-operated Ca2+ entry (SOCE), a Ca2+ influx mechanism coordinated by STIM1 sensors of luminal Ca2+ within the sarcoplasmic reticulum (SR) and Ca2+-permeable Orai1 channels in the sarcolemma, is proposed to contribute to Ca2+-mediated muscle damage in DMD."
Documents the store-operated Orai1-STIM1 calcium-entry route as a contributor to calcium-mediated damage in DMD, supporting the SOCE process on this node. Evidence source is MODEL_ORGANISM because the dystrophic model is the mdx mouse.
+ 1 more reference
Calpain Activation
effector
Sustained cytosolic calcium activates the ubiquitous calcium-dependent cysteine proteases (mu- and m-calpain), which degrade myofibrillar and membrane-cytoskeletal substrates. Inhibiting these calpains with a calpastatin transgene reduces necrosis without changing the upstream membrane damage, placing calpain activation downstream of the primary defect as a killing arm rather than a cause.
Show evidence (1 reference)
"Membrane damage, as assessed by procion orange and creatine kinase assays, was unchanged, supporting the idea that calpains act downstream of the primary muscle defect."
Calpastatin overexpression in mdx muscle reduces necrosis while leaving membrane damage unchanged, establishing calpain activation as a downstream killing step rather than the primary lesion. Evidence source is MODEL_ORGANISM because it is a transgenic mdx mouse.
Mitochondrial Permeability Transition
effector
Cytosolic calcium overload loads the mitochondria with calcium and opens the mitochondrial permeability transition pore (MPTP), whose components include the adenine nucleotide translocase and whose opening requires cyclophilin D. Pore opening collapses the mitochondrial membrane potential and precipitates necrotic fiber death. Genetic deletion of cyclophilin D (Ppif) or of ANT1 (Slc25a4) protects dystrophic muscle, and this arm is shared by non-DGC myopathies (for example collagen VI myopathy) that converge on the pore.
Show evidence (2 references)
"deletion of the gene encoding cyclophilin D (Ppif) rendered mitochondria largely insensitive to the calcium overload-induced swelling associated with a defective sarcolemma, thus reducing myofiber necrosis in two distinct models of muscular dystrophy"
Cyclophilin-D deletion makes mitochondria insensitive to calcium-overload swelling and cuts necrosis in two dystrophy models, establishing the calcium-driven permeability transition as the route to fiber death. Evidence source is MODEL_ORGANISM because it is a mouse knockout study.
"This study provides direct evidence that ANT1 and CypD are required MPTP components governing in vivo cell death"
In vivo deletion of ANT1 and cyclophilin D in a dystrophic mouse shows both are required MPTP components governing necrotic death, identifying the pore molecularly. Evidence source is MODEL_ORGANISM because it is a mouse genetic study.
Myofiber Necrosis
effector
Calpain activity and mitochondrial permeability transition together kill the muscle fiber by necrosis. Mitochondrial-dependent necrosis is a prominent and rate-contributing mechanism of fiber loss across muscular dystrophies, and the dying fiber is the source of the inflammation, regeneration demand, and enzyme leakage that follow.
Downstream
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Creatine Kinase Leakage into Serum
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Necrosis-Driven Muscle Inflammation
Show evidence (2 references)
"Thus, mitochondrial-dependent necrosis represents a prominent disease mechanism in muscular dystrophy"
States that mitochondrial-dependent necrosis is a prominent disease mechanism in muscular dystrophy, the fiber-death node. Evidence source is MODEL_ORGANISM because the conclusion rests on mouse dystrophy models.
"Originating from vulnerable myofibres, muscle cell necrosis and inflammatory processes are present in DMD."
A DMD review states that necrosis of vulnerable myofibers and inflammation are present, linking fiber death to the downstream inflammatory node. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review article.
Creatine Kinase Leakage into Serum
consequence
Because the necrotic fiber's membrane is breached and permeable, soluble cytoplasmic enzymes - most prominently creatine kinase - escape into the circulation, producing the markedly elevated serum creatine kinase that is the hallmark laboratory readout of active myofiber damage in these diseases. This is a systemic consequence of fiber necrosis rather than a step that drives further pathology.
Show evidence (1 reference)
"increased membrane permeability which allows soluble enzymes such as creatine kinase to leak out of the cell and ions such as calcium to enter the cell"
States that the permeable dystrophic membrane lets creatine kinase leak out while calcium enters, the basis of the serum-CK readout node. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review of the permeability mechanism.
Necrosis-Driven Muscle Inflammation
effector
Necrotic fibers release damage signals that recruit and activate macrophages into the muscle. In the dystrophic environment the pro-inflammatory (M1) macrophage phenotype worsens fiber injury, so the inflammatory infiltrate is not merely reactive but amplifies the damage and shapes the regenerative response that follows.
Downstream
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Exhausted Satellite-Cell Regeneration
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Fibro-Adipose Replacement of Muscle
Show evidence (2 references)
"M1 macrophages play a major role in worsening muscle injury in the mdx mouse model of Duchenne muscular dystrophy."
Establishes that M1 macrophages actively worsen muscle injury in dystrophic muscle, supporting inflammation as a damage-amplifying node. Evidence source is MODEL_ORGANISM because the work is in the mdx mouse.
"Originating from vulnerable myofibres, muscle cell necrosis and inflammatory processes are present in DMD."
Links myofiber necrosis to the inflammatory processes of DMD, the necrosis-to-inflammation edge. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review.
Exhausted Satellite-Cell Regeneration
effector
Each round of necrosis demands repair by muscle satellite cells. Repeated degeneration-regeneration cycles progressively deplete the satellite-cell pool and its proliferative capacity, so regeneration eventually fails to keep pace with fiber loss. This cell-autonomous decline in regenerative capacity is a major determinant of disease progression, and in humans satellite-cell / myoblast proliferative capacity is already defective.
Downstream
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Fibro-Adipose Replacement of Muscle
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Progressive Muscle Weakness
Show evidence (2 references)
"DMD progression results, in part, from a cell-autonomous failure of MuSC to maintain the damage-repair cycle initiated by dystrophin deficiency."
The mdx/mTR model shows DMD progression stems from cell-autonomous satellite-cell (MuSC) failure to sustain the repair cycle, the basis of this regeneration-exhaustion node. Evidence source is MODEL_ORGANISM because it is a mouse genetic model.
"A defect in the proliferative capacity of satellite cells, mononucleated precursors of mature muscle fibers, was found in clonal analyses of cells cultured from Duchenne muscular dystrophy (DMD) patients."
Clonal analysis of DMD patient-derived cells shows a defect in satellite cell proliferative capacity, the human correlate of the exhaustion node. Evidence source is IN_VITRO because the defect was measured in cultured patient myoblasts.
Fibro-Adipose Replacement of Muscle
effector
When regeneration can no longer replace lost fibers, resident platelet-derived growth factor receptor alpha (PDGFRalpha)-positive fibro-adipogenic progenitors proliferate and differentiate into collagen-producing fibroblasts and adipocytes, replacing contractile muscle with fibrous and fatty tissue. These interstitial mesenchymal progenitors - distinct from satellite cells - are the common origin of both the fibrosis and the fat. This node is the muscle-specific instance of the generic fibrotic mesenchymal-cell activation step.
Downstream
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Progressive Muscle Weakness
Show evidence (2 references)
"PDGFRalpha(+) mesenchymal progenitors are the major contributor to ectopic fat cell formation in skeletal muscle"
Identifies interstitial PDGFRalpha+ mesenchymal progenitors, distinct from satellite cells, as the source of ectopic muscle fat, the adipose arm of this replacement node. Evidence source is MODEL_ORGANISM because the lineage work was done in mouse muscle.
"PDGFRα(+) cells accumulated in fibrotic areas of the diaphragm in the mdx mouse, a model of Duchenne muscular dystrophy."
Shows the same PDGFRalpha+ progenitors accumulate in and produce the fibrosis of mdx diaphragm, the fibrotic arm of this node and the basis for its conformance to the generic fibrotic mesenchymal-activation step. Evidence source is MODEL_ORGANISM because it is the mdx mouse.
Progressive Muscle Weakness
consequence
The organism-level end state. Cumulative fiber loss, failed regeneration, and replacement of contractile tissue by fibrosis and fat reduce functional muscle mass, so strength declines progressively. This is the shared clinical consequence toward which every conforming dystrophy converges, varying only in tempo and distribution by disorder.
Show evidence (3 references)
"repeated bouts of muscle damage lead to atrophy and fibrosis, and eventually muscle degeneration"
States that repeated muscle damage culminates in atrophy, fibrosis, and muscle degeneration, the progressive-weakness end state. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review.
"Severity was gauged by muscle strength and age at loss of ambulation."
Ties disease severity directly to declining muscle strength and loss of ambulation - the progressive loss of strength this node names.
"Muscular recovery is limited due to the limited number and capacity of satellite cells."
Links limited satellite-cell number and capacity to limited muscular recovery, the regeneration-failure contribution to progressive weakness. Evidence source is OTHER and quote_role REVIEW_SYNTHESIS because this is a review.
Corticosteroid Therapy (Prednisone or Deflazacort)
Platform:
Small molecule
Daily glucocorticoids - prednisone/prednisolone or deflazacort - are the long-standing standard-of-care pharmacotherapy that preserves muscle strength in Duchenne muscular dystrophy. Their precise mechanism is debated - proposed actions include anti-inflammatory effects, membrane stabilization, and effects on regeneration - and the trial evidence shows a clinical strength benefit rather than action on any single node. They are placed on the inflammatory node here because dampening the macrophage-driven inflammation that amplifies myofiber injury is the best-characterized of those actions; they do not restore the upstream mechanical link.
Evidence: 1
Cyclophilin D / mPTP Inhibition (Alisporivir / Debio-025, experimental)
Platform:
Small molecule
An experimental, not yet approved, strategy that targets the permeability-transition node directly. Debio-025 (alisporivir) is a non-immunosuppressive cyclophilin inhibitor that desensitizes the mitochondrial permeability transition pore, reducing calcium-overload-driven necrosis. In mdx and sarcoglycan-null mice it reduces dystrophic pathology at least as effectively as prednisone. It illustrates the module's drug-target pattern of acting on a specific internal node (here the mitochondrial pore) rather than the upstream genetic lesion.
Evidence: 1
Micro-dystrophin Gene Replacement
Platform:
Gene therapy
Gene-replacement therapy delivering a truncated but functional micro-dystrophin by AAV vector aims to restore the cytoskeleton-to-matrix mechanical link at the trigger node, so the sarcolemma regains mechanical protection and the whole downstream chain is pre-empted. Highly functional micro-dystrophins protect dystrophic muscle from contraction-induced damage in mice, and systemic AAV micro-dystrophin has entered clinical testing in DMD.
Evidence: 2