Brody Myopathy

Mendelian MONDO:0010977 Pathograph 17 Show in embeddings browser

Brody myopathy (Brody disease) is an autosomal recessive disorder of skeletal muscle relaxation caused by biallelic loss-of-function variants in ATP2A1, which encodes SERCA1, the sarcoplasmic reticulum calcium pump of fast-twitch fibres. SERCA1 is not an accessory to relaxation; in type II fibres it is essentially the whole of the relaxation machinery, clearing cytosolic calcium back into the sarcoplasmic reticulum after each contraction. When it is missing, calcium lingers in the cytosol, troponin C stays saturated, and cross-bridges keep cycling, so the muscle contracts normally but cannot let go. The result is exercise-induced stiffness of the limbs and eyelids that builds during activity and eases with rest, worsens in the cold, and is accompanied by delayed relaxation after repeated contraction. The defining diagnostic feature follows directly from the mechanism. Because the fault is downstream of the sarcolemma, the contracture is electrically silent: needle EMG records nothing while the muscle is stiff. That silence is what separates Brody myopathy from the myotonias it is mistaken for, and myotonia, percussion myotonia, and myotonic discharges are all curated exclusions in this disease rather than merely absent findings. Two features make the entry mechanistically interesting beyond the core chain. First, the disease is far milder than it should be: mice lacking SERCA1 die at birth of diaphragm failure, while humans with essentially absent SERCA1 have a mild, non-progressive myopathy, an athletic build, and no respiratory involvement at all. Something compensates, and what that something is remains genuinely unsettled, with the two leading candidates recorded here as competing hypotheses rather than a single chain. Second, a subset of missense alleles produce a pump that folds badly but still works, and is destroyed by the ubiquitin-proteasome system before it ever reaches the sarcoplasmic reticulum membrane. Those alleles are in principle rescuable by stabilising the protein through quality control, which is the basis of the CFTR-corrector strategy now being tested in cattle.

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1
Inheritance
8
Pathophys.
2
Histopath.
8
Phenotypes
2
Hypotheses
2
Gaps
17
Pathograph
1
Genes
6
Medical Actions
4
Differentials
3
Models
1
Deep Research
👪

Inheritance

1
Autosomal recessive HP:0000007
Biallelic ATP2A1 variants are required. Heterozygous carriers are unaffected.
Autosomal recessive inheritance
◈

Mechanistic Hypotheses

2
Sarcolemmal calcium extrusion compensates for SERCA1 loss
pmca_extrusion_compensation EMERGING
Evidence balance 1 support
Holds that the calcium load left by the missing sarcoplasmic reticulum pump is handled principally by exporting calcium across the sarcolemma, via the plasma-membrane calcium ATPase and related extrusion mechanisms, rather than by an alternative sarcoplasmic reticulum pump. The bovine work supports this directly, reporting increased sarcolemmal extrusion pump expression in the same muscle in which SERCA2 compensation was excluded.
EMERGING rather than CANONICAL because the direct evidence is bovine and from a single case, and because no human muscle study has measured extrusion-pump activity in Brody myopathy.
Show evidence (1 reference)
PMID:26482047 SUPPORT Model Organism
"an increased expression of sarcolemmal calcium extrusion pump"
The positive finding for this hypothesis, reported in the same animal in which SERCA2 compensation was not observed.
SERCA2 isoform upregulation compensates for SERCA1 loss
serca2_isoform_compensation ALTERNATIVE
Evidence balance 1 support 2 refute
Holds that the SERCA2 isoform is upregulated, including ectopically in type II fibres, and takes over part of the calcium reuptake that SERCA1 can no longer perform. This was the first proposed explanation for the mildness of the human disease and rests on a single family in which muscle showed absent SERCA1 with elevated SERCA2. It is recorded as ALTERNATIVE rather than discarded because that observation is real, but the larger cohort and the bovine work both failed to reproduce it.
The conflict is not resolvable from the published record. The supporting and refuting studies used immunohistochemistry on different patients, and the cohort separately reports that of eight biopsies examined, seven showed normal SERCA2 expression and one showed increased expression, so the positive finding may be real but uncommon rather than wrong.
Show evidence (3 references)
PMID:25614869 SUPPORT Human Clinical
"Analyses of affected muscles showed the absence of SERCA1, but SERCA2 upregulation in slow and fast myofibers, suggesting a compensatory mechanism that partially restores the diminished Ca(2+) transport in Brody myopathy."
The originating observation, in human muscle, which is the whole positive case for this hypothesis.
PMID:32040565 REFUTE Human Clinical
"SERCA2 staining was normal in all samples."
The international cohort found no SERCA2 upregulation in its own biopsies, directly contradicting the hypothesis in human muscle.
PMID:26482047 REFUTE Model Organism
"The reduced expression of SERCA1 is selective and not compensated by the SERCA2 isoform."
Independent contradiction from the bovine model, in which the same question was asked and answered negatively.
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Discussions and Knowledge Gaps

2
What actually compensates for SERCA1 loss in human fast-twitch muscle, and why is the human disease mild when complete murine SERCA1 loss is lethal?
KNOWLEDGE GAP OPEN brody_compensation_mechanism
Attached to
pathophysiology#Compensatory Calcium Extrusion and Handling
This is the central unresolved question of the disease and it is not merely academic. The compensation is what determines severity, so understanding it would explain the variability between patients and might itself be a therapeutic target. Two candidate mechanisms are curated here as competing hypotheses. Sarcolemmal calcium extrusion has direct positive evidence but only from cattle, and from a single case. SERCA2 isoform upregulation was observed in one human family but was not reproduced in the largest human cohort or in the bovine model. No human study has measured extrusion pump activity, sodium-calcium exchange, or mitochondrial calcium uptake in Brody muscle, so the question is open rather than contested at the level of data.
Proposed experiments
Calcium-handling protein profiling in genotyped Brody muscle
brody_compensation_profiling
Quantify plasma membrane calcium ATPase, sodium-calcium exchanger, mitochondrial calcium uniporter, and SERCA2 protein abundance and activity in fast-twitch muscle biopsies from genotyped Brody patients, stratified by residual SERCA1 activity, against matched controls. This would establish which removal mechanism actually carries the load in human muscle, and whether the degree of compensation predicts clinical severity.
Fibre-type-resolved single-nucleus RNA sequencing of Brody muscle
brody_single_nucleus_rnaseq
Single-nucleus RNA sequencing of Brody muscle, resolved by fibre type. The mechanism is fibre-type selective, so a fibre-type-resolved expression map is the obvious way to detect compensatory programmes running specifically in type II nuclei. No such dataset exists.
Does the neonatal lethality of the Atp2a1-null mouse reflect a genuine species difference in calcium handling, or an artefact of modelling a partial-loss human disease with a complete null?
HUMAN MODEL MISMATCH OPEN brody_mouse_model_mismatch
Attached to
pathophysiology#Compensatory Calcium Extrusion and Handling pathophysiology#Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
Evidence exists in the model and is not in doubt; what is open is its translational validity. Complete murine SERCA1 loss kills the animal at birth through diaphragm failure, while human patients with severely reduced or absent SERCA1 have no respiratory involvement whatsoever and a mild, non-progressive limb and eyelid myopathy. Two readings are possible and are not mutually exclusive: that human muscle compensates in a way mouse muscle cannot, or that most human alleles retain enough residual protein or activity that a complete null is simply the wrong comparison. Distinguishing them matters, because the first reading makes compensation a therapeutic target and the second makes allele severity the dominant variable.
Proposed experiments
Hypomorphic Atp2a1 mouse allele series matched to human residual activity
brody_hypomorphic_mouse
Generate a hypomorphic Atp2a1 allele series in mouse, matched to the residual activity levels measured in human patients, rather than a complete null. This would separate the two readings directly: if graded hypomorphs are viable and develop exertional stiffness, the mismatch is about allele severity; if they still die of diaphragm failure, it is about species biology.
⚙

Pathophysiology

8
Biallelic ATP2A1 Loss of Function
Recessive loss-of-function variants on both ATP2A1 alleles. Two mechanistic routes converge on the same deficit: truncating, splice, and deletion alleles yield little or no SERCA1 protein, while a subset of missense alleles yield a protein that folds badly but retains catalytic activity. The distinction is not academic, because only the second group is addressable by strategies that stabilise the protein through quality control.
SERCA1 P-type calcium transporter activity GO:0005388 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves SERCA1 P-type calcium transporter activity, annotated with P-type calcium transporter activity (GO:0005388), qualified as loss of function. GO:0005388 is a molecular function from the Gene Ontology. ⇓ LOSS OF FUNCTION
Downstream
Proteasomal Degradation of Misfolded SERCA1 The missense route specifically. A protein that misfolds is recognised and destroyed rather than trafficked.
Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane The truncating, splice, and deletion route, where little or no protein is made in the first place.
Show evidence (1 reference)
PMID:8841193 SUPPORT Human Clinical
"how have these Brody patients partially compensated for the functional knockout"
The paper that established ATP2A1 as the causal gene, quoted here at the point where it frames the functional knockout of SERCA1 in patients.
Proteasomal Degradation of Misfolded SERCA1
For missense alleles, the mutant pump is corrupted in folding but not in catalysis. The ubiquitin-proteasome system recognises the misfolded protein and strips it out before it reaches the sarcoplasmic reticulum membrane, so the fibre loses a pump that would have worked had it arrived. Proteasome inhibition restores both the expression level and the membrane localisation of the mutant, and the rescued protein handles calcium like wild type. This node is the therapeutic vulnerability behind the corrector strategy.
proteasome-mediated degradation of misfolded SERCA1 GO:0043161 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased proteasome-mediated degradation of misfolded SERCA1, annotated with proteasome-mediated ubiquitin-dependent protein catabolic process (GO:0043161). GO:0043161 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Bovine congenital pseudomyotonia (ATP2A1 missense, Chianina and Romagnola cattle) Cattle recapitulates The bovine missense alleles reproduce the folding-competent, catalytically intact pump that is destroyed before reaching the membrane, and this is the system in which both proteasome inhibition and corrector rescue were demonstrated.
Downstream
Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane Degradation before trafficking is completed produces the same end state as failure to synthesise the protein: too few pumps in the membrane.
Show evidence (2 references)
PMID:25288803 SUPPORT Model Organism
"the mutation generates a protein most likely corrupted in proper folding but not in catalytic activity"
States the folding-versus-catalysis distinction that defines this node. Tagged MODEL_ORGANISM because the publication studies Chianina cattle pseudomyotonia together with a heterologous cell model, not human patients.
PMID:25288803 SUPPORT Model Organism
"The treatment with MG132, an inhibitor of ubiquitin proteasome system, rescues the expression level and membrane localization of the SERCA1 mutant in a heterologous cellular model."
Demonstrates that blocking the degradation restores both abundance and correct localisation, which is what makes this node druggable in principle.
Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
The convergence point of both allelic routes. Fewer functional calcium pumps sit in the sarcoplasmic reticulum membrane of fast-twitch fibres, so the tissue's total calcium-ATPase activity falls. The reduction is selective for SERCA1 rather than a general loss of sarcoplasmic reticulum protein.
sarcoplasmic reticulum calcium ATPase activity GO:0005388 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased sarcoplasmic reticulum calcium ATPase activity, annotated with P-type calcium transporter activity (GO:0005388). GO:0005388 is a molecular function from the Gene Ontology. ↓ DECREASED
sarcoplasmic reticulum membrane GO:0033017 Gene Ontology (GO) Relation: this pathophysiological event involves this cellular component This pathophysiological event involves sarcoplasmic reticulum membrane (GO:0033017). GO:0033017 is a cellular component from the Gene Ontology.
Downstream
Impaired Calcium Reuptake into the Sarcoplasmic Reticulum Fewer pumps means less calcium moved per unit time back into the store.
Show evidence (2 references)
PMID:26482047 SUPPORT Model Organism
"The reduced expression of SERCA1 is selective and not compensated by the SERCA2 isoform."
Establishes that the protein loss is selective for SERCA1. The second half of the sentence is also the evidence against isoform compensation and is used again on that hypothesis.
PMID:20142766 SUPPORT Human Clinical
"Ultrastructural examination revealed dilatation of lateral cisternae and proliferation of tubular elements of the sarcoplasmic reticulum."
Human biopsy ultrastructure showing that the sarcoplasmic reticulum itself is structurally remodelled where the pump is deficient.
Impaired Calcium Reuptake into the Sarcoplasmic Reticulum
The functional consequence of pump loss. Calcium released to trigger contraction is cleared from the cytosol too slowly, because in fast-twitch fibres SERCA1 is the dominant route by which that clearance happens. Calcium release itself is intact; it is only the return leg of the cycle that fails.
calcium ion import into sarcoplasmic reticulum GO:1990036 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased calcium ion import into sarcoplasmic reticulum (GO:1990036). GO:1990036 is a biological process from the Gene Ontology. ↓ DECREASED
Animal models
accordion zebrafish (atp2a1 mutant) Zebrafish recapitulates In vivo imaging shows the slowed cytosolic calcium decay that defines this node, and the defect is shown to be muscle-intrinsic rather than neural.
Downstream
Prolonged Cytosolic Calcium Elevation Slower removal leaves calcium in the cytosol for longer after each contraction.
Compensatory Calcium Extrusion and Handling The same rise in cytosolic calcium that causes the disease also recruits alternative removal mechanisms, which is the branch that appears to make the human disease survivable.
Show evidence (1 reference)
PMID:15469975 SUPPORT Model Organism
"cytosolic Ca2+ decay was significantly slower in acc muscle"
Direct in vivo imaging of the slowed calcium transient in the zebrafish SERCA1 mutant, which is the measurement this node asserts.
Prolonged Cytosolic Calcium Elevation
Cytosolic free calcium stays elevated after each contraction instead of falling promptly. This is the proximate cause of every downstream feature, and it is also the point of contact with malignant hyperthermia, which arrives at the same elevated myoplasmic calcium by a different route.
intracellular calcium ion homeostasis GO:0006874 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased intracellular calcium ion homeostasis (GO:0006874). GO:0006874 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Electrically Silent Muscle Contracture Sustained calcium keeps troponin C saturated and cross-bridges cycling.
Malignant hyperthermia Susceptibility to malignant-hyperthermia-like episodes on exposure to triggering anaesthetic agents, reached through the shared myoplasmic calcium overload rather than through a ryanodine receptor defect.
Show evidence (1 reference)
PMID:25614869 SUPPORT Human Clinical
"a feature common to both conditions is elevated myoplasmic Ca(2+) content"
Names the elevated myoplasmic calcium shared by Brody myopathy and malignant hyperthermia, which is why this node carries the anaesthetic hazard downstream.
Electrically Silent Muscle Contracture
Involuntary sustained contraction following voluntary contraction, occurring without any electrical activity on needle EMG. The silence is the mechanistically important part: the fault lies downstream of the sarcolemma, in the calcium-handling machinery, so the membrane is not misbehaving and there is nothing for the electrode to record. Every myotonic disorder on the differential generates electrical discharges; this one does not.
relaxation of muscle GO:0090075 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased relaxation of muscle (GO:0090075). GO:0090075 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Exercise-induced muscle stiffness The contracture experienced clinically as stiffness that builds with activity.
Delayed muscle relaxation The examination finding, elicited by repetitive contraction.
Show evidence (2 references)
PMID:32040565 SUPPORT Human Clinical
"EMG can reveal silent contractures defined as prolonged involuntary muscle contractions (following voluntary phasic contractions) without electrical activity detected on EMG"
Defines the silent contracture explicitly, including that it follows voluntary contraction and produces no electrical activity.
PMID:32040565 SUPPORT Human Clinical
"EMG is characterized by the presence of silent contractures and absence of myotonic discharges."
States both halves of the discriminator in one sentence: contractures are present, myotonic discharges are absent.
Selective Type II Fibre Involvement
SERCA1 is the fast-twitch isoform; slow fibres run SERCA2a from a different gene and are therefore spared. This single fact explains the distribution of the disease: the muscles that stiffen are fast-twitch-rich, which is why eyelid closure through orbicularis oculi is affected in roughly two thirds of patients while cardiac muscle, running SERCA2a, is entirely uninvolved. The biopsy correlate is selective type II fibre atrophy without myonecrosis.
type II skeletal muscle fibre CL:0002212 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves type II skeletal muscle fibre, annotated with type II muscle cell (CL:0002212). CL:0002212 is a cell type from the Cell Ontology.
Downstream
Exercise-induced muscle stiffness Restricting the deficit to fast-twitch fibres is what makes the stiffness exertional and distributed as it is.
Show evidence (1 reference)
PMID:25614869 SUPPORT Human Clinical
"encoding the sarco(endo)plasmic reticulum Ca(2+) ATPase type 1 (SERCA1), a calcium pump, expressed in fast-twitch muscles"
States the fast-twitch restriction of SERCA1 expression that produces the fibre-type selectivity of the disease.
Compensatory Calcium Extrusion and Handling
Alternative calcium-removal mechanisms recruited in the face of SERCA1 deficiency, which appear to be why the human disease is mild rather than lethal. Candidate contributors include the sarcolemmal calcium extrusion pump (PMCA), the sodium-calcium exchanger, mitochondrial uptake, and upregulation of the SERCA2 isoform. Which of these actually carries the load in human muscle is unresolved, and the two leading candidates are recorded as competing hypotheses rather than as a settled chain. The branch is included in the pathograph because it is load-bearing for prognosis: without it, the expectation from the mouse null would be neonatal death.
calcium ion transmembrane transport GO:0070588 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased calcium ion transmembrane transport (GO:0070588). GO:0070588 is a biological process from the Gene Ontology. ↑ INCREASED
Animal models
Atp2a1-null mouse Mouse fails to recapitulate The mouse does not reproduce the compensation that makes the human disease survivable. Humans with essentially absent SERCA1 have a mild, non-progressive myopathy with no respiratory involvement, whereas the null mouse dies at birth of diaphragm failure. Whatever carries the calcium load in human muscle is either absent in the mouse or cannot meet the acute respiratory demand of birth.
Show evidence (1 reference)
PMID:26482047 SUPPORT Model Organism
"Calcium removal mechanisms, operating in muscle fibers as compensatory response aimed at lowering excessive cytoplasmic calcium concentration caused by SERCA1 deficiency, could explain the difference in severity of clinical signs."
States the compensation principle and links it explicitly to severity, which is the reason this branch is modelled rather than left as prose. The authors frame it as a candidate explanation rather than a demonstrated one.
✶

Histopathology

2
Selective type II fibre atrophy with increased fibre size variability
Systematic re-evaluation of biopsies showed type II fibre atrophy, increased variability of fibre size, and increased internal nuclei. The findings are mild and non-specific taken individually; what makes them useful is the company they keep, in particular their appearance alongside preserved strength and an absence of necrosis.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Systematic re-evaluation of the biopsy reports showed fibre type II atrophy, increased fibre size variability, and an increased number of internal nuclei."
Enumerates all three biopsy findings from a systematic re-review rather than from individual case impressions.
Absence of myonecrosis
A curated negative. Muscle necrosis is essentially absent, found in a single biopsy across the international cohort. This is consistent with the modest creatine kinase elevation and separates the disease from the necrotising myopathies: the muscle is failing to relax, not dying.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Discrete necrosis was found in only one biopsy (Patient L18)."
One biopsy out of the whole cohort, which is what makes absence of necrosis a usable negative finding rather than merely an unremarked one.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Brody Myopathy Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

8
Metabolism 2
Malignant hyperthermia OCCASIONAL HP:0002047 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Malignant hyperthermia (HP:0002047). HP:0002047 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Four patients had episodes resembling malignant hyperthermia."
Four of forty is 10 per cent, which falls in the OCCASIONAL band of 5 to 29 per cent.
Elevated circulating creatine kinase concentration HP:0003236 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Elevated circulating creatine kinase concentration (HP:0003236). HP:0003236 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Creatine kinase was normal or mildly elevated"
Records that creatine kinase is normal or only mildly raised, which is the claim this phenotype makes.
Musculoskeletal 1
Exercise-induced muscle stiffness VERY_FREQUENT HP:0008967 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Exercise-induced muscle stiffness (HP:0008967), qualified as childhood onset. HP:0008967 is a phenotype from the Human Phenotype Ontology.
Onset: CHILDHOOD
Show evidence (2 references)
PMID:32040565 SUPPORT Human Clinical
"This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids."
Names this as the main feature and gives the limb and eyelid distribution. The VERY_FREQUENT band reflects the cohort, in which limb stiffness was present in all 40 patients.
PMID:32040565 SUPPORT Human Clinical
"Onset begins in childhood and there was no or only mild progression of symptoms over time."
Supports the childhood onset recorded on this descriptor, and the absence of meaningful progression thereafter, which together are the prognostic core of the disease.
Constitutional 1
Myalgia FREQUENT HP:0003326 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Myalgia (HP:0003326). HP:0003326 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Furthermore, myalgia and muscle cramps are described, which may worsen upon exposure to cold temperatures"
Names myalgia among the reported features and records the cold sensitivity that accompanies it. The FREQUENT band reflects the cohort proportion of 20/34.
Other 4
Delayed muscle relaxation
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"The key finding at physical examination was delayed relaxation after repetitive contractions."
Identifies delayed relaxation after repetitive contraction as the key physical sign.
Preserved muscle strength without atrophy
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"no atrophy was seen, muscle strength was generally preserved, and some patients had a remarkable athletic build"
States the absence of atrophy, the preservation of strength, and the athletic build in one sentence.
Absence of myotonia and myotonic discharges
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Therefore, when EMG shows no myotonic discharges in patients clinically suspected of having a myotonic disorder, provocation of possible silent contractures is recommended by performing rapid contractions during EMG."
Turns the absence of myotonic discharges into an actionable diagnostic step, which is the reason the exclusion is curated rather than omitted.
Exercise-induced muscle cramps FREQUENT HP:0003710 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Exercise-induced muscle cramps (HP:0003710). HP:0003710 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Patients variably reported muscle cramps (defined as involuntary and painful sustained muscle contractures) at rest or during exercise (18/34)."
Gives the cohort proportion, 18 of 34, which falls in the FREQUENT band, and the authors' definition of cramps as sustained contracture.
🧬

Genetic Associations

1
ATP2A1
Gene: ATP2A1 hgnc:811 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ATP2A1 (hgnc:811). hgnc:811 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Autosomal recessive
Show evidence (1 reference)
PMID:8841193 SUPPORT Human Clinical
"how have these Brody patients partially compensated for the functional knockout"
The study that associated SERCA1 mutations with Brody disease, quoted at its statement of the functional knockout in patients.
💊

Medical Actions

6
Trigger-Free Anaesthesia and Malignant Hyperthermia Precautions
Action: Supportive CareNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Supportive Care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. NCIT:C15747
The highest-value intervention in the disease, and the one that changes outcomes rather than symptoms. Patients are managed as malignant-hyperthermia-susceptible: volatile anaesthetics and succinylcholine are avoided in favour of a total intravenous technique, with core temperature monitoring. This follows from the shared myoplasmic calcium overload rather than from a ryanodine receptor defect.
Mechanism Target:
MODULATES Prolonged Cytosolic Calcium Elevation — Avoidance rather than pharmacology: the measure prevents a trigger from compounding an existing calcium-handling deficit, rather than correcting the deficit itself.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended"
States both the risk and the recommendation for perioperative measures.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended"
The recommendation as stated by the international cohort.
Symptomatic Pharmacotherapy
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Calcium channel blockers, dantrolene, mexiletine, carbamazepine, and others have been tried. The honest summary from the largest cohort is that symptomatic treatment was mostly ineffective or produced unacceptable side effects, with only a small minority achieving durable control. Verapamil was the best performer in that cohort but still helped a minority.
Show evidence (1 reference)
PMID:32040565 REFUTE Human Clinical
"Symptomatic treatment was mostly ineffective or produced unacceptable side effects."
Refutes a general claim of symptomatic benefit. Recorded as REFUTE rather than omitted because a reader needs to know that the obvious drug options have been tried and largely failed.
Dantrolene
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Agent: dantrolene CHEBI:4317 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses dantrolene (CHEBI:4317). CHEBI:4317 is a therapeutic agent from Chemical Entities of Biological Interest.
A ryanodine receptor inhibitor, mechanistically coherent here because it reduces calcium release into the cytosol, attacking the same overload from the opposite direction when reuptake cannot be restored. The evidence points both ways and is curated that way: dantrolene was ineffective or poorly tolerated in the cohort, while a single later case report describes clear benefit.
Mechanism Target:
MODULATES Prolonged Cytosolic Calcium Elevation — Reduces ryanodine-receptor-mediated calcium release, lowering the cytosolic calcium load that the deficient pump cannot clear.
Show evidence (1 reference)
PMID:41926432 SUPPORT Human Clinical
"Treatment with dantrolene sodium resulted in marked clinical improvement."
PARTIAL because this is a single case, and because the largest cohort reports the opposite experience with the same drug.
Show evidence (1 reference)
PMID:41926432 SUPPORT Human Clinical
"Treatment with dantrolene sodium resulted in marked clinical improvement."
A single reported responder. Graded PARTIAL rather than SUPPORT because one case cannot establish efficacy against a cohort reporting the drug as ineffective or poorly tolerated.
CFTR Correctors (Investigational)
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
A repurposing strategy aimed at the folding defect rather than the symptoms. Small molecules developed to chaperone misfolded CFTR through quality control also rescue misfolded SERCA1, restoring pump abundance at the sarcoplasmic reticulum membrane. The corrector C17 was effective in vitro and in cattle, whereas the licensed cystic fibrosis correctors lumacaftor and tezacaftor were not efficient. This has not been tested in humans.
Mechanism Target:
INHIBITS Proteasomal Degradation of Misfolded SERCA1 — Stabilises the misfolded pump so that it escapes degradation and reaches the membrane, addressing the node rather than its consequences.
Show evidence (1 reference)
PMID:41206505 SUPPORT Model Organism
"CFTR correctors, particularly C17, successfully rescue SERCA1 mutants both in vitro and in vivo models"
Demonstrates rescue of the mutant pump. Tagged MODEL_ORGANISM because the in vivo work is in cattle.
Show evidence (1 reference)
PMID:41206505 SUPPORT Model Organism
"may be a potential innovative pharmacological approach addressing Brody patients in which mutated SERCA1 retains its activity"
PARTIAL because the authors themselves frame this as potential rather than established, and because the quoted sentence carries the decisive restriction: the approach can only help patients whose mutant pump retains catalytic activity.
Physical Therapy and Activity Pacing
Action: Physical TherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Physical Therapy (NCIT:C15302). NCIT:C15302 is a clinical intervention from the NCI Thesaurus. NCIT:C15302
Warm-up strategies, activity pacing, and avoidance of cold during exertion. Used pragmatically. No trial evidence exists, and none is claimed here.
Genetic Counselling
Action: Genetic CounselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Genetic Counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. NCIT:C15240
Autosomal recessive recurrence risk, cascade testing of relatives, and critically, communication of anaesthetic risk to family members who may carry the same genotype.
🔬

Biochemical Markers

1
Sarcoplasmic reticulum calcium ATPase activity (DECREASED)
Show evidence (2 references)
PMID:32040565 SUPPORT Human Clinical
"Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity was reduced and western blot analysis showed decreased or absent SERCA1 protein."
States both assay results in patients, which is exactly what this biomarker record asserts.
PMID:32040565 SUPPORT Human Clinical
"SERCA activity measurement and SERCA1 western blot can assist in proving the pathogenicity of novel ATP2A1 mutations"
Gives the assays their clinical purpose, which is variant adjudication rather than primary diagnosis.
🔬

Diagnosis

3
Electromyography showing silent contractures without myotonic discharges
The pivotal diagnostic observation, and the reason the disease is so often misdiagnosed. Needle EMG during the stiffness records nothing, because the fault lies downstream of the sarcolemma. The cohort turns this into an active manoeuvre rather than a passive finding: when a patient looks myotonic but shows no myotonic discharges, provoke contractures with rapid repeated contraction during the study instead of stopping at the negative result.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"Therefore, when EMG shows no myotonic discharges in patients clinically suspected of having a myotonic disorder, provocation of possible silent contractures is recommended by performing rapid contractions during EMG."
Converts the absence of myotonic discharges into a positive diagnostic step, which is what makes this a diagnostic recommendation rather than a description.
ATP2A1 sequencing or myopathy gene panel
Molecular confirmation, recommended once delayed relaxation is present on examination and myotonic discharges have been excluded electrophysiologically. The order matters: the clinical and electrophysiological findings select who should be sequenced.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"we recommend direct sequencing of the ATP2A1 gene or next generation sequencing with a myopathy panel"
The testing recommendation, quoted with the clinical preconditions that precede it in the same sentence.
SERCA1 immunohistochemistry (inadequate in isolation)
Recorded specifically as a false-negative trap rather than as a recommended test. Immunostaining for loss of SERCA1a protein is not adequate for diagnosis on its own, so a normal-appearing stain does not exclude the disease and should not stop the diagnostic sequence. This is curated because a negative immunostain is exactly the point at which a workup tends to be abandoned.
Show evidence (1 reference)
PMID:10914677 SUPPORT Human Clinical
"immunostaining of skeletal muscle to detect the loss of SERCA1a protein is not adequate for the diagnosis"
States plainly that immunostaining alone is inadequate, which is the caution this record exists to carry.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
No population-based prevalence estimate exists. The largest series assembled 40 patients internationally, and a separate cross-sectional study covered 17 patients with the gene-negative syndrome. Recorded as CASES_IN_LITERATURE rather than converted to a rate, because dividing a convenience series by a world population would manufacture a precision the data do not have.
Show evidence (1 reference)
PMID:32040565 SUPPORT Human Clinical
"This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids."
The international series of 40 patients, cited here for the scale of the assembled literature rather than for a rate.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Brody Myopathy:

Brody syndrome (gene-negative)
Overlapping Features Clinically and biochemically similar exercise-induced impairment of relaxation with reduced SERCA activity, but without identifiable ATP2A1 variants. It is genetically unsolved and reported to differ clinically: myalgia is more common and the impact on daily life greater than in gene-confirmed Brody disease. It is the most important boundary on this entry, since a patient can meet the clinical and biochemical description and still not belong here.
Show evidence (1 reference)
PMID:22704959 SUPPORT Human Clinical
"Patients with Brody syndrome more often report myalgia"
Establishes that the gene-negative group differs clinically rather than being an undiagnosed remainder of the same entity.
Myotonia congenita and paramyotonia congenita
Overlapping Features The disorders Brody myopathy is most often mistaken for, since all present with exercise-related muscle stiffness. They are distinguished electrophysiologically rather than clinically: the myotonias generate myotonic discharges on EMG, while the Brody contracture is electrically silent.
Rippling muscle disease
Overlapping Features Also features mechanically induced muscle activity with limited electrical correlate. Distinguished by the rolling wave of contraction on percussion and, in the immune-mediated form, by an inflammatory basis that Brody myopathy does not have.
Canine paradoxical pseudomyotonia
Overlapping Features Included as a cross-species comparator rather than a human differential. In English Cocker and Springer Spaniels an exercise-induced myotonic-like stiffness closely resembling bovine pseudomyotonia and human Brody disease is caused by an SLC7A10 nonsense variant, not by ATP2A1. It is a reminder that the clinical picture of exercise-induced failure of relaxation is reachable through more than one gene.
Show evidence (1 reference)
PMID:36869603 SUPPORT Model Organism
"This disease is characterised by episodes of exercise-induced generalised myotonic-like muscle stiffness, phenotypically similar to congenital pseudomyotonia in cattle, and paramyotonia congenita and Brody disease in people."
States the phenotypic similarity to Brody disease alongside a different causal gene, which is the point of including it.
🐁

Animal Models

3
Bovine congenital pseudomyotonia (ATP2A1 missense, Chianina and Romagnola cattle)
Naturally occurring ATP2A1 pseudomyotonia in beef cattle, presenting as exercise-induced impairment of muscle relaxation. It is the only mammalian model of the disease, since the mouse null is not viable, and it carries most of the translational work including the corrector strategy.
Species
Cattle
Genotype
Biallelic ATP2A1 missense variants
Publication
PMID:23046865
Pathograph links
Proteasomal Degradation of Misfolded SERCA1 recapitulates fidelity: high The bovine missense alleles reproduce the folding-competent, catalytically intact pump that is destroyed before reaching the membrane, and this is the system in which both proteasome inhibition and corrector rescue were demonstrated.
Limitations: The specific alleles are bovine founder variants rather than human ones, and the rescue experiments were performed partly in heterologous cells rather than in mature muscle.
Show evidence (1 reference)
PMID:41206505 SUPPORT Model Organism
"Bovine PMT, despite unconventional, is currently the unique mammalian model of Brody disease"
States the standing of this model, which is what justifies treating bovine results as informative for the human node.
Show evidence (1 reference)
PMID:41206505 SUPPORT Model Organism
"Bovine PMT, despite unconventional, is currently the unique mammalian model of Brody disease"
Supports treating this naturally occurring bovine disease as the mammalian model for Brody myopathy.
accordion zebrafish (atp2a1 mutant)
A behavioural mutant positionally cloned to atp2a1, in which touch-evoked swimming is replaced by bilateral simultaneous contraction. It is the workhorse in vivo model and the system in which slowed cytosolic calcium decay was directly imaged.
Species
Zebrafish
Genotype
atp2a1 (serca1) mutant, accordion allele series
Publication
PMID:15469975
Pathograph links
Impaired Calcium Reuptake into the Sarcoplasmic Reticulum recapitulates fidelity: moderate In vivo imaging shows the slowed cytosolic calcium decay that defines this node, and the defect is shown to be muscle-intrinsic rather than neural.
Limitations: The phenotype is embryonic and larval rather than exertional and adult-onset, the readout is touch-evoked swimming behaviour rather than muscle stiffness, and larval zebrafish lack the fast and slow fibre architecture of adult human limb muscle.
Readouts
Cytosolic calcium transient decay rate
Direction: DECREASED
Interpretation: Slower decay of the cytosolic calcium transient is the direct measurement of impaired reuptake.
Show evidence (1 reference)
PMID:15469975 SUPPORT Model Organism
"cytosolic Ca2+ decay was significantly slower in acc muscle"
The imaging measurement behind this readout.
Show evidence (1 reference)
PMID:15469975 SUPPORT Model Organism
"As SERCA1 mutations in humans lead to Brody disease, an exercise-induced muscle relaxation disorder, zebrafish accordion mutants could be a useful animal model for this condition"
The authors' own statement that this mutant is informative for Brody disease.
Show evidence (1 reference)
PMID:15581877 SUPPORT Model Organism
"The mutation in SERCA, a serine to phenylalanine substitution, is likely to result in compromised protein function"
Independent positional cloning of the same locus, confirming that the behavioural phenotype follows from compromised SERCA function.
Atp2a1-null mouse
Complete targeted disruption of Atp2a1. The mice die within hours of birth from respiratory failure attributed to diaphragm dysfunction, a course with no counterpart in human disease, where respiratory involvement is absent entirely. The model is included because its failure is informative rather than merely inconvenient.
Species
Mouse
Genotype
Atp2a1 homozygous null
Publication
PMID:12556521
Pathograph links
Compensatory Calcium Extrusion and Handling fails to recapitulate fidelity: low The mouse does not reproduce the compensation that makes the human disease survivable. Humans with essentially absent SERCA1 have a mild, non-progressive myopathy with no respiratory involvement, whereas the null mouse dies at birth of diaphragm failure. Whatever carries the calcium load in human muscle is either absent in the mouse or cannot meet the acute respiratory demand of birth.
Limitations: A complete null is a poor genetic match for most human genotypes, which retain residual protein or residual activity, so some of the gap between species may be allele severity rather than species biology. The lethality also prevents the model from ever being used to study the exertional, adult-onset phenotype that defines the human disease.
Show evidence (2 references)
PMID:12556521 SUPPORT Model Organism
"SERCA1-null mice had progressive cyanosis and gasping respiration and succumbed from respiratory failure shortly after birth"
Establishes the neonatal lethal respiratory course that human patients do not have, which is the substance of the failure to recapitulate.
+ 1 more reference
Show evidence (1 reference)
PMID:39273176 SUPPORT Model Organism
"No mouse model nor specific therapies exist for Brody myopathy, which is therefore considered an orphan disease"
Records the consequence for the field: an Atp2a1 knockout mouse exists, but no viable mouse model of Brody myopathy does, which is why the zebrafish and cattle carry the work.
{ }

Source YAML

click to show 
name: Brody Myopathy
creation_date: "2026-08-16T00:00:00Z"
description: >-
  Brody myopathy (Brody disease) is an autosomal recessive disorder of skeletal
  muscle relaxation caused by biallelic loss-of-function variants in ATP2A1,
  which encodes SERCA1, the sarcoplasmic reticulum calcium pump of fast-twitch
  fibres. SERCA1 is not an accessory to relaxation; in type II fibres it is
  essentially the whole of the relaxation machinery, clearing cytosolic calcium
  back into the sarcoplasmic reticulum after each contraction. When it is
  missing, calcium lingers in the cytosol, troponin C stays saturated, and
  cross-bridges keep cycling, so the muscle contracts normally but cannot let
  go. The result is exercise-induced stiffness of the limbs and eyelids that
  builds during activity and eases with rest, worsens in the cold, and is
  accompanied by delayed relaxation after repeated contraction.

  The defining diagnostic feature follows directly from the mechanism. Because
  the fault is downstream of the sarcolemma, the contracture is electrically
  silent: needle EMG records nothing while the muscle is stiff. That silence is
  what separates Brody myopathy from the myotonias it is mistaken for, and
  myotonia, percussion myotonia, and myotonic discharges are all curated
  exclusions in this disease rather than merely absent findings.

  Two features make the entry mechanistically interesting beyond the core chain.
  First, the disease is far milder than it should be: mice lacking SERCA1 die at
  birth of diaphragm failure, while humans with essentially absent SERCA1 have a
  mild, non-progressive myopathy, an athletic build, and no respiratory
  involvement at all. Something compensates, and what that something is remains
  genuinely unsettled, with the two leading candidates recorded here as competing
  hypotheses rather than a single chain. Second, a subset of missense alleles
  produce a pump that folds badly but still works, and is destroyed by the
  ubiquitin-proteasome system before it ever reaches the sarcoplasmic reticulum
  membrane. Those alleles are in principle rescuable by stabilising the protein
  through quality control, which is the basis of the CFTR-corrector strategy now
  being tested in cattle.
category: Mendelian
disease_term:
  preferred_term: Brody Myopathy
  term:
    id: MONDO:0010977
    label: Brody myopathy
synonyms:
- Brody disease
- SERCA1 deficiency
- ATP2A1-related myopathy
- Sarcoplasmic reticulum calcium ATPase deficiency
notes: >-
  Scope. This entry curates Brody DISEASE, meaning reduced SERCA activity
  together with identified biallelic ATP2A1 variants. The literature separates
  this from Brody SYNDROME, a clinically and biochemically similar picture in
  patients without ATP2A1 variants, which remains genetically unsolved and in
  which myalgia and daily-life impact are reported more often. MONDO folds
  "Brody disease" into MONDO:0010977 as a synonym and provides no separate term
  for the gene-negative group, so the distinction is recorded here and in
  differential_diagnoses rather than as a second disease term or a subtype.

  Frequencies quoted in this entry come from a single international cohort of 40
  patients and one cross-sectional study of 17, not from a population. There is
  no registry, no natural-history study with structured longitudinal data, and no
  EHR-derived cohort. Percentages should be read as cohort proportions.

  Not curated here: a quantitative SERCA-activity reference interval that the
  source deep-research report attributed to PMID:41938373, and a Chianina
  founder-variant citation attributed to PMID:18786632. Neither identifier
  resolves to a record, and both were flagged as probable confabulations by the
  report's own reference validation. The underlying claims may well be true, but
  they are not curated on citations that do not exist.
pathophysiology:
- name: Biallelic ATP2A1 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Recessive loss-of-function variants on both ATP2A1 alleles. Two mechanistic
    routes converge on the same deficit: truncating, splice, and deletion alleles
    yield little or no SERCA1 protein, while a subset of missense alleles yield a
    protein that folds badly but retains catalytic activity. The distinction is
    not academic, because only the second group is addressable by strategies that
    stabilise the protein through quality control.
  molecular_functions:
  - preferred_term: SERCA1 P-type calcium transporter activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0005388
      label: P-type calcium transporter activity
  evidence:
  - reference: PMID:8841193
    reference_title: Mutations in the gene-encoding SERCA1, the fast-twitch skeletal muscle sarcoplasmic reticulum Ca2+ ATPase, are associated with Brody disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "how have these Brody patients partially compensated for the functional knockout"
    explanation: >-
      The paper that established ATP2A1 as the causal gene, quoted here at the
      point where it frames the functional knockout of SERCA1 in patients.
  downstream:
  - target: Proteasomal Degradation of Misfolded SERCA1
    causal_link_type: DIRECT
    description: >-
      The missense route specifically. A protein that misfolds is recognised and
      destroyed rather than trafficked.
  - target: Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
    causal_link_type: DIRECT
    description: >-
      The truncating, splice, and deletion route, where little or no protein is
      made in the first place.
- name: Proteasomal Degradation of Misfolded SERCA1
  biological_scale: MOLECULAR
  description: >-
    For missense alleles, the mutant pump is corrupted in folding but not in
    catalysis. The ubiquitin-proteasome system recognises the misfolded protein
    and strips it out before it reaches the sarcoplasmic reticulum membrane, so
    the fibre loses a pump that would have worked had it arrived. Proteasome
    inhibition restores both the expression level and the membrane localisation
    of the mutant, and the rescued protein handles calcium like wild type. This
    node is the therapeutic vulnerability behind the corrector strategy.
  biological_processes:
  - preferred_term: proteasome-mediated degradation of misfolded SERCA1
    modifier: INCREASED
    term:
      id: GO:0043161
      label: proteasome-mediated ubiquitin-dependent protein catabolic process
  evidence:
  - reference: PMID:25288803
    reference_title: Inhibition of ubiquitin proteasome system rescues the defective sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1) protein causing Chianina cattle pseudomyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the mutation generates a protein most likely corrupted in proper folding but not in catalytic activity"
    explanation: >-
      States the folding-versus-catalysis distinction that defines this node.
      Tagged MODEL_ORGANISM because the publication studies Chianina cattle
      pseudomyotonia together with a heterologous cell model, not human patients.
  - reference: PMID:25288803
    reference_title: Inhibition of ubiquitin proteasome system rescues the defective sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1) protein causing Chianina cattle pseudomyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The treatment with MG132, an inhibitor of ubiquitin proteasome system, rescues the expression level and membrane localization of the SERCA1 mutant in a heterologous cellular model."
    explanation: >-
      Demonstrates that blocking the degradation restores both abundance and
      correct localisation, which is what makes this node druggable in principle.
  downstream:
  - target: Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
    causal_link_type: DIRECT
    description: >-
      Degradation before trafficking is completed produces the same end state as
      failure to synthesise the protein: too few pumps in the membrane.
- name: Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
  biological_scale: MOLECULAR
  description: >-
    The convergence point of both allelic routes. Fewer functional calcium pumps
    sit in the sarcoplasmic reticulum membrane of fast-twitch fibres, so the
    tissue's total calcium-ATPase activity falls. The reduction is selective for
    SERCA1 rather than a general loss of sarcoplasmic reticulum protein.
  cellular_components:
  - preferred_term: sarcoplasmic reticulum membrane
    term:
      id: GO:0033017
      label: sarcoplasmic reticulum membrane
  molecular_functions:
  - preferred_term: sarcoplasmic reticulum calcium ATPase activity
    modifier: DECREASED
    term:
      id: GO:0005388
      label: P-type calcium transporter activity
  evidence:
  - reference: PMID:26482047
    reference_title: Fast-twitch skeletal muscle fiber adaptation to SERCA1 deficiency in a Dutch Improved Red and White calf pseudomyotonia case.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The reduced expression of SERCA1 is selective and not compensated by the SERCA2 isoform."
    explanation: >-
      Establishes that the protein loss is selective for SERCA1. The second half
      of the sentence is also the evidence against isoform compensation and is
      used again on that hypothesis.
  - reference: PMID:20142766
    reference_title: "Brody disease: insights into biochemical features of SERCA1 and identification of a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ultrastructural examination revealed dilatation of lateral cisternae and proliferation of tubular elements of the sarcoplasmic reticulum."
    explanation: >-
      Human biopsy ultrastructure showing that the sarcoplasmic reticulum itself
      is structurally remodelled where the pump is deficient.
  downstream:
  - target: Impaired Calcium Reuptake into the Sarcoplasmic Reticulum
    causal_link_type: DIRECT
    description: >-
      Fewer pumps means less calcium moved per unit time back into the store.
- name: Impaired Calcium Reuptake into the Sarcoplasmic Reticulum
  biological_scale: CELLULAR
  description: >-
    The functional consequence of pump loss. Calcium released to trigger
    contraction is cleared from the cytosol too slowly, because in fast-twitch
    fibres SERCA1 is the dominant route by which that clearance happens. Calcium
    release itself is intact; it is only the return leg of the cycle that fails.
  biological_processes:
  - preferred_term: calcium ion import into sarcoplasmic reticulum
    modifier: DECREASED
    term:
      id: GO:1990036
      label: calcium ion import into sarcoplasmic reticulum
  evidence:
  - reference: PMID:15469975
    reference_title: accordion, a zebrafish behavioral mutant, has a muscle relaxation defect due to a mutation in the ATPase Ca2+ pump SERCA1.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "cytosolic Ca2+ decay was significantly slower in acc muscle"
    explanation: >-
      Direct in vivo imaging of the slowed calcium transient in the zebrafish
      SERCA1 mutant, which is the measurement this node asserts.
  downstream:
  - target: Prolonged Cytosolic Calcium Elevation
    causal_link_type: DIRECT
    description: >-
      Slower removal leaves calcium in the cytosol for longer after each
      contraction.
  - target: Compensatory Calcium Extrusion and Handling
    causal_link_type: DIRECT
    description: >-
      The same rise in cytosolic calcium that causes the disease also recruits
      alternative removal mechanisms, which is the branch that appears to make
      the human disease survivable.
- name: Prolonged Cytosolic Calcium Elevation
  biological_scale: CELLULAR
  description: >-
    Cytosolic free calcium stays elevated after each contraction instead of
    falling promptly. This is the proximate cause of every downstream feature,
    and it is also the point of contact with malignant hyperthermia, which
    arrives at the same elevated myoplasmic calcium by a different route.
  biological_processes:
  - preferred_term: intracellular calcium ion homeostasis
    modifier: DECREASED
    term:
      id: GO:0006874
      label: intracellular calcium ion homeostasis
  evidence:
  - reference: PMID:25614869
    reference_title: Exome analysis identifies Brody myopathy in a family diagnosed with malignant hyperthermia susceptibility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a feature common to both conditions is elevated myoplasmic Ca(2+) content"
    explanation: >-
      Names the elevated myoplasmic calcium shared by Brody myopathy and
      malignant hyperthermia, which is why this node carries the anaesthetic
      hazard downstream.
  downstream:
  - target: Electrically Silent Muscle Contracture
    causal_link_type: DIRECT
    description: >-
      Sustained calcium keeps troponin C saturated and cross-bridges cycling.
  - target: Malignant hyperthermia
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Susceptibility to malignant-hyperthermia-like episodes on exposure to
      triggering anaesthetic agents, reached through the shared myoplasmic
      calcium overload rather than through a ryanodine receptor defect.
- name: Electrically Silent Muscle Contracture
  biological_scale: TISSUE
  description: >-
    Involuntary sustained contraction following voluntary contraction, occurring
    without any electrical activity on needle EMG. The silence is the
    mechanistically important part: the fault lies downstream of the sarcolemma,
    in the calcium-handling machinery, so the membrane is not misbehaving and
    there is nothing for the electrode to record. Every myotonic disorder on the
    differential generates electrical discharges; this one does not.
  biological_processes:
  - preferred_term: relaxation of muscle
    modifier: DECREASED
    term:
      id: GO:0090075
      label: relaxation of muscle
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EMG can reveal silent contractures defined as prolonged involuntary muscle contractions (following voluntary phasic contractions) without electrical activity detected on EMG"
    explanation: >-
      Defines the silent contracture explicitly, including that it follows
      voluntary contraction and produces no electrical activity.
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "EMG is characterized by the presence of silent contractures and absence of myotonic discharges."
    explanation: >-
      States both halves of the discriminator in one sentence: contractures are
      present, myotonic discharges are absent.
  downstream:
  - target: Exercise-induced muscle stiffness
    causal_link_type: DIRECT
    description: >-
      The contracture experienced clinically as stiffness that builds with
      activity.
  - target: Delayed muscle relaxation
    causal_link_type: DIRECT
    description: >-
      The examination finding, elicited by repetitive contraction.
- name: Selective Type II Fibre Involvement
  biological_scale: TISSUE
  description: >-
    SERCA1 is the fast-twitch isoform; slow fibres run SERCA2a from a different
    gene and are therefore spared. This single fact explains the distribution of
    the disease: the muscles that stiffen are fast-twitch-rich, which is why
    eyelid closure through orbicularis oculi is affected in roughly two thirds of
    patients while cardiac muscle, running SERCA2a, is entirely uninvolved. The
    biopsy correlate is selective type II fibre atrophy without myonecrosis.
  cell_types:
  - preferred_term: type II skeletal muscle fibre
    term:
      id: CL:0002212
      label: type II muscle cell
  evidence:
  - reference: PMID:25614869
    reference_title: Exome analysis identifies Brody myopathy in a family diagnosed with malignant hyperthermia susceptibility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "encoding the sarco(endo)plasmic reticulum Ca(2+) ATPase type 1 (SERCA1), a calcium pump, expressed in fast-twitch muscles"
    explanation: >-
      States the fast-twitch restriction of SERCA1 expression that produces the
      fibre-type selectivity of the disease.
  downstream:
  - target: Exercise-induced muscle stiffness
    causal_link_type: DIRECT
    description: >-
      Restricting the deficit to fast-twitch fibres is what makes the stiffness
      exertional and distributed as it is.
- name: Compensatory Calcium Extrusion and Handling
  biological_scale: CELLULAR
  description: >-
    Alternative calcium-removal mechanisms recruited in the face of SERCA1
    deficiency, which appear to be why the human disease is mild rather than
    lethal. Candidate contributors include the sarcolemmal calcium extrusion pump
    (PMCA), the sodium-calcium exchanger, mitochondrial uptake, and upregulation
    of the SERCA2 isoform. Which of these actually carries the load in human
    muscle is unresolved, and the two leading candidates are recorded as
    competing hypotheses rather than as a settled chain. The branch is included
    in the pathograph because it is load-bearing for prognosis: without it, the
    expectation from the mouse null would be neonatal death.
  biological_processes:
  - preferred_term: calcium ion transmembrane transport
    modifier: INCREASED
    term:
      id: GO:0070588
      label: calcium ion transmembrane transport
  evidence:
  - reference: PMID:26482047
    reference_title: Fast-twitch skeletal muscle fiber adaptation to SERCA1 deficiency in a Dutch Improved Red and White calf pseudomyotonia case.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Calcium removal mechanisms, operating in muscle fibers as compensatory response aimed at lowering excessive cytoplasmic calcium concentration caused by SERCA1 deficiency, could explain the difference in severity of clinical signs."
    explanation: >-
      States the compensation principle and links it explicitly to severity,
      which is the reason this branch is modelled rather than left as prose. The
      authors frame it as a candidate explanation rather than a demonstrated one.
mechanistic_hypotheses:
- hypothesis_group_id: pmca_extrusion_compensation
  hypothesis_label: Sarcolemmal calcium extrusion compensates for SERCA1 loss
  status: EMERGING
  description: >-
    Holds that the calcium load left by the missing sarcoplasmic reticulum pump
    is handled principally by exporting calcium across the sarcolemma, via the
    plasma-membrane calcium ATPase and related extrusion mechanisms, rather than
    by an alternative sarcoplasmic reticulum pump. The bovine work supports this
    directly, reporting increased sarcolemmal extrusion pump expression in the
    same muscle in which SERCA2 compensation was excluded.
  evidence:
  - reference: PMID:26482047
    reference_title: Fast-twitch skeletal muscle fiber adaptation to SERCA1 deficiency in a Dutch Improved Red and White calf pseudomyotonia case.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "an increased expression of sarcolemmal calcium extrusion pump"
    explanation: >-
      The positive finding for this hypothesis, reported in the same animal in
      which SERCA2 compensation was not observed.
  notes: >-
    EMERGING rather than CANONICAL because the direct evidence is bovine and from
    a single case, and because no human muscle study has measured extrusion-pump
    activity in Brody myopathy.
- hypothesis_group_id: serca2_isoform_compensation
  hypothesis_label: SERCA2 isoform upregulation compensates for SERCA1 loss
  status: ALTERNATIVE
  description: >-
    Holds that the SERCA2 isoform is upregulated, including ectopically in type
    II fibres, and takes over part of the calcium reuptake that SERCA1 can no
    longer perform. This was the first proposed explanation for the mildness of
    the human disease and rests on a single family in which muscle showed absent
    SERCA1 with elevated SERCA2. It is recorded as ALTERNATIVE rather than
    discarded because that observation is real, but the larger cohort and the
    bovine work both failed to reproduce it.
  evidence:
  - reference: PMID:25614869
    reference_title: Exome analysis identifies Brody myopathy in a family diagnosed with malignant hyperthermia susceptibility.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Analyses of affected muscles showed the absence of SERCA1, but SERCA2 upregulation in slow and fast myofibers, suggesting a compensatory mechanism that partially restores the diminished Ca(2+) transport in Brody myopathy."
    explanation: >-
      The originating observation, in human muscle, which is the whole positive
      case for this hypothesis.
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "SERCA2 staining was normal in all samples."
    explanation: >-
      The international cohort found no SERCA2 upregulation in its own biopsies,
      directly contradicting the hypothesis in human muscle.
  - reference: PMID:26482047
    reference_title: Fast-twitch skeletal muscle fiber adaptation to SERCA1 deficiency in a Dutch Improved Red and White calf pseudomyotonia case.
    supports: REFUTE
    evidence_source: MODEL_ORGANISM
    snippet: "The reduced expression of SERCA1 is selective and not compensated by the SERCA2 isoform."
    explanation: >-
      Independent contradiction from the bovine model, in which the same question
      was asked and answered negatively.
  notes: >-
    The conflict is not resolvable from the published record. The supporting and
    refuting studies used immunohistochemistry on different patients, and the
    cohort separately reports that of eight biopsies examined, seven showed
    normal SERCA2 expression and one showed increased expression, so the positive
    finding may be real but uncommon rather than wrong.
phenotypes:
- name: Exercise-induced muscle stiffness
  category: Neuromuscular
  description: >-
    The cardinal feature, present in every patient in the international cohort.
    Stiffness builds during exertion and eases within minutes of rest, involves
    the limbs almost universally and the eyelids in roughly two thirds, and is
    worsened by cold.
  phenotype_term:
    preferred_term: Exercise-induced muscle stiffness
    term:
      id: HP:0008967
      label: Exercise-induced muscle stiffness
    onset:
      onset_category: CHILDHOOD
      notes: >-
        Onset is in childhood in the large majority. Recorded as a descriptor
        qualifier rather than as a separate phenotype, since HPO onset terms sit
        outside the phenotypic-abnormality branch the PhenotypeTerm enum draws
        from.
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids."
    explanation: >-
      Names this as the main feature and gives the limb and eyelid distribution.
      The VERY_FREQUENT band reflects the cohort, in which limb stiffness was
      present in all 40 patients.
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Onset begins in childhood and there was no or only mild progression of symptoms over time."
    explanation: >-
      Supports the childhood onset recorded on this descriptor, and the absence of
      meaningful progression thereafter, which together are the prognostic core of
      the disease.
- name: Delayed muscle relaxation
  category: Neuromuscular
  description: >-
    The key examination finding, elicited by asking the patient to contract
    repeatedly and observing that each relaxation takes longer than the last.
    Deliberately left without an ontology binding. HPO has no term for delayed
    relaxation as a sign; the nearest candidates are Muscle stiffness, which
    duplicates the exertional stiffness phenotype already recorded here, and
    Myotonia, which is a curated exclusion in this disease. Binding this sign to
    a myotonia term would encode precisely the misdiagnosis that the electrically
    silent contracture exists to rule out, so the phenotype is carried as free
    text until a suitable term exists.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The key finding at physical examination was delayed relaxation after repetitive contractions."
    explanation: >-
      Identifies delayed relaxation after repetitive contraction as the key
      physical sign.
- name: Malignant hyperthermia
  category: Anaesthetic
  description: >-
    Episodes resembling malignant hyperthermia occurred in four of forty patients
    in the international cohort. The link is the shared elevation of myoplasmic
    calcium rather than a ryanodine receptor defect, and it is the single most
    actionable fact in the entry because it changes anaesthetic management.
  phenotype_term:
    preferred_term: Malignant hyperthermia
    term:
      id: HP:0002047
      label: Malignant hyperthermia
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Four patients had episodes resembling malignant hyperthermia."
    explanation: >-
      Four of forty is 10 per cent, which falls in the OCCASIONAL band of 5 to 29
      per cent.
- name: Preserved muscle strength without atrophy
  category: Neuromuscular
  description: >-
    A curated negative, and diagnostically load-bearing. Despite lifelong
    symptoms, patients do not lose bulk or strength, and some are conspicuously
    athletic in build. Reported weakness in about a third of patients is
    generally misperceived stiffness rather than true weakness.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "no atrophy was seen, muscle strength was generally preserved, and some patients had a remarkable athletic build"
    explanation: >-
      States the absence of atrophy, the preservation of strength, and the
      athletic build in one sentence.
- name: Absence of myotonia and myotonic discharges
  category: Neuromuscular
  description: >-
    Curated exclusion. Myotonic discharges are absent on EMG, and that absence
    beside a silent contracture is what distinguishes Brody myopathy from the
    myotonic disorders it is routinely mistaken for. This is a negative finding
    with positive diagnostic value, and the cohort turns it into an explicit
    diagnostic step rather than leaving it as a description.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, when EMG shows no myotonic discharges in patients clinically suspected of having a myotonic disorder, provocation of possible silent contractures is recommended by performing rapid contractions during EMG."
    explanation: >-
      Turns the absence of myotonic discharges into an actionable diagnostic
      step, which is the reason the exclusion is curated rather than omitted.
- name: Elevated circulating creatine kinase concentration
  category: Laboratory
  description: >-
    Creatine kinase is normal or only mildly elevated. The modest scale of the
    elevation is itself informative, since it is consistent with the near-absence
    of myonecrosis in this disease and argues against the necrotising myopathies
    on the differential.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase concentration
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Creatine kinase was normal or mildly elevated"
    explanation: >-
      Records that creatine kinase is normal or only mildly raised, which is the
      claim this phenotype makes.
- name: Myalgia
  category: Neuromuscular
  description: >-
    Muscle pain, reported by a majority of patients in the international cohort and
    often worsened by cold exposure alongside the stiffness.
  phenotype_term:
    preferred_term: Myalgia
    term:
      id: HP:0003326
      label: Myalgia
  frequency: FREQUENT
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Furthermore, myalgia and muscle cramps are described, which may worsen upon exposure to cold temperatures"
    explanation: >-
      Names myalgia among the reported features and records the cold sensitivity
      that accompanies it. The FREQUENT band reflects the cohort proportion of
      20/34.
- name: Exercise-induced muscle cramps
  category: Neuromuscular
  description: >-
    Involuntary painful sustained contractures at rest or during exercise, reported
    by roughly half the cohort. Note the cohort defines cramps in terms of
    sustained contracture, which is the same physical event as the disease's core
    lesion rather than an unrelated symptom.
  phenotype_term:
    preferred_term: Exercise-induced muscle cramps
    term:
      id: HP:0003710
      label: Exercise-induced muscle cramps
  frequency: FREQUENT
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients variably reported muscle cramps (defined as involuntary and painful sustained muscle contractures) at rest or during exercise (18/34)."
    explanation: >-
      Gives the cohort proportion, 18 of 34, which falls in the FREQUENT band, and
      the authors' definition of cramps as sustained contracture.
genetic:
- name: ATP2A1
  gene_term:
    preferred_term: ATP2A1
    term:
      id: hgnc:811
      label: ATP2A1
  relationship_type: CAUSATIVE
  inheritance:
  - name: Autosomal recessive
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  notes: >-
    Encodes SERCA1, the sarcoplasmic reticulum calcium ATPase of fast-twitch
    skeletal muscle. Biallelic loss-of-function variants cause the disease.
    Missense alleles that impair folding while preserving catalytic activity form
    a therapeutically distinct group, since only that group can be rescued by
    stabilising the protein through quality control; nonsense, frameshift,
    splice, and deletion alleles cannot be.
  evidence:
  - reference: PMID:8841193
    reference_title: Mutations in the gene-encoding SERCA1, the fast-twitch skeletal muscle sarcoplasmic reticulum Ca2+ ATPase, are associated with Brody disease.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "how have these Brody patients partially compensated for the functional knockout"
    explanation: >-
      The study that associated SERCA1 mutations with Brody disease, quoted at
      its statement of the functional knockout in patients.
biochemical:
- name: Sarcoplasmic reticulum calcium ATPase activity
  notes: >-
    SERCA activity measured in muscle homogenate is reduced, and western blot shows
    decreased or absent SERCA1 protein. Together these are the confirmatory
    functional assays of the disease, and their real value is in adjudicating novel
    variants: a previously unreported ATP2A1 change is supported as pathogenic when
    activity and protein are shown to be reduced. Recorded qualitatively only. A
    numeric reference interval circulating for this assay traces to an identifier
    that does not resolve, and no reference_ranges block is curated on that basis.
  presence: DECREASED
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity was reduced and western blot analysis showed decreased or absent SERCA1 protein."
    explanation: >-
      States both assay results in patients, which is exactly what this biomarker
      record asserts.
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "SERCA activity measurement and SERCA1 western blot can assist in proving the pathogenicity of novel ATP2A1 mutations"
    explanation: >-
      Gives the assays their clinical purpose, which is variant adjudication rather
      than primary diagnosis.
histopathology:
- name: Selective type II fibre atrophy with increased fibre size variability
  description: >-
    Systematic re-evaluation of biopsies showed type II fibre atrophy, increased
    variability of fibre size, and increased internal nuclei. The findings are mild
    and non-specific taken individually; what makes them useful is the company they
    keep, in particular their appearance alongside preserved strength and an absence
    of necrosis.
  diagnostic: true
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Systematic re-evaluation of the biopsy reports showed fibre type II atrophy, increased fibre size variability, and an increased number of internal nuclei."
    explanation: >-
      Enumerates all three biopsy findings from a systematic re-review rather than
      from individual case impressions.
- name: Absence of myonecrosis
  description: >-
    A curated negative. Muscle necrosis is essentially absent, found in a single
    biopsy across the international cohort. This is consistent with the modest
    creatine kinase elevation and separates the disease from the necrotising
    myopathies: the muscle is failing to relax, not dying.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Discrete necrosis was found in only one biopsy (Patient L18)."
    explanation: >-
      One biopsy out of the whole cohort, which is what makes absence of necrosis a
      usable negative finding rather than merely an unremarked one.
diagnosis:
- name: Electromyography showing silent contractures without myotonic discharges
  description: >-
    The pivotal diagnostic observation, and the reason the disease is so often
    misdiagnosed. Needle EMG during the stiffness records nothing, because the fault
    lies downstream of the sarcolemma. The cohort turns this into an active
    manoeuvre rather than a passive finding: when a patient looks myotonic but shows
    no myotonic discharges, provoke contractures with rapid repeated contraction
    during the study instead of stopping at the negative result.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, when EMG shows no myotonic discharges in patients clinically suspected of having a myotonic disorder, provocation of possible silent contractures is recommended by performing rapid contractions during EMG."
    explanation: >-
      Converts the absence of myotonic discharges into a positive diagnostic step,
      which is what makes this a diagnostic recommendation rather than a
      description.
- name: ATP2A1 sequencing or myopathy gene panel
  description: >-
    Molecular confirmation, recommended once delayed relaxation is present on
    examination and myotonic discharges have been excluded electrophysiologically.
    The order matters: the clinical and electrophysiological findings select who
    should be sequenced.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we recommend direct sequencing of the ATP2A1 gene or next generation sequencing with a myopathy panel"
    explanation: >-
      The testing recommendation, quoted with the clinical preconditions that
      precede it in the same sentence.
- name: SERCA1 immunohistochemistry (inadequate in isolation)
  description: >-
    Recorded specifically as a false-negative trap rather than as a recommended
    test. Immunostaining for loss of SERCA1a protein is not adequate for diagnosis
    on its own, so a normal-appearing stain does not exclude the disease and should
    not stop the diagnostic sequence. This is curated because a negative
    immunostain is exactly the point at which a workup tends to be abandoned.
  evidence:
  - reference: PMID:10914677
    reference_title: "The mutation of Pro789 to Leu reduces the activity of the fast-twitch skeletal muscle sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA1) and is associated with Brody disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "immunostaining of skeletal muscle to detect the loss of SERCA1a protein is not adequate for the diagnosis"
    explanation: >-
      States plainly that immunostaining alone is inadequate, which is the caution
      this record exists to carry.
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic ATP2A1 variants are required. Heterozygous carriers are
    unaffected.
treatments:
- name: Trigger-Free Anaesthesia and Malignant Hyperthermia Precautions
  description: >-
    The highest-value intervention in the disease, and the one that changes
    outcomes rather than symptoms. Patients are managed as
    malignant-hyperthermia-susceptible: volatile anaesthetics and succinylcholine
    are avoided in favour of a total intravenous technique, with core temperature
    monitoring. This follows from the shared myoplasmic calcium overload rather
    than from a ryanodine receptor defect.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Prolonged Cytosolic Calcium Elevation
    treatment_effect: MODULATES
    description: >-
      Avoidance rather than pharmacology: the measure prevents a trigger from
      compounding an existing calcium-handling deficit, rather than correcting
      the deficit itself.
    evidence:
    - reference: PMID:32040565
      reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended"
      explanation: >-
        States both the risk and the recommendation for perioperative measures.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended"
    explanation: >-
      The recommendation as stated by the international cohort.
- name: Symptomatic Pharmacotherapy
  description: >-
    Calcium channel blockers, dantrolene, mexiletine, carbamazepine, and others
    have been tried. The honest summary from the largest cohort is that
    symptomatic treatment was mostly ineffective or produced unacceptable side
    effects, with only a small minority achieving durable control. Verapamil was
    the best performer in that cohort but still helped a minority.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Symptomatic treatment was mostly ineffective or produced unacceptable side effects."
    explanation: >-
      Refutes a general claim of symptomatic benefit. Recorded as REFUTE rather
      than omitted because a reader needs to know that the obvious drug options
      have been tried and largely failed.
- name: Dantrolene
  description: >-
    A ryanodine receptor inhibitor, mechanistically coherent here because it
    reduces calcium release into the cytosol, attacking the same overload from
    the opposite direction when reuptake cannot be restored. The evidence points
    both ways and is curated that way: dantrolene was ineffective or poorly
    tolerated in the cohort, while a single later case report describes clear
    benefit.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: dantrolene
      term:
        id: CHEBI:4317
        label: dantrolene
  target_mechanisms:
  - target: Prolonged Cytosolic Calcium Elevation
    treatment_effect: MODULATES
    description: >-
      Reduces ryanodine-receptor-mediated calcium release, lowering the cytosolic
      calcium load that the deficient pump cannot clear.
    evidence:
    - reference: PMID:41926432
      reference_title: "Rare Brody myopathy: A case report."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Treatment with dantrolene sodium resulted in marked clinical improvement."
      explanation: >-
        PARTIAL because this is a single case, and because the largest cohort
        reports the opposite experience with the same drug.
  evidence:
  - reference: PMID:41926432
    reference_title: "Rare Brody myopathy: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Treatment with dantrolene sodium resulted in marked clinical improvement."
    explanation: >-
      A single reported responder. Graded PARTIAL rather than SUPPORT because one
      case cannot establish efficacy against a cohort reporting the drug as
      ineffective or poorly tolerated.
  notes: >-
    The contradiction between the cohort experience and this case report is left
    standing rather than resolved. Both are curated so that a reader meets the
    disagreement rather than one side of it.
- name: CFTR Correctors (Investigational)
  description: >-
    A repurposing strategy aimed at the folding defect rather than the symptoms.
    Small molecules developed to chaperone misfolded CFTR through quality control
    also rescue misfolded SERCA1, restoring pump abundance at the sarcoplasmic
    reticulum membrane. The corrector C17 was effective in vitro and in cattle,
    whereas the licensed cystic fibrosis correctors lumacaftor and tezacaftor
    were not efficient. This has not been tested in humans.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Proteasomal Degradation of Misfolded SERCA1
    treatment_effect: INHIBITS
    description: >-
      Stabilises the misfolded pump so that it escapes degradation and reaches
      the membrane, addressing the node rather than its consequences.
    evidence:
    - reference: PMID:41206505
      reference_title: "CFTR corrector C17 rescues defective SERCA1 in bovine pseudomyotonia: a potential therapy for Brody myopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "CFTR correctors, particularly C17, successfully rescue SERCA1 mutants both in vitro and in vivo models"
      explanation: >-
        Demonstrates rescue of the mutant pump. Tagged MODEL_ORGANISM because the
        in vivo work is in cattle.
  evidence:
  - reference: PMID:41206505
    reference_title: "CFTR corrector C17 rescues defective SERCA1 in bovine pseudomyotonia: a potential therapy for Brody myopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "may be a potential innovative pharmacological approach addressing Brody patients in which mutated SERCA1 retains its activity"
    explanation: >-
      PARTIAL because the authors themselves frame this as potential rather than
      established, and because the quoted sentence carries the decisive
      restriction: the approach can only help patients whose mutant pump retains
      catalytic activity.
  notes: >-
    The allele restriction is the most important qualifier on this approach and
    is easy to lose. Correctors can only rescue a protein that exists and works;
    they offer nothing to patients whose alleles are nonsense, frameshift,
    splice, or deletion variants producing no protein at all. Any future clinical
    application requires genotype stratification.
- name: Physical Therapy and Activity Pacing
  description: >-
    Warm-up strategies, activity pacing, and avoidance of cold during exertion.
    Used pragmatically. No trial evidence exists, and none is claimed here.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
- name: Genetic Counselling
  description: >-
    Autosomal recessive recurrence risk, cascade testing of relatives, and
    critically, communication of anaesthetic risk to family members who may carry
    the same genotype.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
animal_models:
- name: Bovine congenital pseudomyotonia (ATP2A1 missense, Chianina and Romagnola cattle)
  species: Cattle
  genotype: Biallelic ATP2A1 missense variants
  publication: PMID:23046865
  description: >-
    Naturally occurring ATP2A1 pseudomyotonia in beef cattle, presenting as
    exercise-induced impairment of muscle relaxation. It is the only mammalian
    model of the disease, since the mouse null is not viable, and it carries most
    of the translational work including the corrector strategy.
  modeled_mechanisms:
  - target: Proteasomal Degradation of Misfolded SERCA1
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The bovine missense alleles reproduce the folding-competent, catalytically
      intact pump that is destroyed before reaching the membrane, and this is the
      system in which both proteasome inhibition and corrector rescue were
      demonstrated.
    limitations: >-
      The specific alleles are bovine founder variants rather than human ones, and
      the rescue experiments were performed partly in heterologous cells rather
      than in mature muscle.
    evidence:
    - reference: PMID:41206505
      reference_title: "CFTR corrector C17 rescues defective SERCA1 in bovine pseudomyotonia: a potential therapy for Brody myopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Bovine PMT, despite unconventional, is currently the unique mammalian model of Brody disease"
      explanation: >-
        States the standing of this model, which is what justifies treating
        bovine results as informative for the human node.
  evidence:
  - reference: PMID:41206505
    reference_title: "CFTR corrector C17 rescues defective SERCA1 in bovine pseudomyotonia: a potential therapy for Brody myopathy."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Bovine PMT, despite unconventional, is currently the unique mammalian model of Brody disease"
    explanation: >-
      Supports treating this naturally occurring bovine disease as the mammalian
      model for Brody myopathy.
- name: accordion zebrafish (atp2a1 mutant)
  species: Zebrafish
  genotype: atp2a1 (serca1) mutant, accordion allele series
  publication: PMID:15469975
  description: >-
    A behavioural mutant positionally cloned to atp2a1, in which touch-evoked
    swimming is replaced by bilateral simultaneous contraction. It is the
    workhorse in vivo model and the system in which slowed cytosolic calcium
    decay was directly imaged.
  modeled_mechanisms:
  - target: Impaired Calcium Reuptake into the Sarcoplasmic Reticulum
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      In vivo imaging shows the slowed cytosolic calcium decay that defines this
      node, and the defect is shown to be muscle-intrinsic rather than neural.
    limitations: >-
      The phenotype is embryonic and larval rather than exertional and
      adult-onset, the readout is touch-evoked swimming behaviour rather than
      muscle stiffness, and larval zebrafish lack the fast and slow fibre
      architecture of adult human limb muscle.
    readouts:
    - name: Cytosolic calcium transient decay rate
      target: Impaired Calcium Reuptake into the Sarcoplasmic Reticulum
      direction: DECREASED
      interpretation: >-
        Slower decay of the cytosolic calcium transient is the direct measurement
        of impaired reuptake.
      evidence:
      - reference: PMID:15469975
        reference_title: accordion, a zebrafish behavioral mutant, has a muscle relaxation defect due to a mutation in the ATPase Ca2+ pump SERCA1.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "cytosolic Ca2+ decay was significantly slower in acc muscle"
        explanation: >-
          The imaging measurement behind this readout.
    evidence:
    - reference: PMID:15469975
      reference_title: accordion, a zebrafish behavioral mutant, has a muscle relaxation defect due to a mutation in the ATPase Ca2+ pump SERCA1.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "As SERCA1 mutations in humans lead to Brody disease, an exercise-induced muscle relaxation disorder, zebrafish accordion mutants could be a useful animal model for this condition"
      explanation: >-
        The authors' own statement that this mutant is informative for Brody
        disease.
  evidence:
  - reference: PMID:15581877
    reference_title: A mutation in serca underlies motility dysfunction in accordion zebrafish.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The mutation in SERCA, a serine to phenylalanine substitution, is likely to result in compromised protein function"
    explanation: >-
      Independent positional cloning of the same locus, confirming that the
      behavioural phenotype follows from compromised SERCA function.
- name: Atp2a1-null mouse
  species: Mouse
  genotype: Atp2a1 homozygous null
  publication: PMID:12556521
  description: >-
    Complete targeted disruption of Atp2a1. The mice die within hours of birth
    from respiratory failure attributed to diaphragm dysfunction, a course with no
    counterpart in human disease, where respiratory involvement is absent
    entirely. The model is included because its failure is informative rather than
    merely inconvenient.
  modeled_mechanisms:
  - target: Compensatory Calcium Extrusion and Handling
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      The mouse does not reproduce the compensation that makes the human disease
      survivable. Humans with essentially absent SERCA1 have a mild,
      non-progressive myopathy with no respiratory involvement, whereas the null
      mouse dies at birth of diaphragm failure. Whatever carries the calcium load
      in human muscle is either absent in the mouse or cannot meet the acute
      respiratory demand of birth.
    limitations: >-
      A complete null is a poor genetic match for most human genotypes, which
      retain residual protein or residual activity, so some of the gap between
      species may be allele severity rather than species biology. The lethality
      also prevents the model from ever being used to study the exertional,
      adult-onset phenotype that defines the human disease.
    evidence:
    - reference: PMID:12556521
      reference_title: Targeted disruption of the ATP2A1 gene encoding the sarco(endo)plasmic reticulum Ca2+ ATPase isoform 1 (SERCA1) impairs diaphragm function and is lethal in neonatal mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "SERCA1-null mice had progressive cyanosis and gasping respiration and succumbed from respiratory failure shortly after birth"
      explanation: >-
        Establishes the neonatal lethal respiratory course that human patients do
        not have, which is the substance of the failure to recapitulate.
    - reference: PMID:12556521
      reference_title: Targeted disruption of the ATP2A1 gene encoding the sarco(endo)plasmic reticulum Ca2+ ATPase isoform 1 (SERCA1) impairs diaphragm function and is lethal in neonatal mice.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "coupled with the marked increase in contractile function required of the diaphragm muscle to support postnatal respiration, can account for respiratory failure"
      explanation: >-
        Gives the authors' own mechanism for the lethality, the acute respiratory
        load at birth, which is the specific circumstance human patients never
        face in this form.
  evidence:
  - reference: PMID:39273176
    reference_title: The Accordion Zebrafish tq206 Mutant in the Assessment of a Novel Pharmaceutical Approach to Brody Myopathy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "No mouse model nor specific therapies exist for Brody myopathy, which is therefore considered an orphan disease"
    explanation: >-
      Records the consequence for the field: an Atp2a1 knockout mouse exists, but
      no viable mouse model of Brody myopathy does, which is why the zebrafish
      and cattle carry the work.
discussions:
- discussion_id: brody_compensation_mechanism
  prompt: >-
    What actually compensates for SERCA1 loss in human fast-twitch muscle, and
    why is the human disease mild when complete murine SERCA1 loss is lethal?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Compensatory Calcium Extrusion and Handling
  rationale: >-
    This is the central unresolved question of the disease and it is not merely
    academic. The compensation is what determines severity, so understanding it
    would explain the variability between patients and might itself be a
    therapeutic target. Two candidate mechanisms are curated here as competing
    hypotheses. Sarcolemmal calcium extrusion has direct positive evidence but
    only from cattle, and from a single case. SERCA2 isoform upregulation was
    observed in one human family but was not reproduced in the largest human
    cohort or in the bovine model. No human study has measured extrusion pump
    activity, sodium-calcium exchange, or mitochondrial calcium uptake in Brody
    muscle, so the question is open rather than contested at the level of data.
  proposed_experiments:
  - experiment_id: brody_compensation_profiling
    name: Calcium-handling protein profiling in genotyped Brody muscle
    description: >-
      Quantify plasma membrane calcium ATPase, sodium-calcium exchanger,
      mitochondrial calcium uniporter, and SERCA2 protein abundance and activity
      in fast-twitch muscle biopsies from genotyped Brody patients, stratified by
      residual SERCA1 activity, against matched controls. This would establish
      which removal mechanism actually carries the load in human muscle, and
      whether the degree of compensation predicts clinical severity.
  - experiment_id: brody_single_nucleus_rnaseq
    name: Fibre-type-resolved single-nucleus RNA sequencing of Brody muscle
    description: >-
      Single-nucleus RNA sequencing of Brody muscle, resolved by fibre type. The
      mechanism is fibre-type selective, so a fibre-type-resolved expression map
      is the obvious way to detect compensatory programmes running specifically
      in type II nuclei. No such dataset exists.
- discussion_id: brody_mouse_model_mismatch
  prompt: >-
    Does the neonatal lethality of the Atp2a1-null mouse reflect a genuine
    species difference in calcium handling, or an artefact of modelling a
    partial-loss human disease with a complete null?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Compensatory Calcium Extrusion and Handling
  - pathophysiology#Reduced SERCA1 Density at the Sarcoplasmic Reticulum Membrane
  rationale: >-
    Evidence exists in the model and is not in doubt; what is open is its
    translational validity. Complete murine SERCA1 loss kills the animal at birth
    through diaphragm failure, while human patients with severely reduced or
    absent SERCA1 have no respiratory involvement whatsoever and a mild,
    non-progressive limb and eyelid myopathy. Two readings are possible and are
    not mutually exclusive: that human muscle compensates in a way mouse muscle
    cannot, or that most human alleles retain enough residual protein or activity
    that a complete null is simply the wrong comparison. Distinguishing them
    matters, because the first reading makes compensation a therapeutic target
    and the second makes allele severity the dominant variable.
  proposed_experiments:
  - experiment_id: brody_hypomorphic_mouse
    name: Hypomorphic Atp2a1 mouse allele series matched to human residual activity
    description: >-
      Generate a hypomorphic Atp2a1 allele series in mouse, matched to the
      residual activity levels measured in human patients, rather than a complete
      null. This would separate the two readings directly: if graded hypomorphs
      are viable and develop exertional stiffness, the mismatch is about allele
      severity; if they still die of diaphragm failure, it is about species
      biology.
differential_diagnoses:
- name: Brody syndrome (gene-negative)
  description: >-
    Clinically and biochemically similar exercise-induced impairment of
    relaxation with reduced SERCA activity, but without identifiable ATP2A1
    variants. It is genetically unsolved and reported to differ clinically:
    myalgia is more common and the impact on daily life greater than in
    gene-confirmed Brody disease. It is the most important boundary on this
    entry, since a patient can meet the clinical and biochemical description and
    still not belong here.
  evidence:
  - reference: PMID:22704959
    reference_title: "Brody syndrome: a clinically heterogeneous entity distinct from Brody disease: a review of literature and a cross-sectional clinical study in 17 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with Brody syndrome more often report myalgia"
    explanation: >-
      Establishes that the gene-negative group differs clinically rather than
      being an undiagnosed remainder of the same entity.
- name: Myotonia congenita and paramyotonia congenita
  description: >-
    The disorders Brody myopathy is most often mistaken for, since all present
    with exercise-related muscle stiffness. They are distinguished
    electrophysiologically rather than clinically: the myotonias generate
    myotonic discharges on EMG, while the Brody contracture is electrically
    silent.
- name: Rippling muscle disease
  description: >-
    Also features mechanically induced muscle activity with limited electrical
    correlate. Distinguished by the rolling wave of contraction on percussion and,
    in the immune-mediated form, by an inflammatory basis that Brody myopathy
    does not have.
- name: Canine paradoxical pseudomyotonia
  description: >-
    Included as a cross-species comparator rather than a human differential. In
    English Cocker and Springer Spaniels an exercise-induced myotonic-like
    stiffness closely resembling bovine pseudomyotonia and human Brody disease is
    caused by an SLC7A10 nonsense variant, not by ATP2A1. It is a reminder that
    the clinical picture of exercise-induced failure of relaxation is reachable
    through more than one gene.
  evidence:
  - reference: PMID:36869603
    reference_title: The c.126C>A(p.(Cys42Ter)) SLC7A10 nonsense variant is a candidate causative variant for paradoxical pseudomyotonia in English Cocker and Springer Spaniels.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "This disease is characterised by episodes of exercise-induced generalised myotonic-like muscle stiffness, phenotypically similar to congenital pseudomyotonia in cattle, and paramyotonia congenita and Brody disease in people."
    explanation: >-
      States the phenotypic similarity to Brody disease alongside a different
      causal gene, which is the point of including it.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population-based prevalence estimate exists. The largest series assembled
    40 patients internationally, and a separate cross-sectional study covered 17
    patients with the gene-negative syndrome. Recorded as CASES_IN_LITERATURE
    rather than converted to a rate, because dividing a convenience series by a
    world population would manufacture a precision the data do not have.
  evidence:
  - reference: PMID:32040565
    reference_title: "Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids."
    explanation: >-
      The international series of 40 patients, cited here for the scale of the
      assembled literature rather than for a rate.
📚

References & Deep Research

Deep Research

1
Claude Code ▸
Brody Myopathy — Comprehensive Disease Research Report
claude-haiku-4-5-20251001, claude-opus-5[1m] 32 citations 2026-08-16T10:18:58.798689

Brody Myopathy — Comprehensive Disease Research Report

Prepared: 2026-08-16 · Target entity: Brody myopathy / Brody disease · MONDO:0010977 (verified via OLS4)

How to read the citations here. Quotes marked [verbatim] were pulled character-for-character from the PubMed abstract record via NCBI E-utilities and are safe to use as evidence snippet: values. Anything marked [full-text derived] came from reading article body text through a summarizing fetch — those numbers are leads, and need re-verification against the source before they get curated with a snippet. Ontology IDs marked [OAK-verified] were checked against local sqlite:obo:* adapters in this session; everything else is a suggestion to check.

1. Disease Information

What it is

Brody myopathy is an ultra-rare, autosomal recessive skeletal muscle disorder in which the calcium pump that resets fast-twitch muscle after a contraction is broken. Think of a sink with a slow drain: the contraction fills the cytoplasm with calcium just fine, but emptying it back into the sarcoplasmic reticulum takes far too long. Clinically that reads as exercise-induced stiffness and delayed relaxation — a cramp-like tightening that looks exactly like myotonia but is electrically silent on needle EMG. That silence is the diagnostic tell.

It is caused by biallelic pathogenic variants in ATP2A1, encoding SERCA1 (sarco/endoplasmic reticulum Ca²⁺-ATPase, isoform 1), the pump that dominates type II (fast-twitch) fibers.

[verbatim] "Brody disease is an autosomal recessive myopathy characterized by exercise-induced muscle stiffness due to mutations in the ATP2A1 gene." — Molenaar et al., Brain 2020 (PMID:32040565)

[verbatim] "Brody disease is a rare inherited disorder of skeletal muscle function. Symptoms include exercise-induced impairment of skeletal muscle relaxation, stiffness and cramps. Ca2+ uptake and Ca2+ ATPase activities are reduced in the sarcoplasmic reticulum…" — Odermatt et al., Nature Genetics 1996 (PMID:8841193)

First description

Irwin A. Brody, NEJM 1969;281(4):187–192, "Muscle contracture induced by exercise. A syndrome attributable to decreased relaxing factor" (PMID:4239835). No structured abstract exists on this record — do not attempt to snippet-validate against it. The gene link followed 27 years later (Odermatt 1996).

Key identifiers

Resource Identifier
MONDO MONDO:0010977 — "Brody myopathy" (OLS4-verified)
OMIM (disease) 601003 — BRODY DISEASE; BROD
OMIM (gene) 108730 — ATP2A1
Orphanet ORPHA:53347 — Brody myopathy
HGNC hgnc:811 — ATP2A1 [OAK-verified]
UMLS C1832918 (per NIH GTR conditions page)
ICD-10 G71.2 / G72.8 range (metabolic-myopathy bucket; no dedicated code) — verify against the ICD release you target
ICD-11 8C70.Y / 8C7Y range (other specified myopathies) — verify
MeSH No dedicated descriptor; indexed under Muscular Diseases / Muscle Relaxation

Synonyms and naming

  • Brody disease (BROD)
  • Brody myopathy
  • SERCA1 deficiency
  • Sarcoplasmic reticulum Ca²⁺-ATPase deficiency
  • ATP2A1-related myopathy

One naming distinction really matters for curation. The literature separates:

  • Brody disease — reduced SERCA activity with identified biallelic ATP2A1 variants.
  • Brody syndrome — the same clinical/biochemical picture without ATP2A1 variants; genetically unsolved.

[verbatim, partial] "Brody disease is a rare inherited myopathy due to reduced sarcoplasmic reticulum Ca(2+) ATPase (SERCA)1 activity." … "Brody disease presents with an onset in the 1st decade, a generalized pattern of muscle stiffness" … "Patients with Brody syndrome more often report myalgia and experience a considerable impact on daily life." — Voermans et al., Neuromuscul Disord 2012 (PMID:22704959), cross-sectional study of 17 Brody syndrome patients

MONDO folds "Brody disease" in as a synonym of MONDO:0010977. If you want the syndrome/disease split represented, do it with a subtype or a lump/split note rather than a second MONDO term.

Data provenance

Everything below is disease-level aggregated knowledge — case reports, one 40-patient international cohort, and one 17-patient cross-sectional study. There is no registry, no EHR-derived cohort, and no natural-history study with structured longitudinal data. Curate accordingly: frequencies come from n≈40, not from a population.

2. Etiology

Primary cause

Biallelic (homozygous or compound heterozygous) loss-of-function variants in ATP2A1 (16p11.2; older literature maps it to 16p12.1-12.2). Purely Mendelian — no infectious, environmental, or autoimmune contribution to causation.

Two mechanistic flavors of "loss of function," and they matter therapeutically:

  1. Quantitative loss — nonsense, frameshift, splice, large deletion → little or no SERCA1 protein made.
  2. Qualitative/folding loss — missense → protein is often catalytically competent but misfolded, recognized by ER quality control, ubiquitinated, and destroyed before it reaches the SR membrane. This is the CFTR-ΔF508 playbook running in a different gene, and it's the entire basis for the corrector-drug strategy in §12.

[verbatim] "Most mutations generate proteins corrupted in proper folding that although catalytically active, were ubiquitinated and prematurely degraded by the ubiquitin-proteasome system, thus sharing with Cystic Fibrosis the same pathogenetic mechanism." — Sacchetto group, Hum Mol Genet 2025 (PMID:41206505)

Genetic risk factors

  • Causal: biallelic ATP2A1 variants. Heterozygous carriers are clinically unaffected.
  • Not causal: heterozygous ATP2A1 variants alone. Odermatt 2000 explicitly disproved one candidate this way.

[verbatim] "In a fourth family, the heterozygous substitution of T for C2455, mutating Arg819 to Cys, was identified. This mutation was also readily expressed in HEK-293 cells and shown to have near normal Ca2+ transport activity, indicating that it is not causal for Brody disease." — Odermatt et al., Hum Genet 2000 (PMID:10914677)

  • Consanguinity raises risk, as for any AR disorder; the 2023 Turkish case was homozygous, consistent with that.
  • No modifier genes have been identified. Genotype–phenotype correlation is reported as absent (see §4).

Environmental risk / trigger factors

There is a clean distinction here that a knowledge base should preserve: nothing environmental causes Brody myopathy, but several things unmask or worsen it. Triggers, not etiology:

Trigger Effect Evidence
Physical exertion (even mild) Elicits stiffness/delayed relaxation — the defining trigger PMID:32040565, PMID:39273176
Cold exposure Symptom exacerbation, reported in ~72% of the cohort PMID:32040565 [full-text derived]
Volatile anesthetics + succinylcholine Precipitate malignant-hyperthermia-like episodes PMID:32040565, PMID:25614869
Repetitive contraction The physical-exam provocation maneuver PMID:32040565

Suggested ECTO grounding: exposure to cold temperature and exposure to anesthetic agent concepts — verify CURIEs with OAK before binding; I did not verify ECTO terms this session.

Protective factors

  • None documented. No protective allele, dietary factor, or lifestyle exposure has been reported.
  • Pacing, warm environments, and avoidance of maximal exertion are symptom-avoidance strategies, not protective factors in the epidemiological sense.
  • There is no "second wind" phenomenon (that's McArdle disease) — a useful negative for differential diagnosis.

Gene–environment interaction

One real, clinically consequential interaction: genotype (biallelic ATP2A1 LoF) × anesthetic exposure → MH-like crisis. The proposed convergence is shared elevated myoplasmic calcium.

[verbatim, partial] Sambuughin et al. note that "elevated myoplasmic Ca(2+) content" is common to both conditions, explaining the secondary malignant hyperthermia diagnosis alongside the primary Brody myopathy. — Mol Genet Genomic Med 2014 (PMID:25614869)

3. Phenotypes

HPO annotations currently attached to OMIM:601003

Retrieved live from the HPO annotation service. Note the many 0/N entries — these are curated exclusions, and they're arguably the most diagnostically valuable part of the profile:

HP ID Term Annotated frequency
HP:0008967 Exercise-induced muscle stiffness 10/10
HP:0011463 Childhood onset 5/5
HP:0003710 Exercise-induced muscle cramps 1/1
HP:0002047 Malignant hyperthermia 1/1
HP:0001270 Motor delay 1/1
HP:0003623 Neonatal onset 1/1
HP:0009046 Difficulty running 1/5
HP:0000007 Autosomal recessive inheritance —
HP:0002486 Myotonia 0/5 (excluded)
HP:0100284 EMG: myotonic discharges 0/5 (excluded)
HP:0010548 Percussion myotonia 0/10 (excluded)
HP:0001324 Muscle weakness 0/5 (excluded)
HP:0003326 Myalgia 0/5
HP:0002411 Myokymia 0/5 (excluded)
HP:0002380 Fasciculations 0/5 (excluded)
HP:0001371 Flexion contracture 0/5 (excluded)
HP:0003712 Skeletal muscle hypertrophy 0/5
HP:0031826 Abnormal reflex 0/5
HP:0003474 Somatic sensory dysfunction 0/5

All HP IDs above independently [OAK-verified] against sqlite:obo:hp except where the HPO service supplied them directly.

Clinical features with cohort frequencies

From the 40-patient international cohort (Molenaar 2020, PMID:32040565). [full-text derived — re-verify before snippet-curation]

Feature Frequency Suggested HP term
Exercise-induced muscle stiffness (limbs) 40/40 (100%) HP:0008967
Lower-limb involvement 38/38 (100%) HP:0008967
Upper-limb involvement 33/38 (87%) HP:0008967
Cold sensitivity / cold-induced worsening 25/36 (72%) — (qualifier, not a term)
Athletic build (paradoxical) 20/30 (67%) HP:0003712 (approximate)
Eyelid stiffness 24/38 (63%) HP:0008967 + UBERON:0001711 site
Stiffness at exercise onset 19/30 (63%) —
Myalgia 20/34 (59%) HP:0003326 / HP:0003738
Muscle cramps 18/34 (52%) HP:0003710
Reported muscle weakness 11/35 (31%) HP:0001324 — often misperceived stiffness
MH-like episodes 4/40 (10%) HP:0002047
Clinical muscle atrophy 0/33 (0%) (excluded)

The abstract-level statements are safely quotable:

[verbatim] "This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids. Onset begins in childhood and there was no or only mild progression of symptoms over time. Four patients had episodes resembling malignant hyperthermia. The key finding at physical examination was delayed relaxation after repetitive contractions. Additionally, no atrophy was seen, muscle strength was generally preserved, and some patients had a remarkable athletic build." — PMID:32040565

The eyelid involvement isn't a curiosity — it's mechanistically informative. Orbicularis oculi (UBERON:0001578 [OAK-verified]) is a fast-twitch-rich muscle, so it's exactly where a SERCA1-specific defect should show up first.

Phenotype characteristics

  • Age of onset: first decade in the large majority. Mean reported symptom onset 19.2 ± 15.0 yr with 38/40 in childhood [full-text derived] — the mean is skewed by late-recognized cases; the modal onset is childhood. The 2023 Turkish case pushed onset into the second decade (age 14–15).
  • Severity: mild to moderate. Strength preserved. Most patients function independently.
  • Progression: essentially non-progressive or minimally progressive. This is a load-bearing fact for prognosis.
  • Course: episodic/exertional — stiffness appears with activity and resolves with a few minutes of rest.
  • Duration: lifelong.

Laboratory phenotype

  • Creatine kinase (HP:0003236 [OAK-verified]): normal or mildly elevated. Range 50–1,300 IU/L, roughly half normal and half mildly-to-moderately raised [full-text derived].
  • SERCA activity in muscle homogenate: markedly reduced — now with proper reference values, see §10.
  • Rhabdomyolysis (HP:0003201 [OAK-verified]): rare. A 2026 case presented with exercise-induced rhabdomyolysis as the index event (PMID:41926432) — this genuinely expands the recognized presentation.

Quality-of-life impact

Thin evidence, honestly. The 2020 cohort used a Modified Rankin Scale, with 13/23 (57%) at "slight disability but able to look after own affairs" [full-text derived]. No EQ-5D, SF-36, or PROMIS data exist for this disease. Notably, Voermans 2012 reports that Brody syndrome patients (the gene-negative group) report more myalgia and greater daily-life impact than Brody disease patients — a genuine, quotable contrast.

4. Genetic / Molecular Information

Causal gene

ATP2A1 — ATPase sarcoplasmic/endoplasmic reticulum Ca²⁺ transporting 1

  • HGNC: hgnc:811 [OAK-verified] (note repo convention: lowercase hgnc:)
  • OMIM gene: 108730
  • Locus: 16p11.2
  • Reference transcript commonly used in reports: NM_004320.4
  • Protein: SERCA1a, ~994 aa, ~110 kDa P-type ATPase
  • UniProt: O14983 (SERCA1 human) — verify before binding

Splice isoforms. ATP2A1 makes two developmentally regulated isoforms by alternative splicing at the 3′ end: SERCA1a (adult; stop codon in exon 22) and SERCA1b (neonatal; skips exon 22, stop in exon 23). SERCA1a is >99% of SERCA1 in adult skeletal muscle. This matters for in-vitro work — Guglielmi 2013 found the neonatal SERCA1b isoform predominates in cultured human myotubes and in infant muscle, which limits how well cultured fibers model the adult defect.

Pathogenic variant landscape

Variant classes seen in Brody disease (all reported): nonsense, frameshift (deletions and insertions/duplications), canonical splice-site, in-frame single-codon deletions, missense, and large rearrangements including whole-gene deletion.

From the 40-patient cohort, 33 distinct mutations [full-text derived]:

Class Count
Missense 11
Frameshift 7
Nonsense (stop) 6
Splice-site 4
In-frame single-codon deletion 3
Large rearrangement (exon 9 del; whole-gene del) 2

Recurrent variants noted across unrelated families [full-text derived]: p.Leu67del, c.2464dup, exon 9 deletion, p.Arg560Cys. None constitutes an established founder allele.

Individually characterized variants worth curating:

Variant Consequence Source
Intron 3 splice-donor site variant Splice defect PMID:8841193 [verbatim]
Two premature stop codons (two families) Truncated SERCA1, essential domains deleted PMID:8841193 [verbatim]
c.2366C>T, p.Pro789Leu (homozygous) Expressed in HEK-293 but "almost complete loss of Ca²⁺ transport activity because of reduced Ca²⁺ affinity" PMID:10914677 [verbatim]
c.2455C>T, p.Arg819Cys (het) Near-normal transport — NOT causal PMID:10914677 [verbatim]
Two novel in-frame deletions (siblings) Reduced SERCA1 protein amount, normal IHC pattern PMID:20142766 [verbatim]
p.Ile235Asn + p.Glu982Lys (compound het) Absent SERCA1, elevated SERCA2; family carried an MH-susceptibility diagnosis PMID:25614869
Two novel heterozygous exon 3 variants — PMID:23911890 [verbatim]
c.2464delC (frameshift) + c.324+1G>A (novel splice) Compound het in two siblings PMID:37332993 [verbatim]
c.428G>A, p.Arg143Gln (homozygous, NM_004320.4) Very mild, second-decade onset, Turkish patient PMID:38125752 [verbatim]

[verbatim] "Here, we report a Turkish Brody Disease patient with a homozygous c.428G>A p.Arg143Gln (NM_004320.4) missense mutation in the ATP2A1." — PMID:38125752

Variant classification / population frequency — honest gaps:

  • ClinVar: a query on ATP2A1[gene] returns 1,113 variation records total; restricting to pathogenic/likely-pathogenic returns 268. That P/LP number is almost certainly inflated by multi-gene CNV records, because ATP2A1 sits inside the recurrent distal 16p11.2 BP2–BP3 ~220 kb deletion (chr16:28.73–28.95 Mb, ~9 genes including SH2B1; OMIM 613444), which is curated as pathogenic for obesity/developmental delay. Do not curate 268 as "268 pathogenic ATP2A1 variants." Re-derive with an explicit single-gene filter.
  • gnomAD constraint (pLI, LOEUF, o/e): I was unable to retrieve these — the gnomAD browser is a JS app and its API needs POST. Flagging as not-retrieved rather than guessing. What is clinically established: heterozygous carriers are asymptomatic, so ATP2A1 is not haploinsufficient in the disease-causing sense.
  • Carrier frequency: not established anywhere I could find. Given ~47 patients ever reported, it has never been measured directly.

Somatic vs germline

Entirely germline. No somatic ATP2A1 disease has been described. (Incidental note: ATP2A1 shows up in cancer expression literature, but that's not a somatic disease mechanism relevant here.)

Functional consequences

  • Loss of function in all pathogenic cases. Two sub-mechanisms: reduced protein quantity (truncating) and reduced protein stability/trafficking despite retained catalysis (missense; see §6).
  • No gain-of-function or dominant-negative mechanism reported.

Modifier genes, epigenetics, chromosomal abnormalities

  • Modifier genes: none identified.
  • Genotype–phenotype: explicitly reported as absent — "No gradation in severity could be demonstrated in clinical presentation… leading to no particular phenotype-to-genotype correlations." [full-text derived, PMID:32040565]
  • Epigenetics: no DNA methylation, histone, or chromatin studies exist for Brody myopathy. Genuine blank.
  • Chromosomal abnormalities: whole-gene ATP2A1 deletion has been reported as one allele. The distal 16p11.2 BP2–BP3 deletion removes one ATP2A1 copy but is not reported to cause Brody myopathy on its own — it would need a second-hit point variant in trans. This is a plausible-but-unreported compound-heterozygous mechanism worth flagging as a knowledge gap.

5. Environmental Information

Short section, and it should be. Brody myopathy is Mendelian, full stop.

  • Environmental factors: no toxin, radiation, pollutant, or occupational exposure contributes to causation. Cold and exertion are symptom triggers, not causes.
  • Lifestyle factors: no dietary, smoking, or alcohol association. Athletic training is neither causal nor protective; several patients are notably athletic despite the disease.
  • Infectious agents: none. Not applicable.
  • Iatrogenic exposure worth modeling: volatile anesthetics and depolarizing muscle relaxants (succinylcholine, CHEBI:45652 [OAK-verified]) as MH-crisis triggers. This is the one exposure that belongs in an environmental: block with influences_mechanisms.

6. Mechanism / Pathophysiology

Here's the causal chain, laid out for a pathograph.

The normal biology it breaks

SERCA1 is a P-type ATPase with three cytoplasmic domains (A/actuator, N/nucleotide-binding, P/phosphorylation) and ten transmembrane helices carrying two Ca²⁺-binding sites. It runs a Post-Albers E1/E2 cycle, pumping 2 Ca²⁺ into the SR lumen per ATP hydrolyzed against a countertransport of protons. In fast-twitch fibers it is the overwhelmingly dominant route by which cytosolic calcium is cleared after a contraction — i.e., it is the relaxation machinery. It is tonically restrained by small regulatory peptides (sarcolipin, myoregulin); phospholamban does the equivalent job for the SERCA2a isoform in heart and slow muscle. Structural reference: Toyoshima's rabbit SERCA1a structure (PDB 1SU4) — verify PDB before binding.

Causal chain, upstream → downstream

Step 1 (MOLECULAR). Biallelic ATP2A1 LoF variants. → Two routes: - 1a. Truncating/splice/deletion → little or no SERCA1 protein synthesized. - 1b. Missense → protein folds badly, is ubiquitinated, and is stripped out by the ubiquitin–proteasome system before reaching the SR membrane, despite retaining catalytic activity.

[verbatim, partial] Bianchini et al. showed the mutation "impairs protein folding rather than catalytic function," and that proteasome inhibition restores "the same ability of wild type to maintain Ca(2+) homeostasis within cells." — J Biol Chem 2014 (PMID:25288803)

Step 2 (MOLECULAR). Reduced SERCA1 protein at the SR membrane → reduced SR Ca²⁺-ATPase activity. Measured reduction: 50–80% of control activity [full-text derived], and now quantified against proper reference values:

[verbatim] "With the optimized assay, SERCA activity was assessed in muscle samples from healthy controls (n = 28) and patients with Brody disease (n = 4)… demonstrate marked decreased SERCA activity in Brody disease muscle samples (30.0 ± 4.2 mU/mg protein) compared to controls (86.7 ± 25.1 mU/mg protein)." — Biochem Biophys Rep 2026 (PMID:41938373)

Step 3 (CELLULAR). Impaired Ca²⁺ re-uptake into the SR → prolonged elevation of cytosolic free Ca²⁺ after each contraction, i.e. a slow calcium-transient decay. Directly imaged in the zebrafish model:

[verbatim] "In vivo imaging of muscle Ca2+ transients revealed that cytosolic Ca2+ decay was significantly slower in acc muscle. Thus, it appears that the mutant behavior is caused by a muscle relaxation defect due to the impairment of Ca2+ re-uptake." — Hirata et al., Development 2004 (PMID:15469975)

Step 4 (CELLULAR/TISSUE). Sustained cytosolic Ca²⁺ keeps troponin C saturated and cross-bridges cycling → electrically silent contracture. The key word is silent: the sarcolemma isn't misbehaving, so needle EMG records nothing during the stiffness. That's what separates it from every myotonia on the differential.

Step 5 (TISSUE). Selective type II (fast-twitch) fiber involvement, because SERCA1 is the fast-fiber isoform and slow fibers run SERCA2a instead. Explains the muscle distribution (limbs, eyelids), the exertion dependence, and the biopsy finding of type II fiber atrophy.

Step 6 (ORGANISM). Exercise-induced stiffness, delayed relaxation, cramps, myalgia; cold exacerbation (SERCA kinetics slow further at low temperature); MH-like susceptibility on anesthetic exposure via shared myoplasmic Ca²⁺ overload; rarely, exertional rhabdomyolysis.

The compensation branch — why this disease is mild

Here's the biologically interesting bit. A complete SERCA1 knockout is lethal in mice, yet humans with essentially absent SERCA1 walk around with an athletic build and stiff eyelids. Something is picking up the slack.

[verbatim] "…raising the intriguing question: how have these Brody patients partially compensated for the functional knockout of a gene product believed to be essential for fast-twitch skeletal muscle relaxation?" — PMID:8841193

Candidate compensators (all still contested): - SERCA2 upregulation — supported in the MH family (PMID:25614869: "Muscle analysis revealed absent SERCA1 but elevated SERCA2, suggesting compensatory mechanisms partially restoring calcium transport"), but the 2020 cohort found SERCA2 expression normal in 7/8 tested [full-text derived]. Genuinely conflicting. - Plasma membrane Ca²⁺-ATPase (PMCA) upregulation — the bovine model supports this over SERCA2 [full-text derived]. - Na⁺/Ca²⁺ exchanger activation. - Mitochondrial Ca²⁺ uptake. - Reduced myoregulin/sarcolipin inhibition of residual pump.

This unresolved compensation question is an excellent KNOWLEDGE_GAP discussion for a dismech entry — and the SERCA2 contradiction is a textbook case for curating two competing mechanistic_hypotheses rather than one settled chain.

Ontology term suggestions for the mechanism

GO biological process / molecular function / cellular component — all [OAK-verified]:

GO ID Label Use
GO:0005388 P-type calcium transporter activity SERCA1 molecular function; modifier: DECREASED
GO:1990036 calcium ion import into sarcoplasmic reticulum the specific failing process
GO:0070588 calcium ion transmembrane transport broader parent
GO:0006874 intracellular calcium ion homeostasis modifier: DECREASED/disrupted
GO:0032469 endoplasmic reticulum calcium ion homeostasis SR luminal side
GO:0090075 relaxation of muscle the impaired output — modifier: DECREASED
GO:0006936 muscle contraction prolonged/sustained
GO:0051209 release of sequestered calcium ion into cytosol the intact upstream arm
GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process the missense-degradation node — modifier: INCREASED
GO:0034976 response to endoplasmic reticulum stress ER quality-control arm
GO:0014850 response to muscle activity exertion dependence
GO:0016529 sarcoplasmic reticulum cellular component
GO:0033017 sarcoplasmic reticulum membrane where the pump lives / fails to arrive

Cell types — [OAK-verified]; note the numbering is easy to flip:

CL ID Label Note
CL:0002212 type II muscle cell the affected population
CL:0002211 type I muscle cell the spared population — good for a negative annotation
CL:0008002 skeletal muscle fiber general
CL:0000188 cell of skeletal muscle parent

Pathways. KEGG hsa04020 (calcium signaling pathway) and hsa04260/04261; Reactome "Ion homeostasis" (R-HSA-5578775) and "Reduction of cytosolic Ca++ levels" (R-HSA-418359) — verify Reactome IDs before use.

Immune system, metabolism, fibrosis

  • Immune involvement: none. Not an inflammatory or autoimmune myopathy. (Contrast: rippling muscle disease has an immune-mediated form; Brody does not.)
  • Metabolic changes: no primary metabolic defect. Indirect consequence — SERCA pumping is a major consumer of muscle ATP, so a broken pump alters the energy economy of contraction, but there is no documented glycogen, lipid, or amino-acid abnormality. Explicitly not a metabolic myopathy in the McArdle sense.
  • Tissue damage: mild. Type II fiber atrophy, fiber-size variability, internal nuclei. Myonecrosis essentially absent (one exception in the 40-patient cohort) [full-text derived]. No fibrosis, no ischemia, no oxidative-stress mechanism established.

Molecular profiling — a candid inventory

  • Transcriptomics: no Brody-specific human muscle RNA-seq dataset published.
  • Proteomics: no dedicated proteomic study. The protein-level work is targeted western blot and 2D gel (PMID:20142766 used high-resolution 2D electrophoresis).
  • Metabolomics / lipidomics: none.
  • Single-cell / spatial transcriptomics: none. Given the fiber-type-selective mechanism, single-nucleus RNA-seq of Brody muscle is an obvious unexploited experiment — worth curating as a proposed_experiments entry.
  • Functional genomics screens: none disease-specific.
  • Ultrastructure (the one thing that is characterized):

[verbatim] "Ultrastructural examination revealed dilatation of lateral cisternae and proliferation of tubular elements of the sarcoplasmic reticulum." — PMID:20142766

7. Anatomical Structures Affected

Organ level

  • Primary: skeletal muscle — UBERON:0001134 skeletal muscle tissue [OAK-verified]; UBERON:0014892 skeletal muscle organ, vertebrate [OAK-verified].
  • Body system: musculoskeletal only. No cardiac involvement (heart runs SERCA2a from ATP2A2), no CNS/PNS involvement, no respiratory involvement in humans.
  • Secondary organ involvement: essentially none. The exceptions are crisis-related — MH-like hypermetabolic episodes and, rarely, rhabdomyolysis with its downstream renal risk.

Note the striking species contrast: the mouse Atp2a1-null dies of diaphragm failure (UBERON:0001103 [OAK-verified]), a compartment humans with the same defect do not clinically manifest. See §15 — this is a genuine HUMAN_MODEL_MISMATCH.

Regional distribution

Site UBERON Involvement
Lower limb muscles UBERON:0001377 quadriceps femoris [OAK-verified] (biopsy site) ~100%
Upper limb muscles — ~87%
Eyelid UBERON:0001711 eyelid [OAK-verified] ~63%
Orbicularis oculi muscle UBERON:0001578 [OAK-verified] the fast-twitch facial muscle behind eyelid stiffness
Facial muscles — reported
Neck muscles UBERON:0002377 muscle of neck [OAK-verified] occasional

Lateralization: bilateral and symmetric. No asymmetric or focal presentation reported.

Tissue and cell level

  • Tissue type: striated skeletal muscle.
  • Target cell population: type II / fast-twitch muscle fibers (CL:0002212), with type I fibers spared. Biopsies show a shifted fiber composition — mean type II fiber fraction in quadriceps ~75% vs. a 50–65% normal range [full-text derived] — alongside selective type II atrophy.

Subcellular level

  • Sarcoplasmic reticulum (GO:0016529), specifically the SR membrane (GO:0033017) and the longitudinal/free SR where SERCA1 concentrates.
  • Terminal cisternae / lateral cisternae — dilated on EM.
  • Cytosol/myoplasm — the compartment where calcium wrongly lingers.
  • For missense alleles: endoplasmic reticulum quality-control compartment and the proteasome (GO:0043161) are where the protein is lost.

8. Temporal Development

Onset

  • Typical: first decade of life. HPO annotates HP:0011463 (Childhood onset) at 5/5. The 2020 cohort had 38/40 with childhood onset [full-text derived].
  • Range: one neonatal-onset annotation exists (HP:0003623, 1/1); at the other end, the 2023 Turkish case began at 14–15.
  • Pattern: insidious and chronic, punctuated by discrete exertional episodes. Not acute.
  • Diagnostic delay is the norm — mean age at diagnosis 27.3 ± 14.6 yr, mean delay 9.9 ± 13.7 yr [full-text derived]. Nearly a decade. That's the headline number for any "under-recognition" argument.

[verbatim] "Almost 50 years after the initial case presentation, only 18 patients have been reported and many questions regarding the clinical phenotype and results of ancillary investigations remain unanswered, likely leading to incomplete recognition and consequently under-diagnosis." — PMID:32040565

Progression

  • Rate: none to minimal. This is the single most reassuring fact about the disease.

[verbatim] "Onset begins in childhood and there was no or only mild progression of symptoms over time." — PMID:32040565

  • Stages: no staging system exists, and none is warranted for a non-progressive condition.
  • Course: episodic/exertional on a stable chronic baseline. Symptoms appear with activity and remit within minutes of rest.
  • Duration: lifelong.

The mild-progression rule has at least one documented exception at the individual level — the 2023 Turkish patient showed "mild progressive proximal muscle weakness in the lower extremities" [verbatim, PMID:38125752]. Curate that as an individual observation, not a general course.

Patterns

  • Remission: none spontaneous; symptom relief is rest-dependent and immediate rather than a true remission.
  • Critical periods: the actionable ones are perioperative windows (anesthetic exposure) and any planned high-intensity exertion. There is no developmental critical window for intervention.

9. Inheritance and Population

Epidemiology

  • Prevalence: approximately 1 in 10,000,000. Orphanet classes it as <1/1,000,000 (point prevalence, worldwide).

[verbatim] "To date, only thirty-three Brody families with forty-seven patients have been reported in the literature, and the disease prevalence is considered as 1 in 10 million, demonstrating the peculiarity of the disease." — PMID:38125752

For a dismech prevalence block: measure_type: POINT_PREVALENCE, prevalence_class: BELOW_1_IN_1000000, rate_per_100000: 0.01, population: Worldwide, with the verbatim sentence above as the snippet. A parallel CASES_IN_LITERATURE record (47 patients / 33 families as of 2023; the 2020 cohort itself totaled 40 patients from 28 families) captures the other framing.

  • Incidence: never measured.
  • Almost certainly under-diagnosed — the ~10-year diagnostic delay plus the "incomplete recognition" statement above both argue the true figure is higher than the counted figure.

Genetic epidemiology

  • Inheritance: autosomal recessive (HP:0000007). Confirmed repeatedly since 1996.
  • Penetrance: appears complete in biallelic individuals; no unaffected homozygotes reported. But with n≈47 total, "complete penetrance" is an observation, not a measurement.
  • Expressivity: variable — from the very mild second-decade Turkish case to patients with MH crises. Notably, that variability does not track genotype.
  • Genetic anticipation: not applicable (no repeat expansion).
  • Germline mosaicism: not reported.
  • Founder effects: none established. Several recurrent alleles (p.Leu67del, c.2464dup, exon 9 del, p.Arg560Cys) appear in >1 family but haven't been shown to share haplotypes.
  • Consanguinity: contributory, as expected for AR; homozygous cases in consanguineous populations are described.
  • Carrier frequency: not established.

Population demographics

  • Sex ratio: approximately 1:1 — consistent with autosomal inheritance, and reported as roughly equal in the 40-patient cohort [full-text derived].
  • Geographic distribution: no endemic focus. The 2020 cohort drew from France, Netherlands, Canada, UK, Germany, Spain, Italy, Switzerland, and USA [full-text derived]; additional reports from Turkey (2023) and Italy (2023). Ascertainment follows neuromuscular-center density, not biology.
  • Ethnic predisposition: none identified.
  • Age distribution of affected individuals: all ages, since the disease neither kills nor progresses; the reported population skews toward young adults simply because that's when the decade-long diagnostic delay finally resolves.

10. Diagnostics

Diagnostic reasoning in one sentence

Exercise-induced stiffness + delayed relaxation on repetitive contraction + electrically silent EMG during the stiffness → sequence ATP2A1.

[verbatim] "When physical examination shows delayed relaxation, and there are no myotonic discharges at electromyography, we recommend direct sequencing of the ATP2A1 gene or next generation sequencing with a myopathy panel." — PMID:32040565

Clinical / bedside tests

  • Repetitive contraction provocation — repeated forceful eye closure or hand grip, watching for progressively delayed relaxation. The cardinal sign.
  • Percussion myotonia: absent (HP:0010548, 0/10) — this negative is diagnostically load-bearing.
  • No warm-up phenomenon (unlike myotonia congenita); no second wind (unlike McArdle).

Laboratory tests

Test Finding LOINC
Serum creatine kinase Normal to mildly elevated (50–1,300 IU/L) LOINC:2157-6 (CK, serum/plasma) — verify
Serum myoglobin / urine myoglobin Abnormal only in the rare rhabdomyolysis presentation —
Thyroid function Normal — used to exclude hypothyroid pseudomyotonia —

Electrophysiology — the discriminating test

  • Needle EMG: no myotonic discharges (HP:0100284, 0/5 excluded). Instead, silent contractures in roughly 64% of tested patients [full-text derived], defined as "prolonged involuntary muscle contractions following voluntary phasic contractions without electrical activity."
  • The 2020 authors argue for the term "silent contractures" over the older "silent cramps," since the strict electromyographic definition of cramp doesn't apply [full-text derived].
  • Nerve conduction studies: normal.
  • ECG/EEG: normal; not diagnostically relevant.

Muscle biopsy and histopathology

Mild, nonspecific, and supportive rather than diagnostic:

[verbatim] "…muscle biopsy showed mild myopathic changes with selective type II atrophy." — PMID:32040565

Finding Frequency HP term
Type 2 muscle fiber atrophy 13/17 (76%) HP:0003554 [OAK-verified]
Marked fiber-size variability 11/12 (92%) HP:0003557 [OAK-verified]
Increased internal nuclei 14/17 (82%) HP:0003687 [OAK-verified]
Myonecrosis Essentially absent —
SR lateral cisternae dilatation, tubular proliferation (EM) Reported —

(Frequencies [full-text derived].)

Functional / biochemical confirmatory assays

This is where Brody diagnosis has real depth, and where the 2026 paper is a significant advance.

1. SERCA activity assay on muscle homogenate. Now with validated reference values:

[verbatim] "We developed a robust enzyme assay to measure SERCA activity with high discriminative power to distinguish patients with Brody disease from controls. Thus, this assay provides a reliable method of studying this important calcium pump for both clinical and scientific purposes." — PMID:41938373

Reference: controls 86.7 ± 25.1 mU/mg protein (n=28); Brody disease 30.0 ± 4.2 mU/mg protein (n=4). This is a genuinely curatable reference_ranges block with interpretation bands.

2. SERCA1 western blot — decreased or absent protein.

3. What NOT to rely on: immunohistochemistry alone. Two independent groups say this explicitly:

[verbatim] "…immunostaining of skeletal muscle to detect the loss of SERCA1a protein is not adequate for the diagnosis of ATP2A1-linked Brody disease." — PMID:10914677

[verbatim] "SERCA1 reactivity was observed in type 2 muscle fibers of patients with and without ATP2A1 mutations and staining intensity was similar in patients and controls." — PMID:23911890

That's a false-negative trap worth curating as a diagnostic caveat.

Genetic testing

  • First-line: direct ATP2A1 Sanger sequencing, or NGS myopathy/neuromuscular gene panel (PMID:32040565 recommendation).
  • WES: effective and has solved cases — including one misassigned as pure MH susceptibility (PMID:25614869).
  • WGS: useful for deep-intronic and structural variants; no dedicated study.
  • CNV detection required. Whole-gene and exon-9 deletions are documented, so a sequencing-only panel with no dosage analysis will miss alleles. MLPA/CMA/read-depth CNV calling should be part of the workflow.
  • Karyotype / FISH / mtDNA / repeat-expansion testing: not indicated.

Imaging

  • Muscle MRI: no characteristic pattern described; not a diagnostic test for this disease. Reasonable for excluding dystrophies.

Differential diagnosis

The whole diagnostic act is separating this from things that look identical at the bedside:

Condition Gene(s) Distinguishing feature
Myotonia congenita (Thomsen/Becker) CLCN1 Myotonic discharges on EMG; warm-up phenomenon
Paramyotonia congenita SCN4A Myotonic discharges; paradoxical cold-induced worsening with EMG activity
Myotonic dystrophy 1/2 DMPK, CNBP Myotonic discharges; multisystem (cataract, cardiac conduction, endocrine)
Rippling muscle disease CAV3, CAVIN1/BIN1 Also electrically silent; visible rippling/mounding, percussion-induced
McArdle disease PYGM Second wind; high baseline CK; myoglobinuria; forearm exercise test
Schwartz-Jampel syndrome HSPG2 Chondrodysplasia, blepharophimosis, continuous EMG activity
Isaacs syndrome / neuromyotonia acquired, CASPR2 Ab Neuromyotonic/myokymic discharges — electrically noisy, opposite of Brody
Stiff-person syndrome acquired, GAD65 Ab Central; continuous motor unit activity; axial
Hypothyroid pseudomyotonia acquired Abnormal TSH; reversible
Tubular aggregate myopathy / Stormorken STIM1, ORAI1 Also a calcium-handling myopathy; tubular aggregates on biopsy (HP:0100301)
Brody syndrome unknown Same phenotype + reduced SERCA activity but no ATP2A1 variant

The 2026 Muscle & Nerve review is a good single anchor for this whole differential:

[verbatim] "Rippling muscle disease (RMD) and Brody disease are extremely rare nonprogressive myopathies associated with electrical silence on needle EMG during muscle stiffness and delayed muscle relaxation… Brody disease is autosomal recessive myopathy due to defective pumping of calcium from the cytoplasm by sarco(endo)plasmic reticulum Ca2+ adenosine triphosphatase pumps." — Katirji, Muscle Nerve 2026 (PMID:42124386)

Screening

  • Newborn screening: not performed anywhere; not a candidate (no treatment, non-progressive).
  • Carrier screening: not offered as a population program; relevant only for cascade testing in known families.
  • Cascade family testing: appropriate once a proband's biallelic variants are established, particularly to identify relatives at anesthetic risk.

11. Outcome / Prognosis

Survival and mortality

  • Life expectancy: normal. No reduction reported in any series.
  • Disease-specific mortality: essentially zero from the myopathy itself. The one credible mortality pathway is a perioperative MH-like crisis, which is why the anesthetic precautions in §12 carry disproportionate weight.
  • No 5-/10-year survival statistics exist because there is nothing to survive in the actuarial sense.

Morbidity and function

  • Strength is preserved; atrophy is absent clinically; many patients are athletically built.
  • Disability is real but modest: 13/23 (57%) at "slight disability but able to look after own affairs" on the modified Rankin Scale [full-text derived].
  • Functional limits are activity-specific: stairs, running, sustained grip, sustained eye closure, cold-weather activity.
  • Quality-of-life instruments: no EQ-5D, SF-36, or PROMIS data. A genuine gap.

Disease course and complications

Complication Frequency Note
MH-like episode 4/40 (10%) The serious one; anesthetic-triggered
Exertional rhabdomyolysis Rare; ≥1 documented index presentation PMID:41926432
Progressive weakness Rare, mild when present PMID:38125752
Contractures / fixed deformity Not reported (HP:0001371 excluded) —
Cardiac / respiratory involvement Not reported in humans Contrast with the mouse model
  • Recovery potential: the myopathy does not remit, but individual episodes resolve fully within minutes of rest. No cumulative damage.

Prognostic factors

  • Genotype is not prognostic — no genotype–phenotype correlation demonstrated [full-text derived, PMID:32040565].
  • Residual SERCA activity is a plausible but untested severity predictor. Worth flagging as a knowledge gap: the 2026 assay finally makes it measurable at scale.
  • The one practically prognostic variable is whether the patient and their anesthesiology team know the diagnosis before surgery.
  • Prognostic biomarkers: none validated.

12. Treatment

The honest summary

There is no disease-modifying therapy. Symptomatic drug treatment has been mostly disappointing.

[verbatim] "Symptomatic treatment was mostly ineffective or produced unacceptable side effects." — PMID:32040565

Pharmacotherapy tried, and how it went

From the 40-patient cohort [full-text derived — re-verify before curating]:

Drug CHEBI n Outcome
Verapamil (Ca²⁺ channel blocker) CHEBI:9948 [OAK-verified] 9 Improved 3; stopped in 2 for side effects; 1 long-term success — the best performer
Dantrolene (RyR1 inhibitor) CHEBI:4317 [OAK-verified] 5 Ineffective or side effects in this cohort
Mexiletine (Na⁺ channel blocker) CHEBI:6916 [OAK-verified] 2 Improved 1; stopped for side effects
Carbamazepine CHEBI:3387 [OAK-verified] 2 No effect
Ibuprofen CHEBI:5855 [OAK-verified] 2 No effect
Nifedipine CHEBI:7565 [OAK-verified] 2 No effect
Acetazolamide CHEBI:27690 [OAK-verified] 1 Insufficient data

Overall, only 1 of 18 treated patients achieved durable symptom control; 13/31 never pursued pharmacotherapy at all [full-text derived].

A 2026 counter-datapoint on dantrolene. A single case reports clear benefit, which contradicts the cohort experience and is worth curating as a distinct, PARTIAL-strength claim rather than folding into the negative consensus:

[verbatim] "Treatment with dantrolene sodium resulted in marked clinical improvement. The patient demonstrated enhanced muscle relaxation, reduced exercise-induced stiffness, and improved functional capacity following dantrolene therapy." — Edmund, J Am Assoc Nurse Pract 2026 (PMID:41926432)

Mechanistically dantrolene is coherent here — it reduces RyR1-mediated calcium release, attacking the same cytosolic calcium overload from the opposite direction when re-uptake can't be fixed. n=1 is n=1, though.

Advanced / experimental therapeutics — the interesting frontier

Proteasome inhibition (proof of concept, in vitro). Since misfolded-but-active SERCA1 is destroyed by the UPS, blocking that destruction restores the pump:

[verbatim, partial] Proteasome inhibition (MG132) "rescues the expression level and membrane localization of the SERCA1 mutant," and rescued protein has "the same ability of wild type to maintain Ca(2+) homeostasis within cells." — PMID:25288803

CFTR correctors — the most promising translational lead (2025). Repurposing small molecules developed for ΔF508-CFTR to chaperone misfolded SERCA1 through quality control:

[verbatim] "In this study, we show that CFTR correctors, particularly C17, successfully rescue SERCA1 mutants both in vitro and in vivo models. Our findings suggest that CFTR correctors may be a potential innovative pharmacological approach addressing Brody patients in which mutated SERCA1 retains its activity." — Hum Mol Genet 2025 (PMID:41206505)

Details [full-text derived]: twelve correctors screened; C17 best (C4 and C9 also active); the FDA-approved CF correctors VX-809 (lumacaftor) and VX-661 (tezacaftor) were NOT highly efficient. Tested on R164H (Chianina) and G211V (Romagnola) mutants; in vivo work was intramuscular C17 in two Romagnola calves, showing increased SERCA1 in SR membranes and increased Ca²⁺-ATPase activity. Authors' own caveats: tiny sample size, inability to quantify per-allele expression, one animal had a severe contracture crisis two months post-treatment, and therapeutic-index/Cmax work is still ongoing.

The critical scope limit for curation: this strategy only helps patients whose mutant SERCA1 retains catalytic activity — i.e. a subset of missense alleles. It does nothing for nonsense, frameshift, splice, or deletion alleles. That patient-stratification requirement is the single most important qualifier on the whole approach.

  • Gene therapy / gene editing: none reported. ATP2A1 is a plausible AAV target in principle (muscle-tropic serotypes exist), but the ~3 kb coding sequence plus a muscle promoter is a tight but feasible AAV payload. No published program.
  • RNA therapies (ASO, siRNA, mRNA): none. Splice-variant alleles (e.g. c.324+1G>A) are conceptually ASO-addressable but untried.
  • Cell therapy, immunotherapy, targeted oncology-style therapy: not applicable.
  • Registered clinical trials: I found no ClinicalTrials.gov entries specific to Brody myopathy. Treat any claimed NCT ID with suspicion.

Surgical and interventional

No surgical treatment for the myopathy. Surgery matters here only as a hazard.

Perioperative management — the highest-value actionable content

[verbatim] "…patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended." — PMID:32040565

Practical measures [full-text derived]: avoid succinylcholine (CHEBI:45652) and volatile/inhalational anesthetics; use a trigger-free (total intravenous) technique; monitor core temperature and vital functions; treat the patient as MH-susceptible; some patients have had positive in vitro contracture tests.

Supportive and rehabilitative

  • Activity pacing and warm-up strategies — behavioral, low-evidence but low-risk.
  • Avoidance of cold exposure during activity.
  • Physical therapy (NCIT:C15302 Physical Therapy [OAK-verified]) — no trial evidence; used pragmatically.
  • Genetic counseling (NCIT:C15240 [OAK-verified]) — AR recurrence risk, cascade testing, and crucially, flagging anesthetic risk to relatives.
  • Medical-alert documentation of MH-like risk — arguably the highest-yield intervention in the entire management repertoire.

NCIT treatment terms

Treatment treatment_term therapeutic_agent
Verapamil NCIT:C15986 Pharmacotherapy [OAK-verified] CHEBI:9948 verapamil
Dantrolene NCIT:C15986 CHEBI:4317 dantrolene
Mexiletine NCIT:C15986 CHEBI:6916 mexiletine
Physical therapy NCIT:C15302 Physical Therapy —
Genetic counseling NCIT:C15240 Genetic Counseling —
Supportive/symptomatic care NCIT:C15747 Supportive Care [OAK-verified] —
Rehabilitation NCIT:C15315 Rehabilitation [OAK-verified] —

Suggested therapeutic_modality values: SMALL_MOLECULE for all drug entries; BEHAVIORAL for pacing/cold-avoidance/physical therapy.

Pharmacogenomics

No PharmGKB or CPIC guidance for Brody myopathy. The nearest relevant precision-medicine axis is genotype-guided eligibility for corrector therapy (activity-retaining missense only), which is a research proposition, not clinical practice.

13. Prevention

Primary prevention

The disease itself is not preventable — it's a germline recessive condition. What is preventable is essentially everything downstream:

  • Reproductive/genetic prevention: genetic counseling for at-risk couples; carrier testing in families with a known proband; prenatal diagnosis and PGT-M technically feasible once both familial variants are known. Whether that is proportionate for a non-progressive, non-life-shortening condition is a genuine ethical judgment call, and the literature does not push it.
  • Population carrier screening: not recommended and not performed. Prevalence of ~1 in 10 million puts it far outside any screening panel's cost-effectiveness envelope.
  • Immunization: not applicable.

Secondary prevention (early detection)

  • Newborn screening: not performed, not proposed. Fails the classic Wilson–Jungner criteria at the "acceptable treatment exists" step.
  • The real secondary-prevention win is shortening the ~10-year diagnostic delay — clinician education that electrically silent stiffness means Brody, not myotonia, and that a myopathy NGS panel should carry ATP2A1.
  • Cascade testing of siblings and relatives of a proband.

Tertiary prevention (preventing complications)

This is where prevention actually earns its keep for this disease:

  1. Anesthetic-crisis prevention — documented MH-like precautions, trigger-free anesthesia, medical-alert identification. Prevents the only plausibly fatal complication.
  2. Rhabdomyolysis avoidance — counseling against maximal/unaccustomed exertion, especially in heat or after illness.
  3. Cold-exposure avoidance during activity.
  4. Activity pacing to keep patients functional rather than deconditioned.

Behavioral / public health / environmental interventions

  • Behavioral: pacing, warm-up, temperature management — no trial evidence, plausible mechanism.
  • Public health and environmental interventions: not applicable. No sanitation, vector, or exposure dimension exists for a Mendelian pump defect.

Prophylaxis

No prophylactic medication is established. Dantrolene is not used prophylactically in Brody myopathy (it's a treatment for an MH crisis in progress, and prophylactic use is no longer standard even in confirmed MH susceptibility).

14. Other Species / Natural Disease

This is a case where veterinary medicine carries the translational load, because the obvious mouse model died of something the humans don't get.

Bovine congenital pseudomyotonia — the mammalian model

Species: Bos taurus, NCBITaxon:9913. OMIA: OMIA:001464-9913 — Pseudomyotonia, congenital in Bos taurus (ATP2A1-related). A related, more severe ATP2A1 condition is catalogued as OMIA:001450-9913 — Congenital muscular dystonia 1. Gene: bovine ATP2A1 (NCBI Gene ID 281583 — verify).

Affected breeds (VBO terms exist for these; verify CURIEs):

Breed Variant Reference
Chianina c.491G>A, p.Arg164His PMID:18786632 — "Identification of a missense mutation in the bovine ATP2A1 gene in congenital pseudomyotonia of Chianina cattle: an animal model of human Brody disease"
Romagnola novel exon-8 complex variant c.[632G>T; 857G>T] (p.Gly211Val / p.Gly286Val); 3/4 cases compound het with the Chianina c.491G>A PMID:23046865
Belgian Blue "muscular dystonia type II" see OMIA:001450
Dutch Improved Red and White cross-breed single case PMID:20547455; fiber adaptation study PMID:26482047

Commercial genotyping exists (e.g. UC Davis VGL PMT test for Chianina/Romagnola), which tells you the allele is common enough in those breeds to matter economically.

Why it's the model that counts:

[verbatim] "Bovine PMT, despite unconventional, is currently the unique mammalian model of Brody disease." — PMID:41206505

The clinical picture is a near-perfect phenocopy: exercise-induced impaired relaxation, triggered by startle or by moving faster than a slow walk, with an uncoordinated hopping gait during cramping episodes.

Comparative pathology insight: the bovine work identified PMCA upregulation rather than SERCA2 upregulation as the dominant compensation [full-text derived] — and the calf study (PMID:26482047) directly examines fast-twitch fiber adaptation to SERCA1 deficiency. That's the cleanest available handle on the compensation question raised in §6.

Other veterinary conditions on the differential

  • Paradoxical pseudomyotonia in English Cocker and Springer Spaniels — OMIA:002645-9615, Canis lupus familiaris (NCBITaxon:9615), caused by a SLC7A10 nonsense variant (c.126C>A, p.Cys42Ter), not ATP2A1 (PMID:36869603). Useful as a "looks like Brody, isn't Brody" comparator.
  • Equine muscle biology is relevant context rather than disease: horse gluteal muscle expresses ATP2A1 as its predominant SR Ca²⁺-ATPase, but with strikingly low sarcolipin protein — proposed as an adaptation potentiating calcium cycling in a speed-selected prey species (PMID:33202832). No equine Brody-equivalent is described.

Evolutionary conservation

[verbatim] "SERCA protein shows a high degree of conservation among species." — PMID:39273176

That conservation is exactly what makes zebrafish and cattle informative, and it's why the CFTR-corrector result in bovine mutants is taken seriously as a human lead.

Zoonotic potential / cross-species transmission

Not applicable. Purely genetic, non-transmissible.

15. Model Organisms

Mouse — Atp2a1-null: the model that failed, informatively

[verbatim] "…term SERCA1-null mice had progressive cyanosis and gasping respiration and succumbed from respiratory failure shortly after birth." — Pan et al., J Biol Chem 2003 (PMID:12556521)

[verbatim] "…the absence of SERCA1 in type II fibers…coupled with the marked increase in contractile function required of the diaphragm muscle to support postnatal respiration, can account for respiratory failure."

This is a textbook HUMAN_MODEL_MISMATCH, not a KNOWLEDGE_GAP. Evidence exists in the model; what's open is its translational validity. Complete murine SERCA1 loss is neonatally lethal via diaphragm failure, while humans with severely reduced or absent SERCA1 have a mild, non-progressive limb-and-eyelid myopathy with no respiratory involvement whatsoever. The mismatch is not a nuisance — it's the clue that human compensation (PMCA/NCX/SERCA2/mitochondrial uptake) is doing real work that mouse diaphragm cannot manage under the acute respiratory load of birth.

Consequence, stated plainly by two independent groups:

[verbatim] "At present, neither specific therapy, nor mouse model exists for Brody myopathy." — PMID:41206505

[verbatim] "No mouse model nor specific therapies exist for Brody myopathy, which is therefore considered an orphan disease." — PMID:39273176

(To be precise: an Atp2a1 knockout mouse exists; a viable mouse model of Brody myopathy does not. Worth phrasing carefully in an entry.)

Zebrafish — accordion mutants: the workhorse in vivo model

Species: Danio rerio, NCBITaxon:7955. Gene: atp2a1. ZFIN has the accordion allele series.

Two independent 2004 papers positionally cloned it:

[verbatim] "…acc mutants carry a mutation in atp2a1 gene that encodes the sarco(endo)plasmic reticulum Ca2+-ATPase 1 (SERCA1)… As SERCA1 mutations in humans lead to Brody disease, an exercise-induced muscle relaxation disorder, zebrafish accordion mutants could be a useful animal model for this condition." — Hirata et al., Development 2004 (PMID:15469975)

[verbatim] "Positional cloning of acc identified a serca mutation as the cause of the acc phenotype… The mutation in SERCA, a serine to phenylalanine substitution, is likely to result in compromised protein function that accounts for the observed phenotype." — Gleason et al., Dev Biol 2004 (PMID:15581877)

Phenotype recapitulation — strong at the mechanistic level:

Human feature Zebrafish acc Match
Delayed muscle relaxation Relaxation "significantly slower than normal" ✔
Slowed cytosolic Ca²⁺ clearance "cytosolic Ca2+ decay was significantly slower" ✔
Muscle-intrinsic (not neural) "output from the central nervous system is normal in mutants"; "defect is not manifested in neuromuscular transmission" ✔
Exercise-induced, adult-onset, mild course ✘ — embryonic/larval, constitutive ✘
Bilateral simultaneous contraction ("accordion" shortening) Fish-specific behavioral readout n/a

Model limitations to record: the phenotype is embryonic/larval and behavioral, not exertional; there is no fast/slow fiber architecture equivalent to adult human limb muscle; and the readout (touch-evoked coiling) is a swimming-behavior proxy, not muscle stiffness.

Current use. The acc^tq206 line was comprehensively re-characterized in 2024 specifically as a testbed for the corrector strategy:

[verbatim] "In this paper, we focused on a comprehensive characterization of the 'acctq206' zebrafish variant. Our aim was to use this mutant line as an experimental animal model for testing the novel therapeutic approach for BD." — PMID:39273176

An antisense morpholino knockdown of serca reproduces the phenotype in wild-type fish (PMID:15581877) — a clean orthogonal validation.

Cellular / in vitro models

  • HEK-293 heterologous expression — the classic functional assay for novel variants. Used to establish that p.Pro789Leu abolishes transport while p.Arg819Cys does not (PMID:10914677). This is the assay that turns a VUS into a call.
  • Heterologous cell models of bovine mutants — used for the MG132 and CFTR-corrector rescue work (PMID:25288803, PMID:41206505).
  • Cultured human myotubes — available but caveat: they predominantly express the neonatal SERCA1b isoform, not adult SERCA1a (PMID:23911890), which limits fidelity to the adult disease.
  • iPSC-derived skeletal myocytes / organoids: not reported for Brody myopathy. Given that the mouse is unusable and the only mammalian model is a rare cattle breed, an iPSC-myotube platform is arguably the single most valuable missing model system. Strong candidate for a proposed_experiments entry.

Model resources

Resource Relevance
ZFIN accordion alleles incl. acc^tq206; the primary live model
MGI / IMPC / KOMP Atp2a1 alleles; note neonatal lethality of the null
OMIA OMIA:001464-9913 (bovine PMT), OMIA:001450-9913, OMIA:002645-9615 (canine SLC7A10)
Alliance of Genome Resources ATP2A1 orthology across human/mouse/zebrafish
Cellosaurus / ATCC No Brody-specific line

Orthologous genes

Species NCBI Taxon Gene
Human NCBITaxon:9606 ATP2A1 (hgnc:811)
Mouse NCBITaxon:10090 Atp2a1
Zebrafish NCBITaxon:7955 atp2a1
Cattle NCBITaxon:9913 ATP2A1
Rabbit NCBITaxon:9986 ATP2A1 — the source of the canonical SERCA1a structural biology

Appendix A — Reference list with verification status

PMID Short citation Year Abstract verbatim-verified?
4239835 Brody IA, NEJM — original description 1969 ✘ no abstract in record
8841193 Odermatt et al., Nat Genet — ATP2A1 mutations identified 1996 ✔
10914677 Odermatt et al., Hum Genet — p.Pro789Leu functional analysis 2000 ✔
12556521 Pan et al., J Biol Chem — SERCA1-null mouse 2003 ✔ (partial quotes)
15469975 Hirata et al., Development — accordion zebrafish 2004 ✔
15581877 Gleason et al., Dev Biol — serca mutation in accordion 2004 ✔
18786632 Chianina cattle ATP2A1 missense, Genomics 2008 ✘ title only
20142766 Vattemi et al., J Neuropathol Exp Neurol 2010 ✔
20547455 Dutch Red/White calf pseudomyotonia, Neuromuscul Disord 2010 ✘ not fetched
22704959 Voermans et al., Neuromuscul Disord — Brody syndrome vs disease 2012 ✔ (partial)
23046865 Romagnola cattle ATP2A1, BMC Vet Res 2012 ✘ title only
23911890 Guglielmi et al., Mol Genet Metab — SERCA1 expression 2013 ✔ (partial)
25288803 Bianchini et al., J Biol Chem — UPS inhibition rescue 2014 ✔ (partial)
25614869 Sambuughin et al., Mol Genet Genomic Med — exome/MH family 2014 ✔ (partial)
26482047 Calf fast-twitch fiber adaptation, Neuromuscul Disord 2015 ✘ title only
32040565 Molenaar et al., Brain — 40-patient cohort 2020 ✔ full abstract
33202832 Horse gluteal SLN/SERCA, Vet Sci 2020 ✔
36869603 Canine SLC7A10 paradoxical pseudomyotonia, Anim Genet 2023 ✘ title only
37332993 Velardo et al., Front Neurol — two siblings 2023 ✔ (partial)
38125752 Şahin et al., Front Genet — Turkish patient 2023 ✔
39273176 acc^tq206 zebrafish characterization, IJMS 2024 ✔
40637686 Bi-allelic LOF ATP2A1, QJM 2025 ✘ no abstract in record
41206505 CFTR corrector C17, Hum Mol Genet 2025 ✔ full abstract
41926432 Edmund, J Am Assoc Nurse Pract — dantrolene response 2026 ✔
41938373 SERCA activity assay + reference values, Biochem Biophys Rep 2026 ✔ full abstract
42124386 Katirji, Muscle Nerve — muscle stiffness review 2026 ✔

Structured-source references available for citation in dismech format: ORPHA:53347, OMIM:601003, OMIM:108730, OMIA:001464-9913, OMIA:001450-9913, OMIA:002645-9615.

Appendix B — Verified ontology term set

Every ID in this table was checked against a local OAK adapter during this session. IDs not in this table that appear elsewhere in the report (ECTO, LOINC, Reactome, UniProt, PDB, VBO, NCBI Gene) were not verified and must be checked before binding.

HPO — HP:0008967 Exercise-induced muscle stiffness · HP:0003710 Exercise-induced muscle cramps · HP:0003552 Muscle stiffness · HP:0003326 Myalgia · HP:0003738 Exercise-induced myalgia · HP:0003546 Exercise intolerance · HP:0002047 Malignant hyperthermia · HP:0003201 Rhabdomyolysis · HP:0003236 Elevated circulating creatine kinase concentration · HP:0003554 Type 2 muscle fiber atrophy · HP:0003557 Increased variability in muscle fiber diameter · HP:0003687 Centrally nucleated skeletal muscle fibers · HP:0003457 EMG abnormality · HP:0100284 EMG: myotonic discharges (excluded) · HP:0002486 Myotonia (excluded) · HP:0001324 Muscle weakness · HP:0003701 Proximal muscle weakness · HP:0009046 Difficulty running · HP:0000577 Exotropia · HP:0011463 Childhood onset · HP:0000007 Autosomal recessive inheritance

GO — GO:0005388 P-type calcium transporter activity · GO:1990036 calcium ion import into sarcoplasmic reticulum · GO:0070588 calcium ion transmembrane transport · GO:0006874 intracellular calcium ion homeostasis · GO:0032469 endoplasmic reticulum calcium ion homeostasis · GO:0090075 relaxation of muscle · GO:0006936 muscle contraction · GO:0051209 release of sequestered calcium ion into cytosol · GO:0014850 response to muscle activity · GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process · GO:0034976 response to endoplasmic reticulum stress · GO:0016529 sarcoplasmic reticulum · GO:0033017 sarcoplasmic reticulum membrane

CL — CL:0002212 type II muscle cell · CL:0002211 type I muscle cell · CL:0008002 skeletal muscle fiber · CL:0000188 cell of skeletal muscle · CL:0000187 muscle cell

UBERON — UBERON:0001134 skeletal muscle tissue · UBERON:0014892 skeletal muscle organ, vertebrate · UBERON:0001630 muscle organ · UBERON:0001711 eyelid · UBERON:0001578 orbicularis oculi muscle · UBERON:0001377 quadriceps femoris · UBERON:0002377 muscle of neck · UBERON:0001103 diaphragm

CHEBI — CHEBI:29108 calcium(2+) · CHEBI:30616 ATP(4-) · CHEBI:9948 verapamil · CHEBI:4317 dantrolene · CHEBI:6916 mexiletine · CHEBI:7565 nifedipine · CHEBI:27690 acetazolamide · CHEBI:3387 carbamazepine · CHEBI:5855 ibuprofen · CHEBI:45652 succinylcholine

NCIT — NCIT:C15986 Pharmacotherapy · NCIT:C15302 Physical Therapy · NCIT:C15240 Genetic Counseling · NCIT:C15747 Supportive Care · NCIT:C15315 Rehabilitation · NCIT:C49236 Therapeutic Procedure

MONDO — MONDO:0010977 Brody myopathy · HGNC — hgnc:811 ATP2A1

Appendix C — Explicit knowledge gaps for the entry

These are the places where the literature genuinely stops, and they are worth curating as structured discussions rather than leaving as silence:

  1. HUMAN_MODEL_MISMATCH — the mouse. Complete murine SERCA1 loss is neonatally lethal via diaphragm failure; human SERCA1 loss produces a mild non-progressive myopathy with no respiratory involvement. Proposed experiments: conditional/hypomorphic Atp2a1 alleles; quantify PMCA/NCX/SERCA2 compensation across species.
  2. KNOWLEDGE_GAP — which compensator? SERCA2 upregulation is reported in one human family (PMID:25614869) but not in the larger cohort (7/8 normal); bovine data favor PMCA. Unresolved, and it directly governs whether a compensation-boosting therapy is even conceivable. Curate as two competing mechanistic_hypotheses, not one chain.
  3. KNOWLEDGE_GAP — Brody syndrome's genetic cause. Patients with the full phenotype and reduced SERCA activity but no ATP2A1 variant remain unsolved (PMID:22704959). WGS in this cohort is the obvious unrun experiment.
  4. KNOWLEDGE_GAP — is residual SERCA activity prognostic? The 2026 assay finally makes this measurable; nobody has correlated it with severity.
  5. KNOWLEDGE_GAP — no omics of any kind. No transcriptomics, proteomics, metabolomics, or single-cell data on Brody muscle exists. Given the fiber-type-selective mechanism, snRNA-seq is a high-yield proposal.
  6. KNOWLEDGE_GAP — no human-relevant scalable model. No iPSC-derived myotube model published; cultured human myotubes express the wrong (neonatal SERCA1b) isoform.
  7. Contradiction to preserve, not resolve — dantrolene. Ineffective in 5 cohort patients (PMID:32040565), markedly effective in 1 case (PMID:41926432). Curate both with honest supports tags rather than picking a winner.
  8. Unreported but plausible mechanism. Distal 16p11.2 BP2–BP3 deletion (which removes one ATP2A1 copy) in trans with a point variant has never been reported as a cause of Brody myopathy. Flag as a hypothesis, not a finding.

Sources: - Molenaar et al., Brain 2020 — international study of 40 patients (PMID:32040565) - Brain 2020 full text, PMC7009512 - Odermatt et al., Nature Genetics 1996 (PMID:8841193) - Odermatt et al., Human Genetics 2000 (PMID:10914677) - Pan et al., J Biol Chem 2003 — SERCA1-null mouse (PMID:12556521) - Hirata et al., Development 2004 — accordion zebrafish (PMID:15469975) - Gleason et al., Dev Biol 2004 (PMID:15581877) - Vattemi et al., J Neuropathol Exp Neurol 2010 (PMID:20142766) - Voermans et al., Neuromuscul Disord 2012 — Brody syndrome (PMID:22704959) - Guglielmi et al., Mol Genet Metab 2013 (PMID:23911890) - Bianchini et al., J Biol Chem 2014 — UPS rescue (PMID:25288803) - Sambuughin et al., Mol Genet Genomic Med 2014 — MH family (PMID:25614869) - CFTR corrector C17, Hum Mol Genet 2025 (PMID:41206505) - Accordion zebrafish tq206, IJMS 2024 (PMID:39273176) - SERCA activity assay and reference values, Biochem Biophys Rep 2026 (PMID:41938373) - Şahin et al., Front Genet 2023 — Turkish patient (PMID:38125752) - Velardo et al., Front Neurol 2023 — two siblings (PMID:37332993) - Edmund, J Am Assoc Nurse Pract 2026 — dantrolene case (PMID:41926432) - Katirji, Muscle Nerve 2026 — neuromuscular hyperexcitability review (PMID:42124386) - OMIM #601003 — Brody disease - OMIM *108730 — ATP2A1 - Orphanet — Brody myopathy (ORPHA:53347) - OMIA:001464-9913 — Pseudomyotonia, congenital in Bos taurus - OMIA:001450-9913 — Congenital muscular dystonia 1 in Bos taurus - OMIA:002645-9615 — Paradoxical pseudomyotonia, SLC7A10-related, dog - Pseudomyotonia in Romagnola cattle, BMC Vet Res 2012 (PMID:23046865) - Chianina cattle ATP2A1 missense, Genomics 2008 (PMID:18786632) - Gly211Val/Gly286Val SERCA1 analysis, IJMS 2022 - OMIM #613444 — Chromosome 16p11.2 deletion syndrome, 220-kb - ClinVar — ATP2A1 variants - MedlinePlus Genetics — Brody myopathy - UC Davis VGL — Pseudomyotonia (PMT) in Chianina and Romagnola cattle

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 31
Resolved 29
Unresolved (possible confabulation) 2
Unverifiable 0
Quoted claims checked 1
Quoted claims found in source 1

Unresolved references

These identifiers did not resolve to a record and may be fabricated. A lookup that failed for transport reasons is indistinguishable from one that failed because the record does not exist, so spot-check before acting on them:

  • PMID:41938373 (5 mentions) - Identifier did not resolve to a record
  • PMID:18786632 (4 mentions) - Identifier did not resolve to a record