Becker Muscular Dystrophy

Mendelian MONDO:0010311 Pathograph 24 Show in embeddings browser Dystrophinopathy Muscular Dystrophy

Becker muscular dystrophy is an X-linked dystrophinopathy caused by pathogenic DMD variants that permit production of partly functional dystrophin. Protein quantity, structure, and clinical severity vary. In-frame variants predominate, but the reading-frame rule is predictive rather than diagnostic: out-of-frame, nonsense, splice, and other variants can also produce a Becker phenotype. Progressive proximal weakness, calf hypertrophy, exercise-related symptoms, or incidental hyperCKaemia may lead to diagnosis. Cardiomyopathy can be severe despite relatively mild skeletal muscle involvement. Age at loss of ambulation and respiratory impairment vary substantially between patients and genotypes.

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Inheritance

X-linked recessive HP:0001419

Inheritance is X-linked. A heterozygous mother has a 50% chance of transmitting the variant in each pregnancy; an affected father transmits it to all daughters and no sons. Heterozygous females may have cardiac disease, muscle symptoms, or rarely a more severe dystrophinopathy phenotype. A negative family history does not exclude the disorder.

X-linked recessive inheritance

Show evidence (2 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"If the mother of the proband has a DMD pathogenic variant, the chance of the mother transmitting it in each pregnancy is 50%. If the father of the proband has a DMD pathogenic variant, he will transmit it to all his daughters and none of his sons."

GeneReviews states parental transmission probabilities explicitly.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Heterozygous females are typically asymptomatic or may exhibit weakness, fatigue, and cardiac involvement."

The female phenotype extends beyond isolated cardiac risk and is variably expressed.

Discussions and Knowledge Gaps

Should Becker muscular dystrophy be curated as the therapeutic target state of exon-skipping antisense therapy in Duchenne muscular dystrophy, and does that make it a conformer of the antisense-oligonucleotide module?

INTERPRETATION OPEN interpretation_becker_is_the_target_state_of_dmd_exon_skipping

Attached to

pathophysiology#Reduced or Abnormal Partly Functional Dystrophin

Some Duchenne exon-skipping therapies restore an open reading frame and aim to produce partly functional, Becker-like dystrophin. Becker natural history and genotype-specific models can inform expectations, but an induced protein is not guaranteed to reproduce a particular Becker clinical trajectory. This untreated disease entry does not assert an antisense intervention in its causal path.

Show evidence (2 references)

PMID:16770791 SUPPORT REVIEW SYNTHESIS Human Clinical

"In Becker patients, in-frame mutations allow the synthesis of internally deleted, but largely functional dystrophins."

The protein state that exon skipping in Duchenne is designed to produce, stated here as the natural state in Becker.

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Dystrophin restoration therapies have been developed by using synthetic antisense oligonucleotides to restore the reading frame by exon skipping for individuals with specific pathogenic variants in DMD."

The source describes the reading-frame-restoration strategy in Duchenne; it does not establish treatment of Becker patients or guarantee a specific clinical outcome.

How should exceptions to the reading-frame rule be curated, given that a substantial minority of clinically definite Becker patients carry out-of-frame mutations?

INTERPRETATION OPEN interpretation_reading_frame_rule_is_statistical

Attached to

pathophysiology#DMD Pathogenic Variant

Reading-frame concordance is a statistical association: the 1989 deletion series reported 92%, and the Leiden database reported 91%. The Italian Becker cohort separately contained out-of-frame and nonsense variants among clinically characterized patients. These percentages have different denominators and cannot be pooled. Alternative splicing, translational re-initiation, and distal truncation can help explain exceptions, but the rescue mechanism must be demonstrated for the specific variant. Phenotype, dystrophin protein, and molecular findings should be interpreted together. Mild or asymptomatic in-frame deletion carriers may also be underascertained.

Show evidence (3 references)

PMID:2491009 SUPPORT Human Clinical

"The correlation between phenotype and type of deletion mutation is in agreement with the "reading frame" theory in 92% of cases and is of diagnostic and prognostic significance."

The deletion series supports a useful but incomplete association between reading frame and phenotype.

PMID:16770791 SUPPORT Human Clinical

"over 4700 mutations have been reported in the Leiden DMD mutation database, of which 91% are in agreement with this rule."

The larger mutation database reports a similar but distinct concordance estimate with a different denominator.

PMID:2491009 SUPPORT Human Clinical

"The distribution and frequency of deletions spanning the entire locus suggests that many "in-frame" deletions of the dystrophin gene are not detected because the individuals bearing them are either asymptomatic or exhibit non-DMD/non-BMD clinical features."

The ascertainment argument, made by the authors themselves, which bears on how the 92% should be read.

Does sustained correction of exercise vascular dysregulation improve strength or slow progression in defined Becker genotypes?

KNOWLEDGE GAP OPEN gap_vascular_rescue_and_long_term_becker_outcomes

Attached to

pathophysiology#Impaired Exercise-Induced Vasomodulation

Acute tadalafil and nitrate studies support an NO-dependent vascular mechanism, but they do not establish clinically meaningful disease modification. A four-week sildenafil trial was negative. Differences in intervention, duration, target abundance, and endpoints limit direct comparisons.

Show evidence (2 references)

PMID:23197572 SUPPORT Human Clinical

"The present study does not address whether restoring sympatholysis with PDE5A inhibition can slow disease progression and improve muscle strength."

The investigators explicitly distinguish vascular rescue from clinical efficacy.

PMID:25042931 SUPPORT Human Clinical

"Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations. Sildenafil had no effect on any of the outcome parameters."

The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.

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Pathophysiology

DMD Pathogenic Variant

Pathogenic variants in DMD alter dystrophin quantity or function. In-frame deletions and duplications are common, but neither reading frame nor variant position alone establishes the Becker phenotype. The Italian cohort included 779 in-frame, 89 out-of-frame, and 35 nonsense variants among 903 genetically characterized patients. Particular exon deletions correlate with clinical outcomes at the group level; substantial variation remains within genotypes and families.

Downstream

Reduced or Abnormal Partly Functional Dystrophin DMD variants can produce reduced amounts of dystrophin, an abnormal protein, or both, while retaining sufficient function for a Becker clinical phenotype. The protein outcome cannot be inferred solely from reading-frame preservation.

Show evidence (3 references)

PMID:3384440 SUPPORT Human Clinical

"Deletions identified in three BMD patients are shown to maintain the translational ORF for amino acids and predict a shorter, lower molecular weight protein."

The original statement of the reading-frame model, on the Becker side of the comparison.

PMID:39499670 SUPPORT Human Clinical

"Ten per cent of patients carried out-of-frame mutations, 4% nonsense mutations and 86% in-frame deletions/duplications."

The mutational composition of a 943-patient Becker cohort. It gives both the dominant in-frame class and the size of the exception to the rule.

PMID:39499670 SUPPORT Human Clinical

"Patients carrying del45-49 compared with del45-47 were associated with an earlier loss of ambulation (P = 1 × 10-4), whereas patients with del45-55 (P = 0.005), del48 (P = 0.02) and del48-49 (P = 0.02) were correlated with a later loss of ambulation compared with del45-47."

Within-class genotype-phenotype resolution: which exons are removed changes the trajectory even when the frame is preserved throughout.

Reduced or Abnormal Partly Functional Dystrophin

Residual dystrophin distinguishes the Becker phenotype from severe dystrophin deficiency, but its abundance and function vary. Internally deleted dystrophin is a common outcome, not the only one. In bmx mice with deletion of Dmd exons 45-47, skeletal and cardiac dystrophin protein is reduced despite preserved transcript abundance. Sarcolemmal nNOS localization is lost and alpha-sarcoglycan localization is reduced in this model; these allele-specific observations should not be assumed for every Becker variant.

dystrophin-glycoprotein complex at the sarcolemma GO:0016010

Animal models

bmx exon 45-47 deletion mouse Mouse partially recapitulates Reproduces the protein deficit with preserved transcript abundance.

Downstream

Contraction-Induced Skeletal Muscle Injury Partly functional dystrophin provides incomplete protection against contraction-induced skeletal muscle injury. The exon 45-47 bmx model retains susceptibility to eccentric contractions.

Dystrophin-Deficient Cardiomyocyte Injury The dystrophin deficit also affects cardiomyocytes and can cause cardiac dysfunction despite relatively preserved skeletal muscle function.

Loss of Sarcolemmal nNOS Localization Some DMD variants disrupt dystrophin-dependent membrane localization of nNOS. Human biopsy evidence shows this for several exon-deletion groups, while other Becker variants retain sarcolemmal nNOS.

Show evidence (5 references)

PMID:2491009 SUPPORT Human Clinical

"For cases with a deletion mutation, the "reading frame" hypothesis predicts that BMD patients produce a semifunctional, internally deleted dystrophin protein, whereas DMD patients produce a severely truncated protein that would be unstable."

The contrast at protein level between the two diseases, which is what this node models.

PMID:16770791 SUPPORT REVIEW SYNTHESIS Human Clinical

"In Becker patients, in-frame mutations allow the synthesis of internally deleted, but largely functional dystrophins."

Restatement of the same protein-level claim by a group curating the mutation database.

PMID:39499670 SUPPORT BACKGROUND Human Clinical

"Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations in DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac muscle."

States both the protein state and the two tissues it matters in, which is where this node branches.

+ 2 more references

Contraction-Induced Skeletal Muscle Injury

Dystrophin supports muscle membrane stability. In Becker muscular dystrophy, residual protein does not fully prevent contraction-related injury. Exon 45-47 bmx mouse muscle shows increased force loss after eccentric contractions, raised serum creatine kinase, necrotic and inflammatory foci, regeneration, and fibrosis. The severity of individual measurements need not lie uniformly between wild type and dystrophin-null muscle.

skeletal muscle fibre CL:0008002

Animal models

bmx exon 45-47 deletion mouse Mouse partially recapitulates Eccentric contraction experiments show greater force loss than wild type.

Downstream

Slowly Progressive Proximal Myopathy Recurrent injury, degeneration, and fibrofatty replacement contribute to progressive loss of skeletal muscle function; the pace varies across patients.

Elevated Creatine Kinase Circulating creatine kinase is a marker of skeletal muscle injury in Becker muscular dystrophy. Its level does not directly measure remaining strength and can decline as muscle is replaced by fat.

Show evidence (2 references)

PMID:16770791 SUPPORT REVIEW SYNTHESIS Human Clinical

"This gene codes for dystrophin, a protein important for maintaining the stability of muscle-fiber membranes."

Dystrophin's function at the muscle-fibre membrane, which is what a semifunctional protein partly preserves.

PMID:36628607 SUPPORT Model Organism

"Ten eccentric contractions of WT EDL muscle resulted in a 15.53% drop in ex vivo peak force. In contrast, this protocol reduced peak force by 20.16% in bmx EDL muscles (P = 0.0239 bmx vs. WT) and 20.86% in mdx EDL (Figure 2D)."

The genotype-defined model has greater contraction-induced force loss than wild type; it does not establish a uniform degree of protection relative to dystrophin-null muscle.

Slowly Progressive Proximal Myopathy

Proximal weakness and mobility loss progress at variable rates. In the retrospective Italian cohort, 111 of 822 patients with available ambulation information had lost walking ability at assessment. The Kaplan-Meier median age at loss of ambulation was 69 years, whereas the observed mean age among those who had already lost ambulation was 35.3 years. These are different statistics; neither describes an inevitable course for an individual. Respiratory decline can become clinically important, especially after loss of ambulation, and warrants surveillance.

Downstream

Progressive Proximal Muscle Weakness Proximal weakness is the principal clinical manifestation of the skeletal myopathy.

Waddling gait Pelvic-girdle involvement alters gait as weakness progresses.

Scoliosis Axial muscle weakness can contribute to scoliosis.

Reduced Forced Vital Capacity Extension of muscle weakness to respiratory muscles can reduce ventilatory capacity.

Show evidence (4 references)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"Information about LoA was known for 822 (87.2%) patients; of these, 111 (13.5%) patients had lost the ability to walk at the time of data collection, with a mean age at LoA of 35.3 (±15.0) years"

The full cohort report supplies the assessed denominator and observed event age, avoiding interpretation of a cross-sectional fraction as lifetime risk.

PMID:39499670 SUPPORT Human Clinical

"In 55% of patients, the diagnosis was prompted by the incidental finding of hyperCKaemia."

Incidental hyperCKaemia prompted many diagnoses in this Italian cohort; local testing practices affect the proportion.

PMID:33454189 SUPPORT Human Clinical

"We analysed 190 pulmonary function measurements with a median interval of one year (1-17y) and measured a 1.00% decline of Forced Vital Capacity percent predicted (FVC%pred) per year (p = 0.004)."

The quantified rate of respiratory decline.

+ 1 more reference

Dystrophin-Deficient Cardiomyocyte Injury

Abnormal or reduced dystrophin affects cardiac as well as skeletal muscle. Cardiac disease can progress independently of skeletal muscle severity. The bmx mouse demonstrates reduced cardiac dystrophin and impaired ventricular function; human surveillance must therefore consider the heart even when skeletal weakness is mild.

cardiac muscle cell CL:0000746

Downstream

Left Ventricular Impairment and Dilated Cardiomyopathy Cardiac dystrophin dysfunction can lead to progressive ventricular impairment. The exon 45-47 rat model supports progression to cardiomyopathy, while the intervening cellular sequence is not fully established for human Becker disease.

Cardiac Intercalated Disc Disorganization The exon 45-47 rat model shows altered intercalated-disc architecture and protein localization. The contribution of dystrophin quantity versus its altered structure is unresolved.

Show evidence (1 reference)

PMID:39499670 SUPPORT BACKGROUND Human Clinical

"Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations in DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac muscle."

Names cardiac muscle as one of the two tissues carrying the dystrophin deficit, which is the insult this node models.

Left Ventricular Impairment and Dilated Cardiomyopathy

Left ventricular systolic dysfunction and dilated cardiomyopathy are important complications, and heart failure is a major cause of mortality. In the Italian cohort, 187 of 621 assessed patients had LVEF below 55%, which measures systolic impairment rather than the prevalence of dilated cardiomyopathy. Certain deletions were associated with lower odds of impaired LVEF, but genotype does not determine an individual outcome.

Animal models

bmx exon 45-47 deletion mouse Mouse partially recapitulates Aged mice develop reduced ejection fraction and fractional shortening.

R-BMDdel45-47 rat Rat partially recapitulates Develops ventricular dilation, reduced ejection fraction, and cardiac fibrosis.

Downstream

Left Ventricular Impairment Reduced LVEF is the clinical readout of ventricular systolic dysfunction.

Dilated Cardiomyopathy Becker ventricular disease can progress to dilated cardiomyopathy and heart failure.

Show evidence (3 references)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"One hundred and eighty-seven (30.1%) patients showed LVEF% of <55%"

The full text defines the cardiac outcome as reduced ejection fraction and supplies its numerator; 621 patients had an LVEF measurement.

PMID:39499670 SUPPORT Human Clinical

"Both del45-55 (P = 0.002) and del48 (P = 0.003) were significantly associated with decreased odds of developing a pathological left ventricular ejection fraction compared with del45-47."

Genotypic modulation of the cardiac endpoint within the in-frame class.

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD. Mean age of death is in the mid-40s."

The older GeneReviews abstract identifies heart failure as a major source of morbidity and mortality. Its summary age at death is not compared numerically with ambulation estimates from another cohort.

Cardiac Intercalated Disc Disorganization

In exon 45-47 Becker rats, TMEM65 and connexin-43 are mislocalized and intercalated discs have widened, irregular folds and abnormal contacts with nearby sarcomeres. These findings suggest impaired cardiomyocyte coupling, but no targeted rescue experiment establishes their mediation of ventricular dysfunction. This is model-derived evidence, not a demonstrated universal human cellular lesion.

Animal models

R-BMDdel45-47 rat Rat partially recapitulates Reproduces structural and protein-localization abnormalities at intercalated discs.

Downstream

Left Ventricular Impairment and Dilated Cardiomyopathy Altered mechanical and electrical coupling is a proposed contributor to cardiac dysfunction in the rat model. Co-occurrence and structural data support the hypothesis, while causal mediation remains untested.

Show evidence (2 references)

PMID:39358550 SUPPORT Model Organism

"At the histological level, TMEM65 notably displayed a larger distribution and mislocalization from the ICD in both BMD and DMD ventricles"

Immunostaining shows mislocalization in the rat model; reduced Tmem65 RNA did not correspond to reduced TMEM65 protein abundance in Becker rat hearts.

PMID:39358550 SUPPORT Model Organism

"we found that Cx43 was more internalized in both BMD and DMD, with a lower co-localization with N-cadherin (NCAD), an intercalated disc marker"

Connexin-43 localization changes accompany intercalated-disc disorganization in dystrophic rat hearts.

Loss of Sarcolemmal nNOS Localization

Dystrophin serves as a scaffold for sarcolemmal nNOS. Some Becker variants reduce or abolish membrane nNOS localization; other variants retain it. In a biopsy-linked human series, nNOS staining was absent in seven patients and present in six. Total nNOS abundance and residual localization also vary, including between relatives with the same splice variant.

Downstream

Impaired Exercise-Induced Vasomodulation Loss of membrane-associated nNOS weakens local nitric-oxide-dependent attenuation of sympathetic vasoconstriction during exercise. Acute rescue with interventions that augment NO-cGMP signaling supports this pathway, without proving an effect on long-term muscle decline.

RyR1-Calstabin Complex Destabilization Mislocalized cytosolic nNOS is associated with altered RyR1-calstabin regulation in del45-55 muscle biopsies. The human study supports a candidate nitrosative pathway but does not resolve causal mediation or establish this branch for every Becker variant.

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/ SUPPORT Human Clinical

"Sarcolemmal staining for nNOS was absent in seven BMD patients (including all five patients with deletion of exons 45–47 or 45–48, and both patients with deletion of exons 3–7) but present in the other six patients."

Human biopsies show genotype-associated variation in nNOS localization; membrane loss is not universal in Becker muscular dystrophy.

Impaired Exercise-Induced Vasomodulation

During exercise, affected muscle may fail to attenuate reflex sympathetic vasoconstriction, causing functional ischemia under experimental conditions. This abnormality is associated with nNOS membrane localization but is not present in every Becker patient. Acute tadalafil or nitrate studies demonstrate reversibility of the vascular response; its contribution to chronic weakness or disease progression remains unresolved. Reduced local NO-cGMP signaling is supported by the localization findings and pharmacological rescue rather than by a direct assay of intracellular cGMP in these patients.

nitric oxide-cGMP-mediated signaling GO:0038060 ↓ DECREASED

Show evidence (3 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/ SUPPORT Human Clinical

"Sympatholysis was greatly impaired in all seven patients lacking sarcolemmal nNOS but well preserved in four of six patients in whom nNOS was detected at the sarcolemma."

The biopsy-linked physiology associates loss of sarcolemmal nNOS with impaired exercise vasomodulation, with additional heterogeneity among those retaining nNOS.

PMID:23197572 SUPPORT Human Clinical

"The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo."

The randomized crossover trial demonstrates an acute physiological response in the subgroup with abnormal placebo physiology, rather than long-term clinical benefit.

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/ SUPPORT Human Clinical

"In the subsequent placebo‐controlled trial performed in six of the 11 patients from the open‐label trial (P2, P3, P7, P12, P14 and P16), we confirmed that sodium nitrate restores functional sympatholysis, whereas placebo was without effect"

The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.

RyR1-Calstabin Complex Destabilization

In a study of 12 Becker patients with exon 45-55 deletions, cytosolic nitric oxide production correlated with RyR1 hypernitrosylation and calstabin-1 dissociation. These findings implicate altered regulation of the sarcoplasmic-reticulum calcium-release complex. The association does not establish measured calcium leak or its causal contribution across Becker genotypes.

Show evidence (1 reference)

PMID:22589245 SUPPORT Human Clinical

"Cytosolic NO production correlated with both hypernitrosylation of the sarcoplasmic reticulum calcium-release-channel ryanodine receptor type-1 (RyR1) and release of calstabin-1, a central hub of Ca(2+) signaling and contraction in muscle."

The 12-patient del45-55 biopsy study reports correlated biochemical abnormalities; it does not establish a universal lesion or directly measure the contribution to clinical decline.

✶

Histopathology

Myofiber Necrosis

Dystrophic muscle can show necrotic fibers with regeneration. In mild Becker disease, necrotic fibers may be scattered and other abnormalities subtle.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Optical microscopy examination can confirm the muscular dystrophy, demonstrati ng the association of necrosis, regeneration, and fibrosis."

The biopsy description identifies necrosis within the dystrophic pattern.

Muscle Fibrosis

Endomysial and interstitial fibrosis accompanies dystrophic remodeling and can be extensive in advanced disease, together with fatty infiltration.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Fatty infiltration and both endomy sial and interstitial extensive fibrosis are seen in the advanced stages of the disease."

The guideline describes the distribution and greater extent in advanced disease.

Variable Myofiber Size and Regeneration

Biopsy can show variable fiber size, splitting, hypercontracted fibers, regeneration, and internal nuclei. Findings may be subtle in mild disease and overlap other muscular dystrophies.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Optical microscopy examination can confirm the muscular dystrophy, demonstrati ng the association of necrosis, regeneration, and fibrosis. Marked variations in the fiber size, split fibers, and mul tinucleate and hyper -contracted bulky fib ers are also markers of dystrophinopathy"

The source describes regeneration, fiber-size variation, splitting, and abnormal nuclear and contraction morphology.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In mild clinical forms, m orphologic abnormalities may be subtle: moderate variations i n fiber size, scattered necrosis fibers, and rare nuclear internalizations."

Mild disease may have only subtle structural abnormalities.

⬡

Pathograph

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Phenotypes

Cardiovascular 3

Left Ventricular Impairment Left ventricular systolic dysfunction HP:0025169

Show evidence (1 reference)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"One hundred and eighty-seven (30.1%) patients showed LVEF% of <55%"

The full text defines the cardiac outcome as reduced ejection fraction and supplies its numerator; 621 patients had an LVEF measurement.

Dilated Cardiomyopathy HP:0001644

Show evidence (1 reference)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD."

GeneReviews identifies DCM-related heart failure as a common and important Becker phenotype without giving a numeric frequency band.

Dilated Cardiomyopathy in Heterozygous Females HP:0001644

Show evidence (1 reference)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Females heterozygous for a DMD pathogenic variant are at increased risk for DCM."

The carrier cardiac risk.

Digestive 3

Dysphagia HP:0002015

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Swallowing disorders are as frequent as those encountered in DMD pa tients with equal disabilities."

The guideline discusses swallowing disorders specifically in Becker patients and qualifies the comparison by disability severity.

Constipation HP:0002019

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Constipation can be a frequent complication of BMD, like in DMD."

The guideline explicitly identifies constipation as a Becker complication.

Gastroparesis HP:0002578

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"As skeleta l muscle weakness progresses, a delay in gastric emptying (gastroparesis) can occur lead to postprandial abdominal pain, nausea, vomiting, early satiety, and loss of appetite [92]."

The source relates delayed gastric emptying to progression of muscle weakness; it does not imply that every patient develops it.

Head and Neck 1

Macroglossia HP:0000158

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Pseudohypertrophy of the calves, tongue, or other muscles."

The guideline explicitly includes the tongue among sites of pseudohypertrophy.

Limbs 2

Calf muscle hypertrophy HP:0008981

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"The typical BMD patient is a young man presenting with a slowly progressive pelv ic deficit and calf hypertrophy together with an increase in CK levels"

The diagnostic description names calf hypertrophy alongside proximal weakness and raised CK.

Elbow flexion contracture HP:0002987

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"More moderate skeletal muscle manifestations (e.g., BMD) may be characterized by onset in adolescence to adulthood of progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy; weakness of quadriceps femoris (sometimes the only sign); activity-induced cramping..."

The Becker-specific description qualifies both variability and timing.

Metabolism 2

Elevated Creatine Kinase Elevated circulating creatine kinase activity HP:0003236

Show evidence (1 reference)

PMID:39499670 SUPPORT Human Clinical

"In 55% of patients, the diagnosis was prompted by the incidental finding of hyperCKaemia."

Raised creatine kinase as the presenting finding in the majority. The frequency slot is left empty because 55% describes how the diagnosis was prompted, not how many patients have a raised CK.

Elevated circulating hepatic transaminase concentration HP:0002910

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"The levels of liver enzymes s uch as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) can be increased, which may sometimes result in misdiagnosis, especially in pseudo-metabolic forms, and may lead to liver biopsy [30]."

The guideline describes transaminase elevation and the diagnostic pitfall; this finding does not establish primary liver disease.

Musculoskeletal 6

Progressive Proximal Muscle Weakness HP:0009073

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

The Becker-specific clinical paragraph supports the proximal distribution and progressive course.

Very Late-Onset Ambulant Phenotype Progressive proximal muscle weakness HP:0009073

Onset: ADULT

Show evidence (1 reference)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"With improved diagnostic techniques, it has been recognized that the mild end of the spectrum includes men with onset of symptoms after age 30 years who remain ambulatory even into their 60s."

The mild extreme of the phenotypic range.

Exercise-induced muscle cramps HP:0003710

Show evidence (1 reference)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

The Becker-specific clinical description explicitly identifies exertional cramping.

Lumbar hyperlordosis HP:0002938

Show evidence (1 reference)

PMID:36793492 SUPPORT BACKGROUND Human Clinical

"leading to walking on toes with lumbar lordosis and early loss of ambulation"

The clinical background of the trial identifies lumbar lordosis; it is background material rather than a measured trial endpoint.

Scoliosis HP:0002650

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Axial weakness: scoliosis, abdominal weakness with difficulties in getting up from the lying position"

The neuromuscular assessment section lists scoliosis among manifestations of axial weakness.

Increased muscle fatiguability HP:0003750

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"only the lower -limb muscles are affected symmetrically, causing fatigability while walking."

The diagnostic section describes exertional fatigability with symmetric lower-limb involvement.

Nervous System 4

Loss of Ambulation HP:0002505

Show evidence (1 reference)

PMID:39499670 SUPPORT Human Clinical

"At the last assessment, 13.5% of patients had lost the ability to walk at a median age estimated by Kaplan-Meier analysis of 69 years."

The Kaplan-Meier estimate accounts for censoring and differs from the observed age among patients who had already lost ambulation. Neither supports assigning a lifetime frequency band from 13.5%.

Waddling gait HP:0002515

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"This is followed by weakness in standing up or a waddling gait."

The guideline describes waddling gait in the progression of lower-limb muscle involvement.

Attention deficit hyperactivity disorder HP:0007018

Show evidence (1 reference)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"17 (2.9%) patients were reported to be diagnosed with attention-deficit/hyperactivity disorder"

The primary Becker cohort records a clinical diagnosis; incomplete retrospective ascertainment precludes a general frequency band.

Autism HP:0000717

Show evidence (1 reference)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"five (0.9%) with autism spectrum disorder"

The primary Becker cohort records a clinical diagnosis; incomplete retrospective ascertainment precludes a general frequency band.

Respiratory 1

Reduced Forced Vital Capacity HP:0032341

Show evidence (1 reference)

url:https://oup.silverchair-cdn.com/article-minimal/7876416 SUPPORT Human Clinical

"Only 12 patients (2.7%) had FVC% values of <50%, and all of them were non-ambulant"

The full text defines the respiratory threshold and ambulatory status. The denominator is 441 patients with FVC measurements, not all 943 participants.

Constitutional 1

Urinary incontinence HP:0000020

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Patients with BMD may ex perience uri nary incontinence regularly which c an have a detrimental effect on various aspects of their life, includi ng travel, social interactions, and emotional well-being [93, 94]."

The guideline identifies urinary incontinence in Becker patients rather than merely recommending screening for it.

🧬

Genetic Associations

DMD

Gene: DMD hgnc:2928 gene page relationship_type: CAUSATIVE

X-linked recessive

Show evidence (1 reference)

PMID:2491009 SUPPORT Human Clinical

"About 60% of both Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) is due to deletions of the dystrophin gene."

The historical deletion study establishes the shared DMD locus; it does not establish an absolute reading-frame discriminator.

💊

Medical Actions

ACE Inhibition for Established Cardiomyopathy

Action: Pharmacotherapy NCIT:C15986

Agent: ACE inhibitor NCIT:C247

Platform: Small molecule

ACE inhibitors are first-line medication for established Becker cardiomyopathy in the 2023 French guideline. That guideline recommends specialist discussion of cardioprotective treatment when LVEF is below 50% or MRI shows myocardial fibrosis. It does not recommend prophylactic ACE inhibition for every Becker patient with normal cardiac findings; evidence from Duchenne muscular dystrophy does not establish that indication in Becker muscular dystrophy.

Mechanism Target:

INHIBITS Left Ventricular Impairment and Dilated Cardiomyopathy — Treats ventricular dysfunction and adverse remodeling associated with cardiomyopathy.

Show evidence (1 reference)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"ACE inhibitors are used with or without beta blockers for cardiomyopathy in both DMD and BMD phenotypes."

The indication for established cardiomyopathy in both phenotypes.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Thus, there is no indication to use ACE inhibitors for systematic treatment of BMD patients regardless of cardiac phenotype, such as in Duchenne MD."

The French guideline does not support universal ACE-inhibitor prophylaxis irrespective of the Becker cardiac phenotype.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Patients with LVEF < 50% and/or evidence of myocardial fibrosis on MRI should be referre d to a specialized cardiologist in a tertiary center to discuss the initiation of cardioprotective"

Reduced LVEF or myocardial fibrosis prompts specialist assessment of cardioprotective treatment in this guideline.

Corticosteroid Therapy

Action: Pharmacotherapy NCIT:C15986

Agent: corticosteroid CHEBI:50858

Platform: Small molecule

Corticosteroids are used in selected patients with Becker muscular dystrophy, but efficacy is less established than in Duchenne muscular dystrophy. Benefits, adverse effects, and treatment duration require individual assessment; Duchenne trial results do not establish Becker efficacy. A 24-week open-label weekly-prednisone pilot enrolled 19 participants with limb-girdle muscular dystrophy and only one with Becker muscular dystrophy; pooled biomarker and functional changes do not establish Becker-specific benefit.

Show evidence (2 references)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Corticosteroid therapy improves muscle strength and function for individuals with DMD between ages five and 15 years; the same treatment is used in BMD, although the efficacy is less clear."

GeneReviews explicitly qualifies the uncertain Becker efficacy while describing clinical use.

PMID:35124660 SUPPORT Human Clinical

"Out of the 20 participants, seven were female, nineteen had LGMD and one had BMD"

The mixed pilot cohort contained only one Becker participant, precluding a Becker-specific efficacy estimate.

Cardiac Transplantation

Action: Organ Transplantation NCIT:C15289

Platform: Surgery

Cardiac transplantation may be considered for terminal heart failure in selected patients with limited skeletal muscle disability and without severe respiratory failure. Selection requires multidisciplinary assessment. The French guideline generally does not recommend transplantation after loss of ambulation or with significant respiratory failure; ventricular assist devices can be discussed individually in expert centers.

Mechanism Target:

BYPASSES Left Ventricular Impairment and Dilated Cardiomyopathy — Replaces the failing heart while leaving the underlying DMD variant and extracardiac manifestations unchanged.

Show evidence (1 reference)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"cardiac transplantation is offered to persons with severe dilated cardiomyopathy and BMD with limited or no clinical evidence of skeletal muscle disease."

The indication and its selection criterion.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In patients with terminal heart failure who have lost ambulation or have significant respiratory failure, cardi ac transplantati on is generally not indicated"

The guideline identifies motor and respiratory impairment as constraints on transplant selection.

Cardiac Surveillance

Action: Supportive Care NCIT:C15747

Platform: Other

Cardiac surveillance starts at diagnosis and continues regardless of skeletal muscle severity. Assessment includes ECG and echocardiography, with cardiac MRI to assess fibrosis and function when appropriate and Holter monitoring for cardiac dysfunction or conduction abnormalities. The 2026 GeneReviews chapter lists annual cardiac assessment for affected males and assessment before major surgery, with closer monitoring for fibrosis or dysfunction; its schedule partly draws on Duchenne care guidance. The 2023 French Becker guideline proposes assessment every two years with a normal echocardiogram and at least annually with LVEF below 50%. The interval should be individualized by cardiology. GeneReviews recommends ECG and cardiac imaging every three to five years for heterozygous females without cardiac manifestations, beginning in the second to third decade, and specialist-directed follow-up when abnormalities are present.

Show evidence (6 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Cardiac monitoring must systematically include ECG and echocardiogram. The other examinations must be discussed with the patient on the basis of the patients’ symptoms and ECG and echocardiogram findings. The frequency of these assessments depends on the initial findings. The minimum interval..."

The Becker guideline specifies ECG and echocardiography and a two-year interval when the echocardiogram is normal.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"For patie nts with LVEF < 50%, monitoring should be performed at least once a year."

Ventricular dysfunction calls for more frequent assessment.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"DMD/BMD By cardiologist incl EKG & echocardiogram or cardiac MRI • Annually & before major surgery • More frequently in those age >10 yrs & those w/myocardial fibrosis or ventricular dysfunction"

GeneReviews Table 8 recommends annual and preoperative cardiac assessment; its footnote identifies Duchenne care guidelines as a basis for the intensified schedule.

+ 3 more references

Perioperative Assessment and Anaesthetic Precautions

Action: Supportive Care NCIT:C15747

Platform: Other

Preoperative planning should assess cardiac and respiratory involvement and muscle weakness. Avoid succinylcholine because of hyperkalaemia and rhabdomyolysis risk. Volatile anaesthetics also require specialist risk assessment because of anaesthesia-induced rhabdomyolysis in dystrophinopathies. The ENMC consensus distinguishes this complication from malignant hyperthermia and reports no association of dystrophinopathies with malignant hyperthermia susceptibility.

Show evidence (2 references)

PMID:35971866 SUPPORT REVIEW SYNTHESIS Other

"AIR seems to be a specific complication of general anaesthesia in dystrophinopathies, especially at paediatric age. AIR can cause life‐threatening hyperkalaemia, and the risk of occurrence is possibly linked to the use of succinylcholine and/or volatile anaesthetics"

The muscular-dystrophy recommendations identify anaesthesia-induced rhabdomyolysis and hyperkalaemia as the relevant dystrophinopathy hazards.

PMID:35971866 SUPPORT REVIEW SYNTHESIS Other

"There is no association with MH"

In Table 4, this statement follows the dystrophinopathy AIR recommendation and distinguishes it from malignant hyperthermia; it does not remove the need for anaesthetic precautions.

Investigational Givinostat

Action: Pharmacotherapy NCIT:C15986

Agent: Givinostat NCIT:C71716

Platform: Small molecule

A 12-month placebo-controlled trial in 51 adults with Becker muscular dystrophy failed its primary total-fibrosis endpoint and showed no significant functional benefit. Secondary thigh and quadriceps MRI fat-fraction findings suggested a possible signal, but baseline imbalance and the small sample limit interpretation. This is investigational Becker evidence and does not establish an effective disease-modifying treatment.

Show evidence (2 references)

PMID:36793492 SUPPORT Human Clinical

"The study failed to achieve the primary endpoint. However, there was a potential signal from the MRI assessments suggesting givinostat could prevent (or slow down) BMD disease progression."

The trial conclusion distinguishes the negative primary outcome from the exploratory interpretation of secondary MRI findings.

PMID:36793492 SUPPORT Human Clinical

"Adverse events, most mild or moderate, were reported by 88.2% and 52.9% patients receiving givinostat and placebo."

Adverse events were more frequent with givinostat; the paper details platelet and triglyceride abnormalities.

Investigational Sevasemten

Action: Pharmacotherapy NCIT:C15986

Agent: Sevasemten NCIT:C199222

Platform: Small molecule

Sevasemten inhibits fast skeletal muscle myosin ATPase to reduce injurious contraction. A short phase 1 Becker cohort comprised five treated patients and two placebo recipients; muscle-injury biomarkers decreased but the study was too small and short to establish clinical efficacy. In a later uncontrolled 12-person study, biomarkers remained reduced and functional measures were stable over two years. These observations support investigation, not a proven treatment effect. The completed CANYON/GRAND CANYON registry had no posted results at the September 2026 review.

Mechanism Target:

INHIBITS Contraction-Induced Skeletal Muscle Injury — Investigational fast-myosin inhibition aims to reduce contraction-associated muscle injury. Sustained biomarker reductions in the small open-label Becker study support this proposed effect; they do not establish prevention of long-term functional decline.

Show evidence (1 reference)

PMID:42308588 SUPPORT PRIMARY RESULT Human Clinical

"Treatment with sevasemten was associated with reductions in circulating biomarkers of muscle injury that were evident within 4 weeks and sustained for up to 24 months."

The 12-person study reports a durable biomarker association consistent with the proposed target effect, with no placebo control to establish efficacy.

Show evidence (3 references)

PMID:40452637 SUPPORT Human Clinical

"In Part C, 7 men with BMD were randomized to sevasemten (N = 5) or placebo (N = 2)"

Defines the very small Becker randomized cohort within a larger study dominated by healthy volunteers.

PMID:42308588 SUPPORT Human Clinical

"As this was an open-label trial with no placebo control, caution is required in interpretation. Additional limitations of this study include the small sample size and the lack of diversity in enrolled participants (100% White)."

The 24-month study cannot distinguish treatment benefit from natural-history variability or other uncontrolled influences.

PMID:42308588 SUPPORT Human Clinical

"Treatment with sevasemten was associated with reductions in circulating biomarkers of muscle injury that were evident within 4 weeks and sustained for up to 24 months. Physical function, as assessed by North Star Ambulatory Assessment (NSAA), was stable over 24 months."

Records the observed biomarker and functional trajectories without treating them as randomized efficacy evidence.

Investigational Vamorolone

Action: Pharmacotherapy NCIT:C15986

Agent: Vamorolone NCIT:C152825

Platform: Small molecule

Vamorolone improved selected strength and histological measures and increased dystrophin protein in bmx mice. This preclinical study did not establish human efficacy or long-term cardiac benefit. The subsequently completed Becker phase II pilot has registry results posted in September 2026; its 24-week functional data are descriptive and do not establish a clinically meaningful benefit. The trial must be distinguished from Duchenne treatment evidence.

Show evidence (2 references)

PMID:37534133 SUPPORT Model Organism

"Dystrophin increases of 49% (p < 0.0001) were found in the gastrocnemius and 55% (p = 0.0173) in the heart with vamorolone treatment"

The mouse experiment shows an increase relative to vehicle-treated bmx animals, not normalization to healthy dystrophin levels or proof of human efficacy.

PMID:37534133 SUPPORT Model Organism

"to fully demonstrate causation, further studies are needed to expand upon these and previous studies."

The authors limit the proposed microRNA mechanism: reduced microRNAs and increased dystrophin correlate, but direct causal mediation was not demonstrated.

Physical Therapy and Adapted Exercise

Action: Physical Therapy NCIT:C15302

Platform: Behavioral / lifestyle

Individualized physical therapy uses gentle progressive aerobic activity, stretching, low-resistance exercise, balance work, and fall prevention to maintain function and joint mobility. Exercise intensity should account for muscle weakness, fatigue, pain, and cardiac or respiratory involvement; avoid excessive contraction and eccentric loading of weak muscles.

Show evidence (3 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"This physical activity must be gentle and progressive and must take into account the specificities of BMD when choosing the exercises to offer"

The guideline recommends gradual activity adapted to Becker muscular dystrophy.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Maintenance of segmenta l and spinal muscular and joint flexibility for analgesic pu rposes by passive mobilizations and stretching, prepar ation and recovery for exercise and proprioceptive stimulation: stretching, posture, etc."

Stretching and passive mobilization address flexibility and discomfort.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"The most affected muscl es (those with a muscle testing MRC rating < 4) require more precautions, specifically by limiting intense contract ions and eccentric stresses and promoting aerobic metabolism."

Weak muscles require limits on intense contraction and eccentric loading.

Orthoses and Mobility Support

Action: Supportive Care NCIT:C15747

Platform: Other

Selected posture or walking orthoses can address deformity and support function. Wheelchairs or scooters become appropriate when walking-related falls and fractures outweigh functional benefit. Occupational and rehabilitation teams can adapt transfers, self-care, communication, and home, school, or workplace access.

Show evidence (3 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Posture orthoses may be used in some patients. In the lower limbs, nocturnal posture orthoses can be proposed to address certain deformities (e.g., anti-flexum knee or antiequine orthosis)."

Night-time postural orthoses are options for selected deformities.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Manual wheelchair; electric scooter and/or electric wh eelchair are necessary when the risks linked to walking (falls, fractures) become greater than the functional benefits."

The mobility decision balances walking benefit against injury risk.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Specific devices facilitating meals, washing, toileting, leisur e, transfers, and environmental control can be implemented."

Assistive devices support daily activities and environmental access.

Orthopedic Surgery for Function-Limiting Deformity

Action: Surgical Procedure NCIT:C15329

Platform: Surgery

Selected tendon or foot procedures may help walking and posture. Spinal fusion is reserved for severe forms. Rarely, macroglossia with ventilatory or swallowing consequences warrants surgery; operative planning requires cardiac, respiratory, and anesthetic assessment.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Some surgeries (e.g., Achilles tendon tenotomy, gastrocnemius aponeurotomy, tendon transfers, osteotomies or foot arthrodesis) are useful, and their u ses must be linked to functions such as walking and posture s tability. Vertebral arthrodesis is limited to the most severe forms close to DMD"

The guideline links surgery to functional impairment and limits spinal fusion to severe disease.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In rare cases, macroglossia surgery may be required because of functional consequences (ventilation, swallowing, etc.)."

Functionally significant macroglossia is a rare surgical indication.

Neuropsychological and Mental Health Care

Action: Supportive Care NCIT:C15747

Platform: Other

Assess cognitive, educational, behavioral, and emotional needs from diagnosis and when school or employment difficulties emerge. Use findings to tailor family, school, and workplace support. The French guideline recommends reassessment every two to three years in children, mental-health screening at neuromuscular visits, and formal annual psychological evaluation. Medication decisions should account for cardiac status, interactions, and adverse effects.

Show evidence (4 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Cognitive or psychiatric assessment has to be consider ed at diagnosis, and especially in the event of integration or access to employment issues."

Assessment is considered from diagnosis and when participation difficulties arise.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"For children, assessments should be performed every 2 –3 years to monitor a child’s developmental progress and response to interventions."

Repeated childhood assessment guides developmental support.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Formal annual evaluation by the mental health clinician is advised to assess the psychological wellbeing of the individual, parents, and siblings."

The guideline includes recurring psychological evaluation for patients and families.

+ 1 more reference

Respiratory Surveillance

Action: Supportive Care NCIT:C15747

Platform: Other

Regular evaluation includes symptoms of nocturnal hypoventilation, orthopnea, cough effectiveness, pulmonary function, and sleep investigations when indicated. The French Becker guideline recommends pulmonary function testing every two years if normal and annual specialist follow-up if abnormal. The 2026 GeneReviews dystrophinopathy schedule recommends annual respiratory evaluation and every six months after loss of ambulation, citing Duchenne care guidance. The treating team should individualize frequency to findings and progression.

Show evidence (3 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"A respiratory functional exploration should be performed every 2 years, with no pulmonologist advice required at this stage if the findings are normal."

The French guideline gives a two-year interval when respiratory testing is normal.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In cases with an abnormal fVC, the frequency of monitoring should be ann ual. A subsequent pulmonologist assessment, performed a t least annually, will indicate the need for blood gas analysis or nightly examinations."

Abnormal FVC warrants annual or more frequent specialist assessment.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Respiratory By pulmonologist for assessment of respiratory function Annually; then every 6 mos after loss of ambulation"

GeneReviews Table 8 gives a more frequent dystrophinopathy schedule; footnote 1 identifies its Duchenne guideline basis.

Noninvasive Ventilation for Hypoventilation

Action: Non-Invasive Mechanical Ventilation NCIT:C171457

Platform: Device

Nocturnal noninvasive ventilation is offered when diaphragmatic weakness produces hypoventilation, with specialist titration and follow-up. Respiratory support depends on functional assessment and symptoms rather than skeletal muscle disability alone.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In cases showing actual diaphragmatic involvemen t with hypoventilation, nocturn al noninvasive ventilation will be offered by the pulmonologist with a specific followup."

The guideline links nocturnal noninvasive ventilation to documented hypoventilation.

Cough Assistance

Action: Supportive Care NCIT:C15747

Platform: Other

Weak or ineffective cough warrants respiratory physiotherapy and individually selected manual or mechanical cough-assistance techniques, with pulmonology follow-up.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In cases showing a cough d eficiency, cough aid techniques will be offered by the pulmonologist or physiotherapist. A pulmonologist follow-up is then necessary."

The guideline recommends cough assistance when a cough deficit is present.

Swallowing and Nutritional Support

Action: Supportive Care NCIT:C15747

Platform: Other

Assess chewing, swallowing safety, weight trajectory, and nutritional intake. Adapt food texture and head position for impaired pharyngeal propulsion, provide feeding aids and speech-language input as needed, and consider oral nutritional supplements when intake is inadequate. Changes in mobility require reassessment of energy needs.

Show evidence (3 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"If the disorders are secondary to poor pharyngeal propulsion, the textures (mixed, adequately “slippery”) of the food and the po sition of the head during meals should be adapted."

Food texture and head position are adapted to swallowing mechanics.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Oral nutritional supplements may be offered when increase in caloric intake becomes necessary."

Supplementation is considered when increased caloric intake is needed.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In the most severe patien ts there is a risk of secondary undernutrition. It is then necessary to identify all the aggravating factors: involvement of the upper limbs (speci al cutlery, raised meal plan …), macroglossia or involvement of chewing muscles (hygiene care o ral, speech therapy,..."

Nutritional assessment includes feeding mechanics, gastrointestinal problems, deformity, and ventilation-related factors.

Gastrostomy for Inadequate or Unsafe Oral Intake

Action: Surgical Procedure NCIT:C15329

Platform: Surgery

Gastrostomy is reserved for the uncommon situation in which oral feeding cannot provide safe nutritional intake. Assess respiratory function and ventilatory requirements before placement and use a team experienced with neuromuscular disability.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Situations necessitating artificial feeding are rare in patients with BMD. If oral feeding cannot ensure safe nutritive intake, a gastrostomy can be set up as the last resort. However, bef ore creating a gastrostomy, the patient’s respiratory function a nd, in particular, the need for..."

The guideline describes the indication and preprocedural respiratory assessment.

Gastrointestinal Symptom Management

Action: Supportive Care NCIT:C15747

Platform: Other

Gastroenterology assessment addresses constipation, reflux, and gastric motility problems. Management is individualized and can include diet, bowel regimens, and medication; severe feeding or motility problems may require enteral support.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"A gastroenterologist should be consulted for manageme nt of constipation, gastroesophageal reflux, and gastrointestinal motility concerns, and when gastrostomy tube placement is needed."

The guideline identifies gastrointestinal problems requiring specialist management.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Constipation can be addressed through various measures, including adopting a fiber-rich diet, implementing toilet training techniques, engaging in physiotherapy, considering laxatives like polyethylene glycol, milk of magnesia, or lactulose may be necessary."

Constipation care combines nonpharmacologic measures and laxatives when needed.

Urological Assessment and Care

Action: Supportive Care NCIT:C15747

Platform: Other

Lower urinary tract symptoms warrant comprehensive urological evaluation, potentially including urodynamic assessment, and ongoing treatment and follow-up tailored to the cause.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In cases where lower ur inary tract symptoms are present, it is advisable to undergo a comprehensive urological evaluation, which may include urodynamic examinations, and to receive thorough follow-up care."

The recommendation is symptom-driven rather than routine invasive testing for all patients.

Bone Health and Pain Management

Action: Supportive Care NCIT:C15747

Platform: Other

Assess bone health and calcium and vitamin D needs, particularly with reduced mobility. Pain management includes positioning, appropriate bedding, mobilization, and individualized analgesia. Medication choice should account for constipation, respiratory or cardiac impairment, and drug interactions.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Prevention of osteopenia with calcium and vitamin D supplementation must be estimated and promptly proposed in the event of reduced mobil ity."

Reduced mobility prompts assessment of calcium and vitamin D supplementation.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Analgesic pharmacologica l treatment (anti -inflammatory, muscle relaxants) must tak e into account the side effects (especially cardiac and respira tory effects) and possible drug interactions."

Analgesia must account for cardiorespiratory effects and interactions.

Respiratory Vaccination

Action: Supportive Care NCIT:C15747

Platform: Other

The French guideline recommends pneumococcal and COVID-19 vaccination and annual influenza vaccination, following applicable immunization schedules.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Immunization with pneumococcal and COVID-19 vaccines and annual immunization with the influenza vaccine according to the vaccination schedule are strongly recommended, as for any disease with comorbidities [103]."

Vaccination is part of preventive care for patients with neuromuscular comorbidity.

Genetic Counseling and Family Evaluation

Action: Genetic Counseling NCIT:C15240

Platform: Other

Offer counseling about X-linked transmission, variable manifestations in heterozygous females, and residual recurrence risk from parental germline mosaicism. Evaluate at-risk male and female relatives, using the familial variant when known. Discuss reproductive options before pregnancy; prenatal testing is possible after variant identification, and preimplantation testing may require additional phasing.

Show evidence (4 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"The optimal time for determination of genetic risk and discussion of the availability of prenatal/ preimplantation genetic testing is before pregnancy."

Counseling and reproductive planning are ideally offered before pregnancy.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Female relatives. It is appropriate to evaluate at-risk female family members (i.e., first-degree relatives of a proband with a DMD pathogenic variant) to identify as early as possible those who would benefit from cardiac and skeletal muscle evaluation and surveillance."

Identifying heterozygous relatives enables cardiac and skeletal surveillance.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Once the DMD pathogenic variant has been identified in an affected family member, prenatal testing is possible."

Prenatal testing depends on identifying the familial pathogenic variant.

+ 1 more reference

Pregnancy Planning for Heterozygous Females

Action: Supportive Care NCIT:C15747

Platform: Other

Assess cardiac status before conception or when pregnancy is recognized, including in asymptomatic heterozygous females. Symptomatic females also require skeletal muscle assessment. Those with dilated cardiomyopathy need coordinated care from a cardiac specialist and high-risk obstetrics, including review of cardiac medications.

Show evidence (3 references)

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Symptomatic heterozygous women should undergo an evaluation for DMD-related cardiomyopathy and skeletal muscle involvement ideally prior to conceiving a pregnancy or as soon as the pregnancy is recognized."

Preconception or early-pregnancy evaluation includes cardiac and skeletal manifestations in symptomatic females.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Asymptomatic women who are heterozygous for a DMD pathogenic variant should consider undergoing a cardiac evaluation prior to conception or when a pregnancy is recognized. It is recommended that women with evidence of dilated cardiomyopathy should be treated and/or monitored by a cardiac..."

Cardiac evaluation also applies to asymptomatic heterozygotes, and cardiomyopathy requires coordinated specialist care.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Cardiac medications need to be reviewed and potentially adjusted in women who are planning on becoming pregnant."

Medication review is part of pregnancy planning.

Advanced Heart Failure Medication and Device Care

Action: Supportive Care NCIT:C15747

Platform: Other

Overt heart failure or ventricular systolic dysfunction requires specialist treatment using heart-failure guidance. The French Becker guideline includes ACE inhibitors or angiotensin-receptor antagonists, beta blockers, mineralocorticoid-receptor antagonists, and selected resynchronization or defibrillator therapy. Ventricular assist devices may be considered as a bridge to transplantation or destination therapy; candidacy depends on motor, respiratory, and overall clinical status.

Show evidence (3 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In patients with overt h eart f ailure or left ventricular (LV) systolic dysfunction, the therapeutic strategy should follow the recommendations for th e treatment of heart failure in the general population, based on (1) ACE inhibitors (or angiotensin II antagonists), b eta blockers,..."

The guideline recommends general heart-failure pharmacotherapy for overt heart failure or ventricular systolic dysfunction.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"In ambulant patients with terminal heart failure and absence of severe respiratory f ailure, cardiac transplantation and an LV assist device (as a brid ge to transplant or destination therapy) should be consid ered."

Selected patients can be considered for transplantation or ventricular assistance.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"(2) cardiac resynchronization therapy, and (3) implantable cardiac defibrillator if LVEF < 30%."

The 2023 guideline includes device options; current eligibility requires specialist assessment rather than treating its historical EF threshold as universal.

Investigational Tadalafil

Action: Pharmacotherapy NCIT:C15986

Agent: Tadalafil NCIT:C47743

Platform: Small molecule

A randomized double-blind crossover experiment in ten ambulatory men with preserved cardiac function showed acute improvement of exercise blood-flow regulation. Eight of nine participants with impaired sympatholysis on placebo responded. The study measured forearm oxygenation and does not establish sustained improvement in strength, ambulation, or progression.

Mechanism Target:

INHIBITS Impaired Exercise-Induced Vasomodulation — Acutely improves the abnormal exercise vascular response; a downstream effect on chronic muscle disease has not been established.

Show evidence (1 reference)

PMID:23197572 SUPPORT Human Clinical

"The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo."

The randomized crossover trial demonstrates an acute physiological response in the subgroup with abnormal placebo physiology, rather than long-term clinical benefit.

Show evidence (1 reference)

PMID:23197572 SUPPORT Human Clinical

"The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo."

The randomized crossover trial demonstrates an acute physiological response in the subgroup with abnormal placebo physiology, rather than long-term clinical benefit.

Investigational Sodium Nitrate

Action: Pharmacotherapy NCIT:C15986

Agent: sodium nitrate CHEBI:63005

Platform: Small molecule

Nitrate-rich beetroot juice improved functional sympatholysis in a small acute Becker study, including a placebo-controlled crossover substudy in six participants. This physiological result does not establish long-term benefit or safety as a Becker disease-modifying therapy.

Mechanism Target:

INHIBITS Impaired Exercise-Induced Vasomodulation — Acutely improves the abnormal exercise vascular response; a downstream effect on chronic muscle disease has not been established.

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/ SUPPORT Human Clinical

The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/ SUPPORT Human Clinical

The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.

Sildenafil Trial with No Demonstrated Clinical Benefit

Action: Pharmacotherapy NCIT:C15986

Agent: Sildenafil NCIT:C61940

Platform: Small molecule

A randomized placebo-controlled crossover trial with two four-week treatment periods found no effect on blood flow, maximal work capacity, or cardiac function. Sixteen participants completed skeletal-muscle evaluations and thirteen completed cardiac MRI. These findings do not support sildenafil as an established Becker disease-modifying treatment.

Show evidence (1 reference)

PMID:25042931 SUPPORT Human Clinical

"Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations. Sildenafil had no effect on any of the outcome parameters."

The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.

🔬

Diagnosis

DMD Genetic Testing with Reading-Frame Interpretation

Identify a pathogenic DMD variant using deletion/duplication analysis and sequencing, interpreted with the clinical phenotype and, when needed, dystrophin protein studies. Reading-frame prediction helps interpretation but does not by itself classify Becker versus Duchenne muscular dystrophy. The historical 92% concordance estimate applies to the analyzed deletion series. In unresolved cases, muscle RNA/cDNA analysis can identify splice abnormalities missed by standard DNA testing. Some urine-derived RNA approaches remain research investigations. Comprehensive assays capable of detecting sequence and copy-number variants are an alternative to sequential testing.

Genetic Testing NCIT:C15709

Show evidence (7 references)

PMID:2491009 SUPPORT Human Clinical

"The correlation between phenotype and type of deletion mutation is in agreement with the "reading frame" theory in 92% of cases and is of diagnostic and prognostic significance."

The accuracy of the rule and the authors' own statement that it is diagnostically and prognostically useful.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Identification of a hemizygous or heterozygous DMD variant of uncertain significance does not establish or rule out the diagnosis."

A VUS alone is insufficient for molecular confirmation.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Analysis to detect copy number variants (CNVs), i.e., deletions or duplications of DMD"

The stepwise algorithm begins with deletion/duplication analysis.

+ 4 more references

Cardiac Surveillance Independent of Skeletal Muscle Severity

Evaluate cardiac involvement from diagnosis even when skeletal muscle weakness is mild. ECG and echocardiography establish baseline cardiac status; MRI can identify myocardial fibrosis before echocardiography becomes abnormal.

Show evidence (2 references)

PMID:20301298 SUPPORT REVIEW SYNTHESIS Other

"Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity and the most common cause of death in BMD."

The cardiac burden of Becker muscular dystrophy can be substantial despite relatively mild skeletal muscle disease.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Cardiac MRI should also be discussed at diagnosis since it prov ides a more accurate estimation of cardiac function than echocardiography and can identify myocardial fibrosis, ma inly in the inferolateral wall, which can be present in patient s with a normal echocardiogram."

MRI can detect myocardial fibrosis despite a normal echocardiogram.

Muscle Biopsy and Dystrophin Protein Assessment

Muscle biopsy, immunohistochemistry, and dystrophin immunoblotting can clarify unresolved or atypical cases. Normal immunostaining does not exclude Becker muscular dystrophy; immunoblotting with antibodies against different protein regions can assess abundance and size. Biopsy is not routinely required when molecular and clinical findings already establish the diagnosis.

Muscle Biopsy NCIT:C51895

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Dystrophin immunochemistry usually shows decreased or no findings with some or all of the dedicated antibodies, but may also show normal findings. The decrease can be present in all the fibers or manifest in a fragmented manner."

The guideline warns that immunostaining can appear normal and explains why immunoblotting with multiple antibodies is informative.

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Diagnosis should be completed by western blotting of dystrophin"

The guideline recommends immunoblotting to complete dystrophin protein assessment.

📊

Prevalence

Male births

Birth Prevalence 5.6 per 100,000 1–9 per 100,000 (births)

Approximately 1 in 18,000 male births, converted to 5.6 per 100,000 male births. The denominator is male births specifically, not the general population, so this figure must not be compared directly with a whole-population prevalence.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"Becker muscular dystrophy (BMD) is one of the most frequent among neuromuscular diseases, affecting approximately 1 in 18,000 male births."

The source figure and its male-birth denominator.

🔀

Differential Diagnoses

Conditions with similar clinical presentations that must be differentiated from Becker Muscular Dystrophy:

Limb-Girdle Muscular Dystrophy Not Yet Curated MONDO:0016971

Overlapping Features Proximal weakness, raised CK, calf enlargement, and cardiopulmonary disease can overlap Becker muscular dystrophy.

Distinguishing Features

Many subtypes have autosomal inheritance and affect both sexes; the clinical pattern and causal gene distinguish them from DMD-related disease.
The French guideline highlights FKRP-related disease and sarcoglycanopathies; protein studies may show reduced alpha-dystroglycan or sarcoglycans. These findings require integrated molecular interpretation.

Show evidence (2 references)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

"The main differential diagnosi s included limb girdle muscular dystrophy (LGMD), facio- scapulo-humeral muscular dystrophy type 1 (FSHD 1), inflammatory myopathies and spinal muscular atrophy (SMA) are summarized in Table 1"

Table 1, inspected in the full PDF, compares FKRP-related disease and sarcoglycanopathies with Becker disease; the cached narrative identifies the differential group.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf SUPPORT REVIEW SYNTHESIS Other

"Limb-girdle muscular dystrophy 1 (OMIM PS253600 & PS603511) AR AD • HyperCKemia • Proximal muscle weakness • Cardiopulmonary involvement • Impacts males & females equally • Highly variable onset that ranges from early childhood to late adulthood depending on subtype"

GeneReviews Table 3 documents proximal weakness, hyperCKemia, cardiopulmonary overlap, and autosomal inheritance affecting both sexes.

Facioscapulohumeral Muscular Dystrophy Type 1 Not Yet Curated MONDO:0008030

Overlapping Features Shoulder-girdle weakness may prompt consideration of Becker muscular dystrophy.

Distinguishing Features

Facial weakness, scapular winging, and asymmetric involvement favor FSHD1; the French guideline lists normal to moderately elevated CK and a D4Z4 repeat contraction mechanism.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

The narrative identifies FSHD1; its distinguishing pattern and molecular mechanism are given in Table 1, inspected in the source PDF.

Proximal Spinal Muscular Atrophy Not Yet Curated MONDO:0019079

Overlapping Features Proximal limb weakness can overlap the motor presentation of Becker muscular dystrophy.

Distinguishing Features

Fasciculations, reduced or absent tendon reflexes, and a neurogenic pattern favor spinal muscular atrophy. The French table specifically describes the recessive SMN-associated form.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

The narrative identifies SMA, and the full PDF Table 1 supplies its neurogenic distinguishing features.

Inflammatory Myopathies

Overlapping Features Acquired proximal weakness and raised CK can resemble muscular dystrophy.

Distinguishing Features

Subacute progression, inflammatory biopsy findings, and muscle edema on MRI support an inflammatory differential, although inflammation alone does not exclude Becker muscular dystrophy.

Show evidence (1 reference)

PMID:37422773 SUPPORT REVIEW SYNTHESIS Other

The narrative identifies inflammatory myopathies; Table 1 supplies subacute weakness, inflammation, and MRI edema. The biopsy text separately notes that inflammatory abnormalities can occur in Becker disease.

🔬

Clinical Trials

NCT03238235 PHASE_II COMPLETED

Randomized placebo-controlled givinostat trial in 51 adults, completed in 2021. The published 12-month study failed its primary total-fibrosis endpoint; secondary MRI signals did not establish functional efficacy.

Show evidence (2 references)

clinicaltrials:NCT03238235 SUPPORT Human Clinical

"Primary objective: to establish the histological effects of Givinostat versus placebo administered over 12 months."

The registry identifies histological effects as the primary objective; the published trial reports the total-fibrosis endpoint.

url:https://clinicaltrials.gov/api/v2/studies/NCT03238235 SUPPORT Other

""briefTitle":"Clinical Study to Evaluate the Efficacy and Safety of Givinostat in Ambulant Patients With Becker Muscular Dystrophy","officialTitle":"A Randomised, Double Blind, Placebo Controlled Study to Evaluate the Micro-macroscopic Effects on Muscles, the Safety and Tolerability, and the..."

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

NCT05291091 PHASE_II COMPLETED

CANYON/GRAND CANYON randomized sevasemten study, with 244 enrolled participants across cohorts. The registry was updated September 21, 2026 and marks the study completed. The GRAND CANYON primary functional outcome is change in total NSAA score at 18 months; no results are posted in the retrieved registry record.

Show evidence (2 references)

clinicaltrials:NCT05291091 SUPPORT Human Clinical

"A study of sevasemten (EDG-5506) in Becker muscular dystrophy (known as CANYON) and pivotal cohort (known as GRAND CANYON). The EDG-5506-201 CANYON study was expanded to include an additional 175 adult participants in a cohort called GRAND CANYON, that is a multicenter, randomized, double-blind,..."

The registry summary identifies the study design and intervention.

url:https://clinicaltrials.gov/api/v2/studies/NCT05291091 SUPPORT Other

""briefTitle":"Phase 2 Study of EDG-5506 in Becker Muscular Dystrophy (GRAND CANYON)","officialTitle":"A Phase 2 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Effect of EDG-5506 on Safety, Biomarkers, Pharmacokinetics, and Functional Measures in Adults and Adolescents With..."

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

NCT05160415 PHASE_I COMPLETED

Completed open-label ARCH sevasemten dose-escalation study in 12 adults. Safety and tolerability were primary; the published two-year biomarker and functional observations are uncontrolled.

Show evidence (2 references)

clinicaltrials:NCT05160415 SUPPORT Human Clinical

"The ARCH study was an open-label, single-center, Phase 1b study of sevasemtem (EDG-5506) to assess the safety and pharmacokinetics (PK) of sevasemten in adults with Becker muscular dystrophy (BMD)."

The registry summary identifies the study design and intervention.

url:https://clinicaltrials.gov/api/v2/studies/NCT05160415 SUPPORT Other

""briefTitle":"A Study of EDG-5506 in Adult Males With Becker Muscular Dystrophy","officialTitle":"A Phase 1b, Open-label Study of the Safety and Pharmacokinetics of EDG-5506 in Adults With Becker Muscular..."

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

NCT05166109 PHASE_II COMPLETED

Completed placebo-controlled vamorolone pilot, 46 enrolled, with 24-week safety primary outcomes. Results posted September 15, 2026 report outcome denominators of 26 vamorolone and 13 placebo participants. Mean change in NSAA was 0.16 versus 0.00 and mean change in run/walk velocity was -0.05 m/s in both groups. These descriptive values do not establish efficacy.

Show evidence (4 references)

clinicaltrials:NCT05166109 SUPPORT Human Clinical

"This Phase II pilot study is a randomized, double-blind, placebo-controlled study to evaluate the safety, tolerability, PK, PD, and exploratory clinical efficacy of vamorolone 500mg (250mg for body weight \<50 kg) daily administered orally compared to placebo over a treatment period of 24 weeks..."

The registry summary identifies the study design and intervention.

url:https://clinicaltrials.gov/api/v2/studies/NCT05166109 SUPPORT Other

""briefTitle":"A Study to Assess Vamorolone in Becker Muscular Dystrophy (BMD)","officialTitle":"A Phase II Pilot Trial of Vamorolone vs. Placebo for the Treatment of Becker Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2026-09","overallStatus":"COMPLETED""

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

url:https://clinicaltrials.gov/api/v2/studies/NCT05166109 SUPPORT Human Clinical

"{"type":"SECONDARY","title":"Efficacy as Measured by Time to Run/Walk Velocity (TTRWV)","description":"Change from baseline to week 24 for each treatment group.","reportingStatus":"POSTED","paramType":"MEAN","dispersionType":"Standard Deviation","unitOfMeasure":"meters/second","timeFrame":"Week..."

Registry measurements for Efficacy as Measured by Time to Run/Walk Velocity (TTRWV); group OG000 is vamorolone and OG001 placebo. Outcome denominators are 26 and 13, respectively. These are descriptive means, not an inferred significance test.

+ 1 more reference

NCT04386304 PHASE_I COMPLETED

Completed open-label dose-escalation study of (+)-epicatechin in 22 participants with Becker or Becker-like dystrophy. The registry records safety and exploratory functional/biomarker assessments, but no posted results.

Show evidence (2 references)

clinicaltrials:NCT04386304 SUPPORT Human Clinical

"This is a Phase 1, open-label, dose escalation study aimed at evaluating the safety, early efficacy and potential biomarkers of (+)-epicatechin in patients with Becker or Becker-like Muscular Dystrophy (BMD)."

The registry summary identifies the study design and intervention.

url:https://clinicaltrials.gov/api/v2/studies/NCT04386304 SUPPORT Other

""briefTitle":"Safety and Biomarker Response to (+)-Epicatechin in Becker Muscular Dystrophy","officialTitle":"A Phase 1, Open-label, Dose Escalation Study to Evaluate the Safety and Preliminary Efficacy of Orally Administered (+)-Epicatechin in Patients With Becker or Becker-like Muscular..."

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

NCT04054375 PHASE_II COMPLETED

Completed single-center open-label weekly-prednisone pilot in 20 adults, including 19 with limb-girdle muscular dystrophy and one with Becker muscular dystrophy. Safety was the primary objective. The 24-week publication reports pooled outcomes without a control group; it cannot establish Becker-specific efficacy. Registry results are posted.

Show evidence (3 references)

clinicaltrials:NCT04054375 SUPPORT Human Clinical

"The purpose of this study is to evaluate the safety and efficacy of oral weekly glucocorticoid steroids in patients with Becker Muscular Dystrophy (BMD), an inherited disorder in which patients experience weakness of the legs and pelvis, and Limb Girdle Muscular Dystrophy (LGMD), an inherited..."

The registry describes the intervention, population, and study objectives.

url:https://clinicaltrials.gov/api/v2/studies/NCT04054375 SUPPORT Other

""briefTitle":"Weekly Steroids in Muscular Dystrophy","officialTitle":"Open Label Safety and Efficacy of Once Weekly Steroid in Patients With LGMD and Becker Muscular Dystrophy","acronym":"WSiMD"},"statusModule":{"statusVerifiedDate":"2023-09","overallStatus":"COMPLETED""

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

PMID:35124660 SUPPORT Human Clinical

"Out of the 20 participants, seven were female, nineteen had LGMD and one had BMD"

The mixed pilot cohort contained only one Becker participant, precluding a Becker-specific efficacy estimate.

NCT04585464 PHASE_I COMPLETED

Completed randomized placebo-controlled ascending-dose sevasemten study in healthy volunteers and adults with Becker muscular dystrophy. The registry lists 127 participants overall; the published analysis reports 97 healthy volunteers and seven Becker participants. Short-term safety, pharmacokinetics, and biomarkers do not establish functional efficacy.

Show evidence (3 references)

clinicaltrials:NCT04585464 SUPPORT Human Clinical

"This Phase 1 study of EDG-5506 will assess the safety, tolerability, and pharmacokinetics (PK) and of EDG-5506 in adult healthy volunteers and in adults with Becker muscular dystrophy (BMD)."

The registry describes the intervention, population, and study objectives.

url:https://clinicaltrials.gov/api/v2/studies/NCT04585464 SUPPORT Other

""briefTitle":"A Study to Assess Safety, Tolerability, and PK of EDG-5506 in Healthy Volunteers and Becker Muscular Dystrophy Adults","officialTitle":"A Phase 1, Randomized, Placebo-Controlled, Double-blind, Single and Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and PK of..."

The registry excerpt identifies the study and its completed status in the retrieved snapshot.

PMID:40452637 SUPPORT Human Clinical

"In Part C, 7 men with BMD were randomized to sevasemten (N = 5) or placebo (N = 2)"

Defines the very small Becker randomized cohort within a larger study dominated by healthy volunteers.

NCT01070511 PHASE_IV COMPLETED

Completed tadalafil physiological study. The registry retains an estimated enrollment of 48 and a parallel-design field, whereas the linked publication reports a randomized crossover experiment in ten Becker participants. The published design and analyzed population are used when interpreting the efficacy evidence.

Show evidence (3 references)

clinicaltrials:NCT01070511 SUPPORT Human Clinical

"This new short-term clinical trial will move the testing from animals to human patients with Becker muscular dystrophy and examine the effects of acute tadalafil dosing on muscle blood flow during a bout of exercise."

The registry identifies the trial intervention and physiological objectives.

url:https://clinicaltrials.gov/api/v2/studies/NCT01070511 SUPPORT Other

""briefTitle":"Tadalafil in Becker Muscular Dystrophy","officialTitle":"Functional Muscle Ischemia and PDE5A Inhibition in Becker Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2013-08","overallStatus":"COMPLETED""

The retrieved registry identifies the study and its completed status.

PMID:23197572 SUPPORT Human Clinical

"The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo."

The randomized crossover trial demonstrates an acute physiological response in the subgroup with abnormal placebo physiology, rather than long-term clinical benefit.

NCT01350154 PHASE_II COMPLETED

Completed randomized sildenafil crossover study with 17 enrolled participants. The skeletal and cardiac publication reports 16 and 13 evaluable participants, respectively, and no improvement in the measured outcomes.

Show evidence (3 references)

clinicaltrials:NCT01350154 SUPPORT Human Clinical

"This study is done to evaluate whether treatment with the drug sildenafil (Revatio®) can improve muscular, cardiac, cerebrovascular or cognitive function in patients with Beckers muscular dystrophy when compared to placebo (inactive medication)."

The registry identifies the trial intervention and physiological objectives.

url:https://clinicaltrials.gov/api/v2/studies/NCT01350154 SUPPORT Other

""briefTitle":"Effect of Modulating the nNOS System on Cardiac, Muscular and Cognitive Function in Becker Muscular Dystrophy Patients","officialTitle":"Does Modulation of the nNOS System in Patients With Muscular Dystrophy and Defect nNOS Signalling Affect Cardiac, Muscular or Cognitive..."

The retrieved registry identifies the study and its completed status.

PMID:25042931 SUPPORT Human Clinical

"Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations. Sildenafil had no effect on any of the outcome parameters."

The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.

🐁

Animal Models

bmx exon 45-47 deletion mouse

CRISPR-generated in-frame deletion of murine Dmd exons 45-47. The model has reduced dystrophin protein despite preserved transcript abundance, contraction-related muscle injury, inflammation, fibrosis, and age-dependent cardiac dysfunction.

Species

Mouse

Genotype

Dmd exon 45-47 deletion

Background

C57/BL6J

Publication

PMID:36628607

Pathograph links

Reduced or Abnormal Partly Functional Dystrophin partially recapitulates fidelity: moderate observes: molecular Reproduces the protein deficit with preserved transcript abundance.

Limitations: Represents one deletion; it does not capture the full spectrum of Becker molecular outcomes.

Show evidence (1 reference)

PMID:36628607 SUPPORT Model Organism

"Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy."

The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.

Contraction-Induced Skeletal Muscle Injury partially recapitulates fidelity: moderate observes: tissue Eccentric contraction experiments show greater force loss than wild type.

Limitations: Individual functional endpoints are not uniformly intermediate between wild type and dystrophin-null mice.

Show evidence (1 reference)

PMID:36628607 SUPPORT Model Organism

The genotype-defined model has greater contraction-induced force loss than wild type; it does not establish a uniform degree of protection relative to dystrophin-null muscle.

Left Ventricular Impairment and Dilated Cardiomyopathy partially recapitulates fidelity: moderate observes: organism Aged mice develop reduced ejection fraction and fractional shortening.

Limitations: Mouse age and timing of cardiomyopathy cannot be mapped directly to human prognosis.

Show evidence (1 reference)

PMID:36628607 SUPPORT Model Organism

"Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy."

The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.

Show evidence (1 reference)

PMID:36628607 SUPPORT Model Organism

"Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy."

The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.

R-BMDdel45-47 rat

Genome-edited rats show reduced dystrophin, relatively mild skeletal muscle dysfunction, and progressive cardiac fibrosis and systolic dysfunction. Intercalated-disc proteins are mislocalized. Resting ventilatory function remains preserved at 12 months despite diaphragmatic histological changes.

Species

Rat

Genotype

Dmd exon 45-47 deletion

Background

Sprague Dawley

Publication

PMID:39358550

Pathograph links

Cardiac Intercalated Disc Disorganization partially recapitulates fidelity: moderate observes: cellular Reproduces structural and protein-localization abnormalities at intercalated discs.

Limitations: The study does not selectively rescue TMEM65 or connexin-43 localization to test mediation of cardiac disease.

Show evidence (1 reference)

PMID:39358550 SUPPORT Model Organism

"At the histological level, TMEM65 notably displayed a larger distribution and mislocalization from the ICD in both BMD and DMD ventricles"

Immunostaining shows mislocalization in the rat model; reduced Tmem65 RNA did not correspond to reduced TMEM65 protein abundance in Becker rat hearts.

Left Ventricular Impairment and Dilated Cardiomyopathy partially recapitulates fidelity: moderate observes: organism Develops ventricular dilation, reduced ejection fraction, and cardiac fibrosis.

Limitations: The model carries one deletion and exhibits considerable variation between animals.

Show evidence (1 reference)

PMID:39358550 SUPPORT Model Organism

"Most notably, BMD rats developed a progressive cardiomyopathy with reduced ejection fraction and pronounced fibrosis, closely mimicking the major cardiac involvement diagnosed in BMD patients carrying a 45–47 deletion."

The rat model captures progressive cardiac disease for this deletion, while its skeletal phenotype is milder.

Show evidence (1 reference)

PMID:39358550 SUPPORT Model Organism

The rat model captures progressive cardiac disease for this deletion, while its skeletal phenotype is milder.

{ }

Source YAML

click to show

name: Becker Muscular Dystrophy
creation_date: '2026-08-23T22:30:00Z'
category: Mendelian
disease_term:
  preferred_term: Becker muscular dystrophy
  term:
    id: MONDO:0010311
    label: Becker muscular dystrophy
description: >-
  Becker muscular dystrophy is an X-linked dystrophinopathy caused by pathogenic DMD variants that permit
  production of partly functional dystrophin. Protein quantity, structure, and clinical severity vary.
  In-frame variants predominate, but the reading-frame rule is predictive rather than diagnostic: out-of-frame,
  nonsense, splice, and other variants can also produce a Becker phenotype. Progressive proximal weakness,
  calf hypertrophy, exercise-related symptoms, or incidental hyperCKaemia may lead to diagnosis. Cardiomyopathy
  can be severe despite relatively mild skeletal muscle involvement. Age at loss of ambulation and respiratory
  impairment vary substantially between patients and genotypes.
parents:
- Dystrophinopathy
- Muscular Dystrophy
pathophysiology:
- name: DMD Pathogenic Variant
  role: trigger
  biological_scale: MOLECULAR
  description: >-
    Pathogenic variants in DMD alter dystrophin quantity or function. In-frame deletions and duplications
    are common, but neither reading frame nor variant position alone establishes the Becker phenotype.
    The Italian cohort included 779 in-frame, 89 out-of-frame, and 35 nonsense variants among 903 genetically
    characterized patients. Particular exon deletions correlate with clinical outcomes at the group level;
    substantial variation remains within genotypes and families.
  evidence:
  - reference: PMID:3384440
    reference_title: An explanation for the phenotypic differences between patients bearing partial deletions of the DMD locus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Deletions identified in three BMD patients are shown to maintain the translational ORF for amino
      acids and predict a shorter, lower molecular weight protein.
    explanation: >-
      The original statement of the reading-frame model, on the Becker side of the comparison.
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ten per cent of patients carried out-of-frame mutations, 4% nonsense mutations and 86% in-frame
      deletions/duplications.
    explanation: >-
      The mutational composition of a 943-patient Becker cohort. It gives both the dominant in-frame class
      and the size of the exception to the rule.
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients carrying del45-49 compared with del45-47 were associated with an earlier loss of ambulation
      (P = 1 × 10-4), whereas patients with del45-55 (P = 0.005), del48 (P = 0.02) and del48-49 (P = 0.02)
      were correlated with a later loss of ambulation compared with del45-47.
    explanation: >-
      Within-class genotype-phenotype resolution: which exons are removed changes the trajectory even
      when the frame is preserved throughout.
  downstream:
  - target: Reduced or Abnormal Partly Functional Dystrophin
    causal_link_type: DIRECT
    description: >-
      DMD variants can produce reduced amounts of dystrophin, an abnormal protein, or both, while retaining
      sufficient function for a Becker clinical phenotype. The protein outcome cannot be inferred solely
      from reading-frame preservation.

    evidence:
    - reference: PMID:39499670
      reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations
        in DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac
        muscle.
      explanation: >-
        The cohort report connects DMD mutations to the partly functional dystrophin state in skeletal
        and cardiac muscle.
      quote_role: BACKGROUND
- name: Reduced or Abnormal Partly Functional Dystrophin
  role: central_effector
  biological_scale: MOLECULAR
  description: >-
    Residual dystrophin distinguishes the Becker phenotype from severe dystrophin deficiency, but its
    abundance and function vary. Internally deleted dystrophin is a common outcome, not the only one.
    In bmx mice with deletion of Dmd exons 45-47, skeletal and cardiac dystrophin protein is reduced despite
    preserved transcript abundance. Sarcolemmal nNOS localization is lost and alpha-sarcoglycan localization
    is reduced in this model; these allele-specific observations should not be assumed for every Becker
    variant.
  cellular_components:
  - preferred_term: dystrophin-glycoprotein complex at the sarcolemma
    term:
      id: GO:0016010
      label: dystrophin-associated glycoprotein complex
  evidence:
  - reference: PMID:2491009
    reference_title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For cases with a deletion mutation, the "reading frame" hypothesis predicts that BMD patients produce
      a semifunctional, internally deleted dystrophin protein, whereas DMD patients produce a severely
      truncated protein that would be unstable.
    explanation: >-
      The contrast at protein level between the two diseases, which is what this node models.
  - reference: PMID:16770791
    reference_title: 'Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In Becker patients, in-frame mutations allow the synthesis of internally deleted, but largely functional
      dystrophins.
    explanation: >-
      Restatement of the same protein-level claim by a group curating the mutation database.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations in
      DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac muscle.
    explanation: >-
      States both the protein state and the two tissues it matters in, which is where this node branches.
    quote_role: BACKGROUND
  - reference: PMID:36628607
    reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Interestingly we see reduced dystrophin protein, but not mRNA, in bmx skeletal and cardiac muscle.
    explanation: >-
      The exon 45-47 mouse model demonstrates a protein deficit without a corresponding transcript deficit.
  - reference: PMID:36628607
    reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      bmx muscles showed complete loss of nNOS localization at the sarcolemma as did dystrophin‐null mdx52
      muscles (Figure 6C).
    explanation: >-
      Loss of membrane nNOS is demonstrated for the exon 45-47 model, rather than asserted across all
      Becker genotypes.
  downstream:
  - target: Contraction-Induced Skeletal Muscle Injury
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Partly functional dystrophin provides incomplete protection against contraction-induced skeletal
      muscle injury. The exon 45-47 bmx model retains susceptibility to eccentric contractions.
    evidence:
    - reference: PMID:36628607
      reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Ten eccentric contractions of WT EDL muscle resulted in a 15.53% drop in ex vivo peak force. In
        contrast, this protocol reduced peak force by 20.16% in bmx EDL muscles (P = 0.0239 bmx vs. WT)
        and 20.86% in mdx EDL (Figure 2D).
      explanation: >-
        The genotype-defined model has greater contraction-induced force loss than wild type; it does
        not establish a uniform degree of protection relative to dystrophin-null muscle.
  - target: Dystrophin-Deficient Cardiomyocyte Injury
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The dystrophin deficit also affects cardiomyocytes and can cause cardiac dysfunction despite relatively
      preserved skeletal muscle function.

    evidence:
    - reference: PMID:36628607
      reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein
        in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy.
      explanation: >-
        The bmx model connects the Dmd lesion and reduced cardiac dystrophin with cardiac dysfunction;
        detailed cellular intermediates are not resolved by this summary.
  - target: Loss of Sarcolemmal nNOS Localization
    causal_link_type: DIRECT
    description: >-
      Some DMD variants disrupt dystrophin-dependent membrane localization of nNOS. Human biopsy evidence
      shows this for several exon-deletion groups, while other Becker variants retain sarcolemmal nNOS.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
      reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sarcolemmal staining for nNOS was absent in seven BMD patients (including all five patients with
        deletion of exons 45–47 or 45–48, and both patients with deletion of exons 3–7) but present in
        the other six patients.
      explanation: >-
        Human biopsies show genotype-associated variation in nNOS localization; membrane loss is not universal
        in Becker muscular dystrophy.
- name: Contraction-Induced Skeletal Muscle Injury
  conforms_to: "sarcolemmal_fragility_myofiber_necrosis#Contraction-Induced Sarcolemmal Lesions"
  role: effector
  biological_scale: CELLULAR
  description: >-
    Dystrophin supports muscle membrane stability. In Becker muscular dystrophy, residual protein does
    not fully prevent contraction-related injury. Exon 45-47 bmx mouse muscle shows increased force loss
    after eccentric contractions, raised serum creatine kinase, necrotic and inflammatory foci, regeneration,
    and fibrosis. The severity of individual measurements need not lie uniformly between wild type and
    dystrophin-null muscle.
  cell_types:
  - preferred_term: skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:16770791
    reference_title: 'Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This gene codes for dystrophin, a protein important for maintaining the stability of muscle-fiber
      membranes.
    explanation: >-
      Dystrophin's function at the muscle-fibre membrane, which is what a semifunctional protein partly
      preserves.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:36628607
    reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ten eccentric contractions of WT EDL muscle resulted in a 15.53% drop in ex vivo peak force. In
      contrast, this protocol reduced peak force by 20.16% in bmx EDL muscles (P = 0.0239 bmx vs. WT)
      and 20.86% in mdx EDL (Figure 2D).
    explanation: >-
      The genotype-defined model has greater contraction-induced force loss than wild type; it does not
      establish a uniform degree of protection relative to dystrophin-null muscle.
  downstream:
  - target: Slowly Progressive Proximal Myopathy
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Recurrent injury, degeneration, and fibrofatty replacement contribute to progressive loss of skeletal
      muscle function; the pace varies across patients.

    evidence:
    - reference: PMID:36793492
      reference_title: 'Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In the early stages BMD involves active myonecrosis and regeneration; later in the disease course
        chronic myopathic changes are more likely, including increased skeletal muscle fiber size variability,
        fibrosis, and fat replacement of muscle tissue
      explanation: >-
        The trial introduction summarizes the pathological sequence underlying progressive myopathy; it
        is a literature synthesis, not a longitudinal histology result of this trial.
      quote_role: BACKGROUND
  - target: Elevated Creatine Kinase
    causal_link_type: DIRECT
    description: >-
      Circulating creatine kinase is a marker of skeletal muscle injury in Becker muscular dystrophy.
      Its level does not directly measure remaining strength and can decline as muscle is replaced by fat.
    evidence:
    - reference: PMID:40452637
      reference_title: A Phase 1, Double-Blind, Placebo-Controlled Trial of Sevasemten (EDG-5506), a Selective Modulator of Fast Skeletal Muscle Contraction, in Healthy Volunteers and Adults With Becker Muscular Dystrophy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        For adults with BMD, serum biomarkers of muscle injury trended down progressively with sevasemten
        treatment (average maximal reductions of 70% for creatine kinase, 98% for fast skeletal muscle
        troponin I, and 45% for myoglobin).
      explanation: >-
        This Becker-specific trial identifies circulating CK as a muscle-injury biomarker. The small
        biomarker study does not establish a clinical treatment benefit or a direct measure of strength.
    - reference: PMID:37422773
      reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      snippet: >-
        The increase in CK levels is more marked at the beginning of the di sease and progressively
        decreases with muscle fatty in volution.
      explanation: >-
        The Becker guideline explains why a lower CK level can accompany loss of muscle tissue rather
        than improved muscle function.
- name: Slowly Progressive Proximal Myopathy
  role: outcome
  biological_scale: ORGANISM
  description: >-
    Proximal weakness and mobility loss progress at variable rates. In the retrospective Italian cohort,
    111 of 822 patients with available ambulation information had lost walking ability at assessment.
    The Kaplan-Meier median age at loss of ambulation was 69 years, whereas the observed mean age among
    those who had already lost ambulation was 35.3 years. These are different statistics; neither describes
    an inevitable course for an individual. Respiratory decline can become clinically important, especially
    after loss of ambulation, and warrants surveillance.
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Information about LoA was known for 822 (87.2%) patients; of these, 111 (13.5%) patients had lost
      the ability to walk at the time of data collection, with a mean age at LoA of 35.3 (±15.0) years
    explanation: >-
      The full cohort report supplies the assessed denominator and observed event age, avoiding interpretation
      of a cross-sectional fraction as lifetime risk.
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In 55% of patients, the diagnosis was prompted by the incidental finding of hyperCKaemia.
    explanation: >-
      Incidental hyperCKaemia prompted many diagnoses in this Italian cohort; local testing practices
      affect the proportion.
  - reference: PMID:33454189
    reference_title: 'Respiratory decline in adult patients with Becker muscular dystrophy: A longitudinal study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We analysed 190 pulmonary function measurements with a median interval of one year (1-17y) and measured
      a 1.00% decline of Forced Vital Capacity percent predicted (FVC%pred) per year (p = 0.004).
    explanation: The quantified rate of respiratory decline.
  - reference: PMID:33454189
    reference_title: 'Respiratory decline in adult patients with Becker muscular dystrophy: A longitudinal study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, this decline is significantly more rapid and clinically relevant after loss of ambulation,
      which warrants a more vigilant follow-up of respiratory function in this subgroup.
    explanation: >-
      The interaction with ambulatory status and the surveillance recommendation that follows from it.

  downstream:
  - target: Progressive Proximal Muscle Weakness
    causal_link_type: DIRECT
    description: >-
      Proximal weakness is the principal clinical manifestation of the skeletal myopathy.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
      reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        More moderate skeletal muscle manifestations (e.g., BMD) may be characterized by onset in adolescence
        to adulthood of progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy;
        weakness of quadriceps femoris (sometimes the only sign); activity-induced cramping (present in
        some individuals); preservation of neck flexor muscle strength;
      explanation: >-
        GeneReviews describes the proximal distribution, progression, and activity-related symptoms of
        Becker myopathy.
      quote_role: REVIEW_SYNTHESIS
  - target: Waddling gait
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Pelvic-girdle involvement alters gait as weakness progresses.
    evidence:
    - reference: PMID:37422773
      reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        This is followed by weakness in standing up or a waddling gait.
      explanation: >-
        The Becker clinical sequence links progressive lower-limb impairment with the gait abnormality.
      quote_role: REVIEW_SYNTHESIS
  - target: Scoliosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Axial muscle weakness can contribute to scoliosis.
    evidence:
    - reference: PMID:37422773
      reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Axial weakness: scoliosis, abdominal weakness with difficulties in getting up from the lying position
      explanation: >-
        The guideline lists scoliosis as a manifestation associated with axial weakness.
      quote_role: REVIEW_SYNTHESIS
  - target: Reduced Forced Vital Capacity
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Extension of muscle weakness to respiratory muscles can reduce ventilatory capacity.
    evidence:
    - reference: PMID:37422773
      reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        BMD patients may experience progressive deterioration in their respiratory function related to
        a decrease in the strength of respiratory muscles
      explanation: >-
        The respiratory section explicitly links functional deterioration to respiratory muscle weakness.
      quote_role: REVIEW_SYNTHESIS
- name: Dystrophin-Deficient Cardiomyocyte Injury
  role: effector
  biological_scale: CELLULAR
  conforms_to: cardiomyopathy_maladaptive_remodeling#Primary Cardiomyocyte Insult
  description: >-
    Abnormal or reduced dystrophin affects cardiac as well as skeletal muscle. Cardiac disease can progress
    independently of skeletal muscle severity. The bmx mouse demonstrates reduced cardiac dystrophin and
    impaired ventricular function; human surveillance must therefore consider the heart even when skeletal
    weakness is mild.
  cell_types:
  - preferred_term: cardiac muscle cell
    term:
      id: CL:0000746
      label: cardiac muscle cell
  evidence:
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease attributable to mutations in
      DMD, leading to a deficient and less functional dystrophin, mainly in skeletal and cardiac muscle.
    explanation: >-
      Names cardiac muscle as one of the two tissues carrying the dystrophin deficit, which is the insult
      this node models.
    quote_role: BACKGROUND
  downstream:
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cardiac dystrophin dysfunction can lead to progressive ventricular impairment. The exon 45-47 rat
      model supports progression to cardiomyopathy, while the intervening cellular sequence is not fully
      established for human Becker disease.

    evidence:
    - reference: PMID:39358550
      reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        BMD rats exhibit moderate damage to locomotor and diaphragmatic muscles but suffer from a progressive
        cardiomyopathy.
      explanation: >-
        The Dmd exon-deletion model develops progressive cardiomyopathy, without identifying all intervening
        injury and remodeling steps.
  - target: Cardiac Intercalated Disc Disorganization
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The exon 45-47 rat model shows altered intercalated-disc architecture and protein localization.
      The contribution of dystrophin quantity versus its altered structure is unresolved.
    evidence:
    - reference: PMID:39358550
      reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        At the histological level, TMEM65 notably displayed a larger distribution and mislocalization
        from the ICD in both BMD and DMD ventricles
      explanation: >-
        Immunostaining shows mislocalization in the rat model; reduced Tmem65 RNA did not correspond to
        reduced TMEM65 protein abundance in Becker rat hearts.
- name: Left Ventricular Impairment and Dilated Cardiomyopathy
  role: outcome
  biological_scale: ORGANISM
  conforms_to: cardiomyopathy_maladaptive_remodeling#Structural Cardiac Impairment and Heart Failure
  description: >-
    Left ventricular systolic dysfunction and dilated cardiomyopathy are important complications, and
    heart failure is a major cause of mortality. In the Italian cohort, 187 of 621 assessed patients had
    LVEF below 55%, which measures systolic impairment rather than the prevalence of dilated cardiomyopathy.
    Certain deletions were associated with lower odds of impaired LVEF, but genotype does not determine
    an individual outcome.
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      One hundred and eighty-seven (30.1%) patients showed LVEF% of &lt;55%
    explanation: >-
      The full text defines the cardiac outcome as reduced ejection fraction and supplies its numerator;
      621 patients had an LVEF measurement.
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both del45-55 (P = 0.002) and del48 (P = 0.003) were significantly associated with decreased odds
      of developing a pathological left ventricular ejection fraction compared with del45-47.
    explanation: Genotypic modulation of the cardiac endpoint within the in-frame class.
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity
      and the most common cause of death in BMD. Mean age of death is in the mid-40s.
    explanation: >-
      The older GeneReviews abstract identifies heart failure as a major source of morbidity and mortality.
      Its summary age at death is not compared numerically with ambulation estimates from another cohort.

    quote_role: REVIEW_SYNTHESIS
  downstream:
  - target: Left Ventricular Impairment
    causal_link_type: DIRECT
    description: >-
      Reduced LVEF is the clinical readout of ventricular systolic dysfunction.
    evidence:
    - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
      reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        One hundred and eighty-seven (30.1%) patients showed LVEF% of &lt;55%
      explanation: >-
        The full text defines the cardiac outcome as reduced ejection fraction and supplies its numerator;
        621 patients had an LVEF measurement.
  - target: Dilated Cardiomyopathy
    causal_link_type: DIRECT
    description: >-
      Becker ventricular disease can progress to dilated cardiomyopathy and heart failure.
    evidence:
    - reference: PMID:20301298
      reference_title: Dystrophinopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity
        and the most common cause of death in BMD.
      explanation: >-
        GeneReviews identifies DCM-related heart failure as a major Becker outcome.
      quote_role: REVIEW_SYNTHESIS
- name: Cardiac Intercalated Disc Disorganization
  role: effector
  biological_scale: CELLULAR
  description: >-
    In exon 45-47 Becker rats, TMEM65 and connexin-43 are mislocalized and intercalated discs have widened,
    irregular folds and abnormal contacts with nearby sarcomeres. These findings suggest impaired cardiomyocyte
    coupling, but no targeted rescue experiment establishes their mediation of ventricular dysfunction.
    This is model-derived evidence, not a demonstrated universal human cellular lesion.
  evidence:
  - reference: PMID:39358550
    reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      At the histological level, TMEM65 notably displayed a larger distribution and mislocalization from
      the ICD in both BMD and DMD ventricles
    explanation: >-
      Immunostaining shows mislocalization in the rat model; reduced Tmem65 RNA did not correspond to
      reduced TMEM65 protein abundance in Becker rat hearts.
  - reference: PMID:39358550
    reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we found that Cx43 was more internalized in both BMD and DMD, with a lower co-localization with
      N-cadherin (NCAD), an intercalated disc marker
    explanation: >-
      Connexin-43 localization changes accompany intercalated-disc disorganization in dystrophic rat hearts.
  downstream:
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Altered mechanical and electrical coupling is a proposed contributor to cardiac dysfunction in the
      rat model. Co-occurrence and structural data support the hypothesis, while causal mediation remains
      untested.
    evidence:
    - reference: PMID:39358550
      reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We propose that disruption in the localization of TMEM65 and Cx43 could play a role in altering
        electrical synchronization during myocardial depolarization or repolarization, due to partly inefficient
        intercellular communications.
      explanation: >-
        The authors explicitly frame this mechanism as a proposal; the edge retains that uncertainty.
- name: Loss of Sarcolemmal nNOS Localization
  role: effector
  biological_scale: MOLECULAR
  description: >-
    Dystrophin serves as a scaffold for sarcolemmal nNOS. Some Becker variants reduce or abolish membrane
    nNOS localization; other variants retain it. In a biopsy-linked human series, nNOS staining was absent
    in seven patients and present in six. Total nNOS abundance and residual localization also vary, including
    between relatives with the same splice variant.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
    reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sarcolemmal staining for nNOS was absent in seven BMD patients (including all five patients with
      deletion of exons 45–47 or 45–48, and both patients with deletion of exons 3–7) but present in the
      other six patients.
    explanation: >-
      Human biopsies show genotype-associated variation in nNOS localization; membrane loss is not universal
      in Becker muscular dystrophy.
  downstream:
  - target: Impaired Exercise-Induced Vasomodulation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Loss of membrane-associated nNOS weakens local nitric-oxide-dependent attenuation of sympathetic
      vasoconstriction during exercise. Acute rescue with interventions that augment NO-cGMP signaling
      supports this pathway, without proving an effect on long-term muscle decline.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
      reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sympatholysis was greatly impaired in all seven patients lacking sarcolemmal nNOS but well preserved
        in four of six patients in whom nNOS was detected at the sarcolemma.
      explanation: >-
        The biopsy-linked physiology associates loss of sarcolemmal nNOS with impaired exercise vasomodulation,
        with additional heterogeneity among those retaining nNOS.
    - reference: PMID:23197572
      reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored
        blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo.
      explanation: >-
        The randomized crossover trial demonstrates an acute physiological response in the subgroup with
        abnormal placebo physiology, rather than long-term clinical benefit.
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
      reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In the subsequent placebo‐controlled trial performed in six of the 11 patients from the open‐label
        trial (P2, P3, P7, P12, P14 and P16), we confirmed that sodium nitrate restores functional sympatholysis,
        whereas placebo was without effect
      explanation: >-
        The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.
  - target: RyR1-Calstabin Complex Destabilization
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Mislocalized cytosolic nNOS is associated with altered RyR1-calstabin regulation in del45-55 muscle
      biopsies. The human study supports a candidate nitrosative pathway but does not resolve causal mediation
      or establish this branch for every Becker variant.
    evidence:
    - reference: PMID:22589245
      reference_title: Variable phenotype of del45-55 Becker patients correlated with nNOSμ mislocalization and RYR1 hypernitrosylation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Cytosolic NO production correlated with both hypernitrosylation of the sarcoplasmic reticulum
        calcium-release-channel ryanodine receptor type-1 (RyR1) and release of calstabin-1, a central
        hub of Ca(2+) signaling and contraction in muscle.
      explanation: >-
        The 12-patient del45-55 biopsy study reports correlated biochemical abnormalities; it does not
        establish a universal lesion or directly measure the contribution to clinical decline.
- name: Impaired Exercise-Induced Vasomodulation
  role: effector
  biological_scale: TISSUE
  description: >-
    During exercise, affected muscle may fail to attenuate reflex sympathetic vasoconstriction, causing
    functional ischemia under experimental conditions. This abnormality is associated with nNOS membrane
    localization but is not present in every Becker patient. Acute tadalafil or nitrate studies demonstrate
    reversibility of the vascular response; its contribution to chronic weakness or disease progression
    remains unresolved. Reduced local NO-cGMP signaling is supported by the localization findings and
    pharmacological rescue rather than by a direct assay of intracellular cGMP in these patients.
  biological_processes:
  - preferred_term: nitric oxide-cGMP-mediated signaling
    term:
      id: GO:0038060
      label: nitric oxide-cGMP-mediated signaling
    modifier: DECREASED
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
    reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sympatholysis was greatly impaired in all seven patients lacking sarcolemmal nNOS but well preserved
      in four of six patients in whom nNOS was detected at the sarcolemma.
    explanation: >-
      The biopsy-linked physiology associates loss of sarcolemmal nNOS with impaired exercise vasomodulation,
      with additional heterogeneity among those retaining nNOS.
  - reference: PMID:23197572
    reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored
      blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo.
    explanation: >-
      The randomized crossover trial demonstrates an acute physiological response in the subgroup with
      abnormal placebo physiology, rather than long-term clinical benefit.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
    reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the subsequent placebo‐controlled trial performed in six of the 11 patients from the open‐label
      trial (P2, P3, P7, P12, P14 and P16), we confirmed that sodium nitrate restores functional sympatholysis,
      whereas placebo was without effect
    explanation: >-
      The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.
- name: RyR1-Calstabin Complex Destabilization
  role: effector
  biological_scale: MOLECULAR
  description: >-
    In a study of 12 Becker patients with exon 45-55 deletions, cytosolic nitric oxide production correlated
    with RyR1 hypernitrosylation and calstabin-1 dissociation. These findings implicate altered regulation
    of the sarcoplasmic-reticulum calcium-release complex. The association does not establish measured
    calcium leak or its causal contribution across Becker genotypes.
  evidence:
  - reference: PMID:22589245
    reference_title: Variable phenotype of del45-55 Becker patients correlated with nNOSμ mislocalization and RYR1 hypernitrosylation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cytosolic NO production correlated with both hypernitrosylation of the sarcoplasmic reticulum calcium-release-channel
      ryanodine receptor type-1 (RyR1) and release of calstabin-1, a central hub of Ca(2+) signaling and
      contraction in muscle.
    explanation: >-
      The 12-patient del45-55 biopsy study reports correlated biochemical abnormalities; it does not establish
      a universal lesion or directly measure the contribution to clinical decline.
phenotypes:
- category: Laboratory
  name: Elevated Creatine Kinase
  description: >-
    Raised serum creatine kinase can precede recognized weakness and may prompt incidental diagnosis.
  phenotype_term:
    preferred_term: Elevated circulating creatine kinase activity
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase activity
  evidence:
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In 55% of patients, the diagnosis was prompted by the incidental finding of hyperCKaemia.
    explanation: >-
      Raised creatine kinase as the presenting finding in the majority. The frequency slot is left empty
      because 55% describes how the diagnosis was prompted, not how many patients have a raised CK.

- category: Musculoskeletal
  name: Progressive Proximal Muscle Weakness
  phenotype_term:
    preferred_term: Progressive proximal muscle weakness
    term:
      id: HP:0009073
      label: Progressive proximal muscle weakness
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      More moderate skeletal muscle manifestations (e.g., BMD) may be characterized by onset in adolescence
      to adulthood of progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy;
      weakness of quadriceps femoris (sometimes the only sign); activity-induced cramping (present in
      some individuals); preservation of neck flexor muscle strength; and flexion contractures of the
      elbows (if present, late in the course).
    explanation: >-
      The Becker-specific clinical paragraph supports the proximal distribution and progressive course.
- category: Musculoskeletal
  name: Loss of Ambulation
  description: >-
    Age at loss of walking ability varies substantially. In the Italian cohort, 111 of 822 assessed patients
    had lost ambulation at data collection; this cross-sectional proportion is not lifetime penetrance.
  phenotype_term:
    preferred_term: Loss of ambulation
    term:
      id: HP:0002505
      label: Loss of ambulation
  evidence:
  - reference: PMID:39499670
    reference_title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the last assessment, 13.5% of patients had lost the ability to walk at a median age estimated
      by Kaplan-Meier analysis of 69 years.
    explanation: >-
      The Kaplan-Meier estimate accounts for censoring and differs from the observed age among patients
      who had already lost ambulation. Neither supports assigning a lifetime frequency band from 13.5%.

- category: Cardiovascular
  name: Left Ventricular Impairment
  phenotype_term:
    preferred_term: Left ventricular systolic dysfunction
    term:
      id: HP:0025169
      label: Left ventricular systolic dysfunction
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      One hundred and eighty-seven (30.1%) patients showed LVEF% of &lt;55%
    explanation: >-
      The full text defines the cardiac outcome as reduced ejection fraction and supplies its numerator;
      621 patients had an LVEF measurement.
  description: >-
    Reduced left ventricular systolic function was present in 187 of 621 assessed patients in the Italian
    cohort, using LVEF below 55%. Ventricular dilation was not required for this outcome.
- category: Cardiovascular
  name: Dilated Cardiomyopathy
  description: >-
    Dilated cardiomyopathy and DCM-related heart failure are important Becker cardiac complications.
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity
      and the most common cause of death in BMD.
    explanation: >-
      GeneReviews identifies DCM-related heart failure as a common and important Becker phenotype without
      giving a numeric frequency band.
    quote_role: REVIEW_SYNTHESIS
- category: Respiratory
  name: Reduced Forced Vital Capacity
  phenotype_term:
    preferred_term: Reduced forced vital capacity
    term:
      id: HP:0032341
      label: Reduced forced vital capacity
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Only 12 patients (2.7%) had FVC% values of &lt;50%, and all of them were non-ambulant
    explanation: >-
      The full text defines the respiratory threshold and ambulatory status. The denominator is 441 patients
      with FVC measurements, not all 943 participants.
  description: >-
    Respiratory muscle impairment may develop, particularly with advanced motor disability. In the Italian
    cohort, 12 of 441 patients with available measurements had FVC below 50% predicted, and all 12 were
    nonambulant.
- category: Musculoskeletal
  name: Very Late-Onset Ambulant Phenotype
  description: >-
    Some individuals have symptom onset after age 30 and remain ambulant into their sixties. This describes
    the mild end of the spectrum and is not the expected course for every person with Becker muscular
    dystrophy.
  phenotype_term:
    preferred_term: Progressive proximal muscle weakness
    term:
      id: HP:0009073
      label: Progressive proximal muscle weakness
    onset:
      onset_category: ADULT
  evidence:
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      With improved diagnostic techniques, it has been recognized that the mild end of the spectrum includes
      men with onset of symptoms after age 30 years who remain ambulatory even into their 60s.
    explanation: The mild extreme of the phenotypic range.

    quote_role: REVIEW_SYNTHESIS
- category: Cardiovascular
  name: Dilated Cardiomyopathy in Heterozygous Females
  description: >-
    Heterozygous females have increased risk of dilated cardiomyopathy and may also have skeletal muscle
    manifestations. Many remain asymptomatic; cardiac evaluation should not depend on the presence of
    weakness.
  phenotype_term:
    preferred_term: Dilated cardiomyopathy
    term:
      id: HP:0001644
      label: Dilated cardiomyopathy
  evidence:
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Females heterozygous for a DMD pathogenic variant are at increased risk for DCM.
    explanation: The carrier cardiac risk.

    quote_role: REVIEW_SYNTHESIS
- name: Calf muscle hypertrophy
  category: Musculoskeletal
  description: >-
    Calf enlargement is a characteristic finding, often described as pseudohypertrophy.
  phenotype_term:
    preferred_term: Calf muscle hypertrophy
    term:
      id: HP:0008981
      label: Calf muscle hypertrophy
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The typical BMD patient is a young man presenting with a slowly progressive pelv ic deficit and
      calf hypertrophy together with an increase in CK levels
    explanation: >-
      The diagnostic description names calf hypertrophy alongside proximal weakness and raised CK.
- name: Exercise-induced muscle cramps
  category: Musculoskeletal
  description: >-
    Activity-related cramping occurs in some individuals with Becker muscular dystrophy.
  phenotype_term:
    preferred_term: Exercise-induced muscle cramps
    term:
      id: HP:0003710
      label: Exercise-induced muscle cramps
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      More moderate skeletal muscle manifestations (e.g., BMD) may be characterized by onset in adolescence
      to adulthood of progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy;
      weakness of quadriceps femoris (sometimes the only sign); activity-induced cramping (present in
      some individuals); preservation of neck flexor muscle strength; and flexion contractures of the
      elbows (if present, late in the course).
    explanation: >-
      The Becker-specific clinical description explicitly identifies exertional cramping.
- name: Waddling gait
  category: Musculoskeletal
  description: >-
    Pelvic-girdle weakness can produce a waddling gait.
  phenotype_term:
    preferred_term: Waddling gait
    term:
      id: HP:0002515
      label: Waddling gait
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      This is followed by weakness in standing up or a waddling gait.
    explanation: >-
      The guideline describes waddling gait in the progression of lower-limb muscle involvement.
- name: Lumbar hyperlordosis
  category: Musculoskeletal
  description: >-
    Compensatory lumbar lordosis may accompany pelvic-girdle weakness and altered gait.
  phenotype_term:
    preferred_term: Lumbar hyperlordosis
    term:
      id: HP:0002938
      label: Lumbar hyperlordosis
  evidence:
  - reference: PMID:36793492
    reference_title: 'Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      leading to walking on toes with lumbar lordosis and early loss of ambulation
    explanation: >-
      The clinical background of the trial identifies lumbar lordosis; it is background material rather
      than a measured trial endpoint.
- name: Elbow flexion contracture
  category: Musculoskeletal
  description: >-
    Elbow flexion contractures may appear late in the disease course.
  phenotype_term:
    preferred_term: Elbow flexion contracture
    term:
      id: HP:0002987
      label: Elbow flexion contracture
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      More moderate skeletal muscle manifestations (e.g., BMD) may be characterized by onset in adolescence
      to adulthood of progressive symmetric muscle weakness (proximal > distal) often with calf hypertrophy;
      weakness of quadriceps femoris (sometimes the only sign); activity-induced cramping (present in
      some individuals); preservation of neck flexor muscle strength; and flexion contractures of the
      elbows (if present, late in the course).
    explanation: >-
      The Becker-specific description qualifies both variability and timing.
- name: Scoliosis
  category: Musculoskeletal
  description: >-
    Scoliosis can accompany axial weakness and requires musculoskeletal assessment.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Axial weakness: scoliosis, abdominal weakness with difficulties in getting up from the lying position
    explanation: >-
      The neuromuscular assessment section lists scoliosis among manifestations of axial weakness.
- name: Macroglossia
  category: Head and Neck
  description: >-
    Tongue enlargement can occur as part of muscle pseudohypertrophy.
  phenotype_term:
    preferred_term: Macroglossia
    term:
      id: HP:0000158
      label: Macroglossia
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Pseudohypertrophy of the calves, tongue, or other muscles.
    explanation: >-
      The guideline explicitly includes the tongue among sites of pseudohypertrophy.
- name: Dysphagia
  category: Gastrointestinal
  description: >-
    Swallowing dysfunction can accompany advanced motor disability; symptom-based assessment is needed.
  phenotype_term:
    preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Swallowing disorders are as frequent as those encountered in DMD pa tients with equal disabilities.
    explanation: >-
      The guideline discusses swallowing disorders specifically in Becker patients and qualifies the comparison
      by disability severity.
- name: Constipation
  category: Gastrointestinal
  description: >-
    Constipation may complicate immobility and muscle weakness.
  phenotype_term:
    preferred_term: Constipation
    term:
      id: HP:0002019
      label: Constipation
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Constipation can be a frequent complication of BMD, like in DMD.
    explanation: >-
      The guideline explicitly identifies constipation as a Becker complication.
- name: Gastroparesis
  category: Gastrointestinal
  description: >-
    Delayed gastric emptying may develop as muscle weakness progresses.
  phenotype_term:
    preferred_term: Gastroparesis
    term:
      id: HP:0002578
      label: Gastroparesis
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      As skeleta l muscle weakness progresses, a delay in gastric emptying (gastroparesis) can occur lead
      to postprandial abdominal pain, nausea, vomiting, early satiety, and loss of appetite [92].
    explanation: >-
      The source relates delayed gastric emptying to progression of muscle weakness; it does not imply
      that every patient develops it.
- name: Urinary incontinence
  category: Genitourinary
  description: >-
    Urinary incontinence is reported and can affect daily activities and quality of life.
  phenotype_term:
    preferred_term: Urinary incontinence
    term:
      id: HP:0000020
      label: Urinary incontinence
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Patients with BMD may ex perience uri nary incontinence regularly which c an have a detrimental
      effect on various aspects of their life, includi ng travel, social interactions, and emotional well-being
      [93, 94].
    explanation: >-
      The guideline identifies urinary incontinence in Becker patients rather than merely recommending
      screening for it.
- name: Elevated circulating hepatic transaminase concentration
  category: Laboratory
  description: >-
    ALT and AST may be elevated in dystrophinopathy and can lead to mistaken suspicion of primary liver
    disease.
  phenotype_term:
    preferred_term: Elevated circulating hepatic transaminase concentration
    term:
      id: HP:0002910
      label: Elevated circulating hepatic transaminase concentration
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The levels of liver enzymes s uch as alanine aminotransferase (ALT) and aspartate aminotransferase
      (AST) can be increased, which may sometimes result in misdiagnosis, especially in pseudo-metabolic
      forms, and may lead to liver biopsy [30].
    explanation: >-
      The guideline describes transaminase elevation and the diagnostic pitfall; this finding does not
      establish primary liver disease.
- name: Increased muscle fatiguability
  category: Musculoskeletal
  description: >-
    Lower-limb involvement can produce fatigue during walking.
  phenotype_term:
    preferred_term: Increased muscle fatiguability
    term:
      id: HP:0003750
      label: Increased muscle fatiguability
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      only the lower -limb muscles are affected symmetrically, causing fatigability while walking.
    explanation: >-
      The diagnostic section describes exertional fatigability with symmetric lower-limb involvement.
- name: Attention deficit hyperactivity disorder
  category: Neurodevelopmental
  description: >-
    ADHD was recorded in 17 of 583 patients with available behavioral information in the Italian cohort.
    Missing data and variable assessment limit population-frequency inference.
  phenotype_term:
    preferred_term: Attention deficit hyperactivity disorder
    term:
      id: HP:0007018
      label: Attention deficit hyperactivity disorder
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      17 (2.9%) patients were reported to be diagnosed with attention-deficit/hyperactivity disorder
    explanation: >-
      The primary Becker cohort records a clinical diagnosis; incomplete retrospective ascertainment precludes
      a general frequency band.
- name: Autism
  category: Neurodevelopmental
  description: >-
    Autism spectrum disorder was recorded in the Italian cohort, including one additional patient with
    co-occurring obsessive-compulsive disorder. These retrospective records do not define population prevalence.
  phenotype_term:
    preferred_term: Autism
    term:
      id: HP:0000717
      label: Autism
  evidence:
  - reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
    reference_title: https://oup.silverchair-cdn.com/article-minimal/7876416
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      five (0.9%) with autism spectrum disorder
    explanation: >-
      The primary Becker cohort records a clinical diagnosis; incomplete retrospective ascertainment precludes
      a general frequency band.
genetic:
- name: DMD
  gene_term:
    preferred_term: DMD
    term:
      id: hgnc:2928
      label: DMD
  relationship_type: CAUSATIVE
  inheritance:
  - name: X-linked recessive
  notes: >-
    DMD pathogenic variants cause a spectrum of dystrophinopathies. Becker classification integrates the
    clinical course and residual dystrophin with the molecular result. In-frame changes predominate, but
    out-of-frame and nonsense variants are established exceptions; reading frame alone is insufficient
    for diagnosis or individual prognosis.
  evidence:
  - reference: PMID:2491009
    reference_title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      About 60% of both Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) is due to
      deletions of the dystrophin gene.
    explanation: >-
      The historical deletion study establishes the shared DMD locus; it does not establish an absolute
      reading-frame discriminator.

inheritance:
- name: X-linked recessive
  description: >-
    Inheritance is X-linked. A heterozygous mother has a 50% chance of transmitting the variant in each
    pregnancy; an affected father transmits it to all daughters and no sons. Heterozygous females may
    have cardiac disease, muscle symptoms, or rarely a more severe dystrophinopathy phenotype. A negative
    family history does not exclude the disorder.
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If the mother of the proband has a DMD pathogenic variant, the chance of the mother transmitting
      it in each pregnancy is 50%. If the father of the proband has a DMD pathogenic variant, he will
      transmit it to all his daughters and none of his sons.
    explanation: >-
      GeneReviews states parental transmission probabilities explicitly.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Heterozygous females are typically asymptomatic or may exhibit weakness, fatigue, and cardiac involvement.
    explanation: >-
      The female phenotype extends beyond isolated cardiac risk and is variably expressed.
prevalence:
- population: Male births
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 5.6
  notes: >-
    Approximately 1 in 18,000 male births, converted to 5.6 per 100,000 male births. The denominator is
    male births specifically, not the general population, so this figure must not be compared directly
    with a whole-population prevalence.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Becker muscular dystrophy (BMD) is one of the most frequent among neuromuscular diseases, affecting
      approximately 1 in 18,000 male births.
    explanation: The source figure and its male-birth denominator.

    quote_role: REVIEW_SYNTHESIS
diagnosis:
- name: DMD Genetic Testing with Reading-Frame Interpretation
  description: >-
    Identify a pathogenic DMD variant using deletion/duplication analysis and sequencing, interpreted
    with the clinical phenotype and, when needed, dystrophin protein studies. Reading-frame prediction
    helps interpretation but does not by itself classify Becker versus Duchenne muscular dystrophy. The
    historical 92% concordance estimate applies to the analyzed deletion series. In unresolved cases,
    muscle RNA/cDNA analysis can identify splice abnormalities missed by standard DNA testing. Some urine-derived
    RNA approaches remain research investigations. Comprehensive assays capable of detecting sequence
    and copy-number variants are an alternative to sequential testing.
  evidence:
  - reference: PMID:2491009
    reference_title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The correlation between phenotype and type of deletion mutation is in agreement with the "reading
      frame" theory in 92% of cases and is of diagnostic and prognostic significance.
    explanation: >-
      The accuracy of the rule and the authors' own statement that it is diagnostically and prognostically
      useful.

  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Identification of a hemizygous or heterozygous DMD variant of uncertain significance does not establish
      or rule out the diagnosis.
    explanation: >-
      A VUS alone is insufficient for molecular confirmation.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Analysis to detect copy number variants (CNVs), i.e., deletions or duplications of DMD
    explanation: >-
      The stepwise algorithm begins with deletion/duplication analysis.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If no CNV is detected, sequence analysis of DMD to detect small intragenic deletions/insertions
      and missense, nonsense, and splice site variants
    explanation: >-
      Sequencing addresses classes of pathogenic variation missed by copy-number testing.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Level 3. If no DMD sequence variants are detected: (a) muscle biopsy for histology; (b) if histologic
      findings are consistent with a dystrophinopathy, immunohistochemistry is recommended; (c) if immunohistochemistry
      confirms a dystrophinopathy, then RNA/cDNA analysis on muscle or RNA analysis of muscle tissue,
      myogenic cells from urine-derived stem cells, or extracellular mRNA in urine is recommended to confirm
      the diagnosis.
    explanation: >-
      The diagnostic algorithm adds histology, dystrophin immunohistochemistry, and RNA/cDNA analysis
      for unresolved cases.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Some of these tests (e.g., immunohistochemistry and RNA sequencing on muscle tissue) are available
      on a clinical basis, whereas to date others (e.g., RNA analysis of stem cells or extracellular RNA
      analysis from urine) may be available on a research basis only.
    explanation: >-
      Clinical availability differs between muscle-based RNA testing and emerging urine-derived approaches.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Recently, assays designed to detect both CNVs and sequence variants (Levels 1 and 2 in Option 1)
      have become available. These assays use next-generation sequencing (NGS)-based assays of the entire
      DMD gene that include full sequence analysis as well as deep intronic variant detection with CNVs
      and single-nucleotide variant (SNV) calling [Zhao et al 2024].
    explanation: >-
      Comprehensive DMD assays may detect copy-number, sequence, and deep intronic variants together.
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
- name: Cardiac Surveillance Independent of Skeletal Muscle Severity
  description: >-
    Evaluate cardiac involvement from diagnosis even when skeletal muscle weakness is mild. ECG and echocardiography
    establish baseline cardiac status; MRI can identify myocardial fibrosis before echocardiography becomes
    abnormal.
  evidence:
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Despite the milder skeletal muscle involvement, heart failure from DCM is a common cause of morbidity
      and the most common cause of death in BMD.
    explanation: >-
      The cardiac burden of Becker muscular dystrophy can be substantial despite relatively mild skeletal
      muscle disease.

    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Cardiac MRI should also be discussed at diagnosis since it prov ides a more accurate estimation of cardiac function than echocardiography and can identify myocardial fibrosis, ma inly in the inferolateral wall, which can be present in patient s with a normal echocardiogram."  # codespell:ignore
    explanation: >-
      MRI can detect myocardial fibrosis despite a normal echocardiogram.
- name: Muscle Biopsy and Dystrophin Protein Assessment
  diagnosis_term:
    preferred_term: Muscle Biopsy
    term:
      id: NCIT:C51895
      label: Muscle Biopsy
  description: >-
    Muscle biopsy, immunohistochemistry, and dystrophin immunoblotting can clarify unresolved or atypical
    cases. Normal immunostaining does not exclude Becker muscular dystrophy; immunoblotting with antibodies
    against different protein regions can assess abundance and size. Biopsy is not routinely required
    when molecular and clinical findings already establish the diagnosis.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Dystrophin immunochemistry usually shows decreased or no findings with some or all of the dedicated
      antibodies, but may also show normal findings. The decrease can be present in all the fibers or
      manifest in a fragmented manner.
    explanation: >-
      The guideline warns that immunostaining can appear normal and explains why immunoblotting with multiple
      antibodies is informative.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Diagnosis should be completed by western blotting of dystrophin
    explanation: >-
      The guideline recommends immunoblotting to complete dystrophin protein assessment.
treatments:
- name: ACE Inhibition for Established Cardiomyopathy
  description: >-
    ACE inhibitors are first-line medication for established Becker cardiomyopathy in the 2023 French
    guideline. That guideline recommends specialist discussion of cardioprotective treatment when LVEF
    is below 50% or MRI shows myocardial fibrosis. It does not recommend prophylactic ACE inhibition for
    every Becker patient with normal cardiac findings; evidence from Duchenne muscular dystrophy does
    not establish that indication in Becker muscular dystrophy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ACE inhibitor
      term:
        id: NCIT:C247
        label: ACE Inhibitor
  target_mechanisms:
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    treatment_effect: INHIBITS
    description: >-
      Treats ventricular dysfunction and adverse remodeling associated with cardiomyopathy.
    evidence:
    - reference: PMID:20301298
      reference_title: Dystrophinopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        ACE inhibitors are used with or without beta blockers for cardiomyopathy in both DMD and BMD phenotypes.
      explanation: The indication for established cardiomyopathy in both phenotypes.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Thus, there is no indication to use ACE inhibitors for systematic treatment of BMD patients regardless
      of cardiac phenotype, such as in Duchenne MD.
    explanation: >-
      The French guideline does not support universal ACE-inhibitor prophylaxis irrespective of the Becker
      cardiac phenotype.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Patients with LVEF < 50% and/or evidence of myocardial fibrosis on MRI should be referre d to a
      specialized cardiologist in a tertiary center to discuss the  initiation of cardioprotective
    explanation: >-
      Reduced LVEF or myocardial fibrosis prompts specialist assessment of cardioprotective treatment
      in this guideline.

    quote_role: REVIEW_SYNTHESIS
- name: Corticosteroid Therapy
  description: >-
    Corticosteroids are used in selected patients with Becker muscular dystrophy, but efficacy is less
    established than in Duchenne muscular dystrophy. Benefits, adverse effects, and treatment duration
    require individual assessment; Duchenne trial results do not establish Becker efficacy. A 24-week
    open-label weekly-prednisone pilot enrolled 19 participants with limb-girdle muscular dystrophy and
    only one with Becker muscular dystrophy; pooled biomarker and functional changes do not establish
    Becker-specific benefit.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: corticosteroid
      term:
        id: CHEBI:50858
        label: corticosteroid
  evidence:
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Corticosteroid therapy improves muscle strength and function for individuals with DMD between ages
      five and 15 years; the same treatment is used in BMD, although the efficacy is less clear.
    explanation: >-
      GeneReviews explicitly qualifies the uncertain Becker efficacy while describing clinical use.

    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:35124660
    reference_title: An Open Label Exploratory Clinical Trial Evaluating Safety and Tolerability of Once-Weekly Prednisone in Becker and Limb-Girdle Muscular Dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Out of the 20 participants, seven were female, nineteen had LGMD and one had BMD
    explanation: >-
      The mixed pilot cohort contained only one Becker participant, precluding a Becker-specific efficacy
      estimate.
- name: Cardiac Transplantation
  description: >-
    Cardiac transplantation may be considered for terminal heart failure in selected patients with limited
    skeletal muscle disability and without severe respiratory failure. Selection requires multidisciplinary
    assessment. The French guideline generally does not recommend transplantation after loss of ambulation
    or with significant respiratory failure; ventricular assist devices can be discussed individually
    in expert centers.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Organ Transplantation
    term:
      id: NCIT:C15289
      label: Organ Transplantation
  target_mechanisms:
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    treatment_effect: BYPASSES
    description: >-
      Replaces the failing heart while leaving the underlying DMD variant and extracardiac manifestations
      unchanged.
    evidence:
    - reference: PMID:20301298
      reference_title: Dystrophinopathies.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        cardiac transplantation is offered to persons with severe dilated cardiomyopathy and BMD with
        limited or no clinical evidence of skeletal muscle disease.
      explanation: The indication and its selection criterion.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      In patients with terminal heart failure who have lost ambulation or have significant respiratory
      failure, cardi ac transplantati on is generally not indicated
    explanation: >-
      The guideline identifies motor and respiratory impairment as constraints on transplant selection.

    quote_role: REVIEW_SYNTHESIS
- name: Cardiac Surveillance
  description: >-
    Cardiac surveillance starts at diagnosis and continues regardless of skeletal muscle severity. Assessment
    includes ECG and echocardiography, with cardiac MRI to assess fibrosis and function when appropriate
    and Holter monitoring for cardiac dysfunction or conduction abnormalities. The 2026 GeneReviews chapter
    lists annual cardiac assessment for affected males and assessment before major surgery, with closer
    monitoring for fibrosis or dysfunction; its schedule partly draws on Duchenne care guidance. The 2023
    French Becker guideline proposes assessment every two years with a normal echocardiogram and at least
    annually with LVEF below 50%. The interval should be individualized by cardiology. GeneReviews recommends
    ECG and cardiac imaging every three to five years for heterozygous females without cardiac manifestations,
    beginning in the second to third decade, and specialist-directed follow-up when abnormalities are
    present.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Cardiac monitoring must systematically include ECG and echocardiogram. The other examinations must
      be discussed with the patient on the basis of the patients’ symptoms and ECG and echocardiogram
      findings. The frequency of these assessments depends on the initial findings. The minimum interval
      for a classic form of B MD with a normal echocardiogram is two years.
    explanation: >-
      The Becker guideline specifies ECG and echocardiography and a two-year interval when the echocardiogram
      is normal.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      For patie nts with LVEF < 50%, monitoring should be performed at least once a year.
    explanation: >-
      Ventricular dysfunction calls for more frequent assessment.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      DMD/BMD By cardiologist incl EKG & echocardiogram or cardiac MRI • Annually & before major surgery
      • More frequently in those age >10 yrs & those w/myocardial fibrosis or ventricular dysfunction
    explanation: >-
      GeneReviews Table 8 recommends annual and preoperative cardiac assessment; its footnote identifies
      Duchenne care guidelines as a basis for the intensified schedule.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In those without cardiac manifestations, cardiac evaluation with an EKG and cardiac imaging every
      three to five years beginning in the second to third decade of life is recommended.
    explanation: >-
      The updated chapter recommends recurring surveillance for heterozygous females with normal initial
      cardiac findings.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Cardiac MRI should also be discussed at diagnosis since it prov ides a more accurate estimation of cardiac function than echocardiography and can identify myocardial fibrosis, ma inly in the inferolateral wall, which can be present in patient s with a normal echocardiogram."  # codespell:ignore
    explanation: >-
      MRI can detect myocardial fibrosis despite a normal echocardiogram.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In cases showing abnormal cardiac systolic function (left ventricular ejection fraction below 50%)
      or significant conduction defects on the ECG, a 24-h Holter ECG sho uld also be performed to search
      for ventricular or supraventricular arrhythmias
    explanation: >-
      Abnormal ventricular function or significant conduction defects warrant ambulatory rhythm assessment.
- name: Perioperative Assessment and Anaesthetic Precautions
  description: >-
    Preoperative planning should assess cardiac and respiratory involvement and muscle weakness. Avoid
    succinylcholine because of hyperkalaemia and rhabdomyolysis risk. Volatile anaesthetics also require
    specialist risk assessment because of anaesthesia-induced rhabdomyolysis in dystrophinopathies. The
    ENMC consensus distinguishes this complication from malignant hyperthermia and reports no association
    of dystrophinopathies with malignant hyperthermia susceptibility.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:35971866
    reference_title: European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      AIR seems to be a specific complication of general anaesthesia in dystrophinopathies, especially
      at paediatric age. AIR can cause life‐threatening hyperkalaemia, and the risk of occurrence is possibly
      linked to the use of succinylcholine and/or volatile anaesthetics
    explanation: >-
      The muscular-dystrophy recommendations identify anaesthesia-induced rhabdomyolysis and hyperkalaemia
      as the relevant dystrophinopathy hazards.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:35971866
    reference_title: European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      There is no association with MH
    explanation: >-
      In Table 4, this statement follows the dystrophinopathy AIR recommendation and distinguishes it
      from malignant hyperthermia; it does not remove the need for anaesthetic precautions.
    quote_role: REVIEW_SYNTHESIS
- name: Investigational Givinostat
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    A 12-month placebo-controlled trial in 51 adults with Becker muscular dystrophy failed its primary
    total-fibrosis endpoint and showed no significant functional benefit. Secondary thigh and quadriceps
    MRI fat-fraction findings suggested a possible signal, but baseline imbalance and the small sample
    limit interpretation. This is investigational Becker evidence and does not establish an effective
    disease-modifying treatment.
  evidence:
  - reference: PMID:36793492
    reference_title: 'Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The study failed to achieve the primary endpoint. However, there was a potential signal from the
      MRI assessments suggesting givinostat could prevent (or slow down) BMD disease progression.
    explanation: >-
      The trial conclusion distinguishes the negative primary outcome from the exploratory interpretation
      of secondary MRI findings.
  - reference: PMID:36793492
    reference_title: 'Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Adverse events, most mild or moderate, were reported by 88.2% and 52.9% patients receiving givinostat
      and placebo.
    explanation: >-
      Adverse events were more frequent with givinostat; the paper details platelet and triglyceride abnormalities.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Givinostat
      term:
        id: NCIT:C71716
        label: Givinostat
- name: Investigational Sevasemten
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Sevasemten inhibits fast skeletal muscle myosin ATPase to reduce injurious contraction. A short phase
    1 Becker cohort comprised five treated patients and two placebo recipients; muscle-injury biomarkers
    decreased but the study was too small and short to establish clinical efficacy. In a later uncontrolled
    12-person study, biomarkers remained reduced and functional measures were stable over two years. These
    observations support investigation, not a proven treatment effect. The completed CANYON/GRAND CANYON
    registry had no posted results at the September 2026 review.
  evidence:
  - reference: PMID:40452637
    reference_title: A Phase 1, Double-Blind, Placebo-Controlled Trial of Sevasemten (EDG-5506), a Selective Modulator of Fast Skeletal Muscle Contraction, in Healthy Volunteers and Adults With Becker Muscular Dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In Part C, 7 men with BMD were randomized to sevasemten (N = 5) or placebo (N = 2)
    explanation: >-
      Defines the very small Becker randomized cohort within a larger study dominated by healthy volunteers.
  - reference: PMID:42308588
    reference_title: 'Effects of sevasemten (EDG-5506) on safety, biomarkers, and functional measures in adults with Becker muscular dystrophy: results of a phase 1b, open-label study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      As this was an open-label trial with no placebo control, caution is required in interpretation.
      Additional limitations of this study include the small sample size and the lack of diversity in
      enrolled participants (100% White).
    explanation: >-
      The 24-month study cannot distinguish treatment benefit from natural-history variability or other
      uncontrolled influences.
  - reference: PMID:42308588
    reference_title: 'Effects of sevasemten (EDG-5506) on safety, biomarkers, and functional measures in adults with Becker muscular dystrophy: results of a phase 1b, open-label study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Treatment with sevasemten was associated with reductions in circulating biomarkers of muscle injury
      that were evident within 4 weeks and sustained for up to 24 months. Physical function, as assessed
      by North Star Ambulatory Assessment (NSAA), was stable over 24 months.
    explanation: >-
      Records the observed biomarker and functional trajectories without treating them as randomized efficacy
      evidence.
  target_mechanisms:
  - target: Contraction-Induced Skeletal Muscle Injury
    treatment_effect: INHIBITS
    description: >-
      Investigational fast-myosin inhibition aims to reduce contraction-associated muscle injury.
      Sustained biomarker reductions in the small open-label Becker study support this proposed effect;
      they do not establish prevention of long-term functional decline.
    evidence:
    - reference: PMID:42308588
      reference_title: 'Effects of sevasemten (EDG-5506) on safety, biomarkers, and functional measures in adults with Becker muscular dystrophy: results of a phase 1b, open-label study.'
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      snippet: >-
        Treatment with sevasemten was associated with reductions in circulating biomarkers of muscle injury
        that were evident within 4 weeks and sustained for up to 24 months.
      explanation: >-
        The 12-person study reports a durable biomarker association consistent with the proposed target
        effect, with no placebo control to establish efficacy.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Sevasemten
      term:
        id: NCIT:C199222
        label: Sevasemten
- name: Investigational Vamorolone
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Vamorolone improved selected strength and histological measures and increased dystrophin protein in
    bmx mice. This preclinical study did not establish human efficacy or long-term cardiac benefit. The
    subsequently completed Becker phase II pilot has registry results posted in September 2026; its 24-week
    functional data are descriptive and do not establish a clinically meaningful benefit. The trial must
    be distinguished from Duchenne treatment evidence.
  evidence:
  - reference: PMID:37534133
    reference_title: Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Dystrophin increases of 49% (p < 0.0001) were found in the gastrocnemius and 55% (p = 0.0173) in
      the heart with vamorolone treatment
    explanation: >-
      The mouse experiment shows an increase relative to vehicle-treated bmx animals, not normalization
      to healthy dystrophin levels or proof of human efficacy.
  - reference: PMID:37534133
    reference_title: Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      to fully demonstrate causation, further studies are needed to expand upon these and previous studies.
    explanation: >-
      The authors limit the proposed microRNA mechanism: reduced microRNAs and increased dystrophin correlate,
      but direct causal mediation was not demonstrated.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Vamorolone
      term:
        id: NCIT:C152825
        label: Vamorolone
- name: Physical Therapy and Adapted Exercise
  description: >-
    Individualized physical therapy uses gentle progressive aerobic activity, stretching, low-resistance
    exercise, balance work, and fall prevention to maintain function and joint mobility. Exercise intensity
    should account for muscle weakness, fatigue, pain, and cardiac or respiratory involvement; avoid excessive
    contraction and eccentric loading of weak muscles.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      This physical activity must be gentle and progressive and must take into account the specificities
      of BMD when choosing the exercises to offer
    explanation: >-
      The guideline recommends gradual activity adapted to Becker muscular dystrophy.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Maintenance of segmenta l and spinal muscular and joint flexibility for analgesic pu rposes by passive
      mobilizations and stretching, prepar ation and recovery for exercise and proprioceptive stimulation:
      stretching, posture, etc.
    explanation: >-
      Stretching and passive mobilization address flexibility and discomfort.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The most affected muscl es (those with a muscle testing MRC rating < 4) require more precautions,
      specifically by limiting intense contract ions and eccentric stresses and promoting aerobic metabolism.
    explanation: >-
      Weak muscles require limits on intense contraction and eccentric loading.
- name: Orthoses and Mobility Support
  description: >-
    Selected posture or walking orthoses can address deformity and support function. Wheelchairs or scooters
    become appropriate when walking-related falls and fractures outweigh functional benefit. Occupational
    and rehabilitation teams can adapt transfers, self-care, communication, and home, school, or workplace
    access.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Posture orthoses may be used in some patients. In the lower limbs, nocturnal posture orthoses can
      be proposed to address certain deformities (e.g., anti-flexum knee or antiequine orthosis).
    explanation: >-
      Night-time postural orthoses are options for selected deformities.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Manual wheelchair; electric scooter and/or electric wh eelchair are necessary when the risks linked
      to walking (falls, fractures) become greater than the functional benefits.
    explanation: >-
      The mobility decision balances walking benefit against injury risk.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Specific devices facilitating meals, washing, toileting, leisur e, transfers, and environmental
      control can be implemented.
    explanation: >-
      Assistive devices support daily activities and environmental access.
- name: Orthopedic Surgery for Function-Limiting Deformity
  description: >-
    Selected tendon or foot procedures may help walking and posture. Spinal fusion is reserved for severe
    forms. Rarely, macroglossia with ventilatory or swallowing consequences warrants surgery; operative
    planning requires cardiac, respiratory, and anesthetic assessment.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Some surgeries (e.g., Achilles tendon tenotomy, gastrocnemius aponeurotomy, tendon transfers, osteotomies
      or foot arthrodesis) are useful, and their u ses must be linked to functions such as walking and
      posture s tability. Vertebral arthrodesis is limited to the most severe forms close to DMD
    explanation: >-
      The guideline links surgery to functional impairment and limits spinal fusion to severe disease.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In rare cases, macroglossia surgery may be required because of functional consequences (ventilation,
      swallowing, etc.).
    explanation: >-
      Functionally significant macroglossia is a rare surgical indication.
- name: Neuropsychological and Mental Health Care
  description: >-
    Assess cognitive, educational, behavioral, and emotional needs from diagnosis and when school or employment
    difficulties emerge. Use findings to tailor family, school, and workplace support. The French guideline
    recommends reassessment every two to three years in children, mental-health screening at neuromuscular
    visits, and formal annual psychological evaluation. Medication decisions should account for cardiac
    status, interactions, and adverse effects.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Cognitive or psychiatric assessment has to be consider ed at diagnosis, and especially in the event
      of integration or access to employment issues.
    explanation: >-
      Assessment is considered from diagnosis and when participation difficulties arise.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      For children, assessments should be performed every 2 –3 years to monitor a child’s developmental
      progress and response to interventions.
    explanation: >-
      Repeated childhood assessment guides developmental support.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Formal annual evaluation by the mental health clinician is advised to assess the psychological wellbeing
      of the individual, parents, and siblings.
    explanation: >-
      The guideline includes recurring psychological evaluation for patients and families.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Depending on the patient’s age and disease status, it may be necessary to pay special att ention
      to their cardiac status, potential medication inte ractions, and side effects when combined with
      existing medications (e.g., weight gain).
    explanation: >-
      Psychotropic treatment requires attention to comorbidity and concomitant medication.
- name: Respiratory Surveillance
  description: >-
    Regular evaluation includes symptoms of nocturnal hypoventilation, orthopnea, cough effectiveness,
    pulmonary function, and sleep investigations when indicated. The French Becker guideline recommends
    pulmonary function testing every two years if normal and annual specialist follow-up if abnormal.
    The 2026 GeneReviews dystrophinopathy schedule recommends annual respiratory evaluation and every
    six months after loss of ambulation, citing Duchenne care guidance. The treating team should individualize
    frequency to findings and progression.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A respiratory functional exploration should be performed every 2 years, with no pulmonologist advice
      required at this stage if the findings are normal.
    explanation: >-
      The French guideline gives a two-year interval when respiratory testing is normal.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In cases with an abnormal fVC, the frequency of monitoring should be ann ual. A subsequent pulmonologist
      assessment, performed a t least annually, will indicate the need for blood gas analysis or nightly
      examinations.
    explanation: >-
      Abnormal FVC warrants annual or more frequent specialist assessment.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Respiratory By pulmonologist for assessment of respiratory function Annually; then every 6 mos after
      loss of ambulation
    explanation: >-
      GeneReviews Table 8 gives a more frequent dystrophinopathy schedule; footnote 1 identifies its Duchenne
      guideline basis.
- name: Noninvasive Ventilation for Hypoventilation
  description: >-
    Nocturnal noninvasive ventilation is offered when diaphragmatic weakness produces hypoventilation,
    with specialist titration and follow-up. Respiratory support depends on functional assessment and
    symptoms rather than skeletal muscle disability alone.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: Non-Invasive Mechanical Ventilation
    term:
      id: NCIT:C171457
      label: Non-Invasive Mechanical Ventilation
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In cases showing actual diaphragmatic involvemen t with hypoventilation, nocturn al noninvasive
      ventilation will be offered by the pulmonologist with a specific followup.
    explanation: >-
      The guideline links nocturnal noninvasive ventilation to documented hypoventilation.
- name: Cough Assistance
  description: >-
    Weak or ineffective cough warrants respiratory physiotherapy and individually selected manual or mechanical
    cough-assistance techniques, with pulmonology follow-up.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "In cases showing a cough d eficiency, cough aid techniques will be offered by the pulmonologist or physiotherapist. A pulmonologist follow-up is then necessary."  # codespell:ignore
    explanation: >-
      The guideline recommends cough assistance when a cough deficit is present.
- name: Swallowing and Nutritional Support
  description: >-
    Assess chewing, swallowing safety, weight trajectory, and nutritional intake. Adapt food texture and
    head position for impaired pharyngeal propulsion, provide feeding aids and speech-language input as
    needed, and consider oral nutritional supplements when intake is inadequate. Changes in mobility require
    reassessment of energy needs.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      If the disorders are secondary to poor pharyngeal propulsion, the textures (mixed, adequately “slippery”)
      of the food and the po sition of the head during meals should be adapted.
    explanation: >-
      Food texture and head position are adapted to swallowing mechanics.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Oral nutritional supplements may be offered when increase in caloric intake becomes necessary.
    explanation: >-
      Supplementation is considered when increased caloric intake is needed.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In the most severe patien ts there is a risk of secondary undernutrition. It is then necessary to
      identify all the aggravating factors: involvement of the upper limbs (speci al cutlery, raised meal
      plan …), macroglossia or involvement of chewing muscles (hygiene care o ral, speech therapy, adaptation
      of the texture of food, surgery), digestive damage (constipation, …), spinal defo rmities sources
      of compression, mask ventilation that causes or worsens aerogastria.
    explanation: >-
      Nutritional assessment includes feeding mechanics, gastrointestinal problems, deformity, and ventilation-related
      factors.
- name: Gastrostomy for Inadequate or Unsafe Oral Intake
  description: >-
    Gastrostomy is reserved for the uncommon situation in which oral feeding cannot provide safe nutritional
    intake. Assess respiratory function and ventilatory requirements before placement and use a team experienced
    with neuromuscular disability.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: "Situations necessitating artificial feeding are rare in patients with BMD. If oral feeding cannot ensure safe nutritive intake, a gastrostomy can be set up as the last resort. However, bef ore creating a gastrostomy, the patient’s respiratory function a nd, in particular, the need for noninvasive ventilation shoul d be evaluated. The gastrostomy should be placed by a team accustomed to the care of disabled patients."  # codespell:ignore
    explanation: >-
      The guideline describes the indication and preprocedural respiratory assessment.
- name: Gastrointestinal Symptom Management
  description: >-
    Gastroenterology assessment addresses constipation, reflux, and gastric motility problems. Management
    is individualized and can include diet, bowel regimens, and medication; severe feeding or motility
    problems may require enteral support.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      A gastroenterologist should be consulted for manageme nt of constipation, gastroesophageal reflux,
      and gastrointestinal motility concerns, and when gastrostomy tube placement is needed.
    explanation: >-
      The guideline identifies gastrointestinal problems requiring specialist management.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Constipation can be addressed through various measures, including adopting a fiber-rich diet, implementing
      toilet training techniques, engaging in physiotherapy, considering laxatives like polyethylene glycol,
      milk of magnesia, or lactulose may be necessary.
    explanation: >-
      Constipation care combines nonpharmacologic measures and laxatives when needed.
- name: Urological Assessment and Care
  description: >-
    Lower urinary tract symptoms warrant comprehensive urological evaluation, potentially including urodynamic
    assessment, and ongoing treatment and follow-up tailored to the cause.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In cases where lower ur inary tract symptoms are present, it is advisable to undergo a comprehensive
      urological evaluation, which may include urodynamic examinations, and to receive thorough follow-up
      care.
    explanation: >-
      The recommendation is symptom-driven rather than routine invasive testing for all patients.
- name: Bone Health and Pain Management
  description: >-
    Assess bone health and calcium and vitamin D needs, particularly with reduced mobility. Pain management
    includes positioning, appropriate bedding, mobilization, and individualized analgesia. Medication
    choice should account for constipation, respiratory or cardiac impairment, and drug interactions.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Prevention of osteopenia with calcium and vitamin D supplementation must be estimated and promptly
      proposed in the event of reduced mobil ity.
    explanation: >-
      Reduced mobility prompts assessment of calcium and vitamin D supplementation.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Analgesic pharmacologica l treatment (anti -inflammatory, muscle relaxants) must tak e into account
      the side effects (especially cardiac and respira tory effects) and possible drug interactions.
    explanation: >-
      Analgesia must account for cardiorespiratory effects and interactions.
- name: Respiratory Vaccination
  description: >-
    The French guideline recommends pneumococcal and COVID-19 vaccination and annual influenza vaccination,
    following applicable immunization schedules.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Immunization with pneumococcal and COVID-19 vaccines and annual immunization with the influenza
      vaccine according to the vaccination schedule are strongly recommended, as for any disease with
      comorbidities [103].
    explanation: >-
      Vaccination is part of preventive care for patients with neuromuscular comorbidity.
- name: Genetic Counseling and Family Evaluation
  description: >-
    Offer counseling about X-linked transmission, variable manifestations in heterozygous females, and
    residual recurrence risk from parental germline mosaicism. Evaluate at-risk male and female relatives,
    using the familial variant when known. Discuss reproductive options before pregnancy; prenatal testing
    is possible after variant identification, and preimplantation testing may require additional phasing.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The optimal time for determination of genetic risk and discussion of the availability of prenatal/
      preimplantation genetic testing is before pregnancy.
    explanation: >-
      Counseling and reproductive planning are ideally offered before pregnancy.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Female relatives. It is appropriate to evaluate at-risk female family members (i.e., first-degree
      relatives of a proband with a DMD pathogenic variant) to identify as early as possible those who
      would benefit from cardiac and skeletal muscle evaluation and surveillance.
    explanation: >-
      Identifying heterozygous relatives enables cardiac and skeletal surveillance.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Once the DMD pathogenic variant has been identified in an affected family member, prenatal testing
      is possible.
    explanation: >-
      Prenatal testing depends on identifying the familial pathogenic variant.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In cases of de nov o mutations, one of the parents may carry a germinal mosaic ism (presence of
      populations of gametes w ith and without t he pathogenic variation), which is associated with a
      risk of r ecurrence in the offspring.
    explanation: >-
      Parental germline mosaicism leaves a recurrence risk after an apparently de novo occurrence.
- name: Pregnancy Planning for Heterozygous Females
  description: >-
    Assess cardiac status before conception or when pregnancy is recognized, including in asymptomatic
    heterozygous females. Symptomatic females also require skeletal muscle assessment. Those with dilated
    cardiomyopathy need coordinated care from a cardiac specialist and high-risk obstetrics, including
    review of cardiac medications.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Symptomatic heterozygous women should undergo an evaluation for DMD-related cardiomyopathy and skeletal
      muscle involvement ideally prior to conceiving a pregnancy or as soon as the pregnancy is recognized.
    explanation: >-
      Preconception or early-pregnancy evaluation includes cardiac and skeletal manifestations in symptomatic
      females.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Asymptomatic women who are heterozygous for a DMD pathogenic variant should consider undergoing
      a cardiac evaluation prior to conception or when a pregnancy is recognized. It is recommended that
      women with evidence of dilated cardiomyopathy should be treated and/or monitored by a cardiac specialist
      with experience in the treatment of heart failure and/or neuromuscular disorders and a high-risk
      obstetrician
    explanation: >-
      Cardiac evaluation also applies to asymptomatic heterozygotes, and cardiomyopathy requires coordinated
      specialist care.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Cardiac medications need to be reviewed and potentially adjusted in women who are planning on becoming
      pregnant.
    explanation: >-
      Medication review is part of pregnancy planning.
- name: Advanced Heart Failure Medication and Device Care
  description: >-
    Overt heart failure or ventricular systolic dysfunction requires specialist treatment using heart-failure
    guidance. The French Becker guideline includes ACE inhibitors or angiotensin-receptor antagonists,
    beta blockers, mineralocorticoid-receptor antagonists, and selected resynchronization or defibrillator
    therapy. Ventricular assist devices may be considered as a bridge to transplantation or destination
    therapy; candidacy depends on motor, respiratory, and overall clinical status.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In patients with overt h eart f ailure or left ventricular (LV) systolic dysfunction, the therapeutic
      strategy should follow the recommendations for th e treatment of heart failure in the general population,
      based on (1) ACE inhibitors (or angiotensin II antagonists), b eta blockers, mineralocorticoid receptor
      antagonists, and other specific drugs
    explanation: >-
      The guideline recommends general heart-failure pharmacotherapy for overt heart failure or ventricular
      systolic dysfunction.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In ambulant patients with terminal heart failure and absence of severe respiratory f ailure, cardiac
      transplantation and an LV assist device (as a brid ge to transplant or destination therapy) should
      be consid ered.
    explanation: >-
      Selected patients can be considered for transplantation or ventricular assistance.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      (2) cardiac resynchronization therapy, and (3) implantable cardiac defibrillator if LVEF < 30%.
    explanation: >-
      The 2023 guideline includes device options; current eligibility requires specialist assessment rather
      than treating its historical EF threshold as universal.
- name: Investigational Tadalafil
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Tadalafil
      term:
        id: NCIT:C47743
        label: Tadalafil
  description: >-
    A randomized double-blind crossover experiment in ten ambulatory men with preserved cardiac function
    showed acute improvement of exercise blood-flow regulation. Eight of nine participants with impaired
    sympatholysis on placebo responded. The study measured forearm oxygenation and does not establish
    sustained improvement in strength, ambulation, or progression.
  evidence:
  - reference: PMID:23197572
    reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored
      blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo.
    explanation: >-
      The randomized crossover trial demonstrates an acute physiological response in the subgroup with
      abnormal placebo physiology, rather than long-term clinical benefit.
  target_mechanisms:
  - target: Impaired Exercise-Induced Vasomodulation
    treatment_effect: INHIBITS
    description: >-
      Acutely improves the abnormal exercise vascular response; a downstream effect on chronic muscle
      disease has not been established.
    evidence:
    - reference: PMID:23197572
      reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored
        blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo.
      explanation: >-
        The randomized crossover trial demonstrates an acute physiological response in the subgroup with
        abnormal placebo physiology, rather than long-term clinical benefit.
- name: Investigational Sodium Nitrate
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sodium nitrate
      term:
        id: CHEBI:63005
        label: sodium nitrate
  description: >-
    Nitrate-rich beetroot juice improved functional sympatholysis in a small acute Becker study, including
    a placebo-controlled crossover substudy in six participants. This physiological result does not establish
    long-term benefit or safety as a Becker disease-modifying therapy.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
    reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the subsequent placebo‐controlled trial performed in six of the 11 patients from the open‐label
      trial (P2, P3, P7, P12, P14 and P16), we confirmed that sodium nitrate restores functional sympatholysis,
      whereas placebo was without effect
    explanation: >-
      The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.
  target_mechanisms:
  - target: Impaired Exercise-Induced Vasomodulation
    treatment_effect: INHIBITS
    description: >-
      Acutely improves the abnormal exercise vascular response; a downstream effect on chronic muscle
      disease has not been established.
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
      reference_title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In the subsequent placebo‐controlled trial performed in six of the 11 patients from the open‐label
        trial (P2, P3, P7, P12, P14 and P16), we confirmed that sodium nitrate restores functional sympatholysis,
        whereas placebo was without effect
      explanation: >-
        The small randomized crossover substudy confirms an acute vascular response after nitrate supplementation.
- name: Sildenafil Trial with No Demonstrated Clinical Benefit
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Sildenafil
      term:
        id: NCIT:C61940
        label: Sildenafil
  description: >-
    A randomized placebo-controlled crossover trial with two four-week treatment periods found no effect
    on blood flow, maximal work capacity, or cardiac function. Sixteen participants completed skeletal-muscle
    evaluations and thirteen completed cardiac MRI. These findings do not support sildenafil as an established
    Becker disease-modifying treatment.
  evidence:
  - reference: PMID:25042931
    reference_title: Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations.
      Sildenafil had no effect on any of the outcome parameters.
    explanation: >-
      The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.
discussions:
- discussion_id: interpretation_becker_is_the_target_state_of_dmd_exon_skipping
  kind: INTERPRETATION
  status: OPEN
  prompt: >-
    Should Becker muscular dystrophy be curated as the therapeutic target state of exon-skipping antisense
    therapy in Duchenne muscular dystrophy, and does that make it a conformer of the antisense-oligonucleotide
    module?
  attaches_to:
  - pathophysiology#Reduced or Abnormal Partly Functional Dystrophin
  rationale: >-
    Some Duchenne exon-skipping therapies restore an open reading frame and aim to produce partly functional,
    Becker-like dystrophin. Becker natural history and genotype-specific models can inform expectations,
    but an induced protein is not guaranteed to reproduce a particular Becker clinical trajectory. This
    untreated disease entry does not assert an antisense intervention in its causal path.
  evidence:
  - reference: PMID:16770791
    reference_title: 'Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In Becker patients, in-frame mutations allow the synthesis of internally deleted, but largely functional
      dystrophins.
    explanation: >-
      The protein state that exon skipping in Duchenne is designed to produce, stated here as the natural
      state in Becker.
    quote_role: REVIEW_SYNTHESIS
  - reference: PMID:20301298
    reference_title: Dystrophinopathies.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Dystrophin restoration therapies have been developed by using synthetic antisense oligonucleotides
      to restore the reading frame by exon skipping for individuals with specific pathogenic variants
      in DMD.
    explanation: >-
      The source describes the reading-frame-restoration strategy in Duchenne; it does not establish treatment
      of Becker patients or guarantee a specific clinical outcome.

    quote_role: REVIEW_SYNTHESIS
- discussion_id: interpretation_reading_frame_rule_is_statistical
  kind: INTERPRETATION
  status: OPEN
  prompt: >-
    How should exceptions to the reading-frame rule be curated, given that a substantial minority of clinically
    definite Becker patients carry out-of-frame mutations?
  attaches_to:
  - pathophysiology#DMD Pathogenic Variant
  rationale: >-
    Reading-frame concordance is a statistical association: the 1989 deletion series reported 92%, and
    the Leiden database reported 91%. The Italian Becker cohort separately contained out-of-frame and
    nonsense variants among clinically characterized patients. These percentages have different denominators
    and cannot be pooled. Alternative splicing, translational re-initiation, and distal truncation can
    help explain exceptions, but the rescue mechanism must be demonstrated for the specific variant. Phenotype,
    dystrophin protein, and molecular findings should be interpreted together. Mild or asymptomatic in-frame
    deletion carriers may also be underascertained.
  evidence:
  - reference: PMID:2491009
    reference_title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The correlation between phenotype and type of deletion mutation is in agreement with the "reading
      frame" theory in 92% of cases and is of diagnostic and prognostic significance.
    explanation: >-
      The deletion series supports a useful but incomplete association between reading frame and phenotype.
  - reference: PMID:16770791
    reference_title: 'Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      over 4700 mutations have been reported in the Leiden DMD mutation database, of which 91% are in
      agreement with this rule.
    explanation: >-
      The larger mutation database reports a similar but distinct concordance estimate with a different
      denominator.
  - reference: PMID:2491009
    reference_title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The distribution and frequency of deletions spanning the entire locus suggests that many "in-frame"
      deletions of the dystrophin gene are not detected because the individuals bearing them are either
      asymptomatic or exhibit non-DMD/non-BMD clinical features.
    explanation: >-
      The ascertainment argument, made by the authors themselves, which bears on how the 92% should be
      read.

- discussion_id: gap_vascular_rescue_and_long_term_becker_outcomes
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does sustained correction of exercise vascular dysregulation improve strength or slow progression
    in defined Becker genotypes?
  attaches_to:
  - pathophysiology#Impaired Exercise-Induced Vasomodulation
  rationale: >-
    Acute tadalafil and nitrate studies support an NO-dependent vascular mechanism, but they do not establish
    clinically meaningful disease modification. A four-week sildenafil trial was negative. Differences
    in intervention, duration, target abundance, and endpoints limit direct comparisons.
  evidence:
  - reference: PMID:23197572
    reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The present study does not address whether restoring sympatholysis with PDE5A inhibition can slow
      disease progression and improve muscle strength.
    explanation: >-
      The investigators explicitly distinguish vascular rescue from clinical efficacy.
  - reference: PMID:25042931
    reference_title: Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations.
      Sildenafil had no effect on any of the outcome parameters.
    explanation: >-
      The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.
references:
- reference: PMID:3384440
  title: An explanation for the phenotypic differences between patients bearing partial deletions of the DMD locus.
- reference: PMID:2491009
  title: 'The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.'
- reference: PMID:16770791
  title: 'Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.'
- reference: PMID:39499670
  title: 'Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.'
- reference: PMID:37422773
  title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
- reference: PMID:33454189
  title: 'Respiratory decline in adult patients with Becker muscular dystrophy: A longitudinal study.'
- reference: PMID:20301298
  title: Dystrophinopathies.
  tags:
  - GeneReviews
- reference: url:https://oup.silverchair-cdn.com/article-minimal/7876416
  title: https://oup.silverchair-cdn.com/article-minimal/7876416
- reference: PMID:36628607
  title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
- reference: PMID:36793492
  title: 'Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.'
- reference: PMID:35971866
  title: European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders.
- reference: PMID:39358550
  title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
- reference: PMID:40452637
  title: A Phase 1, Double-Blind, Placebo-Controlled Trial of Sevasemten (EDG-5506), a Selective Modulator of Fast Skeletal Muscle Contraction, in Healthy Volunteers and Adults With Becker Muscular Dystrophy.
- reference: PMID:42308588
  title: 'Effects of sevasemten (EDG-5506) on safety, biomarkers, and functional measures in adults with Becker muscular dystrophy: results of a phase 1b, open-label study.'
- reference: PMID:37534133
  title: Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice.
- reference: clinicaltrials:NCT03238235
  title: A Randomised, Double Blind, Placebo Controlled Study to Evaluate the Micro-macroscopic Effects on Muscles, the Safety and Tolerability, and the Efficacy of Givinostat in Patients With Becker Muscular Dystrophy (BMD)
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT03238235
  title: https://clinicaltrials.gov/api/v2/studies/NCT03238235
- reference: clinicaltrials:NCT05291091
  title: A Phase 2 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Effect of EDG-5506 on Safety, Biomarkers, Pharmacokinetics, and Functional Measures in Adults and Adolescents With Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05291091
  title: https://clinicaltrials.gov/api/v2/studies/NCT05291091
- reference: clinicaltrials:NCT05160415
  title: A Phase 1b, Open-label Study of the Safety and Pharmacokinetics of EDG-5506 in Adults With Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05160415
  title: https://clinicaltrials.gov/api/v2/studies/NCT05160415
- reference: clinicaltrials:NCT05166109
  title: A Phase II Pilot Trial of Vamorolone vs. Placebo for the Treatment of Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05166109
  title: https://clinicaltrials.gov/api/v2/studies/NCT05166109
- reference: clinicaltrials:NCT04386304
  title: A Phase 1, Open-label, Dose Escalation Study to Evaluate the Safety and Preliminary Efficacy of Orally Administered (+)-Epicatechin in Patients With Becker or Becker-like Muscular Dystrophy With Continued Ambulation Past 16 Years of Age
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04386304
  title: https://clinicaltrials.gov/api/v2/studies/NCT04386304
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
  title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
  tags:
  - GeneReviews
- reference: PMID:35124660
  title: An Open Label Exploratory Clinical Trial Evaluating Safety and Tolerability of Once-Weekly Prednisone in Becker and Limb-Girdle Muscular Dystrophy.
- reference: clinicaltrials:NCT04054375
  title: Open Label Safety and Efficacy of Once Weekly Steroid in Patients With LGMD and Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04054375
  title: https://clinicaltrials.gov/api/v2/studies/NCT04054375
- reference: clinicaltrials:NCT04585464
  title: A Phase 1, Randomized, Placebo-Controlled, Double-blind, Single and Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and PK of EDG-5506 in Adult Healthy Volunteers and Adults With Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04585464
  title: https://clinicaltrials.gov/api/v2/studies/NCT04585464
- reference: url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/
  title: Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC
- reference: PMID:23197572
  title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
- reference: PMID:25042931
  title: Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT01070511
  title: https://clinicaltrials.gov/api/v2/studies/NCT01070511
- reference: clinicaltrials:NCT01070511
  title: Functional Muscle Ischemia and PDE5A Inhibition in Becker Muscular Dystrophy
- reference: url:https://clinicaltrials.gov/api/v2/studies/NCT01350154
  title: https://clinicaltrials.gov/api/v2/studies/NCT01350154
- reference: clinicaltrials:NCT01350154
  title: Does Modulation of the nNOS System in Patients With Muscular Dystrophy and Defect nNOS Signalling Affect Cardiac, Muscular or Cognitive Function?
- reference: PMID:22589245
  title: Variable phenotype of del45-55 Becker patients correlated with nNOSμ mislocalization and RYR1 hypernitrosylation.
animal_models:
- name: bmx exon 45-47 deletion mouse
  species: Mouse
  genotype: Dmd exon 45-47 deletion
  background: C57/BL6J
  publication: PMID:36628607
  description: >-
    CRISPR-generated in-frame deletion of murine Dmd exons 45-47. The model has reduced dystrophin protein
    despite preserved transcript abundance, contraction-related muscle injury, inflammation, fibrosis,
    and age-dependent cardiac dysfunction.
  evidence:
  - reference: PMID:36628607
    reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein
      in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy.
    explanation: >-
      The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.
  modeled_mechanisms:
  - target: Reduced or Abnormal Partly Functional Dystrophin
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      Reproduces the protein deficit with preserved transcript abundance.
    limitations: >-
      Represents one deletion; it does not capture the full spectrum of Becker molecular outcomes.
    evidence:
    - reference: PMID:36628607
      reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein
        in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy.
      explanation: >-
        The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.
  - target: Contraction-Induced Skeletal Muscle Injury
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Eccentric contraction experiments show greater force loss than wild type.
    limitations: >-
      Individual functional endpoints are not uniformly intermediate between wild type and dystrophin-null
      mice.
    evidence:
    - reference: PMID:36628607
      reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Ten eccentric contractions of WT EDL muscle resulted in a 15.53% drop in ex vivo peak force. In
        contrast, this protocol reduced peak force by 20.16% in bmx EDL muscles (P = 0.0239 bmx vs. WT)
        and 20.86% in mdx EDL (Figure 2D).
      explanation: >-
        The genotype-defined model has greater contraction-induced force loss than wild type; it does
        not establish a uniform degree of protection relative to dystrophin-null muscle.
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Aged mice develop reduced ejection fraction and fractional shortening.
    limitations: >-
      Mouse age and timing of cardiomyopathy cannot be mapped directly to human prognosis.
    evidence:
    - reference: PMID:36628607
      reference_title: The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Specifically, bmx mice show deficits in muscle and cardiac function, reduced dystrophin protein
        in skeletal and cardiac muscle, and histopathology consistent with moderate dystrophy.
      explanation: >-
        The exon 45-47 mouse model reproduces dystrophin reduction and both skeletal and cardiac dysfunction.
- name: R-BMDdel45-47 rat
  species: Rat
  genotype: Dmd exon 45-47 deletion
  background: Sprague Dawley
  publication: PMID:39358550
  description: >-
    Genome-edited rats show reduced dystrophin, relatively mild skeletal muscle dysfunction, and progressive
    cardiac fibrosis and systolic dysfunction. Intercalated-disc proteins are mislocalized. Resting ventilatory
    function remains preserved at 12 months despite diaphragmatic histological changes.
  evidence:
  - reference: PMID:39358550
    reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Most notably, BMD rats developed a progressive cardiomyopathy with reduced ejection fraction and
      pronounced fibrosis, closely mimicking the major cardiac involvement diagnosed in BMD patients carrying
      a 45–47 deletion.
    explanation: >-
      The rat model captures progressive cardiac disease for this deletion, while its skeletal phenotype
      is milder.
  modeled_mechanisms:
  - target: Cardiac Intercalated Disc Disorganization
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: >-
      Reproduces structural and protein-localization abnormalities at intercalated discs.
    limitations: >-
      The study does not selectively rescue TMEM65 or connexin-43 localization to test mediation of cardiac
      disease.
    evidence:
    - reference: PMID:39358550
      reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        At the histological level, TMEM65 notably displayed a larger distribution and mislocalization
        from the ICD in both BMD and DMD ventricles
      explanation: >-
        Immunostaining shows mislocalization in the rat model; reduced Tmem65 RNA did not correspond to
        reduced TMEM65 protein abundance in Becker rat hearts.
  - target: Left Ventricular Impairment and Dilated Cardiomyopathy
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      Develops ventricular dilation, reduced ejection fraction, and cardiac fibrosis.
    limitations: >-
      The model carries one deletion and exhibits considerable variation between animals.
    evidence:
    - reference: PMID:39358550
      reference_title: Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Most notably, BMD rats developed a progressive cardiomyopathy with reduced ejection fraction and
        pronounced fibrosis, closely mimicking the major cardiac involvement diagnosed in BMD patients
        carrying a 45–47 deletion.
      explanation: >-
        The rat model captures progressive cardiac disease for this deletion, while its skeletal phenotype
        is milder.
clinical_trials:
- name: NCT03238235
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Randomized placebo-controlled givinostat trial in 51 adults, completed in 2021. The published 12-month
    study failed its primary total-fibrosis endpoint; secondary MRI signals did not establish functional
    efficacy.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT03238235
    reference_title: A Randomised, Double Blind, Placebo Controlled Study to Evaluate the Micro-macroscopic Effects on Muscles, the Safety and Tolerability, and the Efficacy of Givinostat in Patients With Becker Muscular Dystrophy (BMD)
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Primary objective: to establish the histological effects of Givinostat versus placebo administered
      over 12 months.
    explanation: >-
      The registry identifies histological effects as the primary objective; the published trial reports
      the total-fibrosis endpoint.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT03238235
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT03238235
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Clinical Study to Evaluate the Efficacy and Safety of Givinostat in Ambulant Patients
      With Becker Muscular Dystrophy","officialTitle":"A Randomised, Double Blind, Placebo Controlled
      Study to Evaluate the Micro-macroscopic Effects on Muscles, the Safety and Tolerability, and the
      Efficacy of Givinostat in Patients With Becker Muscular Dystrophy (BMD)"},"statusModule":{"statusVerifiedDate":"2024-03","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
- name: NCT05291091
  phase: PHASE_II
  status: COMPLETED
  description: >-
    CANYON/GRAND CANYON randomized sevasemten study, with 244 enrolled participants across cohorts. The
    registry was updated September 21, 2026 and marks the study completed. The GRAND CANYON primary functional
    outcome is change in total NSAA score at 18 months; no results are posted in the retrieved registry
    record.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT05291091
    reference_title: A Phase 2 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Effect of EDG-5506 on Safety, Biomarkers, Pharmacokinetics, and Functional Measures in Adults and Adolescents With Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A study of sevasemten (EDG-5506) in Becker muscular dystrophy (known as CANYON) and pivotal cohort
      (known as GRAND CANYON). The EDG-5506-201 CANYON study was expanded to include an additional 175
      adult participants in a cohort called GRAND CANYON, that is a multicenter, randomized, double-blind,
      placebo-controlled study to evaluate the safety and efficacy of sevasemten in adults with Becker.
    explanation: >-
      The registry summary identifies the study design and intervention.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05291091
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT05291091
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Phase 2 Study of EDG-5506 in Becker Muscular Dystrophy (GRAND CANYON)","officialTitle":"A
      Phase 2 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Effect of EDG-5506 on
      Safety, Biomarkers, Pharmacokinetics, and Functional Measures in Adults and Adolescents With Becker
      Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2026-09","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
- name: NCT05160415
  phase: PHASE_I
  status: COMPLETED
  description: >-
    Completed open-label ARCH sevasemten dose-escalation study in 12 adults. Safety and tolerability were
    primary; the published two-year biomarker and functional observations are uncontrolled.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT05160415
    reference_title: A Phase 1b, Open-label Study of the Safety and Pharmacokinetics of EDG-5506 in Adults With Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The ARCH study was an open-label, single-center, Phase 1b study of sevasemtem (EDG-5506) to assess
      the safety and pharmacokinetics (PK) of sevasemten in adults with Becker muscular dystrophy (BMD).
    explanation: >-
      The registry summary identifies the study design and intervention.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05160415
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT05160415
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"A Study of EDG-5506 in Adult Males With Becker Muscular Dystrophy","officialTitle":"A
      Phase 1b, Open-label Study of the Safety and Pharmacokinetics of EDG-5506 in Adults With Becker
      Muscular Dystrophy","acronym":"ARCH"},"statusModule":{"statusVerifiedDate":"2025-06","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
- name: NCT05166109
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Completed placebo-controlled vamorolone pilot, 46 enrolled, with 24-week safety primary outcomes.
    Results posted September 15, 2026 report outcome denominators of 26 vamorolone and 13 placebo participants.
    Mean change in NSAA was 0.16 versus 0.00 and mean change in run/walk velocity was -0.05 m/s in both
    groups. These descriptive values do not establish efficacy.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT05166109
    reference_title: A Phase II Pilot Trial of Vamorolone vs. Placebo for the Treatment of Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This Phase II pilot study is a randomized, double-blind, placebo-controlled study to evaluate the
      safety, tolerability, PK, PD, and exploratory clinical efficacy of vamorolone 500mg (250mg for body
      weight \<50 kg) daily administered orally compared to placebo over a treatment period of 24 weeks
      in males with BMD.
    explanation: >-
      The registry summary identifies the study design and intervention.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05166109
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT05166109
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"A Study to Assess Vamorolone in Becker Muscular Dystrophy (BMD)","officialTitle":"A
      Phase II Pilot Trial of Vamorolone vs. Placebo for the Treatment of Becker Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2026-09","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05166109
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT05166109
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      {"type":"SECONDARY","title":"Efficacy as Measured by Time to Run/Walk Velocity (TTRWV)","description":"Change
      from baseline to week 24 for each treatment group.","reportingStatus":"POSTED","paramType":"MEAN","dispersionType":"Standard
      Deviation","unitOfMeasure":"meters/second","timeFrame":"Week 24" ... {"groupId":"OG000","value":"-0.05","spread":"0.272"}
      ... {"groupId":"OG001","value":"-0.05","spread":"0.164"}
    explanation: >-
      Registry measurements for Efficacy as Measured by Time to Run/Walk Velocity (TTRWV); group OG000
      is vamorolone and OG001 placebo. Outcome denominators are 26 and 13, respectively. These are descriptive
      means, not an inferred significance test.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT05166109
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT05166109
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      {"type":"SECONDARY","title":"Efficacy as Measured by North Star Ambulatory Assessment (NSAA) Score","description":"North
      Star Ambulatory Assessment (NSAA). The assessment's score can range from 0 to 34. Higher scores
      indicate a better outcome assessing functional mobility. Data is presented as change from baseline
      to week 24 for each treatment group.","reportingStatus":"POSTED","paramType":"MEAN","dispersionType":"Standard
      Deviation","unitOfMeasure":"Units on a scale","timeFrame":"Week 24" ... {"groupId":"OG000","value":"0.16","spread":"1.599"}
      ... {"groupId":"OG001","value":"0.00","spread":"1.706"}
    explanation: >-
      Registry measurements for Efficacy as Measured by North Star Ambulatory Assessment (NSAA) Score;
      group OG000 is vamorolone and OG001 placebo. Outcome denominators are 26 and 13, respectively. These
      are descriptive means, not an inferred significance test.
- name: NCT04386304
  phase: PHASE_I
  status: COMPLETED
  description: >-
    Completed open-label dose-escalation study of (+)-epicatechin in 22 participants with Becker or Becker-like
    dystrophy. The registry records safety and exploratory functional/biomarker assessments, but no posted
    results.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT04386304
    reference_title: A Phase 1, Open-label, Dose Escalation Study to Evaluate the Safety and Preliminary Efficacy of Orally Administered (+)-Epicatechin in Patients With Becker or Becker-like Muscular Dystrophy With Continued Ambulation Past 16 Years of Age
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This is a Phase 1, open-label, dose escalation study aimed at evaluating the safety, early efficacy
      and potential biomarkers of (+)-epicatechin in patients with Becker or Becker-like Muscular Dystrophy
      (BMD).
    explanation: >-
      The registry summary identifies the study design and intervention.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04386304
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT04386304
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Safety and Biomarker Response to (+)-Epicatechin in Becker Muscular Dystrophy","officialTitle":"A
      Phase 1, Open-label, Dose Escalation Study to Evaluate the Safety and Preliminary Efficacy of Orally
      Administered (+)-Epicatechin in Patients With Becker or Becker-like Muscular Dystrophy With Continued
      Ambulation Past 16 Years of Age"},"statusModule":{"statusVerifiedDate":"2022-03","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
- name: NCT04054375
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Completed single-center open-label weekly-prednisone pilot in 20 adults, including 19 with limb-girdle
    muscular dystrophy and one with Becker muscular dystrophy. Safety was the primary objective. The 24-week
    publication reports pooled outcomes without a control group; it cannot establish Becker-specific efficacy.
    Registry results are posted.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT04054375
    reference_title: Open Label Safety and Efficacy of Once Weekly Steroid in Patients With LGMD and Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The purpose of this study is to evaluate the safety and efficacy of oral weekly glucocorticoid steroids
      in patients with Becker Muscular Dystrophy (BMD), an inherited disorder in which patients experience
      weakness of the legs and pelvis, and Limb Girdle Muscular Dystrophy (LGMD), an inherited disorder
      in which patients experience progressive muscular weakness predominately in their hip and shoulders.
      The primary objective is safety which we the investigators will measure using laboratory testing
      and forced vital capacity (FVC), a breathing test that measures the strength of your lungs. The
      secondary objective is efficacy which will be measured by a change in MRI muscle mass, improved
      muscle performance, and quality of life.
    explanation: >-
      The registry describes the intervention, population, and study objectives.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04054375
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT04054375
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Weekly Steroids in Muscular Dystrophy","officialTitle":"Open Label Safety and Efficacy
      of Once Weekly Steroid in Patients With LGMD and Becker Muscular Dystrophy","acronym":"WSiMD"},"statusModule":{"statusVerifiedDate":"2023-09","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
  - reference: PMID:35124660
    reference_title: An Open Label Exploratory Clinical Trial Evaluating Safety and Tolerability of Once-Weekly Prednisone in Becker and Limb-Girdle Muscular Dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Out of the 20 participants, seven were female, nineteen had LGMD and one had BMD
    explanation: >-
      The mixed pilot cohort contained only one Becker participant, precluding a Becker-specific efficacy
      estimate.
- name: NCT04585464
  phase: PHASE_I
  status: COMPLETED
  description: >-
    Completed randomized placebo-controlled ascending-dose sevasemten study in healthy volunteers and
    adults with Becker muscular dystrophy. The registry lists 127 participants overall; the published
    analysis reports 97 healthy volunteers and seven Becker participants. Short-term safety, pharmacokinetics,
    and biomarkers do not establish functional efficacy.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT04585464
    reference_title: A Phase 1, Randomized, Placebo-Controlled, Double-blind, Single and Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and PK of EDG-5506 in Adult Healthy Volunteers and Adults With Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This Phase 1 study of EDG-5506 will assess the safety, tolerability, and pharmacokinetics (PK) and
      of EDG-5506 in adult healthy volunteers and in adults with Becker muscular dystrophy (BMD).
    explanation: >-
      The registry describes the intervention, population, and study objectives.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT04585464
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT04585464
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"A Study to Assess Safety, Tolerability, and PK of EDG-5506 in Healthy Volunteers and
      Becker Muscular Dystrophy Adults","officialTitle":"A Phase 1, Randomized, Placebo-Controlled, Double-blind,
      Single and Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and PK of EDG-5506
      in Adult Healthy Volunteers and Adults With Becker Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2022-06","overallStatus":"COMPLETED"
    explanation: >-
      The registry excerpt identifies the study and its completed status in the retrieved snapshot.
  - reference: PMID:40452637
    reference_title: A Phase 1, Double-Blind, Placebo-Controlled Trial of Sevasemten (EDG-5506), a Selective Modulator of Fast Skeletal Muscle Contraction, in Healthy Volunteers and Adults With Becker Muscular Dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In Part C, 7 men with BMD were randomized to sevasemten (N = 5) or placebo (N = 2)
    explanation: >-
      Defines the very small Becker randomized cohort within a larger study dominated by healthy volunteers.
- name: NCT01070511
  phase: PHASE_IV
  status: COMPLETED
  description: >-
    Completed tadalafil physiological study. The registry retains an estimated enrollment of 48 and a
    parallel-design field, whereas the linked publication reports a randomized crossover experiment in
    ten Becker participants. The published design and analyzed population are used when interpreting the
    efficacy evidence.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT01070511
    reference_title: Functional Muscle Ischemia and PDE5A Inhibition in Becker Muscular Dystrophy
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This new short-term clinical trial will move the testing from animals to human patients with Becker
      muscular dystrophy and examine the effects of acute tadalafil dosing on muscle blood flow during
      a bout of exercise.
    explanation: >-
      The registry identifies the trial intervention and physiological objectives.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT01070511
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT01070511
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Tadalafil in Becker Muscular Dystrophy","officialTitle":"Functional Muscle Ischemia
      and PDE5A Inhibition in Becker Muscular Dystrophy"},"statusModule":{"statusVerifiedDate":"2013-08","overallStatus":"COMPLETED"
    explanation: >-
      The retrieved registry identifies the study and its completed status.
  - reference: PMID:23197572
    reference_title: Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The key finding of our study is that tadalafil alleviated microvascular ischemia and fully restored
      blood flow regulation in eight of nine BMD patients who lacked sympatholysis when given placebo.
    explanation: >-
      The randomized crossover trial demonstrates an acute physiological response in the subgroup with
      abnormal placebo physiology, rather than long-term clinical benefit.
- name: NCT01350154
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Completed randomized sildenafil crossover study with 17 enrolled participants. The skeletal and cardiac
    publication reports 16 and 13 evaluable participants, respectively, and no improvement in the measured
    outcomes.
  notes: >-
    Registry status checked against the generated ClinicalTrials.gov API cache on 2026-09-28.
  evidence:
  - reference: clinicaltrials:NCT01350154
    reference_title: Does Modulation of the nNOS System in Patients With Muscular Dystrophy and Defect nNOS Signalling Affect Cardiac, Muscular or Cognitive Function?
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study is done to evaluate whether treatment with the drug sildenafil (Revatio®) can improve
      muscular, cardiac, cerebrovascular or cognitive function in patients with Beckers muscular dystrophy
      when compared to placebo (inactive medication).
    explanation: >-
      The registry identifies the trial intervention and physiological objectives.
  - reference: url:https://clinicaltrials.gov/api/v2/studies/NCT01350154
    reference_title: https://clinicaltrials.gov/api/v2/studies/NCT01350154
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      "briefTitle":"Effect of Modulating the nNOS System on Cardiac, Muscular and Cognitive Function in
      Becker Muscular Dystrophy Patients","officialTitle":"Does Modulation of the nNOS System in Patients
      With Muscular Dystrophy and Defect nNOS Signalling Affect Cardiac, Muscular or Cognitive Function?"},"statusModule":{"statusVerifiedDate":"2013-04","overallStatus":"COMPLETED"
    explanation: >-
      The retrieved registry identifies the study and its completed status.
  - reference: PMID:25042931
    reference_title: Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations.
      Sildenafil had no effect on any of the outcome parameters.
    explanation: >-
      The four-week crossover study found no improvement in the measured muscular or cardiac outcomes.
histopathology:
- name: Myofiber Necrosis
  finding_term:
    preferred_term: Necrosis
    term:
      id: NCIT:C36184
      label: Necrosis
  description: >-
    Dystrophic muscle can show necrotic fibers with regeneration. In mild Becker disease, necrotic fibers
    may be scattered and other abnormalities subtle.
  diagnostic: false
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Optical microscopy examination can confirm the muscular dystrophy, demonstrati ng the association
      of necrosis, regeneration, and fibrosis.
    explanation: >-
      The biopsy description identifies necrosis within the dystrophic pattern.
- name: Muscle Fibrosis
  finding_term:
    preferred_term: Fibrosis
    term:
      id: NCIT:C3044
      label: Fibrosis
  description: >-
    Endomysial and interstitial fibrosis accompanies dystrophic remodeling and can be extensive in advanced
    disease, together with fatty infiltration.
  diagnostic: false
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Fatty infiltration and both endomy sial and interstitial extensive fibrosis are seen in the advanced
      stages of the disease.
    explanation: >-
      The guideline describes the distribution and greater extent in advanced disease.
- name: Variable Myofiber Size and Regeneration
  description: >-
    Biopsy can show variable fiber size, splitting, hypercontracted fibers, regeneration, and internal
    nuclei. Findings may be subtle in mild disease and overlap other muscular dystrophies.
  diagnostic: false
  notes: >-
    NCIT searches for muscle fiber regeneration did not identify a faithful specific histopathology binding;
    broad process or gene terms were not substituted.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Optical microscopy examination can confirm the muscular dystrophy, demonstrati ng the association
      of necrosis, regeneration, and fibrosis. Marked variations in the fiber size, split fibers, and
      mul tinucleate and hyper -contracted bulky fib ers are also markers of dystrophinopathy
    explanation: >-
      The source describes regeneration, fiber-size variation, splitting, and abnormal nuclear and contraction
      morphology.
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      In mild clinical forms, m orphologic abnormalities may be subtle: moderate variations i n fiber
      size, scattered necrosis fibers, and rare nuclear internalizations.
    explanation: >-
      Mild disease may have only subtle structural abnormalities.
differential_diagnoses:
- name: Limb-Girdle Muscular Dystrophy
  description: >-
    Proximal weakness, raised CK, calf enlargement, and cardiopulmonary disease can overlap Becker muscular
    dystrophy.
  distinguishing_features:
  - >-
    Many subtypes have autosomal inheritance and affect both sexes; the clinical pattern and causal gene
    distinguish them from DMD-related disease.
  - >-
    The French guideline highlights FKRP-related disease and sarcoglycanopathies; protein studies may
    show reduced alpha-dystroglycan or sarcoglycans. These findings require integrated molecular interpretation.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The main differential diagnosi s included limb girdle muscular dystrophy (LGMD), facio- scapulo-humeral
      muscular dystrophy type 1 (FSHD 1), inflammatory myopathies and spinal muscular atrophy (SMA) are
      summarized in Table 1
    explanation: >-
      Table 1, inspected in the full PDF, compares FKRP-related disease and sarcoglycanopathies with Becker
      disease; the cached narrative identifies the differential group.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    reference_title: https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Limb-girdle muscular dystrophy 1 (OMIM PS253600 & PS603511) AR AD • HyperCKemia • Proximal muscle
      weakness • Cardiopulmonary involvement • Impacts males & females equally • Highly variable onset
      that ranges from early childhood to late adulthood depending on subtype
    explanation: >-
      GeneReviews Table 3 documents proximal weakness, hyperCKemia, cardiopulmonary overlap, and autosomal
      inheritance affecting both sexes.
  disease_term:
    preferred_term: limb-girdle muscular dystrophy
    term:
      id: MONDO:0016971
      label: limb-girdle muscular dystrophy
- name: Facioscapulohumeral Muscular Dystrophy Type 1
  description: >-
    Shoulder-girdle weakness may prompt consideration of Becker muscular dystrophy.
  distinguishing_features:
  - >-
    Facial weakness, scapular winging, and asymmetric involvement favor FSHD1; the French guideline lists
    normal to moderately elevated CK and a D4Z4 repeat contraction mechanism.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The main differential diagnosi s included limb girdle muscular dystrophy (LGMD), facio- scapulo-humeral
      muscular dystrophy type 1 (FSHD 1), inflammatory myopathies and spinal muscular atrophy (SMA) are
      summarized in Table 1
    explanation: >-
      The narrative identifies FSHD1; its distinguishing pattern and molecular mechanism are given in
      Table 1, inspected in the source PDF.
  disease_term:
    preferred_term: facioscapulohumeral muscular dystrophy 1
    term:
      id: MONDO:0008030
      label: facioscapulohumeral muscular dystrophy 1
- name: Proximal Spinal Muscular Atrophy
  description: >-
    Proximal limb weakness can overlap the motor presentation of Becker muscular dystrophy.
  distinguishing_features:
  - >-
    Fasciculations, reduced or absent tendon reflexes, and a neurogenic pattern favor spinal muscular
    atrophy. The French table specifically describes the recessive SMN-associated form.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The main differential diagnosi s included limb girdle muscular dystrophy (LGMD), facio- scapulo-humeral
      muscular dystrophy type 1 (FSHD 1), inflammatory myopathies and spinal muscular atrophy (SMA) are
      summarized in Table 1
    explanation: >-
      The narrative identifies SMA, and the full PDF Table 1 supplies its neurogenic distinguishing features.
  disease_term:
    preferred_term: proximal spinal muscular atrophy
    term:
      id: MONDO:0019079
      label: proximal spinal muscular atrophy
- name: Inflammatory Myopathies
  description: >-
    Acquired proximal weakness and raised CK can resemble muscular dystrophy.
  distinguishing_features:
  - >-
    Subacute progression, inflammatory biopsy findings, and muscle edema on MRI support an inflammatory
    differential, although inflammation alone does not exclude Becker muscular dystrophy.
  evidence:
  - reference: PMID:37422773
    reference_title: 'Diagnosis and management of Becker muscular dystrophy: the French guidelines.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      The main differential diagnosi s included limb girdle muscular dystrophy (LGMD), facio- scapulo-humeral
      muscular dystrophy type 1 (FSHD 1), inflammatory myopathies and spinal muscular atrophy (SMA) are
      summarized in Table 1
    explanation: >-
      The narrative identifies inflammatory myopathies; Table 1 supplies subacute weakness, inflammation,
      and MRI edema. The biopsy text separately notes that inflammatory abnormalities can occur in Becker
      disease.
  notes: >-
    The source describes inflammatory myopathies broadly. MONDO searches returned idiopathic and specific
    subtypes, so no narrower disease binding was imposed.

📚

References & Deep Research

References

PMID:3384440

An explanation for the phenotypic differences between patients bearing partial deletions of the DMD locus.

No top-level findings curated for this source.

PMID:2491009

The molecular basis for Duchenne versus Becker muscular dystrophy: correlation of severity with type of deletion.

No top-level findings curated for this source.

PMID:16770791

Entries in the Leiden Duchenne muscular dystrophy mutation database: an overview of mutation types and paradoxical cases that confirm the reading-frame rule.

No top-level findings curated for this source.

PMID:39499670

Natural history of Becker muscular dystrophy: DMD gene mutations predict clinical severity.

No top-level findings curated for this source.

PMID:37422773

Diagnosis and management of Becker muscular dystrophy: the French guidelines.

No top-level findings curated for this source.

PMID:33454189

Respiratory decline in adult patients with Becker muscular dystrophy: A longitudinal study.

No top-level findings curated for this source.

PMID:20301298

Dystrophinopathies.

No top-level findings curated for this source.

url:https://oup.silverchair-cdn.com/article-minimal/7876416

https://oup.silverchair-cdn.com/article-minimal/7876416

No top-level findings curated for this source.

PMID:36628607

The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47.

No top-level findings curated for this source.

PMID:36793492

Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study.

No top-level findings curated for this source.

PMID:35971866

European Neuromuscular Centre consensus statement on anaesthesia in patients with neuromuscular disorders.

No top-level findings curated for this source.

PMID:39358550

Progressive cardiomyopathy with intercalated disc disorganization in a rat model of Becker dystrophy.

No top-level findings curated for this source.

PMID:40452637

A Phase 1, Double-Blind, Placebo-Controlled Trial of Sevasemten (EDG-5506), a Selective Modulator of Fast Skeletal Muscle Contraction, in Healthy Volunteers and Adults With Becker Muscular Dystrophy.

No top-level findings curated for this source.

PMID:42308588

Effects of sevasemten (EDG-5506) on safety, biomarkers, and functional measures in adults with Becker muscular dystrophy: results of a phase 1b, open-label study.

No top-level findings curated for this source.

PMID:37534133

Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice.

No top-level findings curated for this source.

clinicaltrials:NCT03238235

A Randomised, Double Blind, Placebo Controlled Study to Evaluate the Micro-macroscopic Effects on Muscles, the Safety and Tolerability, and the Efficacy of Givinostat in Patients With Becker Muscular Dystrophy (BMD)

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT03238235

https://clinicaltrials.gov/api/v2/studies/NCT03238235

No top-level findings curated for this source.

clinicaltrials:NCT05291091

A Phase 2 Randomized, Double-blind, Placebo-controlled Study to Evaluate the Effect of EDG-5506 on Safety, Biomarkers, Pharmacokinetics, and Functional Measures in Adults and Adolescents With Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT05291091

https://clinicaltrials.gov/api/v2/studies/NCT05291091

No top-level findings curated for this source.

clinicaltrials:NCT05160415

A Phase 1b, Open-label Study of the Safety and Pharmacokinetics of EDG-5506 in Adults With Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT05160415

https://clinicaltrials.gov/api/v2/studies/NCT05160415

No top-level findings curated for this source.

clinicaltrials:NCT05166109

A Phase II Pilot Trial of Vamorolone vs. Placebo for the Treatment of Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT05166109

https://clinicaltrials.gov/api/v2/studies/NCT05166109

No top-level findings curated for this source.

clinicaltrials:NCT04386304

A Phase 1, Open-label, Dose Escalation Study to Evaluate the Safety and Preliminary Efficacy of Orally Administered (+)-Epicatechin in Patients With Becker or Becker-like Muscular Dystrophy With Continued Ambulation Past 16 Years of Age

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT04386304

https://clinicaltrials.gov/api/v2/studies/NCT04386304

No top-level findings curated for this source.

url:https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf

https://www.ncbi.nlm.nih.gov/sites/books/NBK1119/pdf/Bookshelf_NBK1119.pdf

No top-level findings curated for this source.

PMID:35124660

An Open Label Exploratory Clinical Trial Evaluating Safety and Tolerability of Once-Weekly Prednisone in Becker and Limb-Girdle Muscular Dystrophy.

No top-level findings curated for this source.

clinicaltrials:NCT04054375

Open Label Safety and Efficacy of Once Weekly Steroid in Patients With LGMD and Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT04054375

https://clinicaltrials.gov/api/v2/studies/NCT04054375

No top-level findings curated for this source.

clinicaltrials:NCT04585464

A Phase 1, Randomized, Placebo-Controlled, Double-blind, Single and Multiple Ascending Dose Study to Evaluate the Safety, Tolerability, and PK of EDG-5506 in Adult Healthy Volunteers and Adults With Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT04585464

https://clinicaltrials.gov/api/v2/studies/NCT04585464

No top-level findings curated for this source.

url:https://pmc.ncbi.nlm.nih.gov/articles/PMC4666991/

Sodium nitrate alleviates functional muscle ischaemia in patients with Becker muscular dystrophy - PMC

No top-level findings curated for this source.

PMID:23197572

Tadalafil alleviates muscle ischemia in patients with Becker muscular dystrophy.

No top-level findings curated for this source.

PMID:25042931

Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT01070511

https://clinicaltrials.gov/api/v2/studies/NCT01070511

No top-level findings curated for this source.

clinicaltrials:NCT01070511

Functional Muscle Ischemia and PDE5A Inhibition in Becker Muscular Dystrophy

No top-level findings curated for this source.

url:https://clinicaltrials.gov/api/v2/studies/NCT01350154

https://clinicaltrials.gov/api/v2/studies/NCT01350154

No top-level findings curated for this source.

clinicaltrials:NCT01350154

Does Modulation of the nNOS System in Patients With Muscular Dystrophy and Defect nNOS Signalling Affect Cardiac, Muscular or Cognitive Function?

No top-level findings curated for this source.

PMID:22589245

Variable phenotype of del45-55 Becker patients correlated with nNOSμ mislocalization and RYR1 hypernitrosylation.

No top-level findings curated for this source.

Deep Research

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (1)

Create: Becker Muscular Dystrophy MONDO:0010311 · 2026-08-23T22:12:16Z · View source

Curated de novo from a Perplexity sonar-deep-research report. 'just preflight-dr' returned SKIP for MONDO:0010311 because MONDO records no RO:0004003 causal gene for the term, so the manual NEC preflight was run instead: the report's OMIM ids are 300376 (the MONDO xref for Becker) and 310200 (Duchenne, expected in a Becker report), DMD dominates gene mentions at 109, the ACE hits are angiotensin-converting-enzyme inhibitors rather than a gene, and the eponym trap for this disease - Becker myotonia congenita, an unrelated CLCN1 chloride channelopathy - returns zero mentions of CLCN1, myotonia congenita or Thomsen disease. Three of the six references came from the report's citations file; the other three were found by PubMed query, and every abstract was read before use. The entry is organised around the reading-frame rule as the Becker/Duchenne discriminator, with a central_effector node for the internally deleted semifunctional dystrophin. Two interpretation discussions carry the judgements: Becker is the target state that exon-skipping therapy in Duchenne aims to produce, which is why this entry deliberately does NOT conform to antisense_oligonucleotide_therapy - those nodes are intervention-conditioned and conforming would put an ASO in the causal path of an untreated disease; and the reading-frame rule is statistical not absolute, with three independent figures agreeing at roughly 91-92% and 10 percent of a 943-patient Becker cohort carrying out-of-frame mutations. Conformance to cardiomyopathy_maladaptive_remodeling is claimed at the insult and outcome nodes only, since no reference evidences the intervening remodelling steps in Becker specifically. No treatments curated: all six references grepped for ACE inhibitors, beta-blockers, corticosteroids, ventilation, transplantation, exon skipping and dosing, returning nothing - the cardioprotective regimen exists only in the report's uncited synthesis. Two defects were caught by validation and fixed before commit: HP:0033401 was written for 'Reduced forced vital capacity' but is actually 'Tissue ischemia' (corrected to HP:0032341), and GO:0016010 was placed under biological_processes when it is a cellular component (moved to cellular_components). Validation: 'just validate' passed with 29 of 29 snippets verified, 'just validate-terms' passed, and the ungated CI gates are clean.

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1. Disease Information

sonar-deep-research 21 citations 2026-08-23T21:42:48.778071

1. Disease Information

1.1 Definition, Nosology, and Overall Description

Becker muscular dystrophy is a rare inherited neuromuscular disorder belonging to the group of dystrophinopathies, defined by progressive skeletal muscle weakness with preservation of ambulation into adolescence or adulthood and survival frequently into midlife or later.[2][3][6] Orphanet describes BMD as "a rare, genetic muscular dystrophy characterized by progressive muscle wasting and weakness due to degeneration of skeletal, smooth and cardiac muscle," with onset ranging from childhood to elderly age and X‑linked recessive inheritance.[2] GeneReviews identifies BMD within the broader category of dystrophinopathies, noting that "Becker muscular dystrophy (BMD) is characterized by later-onset skeletal muscle weakness" and that cardiomyopathy is the most common cause of death.[3][8] The Muscular Dystrophy Association similarly characterizes BMD as one of nine major muscular dystrophy types, emphasizing that affected individuals produce dystrophin that is shorter and partially functional, which slows but does not prevent muscle degeneration.[6]

From a nosological perspective, BMD is distinguished from Duchenne muscular dystrophy (OMIM #310200) by its later onset, slower progression, and retention of ambulation beyond age 13, though intermediate phenotypes exist.[1][3][6] Orphanet classifies BMD under neuromuscular diseases with the identifier ORPHA:98895 and lists it as a disorder entity within their rare disease taxonomy.[2] Natural history data from large cohorts, such as the Italian multicenter study of 943 patients, reinforce that BMD is not a single phenotype but rather a spectrum of severity correlated with underlying DMD mutations, ranging from very mild forms discovered by incidental hyperCKemia to more disabling forms with early cardiomyopathy and loss of ambulation.[7][10]

In Human Disease Ontology and MONDO (Mondo Disease Ontology), BMD is represented as a distinct term often cross‑referenced to OMIM and Orphanet identifiers, and is generally categorized under genetic muscular dystrophy and X‑linked disease classes. While MONDO identifiers are not explicitly provided in the search results, BMD is recognized by MONDO as a specific disease entity, typically linked to OMIM #300376 and Orphanet ORPHA:98895.

1.2 Key Identifiers and Coding Systems

Several standardized identifiers and coding systems are used for Becker muscular dystrophy across biomedical databases and clinical classification schemes. Orphanet assigns BMD the identifier ORPHA:98895 and notes that it corresponds to OMIM entries 159050 and 300376.[2] The OMIM entry for "MUSCULAR DYSTROPHY, DUCHENNE TYPE; DMD" (#310200) describes the spectrum of dystrophinopathies from severe DMD to milder BMD, with BMD itself cross‑referenced as OMIM #300376.[1][2] The NIH Genetic Testing Registry associates BMD with the concept identifier C0917713 in the UMLS Metathesaurus, and lists synonyms including "MUSCULAR DYSTROPHY, PSEUDOHYPERTROPHIC PROGRESSIVE, BECKER TYPE."[11]

Regarding international disease classification, Orphanet reports that BMD maps to ICD‑10 code G71.0 (Muscular dystrophy) and ICD‑11 code 8C70.0 (Hereditary muscular dystrophy).[2] These codes are used in clinical documentation and epidemiologic registries to group muscular dystrophy subtypes, although they do not distinguish BMD specifically from DMD in routine practice. In the Human Phenotype Ontology, BMD is not itself a phenotype term, but its characteristic manifestations—such as proximal muscle weakness (HP:0003701), calf muscle hypertrophy (HP:0001846), and cardiomyopathy (HP:0001638)—are well represented.[12] The NIH MedGen concept for calf muscle hypertrophy (C1843057) explicitly notes that "Becker muscular dystrophy (BMD) is characterized by later-onset skeletal muscle weakness" and that incidental hyperCKemia may precede symptom onset.[12]

In the context of ontological integration for a disease knowledge base, BMD can be anchored by MONDO (Becker muscular dystrophy), OMIM #300376, Orphanet ORPHA:98895, UMLS C0917713, ICD‑10 G71.0, and ICD‑11 8C70.0, with further annotation through neuromuscular disease categories and X‑linked recessive inheritance classes.[2][11]

1.3 Synonyms and Alternative Names

Becker muscular dystrophy has accumulated several synonyms historically and across databases. Orphanet lists "BMD," "Becker dystrophinopathy," and "Becker muscular dystrophy" as synonyms, emphasizing that the term "Becker dystrophinopathy" recognizes the shared molecular basis with Duchenne dystrophinopathy.[2] The Genetic Testing Registry includes "MUSCULAR DYSTROPHY, PSEUDOHYPERTROPHIC PROGRESSIVE, BECKER TYPE" as an older descriptive synonym, reflecting earlier clinical terminology before the dystrophin gene was identified.[11] Some literature refers to "Becker’s muscular dystrophy" or "Becker MD," especially in clinical studies comparing multiple muscular dystrophy subtypes.[14]

Within the broader dystrophinopathy spectrum, BMD is sometimes grouped with "intermediate dystrophinopathy" phenotypes that fall between classic DMD and classic BMD in severity.[3][6] However, for ontology alignment and disease knowledge base purposes, it is generally preferable to maintain Becker muscular dystrophy as a distinct diagnostic category, with cross‑references to dystrophinopathies and muscular dystrophy superclasses.

1.4 Source Type: Individual vs Aggregated Information

Most of the information synthesized in this report derives from aggregated disease‑level resources and cohort studies rather than individual patient electronic health records. GeneReviews and StatPearls chapters represent expert‑curated summaries of clinical and genetic knowledge based on multiple primary studies and clinical experience.[3][13] Orphanet provides structured rare disease descriptions based on literature reviews and registry data.[2] Large observational cohorts and meta‑analyses—such as the Italian BMD natural history study including 943 patients,[10] the global prevalence meta‑analysis by Salari et al. including more than 900 million individuals,[4] and the respiratory longitudinal study by De Wel et al. in 23 adult BMD patients[9]—deliver aggregated quantitative information about the typical course, complications, and epidemiology of BMD.

Guideline documents, such as the French BMD diagnosis and management guidelines compiled by Magot and colleagues,[17] synthesize multidisciplinary expert consensus supported by evidence grading. Review articles on cardiomyopathy,[8] dystrophin‑associated complexes,[15] and BMD clinical trials,[19] further integrate diverse datasets and mechanistic insights. Some information—particularly regarding gene–environment interactions and modifier genes—is extrapolated from DMD literature and general knowledge of muscular dystrophy; this is noted where direct BMD‑specific evidence is limited.

2. Etiology

2.1 Primary Causal Factors: Genetic Basis in the DMD Gene

The primary cause of Becker muscular dystrophy is pathogenic variation in the DMD gene on chromosome Xp21.2–Xp21.1, which encodes dystrophin, a large cytoskeletal protein essential for mechanical stabilization and signaling at the sarcolemma of skeletal and cardiac muscle fibers.[2][3][8] Orphanet succinctly notes that "BMD is caused by dystrophin deficiency due to in-frame deletions, mutations or duplications in the DMD gene (Xp21.2)," highlighting that in‑frame variants, which preserve the open reading frame, are typical of BMD.[2] GeneReviews defines dystrophinopathies as conditions "caused by mutations in DMD, the gene that encodes the protein dystrophin," with the absence of dystrophin (usually from out‑of‑frame mutations) causing DMD and reduced or abnormal dystrophin (often from in‑frame mutations) causing BMD.[3][7]

The DMD gene is one of the largest known human genes, spanning 2.2 Mb and comprising 79 exons, multiple promoters, and alternative isoforms expressed in muscle, brain, and other tissues.[15] In BMD, the mutations typically delete or duplicate one or more exons in such a way that the reading frame remains intact, leading to synthesis of a shorter dystrophin protein missing internal spectrin‑like repeats in the rod domain, or other domains, but retaining at least partial functionality.[6][7][15] The large Italian cohort study reports that among 903 BMD patients with known DMD mutations, 85.8% had exon deletions, 5.5% duplications, and 8.6% small variants (including missense, nonsense, splice site, frameshifting, and pathogenic synonymous variants), with 86.3% carrying in‑frame mutations and 9.9% out‑of‑frame mutations that nonetheless were associated with milder BMD phenotypes.[7][10]

Mechanistically, dystrophin deficiency in BMD is less complete than in DMD: truncated dystrophin can still anchor the dystrophin–glycoprotein complex (DGC) to some extent and support sarcolemmal stability, reducing but not eliminating contraction‑induced damage.[6][15] However, the exact impact of specific in‑frame deletions depends on which spectrin repeats, hinge regions, or functional domains are lost, giving rise to significant heterogeneity in clinical severity and organ involvement.[7][8][10] In summary, BMD is a monogenic disease with a well‑defined primary cause: germline DMD mutations that allow at least partial dystrophin expression.

2.2 Genetic Risk Factors and Modifier Influences

Because BMD is monogenic and X‑linked, its primary genetic risk factor is hemizygous inheritance of a pathogenic DMD variant from a carrier mother, or arising de novo in the maternal germline. Salari et al. point out that "DMD or BMD mutations are inherited with a 50% probability in each pregnancy of a carrier mother," with male offspring who inherit the mutation developing disease and female carriers having a variable risk of symptoms depending on X‑inactivation patterns.[4] The genetic testing registry emphasizes X‑linked recessive inheritance and notes that BMD primarily affects males, with females usually carriers.[2][11]

Beyond this deterministic causal variant, several genetic modifiers are thought to influence disease severity, although the evidence is more robust in DMD than in BMD. Candidate modifiers such as polymorphisms in SPP1 (osteopontin) and LTBP4 (latent transforming growth factor beta binding protein 4) have been associated with variability in muscular dystrophy progression, likely via modulation of inflammation and fibrosis pathways.[15] However, direct large‑scale studies of these modifiers in BMD are limited; the Italian natural history cohort instead focuses on the internal structure of DMD mutations themselves as determinants of prognosis. Gorgoglione et al. demonstrate that specific deletion patterns, such as del45–49 vs del45–47, predict earlier loss of ambulation or cardiomyopathy, whereas del45–55 or del48 confer milder phenotypes.[10] These genotype–phenotype correlations show that even within DMD mutations, the exact position and extent of an in‑frame deletion are major internal genetic risk or protective factors.

Carrier females represent another genetic risk category, though they typically display mild or subclinical manifestations. GeneReviews notes that some heterozygous females can develop cardiomyopathy or myalgia depending on skewed X‑inactivation and tissue‑specific expression.[3][8] The French guidelines explicitly provide recommendations for cardiac management in female carriers, recognizing them as a genetically at‑risk population requiring surveillance for late cardiomyopathy.[17]

2.3 Environmental and Lifestyle Risk Factors

There is no evidence that environmental toxins, infections, or occupational exposures cause BMD in the absence of a DMD mutation; thus, environmental factors primarily act as modifiers of disease severity rather than primary etiologic agents. Among lifestyle factors, physical activity intensity and type are important: individuals with BMD are more prone to muscle damage from eccentric contractions and high‑intensity resistance exercise, which can exacerbate weakness and accelerate loss of function.[18] Clinical and patient‑oriented resources emphasize that heavy loads, high‑impact sports, and exercise to exhaustion increase the risk of muscle microtears and may hasten disease progression, whereas mild to moderate, low‑impact exercise is generally beneficial.[6][18]

Body mass index (BMI) is another significant lifestyle‑related risk factor, particularly for respiratory decline. De Wel et al. followed 23 adult BMD patients longitudinally and found that loss of ambulation significantly increased the annual rate of decline in forced vital capacity (FVC), and that higher BMI correlated with even more rapid deterioration in FVC.[9] Their study concludes that "this decline is significantly more rapid and clinically relevant after loss of ambulation, which warrants a more vigilant follow-up of respiratory function in this subgroup," underscoring obesity and sedentary behavior as modifiable environmental contributors to respiratory morbidity.[9]

Cardiovascular risk factors, such as smoking, hypertension, and dyslipidemia, may also worsen cardiomyopathy in BMD, but specific BMD‑focused studies are sparse. Instead, general heart failure literature suggests that standard cardiovascular risk control is prudent. Some case series indicate that viral myocarditis or other acquired cardiac insults can unmask or exacerbate cardiomyopathy in dystrophinopathic hearts, but causality is difficult to establish.[8]

2.4 Protective Factors and Genotype–Phenotype Mitigation

Several intrinsic and extrinsic factors can be considered protective in BMD. On the genetic side, certain in‑frame deletions appear to confer relatively mild phenotypes, preserving ambulation and limiting cardiomyopathy. Gorgoglione et al. report that patients carrying del45–55 or isolated del48 mutations have significantly decreased odds of developing pathological left ventricular ejection fraction and later loss of ambulation compared with those carrying del45–47.[10] The same study shows that del48–49 is associated with later loss of ambulation than del45–47, suggesting that deletion patterns spanning exons 45–55 may be relatively favorable, possibly due to preserving critical binding domains for dystrophin–DGC interactions.[7][10] These mutation classes can be viewed as genetic protective factors within the BMD spectrum.

From an environmental and therapeutic standpoint, early initiation of cardioprotective drugs, such as angiotensin‑converting enzyme (ACE) inhibitors and beta‑blockers, appears to delay or mitigate cardiomyopathy progression in dystrophinopathies, including BMD.[8][17] Ho’s review of cardiomyopathy in BMD notes that standard heart failure therapies are beneficial and recommends beta‑blockers in accordance with heart failure guidelines, while ACE inhibitors are widely used in DMD and BMD to delay onset of cardiomyopathy.[8] The French BMD guidelines similarly advocate early cardiac monitoring and treatment, aiming to preserve left ventricular function and reduce mortality.[17]

Moderate, supervised exercise tailored to avoid eccentric overload is another protective factor. Patient‑oriented guidance emphasizes that light to moderate cardiovascular activity, gentle stretching, and isometric or low‑load strength exercises can improve cardiovascular health, maintain joint mobility, and reduce fatigue without causing excessive muscle damage.[18] Such exercise regimens, combined with adequate rest, hydration, and avoidance of exhaustion, likely ameliorate secondary complications like obesity, deconditioning, and contractures, thereby indirectly protecting respiratory and skeletal muscle function.[18]

2.5 Gene–Environment Interactions

In Becker muscular dystrophy, gene–environment interactions manifest primarily as the interplay between DMD mutations and lifestyle or medical exposures that modulate downstream muscle and cardiac injury. Individuals with more deleterious in‑frame deletions, such as del45–47, may be more vulnerable to high‑intensity exercise or delayed cardioprotective treatment, resulting in earlier loss of ambulation and cardiomyopathy, whereas those with milder deletions like del45–55 can better tolerate moderate physical demands.[10][18] De Wel et al. show that loss of ambulation, which often reflects a combination of genetic severity and environmental factors like inactivity and obesity, is associated with a steeper decline in FVC, indicating that the interaction between genotype and lifestyle can accelerate respiratory compromise.[9]

Medical interventions also create gene–environment interactions. For example, anesthetic agents and perioperative care can pose higher risks for individuals with dystrophinopathies due to their underlying cardiomyopathy and respiratory weakness; thus, careful anesthetic planning and avoidance of certain muscle‑depolarizing agents are recommended.[17] Similarly, the cardiotoxicity of some chemotherapeutic agents or other drugs may be amplified in BMD hearts, making drug–gene interactions clinically important even though they are not primary causes of BMD.

Overall, while BMD is fundamentally a monogenic disease, the interaction between DMD mutations, mechanical loading, cardiometabolic factors, and therapeutic exposures shapes its phenotypic expression. These interactions can be modeled contextually in disease knowledge bases using concepts like gene–environment interaction (GO:0042752) and muscle adaptation to activity (GO:0043500), with environmental entities such as exercise intensity and BMI represented in CHEBI or exposure ontologies.

3. Phenotypes

3.1 Skeletal Muscle Manifestations

The cardinal phenotype of Becker muscular dystrophy is progressive weakness of skeletal muscles, particularly proximal muscles in the lower limbs, with variable involvement of upper limbs and distal muscles over time.[2][3][13] StatPearls describes BMD as presenting with "progressive muscle weakness, most notably of the proximal lower limbs," and notes that onset can range from childhood to adulthood, often between ages 5 and 60.[13][6] Orphanet reports that generalized weakness typically first affects the muscles of the hips, pelvic area, thighs, and shoulders, consistent with a limb‑girdle pattern.[2][6] This phenotype corresponds to HPO terms such as proximal muscle weakness (HP:0003701), difficulty walking (HP:0002355), and Gowers’ sign (HP:0003390), which may be present in more affected individuals.

Calf muscle hypertrophy—or pseudohypertrophy—is another prominent musculoskeletal hallmark. The NIH MedGen entry on calf muscle hypertrophy notes that BMD is characterized by later‑onset weakness and that calf enlargement can be an early sign.[12] Clinically, this represents an increase in calf circumference due to a combination of muscle fiber hypertrophy and fat/connective tissue infiltration, and corresponds to the HPO term calf muscle hypertrophy (HP:0001846).[12] Becker’s original descriptions and subsequent case series frequently mention large calves and a "muscular" appearance in early years, which can delay diagnosis because the child may appear athletic despite underlying weakness.[3][6]

Age of onset of skeletal symptoms is highly variable in BMD. The Muscular Dystrophy Association reports onset ranging widely from 5 to 60 years of age, emphasizing that some boys show symptoms in childhood while others remain well until adulthood.[6] The Italian natural history study found a median age at diagnosis of 7.5 years, with 55% of diagnoses prompted by incidental hyperCKemia rather than overt weakness.[10] Symptom severity is similarly variable; some individuals remain ambulant into their seventh decade, whereas others lose ambulation earlier due to more severe mutations.[10] Progression is generally slow and chronic, but not strictly linear: periods of relative stability may alternate with more rapid decline, especially around major life events such as loss of ambulation or development of cardiomyopathy.[9][10]

The impact of skeletal muscle phenotypes on quality of life is substantial. A study by Ferreira and colleagues assessed quality of life (QoL) in adults with four muscular dystrophy types, including 18 BMD participants, using the SF‑36v2 questionnaire.[14] They found that physical function scores were significantly lower in all muscular dystrophy groups compared with controls, with BMD showing better physical function than DMD but still markedly impaired.[14] Domains such as role physical, bodily pain, social functioning, and general health were also lower in BMD compared to controls, highlighting the broad impact of muscle weakness on daily activities, social participation, and general well‑being.[14] This suggests linking BMD muscle phenotypes to QoL ontologies such as EQ‑5D mobility and SF‑36 physical functioning, to capture functional consequences quantitatively.

3.2 Cardiac Phenotypes

Cardiac involvement is a defining and clinically critical phenotype in Becker muscular dystrophy. Ho’s review emphasizes that "cardiomyopathy represents the number one cause of death in these patients" and that cardiac involvement frequency ranges from 60% to 75%.[8] The typical cardiac phenotype is a dilated cardiomyopathy (DCM) affecting the left ventricle, often with predominant inferolateral wall involvement, progressive systolic dysfunction, and arrhythmias.[8] Echocardiography commonly shows a dilated left ventricle, wall motion abnormalities especially in posterior and lateral walls, impaired diastolic function, and functional mitral and tricuspid regurgitation.[8] Cardiac MRI frequently reveals patchy fibrosis in inferolateral regions, consistent with the distribution of mechanical stress and dystrophin deficiency.[8]

The average age of onset of cardiac involvement in BMD is around 28.7 ± 7.1 years, with severe DCM in individuals younger than 20 being rare.[8] However, the Italian natural history cohort found that 30% of BMD patients had left ventricular impairment at their last assessment, indicating that a substantial fraction develops subclinical or overt cardiomyopathy earlier than previously appreciated.[10] Only about one third of BMD patients develop symptomatic DCM with heart failure signs, but asymptomatic ventricular dysfunction, conduction abnormalities, and arrhythmias are common.[8] Typical ECG changes in BMD include an R:S ratio ≥ 1 in lead V1, tall R waves in right precordial leads, deep Q waves in inferolateral leads, short PR intervals, and longer QTc intervals, along with conduction blocks such as right or left bundle branch block and infra‑His block.[8]

Cardiac phenotypes map to HPO terms such as dilated cardiomyopathy (HP:0001644), left ventricular systolic dysfunction (HP:0005151), ventricular arrhythmia (HP:0004307), atrial arrhythmia (HP:0005110), bundle branch block (HP:0001688), and sudden cardiac death (HP:0001645) in severe cases. Ho’s review notes that there appears to be no consistent correlation between skeletal muscle involvement and the severity or timing of myocardial involvement, indicating that cardiac disease can progress independently and sometimes precede skeletal manifestations.[8] Rare cases exist in which cardiomyopathy is the initial manifestation leading to heart transplantation within a year, after which the underlying dystrophinopathy is recognized.[8] This highlights the need to consider BMD in the differential diagnosis of idiopathic DCM, particularly in young men.

The quality of life impact of cardiac phenotypes in BMD includes limitations in exertional capacity, fatigue, dyspnea, and psychological distress related to chronic heart failure and arrhythmia risk. While the SF‑36 study did not separate cardiac from muscular contributions, lower vitality and general health scores in BMD compared to controls likely reflect combined neuromuscular and cardiac burdens.[14] In disease knowledge bases, it is important to associate cardiomyopathy phenotypes with both UBERON structures such as left ventricle (UBERON:0002084) and CL terms for cardiomyocytes (CL:0000723), alongside process ontologies for cardiac muscle contraction (GO:0060048) and ventricular remodeling (GO:0003228).

3.3 Respiratory Phenotypes

Respiratory involvement in Becker muscular dystrophy has received less attention than in DMD but remains clinically relevant, especially in older or more severely affected individuals. De Wel et al. analyzed 190 pulmonary function measurements over a median 14‑year follow‑up in 23 adult BMD patients, reporting a mean annual decline in forced vital capacity percent predicted (FVC%pred) of 1.00% per year (p = 0.004).[9] They concluded that "adult BMD patients experience a significant but mild respiratory decline," and that the decline becomes significantly more rapid and clinically relevant after loss of ambulation, with higher BMI correlating with even faster deterioration.[9] At the last assessment in the Italian cohort, only 2.7% of BMD patients had documented respiratory involvement, suggesting that clinically significant respiratory failure is relatively uncommon but may be under‑recognized.[10]

Respiratory phenotypes in BMD primarily include restrictive ventilatory defects due to weakness of the diaphragm and accessory respiratory muscles, reduced cough efficacy, and increased risk of nocturnal hypoventilation and respiratory infections in advanced stages.[3][9] These correspond to HPO terms such as restrictive ventilatory defect (HP:0002091), hypoventilation (HP:0002093), recurrent respiratory infections (HP:0002205), and respiratory insufficiency (HP:0002093). The onset of respiratory involvement is typically later than cardiac or skeletal manifestations, often in the fifth or sixth decade of life or after loss of ambulation, and progression is usually mild unless compounded by obesity, severe scoliosis, or advanced cardiomyopathy.[3][9]

The impact on quality of life includes reduced exercise tolerance, sleep disturbances, anxiety related to breathlessness, and a need for ventilatory support in a minority of patients. The De Wel study highlights the importance of vigilant respiratory follow‑up in non‑ambulant BMD patients, suggesting regular spirometry and early intervention with non‑invasive ventilation when indicated.[9] In terms of ontological representation, respiratory phenotypes map to UBERON entities such as lung (UBERON:0002048) and diaphragm (UBERON:0001134), CL terms for respiratory muscle fibers (CL:0000737), and GO processes such as respiratory system process (GO:0003016).

3.4 Other Clinical and Laboratory Phenotypes

Beyond skeletal, cardiac, and respiratory systems, BMD can affect other tissues and produce characteristic laboratory abnormalities. Incidental hyperCKemia, defined as elevated serum creatine kinase (CK) in the absence of overt muscle symptoms, is a common early finding that often prompts diagnosis. GeneReviews and MedGen note that hyperCKemia may be present even earlier than weakness, and that detection of high CK in screening or evaluation for unrelated complaints frequently leads to genetic testing.[3][12][10] This laboratory abnormality corresponds to HPO term elevated serum creatine kinase (HP:0003236) and LOINC codes for CK measurement.

Cognitive and neuropsychiatric phenotypes are less pronounced in BMD than in DMD but can occur due to brain dystrophin isoform deficiency. The Italian cohort reports neuropsychiatric comorbidities as one of the data elements collected, though detailed frequencies are not provided in the abstract.[10] Some case series and reviews describe learning difficulties, attention deficits, and emotional disorders in a subset of BMD patients, similar in nature but milder in frequency compared to DMD.[3] These map to HPO terms such as mild intellectual disability (HP:0001256), attention deficit hyperactivity disorder (HP:0007018), and anxiety (HP:0000739), although careful differentiation is needed because psychosocial impacts of chronic disease may confound primary neurocognitive phenotypes.

Orthopedic complications such as contractures, scoliosis, and joint deformities are less severe and later onset in BMD than in DMD but are still observed, particularly in more advanced stages. Limb‑girdle weakness and imbalanced muscle forces can lead to Achilles tendon contractures, knee flexion contractures, and lumbar hyperlordosis.[3][17] These phenotypes correspond to HPO terms like joint contractures (HP:0001371) and scoliosis (HP:0002650), and can significantly impair mobility and contribute to pain. StatPearls emphasizes orthopedic assessment in BMD management, including monitoring for contractures and spinal deformities.[13]

From a biochemical perspective, dystrophin deficiency is associated with increased serum transaminases (AST and ALT), lactate dehydrogenase, and sometimes troponins, reflecting muscle and cardiac damage.[3][8] Misinterpretation of elevated transaminases as primary liver disease can delay diagnosis; thus, confirming their origin in muscle through CK measurement is important. Quality of life impacts of these multisystem phenotypes include chronic fatigue, pain, reduced self‑efficacy, and psychological distress, as highlighted in the QoL study where fatigue was the most consistently associated factor with multiple QoL domains across muscular dystrophies.[14]

4. Genetic and Molecular Information

4.1 Causal Gene: DMD and Dystrophin

The causal gene for Becker muscular dystrophy is DMD (HGNC:2928), located on chromosome Xp21.2–Xp21.1, encoding dystrophin, a large cytoskeletal protein that forms the core of the dystrophin–glycoprotein complex (DGC).[2][3][8][15] Dystrophin has multiple isoforms generated from distinct promoters and alternative splicing, with the full‑length muscle isoform (Dp427m) expressed in skeletal and cardiac muscle, and shorter isoforms like Dp140 and Dp71 in brain and non‑muscle tissues.[15] The dystrophin protein is approximately 427 kDa and comprises an N‑terminal actin‑binding domain, a central rod domain containing spectrin repeats and hinge regions, a cysteine‑rich domain that binds beta‑dystroglycan, and a C‑terminal domain that associates with syntrophins and dystrobrevins.[6][15]

The dystrophin–glycoprotein complex spans the sarcolemma and connects the intracellular actin cytoskeleton to the extracellular matrix via alpha‑ and beta‑dystroglycan, sarcoglycans, and other associated proteins.[15] This complex stabilizes the muscle cell membrane during contraction and serves as a scaffold for signaling molecules, including neuronal nitric oxide synthase (nNOS), which modulates blood flow and oxidative stress.[6][15] Loss or dysfunction of dystrophin, as in DMD and BMD, destabilizes this complex, leading to membrane fragility, Ca(^{2+}) influx, myofiber necrosis, and progressive muscle degeneration.[15]

In BMD, DMD mutations permit expression of truncated or partially functional dystrophin, which maintains some ability to bind actin and dystroglycan and stabilize the sarcolemma, resulting in milder myofiber damage than in DMD.[6][15] However, the exact consequences depend on the structural domains affected by the mutation, making detailed exon‑level characterization essential for genotype–phenotype correlation.[7][10] OMIM and GeneReviews provide comprehensive descriptions of the DMD gene, its isoforms, and its role in dystrophinopathies.[1][3]

4.2 Pathogenic Variant Spectrum and Classification

The pathogenic variant spectrum in BMD is dominated by exon deletions and duplications that preserve the reading frame, but also includes missense, nonsense, splice site, frameshift, and pathogenic synonymous variants. The Italian natural history study reports that among 903 BMD patients with identified DMD mutations, 775 (85.8%) had deletions, 50 (5.5%) duplications, and 78 (8.6%) small variants.[7] Within the small variant category, there were frameshifting mutations (9.0%), non‑frameshifting indels (9.0%), missense mutations (12.8%), nonsense mutations (44.9%), splicing sequence mutations (20.5%), deep intronic mutations, and pathogenic synonymous mutations.[7] Despite the presence of nonsense and out‑of‑frame variants, many of these BMD patients retained some dystrophin expression, likely due to mechanisms such as exon skipping, alternative splicing, or reinitiation of translation.[7]

When grouped by reading frame maintenance, 86.3% of BMD patients carried in‑frame (IF) mutations, 3.9% nonsense mutations, and 9.9% out‑of‑frame (OF) mutations.[7] Two major mutational hotspots in DMD are recognized: exons 45–55 and exons 1–10, with BMD mutations substantially clustering in these regions.[7] Orphanet notes that BMD is usually caused by in‑frame deletions, mutations, or duplications, while out‑of‑frame mutations cause the severe DMD phenotype.[2] However, Gorgoglione et al. emphasize that the "reading‑frame rule" has exceptions, with some out‑of‑frame mutations producing BMD phenotypes due to compensatory splicing events or expression of alternative isoforms.[7][10]

Variant classification according to ACMG/AMP guidelines depends on the variant type, segregation, functional data, and population frequency. Classic BMD deletions such as del45–48 or del45–55 are well‑established pathogenic variants (P) or likely pathogenic (LP), with extensive clinical correlation.[7][10] Missense, splice site, and synonymous variants often begin as variants of uncertain significance (VUS) until functional studies demonstrate their effect on dystrophin expression. ClinVar and HGMD catalog numerous DMD variants associated with BMD; however, the search results here focus on cohort data rather than specific ClinVar entries.

Allele frequencies of BMD‑causing DMD variants in general population databases such as gnomAD are typically very low, reflecting negative selection against hemizygous males. Carrier frequencies among women are more relevant epidemiologically and can be inferred from disease prevalence. Salari et al. estimate global BMD prevalence at (1.6) per 100,000 people, with dystrophinopathies overall at (3.6) per 100,000.[4] Assuming stable mutation rates and X‑linked recessive inheritance, carrier female frequencies may approximate the square root of male prevalence for non‑founder variants, but direct data from carrier screening programs are sparse.

All BMD‑causing variants are germline rather than somatic, arising in the maternal germline or inherited from carrier mothers. Somatic mosaicism can occur, particularly in mothers of isolated cases, due to post‑zygotic mutations in early embryogenesis; this has implications for recurrence risk but is not itself a disease phenotype. Chromosomal structural abnormalities, such as large Xp21 deletions encompassing DMD and neighboring genes, can produce syndromic dystrophinopathies with cognitive and endocrine features, but these border on DMD rather than classic BMD.[1][3]

4.3 Functional Consequences: Loss of Function and Partial Function

At the functional level, Becker muscular dystrophy arises from partial loss of dystrophin function rather than complete absence. Mutations typically remove spectrin repeats in the central rod domain, hinge regions, or parts of the N‑terminal actin‑binding domain or C‑terminal binding sites, thereby altering dystrophin’s mechanical properties and interactions.[6][15] The Muscular Dystrophy Association explains that "mutations that cause BMD decrease the number of these repeats, leading to muscle weakness" and that the dystrophin protein can still function, albeit imperfectly, with fewer spectrin repeats than normal.[6] People with BMD make a shortened form of the protein, which protects muscles from degenerating as completely or as quickly as in DMD.[6]

Dystrophin’s mechanical role is to transfer force from the contractile apparatus to the extracellular matrix and prevent sarcolemma tearing during contraction.[15] Its non‑mechanical roles include providing a scaffold for signaling molecules, regulating Ca(^{2+}) homeostasis, and localizing nNOS to the sarcolemma.[15] Loss of dystrophin displaces these molecules, disrupting their functions.[6][15] In BMD, truncated dystrophin partially retains these functions, leading to less severe myofiber loss and slower progression. However, some mutations disrupt critical binding sites or hinge flexibility, resulting in more fragile dystrophin and more severe phenotypes despite the retained reading frame.[7][10][15]

Functional studies in cell and animal models show that truncated dystrophin of certain lengths—particularly those preserving the N‑terminal actin‑binding domain and the cysteine‑rich beta‑dystroglycan binding domain—can effectively stabilize the DGC, while deletions removing these domains greatly impair function.[15] This underlies the concept of "internal in‑frame deletions" that can be tolerated, and informs exon‑skipping strategies that attempt to transform out‑of‑frame DMD mutations into in‑frame BMD‑like mutations by skipping specific exons.[15][19] In a knowledge base, these mechanistic consequences can be annotated with GO terms such as structural constituent of muscle (GO:0008307), actin filament binding (GO:0051015), and sarcolemma organization (GO:0003014), and protein dysfunction categories such as partial loss of function.

5. Environmental and Lifestyle Information

5.1 Non‑Genetic Contributing Factors

As a monogenic X‑linked disorder, Becker muscular dystrophy does not have non‑genetic causal factors in the strict sense; however, non‑genetic influences can significantly modulate the clinical course. There is no evidence that environmental toxins, radiation, or pollutants cause BMD, and occupational exposures have not been specifically implicated. Comparative Toxicogenomics and environmental health databases focus more on acquired myopathies than on inherited muscular dystrophies, and the literature on BMD environmental causation is essentially absent.

Nevertheless, environmental stressors such as repeated mechanical overloading, traumatic injuries, and chronic hypoxia can exacerbate muscle and cardiac damage in individuals with BMD. For example, high‑impact sports, heavy lifting, or repetitive eccentric exercise can cause more severe myofiber microtears in dystrophin‑deficient muscles than in healthy muscles, leading to elevated CK, soreness, and potential acceleration of weakness.[18] While this does not cause BMD per se, it contributes to the cumulative burden of structural damage.

5.2 Lifestyle Factors: Exercise, Diet, and Substance Use

Lifestyle factors play a prominent role in modifying disease severity in BMD. Exercise is perhaps the most discussed factor, given the trade‑off between the benefits of physical activity and the risk of muscular damage. Patient‑oriented resources recommend avoiding heavy weights, excessive repetition, and particularly eccentric exercise, defined as contraction while the muscle lengthens.[18] Instead, mild to moderate exercise, such as walking or swimming, is advocated, with the "Talk Test" used to gauge intensity: if the patient can sing, the exercise is light; if they can talk but not sing, it is moderate; if they cannot talk, it is vigorous and should be avoided.[18] These recommendations aim to prevent overexertion and muscle microtears while preserving cardiovascular fitness and joint mobility.

Diet and nutrition also influence BMD outcomes. Obesity exacerbates respiratory decline, as shown by De Wel et al., where higher BMI correlated with faster FVC deterioration.[9] Excess weight additionally increases mechanical load on weakened muscles and joints, contributing to pain and mobility limitations. Conversely, malnutrition can impair muscle repair and immune function. Therefore, balanced nutrition with appropriate caloric intake, adequate protein, and micronutrients is recommended, although specific BMD‑targeted dietary trials are limited.

Substance use, including smoking and excessive alcohol consumption, may worsen cardiovascular and respiratory health, but specific BMD data are lacking. Nonetheless, general medical advice would counsel avoidance of smoking to reduce cardiac and respiratory morbidity, and moderation of alcohol to prevent cardiomyopathy and liver damage, which could complicate disease management.

5.3 Infectious and Immune Factors

No infectious agent is known to cause BMD, and there is no suggestion that BMD is triggered or perpetuated by autoimmunity. However, infections can precipitate acute decompensation. Respiratory infections, particularly pneumonia, pose significant risk in later stages due to weakened cough and respiratory muscle function, potentially leading to hospitalization and increased mortality.[3][9] Viral myocarditis has been reported as an acquired cause of cardiomyopathy in the general population and could be particularly harmful in BMD hearts, although direct evidence is limited.[8] Vaccination against respiratory pathogens, including influenza and pneumococcus, is therefore part of good preventive care but does not alter the underlying genetic disease.

Immune activation contributes to muscle inflammation and fibrosis downstream of dystrophin deficiency, but this is a secondary mechanism rather than a primary etiologic factor.[15] Chronic inflammation in BMD muscles is driven by repeated cycles of necrosis and regeneration and may be potentiated by infections or environmental toxins, but these influences are downstream of the genetic defect.

6. Mechanism and Pathophysiology

6.1 Molecular Pathways: Dystrophin–Glycoprotein Complex Dysfunction

The central pathophysiological mechanism in Becker muscular dystrophy is dysfunction of the dystrophin–glycoprotein complex (DGC) at the sarcolemma of striated muscles. The DGC comprises dystrophin, alpha‑ and beta‑dystroglycan, sarcoglycans (alpha, beta, gamma, delta), sarcospan, syntrophins, dystrobrevins, and associated signaling proteins.[15] The complex links the intracellular actin cytoskeleton to the extracellular matrix, distributing mechanical stress across the sarcolemma and protecting the muscle fiber from contraction‑induced damage.[15] Loss‑of‑function mutations in genes encoding dystrophin or associated proteins destabilize the DGC, leading to membrane instability, increased permeability, and myofiber loss.[15]

In BMD, truncated or reduced dystrophin impairs the mechanical and signaling integrity of the DGC but does not abolish it completely. Spectrin repeats in the central rod domain contribute to dystrophin’s elasticity and ability to transmit force; deletions removing entire blocks of repeats can reduce this capability.[6][15] The cysteine‑rich domain binds beta‑dystroglycan, anchoring the DGC; mutations affecting this domain severely disrupt the complex.[15] The C‑terminal domain interacts with syntrophins and dystrobrevins, which recruit nNOS to the sarcolemma; loss of this domain impairs NO‑mediated vasodilation and perfusion during exercise.[15] In BMD, many mutations remove subsets of spectrin repeats while preserving critical binding domains, resulting in partial mechanical stability and intermediate disease severity.[6][7][10]

Downstream pathways affected by DGC dysfunction include calcium signaling, reactive oxygen species (ROS) production, and inflammatory cascades. Membrane tears and increased permeability lead to dysregulated Ca(^{2+}) influx, activating proteases such as calpains and promoting myofibrillar breakdown.[15] ROS generated by mitochondrial dysfunction and NADPH oxidases further damage lipids and proteins, reinforcing the cycle of injury.[15] Inflammatory pathways, including activation of NF‑κB and cytokine release, recruit macrophages and other immune cells that contribute both to debris clearance and to fibrotic remodeling.[15] Over time, repeated cycles of necrosis and ineffective regeneration result in replacement of muscle tissue with fat and fibrous connective tissue, clinically manifesting as weakness, pseudohypertrophy, and contractures.[6][15]

These mechanisms can be ontologically captured by GO terms such as sarcolemma organization (GO:0003014), regulation of membrane permeability (GO:0006885), positive regulation of inflammatory response (GO:0050729), and skeletal muscle fiber regeneration (GO:0043403). At the protein level, dystrophin’s role can be annotated in UniProt and HGNC with functions such as structural constituent of muscle (GO:0008307) and actin binding (GO:0051015).

6.2 Cellular Processes: Necrosis, Regeneration, and Fibrosis

At the cellular level, BMD pathophysiology unfolds as a sequence of myofiber necrosis, regeneration, and eventual failure of regenerative capacity leading to fibrosis. Dystrophin‑deficient myofibers undergo mechanical damage during normal contraction, leading to focal sarcolemmal lesions and Ca(^{2+}) influx.[15] Elevated intracellular Ca(^{2+}) triggers activation of proteases and mitochondrial dysfunction, culminating in necrotic cell death and release of intracellular contents that evoke an inflammatory response.[15] Macrophages and other immune cells infiltrate damaged muscle, clearing debris and secreting cytokines and growth factors that stimulate satellite cell activation and myoblast proliferation.[15]

Satellite cells, the resident muscle stem cells, attempt to regenerate lost fibers by fusing into new myotubes. Early in disease, regeneration can partially offset necrosis, maintaining muscle mass and function. However, with ongoing cycles of injury, satellite cell pools are depleted or functionally exhausted, and regenerated fibers often remain dystrophin‑deficient due to the underlying DMD mutation.[15] Eventually, fibroblasts and adipocytes proliferate and deposit extracellular matrix components, leading to replacement of muscle tissue by fibrous and fatty tissue.[15] This process corresponds to GO terms such as skeletal muscle tissue regeneration (GO:0043403), muscle cell apoptosis (GO:001065), and extracellular matrix organization (GO:0030198).

In BMD, cellular processes of necrosis and regeneration occur more slowly and less extensively than in DMD, due to partial dystrophin function. This results in more gradual accumulation of fibrosis and fat, preserving muscle fibers for longer. Nevertheless, histopathologic studies show myofiber size variability, central nuclei (indicative of regeneration), necrotic fibers, and endomysial fibrosis in BMD muscles, similar to but milder than in DMD.[3][13] Cardiomyocytes undergo analogous cycles of injury and fibrosis, particularly in inferolateral regions of the left ventricle, leading to dilated cardiomyopathy.[8]

6.3 Protein Dysfunction and Structural Changes

The structural dysfunction of dystrophin in BMD depends on the specific domains affected by mutations. Dystrophin’s N‑terminal calponin homology domains bind F‑actin, anchoring dystrophin to the cytoskeleton.[15] The central rod domain, composed of 24 spectrin‑like repeats and four hinge regions, provides elasticity and length, allowing dystrophin to bridge the distance from actin to the sarcolemma.[15] The cysteine‑rich domain binds beta‑dystroglycan, and the C‑terminal domain interacts with syntrophins and dystrobrevins.[15] BMD mutations often delete segments of the rod domain, reducing length and altering hinge positions but retaining some actin and dystroglycan binding.[6][15]

For example, in‑frame deletions spanning exons 45–55 remove multiple spectrin repeats in the distal rod domain, yet can produce dystrophin variants that remain reasonably functional, as reflected by milder BMD phenotypes.[10][15] Conversely, deletions affecting exons 12 and 14–17 or exons 31–42 disrupt important repeats and hinges, and have been associated with early cardiomyopathy in BMD, suggesting that certain rod domain segments are critical for cardiac muscle resilience.[8] Deletions involving exons 2–9 remove parts of the N‑terminal domain, impairing actin binding, and are associated with risk of dilated cardiomyopathy in the second to third decades of life.[8] These structural insights emphasize the need for detailed domain‑level annotation of dystrophin variants in knowledge bases.

Non‑mechanical protein dysfunction in BMD includes mislocalization of nNOS due to disruption of syntrophin binding sites, leading to impaired NO signaling and reduced vasodilation during exercise.[15] This contributes to hypoperfusion, ischemic stress, and further damage. Binding of Ca(^{2+})-calmodulin to the C‑terminal domain of dystrophin may regulate Ca(^{2+}) signaling and membrane repair; disruption of this interaction by mutations could alter Ca(^{2+}) homeostasis.[15] Structural modeling and AlphaFold predictions can be integrated to visualize how specific in‑frame deletions alter dystrophin’s 3D conformation, bridging molecular structure with clinical phenotypes.

6.4 Metabolic and Immune System Involvement

Metabolic changes in BMD reflect both muscle degeneration and heart failure. Skeletal muscle wasting reduces overall muscle mass, altering basal metabolic rate and insulin sensitivity. Fatty infiltration and reduced physical activity increase risk of metabolic syndrome, although this is more thoroughly studied in DMD. Mitochondrial dysfunction in dystrophin‑deficient muscle fibers impairs oxidative phosphorylation and energy production, contributing to fatigue and exercise intolerance.[15] These metabolic alterations can be represented by GO terms such as oxidative phosphorylation (GO:0006119), ATP metabolic process (GO:0046034), and muscle adaptation (GO:0043500).

The immune system plays a dual role in BMD pathophysiology. Acute inflammation after muscle injury is necessary for debris clearance and regeneration, but chronic inflammation during repeated cycles of necrosis can drive fibrosis and further damage. Macrophages, T cells, and neutrophils infiltrate muscle, and cytokines such as TNF‑α, IL‑6, and TGF‑β modulate the balance between regeneration and fibrosis.[15] Dystrophin deficiency may alter immune cell recruitment and activation, though details are better characterized in DMD models. These processes align with GO terms like inflammatory response (GO:0006954), macrophage activation (GO:0042116), and regulation of TGF‑beta production (GO:0071639).

Autoimmunity per se is not a primary driver, but chronic immune activation can create an environment akin to low‑grade autoimmune myopathy. In the heart, immune responses to necrotic cardiomyocytes may contribute to myocarditis‑like phenotypes and arrhythmogenic substrate. Therapeutic interventions targeting inflammation, such as corticosteroids in DMD, have not been systematically studied in BMD but may influence immune‑mediated components.

6.5 Tissue Damage Mechanisms: Oxidative Stress, Fibrosis, and Necrosis

The mechanisms of tissue damage in BMD encompass oxidative stress, fibrosis, necrosis, and ischemia. ROS generation in dystrophin‑deficient muscles arises from mitochondrial electron transport chain dysfunction, NADPH oxidase activity, and xanthine oxidase, leading to lipid peroxidation, protein carbonylation, and DNA damage.[15] Oxidative stress exacerbates Ca(^{2+}) dysregulation and protease activation, promoting necrosis. Myofiber necrosis, characterized by cell swelling, membrane rupture, and release of intracellular contents, triggers local inflammation and further damage.

Fibrosis is a hallmark of chronic muscular dystrophy. TGF‑β signaling plays a central role, stimulating fibroblasts to produce collagen and other extracellular matrix proteins.[15] In DGC‑deficient mice, severe fibrosis develops in skeletal and cardiac muscle, correlating with functional impairment.[15] In BMD, fibrosis is less pronounced initially but accumulates over decades, particularly in the inferolateral left ventricular wall, as documented by imaging studies.[8] Cardiac fibrosis contributes to ventricular stiffening, dilation, and arrhythmia by disrupting electrical conduction pathways.

Ischemia can result from impaired NO‑mediated vasodilation and microvascular dysfunction in dystrophin‑deficient muscle. Mislocalization of nNOS away from the sarcolemma reduces NO availability, diminishing exercise‑induced vasodilation and leading to muscle ischemia and fatigue.[15] Combined with fibrosis and reduced capillary density, this can cause chronic low‑grade ischemic injury.

These damage mechanisms can be captured with GO terms such as response to oxidative stress (GO:0006979), collagen fibril organization (GO:0030199), regulation of necrotic cell death (GO:0010940), and muscle tissue morphogenesis (GO:0060538). In a knowledge base, linking these processes to specific phenotypes (weakness, cardiomyopathy, respiratory insufficiency) will clarify causal chains.

6.6 Molecular Profiling and Advanced Technologies

Direct molecular profiling studies in BMD are fewer than in DMD, but transcriptomic, proteomic, and imaging data nonetheless illuminate pathogenic pathways. RNA‑seq and microarray studies in dystrophinopathic muscle have shown upregulation of genes involved in inflammation, fibrosis, and apoptosis, and downregulation of genes involved in muscle contraction and metabolism.[15] While many such studies focus on DMD or mdx mice, BMD muscles would be expected to show similar but attenuated patterns. Proteomics analyses reveal altered expression of DGC components, cytoskeletal proteins, and mitochondrial enzymes.[15]

Advanced technologies such as cardiac MRI with late gadolinium enhancement provide spatial profiling of fibrosis in BMD hearts, demonstrating preferential involvement of inferolateral walls and allowing quantification of fibrotic burden.[8] Single‑cell RNA‑seq and spatial transcriptomics have not yet been widely applied in BMD, but in principle could delineate cell‑type specific responses (myofibers, fibroblasts, immune cells, endothelial cells) and regional heterogeneity within muscles. Functional genomics screens using CRISPR or RNAi in muscle cell lines may identify modifier genes that influence dystrophin deficiency, though specific BMD data are limited.

The recent review "An update on Becker muscular dystrophy" highlights increasing use of advanced imaging and biomarker studies in BMD clinical trials.[19] It notes that no treatments are yet approved for BMD but that "the past few years have seen an increased number of interventional clinical trials in BMD with treatments targeting different molecular pathways downstream of the lack of functional dystrophin," implying growing integration of multi‑omic and mechanistic data into therapeutic development.[19]

7. Anatomical Structures Affected

7.1 Organ‑Level Involvement

Becker muscular dystrophy primarily affects skeletal muscle and the heart, with secondary involvement of respiratory muscles and, less frequently, smooth muscle. Skeletal muscles of the pelvic girdle, thighs, shoulders, and calves are most prominently affected, corresponding to UBERON terms such as skeletal muscle tissue (UBERON:0001134), thigh muscles (UBERON:0001638), and shoulder musculature (UBERON:0001450).[2][6] Cardiac involvement focuses on the left ventricle, particularly the inferolateral wall, aligning with UBERON:0002084 (left ventricle) and regional anatomy terms.[8]

Respiratory system involvement includes the diaphragm (UBERON:0001134), intercostal muscles, and accessory muscles of respiration, leading to restrictive ventilatory defects and hypoventilation in advanced disease.[9] Smooth muscle involvement can occur in the gastrointestinal tract and vasculature, although overt clinical manifestations are uncommon in BMD compared to skeletal and cardiac muscle. Central nervous system involvement is limited but includes mild cognitive and neuropsychiatric manifestations linked to brain dystrophin isoforms.[3][10]

Body systems implicated include the muscular system (skeletal and cardiac), cardiovascular system, respiratory system, and, to a lesser degree, nervous and digestive systems. This multi‑organ involvement underscores the need for systems‑level representation in disease ontologies.

7.2 Tissue and Cell‑Level Involvement

At the tissue level, BMD affects striated muscle tissue, both skeletal and cardiac, as well as connective tissue and adipose tissue that replace muscle over time. Skeletal myofibers (CL:0000737) are the primary target cell type, with secondary involvement of cardiac muscle cells (cardiomyocytes, CL:0000723), satellite cells (CL:0002038), fibroblasts (CL:0000057), and adipocytes (CL:0000136).[15] In the heart, conduction system cells such as Purkinje fibers and pacemaker cells are indirectly affected by fibrosis and DGC dysfunction, leading to arrhythmias.[8]

Respiratory muscle fibers in the diaphragm and intercostal muscles, also CL:0000737, experience similar dystrophin deficiency and are subject to the same necrosis‑regeneration‑fibrosis cycle, though clinical consequences are delayed.[9] Vascular smooth muscle cells (CL:0000133) may be affected by dystrophin isoforms and contribute to vasoregulatory changes, though this is less well characterized.

Connective tissue cells such as fibroblasts proliferate in response to chronic muscle damage, depositing collagen and forming fibrotic tissue that compromises function.[15] Immune cells including macrophages (CL:0000584), T cells (CL:0000084), and neutrophils (CL:0000775) infiltrate muscle and modulate inflammation and regeneration. Integrating these cell types with CL (Cell Ontology) terms in a disease knowledge base will facilitate detailed representation of cell‑type specific roles in BMD.

7.3 Subcellular Localization and Compartments

Subcellular compartments involved in BMD pathophysiology include the sarcolemma (GO:0005886), cytoskeleton (GO:0005856), extracellular matrix (GO:0031012), mitochondria (GO:0005739), sarcoplasmic reticulum (GO:0016020), and nucleus (GO:0005634). Dystrophin is localized to the inner surface of the sarcolemma, where it associates with the DGC and actin cytoskeleton.[15] Loss or truncation of dystrophin disrupts sarcolemmal organization and integrity, making this membrane compartment central to disease mechanisms.

Mitochondria are heavily involved due to their role in energy production and ROS generation. Sarcoplasmic reticulum handles Ca(^{2+}) storage and release, and dysregulation of Ca(^{2+}) in dystrophinopathy leads to altered SR function and activation of Ca(^{2+})-dependent pathways.[15] Nuclear compartments are involved in satellite cell activation and differentiation, as well as gene expression changes in myofibers.

In cardiomyocytes, subcellular compartments such as intercalated discs, T‑tubules, and mitochondrial networks play key roles in conduction and contraction; dystrophin deficiency can indirectly affect these structures via cytoskeletal disruption and fibrosis.

7.4 Localization and Lateralization

Clinically, muscle weakness and hypertrophy in BMD are typically bilateral and symmetric, affecting both lower limbs and both shoulders, although individual variation exists. Calf hypertrophy is usually bilateral, and proximal weakness patterns are similarly symmetric.[2][6] Cardiac involvement is systemic but shows regional predilection for the inferolateral left ventricular wall, which is bilateral at the organ level but anatomically localized.[8] Respiratory involvement is symmetric across both hemidiaphragms and intercostal muscles, though scoliosis or asymmetric thoracic deformities can create lateralized functional deficits.

In the context of neuroanatomy, there is no strong lateralization of central nervous system manifestations in BMD; cognitive and behavioral phenotypes are diffuse. Thus, lateralization is less of a defining feature than localization to specific muscle groups and cardiac regions.

8. Temporal Development

8.1 Onset: Age and Pattern

Onset of Becker muscular dystrophy is characteristically variable, ranging from childhood to late adulthood. Orphanet lists age of onset categories as adolescent, adult, childhood, and elderly, reflecting the broad spectrum.[2] The Muscular Dystrophy Association reports onset from 5 to 60 years of age, noting that symptoms often begin with difficulty running, climbing stairs, or lifting objects.[6] GeneReviews describes BMD as having "later-onset skeletal muscle weakness" compared to DMD, which typically presents before age 5.[3]

HyperCKemia may precede clinical symptoms by several years. In the Italian cohort, 55% of BMD diagnoses were prompted by incidental findings of elevated CK, indicating that biochemical evidence of muscle damage often appears before subjective weakness.[10] Onset is generally insidious and chronic rather than acute, with slow emergence of gait clumsiness, fatigue, and difficulty with physical tasks.

Cardiac involvement typically begins in the third decade of life. Ho’s review reports an average age of cardiac involvement of 28.7 ± 7.1 years, with severe DCM before age 20 being uncommon.[8] Respiratory involvement usually begins even later, often after loss of ambulation in the fifth or sixth decade.[9][10] Thus, BMD can be characterized as a chronic, lifelong disease with insidious onset and long preclinical phases.

8.2 Progression: Stages and Rate

Disease progression in Becker muscular dystrophy is slow and heterogeneous. The Italian natural history study reports that at the last assessment (median age 26 years), only 13.5% of BMD patients had lost the ability to walk, with a median age at loss of ambulation estimated by Kaplan–Meier analysis at 69 years.[10] This indicates that most individuals remain ambulant into late adulthood, although a minority experience earlier loss. The same cohort reports that 30% exhibited left ventricular impairment and 2.7% respiratory involvement, suggesting that cardiomyopathy progression is more common than respiratory failure.[10]

Progression can be conceptualized in stages: an early asymptomatic stage with hyperCKemia, a mild symptomatic stage with proximal weakness and calf hypertrophy, an intermediate stage with increasing functional impairment and emerging cardiac dysfunction, and an advanced stage with loss of ambulation, significant cardiomyopathy, and potential respiratory compromise.[3][9][10] The rate of progression varies by genotype, lifestyle, and medical care. Gorgoglione et al. demonstrate that patients carrying del45–49 deletions lose ambulation earlier than those with del45–47 deletions, whereas del45–55 and del48 deletions are associated with later loss of ambulation and lower risk of cardiomyopathy.[10] This underscores that progression rate is strongly influenced by underlying DMD mutation.

Respiratory progression, as quantified by De Wel et al., shows a mean FVC decline of 1% per year, which is mild but clinically significant over decades.[9] After loss of ambulation, the decline accelerates and becomes more clinically relevant, indicating that transition to non‑ambulant status is a critical period for respiratory surveillance and intervention.[9] Cardiac progression depends on both dystrophin genotype and heart failure management; early use of ACE inhibitors and beta‑blockers may slow decline, while untreated cardiomyopathy can progress to end‑stage heart failure requiring transplant.[8][17]

8.3 Patterns: Remission, Critical Periods, and Intervention Windows

Spontaneous remission does not occur in BMD; it is a chronic, lifelong condition. However, progression may plateau during certain periods, especially in milder genotypes, leading to relatively stable function for many years. Treatment‑induced stabilization or partial improvement may occur with cardioprotective therapies, physical rehabilitation, and optimized lifestyle, but reversal of established muscle degeneration is limited.

Critical periods in BMD include adolescence and early adulthood, when joint contractures and orthopedic complications may develop, and the third decade, when cardiomyopathy commonly emerges.[8][10][17] Loss of ambulation represents a major transition period, associated with increased risk of respiratory decline and psychosocial challenges.[9][14] These windows offer opportunities for intervention: early orthopedic care to prevent contractures, proactive cardiac screening and ACE inhibitor initiation, and enhanced respiratory monitoring and support after loss of ambulation.

In the context of clinical trials, early symptomatic or pre‑symptomatic stages may be ideal for interventions targeting downstream molecular pathways, as suggested by the BMD clinical trial review.[19] The review notes that trials have targeted inflammation, fibrosis, and other pathways rather than dystrophin restoration, making timing critical for maximal efficacy.[19]

9. Inheritance and Population Characteristics

9.1 Inheritance Pattern, Penetrance, and Expressivity

Becker muscular dystrophy follows an X‑linked recessive inheritance pattern. Orphanet explicitly states that BMD has "X-linked recessive" inheritance and primarily affects males, with female carriers usually asymptomatic.[2] The Genetic Testing Registry similarly lists X‑linked recessive inheritance and notes synonyms reflecting pseudohypertrophic muscular dystrophy.[11] In this pattern, hemizygous males carrying a pathogenic DMD mutation develop disease, while heterozygous females are carriers and may or may not exhibit symptoms depending on X‑inactivation skewing.

Penetrance in hemizygous males is essentially complete: virtually all males with a BMD‑associated DMD mutation will develop some degree of muscle weakness or cardiomyopathy, though severity varies.[3][7][10] Expressivity is highly variable, influenced by the specific mutation, modifier genes, lifestyle factors, and medical care. Some men present only with hyperCKemia and mild weakness, whereas others develop significant disability and cardiomyopathy.[10]

In female carriers, penetrance of skeletal manifestations is low, but cardiac involvement is more frequent than previously appreciated. GeneReviews and guideline documents note that a subset of carriers develop cardiomyopathy, particularly with skewed X‑inactivation favoring expression of the mutant allele in cardiac tissue.[3][17] Expression of symptoms in carriers is thus incomplete and variable, necessitating cardiac surveillance.

Genetic anticipation—progressive worsening across generations—is not a feature of BMD because DMD mutations are not repeat expansions. Germline mosaicism in mothers of isolated cases can occur and affects recurrence risk counseling, but does not alter disease expression in individual patients. Founder effects are possible in specific populations where particular DMD deletions reached higher frequencies, but large‑scale data are limited.

9.2 Epidemiology: Prevalence, Incidence, and Geographic Variation

Global prevalence estimates of Becker muscular dystrophy come from systematic reviews and meta‑analyses. Salari et al. conducted a meta‑analysis of 25 studies involving over 901 million people and estimated the overall prevalence of muscular dystrophy at (3.6) per 100,000, with prevalence of DMD and BMD at (4.8) and (1.6) per 100,000, respectively.[4] They reported that the Americas have the highest prevalence of muscular dystrophy at (5.1) per 100,000 (95% CI 3.4–7.8), while Africa has the lowest prevalence at (1.7) per 100,000 (95% CI 1.1–4.5).[4] Orphanet notes that in Europe, the estimated prevalence of BMD ranges between 1:16,700 and 1:18,500 male births.[2]

Magot et al.’s French guidelines state that BMD is "one of the most frequent among neuromuscular diseases, affecting approximately 1 in 18,000 male births," highlighting its relative frequency within rare neuromuscular disorders.[17] Incidence data are less robust than prevalence but can be inferred from birth prevalence estimates and carrier frequencies. Dystrophinopathy incidence is generally considered relatively uniform across ethnic groups, though diagnostic rates and registry completeness vary.

Sex ratio is strongly skewed toward males due to X‑linked recessive inheritance. BMD primarily affects boys and men; Orphanet and MDA emphasize this male predominance.[2][6] Female carriers may be counted in some registries but are typically classified separately. Age distribution of affected individuals spans childhood to elderly, reflecting variable onset and survival into later decades.[2][4][10]

Geographic distribution of specific DMD variants may show regional clustering due to founder effects, but detailed mapping is sparse. However, mutational hotspots around exons 45–55 and exons 1–10 are consistent across populations.[7] Global burden of BMD in terms of disability‑adjusted life years (DALYs) has not been specifically quantified, though muscular dystrophies overall contribute to chronic disability and health care utilization.

9.3 Carrier Frequency, Consanguinity, and Population Demographics

Carrier frequency of BMD‑associated DMD mutations among women depends on male prevalence and mutation dynamics. With a male prevalence of around 1 in 18,000 births, carrier frequency may be approximated at similar levels or slightly higher due to segregation and new mutations, but direct screening data are limited.[2][4][17] Consanguinity plays a lesser role in X‑linked disorders than in autosomal recessive disorders, though consanguineous unions can increase the likelihood of interacting genetic factors or unmasking other recessive traits.

Population demographics show that BMD occurs across all ethnic and racial groups, with differences largely reflecting health care access, diagnostic infrastructure, and registry efficiency rather than underlying genetic variation. Registries and cohort studies from Italy,[10] France,[17] and other European countries dominate the literature, but data from the Americas,[4] Asia, and Africa are emerging.

10. Diagnostics

10.1 Clinical and Laboratory Evaluation

Diagnosis of Becker muscular dystrophy begins with clinical assessment of muscle weakness, calf hypertrophy, and functional limitations, followed by laboratory confirmation. Elevated serum creatine kinase (CK) is a hallmark laboratory finding and often the earliest abnormality. GeneReviews notes that hyperCKemia can precede symptoms, and the Italian cohort found that incidental hyperCKemia prompted diagnosis in 55% of patients.[3][10] CK levels in BMD are typically elevated 5–100 times above normal, similar to DMD but with more variability.

Other laboratory tests include serum transaminases (AST, ALT), which are often elevated due to muscle damage rather than liver disease, and lactate dehydrogenase. Cardiac biomarkers such as BNP and troponins may be elevated in cardiomyopathy.[8] Pulmonary function tests, particularly spirometry measuring FVC and FEV1, assess respiratory involvement; De Wel et al. used serial spirometry to quantify FVC decline.[9]

Electrophysiological tests can support diagnosis. Electromyography (EMG) shows myopathic motor unit potentials—short duration, low amplitude—and may reveal spontaneous activity. Nerve conduction studies are usually normal. ECG and Holter monitoring detect conduction abnormalities and arrhythmias typical of BMD cardiomyopathy, including bundle branch blocks, tall R waves, deep Q waves, and prolonged QTc.[8]

Imaging studies such as muscle MRI reveal patterns of fatty infiltration and edema in specific muscle groups, aiding differential diagnosis from other myopathies. Cardiac echocardiography assesses left ventricular size, systolic function, diastolic function, and valvular regurgitation.[8] Cardiac MRI offers more detailed visualization of regional wall motion abnormalities and late gadolinium enhancement for fibrosis.[8]

10.2 Muscle Biopsy and Histopathology

Before widespread genetic testing, muscle biopsy was central to BMD diagnosis. Histopathology typically shows myofiber size variability, necrosis, regeneration with central nuclei, endomysial fibrosis, and fatty replacement, consistent with dystrophic changes.[3][13] Immunohistochemistry for dystrophin demonstrates reduced quantity or abnormal size of dystrophin, as opposed to near‑complete absence in DMD.[3][15] Western blot analysis quantifies dystrophin expression and shows shortened bands corresponding to truncated dystrophin in BMD.[3][15]

Although muscle biopsy is less frequently required today due to genetic testing, it remains valuable when genetic results are inconclusive or when novel variants are identified whose pathogenicity needs functional confirmation. Biopsy findings can be coded using SNOMED CT terms for muscular dystrophy and histologic features.

10.3 Genetic Testing Strategies

Genetic testing is the gold standard for confirming BMD diagnosis and characterizing the causative DMD mutation. GeneReviews and the Genetic Testing Registry advise a stepwise approach starting with methods optimized for detecting exon deletions and duplications, such as multiplex ligation‑dependent probe amplification (MLPA) or comparative genomic hybridization (array‑CGH), followed by sequencing of exons and splice junctions if no large rearrangement is found.[3][11] MLPA can detect deletions or duplications across the 79 exons of DMD, identifying the majority of BMD mutations.[7][10]

Next‑generation sequencing (NGS) approaches, including targeted dystrophin gene panels, whole exome sequencing (WES), or whole genome sequencing (WGS), are increasingly used when initial testing is negative or to identify small variants such as missense, splice site, frameshift, or deep intronic changes.[3] WES is particularly useful in patients with atypical presentation or when multiple genes are suspected, while WGS may uncover complex rearrangements or regulatory variants.

The NIH Genetic Testing Registry lists multiple laboratory tests for BMD, including DMD sequencing, deletion/duplication analysis, and panel tests that include DMD among other neuromuscular genes.[11] Prenatal and preimplantation genetic testing are possible when the familial mutation is known, enabling carrier couples to make informed reproductive decisions.

Chromosomal microarray (CMA) and karyotyping are rarely needed unless syndromic features suggest larger Xp21 deletions involving neighboring genes. FISH can be used to detect specific deletions but is less common. Mitochondrial DNA testing and repeat expansion tests are not relevant to BMD.

10.4 Omics‑Based Diagnostics and Biomarkers

Omics‑based diagnostics have not yet replaced conventional genetic testing in BMD but provide complementary information. RNA‑seq from muscle biopsy can detect aberrant splicing, exon skipping, and low‑level expression of mutant transcripts, confirming functional impact of variants.[15] Proteomics can quantify dystrophin and DGC component levels, while metabolomics may identify signatures of muscle degeneration and cardiomyopathy.

Biomarker development in BMD includes imaging biomarkers (MRI fibrosis patterns), serum biomarkers (CK, cardiac troponins, NT‑proBNP), and emerging molecular markers such as microRNAs associated with muscle damage. However, no specific BMD biomarkers have been validated for regulatory use. The review "An update on Becker muscular dystrophy" notes increasing interest in biomarkers for clinical trials and natural history studies.[19]

10.5 Clinical Criteria and Differential Diagnosis

Standardized clinical criteria for BMD revolve around later onset of weakness, preservation of ambulation beyond age 13, elevated CK, and partial dystrophin expression. Distinguishing BMD from DMD depends on age at onset, age at loss of ambulation, and dystrophin status. Intermediate phenotypes may complicate classification, requiring careful genotypic and phenotypic evaluation.[3][6]

Differential diagnoses include limb‑girdle muscular dystrophies (LGMD), facioscapulohumeral muscular dystrophy (FSHD), metabolic myopathies, inflammatory myopathies, and other neuromuscular disorders. Ferreira et al. compared QoL across DMD, BMD, LGMD, and FSHD, highlighting overlapping physical function impairment but distinct disease courses.[14] LGMD often lacks calf hypertrophy and is autosomal recessive, while FSHD preferentially affects facial and shoulder girdle muscles and has characteristic genetic features. Metabolic and inflammatory myopathies may present with similar weakness but differ in CK patterns, biopsy features, and autoantibody profiles.

UpToDate and other clinical decision support tools provide differential diagnosis frameworks based on age, distribution of weakness, CK level, family history, and biopsy/genetic findings. In BMD, family history of X‑linked muscular dystrophy, male predominance, and dystrophin deficiency are key distinguishing features.

10.6 Screening and Early Detection

Population‑based newborn screening for BMD does not currently exist, although CK testing in newborns has been proposed for DMD detection. Carrier screening for DMD in high‑risk families is standard practice, using targeted mutation analysis.[3][17] Cascade screening of relatives after a proband’s diagnosis is recommended to identify affected males and at‑risk female carriers, enabling early cardiac surveillance and reproductive counseling.[3][17]

Prenatal testing via chorionic villus sampling or amniocentesis can detect familial DMD mutations. Preimplantation genetic diagnosis (PGD) enables selection of embryos free of DMD mutations in assisted reproduction. These measures constitute secondary prevention by enabling early detection and informed choices, though they do not affect disease course in existing patients.

11. Outcome and Prognosis

11.1 Survival, Life Expectancy, and Mortality

Life expectancy in Becker muscular dystrophy is generally longer than in Duchenne muscular dystrophy but still reduced compared to the general population. Many BMD patients live into the fifth or sixth decade, and some beyond, with cardiomyopathy representing the primary cause of death.[8][3] Ho’s review notes that "BMD patients may live until the fifth or sixth decade of life and cardiomyopathy represents the number one cause of death in these patients."[8] GeneReviews similarly emphasizes that cardiomyopathy is the most common cause of death in BMD.[3]

Precise survival rates (5‑year, 10‑year) are not widely reported for BMD, but natural history data provide proxies. The Italian cohort’s Kaplan–Meier estimate of median age at loss of ambulation (69 years) implies survival well into older adulthood for many patients, though this does not directly measure mortality.[10] Mortality rates depend on access to cardiac care, ventilatory support, and multidisciplinary management.

Disease‑specific mortality is driven by heart failure, arrhythmias, and sudden cardiac death due to dilated cardiomyopathy, as well as respiratory failure in advanced stages.[8][9] Infections, particularly pneumonia and sepsis, may contribute. Accurate mortality statistics require linkage of neuromuscular registries with national death registries, an area of ongoing development.

11.2 Morbidity, Disability, and Quality of Life

Morbidity in BMD encompasses muscle weakness, fatigue, pain, cardiomyopathy, respiratory compromise, orthopedic complications, and psychosocial impacts. Disability outcomes include difficulty walking, climbing stairs, lifting objects, and performing activities of daily living (ADLs). Gait abnormalities, frequent falls, and eventually wheelchair dependence characterize motor disability. Orthopedic complications such as contractures and scoliosis can further limit mobility and cause pain.[3][13][17]

Ferreira et al.’s SF‑36 study found that all muscular dystrophy groups, including BMD, had lower quality of life across many domains compared to controls.[14] Physical function scores in BMD were significantly lower than controls but higher than DMD, aligning with milder physical morbidity.[14] Vitality scores were lower in BMD compared to controls, indicating fatigue as a prominent symptom.[14] Bodily pain, social function, and general health domains were also reduced, suggesting that BMD affects not only physical capabilities but also pain levels, social engagement, and perceived health.[14] Mental health domains were less different between BMD and controls, though some subtle differences existed.

Fatigue emerged as the factor most consistently associated with QoL domains across muscular dystrophies, reinforcing its central role in BMD morbidity.[14] Self‑efficacy and ADLs were also strongly associated with QoL, implying that interventions boosting confidence and functional independence may improve well‑being.[14] These findings support linking BMD phenotypes to PROMIS measures and SF‑36 domains in knowledge bases.

11.3 Disease Course, Complications, and Recovery Potential

Disease course in BMD is progressive and chronic, with limited recovery potential. Muscle weakness and cardiomyopathy progress slowly, with intermittent stabilization. Complications include dilated cardiomyopathy, heart failure, arrhythmias, respiratory insufficiency, orthopedic deformities, and psychosocial issues such as depression and anxiety.[3][8][9][14] Recovery from acute exacerbations, such as heart failure episodes or respiratory infections, is possible with appropriate treatment, but underlying disease continues to progress.

Heart failure complications in BMD mirror those in other cardiomyopathies: edema, dyspnea, reduced ejection fraction, and risk of sudden death.[8] Arrhythmias, including atrial fibrillation and ventricular tachycardia, can necessitate device implantation or antiarrhythmic drugs.[8] Respiratory complications include nocturnal hypoventilation and recurrent infections, particularly after loss of ambulation.[9] Orthopedic complications may be addressed surgically or with braces but often recur.

Recovery potential is limited in terms of reversing muscle degeneration, but functional gains can be achieved through rehabilitation, assistive technologies, and optimized cardiovascular and respiratory care. Regenerative therapies and gene‑modifying approaches hold theoretical potential for future disease modification, but no approved treatments currently achieve this in BMD.[19]

11.4 Prognostic Factors and Biomarkers

Prognostic factors in Becker muscular dystrophy include genotype, age at onset, CK levels, functional status, cardiac imaging and ejection fraction, respiratory function, BMI, and treatment adherence. Gorgoglione et al. show that specific DMD deletions, such as del45–49 vs del45–47, significantly influence age at loss of ambulation and risk of left ventricular impairment, making mutation class a key prognostic factor.[10] Del45–55 and del48 deletions are associated with decreased odds of pathological left ventricular ejection fraction and later loss of ambulation, indicating favorable genotypes.[10]

De Wel et al. identify loss of ambulation and higher BMI as risk factors for accelerated FVC decline, making them prognostic for respiratory outcomes.[9] Cardiac biomarkers such as ejection fraction, MRI fibrosis burden, and NT‑proBNP levels are prognostic for heart failure progression and mortality.[8] Elevated CK indicates ongoing muscle damage but is less predictive of long‑term outcomes than functional and cardiac measures.

Prognostic biomarkers in development include imaging markers of fibrosis, serum microRNAs linked to muscle damage, and perhaps circulating proteins reflective of inflammation and fibrosis. However, BMD‑specific biomarkers have not yet been validated for routine clinical use. Still, knowledge bases can incorporate these candidate markers as investigational prognostic indicators.

12. Treatment

12.1 Pharmacotherapy: Corticosteroids and Cardioprotective Drugs

Pharmacological treatment of Becker muscular dystrophy has historically paralleled that of Duchenne muscular dystrophy, particularly with corticosteroids and cardioprotective therapies, although evidence is less robust. A population‑based cohort study of boys with DMD and BMD (MD STARnet) reviewed corticosteroid use from 1991 to 2005, finding that usage increased from 20% in 1991 to 44% in 2005, with median initiation age 6.9 years.[16] The study notes that "only corticosteroids such as prednisone and deflazacort have been shown to improve and/or preserve functional status," and that their clearest benefit is improvement in muscle strength and preservation of independent ambulation by 2–3 years.[16] The American Academy of Neurology Practice Parameter recommends offering corticosteroids (prednisone 0.75 mg/kg/d or deflazacort 0.9 mg/kg/d) to individuals with DMD and BMD.[16]

However, corticosteroid use in BMD is more variable, and many clinicians reserve steroids for more severe or intermediate phenotypes due to concerns about side effects such as weight gain, behavioral changes, gastrointestinal complications, hypertension, and hirsutism.[16] In a knowledge base, corticosteroid therapy can be represented by NCIT terms for "prednisone therapy" and "deflazacort therapy," with mechanisms of action involving anti‑inflammatory and immunosuppressive effects.

Cardioprotective drugs are central to BMD management. ACE inhibitors (e.g., enalapril, perindopril) and beta‑blockers (e.g., carvedilol, bisoprolol) are recommended in accordance with heart failure guidelines.[8][17] Ho’s review states that beta‑blockers are beneficial in DCM and may have positive effects in BMD cardiomyopathy, and that they should be used according to current heart failure guidelines.[8] ACE inhibitors have been shown in DMD to delay onset and progression of cardiomyopathy; similar benefits are presumed in BMD.[8][17] Diuretics and digoxin can be used for symptom relief, though no mortality benefit has been demonstrated.[8]

Other heart failure medications, such as mineralocorticoid receptor antagonists (spironolactone, eplerenone), angiotensin receptor–neprilysin inhibitors, and SGLT2 inhibitors, may be applied based on general cardiomyopathy guidelines, though BMD‑specific data are sparse. Antiarrhythmic drugs and anticoagulants may be needed for arrhythmia management.

12.2 Advanced Therapeutics: Gene, RNA, and Cell Therapies

To date, no gene therapy or RNA‑based therapy is approved specifically for Becker muscular dystrophy, but advances in DMD therapeutics have implications for BMD. Exon‑skipping antisense oligonucleotides (ASOs) aim to convert out‑of‑frame DMD mutations into in‑frame deletions, producing truncated dystrophin similar to BMD and thereby attenuating disease.[15] While these ASOs target specific exons (e.g., exon 51, exon 53) in DMD, they conceptually leverage BMD biology. For existing BMD patients, exon‑skipping is less directly relevant, though ASOs could theoretically be used to modulate splicing in cases with deleterious splice site mutations.

Gene replacement therapies using adeno‑associated virus (AAV) vectors expressing micro‑dystrophin—shortened dystrophin constructs designed to fit within AAV packaging—are in advanced clinical development for DMD. These micro‑dystrophins are modeled on naturally occurring mild BMD variants, preserving critical domains while truncating others.[15][19] BMD patients already express truncated dystrophin, so gene replacement therapy may have less clear benefit, but in cases with severely dysfunctional dystrophin, micro‑dystrophin gene therapy might be considered in the future. The "update on BMD" review highlights ongoing and planned trials in BMD targeting downstream pathways rather than dystrophin restoration.[19]

Cell therapies, such as stem cell transplantation and myoblast transfer, have been explored in dystrophinopathies but face challenges of engraftment, immune rejection, and limited distribution. No approved cell therapies exist for BMD. RNA‑based therapies, including siRNAs and mRNA therapies, are also under investigation primarily in DMD.

Targeted therapies aimed at fibrosis, inflammation, and oxidative stress are more prominent in BMD trials. The BMD review references a randomized, placebo‑controlled, double‑blind study (details not fully shown) that, although it failed to meet its primary endpoint, paved the way for further trials targeting molecular pathways downstream of dystrophin deficiency.[19] Neuroprotective agents like idebenone have been tested in DMD and may have ancillary benefits in BMD, but data are limited.

12.3 Surgical and Interventional Approaches

Surgical interventions in BMD primarily address orthopedic and cardiac complications. Orthopedic surgeries include tendon lengthening to correct contractures, spinal fusion for severe scoliosis, and joint replacement for degenerative changes.[17] These procedures aim to preserve function, relieve pain, and improve posture. Timing depends on severity and progression and must consider respiratory and cardiac risks.

Cardiac interventions include implantation of pacemakers and implantable cardioverter‑defibrillators (ICDs) for conduction abnormalities and arrhythmias, as well as heart transplantation for end‑stage cardiomyopathy.[8] Ho’s review mentions that some BMD patients require cardiac transplant due to severe DCM.[8] Cardiac resynchronization therapy (CRT) may improve function in patients with dyssynchronous ventricular contraction, though BMD‑specific data are limited.

Respiratory interventions include tracheostomy for advanced ventilatory failure, though non‑invasive ventilation is preferred where possible.[9][17] Surgical decision‑making must integrate neuromuscular, cardiac, and respiratory considerations.

12.4 Supportive and Rehabilitative Care

Supportive care and rehabilitation are fundamental to BMD management. Physical therapy focuses on maintaining muscle strength, joint mobility, and balance while avoiding overexertion and eccentric overload. Exercise programs emphasize low‑impact cardiovascular activity (walking, swimming), gentle stretching, and light strength exercises performed with controlled movements and proper form.[18] The ImagingNMD guidance stresses starting with low‑intensity exercise, resting between sets, monitoring breathing, and avoiding exercise to exhaustion.[18]

Occupational therapy assists with ADLs, recommending adaptive devices for dressing, bathing, and mobility. Orthotic devices such as ankle‑foot orthoses and braces support weak muscles and correct gait. Respiratory therapy monitors lung function, teaches breathing exercises, and provides cough assist devices to improve secretion clearance.[9][17] Nutritional support aims to maintain optimal BMI and prevent obesity or malnutrition.

Psychological and social support address depression, anxiety, and coping with chronic illness. Counseling, support groups, and social services help individuals and families manage the emotional and practical aspects of BMD.

12.5 Experimental Treatments and Clinical Trials

Recent years have seen increased numbers of interventional clinical trials in BMD. The "update on BMD" review notes that no treatments are approved specifically for BMD but that various agents targeting molecular pathways downstream of dystrophin deficiency have been tested.[19] These include anti‑inflammatory drugs, antioxidant agents, metabolic modulators, and perhaps anti‑fibrotic compounds. One randomized, placebo‑controlled, double‑blind study in BMD is mentioned, though details are not fully provided; the trial failed its primary endpoint but contributed important data for future trial design.[19]

Therapies such as ACE inhibitors and beta‑blockers for cardiomyopathy are supported by general cardiomyopathy trials, while corticosteroid use is informed by DMD and dystrophinopathy practice parameters.[16] Investigational therapies in DMD, such as utrophin upregulators, TGF‑β inhibitors, and myostatin blockers, may eventually be tested in BMD. ClinicalTrials.gov and EU registries list multiple ongoing or completed BMD studies, though specifics are beyond the scope of the current search results.

12.6 Treatment Outcomes, Side Effects, and Strategy

Treatment outcomes in BMD are heterogeneous. Corticosteroids can improve strength and delay loss of ambulation by several years, but side effects such as weight gain, behavior changes, hypertension, and osteopenia limit long‑term use.[16] ACE inhibitors and beta‑blockers improve cardiac function, reduce symptoms, and likely extend survival, with side effects including hypotension, electrolyte abnormalities, and renal function changes.[8][17] Surgical interventions can significantly improve function and pain but carry perioperative risks.

Experimental therapies have shown mixed results, with some failing to meet primary endpoints but demonstrating safety and biomarker changes. Overall, treatment strategy in BMD emphasizes early diagnosis, genotype‑informed risk assessment, proactive cardiac and respiratory monitoring, and individualized use of pharmacologic and rehabilitative interventions. Personalized medicine approaches consider DMD mutation type, cardiac status, respiratory function, lifestyle, and patient preferences.

In a knowledge base, treatments can be annotated with NCIT terms such as "beta‑blocker therapy," "ACE inhibitor therapy," "corticosteroid therapy," "physical therapy," "cardiac transplantation," and "non‑invasive ventilation," linked to indications (cardiomyopathy, muscle weakness, respiratory failure) and evidence levels.

13. Prevention

13.1 Primary, Secondary, and Tertiary Prevention

Primary prevention of Becker muscular dystrophy, in the sense of preventing disease occurrence, is challenging because it is an inherited monogenic disorder. However, genetic counseling, carrier testing, and reproductive options constitute primary prevention at the family level. Identifying female carriers and informing them about recurrence risks enables choices such as PGD or prenatal diagnosis to prevent affected offspring.[3][17]

Secondary prevention focuses on early detection and timely intervention to reduce morbidity. Cascade screening of relatives after a proband’s diagnosis, including CK testing and genetic analysis, can identify affected males in early stages and carriers requiring surveillance.[3][17] Early cardiac screening with echocardiography and ECG, beginning in adolescence or earlier, allows detection of subclinical cardiomyopathy and initiation of ACE inhibitors or beta‑blockers.[8][17] Respiratory screening with spirometry, especially after loss of ambulation, detects declining FVC and enables early non‑invasive ventilation.[9]

Tertiary prevention aims to prevent complications and optimize function in individuals with established BMD. This includes orthopedic monitoring and interventions to prevent contractures and scoliosis, fall prevention strategies, infection prophylaxis (vaccination, respiratory care), and pain management.[17][18] Lifestyle modifications such as tailored exercise and nutrition reduce secondary complications like obesity and deconditioning.[9][18]

13.2 Immunization, Screening, and Behavioral Interventions

Immunization against respiratory pathogens (influenza, pneumococcus) is recommended to reduce infection risk but does not alter the underlying genetic disease.[3][9] Screening programs for BMD are not population‑based but family‑based, focusing on carrier detection and at‑risk males. Genetic screening for DMD mutations in families with known dystrophinopathy is standard practice, guided by ACMG and NSGC recommendations.[3][17]

Behavioral interventions include exercise counseling, emphasizing low‑to‑moderate intensity activity, avoidance of heavy eccentric loading, adequate hydration, rest periods, and monitoring for pain.[18] Smoking cessation and moderation of alcohol intake are advised to protect cardiac and respiratory health. Sleep hygiene and stress management support mental health.

13.3 Genetic Counseling and Public Health Considerations

Genetic counseling is central to BMD prevention and management. Counselors inform families about inheritance patterns, recurrence risks, carrier testing options, prenatal and preimplantation diagnosis, and implications for extended relatives.[3][17] They also discuss psychosocial aspects of chronic disease and reproductive choices.

Public health interventions for BMD focus on improving access to neuromuscular care, raising awareness among clinicians, and supporting registries and research. Environmental interventions to reduce risk factors (e.g., obesity, smoking) are generic but beneficial. Because BMD is not infectious or environmentally caused, traditional public health measures like sanitation or vector control are irrelevant.

Prophylactic medications, such as ACE inhibitors in pre‑symptomatic carriers at high risk for cardiomyopathy, can be considered tertiary preventive measures. However, evidence for prophylactic ACE inhibitor use in asymptomatic BMD patients is extrapolated from DMD and general cardiomyopathy data rather than BMD‑specific trials.[8][17]

14. Other Species and Natural Disease

14.1 Species and Orthologous Genes

Dystrophinopathies occur not only in humans but also in other species, particularly dogs and mice. The orthologous gene to human DMD exists in many vertebrates, including mouse (Dmd), dog, and others, encoding dystrophin homologs with similar domain structures and functions.[15] Mutations in these orthologs produce muscular dystrophy phenotypes reminiscent of DMD more often than BMD, due to severe loss of dystrophin.

The mdx mouse, for example, carries a nonsense mutation in exon 23 of Dmd, leading to absence of dystrophin and a DMD‑like phenotype.[15] Canine models, such as golden retriever muscular dystrophy (GRMD), result from dystrophin deficiency and exhibit severe progressive muscle wasting akin to DMD. Naturally occurring BMD‑like phenotypes—where truncated dystrophin is produced and disease is milder—are less well documented, but transgenic mice expressing truncated dystrophin constructs mimic BMD to some extent.[15]

14.2 Natural Disease in Companion Animals and Comparative Pathology

Muscular dystrophies in dogs, cats, and other companion animals are veterinary relevance concerns. However, most documented dystrophinopathies in animals resemble DMD more than BMD, with early onset and severe disease. BMD‑like disorders may exist but are less recognized, as veterinary diagnostics may not routinely characterize dystrophin structure and function in detail.

Comparative pathology studies of mdx mice and GRMD dogs provide insights into dystrophin deficiency, muscle degeneration, and cardiomyopathy that are applicable to both DMD and BMD. They show similar cycles of necrosis, regeneration, fibrosis, and cardiac involvement, supporting the generality of DGC dysfunction mechanisms.[15] Differences arise in disease severity and progression due to species‑specific muscle physiology and immune responses.

Evolutionary conservation of dystrophin and DGC components across species supports their fundamental role in muscle stability. HomoloGene and OrthoMCL data show conserved domains and interaction networks, indicating that insights from animal models on dystrophin function and pathogenic mechanisms are broadly translatable.

14.3 Transmission and Zoonotic Potential

Dystrophinopathies are inherited genetic disorders and are not transmissible between individuals or species. There is no zoonotic potential for Becker muscular dystrophy; it does not arise from infectious agents and cannot be transmitted through contact or vectors. Cross‑species susceptibility to dystrophin mutations is limited to inheriting orthologous gene variants within a species.

15. Model Organisms

15.1 Types of Model Systems

Model organisms used to study dystrophinopathies include mice, dogs, zebrafish, and cell culture systems. The mdx mouse is the most widely used model, carrying a nonsense mutation in exon 23 of Dmd and developing a relatively mild muscular dystrophy phenotype compared to human DMD, with near‑normal lifespan but significant muscle pathology.[15] GRMD dogs provide a more severe, DMD‑like phenotype with progressive weakness and cardiomyopathy.[15]

To model BMD specifically, researchers have generated transgenic mice expressing truncated dystrophin constructs mimicking common BMD deletions, such as internal deletions in the rod domain or hybrid dystrophin–utrophin proteins.[15] These models attempt to recapitulate partial dystrophin function and intermediate disease severity. Cell culture systems, including myoblasts and myotubes derived from BMD patients or induced pluripotent stem cell (iPSC)–derived muscle cells, are used to study dystrophin expression, membrane stability, and drug responses in vitro.

15.2 Genetic Models and Phenotype Recapitulation

Genetic models of BMD involve knock‑in of specific in‑frame deletions into the murine Dmd gene or transgenic expression of truncated dystrophin in mdx mice. For example, mice expressing a dystrophin variant with deletion of spectrin repeats 17–23 show milder muscle pathology than mdx mice, resembling BMD.[15] These models display partial preservation of DGC localization, reduced CK levels, and improved muscle strength compared to dystrophin‑null models.

Phenotype recapitulation in these models includes muscle necrosis, regeneration, fibrosis, and some degree of cardiomyopathy, but species differences and compensatory mechanisms (such as upregulation of utrophin) limit direct extrapolation. The mdx mouse, for instance, has a less severe cardiomyopathy than human DMD, and BMD‑like models may therefore underrepresent cardiac involvement seen in human BMD.[15]

15.3 Model Limitations and Applications

Models of BMD and dystrophinopathies have several limitations. Murine and canine muscle physiology differs from human physiology, and immune responses and regenerative capacity vary across species. mdx mice often show robust muscle regeneration that mitigates functional deficits, while human BMD patients experience more progressive degeneration.[15] BMD‑like mouse models may not fully capture the heterogeneity of human DMD mutations and their cardiomyopathy patterns.

Despite these limitations, model organisms are invaluable for studying DGC structure and function, testing exon‑skipping and gene therapies, and exploring downstream pathogenic pathways such as inflammation, fibrosis, and oxidative stress.[15][19] They allow controlled experimental manipulation and functional genomics screens (e.g., CRISPR knockout libraries) to identify modifier genes and drug targets.

Conclusion

Becker muscular dystrophy is a paradigmatic X‑linked dystrophinopathy characterized by progressive skeletal muscle weakness, variable cardiomyopathy, and relatively mild respiratory involvement, caused by DMD mutations that permit expression of shortened or partially functional dystrophin.[2][3][7] Its clinical phenotype spans a broad spectrum, from asymptomatic hyperCKemia with minimal weakness to significant disability and heart failure, underscoring the importance of detailed genotype–phenotype correlation. Epidemiologic data from meta‑analyses and registries position BMD as a relatively common rare neuromuscular disease, with prevalence around (1.6) per 100,000 individuals and approximately 1 in 18,000 male births.[2][4][17]

At the mechanistic level, BMD exemplifies partial loss of function in a critical structural protein and its associated complex, the DGC, leading to sarcolemmal fragility, Ca(^{2+}) dysregulation, oxidative stress, inflammation, and fibrosis, yet with slower progression than complete dystrophin absence.[6][15] Mutations in DMD cluster in hotspots such as exons 45–55, and specific in‑frame deletions differentially affect dystrophin domains and clinical outcomes.[7][10] Cardiac involvement, with dilated cardiomyopathy and arrhythmias, is frequent and represents the leading cause of death, necessitating proactive surveillance and cardioprotective therapy.[8][10][17] Respiratory decline is mild but accelerates after loss of ambulation and with higher BMI, highlighting the interplay of genotype and lifestyle factors.[9]

Diagnostics rely on clinical assessment, elevated CK, imaging, electrophysiology, and, critically, genetic testing to identify DMD mutations and distinguish BMD from DMD and other myopathies.[3][10][11] Muscle biopsy and dystrophin immunohistochemistry remain valuable in complex cases. Outcome and prognosis are shaped by mutation type, cardiac status, respiratory function, BMI, and treatment access; median age at loss of ambulation can extend into late adulthood, but cardiomyopathy often limits life expectancy to the fifth or sixth decade.[8][10] Quality of life, as measured by SF‑36, is significantly reduced in BMD compared to controls, with fatigue and physical function impairments prominent across domains.[14]

Treatment strategies integrate corticosteroids in selected cases, ACE inhibitors and beta‑blockers for cardiomyopathy, orthopedic and respiratory interventions, and comprehensive rehabilitation and psychosocial support.[8][16][17][18] Experimental therapies in BMD increasingly target downstream molecular pathways of dystrophin deficiency, building on insights from DMD and model organisms.[19] Prevention is largely genetic, through counseling and reproductive options, complemented by secondary and tertiary preventive measures such as early cardiac and respiratory screening and lifestyle modifications.[3][17]

For knowledge base construction, BMD can be anchored by ontology terms including MONDO (Becker muscular dystrophy), OMIM #300376, Orphanet ORPHA:98895, UMLS C0917713, ICD‑10 G71.0, ICD‑11 8C70.0, with phenotypes mapped to HPO terms (proximal weakness, calf hypertrophy, cardiomyopathy, respiratory insufficiency, hyperCKemia), molecular functions and processes to GO terms (structural constituent of muscle, sarcolemma organization, inflammatory response, fibrosis), cell types to CL terms (skeletal myofibers, cardiomyocytes, satellite cells, fibroblasts, immune cells), and anatomical structures to UBERON terms (skeletal muscle, heart, left ventricle, diaphragm).[2][3][8][12][15] Treatment annotations can leverage NCIT terms for pharmacologic, surgical, and rehabilitative interventions.

Future research directions include deeper multi‑omic profiling of BMD muscles and hearts, refined genotype–phenotype maps for specific DMD variants, identification of modifier genes and precise gene–environment interactions, development of BMD‑specific prognostic biomarkers, and evaluation of emerging gene and cell therapies in BMD populations. As clinical trials targeting BMD expand and precision medicine approaches mature, integrating detailed mechanistic, phenotypic, and therapeutic data into structured knowledge bases will be crucial to support evidence‑based care and research for individuals living with Becker muscular dystrophy.

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Deep Research

1. Disease Information

1.1 Definition, Nosology, and Overall Description

1.2 Key Identifiers and Coding Systems

1.3 Synonyms and Alternative Names

1.4 Source Type: Individual vs Aggregated Information

2. Etiology

2.1 Primary Causal Factors: Genetic Basis in the DMD Gene

2.2 Genetic Risk Factors and Modifier Influences

2.3 Environmental and Lifestyle Risk Factors

2.4 Protective Factors and Genotype–Phenotype Mitigation

2.5 Gene–Environment Interactions

3. Phenotypes

3.1 Skeletal Muscle Manifestations

3.2 Cardiac Phenotypes

3.3 Respiratory Phenotypes

3.4 Other Clinical and Laboratory Phenotypes

4. Genetic and Molecular Information

4.1 Causal Gene: DMD and Dystrophin

4.2 Pathogenic Variant Spectrum and Classification

4.3 Functional Consequences: Loss of Function and Partial Function

5. Environmental and Lifestyle Information

5.1 Non‑Genetic Contributing Factors

5.2 Lifestyle Factors: Exercise, Diet, and Substance Use

5.3 Infectious and Immune Factors

6. Mechanism and Pathophysiology

6.1 Molecular Pathways: Dystrophin–Glycoprotein Complex Dysfunction

6.2 Cellular Processes: Necrosis, Regeneration, and Fibrosis

6.3 Protein Dysfunction and Structural Changes

6.4 Metabolic and Immune System Involvement

6.5 Tissue Damage Mechanisms: Oxidative Stress, Fibrosis, and Necrosis

6.6 Molecular Profiling and Advanced Technologies

7. Anatomical Structures Affected

7.1 Organ‑Level Involvement

7.2 Tissue and Cell‑Level Involvement

7.3 Subcellular Localization and Compartments

7.4 Localization and Lateralization

8. Temporal Development

8.1 Onset: Age and Pattern

8.2 Progression: Stages and Rate

8.3 Patterns: Remission, Critical Periods, and Intervention Windows

9. Inheritance and Population Characteristics

9.1 Inheritance Pattern, Penetrance, and Expressivity

9.2 Epidemiology: Prevalence, Incidence, and Geographic Variation

9.3 Carrier Frequency, Consanguinity, and Population Demographics

10. Diagnostics

10.1 Clinical and Laboratory Evaluation

10.2 Muscle Biopsy and Histopathology

10.3 Genetic Testing Strategies

10.4 Omics‑Based Diagnostics and Biomarkers

10.5 Clinical Criteria and Differential Diagnosis

10.6 Screening and Early Detection

11. Outcome and Prognosis

11.1 Survival, Life Expectancy, and Mortality

11.2 Morbidity, Disability, and Quality of Life

11.3 Disease Course, Complications, and Recovery Potential

11.4 Prognostic Factors and Biomarkers

12. Treatment

12.1 Pharmacotherapy: Corticosteroids and Cardioprotective Drugs

12.2 Advanced Therapeutics: Gene, RNA, and Cell Therapies

12.3 Surgical and Interventional Approaches

12.4 Supportive and Rehabilitative Care