Bethlem Myopathy: Disease Characteristics Research Report

Scope and evidence basis. This report treats Bethlem myopathy (BM) as the mild end of the collagen-VI-related dystrophy (COL6-RD) spectrum. Evidence is primarily aggregated disease-level literature, specialist cohorts, family studies, experimental models, and ClinicalTrials.gov records—not routine EHR-derived data. Exact HPO/GO/CL/UBERON accessions should be validated against the current ontology release before database import; names below are suggested mappings.

Executive summary

Bethlem myopathy is a rare, chronic Mendelian muscle/connective-tissue disorder caused by pathogenic variants in COL6A1, COL6A2, or COL6A3. It is usually autosomal dominant but can be recessive. The characteristic combination is slowly progressive axial/proximal weakness, early distal laxity followed by contractures—particularly long finger flexors, elbows, ankles, knees, and neck—and variably abnormal skin. Ambulation is generally retained into adulthood, although meaningful weakness, wheelchair use, and restrictive respiratory disease occur in a subset. Cardiac involvement is not a usual primary feature. Open Targets recognizes all three genes as associated with MONDO:0008029 (OpenTargets Search: Bethlem myopathy-COL6A1,COL6A2,COL6A3).

No approved disease-modifying treatment exists. Current practice is multidisciplinary supportive management, especially contracture prevention, mobility preservation, respiratory surveillance, and noninvasive ventilation when indicated. Experimental approaches target defective autophagy/mitophagy, mitochondrial permeability-transition-pore dysfunction, abnormal extracellular-matrix signaling, or the causal allele.

Table: This compact table summarizes the most actionable Bethlem myopathy knowledge-base elements across identifiers, genes, phenotypes, mechanisms, diagnosis, management, trials, and models. It is designed for rapid curation and highlights where exact ontology IDs are suggested versus where only ontology names are appropriate.

1. Disease information

Definition and nomenclature

BM is a relatively mild, slowly progressive collagen-VI-related myopathy characterized by axial and proximal weakness, contractures, distal joint laxity, and skin manifestations. Onset can range from prenatal life to adulthood; retention of walking into adult life is often used as an operational distinction from intermediate and Ullrich phenotypes (merlini2023newclinicaland pages 1-2).

Identifiers and synonyms

• MONDO: MONDO:0008029.
• OMIM/MIM: 158810.
• Orphanet: Bethlem myopathy is represented within Orphanet’s collagen-VI-related disease nomenclature; the exact current ORPHA accession should be verified before ingestion.
• MeSH: generally indexed through Muscular Diseases, Muscular Dystrophies, and collagen type VI rather than a consistently used BM-specific descriptor.
• ICD-10: no specific BM code; commonly mapped to congenital/hereditary myopathy or muscular-dystrophy categories according to local coding rules.
• ICD-11: map under congenital myopathy/muscular dystrophy; a dedicated universally implemented BM code was not established in the retrieved evidence.
• Synonyms: Bethlem myopathy, Bethlem muscular dystrophy, collagen VI-related myopathy—Bethlem phenotype, mild collagen VI-related dystrophy.

BM was described in 1976 as an autosomal-dominant early-onset “benign” myopathy with contractures; causal collagen-VI variants were identified during 1996–1998. “Benign” is now discouraged because respiratory and functional morbidity may be substantial (bonnemann2011thecollagenvirelateda pages 1-2).

2. Etiology, risk, and protective factors

Causal factors

The primary cause is a germline pathogenic variant in COL6A1, COL6A2, or COL6A3, genes encoding the α1(VI), α2(VI), and α3(VI) chains of collagen VI. Pathogenic mechanisms include monoallelic assembly-competent variants producing dominant-negative microfibrils and biallelic loss-of-function, splice, or structural variants that reduce or abolish collagen production. Both dominant and recessive molecular defects are established across the spectrum (OpenTargets Search: Bethlem myopathy-COL6A1,COL6A2,COL6A3, zanotti2023extracellularmatrixdisorganization pages 1-2, mohassel2023collagentypevi pages 1-6).

Genetic risk factors

Risk is determined principally by inheriting or acquiring a pathogenic COL6 allele. Relevant variant classes include glycine substitutions in the triple-helical region, missense variants, exon-skipping splice variants, nonsense/frameshift alleles, in-frame deletions, deep-intronic variants, and copy-number changes. Dominant-negative variants near the amino-terminal portion of the triple helix can interfere with assembly; biallelic null alleles generally reduce chain availability. Examples described in the literature include dominant COL6A1 p.Lys121Arg and COL6A2 p.Asp630Asn, although any individual variant requires contemporary ACMG/AMP and ClinVar review (bonnemann2011thecollagenvirelateda pages 6-7).

Variant frequencies are usually extremely low or absent in population databases because BM is rare and pathogenic alleles are family-specific. No single population allele frequency should be generalized. Variant-level gnomAD frequency, ClinVar assertions, segregation, RNA effect, and collagen secretion/deposition should be curated separately.

Environmental, lifestyle, infectious, and protective factors

There is no evidence that toxin, infection, smoking, alcohol, diet, occupation, radiation, sex, or another environmental exposure causes BM. Activity, nutrition, respiratory infection, surgery, immobilization, and weight may alter functional burden or complications but do not create the disease. No validated genetic protective allele, modifier gene, diet, medication, or exposure prevents penetrance. Apparent gene–environment effects are therefore best framed as modification of functional reserve, not causation. Avoiding prolonged immobility, maintaining safe activity, and prompt respiratory care are tertiary prevention measures, not primary protection.

3. Phenotypes

Musculoskeletal manifestations

• Axial and proximal weakness: usually mild-to-moderate early, chronic and slowly progressive; pelvic-girdle, shoulder-girdle, neck, and trunk muscles are prominent. Suggested HPO: Proximal muscle weakness, Axial muscle weakness, Muscular hypotonia when present.
• Contractures: long finger flexors/interphalangeal joints are particularly characteristic; elbows, Achilles tendons/ankles, knees, hips, neck, and spine may be involved. Suggested HPO: Flexion contracture of finger, Elbow flexion contracture, Knee flexion contracture, Achilles tendon contracture, Rigid spine (merlini2023newclinicaland pages 1-2, bonnemann2011thecollagenvirelateda pages 6-7).
• Distal hyperlaxity: often more evident in childhood and may transition to contracture with age. Suggested HPO: Distal joint hypermobility (bonnemann2011thecollagenvirelateda pages 1-2).
• Motor delay, difficulty running/climbing stairs/rising, and reduced endurance: variable; walking is usually achieved and retained into adulthood.
• Scoliosis/kyphosis and rigid spine: less severe than in classic Ullrich disease but clinically relevant in some patients.
• Myopathic facies/ptosis: occasional rather than defining. In one mixed 15-patient COL6 cohort, rigid spine occurred in four and myopathic face with ptosis in three (zanotti2023extracellularmatrixdisorganization pages 2-3).

Contemporary quantitative evidence shows that “mild” does not mean trivial. In a 2023 cohort of 33 BM patients, only one-third retained knee-extension strength above 50% predicted and only one-tenth retained elbow-flexion strength above 50%. Forty-five percent had FVC below 70% predicted, and 15% used wheelchairs (merlini2023newclinicaland pages 14-15, merlini2023newclinicaland pages 1-2).

Respiratory manifestations

Restrictive impairment results from respiratory-muscle/diaphragmatic weakness and chest-wall stiffness. Nocturnal hypoventilation, sleep-disordered breathing, ineffective cough, and eventual respiratory insufficiency can occur, although ventilator dependence is much less common than in Ullrich disease. Suggested HPO: Restrictive ventilatory defect, Respiratory insufficiency, Sleep hypoventilation. A 2023 mixed COL6 cohort found restrictive respiratory involvement in 6/15 patients, including two severe cases; one had obstructive sleep apnea (zanotti2023extracellularmatrixdisorganization pages 2-3). Historical expert analysis recommends pulmonary function and sleep monitoring even when limb weakness appears mild (bonnemann2011thecollagenvirelateda pages 6-7).

Skin and connective-tissue manifestations

Follicular hyperkeratosis, abnormal scarring/keloids, soft or velvety skin, and other subtle connective-tissue changes may occur. Skin findings support a COL6 diagnosis and help distinguish it from Emery–Dreifuss muscular dystrophy. Suggested HPO: Follicular hyperkeratosis, Keloids, Abnormality of skin morphology (bonnemann2011thecollagenvirelateda pages 12-14).

Laboratory and cardiac findings

Creatine kinase is often normal or mildly elevated. In a 2023 mixed cohort it was normal in three patients and commonly 2–10× elevated, with an exceptional 60× congenital case; such marked elevation should prompt careful differential diagnosis (zanotti2023extracellularmatrixdisorganization pages 2-3). EMG is usually myopathic and nonspecific. Cardiac disease is not considered a typical direct manifestation: cardiac testing was normal throughout that 2023 cohort, and historical reviews describe only rare possibly coincidental abnormalities (zanotti2023extracellularmatrixdisorganization pages 2-3, bonnemann2011thecollagenvirelateda pages 6-7).

Quality of life

Contractures impair hand use, dressing, transfers, gait, and self-care; weakness and fatigue restrict schooling, employment, recreation, and community participation; respiratory support and orthopedic procedures increase care burden. BM-specific EQ-5D, SF-36, or PROMIS datasets remain sparse. The global registry collects pain, hospitalization, mobility, respiratory, medication, imaging, and quality-of-life data, but mature published BM-specific estimates were unavailable (NCT04020159 chunk 1).

4. Genetic and molecular information

Genes and chromosomes

• COL6A1 and COL6A2: chromosome 21; encode α1(VI) and α2(VI).
• COL6A3: chromosome 2; encodes α3(VI).

COL6A1/A2/A3 form the canonical heterotrimer. Although COL6A4–COL6A6 encode additional collagen-VI-like chains, they are not established primary BM genes. Open Targets reports disease associations only for COL6A1/A2/A3 in BM (OpenTargets Search: Bethlem myopathy-COL6A1,COL6A2,COL6A3).

Variant interpretation

Variants must be classified individually under ACMG/AMP criteria. Important evidence includes rarity, affected-domain location, segregation, de novo status, RNA splicing, collagen-VI secretion/deposition, and microfibril morphology. Germline origin is expected; BM is not a somatic neoplasm. Germline or parental mosaicism is possible and should be considered when an apparently de novo dominant variant recurs, although its frequency is unknown.

Standard sequencing historically detected only approximately 60–65% of clinically diagnosed BM, partly because deep-intronic and copy-number variants were missed. A deep-intronic COL6A2 deletion was detected by custom CGH and shown by RNA analysis to cause monoallelic transcription, illustrating the need for complementary assays (DOI 10.1186/1471-2350-11-44).

Modifiers, epigenetics, and chromosomal abnormalities

Marked intrafamilial variability suggests genetic, developmental, and environmental modifiers, but no modifier gene is clinically validated. There is no established BM-specific epigenetic signature used diagnostically. Large deletions/CNVs involving COL6 loci can be causal, but recurrent aneuploidy, translocation, or inversion is not characteristic. Conventional karyotyping and FISH are therefore low-yield unless another chromosomal disorder is suspected.

5. Environmental information

BM has no infectious agent, zoonotic trigger, toxicant, or occupational cause. Lifestyle does not determine occurrence. Exercise should be individualized: moderate, non-eccentric aerobic activity may support conditioning, whereas overwork, pain-provoking eccentric loading, falls, and prolonged immobilization should be avoided. Vaccination against respiratory pathogens follows standard neuromuscular respiratory-risk practice but does not prevent BM itself.

6. Mechanism and pathophysiology

Upstream causal chain

1. A pathogenic COL6A1/A2/A3 allele alters chain quantity or structure.
2. In the endoplasmic reticulum, α1/α2/α3 chains normally assemble into approximately 500-kDa monomers, then disulfide-linked dimers and tetramers; secreted tetramers form extracellular beaded microfibrils.
3. Mutant or absent chains impair secretion, microfibril assembly, or interaction with collagens I/II, fibronectin, glycosaminoglycans, and proteoglycans.
4. The muscle interstitial/basement-membrane matrix becomes disorganized and mechanically/signally abnormal.
5. Sarcolemmal stress, dysregulated calcium handling, mitochondrial permeability-transition-pore opening, reduced ATP production, and apoptosis injure myofibers.
6. Defective autophagy/mitophagy fails to clear damaged mitochondria; impaired regeneration and fibrosis compound weakness and contractures (castagnaro2018extracellularcollagenvi pages 10-14, bernardi2013mitochondrialdysfunctionand pages 1-2, zanotti2023extracellularmatrixdisorganization pages 1-2).

A 2023 human pathology series directly documented heterogeneous collagen-VI distribution, extracellular-matrix disorganization, sarcolemmal alterations, internal nuclei, fiber-size variation, and interstitial fibrosis. Its abstract states that combined histological, immunological, and ultrastructural methods are “pivotal in the diagnosis of COL6 patients” (published March 2023; DOI 10.3390/ijms24065551) (zanotti2023extracellularmatrixdisorganization pages 2-3, zanotti2023extracellularmatrixdisorganization pages 1-2).

Cellular pathways

Mitochondria and apoptosis. Persistent mPTP opening promotes depolarization, swelling, impaired bioenergetics, and intrinsic apoptosis. Cyclosporin A/cyclophilin-D inhibition normalizes several defects in cells and models, supporting causality rather than mere association (telfer2010zebrafishmodelsof pages 1-2, bernardi2013mitochondrialdysfunctionand pages 1-2, merlini2023newclinicaland pages 1-2).

Autophagy/mitophagy. Reduced BECN1/Beclin-1 and BNIP3 signaling and abnormal AKT–mTOR activity diminish autophagic flux. Dysfunctional mitochondria accumulate, amplifying oxidative and apoptotic stress. Suggested GO: autophagy, mitophagy, regulation of mitochondrial membrane permeability, intrinsic apoptotic signaling (castagnaro2018extracellularcollagenvi pages 10-14).

Regeneration. Collagen VI supports satellite-cell self-renewal and regenerative niches. Deficiency reduces regenerative reserve and delays repair. Suggested cells: fibroblast/fibroadipogenic progenitor, skeletal myofiber, satellite cell; suggested GO: skeletal muscle tissue regeneration (mohassel2023collagentypevi pages 6-10, mohassel2023collagentypevi pages 38-41).

TGF-β signaling—emerging evidence. A June 2023 Col6a2-null mouse preprint proposed that collagen VI regulates TGF-β bioavailability and that matrix deficiency produces early TGF-β dysregulation. This is biologically coherent with fibrosis but remains less established than mitochondrial/autophagy mechanisms and should be annotated as preclinical/emerging (mohassel2023collagentypevi pages 6-10, mohassel2023collagentypevi pages 1-6).

Molecular profiling

Deep RNA profiling of patient and Col6a1-null muscle identified CLOCK and molecular-clock gene signatures (2016; DOI 10.1242/jcs.175927). These are research signatures, not validated biomarkers. Proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, and multi-omic BM-specific datasets remain limited. The principal reproducible biochemical abnormalities are defective collagen deposition, mitochondrial dysfunction, and altered autophagic markers.

7. Anatomical structures affected

The primary organ is skeletal muscle, especially axial, pelvic-girdle, shoulder-girdle, and proximal limb musculature; diaphragm and intercostal muscles may be affected secondarily. Tendons, fascia, joint capsules, skin, and muscle connective tissue contribute to contractures and tissue stiffness. Disease is typically bilateral and relatively symmetric, although severity between muscles varies.

Suggested mappings include UBERON: skeletal muscle tissue, diaphragm, tendon, muscle fascia, joint capsule, skin; CL: fibroblast, skeletal muscle fiber, skeletal muscle satellite cell, fibroadipogenic progenitor; GO cellular components: collagen-containing extracellular matrix, basement membrane, endoplasmic reticulum, mitochondrial inner membrane, autophagosome, lysosome.

8. Temporal development

Onset may be congenital, childhood, adolescent, or adult and is usually insidious. Congenital presentations can include hypotonia, torticollis, hip dislocation, clubfoot, or delayed milestones. Childhood may show distal laxity and modest weakness; contractures become progressively more prominent. Weakness may appear stable or improve around puberty, followed by slow deterioration from the third or fourth decade. Historical series suggest approximately two-thirds of patients older than 60 require some ambulation assistance (bonnemann2011thecollagenvirelateda pages 6-7).

BM is lifelong and generally progressive, not episodic or relapsing-remitting. There is no true spontaneous remission. Critical intervention windows include early maintenance of range of motion, timely correction of function-threatening contractures, and detection of nocturnal hypoventilation before daytime respiratory failure.

9. Inheritance and population

Classic BM is autosomal dominant, frequently with variable expressivity; recessive BM-like presentations are also established. Penetrance is high for many clearly pathogenic dominant variants but can be age-dependent and mild, so apparently unaffected adults need careful examination. Anticipation is not established. Consanguinity increases risk for biallelic disease but is irrelevant to most dominant families.

A Newcastle estimate placed prevalence at 0.77 per 100,000; modern incidence, carrier frequency, and population-specific prevalence are uncertain (bonnemann2011thecollagenvirelateda pages 1-2). There is no established sex bias or endemic geography. Founder variants may occur in individual populations, but most families have private variants. The 2024 report of a recessive COL6A2 splice variant in a consanguineous Saudi family illustrates population-specific ascertainment rather than proven increased regional prevalence.

10. Diagnostics

Clinical assessment

Suspect BM when chronic proximal/axial weakness coexists with long finger-flexor or Achilles contractures, early distal laxity, characteristic skin findings, preserved adult ambulation, and a dominant family history. Assess range of motion, MRC/quantitative strength, gait, transfers, six-minute walk where feasible, pulmonary function sitting and supine, cough strength, oximetry/capnography, and sleep symptoms.

Tests

• CK: normal or mildly elevated in typical disease; marked elevation warrants broader evaluation.
• EMG/NCS: myopathic EMG; nerve conduction usually normal.
• Pulmonary: serial FVC, maximal inspiratory/expiratory pressures, peak cough flow, sleep oximetry/capnography or polysomnography.
• Cardiac: baseline ECG/echocardiogram is reasonable, especially before anesthesia or if symptoms/family history exist, but routine progressive cardiomyopathy is not characteristic.
• Muscle MRI: perifascial fatty/connective-tissue replacement, especially the rectus femoris “central shadow/central cloud” and peripheral vastus lateralis pattern. Ultrasound can show a rectus-femoris central cloud (bonnemann2011thecollagenvirelateda pages 12-14).
• Biopsy: variable myopathic/dystrophic change, fiber-size disproportion, internal nuclei, fibrosis, and relatively limited necrosis. Collagen-VI immunostaining may be subtly abnormal or apparently normal in mild BM, so normal staining does not exclude disease (zanotti2023extracellularmatrixdisorganization pages 1-2, bonnemann2011thecollagenvirelateda pages 12-14).
• Fibroblast assay: dermal fibroblasts can demonstrate abnormal collagen secretion/deposition; RT-PCR can reveal exon skipping or deep-intronic effects (bonnemann2011thecollagenvirelateda pages 14-15).

Genetic testing algorithm

1. Use a neuromuscular/congenital-myopathy panel including COL6A1, COL6A2, COL6A3, with robust CNV calling, or exome/genome sequencing.
2. Confirm and segregate candidate variants; determine de novo versus inherited status.
3. For VUS or negative sequencing with a strong phenotype, add fibroblast collagen studies and RNA sequencing/targeted RT-PCR.
4. Use MLPA, exon-level array/CGH, or genome sequencing for deletions, duplications, structural and deep-intronic variants.
5. WGS is particularly useful after nondiagnostic panel/WES because it interrogates intronic and structural variation. CMA, karyotype, FISH, mtDNA testing, and repeat-expansion testing are not routine unless the phenotype suggests another diagnosis (bonnemann2011thecollagenvirelateda pages 14-15).

Differential diagnosis

Key alternatives are Emery–Dreifuss muscular dystrophy/LMNA-related disease, LAMA2-related dystrophy, SEPN1/SELENON myopathy, RYR1-related congenital myopathy, LMNA congenital muscular dystrophy, other limb-girdle muscular dystrophies, Ehlers–Danlos/connective-tissue disorders, and myosclerosis myopathy. Long finger-flexor contractures, skin changes, collagen-VI MRI pattern, absence of significant primary cardiomyopathy, and COL6 molecular evidence favor BM (bonnemann2011thecollagenvirelateda pages 12-14).

Screening

There is no population or newborn screening program. Once a familial variant is known, cascade testing, targeted prenatal diagnosis, and preimplantation genetic testing are possible. Asymptomatic relatives require age-aware counseling because expression can be subtle.

11. Outcome and prognosis

Life expectancy is often near normal in mild BM if respiratory complications are recognized, but robust survival-rate or mortality estimates are unavailable. Most patients remain ambulant into adulthood; late walking aids or wheelchair use occur. In the 2023 cohort, wheelchair use was 15%, underscoring a broader severity range than historic pre-molecular series (merlini2023newclinicaland pages 14-15).

Major morbidity includes progressive weakness, hand and lower-limb contractures, falls, reduced endurance, scoliosis/rigid spine, pain, impaired self-care, and restrictive respiratory disease. Cardiac mortality is not typical. Prognostic factors include respiratory trajectory, severity and distribution of contractures, quantitative strength, mutation mechanism, and phenotype position within the COL6 continuum. No validated circulating prognostic biomarker exists. Collagen immunofluorescence correlates with phenotype at group level but is age-dependent and unsuitable as a stand-alone prognostic marker: serial biopsies showed increasing expression over time, an important consideration for genetic-correction trials (merlini2023newclinicaland pages 14-15, merlini2023newclinicaland pages 1-2).

12. Treatment and current applications

Standard supportive care

• Physiotherapy and occupational therapy: daily gentle stretching, range-of-motion maintenance, posture, safe low-impact aerobic conditioning, energy conservation, and adaptive equipment. Suggested NCIT concepts: Physical Therapy, Occupational Therapy, Exercise Intervention.
• Splints/orthoses: dynamic finger splints and ankle-foot orthoses where tolerated. Suggested NCIT: Splinting, Orthotic Device.
• Orthopedic surgery: selected Achilles-tendon or other contracture release may preserve walking, but recurrence is common; scoliosis bracing is temporizing and surgery requires specialist respiratory/anesthetic planning (bonnemann2011thecollagenvirelateda pages 14-15).
• Respiratory care: regular pulmonary/sleep surveillance, airway-clearance support, cough-assist when indicated, prompt infection treatment, and nocturnal noninvasive ventilation for hypoventilation. Suggested NCIT: Pulmonary Function Test, Noninvasive Ventilation.
• Nutrition/pain/bone health: maintain healthy weight and adequate nutrition; treat pain and osteoporosis risk conventionally. Avoid unmonitored protein restriction.

Experimental pharmacologic and nutritional strategies

Cyclosporin A and non-immunosuppressive cyclophilin inhibitors. Human proof-of-concept and animal/cellular studies show correction of mitochondrial dysfunction and apoptosis, but immunosuppression and limited clinical efficacy evidence preclude routine disease-modifying use. NIM811 and related mPTP modulators remain preclinical (bernardi2013mitochondrialdysfunctionand pages 1-2, merlini2023newclinicaland pages 1-2).

Autophagy activation. A one-year pilot low-protein diet increased autophagic markers and was reported safe/tolerable in seven analyzed adults, with preserved body composition and function and reduced myofiber apoptosis. The abstract states: “These data provide evidence that a low-protein diet is able to activate autophagy and is safe and tolerable in patients with COL6 myopathies” (published November 2016; DOI 10.1080/15548627.2016.1231279). This was mechanistic proof-of-concept, not evidence for routine clinical efficacy. Pterostilbene improved pathology in Col6-deficient mice but remains preclinical.

Gene/RNA therapy. Allele-specific silencing, splice correction, and CRISPR disruption/correction are experimental. A November 2024 fibroblast study achieved 32% editing of a dominant mutant COL6A1 allele with negligible wild-type editing and restored collagen secretion and microfibril ultrastructure; it involved UCMD fibroblasts, so translation to BM and muscle in vivo remains unproven (DOI 10.3390/biom14111412).

There is no established pharmacogenomic dosing algorithm, approved gene therapy, cell therapy, ASO, or combination regimen for BM.

Clinical studies and real-world infrastructure

• NCT01438788: completed Phase II, open-label low-protein-diet pilot; eight adults; 0.6–0.8 g protein/kg/day; Beclin-1/autophagy endpoint (NCT01438788 chunk 1). URL: https://clinicaltrials.gov/study/NCT01438788
• NCT03693898: diagnostic MRI study, planned n=20 adults with BM/Ullrich disease; Dixon MRI fat fraction and strength testing (NCT03693898 chunk 1). URL: https://clinicaltrials.gov/study/NCT03693898
• NCT04020159: prospective Global Registry for COL6-related Dystrophies, target n=1,000; annual genetics, motor, respiratory, contracture, pain, hospitalization, QoL, medication, and imaging data (NCT04020159 chunk 1). URL: https://clinicaltrials.gov/study/NCT04020159

Status labels should be rechecked live because registry records retrieved here had differing historical and aggregate status displays.

13. Prevention

Primary prevention through lifestyle or vaccination is impossible because BM is genetic. Secondary prevention consists of family recognition, cascade testing, early molecular diagnosis, and surveillance before irreversible contractures or respiratory failure. Tertiary prevention includes stretching/orthoses, fall prevention, bone health, respiratory vaccination, airway clearance, sleep assessment, and timely ventilation.

Genetic counseling should cover autosomal-dominant and recessive possibilities, variable expressivity, de novo and mosaic recurrence risk, and reproductive options. Targeted prenatal diagnosis and preimplantation genetic testing are possible once the familial pathogenic variant is established; older approaches included haplotype analysis and chorionic-villus collagen-VI staining (bonnemann2011thecollagenvirelateda pages 14-15).

14. Other species and natural disease

The causal genes are evolutionarily conserved across vertebrates. Relevant taxa include Mus musculus (NCBI Taxon 10090) and Danio rerio (7955). No well-established naturally occurring companion-animal or wildlife disease equivalent to human Bethlem myopathy was identified in the retrieved literature; veterinary breed ontology mapping is therefore not applicable. BM is not transmissible or zoonotic.

15. Model organisms and experimental systems

Mouse

Col6a1−/− mice lack collagen-VI assembly/secretion and show myopathy, abnormal mitochondria, spontaneous myofiber apoptosis, defective autophagy/mitophagy, and impaired regeneration. They are highly useful for mechanistic and drug studies but have a milder motor phenotype than severe human COL6 disease (castagnaro2018extracellularcollagenvi pages 10-14, bernardi2013mitochondrialdysfunctionand pages 1-2).

A Col6a2−/− model, characterized in 2023, showed early postnatal atrophy and weakness, fiber-size variability, central nuclei, delayed regeneration, sarcolemmal fragility, and altered TGF-β bioavailability. This supports matrix-signaling and non-cell-autonomous mechanisms; the work was initially reported as a preprint and requires appropriate evidence grading (mohassel2023collagentypevi pages 6-10, mohassel2023collagentypevi pages 1-6).

Zebrafish

Exon-specific col6a1 morphants produced severe UCMD-like disease when exon 9 was targeted and a milder BM-like phenotype with exon 13 targeting. Severe morphants had abnormal mitochondria and increased cell death; cyclosporin A improved motor function but not sarcolemmal membrane damage. The model is valuable for rapid in-vivo pharmacology but transient morpholino biology and developmental timing limit direct human extrapolation. The abstract reports that the authors generated “zebrafish models of the collagen VI myopathies” and that CsA “improved the motor deficits” in the severe model (published March 2010; DOI 10.1093/hmg/ddq126) (telfer2010zebrafishmodelsof pages 1-2).

Cellular systems

Patient dermal fibroblasts and myoblasts support collagen secretion/deposition assays, RNA studies, mitochondrial/autophagy phenotyping, and editing experiments. Col6a1-null mouse fibroblasts show impaired autophagosome clearance, defective Parkin-dependent mitophagy, AKT–mTOR activation, and increased apoptosis under nutrient stress; adhesion to purified collagen VI improves autophagic flux, demonstrating an extracellular instructive signal (castagnaro2018extracellularcollagenvi pages 10-14). Patient-derived iPSC, organoid, single-cell, and spatial models are promising but not yet mature enough for routine BM annotation.

Recent developments, expert interpretation, and evidence gaps

The strongest 2023 clinical advance was quantitative phenotyping in a 69-person COL6 cohort, including 33 BM patients. It demonstrated unexpectedly substantial strength and pulmonary deficits and age-dependent collagen-VI immunofluorescence, directly affecting endpoint and biopsy interpretation in future trials (merlini2023newclinicaland pages 14-15, merlini2023newclinicaland pages 1-2). A separate March 2023 human study identified three previously unreported variants among 14 pathogenic variants and emphasized integrating genetics with histology, immunology, and ultrastructure (zanotti2023extracellularmatrixdisorganization pages 2-3, zanotti2023extracellularmatrixdisorganization pages 1-2). Emerging 2023 work links collagen VI to TGF-β bioavailability, while 2024 CRISPR work provides allele-selective fibroblast rescue; both are translationally important but not clinical therapies.

Authoritative expert consensus is that BM should be managed as a multisystem neuromuscular/connective-tissue disorder, not dismissed as a benign contracture syndrome. Key unresolved issues are contemporary prevalence and incidence, variant-specific penetrance, validated BM-specific patient-reported outcomes, prospective respiratory trajectories, circulating biomarkers, and controlled disease-modifying trials. Most mechanistic data derive from mixed COL6 phenotypes or models; phenotype-specific extrapolation should therefore be labeled explicitly.

Selected primary/recent sources

1. Merlini L et al. New Clinical and Immunofluorescence Data of Collagen VI-Related Myopathy: A Single Center Cohort of 69 Patients. August 2023. DOI/URL: https://doi.org/10.3390/ijms241512474 (merlini2023newclinicaland pages 14-15, merlini2023newclinicaland pages 1-2)
2. Zanotti S et al. Extracellular Matrix Disorganization and Sarcolemmal Alterations in COL6-Related Myopathy Patients with New Variants of COL6 Genes. March 2023. DOI/URL: https://doi.org/10.3390/ijms24065551 (zanotti2023extracellularmatrixdisorganization pages 2-3, zanotti2023extracellularmatrixdisorganization pages 1-2)
3. Mohassel P et al. Collagen type VI regulates TGFβ bioavailability in skeletal muscle. June 2023 preprint. DOI/URL: https://doi.org/10.1101/2023.06.22.545964 (mohassel2023collagentypevi pages 6-10, mohassel2023collagentypevi pages 1-6)
4. Telfer WR et al. Zebrafish models of collagen VI-related myopathies. March 2010. DOI/URL: https://doi.org/10.1093/hmg/ddq126 (telfer2010zebrafishmodelsof pages 1-2)
5. Bernardi P, Bonaldo P. Mitochondrial dysfunction and defective autophagy in the pathogenesis of collagen VI muscular dystrophies. May 2013. DOI/URL: https://doi.org/10.1101/cshperspect.a011387 (bernardi2013mitochondrialdysfunctionand pages 1-2)

PMID note: PMID values were not consistently exposed in the retrieved full-text metadata. To avoid erroneous identifiers, DOI and direct registry URLs are supplied above; database curators should resolve PMIDs through Crossref/PubMed during ingestion.

References

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