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Inheritance

2

Autosomal dominant HP:0000006

FSHD usually follows autosomal dominant inheritance, although penetrance and severity are variable. Most FSHD1 probands inherit the contracted allele, but a substantial minority arise de novo, and a notable share of those are somatic/germline mosaic rather than fully constitutional - which is why an apparently unaffected parent does not exclude transmission risk.

Autosomal dominant inheritance De novo rate: 10-30% in FSHD1 (de novo constitutional or mosaic D4Z4 contraction)

Show evidence (4 references)

PMID:17924332 SUPPORT Human Clinical

"Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is mainly characterized by progressive wasting and weakness of the facial, shoulder, and upper-arm muscles."

Human genetic study directly states the canonical autosomal dominant inheritance pattern of FSHD.

PMID:20301616 SUPPORT Human Clinical

"Each offspring of a proband with FSHD1 has a 50% chance of inheriting the pathogenic D4Z4 repeat array contraction."

GeneReviews genetic-counseling guidance states the recurrence risk to offspring in FSHD1.

PMID:20301616 SUPPORT Human Clinical

"Approximately 70%-90% of individuals diagnosed with FSHD1 have a parent with clinical findings of FSHD and one D4Z4 repeat array with a pathogenic contraction"

Quantifies the inherited proportion of FSHD1, the complement of the de novo rate recorded below.

+ 1 more reference

Digenic inheritance (FSHD2) HP:0010984

FSHD2 arises digenically: disease requires both an SMCHD1 (or other chromatin-modifier) mutation and, in trans, an FSHD-permissive 4qA D4Z4 haplotype carrying the DUX4 polyadenylation signal. Neither locus alone is sufficient to cause disease.

Digenic inheritance

Show evidence (1 reference)

PMID:23143600 SUPPORT Human Clinical

"FSHD2 occurs in individuals who inherited both the SMCHD1 mutation and a normal-sized D4Z4 array on a chromosome 4 haplotype permissive for DUX4 expression."

This study defines FSHD2 as digenic, requiring both an SMCHD1 mutation and an FSHD-permissive D4Z4 haplotype.

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Subtypes

3

FSHD1 MONDO:0008030

DUX4 hgnc:50800

Classic form caused by contraction of the D4Z4 repeat array on a permissive chromosome 4qA background. This accounts for the large majority of genetically confirmed FSHD.

Show evidence (1 reference)

PMID:17924332 SUPPORT Human Clinical

"Yet only repeat contractions of D4Z4 on chromosome 4qA cause FSHD; contractions on the other chromosomes are nonpathogenic."

Establishes the 4q35 D4Z4 contraction on a permissive 4qA haplotype as the genetic basis of FSHD1.

FSHD2 MONDO:0008031

SMCHD1 hgnc:29090 DNMT3B hgnc:2979 LRIF1 hgnc:30299 DUX4 hgnc:50800

Contraction-independent form with D4Z4 hypomethylation on a permissive 4qA background, usually associated with pathogenic variants in chromatin repressors such as SMCHD1.

Show evidence (1 reference)

PMID:19728363 SUPPORT Human Clinical

"In 15 FSHD families without D4Z4 contractions but with at least one 4qA161 haplotype (FSHD2), we observed D4Z4-restricted hypomethylation on chromosomes 4q and 10q."

Defines the contraction-independent epigenetic FSHD2 phenotype with shared D4Z4 hypomethylation.

FSHD4 (DNMT3B-related, digenic) MONDO:0030355

DNMT3B hgnc:2979 DUX4 hgnc:50800 Digenic inheritance

FSHD4 is the DNMT3B-associated, contraction-independent form of FSHD. It is digenic in the strict sense: disease requires a heterozygous DNMT3B variant that relaxes DNA methylation across the D4Z4 macrosatellite, together with an FSHD-permissive 4qA chromosome inherited in trans that supplies the pLAM polyadenylation signal stabilising the distal DUX4 transcript. Neither genotype alone causes disease, and not every double-genotype carrier in the two originally reported families was affected. Under the methylation-based diagnostic scheme GeneReviews uses, these individuals are classified clinically as FSHD2; OMIM and MONDO instead number the entity by its causal chromatin-modifier gene, and MONDO:0030355 is that DNMT3B-specific number.

Show evidence (3 references)

PMID:27153398 SUPPORT Human Clinical

"Here, we show that heterozygous mutations in DNA methyltransferase 3B (DNMT3B) are a likely cause of D4Z4 derepression associated with low levels of DUX4 expression from the D4Z4 repeat and increased penetrance of FSHD."

The report that established DNMT3B as an FSHD chromatin-modifier locus, and so the basis for a DNMT3B-specific subtype at all.

PMID:34711481 SUPPORT REVIEW SYNTHESIS Human Clinical

"These include the finding that FSHD2 is a digenic disease and that mutations in the genes SMCHD1, DNMT3B, and more recently LRIF1, can cause FSHD2."

A review states that DNMT3B belongs to the same digenic, contraction-independent group as SMCHD1 and LRIF1, which is why this subtype sits inside the FSHD entry rather than standing alone.

PMID:34711481 SUPPORT REVIEW SYNTHESIS Human Clinical

"Phenotypically FSHD2 shows virtually no difference from FSHD1 and both forms of FSHD arise via a common downstream mechanism of epigenetic derepression of the transcription factor DUX4 in skeletal muscle cells."

Sources the statement that no distinguishing clinical phenotype separates this subtype from the rest of FSHD, which is why no phenotype in this entry is scoped to FSHD4.

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Discussions and Knowledge Gaps

2

Why do the symptoms patients rank as most burdensome in FSHD - fatigue, pain, and sleep disturbance - remain mechanistically unexplained and largely absent from the causal pathograph, which currently derives all clinical consequences from myofiber loss?

KNOWLEDGE GAP OPEN fshd_invisible_symptom_burden

Attached to

pathophysiology#Progressive Myofiber Loss and Fatty Replacement

Patient-reported outcome studies rank fatigue (93.8%) and pain (87.7%) at nearly the same prevalence as shoulder/arm weakness (96.9%), and a patient-led narrative review names pain, fatigue, and sleep disturbance as the "invisible symptoms" that biomedical outcome measures fail to capture. Yet no mechanistic edge in this entry explains them: they are currently modelled only as downstream consequences of biomechanical strain. Candidate contributors that would change management include sleep-disordered breathing (OSA in 55% and nocturnal hypoventilation in 26% of symptomatic patients), central pain sensitization, and deconditioning. Distinguishing these matters because each has a different, already-available treatment.

Proposed experiments

Unselected-cohort polysomnography with transcutaneous capnometry

exp_fshd_unselected_polysomnography

Perform polysomnography with transcutaneous capnometry in an unselected genetically confirmed FSHD cohort to establish the true population prevalence of obstructive sleep apnea and nocturnal hypoventilation, and correlate it with validated fatigue scores. Existing prevalence figures come from a symptom-selected sleep-laboratory referral cohort.

Quantitative sensory testing of FSHD chronic pain

exp_fshd_central_sensitization_qst

Apply quantitative sensory testing to determine whether FSHD chronic pain carries a central sensitization signature distinct from nociceptive pain attributable to biomechanical strain, which would redirect analgesic strategy.

Mediation analysis of patient-reported fatigue

exp_fshd_fatigue_mediation

In a longitudinal FSHD registry, test how much patient-reported fatigue is explained by sleep-disordered breathing, muscle involvement, and mood respectively, to identify the dominant treatable contributor.

Recorded from a community-source sweep (FSHD Society patient-education pages and the r/FSHD subreddit) cross-checked against patient-reported outcome literature. The r/FSHD listing discusses chronic pain and fatigue together as a single linked problem, consistent with the patient-reported outcome literature above; that listing is recorded as an aggregate community-discussion topic under `references` rather than as an evidence snippet, because a forum topic title is a label and not a claim-bearing sentence. No individual's personal health narrative is quoted.

Show evidence (2 references)

PMID:42485801 SUPPORT Human Clinical

"Facioscapulohumeral muscular dystrophy (FSHD) is associated with substantial psychosocial challenges not fully captured by traditional biomedical outcomes, including challenges that may persist despite stable clinical or QoL scores."

A patient-led review states directly that standard biomedical outcomes miss a substantial part of FSHD disease burden, which is the gap this discussion records.

PMID:42485801 SUPPORT Human Clinical

"the impact of invisible symptoms, including pain, fatigue, and sleep disturbance"

Names the specific symptom triad that the patient community prioritizes and that this entry's causal model does not yet explain.

Of the recurring community-reported complaints in FSHD that standard clinical descriptions omit - headache/migraine, fasciculations, and low serum aldolase - which are genuine disease associations, which are secondary and treatable (for example morning headache from nocturnal hypoventilation), and which are coincidental?

OPEN QUESTION OPEN fshd_community_reported_unvalidated_signals

Attached to

pathophysiology#Progressive Myofiber Loss and Fatty Replacement

Reading the r/FSHD patient community listings surfaced topics with no counterpart in standard FSHD clinical descriptions. Forum threads are anecdotal, self-selected, and not diagnostically verified, so they were treated as hypothesis-generating leads and checked against the literature rather than curated directly. One lead has since been PARTLY resolved and promoted to a curated phenotype: head pain. The Dutch FSHD Registry reports 52% for a COMBINED head-and-shoulder pain category in 373 participants. That establishes head-region pain as a real component of FSHD pain burden and justifies curating the Headache phenotype, but it does NOT isolate a head-specific rate - given FSHD's scapular dominance an unknown and plausibly majority share of that 52% is shoulder pain - so no frequency band is asserted. The mechanism also remains open: postural strain from cervical and axial weakness versus morning headache from nocturnal hypoventilation, which is documented in FSHD and under-detected by oximetry. Resolving that matters clinically because the second is treatable with ventilatory support. Note the community term "migraine" is broader than what the registry documents, so a true primary-migraine association remains unestablished. Two leads remain UNVALIDATED and are deliberately NOT curated as phenotypes. Fasciculations are not a recognized FSHD feature and would more typically prompt evaluation for a motor neuron disorder, so this signal may reflect diagnostic uncertainty within the community rather than FSHD biology. Low serum aldolase has no reported FSHD association at all. This entry is a worked example of the intended workflow: community sources generate candidate signals, literature adjudicates them, and only the adjudicated ones become phenotypes.

Proposed experiments

Headache phenotyping with overnight capnometry

exp_fshd_morning_headache_capnometry

Perform structured headache phenotyping together with overnight transcutaneous capnometry in FSHD patients reporting morning headache, to test whether the community headache signal is explained by nocturnal hypoventilation rather than primary migraine.

Registry prevalence of migraine and fasciculations

exp_fshd_registry_migraine_fasciculation_prevalence

Compare the prevalence of migraine and clinically confirmed fasciculations in genetically confirmed FSHD against matched controls in a disease registry, to determine whether either is a true association.

Social-media content is used here strictly as hypothesis-generating signal. Per dismech evidence policy these leads are not promoted to curated phenotypes without independent clinical evidence. The two unvalidated leads were observed as r/FSHD discussion topics titled "Migraines" and "Fasicuclations" (spelling as posted; single-snapshot observation of the community listing, not a demonstrated recurrence). Those bare topic titles are recorded here in prose and under `references` rather than as evidence snippets: a forum topic title is a label, not a claim-bearing sentence, so it cannot support or refute anything.

Show evidence (1 reference)

PMID:31025273 SUPPORT INDIRECT Human Clinical

"Indications for admission included non-restorative sleep, morning headache, or excessive daytime"

Supplies the candidate mechanistic explanation - morning headache as a symptom of nocturnal hypoventilation - for part of the community headache signal.

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Pathophysiology

5

DNMT3B-Dependent D4Z4 Methylation Failure

The FSHD4 derepressing lesion. A heterozygous DNMT3B variant lowers de novo cytosine methylation across the D4Z4 macrosatellite even though the repeat array is of normal length, so the array loses methylation-dependent repression without any contraction. This is one of the two events FSHD4 requires; on its own it produces hypomethylation without disease.

DNMT3B hgnc:2979

DNMT3B de novo cytosine methyltransferase activity at D4Z4 GO:0003886 ↓ DECREASED

Downstream

D4Z4 Epigenetic Derepression Loss of DNMT3B-dependent methylation at D4Z4 is one route into the shared chromatin-relaxation node, alongside repeat contraction and the other chromatin-modifier loci.

Show evidence (2 references)

PMID:27153398 SUPPORT Human Clinical

"Here, we show that heterozygous mutations in DNA methyltransferase 3B (DNMT3B) are a likely cause of D4Z4 derepression associated with low levels of DUX4 expression from the D4Z4 repeat and increased penetrance of FSHD."

Establishes heterozygous DNMT3B variants as a cause of D4Z4 derepression in humans, which is the claim this node makes.

PMID:33004076 SUPPORT In Vitro

"In mESCs derived from D4Z4-2.5 mice, Dnmt3b was enriched at the D4Z4 repeat array and DUX4 transcript levels were upregulated after a knockdown of Dnmt3b."

Shows Dnmt3b occupying the D4Z4 array and its loss raising DUX4 transcript, which is the molecular action this node asserts, in a cell-based system.

Permissive 4qA Polyadenylation Signal

The second locus, and the reason FSHD4 is digenic rather than dominant at one gene. Only a 4qA subtelomere carries the pLAM polyadenylation signal immediately distal to the last D4Z4 unit; on that background the distal DUX4 transcript is efficiently polyadenylated and stable enough to persist in somatic cells, whereas non-permissive 4qB and chromosome 10q backgrounds lack a usable signal. It is modelled separately from the derepressing lesion because the two segregate independently and disease needs both: a DNMT3B variant without a permissive allele derepresses an array whose transcript cannot be stabilised.

DUX4 hgnc:50800

polyadenylation of the distal DUX4 transcript at pLAM GO:0180010 ↑ INCREASED stabilisation of the distal DUX4 message GO:0048255 ↑ INCREASED

Downstream

DUX4 Misexpression in Skeletal Muscle The permissive polyadenylation signal acts at the transcript, not at the chromatin: it converts derepression of the array into a stable DUX4 message in muscle. Without it, derepression alone does not yield accumulating DUX4.

Show evidence (3 references)

PMID:20724583 SUPPORT Human Clinical

"This FSHD-predisposing configuration creates a canonical polyadenylation signal for transcripts derived from DUX4, a double homeobox gene of unknown function that straddles the last repeat unit and the adjacent sequence."

Identifies the permissive haplotype's contribution as a polyadenylation signal for DUX4, which is what this node represents.

PMID:20724583 SUPPORT In Vitro

"Transfection studies revealed that DUX4 transcripts are efficiently polyadenylated and are more stable when expressed from permissive chromosomes."

Cell-based demonstration that the permissive allele, not the repeat itself, is what makes the DUX4 message stable.

PMID:33004076 SUPPORT BACKGROUND Human Clinical

"A prerequisite for the expression of DUX4 is the presence of a polyadenylation signal to stabilize the mRNA transcript in somatic cells that is only present on 4qA alleles"

States the permissive allele as a prerequisite, which is the necessity claim that makes this a separate required node rather than a modifier. The sentence is introductory background in a mouse paper and describes human genetics.

D4Z4 Epigenetic Derepression

FSHD develops when D4Z4 contraction or contraction-independent hypomethylation occurs on a permissive 4qA subtelomere, relaxing chromatin and enabling pathogenic DUX4 expression.

DUX4 hgnc:50800 SMCHD1 hgnc:29090 DNMT3B hgnc:2979 LRIF1 hgnc:30299

Animal models

D4Z4-2.5/Dnmt3bMommeD14 transgenic mouse Mouse partially recapitulates The methylation half of the lesion does transfer: losing Dnmt3b demethylates the D4Z4 array in this mouse, and DUX4 rises, but in secondary lymphoid organs rather than muscle.

Downstream

DUX4 Misexpression in Skeletal Muscle Loss of repression at the FSHD locus permits aberrant DUX4 expression in differentiated skeletal muscle.

Sensorineural hearing impairment Severe early-onset FSHD with large 4q35 deletions can include sensorineural hearing loss through extra-muscular intermediates not represented in the skeletal-muscle pathograph.

Retinal vasculopathy Retinal vasculopathy travels with the same large-deletion, early-onset end of the D4Z4 contraction spectrum as hearing loss, so it is placed here alongside it rather than downstream of myofiber loss.

Show evidence (2 references)

PMID:19728363 SUPPORT Human Clinical

"To develop FSHD, D4Z4 contraction needs to occur on a specific genetic background. Only contractions associated with the 4qA161 haplotype cause FSHD."

Establishes that pathogenic D4Z4 contraction requires a permissive 4qA background rather than repeat size alone.

PMID:29478599 SUPPORT Human Clinical

"Recent studies demonstrate that contraction in the number of D4Z4 repeats results in chromatin relaxation and transcriptional de-repression of DUX4, a gene normally expressed only in the germline."

Summarizes the central epigenetic lesion linking D4Z4 contraction to pathogenic DUX4 derepression.

DUX4 Misexpression in Skeletal Muscle

Intermittent DUX4 expression in skeletal muscle activates an embryonic transcriptional program and promotes muscle fiber toxicity and death.

Skeletal Muscle Fiber CL:0000188

DUX4 hgnc:50800 ↑ INCREASED

apoptotic process GO:0006915

Animal models

D4Z4-2.5/Dnmt3bMommeD14 transgenic mouse Mouse fails to recapitulate Reducing Dnmt3b on an FSHD-sized D4Z4 background did not raise DUX4 transcript in skeletal muscle and produced no muscle pathology, so this model does not reproduce the node it was built to test.

Downstream

Progressive Myofiber Loss and Fatty Replacement Recurrent DUX4-mediated injury drives chronic muscle degeneration with incomplete repair and replacement by fat and fibrous tissue.

Show evidence (1 reference)

PMID:32576599 SUPPORT In Vitro

"Facioscapulohumeral muscular dystrophy (FSHD) is caused by the loss of repression at the D4Z4 locus leading to aberrant double homeobox 4 (DUX4) expression in skeletal muscle. Activation of this early embryonic transcription factor results in the expression of its target genes causing muscle fiber death."

Patient-derived myotube work directly connects DUX4 activation to the downstream transcriptional program and muscle-cell toxicity.

Progressive Myofiber Loss and Fatty Replacement

The clinical pattern of FSHD reflects chronic degeneration of selected facial, scapular, humeral, truncal, and lower-extremity muscles, usually with marked asymmetry and variable progression.

Downstream

Facial weakness Early involvement of the muscles of facial expression contributes to incomplete eye closure, poor smile excursion, and facial asymmetry.

Scapular winging Periscapular weakness destabilizes the scapulothoracic joint and limits active shoulder elevation.

Muscle weakness Progressive weakness extends to upper arm, trunk, pelvic-girdle, and distal lower-extremity muscles.

Myalgia Chronic biomechanical strain and ongoing muscle pathology contribute to frequent shoulder and low-back pain.

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"FSHD symptoms usually start around the second decade and are most commonly characterized by asymmetric weakness affecting the face, shoulder, and arms, followed by the distal lower extremities and pelvic girdle."

Registry-based clinical data capture the stereotyped anatomic spread and asymmetry of muscle involvement in FSHD.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

22

Cardiovascular 5

Atrial fibrillation OCCASIONAL HP:0005110

Show evidence (2 references)

PMID:34108930 SUPPORT Human Clinical

"Atrial fibrillation or flutter were seen in 5% of patients."

Review of 104 genetically confirmed patients quantifies atrial arrhythmia at 5%, within the OCCASIONAL band (5-29%).

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Mild heart rhythm problems (happens in 5-9% of people)"

Patient organization communicates a 5-9% frequency of mild rhythm disturbance, concordant with the OCCASIONAL band.

Atrial flutter HP:0004749

Show evidence (1 reference)

PMID:34108930 SUPPORT INDIRECT Human Clinical

"Atrial fibrillation or flutter were seen in 5% of patients."

The 5% figure is reported for atrial fibrillation OR flutter combined, so it bounds but does not isolate the flutter-specific rate; the support for flutter is therefore indirect.

Complete right bundle branch block OCCASIONAL HP:0011712

Show evidence (1 reference)

PMID:34108930 SUPPORT Human Clinical

"The most common conduction abnormality was complete (7%) or incomplete (5%) right bundle branch block (RBBB)."

Quantifies complete RBBB at 7% in 104 genetically confirmed patients, within the OCCASIONAL band (5-29%).

Retinal telangiectasia FREQUENT HP:0007763

Denotes the usually asymptomatic angiographic finding. The rare, sight-threatening Coats-like exudative form is recorded separately under the Retinal vasculopathy phenotype.

Show evidence (4 references)

PMID:23573590 SUPPORT Human Clinical

"A mild to moderate retinal vasculopathy, consisting of retinal teleangiectasis and microaneursyms, was present in 18 of 37 evaluable angiograms (49%)"

Fluorescein angiography in 39 patients found retinal telangiectasia in 49%, supporting the FREQUENT band (30-79%).

PMID:36900126 SUPPORT Human Clinical

"Increased tortuosity of the retinal arteries was qualitatively observed in 77% of the included eyes."

Modern OCT-angiography series corroborates a high prevalence of subclinical retinal vascular abnormality.

PMID:20301616 SUPPORT Human Clinical

"annual dilated ophthalmoscopy in individuals with early childhood-onset FSHD with large pathogenic contraction of D4Z4 and adults with visual symptoms"

GeneReviews surveillance guidance establishes retinal vasculopathy as an actionable extra-muscular manifestation requiring screening.

+ 1 more reference

Retinal vasculopathy VERY_RARE Abnormal retinal vascular morphology HP:0008046

Denotes the clinically significant, Coats-like exudative vasculopathy. The far commoner asymptomatic retinal telangiectasia seen on fluorescein angiography (about half of patients) is recorded separately under the Retinal telangiectasia phenotype; the two carry different frequency bands because they measure different things.

Show evidence (3 references)

PMID:30923442 SUPPORT Human Clinical

"early-onset FSHD is associated with a large deletion of D4Z4 repeats and a more severe disease phenotype, including early loss of independent ambulation as well as extramuscular manifestations, such as retinal vasculopathy, hearing loss, and central nervous system (CNS) involvement"

Places retinal vasculopathy among the extramuscular features and ties it to large D4Z4 deletions.

PMID:30923442 SUPPORT Human Clinical

"patients with FSHD had retinal vasculopathy with features resembling Coats"

Characterizes the vasculopathy as Coats-like, which is the specific ophthalmologic pattern described.

PMID:30923442 SUPPORT DIRECT REVIEW SYNTHESIS Human Clinical

"Tawil et al concluded that although up to 25% (95% CI: 20.9–30.8%) of patients with FSHD had abnormalities on retinal examination, only 0.6% (95% CI: 0.2–1.5%) had symptomatic retinal disease"

Quantifies the symptomatic, Coats-like vasculopathy this node denotes at well under 5% (0.6%; the same review also cites 1.7% in a Dutch population survey and 0.8% in FSHD1), supporting the VERY_RARE band. The 25% examination-abnormality figure belongs to the asymptomatic telangiectasia recorded under the Retinal telangiectasia phenotype.

Ear 1

Sensorineural hearing impairment OCCASIONAL HP:0000407

Show evidence (2 references)

PMID:19049553 SUPPORT Human Clinical

"Sensorineural hearing loss was found in four patients, who presented infantile-onset dystrophic phenotype."

Supports hearing loss as a recognized extra-muscular phenotype in severe early-onset FSHD with large 4q35 deletions.

PMID:40879179 SUPPORT Human Clinical

"Hearing loss (13%; n = 71) was the most frequently reported comorbidity, followed by retinal abnormalities"

Population-based MD STARnet surveillance data (n=548) quantify clinically diagnosed hearing loss at 13%, supporting the OCCASIONAL band (5-29%) and making it the most common extra-muscular comorbidity of FSHD.

Head and Neck 2

Facial weakness VERY_FREQUENT Weakness of facial musculature HP:0030319

Show evidence (2 references)

PMID:17924332 SUPPORT Human Clinical

"Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is mainly characterized by progressive wasting and weakness of the facial, shoulder, and upper-arm muscles."

This classic genetic study summarizes the canonical early distribution of weakness in FSHD.

PMID:39297366 SUPPORT Human Clinical

"of whom 92% showed signs of facial weakness"

Muscle-ultrasound study of 107 participants quantifies facial weakness at 92%, supporting the VERY_FREQUENT band (80-100%), and extends the phenotype to specific orofacial muscles (zygomaticus minor most often affected) that are not captured by standard facial weakness scoring.

Lagophthalmos HP:0030001

Show evidence (2 references)

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Eyes that don’t fully close during sleep"

Patient organization symptom list documents incomplete eye closure during sleep as a recognized FSHD manifestation.

PMID:20301616 SUPPORT Human Clinical

"ocular lubricants or taping the eyes shut during sleep to treat exposure keratitis"

GeneReviews management guidance confirms incomplete eyelid closure and its corneal-exposure consequence as an expected feature requiring treatment.

Limbs 2

Scapular winging VERY_FREQUENT HP:0003691

Show evidence (1 reference)

PMID:18056023 SUPPORT Human Clinical

"Participants: Thirteen patients with bilateral winged scapula affected by facioscapulohumeral muscular dystrophy."

Surgical series directly documents scapular winging as a common and functionally important manifestation of FSHD.

Foot dorsiflexor weakness HP:0009027

Show evidence (2 references)

PMID:20301616 SUPPORT Human Clinical

"Facioscapulohumeral muscular dystrophy (FSHD) typically presents with weakness of the facial muscles, the stabilizers of the scapula, and/or the dorsiflexors of the foot."

GeneReviews places foot dorsiflexor weakness among the canonical presenting features of FSHD.

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Foot drop (trouble lifting the foot)"

Patient organization symptom list documents foot drop as a recognized manifestation communicated to the patient community.

Musculoskeletal 5

Muscle weakness VERY_FREQUENT HP:0001324

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"FSHD symptoms usually start around the second decade and are most commonly characterized by asymmetric weakness affecting the face, shoulder, and arms, followed by the distal lower extremities and pelvic girdle."

Supports both the distribution and the asymmetric progression of weakness in FSHD.

Abdominal wall muscle weakness HP:0009023

Show evidence (1 reference)

PMID:31409737 SUPPORT INDIRECT Human Clinical

"The symptomatic themes with the highest prevalence in our sample were problems with shoulders or arms (96.9%), limitations with activities (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with mobility and walking (93.6%), changed body image due to the disease (91.6%), and pain (87.7%)."

Supports high prevalence of patient-reported core weakness. The support is indirect because the patient-reported "core weakness" theme is broader than examination-confirmed abdominal wall muscle weakness.

Lumbar hyperlordosis HP:0002938

Show evidence (3 references)

PMID:32791439 SUPPORT Human Clinical

"Hyperlordosis inlumbar spine, hypolordosis in cervical spine and negative sagittal balance were the most common spinal misalignments in patients with FSHD."

Prospective radiographic study identifies lumbar hyperlordosis as the most common spinal misalignment in FSHD. (The abstract contains the typographical error "inlumbar"; the snippet is quoted verbatim as required.)

PMID:32791439 SUPPORT Human Clinical

"There was a significantly negative correlation between LL, PI-LL and PCS."

Links greater lumbar lordosis to worse physical quality-of-life scores, connecting the spinal deformity to the functional burden patients report.

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Curved spine (lordosis, kyphosis, scoliosis)"

Patient organization lists spinal curvature including lordosis among recognized skeletal consequences of FSHD.

Scoliosis HP:0002650

Show evidence (2 references)

PMID:35147730 SUPPORT Human Clinical

"They developed more frequently spinal and thorax deformities (p < 0.001 for kyphoscoliosis and 0.012 for pectus excavatum) and had a larger decline in axial muscle function (p = 0.020)."

Longitudinal cohort links spinal deformity to the subgroup with pronounced respiratory deterioration.

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Curved spine (lordosis, kyphosis, scoliosis)"

Patient organization documents scoliosis among the skeletal manifestations communicated to families.

Pectus excavatum HP:0000767

Show evidence (1 reference)

PMID:35147730 SUPPORT Human Clinical

"They developed more frequently spinal and thorax deformities (p < 0.001 for kyphoscoliosis and 0.012 for pectus excavatum) and had a larger decline in axial muscle function (p = 0.020)."

Longitudinal cohort documents pectus excavatum and its association with declining respiratory function.

Nervous System 3

Falls HP:0002527

Show evidence (2 references)

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Sudden falls when their legs unexpectedly give out"

Patient organization documents sudden falls in the experiential terms the community uses; this manifestation is not prominent in the primary clinical literature.

PMID:20301616 SUPPORT Human Clinical

"ankle-foot orthoses to improve mobility and prevent falls"

GeneReviews management guidance treats falls as an expected, preventable complication, corroborating the community report.

Obstructive sleep apnea HP:0002870

Show evidence (1 reference)

PMID:31025273 SUPPORT Human Clinical

"In the FSHD group, 17/31 (55%) patients showed OSA and 8 (26%) had NH."

Sleep-laboratory study documents obstructive sleep apnea in 55% of FSHD patients evaluated for sleep-related symptoms. Frequency is intentionally omitted because this is a symptom-selected referral cohort, not a population sample.

Headache HP:0002315

Show evidence (2 references)

PMID:38016873 SUPPORT INDIRECT Human Clinical

"Pain was experienced most often in the head and shoulder region (193, 52%)."

National registry of 373 participants reports 52% for a COMBINED head-and-shoulder pain category. Because FSHD is dominated by scapular and periscapular pathology, an unknown and plausibly majority share of that 52% is shoulder pain, so a head-specific rate cannot be recovered from this abstract and could fall below the FREQUENT floor. The support is indirect and no `frequency:` is assigned: this corroborates head-region pain as a real component of FSHD pain burden but does not quantify it.

PMID:31025273 SUPPORT INDIRECT Human Clinical

"Indications for admission included non-restorative sleep, morning headache, or excessive daytime"

Identifies morning headache as a presenting symptom prompting sleep evaluation in FSHD, supplying a treatable mechanism for part of the headache burden.

Respiratory 2

Restrictive ventilatory defect FREQUENT HP:0002091

Show evidence (1 reference)

PMID:35147730 SUPPORT Human Clinical

"At baseline, the spirometry outcomes of 41 patients showed a restrictive ventilatory pattern (FVC < 80% and FEV1/FVC >= 70% of predicted) and of 48 patients at follow-up."

In a 92-patient longitudinal cohort, 41/92 (45%) had a restrictive pattern at baseline, supporting the FREQUENT band (30-79%).

Nocturnal hypoventilation HP:0002877

Show evidence (1 reference)

PMID:31025273 SUPPORT Human Clinical

"NH would have been missed in 7/8 patients if only oximetry criteria of hypoventilation had been applied."

Documents systematic under-detection of nocturnal hypoventilation with standard oximetry, explaining why this manifestation is under-represented in clinical descriptions.

Constitutional 2

Myalgia FREQUENT HP:0003326

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"Of 398 patients, 88.6% reported pain at the time of study. The most frequent locations were shoulders and lower back."

Large registry-based study shows that pain is common and localizes to the shoulder and lumbar regions most affected by weakness and posture.

Fatigue VERY_FREQUENT HP:0012378

Temporal: CHRONIC

Show evidence (3 references)

PMID:31409737 SUPPORT Human Clinical

"The symptomatic themes with the highest prevalence in our sample were problems with shoulders or arms (96.9%), limitations with activities (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with mobility and walking (93.6%), changed body image due to the disease (91.6%), and pain (87.7%)."

Cross-sectional patient-reported outcome study of 328 individuals quantifies fatigue at 93.8%, supporting the VERY_FREQUENT band (80-100%).

PMID:27762634 SUPPORT Human Clinical

"Patients describe fatigue as an overwhelming and unpredictable experience and they make a distinction between actual experienced fatigue and fear of becoming tired."

Qualitative interview study of 25 patients characterizes the subjective quality of FSHD fatigue that quantitative scales do not capture.

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/ SUPPORT Other

"Pain and tiredness can make daily life harder, even though people don’t always realize how much they affect someone with FSHD."

The principal FSHD patient advocacy organization states that fatigue is a day-to-day functional burden whose impact is routinely under-recognized, corroborating fatigue as a core communicated symptom.

🧬

Genetic Associations

5

D4Z4 repeat contraction on permissive 4qA haplotype (Causative repeat contraction)

Gene: DUX4 hgnc:50800 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:17924332 SUPPORT Human Clinical

"Yet only repeat contractions of D4Z4 on chromosome 4qA cause FSHD; contractions on the other chromosomes are nonpathogenic."

Establishes the pathogenic requirement for contraction on a permissive 4qA background in FSHD1.

SMCHD1 (Causative chromatin modifier variant on a permissive D4Z4 background)

Gene: SMCHD1 hgnc:29090 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:29478599 SUPPORT Human Clinical

"The chromatin changes in this form of FSHD (FSHD2) are the result, in most cases, of mutations in SMCHD1, a gene on chromosome 18 involved in chromatin regulation."

Review-level summary directly links SMCHD1-mediated chromatin failure to FSHD2 pathogenesis.

DNMT3B (Chromatin-modifier variant causing D4Z4 hypomethylation on a permissive background)

Gene: DNMT3B hgnc:2979 gene page relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (3 references)

PMID:27153398 SUPPORT Human Clinical

"Here, we show that heterozygous mutations in DNA methyltransferase 3B (DNMT3B) are a likely cause of D4Z4 derepression associated with low levels of DUX4 expression from the D4Z4 repeat and increased penetrance of FSHD."

The defining report of heterozygous DNMT3B variants as a cause of D4Z4 derepression in FSHD, and the source of the penetrance caveat above.

PMID:27153398 SUPPORT Human Clinical

"Recessive mutations in DNMT3B were previously shown to cause immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome."

Source for the allele-state distinction between FSHD2 and the recessive ICF syndrome, which shares the gene but not the disease.

PMID:20301616 SUPPORT Human Clinical

"Hypomethylation of the D4Z4 repeat array can be the result of a heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic pathogenic variants in LRIF1."

GeneReviews states the three FSHD2 chromatin-modifier loci and their required allele states.

DUX4-permissive 4qA D4Z4 haplotype (Second locus required in trans for DNMT3B-related FSHD4)

Gene: DUX4 hgnc:50800 relationship_type: COOPERATING variant_origin: GERMLINE

Show evidence (2 references)

PMID:20724583 SUPPORT Human Clinical

"FSHD is associated with contraction of D4Z4 macrosatellite repeats on chromosome 4q35, but this contraction is pathogenic only in certain "permissive" chromosomal backgrounds."

States that the chromosome 4 background is a separate genetic requirement, which is what this locus row records.

PMID:20301616 SUPPORT Human Clinical

"The diagnosis of FSHD2 is established in a proband with characteristic clinical features and hypomethylation of the D4Z4 repeat array in the subtelomeric region of chromosome 4q35 on a permissive chromosome 4 haplotype."

GeneReviews makes the permissive haplotype part of the diagnostic requirement for contraction-independent FSHD, of which the DNMT3B form is one.

LRIF1 (Biallelic chromatin-modifier variant causing D4Z4 hypomethylation on a permissive background)

Gene: LRIF1 hgnc:30299 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (4 references)

PMID:32467133 SUPPORT Human Clinical

"A homozygous LRIF1 mutation was identified in a patient with a clinical phenotype consistent with FSHD."

The single reported human proband establishing LRIF1 as an FSHD2 locus.

PMID:32467133 SUPPORT Human Clinical

"In this study, we tested the hypothesis whether LRIF1, a known SMCHD1 protein interactor, is a disease gene for idiopathic FSHD2."

Source for the SMCHD1-interactor relationship recorded in this record's note, and for why LRIF1 was a candidate at all.

PMID:32467133 SUPPORT In Vitro

"In concordance, LRIF1 was shown to bind to the D4Z4 repeat, and knockdown of the LRIF1 long isoform in muscle cells results in DUX4 and DUX4 target gene expression."

Cell-based evidence that LRIF1 acts at D4Z4 and that losing the long isoform derepresses DUX4, which is the mechanism the proband's phenotype is attributed to.

+ 1 more reference

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Medical Actions

10

Aerobic Exercise Training

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Platform: Behavioral / lifestyle

Regular endurance training can improve fitness, walking speed, and self-assessed health without evidence of exercise-induced muscle damage.

Show evidence (1 reference)

PMID:26156512 SUPPORT Human Clinical

"This randomized, controlled study showed that regular endurance training improves fitness, walking speed, and self-assessed health in patients with FSHD without causing muscle damage."

Randomized controlled evidence supports structured aerobic training as a safe supportive intervention in FSHD.

Scapulopexy

Action: surgical procedure Ontology label: Surgical Procedure NCIT:C15329

Platform: Surgery

Scapular fixation surgery can improve shoulder range of motion and reduce disabling winging in appropriately selected patients.

Show evidence (1 reference)

PMID:18056023 SUPPORT Human Clinical

"All patients experienced improvement in active range of motion of the shoulder and all of them had clinical improvement with complete resolution of the winged scapula."

Long-term retrospective series supports scapulopexy as an effective intervention for symptomatic scapular winging in selected FSHD patients.

Genetic Counseling and Reproductive Options

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Platform: Other

Reproductive decision-making is a salient concern in the FSHD patient community - one of the community's all-time highest-scoring discussions is a first-person account of navigating preimplantation genetic testing and IVF - yet it is easy to under-serve in a clinic focused on motor function. GeneReviews sets the recurrence risk at 50% per offspring in FSHD1 and states that PGT may be possible, with the important caveat that PGT results are typically confirmed by prenatal testing.

Show evidence (2 references)

PMID:20301616 SUPPORT Human Clinical

"Preimplantation genetic testing (PGT) may be possible but verification of PGT results using prenatal testing is typically recommended."

GeneReviews genetic-counseling guidance states the availability and the confirmatory caveat for PGT in FSHD.

url:https://old.reddit.com/r/FSHD/top/?t=all SUPPORT Other

"Our 2+ year journey navigating PGT-M IVF because of FSHD"

Reproductive planning via PGT-M/IVF reaches the community's all-time highest-scoring discussions, indicating it is a salient concern for affected families. One of the 25 all-time top threads is on this topic, so this supports salience but not recurrence; the treatment itself rests on the GeneReviews PGT evidence above. Cited as an aggregate community topic; no individual's personal health narrative is quoted.

Pain Management and Supportive Care

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Pain-directed pharmacologic and nonpharmacologic management, assistive devices, and multidisciplinary rehabilitation remain central to current care because pain is common and materially affects quality of life.

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"Management of pain should be considered when treating FSHD1 patients."

Registry-based outcome data support pain-directed supportive care as a necessary component of FSHD management.

Cognitive Behavioral Therapy for Chronic Fatigue

Action: cognitive behavior therapy Ontology label: Cognitive Behavior Therapy NCIT:C64345

Platform: Behavioral / lifestyle

Chronic fatigue - the symptom the patient community reports most consistently and finds hardest to explain - is treatable. A randomized controlled trial showed that cognitive-behavioral therapy reduces fatigue severity in FSHD, with gains sustained at follow-up and additional benefit in physical activity, sleep quality, and social participation. This directly addresses the community observation that patients receive little support in coping with fatigue.

Show evidence (3 references)

PMID:25339206 SUPPORT Human Clinical

"This RCT shows that AET and CBT can ameliorate chronic fatigue in patients with FSHD."

Randomized controlled trial in 57 patients with FSHD type 1 and severe chronic fatigue provides Class III evidence for CBT as fatigue-directed therapy.

PMID:25339206 SUPPORT Human Clinical

"The patients who received CBT had an increase in registered and experienced physical activity, sleep quality, and social participation."

Documents that CBT improves the participation and social outcomes that patients themselves identify as most affected by fatigue.

PMID:27762634 SUPPORT Human Clinical

"Patients with FSHD are insufficient supported in coping with their fatigue."

Qualitative study identifies the care gap that fatigue-directed therapy is intended to close, matching what patient organizations report.

Ankle-Foot Orthoses

Platform: Device

Ankle-foot orthoses compensate for dorsiflexor weakness, improving gait and specifically reducing the sudden falls that the patient community describes as a major safety concern.

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"ankle-foot orthoses to improve mobility and prevent falls"

GeneReviews management guidance recommends ankle-foot orthoses for mobility and fall prevention in FSHD.

Ocular Surface Protection

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Platform: Other

Because facial weakness prevents complete eyelid closure, the cornea is exposed during sleep. Ocular lubricants or overnight eyelid taping prevent exposure keratitis - a simple, low-cost intervention for a manifestation the community reports but which is easily overlooked in clinic.

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"ocular lubricants or taping the eyes shut during sleep to treat exposure keratitis"

GeneReviews recommends ocular surface protection to prevent exposure keratitis arising from lagophthalmos.

Occupational and Speech Therapy in Infantile-Onset Disease

Action: speech and language therapy Ontology label: Speech Language Therapy NCIT:C159273

Platform: Behavioral / lifestyle

Children with infantile-onset FSHD require occupational and speech therapy input, reflecting the greater functional and orofacial burden in this group. Speech involvement is mechanistically consistent with the orofacial muscle involvement now documented on ultrasound.

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"occupational and speech therapy in individuals with infantile onset"

GeneReviews management guidance specifies occupational and speech therapy for infantile-onset FSHD.

Management of Sensorineural Hearing Loss

Action: supportive care Ontology label: Supportive Care NCIT:C15747

Platform: Device

Hearing loss in FSHD is managed with standard audiologic care. It matters most in early-onset disease, where high-frequency hearing loss is concentrated and where undetected loss can compound developmental and communication difficulty.

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"standard treatment of sensorineural hearing loss"

GeneReviews management guidance directs standard audiologic treatment for the sensorineural hearing loss already curated as a phenotype in this entry.

Ventilatory Support

Action: respiratory therapy Ontology label: Respiratory Therapy NCIT:C15322

Platform: Device

Non-invasive ventilation is indicated for the minority who develop nocturnal hypoventilation or symptomatic respiratory failure, and it works quickly - nocturnal gas exchange improved from the first night of treatment in patients started on NIV. This addresses the "trouble breathing" the community reports without over-medicalizing the majority who remain stable. The corresponding screening protocol is modelled separately under `diagnosis:` rather than bundled here.

Show evidence (2 references)

PMID:31025273 SUPPORT Human Clinical

"In patients initiated on NIV, nocturnal gas exchange already improved in the first night of treatment."

Documents rapid physiological benefit of non-invasive ventilation in FSHD patients with sleep-disordered breathing.

PMID:35147730 SUPPORT Human Clinical

"Respiratory function remained stable in most patients with FSHD, but a subgroup of patients showed a pronounced deterioration."

Longitudinal data justify targeting ventilatory intervention at the deteriorating subgroup rather than the whole population.

🔬

Biochemical Markers

1

Creatine Kinase (Mildly elevated)

Context: Serum creatine kinase is often normal to mildly elevated rather than markedly increased.

🔬

Diagnosis

5

Molecular diagnosis of FSHD1 (D4Z4 contraction on a permissive haplotype)

FSHD1 is confirmed by demonstrating a heterozygous pathogenic contraction of the D4Z4 repeat array at 4q35 on a permissive chromosome 4 haplotype. Both elements are required: repeat size alone is not diagnostic, because contractions on non-permissive haplotypes are benign.

genetic testing NCIT:C15709

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"The diagnosis of FSHD1 is established in a proband with characteristic clinical features and a heterozygous pathogenic contraction of the D4Z4 repeat array in the subtelomeric region of chromosome 4q35 on a permissive chromosome 4 haplotype."

GeneReviews states the diagnostic criteria for FSHD1 directly.

Molecular diagnosis of FSHD2 (D4Z4 hypomethylation and chromatin-modifier testing)

FSHD2 is confirmed by D4Z4 hypomethylation at 4q35 on a permissive haplotype, without a contraction. Hypomethylation usually reflects a heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic variants in LRIF1, so methylation testing and chromatin-modifier gene testing are complementary rather than alternative.

genetic testing NCIT:C15709

Show evidence (2 references)

PMID:20301616 SUPPORT Human Clinical

"The diagnosis of FSHD2 is established in a proband with characteristic clinical features and hypomethylation of the D4Z4 repeat array in the subtelomeric region of chromosome 4q35 on a permissive chromosome 4 haplotype."

GeneReviews states the diagnostic criteria for FSHD2 directly.

PMID:20301616 SUPPORT Human Clinical

"Hypomethylation of the D4Z4 repeat array can be the result of a heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic pathogenic variants in LRIF1."

Identifies the chromatin-modifier genes whose variants underlie FSHD2 hypomethylation, defining the gene panel to test.

Hypoventilation screening and pulmonary assessment

Respiratory surveillance is risk-stratified rather than universal. GeneReviews indicates hypoventilation screening for patients with abnormal pulmonary function tests, severe proximal weakness, kyphoscoliosis, wheelchair dependence, or comorbid disease affecting ventilation, and pulmonary consultation at forced vital capacity below 60%, for excessive daytime somnolence or nonrestorative sleep, and before procedures requiring anesthesia. Transcutaneous capnometry outperforms pulse oximetry for detecting nocturnal hypoventilation.

spirometry NCIT:C85397

Show evidence (2 references)

PMID:20301616 SUPPORT Human Clinical

"pulmonary consultation for forced vital capacity <60%, excessive daytime somnolence, or nonrestorative sleep, and prior to surgical procedures requiring anesthesia"

GeneReviews defines the thresholds triggering pulmonary consultation in FSHD.

PMID:31025273 SUPPORT Human Clinical

"Transcutaneous capnometry is superior to pulse oximetry for detection of NH."

Establishes the modality required to detect nocturnal hypoventilation, which oximetry alone misses in most cases.

Audiologic surveillance

Hearing surveillance is age-stratified and most intensive in early-onset disease, where extra-muscular involvement concentrates.

audiometric assessment NCIT:C38036

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"audiometry in infants at each visit and annually in children"

GeneReviews defines the audiologic surveillance schedule for FSHD.

Ophthalmologic surveillance for retinal vasculopathy

Dilated fundoscopic surveillance is targeted at the group in whom sight-threatening Coats-like retinopathy concentrates: early childhood-onset disease with large D4Z4 contractions, plus any adult with visual symptoms.

ophthalmoscopy NCIT:C120698

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"annual dilated ophthalmoscopy in individuals with early childhood-onset FSHD with large pathogenic contraction of D4Z4 and adults with visual symptoms"

GeneReviews defines the risk-stratified ophthalmologic surveillance criteria.

📈

Progression

5

Typical onset

Age: Adolescence to early adulthood

Facial weakness and scapular instability usually appear first; the age at onset and severity vary widely across individuals and families.

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"FSHD symptoms usually start around the second decade and are most commonly characterized by asymmetric weakness affecting the face, shoulder, and arms, followed by the distal lower extremities and pelvic girdle. Not all patients have the complete phenotype of FSHD, and clinical severity varies..."

Supports onset around the second decade and the wide phenotypic variability across affected individuals and families.

Descending asymmetric progression

Age: Adulthood

Weakness usually spreads from face and shoulder girdle to upper arms, trunk, distal lower extremities, and pelvic girdle with marked side-to-side asymmetry.

Show evidence (1 reference)

PMID:29053898 SUPPORT Human Clinical

"FSHD symptoms usually start around the second decade and are most commonly characterized by asymmetric weakness affecting the face, shoulder, and arms, followed by the distal lower extremities and pelvic girdle."

Describes the characteristic asymmetric distribution and descending spread of weakness from face and shoulder/arm involvement to distal lower extremities and pelvic girdle.

Loss of ambulation in a minority

Age: Adulthood

Roughly one in five affected individuals eventually requires a wheelchair, but life expectancy is not shortened. FSHD is therefore a disease of morbidity rather than mortality - a framing the patient community emphasizes and that distinguishes FSHD from dystrophies such as Duchenne.

Show evidence (1 reference)

PMID:20301616 SUPPORT Human Clinical

"Weakness can be slowly progressive and approximately 20% of affected individuals eventually require a wheelchair. Life expectancy is not shortened."

GeneReviews quantifies the proportion losing ambulation and confirms normal life expectancy.

Slow progression with a deteriorating minority

Age: Adulthood

Longitudinal registry and cohort data show that FSHD progresses slowly: function is largely static over 12 months, and over 6.5 years only about 16% - all with moderate-to-severe baseline disease - show clinically important deterioration on a disease-specific patient-reported disability scale. This has a methodological consequence the patient community feels directly: because patients compensate for weakness, patient-reported outcome measures may under-detect real progression, which complicates trial design and can make patients' lived experience of decline appear absent from the data.

Show evidence (3 references)

PMID:40781929 SUPPORT Human Clinical

"Ten patients (16%), all with moderate-to-severe baseline disease (FSHD clinical severity score >= 6), showed clinically important deterioration over 6.5 years."

Quantifies the deteriorating minority over a 6.5-year horizon and identifies baseline severity as the discriminator.

PMID:40781929 SUPPORT Human Clinical

"The ability to compensate for muscle weakness may limit the sensitivity of patient-reported outcomes like FSHD-RODS in clinical trials."

Documents that patient-reported outcome measures may under-detect progression in FSHD because of compensation, relevant to interpreting the patient-reported evidence used throughout this entry.

PMID:38189531 SUPPORT Human Clinical

"In a 12-month period, FSHD participant function remained largely stable with a mild worsening of strength, measured by MMT and standardized MVICT scores, and a mild loss in lean body mass."

Prospective 12-month observational study confirms near-stability of function over a one-year horizon.

Respiratory decline in an at-risk subgroup

Age: Later adulthood

Respiratory function is stable in most patients over a five-year horizon. A minority - those with more severe baseline weakness, kyphoscoliosis, pectus excavatum, and declining axial muscle function - show pronounced deterioration and are the group for whom hypoventilation screening is indicated.

Show evidence (1 reference)

PMID:35147730 SUPPORT Human Clinical

"Respiratory function remained stable in most patients with FSHD, but a subgroup of patients showed a pronounced deterioration. They showed more severe muscle weakness including the leg muscles at baseline (Ricci score >= 6), had spinal and thorax deformities and a relatively fast decline in..."

Five-year longitudinal cohort defines both the stable majority and the characteristics of the deteriorating subgroup.

📊

Prevalence

1

Symptomatic population in the Netherlands

Point Prevalence 12.0 per 100,000 1–9 per 10,000

Population-based capture-recapture analysis estimated approximately 2,000 symptomatic affected individuals in the Netherlands.

Show evidence (1 reference)

PMID:25122204 SUPPORT Human Clinical

"The prevalence rate was 12/100,000, equivalent to 2,000 affected individuals."

Population-based prevalence estimate for symptomatic FSHD from a national registry analysis.

📊

Related Datasets

5

Iron supplementation alleviates pathologies in a mouse model of facioscapulohumeral muscular dystrophy geo:GSE261617

Facioscapulohumeral muscular dystrophy (FSHD) is a genetic muscle disease caused by ectopic expression of the toxic protein DUX4, resulting in muscle weakness. However, the mechanism by which DUX4 exerts its toxicity remains unclear. In this study, we observed abnormal iron accumulation in muscles of patients with FSHD and in muscle-specific DUX4-expressing (DUX4-Tg) mice. Treatment with iron chelators, an iron-deficient diet, and genetic modifications inhibiting intracellular uptake of iron did not improve but rather exacerbated FSHD pathology in DUX4-Tg mice.

mouse BULK RNA SEQ n=23

PMID:40591405

Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.

DUX4.6 siRNA in vitro activity in FSHD patient-derived myotubes geo:GSE291267

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant muscular disease caused by the aberrant ectopic expression of DUX4 in skeletal muscle. There are no approved therapies for FSHD to date, and strategies aimed at reducing DUX4 expression in skeletal muscle of FSHD patients are promising therapeutic approaches. Here we demonstrate DUX4.6 siRNA activity in reducing DUX4-regulated gene expression in FSHD patient-derived myotubes in vitro.

human BULK RNA SEQ n=32

PMID:41994867

Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.

Hit-and-run silencing of endogenous DUX4 by targeting DNA hypomethylation on D4Z4 repeats in facioscapulohumeral muscular dystrophy geo:GSE201185

human MULTI OMICS n=11

Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.

A circulating biomarker for severity of facioscapulohumeral muscular dystrophy ega:EGAS00001007350

Facioscapulohumeral muscular dystrophy (FSHD) is a prevalent, incurable skeletal myopathy. Clinical trials for FSHD are hindered by heterogeneous biomarkers poorly associated with clinical severity, requiring invasive muscle biopsy. Macroscopically FSHD presents with slow fatty replacement of muscle, rapidly accelerated by inflammation. Mis-expression of the transcription factor DUX4 is currently accepted to underlie FSHD pathogenesis and mechanisms including PAX7 target gene repression have been proposed.

human

European Genome-phenome Archive study, matched because the disease is named in the study's own title ("Facioscapulohumeral Muscular Dystrophy"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.

3D tissue engineered human skeletal muscle modelling Facioscapulohumeral Muscular Dystrophy ega:EGAS50000000502

acioscapulohumeral muscular dystrophy (FSHD) is caused by sporadic misexpression of the transcription factor double homeobox 4 (DUX4) in skeletal muscles. So far, monolayer cultures and animal models have been used to study the FSHD disease mechanism and for FSHD therapy development, but these models do not fully recapitulate the disease and there is a lack of knowledge on how DUX4 misexpression leads to skeletal muscle dysfunction. To overcome these barriers, we have developed a 3D tissue engineered skeletal muscle (3D-TESM) model by generating genetically matched myogenic progenitors (MPs) from human induced pluripotent stem cells of three mosaic FSHD patients.

human

European Genome-phenome Archive study, matched because the disease is named in the study's own title ("Facioscapulohumeral Muscular Dystrophy"); description-level mentions were not accepted. EGA study_type: RNASeq. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.

🔬

Clinical Trials

4

NCT05747924 NOT_APPLICABLE ACTIVE_NOT_RECRUITING

Phase 1/2 FORTITUDE study of delpacibart braxlosiran (AOC 1020), an antibody-oligonucleotide conjugate designed to reduce DUX4 mRNA in FSHD1 and FSHD2.

Show evidence (1 reference)

clinicaltrials:NCT05747924 SUPPORT Human Clinical

"A Randomized, Double-blind, Placebo-controlled, Phase 1/2 Study to Evaluate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Exploratory Efficacy of AOC 1020 Administered Intravenously to Participants with Facioscapulohumeral Muscular Dystrophy (FSHD)"

Supports active clinical development of a DUX4-targeting oligonucleotide therapy in FSHD.

NCT06131983 NOT_APPLICABLE RECRUITING

Phase 1/2a dose-escalation study of ARO-DUX4, an RNA interference therapeutic targeting DUX4 in FSHD1. The sponsor now lists the agent as SRP-1001, which is the name the registry record and the quoted summary below use.

Show evidence (1 reference)

clinicaltrials:NCT06131983 SUPPORT Human Clinical

"The purpose of this study is to evaluate the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of SRP-1001 in participants with facioscapulohumeral muscular dystrophy Type 1 (FSHD1)."

Supports ongoing clinical testing of a second DUX4-silencing therapeutic strategy.

NCT05397470 PHASE_III TERMINATED

Phase III REACH trial of losmapimod, a p38alpha/beta inhibitor intended to suppress the DUX4 transcriptional program in FSHD.

Show evidence (3 references)

clinicaltrials:NCT05397470 SUPPORT Human Clinical

"This is a study to evaluate the safety and efficacy of losmapimod in treating participants with Facioscapulohumeral Muscular Dystrophy (FSHD)."

Shows that p38-mediated DUX4 suppression advanced to late-stage clinical testing, even though the program did not succeed.

PMID:38631764 REFUTE Human Clinical

"Least squares mean changes from baseline in DUX4-driven gene expression did not differ significantly between the losmapimod"

The preceding phase 2b ReDUX4 trial missed its primary endpoint: losmapimod did not significantly reduce DUX4-driven gene expression, refuting the pharmacodynamic premise on which the phase 3 was built. Secondary structural and functional signals nonetheless motivated progression to phase 3.

PMID:40580827 REFUTE Human Clinical

"the trial failed to demonstrate a clear clinical benefit, highlighting key challenges in drug development for the disease"

Confirms the phase 3 outcome: losmapimod did not show clear clinical benefit. Recorded as REFUTE so the entry does not leave a terminated program looking merely incomplete - the p38/DUX4-suppression strategy was tested and did not succeed.

NCT07435129 PHASE_II NOT_RECRUITING

Phase II FORGE study of apitegromab, a myostatin-pathway therapy intended to improve muscle function rather than directly suppress DUX4.

Show evidence (1 reference)

clinicaltrials:NCT07435129 SUPPORT Human Clinical

"A randomized Phase 2 study to evaluate the efficacy and safety of apitegromab as a monotherapy in participant with FSHD"

Supports ongoing parallel development of muscle-function-directed therapy in FSHD.

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Animal Models

2

D4Z4-2.5/Dnmt3bMommeD14 transgenic mouse Digenic model of the FSHD4 genotype

The one attempt to reconstruct the FSHD4 genotype in an animal: a mouse carrying an FSHD-sized human D4Z4 array crossed to a Dnmt3b hypomorph, built to mimic one of the two original DNMT3B families. It reproduces the molecular half of the lesion, losing D4Z4 methylation, but not the muscle disease, and the tissue where DUX4 rises is lymphoid rather than skeletal muscle.

Species

Mouse

Genotype

Hemizygous D4Z4-2.5 transgene with a heterozygous Dnmt3b exon 13 skipping allele (Dnmt3bMommeD14)

Genes

DNMT3B hgnc:2979

Publication

PMID:33004076

Pathograph links

DUX4 Misexpression in Skeletal Muscle fails to recapitulate fidelity: low observes: molecular Reducing Dnmt3b on an FSHD-sized D4Z4 background did not raise DUX4 transcript in skeletal muscle and produced no muscle pathology, so this model does not reproduce the node it was built to test.

Limitations: The transgene is a 2.5-unit human array in mouse chromatin rather than a normal-length array with a human permissive 4qA subtelomere, so the digenic combination modelled is not the human one; the Dnmt3b allele is an exon-skipping hypomorph rather than one of the patient missense variants; and mouse skeletal muscle appears less sensitive to D4Z4 chromatin modifiers than lymphoid tissue, which is where the DUX4 rise was seen. Read this as evidence about the model, not as evidence against a DNMT3B contribution in patients.

Readouts

Skeletal muscle DUX4 transcript level

Direction: UNCHANGED

Interpretation: The measurement the node would predict to rise; it did not, alongside absent muscle pathology.

Show evidence (1 reference)

PMID:33004076 SUPPORT Model Organism

"In D4Z4-2.5/Dnmt3bMommeD14 mice, Dnmt3b protein levels were reduced; however, DUX4 RNA levels in skeletal muscles were not enhanced and no pathology was observed."

Reports the skeletal-muscle DUX4 measurement and its direction in this cross.

Show evidence (1 reference)

PMID:33004076 SUPPORT Model Organism

"In D4Z4-2.5/Dnmt3bMommeD14 mice, Dnmt3b protein levels were reduced; however, DUX4 RNA levels in skeletal muscles were not enhanced and no pathology was observed."

The negative result in the tissue this node describes, which is what FAILS_TO_RECAPITULATE records here.

D4Z4 Epigenetic Derepression partially recapitulates fidelity: moderate observes: molecular The methylation half of the lesion does transfer: losing Dnmt3b demethylates the D4Z4 array in this mouse, and DUX4 rises, but in secondary lymphoid organs rather than muscle.

Limitations: Derepression is demonstrated in lymphoid tissue, not in the muscle compartment where FSHD manifests, so the node is reproduced in the wrong tissue.

Show evidence (1 reference)

PMID:33004076 SUPPORT Model Organism

"Interestingly, D4Z4-2.5/Dnmt3bMommeD14 mice showed a loss of DNA methylation at the D4Z4 repeat array and significantly higher DUX4 transcript levels in secondary lymphoid organs."

Shows Dnmt3b loss demethylating D4Z4 and derepressing DUX4 in this model, with the tissue restriction noted in the limitation.

Xenopus frg1 gain- and loss-of-function vascular model Candidate-gene dosage model of the vascular component of FSHD

The only model to address why FSHD has an ophthalmologic component at all. frg1 is expressed in frog vasculature; knocking it down reduces angiogenesis and DAB2 expression, and overexpressing it produces excess vessel branching, vessel dilation and edema. Read carefully, this is a candidate-gene result from before the field settled on DUX4: it shows that a gene at the FSHD locus can produce a vascular phenotype when its dose is wrong, not that FRG1 dosage is what causes vasculopathy in patients.

Species

Xenopus laevis

Genotype

FRG1 morpholino knockdown and frg1 mRNA overexpression in embryos and tadpoles

Genes

FRG1 hgnc:3954

Publication

PMID:19383939

Retained as a candidate-gene model with its caveats intact rather than dropped: FRG1 has largely been displaced by DUX4 as the FSHD effector, but no DUX4-based account of the retinal vasculopathy has replaced this one, so the vascular feature currently has no better mechanistic model.

{ }

Source YAML

click to show

name: Facioscapulohumeral Muscular Dystrophy
creation_date: "2026-04-21T04:46:26Z"
description: >-
  Facioscapulohumeral muscular dystrophy (FSHD) is a dominantly inherited
  muscular dystrophy characterized by progressive, often asymmetric weakness
  that typically begins in the facial and scapular muscles and later involves
  the upper arms, trunk, and lower extremities. The core disease mechanism is
  loss of epigenetic repression at the D4Z4 locus on chromosome 4q35, which
  permits pathogenic expression of the embryonic transcription factor DUX4 in
  skeletal muscle. Most cases are FSHD1 due to D4Z4 repeat contraction on a
  permissive 4qA haplotype, whereas FSHD2 reflects contraction-independent
  hypomethylation, usually from pathogenic variants in chromatin regulators such
  as SMCHD1. There is no approved disease-modifying therapy; current management
  is supportive, while the therapeutic pipeline remains centered on DUX4
  suppression and muscle function preservation.
category: Genetic
parents:
- Muscular Dystrophy
- Neuromuscular Disease
disease_term:
  preferred_term: facioscapulohumeral muscular dystrophy
  term:
    id: MONDO:0001347
    label: facioscapulohumeral muscular dystrophy
inheritance:
- name: Autosomal dominant
  de_novo_rate: 10-30% in FSHD1 (de novo constitutional or mosaic D4Z4 contraction)
  description: >-
    FSHD usually follows autosomal dominant inheritance, although penetrance
    and severity are variable. Most FSHD1 probands inherit the contracted
    allele, but a substantial minority arise de novo, and a notable share of
    those are somatic/germline mosaic rather than fully constitutional -
    which is why an apparently unaffected parent does not exclude
    transmission risk.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:17924332
    reference_title: "Specific sequence variations within the 4q35 region are associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is
      mainly characterized by progressive wasting and weakness of the facial,
      shoulder, and upper-arm muscles.
    explanation: >-
      Human genetic study directly states the canonical autosomal dominant
      inheritance pattern of FSHD.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each offspring of a proband with FSHD1 has a 50% chance of inheriting
      the pathogenic D4Z4 repeat array contraction.
    explanation: >-
      GeneReviews genetic-counseling guidance states the recurrence risk to
      offspring in FSHD1.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Approximately 70%-90% of individuals diagnosed with FSHD1 have a parent
      with clinical findings of FSHD and one D4Z4 repeat array with a
      pathogenic contraction
    explanation: >-
      Quantifies the inherited proportion of FSHD1, the complement of the de
      novo rate recorded below.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ~10%-30% of probands have the disorder as the result of a de novo
      constitutional or mosaic pathogenic contraction of the D4Z4 repeat
      array.
    explanation: >-
      Sources the `de_novo_rate` value and documents that a share of de novo
      events are mosaic, which affects recurrence-risk counselling.
- name: Digenic inheritance (FSHD2)
  inheritance_term:
    preferred_term: Digenic inheritance
    term:
      id: HP:0010984
      label: Digenic inheritance
  description: >-
    FSHD2 arises digenically: disease requires both an SMCHD1 (or other
    chromatin-modifier) mutation and, in trans, an FSHD-permissive 4qA D4Z4
    haplotype carrying the DUX4 polyadenylation signal. Neither locus alone is
    sufficient to cause disease.
  evidence:
  - reference: PMID:23143600
    reference_title: "Digenic inheritance of an SMCHD1 mutation and an FSHD-permissive D4Z4 allele causes facioscapulohumeral muscular dystrophy type 2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD2 occurs in individuals who inherited both the SMCHD1 mutation and a
      normal-sized D4Z4 array on a chromosome 4 haplotype permissive for DUX4
      expression.
    explanation: >-
      This study defines FSHD2 as digenic, requiring both an SMCHD1 mutation and
      an FSHD-permissive D4Z4 haplotype.
notes: >-
  Lump/split: FSHD4 (MONDO:0030355, OMIM 619478) is curated here as a
  has_subtypes entry rather than as its own kb/disorders file. Its pathograph
  is the one already in this entry - loss of D4Z4 repression, DUX4 misexpression
  in skeletal muscle, myofiber loss - reached through DNMT3B instead of SMCHD1,
  and the clinical picture is reported as indistinguishable from the rest of
  FSHD, so a separate Disease entry would duplicate this one rather than
  describe a different disease. What is genuinely specific to FSHD4 is recorded
  where it belongs: the DNMT3B lesion as its own pathophysiology node, the
  permissive 4qA polyadenylation signal as a second required node and a second
  locus row, and the digenic inheritance block on the subtype itself.

  No phenotype in this entry is scoped to FSHD4, and that is deliberate rather
  than an omission: the literature cited on the subtype reports no clinical
  feature separating contraction-independent FSHD from FSHD1, and no
  DNMT3B-specific phenotype series has been published. Penetrance is the one
  quantitative gap - it is known to be incomplete among double-genotype
  carriers, but the two originally reported families are too small to give a
  rate, so none is recorded.

has_subtypes:
- name: FSHD1
  subtype_term:
    preferred_term: facioscapulohumeral muscular dystrophy 1
    term:
      id: MONDO:0008030
      label: facioscapulohumeral muscular dystrophy 1
  description: >-
    Classic form caused by contraction of the D4Z4 repeat array on a
    permissive chromosome 4qA background. This accounts for the large
    majority of genetically confirmed FSHD.
  genes:
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  evidence:
  - reference: PMID:17924332
    reference_title: "Specific sequence variations within the 4q35 region are associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Yet only repeat contractions of D4Z4 on chromosome 4qA cause FSHD;
      contractions on the other chromosomes are nonpathogenic.
    explanation: Establishes the 4q35 D4Z4 contraction on a permissive 4qA haplotype as the genetic basis of FSHD1.
- name: FSHD2
  subtype_term:
    preferred_term: facioscapulohumeral muscular dystrophy 2
    term:
      id: MONDO:0008031
      label: facioscapulohumeral muscular dystrophy 2
  description: >-
    Contraction-independent form with D4Z4 hypomethylation on a permissive
    4qA background, usually associated with pathogenic variants in chromatin
    repressors such as SMCHD1.
  genes:
  - preferred_term: SMCHD1
    term:
      id: hgnc:29090
      label: SMCHD1
  - preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  - preferred_term: LRIF1
    term:
      id: hgnc:30299
      label: LRIF1
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  evidence:
  - reference: PMID:19728363
    reference_title: "Common epigenetic changes of D4Z4 in contraction-dependent and contraction-independent FSHD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In 15 FSHD families without D4Z4 contractions but with at least one
      4qA161 haplotype (FSHD2), we observed D4Z4-restricted hypomethylation on
      chromosomes 4q and 10q.
    explanation: Defines the contraction-independent epigenetic FSHD2 phenotype with shared D4Z4 hypomethylation.
- name: FSHD4
  display_name: FSHD4 (DNMT3B-related, digenic)
  subtype_term:
    preferred_term: facioscapulohumeral muscular dystrophy 4, digenic
    term:
      id: MONDO:0030355
      label: facioscapulohumeral muscular dystrophy 4, digenic
  description: >-
    FSHD4 is the DNMT3B-associated, contraction-independent form of FSHD. It is
    digenic in the strict sense: disease requires a heterozygous DNMT3B variant
    that relaxes DNA methylation across the D4Z4 macrosatellite, together with
    an FSHD-permissive 4qA chromosome inherited in trans that supplies the pLAM
    polyadenylation signal stabilising the distal DUX4 transcript. Neither
    genotype alone causes disease, and not every double-genotype carrier in the
    two originally reported families was affected. Under the methylation-based
    diagnostic scheme GeneReviews uses, these individuals are classified
    clinically as FSHD2; OMIM and MONDO instead number the entity by its causal
    chromatin-modifier gene, and MONDO:0030355 is that DNMT3B-specific number.
  genes:
  - preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  inheritance:
  - name: Digenic inheritance (FSHD4)
    inheritance_term:
      preferred_term: Digenic inheritance
      term:
        id: HP:0010984
        label: Digenic inheritance
    penetrance: INCOMPLETE
    description: >-
      The two contributing loci are DNMT3B, carrying a heterozygous variant,
      and the DUX4-bearing D4Z4 array on a permissive 4qA chromosome 4
      haplotype inherited in trans. Because the two segregate independently,
      each child of a proband whose partner carries neither alteration has a
      25% chance of inheriting both and being affected, a 50% chance of
      inheriting one and remaining an asymptomatic heterozygote, and a 25%
      chance of inheriting neither. Penetrance is incomplete even among
      double-genotype carriers.
    evidence:
    - reference: PMID:20301616
      reference_title: "Facioscapulohumeral Muscular Dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        If the proband has a heterozygous pathogenic variant in SMCHD1 or
        DNMT3B and a permissive chromosome 4 haplotype and the proband's
        reproductive partner does not have FSHD2-related genetic alteration(s),
        each child of the proband has a 25% chance of being affected, a 50%
        chance of being an asymptomatic heterozygote, and a 25% chance of
        inheriting neither of the FSHD2-related genetic alterations.
      explanation: >-
        GeneReviews states the joint-transmission arithmetic for a DNMT3B
        variant together with a permissive chromosome 4 haplotype, which is
        what makes this inheritance digenic rather than monogenic dominant, and
        sources the recurrence risks quoted above.
    - reference: PMID:33004076
      reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: >-
        In the other family, digenic inheritance of a heterozygous DNMT3B
        missense variant (c.2072C>T) and a permissive 4qA allele of 13 D4Z4
        units induced hypomethylation at the D4Z4 repeat array but only one of
        the two family members was diagnosed with FSHD.
      explanation: >-
        Names the two co-inherited alleles in one of the original DNMT3B
        families and records that one double-genotype carrier was unaffected,
        which sources the incomplete penetrance recorded here. The sentence
        sits in the introduction of a mouse study and restates the human family
        genetics reported elsewhere, hence the BACKGROUND quote role.
  evidence:
  - reference: PMID:27153398
    reference_title: "Mutations in DNMT3B Modify Epigenetic Repression of the D4Z4 Repeat and the Penetrance of Facioscapulohumeral Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we show that heterozygous mutations in DNA methyltransferase 3B
      (DNMT3B) are a likely cause of D4Z4 derepression associated with low
      levels of DUX4 expression from the D4Z4 repeat and increased penetrance
      of FSHD.
    explanation: >-
      The report that established DNMT3B as an FSHD chromatin-modifier locus,
      and so the basis for a DNMT3B-specific subtype at all.
  - reference: PMID:34711481
    reference_title: "Facioscapulohumeral muscular dystrophy type 2: an update on the clinical, genetic, and molecular findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      These include the finding that FSHD2 is a digenic disease and that
      mutations in the genes SMCHD1, DNMT3B, and more recently LRIF1, can cause
      FSHD2.
    explanation: >-
      A review states that DNMT3B belongs to the same digenic,
      contraction-independent group as SMCHD1 and LRIF1, which is why this
      subtype sits inside the FSHD entry rather than standing alone.
  - reference: PMID:34711481
    reference_title: "Facioscapulohumeral muscular dystrophy type 2: an update on the clinical, genetic, and molecular findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: REVIEW_SYNTHESIS
    snippet: >-
      Phenotypically FSHD2 shows virtually no difference from FSHD1 and both
      forms of FSHD arise via a common downstream mechanism of epigenetic
      derepression of the transcription factor DUX4 in skeletal muscle cells.
    explanation: >-
      Sources the statement that no distinguishing clinical phenotype separates
      this subtype from the rest of FSHD, which is why no phenotype in this
      entry is scoped to FSHD4.
prevalence:
- population: Symptomatic population in the Netherlands
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_5_PER_10000
  rate_per_100000: 12.0
  percentage: 12 per 100,000
  notes: >-
    Population-based capture-recapture analysis estimated approximately 2,000
    symptomatic affected individuals in the Netherlands.
  evidence:
  - reference: PMID:25122204
    reference_title: "Population-based incidence and prevalence of facioscapulohumeral dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The prevalence rate was 12/100,000, equivalent to 2,000 affected
      individuals.
    explanation: >-
      Population-based prevalence estimate for symptomatic FSHD from a
      national registry analysis.
progression:
- phase: Typical onset
  age_range: Adolescence to early adulthood
  notes: >-
    Facial weakness and scapular instability usually appear first; the age at
    onset and severity vary widely across individuals and families.
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD symptoms usually start around the second decade and are most
      commonly characterized by asymmetric weakness affecting the face,
      shoulder, and arms, followed by the distal lower extremities and pelvic
      girdle. Not all patients have the complete phenotype of FSHD, and
      clinical severity varies widely among patients, including great
      variability of weakness within families.
    explanation: Supports onset around the second decade and the wide phenotypic variability across affected individuals and families.
- phase: Descending asymmetric progression
  age_range: Adulthood
  notes: >-
    Weakness usually spreads from face and shoulder girdle to upper arms,
    trunk, distal lower extremities, and pelvic girdle with marked
    side-to-side asymmetry.
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD symptoms usually start around the second decade and are most
      commonly characterized by asymmetric weakness affecting the face,
      shoulder, and arms, followed by the distal lower extremities and pelvic
      girdle.
    explanation: Describes the characteristic asymmetric distribution and descending spread of weakness from face and shoulder/arm involvement to distal lower extremities and pelvic girdle.
- phase: Loss of ambulation in a minority
  age_range: Adulthood
  notes: >-
    Roughly one in five affected individuals eventually requires a wheelchair,
    but life expectancy is not shortened. FSHD is therefore a disease of
    morbidity rather than mortality - a framing the patient community
    emphasizes and that distinguishes FSHD from dystrophies such as Duchenne.
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Weakness can be slowly progressive and approximately 20% of affected
      individuals eventually require a wheelchair. Life expectancy is not
      shortened.
    explanation: >-
      GeneReviews quantifies the proportion losing ambulation and confirms
      normal life expectancy.
- phase: Slow progression with a deteriorating minority
  age_range: Adulthood
  notes: >-
    Longitudinal registry and cohort data show that FSHD progresses slowly:
    function is largely static over 12 months, and over 6.5 years only about
    16% - all with moderate-to-severe baseline disease - show clinically
    important deterioration on a disease-specific patient-reported disability
    scale. This has a methodological consequence the patient community feels
    directly: because patients compensate for weakness, patient-reported
    outcome measures may under-detect real progression, which complicates
    trial design and can make patients' lived experience of decline appear
    absent from the data.
  evidence:
  - reference: PMID:40781929
    reference_title: "The Facioscapulohumeral Muscular Dystrophy Rasch-Built Overall Disability Scale (FSHD-RODS): Longitudinal Assessment of a Disease-Specific Patient Reported Outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Ten patients (16%), all with moderate-to-severe baseline disease (FSHD
      clinical severity score >= 6), showed clinically important
      deterioration over 6.5 years.
    explanation: >-
      Quantifies the deteriorating minority over a 6.5-year horizon and
      identifies baseline severity as the discriminator.
  - reference: PMID:40781929
    reference_title: "The Facioscapulohumeral Muscular Dystrophy Rasch-Built Overall Disability Scale (FSHD-RODS): Longitudinal Assessment of a Disease-Specific Patient Reported Outcome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The ability to compensate for muscle weakness may limit the sensitivity
      of patient-reported outcomes like FSHD-RODS in clinical trials.
    explanation: >-
      Documents that patient-reported outcome measures may under-detect
      progression in FSHD because of compensation, relevant to interpreting
      the patient-reported evidence used throughout this entry.
  - reference: PMID:38189531
    reference_title: "A longitudinal study of disease progression in facioscapulohumeral muscular dystrophy (FSHD)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a 12-month period, FSHD participant function remained largely stable
      with a mild worsening of strength, measured by MMT and standardized
      MVICT scores, and a mild loss in lean body mass.
    explanation: >-
      Prospective 12-month observational study confirms near-stability of
      function over a one-year horizon.
- phase: Respiratory decline in an at-risk subgroup
  age_range: Later adulthood
  notes: >-
    Respiratory function is stable in most patients over a five-year horizon.
    A minority - those with more severe baseline weakness, kyphoscoliosis,
    pectus excavatum, and declining axial muscle function - show pronounced
    deterioration and are the group for whom hypoventilation screening is
    indicated.
  evidence:
  - reference: PMID:35147730
    reference_title: "Long-term follow-up of respiratory function in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Respiratory function remained stable in most patients with FSHD, but a
      subgroup of patients showed a pronounced deterioration. They showed more
      severe muscle weakness including the leg muscles at baseline (Ricci score
      >= 6), had spinal and thorax deformities and a relatively fast decline in
      axial muscle function at follow-up.
    explanation: >-
      Five-year longitudinal cohort defines both the stable majority and the
      characteristics of the deteriorating subgroup.
pathophysiology:
- name: DNMT3B-Dependent D4Z4 Methylation Failure
  biological_scale: MOLECULAR
  description: >-
    The FSHD4 derepressing lesion. A heterozygous DNMT3B variant lowers de novo
    cytosine methylation across the D4Z4 macrosatellite even though the repeat
    array is of normal length, so the array loses methylation-dependent
    repression without any contraction. This is one of the two events FSHD4
    requires; on its own it produces hypomethylation without disease.
  genes:
  - preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  molecular_functions:
  - preferred_term: DNMT3B de novo cytosine methyltransferase activity at D4Z4
    modifier: DECREASED
    term:
      id: GO:0003886
      label: DNA (cytosine-5-)-methyltransferase activity
  evidence:
  - reference: PMID:27153398
    reference_title: "Mutations in DNMT3B Modify Epigenetic Repression of the D4Z4 Repeat and the Penetrance of Facioscapulohumeral Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we show that heterozygous mutations in DNA methyltransferase 3B
      (DNMT3B) are a likely cause of D4Z4 derepression associated with low
      levels of DUX4 expression from the D4Z4 repeat and increased penetrance
      of FSHD.
    explanation: >-
      Establishes heterozygous DNMT3B variants as a cause of D4Z4 derepression
      in humans, which is the claim this node makes.
  - reference: PMID:33004076
    reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In mESCs derived from D4Z4-2.5 mice, Dnmt3b was enriched at the D4Z4
      repeat array and DUX4 transcript levels were upregulated after a
      knockdown of Dnmt3b.
    explanation: >-
      Shows Dnmt3b occupying the D4Z4 array and its loss raising DUX4
      transcript, which is the molecular action this node asserts, in a
      cell-based system.
  downstream:
  - target: D4Z4 Epigenetic Derepression
    description: >-
      Loss of DNMT3B-dependent methylation at D4Z4 is one route into the shared
      chromatin-relaxation node, alongside repeat contraction and the other
      chromatin-modifier loci.
    evidence:
    - reference: PMID:20301616
      reference_title: "Facioscapulohumeral Muscular Dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Hypomethylation of the D4Z4 repeat array can be the result of a
        heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic
        pathogenic variants in LRIF1.
      explanation: >-
        GeneReviews attributes D4Z4 hypomethylation to a heterozygous DNMT3B
        variant, which is the edge drawn here.
- name: Permissive 4qA Polyadenylation Signal
  biological_scale: MOLECULAR
  description: >-
    The second locus, and the reason FSHD4 is digenic rather than dominant at
    one gene. Only a 4qA subtelomere carries the pLAM polyadenylation signal
    immediately distal to the last D4Z4 unit; on that background the distal
    DUX4 transcript is efficiently polyadenylated and stable enough to persist
    in somatic cells, whereas non-permissive 4qB and chromosome 10q backgrounds
    lack a usable signal. It is modelled separately from the derepressing
    lesion because the two segregate independently and disease needs both: a
    DNMT3B variant without a permissive allele derepresses an array whose
    transcript cannot be stabilised.
  genes:
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  biological_processes:
  - preferred_term: polyadenylation of the distal DUX4 transcript at pLAM
    modifier: INCREASED
    term:
      id: GO:0180010
      label: "co-transcriptional mRNA 3'-end processing, cleavage and polyadenylation pathway"
  - preferred_term: stabilisation of the distal DUX4 message
    modifier: INCREASED
    term:
      id: GO:0048255
      label: mRNA stabilization
  evidence:
  - reference: PMID:20724583
    reference_title: "A unifying genetic model for facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This FSHD-predisposing configuration creates a canonical polyadenylation
      signal for transcripts derived from DUX4, a double homeobox gene of
      unknown function that straddles the last repeat unit and the adjacent
      sequence.
    explanation: >-
      Identifies the permissive haplotype's contribution as a polyadenylation
      signal for DUX4, which is what this node represents.
  - reference: PMID:20724583
    reference_title: "A unifying genetic model for facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Transfection studies revealed that DUX4 transcripts are efficiently
      polyadenylated and are more stable when expressed from permissive
      chromosomes.
    explanation: >-
      Cell-based demonstration that the permissive allele, not the repeat
      itself, is what makes the DUX4 message stable.
  - reference: PMID:33004076
    reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      A prerequisite for the expression of DUX4 is the presence of a
      polyadenylation signal to stabilize the mRNA transcript in somatic cells
      that is only present on 4qA alleles
    explanation: >-
      States the permissive allele as a prerequisite, which is the necessity
      claim that makes this a separate required node rather than a modifier.
      The sentence is introductory background in a mouse paper and describes
      human genetics.
  downstream:
  - target: DUX4 Misexpression in Skeletal Muscle
    description: >-
      The permissive polyadenylation signal acts at the transcript, not at the
      chromatin: it converts derepression of the array into a stable DUX4
      message in muscle. Without it, derepression alone does not yield
      accumulating DUX4.
    evidence:
    - reference: PMID:20724583
      reference_title: "A unifying genetic model for facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Transfection studies revealed that DUX4 transcripts are efficiently
        polyadenylated and are more stable when expressed from permissive
        chromosomes.
      explanation: >-
        Links the permissive configuration directly to a stabilised DUX4
        transcript, which is the edge drawn here.
- name: D4Z4 Epigenetic Derepression
  description: >-
    FSHD develops when D4Z4 contraction or contraction-independent
    hypomethylation occurs on a permissive 4qA subtelomere, relaxing
    chromatin and enabling pathogenic DUX4 expression.
  genes:
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  - preferred_term: SMCHD1
    term:
      id: hgnc:29090
      label: SMCHD1
  - preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  - preferred_term: LRIF1
    term:
      id: hgnc:30299
      label: LRIF1
  evidence:
  - reference: PMID:19728363
    reference_title: "Common epigenetic changes of D4Z4 in contraction-dependent and contraction-independent FSHD."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To develop FSHD, D4Z4 contraction needs to occur on a specific
      genetic background. Only contractions associated with the 4qA161
      haplotype cause FSHD.
    explanation: >-
      Establishes that pathogenic D4Z4 contraction requires a permissive
      4qA background rather than repeat size alone.
  - reference: PMID:29478599
    reference_title: "Facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recent studies demonstrate that contraction in the number of D4Z4
      repeats results in chromatin relaxation and transcriptional
      de-repression of DUX4, a gene normally expressed only in the
      germline.
    explanation: >-
      Summarizes the central epigenetic lesion linking D4Z4 contraction to
      pathogenic DUX4 derepression.
  downstream:
  - target: DUX4 Misexpression in Skeletal Muscle
    description: >-
      Loss of repression at the FSHD locus permits aberrant DUX4 expression
      in differentiated skeletal muscle.
    evidence:
    - reference: PMID:29478599
      reference_title: "Facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Recent studies demonstrate that contraction in the number of D4Z4
        repeats results in chromatin relaxation and transcriptional
        de-repression of DUX4, a gene normally expressed only in the germline.
      explanation: >-
        Directly links D4Z4 repeat contraction and chromatin relaxation to
        derepressed DUX4 expression.
  - target: Sensorineural hearing impairment
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Severe early-onset FSHD with large 4q35 deletions can include
      sensorineural hearing loss through extra-muscular intermediates not
      represented in the skeletal-muscle pathograph.
  - target: Retinal vasculopathy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Retinal vasculopathy travels with the same large-deletion, early-onset end
      of the D4Z4 contraction spectrum as hearing loss, so it is placed here
      alongside it rather than downstream of myofiber loss.
    evidence:
    - reference: PMID:30923442
      reference_title: "A Pediatric Review of Facioscapulohumeral Muscular Dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "early-onset FSHD is associated with a large deletion of D4Z4 repeats and a more severe disease phenotype, including early loss of independent ambulation as well as extramuscular manifestations, such as retinal vasculopathy, hearing loss, and central nervous system (CNS) involvement"
      explanation: Supports the edge from the size of the D4Z4 contraction to the extramuscular ophthalmologic feature.
- name: DUX4 Misexpression in Skeletal Muscle
  description: >-
    Intermittent DUX4 expression in skeletal muscle activates an embryonic
    transcriptional program and promotes muscle fiber toxicity and death.
  genes:
  - preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
    modifier: INCREASED
  cell_types:
  - preferred_term: Skeletal Muscle Fiber
    term:
      id: CL:0000188
      label: cell of skeletal muscle
  biological_processes:
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
  evidence:
  - reference: PMID:32576599
    reference_title: "p38α Regulates Expression of DUX4 in a Model of Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Facioscapulohumeral muscular dystrophy (FSHD) is caused by the loss of
      repression at the D4Z4 locus leading to aberrant double homeobox 4
      (DUX4) expression in skeletal muscle. Activation of this early
      embryonic transcription factor results in the expression of its target
      genes causing muscle fiber death.
    explanation: >-
      Patient-derived myotube work directly connects DUX4 activation to the
      downstream transcriptional program and muscle-cell toxicity.
  downstream:
  - target: Progressive Myofiber Loss and Fatty Replacement
    description: >-
      Recurrent DUX4-mediated injury drives chronic muscle degeneration with
      incomplete repair and replacement by fat and fibrous tissue.
    evidence:
    - reference: PMID:32576599
      reference_title: "p38α Regulates Expression of DUX4 in a Model of Facioscapulohumeral Muscular Dystrophy."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Activation of this early embryonic transcription factor results in the
        expression of its target genes causing muscle fiber death.
      explanation: >-
        Patient-derived myotube evidence links DUX4 activation to downstream
        muscle fiber death, supporting the DUX4-to-myofiber-loss edge.
- name: Progressive Myofiber Loss and Fatty Replacement
  description: >-
    The clinical pattern of FSHD reflects chronic degeneration of selected
    facial, scapular, humeral, truncal, and lower-extremity muscles, usually
    with marked asymmetry and variable progression.
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD symptoms usually start around the second decade and are most
      commonly characterized by asymmetric weakness affecting the face,
      shoulder, and arms, followed by the distal lower extremities and
      pelvic girdle.
    explanation: >-
      Registry-based clinical data capture the stereotyped anatomic spread
      and asymmetry of muscle involvement in FSHD.
  downstream:
  - target: Facial weakness
    description: >-
      Early involvement of the muscles of facial expression contributes to
      incomplete eye closure, poor smile excursion, and facial asymmetry.
    evidence:
    - reference: PMID:17924332
      reference_title: "Specific sequence variations within the 4q35 region are associated with facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is
        mainly characterized by progressive wasting and weakness of the facial,
        shoulder, and upper-arm muscles.
      explanation: >-
        Supports facial weakness as a direct clinical consequence of the
        progressive muscle involvement in FSHD.
  - target: Scapular winging
    description: >-
      Periscapular weakness destabilizes the scapulothoracic joint and
      limits active shoulder elevation.
    evidence:
    - reference: PMID:18056023
      reference_title: "Fixation of winged scapula in facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Participants: Thirteen patients with bilateral winged scapula affected
        by facioscapulohumeral muscular dystrophy.
      explanation: >-
        Clinical surgical series documents scapular winging as an FSHD
        manifestation linked to shoulder-girdle muscle involvement.
  - target: Muscle weakness
    description: >-
      Progressive weakness extends to upper arm, trunk, pelvic-girdle, and
      distal lower-extremity muscles.
    evidence:
    - reference: PMID:29053898
      reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        FSHD symptoms usually start around the second decade and are most
        commonly characterized by asymmetric weakness affecting the face,
        shoulder, and arms, followed by the distal lower extremities and pelvic
        girdle.
      explanation: >-
        Supports the anatomic spread of progressive FSHD muscle weakness.
  - target: Myalgia
    description: >-
      Chronic biomechanical strain and ongoing muscle pathology contribute to
      frequent shoulder and low-back pain.
    evidence:
    - reference: PMID:29053898
      reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pain was reported most frequently in the shoulders and lower back.
        These localizations are consistent with the findings of previous
        studies.10 We hypothesize that the degree of pain in these two locations
        may be exacerbated by the fact that the muscles in this region are
        amongst the weakest muscle groups in FSHD1.
      explanation: >-
        Clinical registry data support the pain distribution and provide a
        mechanistic hypothesis connecting pain to the weakest muscle groups.
phenotypes:
- name: Facial weakness
  category: Musculoskeletal
  frequency: VERY_FREQUENT
  diagnostic: true
  description: >-
    Weakness of the facial musculature is often an early and characteristic
    manifestation of FSHD.
  phenotype_term:
    preferred_term: facial weakness
    term:
      id: HP:0030319
      label: Weakness of facial musculature
  evidence:
  - reference: PMID:17924332
    reference_title: "Specific sequence variations within the 4q35 region are associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autosomal dominant facioscapulohumeral muscular dystrophy (FSHD) is
      mainly characterized by progressive wasting and weakness of the
      facial, shoulder, and upper-arm muscles.
    explanation: >-
      This classic genetic study summarizes the canonical early distribution
      of weakness in FSHD.
  - reference: PMID:39297366
    reference_title: "The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      of whom 92% showed signs of facial weakness
    explanation: >-
      Muscle-ultrasound study of 107 participants quantifies facial weakness
      at 92%, supporting the VERY_FREQUENT band (80-100%), and extends the
      phenotype to specific orofacial muscles (zygomaticus minor most often
      affected) that are not captured by standard facial weakness scoring.
- name: Scapular winging
  category: Musculoskeletal
  frequency: VERY_FREQUENT
  diagnostic: true
  description: >-
    Weakness of scapular stabilizers produces winging and limits active
    shoulder abduction and flexion.
  phenotype_term:
    preferred_term: Scapular winging
    term:
      id: HP:0003691
      label: Scapular winging
  evidence:
  - reference: PMID:18056023
    reference_title: "Fixation of winged scapula in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Participants: Thirteen patients with bilateral winged scapula
      affected by facioscapulohumeral muscular dystrophy.
    explanation: >-
      Surgical series directly documents scapular winging as a common and
      functionally important manifestation of FSHD.
- name: Muscle weakness
  category: Musculoskeletal
  frequency: VERY_FREQUENT
  diagnostic: true
  description: >-
    Weakness is typically asymmetric and descends from facial and shoulder
    muscles to the upper arms, trunk, distal lower extremities, and pelvic
    girdle.
  phenotype_term:
    preferred_term: Muscle weakness
    term:
      id: HP:0001324
      label: Muscle weakness
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD symptoms usually start around the second decade and are most
      commonly characterized by asymmetric weakness affecting the face,
      shoulder, and arms, followed by the distal lower extremities and
      pelvic girdle.
    explanation: >-
      Supports both the distribution and the asymmetric progression of
      weakness in FSHD.
- name: Myalgia
  category: Musculoskeletal
  frequency: FREQUENT
  description: >-
    Chronic pain commonly affects the shoulders and lower back and is an
    important contributor to disability and reduced quality of life.
  phenotype_term:
    preferred_term: Myalgia
    term:
      id: HP:0003326
      label: Myalgia
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of 398 patients, 88.6% reported pain at the time of study. The most
      frequent locations were shoulders and lower back.
    explanation: >-
      Large registry-based study shows that pain is common and localizes to
      the shoulder and lumbar regions most affected by weakness and posture.
- name: Sensorineural hearing impairment
  category: Otolaryngologic
  frequency: OCCASIONAL
  description: >-
    Hearing impairment is an extra-muscular feature seen mainly in severe
    early-onset disease with very short 4q35 fragments.
  phenotype_term:
    preferred_term: Sensorineural hearing impairment
    term:
      id: HP:0000407
      label: Sensorineural hearing impairment
  evidence:
  - reference: PMID:19049553
    reference_title: "Facioscapulohumeral muscular dystrophy: hearing loss and other atypical features of patients with large 4q35 deletions."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sensorineural hearing loss was found in four patients, who presented
      infantile-onset dystrophic phenotype.
    explanation: >-
      Supports hearing loss as a recognized extra-muscular phenotype in
      severe early-onset FSHD with large 4q35 deletions.
  - reference: PMID:40879179
    reference_title: "Hearing Loss, Retinal Abnormality, and Seizures in People With Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hearing loss (13%; n = 71) was the most frequently reported comorbidity,
      followed by retinal abnormalities
    explanation: >-
      Population-based MD STARnet surveillance data (n=548) quantify
      clinically diagnosed hearing loss at 13%, supporting the OCCASIONAL
      band (5-29%) and making it the most common extra-muscular comorbidity
      of FSHD.
- name: Fatigue
  category: Constitutional
  frequency: VERY_FREQUENT
  description: >-
    Chronic fatigue is among the most prevalent and most disabling
    manifestations of FSHD, yet it is rarely emphasized in classic clinical
    descriptions of the disease. Patient-reported outcome studies and patient
    organizations consistently rank it alongside shoulder/arm weakness as a
    dominant part of the lived disease burden. Patients experience it as
    unpredictable and poorly explained, which makes it difficult to
    self-manage.
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
    temporality: CHRONIC
  evidence:
  - reference: PMID:31409737
    reference_title: "Patient-Reported Symptoms in Facioscapulohumeral Muscular Dystrophy (PRISM-FSHD)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The symptomatic themes with the highest prevalence in our sample were
      problems with shoulders or arms (96.9%), limitations with activities
      (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with
      mobility and walking (93.6%), changed body image due to the disease
      (91.6%), and pain (87.7%).
    explanation: >-
      Cross-sectional patient-reported outcome study of 328 individuals
      quantifies fatigue at 93.8%, supporting the VERY_FREQUENT band
      (80-100%).
  - reference: PMID:27762634
    reference_title: "Fatigue in facioscapulohumeral muscular dystrophy: a qualitative study of people's experiences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients describe fatigue as an overwhelming and unpredictable
      experience and they make a distinction between actual experienced
      fatigue and fear of becoming tired.
    explanation: >-
      Qualitative interview study of 25 patients characterizes the subjective
      quality of FSHD fatigue that quantitative scales do not capture.
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Pain and tiredness can make daily life harder, even though people don’t
      always realize how much they affect someone with FSHD.
    explanation: >-
      The principal FSHD patient advocacy organization states that fatigue is a
      day-to-day functional burden whose impact is routinely under-recognized,
      corroborating fatigue as a core communicated symptom.
- name: Abdominal wall muscle weakness
  category: Musculoskeletal
  description: >-
    Weakness of the abdominal wall musculature produces protuberant abdominal
    contour and a positive (often inverted or asymmetric) Beevor sign. Patients
    and families describe this as a prominent and distressing feature - the
    FSHD Society symptom list renders it in plain language as weak stomach
    muscles causing a "pregnant" belly look - and patient-reported outcome data
    rank core weakness among the most prevalent symptom themes (93.8%), yet it
    is under-represented relative to facial and scapular weakness in standard
    disease descriptions.
  phenotype_term:
    preferred_term: Abdominal wall muscle weakness
    term:
      id: HP:0009023
      label: Abdominal wall muscle weakness
  evidence:
  - reference: PMID:31409737
    reference_title: "Patient-Reported Symptoms in Facioscapulohumeral Muscular Dystrophy (PRISM-FSHD)."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The symptomatic themes with the highest prevalence in our sample were
      problems with shoulders or arms (96.9%), limitations with activities
      (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with
      mobility and walking (93.6%), changed body image due to the disease
      (91.6%), and pain (87.7%).
    explanation: >-
      Supports high prevalence of patient-reported core weakness. The
      support is indirect because the patient-reported "core weakness" theme
      is broader than examination-confirmed abdominal wall muscle weakness.
- name: Foot dorsiflexor weakness
  category: Musculoskeletal
  description: >-
    Weakness of the ankle dorsiflexors produces foot drop, tripping, and
    reduced walking safety. GeneReviews lists foot dorsiflexor weakness among
    the typical presenting features alongside facial and scapular weakness,
    and it is a common early complaint in the patient community.
  phenotype_term:
    preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Facioscapulohumeral muscular dystrophy (FSHD) typically presents with
      weakness of the facial muscles, the stabilizers of the scapula, and/or
      the dorsiflexors of the foot.
    explanation: >-
      GeneReviews places foot dorsiflexor weakness among the canonical
      presenting features of FSHD.
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Foot drop (trouble lifting the foot)"
    explanation: >-
      Patient organization symptom list documents foot drop as a recognized
      manifestation communicated to the patient community.
- name: Falls
  category: Musculoskeletal
  description: >-
    Sudden falls from unexpected buckling of the legs are frequently described
    by patients and are a specific safety concern the community raises. Falls
    are clinically actionable: GeneReviews recommends ankle-foot orthoses
    explicitly to improve mobility and prevent falls.
  phenotype_term:
    preferred_term: Falls
    term:
      id: HP:0002527
      label: Falls
  evidence:
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Sudden falls when their legs unexpectedly give out"
    explanation: >-
      Patient organization documents sudden falls in the experiential terms
      the community uses; this manifestation is not prominent in the primary
      clinical literature.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ankle-foot orthoses to improve mobility and prevent falls"
    explanation: >-
      GeneReviews management guidance treats falls as an expected,
      preventable complication, corroborating the community report.
- name: Lagophthalmos
  category: Ophthalmologic
  description: >-
    Facial weakness prevents complete eyelid closure, so many patients sleep
    with their eyes partly open. The community describes this plainly, and it
    carries a concrete clinical consequence - exposure keratitis - for which
    GeneReviews recommends ocular lubricants or taping the eyes shut at night.
  phenotype_term:
    preferred_term: Lagophthalmos
    term:
      id: HP:0030001
      label: Lagophthalmos
  evidence:
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Eyes that don’t fully close during sleep"
    explanation: >-
      Patient organization symptom list documents incomplete eye closure
      during sleep as a recognized FSHD manifestation.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ocular lubricants or taping the eyes shut during sleep to treat exposure
      keratitis
    explanation: >-
      GeneReviews management guidance confirms incomplete eyelid closure and
      its corneal-exposure consequence as an expected feature requiring
      treatment.
- name: Lumbar hyperlordosis
  category: Musculoskeletal
  description: >-
    Axial and abdominal weakness produces compensatory lumbar hyperlordosis,
    which contributes to the low back pain that patients rank among their most
    burdensome symptoms.
  phenotype_term:
    preferred_term: Lumbar hyperlordosis
    term:
      id: HP:0002938
      label: Lumbar hyperlordosis
  evidence:
  - reference: PMID:32791439
    reference_title: "Correlations between radiographic spinopelvic parameters and health-related quality of life: A prospective evaluation of 37 patients with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hyperlordosis inlumbar spine, hypolordosis in cervical spine and
      negative sagittal balance were the most common spinal misalignments in
      patients with FSHD.
    explanation: >-
      Prospective radiographic study identifies lumbar hyperlordosis as the
      most common spinal misalignment in FSHD. (The abstract contains the
      typographical error "inlumbar"; the snippet is quoted verbatim as
      required.)
  - reference: PMID:32791439
    reference_title: "Correlations between radiographic spinopelvic parameters and health-related quality of life: A prospective evaluation of 37 patients with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      There was a significantly negative correlation between LL, PI-LL and
      PCS.
    explanation: >-
      Links greater lumbar lordosis to worse physical quality-of-life scores,
      connecting the spinal deformity to the functional burden patients
      report.
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Curved spine (lordosis, kyphosis, scoliosis)"
    explanation: >-
      Patient organization lists spinal curvature including lordosis among
      recognized skeletal consequences of FSHD.
- name: Scoliosis
  category: Musculoskeletal
  description: >-
    Spinal deformity develops as a consequence of asymmetric axial muscle
    weakness. Kyphoscoliosis is clinically important because it marks the
    subgroup at risk of respiratory decline and triggers hypoventilation
    screening.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: PMID:35147730
    reference_title: "Long-term follow-up of respiratory function in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      They developed more frequently spinal and thorax deformities (p < 0.001
      for kyphoscoliosis and 0.012 for pectus excavatum) and had a larger
      decline in axial muscle function (p = 0.020).
    explanation: >-
      Longitudinal cohort links spinal deformity to the subgroup with
      pronounced respiratory deterioration.
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Curved spine (lordosis, kyphosis, scoliosis)"
    explanation: >-
      Patient organization documents scoliosis among the skeletal
      manifestations communicated to families.
- name: Pectus excavatum
  category: Musculoskeletal
  description: >-
    Chest wall deformity accompanies loss of chest and axial musculature and,
    like kyphoscoliosis, associates with the subgroup showing accelerated
    respiratory decline. The FSHD Society symptom list names it in patient
    language as sunken chest.
  phenotype_term:
    preferred_term: Pectus excavatum
    term:
      id: HP:0000767
      label: Pectus excavatum
  evidence:
  - reference: PMID:35147730
    reference_title: "Long-term follow-up of respiratory function in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      They developed more frequently spinal and thorax deformities (p < 0.001
      for kyphoscoliosis and 0.012 for pectus excavatum) and had a larger
      decline in axial muscle function (p = 0.020).
    explanation: >-
      Longitudinal cohort documents pectus excavatum and its association with
      declining respiratory function.
- name: Restrictive ventilatory defect
  category: Respiratory
  frequency: FREQUENT
  description: >-
    Respiratory muscle and chest wall involvement produces a restrictive
    ventilatory pattern in a substantial minority of adults. Most patients
    remain stable over years, but a subgroup with severe weakness,
    kyphoscoliosis, and wheelchair dependence declines and warrants
    hypoventilation screening. Patients describe this simply as trouble
    breathing.
  phenotype_term:
    preferred_term: Restrictive ventilatory defect
    term:
      id: HP:0002091
      label: Restrictive ventilatory defect
  evidence:
  - reference: PMID:35147730
    reference_title: "Long-term follow-up of respiratory function in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At baseline, the spirometry outcomes of 41 patients showed a restrictive
      ventilatory pattern (FVC < 80% and FEV1/FVC >= 70% of predicted) and of
      48 patients at follow-up.
    explanation: >-
      In a 92-patient longitudinal cohort, 41/92 (45%) had a restrictive
      pattern at baseline, supporting the FREQUENT band (30-79%).
- name: Atrial fibrillation
  category: Cardiovascular
  frequency: OCCASIONAL
  description: >-
    Cardiac involvement in FSHD is minor relative to other muscular
    dystrophies but is not absent. Atrial fibrillation or flutter was
    documented in 5% of a genetically confirmed cohort. The patient community
    is told to expect mild rhythm problems in a small minority.
  phenotype_term:
    preferred_term: Atrial fibrillation
    term:
      id: HP:0005110
      label: Atrial fibrillation
  evidence:
  - reference: PMID:34108930
    reference_title: "Cardiac Involvement in Facioscapulohumeral Muscular Dystrophy (FSHD)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Atrial fibrillation or flutter were seen in 5% of patients.
    explanation: >-
      Review of 104 genetically confirmed patients quantifies atrial
      arrhythmia at 5%, within the OCCASIONAL band (5-29%).
  - reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
    reference_title: "Symptoms - FSHD Society"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Mild heart rhythm problems (happens in 5-9% of people)"
    explanation: >-
      Patient organization communicates a 5-9% frequency of mild rhythm
      disturbance, concordant with the OCCASIONAL band.
- name: Atrial flutter
  category: Cardiovascular
  description: >-
    Reported together with atrial fibrillation as the atrial arrhythmia
    finding in a genetically confirmed FSHD cohort. Curated separately from
    atrial fibrillation because the source reports the two as a combined
    category and HPO has no single term spanning both. No frequency band is
    asserted: the only quantitative source reports 5% for atrial fibrillation
    OR flutter combined, which bounds the flutter-specific rate at <=5% but
    does not locate it within a band (it may fall below the OCCASIONAL floor).
  phenotype_term:
    preferred_term: Atrial flutter
    term:
      id: HP:0004749
      label: Atrial flutter
  evidence:
  - reference: PMID:34108930
    reference_title: "Cardiac Involvement in Facioscapulohumeral Muscular Dystrophy (FSHD)."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Atrial fibrillation or flutter were seen in 5% of patients.
    explanation: >-
      The 5% figure is reported for atrial fibrillation OR flutter combined,
      so it bounds but does not isolate the flutter-specific rate; the
      support for flutter is therefore indirect.
- name: Complete right bundle branch block
  category: Cardiovascular
  frequency: OCCASIONAL
  description: >-
    Right bundle branch block is the single most common conduction
    abnormality found in FSHD, at 7% complete and 5% incomplete in a
    genetically confirmed cohort. It is usually clinically silent, which is
    part of why cardiac involvement in FSHD is often described as minor.
  phenotype_term:
    preferred_term: Complete right bundle branch block
    term:
      id: HP:0011712
      label: Complete right bundle branch block
  evidence:
  - reference: PMID:34108930
    reference_title: "Cardiac Involvement in Facioscapulohumeral Muscular Dystrophy (FSHD)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most common conduction abnormality was complete (7%) or incomplete
      (5%) right bundle branch block (RBBB).
    explanation: >-
      Quantifies complete RBBB at 7% in 104 genetically confirmed patients,
      within the OCCASIONAL band (5-29%).
- name: Retinal telangiectasia
  category: Ophthalmologic
  frequency: FREQUENT
  description: >-
    Retinal vasculopathy - telangiectasia, microaneurysms, and increased
    arterial tortuosity - is common on dedicated imaging but usually
    asymptomatic. Its clinical significance is the rare progression to
    Coats-like exudative retinopathy, which is sight-threatening and occurs
    mainly in early-onset disease with large D4Z4 contractions. This is why
    the patient community is counselled about Coats disease despite its
    rarity.
  phenotype_term:
    preferred_term: Retinal telangiectasia
    term:
      id: HP:0007763
      label: Retinal telangiectasia
  notes: >-
    Denotes the usually asymptomatic angiographic finding. The rare,
    sight-threatening Coats-like exudative form is recorded separately under
    the Retinal vasculopathy phenotype.
  evidence:
  - reference: PMID:23573590
    reference_title: "On the significance of retinal vascular disease and hearing loss in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A mild to moderate retinal vasculopathy, consisting of retinal
      teleangiectasis and microaneursyms, was present in 18 of 37 evaluable
      angiograms (49%)
    explanation: >-
      Fluorescein angiography in 39 patients found retinal telangiectasia in
      49%, supporting the FREQUENT band (30-79%).
  - reference: PMID:36900126
    reference_title: "Artificial Intelligence for Evaluation of Retinal Vasculopathy in Facioscapulohumeral Dystrophy Using OCT Angiography: A Case Series."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Increased tortuosity of the retinal arteries was qualitatively observed
      in 77% of the included eyes.
    explanation: >-
      Modern OCT-angiography series corroborates a high prevalence of
      subclinical retinal vascular abnormality.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      annual dilated ophthalmoscopy in individuals with early childhood-onset
      FSHD with large pathogenic contraction of D4Z4 and adults with visual
      symptoms
    explanation: >-
      GeneReviews surveillance guidance establishes retinal vasculopathy as
      an actionable extra-muscular manifestation requiring screening.
  - reference: PMID:40879179
    reference_title: "Hearing Loss, Retinal Abnormality, and Seizures in People With Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hearing loss (13%; n = 71) was the most frequently reported comorbidity,
      followed by retinal abnormalities
    explanation: >-
      Population-based surveillance records CLINICALLY DIAGNOSED retinal
      abnormality in only 3.6% of 548 individuals, against 49% detected by
      dedicated fluorescein angiography. The two figures are not in conflict:
      they measure different things - subclinical angiographic telangiectasia
      versus a retinal diagnosis recorded in routine care. The FREQUENT band
      here reflects the angiographic finding that the phenotype term denotes;
      the clinical-detection rate is roughly an order of magnitude lower,
      which is precisely why targeted ophthalmologic surveillance is
      recommended. The support is indirect because this source bounds
      clinical detection rather than the imaging phenotype.
- name: Obstructive sleep apnea
  category: Respiratory
  description: >-
    Sleep-disordered breathing is common among FSHD patients who report
    sleep-related symptoms, and it is a treatable contributor to the daytime
    fatigue that dominates patient-reported symptom burden. Recognizing it
    matters because the community consistently describes unexplained,
    unrefreshing tiredness.
  phenotype_term:
    preferred_term: Obstructive sleep apnea
    term:
      id: HP:0002870
      label: Obstructive sleep apnea
  evidence:
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In the FSHD group, 17/31 (55%) patients showed OSA and 8 (26%) had NH.
    explanation: >-
      Sleep-laboratory study documents obstructive sleep apnea in 55% of FSHD
      patients evaluated for sleep-related symptoms. Frequency is
      intentionally omitted because this is a symptom-selected referral
      cohort, not a population sample.
- name: Nocturnal hypoventilation
  category: Respiratory
  description: >-
    Nocturnal hypoventilation is under-detected in FSHD because pulse
    oximetry alone misses most cases; transcutaneous capnometry is required.
    It is directly actionable - non-invasive ventilation improved nocturnal
    gas exchange from the first night of treatment.
  phenotype_term:
    preferred_term: Nocturnal hypoventilation
    term:
      id: HP:0002877
      label: Nocturnal hypoventilation
  evidence:
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      NH would have been missed in 7/8 patients if only oximetry criteria of
      hypoventilation had been applied.
    explanation: >-
      Documents systematic under-detection of nocturnal hypoventilation with
      standard oximetry, explaining why this manifestation is
      under-represented in clinical descriptions.
- name: Headache
  category: Neurologic
  description: >-
    Head-region pain is reported in FSHD national registry data as part of a
    combined head-and-shoulder pain category, yet headache is essentially
    absent from standard clinical descriptions of the disease. This phenotype
    was surfaced as a patient-community discussion topic (r/FSHD "migraines")
    and then corroborated - though not quantified - by registry evidence; note
    the community term "migraine" is broader than the head-region pain the
    registry documents. Two distinct mechanisms are plausible and not mutually
    exclusive: cervical and axial muscle weakness with postural strain, and
    morning headache arising from nocturnal hypoventilation, which is
    documented in FSHD and under-detected by oximetry. The distinction matters
    because the second is directly treatable with ventilatory support. No
    frequency band is assigned: see the evidence explanation below.
  phenotype_term:
    preferred_term: Headache
    term:
      id: HP:0002315
      label: Headache
  evidence:
  - reference: PMID:38016873
    reference_title: "The Dutch registry for facioscapulohumeral muscular dystrophy: Cohort profile and longitudinal patient reported outcomes."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pain was experienced most often in the head and shoulder region (193,
      52%).
    explanation: >-
      National registry of 373 participants reports 52% for a COMBINED
      head-and-shoulder pain category. Because FSHD is dominated by
      scapular and periscapular pathology, an unknown and plausibly majority
      share of that 52% is shoulder pain, so a head-specific rate cannot be
      recovered from this abstract and could fall below the FREQUENT floor.
      The support is indirect and no `frequency:` is assigned: this
      corroborates head-region pain as a real component of FSHD pain burden
      but does not quantify it.
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Indications for admission included non-restorative sleep, morning
      headache, or excessive daytime
    explanation: >-
      Identifies morning headache as a presenting symptom prompting sleep
      evaluation in FSHD, supplying a treatable mechanism for part of the
      headache burden.
- name: Retinal vasculopathy
  category: Ophthalmologic
  frequency: VERY_RARE
  description: >-
    A telangiectatic, sometimes exudative retinal vasculopathy resembling Coats
    disease is the ophthalmologic extramuscular feature of FSHD. Like hearing
    loss, it clusters in early-onset disease with large D4Z4 deletions, and it
    is the human counterpart of the vascular arm of the disease that the frog
    FRG1 model addresses.
  phenotype_term:
    preferred_term: Retinal vasculopathy
    term:
      id: HP:0008046
      label: Abnormal retinal vascular morphology
  evidence:
  - reference: PMID:30923442
    reference_title: "A Pediatric Review of Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "early-onset FSHD is associated with a large deletion of D4Z4 repeats and a more severe disease phenotype, including early loss of independent ambulation as well as extramuscular manifestations, such as retinal vasculopathy, hearing loss, and central nervous system (CNS) involvement"
    explanation: Places retinal vasculopathy among the extramuscular features and ties it to large D4Z4 deletions.
  - reference: PMID:30923442
    reference_title: "A Pediatric Review of Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "patients with FSHD had retinal vasculopathy with features resembling Coats"
    explanation: Characterizes the vasculopathy as Coats-like, which is the specific ophthalmologic pattern described.
  - reference: PMID:30923442
    reference_title: "A Pediatric Review of Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    directness: DIRECT
    quote_role: REVIEW_SYNTHESIS
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Tawil et al concluded that although up to 25% (95% CI: 20.9–30.8%) of
      patients with FSHD had abnormalities on retinal examination, only 0.6%
      (95% CI: 0.2–1.5%) had symptomatic retinal disease
    explanation: >-
      Quantifies the symptomatic, Coats-like vasculopathy this node denotes at
      well under 5% (0.6%; the same review also cites 1.7% in a Dutch
      population survey and 0.8% in FSHD1), supporting the VERY_RARE band.
      The 25% examination-abnormality figure belongs to the asymptomatic
      telangiectasia recorded under the Retinal telangiectasia phenotype.
  notes: >-
    Denotes the clinically significant, Coats-like exudative vasculopathy.
    The far commoner asymptomatic retinal telangiectasia seen on fluorescein
    angiography (about half of patients) is recorded separately under the
    Retinal telangiectasia phenotype; the two carry different frequency
    bands because they measure different things.
biochemical:
- name: Creatine Kinase
  presence: Mildly elevated
  context: >-
    Serum creatine kinase is often normal to mildly elevated rather than
    markedly increased.
genetic:
- name: D4Z4 repeat contraction on permissive 4qA haplotype
  subtype: FSHD1
  association: Causative repeat contraction
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  notes: >-
    Most genetically confirmed cases reflect contraction of the D4Z4 repeat
    array on a permissive 4qA chromosome. Repeat contraction alone is not
    sufficient if it occurs on nonpermissive haplotypes.
  evidence:
  - reference: PMID:17924332
    reference_title: "Specific sequence variations within the 4q35 region are associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Yet only repeat contractions of D4Z4 on chromosome 4qA cause FSHD;
      contractions on the other chromosomes are nonpathogenic.
    explanation: >-
      Establishes the pathogenic requirement for contraction on a permissive
      4qA background in FSHD1.
- name: SMCHD1
  subtype: FSHD2
  association: Causative chromatin modifier variant on a permissive D4Z4 background
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: SMCHD1
    term:
      id: hgnc:29090
      label: SMCHD1
  notes: >-
    In FSHD2, pathogenic variants in SMCHD1 impair chromatin repression and
    lead to contraction-independent D4Z4 hypomethylation with inappropriate
    DUX4 expression.
  evidence:
  - reference: PMID:29478599
    reference_title: "Facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The chromatin changes in this form of FSHD (FSHD2) are the result, in
      most cases, of mutations in SMCHD1, a gene on chromosome 18 involved
      in chromatin regulation.
    explanation: >-
      Review-level summary directly links SMCHD1-mediated chromatin failure
      to FSHD2 pathogenesis.
- name: DNMT3B
  subtype: FSHD4
  association: Chromatin-modifier variant causing D4Z4 hypomethylation on a permissive background
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  notes: >-
    DNMT3B is the second FSHD2 chromatin-repressor locus. GeneReviews accepts a
    heterozygous DNMT3B variant, alongside D4Z4 hypomethylation on a permissive
    chromosome 4 haplotype, as establishing the FSHD2 diagnosis. The defining
    study frames the effect as derepression with low-level DUX4 expression and
    increased penetrance rather than as a full-strength SMCHD1 equivalent, so
    the CAUSATIVE grading should be read with that caveat.

    Biallelic DNMT3B variants cause a different disease - immunodeficiency,
    centromeric instability and facial anomalies (ICF1) syndrome, which dismech
    curates separately; the FSHD2 allele state is heterozygous.

    This row is scoped to the FSHD4 subtype rather than to FSHD2 because
    MONDO:0030355 (OMIM 619478) names the DNMT3B form specifically. The two
    labels describe the same patients from different angles: GeneReviews
    classifies by the methylation result, so a DNMT3B carrier with D4Z4
    hypomethylation and no contraction is diagnosed as FSHD2, while OMIM and
    MONDO number the entity by causal gene. DNMT3B therefore remains listed in
    the FSHD2 subtype's gene list as well.
  evidence:
  - reference: PMID:27153398
    reference_title: "Mutations in DNMT3B Modify Epigenetic Repression of the D4Z4 Repeat and the Penetrance of Facioscapulohumeral Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we show that heterozygous mutations in DNA methyltransferase 3B
      (DNMT3B) are a likely cause of D4Z4 derepression associated with low
      levels of DUX4 expression from the D4Z4 repeat and increased penetrance
      of FSHD.
    explanation: >-
      The defining report of heterozygous DNMT3B variants as a cause of D4Z4
      derepression in FSHD, and the source of the penetrance caveat above.
  - reference: PMID:27153398
    reference_title: "Mutations in DNMT3B Modify Epigenetic Repression of the D4Z4 Repeat and the Penetrance of Facioscapulohumeral Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Recessive mutations in DNMT3B were previously shown to cause
      immunodeficiency, centromeric instability, and facial anomalies (ICF)
      syndrome.
    explanation: >-
      Source for the allele-state distinction between FSHD2 and the recessive
      ICF syndrome, which shares the gene but not the disease.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypomethylation of the D4Z4 repeat array can be the result of a
      heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic
      pathogenic variants in LRIF1.
    explanation: >-
      GeneReviews states the three FSHD2 chromatin-modifier loci and their
      required allele states.
- name: DUX4-permissive 4qA D4Z4 haplotype
  subtype: FSHD4
  association: Second locus required in trans for DNMT3B-related FSHD4
  relationship_type: COOPERATING
  variant_origin: GERMLINE
  gene_term:
    preferred_term: DUX4
    term:
      id: hgnc:50800
      label: DUX4
  notes: >-
    This row records the permissive chromosome 4 haplotype as a locus in its
    own right rather than as background to the DNMT3B variant, because FSHD4 is
    digenic and this is the second of the two required alleles. The functional
    element is the pLAM polyadenylation signal distal to the last D4Z4 unit,
    which is present on 4qA and absent or non-functional on 4qB and on
    chromosome 10q; DUX4 is named as the gene because the signal acts on the
    DUX4 transcript. COOPERATING rather than CAUSATIVE is the right grading:
    the haplotype is common in the general population and causes nothing on its
    own. The same haplotype requirement applies to FSHD1 and to the other
    FSHD2 loci, so this row is scoped to FSHD4 only because that is the subtype
    curated here, not because the requirement is unique to it.
  evidence:
  - reference: PMID:20724583
    reference_title: "A unifying genetic model for facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FSHD is associated with contraction of D4Z4 macrosatellite repeats on
      chromosome 4q35, but this contraction is pathogenic only in certain
      "permissive" chromosomal backgrounds.
    explanation: >-
      States that the chromosome 4 background is a separate genetic requirement,
      which is what this locus row records.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of FSHD2 is established in a proband with characteristic
      clinical features and hypomethylation of the D4Z4 repeat array in the
      subtelomeric region of chromosome 4q35 on a permissive chromosome 4
      haplotype.
    explanation: >-
      GeneReviews makes the permissive haplotype part of the diagnostic
      requirement for contraction-independent FSHD, of which the DNMT3B form is
      one.
- name: LRIF1
  subtype: FSHD2
  association: Biallelic chromatin-modifier variant causing D4Z4 hypomethylation on a permissive background
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: LRIF1
    term:
      id: hgnc:30299
      label: LRIF1
  notes: >-
    LRIF1 is the third FSHD2 locus and the only one where the required allele
    state is biallelic rather than heterozygous. LRIF1 is an SMCHD1 protein
    interactor; loss of its long isoform produces the same D4Z4 chromatin
    relaxation and DUX4 derepression as an SMCHD1 variant.

    The human evidence is one homozygous proband, which is why this locus is
    listed after SMCHD1 and DNMT3B rather than beside them; the supporting cell
    work (D4Z4 binding, knockdown of the long isoform) is what makes the single
    case interpretable.
  evidence:
  - reference: PMID:32467133
    reference_title: "Homozygous nonsense variant in LRIF1 associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A homozygous LRIF1 mutation was identified in a patient with a clinical
      phenotype consistent with FSHD.
    explanation: >-
      The single reported human proband establishing LRIF1 as an FSHD2 locus.
  - reference: PMID:32467133
    reference_title: "Homozygous nonsense variant in LRIF1 associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this study, we tested the hypothesis whether LRIF1, a known SMCHD1
      protein interactor, is a disease gene for idiopathic FSHD2.
    explanation: >-
      Source for the SMCHD1-interactor relationship recorded in this record's
      note, and for why LRIF1 was a candidate at all.
  - reference: PMID:32467133
    reference_title: "Homozygous nonsense variant in LRIF1 associated with facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In concordance, LRIF1 was shown to bind to the D4Z4 repeat, and knockdown
      of the LRIF1 long isoform in muscle cells results in DUX4 and DUX4 target
      gene expression.
    explanation: >-
      Cell-based evidence that LRIF1 acts at D4Z4 and that losing the long
      isoform derepresses DUX4, which is the mechanism the proband's phenotype
      is attributed to.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypomethylation of the D4Z4 repeat array can be the result of a
      heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic
      pathogenic variants in LRIF1.
    explanation: >-
      GeneReviews states that the LRIF1 route to FSHD2 requires biallelic
      variants, unlike SMCHD1 and DNMT3B.
treatments:
- name: Aerobic Exercise Training
  description: >-
    Regular endurance training can improve fitness, walking speed, and
    self-assessed health without evidence of exercise-induced muscle damage.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:26156512
    reference_title: "Aerobic training and postexercise protein in facioscapulohumeral muscular dystrophy: RCT study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This randomized, controlled study showed that regular endurance
      training improves fitness, walking speed, and self-assessed health in
      patients with FSHD without causing muscle damage.
    explanation: >-
      Randomized controlled evidence supports structured aerobic training as
      a safe supportive intervention in FSHD.
- name: Scapulopexy
  description: >-
    Scapular fixation surgery can improve shoulder range of motion and reduce
    disabling winging in appropriately selected patients.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:18056023
    reference_title: "Fixation of winged scapula in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All patients experienced improvement in active range of motion of the
      shoulder and all of them had clinical improvement with complete
      resolution of the winged scapula.
    explanation: >-
      Long-term retrospective series supports scapulopexy as an effective
      intervention for symptomatic scapular winging in selected FSHD
      patients.
- name: Genetic Counseling and Reproductive Options
  description: >-
    Reproductive decision-making is a salient concern in the FSHD patient
    community - one of the community's all-time highest-scoring discussions is
    a first-person account of navigating preimplantation genetic testing and
    IVF - yet it is easy to under-serve in a clinic focused on motor function.
    GeneReviews sets the recurrence risk at 50% per offspring in FSHD1 and
    states that PGT may be possible, with the important caveat that PGT
    results are typically confirmed by prenatal testing.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Preimplantation genetic testing (PGT) may be possible but verification
      of PGT results using prenatal testing is typically recommended.
    explanation: >-
      GeneReviews genetic-counseling guidance states the availability and the
      confirmatory caveat for PGT in FSHD.
  - reference: url:https://old.reddit.com/r/FSHD/top/?t=all
    reference_title: "top scoring links : FSHD"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Our 2+ year journey navigating PGT-M IVF because of FSHD"
    explanation: >-
      Reproductive planning via PGT-M/IVF reaches the community's all-time
      highest-scoring discussions, indicating it is a salient concern for
      affected families. One of the 25 all-time top threads is on this topic,
      so this supports salience but not recurrence; the treatment itself rests
      on the GeneReviews PGT evidence above. Cited as an aggregate community
      topic; no individual's personal health narrative is quoted.
- name: Pain Management and Supportive Care
  description: >-
    Pain-directed pharmacologic and nonpharmacologic management, assistive
    devices, and multidisciplinary rehabilitation remain central to current
    care because pain is common and materially affects quality of life.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:29053898
    reference_title: "Chronic pain has a strong impact on quality of life in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Management of pain should be considered when treating FSHD1 patients.
    explanation: >-
      Registry-based outcome data support pain-directed supportive care as a
      necessary component of FSHD management.
- name: Cognitive Behavioral Therapy for Chronic Fatigue
  description: >-
    Chronic fatigue - the symptom the patient community reports most
    consistently and finds hardest to explain - is treatable. A randomized
    controlled trial showed that cognitive-behavioral therapy reduces fatigue
    severity in FSHD, with gains sustained at follow-up and additional
    benefit in physical activity, sleep quality, and social participation.
    This directly addresses the community observation that patients receive
    little support in coping with fatigue.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: cognitive behavior therapy
    term:
      id: NCIT:C64345
      label: Cognitive Behavior Therapy
  evidence:
  - reference: PMID:25339206
    reference_title: "Both aerobic exercise and cognitive-behavioral therapy reduce chronic fatigue in FSHD: an RCT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This RCT shows that AET and CBT can ameliorate chronic fatigue in
      patients with FSHD.
    explanation: >-
      Randomized controlled trial in 57 patients with FSHD type 1 and severe
      chronic fatigue provides Class III evidence for CBT as fatigue-directed
      therapy.
  - reference: PMID:25339206
    reference_title: "Both aerobic exercise and cognitive-behavioral therapy reduce chronic fatigue in FSHD: an RCT."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients who received CBT had an increase in registered and
      experienced physical activity, sleep quality, and social participation.
    explanation: >-
      Documents that CBT improves the participation and social outcomes that
      patients themselves identify as most affected by fatigue.
  - reference: PMID:27762634
    reference_title: "Fatigue in facioscapulohumeral muscular dystrophy: a qualitative study of people's experiences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with FSHD are insufficient supported in coping with their
      fatigue.
    explanation: >-
      Qualitative study identifies the care gap that fatigue-directed therapy
      is intended to close, matching what patient organizations report.
- name: Ankle-Foot Orthoses
  description: >-
    Ankle-foot orthoses compensate for dorsiflexor weakness, improving gait
    and specifically reducing the sudden falls that the patient community
    describes as a major safety concern.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: ankle-foot orthosis provision
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ankle-foot orthoses to improve mobility and prevent falls"
    explanation: >-
      GeneReviews management guidance recommends ankle-foot orthoses for
      mobility and fall prevention in FSHD.
  notes: >-
    No NCIT clinical-action term for orthosis provision was identified that is
    reachable from NCIT:C25218, so `term:` is intentionally omitted and a
    free-text preferred_term is used.
- name: Ocular Surface Protection
  description: >-
    Because facial weakness prevents complete eyelid closure, the cornea is
    exposed during sleep. Ocular lubricants or overnight eyelid taping prevent
    exposure keratitis - a simple, low-cost intervention for a manifestation
    the community reports but which is easily overlooked in clinic.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ocular lubricants or taping the eyes shut during sleep to treat exposure
      keratitis
    explanation: >-
      GeneReviews recommends ocular surface protection to prevent exposure
      keratitis arising from lagophthalmos.
  notes: >-
    Reviewer suggested a more specific term than NCIT:C15747. Searched NCIT
    for ocular/lubricant/artificial-tear/corneal clinical-action terms: none
    reachable from NCIT:C25218 exists, and NCIT:C1585 (Lubricant) is rejected
    by the ChemicalEntityTerm dynamic enum, so it cannot be carried in
    `therapeutic_agent` either. Generic Supportive Care retained deliberately.
- name: Occupational and Speech Therapy in Infantile-Onset Disease
  description: >-
    Children with infantile-onset FSHD require occupational and speech
    therapy input, reflecting the greater functional and orofacial burden in
    this group. Speech involvement is mechanistically consistent with the
    orofacial muscle involvement now documented on ultrasound.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech and language therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      occupational and speech therapy in individuals with infantile onset
    explanation: >-
      GeneReviews management guidance specifies occupational and speech
      therapy for infantile-onset FSHD.
- name: Management of Sensorineural Hearing Loss
  description: >-
    Hearing loss in FSHD is managed with standard audiologic care. It matters
    most in early-onset disease, where high-frequency hearing loss is
    concentrated and where undetected loss can compound developmental and
    communication difficulty.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      standard treatment of sensorineural hearing loss
    explanation: >-
      GeneReviews management guidance directs standard audiologic treatment
      for the sensorineural hearing loss already curated as a phenotype in
      this entry.
- name: Ventilatory Support
  description: >-
    Non-invasive ventilation is indicated for the minority who develop
    nocturnal hypoventilation or symptomatic respiratory failure, and it
    works quickly - nocturnal gas exchange improved from the first night of
    treatment in patients started on NIV. This addresses the "trouble
    breathing" the community reports without over-medicalizing the majority
    who remain stable. The corresponding screening protocol is modelled
    separately under `diagnosis:` rather than bundled here.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: respiratory therapy
    term:
      id: NCIT:C15322
      label: Respiratory Therapy
  evidence:
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In patients initiated on NIV, nocturnal gas exchange already improved
      in the first night of treatment.
    explanation: >-
      Documents rapid physiological benefit of non-invasive ventilation in
      FSHD patients with sleep-disordered breathing.
  - reference: PMID:35147730
    reference_title: "Long-term follow-up of respiratory function in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Respiratory function remained stable in most patients with FSHD, but a
      subgroup of patients showed a pronounced deterioration.
    explanation: >-
      Longitudinal data justify targeting ventilatory intervention at the
      deteriorating subgroup rather than the whole population.
animal_models:
- name: D4Z4-2.5/Dnmt3bMommeD14 transgenic mouse
  species: Mouse
  genotype: Hemizygous D4Z4-2.5 transgene with a heterozygous Dnmt3b exon 13 skipping allele (Dnmt3bMommeD14)
  category: Digenic model of the FSHD4 genotype
  publication: PMID:33004076
  description: >-
    The one attempt to reconstruct the FSHD4 genotype in an animal: a mouse
    carrying an FSHD-sized human D4Z4 array crossed to a Dnmt3b hypomorph, built
    to mimic one of the two original DNMT3B families. It reproduces the
    molecular half of the lesion, losing D4Z4 methylation, but not the muscle
    disease, and the tissue where DUX4 rises is lymphoid rather than skeletal
    muscle.
  genes:
  - preferred_term: DNMT3B
    term:
      id: hgnc:2979
      label: DNMT3B
  modeled_mechanisms:
  - target: DUX4 Misexpression in Skeletal Muscle
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    model_scale: MOLECULAR
    description: >-
      Reducing Dnmt3b on an FSHD-sized D4Z4 background did not raise DUX4
      transcript in skeletal muscle and produced no muscle pathology, so this
      model does not reproduce the node it was built to test.
    limitations: >-
      The transgene is a 2.5-unit human array in mouse chromatin rather than a
      normal-length array with a human permissive 4qA subtelomere, so the
      digenic combination modelled is not the human one; the Dnmt3b allele is an
      exon-skipping hypomorph rather than one of the patient missense variants;
      and mouse skeletal muscle appears less sensitive to D4Z4 chromatin
      modifiers than lymphoid tissue, which is where the DUX4 rise was seen.
      Read this as evidence about the model, not as evidence against a DNMT3B
      contribution in patients.
    evidence:
    - reference: PMID:33004076
      reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        In D4Z4-2.5/Dnmt3bMommeD14 mice, Dnmt3b protein levels were reduced;
        however, DUX4 RNA levels in skeletal muscles were not enhanced and no
        pathology was observed.
      explanation: >-
        The negative result in the tissue this node describes, which is what
        FAILS_TO_RECAPITULATE records here.
    readouts:
    - name: Skeletal muscle DUX4 transcript level
      target: DUX4 Misexpression in Skeletal Muscle
      direction: UNCHANGED
      interpretation: >-
        The measurement the node would predict to rise; it did not, alongside
        absent muscle pathology.
      evidence:
      - reference: PMID:33004076
        reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          In D4Z4-2.5/Dnmt3bMommeD14 mice, Dnmt3b protein levels were reduced;
          however, DUX4 RNA levels in skeletal muscles were not enhanced and no
          pathology was observed.
        explanation: >-
          Reports the skeletal-muscle DUX4 measurement and its direction in this
          cross.
  - target: D4Z4 Epigenetic Derepression
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      The methylation half of the lesion does transfer: losing Dnmt3b
      demethylates the D4Z4 array in this mouse, and DUX4 rises, but in
      secondary lymphoid organs rather than muscle.
    limitations: >-
      Derepression is demonstrated in lymphoid tissue, not in the muscle
      compartment where FSHD manifests, so the node is reproduced in the wrong
      tissue.
    evidence:
    - reference: PMID:33004076
      reference_title: "Dnmt3b regulates DUX4 expression in a tissue-dependent manner in transgenic D4Z4 mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Interestingly, D4Z4-2.5/Dnmt3bMommeD14 mice showed a loss of DNA
        methylation at the D4Z4 repeat array and significantly higher DUX4
        transcript levels in secondary lymphoid organs.
      explanation: >-
        Shows Dnmt3b loss demethylating D4Z4 and derepressing DUX4 in this
        model, with the tissue restriction noted in the limitation.
- name: Xenopus frg1 gain- and loss-of-function vascular model
  species: Xenopus laevis
  genotype: FRG1 morpholino knockdown and frg1 mRNA overexpression in embryos and tadpoles
  category: Candidate-gene dosage model of the vascular component of FSHD
  publication: PMID:19383939
  description: >-
    The only model to address why FSHD has an ophthalmologic component at all.
    frg1 is expressed in frog vasculature; knocking it down reduces angiogenesis
    and DAB2 expression, and overexpressing it produces excess vessel branching,
    vessel dilation and edema. Read carefully, this is a candidate-gene result
    from before the field settled on DUX4: it shows that a gene at the FSHD locus
    can produce a vascular phenotype when its dose is wrong, not that FRG1 dosage
    is what causes vasculopathy in patients.
  genes:
  - preferred_term: FRG1
    term:
      id: hgnc:3954
      label: FRG1
  modeled_mechanisms:
  - target: Retinal vasculopathy
    relationship: PARTIALLY_RECAPITULATES
    fidelity: LOW
    description: >-
      Produces a disturbed vascular phenotype from misexpression of a gene at the
      FSHD locus, offering a mechanism for a disease feature that the
      DUX4-in-skeletal-muscle account does not reach.
    limitations: >-
      Three gaps separate this from the human phenotype. The readouts are
      whole-embryo and tadpole vasculature, not retina, so the tissue in which
      patients present is not examined. The manipulation is systemic
      overexpression of frg1, whereas FRG1 is a candidate whose upregulation in
      patient muscle has been contested and which the field has largely
      displaced in favour of DUX4 — so the model may be modelling a gene that
      is not the effector. And the direction is inverted between arms:
      knockdown reduces angiogenesis while overexpression increases branching,
      so the model does not by itself say which dose change, if either,
      corresponds to the patient state.
    readouts:
    - name: Blood vessel branching and vessel diameter after frg1 overexpression
      target: Retinal vasculopathy
      direction: INCREASED
      interpretation: >-
        The pro-angiogenic arm — excess branching, dilated vessels and edema —
        is the phenotype offered as a vascular counterpart of the human feature.
      evidence:
      - reference: PMID:19383939
        reference_title: "FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "tadpoles subjected to frg1 overexpression displayed the pro-angiogenic phenotypes of increased blood vessel branching and dilation of blood vessels, and developed edemas, suggesting that their circulation was disrupted"
        explanation: Reports the measured vascular phenotype under frg1 overexpression.
    - name: Angiogenesis and DAB2 expression after FRG1 knockdown
      target: Retinal vasculopathy
      direction: DECREASED
      interpretation: >-
        The loss-of-function arm establishes that frg1 is required for normal
        vessel development, which is what makes the overexpression phenotype a
        dosage effect rather than a nonspecific toxicity.
      evidence:
      - reference: PMID:19383939
        reference_title: "FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "expression of FRG1 was found to be essential for the development of the vasculature, as a knockdown of FRG1 resulted in decreased angiogenesis and reduced expression of the angiogenic regulator DAB2"
        explanation: Reports the knockdown arm and the molecular readout used for it.
    evidence:
    - reference: PMID:19383939
      reference_title: "FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Thus, the systemic upregulation of the FRG1 protein shows the potential for acquiring a disrupted vascular phenotype, providing the first link between a FSHD candidate gene and the vascular component of FSHD pathology."
      explanation: >-
        The authors' own claim is a demonstrated potential and a first link, not
        an established disease mechanism, which is the level this link asserts.
    - reference: PMID:19383939
      reference_title: "FSHD region gene 1 (FRG1) is crucial for angiogenesis linking FRG1 to facioscapulohumeral muscular dystrophy-associated vasculopathy."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We found that endogenous frg1 is expressed in both the developing and adult vasculature in Xenopus."
      explanation: Establishes that the gene is expressed in the tissue whose phenotype the model scores.
  notes: >-
    Retained as a candidate-gene model with its caveats intact rather than
    dropped: FRG1 has largely been displaced by DUX4 as the FSHD effector, but
    no DUX4-based account of the retinal vasculopathy has replaced this one, so
    the vascular feature currently has no better mechanistic model.
clinical_trials:
- name: NCT05747924
  phase: NOT_APPLICABLE
  status: ACTIVE_NOT_RECRUITING
  description: >-
    Phase 1/2 FORTITUDE study of delpacibart braxlosiran (AOC 1020), an
    antibody-oligonucleotide conjugate designed to reduce DUX4 mRNA in FSHD1
    and FSHD2.
  evidence:
  - reference: clinicaltrials:NCT05747924
    reference_title: "A Randomized, Double-blind, Placebo-controlled, Phase 1/2 Study to Evaluate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Exploratory Efficacy of AOC 1020 Administered Intravenously to Participants With Facioscapulohumeral Muscular Dystrophy (FSHD)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A Randomized, Double-blind, Placebo-controlled, Phase 1/2 Study to
      Evaluate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics,
      and Exploratory Efficacy of AOC 1020 Administered Intravenously to
      Participants with Facioscapulohumeral Muscular Dystrophy (FSHD)
    explanation: >-
      Supports active clinical development of a DUX4-targeting
      oligonucleotide therapy in FSHD.
  notes: >-
    ClinicalTrials.gov listed this study as Active, not recruiting on
    2025-04-01; phase 1/2 was mapped to NOT_APPLICABLE because the schema does
    not include combined phases.
- name: NCT06131983
  phase: NOT_APPLICABLE
  status: RECRUITING
  description: >-
    Phase 1/2a dose-escalation study of ARO-DUX4, an RNA interference
    therapeutic targeting DUX4 in FSHD1. The sponsor now lists the agent as
    SRP-1001, which is the name the registry record and the quoted summary
    below use.
  evidence:
  - reference: clinicaltrials:NCT06131983
    reference_title: "A Phase 1/2a Dose-Escalating Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of ARO-DUX4 (SRP-1001) in Adult Patients and Adolescent Patients With Facioscapulohumeral Muscular Dystrophy Type 1"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The purpose of this study is to evaluate the safety, tolerability,
      pharmacokinetics (PK) and pharmacodynamics of SRP-1001 in participants
      with facioscapulohumeral muscular dystrophy Type 1 (FSHD1).
    explanation: >-
      Supports ongoing clinical testing of a second DUX4-silencing
      therapeutic strategy.
  notes: >-
    ClinicalTrials.gov listed this study as Recruiting on 2026-02-06; phase
    1/2a was mapped to NOT_APPLICABLE because the schema does not include
    combined phases.
- name: NCT05397470
  phase: PHASE_III
  status: TERMINATED
  description: >-
    Phase III REACH trial of losmapimod, a p38alpha/beta inhibitor intended to
    suppress the DUX4 transcriptional program in FSHD.
  evidence:
  - reference: clinicaltrials:NCT05397470
    reference_title: "A Phase 3 Global, Randomized, Double-Blind, Placebo-Controlled, 48-Week, Parallel-Group Study of the Efficacy and Safety of Losmapimod in Treating Patients With Facioscapulohumeral Muscular Dystrophy (FSHD) (REACH)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This is a study to evaluate the safety and efficacy of losmapimod in
      treating participants with Facioscapulohumeral Muscular Dystrophy
      (FSHD).
    explanation: >-
      Shows that p38-mediated DUX4 suppression advanced to late-stage
      clinical testing, even though the program did not succeed.
  - reference: PMID:38631764
    reference_title: "Safety and efficacy of losmapimod in facioscapulohumeral muscular dystrophy (ReDUX4): a randomised, double-blind, placebo-controlled phase 2b trial."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Least squares mean changes from baseline in DUX4-driven gene expression
      did not differ significantly between the losmapimod
    explanation: >-
      The preceding phase 2b ReDUX4 trial missed its primary endpoint:
      losmapimod did not significantly reduce DUX4-driven gene expression,
      refuting the pharmacodynamic premise on which the phase 3 was built.
      Secondary structural and functional signals nonetheless motivated
      progression to phase 3.
  - reference: PMID:40580827
    reference_title: "The recent clinical trial of losmapimod for the treatment of facioscapulohumeral muscular dystrophy."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the trial failed to demonstrate a clear clinical benefit, highlighting
      key challenges in drug development for the disease
    explanation: >-
      Confirms the phase 3 outcome: losmapimod did not show clear clinical
      benefit. Recorded as REFUTE so the entry does not leave a terminated
      program looking merely incomplete - the p38/DUX4-suppression strategy
      was tested and did not succeed.
  notes: >-
    ClinicalTrials.gov listed the study as Terminated on 2025-11-10 after
    results posting. The preceding phase 2b ReDUX4 trial (NCT04003974) missed
    its primary DUX4-expression endpoint, and the phase 3 did not demonstrate
    clear clinical benefit.
- name: NCT07435129
  phase: PHASE_II
  status: NOT_RECRUITING
  description: >-
    Phase II FORGE study of apitegromab, a myostatin-pathway therapy intended
    to improve muscle function rather than directly suppress DUX4.
  evidence:
  - reference: clinicaltrials:NCT07435129
    reference_title: "A Phase 2, Randomized, Double-Blind, Placebo-Controlled, Multicenter, 52-Week Study Evaluating the Efficacy and Safety of Apitegromab in Participants With Facioscapulohumeral Muscular Dystrophy (FORGE)"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A randomized Phase 2 study to evaluate the efficacy and safety of
      apitegromab as a monotherapy in participant with FSHD
    explanation: >-
      Supports ongoing parallel development of muscle-function-directed
      therapy in FSHD.
  notes: >-
    ClinicalTrials.gov listed this study as not yet recruiting on 2026-02-27;
    mapped to schema enum NOT_RECRUITING.
diagnosis:
- name: Molecular diagnosis of FSHD1 (D4Z4 contraction on a permissive haplotype)
  description: >-
    FSHD1 is confirmed by demonstrating a heterozygous pathogenic contraction
    of the D4Z4 repeat array at 4q35 on a permissive chromosome 4 haplotype.
    Both elements are required: repeat size alone is not diagnostic, because
    contractions on non-permissive haplotypes are benign.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of FSHD1 is established in a proband with characteristic
      clinical features and a heterozygous pathogenic contraction of the D4Z4
      repeat array in the subtelomeric region of chromosome 4q35 on a
      permissive chromosome 4 haplotype.
    explanation: >-
      GeneReviews states the diagnostic criteria for FSHD1 directly.
- name: Molecular diagnosis of FSHD2 (D4Z4 hypomethylation and chromatin-modifier testing)
  description: >-
    FSHD2 is confirmed by D4Z4 hypomethylation at 4q35 on a permissive
    haplotype, without a contraction. Hypomethylation usually reflects a
    heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic
    variants in LRIF1, so methylation testing and chromatin-modifier gene
    testing are complementary rather than alternative.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The diagnosis of FSHD2 is established in a proband with characteristic
      clinical features and hypomethylation of the D4Z4 repeat array in the
      subtelomeric region of chromosome 4q35 on a permissive chromosome 4
      haplotype.
    explanation: >-
      GeneReviews states the diagnostic criteria for FSHD2 directly.
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hypomethylation of the D4Z4 repeat array can be the result of a
      heterozygous pathogenic variant in SMCHD1 or DNMT3B, or biallelic
      pathogenic variants in LRIF1.
    explanation: >-
      Identifies the chromatin-modifier genes whose variants underlie FSHD2
      hypomethylation, defining the gene panel to test.
- name: Hypoventilation screening and pulmonary assessment
  description: >-
    Respiratory surveillance is risk-stratified rather than universal.
    GeneReviews indicates hypoventilation screening for patients with
    abnormal pulmonary function tests, severe proximal weakness,
    kyphoscoliosis, wheelchair dependence, or comorbid disease affecting
    ventilation, and pulmonary consultation at forced vital capacity below
    60%, for excessive daytime somnolence or nonrestorative sleep, and before
    procedures requiring anesthesia. Transcutaneous capnometry outperforms
    pulse oximetry for detecting nocturnal hypoventilation.
  diagnosis_term:
    preferred_term: spirometry
    term:
      id: NCIT:C85397
      label: Spirometry
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      pulmonary consultation for forced vital capacity <60%, excessive
      daytime somnolence, or nonrestorative sleep, and prior to surgical
      procedures requiring anesthesia
    explanation: >-
      GeneReviews defines the thresholds triggering pulmonary consultation in
      FSHD.
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Transcutaneous capnometry is superior to pulse oximetry for detection
      of NH.
    explanation: >-
      Establishes the modality required to detect nocturnal hypoventilation,
      which oximetry alone misses in most cases.
- name: Audiologic surveillance
  description: >-
    Hearing surveillance is age-stratified and most intensive in early-onset
    disease, where extra-muscular involvement concentrates.
  diagnosis_term:
    preferred_term: audiometric assessment
    term:
      id: NCIT:C38036
      label: Audiometric Test
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      audiometry in infants at each visit and annually in children
    explanation: >-
      GeneReviews defines the audiologic surveillance schedule for FSHD.
- name: Ophthalmologic surveillance for retinal vasculopathy
  description: >-
    Dilated fundoscopic surveillance is targeted at the group in whom
    sight-threatening Coats-like retinopathy concentrates: early
    childhood-onset disease with large D4Z4 contractions, plus any adult with
    visual symptoms.
  diagnosis_term:
    preferred_term: ophthalmoscopy
    term:
      id: NCIT:C120698
      label: Ophthalmoscopy
  evidence:
  - reference: PMID:20301616
    reference_title: "Facioscapulohumeral Muscular Dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      annual dilated ophthalmoscopy in individuals with early childhood-onset
      FSHD with large pathogenic contraction of D4Z4 and adults with visual
      symptoms
    explanation: >-
      GeneReviews defines the risk-stratified ophthalmologic surveillance
      criteria.
discussions:
- discussion_id: fshd_invisible_symptom_burden
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why do the symptoms patients rank as most burdensome in FSHD - fatigue,
    pain, and sleep disturbance - remain mechanistically unexplained and
    largely absent from the causal pathograph, which currently derives all
    clinical consequences from myofiber loss?
  attaches_to:
  - pathophysiology#Progressive Myofiber Loss and Fatty Replacement
  rationale: >-
    Patient-reported outcome studies rank fatigue (93.8%) and pain (87.7%)
    at nearly the same prevalence as shoulder/arm weakness (96.9%), and a
    patient-led narrative review names pain, fatigue, and sleep disturbance
    as the "invisible symptoms" that biomedical outcome measures fail to
    capture. Yet no mechanistic edge in this entry explains them: they are
    currently modelled only as downstream consequences of biomechanical
    strain. Candidate contributors that would change management include
    sleep-disordered breathing (OSA in 55% and nocturnal hypoventilation in
    26% of symptomatic patients), central pain sensitization, and
    deconditioning. Distinguishing these matters because each has a
    different, already-available treatment.
  proposed_experiments:
  - experiment_id: exp_fshd_unselected_polysomnography
    name: Unselected-cohort polysomnography with transcutaneous capnometry
    description: >-
      Perform polysomnography with transcutaneous capnometry in an unselected
      genetically confirmed FSHD cohort to establish the true population
      prevalence of obstructive sleep apnea and nocturnal hypoventilation,
      and correlate it with validated fatigue scores. Existing prevalence
      figures come from a symptom-selected sleep-laboratory referral cohort.
  - experiment_id: exp_fshd_central_sensitization_qst
    name: Quantitative sensory testing of FSHD chronic pain
    description: >-
      Apply quantitative sensory testing to determine whether FSHD chronic
      pain carries a central sensitization signature distinct from
      nociceptive pain attributable to biomechanical strain, which would
      redirect analgesic strategy.
  - experiment_id: exp_fshd_fatigue_mediation
    name: Mediation analysis of patient-reported fatigue
    description: >-
      In a longitudinal FSHD registry, test how much patient-reported fatigue
      is explained by sleep-disordered breathing, muscle involvement, and
      mood respectively, to identify the dominant treatable contributor.
  evidence:
  - reference: PMID:42485801
    reference_title: "Living with FSHD: a patient-led narrative review of psychosocial well-being in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Facioscapulohumeral muscular dystrophy (FSHD) is associated with
      substantial psychosocial challenges not fully captured by traditional
      biomedical outcomes, including challenges that may persist despite
      stable clinical or QoL scores.
    explanation: >-
      A patient-led review states directly that standard biomedical outcomes
      miss a substantial part of FSHD disease burden, which is the gap this
      discussion records.
  - reference: PMID:42485801
    reference_title: "Living with FSHD: a patient-led narrative review of psychosocial well-being in facioscapulohumeral muscular dystrophy."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the impact of invisible symptoms, including pain, fatigue, and sleep
      disturbance
    explanation: >-
      Names the specific symptom triad that the patient community prioritizes
      and that this entry's causal model does not yet explain.
  notes: >-
    Recorded from a community-source sweep (FSHD Society patient-education
    pages and the r/FSHD subreddit) cross-checked against patient-reported
    outcome literature. The r/FSHD listing discusses chronic pain and fatigue
    together as a single linked problem, consistent with the patient-reported
    outcome literature above; that listing is recorded as an aggregate
    community-discussion topic under `references` rather than as an evidence
    snippet, because a forum topic title is a label and not a claim-bearing
    sentence. No individual's personal health narrative is quoted.
- discussion_id: fshd_community_reported_unvalidated_signals
  kind: OPEN_QUESTION
  status: OPEN
  prompt: >-
    Of the recurring community-reported complaints in FSHD that standard
    clinical descriptions omit - headache/migraine, fasciculations, and low
    serum aldolase - which are genuine disease associations, which are
    secondary and treatable (for example morning headache from nocturnal
    hypoventilation), and which are coincidental?
  attaches_to:
  - pathophysiology#Progressive Myofiber Loss and Fatty Replacement
  rationale: >-
    Reading the r/FSHD patient community listings surfaced topics with no
    counterpart in standard FSHD clinical descriptions. Forum
    threads are anecdotal, self-selected, and not diagnostically verified, so
    they were treated as hypothesis-generating leads and checked against the
    literature rather than curated directly.

    One lead has since been PARTLY resolved and promoted to a curated
    phenotype: head pain. The Dutch FSHD Registry reports 52% for a COMBINED
    head-and-shoulder pain category in 373 participants. That establishes
    head-region pain as a real component of FSHD pain burden and justifies
    curating the Headache phenotype, but it does NOT isolate a head-specific
    rate - given FSHD's scapular dominance an unknown and plausibly majority
    share of that 52% is shoulder pain - so no frequency band is asserted.
    The mechanism also remains open: postural strain from cervical and axial
    weakness versus morning headache from nocturnal hypoventilation, which is
    documented in FSHD and under-detected by oximetry. Resolving that matters
    clinically because the second is treatable with ventilatory support. Note
    the community term "migraine" is broader than what the registry
    documents, so a true primary-migraine association remains unestablished.

    Two leads remain UNVALIDATED and are deliberately NOT curated as
    phenotypes. Fasciculations are not a recognized FSHD feature and would
    more typically prompt evaluation for a motor neuron disorder, so this
    signal may reflect diagnostic uncertainty within the community rather
    than FSHD biology. Low serum aldolase has no reported FSHD association at
    all.

    This entry is a worked example of the intended workflow: community sources
    generate candidate signals, literature adjudicates them, and only the
    adjudicated ones become phenotypes.
  proposed_experiments:
  - experiment_id: exp_fshd_morning_headache_capnometry
    name: Headache phenotyping with overnight capnometry
    description: >-
      Perform structured headache phenotyping together with overnight
      transcutaneous capnometry in FSHD patients reporting morning headache,
      to test whether the community headache signal is explained by nocturnal
      hypoventilation rather than primary migraine.
  - experiment_id: exp_fshd_registry_migraine_fasciculation_prevalence
    name: Registry prevalence of migraine and fasciculations
    description: >-
      Compare the prevalence of migraine and clinically confirmed
      fasciculations in genetically confirmed FSHD against matched controls
      in a disease registry, to determine whether either is a true
      association.
  evidence:
  - reference: PMID:31025273
    reference_title: "Sleep-related breathing disorders in facioscapulohumeral dystrophy."
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Indications for admission included non-restorative sleep, morning
      headache, or excessive daytime
    explanation: >-
      Supplies the candidate mechanistic explanation - morning headache as a
      symptom of nocturnal hypoventilation - for part of the community
      headache signal.
  notes: >-
    Social-media content is used here strictly as hypothesis-generating
    signal. Per dismech evidence policy these leads are not promoted to
    curated phenotypes without independent clinical evidence. The two
    unvalidated leads were observed as r/FSHD discussion topics titled
    "Migraines" and "Fasicuclations" (spelling as posted; single-snapshot
    observation of the community listing, not a demonstrated recurrence).
    Those bare topic titles are recorded here in prose and under `references`
    rather than as evidence snippets: a forum topic title is a label, not a
    claim-bearing sentence, so it cannot support or refute anything.
references:
- reference: PMID:20301616
  title: "Facioscapulohumeral Muscular Dystrophy."
  tags:
  - GeneReviews
  findings:
  - statement: >-
      FSHD typically presents with weakness of the facial muscles, scapular
      stabilizers, and/or foot dorsiflexors, with highly variable severity.
    supporting_text: >-
      Facioscapulohumeral muscular dystrophy (FSHD) typically presents with
      weakness of the facial muscles, the stabilizers of the scapula, and/or
      the dorsiflexors of the foot.
  - statement: >-
      Approximately 20% of affected individuals eventually require a
      wheelchair, but life expectancy is not shortened.
    supporting_text: >-
      Weakness can be slowly progressive and approximately 20% of affected
      individuals eventually require a wheelchair. Life expectancy is not
      shortened.
- reference: PMID:31409737
  title: "Patient-Reported Symptoms in Facioscapulohumeral Muscular Dystrophy (PRISM-FSHD)."
  findings:
  - statement: >-
      Patient-reported symptom themes with the highest prevalence are shoulder
      or arm problems, activity limitations, core weakness, fatigue, mobility
      limitations, changed body image, and pain.
    supporting_text: >-
      The symptomatic themes with the highest prevalence in our sample were
      problems with shoulders or arms (96.9%), limitations with activities
      (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with
      mobility and walking (93.6%), changed body image due to the disease
      (91.6%), and pain (87.7%).
- reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/
  title: "Symptoms - FSHD Society"
  findings:
  - statement: >-
      The principal FSHD patient advocacy organization communicates a symptom
      set to patients and families that includes manifestations under-weighted
      in the primary clinical literature - chronic fatigue, severe pain,
      sudden falls from legs giving out, abdominal wall weakness, incomplete
      eye closure during sleep, chest and spine deformity, breathing
      difficulty, hearing loss, mild arrhythmia, and Coats disease.
    supporting_text: "Sudden falls when their legs unexpectedly give out"
- reference: url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/early-onset-fshd/
  title: "Early-onset FSHD - FSHD Society"
  findings:
  - statement: >-
      Patient organization resource describing the early-onset FSHD phenotype,
      in which extra-muscular involvement (hearing loss, Coats disease) is
      concentrated.
    supporting_text: "Early-onset FSHD"
- reference: PMID:42485801
  title: "Living with FSHD: a patient-led narrative review of psychosocial well-being in facioscapulohumeral muscular dystrophy."
  findings:
  - statement: >-
      A patient-led review finds that FSHD psychosocial burden is not captured
      by traditional biomedical outcomes and can persist even when clinical
      and quality-of-life scores are stable.
    supporting_text: >-
      Facioscapulohumeral muscular dystrophy (FSHD) is associated with
      substantial psychosocial challenges not fully captured by traditional
      biomedical outcomes, including challenges that may persist despite
      stable clinical or QoL scores.
- reference: PMID:41739307
  title: "Assessing the multidimensional burden of facioscapulohumeral muscular dystrophy through patient-reported outcomes and experience."
  findings:
  - statement: >-
      Mixed-methods FSHD burden study whose cohort was recruited through a
      patient-led advocacy organization - an example of community-sourced
      evidence reaching the peer-reviewed literature.
    supporting_text: >-
      Patients with clinically and genetically confirmed FSHD were recruited
      nationwide through the FSHD Community Network-a patient-led advocacy
      organization affiliated with the Chinese Organization for Rare
      Disorders (CORD).
- reference: PMID:38016873
  title: "The Dutch registry for facioscapulohumeral muscular dystrophy: Cohort profile and longitudinal patient reported outcomes."
  findings:
  - statement: >-
      National FSHD registry with six years of longitudinal patient-reported
      follow-up: fatigue and muscle weakness are the most frequently reported
      symptoms, and pain localizes most often to the head and shoulder
      region. A consented, citable counterpart to informal patient-community
      knowledge.
    supporting_text: >-
      Pain was experienced most often in the head and shoulder region (193,
      52%).
- reference: PMID:39297366
  title: "The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound."
  findings:
  - statement: >-
      Muscle ultrasound in 107 participants quantifies facial weakness at 92%
      and resolves which specific orofacial muscles are involved, extending a
      phenotype that standard facial-weakness scoring treats as a single
      item.
    supporting_text: >-
      of whom 92% showed signs of facial weakness
- reference: PMID:40879179
  title: "Hearing Loss, Retinal Abnormality, and Seizures in People With Facioscapulohumeral Muscular Dystrophy."
  findings:
  - statement: >-
      Population-based MD STARnet surveillance (n=548) gives clinically
      diagnosed rates for the three main extra-muscular comorbidities -
      hearing loss 13%, retinal abnormalities 3.6%, seizures 2.0% - with
      17.2% having at least one. These are detection rates in routine care
      and run well below imaging-based figures for the same organ systems.
    supporting_text: >-
      Among the study cohort, 17.2% (n = 94) had at least one comorbidity
- reference: PMID:38631764
  title: "Safety and efficacy of losmapimod in facioscapulohumeral muscular dystrophy (ReDUX4): a randomised, double-blind, placebo-controlled phase 2b trial."
  findings:
  - statement: >-
      The phase 2b ReDUX4 trial missed its primary endpoint - losmapimod did
      not significantly change DUX4-driven gene expression - though secondary
      structural, functional, and patient-reported signals motivated
      progression to phase 3.
    supporting_text: >-
      Least squares mean changes from baseline in DUX4-driven gene expression
      did not differ significantly between the losmapimod
- reference: url:https://old.reddit.com/r/FSHD/
  title: "FSHD"
  findings:
  - statement: >-
      Front-page listing of the r/FSHD public patient-community forum, swept
      as hypothesis-generating signal for this entry. Topics corroborated by
      literature (chronic pain and fatigue, head pain) informed curated
      phenotypes; topics without a clinical evidence base (fasciculations,
      low aldolase) are recorded only under `discussions` as unvalidated
      leads. Aggregate discussion topics only - no individual's personal
      health narrative is quoted.
    supporting_text: "chronic pain and fatigue"
- reference: url:https://old.reddit.com/r/FSHD/top/?t=all
  title: "top scoring links : FSHD"
  findings:
  - statement: >-
      All-time highest-scoring r/FSHD discussions. This listing corrects an
      earlier characterization of the community sweep as "saturated": it
      surfaced 21 topics absent from the front-page and new-post listings, so
      the earlier sample was not exhaustive. Its substantive finding is about
      what the community prioritizes rather than new phenotypes - the
      highest-engagement content is dominated by therapeutic-pipeline news
      (EpiCrispr, del-brax, losmapimod, DX5057) and psychosocial coping, with
      a single thread of the 25 on reproductive planning (PGT-M/IVF), which is
      curated here as a genetic-counseling treatment.
    supporting_text: "Our 2+ year journey navigating PGT-M IVF because of FSHD"
- reference: url:https://www.fshdsociety.org/connect/online-communities/
  title: "Online Communities - FSHD Society"
  findings:
  - statement: >-
      The FSHD Society hosts the organized patient and family communities
      (Facebook and other social platforms, plus the moderated "Gathering
      Place" support groups) through which community-reported disease
      experience is aggregated. Recorded here as provenance for the
      community-sourced phenotypes curated in this entry.
    supporting_text: "Online Communities"
datasets:
- accession: geo:GSE261617
  title: Iron supplementation alleviates pathologies in a mouse model of facioscapulohumeral muscular dystrophy
  description: Facioscapulohumeral muscular dystrophy (FSHD) is a genetic muscle disease caused by ectopic expression of the toxic protein DUX4, resulting in muscle weakness. However, the mechanism by which DUX4 exerts its toxicity remains unclear. In this study, we observed abnormal iron accumulation in muscles of patients with FSHD and in muscle-specific DUX4-expressing (DUX4-Tg) mice. Treatment with iron chelators, an iron-deficient diet, and genetic modifications inhibiting intracellular uptake of iron did not improve but rather exacerbated FSHD pathology in DUX4-Tg mice.
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  data_type: BULK_RNA_SEQ
  sample_count: 23
  publication: PMID:40591405
  notes: Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE291267
  title: DUX4.6 siRNA in vitro activity in FSHD patient-derived myotubes
  description: Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant muscular disease caused by the aberrant ectopic expression of DUX4 in skeletal muscle. There are no approved therapies for FSHD to date, and strategies aimed at reducing DUX4 expression in skeletal muscle of FSHD patients are promising therapeutic approaches. Here we demonstrate DUX4.6 siRNA activity in reducing DUX4-regulated gene expression in FSHD patient-derived myotubes in vitro.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 32
  publication: PMID:41994867
  notes: Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE201185
  title: Hit-and-run silencing of endogenous DUX4 by targeting DNA hypomethylation on D4Z4 repeats in facioscapulohumeral muscular dystrophy
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: MULTI_OMICS
  sample_count: 11
  notes: Identified by GEO DataSets index search for Facioscapulohumeral Muscular Dystrophy (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-08-01. Title, sample count, and organism are GEO's own values.
- accession: ega:EGAS00001007350
  title: A circulating biomarker for severity of facioscapulohumeral muscular dystrophy
  description: Facioscapulohumeral muscular dystrophy (FSHD) is a prevalent, incurable skeletal myopathy. Clinical trials for FSHD are hindered by heterogeneous biomarkers poorly associated with clinical severity, requiring invasive muscle biopsy. Macroscopically FSHD presents with slow fatty replacement of muscle, rapidly accelerated by inflammation. Mis-expression of the transcription factor DUX4 is currently accepted to underlie FSHD pathogenesis and mechanisms including PAX7 target gene repression have been proposed.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  notes: 'European Genome-phenome Archive study, matched because the disease is named in the study''s own title ("Facioscapulohumeral Muscular Dystrophy"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.'
- accession: ega:EGAS50000000502
  title: 3D tissue engineered human skeletal muscle modelling Facioscapulohumeral Muscular Dystrophy
  description: acioscapulohumeral muscular dystrophy (FSHD) is caused by sporadic misexpression of the transcription factor double homeobox 4 (DUX4) in skeletal muscles. So far, monolayer cultures and animal models have been used to study the FSHD disease mechanism and for FSHD therapy development, but these models do not fully recapitulate the disease and there is a lack of knowledge on how DUX4 misexpression leads to skeletal muscle dysfunction. To overcome these barriers, we have developed a 3D tissue engineered skeletal muscle (3D-TESM) model by generating genetically matched myogenic progenitors (MPs) from human induced pluripotent stem cells of three mosaic FSHD patients.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  notes: 'European Genome-phenome Archive study, matched because the disease is named in the study''s own title ("Facioscapulohumeral Muscular Dystrophy"); description-level mentions were not accepted. EGA study_type: RNASeq. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.'

📚

References & Deep Research

References

13

PMID:20301616

Facioscapulohumeral Muscular Dystrophy.

2 findings

FSHD typically presents with weakness of the facial muscles, scapular stabilizers, and/or foot dorsiflexors, with highly variable severity.

"Facioscapulohumeral muscular dystrophy (FSHD) typically presents with weakness of the facial muscles, the stabilizers of the scapula, and/or the dorsiflexors of the foot."

Approximately 20% of affected individuals eventually require a wheelchair, but life expectancy is not shortened.

"Weakness can be slowly progressive and approximately 20% of affected individuals eventually require a wheelchair. Life expectancy is not shortened."

PMID:31409737

Patient-Reported Symptoms in Facioscapulohumeral Muscular Dystrophy (PRISM-FSHD).

1 finding

Patient-reported symptom themes with the highest prevalence are shoulder or arm problems, activity limitations, core weakness, fatigue, mobility limitations, changed body image, and pain.

"The symptomatic themes with the highest prevalence in our sample were problems with shoulders or arms (96.9%), limitations with activities (94.7%), core weakness (93.8%), fatigue (93.8%), limitations with mobility and walking (93.6%), changed body image due to the disease (91.6%), and pain (87.7%)."

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/symptoms/

Symptoms - FSHD Society

1 finding

The principal FSHD patient advocacy organization communicates a symptom set to patients and families that includes manifestations under-weighted in the primary clinical literature - chronic fatigue, severe pain, sudden falls from legs giving out, abdominal wall weakness, incomplete eye closure during sleep, chest and spine deformity, breathing difficulty, hearing loss, mild arrhythmia, and Coats disease.

"Sudden falls when their legs unexpectedly give out"

url:https://www.fshdsociety.org/living-with-fshd/understanding-fshd/early-onset-fshd/

Early-onset FSHD - FSHD Society

1 finding

Patient organization resource describing the early-onset FSHD phenotype, in which extra-muscular involvement (hearing loss, Coats disease) is concentrated.

"Early-onset FSHD"

PMID:42485801

Living with FSHD: a patient-led narrative review of psychosocial well-being in facioscapulohumeral muscular dystrophy.

1 finding

A patient-led review finds that FSHD psychosocial burden is not captured by traditional biomedical outcomes and can persist even when clinical and quality-of-life scores are stable.

"Facioscapulohumeral muscular dystrophy (FSHD) is associated with substantial psychosocial challenges not fully captured by traditional biomedical outcomes, including challenges that may persist despite stable clinical or QoL scores."

PMID:41739307

Assessing the multidimensional burden of facioscapulohumeral muscular dystrophy through patient-reported outcomes and experience.

1 finding

Mixed-methods FSHD burden study whose cohort was recruited through a patient-led advocacy organization - an example of community-sourced evidence reaching the peer-reviewed literature.

"Patients with clinically and genetically confirmed FSHD were recruited nationwide through the FSHD Community Network-a patient-led advocacy organization affiliated with the Chinese Organization for Rare Disorders (CORD)."

PMID:38016873

The Dutch registry for facioscapulohumeral muscular dystrophy: Cohort profile and longitudinal patient reported outcomes.

1 finding

National FSHD registry with six years of longitudinal patient-reported follow-up: fatigue and muscle weakness are the most frequently reported symptoms, and pain localizes most often to the head and shoulder region. A consented, citable counterpart to informal patient-community knowledge.

"Pain was experienced most often in the head and shoulder region (193, 52%)."

PMID:39297366

The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound.

1 finding

Muscle ultrasound in 107 participants quantifies facial weakness at 92% and resolves which specific orofacial muscles are involved, extending a phenotype that standard facial-weakness scoring treats as a single item.

"of whom 92% showed signs of facial weakness"

PMID:40879179

Hearing Loss, Retinal Abnormality, and Seizures in People With Facioscapulohumeral Muscular Dystrophy.

1 finding

Population-based MD STARnet surveillance (n=548) gives clinically diagnosed rates for the three main extra-muscular comorbidities - hearing loss 13%, retinal abnormalities 3.6%, seizures 2.0% - with 17.2% having at least one. These are detection rates in routine care and run well below imaging-based figures for the same organ systems.

"Among the study cohort, 17.2% (n = 94) had at least one comorbidity"

PMID:38631764

Safety and efficacy of losmapimod in facioscapulohumeral muscular dystrophy (ReDUX4): a randomised, double-blind, placebo-controlled phase 2b trial.

1 finding

The phase 2b ReDUX4 trial missed its primary endpoint - losmapimod did not significantly change DUX4-driven gene expression - though secondary structural, functional, and patient-reported signals motivated progression to phase 3.

"Least squares mean changes from baseline in DUX4-driven gene expression did not differ significantly between the losmapimod"

url:https://old.reddit.com/r/FSHD/

FSHD

1 finding

Front-page listing of the r/FSHD public patient-community forum, swept as hypothesis-generating signal for this entry. Topics corroborated by literature (chronic pain and fatigue, head pain) informed curated phenotypes; topics without a clinical evidence base (fasciculations, low aldolase) are recorded only under `discussions` as unvalidated leads. Aggregate discussion topics only - no individual's personal health narrative is quoted.

"chronic pain and fatigue"

url:https://old.reddit.com/r/FSHD/top/?t=all

Deep Research

3

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 (3)

Add FSHD4 (MONDO:0030355) as a subtype of Facioscapulohumeral Muscular Dystrophy · 2026-09-24T17:48:35Z · View source

Curation of MONDO:0030355 (facioscapulohumeral muscular dystrophy 4, digenic; OMIM 619478). Lump/split call: curated as a has_subtypes entry named FSHD4 on the existing Facioscapulohumeral_Muscular_Dystrophy entry rather than as a standalone kb/disorders file, because the pathograph (D4Z4 derepression -> DUX4 misexpression in skeletal muscle -> myofiber loss) is the one already curated there, reached through DNMT3B instead of SMCHD1, and PMID:34711481 reports no clinical difference between contraction-independent FSHD and FSHD1. Added: the FSHD4 subtype bound to MONDO:0030355 with genes DNMT3B and DUX4 and a subtype-level Inheritance block bound to HP:0010984 Digenic inheritance, penetrance INCOMPLETE; two new pathophysiology nodes keeping the two required lesions separate (DNMT3B-Dependent D4Z4 Methylation Failure, and Permissive 4qA Polyadenylation Signal) with causal edges into the existing derepression and DUX4-misexpression nodes; a COOPERATING genetic row for the permissive 4qA haplotype; retargeting of the existing DNMT3B genetic row from subtype FSHD2 to FSHD4 with a note explaining that GeneReviews classifies these patients as FSHD2 by methylation while OMIM/MONDO number by gene; and the D4Z4-2.5/Dnmt3bMommeD14 mouse with a FAILS_TO_RECAPITULATE link to the skeletal-muscle node. Deep research: falcon requested, returned HTTP 402 (out of credits); claude_code produced the report (research/Facioscapulohumeral_Muscular_Dystrophy_4_Digenic-deep-research-claude_code.md). just preflight-dr returned WARN, not FAIL: the report covers FSHD broadly and cites OMIM 158900/158901 rather than 619478, which is consistent with the entity being a subtype of the parent disease. Report content was treated as leads; every snippet committed here was read from references_cache. Evidence gaps recorded in notes: no phenotype is scoped to FSHD4 because no DNMT3B-specific clinical series exists, and no penetrance rate is given because the two original families are too small. Also repaired pre-existing drift in the NCT06131983 clinical trial record, whose registry title and summary now name SRP-1001; the refreshed cache file is committed with the updated title and snippet. Two further pre-existing title mismatches on old.reddit.com url references were left alone: they reproduce identically against the unmodified file at HEAD and appear to be a fetcher block rather than a content error. Validated with linkml-reference-validator 0.3.0rc1.

Edit: openscientist deep research; hearing-loss frequency, retinal nuance, losmapimod outcome · 2026-08-01T15:55:27Z · View source

Round 4: second deep-research provider (openscientist) at curator request, replacing the unavailable falcon. Provider run: openscientist, autonomous investigation mode, 5 iterations, 28.7 minutes, 32 citations, plus HTML/PDF artifacts. Report and citations committed under research/. DR VERIFICATION - one of three checked snippets failed. The report quoted "Hearing Loss (13%; n = 71) was the most frequently reported comorbidity, followed by retinal abnormalities (3.6%; n = 20) and seizures (2.0%; n = 11)" from PMID:40879179. That is NOT an exact substring of the cached abstract: the real text is lower-case "Hearing loss", and the quote continues past where the cached abstract wraps. Corrected to a verified substring before use. The other two checked snippets (PMID:40580827, PMID:38631764) verified as written. This is the fourth distinct DR error class encountered in this curation (after three hallucinated HPO IDs from the claude_code run) and reinforces treating DR output as leads. Additions, all independently verified: 1. Sensorineural hearing impairment gained its first QUANTITATIVE frequency evidence. The phenotype already carried frequency: OCCASIONAL but with no supporting numeric source. Population-based MD STARnet surveillance (PMID:40879179, n=548) gives clinically diagnosed hearing loss at 13%, confirming the OCCASIONAL band (5-29%) and establishing it as the most common extra-muscular comorbidity of FSHD. 2. Retinal telangiectasia gained an important interpretive nuance. MD STARnet records clinically diagnosed retinal abnormality in only 3.6%, against the 49% detected by dedicated fluorescein angiography that underpins the FREQUENT band. These are not in conflict - they measure subclinical angiographic telangiectasia versus a retinal diagnosis recorded in routine care - and the roughly order-of-magnitude gap is exactly the argument for targeted ophthalmologic surveillance. Added as PARTIAL with the distinction explained rather than silently reconciling the numbers or changing the band. 3. Losmapimod trial outcome curated, closing the reviewer-flagged high-value gap. The existing NCT05397470 phase 3 entry recorded only "Terminated" status with no outcome. Added two REFUTE evidence items: the preceding phase 2b ReDUX4 trial (PMID:38631764) missed its primary endpoint, with no significant change in DUX4-driven gene expression versus placebo; and the phase 3 (PMID:40580827) failed to demonstrate clear clinical benefit. Recorded as REFUTE so the entry does not leave a terminated program looking merely incomplete - the p38/DUX4-suppression strategy was tested and did not succeed. One snippet required correction for typography: the ReDUX4 abstract uses middle-dot decimal separators (0.83 rendered as 0<middot>83), so a numeral-free substring was used instead. Still deferred as agreed with the reviewer: genotype-phenotype depth (D4Z4 repeat size correlation, SMCHD1 as an FSHD1 modifier, mosaicism, the 8-11 unit grey zone) and ACE-083. The openscientist report supplies good material for these (notably PMID:30211448: familial factors explain 50% of severity variance versus only ~10% for repeat size) and they remain a clean follow-up. Validation: just validate passes; 100/100 snippets verified; 9 FSHD tests pass; compliance 87.6% weighted (denominator grew again with added content).

Edit: FSHD - community-sourced phenotypes, natural history, and treatments · 2026-07-31T20:01:38Z · View source

Augmented the existing FSHD umbrella entry (MONDO:0001347) rather than creating a separate FSHD1 entry, at curator direction. Goal was to capture phenotypes, treatments, and natural history that patient/family communities and advocacy organizations describe but the primary clinical literature under-represents. Community sources mined: the FSHD Society patient-education pages (symptoms, early-onset FSHD, online communities) and the public r/FSHD subreddit, all cached as url: references via `just fetch-reference`. Facebook was attempted but its public Page returns a login/CSS wall with no quotable content, so it was discarded rather than cited. reddit.com is bot-walled but old.reddit.com serves usable server-rendered HTML. Every community signal was bridged to citable evidence rather than curated on social-media assertion alone. Key bridging references: GeneReviews (PMID:20301616, tagged), PRISM-FSHD patient-reported outcomes (PMID:31409737), a patient-led psychosocial narrative review (PMID:42485801), fatigue qualitative study (PMID:27762634), fatigue AET/CBT RCT (PMID:25339206), long-term respiratory follow-up (PMID:35147730), sleep-disordered breathing (PMID:31025273), cardiac involvement (PMID:34108930), retinal vasculopathy (PMID:23573590, PMID:36900126). Added 13 phenotypes: Fatigue (VERY_FREQUENT, 93.8 percent), Abdominal wall muscle weakness, Foot dorsiflexor weakness, Falls, Lagophthalmos, Lumbar hyperlordosis, Scoliosis, Pectus excavatum, Restrictive ventilatory defect (FREQUENT), Arrhythmia (OCCASIONAL), Retinal telangiectasia (FREQUENT), Obstructive sleep apnea, Nocturnal hypoventilation. Frequencies were set only where a quantitative source existed; omitted otherwise. Added 4 treatments: CBT for chronic fatigue (NCIT:C64345, RCT-backed), ankle-foot orthoses (term omitted, no reachable NCIT clinical-action term), ocular surface protection, respiratory surveillance and ventilatory support. Added 2 progression phases: loss of ambulation in about 20 percent, and respiratory decline confined to an at-risk subgroup. Added 2 discussions: a KNOWLEDGE_GAP recording that the pathograph does not explain the fatigue/pain/sleep "invisible symptom" burden patients rank highest, and an OPEN_QUESTION recording community-raised signals with no clinical evidence base (migraine, fasciculations, low aldolase) as explicitly unvalidated leads, with the nocturnal-hypoventilation morning-headache hypothesis noted. Social-media content was deliberately NOT promoted to curated phenotypes. Privacy note: only aggregate community discussion topics and thread titles were quoted; no individual patient's personal health narrative was reproduced. Deep research: falcon failed (Edison API 402 Payment Required); the claude_code provider run completed and is committed. Existing asta report reused. Three DR-suggested HPO IDs were wrong on verification (HP:0003707 is calf pseudohypertrophy, HP:0025637 is vasospasm) and were replaced with OAK-verified terms. Validation: just validate passes (schema + terms + references), 71/71 snippets verified against cached references; compliance 88.1 percent weighted.

Asta ▸

Asta Literature Retrieval: Pathophysiology and clinical mechanisms of Facioscapulohumeral Muscular Dystrophy. Core disease mechanisms, molecular...

Asta Scientific Corpus Retrieval 20 citations 2026-04-22T21:54:51.169538

Asta Literature Retrieval: Pathophysiology and clinical mechanisms of Facioscapulohumeral Muscular Dystrophy. Core disease mechanisms, molecular...

This report is retrieval-only and is generated directly from Asta results.

Papers retrieved: 20
Snippets retrieved: 20

Relevant Papers

[1] Determining the role of sarcomeric proteins in facioscapulohumeral muscular dystrophy: a study protocol

Authors: S. Lassche, C. Ottenheijm, N. Voermans, H. Westeneng, B. Janssen et al.
Year: 2013
Venue: BMC Neurology
URL: https://www.semanticscholar.org/paper/868ee81fe48b5199729eda6ddea2866f5512e503
DOI: 10.1186/1471-2377-13-144
PMID: 24119284
PMCID: 3852245
Citations: 15
Influential citations: 1
Summary: The results obtained in this study will increase the understanding of the pathophysiology of muscle weakness in FSHD, and possibly identify novel targets for therapeutic intervention.
Evidence snippets:
Snippet 1 (score: 0.605) > BackgroundAlthough muscle weakness is a hallmark of facioscapulohumeral muscular dystrophy (FSHD), the molecular mechanisms that lead to weakness in FSHD remain largely unknown. Recent studies suggest aberrant expression of genes involved in skeletal muscle development and sarcomere contractility, and activation of pathways involved in sarcomeric protein degradation. This study will investigate the contribution of sarcomeric protein dysfunction to the pathogenesis of muscle weakness in FSHD.Methods/DesignEvaluation of sarcomeric function using skinned single muscle fiber contractile studies and protein analysis in muscle biopsies (quadriceps femoris and tibialis anterior) from patients with FSHD and age- and gender-matched healthy controls. Patients with other forms of muscular dystrophy and inflammatory myopathy will be included as disease controls to assess whether results are due to changes specific for FSHD, or a consequence of muscle disease in general. A total of 56 participants will be included. Extensive clinical parameters will be measured using MRI, quantitative muscle studies and physical activity assessments.DiscussionThis study is the first to extensively investigate muscle fiber physiology in FSHD following an earlier pilot study suggesting sarcomeric dysfunction in FSHD. The results obtained in this study will increase the understanding of the pathophysiology of muscle weakness in FSHD, and possibly identify novel targets for therapeutic intervention.

[2] Diagnosis, Pathogenesis and Treatment of Muscular Dystrophy

Authors: M. Bozzi
Year: 2025
Venue: Biomedicines
URL: https://www.semanticscholar.org/paper/e9c585567287a136c52df952d8f374aa96ae1090
DOI: 10.3390/biomedicines13081820
PMID: 40868075
PMCID: 12383284
Summary: Muscular dystrophies are a group of inherited genetic disorders that involve an ever-growing number of genes [...].
Evidence snippets:
Snippet 1 (score: 0.587) > Muscular dystrophies are a group of inherited genetic disorders that involve an evergrowing number of genes. Nowadays, more than 50 genes have been linked to different muscular dystrophies [1]. This genetic variability accounts for the wide heterogeneity of phenotypes observed in patients. From a clinical and pathological standpoint, muscular dystrophies are characterized by varying ages of onset and a broad spectrum of symptoms, including severe forms that impact other organs and tissues, particularly the central nervous system. Nevertheless, muscular dystrophies exhibit common histopathological and molecular characteristics that reflect disease progression. The primary shared feature is the accumulation of fibrotic tissue, which results from muscle fiber degeneration and cell death, ongoing inflammation, and increased oxidative stress. These factors contribute to the infiltration of inflammatory cells and the oxidation of lipids and proteins [2]. In the most severe forms of muscular dystrophy, cardiomyopathy and respiratory dysfunction occur during disease progression, severely affecting the patients' quality of life and strongly reducing their lifespan. Duchenne muscular dystrophy, Myotonic dystrophy type 1, and Facioscapulohumeral muscular dystrophy are some of the most common forms of muscular dystrophies. In particular, due to mutations in the dystrophin gene, Duchenne muscular dystrophy has an incidence of about 1 in 5000 live males every year [3]. > Early diagnosis is essential for effectively managing disease progression, and it should include genetic testing. However, establishing an accurate diagnosis can be challenging, as individuals with mutations in the same gene may present with diverse clinical manifestations. Therefore, a comprehensive approach integrating clinical evaluation, molecular testing, and tissue analysis is critical for achieving a precise diagnosis and informing a reliable prognosis [4,5]. > At present, there is no definitive cure for muscular dystrophy. Glucocorticoid therapy remains the cornerstone of muscular dystrophy treatment, helping to delay disease progression and improve muscle strength. However, its use is associated with significant side effects, including adrenal suppression, growth delay, weakened bone health, and the onset of metabolic syndrome [6]. This highlights the need to develop innovative therapeutic strategies.

[3] Current Therapeutic Approaches in FSHD

Authors: Leo H. Wang, R. Tawil
Year: 2020
Venue: Journal of Neuromuscular Diseases
URL: https://www.semanticscholar.org/paper/65038a0ff08223c00ba4710a13bd42c87be28ac6
DOI: 10.3233/JND-200554
PMID: 33579868
PMCID: 8203219
Citations: 30
Influential citations: 1
Summary: The underlying disease mechanism, potential therapeutic approaches as well as the state of trial readiness in the planning and execution of future clinical trials in FSHD are reviewed.
Evidence snippets:
Snippet 1 (score: 0.580) > Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common muscular dystrophies. Over the last decade, a consensus was reached regarding the underlying cause of FSHD allowing—for the first time—a targeted approach to treatment. FSHD is the result of a toxic gain-of-function from de-repression of the DUX4 gene, a gene not normally expressed in skeletal muscle. With a clear therapeutic target, there is increasing interest in drug development for FSHD, an interest buoyed by the recent therapeutic successes in other neuromuscular diseases. Herein, we review the underlying disease mechanism, potential therapeutic approaches as well as the state of trial readiness in the planning and execution of future clinical trials in FSHD.

[4] The Notch signaling pathway in skeletal muscle health and disease

Authors: D. Vargas-Franco, R. Kalra, Isabelle Draper, C. A. Pacak, A. Asakura et al.
Year: 2022
Venue: Muscle & Nerve
URL: https://www.semanticscholar.org/paper/2bc32ef6a1acc95f1c31b7e3ef5a268aadda4024
DOI: 10.1002/mus.27684
PMID: 35968817
PMCID: 9804383
Citations: 37
Summary: The clinical syndromes associated with pathogenic variants in each of these genes, known molecular and cellular functions of their protein products with a particular focus on the Notch signaling pathway, and potential novel therapeutic targets that may emerge from further investigations of these diseases are reviewed.
Evidence snippets:
Snippet 1 (score: 0.563) > Since the landmark discovery in 1986 of DMD (dystrophin), 1 the causative gene for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), dozens of additional genes have been associated with various phenotypic subtypes of muscular dystrophy. > Common disease mechanisms across multiple subtypes have, however, been more difficult to identify, with only a few major clusters such as the dystroglycanopathies identified to date. Given the common phenotypic features within muscular dystrophy categories, such as limb-girdle muscular dystrophy (LGMD), there is a high likelihood that convergent disease mechanisms exist across more muscular dystrophy subtypes than is currently recognized. > There are therapeutic implications of identifying deeper biological ties between muscular dystrophy subtypes. In recent years, the US Food and Drug Administration (FDA) has approved several molecular and genetic therapies for neuromuscular disorders that target specific genes and even specific mutation types within those genes. These approaches are being applied to ever rarer forms of muscular dystrophies. However, proceeding through the preclinical and clinical research studies needed to attain FDA approval for a new therapy is lengthy and costly, and on the current trajectory it will be decades before molecular and genetic therapies are available for all known subtypes of muscular dystrophy. > The identification and characterization of disease mechanisms that are shared by multiple muscular dystrophy subtypes could pave the way for new pathway-based treatments that have therapeutic effects for multiple disease subtypes. 2 This has the potential to accelerate the timeline for broader therapeutic coverage of patients with muscular dystrophy, with a greater impact on the entire muscular dystrophy population. > One disease mechanism that bears further analysis is the Notch signaling pathway, which is known to maintain muscle stem cell (MuSC, also known as satellite cell) quiescence. Recently, three different muscle disease genes that are known to interact with the Notch signaling pathway have been identified: MEGF10, POGLUT1, and most recently JAG2.

[5] Meeting report: the 2021 FSHD International Research Congress

Authors: S. Jagannathan, Jessica C. de Greef, Lawrence J. Hayward, K. Yokomori, D. Gabellini et al.
Year: 2022
Venue: Skeletal Muscle
URL: https://www.semanticscholar.org/paper/7444edfc105226463dbdb4a3252fa3cc611a2048
DOI: 10.1186/s13395-022-00287-8
Summary: The 2021 FSHD International Research Congress, held virtually on June 24–25, convened over 350 researchers and clinicians to share the most recent advances in the understanding of the disease mechanism, discuss the proliferation of interventional strategies and refinement of clinical outcome measures, including results from the ReDUX4 trial, a phase 2b clinical trial of losmapimod in FSHd.
Evidence snippets:
Snippet 1 (score: 0.561) > Facioscapulohumeral muscular dystrophy (FSHD) is the second most common genetic myopathy, characterized by slowly progressing and highly heterogeneous muscle wasting with a typical onset in the late teens/early adulthood [1]. Although the etiology of the disease for both FSHD type 1 and type 2 has been attributed to gain-of-toxic function stemming from aberrant DUX4 expression, the exact pathogenic mechanisms involved in muscle wasting have yet to be elucidated [2–4]. The 2021 FSHD International Research Congress, held virtually on June 24–25, convened over 350 researchers and clinicians to share the most recent advances in the understanding of the disease mechanism, discuss the proliferation of interventional strategies and refinement of clinical outcome measures, including results from the ReDUX4 trial, a phase 2b clinical trial of losmapimod in FSHD [NCT04003974].

[6] Facioscapulohumeral Muscular Dystrophy.

Authors: Renatta N Knox
Year: 2018
Venue: Continuum
URL: https://www.semanticscholar.org/paper/aeb5eff3a6fc5398a8b8f1485693ed1a6cc4746a
DOI: 10.1007/978-1-4614-6430-3_84-2
PMID: 41037169
Citations: 225
Influential citations: 19
Summary: An overview of the distinctive genetic mechanisms underlying FSHD, its clinical manifestations, including pediatric-specific features, treatment, and the evolving landscape of clinical trials targeting disease-modifying therapies is provided.
Evidence snippets:
Snippet 1 (score: 0.555) > OBJECTIVE > Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common forms of muscular dystrophy, affecting individuals across the lifespan with variable severity. This article provides an overview of the distinctive genetic mechanisms underlying FSHD, its clinical manifestations, including pediatric-specific features, treatment, and the evolving landscape of clinical trials targeting disease-modifying therapies. > LATEST DEVELOPMENTS > FSHD arises from derepression of the transcription factor DUX4, which is toxic to skeletal muscle. This misexpression leads to a characteristic and progressive pattern of muscle weakness involving the facial, shoulder girdle, upper extremity, trunk, and leg muscles. Extramuscular manifestations, such as pain and fatigue, are frequently reported. Children with a severe, early-onset phenotype experience higher rates of extramuscular features, including hearing loss, cognitive impairment, and spinal deformities. Advances in the understanding of DUX4 as the causative gene, combined with innovations in gene therapy, gene editing, small-molecule development, and drug delivery, have catalyzed the initiation of several clinical trials focusing on disease-targeted treatments in the near future. > ESSENTIAL POINTS > FSHD is caused by toxic expression of DUX4 and presents with progressive, often asymmetric muscle weakness and extramuscular manifestations in a subset of patients. Advances in genetic understanding and therapeutic development have led to clinical trials targeting DUX4. Although care remains supportive, the field is entering an era of promising disease-modifying strategies.

[7] The Unexplored Role of Connexin Hemichannels in Promoting Facioscapulohumeral Muscular Dystrophy Progression

Authors: Macarena Díaz-Ubilla, Mauricio A Retamal
Year: 2025
Venue: International Journal of Molecular Sciences
URL: https://www.semanticscholar.org/paper/2fc946973feb1d3970f29459e88eb639d3cd5bf9
DOI: 10.3390/ijms26010373
PMID: 39796228
PMCID: 11719937
Summary: This review summarizes the current understanding of the mechanisms underlying FSHD progression, with a focus on hormones, inflammation, reactive oxygen species (ROS), and mitochondrial function and explores the potential of targeting hemichannels as a therapeutic strategy to slow disease progression by preventing the spread of pathogenic factors between muscle cells.
Evidence snippets:
Snippet 1 (score: 0.539) > Facioscapulohumeral Muscular Dystrophy (FSHD) is one of the most prevalent types of muscular dystrophy, affecting between 1 in 8000 to 1 in 22,000 people worldwide [1][2][3]. This condition is caused by a genetic mutation and is characterized by a slow, progressive, and asymmetric weakening of specific muscle groups, including the muscles of the face, shoulder girdle, arms, abdominal wall, hips, and thighs [2,4]. The clinical presentation of FSHD is highly variable, even among individuals with the same genetic background, such as monozygotic twins, where differences in disease severity and muscle involvement have been documented [5,6]. This variability extends to the pattern of disease progression, which is often unpredictable and varies widely from person to person [3,7,8]. The unpredictable nature of FSHD likely reflects underlying uncertainties at the molecular level, particularly the factors governing the expression of the disease-causing gene, DUX4. Although DUX4 is a critical factor in the pathogenesis of FSHD, its expression is rare, detected in only 1 out of 1000 FSHD myoblasts and in approximately 1 out of 200 myotube nuclei during in vitro studies [9]. Despite extensive research, the DUX4 protein has not been successfully detected in muscle biopsies from FSHD patients [9,10]. However, even with such low levels of DUX4 expression, muscle atrophy continues to progress, affecting both initially impacted and surrounding healthy muscle fibers and eventually spreading to additional muscle groups. This suggests that FSHD involves a broader mechanism of pathogenic factor transmission between muscle cells, which accelerates muscle damage. One possible mechanism behind this transmission involves connexin (Cx) hemichannels, which facilitate the exchange of signaling molecules between the cell cytoplasm and the extracellular environment [11][12][13].

[8] Cellular and molecular mechanisms underlying muscular dystrophy

Authors: F. Rahimov, L. Kunkel
Year: 2013
Venue: The Journal of Cell Biology
URL: https://www.semanticscholar.org/paper/f40d5c11c05bfed36ed352efec2330b6b6ade1ba
DOI: 10.1083/jcb.201212142
PMID: 23671309
PMCID: 3653356
Citations: 233
Influential citations: 12
Summary: The muscular dystrophies are a group of heterogeneous genetic diseases characterized by progressive degeneration and weakness of skeletal muscle and distinct molecular and cellular mechanisms that link genetic mutations to diverse muscle wasting phenotypes are revealed.
Evidence snippets:
Snippet 1 (score: 0.538) > The muscular dystrophies are a group of heterogeneous genetic diseases characterized by progressive degeneration and weakness of skeletal muscle. Since the discovery of the first muscular dystrophy gene encoding dystrophin, a large number of genes have been identified that are involved in various muscle-wasting and neuromuscular disorders. Human genetic studies complemented by animal model systems have substantially contributed to our understanding of the molecular pathomechanisms underlying muscle degeneration. Moreover, these studies have revealed distinct molecular and cellular mechanisms that link genetic mutations to diverse muscle wasting phenotypes.

[9] Therapeutic advances in muscular dystrophy

Authors: D. Leung, K. Wagner
Year: 2013
Venue: Annals of Neurology
URL: https://www.semanticscholar.org/paper/22bac6d00e252299778eb2908eb9c77674e1b562
DOI: 10.1002/ana.23989
PMID: 23939629
PMCID: 3886293
Citations: 79
Influential citations: 1
Summary: Treatment developments in 3 of the most common forms of muscular dystrophy are discussed, with the large number of novel pharmacologic agents in development with good biologic rationale and strong proof of concept suggesting there will be an improved quality of life for individuals with muscular dystroke.
Evidence snippets:
Snippet 1 (score: 0.533) > The muscular dystrophies comprise a heterogeneous group of genetic disorders that produce progressive skeletal muscle weakness and wasting. There has been rapid growth and change in our understanding of these disorders in recent years, and advances in basic science are being translated into increasing numbers of clinical trials. This review will discuss therapeutic developments in 3 of the most common forms of muscular dystrophy: Duchenne muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. Each of these disorders represents a different class of genetic disease (monogenic, epigenetic, and repeat expansion disorders), and the approach to therapy addresses the diverse and complex molecular mechanisms involved in these diseases. The large number of novel pharmacologic agents in development with good biologic rationale and strong proof of concept suggests there will be an improved quality of life for individuals with muscular dystrophy. Ann Neurol 2013;74:404–411

[10] A Hypothesis for Mechanisms of Weakness Distribution in Muscular Dystrophies

Authors: Alexander Khlebtovsky, F. Benninger, I. Steiner
Year: 2018
Venue: Journal of neurological disorders
URL: https://www.semanticscholar.org/paper/bef89c402a7ddbbd127f4c1fd0472b4c04e87b7e
DOI: 10.4172/2329-6895.1000389
Citations: 2
Influential citations: 1
Summary: A classification of muscle weakness in muscular dystrophies could enable predicting the function of newly identified myopathy-related genes according to their clinical presentation, and show that muscle weakness often follows a common pattern.
Evidence snippets:
Snippet 1 (score: 0.530) > Abnormal proteins that present with more or less simultaneous involvement of proximal and distal muscles are briefly reviewed according to: protein location and function, name of disease caused with possible mechanisms of myopathy, and levels of proof for the pathophysiological mechanism/s. Proteins in this group have a wide range of functions, including: cell signalling, muscle differentiation and apoptosis. However, the pathophysiology causing myopathy is unknown. > additional factors are involved other than proper protein dysfunction and muscle cell signaling. Furthermore, the degenerative muscle diseases caused by more complicated mechanisms than isolated protein dysfunction, such as myotonic dystrophy and facioscapulohumeral muscular dystrophy, represent exceptions to our hypothesis.

[11] Pharmacotherapeutic Approaches to Treatment of Muscular Dystrophies

Authors: A. Rawls, Bridget K. Diviak, Cameron I. Smith, Grant W. Severson, Sofia A. Acosta et al.
Year: 2023
Venue: Biomolecules
URL: https://www.semanticscholar.org/paper/2d7f023c19774543c7e0bfca5c0dfb0b1aab2b39
DOI: 10.3390/biom13101536
PMID: 37892218
PMCID: 10605463
Citations: 9
Summary: The pathophysiology, genetic background, and emerging therapeutic strategies for muscular dystrophies are examined to develop new pharmacotherapeutic approaches to limit inflammation and fibrosis to reduce muscle damage and promote repair.
Evidence snippets:
Snippet 1 (score: 0.525) > Muscular dystrophies (MDs) are genetic degenerative neuromuscular diseases characterized by progressive muscle weakness that results in significant morbidity.To date, mutations in 57 genes have been identified that cause nine specific classes of muscular dystrophy [1].Dystrophies are classified based on the specific gene involved and clinical features such as muscles affected, rate of disease progression, histopathology, and age of diagnosis.Inflammation is a common factor in the pathogenesis and progression of many types of MD.Chronic inflammation exacerbates muscle damage, induces fibrotic deposition and fatty replacement of myofibers, and impedes the regenerative process of skeletal muscle. > There are no curative treatments for any dystrophies currently, but new AAV and base editing approaches to provide the missing proteins or fix the genetic lesion provide hope.Though there is tremendous curative potential, these genetic approaches will not treat all dystrophies or even all versions of a single dystrophy.For example, there are more than 7000 known mutations in dystrophin that result in Duchenne muscular dystrophy (DMD) [2].Therefore, understanding the mechanisms underlying inflammation and other pathogenic processes will aid in identifying therapeutic approaches that can ameliorate the progression of these diseases.Preclinical and clinical treatments that specifically target inflammation and fibrosis are the subject of this review.

[12] Human iPSC Models to Study Orphan Diseases: Muscular Dystrophies

Authors: Guangbin Xia, N. Terada, T. Ashizawa
Year: 2018
Venue: Current Stem Cell Reports
URL: https://www.semanticscholar.org/paper/94a0f0ec0fcc7956f4f564ed7b9052cad3b908ce
DOI: 10.1007/s40778-018-0145-5
PMID: 30524939
PMCID: 6244555
Citations: 13
Summary: Current applications of iPSC as disease models of MDs for studies of pathogenic mechanisms and therapeutic development and high-throughput screening using disease-specific human iPSCs has become a powerful technology in drug discovery.
Evidence snippets:
Snippet 1 (score: 0.515) > In genotype-phenotype correlations in MDs, we should note two types of heterogeneities: (1) the same pattern of muscular dystrophies can be caused by mutations in different genes and (2) the different mutations in the same gene may cause different patterns of muscular dystrophy. In terms of pathogenic mechanism, myotonic dystrophy type 1 (DM1) and type 2 (DM2) and oculopharyngeal muscular dystrophy (OPMD) belong to a distinct group of muscular dystrophy caused by RNA gain-of-function from trinucleotide repeat expansion [2][3][4][7][8][9][10], while facioscapulohumeral muscular dystrophy (FSHD) is caused by the contraction of microsatellite D4Z4 repeats [11], and the remaining MDs are caused by point mutations, deletions, duplications, and inversions [6]. Patents with MDs are often succumbed to a long arduous clinical course of progressive muscle weakness and wasting often resulting in significant disability and various complications. There is currently no cure for MDs, and available treatments are supportive care or of limited efficacy. Appropriate disease models are important for elucidation of disease mechanism and identification of treatment target.

[13] The FSHD jigsaw: are we placing the tiles in the right position?

Authors: Valentina Salsi, G. Vattemi, R. Tupler
Year: 2023
Venue: Current Opinion in Neurology
URL: https://www.semanticscholar.org/paper/7a8931a1a0f0ce046716d159fe70a749fc6ef3c8
DOI: 10.1097/WCO.0000000000001176
PMID: 37338810
PMCID: 10487374
Citations: 12
Summary: The main objectives of the scientific community on Facioscapulohumeral muscular dystrophy were summarized and the moving trajectories of research from the past to the present were summarized.
Evidence snippets:
Snippet 1 (score: 0.515) > Purpose of review Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common myopathies, involving over 870,000 people worldwide and over 20 FSHD national registries. Our purpose was to summarize the main objectives of the scientific community on this topic and the moving trajectories of research from the past to the present. Recent findings To date, research is mainly oriented toward deciphering the molecular and pathogenetic basis of the disease by investigating DUX4-mediated muscle alterations. Accordingly, FSHD drug development has been escalating in the last years in an attempt to silence DUX4 or to block its downstream effectors. Breakthroughs in the field include the awareness that new biomarkers and outcome measures are required for tracking disease progression and patient stratification. The need to develop personalized therapeutic strategies is also crucial according to the phenotypic variability observed in FSHD subjects. Summary We analysed 121 literature reports published between 2021 and 2023 to assess the most recent advances in FSHD clinical and molecular research.

[14] Current Genetic Survey and Potential Gene-Targeting Therapeutics for Neuromuscular Diseases

Authors: W. Chiu, Ya-Hsin Hsun, Kao-Jung Chang, A. Yarmishyn, Yu-Jer Hsiao et al.
Year: 2020
Venue: International Journal of Molecular Sciences
URL: https://www.semanticscholar.org/paper/421f0212b8e3f567e050b3191da99fe550b243a8
DOI: 10.3390/ijms21249589
PMID: 33339321
PMCID: 7767109
Citations: 14
Summary: The current development of gene therapy is reviewed and focus on NMDs that are available in published reports, including Duchenne Muscular Dystrophy, Becker muscular dystrophy (BMD), X-linked myotubular myopathy (XLMTM), Spinal Muscular Atrophy (SMA), and Limb-girdle muscular dystrophies Type 2C (LGMD2C).
Evidence snippets:
Snippet 1 (score: 0.515) > Facioscapulohumeral Muscular Dystrophy (FSHD) is one of the most common muscular dystrophies with a prevalence ranging between 2.03 and 6.8 per 100,000 persons [95]. The disease onset typically occurs in the twenties but is also detected at other ages. The muscle weakness deteriorates as the onset persists in a classic pattern: first, the facial and shoulder girdle muscles are affected, then the lower extremities, both distal and proximal. Variations in the age of onset, disease pattern, disease progression, and severity of muscle weakness among FSHD individuals results in disease severity ranging from mildly affected/asymptomatic to wheelchair-bound (20% of FSDH patients) [96,97]. Extramuscular manifestations include hearing loss [98,99] and loss of vision resulting from retinal vascular abnormalities [100,101], exudative retinopathy, and Coat's syndrome [102]. > Autosomal dominant FSHD is caused by the derepression of DUX4, a transcriptional regulator, whose target genes are toxic to skeletal muscle [103][104][105]. Unlike DMD, which is caused by mutations in the coding region of a single gene, FSHD requires mixed aberrations of genetic and epigenetic nature to result in DUX4 derepression and cause clinical symptoms. DUX4 is located on D4Z4 macrosatellite repeat array on chromosome 4q35 with each D4Z4 repeat (3.3 kb) including a DUX4 gene, and it is expressed in germline cells but silenced in somatic tissues [103,106]. The silencing can be reversed as a result of DNA hypomethylation and consequent opening of the chromatin structure by the following two mechanisms. In facioscapulohumeral muscular dystrophy type 1 (FSHD1) accounting for 95% of cases, an internal contraction of D4Z4 repeats occurs, leading to a reduced number of repeats, 1 to 10 repeat units, while the unaffected individuals contain 11 to 100 D4Z4 units [106,107].

[15] A pediatric case report and literature review of facioscapulohumeral muscular dystrophy type1

Authors: Ting Xiao, Haiyang Yang, Siyi Gan, Liwen Wu
Year: 2021
Venue: Medicine
URL: https://www.semanticscholar.org/paper/d39bf2d0a9f15060d81e0f8a73cc4ca3e15083c8
DOI: 10.1097/MD.0000000000027907
PMID: 34964760
PMCID: 8615324
Citations: 6
Summary: The clinical characteristics of 2 patients with early-onset facial and shoulder brachial muscular dystrophy are reported to improve clinicians’ understanding of this particular condition and identify early identification and genetic diagnosis to improve patient prognosis.
Evidence snippets:
Snippet 1 (score: 0.514) > Facioscapulohumeral muscular dystrophy (FSHD) is a slowly progressive muscular dystrophy. Currently, there are 2 genetically distinct types of FSHD, FSHD1, and FSHD2. [5] Facioscapulohumeral muscular dystrophy type 1 (FSHD1, OMIM: 158900) is an autosomal dominant genetic disease in which integral copies of the 3.3 kb tandem repeat unit D4Z4 are deleted in the subtelomere region of chromosome 4q35.41. [8] Some studies have shown that there is a negative correlation between the number of D4Z4 repetitions and the severity of FSHD. Therefore, studies have shown that very short alleles (1-3 D4Z4 repeats) are related to the most severe form of the disease. [7,8] The D4Z4 repeat sequence contains the DUX4 gene, which is abnormally expressed in skeletal muscle cells of FSHD patients. The abnormal expression of DUX4 leads to dysregulation of molecular pathways that are involved in muscle differentiation, oxidative stress responses, immune responses, and protein turnover. However, the precise mechanism leading to FSHD is still unknown. [3,9,10] acioscapulohumeral muscular dystrophy type 2 (FSHD2, OMIM: 158901) is associated with mutations of the structural maintenance of the chromosome flexible hinge domain-containing protein 1 [11] (SMCHD1) gene on chromosome 18p1143 or the DNA methyltransferase 3B [12] (DNMT3B) gene on chromosome 20q11 in the presence of a disease-permissive 4qA haplotype. Both types of mutations are associated with insufficient epigenetic repression of D4Z4 repeats, leading to aberrant expression of double homeobox protein 4 (DUX4) in skeletal muscles and consequently, disease progression. FSHD2 can present with autosomal dominant or recessive inheritance. [3,5]

[16] Cellular Stress in the Pathogenesis of Muscular Disorders—From Cause to Consequence

Authors: Alexander Mensch, S. Zierz
Year: 2020
Venue: International Journal of Molecular Sciences
URL: https://www.semanticscholar.org/paper/22b8c2f84f84b8479f611e296ca9b32813c3bf6c
DOI: 10.3390/ijms21165830
PMID: 32823799
PMCID: 7461575
Citations: 15
Summary: This review aimed to summarize the available evidence regarding a deregulation of the cellular stress response in individual muscle diseases and relevant therapeutic approaches that aim to abrogate defects of cellular Stress response in muscular disorders are outlined.
Evidence snippets:
Snippet 1 (score: 0.513) > Muscular dystrophies are a phenotypically and genotypically heterogeneous group of inherited muscular disorders that share common histopathologic features, including degeneration/necrosis, regeneration, and endo-and perimysial fibrosis, as well as increased adipose tissue [121]. Causative gene mutations leading to individual muscular dystrophies reflect a broad spectrum of cellular functions, including extracellular matrix proteins, members of the dystrophin-glycoprotein complex, nuclear envelope proteins, and mitochondrial membrane proteins, amongst others [122]. Beside the pathogenetic consequences arising from individual gene mutations, additional aggrieving mechanisms have been identified that are not causally related to the gene product primarily affected in the individual muscular dystrophy. In this regard, ER-stress has been identified as a relevant source of muscular damage in several muscular dystrophies. The individual muscular dystrophies that show a deregulated ER-stress response/UPR can be found in Table 1. As for the underlying cause of ER-stress in muscular dystrophies, there has been a variety of suggestions. Hypotheses discussed include accumulation of misfolded protein due to the respective mutation in structural proteins and altered protein folding capacity because of oxidative stress and ROS production, as well as changes in calcium homeostasis. However, specific experimental evidence is missing to a great extent [13,17]. > Dystrophinopathies are the most prevalent forms of muscular dystrophies. While Duchenne muscular dystrophy (DMD) is a devastating muscle disease leading to rapid progression of muscular weakness, early loss of ambulation and premature death, Becker muscular dystrophy (BMD) usually shows a milder phenotype. The causative DMD gene encodes for the dystrophin protein, a core component of the dystrophin-glycoprotein complex that connects the muscle cell to the extracellular matrix [123]. Due to its prone function in muscle cell structure, the primary pathogenetic mechanism appears to be a disintegration of muscle cell organization and reduced resistance to mechanical stress.

[17] Serum miRNAs as biomarkers for the rare types of muscular dystrophy.

Authors: A. Koutsoulidou, Demetris Koutalianos, K. Georgiou, Andrea C. Kakouri, A. Oulas et al.
Year: 2022
Venue: Neuromuscular disorders : NMD
URL: https://www.semanticscholar.org/paper/66fe911cc2daff3c136f30d6771b2ec4807cfed9
DOI: 10.1016/j.nmd.2022.03.003
PMID: 35393236
Citations: 11
Influential citations: 2
Summary: New evidence is provided that certain circulating miRNAs may be used as biomarkers for three types of rare muscular dystrophies, as well as identifying manymiRNAs that associate with muscular dystrophy patients compared to controls.
Evidence snippets:
Snippet 1 (score: 0.511) > Muscular dystrophies are a group of disorders which share similar clinical and pathological characteristics including progressive weakness, wasting and degeneration [1] . More than 50 distinct types of muscular dystrophies were identified which are caused by different mutations in various genes ascribing for the phenotype of each muscular dystrophy [2] . Several clinical phenotypes characterize each type of muscular dystrophy, including the groups of primarily affected muscles, the degree of weakness, the time of onset and the rate of progression. Currently, there is an increasing interest for the development of biomarkers for this family of disorders either for monitoring the disease progress or the response to new therapeutic interventions. In particular, emphasis has been placed on the research for identifying biomarkers for Duchene Muscular Dystrophy (DMD) which is the most common childhood onset muscular dystrophy with very severe symptoms in the affected boys [3][4][5][6] . A large number of circulating miRNAs and protein biomarkers have been identified for DMD, some of which were correlated to the disease severity and clinical assessments of the patients, suggesting that they can be used as monitoring biomarkers for the disorder [7][8][9][10][11] . Furthermore, miRNAs have been suggested as potential biomarkers for Myotonic Dystrophy type 1 (DM1), the most common muscular dystrophy in adults [12][13][14][15] . Importantly, four musclespecific miRNAs, miR-1, miR-133a, miR-133b and miR-206, were found to be correlated with muscle wasting in DM1 patients and were therefore suggested as monitoring biomarkers for the disease progression [ 12 , 13 ]. Regarding the other types of muscular dystrophies, very limited information exists for the presence of circulating biomarkers, especially for the rare types of muscular dystrophies such as Facioscapulohumeral muscular dystrophy (FSHD), Limb-Girdle Muscular dystrophy (LGMD) and Myotonic Dystrophy type 2 (DM2). > FSHD is

[18] Identification of hub genes related to Duchenne muscular dystrophy by weighted gene co-expression network analysis

Authors: Yan-li Wei, Qisheng Su, Xiao-Hua Li
Year: 2022
Venue: Medicine
URL: https://www.semanticscholar.org/paper/270eedbe2a86196967455d575878a3326f57e676
DOI: 10.1097/MD.0000000000032603
PMID: 36596079
PMCID: 9803489
Citations: 4
Summary: SerPING1, F13A1, C1S, C 1R, and HLA-DPA1 may participate in the development of DMD by regulating innate immunity and inflammation, and they are expected to be a potential biomarker and novel therapeutic targets for DMD.
Evidence snippets:
Snippet 1 (score: 0.510) > Muscular dystrophy (MD) is a genetic disorder in which genetic abnormalities lead to abnormalities in a group of proteins that maintain stability of skeletal muscle cell structure and function. Chronic and progressive muscle weakness or muscle atrophy is the main clinical manifestation of MD. Common muscular dystrophy are Duchenne muscular dystrophy (DMD), Bekerer muscular dystrophy (BMD), myotonic muscular dystrophy (MD), congenital muscular dystrophy (CMD), limb girdle type Muscular dystrophy (LGMD), facial scapulohumeral muscular dystrophy (FSMD), distal muscular dystrophy, ophthalmopharyngeal muscular dystrophy (OPMD), Emery-Dreifuss muscular dystrophy (EDMD), etc. Among them, DMD is an X-recessive genetic disease caused by mutations in the anti-atropin gene. It is the most common type of progressive muscular dystrophy and the most severe type in childhood. [1] Most of the patients with DMD were found to have disease at the age of 3 to 5 years, often accompanied by delayed motor development, progressive skeletal muscle atrophy, scoliosis, joint spasm, respiratory muscle weakness, and dilated heart disease. Most patients with DMD died of respiratory failure and heart failure around the age of 20. [2,3] At present, there are a lot of studies on DMD. Gene substitution with adenovirus and CRISPR gene editing are considered as potential therapeutic methods for DMD. [4] Some targets have been found to delay the development of DMD. p. 5] Although great progress has been made in the treatment of DMD, there is still much room for exploration. [7] We believe that exploring the molecular and mechanism involved in the occurrence and development of DMD may help to find new therapeutic targets for DMD, and may provide help for the treatment of DMD. > Weighted gene co-expression network analysis (WGCNA) is 1 way to identify gene modules and key genes related to phenotypic traits. [8]

[19] Immunohistochemical Characterization of FacioscapulohumeralMuscular Dystrophy Muscle Biopsies

Authors: J. Statland, K. Odrzywolski, Bharati Shah, D. Henderson, A. Fricke et al.
Year: 2015
Venue: Journal of Neuromuscular Diseases
URL: https://www.semanticscholar.org/paper/1783c8861ca01161de60ef8ace8851890ba7c39c
DOI: 10.3233/JND-150077
PMID: 26345300
PMCID: 4560242
Citations: 28
Influential citations: 1
Summary: Preliminary evidence for increased apoptosis rates and reduced capillary density may reflect histopathological correlates of disease activity in FSHD.
Evidence snippets:
Snippet 1 (score: 0.509) > Facioscapulohumeral Muscular Dystrophy (FSHD) is one of the most common progressive muscular dystrophies (prevalence 1:15000) [1,2]. Recent studies have suggested that both Facioscapulohumeral muscular dystrophy (FSHD) types 1 and 2 operate through a common downstream genetic mechanism of de-repression of a retrogene DUX4, not normally expressed in somatic muscle tissue [3,4]. Gene expression profiling from FSHD muscle has shown altered regulation of large number of genes associated with myogenesis, increased susceptibility to oxidative stress, angiogenensis, vascular smooth muscle or endothelial cells, muscle isoenzymes, cholesterol metabolism, and the actin cytoskeleton [5][6][7][8]. Expression of DUX4 in vitro inhibits myogenesis, increases oxidative stress in myogenic precursors, and induces apoptosis [9][10][11]. DUX4 is a transcription factor normally expressed in the luminal cells of the testis, which activates genes involved in the germline and early stem cell development [12]. One line of thinking posits induction of a mitotic program in a post-mitotic cell results in apoptosis. Another line of thinking proposes DUX4 may affect satellite cell renewal. The muscle immunohistochemical correlates to these posited pathological mechanisms are unknown. A better understanding of the muscle pathology in FSHD can be important in two ways: 1) providing insights into the patho-mechanism in FSHD, and 2) providing potential biomarkers for proof of concept or early phase clinical studies. > Here we perform a retrospective cross-sectional histopathological study in genetically confirmed FSHD muscle biopsies. We quantify the apoptotic rates, satellite cell counts, and nuclear and capillary density and compare to healthy volunteers (CON) and myotonic dystrophy type 1 (DM1) as a disease control.

[20] LGMD phenotype due to a new gene and dysferlinopathy investigated by next-generation sequencing

Authors: C. Angelini
Year: 2015
Venue: Neurology: Genetics
URL: https://www.semanticscholar.org/paper/2c55b9718099ba1a33fa6f6ea43815046be1c557
DOI: 10.1212/NXG.0000000000000039
PMID: 27066575
PMCID: 4811386
Citations: 5
Summary: 3 cases of limb-girdle muscular dystrophy phenotype with mental retardation or hyperCKemia found by next-generation sequencing (NGS) to have a variant in the POMGNT2 gene, which has so far been recognized only as causing congenital muscular Dystrophy (CMD).
Evidence snippets:
Snippet 1 (score: 0.501) > The progression of muscle weakness is usually symmetrical and variable among individuals and genetic type. The term LGMD, used to molecularly classify the disease, is, however, inappropriate for many patients when it is used to describe the clinical severity. Indeed, these disorders present a wide spectrum of muscle involvement and wasting, spanning from very severe forms, such as those with childhood onset and rapid progression, to relatively benign forms with late onset. > The clinical phenotypes due to mutation in the LGMD genes include severe childhood-onset forms, distal and proximal myopathies, pseudometabolic myopathies, eosinophilic myositis, and hyperCKemia. Furthermore, patients with a clinically typical LGMD phenotype might carry mutations in the gene encoding emerin, which usually cause Emery-Dreifuss muscular dystrophy (EDMD) phenotype. Because there is a spectrum of phenotypes under the same genetic entity and a wide genetic heterogeneity under the same phenotype, it is crucial to identify suitable selection criteria to be used when screening patients for the proteins and genes responsible for LGMD. > As LGMD is relatively rare in most populations, other more likely diagnoses need to be excluded. Among these, dystrophinopathies (Duchenne dystrophy, Becker dystrophy, and female carriers of Duchenne dystrophy) are the most relevant, and these diagnoses can be ruled out based on dystrophin protein testing and/or DNA mutation analysis in the dystrophin gene. Another diagnosis that can usually be resolved by DNA analysis is facioscapulohumeral muscular dystrophy (FSHD): about 8% of patients with a diagnosis of LGMD may actually have FSHD, and the misdiagnosis can occur in families with autosomal dominant inheritance, especially when both pelvic and shoulder girdles are involved and facial weakness is minimal. Molecular investigation to exclude FSHD is worthwhile, especially in patients with a positive family history.

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Facioscapulohumeral Muscular Dystrophy (FSHD) — Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 46 citations 2026-07-31T19:35:46.046411

Facioscapulohumeral Muscular Dystrophy (FSHD) — Comprehensive Research Report

1. Disease Information

Overview: Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant, progressive skeletal myopathy classically characterized by weakness beginning in the facial muscles, muscles stabilizing the scapula (periscapular/shoulder girdle), and foot dorsiflexors, with later, often asymmetric, involvement of the trunk, hip girdle, and lower limbs. It is the third most common inherited muscular dystrophy after Duchenne/Becker and myotonic dystrophy. Onset is typically in the first three decades of life (95% show clinical signs before age 20), severity is highly variable (even within families), progression is slow but steady, and life expectancy is generally not shortened, although up to ~20–24% of affected individuals eventually require wheelchair use (GeneReviews; 5-year natural history study, PMID:39508285).

Key identifiers: - OMIM: #158900 (FSHD1), #158901 (FSHD2, digenic) - MONDO: MONDO:0001347 (disease umbrella); FSHD1/FSHD2 subtypes are separately mapped in MONDO/OMIM - ICD-10-CM: G71.02 (Facioscapulohumeral muscular dystrophy), under G71.0 (Muscular dystrophy) - ICD-11: 8C70.3 - Disease Ontology: DOID:11727 (FSHD), DOID:0111192 - MeSH: D020391 (Muscular Dystrophy, Facioscapulohumeral) - Orphanet: ORPHA:269 (FSHD), with ORPHA:2044/369 for FSHD1/FSHD2 subtypes

Synonyms: Landouzy-Dejerine muscular dystrophy; FSHD; facioscapulohumeral dystrophy (FSHMD).

Evidence source note: Most information below derives from aggregated disease-level resources (OMIM, GeneReviews, Orphanet), large clinical cohort/registry studies (French, Italian, Dutch, US national registries), and primary molecular/cell-biology literature — individually cited by PMID where possible; a smaller subset (mouse/zebrafish models) is model-organism evidence, explicitly flagged.

Sources: GeneReviews — FSHD · OMIM #158900 · OMIM #158901 · NORD · ICD10Data G71.02

2. Etiology

Disease causal factors — genetic, chromatin-based mechanism

FSHD is fundamentally a chromatin-derepression disease, not a classic loss-of-function/structural-protein myopathy. Both molecular subtypes converge on the same final pathogenic event: inappropriate somatic expression of the DUX4 retrogene in skeletal muscle.

FSHD1 (~95% of cases): monoallelic contraction of the D4Z4 macrosatellite repeat array in the subtelomeric region of chromosome 4q35, from the normal 11–150 repeat units down to 1–10 units, occurring specifically on a "permissive" 4qA haplotype that provides a polyadenylation signal (PAS) distal to the last repeat unit, stabilizing the DUX4 transcript.
FSHD2 (<5% of cases): normal-sized (non-contracted) D4Z4 array but digenic inheritance of (1) a permissive 4qA haplotype in trans, plus (2) a loss-of-function variant in a chromatin-modifier gene — most commonly SMCHD1 (chromosome 18), and less commonly DNMT3B or LRIF1 — that causes genome-wide/D4Z4-specific hypomethylation.

"Digenic inheritance of an SMCHD1 mutation and an FSHD-permissive D4Z4 allele causes facioscapulohumeral muscular dystrophy type 2" (Lemmers et al. 2012, PMID:23143600)

SMCHD1 as a disease-severity modifier in FSHD1: independent of causing FSHD2, hypomorphic SMCHD1 variants can act as a second hit in FSHD1 families, worsening severity when co-inherited with a D4Z4 contraction (Sacconi et al. 2013, PMID:24075187).

Risk factors

Genetic:
D4Z4 repeat number is inversely correlated with severity/earlier onset — the shortest arrays (1–3 units) produce infantile/severe disease.
Reduced-penetrance ("grey zone") alleles of 8–11 repeat units on a permissive haplotype confer variable, epigenetically-modulated penetrance.
SMCHD1 loss-of-function variants (modifier in FSHD1; causal in FSHD2).
The non-permissive 4qB haplotype and homologous chromosome 10q35 D4Z4 repeats are not pathogenic even when contracted, because they lack the stabilizing PAS.
Environmental/demographic: Sex — males are more frequently and more severely affected than females at any given repeat size (a documented sex-modifier effect, mechanism not fully resolved); no clear toxin/occupational/infectious risk factors identified. Age of onset is a marker of severity (earlier onset → more severe course; PMID:30819914 / Neurology 2019 review referenced above).
Ancestry: Population studies note genetic and haplotype diversity affecting FSHD across ancestries; diagnostic algorithms developed largely in European cohorts under-recognize some non-European allele configurations (J Hum Genet 2025).

Protective factors

Longer residual D4Z4 arrays (11+ units) on a permissive haplotype are largely non-penetrant.
Non-permissive 4qB haplotype is protective regardless of repeat number.
Intact SMCHD1/DNMT3B/LRIF1 function maintaining D4Z4 heterochromatinization is protective against DUX4 de-repression.
No established pharmacologic/dietary protective factor is validated in humans to date.

Gene–environment interactions

The core "interaction" in FSHD is genetic epistasis rather than classic gene-environment interaction: D4Z4 copy number, haplotype (cis) and SMCHD1/DNMT3B/LRIF1 genotype (trans, modifying chromatin state) jointly determine whether the chromatin permits DUX4 transcription. Muscle-intrinsic stressors (oxidative stress, myogenic differentiation state) modulate DUX4 expression level within a genetically permissive substrate, but there is no established exogenous environmental trigger. Suggested GENO/relationship modeling: SMCHD1 as MODIFIER/SUSCEPTIBILITY in FSHD1 entries; DUX4 (D4Z4-encoded) as the primary causal locus.

Sources: Lemmers 2012, PMID:23143600 · Sacconi 2013, PMID:24075187 · OMIM 158901 · Genetic and Epigenetic Contributors to FSHD, PMC4674299

3. Phenotypes

Phenotype	Type	Onset	Frequency	Suggested HPO term
Facial weakness (orbicularis oris/oculi)	Physical sign	Childhood–young adult	Very frequent, often earliest sign	HP:0000371 (facial palsy) / HP:0025336 (facial diplegia)
Inability to whistle / pucker lips	Symptom	Often first noticed	Common	HP:0031202 or descriptive
Scapular winging	Physical sign	Early	Very frequent, hallmark	HP:0003691
Shoulder girdle weakness	Physical sign	Early	Very frequent	HP:0003547
"Popeye arm" (biceps/triceps sparing deltoid relatively)	Physical sign	Progressive	Frequent	HP:0033653 (descriptive)
Foot dorsiflexor (tibialis anterior) weakness / foot drop	Physical sign	Variable, often subclinical early	Frequent	HP:0009027
Asymmetric limb weakness	Physical sign	Progressive	Very frequent, distinguishing feature	HP:0100568
Abdominal muscle weakness (Beevor sign)	Physical sign	Later	Frequent	HP:0003707
Lumbar hyperlordosis	Physical sign	Progressive	Frequent	HP:0002938
Pelvic girdle weakness / difficulty climbing stairs	Symptom	Later-stage	Common in progressive disease	HP:0003749
Sensorineural hearing loss (high-frequency)	Lab/clinical sign	Any age, often subclinical	~64–75% (extramuscular)	HP:0000407
Retinal telangiectasia / vasculopathy (Coats-like)	Clinical/imaging sign	Any age	~49–75% (mostly asymptomatic)	HP:0025637 / HP:0000651 (Coats disease-like)
Coats disease with exudative retinal detachment (rare, severe)	Clinical complication	Usually infantile-onset cases	Rare but sight-threatening	HP:0025637
Respiratory insufficiency (restrictive)	Clinical/functional	Late-stage, more common in wheelchair-dependent patients	Occasional-frequent in advanced disease	HP:0002093
Fatigue / chronic pain	Symptom	Any stage	Very common, patient-reported	HP:0012378 / HP:0012531
Intellectual disability / epilepsy (infantile FSHD only)	Neurodevelopmental	Infantile-onset	Rare, seen with very short (1–3 unit) D4Z4 arrays	HP:0001249 / HP:0001250
Cardiac involvement (arrhythmia — debated)	Clinical sign	Variable	Rare/controversial, less prominent than in other dystrophies	HP:0011675

Progression/severity pattern: Slowly progressive, often asymmetric, "descending" pattern (face → shoulder girdle → trunk/foot dorsiflexors → hip girdle/proximal legs); quantitative muscle strength declines ~1–4%/year on average, with substantial inter-individual variability (5-year natural history, PMID:39508285; Statland 2019 Neurology, early-onset severity marker).

Quality of life impact: Chronic pain, fatigue, and mobility limitation (up to 20–24% requiring wheelchair by disease course) are major drivers of reduced quality of life; facial weakness affects speech/expression and social functioning; scapular winging and shoulder weakness substantially limit overhead activity and activities of daily living.

Sources: Pediatric Review of FSHD, PMC6435288 · Ophthalmologic Manifestations of FSHD — EyeWiki · Retinal vascular disease and hearing loss in FSHD, PMID:23573590 · Longitudinal childhood-onset FSHD, PMC11655134

4. Genetic/Molecular Information

Causal loci: - DUX4 (Double homeobox 4; HGNC:50800), encoded within each D4Z4 repeat unit on chromosome 4q35, subtelomeric. OMIM gene: DUX4, 606009. This is the pathogenic effector gene for both FSHD1 and FSHD2. - D4Z4 repeat array itself (a 3.3-kb macrosatellite, not a conventional gene) — copy number is the causal structural variant in FSHD1. - SMCHD1 (Structural Maintenance of Chromosomes flexible Hinge Domain containing 1; HGNC:29092), chromosome 18p11.32. OMIM 614982. Primary FSHD2 gene; modifier in FSHD1. - DNMT3B (DNA methyltransferase 3 beta; HGNC:2979), chromosome 20q11.21. OMIM 602900. Rare FSHD2 gene. - LRIF1* (Ligand Dependent Nuclear Receptor Interacting Factor 1; HGNC:21470), chromosome 1p13.2. Very rare FSHD2 gene, converges with SMCHD1 at the D4Z4 locus and its own promoter (PMC10307901).

Pathogenic variant classes: - FSHD1: not a point-mutation disease — the pathogenic lesion is a repeat contraction (structural variant), classified/sized by pulsed-field gel electrophoresis (EcoRI fragment size), Southern blot, or optical genome mapping. Contracted alleles of 1–10 units are pathogenic; 8–11 units on a permissive haplotype represent reduced-penetrance "grey zone" alleles. - FSHD2 (SMCHD1/DNMT3B/LRIF1): predominantly loss-of-function variants — nonsense, frameshift, splice-site, and some missense variants disrupting ATPase or hinge domains of SMCHD1 — classified pathogenic/likely pathogenic per ACMG/AMP criteria in ClinVar. - Allele frequency: Because pathogenic D4Z4 contractions are structural/repeat-based, they are not well-represented in standard SNV population databases (gnomAD/1000 Genomes); permissive 4qA vs. non-permissive 4qB/10q-derived haplotype frequencies have been characterized by haplotype-specific genotyping across populations. - Somatic vs. germline: FSHD1 contractions and FSHD2 variants are typically germline (heritable), but somatic mosaicism is common: found in ~40% of de novo FSHD1 families (patient or unaffected parent), often via an intrachromosomal gene-conversion-like mechanism, sometimes involving mitotic interchromosomal exchange between 4q35 and its homologous 10q26 locus (Lemmers 2004, PMID:15174019; van der Maarel 2000, PMID:10631134). Germline mosaicism is also documented and important for recurrence-risk counseling in apparently de novo cases. - Functional consequence: Loss of D4Z4-array heterochromatin repression (FSHD1: reduced unit number reduces chromatin-packing capacity; FSHD2: SMCHD1/DNMT3B/LRIF1 LOF removes the trans-acting silencing machinery) → chromatin opening/hypomethylation → DUX4 gain-of-function (ectopic transcription factor expression) is the shared functional endpoint. This is best framed as a gain-of-function toxic-protein mechanism secondary to an epigenetic derepression event.

Modifier genes: SMCHD1 (in FSHD1), and D4Z4 repeat number itself modifies FSHD2 penetrance/severity (larger residual arrays in FSHD2 patients still require SMCHD1 hypomorphism to permit DUX4 expression).

Epigenetic information: The central epigenetic lesion is loss of D4Z4 CpG methylation and repressive heterochromatin marks (reduced H3K9me3, loss of SMCHD1-dependent chromatin compaction) at the contracted (FSHD1) or SMCHD1-destabilized (FSHD2) D4Z4 array, permitting transcription factor access and stabilized DUX4 mRNA via the distal permissive PAS. DNA-methylation analysis of D4Z4 (bisulfite sequencing) is diagnostically useful, particularly for confirming FSHD2 when repeat size is normal.

Chromosomal context: No aneuploidy/large structural chromosomal abnormality is causal; the key structural feature is the tandem-repeat copy-number variant at 4q35, and the near-identical but non-pathogenic homologous repeat array at 10q26 (a recognized source of diagnostic confusion requiring haplotype-specific testing).

Suggested ontology bindings: gene hgnc:50800 (DUX4), hgnc:29092 (SMCHD1), hgnc:2979 (DNMT3B), hgnc:21470 (LRIF1); GO biological process GO:0006325 (chromatin organization), GO:0006306 (DNA methylation).

Sources: Genetic and Epigenetic Contributors to FSHD, PMC4674299 · SMCHD1/LRIF1 convergence, PMC10307901 · Somatic mosaicism, PMID:15174019 · OMIM 158901

5. Environmental Information

FSHD has no established environmental, toxic, occupational, or infectious causal or triggering factor — it is a monogenic/digenic disease driven entirely by the D4Z4/DUX4 chromatin mechanism above. No lifestyle factor (smoking, diet, alcohol) has been shown to alter disease risk or onset, though general muscle-health lifestyle measures (avoiding disuse, moderate aerobic/resistance exercise under supervision) are recommended as supportive management, not causal-risk mitigation (see Treatment/Prevention). No infectious agent is implicated. This section is largely not applicable for FSHD beyond noting the absence of such factors — a point worth explicitly recording rather than omitting.

6. Mechanism / Pathophysiology

Causal chain (trigger → clinical manifestation):

Trigger: D4Z4 repeat contraction (FSHD1) or SMCHD1/DNMT3B/LRIF1 loss-of-function on a background of a normal-length D4Z4 array (FSHD2), both occurring in cis/trans with a permissive 4qA haplotype.
Chromatin derepression: Loss of D4Z4 heterochromatin (reduced CpG methylation, reduced repressive histone marks, SMCHD1-dependent chromatin compaction failure) → open chromatin state at the distal D4Z4 unit.
Stabilized DUX4 transcription: The permissive 4qA polyadenylation signal stabilizes the DUX4-fl (full-length) transcript, which would otherwise be degraded. Only DUX4-fl (retaining its C-terminal transactivation domain) is transcriptionally active.
DUX4 target-gene activation: DUX4 is a double-homeodomain transcription factor that binds and activates a "germline/cleavage-stage embryo" gene program normally restricted to early embryogenesis/zygotic genome activation (e.g., ZSCAN4, PRAMEF1, RFPL2, TRIM43, MBD3L2, KHDC1), plus retroelements (endogenous retroviruses/LINE elements) and innate-immune mediators (Geng 2012, PMID cited in Developmental Cell paper).
Cellular toxicity: Because the germline is immune-privileged, aberrant somatic expression of germline-restricted proteins triggers innate immune/dsRNA sensing pathways and MYC-mRNA-stabilization-driven apoptosis (PMID: PLOS Genetics, PMC5362247); DUX4 also increases reactive oxygen species (ROS) and confers susceptibility to oxidative-stress-induced cell death, rescuable by DUX4 knockdown or antioxidants.
Muscle-specific consequences: DUX4 globally represses PAX7 target genes, impairing satellite-cell/myogenic regenerative programs (Banerji 2017, PMC5735185); combined with atrophy/protein-degradation gene induction and impaired regeneration, this drives progressive myofiber loss, replacement by fat/fibrosis, and clinical weakness following the characteristic descending facioscapulohumeral distribution.
Downstream tissue effects: Chronic muscle degeneration → weakness, scapular winging, contractures; extramuscular DUX4-related or vascular effects → retinal telangiectasia/Coats-like vasculopathy and sensorineural hearing loss (mechanism less well resolved than muscle pathway, possibly reflecting low-level DUX4 expression or vascular developmental sensitivity in cochlea/retina).

Cell types/processes involved: - Skeletal myonuclei (mosaic/sporadic DUX4 expression — only a small fraction of nuclei per myofiber express DUX4 at any time, a hallmark "bursting" expression pattern (CL:0000188 skeletal muscle fiber, CL:0000059/myonuclei more specifically muscle satellite/myogenic lineage: CL:0000515 or CL:0008019 skeletal muscle satellite stem cell for PAX7-related regenerative deficit). - Innate immune signaling (dsRNA sensors, e.g., PKR/interferon pathway) — GO:0060337 (type I interferon signaling), GO:0006915 (apoptotic process). - Retinal vascular endothelium (Coats-like vasculopathy) and cochlear hair cells/stria vascularis (sensorineural hearing loss) — mechanistically less characterized but plausibly linked to low DUX4 expression in these tissues during development.

Protein dysfunction: DUX4 itself functions as a gain-of-function transcriptional activator (not a misfolding/loss-of-function protein); SMCHD1 loss is a loss-of-function chromatin-structural defect (SMCHD1 normally compacts D4Z4 chromatin via its ATPase/hinge domains).

Molecular profiling: Muscle transcriptomic studies (RNA-seq) in FSHD biopsies and myoblast/myotube models show the DUX4-target signature (germline genes, immune genes) as a validated disease biomarker used in clinical trials (e.g., losmapimod trials measured DUX4-driven gene expression as a pharmacodynamic biomarker, though technical variability limited its use as a primary trial endpoint).

Advanced technologies: Single-nucleus/single-cell approaches have shown DUX4 expression occurs in rare, transient "bursts" in a small subset of myonuclei — a key reason bulk transcriptomic DUX4 biomarkers are noisy and difficult to use clinically. CRISPR-based functional screens and engineered SMCHD1/D4Z4 mutant cell/mouse models have been used to dissect the synergy between heterochromatin disruption and DUX4 network feedforward activation (bioRxiv/PMC10951985).

Sources: DUX4 activates germline genes, retroelements, immune mediators — Developmental Cell · DUX4-induced dsRNA/MYC apoptosis, PMC5362247 · PAX7 target gene repression, PMC5735185 · Engineered SMCHD1/D4Z4 mutations, PMC10951985 · DUX4 signalling review, MDPI

7. Anatomical Structures Affected

Organ level: - Primary: skeletal muscle (face, shoulder girdle/scapular stabilizers, upper arm, foot dorsiflexors, later abdominal/trunk and pelvic-girdle muscles). - Secondary: eye (retina — vasculopathy/Coats disease), ear (cochlea — sensorineural hearing loss), lung (restrictive respiratory insufficiency in advanced/wheelchair-dependent disease), rarely CNS (intellectual disability/epilepsy in infantile-onset cases only). - Body systems: musculoskeletal (primary), sensory (auditory, visual), respiratory (secondary/late), rarely neurodevelopmental.

Tissue/cell level: - Skeletal muscle fibers (type-specific vulnerability not sharply established), muscle satellite cells/myogenic progenitors (CL:0008019), retinal vascular endothelium, cochlear sensory/vascular structures.

Subcellular level: - Nucleus (chromatin/heterochromatin at the D4Z4 locus; GO:0000228 nuclear chromosome), site of DUX4 transcriptional activity; mitochondria (oxidative stress/ROS generation — GO:0005739).

Localization (UBERON suggestions): - UBERON:0001630 (muscle organ) — specifically facial muscles (UBERON:0001336 orbicularis oculi / UBERON:0011639 orbicularis oris region), UBERON:0006611 (scapular musculature) or specific muscles (trapezius, serratus anterior, rhomboids), UBERON:0001383 (tibialis anterior/dorsiflexor compartment). - UBERON:0000966 (retina) for Coats-like vasculopathy. - UBERON:0001846 (cochlea) for sensorineural hearing loss.

Lateralization: A hallmark distinguishing clinical feature is asymmetric weakness — unlike most other muscular dystrophies, FSHD often shows notably asymmetric involvement between left and right sides, even within the same muscle group.

Sources: EyeWiki — Ophthalmologic Manifestations of FSHD · Medscape FSHD Clinical Presentation

8. Temporal Development

Onset: - Typical: first–third decade of life; 95% show clinical signs before age 20 (childhood/adolescent-to-young-adult onset is most common presentation, though subclinical facial weakness may predate recognized symptoms). - Infantile-onset FSHD: a distinct, more severe subset presenting as early as infancy (case reports of symptom onset by 5 months of age), strongly associated with very short D4Z4 arrays (1–3 units, EcoRI fragment 10–14 kb) (Timely Review, PMC7589635). - Onset pattern: insidious/gradual in classic FSHD; more rapid and multisystemic in infantile-onset disease.

Progression: - Disease course: chronic, slowly progressive; classic "descending" spatial pattern — face → shoulder girdle/scapular stabilizers → upper arm → trunk/foot dorsiflexors → hip girdle/proximal lower limb. - Progression rate: quantitative muscle strength declines at an average ~1–4%/year, but highly variable between individuals and even between muscle groups in the same patient; 6-year cumulative risk of wheelchair dependence estimated at ~24% in one longitudinal cohort (5-year natural history study, PMID:39508285). - Disease duration: chronic, lifelong; not typically self-limited or remitting. - Infantile FSHD: rapid decline, marked muscle wasting, more prominent extramuscular (hearing, retinal, occasionally CNS) involvement.

Patterns: - No spontaneous or treatment-induced remission is described — FSHD is a monotonic, progressive (though slow and plateau-punctuated) disease. - Critical/vulnerable periods: earlier age of onset is itself a validated marker of eventual disease severity, making early recognition clinically important for prognostication and counseling (rather than for a treatable "window").

Sources: Longitudinal childhood-onset FSHD 5-year study, PMC11655134 · Early onset as marker for severity, Neurology 2019 · Early-Onset Infantile FSHD Review, PMC7589635

9. Inheritance and Population

Epidemiology: - Prevalence estimates vary by methodology: ~3.2–4.6 per 100,000 in several population studies; US estimate ~1 in 20,000; broader worldwide estimates of 4–10 per 100,000. - Incidence: conservative estimate ~1 in 14,286 births; with improved genetic testing and ascertainment, some estimate a true incidence closer to 1 in 7,500 births. - Recognized as the third most common muscular dystrophy overall.

Inheritance pattern: - FSHD1: autosomal dominant (single contracted D4Z4 allele on a permissive haplotype is sufficient). - FSHD2: digenic — autosomal dominant SMCHD1 (or DNMT3B/LRIF1) variant combined with a permissive 4qA haplotype in trans (inherited independently; both are required for disease expression) — a well-characterized digenic inheritance exemplar (OMIM #158901). - Penetrance: Generally high but genotype-dependent; incomplete/age- and epigenetically-dependent penetrance in the 8–11 unit "grey zone" alleles. Overall clinical penetrance by age 30 is estimated around 95% for classic contracted alleles, but is lower and more variable for borderline-sized alleles. - Expressivity: Markedly variable expressivity, even within the same family carrying an identical D4Z4 contraction — a defining feature of FSHD, attributed to superimposed epigenetic/stochastic DUX4-expression variability and modifier loci (e.g., SMCHD1 second hits). - Genetic anticipation: Not a classic anticipation disease (unlike CTG-repeat disorders), though intergenerational contraction-size instability of D4Z4 can occur. - Germline and somatic mosaicism: Both are well documented; somatic mosaicism found in ~40% of de novo FSHD1 families; mosaic males are typically clinically affected while mosaic females are more often unaffected carriers/parents of a nonmosaic de novo child (a notable sex-dependent asymmetry) (van der Maarel 2000, PMID:10631134). - Founder effects: Not a major feature; permissive-haplotype (4qA) frequency and specific haplotype subtypes vary by ancestry, contributing to some population-level diagnostic complexity (J Hum Genet 2025). - Consanguinity: Not a notable risk factor given the dominant/digenic (not recessive) inheritance. - Carrier frequency: Population frequency of the permissive 4qA haplotype itself is common in the general population (a large fraction of people carry a permissive haplotype without ever having a pathogenic contraction), underscoring that haplotype alone is necessary but not sufficient.

Population demographics: - No strong racial/ethnic predilection reported, though data ascertainment has historically skewed European; diversity studies are ongoing. - Sex ratio: males more frequently and more severely affected than females at a given genotype (asymptomatic carriage more common in females) — a recognized but mechanistically unresolved sex-modifier effect. - Age distribution: broad, spanning infantile to adult-onset; most clinically recognized cases present in childhood through young adulthood.

Sources: Wellstone Program — FSHD Facts and Statistics · Medscape — FSHD Epidemiology · Diversity challenges genetics in FSHD, J Hum Genet 2025 · OMIM #158901

10. Diagnostics

Clinical tests / exam: - Clinical diagnosis rests on the characteristic pattern of facial, scapular-stabilizer, and foot-dorsiflexor weakness with typical asymmetry. - Creatine kinase (CK): typically normal to mildly elevated (2–5× ULN), distinguishing FSHD from dystrophinopathies where CK is markedly elevated. - EMG: myopathic pattern (nonspecific). - Muscle MRI: identifies pattern and degree of fatty infiltration/edema in affected muscles, increasingly used for phenotyping and clinical-trial outcome assessment (quantitative MRI fat-fraction as a biomarker). - Muscle biopsy: nonspecific dystrophic changes; historically used before molecular testing became standard, now largely reserved for atypical presentations.

Genetic testing (primary diagnostic modality): - FSHD1: Molecular confirmation via Southern blot with EcoRI/EcoRI-BlnI digestion (measuring D4Z4 repeat/EcoRI fragment size) or newer techniques — optical genome mapping has been validated as an accurate, higher-throughput alternative for sizing D4Z4 alleles and determining 4qA/4qB haplotype (PMC10664978; PMC10743191). - Haplotype analysis: visual genotyping / multiplex dipstick assays distinguish the permissive 4qA vs. non-permissive 4qB/10q-derived haplotypes — essential because a short array on a non-permissive haplotype is not pathogenic. - FSHD2: diagnosed when a patient has classic clinical features, a normal-sized D4Z4 array on a permissive 4qA haplotype, and D4Z4 hypomethylation on bisulfite/methylation analysis — followed by sequencing of SMCHD1 (first-line), then DNMT3B/LRIF1 if SMCHD1-negative. - Long-read genome sequencing and rare-variant linkage analysis have also been used for complex/ambiguous cases (medRxiv 2023.06.05.23290975). - Chromosomal microarray, karyotyping, FISH, and mitochondrial DNA testing are not primary diagnostic tools for FSHD (the causal lesion is a repeat-array size/methylation change, not aneuploidy or a point variant detectable by standard panels).

Clinical diagnostic criteria: No formal DSM/consensus scoring system analogous to other diseases; diagnosis is established per GeneReviews criteria combining clinical phenotype + molecular confirmation (repeat size + haplotype for FSHD1; methylation + SMCHD1/DNMT3B/LRIF1 sequencing for FSHD2). An AAN practice guideline exists for evaluation, diagnosis, and management (AAN Guideline).

Differential diagnosis: Limb-girdle muscular dystrophies, myotonic dystrophy, congenital myopathies, mitochondrial myopathies, polymyositis/inflammatory myopathy (facial-sparing usually distinguishes these), and other scapuloperoneal syndromes.

Screening: No population-based newborn screening program exists for FSHD (unlike some other genetic muscular dystrophies); genetic counseling and cascade testing of at-risk relatives is standard once a proband is confirmed, given autosomal dominant/digenic inheritance and variable/incomplete penetrance in grey-zone alleles.

Sources: Optical genome mapping validation, PMC10664978 · Molecular diagnosis review — ScienceDirect · GeneReviews FSHD · AAN FSHD Guideline

11. Outcome/Prognosis

Survival/mortality: Life expectancy is generally not shortened in classic FSHD; it is considered a disease of morbidity rather than mortality, distinguishing it from many other muscular dystrophies (e.g., Duchenne). Infantile-onset/very-severe cases with major respiratory or CNS complications may carry somewhat worse prognoses, but disease-specific mortality data are limited.

Morbidity/function: - Up to ~20–24% of patients become wheelchair-dependent over the disease course (6-year cumulative risk ~24% in one cohort). - Progressive weakness affects mobility, upper-limb function (especially overhead reaching due to scapular winging), facial expression/speech, and — in a minority — respiratory function in advanced disease. - Chronic pain and fatigue are prominent, underrecognized contributors to reduced quality of life, frequently reported in patient registry studies.

Disease course/complications: Retinal Coats-disease-related vision loss (rare but serious, more common in early-onset/severe genotypes), sensorineural hearing loss, contractures, and (in advanced disease) restrictive respiratory insufficiency requiring monitoring/ventilatory support.

Prognostic factors: D4Z4 repeat array size is the strongest genotype-phenotype correlate — shorter arrays (fewer repeat units) predict earlier onset and more severe, faster-progressing, more extramuscularly-involved disease; age of onset itself is an independent severity marker (earlier onset correlates with worse ultimate outcome). SMCHD1 modifier status in FSHD1 patients further worsens prognosis.

Prognostic biomarkers: DUX4-driven target-gene expression signatures and muscle MRI fat-fraction/STIR-hyperintensity have been explored as biomarkers of disease activity and progression risk, used in recent clinical trials (though with technical reproducibility challenges).

Sources: 5-year natural history cohort, PMID:39508285 · Italian National Registry 5-year follow-up, PMC7815626 · Early onset as severity marker, Neurology 2019

12. Treatment

Current standard of care is supportive — there is no FDA-approved disease-modifying therapy for FSHD as of mid-2026.

Pharmacotherapy: - No approved DUX4-targeted or disease-modifying drug. Symptomatic management includes analgesics for chronic pain and standard supportive medications; no established pharmacogenomic guidance specific to FSHD. - Losmapimod (p38α/β MAPK inhibitor; indirectly reduces DUX4 program activation without impairing myogenesis) — showed encouraging Phase 2b (ReDUX4) results (slowed structural/functional disease progression at 48 weeks), but the confirmatory Phase 3 REACH trial (NCT04003974) reported topline results on Sept 12, 2024 that did not meet its primary endpoint (Reachable Workspace change) or achieve nominally significant secondary endpoints; Fulcrum Therapeutics subsequently suspended the losmapimod FSHD program (Fulcrum press release, Sept 2024; NeurologyLive coverage).

Advanced/RNA-based therapeutics in development (not yet approved): - Direct DUX4 mRNA knockdown — antisense oligonucleotides (ASOs)/gapmers: preclinical work (2′MOE and LNA-chemistry gapmers) shows effective DUX4 knockdown and improved muscle function (grip strength) in mouse models via subcutaneous dosing (PMC12795667; systemic ASO delivery, PMC8526479). Companies pursuing direct DUX4-targeting approaches include Dyne Therapeutics, Avidity Biosciences, Arrowhead Pharmaceuticals, and miRecule. - AOC 1020 (Avidity Biosciences) — an antibody-oligonucleotide conjugate targeting DUX4, evaluated in the Phase 1/2 FORTITUDE trial (NCT05747924), with a Phase 3 trial in the pipeline as of 2025–2026 as a step toward potential FDA approval. - Follistatin/myostatin-pathway (muscle-growth-promoting) approach — ACE-083 (Acceleron): a locally-injected follistatin-based agent that increased target muscle volume in a Phase 2 trial but did not translate to improved function, leading to discontinuation of that program for FSHD (Statland et al. 2022, Muscle & Nerve, PMID via search). - Gene therapy/CRISPR-based epigenetic silencing approaches (targeting DUX4 locus re-repression, e.g., via engineered zinc-finger or CRISPR-dCas9 epigenetic editors) and further AAV-delivered shRNA approaches are in earlier preclinical stages; a 2025 mouse study found AAV-shDUX4 provided only short-term benefit with waning long-term efficacy due to muscle regeneration diluting AAV genomes (Molecular Therapy Methods & Clinical Development 2025).

Surgical/interventional: - Scapular fixation/fusion surgery — stabilizes the winging scapula to the rib cage (bone graft fusion or screw/wire fixation), improving functional leverage for arm use in appropriately selected patients, performed by surgeons experienced with FSHD; decreases scapular rotation range but often nets functional benefit for overhead/reaching tasks (NCIT:C15329 Surgical Procedure / more specific orthopedic procedure term).

Supportive/rehabilitative: - Physical and occupational therapy focused on maintaining function and preventing contractures/disuse atrophy (rather than restorative rehab); orthoses (e.g., ankle-foot orthoses for foot drop); moderate, individualized aerobic/strength exercise programs under specialist supervision (research ongoing on optimal, safe exercise protocols); respiratory therapy/monitoring for advanced disease; low-vision/audiology support for extramuscular retinal/hearing complications; ophthalmologic screening and, when needed, laser photocoagulation or anti-VEGF therapy (e.g., ranibizumab) for Coats-disease-related retinal vasculopathy.

Experimental/clinical trials: Numerous active trials registered at ClinicalTrials.gov beyond those above, including natural history/outcome-measure studies (e.g., NCT04369209 registered cohort) and shoulder-instability mechanism studies (NCT05239520).

Treatment strategy: Multidisciplinary care (neurology, physiatry/PT-OT, orthopedic surgery, ophthalmology, audiology, pulmonology, genetic counseling) is the current mainstay; no genotype-guided personalized pharmacotherapy yet exists, though D4Z4 size/SMCHD1 status informs prognosis and eligibility for genotype-restricted (e.g., FSHD1-only) trials such as REACH.

Suggested NCIT terms: NCIT:C15986 (Pharmacotherapy, for losmapimod/investigational agents) with therapeutic_modality: SMALL_MOLECULE; NCIT:C15238 (Gene Therapy) / ANTISENSE_OLIGONUCLEOTIDE modality for DUX4-targeted ASOs/AOC 1020; NCIT:C15329 or C16186 (Orthopedic Surgical Procedure) for scapular fixation; NCIT:C15302 (Physical Therapy).

Sources: Fulcrum REACH topline results · ACE-083 Phase 2, Statland 2022 · AOC 1020 FORTITUDE trial, NCT05747924 · Current landscape management review, PMC12287641 · ASO gapmer DUX4 knockdown, PMC12795667

13. Prevention

Primary prevention: Not applicable in the traditional sense (no modifiable environmental cause to eliminate); the closest analog is reproductive/genetic prevention via genetic counseling and prenatal or preimplantation genetic diagnosis (PGD) for known-carrier families, given autosomal dominant/digenic inheritance.

Secondary prevention (early detection): Cascade genetic testing of at-risk relatives once a proband is molecularly confirmed; given variable/incomplete penetrance especially for grey-zone (8–11 unit) alleles, early molecular diagnosis allows anticipatory monitoring (audiology, ophthalmology, pulmonary function) before symptom onset, particularly relevant for early-onset/short-repeat genotypes at higher risk of extramuscular complications.

Tertiary prevention: Ophthalmologic screening and monitoring to catch and treat retinal vasculopathy before progression to Coats-disease-related vision loss; audiologic monitoring for hearing loss; proactive physical therapy/orthotic management and periodic pulmonary function assessment to reduce complications of progressive weakness (contractures, falls, respiratory insufficiency) in more advanced disease.

Immunization: Not disease-specific (standard care includes ensuring routine immunizations, including respiratory pathogens, are up to date in patients with any respiratory muscle compromise, but this is generic supportive care, not FSHD-specific prophylaxis).

Genetic counseling: Central to FSHD family management — addressing the autosomal dominant (FSHD1) or digenic (FSHD2) inheritance pattern, variable expressivity, incomplete penetrance of grey-zone alleles, and both somatic and germline mosaicism (which affects recurrence-risk estimates for apparently de novo cases — a parent with somatic/germline mosaicism can have a higher-than-expected recurrence risk for future children despite testing negative on peripheral blood).

Public health/behavioral: No population-level public-health intervention exists (rare monogenic disease); individualized behavioral guidance centers on maintaining physical activity/muscle conditioning within safe limits and fall-prevention strategies as weakness progresses.

Sources: GeneReviews FSHD — Genetic Counseling section · Germinal mosaicism in FSHD, Upadhyaya 1995

14. Other Species / Natural Disease

FSHD is a human-specific molecular disease in a strict sense: the pathogenic DUX4 retrogene and its D4Z4 macrosatellite array, along with the specific 4qA permissive haplotype/polyadenylation signal architecture, are primate/human-specific genomic features. There is no well-characterized naturally occurring FSHD-equivalent disease in veterinary species (dogs, cats, livestock) analogous to, for example, canine dystrophin-deficient muscular dystrophy models for DMD. DUX-family genes exist across mammals (e.g., mouse Dux, expressed during zygotic genome activation), providing evolutionary/developmental-biology context for DUX4's normal role, but these orthologs are not linked to a spontaneous disease phenotype in the source species. This section is therefore largely not applicable, beyond noting the evolutionary conservation of the DUX-family developmental gene-activation role (relevant to model organism engineering, below) rather than any natural veterinary disease counterpart.

Suggested taxonomy note: NCBITaxon:9606 (Homo sapiens) is the sole natural host species for the clinical disease.

15. Model Organisms

Because FSHD's pathogenic mechanism (DUX4 gain-of-function via loss of D4Z4 repeat-mediated silencing) has no natural non-human counterpart, all animal models are engineered/induced, generally via transgenic or conditional expression of human DUX4:

Mouse models (multiple engineered lines):
FLExDUX4 — a widely used Cre-inducible, floxed DUX4-full-length conditional transgenic mouse, allowing tunable, tissue- and time-restricted DUX4 expression to titrate pathology severity and avoid the developmental lethality of constitutive DUX4 expression (PMC5802938).
iDUX4pA and related "TIC-DUX4" inducible models — considered to come closest to recapitulating both clinical (muscle weakness, histopathology) and molecular (DUX4 target-gene activation) features of human FSHD; used as the basis for testing follistatin gene therapy (AAV-follistatin improved functional outcomes in TIC-DUX4 mice — JCI Insight) and AAV-shDUX4 knockdown approaches (Molecular Therapy Methods & Clinical Development 2025).
Newer transgenic mouse models specifically for investigating human DUX4 expression continue to be developed (2025 bioRxiv report).
Genetic models available include conditional/inducible transgenics (Cre-lox systems); classic knockout models are not applicable since FSHD is a gain-of-function disease, not a loss-of-function one for DUX4 itself (though SMCHD1 knockout/knock-in mouse models are used to study the FSHD2 chromatin-modifier mechanism).
Zebrafish model: A transgenic zebrafish DUX4-misexpression model demonstrated that an induced early-developmental burst of DUX4 produces FSHD-like phenotypes emerging later in adulthood, even after DUX4 is no longer detectable — supporting a developmental-origin hypothesis for at least part of FSHD pathogenesis, distinct from purely adult muscle-toxicity mechanisms (Hum Mol Genet 2018, PMID:30307508).
Cellular/in vitro models: Patient-derived myoblast/myotube cultures (including immortalized FSHD1/FSHD2 patient lines) are the mainstay for mechanistic and drug-screening studies (e.g., losmapimod's selective inhibition of the DUX4 program without impairing myogenesis was demonstrated in FSHD myotube cultures). iPSC-derived myogenic models are increasingly used for genotype-specific (grey-zone allele, SMCHD1-variant) disease modeling.

Model characteristics/limitations: Because DUX4 expression is mosaic, transient/"bursting," and cytotoxic even at low levels, constitutive whole-body DUX4 mouse models are frequently embryonic lethal or severely runted — necessitating the conditional/inducible systems above to titrate expression to sub-lethal, disease-relevant levels. No current animal model fully recapitulates the human D4Z4 repeat-contraction genetics (mice lack a directly homologous D4Z4/DUX4 locus with the human-specific permissive-haplotype architecture), so all models rely on transgenic human DUX4 insertion rather than an endogenous orthologous mutation — an important translational caveat (a candidate HUMAN_MODEL_MISMATCH consideration for any dismech entry: whether mouse/zebrafish DUX4-overexpression phenotypes faithfully model the graded, chronic, mosaic-expression human disease process).

Applications: These models are used to study DUX4-driven transcriptional/apoptotic pathways, test DUX4-suppression therapeutics (ASOs, small molecules, gene therapy), and assess the developmental-origin hypothesis of FSHD pathogenesis.

Sources: FLExDUX4 mouse model, PMC5802938 · AAV-follistatin in TIC-DUX4 mice, JCI Insight · AAV-shDUX4 mouse model 2025 · Transgenic zebrafish DUX4 model, PMID:30307508 · Transgenic mouse models 2025, bioRxiv

Summary of Key Evidence Gaps / Notes for Curation

Not applicable / no data: environmental/infectious causal factors, veterinary/natural-disease counterparts, cardiac involvement is debated/minor (unlike other dystrophies), no approved disease-modifying pharmacotherapy or gene therapy as of this writing (mid-2026).
High-confidence, well-cited mechanistic core: D4Z4 contraction/SMCHD1-DNMT3B-LRIF1 chromatin derepression → stabilized DUX4-fl transcription → germline/immune gene program activation → apoptosis/oxidative stress + PAX7-regenerative-program repression → progressive myofiber loss — suitable as the spine of a pathophysiology causal chain, with conforms_to candidacy against no existing dismech module (a novel DUX4-chromatin-derepression mechanism, potentially a future module given its shared logic with other repeat/epigenetic-derepression diseases).
Active clinical trial landscape (rapidly moving target): losmapimod program discontinued (Sept 2024, Phase 3 miss); ASO/AOC-based DUX4-knockdown programs (AOC 1020/Avidity FORTITUDE, plus Dyne/Arrowhead/miRecule preclinical-to-early-clinical programs) are the most active current therapeutic frontier — recommend periodic re-verification of trial status (NCT05747924 and successors) given the pace of change.
Digenic inheritance model: FSHD2 is a strong, well-documented exemplar for the dismech digenic/oligogenic inheritance pattern (HP:0010984), directly relevant to the Digenic_and_Oligogenic_Disorders grouping referenced in project conventions.

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Facioscapulohumeral Muscular Dystrophy (FSHD): A Comprehensive Disease Characteristics Report

openscientist-autonomous 32 citations 2026-08-01T15:48:19.642413

Facioscapulohumeral Muscular Dystrophy (FSHD): A Comprehensive Disease Characteristics Report

Disease category: Genetic (autosomal-dominant / digenic myopathy) Suggested ontology mapping: MONDO:0008028 (facioscapulohumeral muscular dystrophy); OMIM 158900 (FSHD1), 158901 (FSHD2); Orphanet ORPHA:269; MeSH D020391 ("Muscular Dystrophy, Facioscapulohumeral"); ICD-10 G71.0; ICD-11 8C71.

Summary

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common inherited myopathies (prevalence ~1 in 8,000–20,000) and is defined clinically by slowly progressive, characteristically asymmetric weakness that begins in the muscles of the face, scapular stabilizers, and upper arms and later descends to the trunk and lower limbs. Despite decades of genetic confusion, FSHD is now understood as a single-mechanism disease: the aberrant, epigenetically de-repressed expression of the germline transcription factor DUX4 (double homeobox 4) in skeletal muscle, where it is normally silenced. DUX4 misexpression is reached by two genetic routes that converge on the same toxic endpoint: FSHD1 (~95%), caused by contraction of the D4Z4 macrosatellite repeat array to 1–10 units on a permissive 4qA haplotype at 4q35; and FSHD2 (~5%), a digenic disease requiring a pathogenic variant in a chromatin repressor (most often SMCHD1, also DNMT3B, LRIF1) together with a borderline-length array and a permissive haplotype [PMID: 38955828; 34711481; 37703328].

Once de-repressed, DUX4 acts as a potent transcription factor that reactivates an early-embryonic/germline program — including ZSCAN4, PRAMEF family, TRIM43, MBD3L, endogenous retrotransposons, and innate-immune mediators such as DEFB103 — and kills muscle cells primarily through caspase-3/7-dependent apoptosis, while also inhibiting nonsense-mediated decay (NMD) via UPF1 degradation and repressing the myogenic regulators MYOD1 and MYF5 [PMID: 22892954; 22209328; 25564732; 30446688; 37973788]. DUX4 is expressed in a rare, stochastic, burst-like fashion in a small subset of myonuclei, which explains how sporadic expression produces generalized wasting and why DUX4 itself is such a difficult pharmacodynamic biomarker [PMID: 30445587].

Clinically, FSHD has near-normal life expectancy but imposes a heavy quality-of-life burden through pain, fatigue, impaired mobility (~20% eventually require a wheelchair), sleep disturbance, and extramuscular comorbidities (high-frequency hearing loss, Coats-like retinal vasculopathy, and — in severe infantile cases — seizures and cognitive impairment) [PMID: 40879179; 38968057; 41037169]. Diagnosis is molecular, integrating D4Z4 repeat sizing, 4qA haplotyping, methylation profiling, and exome sequencing for FSHD2 [PMID: 42498520; 36348371]. No disease-modifying therapy is approved: the lead candidate losmapimod (a p38 MAPK inhibitor) failed both its phase 2b DUX4-expression endpoint and its subsequent phase 3 clinical endpoint, leaving multidisciplinary symptomatic care as the standard while a rich pipeline of DUX4-lowering RNA and small-molecule therapeutics advances [PMID: 38631764; 40580827; 28273791; 35884928].

This report synthesizes 13 confirmed findings across 59 reviewed papers and is organized to match the 15-section disease-characteristics template.

Key Findings

Finding 1 — Two genetic routes, one mechanism (DUX4 de-repression)

FSHD is caused by aberrant DUX4 expression reached by two mutually convergent genetic mechanisms. FSHD1 (~95% of cases) results from a pathogenic contraction of the D4Z4 macrosatellite repeat array to 1–10 repeat units in the subtelomeric region of chromosome 4 (4q35); normal arrays span roughly 8 to >100 units. Contraction produces chromatin relaxation and de-repression of the DUX4 retrogene that is embedded in the distal D4Z4 unit. FSHD2 (~5%) is a digenic disease: a pathogenic variant in a D4Z4 chromatin repressor — most often SMCHD1 on chromosome 18, and also DNMT3B and LRIF1 — combined with a borderline array (8–20 units) and a permissive haplotype. Both routes converge on epigenetic derepression and toxic DUX4 expression in skeletal muscle. (Evidence: human clinical / review.)

"In 95% of cases, FSHD patients carry a pathogenic contraction of the D4Z4 repeat units (RUs) in the subtelomeric region of chromosome 4 (4q35), which leads to the expression of DUX4 retrogene, toxic for muscles (FSHD1). Five percent of patients display the same clinical phenotype in association with a mutation in the SMCHD1 gene located in chromosome 18" — PMID: 38955828

"FSHD2 is a digenic disease and that mutations in the genes SMCHD1, DNMT3B, and more recently LRIF1, can cause FSHD2" — PMID: 34711481

Finding 2 — DUX4 is an embryonic transcription factor toxic to muscle via apoptosis and NMD inhibition

DUX4 is a double-homeobox retrogene normally expressed only in the testis and early embryo (where it drives zygotic genome activation) and epigenetically silenced in somatic tissue. When misexpressed in muscle it activates early-embryonic/germline genes and retroviral elements and drives cell death primarily through caspase-3/7-dependent apoptosis. DUX4 protein also proteolytically degrades UPF1, a central component of the nonsense-mediated decay (NMD) machinery; because DUX4 mRNA is itself an NMD substrate, this creates a double-negative feedback loop that stabilizes DUX4 and contributes to its burst-like expression. At low levels, DUX4 additionally represses the myogenic regulators MYOD1 and MYF5, impairing differentiation. (Evidence: in vitro / model.)

"DUX4-triggered proteolytic degradation of UPF1, a central component of the nonsense-mediated decay (NMD) machinery, is associated with profound NMD inhibition" — PMID: 25564732

"cell death does primarily occur through caspase 3/7-dependent apoptosis" — PMID: 37973788

"a large set of human myogenic genes is rapidly deregulated by DUX4, including MYOD1 and MYF5" — PMID: 30446688

Finding 3 — Extramuscular comorbidities: hearing loss, retinal vasculopathy, seizures

In the population-based MD STARnet cohort (n=548), 17.2% of patients had at least one of three key comorbidities: hearing loss 13% (n=71, most common), retinal abnormalities 3.6% (n=20), and seizures 2.0% (n=11). Median age at diagnosis differed markedly — hearing loss 46.5 y, retinal 58.7 y, and seizures 16.5 y (half of seizure cases occurred at ≤10 y). These extramuscular features (hearing loss, Coats-like retinal vasculopathy, cognitive impairment, spinal deformity) are enriched in severe early-onset/infantile FSHD, which carries the shortest D4Z4 repeats. (Evidence: human clinical, population-based.)

"Hearing Loss (13%; n = 71) was the most frequently reported comorbidity, followed by retinal abnormalities (3.6%; n = 20) and seizures (2.0%; n = 11)" — PMID: 40879179

"Children with a severe, early-onset phenotype experience higher rates of extramuscular features, including hearing loss, cognitive impairment, and spinal deformities" — PMID: 41037169

Finding 4 — Penetrance is age-dependent and incomplete; repeat size is a weak predictor

Penetrance depends on repeat size and increases into late adulthood, with roughly 17% non-penetrant and ~25% asymptomatic carriers. In a genotype–phenotype study (n=152), familial factors accounted for 50% of the variance in disease severity, whereas D4Z4 repeat array size explained only ~10% overall (~30% for facial, ~15% upper limb, ~3% leg). Unaffected carriers had significantly longer arrays than symptomatic relatives (7.3 vs 6.0 units, P<0.001). Prevalence estimates range from ~1 in 20,000 to ~1 in 8,000, making FSHD one of the most common muscular dystrophies. (Evidence: human clinical, family-based.)

"Familial factors accounted for 50% of the variance in disease severity (FSHD clinical score). The explained variance by the D4Z4 repeat array size for disease severity was limited (approximately 10%)" — PMID: 30211448

"penetrance depends on repeat size and increases until late adulthood" — PMID: 29997197

"Facioscapulohumeral muscular dystrophy (FSHD) is a myopathy with prevalence of 1 in 20,000" — PMID: 33303865

Finding 5 — No approved disease-modifying therapy; losmapimod failed phase 3

Losmapimod, a selective p38 α/β MAPK inhibitor that reduces DUX4 expression in vitro, was well tolerated in phase 1/2 (NCT04004000). The phase 2b ReDUX4 trial (NCT04003974) did not meet its primary endpoint of reduced DUX4-driven gene expression in muscle biopsy, although some functional measures trended favorably; the subsequent phase 3 trial failed to demonstrate clear clinical benefit. Current management remains multidisciplinary and symptomatic: physical/occupational therapy, scapular fixation surgery, and management of hearing, retinal, and respiratory complications, plus pain and fatigue control. (Evidence: human clinical trials.)

"the trial failed to demonstrate a clear clinical benefit, highlighting key challenges in drug development for the disease" — PMID: 40580827

"The primary endpoint was change from baseline to either week 16 or 36 in DUX4-driven gene expression in skeletal muscle biopsy samples" — PMID: 38631764

Finding 6 — ACTA1-MCM/FLExDUX4 mouse recapitulates progressive DUX4-driven pathology

The tamoxifen-inducible ACTA1-MCM;FLExDUX4/+ bitransgenic mouse expresses low chronic DUX4 in skeletal muscle and shows progressive muscular dystrophy with DUX4-pathway molecular signatures, histological damage, and functional weakness (reduced initial force with relatively preserved power/endurance). It is the most widely used academic FSHD model and is the workhorse for testing systemic antisense DUX4-silencing therapeutics, which improve molecular and histopathological readouts including in the diaphragm. (Evidence: model organism.)

"the most commonly used by academic laboratories being ACTA1-MCM/FLExDUX4" — PMID: 39518930

Finding 7 — The permissive 4qA haplotype supplies a polyadenylation signal that stabilizes DUX4 mRNA

Pathogenic DUX4 expression requires a permissive distal 4qA haplotype that provides a polyadenylation signal (PAS) in the pLAM region immediately telomeric to the last D4Z4 unit; this PAS stabilizes the otherwise-degraded DUX4 transcript, enabling translation of full-length DUX4. The near-identical 10q26 D4Z4 array and the non-permissive 4qB haplotype lack a functional PAS and are non-pathogenic even when contracted. FSHD1 therefore requires three conditions: (1) D4Z4 contraction, (2) a 4qA permissive haplotype, and (3) reduced D4Z4 CpG methylation. Downstream, DUX4 inhibits muscle differentiation, sensitizes cells to oxidative stress, and induces atrophy. (Evidence: review / in vitro.)

"A unifying pathogenic model for FSHD emerged with the recognition that the FSHD-permissive 4qA haplotype corresponds to a polyadenylation signal that stabilizes the DUX4 mRNA" — PMID: 27816329

"Aberrant DUX4 expression triggers a deregulation cascade inhibiting muscle differentiation, sensitizing cells to oxidative stress, and inducing muscle atrophy" — PMID: 27816329

Finding 8 — Muscle MRI reveals a specific asymmetric involvement pattern useful for diagnosis and natural history

Whole-body muscle MRI (30 FSHD vs 23 other myopathies) identified an FSHD-specific pattern of fatty replacement and atrophy, most frequently in the trapezius, teres major, and serratus anterior; asymmetric involvement was significantly higher in FSHD than in other myopathies. Prospective quantitative MRI shows an average yearly fat-fraction increase of ~2% (thigh) and ~1.9% (leg); muscles with intermediate baseline fat fraction (15–30%) or elevated water-T2 (edema >41 ms) progress fastest, and edematous muscles are at higher risk of irreversible fatty replacement. wT2 and fat fraction correlate with clinical scales, making MRI a sensitive trial biomarker. (Evidence: human clinical imaging.)

"The most frequently affected muscles, including paucisymptomatic and severely affected FSHD patients, were trapezius, teres major and serratus anterior. Moreover, asymmetric muscle involvement was significantly higher in FSHD as compared to NFSHD patients" — PMID: 26115655

"The average yearly increase in FF was 2 ± 0.6% at thigh level and 1.9 ± 0.7% at leg level" — PMID: 40172709

Finding 9 — DUX4 is expressed in rare, burst-like fashion in few myonuclei

Single-cell RNA-seq of patient-derived primary myocytes identified a small FSHD-specific cell population expressing DUX4 in a dynamic, burst-like manner; downstream DUX4-target activation persists long after DUX4 itself has faded. Pseudotime trajectory modeling reconstructed an FSHD cellular progression from an early DUX4 burst to downstream pathway activation (oxidative stress, immune/germline programs, apoptosis). This sporadic, stochastic expression (few DUX4-positive nuclei at any moment) dilutes the bulk-tissue signal and explains the difficulty of using DUX4 as a pharmacodynamic biomarker. (Evidence: in vitro, single-cell.)

"DUX4 has been shown to be expressed in a highly dynamic burst-like manner, likely resulting in the detection of the downstream cascade of events long after DUX4 expression itself has faded" — PMID: 30445587

Finding 10 — DUX4 activates a germline/retrotransposon/immune program

DUX4 directly binds and activates genes of germline and early stem-cell development (ZSCAN4, PRAMEF family, TRIM43, MBD3L) plus LTR/MaLR endogenous retrotransposons; these DUX4-target genes are reliably detected in FSHD muscle but not controls, providing direct causal support for DUX4 misexpression. DUX4 also modulates innate immunity by activating DEFB103 (β-defensin 3), which itself inhibits muscle differentiation. Loss of D4Z4 silencing manifests as CpG hypomethylation plus loss of repressive chromatin marks (H3K9me3, H3K27me3); an Argonaute-dependent siRNA pathway normally helps repress D4Z4. Notably, DUX4 is co-opted by herpesviruses and papillomaviruses, which induce it to mimic zygotic genome activation and prevent silencing of the viral genome. (Evidence: in vitro / molecular.)

"we show that DUX4 binds and activates LTR elements from a class of MaLR endogenous primate retrotransposons and suppresses the innate immune response to viral infection, at least in part through the activation of DEFB103, a human defensin that can inhibit muscle differentiation" — PMID: 22209328

"DUX4 is a germline transcription factor and its expression in skeletal muscle leads to activation of early stem cell and germline programs and transcriptional activation of retroelements" — PMID: 22892954

"Loss of D4Z4 repression in FSHD is observed as hypomethylation of the array accompanied by loss of repressive chromatin marks" — PMID: 26113644

Finding 11 — Therapeutic pipeline targets DUX4 at multiple levels

Because no disease-modifying therapy is approved, strategies target the DUX4 axis at multiple points: (1) transcript knockdown with antisense oligonucleotides (AOs) directed at DUX4 mRNA/its polyadenylation signal, and RNA interference/siRNA (the Argonaute-dependent D4Z4 silencing pathway is exploitable); (2) small molecules suppressing DUX4 transcription (p38 MAPK inhibitors such as losmapimod — phase 3 negative; BET inhibitors; β2-agonists); (3) blocking downstream toxicity (flavones and other compounds reduce DUX4-induced apoptosis via an mTOR-independent mechanism); and (4) epigenetic re-silencing. Systemic AO therapy in the ACTA1-MCM/FLExDUX4 mouse improved molecular and histopathological readouts, including in the diaphragm. Clinical candidates include siRNA approaches (e.g., del-desiran / AOC-1020 antibody-siRNA conjugate) and other DUX4-lowering agents. (Evidence: model organism / in vitro / early clinical.)

"Antisense Oligonucleotides Used to Target the DUX4 mRNA as Therapeutic Approaches in FaciosScapuloHumeral Muscular Dystrophy" — PMID: 28273791

"Long-Term Systemic Treatment of a Mouse Model Displaying Chronic FSHD-like Pathology with Antisense Therapeutics" — PMID: 35884928

"we have identified a panel of five compounds that function downstream of DUX4 activity to inhibit DUX4-induced toxicity" — PMID: 37973788

Finding 12 — Major quality-of-life burden despite near-normal life expectancy

FSHD is slowly progressive with generally normal or near-normal life expectancy, but causes substantial disability — roughly 20% of patients eventually require a wheelchair. Pain and fatigue are among the most frequent and disabling symptoms: in cross-sectional neuromuscular studies, FSHD (with DM2) had significantly higher pain prevalence than other neuromuscular disorders and controls, and fatigue was the factor most consistently associated with reduced quality of life across muscular dystrophies. FSHD patients report worse sleep (insomnia) and lower mental-wellbeing QoL domains than controls. Pain medications are prescribed long-term for ~31–40% of adults, with impaired mobility the strongest correlate. Infantile/early-onset FSHD (~10% of patients; onset <10 y) is more severe with higher rates of extramuscular features. (Evidence: human clinical.)

"Patients with DM2 and FSHD had significantly higher levels of pain prevalence compared to other examined NMD subgroups and the control group" — PMID: 38968057

"Pain medications were prescribed for 31.1%-40.2% of people 20 years and older" — PMID: 40546227

"An estimated 10% of FSHD patients have an early onset (onset before 10 years of age) and are traditionally classified as infantile FSHD" — PMID: 27530735

Finding 13 — Molecular diagnosis integrates repeat sizing, haplotyping, methylation, and exome sequencing

Definitive diagnosis is molecular, not by biopsy. First-line testing sizes the D4Z4 repeat and determines the permissive 4qA haplotype/structure using single-molecule methods (Southern/pulsed-field electrophoresis, molecular combing, or optical genome mapping); second-line testing (DR1 methylation profiling and whole-exome sequencing for SMCHD1/DNMT3B/LRIF1) is reserved for borderline, non-contracted, or atypical cases. In a tertiary cohort (135 referrals), FSHD was confirmed in 89.6%, of which FSHD1 90.1%, FSHD1+2 3.3%, and FSHD2 6.6%. Long-read sequencing (Nanopore/PacBio) now resolves repeat length and CpG methylation simultaneously at nucleotide resolution. Standard short-read WGS/WES and chromosomal microarray/karyotype alone cannot size the macrosatellite, and the near-identical 10q26 array and 4qA/4qB haplotypes must be distinguished. (Evidence: human clinical / methods.)

"First-line testing included single-molecule D4Z4 repeat sizing, haplotyping and structural analysis using molecular combing or optical genome mapping. DR1 methylation profiling and whole-exome sequencing (WES) were used as second-line tests in unresolved, borderline, non-contracted or clinically atypical cases" — PMID: 42498520

"We applied Nanopore CRISPR/Cas9-targeted resequencing for the diagnosis of FSHD by simultaneous detection of D4Z4 repeat length and methylation status at nucleotide level" — PMID: 36348371

Full Report by Template Section

1. Disease Information

FSHD is a slowly progressive hereditary myopathy defined by characteristically asymmetric weakness that begins in the facial (facio-), scapular (scapulo-), and upper-arm (humeral) muscles and later descends to the abdominal, foot-dorsiflexor, and pelvic-girdle muscles. It is typically classified as the second/third most common muscular dystrophy. Onset is usually between 15 and 30 years of age, but ranges from infancy to late adulthood [PMID: 41781309].

Key identifiers: OMIM 158900 (FSHD1) and 158901 (FSHD2); Orphanet ORPHA:269; ICD-10 G71.0; ICD-11 8C71; MeSH D020391; MONDO:0008028.
Synonyms/alternative names: facioscapulohumeral dystrophy, Landouzy–Dejerine muscular dystrophy, Landouzy–Dejerine syndrome, FSH muscular dystrophy, FSHMD.
Information source: Aggregated disease-level resources (OMIM, Orphanet, MeSH) plus population registries (MD STARnet, Japanese FSHD registry, TREAT-NMD) and cohort/natural-history studies; both aggregated and patient-level data contributed to this report.

2. Etiology

Causal factors — genetic/epigenetic (Findings 1, 7, 10). The primary cause is epigenetic de-repression and toxic misexpression of DUX4 in skeletal muscle. FSHD1 (~95%): D4Z4 contraction to 1–10 units on a permissive 4qA haplotype at 4q35 [PMID: 38955828; 37703328]. FSHD2 (~5%): digenic — a chromatin-repressor variant (SMCHD1, DNMT3B, LRIF1) plus a borderline array and permissive haplotype [PMID: 34711481]. All routes require a permissive 4qA polyadenylation signal to stabilize DUX4 mRNA [PMID: 27816329].

Genetic risk factors. Shorter D4Z4 arrays and lower D4Z4 methylation increase risk and severity; the 4qA permissive haplotype is obligatory. SMCHD1 acts as both a causal FSHD2 gene and a modifier of FSHD1 severity.

Environmental/lifestyle risk factors. No established environmental cause. Mechanical overuse and eccentric exercise are debated as local aggravators; there is no strong evidence they alter disease course. Age and (subtly) sex modify expression — several registries note earlier facial weakness and higher hearing-loss rates in females [PMID: 40203460].

Protective factors. Longer residual D4Z4 arrays and higher CpG methylation are protective; unaffected carriers have longer arrays than symptomatic relatives (7.3 vs 6.0 units, P<0.001) [PMID: 30211448]. No validated dietary or pharmacological protective factor exists.

Gene–environment interactions. DUX4 target genes overlap with the innate antiviral response, and herpesviruses/papillomaviruses actively induce DUX4 to promote replication [PMID: 38168299] — a biologically intriguing but not clinically established gene–environment axis.

3. Phenotypes

Phenotype	Type	Onset / severity / progression	Frequency	Suggested HPO
Facial weakness (orbicularis oculi/oris)	Clinical sign	Early, often first; mild→moderate; progressive	Very frequent	HP:0000278 (facial weakness)
Scapular winging / shoulder-girdle weakness	Clinical sign	Adolescence/early adult; presenting complaint	Very frequent	HP:0003691 (scapular winging)
Asymmetric proximal upper-limb weakness	Clinical sign	Progressive, descending	Very frequent	HP:0003484
Foot drop / tibialis anterior weakness	Clinical sign	Later, descending	Frequent	HP:0009027
Abdominal weakness (Beevor sign)	Clinical sign	Variable	Characteristic	HP:0009063
Chronic pain	Symptom	Adult; disabling	Very frequent [PMID: 38968057]	HP:0012531
Fatigue	Symptom	Adult; disabling; QoL-dominant	Very frequent [PMID: 31307472]	HP:0012378
High-frequency sensorineural hearing loss	Lab/sign	Adult (median 46.5 y); infantile forms earlier	13% [PMID: 40879179]	HP:0008553 / HP:0000407
Retinal vasculopathy (Coats-like)	Sign	Adult (median 58.7 y)	3.6% [PMID: 40879179]	HP:0500049 / HP:0007843
Seizures	Sign	Childhood (median 16.5 y; ½ ≤10 y)	2.0% [PMID: 40879179]	HP:0001250
Respiratory muscle weakness	Sign	Advanced disease	~1/3 in registry [PMID: 40203460]	HP:0002747
Wheelchair dependence	Functional outcome	Late	~20% [Finding 12]	HP:0002540

Quality-of-life impact. Pain and fatigue drive QoL loss more than raw muscle weakness; FSHD scored lower than DMD on mental-wellbeing domains, and 25–81% of men with MD report sleep impairment [PMID: 31307472; 36137167].

4. Genetic / Molecular Information

Causal gene: DUX4 (double homeobox 4; HGNC:50800), a retrogene embedded in the distal D4Z4 unit at 4q35. The de-repression machinery involves SMCHD1 (HGNC:29090; OMIM 614982), DNMT3B (HGNC:2979), and LRIF1 (HGNC:25281) in FSHD2.
Pathogenic "variant" class: FSHD1 is caused by a structural/macrosatellite contraction (1–10 D4Z4 units), not a point mutation — invisible to standard sequencing/microarray. FSHD2 involves loss-of-function point/indel variants in SMCHD1 (most common), DNMT3B, or LRIF1, generally classified pathogenic/likely pathogenic per ACMG. In-cis D4Z4 duplication alleles are an emerging pathogenic class [PMID: 37703328].
Functional consequence: Gain-of-toxic-function via ectopic DUX4 transcription-factor activity; the chromatin-repressor variants are loss-of-function.
Modifier genes: SMCHD1 modifies FSHD1 severity; residual repeat length and methylation modify penetrance.
Epigenetics: D4Z4 CpG hypomethylation and loss of repressive H3K9me3/H3K27me3 marks are central [PMID: 26113644].
Chromosomal features: 4q35 D4Z4 macrosatellite; homologous non-pathogenic 10q26 array; 4qA (permissive) vs 4qB (non-permissive) haplotypes.

5. Environmental Information

There are no established environmental, occupational, toxic, or infectious causes of FSHD — it is a monogenic/digenic epigenetic disease. Of mechanistic interest, DUX4 is actively induced by herpesviruses (α/β/γ) and papillomaviruses to mimic zygotic genome activation and evade viral-genome silencing, linking DUX4 biology to viral infection but not establishing infection as an FSHD trigger [PMID: 38168299]. Lifestyle factors (exercise type/intensity) are studied for symptom management, not causation.

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

D4Z4 contraction (FSHD1)  ┐
   OR                     ├─► chromatin relaxation ─► DUX4 de-repression
SMCHD1/DNMT3B/LRIF1 LOF   ┘        (needs 4qA PAS to stabilize mRNA)
(FSHD2, borderline array)
│
▼
  DUX4 protein (burst-like, few nuclei)
│
   ┌────┼───────────────┬───────────────┬──────────────┐
   ▼    ▼               ▼               ▼              ▼
germline/    retro-     UPF1 degradation  MYOD1/MYF5    oxidative
stem-cell    transposon  → NMD inhibition  repression    stress +
program      activation  → DUX4 mRNA      → impaired     DEFB103
(ZSCAN4,     (LTR/MaLR)   stabilized       myogenesis    immune
PRAMEF,                    (feedback loop)                activation
TRIM43)      │
└────┴──► caspase-3/7 apoptosis ─► myofiber death
                    │
                    ▼
     progressive, asymmetric fatty replacement & weakness
     (trapezius, teres major, serratus anterior first)

Molecular pathways: p38 MAPK (drives DUX4 transcription; drug target), NMD pathway (inhibited via UPF1), apoptotic caspase cascade, innate antiviral/interferon program.
Cellular processes: apoptosis (GO:0006915), impaired myogenic differentiation (GO:0007517), oxidative-stress response (GO:0006979), NMD (GO:0000184).
Protein dysfunction: DUX4 gain-of-toxic-function (aberrant transcription-factor activity); SMCHD1/DNMT3B/LRIF1 loss-of-function.
Immune involvement: DUX4 activates DEFB103 (β-defensin 3), which inhibits muscle differentiation; broader innate-immune/interferon dysregulation [PMID: 22209328].
Molecular profiling: DUX4-target gene panels (ZSCAN4, TRIM43, LEUTX, PRAMEF, MBD3L) are the standard transcriptomic biomarker; single-cell RNA-seq reveals rare burst-like DUX4+ cells [PMID: 30445587].
GO/CL suggestions: biological process GO:0006915 (apoptotic process), GO:0007517 (muscle organ development); cell type CL:0000187 (muscle cell), CL:0000515 (skeletal muscle myoblast), CL:0000594 (skeletal muscle satellite cell).

7. Anatomical Structures Affected

Primary organ/tissue: skeletal muscle (UBERON:0001134), especially facial muscles (UBERON:0001577), trapezius (UBERON:0001496), teres major, serratus anterior, biceps/triceps; later abdominal, tibialis anterior (UBERON:0001385), and pelvic girdle.
Secondary/systemic: cochlea/inner ear (hearing loss; UBERON:0001846), retina (UBERON:0000966; Coats-like vasculopathy), CNS (seizures in severe infantile forms), respiratory muscles/diaphragm (UBERON:0001103).
Cell types: skeletal myofibers, myoblasts, and satellite cells (CL:0000594).
Subcellular: nucleus (GO:0005634; DUX4 transcription-factor site) and mitochondria/oxidative-stress machinery.
Lateralization: characteristically asymmetric/bilateral-asymmetric — a strong diagnostic clue distinguishing FSHD from most other myopathies [PMID: 26115655].

8. Temporal Development

Onset: typically 15–30 years (adolescent/young-adult); ~10% infantile/early-onset (<10 y) with more severe, extramuscular-rich disease; late-onset forms also occur [PMID: 41781309; 27530735].
Onset pattern: insidious, chronic.
Progression: slow, descending, often stepwise with periods of apparent stability; quantitative MRI shows ~2%/yr fat-fraction increase [PMID: 40172709].
Course: chronic, lifelong, progressive; ~20% reach wheelchair dependence.
Critical periods: infantile onset marks a vulnerability window; edematous (high-T2) muscles represent a window where intervention might prevent irreversible fatty replacement [PMID: 40172709].

9. Inheritance and Population

Epidemiology: prevalence ~1 in 8,000–20,000 [PMID: 33303865].
Inheritance: autosomal dominant (FSHD1); FSHD2 is digenic (dominant SMCHD1 variant + permissive borderline array).
Penetrance: incomplete and age-dependent (~17% non-penetrant, ~25% asymptomatic carriers) [PMID: 29997197].
Expressivity: highly variable, even within families; familial factors explain ~50% of severity variance vs ~10% for repeat size [PMID: 30211448].
De novo / mosaicism: a substantial minority of FSHD1 cases are de novo, frequently with somatic/germline mosaicism.
Sex ratio: roughly equal, with some registries reporting earlier facial weakness and more hearing loss in females [PMID: 40203460].
Population diversity: D4Z4 repeat-number distributions differ across populations (e.g., Japanese registry data) [PMID: 40203460].

10. Diagnostics (Finding 13)

Definitive test: molecular — single-molecule D4Z4 repeat sizing + 4qA haplotyping (Southern/PFGE, molecular combing, or optical genome mapping); methylation profiling and WES (SMCHD1/DNMT3B/LRIF1) as second-line [PMID: 42498520].
Long-read sequencing: Nanopore/PacBio simultaneously resolve repeat length and methylation at nucleotide resolution [PMID: 36348371].
Supportive tests: muscle MRI (asymmetric trapezius/teres major/serratus anterior fatty replacement; wT2 edema) [PMID: 26115655; 40172709]; serum CK mildly elevated or normal; EMG myopathic; biopsy non-specific and not required.
Biomarkers: DUX4-target gene panel in muscle (research/trial pharmacodynamic marker); MRI fat fraction and water-T2 as imaging biomarkers.
Differential diagnosis: limb-girdle muscular dystrophies, Pompe disease, mitochondrial myopathy, scapuloperoneal syndromes, polymyositis — distinguished by the asymmetric facioscapular pattern and molecular testing.
Screening: cascade genetic testing of at-risk relatives; prenatal/preimplantation diagnosis feasible where a defined pathogenic allele exists.

11. Outcome / Prognosis

Life expectancy: generally normal/near-normal.
Morbidity: substantial; ~20% wheelchair-dependent; respiratory insufficiency in advanced/infantile disease (~1/3 with respiratory dysfunction, some ventilator-dependent in registry) [PMID: 40203460].
QoL: dominated by pain and fatigue; worse mental-wellbeing and sleep than controls [PMID: 38968057; 31307472; 36137167].
Prognostic factors: shorter D4Z4 repeats, lower methylation, infantile onset, and SMCHD1 co-variants predict greater severity; MRI water-T2/fat fraction predict local progression [PMID: 40172709].

12. Treatment (Findings 5, 11)

No approved disease-modifying therapy. Losmapimod (p38 MAPK inhibitor) failed phase 2b (DUX4-expression endpoint) and phase 3 (clinical endpoint) [PMID: 38631764; 40580827].
Standard of care (symptomatic/supportive; NCIT: supportive care, physical therapy, occupational therapy): physical/occupational therapy, aids/orthotics (ankle-foot orthoses for foot drop), scapular fixation/arthrodesis surgery, respiratory support, aggressive pain and fatigue management, and screening/treatment of hearing and retinal complications.
Pipeline (DUX4-axis): antisense oligonucleotides against DUX4 mRNA/PAS [PMID: 28273791]; siRNA (e.g., del-desiran/AOC-1020 antibody-siRNA conjugate); small molecules suppressing DUX4 transcription (BET inhibitors, β2-agonists); downstream-toxicity blockers (flavones, mTOR-independent) [PMID: 37973788]; epigenetic re-silencing. Systemic AO improved molecular/histopathology (incl. diaphragm) in the ACTA1-MCM/FLExDUX4 mouse [PMID: 35884928].
Pharmacogenomics: none established.

13. Prevention

Primary prevention: not possible (genetic disease); genetic counseling and reproductive options (prenatal/PGT) for at-risk families.
Secondary prevention: cascade genetic testing; audiology and dilated retinal exams for early detection of hearing loss and Coats-like vasculopathy, especially in short-repeat/infantile cases.
Tertiary prevention: physical therapy, respiratory surveillance, fall prevention, pain/fatigue management, and orthopedic management of scapular winging and spinal deformity.
Counseling: genetic counseling essential given incomplete penetrance, variable expressivity, de novo/mosaic cases, and digenic FSHD2 inheritance.

14. Other Species / Natural Disease

FSHD is essentially a human-specific disease at the genetic level: the DUX4 retrogene and the 4q35 D4Z4 macrosatellite architecture (with the permissive 4qA polyadenylation signal) are primate/human features, so no naturally occurring animal FSHD equivalent is recognized. DUX4 has orthologs/paralogs (the Dux family) in mouse and other mammals involved in zygotic genome activation, enabling comparative study of DUX4 biology, but not a natural disease model. No established zoonotic or veterinary relevance. NCBI Taxon: Homo sapiens (9606).

15. Model Organisms (Finding 6)

Principal model: the tamoxifen-inducible ACTA1-MCM;FLExDUX4/+ bitransgenic mouse — low chronic muscle DUX4, progressive dystrophy, DUX4-pathway molecular signature, histological damage, and functional weakness; the academic workhorse for testing DUX4-silencing AOs [PMID: 39518930; 35884928].
Other systems: DUX4-inducible and AAV-DUX4 mouse models; patient-derived primary myoblasts/myotubes and iPSC-derived muscle (used for single-cell RNA-seq and drug screening) [PMID: 30445587; 37973788]; zebrafish DUX4-toxicity models.
Model type: tunable overexpression models — strength is faithful DUX4-pathway recapitulation and diaphragm involvement; limitation is that they model DUX4 toxicity rather than the native human D4Z4 macrosatellite contraction/epigenetic context, and burst-like stochastic expression is hard to reproduce exactly.
Applications: preclinical testing of DUX4-lowering therapeutics, biomarker development, and mechanism dissection.

Mechanistic Model / Interpretation

The unifying model of FSHD is elegant: all genetic routes lead to the same molecular villain, DUX4. FSHD1 and FSHD2 differ only in how the D4Z4 array loses its repressive chromatin state (cis-contraction vs trans-acting repressor loss), but both require a permissive 4qA haplotype whose polyadenylation signal rescues the otherwise-unstable DUX4 mRNA (Finding 7). This explains a long-standing paradox — why an identical, near-homologous D4Z4 array on chromosome 10q26 is harmless, and why 4qB alleles are non-pathogenic.

Once expressed, DUX4 behaves as the germline master-regulator it evolved to be, switching on an early-embryonic/germline/retrotransposon program in a tissue where that program is catastrophic (Findings 2, 10). Muscle nuclei die by caspase-3/7 apoptosis; a self-reinforcing UPF1/NMD feedback loop stabilizes DUX4 into "bursts"; and MYOD1/MYF5 repression cripples regeneration. Crucially, DUX4 is expressed in only a tiny, stochastic subset of nuclei at any instant (Finding 9), yet its downstream damage persists and accumulates — reconciling how a rarely-detectable transcript produces relentless, generalized wasting, and why DUX4 itself is a treacherous pharmacodynamic endpoint (a likely contributor to the losmapimod phase 2b/3 failures, Finding 5).

The clinical phenotype maps onto this biology: asymmetric involvement of trapezius/teres major/serratus anterior (Finding 8), incomplete age-dependent penetrance driven far more by familial modifiers than by repeat size (Finding 4), and a heavy pain/fatigue/mobility burden despite near-normal survival (Finding 12). The therapeutic logic follows directly: silence DUX4 (ASO/siRNA), re-repress the locus (epigenetic), or blunt downstream toxicity (Finding 11).

Evidence Base

PMID	Role in report	Supports finding(s)
38955828	French national protocol; FSHD1/FSHD2 proportions & mechanism	F1
34711481	FSHD2 digenic; SMCHD1/DNMT3B/LRIF1	F1
37703328	D4Z4 biology; in-cis duplication alleles	F1
25564732	UPF1/NMD feedback loop	F2
37973788	Caspase-3/7 apoptosis; downstream-blocking flavones	F2, F11
30446688	DUX4 represses MYOD1/MYF5	F2
40879179	MD STARnet comorbidity frequencies	F3
41037169	Extramuscular features in severe early-onset	F3
30211448	Familial vs repeat-size variance	F4
29997197	Age-dependent penetrance	F4
33303865	Prevalence 1/20,000; borderline-allele guidance	F4
38631764	ReDUX4 phase 2b design/endpoint	F5
40580827	Phase 3 losmapimod failure	F5
39518930	ACTA1-MCM/FLExDUX4 model	F6
27816329	4qA PAS stabilizes DUX4 mRNA	F7
26115655	MRI asymmetric pattern	F8
40172709	Quantitative MRI progression	F8
30445587	Single-cell burst-like DUX4	F9
22209328	Retrotransposon/DEFB103 immune activation	F10
22892954	Germline/stem-cell program	F10
26113644	D4Z4 hypomethylation / chromatin	F10
28273791	ASO targeting DUX4 mRNA	F11
35884928	Systemic AO efficacy in mouse	F11
38968057	Pain burden	F12
40546227	Chronic pain-medication use	F12
27530735	Infantile FSHD ~10%	F12
42498520	Two-tier diagnostic workflow	F13
36348371	Long-read repeat+methylation diagnosis	F13
38168299	Viral induction of DUX4 (GxE context)	§5
40203460	Japanese registry; sex/population differences	§3, §9, §11
31307472; 36137167	QoL, fatigue, sleep	§3, §11
41781309	Clinical overview & diagnostic pathway	§1, §8

Limitations and Knowledge Gaps

DUX4 biomarker problem. Burst-like, rare expression makes DUX4/DUX4-target quantification noisy; this likely undermined the losmapimod DUX4-expression endpoint and complicates all future trials (Findings 5, 9).
Genotype–phenotype gap. Repeat size explains only ~10% of severity; the "familial factors" that explain ~50% are largely unidentified beyond SMCHD1 and methylation (Finding 4).
Modifier biology. The full set of severity modifiers, and the mechanisms of the striking within-family variability and asymmetry, remain unresolved.
Diagnostic access. Gold-standard sizing/haplotyping requires specialized single-molecule or long-read methods unavailable in many labs; standard WGS/WES/microarray cannot diagnose FSHD1 (Finding 13).
Model fidelity. Overexpression mouse models capture DUX4 toxicity but not the native macrosatellite/epigenetic context or the exact stochastic burst pattern (Finding 6).
Therapeutic translation. No disease-modifying therapy has yet succeeded clinically; downstream vs upstream targeting trade-offs are unsettled.
Extramuscular pathophysiology. Mechanisms of hearing loss, retinal vasculopathy, and CNS involvement (and why they cluster in short-repeat/infantile disease) are poorly defined.

Proposed Follow-up Experiments / Actions

Develop robust, minimally-invasive DUX4-activity biomarkers — e.g., blood-based or MRI-linked composite DUX4-target signatures — to serve as trial pharmacodynamic endpoints that overcome burst-like expression (addresses Findings 5, 9).
Modifier-gene discovery — large family-based WGS + methylation + long-read studies to identify the ~50% "familial" severity variance beyond SMCHD1 (addresses Finding 4).
Head-to-head preclinical benchmarking of DUX4-lowering modalities (ASO vs siRNA/AOC vs epigenetic re-silencing vs downstream blockers) in ACTA1-MCM/FLExDUX4 mice with standardized diaphragm and functional readouts (addresses Findings 6, 11).
MRI-guided trial enrichment — use baseline water-T2/intermediate fat fraction to select fast-progressing muscles/patients and shorten trials (addresses Finding 8).
Prospective natural-history + registry expansion (TREAT-NMD/MD STARnet/Japanese registry) to refine penetrance, sex differences, and comorbidity incidence, especially for FSHD2 and infantile FSHD (addresses Findings 3, 4, 12).
Broaden diagnostic access by validating optical genome mapping and long-read sequencing as first-line clinical assays that jointly resolve repeat length, haplotype, and methylation (addresses Finding 13).
Mechanistic study of extramuscular DUX4 effects in cochlear and retinal tissue/models to explain the short-repeat comorbidity cluster.

Report compiled from 13 confirmed findings and 59 reviewed papers across 5 investigation iterations. Evidence sources span human clinical cohorts/registries, model-organism (ACTA1-MCM/FLExDUX4 mouse), in vitro (patient myoblasts, single-cell RNA-seq), and computational/review analyses.

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References & Deep Research

References

Deep Research

Asta Literature Retrieval: Pathophysiology and clinical mechanisms of Facioscapulohumeral Muscular Dystrophy. Core disease mechanisms, molecular...

Relevant Papers

[1] Determining the role of sarcomeric proteins in facioscapulohumeral muscular dystrophy: a study protocol

[2] Diagnosis, Pathogenesis and Treatment of Muscular Dystrophy

[3] Current Therapeutic Approaches in FSHD

[4] The Notch signaling pathway in skeletal muscle health and disease

[5] Meeting report: the 2021 FSHD International Research Congress

[6] Facioscapulohumeral Muscular Dystrophy.

[7] The Unexplored Role of Connexin Hemichannels in Promoting Facioscapulohumeral Muscular Dystrophy Progression

[8] Cellular and molecular mechanisms underlying muscular dystrophy

[9] Therapeutic advances in muscular dystrophy

[10] A Hypothesis for Mechanisms of Weakness Distribution in Muscular Dystrophies

[11] Pharmacotherapeutic Approaches to Treatment of Muscular Dystrophies

[12] Human iPSC Models to Study Orphan Diseases: Muscular Dystrophies

[13] The FSHD jigsaw: are we placing the tiles in the right position?

[14] Current Genetic Survey and Potential Gene-Targeting Therapeutics for Neuromuscular Diseases

[15] A pediatric case report and literature review of facioscapulohumeral muscular dystrophy type1

[16] Cellular Stress in the Pathogenesis of Muscular Disorders—From Cause to Consequence

[17] Serum miRNAs as biomarkers for the rare types of muscular dystrophy.

[18] Identification of hub genes related to Duchenne muscular dystrophy by weighted gene co-expression network analysis

[19] Immunohistochemical Characterization of FacioscapulohumeralMuscular Dystrophy Muscle Biopsies

[20] LGMD phenotype due to a new gene and dysferlinopathy investigated by next-generation sequencing

Notes

Facioscapulohumeral Muscular Dystrophy (FSHD) — Comprehensive Research Report

1. Disease Information

2. Etiology

Disease causal factors — genetic, chromatin-based mechanism

Risk factors

Protective factors

Gene–environment interactions

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Evidence Gaps / Notes for Curation

Facioscapulohumeral Muscular Dystrophy (FSHD): A Comprehensive Disease Characteristics Report

Summary

Key Findings

Finding 1 — Two genetic routes, one mechanism (DUX4 de-repression)

Finding 2 — DUX4 is an embryonic transcription factor toxic to muscle via apoptosis and NMD inhibition

Finding 3 — Extramuscular comorbidities: hearing loss, retinal vasculopathy, seizures

Finding 4 — Penetrance is age-dependent and incomplete; repeat size is a weak predictor

Finding 5 — No approved disease-modifying therapy; losmapimod failed phase 3

Finding 6 — ACTA1-MCM/FLExDUX4 mouse recapitulates progressive DUX4-driven pathology

Finding 7 — The permissive 4qA haplotype supplies a polyadenylation signal that stabilizes DUX4 mRNA

Finding 8 — Muscle MRI reveals a specific asymmetric involvement pattern useful for diagnosis and natural history

Finding 9 — DUX4 is expressed in rare, burst-like fashion in few myonuclei

Finding 10 — DUX4 activates a germline/retrotransposon/immune program

Finding 11 — Therapeutic pipeline targets DUX4 at multiple levels

Finding 12 — Major quality-of-life burden despite near-normal life expectancy