Schwartz-Jampel Syndrome

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Classifications

ISDS Skeletal Nosology

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Mappings

MONDO

MONDO:0100435 Schwartz-Jampel syndrome type 1 Not Yet Curated

MONDO:0100435 is the OMIM-anchored "type 1" child of MONDO:0009717. Since the former "type 2" was reassigned to LIFR-related Stuve-Wiedemann syndrome, type 1 is in practice coextensive with the HSPG2 disorder modeled here, but it is recorded as a narrowMatch because MONDO still maintains the two terms separately.

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Inheritance

1

Autosomal recessive inheritance HP:0000007

SJS segregates as an autosomal recessive trait; affected individuals carry biallelic (homozygous or compound heterozygous) hypomorphic HSPG2 variants and heterozygous parents are unaffected.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:11101850 SUPPORT Human Clinical

"Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia"

The disease-gene identification paper states the autosomal recessive mode of inheritance.

PMID:33767660 SUPPORT Human Clinical

"This mutation carried by the asymptomatic parents was previously registered in a single-nucleotide polymorphism database"

Carriage of the pathogenic allele by asymptomatic parents is direct evidence of recessive inheritance with unaffected heterozygotes.

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Subtypes

2

SJS type 1A (milder phenotype)

The milder of the two clinical severity grades of the HSPG2 disorder, with later recognition of myotonic signs and less severe skeletal involvement.

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"SJS1 is further divided into SJS1A, a milder phenotype, and SJS1B, a severe form with neonatal onset"

Establishes the two clinical severity grades used as subtypes here.

SJS type 1B (severe, neonatal onset)

The severe, neonatal-onset grade of the HSPG2 disorder. Distinct from the historical "SJS type 2", which is now Stuve-Wiedemann syndrome (LIFR).

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"SJS1 is further divided into SJS1A, a milder phenotype, and SJS1B, a severe form with neonatal onset"

Establishes the two clinical severity grades used as subtypes here.

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Discussions and Knowledge Gaps

2

Is endplate acetylcholinesterase deficiency sufficient to generate the spontaneous muscle activity of Schwartz-Jampel syndrome, or are additional perlecan-dependent changes required?

KNOWLEDGE GAP OPEN sjs_ache_sufficiency_gap

Attached to

pathophysiology#Endplate Acetylcholinesterase Deficiency pathophysiology#Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling

The mouse model that established the endplate AChE deficiency in vivo also showed that the deficiency alone did not produce resting spontaneous EMG activity in the diaphragm, so the causal chain from AChE loss to continuous muscle hyperactivity is necessary-but-not-obviously-sufficient. The human biopsy study points to a combination of synaptic AChE deficiency, preterminal amyelination and junctional remodeling acting synergistically. Which of those is rate-limiting is unresolved, and it matters therapeutically: an AChE-directed strategy would only help if that arm dominates.

Proposed experiments

Muscle-specific perlecan restoration in the SJS mouse

sjs_nmj_perlecan_restoration

Restore synaptic perlecan (and hence endplate AChE) selectively at the neuromuscular junction in the C1532Yneo line and test whether spontaneous EMG activity resolves without correcting preterminal myelination.

Show evidence (1 reference)

PMID:18647752 SUPPORT Model Organism

"However, physiological endplate AChE deficiency was not associated with spontaneous activity at rest on EMG in the diaphragm, suggesting that additional changes are required to generate such activity characteristic of SJS."

The authors state the insufficiency directly; this is the gap recorded here.

Why does the SJS-associated HSPG2 C1532Y substitution cause disease in the human family in which it was found but only a mild, non-SJS phenotype when knocked into mouse without a transcription-lowering cassette?

HUMAN MODEL MISMATCH OPEN sjs_c1532y_mouse_human_mismatch

Attached to

pathophysiology#HSPG2 Hypomorphic Variation pathophysiology#Chondrodysplasia and Skeletal Deformity animal_models#Perlecan C1532Y point-mutation-only mouse

The knock-in series separates the missense change from the transcriptional down-regulation supplied by the retained Neo cassette. Only the down-regulated line reproduces SJS, which led the authors to question whether C1532Y is the sole causative factor in the human family. Two readings remain open — that the human allele carries an additional transcriptional effect the mouse construct does not reproduce, or that mouse tolerates a perlecan level that human does not — and they imply different things about how faithfully hypomorphic-allele mouse models can be used to rank SJS variant severity.

Proposed experiments

Re-sequencing and expression analysis of the original C1532Y family

sjs_c1532y_family_expression_reanalysis

Determine HSPG2 transcript level and search for a second cis-acting regulatory variant in the family carrying C1532Y, to test whether the human genotype includes a transcriptional component absent from the mouse knock-in.

Show evidence (1 reference)

PMID:17213231 SUPPORT Model Organism

"These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS."

States the mismatch and the authors' proposed resolution.

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Pathophysiology

8

HSPG2 Hypomorphic Variation

Biallelic partial loss-of-function variants distributed across the 97 exons of HSPG2 are the initiating lesion. Two molecularly distinct routes reduce the amount of functional perlecan reaching the extracellular space: truncating alleles destabilize HSPG2 mRNA through nonsense-mediated decay, while missense alleles affecting cysteine residues cause intracellular retention of the mutant core protein by ER quality control. Crucially, these are hypomorphic rather than null alleles — the same gene's functional null alleles cause dyssegmental dysplasia, Silverman-Handmaker type.

HSPG2 hgnc:5273

Genetic context HSPG2 hgnc:5273 variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: PARTIAL_LOSS_OF_FUNCTION

Homozygous or compound heterozygous hypomorphic germline HSPG2 alleles; compound heterozygosity is common because almost all reported mutations are private.

Downstream

Reduced Perlecan Secretion into Basement Membranes Both truncating (NMD) and cysteine-missense (intracellular retention) alleles converge on less perlecan being secreted.

Show evidence (3 references)

PMID:11101850 SUPPORT Human Clinical

"Here we describe mutations, including missense and splicing mutations, of the gene encoding perlecan (HSPG2) in three SJS1 families."

Identifies HSPG2 as the SJS disease gene, the initiating lesion of this pathograph.

PMID:16927315 SUPPORT Human Clinical

"Mutations included nine deletion or insertion (41%), six splice site (27%), five missense (23%), and two nonsense mutations (9%)."

Documents the allelic spectrum across 23 families, supporting the variety of variant classes recorded on this node.

PMID:16927315 SUPPORT Human Clinical

"Our analyses strengthen the idea that SJS results from hypomorphic mutations of the HSPG2 gene."

Establishes that SJS-causing alleles are hypomorphic, not null — the distinction that separates SJS from DDSH.

Reduced Perlecan Secretion into Basement Membranes

Perlecan is the major heparan sulfate proteoglycan of basement membranes and of the cartilage pericellular matrix. Reduced secretion lowers its concentration in basement membranes throughout the body, and the residual level sets disease severity: perlecan abundance and phenotype severity are inversely correlated in allelic mouse lines, and complete absence produces the lethal DDSH phenotype instead. From this single molecular deficit the pathograph branches into an ECM/cartilage arm and a synaptic/neuromuscular arm.

extracellular matrix organization GO:0030198 ⚠ ABNORMAL

basement membrane GO:0005604

Experimental models

SJS patient-derived primary dermal fibroblasts PRIMARY CELL CULTURE Directly quantifies secreted perlecan from cells carrying a patient genotype.

Animal models

Perlecan-null (Hspg2 knockout) mouse Mouse partially recapitulates Complete absence of perlecan produces a severe chondrodysplasia with dyssegmental ossification, delimiting the null end of the dosage series that this node models.

Downstream

Endplate Acetylcholinesterase Deficiency Perlecan is the basement-membrane anchor that concentrates acetylcholinesterase in the synaptic cleft, so synaptic perlecan loss lowers endplate AChE.

Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation Perlecan deposited in the pericellular matrix around chondrocytes is required for prechondrocyte condensation and growth-plate organization.

Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation A third, cell-autonomous consequence of the perlecan deficit, independent of the endplate AChE route: perlecan loss releases myostatin restraint in fast-twitch muscle and lowers Akt/mTORC1 tone in slow-twitch muscle.

Show evidence (3 references)

PMID:16550923 SUPPORT Other

"Perlecan is the major heparan sulfate proteoglycan of extracellular matrix and basement membranes that displays various functions."

Establishes the molecular identity and localization of the deficient product.

PMID:16550923 SUPPORT Other

"A gene-dosage effect seems to account for the correlation between the phenotype and the mutations within the gene: SJS would be associated with hypomorph mutations of the perlecan gene and DDSH would be due to the absence of functional perlecan."

States the dosage relationship that makes residual perlecan level, rather than the identity of the mutation, the proximate determinant of phenotype.

PMID:18647752 SUPPORT Model Organism

"An inverse correlation between disease severity and perlecan secretion in the BMs was observed at the macroscopic and microscopic levels, consistent with a dosage effect."

In vivo demonstration in allelic mouse lines that severity tracks residual basement-membrane perlecan.

Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation

A signalling account of the muscle-bulk changes in perlecan deficiency that is separate from, and potentially additive to, the neuromuscular-hyperactivity account of hypertrophy. Perlecan is a myostatin-binding basement-membrane proteoglycan, so its loss reduces myostatin (TGF-beta family) growth restraint and drives hypertrophy selectively in fast-twitch muscle; in slow-twitch muscle the same deficit is associated instead with reduced Akt/mTORC1 signalling and disinhibited autophagy, producing atrophy. The entry records this as PROVISIONAL and the atrophy arm explicitly as hypothesised, because the source itself hedges the Akt/mTORC1-autophagy limb ("possibly through") and because the fibre-type dissection rests on mouse work rather than on SJS patient muscle. Curated so the entry does not silently assert only the weaker of the two available explanations for the Skeletal Muscle Hypertrophy phenotype.

skeletal muscle fiber CL:0008002

myostatin (TGF-beta family) receptor signaling GO:0007179 ↓ DECREASED Akt/mTORC1 signaling in slow-twitch muscle GO:0043491 ↓ DECREASED TOR signaling GO:0031929 ↓ DECREASED autophagy (disinhibited in slow-twitch muscle) GO:0006914 ↑ INCREASED

Show evidence (1 reference)

PMID:33767660 SUPPORT Model Organism

"In addition, perlecan deficiency causes hypertrophy in fast-twitch muscles by reducing myostatin signaling (1) and also can cause atrophy in the slow-twitch muscles, possibly through disinhibition of autophagy related to reduced Akt/mTORC1 signaling (2)."

The single sentence supporting both limbs of this node. Tagged MODEL_ORGANISM although PMID:33767660 is a human case report, because this particular sentence relays the fibre-type dissection from the mouse literature rather than the authors' own patient data. Note the source's own hedge ("possibly through") on the Akt/mTORC1-autophagy limb, which is why the node carries PROVISIONAL rather than ESTABLISHED confidence.

Endplate Acetylcholinesterase Deficiency

Perlecan tethers acetylcholinesterase in the synaptic basal lamina of the neuromuscular junction. In SJS the postsynaptic apparatus is structurally well formed, but synaptic AChE is deficient, so acetylcholine released at the endplate is cleared too slowly and its action is prolonged. This is a synapse-specific consequence of the same basement-membrane perlecan deficit, and is the mechanism that distinguishes SJS from the muscle chloride- and sodium-channel myotonias.

skeletal muscle fiber CL:0008002

acetylcholinesterase activity GO:0003990 ↓ DECREASED

synaptic cleft GO:0043083

neuromuscular junction GO:0031594

Animal models

Perlecan C1532Yneo hypomorphic knock-in mouse Mouse recapitulates Endplate AChE is reduced as a direct consequence of synaptic perlecan deficiency, with an otherwise intact junction.

Downstream

Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling Prolonged cholinergic action at a structurally remodeled, partly amyelinated preterminal axon generates ectopic distal nerve activity.

Show evidence (2 references)

PMID:24011702 SUPPORT Human Clinical

"The study of muscle biopsies containing neuromuscular junctions showed well-formed post-synaptic element, synaptic acetylcholinesterase deficiency, denervation of synaptic gutters with reinnervation by terminal sprouting, and long nonmyelinated preterminal nerve segments."

Human muscle-biopsy confirmation of synaptic AChE deficiency with an intact postsynaptic apparatus.

PMID:18647752 SUPPORT Model Organism

"Studies of muscle contractile properties showed muscle fatigability at low frequencies of nerve stimulation and suggested that partial endplate AChE deficiency might contribute to SJS muscle stiffness by potentiating muscle force."

Links the endplate AChE deficit functionally to the muscle stiffness phenotype.

Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling

The neuromuscular arm of SJS behaves as a congenital distal peripheral nerve hyperexcitability rather than as a myopathy or a nerve-trunk neuropathy. Nerve conduction along the trunk, neuromuscular transmission and compound nerve action potentials are normal, while the preterminal axon shows long non-myelinated segments and the synaptic gutters are denervated and reinnervated by terminal sprouting. Needle EMG detects complex repetitive discharges without transmission failure.

motor neuron CL:0000100 Schwann cell CL:0002573

neuromuscular junction GO:0031594

Downstream

Continuous Muscle Fiber Hyperactivity Ectopic distal discharges drive sustained involuntary muscle-fiber activity, clinically expressed as myotonia/neuromyotonia and stiffness.

Show evidence (3 references)

PMID:24011702 SUPPORT Human Clinical

"Needle electromyography detected complex repetitive discharges without any evidence for neuromuscular transmission failure."

Electrophysiological signature of the hyperexcitability node in a human patient.

PMID:24011702 SUPPORT Human Clinical

"Electroneuromyography showed normal nerve conduction, neuromuscular transmission, and compound nerve action potentials while multiple measures of peripheral nerve excitability along the nerve trunk did not detect changes."

Constrains the node: the abnormality is distal and local, not a generalized nerve-trunk excitability change. Recorded as PARTIAL because it refines rather than simply confirms the claim, and rests on a single adult patient.

PMID:33767660 SUPPORT Human Clinical

"Needle electromyography revealed extensive complex repetitive discharges and multiple polyphasic motor unit action potentials in axial and limb muscles at rest."

Independent patient with the same resting-discharge signature.

Continuous Muscle Fiber Hyperactivity

Sustained involuntary activity of skeletal muscle fibers produces the permanent myotonia (prolonged failure of muscle relaxation), generalized stiffness and percussion myotonia that define the disorder clinically, and contributes with the skeletal arm to fixed joint contractures and the characteristic facial appearance.

skeletal muscle fiber CL:0008002

skeletal muscle contraction GO:0003009 ↑ INCREASED

Animal models

Perlecan C1532Yneo hypomorphic knock-in mouse Mouse recapitulates The line reproduces SJS neuromyotonia with spontaneous EMG activity.

Show evidence (2 references)

PMID:11101850 SUPPORT Human Clinical

"Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia"

Defines permanent myotonia as a cardinal feature of the disorder.

PMID:18647752 SUPPORT Model Organism

"These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG)."

The perlecan-hypomorphic mouse lines reproduce the spontaneous activity that characterizes this node.

Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation

Perlecan is deposited in the pericellular matrix surrounding chondrocytes, where domain IV of the core protein drives prechondrocyte clustering — the condensation step that initiates cartilage formation — through deactivation of FAK/Src and reduced ERK signaling, with induction of Sox9, N-cadherin, collagen II and aggrecan. An SJS-associated domain IV missense change (R3452Q) limits this clustering activity, and SJS-associated mutations in the disulfide-rich region 3 destabilize the protein.

chondrocyte CL:0000138

cartilage development GO:0051216 ↓ DECREASED chondrocyte differentiation GO:0002062 ⚠ ABNORMAL

Experimental models

ATDC5 prechondrocyte clustering assay with perlecan domain IV constructs CELL LINE Introducing the SJS patient allele into the domain IV construct reduces its clustering activity, connecting the mutation to the condensation step.

Downstream

Chondrodysplasia and Skeletal Deformity Failure of the condensation and growth-plate program yields the chondrodysplastic skeleton.

Show evidence (3 references)

PMID:30203597 SUPPORT In Vitro

"A region within domain IV of perlecan (HSPG2 IV-3) was found to promote rapid prechondrocyte clustering."

Establishes the normal function that is lost at this node.

PMID:30203597 SUPPORT In Vitro

"Introduction of the mutation (R3452Q) associated with the human skeletal disorder Schwartz-Jampel syndrome limited HSPG2 IV-3-induced clustering."

Directly ties an SJS patient allele to loss of the chondrocyte-clustering function.

PMID:40118124 SUPPORT In Vitro

"Four of the mutations resulted in decreased yields and thermal stability compared to the wild-type protein."

Structural work showing most tested SJS mutations destabilize perlecan region 3. Recorded as PARTIAL because the same study found one SJS mutation (P1019L) that was more thermally stable than wild type, so destabilization is not a universal mechanism.

Chondrodysplasia and Skeletal Deformity

The skeletal arm of the disorder: reduced stature, kyphoscoliosis, bowing of the diaphyses, irregular epiphyses and joint contractures, with growth-plate disorganization. In perlecan-hypomorphic mice the same reduction produces smaller size, impaired mineralization, misshapen bones, a flat face and joint dysplasia, together with transient expansion of hypertrophic cartilage in the growth plate.

hypertrophic chondrocyte CL:0000743

ossification GO:0001503 ⚠ ABNORMAL bone development GO:0060348 ⚠ ABNORMAL

Animal models

Perlecan C1532Yneo hypomorphic knock-in mouse Mouse recapitulates Reduced perlecan secretion produces a skeletal phenotype characteristic of SJS patients, with growth-plate changes.

Perlecan C1532Y point-mutation-only mouse Mouse fails to recapitulate Mice carrying only the SJS-associated C1532Y substitution show a mild phenotype inconsistent with SJS.

Show evidence (3 references)

PMID:11101850 SUPPORT Human Clinical

"skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses"

Enumerates the skeletal features modeled at this node.

PMID:17213231 SUPPORT Model Organism

"Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis."

In vivo recapitulation of the skeletal arm when perlecan is reduced.

PMID:17213231 SUPPORT Model Organism

"Moreover, C1532Yneo mice displayed transient expansion of hypertrophic cartilage in the growth plate concomitant with radial trabecular bone orientation."

Growth-plate correlate of the chondrodysplasia, supporting the hypertrophic-chondrocyte annotation on this node.

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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

24

Digestive 1

Feeding Difficulties HP:0011968

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"The patient had difficulty opening her mouth and swallowing. She was unable to eat solid foods and was bottle fed."

Case-level documentation of the feeding difficulty.

Ear 1

Abnormal Pinna Morphology HP:0000377

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast"

Lists unusual pinnae in the SJS1 clinical spectrum.

Eye 2

Myopia HP:0000545

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast"

Lists myopia in the SJS1 clinical spectrum.

Ectopia Lentis HP:0001083

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"myopia (25), ectopia lentis (26), blepharophimosis, decreased subcutaneous tissue, small testis, malignant hyperpyrexia"

Lists ectopia lentis among the ocular manifestations of other organ systems in SJS.

Head and Neck 3

Narrow Mouth HP:0000160

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present."

Case-level documentation of microstomia with pursed lips.

Cleft Palate HP:0000175

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present."

Case-level documentation of posterior cleft palate.

Micrognathia HP:0000347

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia"

Lists micrognathia among the developmental skeletal features of the disorder.

Limbs 1

Bowing of the Long Bones HP:0006487

Show evidence (1 reference)

PMID:11101850 SUPPORT Human Clinical

"skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses"

Names bowing of the diaphyses among the skeletal features.

Metabolism 1

Malignant Hyperthermia Susceptibility HP:0002047

Show evidence (2 references)

PMID:38285320 SUPPORT Human Clinical

"the presence of jaw muscle tightness, bony deformities, and the risk of malignant hyperthermia may increase surgical complications"

States the malignant-hyperthermia risk explicitly and ties it to increased surgical complications, which is why it is curated as a management-relevant phenotype.

PMID:33767660 SUPPORT Human Clinical

"myopia (25), ectopia lentis (26), blepharophimosis, decreased subcutaneous tissue, small testis, malignant hyperpyrexia"

Independently lists malignant hyperpyrexia among the reported manifestations, corroborating the susceptibility.

Musculoskeletal 10

Myotonia HP:0002486

Show evidence (1 reference)

PMID:11101850 SUPPORT Human Clinical

"permanent myotonia (prolonged failure of muscle relaxation)"

Names myotonia as a defining feature of the disorder.

Generalized Muscle Stiffness HP:0003552

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterized by typical facial dysmorphism, generalized muscle stiffness, joint contracture, and skeletal abnormalities."

Lists generalized muscle stiffness among the defining clinical features.

Kyphoscoliosis HP:0002751

Show evidence (1 reference)

PMID:11101850 SUPPORT Human Clinical

"skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses"

Names kyphoscoliosis among the skeletal features.

Epiphyseal Dysplasia HP:0002656

Show evidence (1 reference)

PMID:11101850 SUPPORT Human Clinical

"skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses"

Names irregular epiphyses among the skeletal features.

Joint Contractures Flexion contracture HP:0001371

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"Skeletal abnormalities include short stature and contractures of large joints"

States contractures of large joints as a skeletal feature of SJS1.

Camptodactyly HP:0012385

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"long thin fingers and campodactyly in the bilateral 5th fingers were present"

Case-level documentation of camptodactyly (spelled "campodactyly" in the source).

Pectus Carinatum HP:0000768

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast"

Lists pigeon breast (pectus carinatum) in the SJS1 clinical spectrum.

Platyspondyly HP:0000926

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia"

Lists platyspondyly among the developmental skeletal features.

Coronal Cleft Vertebrae HP:0003417

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia"

Lists coronal clefting of the vertebral body among the developmental skeletal features.

Hip Dysplasia HP:0001385

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia"

Names developmental hip dysplasia among the developmental skeletal features.

Growth 1

Short Stature HP:0004322

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"Skeletal abnormalities include short stature and contractures of large joints"

States short stature as a skeletal feature of SJS1.

Other 4

Mask-Like Facies HP:0000298

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"a distinctive facial appearance with a pointed mouth and narrowed eye fissures"

Describes the characteristic facial appearance recorded here.

Blepharophimosis HP:0000581

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"is characterized by congenital blepharophimosis, distinctive facies, muscle stiffness, and joint deformities"

Records congenital blepharophimosis as a characteristic feature.

Blepharospasm HP:0000643

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present."

Case-level documentation of blepharospasm.

Skeletal Muscle Hypertrophy HP:0003712

Show evidence (3 references)

PMID:33767660 SUPPORT Human Clinical

"Neuromuscular hyperactivity leads to muscle cramps, blepharospasm, pursed lip, mask face, and muscle hypertrophy"

Attributes muscle hypertrophy directly to the neuromuscular hyperactivity that this entry models, placing it downstream of the same mechanism as the myotonia and blepharospasm.

PMID:33767660 SUPPORT Model Organism

"In addition, perlecan deficiency causes hypertrophy in fast-twitch muscles by reducing myostatin signaling (1) and also can cause atrophy in the slow-twitch muscles, possibly through disinhibition of autophagy related to reduced Akt/mTORC1 signaling (2)."

The competing molecular account from the same review, curated as PARTIAL because it applies specifically to fast-twitch fibres and predicts the opposite change in slow-twitch fibres, and MODEL_ORGANISM because the sentence relays mouse work cited by this human case report. Modeled at the "Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation" node.

PMID:37761893 SUPPORT Human Clinical

"Global hypertrophy was evident and motility was completed but clumsy and limited by stiffness."

Independent case-level observation of the hypertrophy in a molecularly confirmed SJS1 patient.

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Genetic Associations

1

HSPG2

Gene: HSPG2 hgnc:5273 relationship_type: CAUSATIVE variant_origin: GERMLINE

Autosomal recessive inheritance

Show evidence (3 references)

PMID:11101850 SUPPORT Human Clinical

"In so doing, we have identified the first human mutations in HSPG2"

The original gene-identification report establishing HSPG2 as causal.

PMID:16927315 SUPPORT Human Clinical

"All but four mutations were private, and we found no evidence for a founder effect."

Supports the allelic-heterogeneity statement recorded in this block.

PMID:37761893 SUPPORT Human Clinical

"Schwartz-Jampel syndrome type 1 (SJS1) is a rare autosomal recessive musculoskeletal disorder caused by various mutations in the HSPG2 gene encoding the protein perlecan, a major component of basement membranes."

Contemporary confirmation of HSPG2 as the causal gene for SJS1.

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Medical Actions

9

Carbamazepine

Action: Pharmacotherapy NCIT:C15986

Agent: carbamazepine CHEBI:3387

Sodium-channel-blocking antiepileptic used off-label as an antimyotonic; a reported case showed reduced muscle rigidity and improved motor skills within about six weeks of starting oral therapy.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Reduces the sustained involuntary muscle activity responsible for stiffness and rigidity; it does not address the perlecan deficit.

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"Oral carbamazepine therapy was initiated and 1.5 months later the patient`s muscle rigidity had decreased and her motor skills had improved."

Reports the clinical response — reduced muscle rigidity — which is the symptom the muscle-hyperactivity node models. Note the source's backtick apostrophe is reproduced verbatim.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms."

Places carbamazepine within the standard antimyotonic pharmacotherapy options for SJS.

Mexiletine

Action: Pharmacotherapy NCIT:C15986

Agent: mexiletine CHEBI:6916

Sodium-channel-blocking antiarrhythmic used as an antimyotonic agent, one of the pharmacologic options commonly used to reduce myotonic symptoms in SJS.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Symptomatic suppression of the sustained muscle activity.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms."

Names mexiletine among the agents used to reduce the myotonic symptoms modeled at this node.

Lamotrigine

Action: Pharmacotherapy NCIT:C15986

Agent: lamotrigine CHEBI:6367

Sodium-channel-blocking antiepileptic listed among the pharmacologic agents commonly used to reduce myotonic symptoms in SJS.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Symptomatic suppression of the sustained muscle fiber activity; like the other antimyotonics it acts distal to the perlecan deficit.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms."

Names lamotrigine among the agents used to reduce the myotonic symptoms modeled at this node.

Flecainide

Action: Pharmacotherapy NCIT:C15986

Agent: flecainide CHEBI:75984

Class Ic sodium-channel-blocking antiarrhythmic listed among the pharmacologic agents commonly used to reduce myotonic symptoms in SJS.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Symptomatic suppression of the sustained muscle fiber activity through sodium-channel block.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms."

Names flecainide among the agents used to reduce the myotonic symptoms modeled at this node.

Phenytoin

Action: Pharmacotherapy NCIT:C15986

Agent: phenytoin CHEBI:8107

Sodium-channel-blocking anticonvulsant used as an antimyotonic. In a genetically confirmed SJS type 1A case it was given with carbamazepine from age 3 and effectively alleviated the myotonic symptoms before the myotonia later worsened.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Membrane stabilization of excitable tissue by sodium-channel block, reducing the sustained fiber activity.

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"However, anticonvulsivants, such as carbamazepine or phenytoin, blocking sodium channels with stabilization of the membrane of excitable tissues, represent the most used drugs, followed by antiarrhythmic therapies such as mexiletine, procainamide and quinidine."

States both the mechanism (sodium-channel block stabilizing excitable membrane) and phenytoin's place as one of the two most-used drugs.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Since the age of 3, he had been prescribed carbamazepine and phenytoin, which effectively alleviated his myotonic symptoms."

Case-level report of symptomatic benefit in a molecularly confirmed patient, though given in combination with carbamazepine.

Non-Pharmacologic Physical Modalities

Action: Physical Therapy NCIT:C15302

Warming, massage, pre-exercise warm-up and gradual stretching, used in combination with antimyotonic medication to reduce stiffness. Reported in the SJS management literature rather than trialed.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Reduces the stiffness produced by sustained fiber activity; adjunctive to pharmacotherapy rather than an alternative to it.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Non-pharmacologic modalities, such as warming, massage, pre-exercise warm-up, and gradual stretching combined with medications, have also been reported."

Names the physical modalities and states they are used combined with medication.

Oculoplastic Surgery for Blepharophimosis and Blepharospasm

Action: Surgical Procedure NCIT:C15329

Myectomy, levator resection and lateral canthopexy for the eyelid anomalies and facial spasm, reported to give excellent and long-lasting relief. Outcomes in SJS specifically are mixed — one molecularly confirmed patient underwent blepharophimosis surgery without significant improvement. Anesthetic and surgical risk is materially raised in SJS (see the Malignant Hyperthermia phenotype), which is why this is not a first-line option.

Target Phenotypes: Blepharospasm HP:0000643

Show evidence (3 references)

PMID:38285320 SUPPORT Human Clinical

"Surgical techniques, such as myectomy, levator resection, and lateral canthopexy, offer excellent and long-lasting relief for blepharospasm and eyelid anomalies"

Names the specific procedures and the reported benefit.

PMID:38285320 SUPPORT Human Clinical

"However, the presence of jaw muscle tightness, bony deformities, and the risk of malignant hyperthermia may increase surgical complications"

The safety qualifier from the same source; recorded as PARTIAL because it constrains rather than supports the intervention.

PMID:37761893 SUPPORT Human Clinical

"He underwent surgery for blepharophimosis, without significant improvement."

A negative case-level outcome, curated so the entry does not report only the favorable surgical series.

Botulinum Toxin Type A Injection

Action: Pharmacotherapy NCIT:C15986

Agent: botulinum toxin type A CHEBI:3160

Local chemodenervation of overactive facial muscles. Reported to produce significant clinical improvement in a patient with SJS type 1A whose difficulty opening the eyes and mouth was limiting daily activity; dose and interval must be individually tailored, and pediatric dosing kept minimal.

Mechanism Target:

INHIBITS Continuous Muscle Fiber Hyperactivity — Blocks neuromuscular transmission in the injected muscles, interrupting the sustained hyperactivity locally. Acts distal to the perlecan deficit and is purely symptomatic and focal.

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"Botulinum toxin A injection was administered and demonstrated significant clinical improvement after the treatment."

Reports the clinical effect of focal chemodenervation on the muscle hyperactivity.

Target Phenotypes: Blepharospasm HP:0000643

Show evidence (1 reference)

PMID:38285320 SUPPORT Human Clinical

"However, the optimal doses and intervals must be individually tailored to optimize symptom control."

Recorded as PARTIAL because the supporting evidence is a single case and the source itself notes that dosing is not standardized.

Symptomatic and Supportive Management

Action: Supportive Care NCIT:C15747

Care is directed at symptom control rather than at the underlying perlecan deficiency; several drugs have been used with variable efficacy, and management is otherwise supportive.

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"Therapy is mainly focused on symptom management and several drugs have been administered with different efficacy."

States that management is symptomatic with variable drug efficacy.

🔬

Biochemical Markers

2

Elevated Serum Creatine Kinase (Present)

Context: Routine neuromuscular work-up before molecular confirmation

Show evidence (2 references)

PMID:37761893 SUPPORT Human Clinical

"The creatine kinacse (CK) level was elevated (750 U/L), and electromyograph (EMG) revealed myotonic discharges with high-frequency repetitive activity."

The first of two serial CK values in a molecularly confirmed SJS1 case. The source's misspelling of "kinacse" is reproduced verbatim.

PMID:37761893 SUPPORT Human Clinical

"The CK was 800 U/L, while other blood tests, including potassium and sodium, were normal."

The second serial value, at age 6.

Normal Serum Potassium and Sodium (Present)

Context: Differential diagnosis against the periodic paralyses

Show evidence (1 reference)

PMID:37761893 SUPPORT Human Clinical

"The CK was 800 U/L, while other blood tests, including potassium and sodium, were normal."

States the normal potassium and sodium in a molecularly confirmed SJS1 patient presenting with stiffness and myotonia.

🔬

Diagnosis

2

Clinical recognition with molecular confirmation

The diagnostic route for SJS1. The combination of myotonic signs with the typical facial features and skeletal dysplasia is regarded as pathognomonic, so the diagnosis is made clinically and then confirmed by sequencing HSPG2; instrumental studies are supportive rather than discriminating.

genetic testing NCIT:C15709

Worth flagging for anyone extending this section: the same review states that EMG and muscle biopsy "do not provide any additional clues useful for the diagnosis of SJS1", so their role is to place the patient in the myotonic-disorder differential, not to establish SJS.

Show evidence (2 references)

PMID:37761893 SUPPORT Human Clinical

"Hence, SJS1 diagnosis mainly relies on clinical data, then needing molecular confirmation."

States the diagnostic strategy directly — clinical recognition first, molecular confirmation second.

PMID:38285320 SUPPORT Human Clinical

"While electromyography (EMG) signs of myotonia and X-ray abnormalities are commonly used in diagnosing SJS, we opted for genetic confirmation instead of EMG"

A worked case in which molecular testing substituted for EMG, supporting genetic confirmation as sufficient.

Needle electromyography

EMG in SJS shows continuous high-frequency repetitive discharges — often complex repetitive discharges lacking the waxing-and-waning of classical myotonia. It establishes that the stiffness is of neuromuscular origin and is the instrumental correlate of the Continuous Muscle Fiber Hyperactivity node, but it does not by itself distinguish SJS from other myotonic disorders.

electromyography NCIT:C38056

Show evidence (2 references)

PMID:37761893 SUPPORT Human Clinical

"The creatine kinacse (CK) level was elevated (750 U/L), and electromyograph (EMG) revealed myotonic discharges with high-frequency repetitive activity."

Reports the characteristic EMG finding in a molecularly confirmed case.

PMID:33767660 SUPPORT Human Clinical

"In previous literature, needle EMG often reveals CRDs with higher frequency and lack of typical waxing and waning compared to typical myotonia discharge"

Characterizes the discharge morphology and, importantly, distinguishes it from classical myotonic discharges.

📊

Prevalence

2

Worldwide

Point Prevalence <1 in 1,000,000

Reported as a prevalence below 1 in 1,000,000. The source renders the figure as "<1/106" (i.e. 1/10^6) after superscript flattening.

Show evidence (1 reference)

PMID:33767660 SUPPORT Human Clinical

"a rare autosomal recessive disease with a prevalence of <1/106"

States the population prevalence band used for this record.

Worldwide (published cases)

Cases In Literature Ultra Rare

Cumulative published case count as of 2019; complements rather than duplicates the population-rate record above.

Show evidence (1 reference)

PMID:32134596 SUPPORT Human Clinical

"Approximately 150 cases have been reported in literature."

Gives the cumulative number of reported cases, the appropriate measure for an ultra-rare disorder with no population-based ascertainment.

🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Schwartz-Jampel Syndrome:

Stuve-Wiedemann syndrome (formerly "Schwartz-Jampel syndrome type 2")

Overlapping Features Severe neonatal condition with bowed long bones, respiratory distress, feeding difficulties and hyperthermic episodes causing early lethality. Historically classified as SJS type 2 on clinical overlap, it is caused by null LIFR mutations with impaired JAK/STAT3 signaling and is a genetically distinct disorder — not an allelic form of the HSPG2 disease modeled here.

Distinguishing Features

Causal gene LIFR (5p13.1) rather than HSPG2
Hyperthermic episodes causing early lethality
No perlecan deficiency

Show evidence (1 reference)

PMID:14740318 SUPPORT Human Clinical

"We conclude, therefore, that SWS and SJS2 represent a single clinically and genetically homogeneous condition due to null mutations in the LIFR gene on chromosome 5p13."

Establishes that the historical "SJS type 2" is Stuve-Wiedemann syndrome, a distinct LIFR disorder.

Dyssegmental dysplasia, Silverman-Handmaker type (DDSH)

Overlapping Features Lethal autosomal recessive neonatal skeletal dysplasia caused by functional null mutations of the same gene, HSPG2. Allelic with SJS but at the null end of the perlecan dosage series.

Distinguishing Features

Functional-null rather than hypomorphic HSPG2 alleles
Truncated perlecan is not secreted at all, rather than secreted at reduced level
Neonatal lethality with dyssegmental ossification of the spine

Show evidence (2 references)

PMID:11279527 SUPPORT Human Clinical

"Thus, DDSH is caused by a functional null mutation of HSPG2."

Establishes the allelic but mechanistically distinct null disorder.

PMID:11279527 SUPPORT In Vitro

"Biochemically, truncated perlecan was not secreted by the patient fibroblasts, but was degraded to smaller fragments within the cells."

Gives the biochemical distinction from the hypomorphic SJS alleles, which still permit reduced secretion.

🧫

Experimental Models

2

SJS patient-derived primary dermal fibroblasts PRIMARY_CELL_CULTURE

Primary fibroblasts from a patient homozygous for HSPG2 c.1125C>G (p.Cys375Trp), used to test the functional consequence of the variant. Secreted perlecan and migration were reduced while proliferation was unaffected, giving a cell-level readout of the hypomorphic effect.

Organism

human NCBITaxon:9606

Publication

PMID:33767660

Pathograph links

Reduced Perlecan Secretion into Basement Membranes measures fidelity: moderate Directly quantifies secreted perlecan from cells carrying a patient genotype.

Limitations: Dermal fibroblasts are not the disease-relevant chondrocyte or neuromuscular-junction compartment, so they report the secretion defect but not its tissue-specific consequences; n = 1 genotype.

Readouts

Secreted perlecan level

Direction: DECREASED

Interpretation: Cell-level confirmation that the patient allele reduces perlecan secretion.

Show evidence (1 reference)

PMID:33767660 SUPPORT In Vitro

"At cellular levels, mutant primary fibroblasts had reduced levels of secreted perlecan and impaired migration ability but normal capability of proliferation."

Reports the measured reduction in secreted perlecan.

Show evidence (1 reference)

PMID:33767660 SUPPORT In Vitro

"The pathogenic nature of this missense mutation was demonstrated by in silico pathogenicity assessment, clinical presentations, and cellular function of primary fibroblast derived from patients."

States that the patient fibroblast assay is the functional evidence for the variant's effect, making it informative for this node.

ATDC5 prechondrocyte clustering assay with perlecan domain IV constructs CELL_LINE

ATDC5 cells, a model of early chondrogenesis, exposed to recombinant perlecan domain IV subdomain (HSPG2 IV-3) with and without the SJS-associated R3452Q substitution, reading out prechondrocyte clustering and condensation markers.

Organism

mouse NCBITaxon:10090

Publication

PMID:30203597

Pathograph links

Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation perturbs fidelity: moderate Introducing the SJS patient allele into the domain IV construct reduces its clustering activity, connecting the mutation to the condensation step.

Limitations: An immortalized murine cell line exposed to an isolated recombinant subdomain, not full-length perlecan in native pericellular matrix; the assay also required thermal unfolding to maximize activity, so the relationship between assay activity and in vivo function is indirect.

Readouts

Prechondrocyte clustering

Direction: DECREASED

Interpretation: Loss of clustering activity when the SJS allele is present is the cell-level correlate of impaired condensation.

Show evidence (1 reference)

PMID:30203597 SUPPORT In Vitro

"Introduction of the mutation (R3452Q) associated with the human skeletal disorder Schwartz-Jampel syndrome limited HSPG2 IV-3-induced clustering."

Reports the measured reduction in clustering.

Show evidence (1 reference)

PMID:30203597 SUPPORT In Vitro

"Perlecan subdomains were tested for chondrogenic properties in ATDC5 cells, a model for early chondrogenesis."

Identifies the assay system and its purpose, supporting its use for this node.

🐁

Animal Models

3

Perlecan C1532Yneo hypomorphic knock-in mouse

Knock-in of a human SJS missense allele with the Neo cassette retained, which down-regulates Hspg2 transcription and so lowers secreted perlecan further than the point mutation alone. The line reproduces both arms of the human disease and was the first animal model of SJS neuromyotonia.

Species

Mouse

Genotype

Hspg2 p.C1532Y knock-in retaining the Neo selection cassette (C1532Yneo)

Genes

HSPG2 hgnc:5273

Publication

PMID:18647752

Pathograph links

Endplate Acetylcholinesterase Deficiency recapitulates fidelity: high Endplate AChE is reduced as a direct consequence of synaptic perlecan deficiency, with an otherwise intact junction.

Limitations: The reduction is partial and, on its own, was not sufficient to generate resting spontaneous EMG activity in the diaphragm, so the model shows that AChE deficiency is necessary but leaves the sufficiency question open.

Readouts

Endplate acetylcholinesterase level

Direction: DECREASED

Interpretation: Direct measurement of the synaptic AChE deficit at the node.

Show evidence (1 reference)

PMID:18647752 SUPPORT Model Organism

"Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization."

Reports the measured endplate AChE reduction.

Show evidence (1 reference)

PMID:18647752 SUPPORT Model Organism

"It has been suggested that SJS neuromyotonia may result from endplate acetylcholinesterase (AChE) deficiency, but this hypothesis has never been investigated in vivo due to the lack of an animal model for neuromyotonia."

Establishes that this model exists precisely to test the endplate-AChE mechanism in vivo, making it informative for this node.

Continuous Muscle Fiber Hyperactivity recapitulates fidelity: high The line reproduces SJS neuromyotonia with spontaneous EMG activity.

Limitations: Spontaneous activity was absent at rest in the diaphragm despite the AChE deficiency, indicating that additional changes contribute in vivo.

Readouts

Spontaneous activity on electromyogram

Direction: INCREASED

Interpretation: Electrophysiological correlate of the human myotonia/neuromyotonia phenotype.

Show evidence (1 reference)

PMID:18647752 SUPPORT Model Organism

"These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG)."

Reports the spontaneous EMG activity measured in the model.

Show evidence (1 reference)

PMID:18647752 SUPPORT Model Organism

"These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG)."

The model reproduces the defining neuromuscular phenotype, so it is informative for this node.

Chondrodysplasia and Skeletal Deformity recapitulates fidelity: moderate Reduced perlecan secretion produces a skeletal phenotype characteristic of SJS patients, with growth-plate changes.

Limitations: The skeletal readouts include joint changes described as reminiscent of osteoarthritis and osteonecrosis, which are not the way the human phenotype is characterized, and the hypertrophic-cartilage expansion is transient.

Readouts

Skeletal size, mineralization and bone shape

Direction: ALTERED

Interpretation: Composite skeletal-survey correlate of the human chondrodysplasia.

Show evidence (1 reference)

PMID:17213231 SUPPORT Model Organism

"Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis."

Reports the measured skeletal abnormalities.

Show evidence (1 reference)

PMID:17213231 SUPPORT Model Organism

"Immunostaining, biochemistry, size measurements, skeletal studies and histology revealed Hspg2 transcriptional changes in C1532Yneo mice, leading to reduced perlecan secretion and a skeletal disease phenotype characteristic of SJS patients."

States that this line's skeletal phenotype is characteristic of SJS patients, supporting its use for this node.

Perlecan C1532Y point-mutation-only mouse

The control arm of the same knock-in series, carrying only the human SJS missense change. Its mild phenotype is a substantive negative result: it implies that the point mutation alone is not sufficient to produce the SJS skeletal phenotype in mouse, and that transcriptional down-regulation of perlecan is what drives disease in this system.

Species

Mouse

Genotype

Hspg2 p.C1532Y knock-in without the Neo cassette (C1532Y)

Genes

HSPG2 hgnc:5273

Publication

PMID:17213231

Pathograph links

Chondrodysplasia and Skeletal Deformity fails to recapitulate fidelity: low Mice carrying only the SJS-associated C1532Y substitution show a mild phenotype inconsistent with SJS.

Limitations: This is a species/allele-level mismatch rather than a technical failure: the same substitution is associated with disease in the human family in which it was found. It leaves open whether the human allele acts through an additional transcriptional effect not reproduced in mouse, or whether the human family carries a second contributing lesion.

Readouts

Skeletal phenotype severity

Direction: UNCHANGED

Interpretation: A negative result: the isolated missense allele does not reproduce the SJS skeleton in mouse.

Show evidence (1 reference)

PMID:17213231 SUPPORT Model Organism

"In contrast, C1532Y mice, harboring only the mutation associated with SJS, displayed a mild phenotype, inconsistent with SJS."

Reports the negative skeletal result for this line.

Show evidence (1 reference)

PMID:17213231 SUPPORT Model Organism

"These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS."

The authors draw the explicit negative inference recorded by this FAILS_TO_RECAPITULATE link.

Perlecan-null (Hspg2 knockout) mouse

The complete-null end of the perlecan dosage series. It models the allelic lethal disorder DDSH rather than SJS, and is included here because the contrast is what establishes SJS as a hypomorphic, dosage-dependent condition.

Species

Mouse

Genotype

Hspg2 null (knockout)

Genes

HSPG2 hgnc:5273

Publication

PMID:11279527

Pathograph links

Reduced Perlecan Secretion into Basement Membranes partially recapitulates fidelity: moderate Complete absence of perlecan produces a severe chondrodysplasia with dyssegmental ossification, delimiting the null end of the dosage series that this node models.

Limitations: The null genotype models DDSH, not SJS: it overshoots the partial reduction that characterizes SJS, so it bounds the mechanism rather than reproducing the disease.

Readouts

Chondro-osseous morphology

Direction: ALTERED

Interpretation: Establishes the phenotype produced when perlecan is absent rather than merely reduced.

Show evidence (1 reference)

PMID:11279527 SUPPORT Model Organism

"Mice lacking the perlecan gene (Hspg2) have a severe chondrodysplasia with dyssegmental ossification of the spine"

Reports the null-mouse skeletal phenotype.

Show evidence (1 reference)

PMID:11279527 SUPPORT Model Organism

"show radiographic, clinical and chondro-osseous morphology similar to a lethal autosomal recessive disorder in humans termed dyssegmental dysplasia, Silverman-Handmaker type (DDSH; MIM 224410)"

Identifies the null mouse as a model of DDSH, the allelic disorder that anchors the null end of the dosage series.

{ }

Source YAML

click to show

name: Schwartz-Jampel Syndrome
creation_date: "2026-08-17T00:00:00Z"
category: Mendelian
description: >-
  Schwartz-Jampel syndrome (SJS, chondrodystrophic myotonia) is a rare
  autosomal recessive disorder in which hypomorphic mutations of HSPG2 reduce
  secretion of perlecan, the major heparan sulfate proteoglycan of basement
  membranes and of the cartilage pericellular matrix. The resulting perlecan
  deficiency produces a two-armed phenotype that is unusual among skeletal
  dysplasias: a chondrodysplasia with short stature, kyphoscoliosis, bowed
  diaphyses and irregular epiphyses, together with continuous muscle
  hyperactivity (myotonia/neuromyotonia) with a characteristic mask-like face,
  blepharophimosis, blepharospasm and pursed lips. The neuromuscular arm is
  best explained by distal peripheral nerve hyperexcitability arising from
  synaptic acetylcholinesterase deficiency at the motor endplate — perlecan is
  the basement-membrane anchor that concentrates AChE in the synaptic cleft —
  together with preterminal nerve and neuromuscular-junction remodeling, rather
  than by a muscle-membrane channelopathy. Allelic functional-null HSPG2
  mutations instead cause the lethal neonatal dyssegmental dysplasia,
  Silverman-Handmaker type, so SJS and DDSH form a perlecan gene-dosage series.
disease_term:
  preferred_term: Schwartz-Jampel syndrome
  term:
    id: MONDO:0009717
    label: Schwartz-Jampel syndrome
parents:
- hereditary disease
- Skeletal Dysplasia
- Neuromuscular Disease
synonyms:
- chondrodystrophic myotonia
- myotonic chondrodystrophy
- Schwartz-Jampel-Aberfeld syndrome
- Aberfeld syndrome
- osteochondromuscular dystrophy
- SJS1
notes: >-
  ENTITY-IDENTITY NOTE (do not "fix" by splitting or by re-pointing the
  disease_term). Historically "Schwartz-Jampel syndrome type 2" (SJS2, neonatal
  Schwartz-Jampel syndrome) was treated as a severe allelic variant of this
  disorder. It is not: SJS2 was shown to be caused by null mutations of LIFR
  and is now recognized as Stuve-Wiedemann syndrome, a clinically and
  genetically distinct condition (PMID:14740318). This entry therefore models
  only the HSPG2/perlecan disorder — which the modern literature calls SJS
  type 1 — and MONDO:0100435 (Schwartz-Jampel syndrome type 1) is recorded as a
  narrowMatch rather than as the primary anchor, because the top-level
  Orphanet-backed MONDO:0009717 concept is the one the SJS literature uses.
  Curators using deep-research output for this disease should treat any report
  that discusses LIFR, JAK/STAT3 or hyperthermic episodes as describing a
  different entity (CLAUDE.md section 2b, Named Entity Confusion).

  The allelic severe disorder dyssegmental dysplasia, Silverman-Handmaker type
  (DDSH; HSPG2 functional null) is deliberately NOT modeled here as a subtype:
  it is a separate lethal neonatal entity with its own MONDO term and is listed
  alongside SJS as a separate row of the ISDS nosology. It is referenced in
  this entry only as the null end of the perlecan dosage series and as a
  differential diagnosis, and remains an open curation target of
  monarch-initiative/dismech#7867.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0100435
      label: Schwartz-Jampel syndrome type 1
    mapping_predicate: skos:narrowMatch
    mapping_source: MONDO (OMIM:255800)
    mapping_justification: >-
      MONDO:0100435 is the OMIM-anchored "type 1" child of MONDO:0009717. Since
      the former "type 2" was reassigned to LIFR-related Stuve-Wiedemann
      syndrome, type 1 is in practice coextensive with the HSPG2 disorder
      modeled here, but it is recorded as a narrowMatch because MONDO still
      maintains the two terms separately.
classifications:
  isds_skeletal_category:
  - classification_value: proteoglycan_core_protein_disorders
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (11th edition;
      Unger et al., PMID:36779427), group 7 "Proteoglycan core proteins
      disorders", listed there as "Schwartz-Jampel syndrome (myotonic
      chondrodystrophy)" with HSPG2. In the 2019 revision (PMID:31633310) the
      same disorder sat in the separate "Perlecan group"; the 2023 revision
      merged the perlecan and aggrecan groups into this single group.
    evidence:
    - reference: PMID:36779427
      reference_title: "Nosology of genetic skeletal disorders: 2023 revision."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        the previous “Perlecan group” and “Aggrecan group” were incorporated into the new group of “Proteoglycan core protein disorders”
      explanation: >-
        Supports the group's identity and its provenance from the merged 2019
        perlecan group. Note the scope of this citation: the consensus paper's
        text documents the restructuring, while the assignment of Schwartz-Jampel
        syndrome specifically to that group comes from the revision's Table 1
        row for the disorder, which is not quotable from the cached record.
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    SJS segregates as an autosomal recessive trait; affected individuals carry
    biallelic (homozygous or compound heterozygous) hypomorphic HSPG2 variants
    and heterozygous parents are unaffected.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia
    explanation: >-
      The disease-gene identification paper states the autosomal recessive mode
      of inheritance.
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This mutation carried by the asymptomatic parents was previously registered in a single-nucleotide polymorphism database
    explanation: >-
      Carriage of the pathogenic allele by asymptomatic parents is direct
      evidence of recessive inheritance with unaffected heterozygotes.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    Reported as a prevalence below 1 in 1,000,000. The source renders the
    figure as "<1/106" (i.e. 1/10^6) after superscript flattening.
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a rare autosomal recessive disease with a prevalence of <1/106
    explanation: >-
      States the population prevalence band used for this record.
- population: Worldwide (published cases)
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Cumulative published case count as of 2019; complements rather than
    duplicates the population-rate record above.
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Approximately 150 cases have been reported in literature.
    explanation: >-
      Gives the cumulative number of reported cases, the appropriate measure
      for an ultra-rare disorder with no population-based ascertainment.
has_subtypes:
- name: SJS1A
  display_name: SJS type 1A (milder phenotype)
  description: >-
    The milder of the two clinical severity grades of the HSPG2 disorder, with
    later recognition of myotonic signs and less severe skeletal involvement.
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SJS1 is further divided into SJS1A, a milder phenotype, and SJS1B, a severe form with neonatal onset
    explanation: >-
      Establishes the two clinical severity grades used as subtypes here.
- name: SJS1B
  display_name: SJS type 1B (severe, neonatal onset)
  description: >-
    The severe, neonatal-onset grade of the HSPG2 disorder. Distinct from the
    historical "SJS type 2", which is now Stuve-Wiedemann syndrome (LIFR).
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      SJS1 is further divided into SJS1A, a milder phenotype, and SJS1B, a severe form with neonatal onset
    explanation: >-
      Establishes the two clinical severity grades used as subtypes here.
pathophysiology:
- name: HSPG2 Hypomorphic Variation
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Biallelic partial loss-of-function variants distributed across the 97 exons
    of HSPG2 are the initiating lesion. Two molecularly distinct routes reduce
    the amount of functional perlecan reaching the extracellular space:
    truncating alleles destabilize HSPG2 mRNA through nonsense-mediated decay,
    while missense alleles affecting cysteine residues cause intracellular
    retention of the mutant core protein by ER quality control. Crucially,
    these are hypomorphic rather than null alleles — the same gene's functional
    null alleles cause dyssegmental dysplasia, Silverman-Handmaker type.
  genes:
  - preferred_term: HSPG2
    term:
      id: hgnc:5273
      label: HSPG2
  genetic_context:
    gene:
      preferred_term: HSPG2
      term:
        id: hgnc:5273
        label: HSPG2
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: PARTIAL_LOSS_OF_FUNCTION
    description: >-
      Homozygous or compound heterozygous hypomorphic germline HSPG2 alleles;
      compound heterozygosity is common because almost all reported mutations
      are private.
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here we describe mutations, including missense and splicing mutations, of the gene encoding perlecan (HSPG2) in three SJS1 families.
    explanation: >-
      Identifies HSPG2 as the SJS disease gene, the initiating lesion of this
      pathograph.
  - reference: PMID:16927315
    reference_title: Spectrum of HSPG2 (Perlecan) mutations in patients with Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutations included nine deletion or insertion (41%), six splice site (27%), five missense (23%), and two nonsense mutations (9%).
    explanation: >-
      Documents the allelic spectrum across 23 families, supporting the
      variety of variant classes recorded on this node.
  - reference: PMID:16927315
    reference_title: Spectrum of HSPG2 (Perlecan) mutations in patients with Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our analyses strengthen the idea that SJS results from hypomorphic mutations of the HSPG2 gene.
    explanation: >-
      Establishes that SJS-causing alleles are hypomorphic, not null — the
      distinction that separates SJS from DDSH.
  downstream:
  - target: Reduced Perlecan Secretion into Basement Membranes
    causal_link_type: DIRECT
    description: >-
      Both truncating (NMD) and cysteine-missense (intracellular retention)
      alleles converge on less perlecan being secreted.
    evidence:
    - reference: PMID:16927315
      reference_title: Spectrum of HSPG2 (Perlecan) mutations in patients with Schwartz-Jampel syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        truncating mutations resulted in instability of HSPG2 mRNA through nonsense mRNA-mediated decay, whereas missense mutations involving cysteine residues led to intracellular retention of perlecan, probably due to quality control pathways
      explanation: >-
        Gives the two molecular routes by which HSPG2 variants reduce secreted
        perlecan.
    - reference: PMID:33767660
      reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        At cellular levels, mutant primary fibroblasts had reduced levels of secreted perlecan and impaired migration ability but normal capability of proliferation.
      explanation: >-
        Patient-derived fibroblasts directly demonstrate reduced perlecan
        secretion downstream of the HSPG2 variant.
- name: Reduced Perlecan Secretion into Basement Membranes
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Perlecan is the major heparan sulfate proteoglycan of basement membranes
    and of the cartilage pericellular matrix. Reduced secretion lowers its
    concentration in basement membranes throughout the body, and the residual
    level sets disease severity: perlecan abundance and phenotype severity are
    inversely correlated in allelic mouse lines, and complete absence produces
    the lethal DDSH phenotype instead. From this single molecular deficit the
    pathograph branches into an ECM/cartilage arm and a synaptic/neuromuscular
    arm.
  gene_products:
  - preferred_term: perlecan
    term:
      id: NCIT:C95448
      label: Basement Membrane-Specific Heparan Sulfate Proteoglycan Core Protein
    modifier: DECREASED
  cellular_components:
  - preferred_term: basement membrane
    term:
      id: GO:0005604
      label: basement membrane
    modifier: DECREASED
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:16550923
    reference_title: Schwartz-Jampel syndrome and perlecan deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Perlecan is the major heparan sulfate proteoglycan of extracellular matrix and basement membranes that displays various functions.
    explanation: >-
      Establishes the molecular identity and localization of the deficient
      product.
  - reference: PMID:16550923
    reference_title: Schwartz-Jampel syndrome and perlecan deficiency.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      A gene-dosage effect seems to account for the correlation between the phenotype and the mutations within the gene: SJS would be associated with hypomorph mutations of the perlecan gene and DDSH would be due to the absence of functional perlecan.
    explanation: >-
      States the dosage relationship that makes residual perlecan level, rather
      than the identity of the mutation, the proximate determinant of
      phenotype.
  - reference: PMID:18647752
    reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      An inverse correlation between disease severity and perlecan secretion in the BMs was observed at the macroscopic and microscopic levels, consistent with a dosage effect.
    explanation: >-
      In vivo demonstration in allelic mouse lines that severity tracks
      residual basement-membrane perlecan.
  downstream:
  - target: Endplate Acetylcholinesterase Deficiency
    causal_link_type: DIRECT
    description: >-
      Perlecan is the basement-membrane anchor that concentrates
      acetylcholinesterase in the synaptic cleft, so synaptic perlecan loss
      lowers endplate AChE.
    evidence:
    - reference: PMID:18647752
      reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization.
      explanation: >-
        Attributes the endplate AChE deficit specifically to synaptic perlecan
        loss, excluding gross junctional disorganization as the cause.
  - target: Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation
    causal_link_type: DIRECT
    description: >-
      Perlecan deposited in the pericellular matrix around chondrocytes is
      required for prechondrocyte condensation and growth-plate organization.
    evidence:
    - reference: PMID:11101850
      reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        which underscore the importance of perlecan not only in maintaining cartilage integrity but also in regulating muscle excitability
      explanation: >-
        States both arms of the branch modeled here — cartilage integrity and
        muscle excitability — as perlecan-dependent.
  - target: Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation
    causal_link_type: DIRECT
    description: >-
      A third, cell-autonomous consequence of the perlecan deficit, independent
      of the endplate AChE route: perlecan loss releases myostatin restraint in
      fast-twitch muscle and lowers Akt/mTORC1 tone in slow-twitch muscle.
    evidence:
    - reference: PMID:33767660
      reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        In addition, perlecan deficiency causes hypertrophy in fast-twitch muscles by reducing myostatin signaling (1) and also can cause atrophy in the slow-twitch muscles, possibly through disinhibition of autophagy related to reduced Akt/mTORC1 signaling (2).
      explanation: >-
        States the perlecan-to-myostatin and perlecan-to-Akt/mTORC1 links that
        this edge models, and marks them as separate from the endplate route.
        MODEL_ORGANISM because the sentence relays mouse findings cited by this
        human case report, not the report's own patient observations.
- name: Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation
  biological_scale: MOLECULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    A signalling account of the muscle-bulk changes in perlecan deficiency that
    is separate from, and potentially additive to, the neuromuscular-hyperactivity
    account of hypertrophy. Perlecan is a myostatin-binding basement-membrane
    proteoglycan, so its loss reduces myostatin (TGF-beta family) growth
    restraint and drives hypertrophy selectively in fast-twitch muscle; in
    slow-twitch muscle the same deficit is associated instead with reduced
    Akt/mTORC1 signalling and disinhibited autophagy, producing atrophy. The
    entry records this as PROVISIONAL and the atrophy arm explicitly as
    hypothesised, because the source itself hedges the Akt/mTORC1-autophagy
    limb ("possibly through") and because the fibre-type dissection rests on
    mouse work rather than on SJS patient muscle. Curated so the entry does not
    silently assert only the weaker of the two available explanations for the
    Skeletal Muscle Hypertrophy phenotype.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: myostatin (TGF-beta family) receptor signaling
    term:
      id: GO:0007179
      label: transforming growth factor beta receptor signaling pathway
    modifier: DECREASED
  - preferred_term: Akt/mTORC1 signaling in slow-twitch muscle
    term:
      id: GO:0043491
      label: phosphatidylinositol 3-kinase/protein kinase B signal transduction
    modifier: DECREASED
  - preferred_term: TOR signaling
    term:
      id: GO:0031929
      label: TOR signaling
    modifier: DECREASED
  - preferred_term: autophagy (disinhibited in slow-twitch muscle)
    term:
      id: GO:0006914
      label: autophagy
    modifier: INCREASED
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In addition, perlecan deficiency causes hypertrophy in fast-twitch muscles by reducing myostatin signaling (1) and also can cause atrophy in the slow-twitch muscles, possibly through disinhibition of autophagy related to reduced Akt/mTORC1 signaling (2).
    explanation: >-
      The single sentence supporting both limbs of this node. Tagged
      MODEL_ORGANISM although PMID:33767660 is a human case report, because
      this particular sentence relays the fibre-type dissection from the mouse
      literature rather than the authors' own patient data. Note the source's
      own hedge ("possibly through") on the Akt/mTORC1-autophagy limb, which is
      why the node carries PROVISIONAL rather than ESTABLISHED confidence.
  notes: >-
    Deliberately NOT wired downstream to Continuous Muscle Fiber Hyperactivity:
    this is a parallel, activity-independent route to altered muscle bulk, and
    collapsing the two would assert a causal ordering the source does not make.
- name: Endplate Acetylcholinesterase Deficiency
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Perlecan tethers acetylcholinesterase in the synaptic basal lamina of the
    neuromuscular junction. In SJS the postsynaptic apparatus is structurally
    well formed, but synaptic AChE is deficient, so acetylcholine released at
    the endplate is cleared too slowly and its action is prolonged. This is a
    synapse-specific consequence of the same basement-membrane perlecan
    deficit, and is the mechanism that distinguishes SJS from the muscle
    chloride- and sodium-channel myotonias.
  locations:
  - preferred_term: neuromuscular junction
    term:
      id: GO:0031594
      label: neuromuscular junction
  molecular_functions:
  - preferred_term: acetylcholinesterase activity
    term:
      id: GO:0003990
      label: acetylcholinesterase activity
    modifier: DECREASED
  cellular_components:
  - preferred_term: synaptic cleft
    term:
      id: GO:0043083
      label: synaptic cleft
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  evidence:
  - reference: PMID:24011702
    reference_title: Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The study of muscle biopsies containing neuromuscular junctions showed well-formed post-synaptic element, synaptic acetylcholinesterase deficiency, denervation of synaptic gutters with reinnervation by terminal sprouting, and long nonmyelinated preterminal nerve segments.
    explanation: >-
      Human muscle-biopsy confirmation of synaptic AChE deficiency with an
      intact postsynaptic apparatus.
  - reference: PMID:18647752
    reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Studies of muscle contractile properties showed muscle fatigability at low frequencies of nerve stimulation and suggested that partial endplate AChE deficiency might contribute to SJS muscle stiffness by potentiating muscle force.
    explanation: >-
      Links the endplate AChE deficit functionally to the muscle stiffness
      phenotype.
  downstream:
  - target: Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling
    causal_link_type: DIRECT
    description: >-
      Prolonged cholinergic action at a structurally remodeled, partly
      amyelinated preterminal axon generates ectopic distal nerve activity.
    evidence:
    - reference: PMID:24011702
      reference_title: Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        These data support the notion of peripheral nerve hyperexcitability in SJS, which would originate distally from synergistic actions of peripheral nerve and neuromuscular junction changes as a result of perlecan deficiency.
      explanation: >-
        States the causal chain from perlecan deficiency through junctional and
        nerve changes to distal hyperexcitability.
- name: Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    The neuromuscular arm of SJS behaves as a congenital distal peripheral
    nerve hyperexcitability rather than as a myopathy or a nerve-trunk
    neuropathy. Nerve conduction along the trunk, neuromuscular transmission
    and compound nerve action potentials are normal, while the preterminal
    axon shows long non-myelinated segments and the synaptic gutters are
    denervated and reinnervated by terminal sprouting. Needle EMG detects
    complex repetitive discharges without transmission failure.
  cell_types:
  - preferred_term: motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  - preferred_term: Schwann cell
    term:
      id: CL:0002573
      label: Schwann cell
  locations:
  - preferred_term: neuromuscular junction
    term:
      id: GO:0031594
      label: neuromuscular junction
  evidence:
  - reference: PMID:24011702
    reference_title: Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Needle electromyography detected complex repetitive discharges without any evidence for neuromuscular transmission failure.
    explanation: >-
      Electrophysiological signature of the hyperexcitability node in a human
      patient.
  - reference: PMID:24011702
    reference_title: Peripheral nerve hyperexcitability with preterminal nerve and neuromuscular junction remodeling is a hallmark of Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Electroneuromyography showed normal nerve conduction, neuromuscular transmission, and compound nerve action potentials while multiple measures of peripheral nerve excitability along the nerve trunk did not detect changes.
    explanation: >-
      Constrains the node: the abnormality is distal and local, not a
      generalized nerve-trunk excitability change. Recorded as PARTIAL because
      it refines rather than simply confirms the claim, and rests on a single
      adult patient.
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Needle electromyography revealed extensive complex repetitive discharges and multiple polyphasic motor unit action potentials in axial and limb muscles at rest.
    explanation: >-
      Independent patient with the same resting-discharge signature.
  downstream:
  - target: Continuous Muscle Fiber Hyperactivity
    causal_link_type: DIRECT
    description: >-
      Ectopic distal discharges drive sustained involuntary muscle-fiber
      activity, clinically expressed as myotonia/neuromyotonia and stiffness.
    evidence:
    - reference: PMID:11101850
      reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Electromyographic investigations reveal repetitive muscle discharges, which may originate from both neurogenic and myogenic alterations.
      explanation: >-
        Connects the repetitive discharges to the sustained muscle activity,
        while preserving the original authors' agnosticism about the neurogenic
        versus myogenic origin.
- name: Continuous Muscle Fiber Hyperactivity
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    Sustained involuntary activity of skeletal muscle fibers produces the
    permanent myotonia (prolonged failure of muscle relaxation), generalized
    stiffness and percussion myotonia that define the disorder clinically, and
    contributes with the skeletal arm to fixed joint contractures and the
    characteristic facial appearance.
  cell_types:
  - preferred_term: skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: skeletal muscle contraction
    term:
      id: GO:0003009
      label: skeletal muscle contraction
    modifier: INCREASED
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Schwartz-Jampel syndrome (SJS1) is a rare autosomal recessive disorder characterized by permanent myotonia (prolonged failure of muscle relaxation) and skeletal dysplasia
    explanation: >-
      Defines permanent myotonia as a cardinal feature of the disorder.
  - reference: PMID:18647752
    reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG).
    explanation: >-
      The perlecan-hypomorphic mouse lines reproduce the spontaneous activity
      that characterizes this node.
- name: Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Perlecan is deposited in the pericellular matrix surrounding chondrocytes,
    where domain IV of the core protein drives prechondrocyte clustering — the
    condensation step that initiates cartilage formation — through
    deactivation of FAK/Src and reduced ERK signaling, with induction of Sox9,
    N-cadherin, collagen II and aggrecan. An SJS-associated domain IV missense
    change (R3452Q) limits this clustering activity, and SJS-associated
    mutations in the disulfide-rich region 3 destabilize the protein.
  cell_types:
  - preferred_term: chondrocyte
    term:
      id: CL:0000138
      label: chondrocyte
  biological_processes:
  - preferred_term: cartilage development
    term:
      id: GO:0051216
      label: cartilage development
    modifier: DECREASED
  - preferred_term: chondrocyte differentiation
    term:
      id: GO:0002062
      label: chondrocyte differentiation
    modifier: ABNORMAL
  evidence:
  - reference: PMID:30203597
    reference_title: "Perlecan/HSPG2: Signaling role of domain IV in chondrocyte clustering with implications for Schwartz-Jampel Syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      A region within domain IV of perlecan (HSPG2 IV-3) was found to promote rapid prechondrocyte clustering.
    explanation: >-
      Establishes the normal function that is lost at this node.
  - reference: PMID:30203597
    reference_title: "Perlecan/HSPG2: Signaling role of domain IV in chondrocyte clustering with implications for Schwartz-Jampel Syndrome."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Introduction of the mutation (R3452Q) associated with the human skeletal disorder Schwartz-Jampel syndrome limited HSPG2 IV-3-induced clustering.
    explanation: >-
      Directly ties an SJS patient allele to loss of the chondrocyte-clustering
      function.
  - reference: PMID:40118124
    reference_title: Structural insights on perlecan and Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Four of the mutations resulted in decreased yields and thermal stability compared to the wild-type protein.
    explanation: >-
      Structural work showing most tested SJS mutations destabilize perlecan
      region 3. Recorded as PARTIAL because the same study found one SJS
      mutation (P1019L) that was more thermally stable than wild type, so
      destabilization is not a universal mechanism.
  downstream:
  - target: Chondrodysplasia and Skeletal Deformity
    causal_link_type: DIRECT
    description: >-
      Failure of the condensation and growth-plate program yields the
      chondrodysplastic skeleton.
    evidence:
    - reference: PMID:30203597
      reference_title: "Perlecan/HSPG2: Signaling role of domain IV in chondrocyte clustering with implications for Schwartz-Jampel Syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        These findings point to a critical role for perlecan domain IV in cartilage development through triggering chondrocyte condensation.
      explanation: >-
        Supports the edge from impaired condensation to abnormal cartilage
        development.
- name: Chondrodysplasia and Skeletal Deformity
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    The skeletal arm of the disorder: reduced stature, kyphoscoliosis, bowing
    of the diaphyses, irregular epiphyses and joint contractures, with
    growth-plate disorganization. In perlecan-hypomorphic mice the same
    reduction produces smaller size, impaired mineralization, misshapen bones,
    a flat face and joint dysplasia, together with transient expansion of
    hypertrophic cartilage in the growth plate.
  biological_processes:
  - preferred_term: ossification
    term:
      id: GO:0001503
      label: ossification
    modifier: ABNORMAL
  - preferred_term: bone development
    term:
      id: GO:0060348
      label: bone development
    modifier: ABNORMAL
  cell_types:
  - preferred_term: hypertrophic chondrocyte
    term:
      id: CL:0000743
      label: hypertrophic chondrocyte
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses
    explanation: >-
      Enumerates the skeletal features modeled at this node.
  - reference: PMID:17213231
    reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis.
    explanation: >-
      In vivo recapitulation of the skeletal arm when perlecan is reduced.
  - reference: PMID:17213231
    reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Moreover, C1532Yneo mice displayed transient expansion of hypertrophic cartilage in the growth plate concomitant with radial trabecular bone orientation.
    explanation: >-
      Growth-plate correlate of the chondrodysplasia, supporting the
      hypertrophic-chondrocyte annotation on this node.
phenotypes:
- category: Neuromuscular
  name: Myotonia
  description: >-
    Permanent myotonia — prolonged failure of muscle relaxation — is a cardinal
    diagnostic feature and may appear at any age in the disease course.
  phenotype_term:
    preferred_term: Myotonia
    term:
      id: HP:0002486
      label: Myotonia
  diagnostic: true
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      permanent myotonia (prolonged failure of muscle relaxation)
    explanation: >-
      Names myotonia as a defining feature of the disorder.
- category: Neuromuscular
  name: Generalized Muscle Stiffness
  description: >-
    Generalized stiffness and cramping from continuous muscle hyperactivity;
    this is the symptom that treatment principally targets.
  phenotype_term:
    preferred_term: Muscle stiffness
    term:
      id: HP:0003552
      label: Muscle stiffness
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterized by typical facial dysmorphism, generalized muscle stiffness, joint contracture, and skeletal abnormalities.
    explanation: >-
      Lists generalized muscle stiffness among the defining clinical features.
- category: Craniofacial
  name: Mask-Like Facies
  description: >-
    A distinctive fixed facial appearance with narrowed eye fissures and a
    small, pointed/pursed mouth, produced by the combination of facial muscle
    hyperactivity and craniofacial dysmorphism.
  phenotype_term:
    preferred_term: Mask-like facies
    term:
      id: HP:0000298
      label: Mask-like facies
  diagnostic: true
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a distinctive facial appearance with a pointed mouth and narrowed eye fissures
    explanation: >-
      Describes the characteristic facial appearance recorded here.
- category: Ophthalmological
  name: Blepharophimosis
  description: Narrowed palpebral fissures, part of the characteristic facies.
  phenotype_term:
    preferred_term: Blepharophimosis
    term:
      id: HP:0000581
      label: Blepharophimosis
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      is characterized by congenital blepharophimosis, distinctive facies, muscle stiffness, and joint deformities
    explanation: >-
      Records congenital blepharophimosis as a characteristic feature.
- category: Ophthalmological
  name: Blepharospasm
  description: >-
    Involuntary eyelid closure that can significantly limit daily activities
    and is a principal target of botulinum toxin treatment.
  phenotype_term:
    preferred_term: Blepharospasm
    term:
      id: HP:0000643
      label: Blepharospasm
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present.
    explanation: >-
      Case-level documentation of blepharospasm.
- category: Craniofacial
  name: Narrow Mouth
  description: Microstomia with pursed lips, part of the characteristic facies.
  phenotype_term:
    preferred_term: Narrow mouth
    term:
      id: HP:0000160
      label: Narrow mouth
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present.
    explanation: >-
      Case-level documentation of microstomia with pursed lips.
- category: Craniofacial
  name: Cleft Palate
  description: Posterior cleft palate reported in affected individuals.
  phenotype_term:
    preferred_term: Cleft palate
    term:
      id: HP:0000175
      label: Cleft palate
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Bilateral blepharospasm, posterior cleft palate, microstomia, pursed lips, kyphoscoliosis, contracture in the elbows, long thin fingers and campodactyly in the bilateral 5th fingers were present.
    explanation: >-
      Case-level documentation of posterior cleft palate.
- category: Skeletal
  name: Short Stature
  description: Reduced stature is a consistent feature of the chondrodysplasia.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Skeletal abnormalities include short stature and contractures of large joints
    explanation: >-
      States short stature as a skeletal feature of SJS1.
- category: Skeletal
  name: Kyphoscoliosis
  description: Spinal deformity arising from the chondrodysplasia.
  phenotype_term:
    preferred_term: Kyphoscoliosis
    term:
      id: HP:0002751
      label: Kyphoscoliosis
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses
    explanation: >-
      Names kyphoscoliosis among the skeletal features.
- category: Skeletal
  name: Bowing of the Long Bones
  description: Bowing of the diaphyses of the long bones.
  phenotype_term:
    preferred_term: Bowing of the long bones
    term:
      id: HP:0006487
      label: Bowing of the long bones
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses
    explanation: >-
      Names bowing of the diaphyses among the skeletal features.
- category: Skeletal
  name: Epiphyseal Dysplasia
  description: Irregular epiphyses on skeletal survey.
  phenotype_term:
    preferred_term: Epiphyseal dysplasia
    term:
      id: HP:0002656
      label: Epiphyseal dysplasia
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      skeletal dysplasia, resulting in reduced stature, kyphoscoliosis, bowing of the diaphyses and irregular epiphyses
    explanation: >-
      Names irregular epiphyses among the skeletal features.
- category: Skeletal
  name: Joint Contractures
  description: >-
    Flexion contractures of the large joints, contributed to by both the
    skeletal dysplasia and the sustained muscle hyperactivity.
  phenotype_term:
    preferred_term: Flexion contracture
    term:
      id: HP:0001371
      label: Flexion contracture
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Skeletal abnormalities include short stature and contractures of large joints
    explanation: >-
      States contractures of large joints as a skeletal feature of SJS1.
- category: Skeletal
  name: Camptodactyly
  description: Fixed flexion of the fifth fingers reported in affected children.
  phenotype_term:
    preferred_term: Camptodactyly
    term:
      id: HP:0012385
      label: Camptodactyly
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      long thin fingers and campodactyly in the bilateral 5th fingers were present
    explanation: >-
      Case-level documentation of camptodactyly (spelled "campodactyly" in the
      source).
- category: Ophthalmological
  name: Myopia
  description: Myopia is part of the recognized SJS1 clinical spectrum.
  phenotype_term:
    preferred_term: Myopia
    term:
      id: HP:0000545
      label: Myopia
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast
    explanation: >-
      Lists myopia in the SJS1 clinical spectrum.
- category: Skeletal
  name: Pectus Carinatum
  description: Pigeon-breast chest deformity.
  phenotype_term:
    preferred_term: Pectus carinatum
    term:
      id: HP:0000768
      label: Pectus carinatum
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast
    explanation: >-
      Lists pigeon breast (pectus carinatum) in the SJS1 clinical spectrum.
- category: Craniofacial
  name: Abnormal Pinna Morphology
  description: Unusual pinnae are part of the recognized clinical spectrum.
  phenotype_term:
    preferred_term: Abnormal pinna morphology
    term:
      id: HP:0000377
      label: Abnormal pinna morphology
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      short stature, myotonia, chondrodysplasia, joint contractures, unusual pinnae, myopia and pigeon breast
    explanation: >-
      Lists unusual pinnae in the SJS1 clinical spectrum.
- category: Gastrointestinal
  name: Feeding Difficulties
  description: >-
    Difficulty opening the mouth and swallowing, with inability to take solid
    food, arising from the facial and masticatory muscle hyperactivity and
    microstomia.
  phenotype_term:
    preferred_term: Feeding difficulties
    term:
      id: HP:0011968
      label: Feeding difficulties
  evidence:
  - reference: PMID:32134596
    reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patient had difficulty opening her mouth and swallowing. She was unable to eat solid foods and was bottle fed.
    explanation: >-
      Case-level documentation of the feeding difficulty.
- category: Neuromuscular
  name: Skeletal Muscle Hypertrophy
  description: >-
    Increased muscle bulk, not attributable to training, and part of the
    cardinal SJS presentation alongside the myotonia and stiffness. The same
    source offers two non-exclusive mechanistic accounts, both curated here:
    a consequence of the sustained neuromuscular hyperactivity, and a
    fibre-type-specific signalling effect of the perlecan deficit itself
    (reduced myostatin restraint in fast-twitch muscle). Global hypertrophy in
    a genetically confirmed patient was observed to regress over follow-up.
  phenotype_term:
    preferred_term: Skeletal muscle hypertrophy
    term:
      id: HP:0003712
      label: Skeletal muscle hypertrophy
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuromuscular hyperactivity leads to muscle cramps, blepharospasm, pursed lip, mask face, and muscle hypertrophy
    explanation: >-
      Attributes muscle hypertrophy directly to the neuromuscular hyperactivity
      that this entry models, placing it downstream of the same mechanism as the
      myotonia and blepharospasm.
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      In addition, perlecan deficiency causes hypertrophy in fast-twitch muscles by reducing myostatin signaling (1) and also can cause atrophy in the slow-twitch muscles, possibly through disinhibition of autophagy related to reduced Akt/mTORC1 signaling (2).
    explanation: >-
      The competing molecular account from the same review, curated as PARTIAL
      because it applies specifically to fast-twitch fibres and predicts the
      opposite change in slow-twitch fibres, and MODEL_ORGANISM because the
      sentence relays mouse work cited by this human case report. Modeled at
      the "Fiber-Type-Specific Myostatin and Akt-mTORC1 Dysregulation" node.
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Global hypertrophy was evident and motility was completed but clumsy and limited by stiffness.
    explanation: >-
      Independent case-level observation of the hypertrophy in a molecularly
      confirmed SJS1 patient.
- category: Craniofacial
  name: Micrognathia
  description: >-
    Mandibular hypoplasia, one of the developmental skeletal features of the
    facial dysmorphism; it also contributes to the jaw tightness that
    complicates airway management.
  phenotype_term:
    preferred_term: Micrognathia
    term:
      id: HP:0000347
      label: Micrognathia
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia
    explanation: >-
      Lists micrognathia among the developmental skeletal features of the
      disorder.
- category: Skeletal
  name: Platyspondyly
  description: >-
    Flattened vertebral bodies, part of the developmental vertebral involvement
    that accompanies the kyphoscoliosis.
  phenotype_term:
    preferred_term: Platyspondyly
    term:
      id: HP:0000926
      label: Platyspondyly
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia
    explanation: >-
      Lists platyspondyly among the developmental skeletal features.
- category: Skeletal
  name: Coronal Cleft Vertebrae
  description: >-
    Coronal clefting of the vertebral bodies, reflecting two rather than one
    primary ossification centre, reported together with failure of ossification
    of the anterior half of the vertebral body.
  phenotype_term:
    preferred_term: Coronal cleft vertebrae
    term:
      id: HP:0003417
      label: Coronal cleft vertebrae
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia
    explanation: >-
      Lists coronal clefting of the vertebral body among the developmental
      skeletal features.
- category: Skeletal
  name: Hip Dysplasia
  description: >-
    Developmental dysplasia of the hip, part of the skeletal dysplasia component
    of the disorder.
  phenotype_term:
    preferred_term: Hip dysplasia
    term:
      id: HP:0001385
      label: Hip dysplasia
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Developmental skeletal symptoms include short stature, prominent supraorbital ridge, micrognathia, low-set ears, pectus carinatum, kyphoscoliosis, platyspondyly, anisospondyly, coronal cleft and failure of the anterior half of the vertebral body, pes planus, and developmental hip dysplasia
    explanation: >-
      Names developmental hip dysplasia among the developmental skeletal
      features.
- category: Ophthalmological
  name: Ectopia Lentis
  description: >-
    Dislocation or malposition of the crystalline lens, an ocular feature
    reported beyond the more common myopia and blepharophimosis.
  phenotype_term:
    preferred_term: Ectopia lentis
    term:
      id: HP:0001083
      label: Ectopia lentis
  evidence:
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      myopia (25), ectopia lentis (26), blepharophimosis, decreased subcutaneous tissue, small testis, malignant hyperpyrexia
    explanation: >-
      Lists ectopia lentis among the ocular manifestations of other organ
      systems in SJS.
- category: Neuromuscular
  name: Malignant Hyperthermia Susceptibility
  description: >-
    Susceptibility to malignant hyperthermia is the most safety-critical
    management consideration in SJS: together with the jaw muscle tightness and
    bony deformities it raises the risk of any procedure requiring general
    anaesthesia, including the myectomy, levator resection and canthopexy used
    for the blepharospasm. Recorded here as a susceptibility feature of the
    disorder rather than as an observed event in a specific patient.
  phenotype_term:
    preferred_term: Malignant hyperthermia
    term:
      id: HP:0002047
      label: Malignant hyperthermia
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the presence of jaw muscle tightness, bony deformities, and the risk of malignant hyperthermia may increase surgical complications
    explanation: >-
      States the malignant-hyperthermia risk explicitly and ties it to increased
      surgical complications, which is why it is curated as a management-relevant
      phenotype.
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      myopia (25), ectopia lentis (26), blepharophimosis, decreased subcutaneous tissue, small testis, malignant hyperpyrexia
    explanation: >-
      Independently lists malignant hyperpyrexia among the reported
      manifestations, corroborating the susceptibility.
biochemical:
- name: Elevated Serum Creatine Kinase
  presence: Present
  context: Routine neuromuscular work-up before molecular confirmation
  biomarker_term:
    preferred_term: creatine kinase measurement
    term:
      id: NCIT:C64489
      label: Creatine Kinase Measurement
  notes: >-
    CK is raised but only modestly so — 750-800 U/L in the two serial
    measurements reported for one molecularly confirmed SJS1 patient, an order
    of magnitude below the values typical of Duchenne muscular dystrophy. The
    elevation is a non-specific marker of the muscle involvement and does not
    distinguish SJS from the other myotonic disorders; it is diagnostically
    useful mainly in prompting a neuromuscular work-up.
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The creatine kinacse (CK) level was elevated (750 U/L), and electromyograph (EMG) revealed myotonic discharges with high-frequency repetitive activity.
    explanation: >-
      The first of two serial CK values in a molecularly confirmed SJS1 case.
      The source's misspelling of "kinacse" is reproduced verbatim.
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The CK was 800 U/L, while other blood tests, including potassium and sodium, were normal.
    explanation: >-
      The second serial value, at age 6.
- name: Normal Serum Potassium and Sodium
  presence: Present
  context: Differential diagnosis against the periodic paralyses
  notes: >-
    Curated as a discriminating NEGATIVE finding rather than an abnormality.
    Muscle stiffness with a normal serum potassium argues against the
    hyperkalaemic and hypokalaemic periodic paralyses, which share the episodic
    weakness/stiffness presentation but are defined by a potassium shift. No
    biomarker_term is bound because the finding is the normality of the
    electrolytes, not a positive analyte abnormality.
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The CK was 800 U/L, while other blood tests, including potassium and sodium, were normal.
    explanation: >-
      States the normal potassium and sodium in a molecularly confirmed SJS1
      patient presenting with stiffness and myotonia.
diagnosis:
- name: Clinical recognition with molecular confirmation
  description: >-
    The diagnostic route for SJS1. The combination of myotonic signs with the
    typical facial features and skeletal dysplasia is regarded as
    pathognomonic, so the diagnosis is made clinically and then confirmed by
    sequencing HSPG2; instrumental studies are supportive rather than
    discriminating.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hence, SJS1 diagnosis mainly relies on clinical data, then needing molecular confirmation.
    explanation: >-
      States the diagnostic strategy directly — clinical recognition first,
      molecular confirmation second.
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      While electromyography (EMG) signs of myotonia and X-ray abnormalities are commonly used in diagnosing SJS, we opted for genetic confirmation instead of EMG
    explanation: >-
      A worked case in which molecular testing substituted for EMG, supporting
      genetic confirmation as sufficient.
  notes: >-
    Worth flagging for anyone extending this section: the same review states
    that EMG and muscle biopsy "do not provide any additional clues useful for
    the diagnosis of SJS1", so their role is to place the patient in the
    myotonic-disorder differential, not to establish SJS.
- name: Needle electromyography
  description: >-
    EMG in SJS shows continuous high-frequency repetitive discharges — often
    complex repetitive discharges lacking the waxing-and-waning of classical
    myotonia. It establishes that the stiffness is of neuromuscular origin and
    is the instrumental correlate of the Continuous Muscle Fiber Hyperactivity
    node, but it does not by itself distinguish SJS from other myotonic
    disorders.
  diagnosis_term:
    preferred_term: electromyography
    term:
      id: NCIT:C38056
      label: Electromyography
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The creatine kinacse (CK) level was elevated (750 U/L), and electromyograph (EMG) revealed myotonic discharges with high-frequency repetitive activity.
    explanation: >-
      Reports the characteristic EMG finding in a molecularly confirmed case.
  - reference: PMID:33767660
    reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In previous literature, needle EMG often reveals CRDs with higher frequency and lack of typical waxing and waning compared to typical myotonia discharge
    explanation: >-
      Characterizes the discharge morphology and, importantly, distinguishes it
      from classical myotonic discharges.
genetic:
- name: HSPG2
  gene_term:
    preferred_term: HSPG2
    term:
      id: hgnc:5273
      label: HSPG2
  presence: PRESENT
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: Autosomal recessive inheritance
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
  frequency: >-
    The only gene known to cause Schwartz-Jampel syndrome; almost all reported
    alleles are private, with no founder effect identified.
  notes: >-
    Variants are distributed across the whole gene rather than clustering in a
    hotspot, and both truncating and missense classes are pathogenic. Whether a
    given allele produces a hypomorphic or a functional-null protein determines
    whether the phenotype is SJS or the lethal allelic disorder DDSH.
  evidence:
  - reference: PMID:11101850
    reference_title: "Perlecan, the major proteoglycan of basement membranes, is altered in patients with Schwartz-Jampel syndrome (chondrodystrophic myotonia)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In so doing, we have identified the first human mutations in HSPG2
    explanation: >-
      The original gene-identification report establishing HSPG2 as causal.
  - reference: PMID:16927315
    reference_title: Spectrum of HSPG2 (Perlecan) mutations in patients with Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All but four mutations were private, and we found no evidence for a founder effect.
    explanation: >-
      Supports the allelic-heterogeneity statement recorded in this block.
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Schwartz-Jampel syndrome type 1 (SJS1) is a rare autosomal recessive musculoskeletal disorder caused by various mutations in the HSPG2 gene encoding the protein perlecan, a major component of basement membranes.
    explanation: >-
      Contemporary confirmation of HSPG2 as the causal gene for SJS1.
treatments:
- name: Carbamazepine
  description: >-
    Sodium-channel-blocking antiepileptic used off-label as an antimyotonic; a
    reported case showed reduced muscle rigidity and improved motor skills
    within about six weeks of starting oral therapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: carbamazepine
      term:
        id: CHEBI:3387
        label: carbamazepine
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Reduces the sustained involuntary muscle activity responsible for
      stiffness and rigidity; it does not address the perlecan deficit.
    evidence:
    - reference: PMID:32134596
      reference_title: "Schwartz Jampel syndrome responding positively to carbamazepine therapy: a case report and a novel mutation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Oral carbamazepine therapy was initiated and 1.5 months later the patient`s muscle rigidity had decreased and her motor skills had improved.
      explanation: >-
        Reports the clinical response — reduced muscle rigidity — which is the
        symptom the muscle-hyperactivity node models. Note the source's
        backtick apostrophe is reproduced verbatim.
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms.
    explanation: >-
      Places carbamazepine within the standard antimyotonic pharmacotherapy
      options for SJS.
  notes: >-
    Evidence is at the level of single case reports; no controlled trial exists
    in this ultra-rare disorder.
- name: Mexiletine
  description: >-
    Sodium-channel-blocking antiarrhythmic used as an antimyotonic agent, one
    of the pharmacologic options commonly used to reduce myotonic symptoms in
    SJS.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: mexiletine
      term:
        id: CHEBI:6916
        label: mexiletine
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Symptomatic suppression of the sustained muscle activity.
    evidence:
    - reference: PMID:38285320
      reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms.
      explanation: >-
        Names mexiletine among the agents used to reduce the myotonic symptoms
        modeled at this node.
- name: Lamotrigine
  description: >-
    Sodium-channel-blocking antiepileptic listed among the pharmacologic agents
    commonly used to reduce myotonic symptoms in SJS.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: lamotrigine
      term:
        id: CHEBI:6367
        label: lamotrigine
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Symptomatic suppression of the sustained muscle fiber activity; like the
      other antimyotonics it acts distal to the perlecan deficit.
    evidence:
    - reference: PMID:38285320
      reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms.
      explanation: >-
        Names lamotrigine among the agents used to reduce the myotonic symptoms
        modeled at this node.
  notes: >-
    Named in a narrative review of SJS management; no SJS-specific efficacy
    data are reported, so this is weaker evidence than the carbamazepine and
    botulinum-toxin entries, which rest on reported case outcomes.
- name: Flecainide
  description: >-
    Class Ic sodium-channel-blocking antiarrhythmic listed among the
    pharmacologic agents commonly used to reduce myotonic symptoms in SJS.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: flecainide
      term:
        id: CHEBI:75984
        label: flecainide
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Symptomatic suppression of the sustained muscle fiber activity through
      sodium-channel block.
    evidence:
    - reference: PMID:38285320
      reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Pharmacologic treatment, including mexiletine, carbamazepine, lamotrigine, and flecainide, is commonly used to reduce myotonic symptoms.
      explanation: >-
        Names flecainide among the agents used to reduce the myotonic symptoms
        modeled at this node.
  notes: >-
    As with lamotrigine, named in a management review without SJS-specific
    efficacy data.
- name: Phenytoin
  description: >-
    Sodium-channel-blocking anticonvulsant used as an antimyotonic. In a
    genetically confirmed SJS type 1A case it was given with carbamazepine from
    age 3 and effectively alleviated the myotonic symptoms before the myotonia
    later worsened.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: phenytoin
      term:
        id: CHEBI:8107
        label: phenytoin
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Membrane stabilization of excitable tissue by sodium-channel block,
      reducing the sustained fiber activity.
    evidence:
    - reference: PMID:37761893
      reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        However, anticonvulsivants, such as carbamazepine or phenytoin, blocking sodium channels with stabilization of the membrane of excitable tissues, represent the most used drugs, followed by antiarrhythmic therapies such as mexiletine, procainamide and quinidine.
      explanation: >-
        States both the mechanism (sodium-channel block stabilizing excitable
        membrane) and phenytoin's place as one of the two most-used drugs.
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Since the age of 3, he had been prescribed carbamazepine and phenytoin, which effectively alleviated his myotonic symptoms.
    explanation: >-
      Case-level report of symptomatic benefit in a molecularly confirmed
      patient, though given in combination with carbamazepine.
  notes: >-
    Procainamide and quinidine are named alongside phenytoin in the same
    review sentence as second-line antiarrhythmic options, but are not modeled
    as separate treatments here because no SJS case outcome is reported for
    them and no cached source describes their use beyond the list.
- name: Non-Pharmacologic Physical Modalities
  description: >-
    Warming, massage, pre-exercise warm-up and gradual stretching, used in
    combination with antimyotonic medication to reduce stiffness. Reported in
    the SJS management literature rather than trialed.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Physical Therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Reduces the stiffness produced by sustained fiber activity; adjunctive to
      pharmacotherapy rather than an alternative to it.
    evidence:
    - reference: PMID:38285320
      reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Non-pharmacologic modalities, such as warming, massage, pre-exercise warm-up, and gradual stretching combined with medications, have also been reported.
      explanation: >-
        Names the physical modalities and states they are used combined with
        medication.
- name: Oculoplastic Surgery for Blepharophimosis and Blepharospasm
  description: >-
    Myectomy, levator resection and lateral canthopexy for the eyelid
    anomalies and facial spasm, reported to give excellent and long-lasting
    relief. Outcomes in SJS specifically are mixed — one molecularly confirmed
    patient underwent blepharophimosis surgery without significant improvement.
    Anesthetic and surgical risk is materially raised in SJS (see the Malignant
    Hyperthermia phenotype), which is why this is not a first-line option.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_phenotypes:
  - preferred_term: Blepharospasm
    term:
      id: HP:0000643
      label: Blepharospasm
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Surgical techniques, such as myectomy, levator resection, and lateral canthopexy, offer excellent and long-lasting relief for blepharospasm and eyelid anomalies
    explanation: >-
      Names the specific procedures and the reported benefit.
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, the presence of jaw muscle tightness, bony deformities, and the risk of malignant hyperthermia may increase surgical complications
    explanation: >-
      The safety qualifier from the same source; recorded as PARTIAL because it
      constrains rather than supports the intervention.
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      He underwent surgery for blepharophimosis, without significant improvement.
    explanation: >-
      A negative case-level outcome, curated so the entry does not report only
      the favorable surgical series.
- name: Botulinum Toxin Type A Injection
  description: >-
    Local chemodenervation of overactive facial muscles. Reported to produce
    significant clinical improvement in a patient with SJS type 1A whose
    difficulty opening the eyes and mouth was limiting daily activity; dose and
    interval must be individually tailored, and pediatric dosing kept minimal.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: botulinum toxin type A
      term:
        id: CHEBI:3160
        label: Botulinum toxin type A
  target_phenotypes:
  - preferred_term: Blepharospasm
    term:
      id: HP:0000643
      label: Blepharospasm
  target_mechanisms:
  - target: Continuous Muscle Fiber Hyperactivity
    treatment_effect: INHIBITS
    description: >-
      Blocks neuromuscular transmission in the injected muscles, interrupting
      the sustained hyperactivity locally. Acts distal to the perlecan deficit
      and is purely symptomatic and focal.
    evidence:
    - reference: PMID:38285320
      reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Botulinum toxin A injection was administered and demonstrated significant clinical improvement after the treatment.
      explanation: >-
        Reports the clinical effect of focal chemodenervation on the muscle
        hyperactivity.
  evidence:
  - reference: PMID:38285320
    reference_title: Successful Treatment of Schwartz-Jampel Syndrome with Botulinum Toxin Type A.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, the optimal doses and intervals must be individually tailored to optimize symptom control.
    explanation: >-
      Recorded as PARTIAL because the supporting evidence is a single case and
      the source itself notes that dosing is not standardized.
  notes: >-
    therapeutic_modality is OTHER, not SMALL_MOLECULE: botulinum neurotoxin A
    is a ~150 kDa bacterial protein toxin. PEPTIDE would also be wrong at that
    size, and PROTEIN_REPLACEMENT describes replacing a deficient host protein,
    which this is not. OTHER is the honest value until the enum carries a
    protein-biologic/toxin category.
- name: Symptomatic and Supportive Management
  description: >-
    Care is directed at symptom control rather than at the underlying perlecan
    deficiency; several drugs have been used with variable efficacy, and
    management is otherwise supportive.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:37761893
    reference_title: "Novel HSPG2 Gene Mutation Causing Schwartz-Jampel Syndrome in a Moroccan Family: A Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Therapy is mainly focused on symptom management and several drugs have been administered with different efficacy.
    explanation: >-
      States that management is symptomatic with variable drug efficacy.
animal_models:
- name: Perlecan C1532Yneo hypomorphic knock-in mouse
  species: Mouse
  genotype: Hspg2 p.C1532Y knock-in retaining the Neo selection cassette (C1532Yneo)
  publication: PMID:18647752
  description: >-
    Knock-in of a human SJS missense allele with the Neo cassette retained,
    which down-regulates Hspg2 transcription and so lowers secreted perlecan
    further than the point mutation alone. The line reproduces both arms of the
    human disease and was the first animal model of SJS neuromyotonia.
  genes:
  - preferred_term: HSPG2
    term:
      id: hgnc:5273
      label: HSPG2
  modeled_mechanisms:
  - target: Endplate Acetylcholinesterase Deficiency
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Endplate AChE is reduced as a direct consequence of synaptic perlecan
      deficiency, with an otherwise intact junction.
    limitations: >-
      The reduction is partial and, on its own, was not sufficient to generate
      resting spontaneous EMG activity in the diaphragm, so the model shows
      that AChE deficiency is necessary but leaves the sufficiency question
      open.
    readouts:
    - name: Endplate acetylcholinesterase level
      target: Endplate Acetylcholinesterase Deficiency
      direction: DECREASED
      interpretation: >-
        Direct measurement of the synaptic AChE deficit at the node.
      evidence:
      - reference: PMID:18647752
        reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization.
        explanation: Reports the measured endplate AChE reduction.
    evidence:
    - reference: PMID:18647752
      reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        It has been suggested that SJS neuromyotonia may result from endplate acetylcholinesterase (AChE) deficiency, but this hypothesis has never been investigated in vivo due to the lack of an animal model for neuromyotonia.
      explanation: >-
        Establishes that this model exists precisely to test the endplate-AChE
        mechanism in vivo, making it informative for this node.
  - target: Continuous Muscle Fiber Hyperactivity
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The line reproduces SJS neuromyotonia with spontaneous EMG activity.
    limitations: >-
      Spontaneous activity was absent at rest in the diaphragm despite the AChE
      deficiency, indicating that additional changes contribute in vivo.
    readouts:
    - name: Spontaneous activity on electromyogram
      target: Continuous Muscle Fiber Hyperactivity
      direction: INCREASED
      interpretation: >-
        Electrophysiological correlate of the human myotonia/neuromyotonia
        phenotype.
      evidence:
      - reference: PMID:18647752
        reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG).
        explanation: Reports the spontaneous EMG activity measured in the model.
    evidence:
    - reference: PMID:18647752
      reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG).
      explanation: >-
        The model reproduces the defining neuromuscular phenotype, so it is
        informative for this node.
  - target: Chondrodysplasia and Skeletal Deformity
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reduced perlecan secretion produces a skeletal phenotype characteristic
      of SJS patients, with growth-plate changes.
    limitations: >-
      The skeletal readouts include joint changes described as reminiscent of
      osteoarthritis and osteonecrosis, which are not the way the human
      phenotype is characterized, and the hypertrophic-cartilage expansion is
      transient.
    readouts:
    - name: Skeletal size, mineralization and bone shape
      target: Chondrodysplasia and Skeletal Deformity
      direction: ALTERED
      interpretation: >-
        Composite skeletal-survey correlate of the human chondrodysplasia.
      evidence:
      - reference: PMID:17213231
        reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis.
        explanation: Reports the measured skeletal abnormalities.
    evidence:
    - reference: PMID:17213231
      reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Immunostaining, biochemistry, size measurements, skeletal studies and histology revealed Hspg2 transcriptional changes in C1532Yneo mice, leading to reduced perlecan secretion and a skeletal disease phenotype characteristic of SJS patients.
      explanation: >-
        States that this line's skeletal phenotype is characteristic of SJS
        patients, supporting its use for this node.
- name: Perlecan C1532Y point-mutation-only mouse
  species: Mouse
  genotype: Hspg2 p.C1532Y knock-in without the Neo cassette (C1532Y)
  publication: PMID:17213231
  description: >-
    The control arm of the same knock-in series, carrying only the human SJS
    missense change. Its mild phenotype is a substantive negative result: it
    implies that the point mutation alone is not sufficient to produce the SJS
    skeletal phenotype in mouse, and that transcriptional down-regulation of
    perlecan is what drives disease in this system.
  genes:
  - preferred_term: HSPG2
    term:
      id: hgnc:5273
      label: HSPG2
  modeled_mechanisms:
  - target: Chondrodysplasia and Skeletal Deformity
    relationship: FAILS_TO_RECAPITULATE
    fidelity: LOW
    description: >-
      Mice carrying only the SJS-associated C1532Y substitution show a mild
      phenotype inconsistent with SJS.
    limitations: >-
      This is a species/allele-level mismatch rather than a technical failure:
      the same substitution is associated with disease in the human family in
      which it was found. It leaves open whether the human allele acts through
      an additional transcriptional effect not reproduced in mouse, or whether
      the human family carries a second contributing lesion.
    readouts:
    - name: Skeletal phenotype severity
      target: Chondrodysplasia and Skeletal Deformity
      direction: UNCHANGED
      interpretation: >-
        A negative result: the isolated missense allele does not reproduce the
        SJS skeleton in mouse.
      evidence:
      - reference: PMID:17213231
        reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          In contrast, C1532Y mice, harboring only the mutation associated with SJS, displayed a mild phenotype, inconsistent with SJS.
        explanation: Reports the negative skeletal result for this line.
    evidence:
    - reference: PMID:17213231
      reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS.
      explanation: >-
        The authors draw the explicit negative inference recorded by this
        FAILS_TO_RECAPITULATE link.
- name: Perlecan-null (Hspg2 knockout) mouse
  species: Mouse
  genotype: Hspg2 null (knockout)
  publication: PMID:11279527
  description: >-
    The complete-null end of the perlecan dosage series. It models the allelic
    lethal disorder DDSH rather than SJS, and is included here because the
    contrast is what establishes SJS as a hypomorphic, dosage-dependent
    condition.
  genes:
  - preferred_term: HSPG2
    term:
      id: hgnc:5273
      label: HSPG2
  modeled_mechanisms:
  - target: Reduced Perlecan Secretion into Basement Membranes
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Complete absence of perlecan produces a severe chondrodysplasia with
      dyssegmental ossification, delimiting the null end of the dosage series
      that this node models.
    limitations: >-
      The null genotype models DDSH, not SJS: it overshoots the partial
      reduction that characterizes SJS, so it bounds the mechanism rather than
      reproducing the disease.
    readouts:
    - name: Chondro-osseous morphology
      target: Reduced Perlecan Secretion into Basement Membranes
      direction: ALTERED
      interpretation: >-
        Establishes the phenotype produced when perlecan is absent rather than
        merely reduced.
      evidence:
      - reference: PMID:11279527
        reference_title: Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Mice lacking the perlecan gene (Hspg2) have a severe chondrodysplasia with dyssegmental ossification of the spine
        explanation: Reports the null-mouse skeletal phenotype.
    evidence:
    - reference: PMID:11279527
      reference_title: Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        show radiographic, clinical and chondro-osseous morphology similar to a lethal autosomal recessive disorder in humans termed dyssegmental dysplasia, Silverman-Handmaker type (DDSH; MIM 224410)
      explanation: >-
        Identifies the null mouse as a model of DDSH, the allelic disorder that
        anchors the null end of the dosage series.
experimental_models:
- name: SJS patient-derived primary dermal fibroblasts
  description: >-
    Primary fibroblasts from a patient homozygous for HSPG2 c.1125C>G
    (p.Cys375Trp), used to test the functional consequence of the variant.
    Secreted perlecan and migration were reduced while proliferation was
    unaffected, giving a cell-level readout of the hypomorphic effect.
  experimental_model_type: PRIMARY_CELL_CULTURE
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  publication: PMID:33767660
  modeled_mechanisms:
  - target: Reduced Perlecan Secretion into Basement Membranes
    relationship: MEASURES
    fidelity: MODERATE
    description: >-
      Directly quantifies secreted perlecan from cells carrying a patient
      genotype.
    limitations: >-
      Dermal fibroblasts are not the disease-relevant chondrocyte or
      neuromuscular-junction compartment, so they report the secretion defect
      but not its tissue-specific consequences; n = 1 genotype.
    readouts:
    - name: Secreted perlecan level
      target: Reduced Perlecan Secretion into Basement Membranes
      direction: DECREASED
      interpretation: >-
        Cell-level confirmation that the patient allele reduces perlecan
        secretion.
      evidence:
      - reference: PMID:33767660
        reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          At cellular levels, mutant primary fibroblasts had reduced levels of secreted perlecan and impaired migration ability but normal capability of proliferation.
        explanation: Reports the measured reduction in secreted perlecan.
    evidence:
    - reference: PMID:33767660
      reference_title: A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The pathogenic nature of this missense mutation was demonstrated by in silico pathogenicity assessment, clinical presentations, and cellular function of primary fibroblast derived from patients.
      explanation: >-
        States that the patient fibroblast assay is the functional evidence for
        the variant's effect, making it informative for this node.
- name: ATDC5 prechondrocyte clustering assay with perlecan domain IV constructs
  description: >-
    ATDC5 cells, a model of early chondrogenesis, exposed to recombinant
    perlecan domain IV subdomain (HSPG2 IV-3) with and without the
    SJS-associated R3452Q substitution, reading out prechondrocyte clustering
    and condensation markers.
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  publication: PMID:30203597
  modeled_mechanisms:
  - target: Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation
    relationship: PERTURBS
    fidelity: MODERATE
    description: >-
      Introducing the SJS patient allele into the domain IV construct reduces
      its clustering activity, connecting the mutation to the condensation
      step.
    limitations: >-
      An immortalized murine cell line exposed to an isolated recombinant
      subdomain, not full-length perlecan in native pericellular matrix; the
      assay also required thermal unfolding to maximize activity, so the
      relationship between assay activity and in vivo function is indirect.
    readouts:
    - name: Prechondrocyte clustering
      target: Cartilage Pericellular Matrix Failure and Impaired Chondrocyte Condensation
      direction: DECREASED
      interpretation: >-
        Loss of clustering activity when the SJS allele is present is the
        cell-level correlate of impaired condensation.
      evidence:
      - reference: PMID:30203597
        reference_title: "Perlecan/HSPG2: Signaling role of domain IV in chondrocyte clustering with implications for Schwartz-Jampel Syndrome."
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          Introduction of the mutation (R3452Q) associated with the human skeletal disorder Schwartz-Jampel syndrome limited HSPG2 IV-3-induced clustering.
        explanation: Reports the measured reduction in clustering.
    evidence:
    - reference: PMID:30203597
      reference_title: "Perlecan/HSPG2: Signaling role of domain IV in chondrocyte clustering with implications for Schwartz-Jampel Syndrome."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Perlecan subdomains were tested for chondrogenic properties in ATDC5 cells, a model for early chondrogenesis.
      explanation: >-
        Identifies the assay system and its purpose, supporting its use for
        this node.
differential_diagnoses:
- name: Stuve-Wiedemann syndrome (formerly "Schwartz-Jampel syndrome type 2")
  description: >-
    Severe neonatal condition with bowed long bones, respiratory distress,
    feeding difficulties and hyperthermic episodes causing early lethality.
    Historically classified as SJS type 2 on clinical overlap, it is caused by
    null LIFR mutations with impaired JAK/STAT3 signaling and is a genetically
    distinct disorder — not an allelic form of the HSPG2 disease modeled here.
  distinguishing_features:
  - Causal gene LIFR (5p13.1) rather than HSPG2
  - Hyperthermic episodes causing early lethality
  - No perlecan deficiency
  evidence:
  - reference: PMID:14740318
    reference_title: Null leukemia inhibitory factor receptor (LIFR) mutations in Stuve-Wiedemann/Schwartz-Jampel type 2 syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We conclude, therefore, that SWS and SJS2 represent a single clinically and genetically homogeneous condition due to null mutations in the LIFR gene on chromosome 5p13.
    explanation: >-
      Establishes that the historical "SJS type 2" is Stuve-Wiedemann syndrome,
      a distinct LIFR disorder.
- name: Dyssegmental dysplasia, Silverman-Handmaker type (DDSH)
  description: >-
    Lethal autosomal recessive neonatal skeletal dysplasia caused by functional
    null mutations of the same gene, HSPG2. Allelic with SJS but at the null
    end of the perlecan dosage series.
  distinguishing_features:
  - Functional-null rather than hypomorphic HSPG2 alleles
  - Truncated perlecan is not secreted at all, rather than secreted at reduced level
  - Neonatal lethality with dyssegmental ossification of the spine
  evidence:
  - reference: PMID:11279527
    reference_title: Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thus, DDSH is caused by a functional null mutation of HSPG2.
    explanation: >-
      Establishes the allelic but mechanistically distinct null disorder.
  - reference: PMID:11279527
    reference_title: Dyssegmental dysplasia, Silverman-Handmaker type, is caused by functional null mutations of the perlecan gene.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Biochemically, truncated perlecan was not secreted by the patient fibroblasts, but was degraded to smaller fragments within the cells.
    explanation: >-
      Gives the biochemical distinction from the hypomorphic SJS alleles, which
      still permit reduced secretion.
discussions:
- discussion_id: sjs_ache_sufficiency_gap
  prompt: >-
    Is endplate acetylcholinesterase deficiency sufficient to generate the
    spontaneous muscle activity of Schwartz-Jampel syndrome, or are additional
    perlecan-dependent changes required?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Endplate Acetylcholinesterase Deficiency
  - pathophysiology#Distal Peripheral Nerve Hyperexcitability and Junctional Remodeling
  rationale: >-
    The mouse model that established the endplate AChE deficiency in vivo also
    showed that the deficiency alone did not produce resting spontaneous EMG
    activity in the diaphragm, so the causal chain from AChE loss to continuous
    muscle hyperactivity is necessary-but-not-obviously-sufficient. The human
    biopsy study points to a combination of synaptic AChE deficiency,
    preterminal amyelination and junctional remodeling acting synergistically.
    Which of those is rate-limiting is unresolved, and it matters
    therapeutically: an AChE-directed strategy would only help if that arm
    dominates.
  proposed_experiments:
  - experiment_id: sjs_nmj_perlecan_restoration
    name: Muscle-specific perlecan restoration in the SJS mouse
    description: >-
      Restore synaptic perlecan (and hence endplate AChE) selectively at the
      neuromuscular junction in the C1532Yneo line and test whether spontaneous
      EMG activity resolves without correcting preterminal myelination.
  evidence:
  - reference: PMID:18647752
    reference_title: Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      However, physiological endplate AChE deficiency was not associated with spontaneous activity at rest on EMG in the diaphragm, suggesting that additional changes are required to generate such activity characteristic of SJS.
    explanation: >-
      The authors state the insufficiency directly; this is the gap recorded
      here.
- discussion_id: sjs_c1532y_mouse_human_mismatch
  prompt: >-
    Why does the SJS-associated HSPG2 C1532Y substitution cause disease in the
    human family in which it was found but only a mild, non-SJS phenotype when
    knocked into mouse without a transcription-lowering cassette?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#HSPG2 Hypomorphic Variation
  - pathophysiology#Chondrodysplasia and Skeletal Deformity
  - animal_models#Perlecan C1532Y point-mutation-only mouse
  rationale: >-
    The knock-in series separates the missense change from the transcriptional
    down-regulation supplied by the retained Neo cassette. Only the
    down-regulated line reproduces SJS, which led the authors to question
    whether C1532Y is the sole causative factor in the human family. Two
    readings remain open — that the human allele carries an additional
    transcriptional effect the mouse construct does not reproduce, or that
    mouse tolerates a perlecan level that human does not — and they imply
    different things about how faithfully hypomorphic-allele mouse models can
    be used to rank SJS variant severity.
  proposed_experiments:
  - experiment_id: sjs_c1532y_family_expression_reanalysis
    name: Re-sequencing and expression analysis of the original C1532Y family
    description: >-
      Determine HSPG2 transcript level and search for a second cis-acting
      regulatory variant in the family carrying C1532Y, to test whether the
      human genotype includes a transcriptional component absent from the
      mouse knock-in.
  evidence:
  - reference: PMID:17213231
    reference_title: Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS.
    explanation: >-
      States the mismatch and the authors' proposed resolution.
tracked_issues:
- url: https://github.com/monarch-initiative/dismech/issues/7867
  title: "Coverage gap: 4 ISDS skeletal-nosology groups have zero dismech entries"
  tracked_issue_role: SOURCE
  notes: >-
    This entry is the first dismech member of the ISDS 2023 group 7
    (proteoglycan core protein disorders). The remaining members listed in that
    issue — dyssegmental dysplasia (HSPG2) and the three ACAN disorders —
    are still uncurated.
review_notes: >-
  Second-pass curation targets deliberately left open in this first pass:
  (1) no Orphanet provenance — ORPHA:800 is not in references_cache and would
  need an Orphadata refresh, which would also supply HPO frequency annotations;
  (2) no phenotype frequency: bands, per docs/frequency-evidence-guidelines.md,
  since no source in the evidence set quantifies them;
  (3) no histopathology or imaging_findings blocks (the muscle-biopsy and
  skeletal-survey findings are currently carried as pathophysiology evidence);
  (4) no conforms_to declared — there is no basement-membrane / pericellular
  proteoglycan module in kb/modules/, and the endochondral-ossification
  mechanism here is not the FGFR gain-of-function pattern; a module covering
  proteoglycan core-protein deficiency would be a reasonable follow-up once the
  ACAN and DDSH entries exist to conform to it.

Schwartz-Jampel Syndrome

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