Neurodevelopmental Disorder with Neuromuscular and Skeletal Abnormalities (NEDNMSA): A Comprehensive Disease Characteristics Report

Disease: Neurodevelopmental Disorder with Neuromuscular and Skeletal Abnormalities (NEDNMSA) MONDO ID: MONDO:0859236 · OMIM: 619833 · Category: Mendelian (autosomal recessive) Causal gene: NRCAM (HGNC:7994; NCBI Gene 4897; locus 7q31.1)

Summary

Neurodevelopmental Disorder with Neuromuscular and Skeletal Abnormalities (NEDNMSA) is an ultra-rare autosomal recessive Mendelian syndrome caused by biallelic loss-of-function or deleterious missense variants in NRCAM, the gene encoding the neuronal cell-adhesion molecule NrCAM (neuron-glia-related cell adhesion molecule). The disorder was first defined by Kurolap and colleagues in 2022 in a cohort of ten affected individuals from eight families (PMID: 35108495), and independently confirmed in 2023 by a second report describing a homozygous nonsense variant (PMID: 36606341). The clinical syndrome is characterized by a triad-plus phenotype: developmental delay/intellectual disability, hypotonia, and peripheral neuropathy and/or spasticity, accompanied by a variable constellation of skeletal (scoliosis, hip dysplasia, foot deformities, distal arthrogryposis), central nervous system structural (thin corpus callosum, ventriculomegaly, delayed myelination, periventricular heterotopia), and ophthalmologic anomalies.

Mechanistically, NrCAM is an L1-family immunoglobulin-superfamily axonal/glial adhesion molecule that, together with its partners gliomedin and neurofascin-186 (NF186), orchestrates the assembly of nodes of Ranvier and axon initial segments by recruiting ankyrin-G and clustering voltage-gated sodium channels. Loss of NrCAM function destabilizes this nodal complex, degrades saltatory conduction, and disrupts axon guidance and brain morphogenesis — providing a direct causal chain from gene dysfunction to the observed neuromuscular and neurodevelopmental phenotypes. Population-genetic constraint metrics from gnomAD (pLI ≈ 0; LOEUF = 0.636; observed/expected LoF = 0.53) confirm that NRCAM is not haploinsufficient, consistent with a recessive rather than dominant mechanism, and animal models (Nrcam-null mice, nrcama-deficient zebrafish) recapitulate axon-guidance and brain-structural defects.

The disorder is congenital in onset, non-progressive to slowly variable in course, and lifelong. Because only ~11 individuals have been reported worldwide, no prevalence estimate, natural-history study, disease-specific therapy, or clinical trial exists. Diagnosis is molecular (trio-based whole-exome or whole-genome sequencing) supported by nerve conduction studies and brain MRI, and management is entirely supportive and multidisciplinary. This report synthesizes eight confirmed findings across 15 disease-characteristic domains, flagging clearly where evidence is absent.

Key Findings

Finding 1 — NEDNMSA is caused by biallelic NRCAM variants (autosomal recessive)

Ontology cross-referencing links MONDO:0859236 → OMIM:619833 → UMLS:C5676965 / MedGen:1803456, and identifies a single causal gene, NRCAM (HGNC:7994; gene OMIM 601581; locus 7q31.1). The defining cohort (Kurolap et al., 2022) reported ten affected individuals from eight families carrying bi-allelic NRCAM variants. A second, independent report (Elahi et al., 2023) confirmed the gene–disease relationship with a homozygous nonsense variant c.73C>T (p.Gln25*), establishing the association beyond a single family.

"Here, we describe ten affected individuals with bi-allelic variants in the neuronal cell adhesion molecule NRCAM that lead to a neurodevelopmental syndrome of varying severity; the individuals are from eight families. This syndrome is characterized by developmental delay/intellectual disability, hypotonia, peripheral neuropathy, and/or spasticity." — PMID: 35108495

"This study is the second report of an association between biallelic NRCAM gene variants and a Mendelian disorder." — PMID: 36606341

Evidence type: Human clinical (two independent cohorts). This finding anchors Section 1 (Disease Information), Section 4 (Genetic/Molecular), and Section 9 (Inheritance).

Finding 2 — NrCAM mediates node-of-Ranvier assembly and Na⁺-channel clustering

NrCAM is an axonal/glial Ig-superfamily cell-adhesion molecule of the L1 family. Together with gliomedin and neurofascin-186 (NF186), it clusters ankyrin-G and voltage-gated Na⁺ channels at nodes of Ranvier (Lustig et al., 2001, PMID: 11728309; Eshed et al., 2005, PMID: 16039564). Combined genetic loss of gliomedin and NrCAM in mice causes progressive loss of nodal Na⁺ channels, "binary nodes," dysregulated nodal gap length, neurological abnormalities, and slowed nerve conduction (Amor et al., 2014).

"absence of both molecules (and hence the glial clustering signal) resulted in a gradual loss of Na(+) channels and other axonal components from the nodes, the formation of binary nodes, and dysregulation of nodal gap length. Therefore, these mice exhibit neurological abnormalities and slower nerve conduction." — PMID: 24719088

"These results provide the first evidence that neurofascin plays a major role in the formation of nodes, possibly via interactions with Nr-CAM." — PMID: 11728309

Evidence type: Model organism + in vitro. This is the central mechanistic finding explaining the neuropathy/spasticity phenotype (Section 6).

Finding 3 — gnomAD constraint supports a recessive loss-of-function mechanism

Constraint metrics for NRCAM (ENSG00000091129; chr7:108,147,623–108,456,717 GRCh38; canonical ENST00000379028) are: pLI ≈ 0 (2.58×10⁻¹¹), LOEUF (oe_lof upper) = 0.636, observed/expected LoF = 0.53 (83 observed vs 156.5 expected), LoF Z = 4.99; missense oe = 0.89, mis_Z = 1.92. The near-zero pLI indicates NRCAM tolerates heterozygous loss of function (i.e., is not haploinsufficient), while the elevated LoF Z-score shows selection against biallelic depletion. This population-genetic signature is exactly what is expected for a gene causing a recessive disorder — heterozygous carriers are unaffected, and disease requires two damaged alleles.

Evidence type: Computational/population genetics (gnomAD v2/v4). Supports the inheritance model of Section 9.

Finding 4 — Animal models recapitulate axon-guidance and brain-structural defects

Nrcam-null mice show disturbed olfactory-nerve axon guidance and altered size of the ventricular system and cerebellar vermis (Heyden et al., 2008). NrCAM also regulates postnatal hypothalamic tanycyte differentiation, proliferation, and neurogenesis (Moore et al., 2022, PMID: 35464310). The defining human study used zebrafish nrcama loss-of-function to corroborate the gene–disease link.

"in both mutants, CHL1 and NrCAM, the guidance of the olfactory nerve projections is disturbed. Both mutations also alter the size of the ventricular system and the vermis" — PMID: 18588951

"These findings are corroborated by previous in vitro studies of murine Nrcam-deficient cells, revealing abnormal neurite outgrowth, synaptogenesis, and formation of nodes of Ranvier on myelinated axons." — PMID: 35108495

The mouse ventricular/vermis changes mirror the human ventriculomegaly and CNS anomalies, and the neurite-outgrowth/synaptogenesis/node-formation deficits provide cellular-level parallels to the human disease (Sections 6, 15).

Evidence type: Model organism (mouse, zebrafish) + in vitro.

Finding 5 — Pathogenic missense variants cluster in the third fibronectin type-III domain

Human NRCAM (UniProt Q92823) is a 1,304-aa type-I transmembrane L1-family protein comprising 6 Ig-like domains (aa 46–632), 5 fibronectin type-III (Fn-III) domains (aa 649–1156), a transmembrane segment, and a cytoplasmic tail. The third Fn-III domain (aa ~848–950) is a mutational hotspot: many disease-associated missense variants cluster there and are computationally predicted to be deleterious to protein structure and protein–protein interactions.

"Computational analyses of NRCAM variants, many of which cluster in the third fibronectin type III (Fn-III) domain, strongly suggest a deleterious effect on NRCAM structure and function, including possible disruption of its interactions with other proteins." — PMID: 35108495

Evidence type: Human clinical + computational. Informs variant interpretation (Section 4) and protein-dysfunction mechanism (Section 6).

Finding 6 — Phenotype spectrum and frequencies (HPO-annotated cohort, n ≈ 10)

The table below consolidates HPOA/Monarch frequencies for MONDO:0859236 with suggested HPO terms. Frequencies are derived from the small defining cohort and should be read as indicative, not population-representative.

ClinVar lists 289 NRCAM records, of which 38 are pathogenic/likely-pathogenic.

"This syndrome is characterized by developmental delay/intellectual disability, hypotonia, peripheral neuropathy, and/or spasticity." — PMID: 35108495

Evidence type: Human clinical (HPO annotation). Populates Section 3 (Phenotypes).

Finding 7 — Epidemiology, inheritance, and diagnostic/management framework

The disorder is ultra-rare: the entire published literature comprises ~11 individuals (10 from 8 families, Kurolap 2022; +1, Elahi 2023). No prevalence or incidence estimate exists, and there is no Orphanet ORPHAcode. Inheritance is autosomal recessive with biallelic homozygous or compound-heterozygous variants; homozygous variants in several families implicate consanguinity. Diagnosis is molecular via trio-based whole-exome or whole-genome sequencing, supported by EMG/nerve conduction studies (documenting axonal and/or demyelinating peripheral neuropathy) and brain MRI (thin corpus callosum, ventriculomegaly, delayed myelination, periventricular heterotopia). No disease-specific pharmacotherapy, gene therapy, or clinical trial exists; management is supportive and multidisciplinary. Severity is variable and not strictly determined by variant type, indicating variable expressivity relevant to prognostic counseling.

"we show that type of the pathogenic variant does not necessarily determine the severity of this phenotype." — PMID: 36606341

"the individuals are from eight families" — PMID: 35108495

Evidence type: Human clinical. Populates Sections 8–13.

Finding 8 — Evolutionary conservation and orthologs

NCBI Gene confirms conserved NRCAM orthologs across model species: human NRCAM (Gene 4897; HGNC:7994), mouse Nrcam (Gene 319504; NCBI:txid10090), rat Nrcam (Gene 497815; NCBI:txid10116), zebrafish nrcama (Gene 556537; NCBI:txid7955; paralog nrcamb). NRCAM belongs to the L1 immunoglobulin-superfamily cell-adhesion molecule family, with paralogs L1CAM, CHL1, and NFASC.

Evidence type: Computational/comparative genomics. Populates Sections 14–15.

Section-by-Section Report

1. Disease Information

Overview. NEDNMSA is a Mendelian, autosomal recessive neurodevelopmental syndrome combining neurological, neuromuscular, and skeletal features. Its defining triad is developmental delay/intellectual disability, hypotonia, and peripheral neuropathy and/or spasticity, with additional variable skeletal, brain-structural, and eye findings.

Key identifiers: MONDO:0859236 · OMIM:619833 · UMLS:C5676965 · MedGen:1803456. No Orphanet ORPHAcode has been assigned (reflecting ultra-rarity). ICD-10/ICD-11 and MeSH lack a specific code; the disorder maps to broad categories and is best referenced by its MONDO/OMIM identifiers.

Synonyms: "Neurodevelopmental disorder with neuromuscular and skeletal abnormalities"; "NRCAM-related neurodevelopmental disorder"; "NRCAM-related bi-allelic disorder." Gene-level synonyms for NrCAM include neuron-glia-related cell adhesion molecule and neuronal cell adhesion molecule.

Information source: Aggregated disease-level resources (OMIM/MONDO) built from two individual-patient case series (clinical phenotyping of ~11 patients), not from population EHR datasets.

2. Etiology

Causal factors. The disorder is purely genetic (monogenic, recessive): biallelic pathogenic variants in NRCAM. There is no known environmental, infectious, or mechanistic (non-genetic) cause.

Genetic risk factors. The only established risk factor is inheritance of two damaged NRCAM alleles. Consanguinity is a major contributor (multiple homozygous families). No modifier genes or susceptibility loci have been identified (the cohort is too small).

Environmental / lifestyle / protective factors. Not applicable / not reported. No environmental risk factors, protective variants, protective exposures, or gene–environment interactions have been described for this ultra-rare Mendelian disorder. Standard prenatal care applies but does not modify the genetic risk.

3. Phenotypes

See Finding 6 table for the full HPO-annotated phenotype list with frequencies. Key characteristics:

• Phenotype types: clinical signs (hypotonia, spasticity, neuropathy), developmental/behavioral (developmental delay, intellectual disability, self-injurious/aggressive behavior), physical/skeletal manifestations (scoliosis, hip dysplasia, pes cavus, hammertoe, distal arthrogryposis, micrognathia, microcephaly), and neuroimaging abnormalities (thin corpus callosum, ventriculomegaly, delayed myelination, periventricular heterotopia).
• Age of onset: congenital/neonatal (hypotonia, structural anomalies) to early childhood (developmental delay).
• Severity: variable (mild to severe), not strictly predicted by variant type (Elahi 2023).
• Progression: largely static/stable neurodevelopmental course; peripheral neuropathy may be slowly progressive.
• Quality-of-life impact: substantial — motor and cognitive impairment, feeding difficulty (G-tube in ~22%), and orthopedic disability affect daily functioning and independence. Formal QoL instrument data (EQ-5D/SF-36/PROMIS) are not available for this ultra-rare disorder.

4. Genetic/Molecular Information

• Causal gene: NRCAM (HGNC:7994; NCBI Gene 4897; gene OMIM 601581; 7q31.1; ENSG00000091129; canonical ENST00000379028).
• Protein: NrCAM, UniProt Q92823, 1,304 aa, type-I transmembrane; 6 Ig-like domains (aa 46–632), 5 Fn-III domains (aa 649–1156); the 3rd Fn-III domain (~aa 848–950) is a missense hotspot (Finding 5).
• Variant classes: nonsense (e.g., c.73C>T p.Gln25*), other loss-of-function, and deleterious missense (clustered in Fn-III #3). ClinVar: 289 records, 38 pathogenic/likely-pathogenic.
• Functional consequence: loss of function (recessive). gnomAD constraint (pLI ≈ 0; LOEUF 0.636; oe_LoF 0.53) confirms NRCAM is not haploinsufficient — disease requires biallelic hits (Finding 3).
• Allele frequency: individual pathogenic alleles are private/ultra-rare in gnomAD.
• Origin: germline (inherited, recessive). No somatic disease role in this Mendelian phenotype (though somatic/epigenetic NRCAM dysregulation is separately implicated in gliomas and colorectal cancer — see Evidence Base; this is unrelated to NEDNMSA).
• Modifier genes / epigenetics / chromosomal abnormalities: not reported for NEDNMSA.

5. Environmental Information

Not applicable. NEDNMSA is a monogenic recessive disorder with no established environmental factors, lifestyle contributors, or infectious triggers.

6. Mechanism / Pathophysiology

The core mechanism is failure of node-of-Ranvier and axon-initial-segment assembly plus disrupted axon guidance (Findings 2, 4, 5).

Causal chain:

Biallelic NRCAM LoF / deleterious missense (Fn-III #3 hotspot)
│
▼
Loss of NrCAM adhesion function (Ig + Fn-III interactions with
gliomedin, NF186 disrupted)
│
├─► Failure to recruit ankyrin-G  ──► Na⁺ channels not clustered
│        at nodes of Ranvier / axon initial segments
│        │
│        ▼
│   Degraded saltatory conduction ──► PERIPHERAL NEUROPATHY,
│        SPASTICITY, MOTOR DELAY, HYPOTONIA
│
└─► Abnormal axon guidance, neurite outgrowth, synaptogenesis
 │
 ▼
    Brain morphogenesis defects (ventriculomegaly, thin corpus
    callosum, delayed myelination, periventricular heterotopia)
 │
 ▼
    DEVELOPMENTAL DELAY / INTELLECTUAL DISABILITY, MICROCEPHALY

• Upstream: loss of NrCAM adhesion; failure of the gliomedin–NF186–NrCAM glial clustering signal.
• Downstream: ankyrin-G / Na⁺-channel declustering → conduction failure; axon-guidance/synaptic defects → structural brain anomalies.
• Cell types (CL terms): neurons (CL:0000540), myelinating Schwann cells (CL:0002573), oligodendrocytes (CL:0000128), hypothalamic tanycytes (Moore 2022).
• Biological processes (GO terms): node of Ranvier assembly / GO:0033268; axon guidance / GO:0007411; cell adhesion / GO:0007155; myelination / GO:0042552; neuron projection development / GO:0031175; regulation of sodium ion transmembrane transport.
• Subcellular compartments (GO CC): node of Ranvier (GO:0033268), axon initial segment (GO:0043194), plasma membrane (GO:0005886), paranode region of axon (GO:0033270).
• Molecular pathways: L1-family cell-adhesion/axon-guidance signaling; ankyrin-G/βIV-spectrin cytoskeletal scaffolding. (NrCAM is also a Wnt-pathway target in cancer contexts — not relevant to NEDNMSA pathogenesis.)
• Metabolic / immune involvement: not implicated.

7. Anatomical Structures Affected

• Organ level (UBERON): brain (UBERON:0000955), peripheral nervous system / peripheral nerve (UBERON:0000010, UBERON:0001021), spinal cord (UBERON:0002240); secondary: skeletal system — vertebral column (UBERON:0001130), hip joint (UBERON:0001464), foot (UBERON:0002387); eye (UBERON:0000970).
• Body systems: nervous (central + peripheral), musculoskeletal, ophthalmologic.
• Tissue/cell level: nervous tissue, skeletal muscle (secondary, via denervation/hypotonia), connective/skeletal tissue; targeted cells — neurons, Schwann cells, oligodendrocytes (Findings 2, 4).
• Subcellular: node of Ranvier, axon initial segment, axolemma (Finding 2).
• Specific sites / lateralization: corpus callosum (UBERON:0002336), lateral ventricles (ventriculomegaly), cerebellar vermis (UBERON:0004720), periventricular zone; anomalies are typically bilateral/symmetric where reported.

8. Temporal Development

• Onset: congenital / neonatal (hypotonia, structural anomalies) to early-childhood (developmental delay); onset pattern is chronic/insidious, not acute.
• Progression: neurodevelopmental features are largely static; peripheral neuropathy and orthopedic features (e.g., scoliosis) may be slowly progressive. No defined disease stages.
• Course: chronic, lifelong. No remission. Severity variable and not determined by variant type (Finding 7).
• Critical periods: prenatal/early-postnatal neurodevelopment (axon guidance, myelination) is the window of vulnerability; no proven intervention window exists.

9. Inheritance and Population

• Epidemiology: prevalence and incidence unknown (ultra-rare; ~11 reported individuals; no registry).
• Inheritance: autosomal recessive; biallelic homozygous or compound-heterozygous NRCAM variants (Findings 1, 3).
• Penetrance: presumed high/complete in biallelic carriers (all reported biallelic individuals affected), though small n limits certainty.
• Expressivity: variable (severity independent of variant type; Finding 7).
• Anticipation / mosaicism: not reported / not applicable (no repeat expansion).
• Founder effects: none established; consanguinity is a recurring factor (multiple homozygous families).
• Carrier frequency: not formally estimated; heterozygous LoF alleles are tolerated per gnomAD constraint (Finding 3).
• Demographics: no ethnic predilection established; the small cohort spans multiple families/populations. Sex ratio not established (expected ~1:1 for autosomal recessive). Age distribution: pediatric at ascertainment.

10. Diagnostics

• Genetic testing (primary): trio-based whole-exome (WES) or whole-genome sequencing (WGS) is the diagnostic gold standard; targeted NRCAM analysis / neurodevelopmental gene panels can confirm. Chromosomal microarray/karyotype are typically normal (this is a sequence-level disorder, not a CNV syndrome).
• Electrophysiology: EMG/nerve conduction studies documenting axonal and/or demyelinating peripheral neuropathy (Finding 7).
• Imaging: brain MRI — thin corpus callosum, ventriculomegaly, delayed myelination, periventricular heterotopia (Findings 6, 7).
• Laboratory/biomarkers: no specific biochemical biomarker; diagnosis rests on genotype + phenotype.
• Clinical criteria: no formal consensus criteria; diagnosis is molecular + clinical gestalt.
• Differential diagnosis: other autosomal-recessive neurodevelopmental syndromes with neuropathy/spasticity and skeletal features (e.g., L1CAM-spectrum disorders, other L1-family conditions, hereditary motor-sensory neuropathies with CNS involvement, arthrogryposis-associated neurodevelopmental disorders). Molecular testing distinguishes them.
• Screening: no population newborn screening; cascade carrier testing of at-risk relatives is appropriate once a familial variant is known.

11. Outcome/Prognosis

• Survival/mortality: no disease-specific mortality data; the disorder is not reported as lethal in childhood, but survival statistics are unavailable (n too small).
• Morbidity/function: significant lifelong disability driven by intellectual disability, motor impairment, neuropathy/spasticity, feeding difficulty, and orthopedic complications (scoliosis, hip dysplasia).
• Complications: feeding failure/failure-to-thrive (G-tube ~22%), orthopedic deterioration, contractures, visual impairment (cataract/optic atrophy/retinal detachment).
• Recovery potential: none (structural/developmental); supportive care can improve function.
• Prognostic factors: severity is variable and not predicted by variant type (Finding 7); no validated prognostic biomarkers.

12. Treatment

No disease-specific pharmacotherapy, gene therapy, cell therapy, RNA therapy, or targeted/immunotherapy exists. No clinical trials (NCT) are registered. Management is supportive and multidisciplinary (Finding 7):

• Supportive/rehabilitative (NCIT-type interventions): physical therapy (NCIT:C15216), occupational therapy, speech therapy; nutritional support / gastrostomy feeding for failure-to-thrive.
• Symptomatic pharmacotherapy: antispasticity agents (e.g., baclofen) for spasticity; standard management of seizures/behavioral symptoms as needed (no disorder-specific evidence).
• Surgical/interventional: orthopedic correction of scoliosis, hip dysplasia, and foot deformities; ophthalmologic surgery (e.g., cataract, retinal detachment) as indicated.
• Pharmacogenomics / personalized medicine: not applicable / not developed.

13. Prevention

• Primary prevention: none for the genetic cause; genetic counseling for consanguineous or carrier families.
• Secondary/tertiary prevention: early developmental intervention; surveillance for and management of scoliosis, hip dysplasia, feeding, and ophthalmologic complications.
• Genetic screening: carrier testing, cascade screening, and prenatal/preimplantation genetic diagnosis available once a familial variant is identified.
• Public health / immunization / behavioral / prophylaxis: not applicable.

14. Other Species / Natural Disease

• Taxonomy / orthologs (Finding 8): mouse Nrcam (Gene 319504; txid10090), rat Nrcam (Gene 497815; txid10116), zebrafish nrcama (Gene 556537; txid7955; paralog nrcamb). NrCAM is an L1-family CAM (paralogs L1CAM, CHL1, NFASC).
• Natural disease in other species: no naturally occurring NRCAM-equivalent disorder is catalogued (e.g., in OMIA) — the disease is known only from engineered/experimental models, not spontaneous animal disease.
• Comparative biology: node-of-Ranvier assembly and NrCAM function are highly evolutionarily conserved across mammals and teleosts, validating cross-species modeling.
• Zoonotic potential: not applicable (genetic disorder).

15. Model Organisms

• Mouse (Mus musculus, MGI): Nrcam-null mice — disturbed olfactory-nerve axon guidance, altered ventricular-system and cerebellar-vermis size (Heyden 2008); tanycyte differentiation/neurogenesis defects (Moore 2022); combined gliomedin+NrCAM loss — node disintegration, conduction slowing (Amor 2014). Recapitulation: good for axon-guidance, brain-structural, and nodal/conduction phenotypes.
• Zebrafish (Danio rerio, ZFIN): nrcama loss-of-function used to corroborate the human gene–disease link (Kurolap 2022).
• In vitro: murine Nrcam-deficient cells — abnormal neurite outgrowth, synaptogenesis, and node-of-Ranvier formation (Finding 4).
• Model types available: knockout mice; morphant/mutant zebrafish; primary neuronal cultures. Humanized/conditional/iPSC-organoid models are not yet reported for this disorder.
• Limitations: models capture axonal/nodal and brain-structural biology but not the full human skeletal spectrum; small human cohort limits genotype–phenotype validation.

Mechanistic Model / Interpretation

NEDNMSA is best understood as an axonal cell-adhesion / node-of-Ranvier assembly disorder. NrCAM sits at the intersection of two conserved neurodevelopmental processes: (1) axon guidance and neurite/synapse formation during brain morphogenesis, and (2) nodal/AIS assembly required for saltatory conduction. Biallelic loss of NrCAM function — whether through truncating variants or missense variants that disrupt the third Fn-III domain's protein interactions — degrades both processes simultaneously. This dual role explains the disorder's characteristic combination of central (intellectual disability, brain malformations) and peripheral (neuropathy, hypotonia, spasticity) features, with skeletal abnormalities arising secondary to the neuromuscular deficit and developmental disruption.

The convergence of population-genetic constraint (recessive signature), conserved animal-model phenotypes, and human clinical/molecular data yields a coherent, well-supported causal narrative with no major internal contradictions.

Evidence Base

Non-NEDNMSA context (excluded from pathogenesis): NRCAM is separately dysregulated in gliomas via CNV/methylation (PMID: 41663200) and overexpressed in colorectal cancer (PMID: 21718388) as a Wnt target — these are somatic/oncologic roles unrelated to the germline recessive Mendelian disorder and are noted only to avoid conflation.

Limitations and Knowledge Gaps

1. Extremely small evidence base (~11 individuals). All human phenotype frequencies derive from ≤10 patients; percentages are indicative, not population estimates.
2. No epidemiology. Prevalence, incidence, carrier frequency, sex ratio, and geographic distribution are unknown; no Orphanet code or registry exists.
3. No natural-history or QoL data. Progression rate, life expectancy, and validated QoL metrics are undefined.
4. Genotype–phenotype correlation unresolved. Severity is not predicted by variant type, but the sample is too small to establish modifiers.
5. No disease-specific therapy or trials. Management is empirical/supportive.
6. Mechanistic gaps. The precise contribution of each missense variant to specific interaction disruptions, and the relative weight of central vs. peripheral pathology, remain to be functionally dissected. No human iPSC/organoid model yet exists.
7. Ontology mapping incomplete. No dedicated ICD-11/MeSH/Orphanet identifiers.

Proposed Follow-up Experiments / Actions

1. International matchmaking (GeneMatcher, Matchmaker Exchange) to expand the cohort, refine phenotype frequencies, and enable genotype–phenotype analysis.
2. Functional validation of Fn-III #3 missense variants — in vitro binding assays (NrCAM–gliomedin/NF186), node-of-Ranvier reconstitution, and structural modeling (AlphaFold + PDB comparison) to classify VUS per ACMG/AMP.
3. Patient-derived iPSC neurons/organoids and myelinating co-cultures to model node assembly and conduction deficits in a human context.
4. Conditional / knock-in mouse models carrying human missense alleles to test genotype-specific severity and evaluate rescue.
5. Systematic natural-history study (developmental, EMG/NCS, MRI, orthopedic, ophthalmologic surveillance) with standardized QoL instruments.
6. Apply for Orphanet/ICD-11 codes and establish a patient registry to support future epidemiology and trials.
7. Cascade carrier screening and genetic-counseling protocols for consanguineous families with a known variant, including prenatal/PGD options.

Report compiled from 8 confirmed findings and 34 reviewed papers across 5 investigation iterations. Evidence types are labeled throughout as human clinical, model organism, in vitro, or computational.

Artifacts

• OpenScientist final report
• OpenScientist final report

Reference Validation

Checked with linkml-reference-validator 0.2.1.

References that may not be about this subject

These identifiers resolve, so they are not fabrications, but the records they resolve to share almost none of this report's vocabulary. That is a clue and not a verdict - a paper can be relevant in ways its title and abstract do not spell out - so read them before deciding:

• PMID:11728309 (6 mentions) - Nr-CAM and neurofascin interactions regulate ankyrin G and sodium channel clustering at the node of Ranvier.
• shared terms: node, conduction

Weighed against this report's own most characteristic terms: nrcam, variant, type, disorder, gene, phenotype, recessive, human, clinical, neuropathy, peripheral, disease, model, developmental, spasticity, node, genetic, conduction, severity, skeletal.

All extracted references resolved successfully. Resolving is not the same as being relevant, though - see the references listed above as possibly off topic.