CCN2-Related Kyphomelic Dysplasia

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Classifications

Harrison's Part

ISDS Skeletal Nosology

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Mappings

MONDO

MONDO:0008881 kyphomelic dysplasia Not Yet Curated

MONDO's machine-actionable identifiers on MONDO:0008881 point at this entity specifically: it xrefs OMIM:211350 (the CCN2-anchored recessive form) and asserts RO:0004003 HGNC:2500 CCN2 as the causal gene. Only the human-readable definition is stale — it still states that kyphomelic dysplasia is no longer its own entity and that cases should be reclassified, a position from PMID:11038441 (2000) predating the 2022 KIF5B and 2024 CCN2 gene discoveries. closeMatch rather than exactMatch because the term simultaneously carries the broader historical clinical-radiographic concept that the `Kyphomelic_Dysplasia` grouping models, so it cannot be cleanly equated with this member alone. Under the CLAUDE.md mapping-predicate rule, closeMatch correctly does not retire MONDO:0008881 from MONDO coverage tooling.

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Inheritance

1

Autosomal recessive inheritance HP:0000007

Two unrelated consanguineous families with six affected offspring between them, each segregating a homozygous CCN2 variant with the phenotype. The consanguinity and the segregation together establish recessive inheritance, and distinguish this form from the dominant de novo KIF5B form.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:39506047 SUPPORT Human Clinical

"We ascertained two unrelated consanguineous families with kyphomelic dysplasia."

Documents the consanguineous family structure consistent with recessive inheritance.

PMID:39506047 SUPPORT Human Clinical

"We noted two novel homozygous variants in CCN2 as possible candidates that segregated with the phenotype in the families: a missense variant c.443G>A; p.(Cys148Tyr) in exon 3 and a frameshift variant, c.779_786del; p.(Pro260LeufsTer7) in exon 5."

Records the homozygous genotypes and their segregation with the phenotype.

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Discussions and Knowledge Gaps

2

Does the mouse-derived chain from CCN2 loss through hypertrophic-zone matrix disturbance and reduced VEGF to impaired growth-plate angiogenesis operate in human CCN2-related kyphomelic dysplasia?

HUMAN MODEL MISMATCH OPEN ccn2_kd_intermediate_chain_is_mouse_derived

Attached to

pathophysiology#Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis pathophysiology#Impaired Chondrocyte Proliferation and Differentiation

Evidence exists in the model; its translational validity is the open question. The human data establish gene-disease causality — two consanguineous families, segregating homozygous variants, a concordant clinical phenotype — but say nothing about the intermediate steps. Every element of the mechanistic chain curated here (impaired chondrocyte proliferation, hypertrophic-zone matrix composition, reduced VEGF, failed vascular invasion) comes from the Ctgf-null mouse, and the zebrafish crispant contributes cartilage phenotype rather than mechanism. No human growth-plate tissue from a CCN2 patient has been examined. This matters because the angiogenic coupling is the part of the model that would be therapeutically interesting, and it is also the part furthest from human observation.

Proposed experiments

Growth-plate histology and VEGF in human CCN2 patient tissue

exp_ccn2_kd_human_growth_plate_histology

Where surgical specimens or post-mortem tissue are available from CCN2 patients, examine growth-plate zonal architecture, matrix composition and VEGF expression against age-matched controls, to test whether the mouse chain holds in human bone.

Patient-variant chondrocyte differentiation model

exp_ccn2_kd_patient_chondrocyte_model

Introduce the p.(Cys148Tyr) and p.(Pro260LeufsTer7) alleles into human induced pluripotent stem cell-derived chondrocytes and measure proliferation, matrix output and VEGF secretion, providing a human cellular test of the mouse-derived steps.

What distinguishes biallelic CCN2 loss causing recessive kyphomelic dysplasia from the monoallelic CCN2 variant causing dominant spondyloepimetaphyseal dysplasia with low bone mass?

KNOWLEDGE GAP OPEN ccn2_kd_allelic_series_with_dominant_semd

Attached to

pathophysiology#CCN2 Loss of Function

CCN2 is not a one-disease gene. A monoallelic signal-peptide variant, p.Arg22Pro, causes an autosomal dominant spondyloepimetaphyseal dysplasia with low bone mass through impaired secretion and intracellular retention — a different skeletal phenotype, a different inheritance mode and a different proximal defect from the biallelic loss-of-function alleles curated here. Both act in a loss-of-secretion or loss-of-function direction, so this reads as a genuine allelic series rather than opposed mechanisms, but nothing establishes whether dosage alone explains the phenotypic difference or whether signal-peptide retention has consequences that simple absence does not. The practical consequence is that a CCN2 variant found on a skeletal dysplasia panel cannot be interpreted from the gene alone.

Proposed experiments

Secretion and retention comparison across the CCN2 allelic series

exp_ccn2_allelic_series_secretion_comparison

Express p.Arg22Pro alongside the kyphomelic dysplasia alleles in a common background and compare secreted versus retained CCN2, endoplasmic reticulum stress markers and dominant-negative effect on co-expressed wild-type protein.

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Pathophysiology

4

CCN2 Loss of Function

Biallelic loss-of-function variants in CCN2 remove or impair the matricellular protein CCN2 (connective tissue growth factor). Two homozygous alleles are reported: a missense c.443G>A p.(Cys148Tyr) in exon 3 and a frameshift c.779_786del p.(Pro260LeufsTer7) in exon 5.

CCN2 hgnc:2500

Genetic context variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Homozygous germline missense and frameshift alleles in two consanguineous families.

Downstream

Impaired Chondrocyte Proliferation and Differentiation

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"We noted two novel homozygous variants in CCN2 as possible candidates that segregated with the phenotype in the families: a missense variant c.443G>A; p.(Cys148Tyr) in exon 3 and a frameshift variant, c.779_786del; p.(Pro260LeufsTer7) in exon 5."

Identifies both pathogenic alleles at nucleotide and protein level.

Impaired Chondrocyte Proliferation and Differentiation

CCN2 is required for chondrocyte proliferation and differentiation. Losing it disrupts the orderly progression of growth plate chondrocytes on which endochondral bone formation depends, so the long bones that form by that route are laid down abnormally.

Chondrocyte CL:0000138

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

Animal models

ccn2a F0 CRISPR knockout zebrafish Zebrafish recapitulates Reproduces impaired cartilage formation on loss of the CCN2 orthologue, supporting the chondrocyte node.

Downstream

Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis

Show evidence (2 references)

PMID:39506047 SUPPORT Other

"CCN2 is crucial for proliferation and differentiation of chondrocytes."

States the cellular function of CCN2 whose loss drives this node.

PMID:39506047 SUPPORT Model Organism

"F0 knockouts of ccn2a in zebrafish showed altered body curvature, impaired cartilage formation in craniofacial region and either bent or missing tails."

Demonstrates impaired cartilage formation on CCN2 loss in an independent model organism.

Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis

Mouse work on the Ctgf null defines the step between the chondrocyte defect and the malformed bone: matrix composition within the growth plate's hypertrophic zone is disturbed, and VEGF expression in that zone falls, coupling the cartilage defect to failure of the vascular invasion that endochondral ossification depends on. CCN2 is on this account a coordinator of chondrogenesis and angiogenesis rather than a chondrocyte-autonomous factor. The node is PROVISIONAL because this entire intermediate chain is mouse-derived: the human evidence establishes that CCN2 causes the disease, not that these are the steps by which it does so.

Hypertrophic chondrocyte CL:0000743

cartilage development GO:0051216 ⚠ ABNORMAL

Downstream

Bent Bone Skeletal Dysplasia

Show evidence (2 references)

PMID:12736220 SUPPORT Model Organism

"Ctgf deficiency leads to skeletal dysmorphisms as a result of impaired chondrocyte proliferation and extracellular matrix composition within the hypertrophic zone."

Establishes the hypertrophic-zone matrix defect as the route from CCN2 loss to skeletal dysmorphism in the mouse.

PMID:12736220 SUPPORT Model Organism

"These defects are linked to decreased expression of vascular endothelial growth factor (VEGF) in the hypertrophic zones of Ctgf mutants."

Links the matrix defect to reduced VEGF and therefore to impaired growth-plate angiogenesis.

Bent Bone Skeletal Dysplasia

The skeletal endpoint: sharply angulated (kyphomelic) femora with bowing of the long bones, radial head dislocations and mild platyspondyly, together with the craniofacial features — cleft palate and micro-retrognathia — that follow from the same chondrocyte defect acting on craniofacial cartilage.

Animal models

Ccn2 knockout mouse Mouse recapitulates Reproduces both the limb and craniofacial arms of the human phenotype, including twisted limbs and cleft palate.

Show evidence (2 references)

PMID:39506047 SUPPORT Human Clinical

"Radiographs revealed kyphomelic femora, bowing of long bones, radial head dislocations and mild platyspondyly."

Documents the radiographic skeletal phenotype.

PMID:39506047 SUPPORT Model Organism

"Earlier studies have shown that Ccn2-deficient mice exhibit twisted limbs, short and kinked sterna, broad vertebrae, domed cranial vault, shorter mandibles, and cleft palate."

Shows the mouse null reproduces both the limb-bowing and the cleft palate arms of the human phenotype.

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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

6

Head and Neck 1

Cleft Palate HP:0000175

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"All the probands had short stature, cleft palate, and micro-retrognathia."

Documents cleft palate in all reported probands.

Limbs 2

Kyphomelic Femora and Long Bone Bowing Femoral bowing HP:0002980

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"Radiographs revealed kyphomelic femora, bowing of long bones, radial head dislocations and mild platyspondyly."

Documents femoral kyphomelia and long bone bowing.

Radial Head Dislocation Dislocated radial head HP:0003083

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"Radiographs revealed kyphomelic femora, bowing of long bones, radial head dislocations and mild platyspondyly."

Documents radial head dislocation.

Musculoskeletal 1

Platyspondyly HP:0000926

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"Radiographs revealed kyphomelic femora, bowing of long bones, radial head dislocations and mild platyspondyly."

Documents mild platyspondyly.

Growth 1

Short Stature HP:0004322

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"All the probands had short stature, cleft palate, and micro-retrognathia."

Documents short stature in all reported probands.

Other 1

Micro-retrognathia HP:0000308

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"All the probands had short stature, cleft palate, and micro-retrognathia."

Documents micro-retrognathia in all reported probands.

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Genetic Associations

1

CCN2

Gene: CCN2 hgnc:2500 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:39506047 SUPPORT Human Clinical

"Our observations in humans and zebrafish combined with previously described skeletal phenotype of Ccn2 knock out mice, confirm that biallelic loss of function variants in CCN2 result in an autosomal recessive kyphomelic dysplasia."

The authors' summary of the multi-species evidence for the gene-disease relationship.

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External Assertions

1

OMIM kyphomelic dysplasia record

OMIM disease record OMIM:211350

OMIM's record for the recessive CCN2-anchored form. This is the identifier MONDO:0008881 xrefs, and the one that separates this entity from OMIM:621644 (the KIF5B-related dominant form). The split at OMIM is the external evidence that the clinical label covers more than one entity.

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Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from CCN2-Related Kyphomelic Dysplasia:

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Animal Models

2

ccn2a F0 CRISPR knockout zebrafish

CRISPR-Cas9 F0 knockout of ccn2a, generated as part of the study reporting the human CCN2 variants.

Species

Zebrafish

Genotype

ccn2a F0 CRISPR-Cas9 knockout

Publication

PMID:39506047

Pathograph links

Impaired Chondrocyte Proliferation and Differentiation recapitulates fidelity: moderate Reproduces impaired cartilage formation on loss of the CCN2 orthologue, supporting the chondrocyte node.

Limitations: F0 crispant rather than a stable germline line, so mosaicism is expected; zebrafish carry ccn2a and ccn2b paralogues, and the human disease alleles include a missense whose specific consequence a knockout cannot model.

Readouts

Craniofacial cartilage formation

Direction: DECREASED

Interpretation: Impaired craniofacial cartilage in crispants, the counterpart of the human cleft palate and micro-retrognathia.

Show evidence (1 reference)

PMID:39506047 SUPPORT Model Organism

"F0 knockouts of ccn2a in zebrafish showed altered body curvature, impaired cartilage formation in craniofacial region and either bent or missing tails."

The cartilage measurement underlying this readout.

Show evidence (1 reference)

PMID:39506047 SUPPORT Model Organism

"We studied the impact of CCN2 knockout in zebrafish models via CRISPR-Cas9 gene editing."

Establishes the model and the perturbation used to test the chondrocyte node.

Ccn2 knockout mouse

Previously described Ccn2-deficient mouse, cited as cross-species support for the human gene-disease relationship.

Species

Mouse

Genotype

Ccn2 null

Publication

PMID:39506047

Pathograph links

Bent Bone Skeletal Dysplasia recapitulates fidelity: moderate Reproduces both the limb and craniofacial arms of the human phenotype, including twisted limbs and cleft palate.

Limitations: A complete null, whereas the human alleles include a missense; the mouse phenotype is described in the CCN2 report as previously established rather than generated alongside the patient data, so assay comparability with the human skeletal survey is limited.

Readouts

Limb and craniofacial skeletal morphology

Direction: ALTERED

Interpretation: Twisted limbs, kinked sterna, broad vertebrae, domed cranial vault, shortened mandibles and cleft palate.

Show evidence (1 reference)

PMID:39506047 SUPPORT Model Organism

"Earlier studies have shown that Ccn2-deficient mice exhibit twisted limbs, short and kinked sterna, broad vertebrae, domed cranial vault, shorter mandibles, and cleft palate."

The skeletal phenotype underlying this readout.

Show evidence (1 reference)

PMID:39506047 SUPPORT Model Organism

"Our observations in humans and zebrafish combined with previously described skeletal phenotype of Ccn2 knock out mice, confirm that biallelic loss of function variants in CCN2 result in an autosomal recessive kyphomelic dysplasia."

Records the authors' use of the mouse phenotype as support for the gene-disease relationship.

{ }

Source YAML

click to show

name: CCN2-Related Kyphomelic Dysplasia
creation_date: "2026-08-22T00:00:00Z"
description: >-
  CCN2-related kyphomelic dysplasia is an autosomal recessive bent-bone skeletal
  dysplasia caused by biallelic loss-of-function variants in CCN2 (formerly
  CTGF), a matricellular protein required for chondrocyte proliferation and
  differentiation. It is one of two molecularly defined forms of kyphomelic
  dysplasia, the other being the dominant, de novo KIF5B-related form; the two
  share a bent-bone radiographic phenotype but differ in gene, inheritance and
  mechanism. Affected individuals have short stature, cleft palate and
  micro-retrognathia, with kyphomelic (sharply angulated) femora, bowing of the
  long bones, radial head dislocations and mild platyspondyly. The gene-disease
  relationship rests on segregation in two consanguineous families together with
  concordant skeletal phenotypes in Ccn2-deficient mice and CRISPR-generated
  ccn2a-knockout zebrafish.
category: Mendelian
parents:
- hereditary disease
synonyms:
- CCN2-related kyphomelic dysplasia
- autosomal recessive kyphomelic dysplasia
- CTGF-related kyphomelic dysplasia
- kyphomelic dysplasia, CCN2 type
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
    evidence:
    - reference: PMID:39506047
      reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Our observations in humans and zebrafish combined with previously
        described skeletal phenotype of Ccn2 knock out mice, confirm that
        biallelic loss of function variants in CCN2 result in an autosomal
        recessive kyphomelic dysplasia.
      explanation: >-
        Establishes a single-gene autosomal recessive Mendelian basis.
  isds_skeletal_category:
  - classification_value: bent_bone_dysplasia
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (11th edition;
      Unger et al., PMID:36779427), group 20 "Bent bones dysplasia group". The
      2023 table carries one kyphomelic row, NOS 20-0040, and that row is the
      pre-split conflated concept: it is named "Kyphomelic dysplasia with facial
      dysmorphism, KIF5B-related" but is keyed to MIM 211350, the identifier
      OMIM now anchors to this recessive CCN2 form (OMIM:621644 is the
      KIF5B-related dominant form). The row's own caveat, that "the name
      'kyphomelic dysplasia' has been applied to heterogeneous conditions",
      says the committee knew it was covering more than one entity.

      This entity is therefore assigned to group 20 on the MIM anchor of NOS
      20-0040, not on its gene attribution, which names the other form. The
      assignment is an extension of the table rather than a transcription of
      it: CCN2 was published (PMID:39506047, 2024) after the 2023 revision
      closed, so the committee could not have listed it. Recorded here rather
      than withheld because leaving the entity unclassified would drop a bona
      fide bent-bone dysplasia out of the group entirely; re-verify against the
      next revision, which should split NOS 20-0040 into two rows.
references:
- reference: PMID:39506047
  title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
- reference: PMID:35342932
  title: "De novo heterozygous variants in KIF5B cause kyphomelic dysplasia."
- reference: PMID:12736220
  title: "Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development."
- reference: PMID:39414788
  title: "A monoallelic variant in CCN2 causes an autosomal dominant spondyloepimetaphyseal dysplasia with low bone mass."
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0008881
      label: kyphomelic dysplasia
    mapping_predicate: skos:closeMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO's machine-actionable identifiers on MONDO:0008881 point at this
      entity specifically: it xrefs OMIM:211350 (the CCN2-anchored recessive
      form) and asserts RO:0004003 HGNC:2500 CCN2 as the causal gene. Only the
      human-readable definition is stale — it still states that kyphomelic
      dysplasia is no longer its own entity and that cases should be
      reclassified, a position from PMID:11038441 (2000) predating the 2022
      KIF5B and 2024 CCN2 gene discoveries. closeMatch rather than exactMatch
      because the term simultaneously carries the broader historical
      clinical-radiographic concept that the `Kyphomelic_Dysplasia` grouping
      models, so it cannot be cleanly equated with this member alone. Under the
      CLAUDE.md mapping-predicate rule, closeMatch correctly does not retire
      MONDO:0008881 from MONDO coverage tooling.
external_assertions:
- name: OMIM kyphomelic dysplasia record
  source: OMIM
  assertion_type: disease_record
  external_id: OMIM:211350
  url: https://omim.org/entry/211350
  description: >-
    OMIM's record for the recessive CCN2-anchored form. This is the identifier
    MONDO:0008881 xrefs, and the one that separates this entity from
    OMIM:621644 (the KIF5B-related dominant form). The split at OMIM is the
    external evidence that the clinical label covers more than one entity.
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Two unrelated consanguineous families with six affected offspring between
    them, each segregating a homozygous CCN2 variant with the phenotype. The
    consanguinity and the segregation together establish recessive inheritance,
    and distinguish this form from the dominant de novo KIF5B form.
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We ascertained two unrelated consanguineous families with kyphomelic
      dysplasia.
    explanation: >-
      Documents the consanguineous family structure consistent with recessive
      inheritance.
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We noted two novel homozygous variants in CCN2 as possible candidates that
      segregated with the phenotype in the families: a missense variant c.443G>A;
      p.(Cys148Tyr) in exon 3 and a frameshift variant, c.779_786del;
      p.(Pro260LeufsTer7) in exon 5.
    explanation: >-
      Records the homozygous genotypes and their segregation with the phenotype.
pathophysiology:
- name: CCN2 Loss of Function
  biological_scale: MOLECULAR
  role: trigger
  mechanism_confidence: ESTABLISHED
  description: >-
    Biallelic loss-of-function variants in CCN2 remove or impair the
    matricellular protein CCN2 (connective tissue growth factor). Two homozygous
    alleles are reported: a missense c.443G>A p.(Cys148Tyr) in exon 3 and a
    frameshift c.779_786del p.(Pro260LeufsTer7) in exon 5.
  genes:
  - preferred_term: CCN2
    term:
      id: hgnc:2500
      label: CCN2
  genetic_context:
    functional_impact_category: LOSS_OF_FUNCTION
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    description: >-
      Homozygous germline missense and frameshift alleles in two consanguineous
      families.
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We noted two novel homozygous variants in CCN2 as possible candidates that
      segregated with the phenotype in the families: a missense variant c.443G>A;
      p.(Cys148Tyr) in exon 3 and a frameshift variant, c.779_786del;
      p.(Pro260LeufsTer7) in exon 5.
    explanation: >-
      Identifies both pathogenic alleles at nucleotide and protein level.
  downstream:
  - target: Impaired Chondrocyte Proliferation and Differentiation
- name: Impaired Chondrocyte Proliferation and Differentiation
  biological_scale: CELLULAR
  role: central_effector
  mechanism_confidence: ESTABLISHED
  description: >-
    CCN2 is required for chondrocyte proliferation and differentiation. Losing it
    disrupts the orderly progression of growth plate chondrocytes on which
    endochondral bone formation depends, so the long bones that form by that
    route are laid down abnormally.
  biological_processes:
  - preferred_term: chondrocyte differentiation
    modifier: DECREASED
    term:
      id: GO:0002062
      label: chondrocyte differentiation
  - preferred_term: cartilage development
    modifier: ABNORMAL
    term:
      id: GO:0051216
      label: cartilage development
  cell_types:
  - preferred_term: Chondrocyte
    term:
      id: CL:0000138
      label: chondrocyte
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      CCN2 is crucial for proliferation and differentiation of chondrocytes.
    explanation: >-
      States the cellular function of CCN2 whose loss drives this node.
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      F0 knockouts of ccn2a in zebrafish showed altered body curvature, impaired
      cartilage formation in craniofacial region and either bent or missing tails.
    explanation: >-
      Demonstrates impaired cartilage formation on CCN2 loss in an independent
      model organism.
  downstream:
  - target: Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis
- name: Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis
  biological_scale: TISSUE
  role: central_effector
  mechanism_confidence: PROVISIONAL
  description: >-
    Mouse work on the Ctgf null defines the step between the chondrocyte defect
    and the malformed bone: matrix composition within the growth plate's
    hypertrophic zone is disturbed, and VEGF expression in that zone falls,
    coupling the cartilage defect to failure of the vascular invasion that
    endochondral ossification depends on. CCN2 is on this account a coordinator
    of chondrogenesis and angiogenesis rather than a chondrocyte-autonomous
    factor. The node is PROVISIONAL because this entire intermediate chain is
    mouse-derived: the human evidence establishes that CCN2 causes the disease,
    not that these are the steps by which it does so.
  biological_processes:
  - preferred_term: cartilage development
    modifier: ABNORMAL
    term:
      id: GO:0051216
      label: cartilage development
  cell_types:
  - preferred_term: Hypertrophic chondrocyte
    term:
      id: CL:0000743
      label: hypertrophic chondrocyte
  evidence:
  - reference: PMID:12736220
    reference_title: "Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ctgf deficiency leads to skeletal dysmorphisms as a result of impaired
      chondrocyte proliferation and extracellular matrix composition within the
      hypertrophic zone.
    explanation: >-
      Establishes the hypertrophic-zone matrix defect as the route from CCN2 loss
      to skeletal dysmorphism in the mouse.
  - reference: PMID:12736220
    reference_title: "Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      These defects are linked to decreased expression of vascular endothelial
      growth factor (VEGF) in the hypertrophic zones of Ctgf mutants.
    explanation: >-
      Links the matrix defect to reduced VEGF and therefore to impaired
      growth-plate angiogenesis.
  downstream:
  - target: Bent Bone Skeletal Dysplasia
- name: Bent Bone Skeletal Dysplasia
  biological_scale: ORGANISM
  role: consequence
  mechanism_confidence: ESTABLISHED
  description: >-
    The skeletal endpoint: sharply angulated (kyphomelic) femora with bowing of
    the long bones, radial head dislocations and mild platyspondyly, together
    with the craniofacial features — cleft palate and micro-retrognathia — that
    follow from the same chondrocyte defect acting on craniofacial cartilage.
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiographs revealed kyphomelic femora, bowing of long bones, radial head
      dislocations and mild platyspondyly.
    explanation: >-
      Documents the radiographic skeletal phenotype.
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Earlier studies have shown that Ccn2-deficient mice exhibit twisted limbs,
      short and kinked sterna, broad vertebrae, domed cranial vault, shorter
      mandibles, and cleft palate.
    explanation: >-
      Shows the mouse null reproduces both the limb-bowing and the cleft palate
      arms of the human phenotype.
phenotypes:
- category: Musculoskeletal
  name: Kyphomelic Femora and Long Bone Bowing
  description: >-
    The defining radiographic feature: sharply angulated femora with bowing of
    the other long bones.
  phenotype_term:
    preferred_term: Femoral bowing
    term:
      id: HP:0002980
      label: Femoral bowing
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiographs revealed kyphomelic femora, bowing of long bones, radial head
      dislocations and mild platyspondyly.
    explanation: >-
      Documents femoral kyphomelia and long bone bowing.
- category: Musculoskeletal
  name: Radial Head Dislocation
  description: >-
    Present on skeletal survey in the reported probands.
  phenotype_term:
    preferred_term: Dislocated radial head
    term:
      id: HP:0003083
      label: Dislocated radial head
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiographs revealed kyphomelic femora, bowing of long bones, radial head
      dislocations and mild platyspondyly.
    explanation: >-
      Documents radial head dislocation.
- category: Musculoskeletal
  name: Platyspondyly
  description: >-
    Mild vertebral body flattening, indicating that the chondrocyte defect
    affects the axial as well as the appendicular skeleton.
  phenotype_term:
    preferred_term: Platyspondyly
    term:
      id: HP:0000926
      label: Platyspondyly
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiographs revealed kyphomelic femora, bowing of long bones, radial head
      dislocations and mild platyspondyly.
    explanation: >-
      Documents mild platyspondyly.
- category: Craniofacial
  name: Cleft Palate
  description: >-
    Present in all probands, and reproduced in the Ccn2-null mouse, which links
    it to the same chondrocyte defect rather than to an independent lesion.
  phenotype_term:
    preferred_term: Cleft palate
    term:
      id: HP:0000175
      label: Cleft palate
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the probands had short stature, cleft palate, and micro-retrognathia.
    explanation: >-
      Documents cleft palate in all reported probands.
- category: Craniofacial
  name: Micro-retrognathia
  description: >-
    Small, posteriorly set mandible, present in all probands and mirrored by the
    shorter mandibles of the Ccn2-null mouse.
  phenotype_term:
    preferred_term: Microretrognathia
    term:
      id: HP:0000308
      label: Microretrognathia
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the probands had short stature, cleft palate, and micro-retrognathia.
    explanation: >-
      Documents micro-retrognathia in all reported probands.
- category: Growth
  name: Short Stature
  description: >-
    Present in all probands, the expected growth consequence of a growth plate
    chondrocyte defect.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the probands had short stature, cleft palate, and micro-retrognathia.
    explanation: >-
      Documents short stature in all reported probands.
genetic:
- name: CCN2
  gene_term:
    preferred_term: CCN2
    term:
      id: hgnc:2500
      label: CCN2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  presence: PRESENT
  frequency: Biallelic in all reported patients
  notes: >-
    CCN2 (formerly CTGF) encodes a matricellular protein of the CCN family
    required for chondrocyte proliferation and differentiation. The two reported
    pathogenic alleles are homozygous: a missense p.(Cys148Tyr) and a frameshift
    p.(Pro260LeufsTer7). Cross-species support is unusually good for a
    two-family gene-disease assertion — the Ccn2-null mouse and a CRISPR-Cas9
    ccn2a zebrafish knockout both show concordant skeletal and craniofacial
    phenotypes.
  evidence:
  - reference: PMID:39506047
    reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our observations in humans and zebrafish combined with previously described
      skeletal phenotype of Ccn2 knock out mice, confirm that biallelic loss of
      function variants in CCN2 result in an autosomal recessive kyphomelic
      dysplasia.
    explanation: >-
      The authors' summary of the multi-species evidence for the gene-disease
      relationship.
animal_models:
- name: ccn2a F0 CRISPR knockout zebrafish
  species: Zebrafish
  genotype: ccn2a F0 CRISPR-Cas9 knockout
  publication: PMID:39506047
  description: >-
    CRISPR-Cas9 F0 knockout of ccn2a, generated as part of the study reporting
    the human CCN2 variants.
  modeled_mechanisms:
  - target: Impaired Chondrocyte Proliferation and Differentiation
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces impaired cartilage formation on loss of the CCN2 orthologue,
      supporting the chondrocyte node.
    limitations: >-
      F0 crispant rather than a stable germline line, so mosaicism is expected;
      zebrafish carry ccn2a and ccn2b paralogues, and the human disease alleles
      include a missense whose specific consequence a knockout cannot model.
    readouts:
    - name: Craniofacial cartilage formation
      target: Impaired Chondrocyte Proliferation and Differentiation
      direction: DECREASED
      interpretation: >-
        Impaired craniofacial cartilage in crispants, the counterpart of the human
        cleft palate and micro-retrognathia.
      evidence:
      - reference: PMID:39506047
        reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          F0 knockouts of ccn2a in zebrafish showed altered body curvature,
          impaired cartilage formation in craniofacial region and either bent or
          missing tails.
        explanation: >-
          The cartilage measurement underlying this readout.
    evidence:
    - reference: PMID:39506047
      reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We studied the impact of CCN2 knockout in zebrafish models via CRISPR-Cas9
        gene editing.
      explanation: >-
        Establishes the model and the perturbation used to test the chondrocyte
        node.
- name: Ccn2 knockout mouse
  species: Mouse
  genotype: Ccn2 null
  publication: PMID:39506047
  description: >-
    Previously described Ccn2-deficient mouse, cited as cross-species support for
    the human gene-disease relationship.
  modeled_mechanisms:
  - target: Bent Bone Skeletal Dysplasia
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces both the limb and craniofacial arms of the human phenotype,
      including twisted limbs and cleft palate.
    limitations: >-
      A complete null, whereas the human alleles include a missense; the mouse
      phenotype is described in the CCN2 report as previously established rather
      than generated alongside the patient data, so assay comparability with the
      human skeletal survey is limited.
    readouts:
    - name: Limb and craniofacial skeletal morphology
      target: Bent Bone Skeletal Dysplasia
      direction: ALTERED
      interpretation: >-
        Twisted limbs, kinked sterna, broad vertebrae, domed cranial vault,
        shortened mandibles and cleft palate.
      evidence:
      - reference: PMID:39506047
        reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Earlier studies have shown that Ccn2-deficient mice exhibit twisted
          limbs, short and kinked sterna, broad vertebrae, domed cranial vault,
          shorter mandibles, and cleft palate.
        explanation: >-
          The skeletal phenotype underlying this readout.
    evidence:
    - reference: PMID:39506047
      reference_title: "Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Our observations in humans and zebrafish combined with previously
        described skeletal phenotype of Ccn2 knock out mice, confirm that
        biallelic loss of function variants in CCN2 result in an autosomal
        recessive kyphomelic dysplasia.
      explanation: >-
        Records the authors' use of the mouse phenotype as support for the
        gene-disease relationship.
differential_diagnoses:
- name: KIF5B-Related Kyphomelic Dysplasia
  description: >-
    The other molecularly defined form of kyphomelic dysplasia, and the primary
    differential. It is caused by de novo heterozygous KIF5B variants and is
    therefore dominant rather than recessive, arises in a kinesin motor protein
    rather than a matricellular protein, and characteristically adds postnatal
    osteoporosis with fractures and optic atrophy — none of which are features of
    the CCN2 form. Family structure alone is suggestive (consanguinity and
    sibling recurrence versus a sporadic de novo case), but the two are properly
    separated by sequencing.
  evidence:
  - reference: PMID:35342932
    reference_title: "De novo heterozygous variants in KIF5B cause kyphomelic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings suggest that heterozygous KIF5B deleterious variants cause a
      specific form of kyphomelic dysplasia.
    explanation: >-
      Establishes the KIF5B form as a distinct entity under the same clinical
      label.
discussions:
- discussion_id: ccn2_kd_intermediate_chain_is_mouse_derived
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Does the mouse-derived chain from CCN2 loss through hypertrophic-zone matrix
    disturbance and reduced VEGF to impaired growth-plate angiogenesis operate in
    human CCN2-related kyphomelic dysplasia?
  attaches_to:
  - "pathophysiology#Impaired Hypertrophic-Zone Matrix Remodeling and Growth-Plate Angiogenesis"
  - "pathophysiology#Impaired Chondrocyte Proliferation and Differentiation"
  rationale: >-
    Evidence exists in the model; its translational validity is the open
    question. The human data establish gene-disease causality — two consanguineous
    families, segregating homozygous variants, a concordant clinical phenotype —
    but say nothing about the intermediate steps. Every element of the mechanistic
    chain curated here (impaired chondrocyte proliferation, hypertrophic-zone
    matrix composition, reduced VEGF, failed vascular invasion) comes from the
    Ctgf-null mouse, and the zebrafish crispant contributes cartilage phenotype
    rather than mechanism. No human growth-plate tissue from a CCN2 patient has
    been examined. This matters because the angiogenic coupling is the part of the
    model that would be therapeutically interesting, and it is also the part
    furthest from human observation.
  proposed_experiments:
  - experiment_id: exp_ccn2_kd_human_growth_plate_histology
    name: Growth-plate histology and VEGF in human CCN2 patient tissue
    description: >-
      Where surgical specimens or post-mortem tissue are available from CCN2
      patients, examine growth-plate zonal architecture, matrix composition and
      VEGF expression against age-matched controls, to test whether the mouse
      chain holds in human bone.
  - experiment_id: exp_ccn2_kd_patient_chondrocyte_model
    name: Patient-variant chondrocyte differentiation model
    description: >-
      Introduce the p.(Cys148Tyr) and p.(Pro260LeufsTer7) alleles into human
      induced pluripotent stem cell-derived chondrocytes and measure
      proliferation, matrix output and VEGF secretion, providing a human cellular
      test of the mouse-derived steps.
- discussion_id: ccn2_kd_allelic_series_with_dominant_semd
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What distinguishes biallelic CCN2 loss causing recessive kyphomelic dysplasia
    from the monoallelic CCN2 variant causing dominant spondyloepimetaphyseal
    dysplasia with low bone mass?
  attaches_to:
  - "pathophysiology#CCN2 Loss of Function"
  rationale: >-
    CCN2 is not a one-disease gene. A monoallelic signal-peptide variant,
    p.Arg22Pro, causes an autosomal dominant spondyloepimetaphyseal dysplasia
    with low bone mass through impaired secretion and intracellular retention —
    a different skeletal phenotype, a different inheritance mode and a different
    proximal defect from the biallelic loss-of-function alleles curated here.
    Both act in a loss-of-secretion or loss-of-function direction, so this reads
    as a genuine allelic series rather than opposed mechanisms, but nothing
    establishes whether dosage alone explains the phenotypic difference or
    whether signal-peptide retention has consequences that simple absence does
    not. The practical consequence is that a CCN2 variant found on a skeletal
    dysplasia panel cannot be interpreted from the gene alone.
  proposed_experiments:
  - experiment_id: exp_ccn2_allelic_series_secretion_comparison
    name: Secretion and retention comparison across the CCN2 allelic series
    description: >-
      Express p.Arg22Pro alongside the kyphomelic dysplasia alleles in a common
      background and compare secreted versus retained CCN2, endoplasmic reticulum
      stress markers and dominant-negative effect on co-expressed wild-type
      protein.
notes: >-
  Scope. This entry curates the CCN2-anchored autosomal recessive form of
  kyphomelic dysplasia. It is a member of the `Kyphomelic_Dysplasia` grouping,
  which unions it with the KIF5B-related dominant form; the grouping carries the
  MONDO:0008881 mapping and the reasoning for why the clinical label is a
  grouping rather than a single disease.

  Why this is not curated as "kyphomelic dysplasia". Both papers that
  molecularly defined a form of this condition describe the clinical label as a
  heterogeneous group of skeletal dysplasias. Curating a single Disease entry
  under that label would have merged a dominant kinesin-motor disorder with a
  recessive matricellular-protein disorder on the strength of a shared
  radiographic appearance. Note that MONDO attaches CCN2 to MONDO:0008881 as the
  causal gene, which is the assertion that brought this stub into the queue with
  one gene attached; the literature does not support treating that as the whole
  entity.

  Allelic series. CCN2 also causes an autosomal dominant spondyloepimetaphyseal
  dysplasia with low bone mass via a monoallelic signal-peptide variant
  (p.Arg22Pro), which is a distinct entity from this one and is curated as an open
  discussion rather than folded in. A CCN2 variant on a skeletal dysplasia panel
  therefore needs zygosity and variant position before it can be interpreted.

  Evidence base. Two consanguineous families with six affected offspring, plus
  concordant mouse and zebrafish models. That is a small human series, but the
  cross-species concordance is unusually strong for a recent gene-disease
  assertion. No treatment evidence exists, so no treatments block is curated.

📚

References & Deep Research

References

4

PMID:39506047

Biallelic variants in CCN2 underlie an autosomal recessive kyphomelic dysplasia.

No top-level findings curated for this source.

PMID:35342932

De novo heterozygous variants in KIF5B cause kyphomelic dysplasia.

No top-level findings curated for this source.

PMID:12736220

Connective tissue growth factor coordinates chondrogenesis and angiogenesis during skeletal development.

No top-level findings curated for this source.

PMID:39414788

A monoallelic variant in CCN2 causes an autosomal dominant spondyloepimetaphyseal dysplasia with low bone mass.

No top-level findings curated for this source.

CCN2-Related Kyphomelic Dysplasia

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References