Chondrodysplasia Punctata (CDP)

name: Chondrodysplasia Punctata
display_name: Chondrodysplasia Punctata (CDP)
creation_date: "2026-07-01T00:00:00Z"
description: >-
  Chondrodysplasia punctata (CDP) is a clinically defined, etiologically heterogeneous
  family of skeletal disorders unified by a single radiographic hallmark: punctate
  ("stippled") foci of abnormal calcification in the epiphyseal and other cartilaginous
  regions during infancy. Beyond that shared imaging signature the group is mechanistically
  diverse, and its diversity is the point of assembling it. It spans peroxisomal disorders
  (defective PTS2 matrix-protein import in RCDP1 and RCDP5, and single-enzyme ether-lipid
  biosynthesis defects in RCDP2/3/4), disorders of post-squalene cholesterol biosynthesis
  (CDPX2 at the delta8-delta7 isomerase, CHILD syndrome at NSDHL, Greenberg dysplasia at
  the C14 reductase carried by LBR), a sulfatase deficiency whose substrate is still
  unknown (CDPX1), the loss of an inhibitor of mineralization (Keutel syndrome), and an
  entity with no molecular cause at all (the tibial-metacarpal type). It also has a set of
  acquired phenocopies - maternal warfarin exposure, early-gestation vitamin K deficiency,
  maternal autoimmune disease - which reach the same radiographic endpoint without a
  germline lesion and are deliberately excluded from membership here. Members converge on
  the chondrodysplasia punctata radiographic phenotype while diverging in causal gene,
  metabolic pathway, inheritance, and extraskeletal features: rhizomelic versus
  brachytelephalangic versus tibial-metacarpal limb patterns, cataract, ichthyosis,
  developmental impairment, cardiovascular disease, and outcomes from perinatal lethality
  to a normal adult life.
grouping_basis:
- SHARED_PHENOTYPE
- CLINICAL_CONVENTION
grouping_rationale: >-
  The members are lumped by a shared *radiographic* phenotype - punctate calcification of
  cartilage - which is the defining, historically diagnostic feature, the basis of the
  clinical "chondrodysplasia punctata" convention, and the organizing principle of group 23
  of the ISDS Nosology of Genetic Skeletal Disorders (2023 revision, Unger et al.,
  PMID:36779427). They are kept as separate Disease entries because the underlying
  mechanisms have almost nothing in common: three distinct arms of peroxisomal biology, two
  different enzymatic steps of post-squalene cholesterol synthesis plus a third carried by a
  nuclear-envelope protein, an unsolved sulfatase deficiency, and a lost calcification
  inhibitor whose lesion runs in the opposite direction from all the others. Grouping by the
  convergent radiographic phenotype makes the family navigable - it is how a stippled
  newborn is actually worked up - while preserving the mechanistic distinctions that drive
  biochemical testing, prognosis, and counselling. Both criteria are stated as NECESSARY:
  each is entailed by membership, but neither establishes it, since the punctate-calcification
  finding is shared with acquired phenocopies that carry no germline lesion and are not
  members.
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0019701
      label: chondrodysplasia punctata
    mapping_predicate: skos:closeMatch
    mapping_source: MONDO
    mapping_justification: >-
      MONDO:0019701 (chondrodysplasia punctata) is the clinical umbrella class for the CDP
      family, and this grouping now enumerates the genetic CDP entities the ISDS nosology
      recognizes - both X-linked forms, all the rhizomelic forms, CHILD syndrome, Greenberg
      dysplasia, Keutel syndrome, and the tibial-metacarpal type. A closeMatch rather than an
      exactMatch is used because the two sets still differ at the edges: MONDO's subtree also
      subsumes chromosomal and acquired phenocopy descendants, which this grouping
      deliberately excludes, and the grouping lumps RCDP2/3/4 into a single member entry that
      MONDO splits.
    consistency:
    - reference: MONDO
      consistent: CONSISTENT
      notes: >-
        Every listed member is an is-a descendant of MONDO:0019701 (chondrodysplasia
        punctata) or, in the case of CHILD syndrome (MONDO:0010621), classified beneath it in
        MONDO. The grouping is a consistent subset that does not enumerate the acquired and
        chromosomal phenocopy descendants.
membership_criteria:
- description: >-
    A member is listed in group 23 "Chondrodysplasia punctata (CDP) group" of the ISDS
    Nosology of Genetic Skeletal Disorders, 2023 revision (Unger et al., PMID:36779427), and
    carries that assignment on its Disease entry.
  criteria_semantics: NECESSARY
  logic:
    criterion_predicate: HAS_CLASSIFICATION
    classification: "isds_skeletal_category:chondrodysplasia_punctata"
    description: >-
      Assigned to ISDS group 23 via classifications.isds_skeletal_category on the member
      Disease entry. Stated in the keyed `<slot>:<value>` form so the audit reads the
      structured classifications block. This criterion is what fixes the grouping's scope to
      recognized genetic entities and excludes the acquired phenocopies (warfarin
      embryopathy, vitamin-K-deficiency and maternal-autoimmune brachytelephalangic CDP),
      which the nosology does not list because they are not inherited skeletal disorders.
- description: >-
    A member exhibits punctate or stippled calcification of cartilage on infantile
    radiographs - the defining radiographic hallmark of the CDP family.
  criteria_semantics: NECESSARY
  logic:
    criterion_predicate: HAS_PHENOTYPE
    description: >-
      Anchored at HP:0010766 (Ectopic calcification) rather than at the narrower
      HP:0010655 (Epiphyseal stippling) so that HP closure covers the different descendant
      terms the members legitimately use: most carry HP:0010655, CHILD syndrome carries
      HP:0002764 (Stippled chondral calcification), and Keutel syndrome additionally carries
      HP:0100593 (Calcification of cartilage) and HP:0002787 (Tracheal calcification) for
      calcification at sites outside the epiphyses. HP:0010655 and HP:0002764 are siblings
      rather than ancestor and descendant, so a criterion stated at either one would report
      a false negative for members annotated with the other.
    phenotype_term:
      preferred_term: Ectopic calcification
      term:
        id: HP:0010766
        label: Ectopic calcification
members:
- member: Rhizomelic Chondrodysplasia Punctata Type 1
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Autosomal recessive peroxisome biogenesis disorder caused by biallelic PEX7 loss of
      function. PEX7 is the cytosolic receptor for PTS2-targeted peroxisomal matrix enzymes,
      so its loss mislocalizes plasmalogen-synthesis enzymes (DHAPAT/GNPAT and alkyl-DHAP
      synthase/AGPS) *and* phytanoyl-CoA hydroxylase - producing plasmalogen deficiency
      together with phytanic-acid accumulation. Distinguished from the single-enzyme forms by
      the receptor-level (import) defect and by elevated phytanic acid.
    gene:
      preferred_term: PEX7
      term:
        id: hgnc:8860
        label: PEX7
- member: Rhizomelic Chondrodysplasia Punctata Type 5
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      The other import-receptor form, reached from the opposite side of the same receptor
      complex. A frameshift in the PEX5L-specific exon 9 removes only the long isoform of
      PEX5, which is the co-receptor through which PEX7 delivers PTS2 cargo; PTS1 import
      survives through PEX5S. The resulting selective PTS2 import failure is biochemically
      indistinguishable from RCDP1, so the two can be separated only by sequencing. Variants
      hitting both PEX5 isoforms instead cause a Zellweger spectrum disorder, making this one
      gene the source of two unrelated diseases.
    gene:
      preferred_term: PEX5
      term:
        id: hgnc:9719
        label: PEX5
- member: Rhizomelic Chondrodysplasia Punctata, Plasmalogen-Synthesis Defect
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Autosomal recessive single-enzyme defects of ether-phospholipid (plasmalogen)
      biosynthesis - RCDP2 (GNPAT/DHAPAT) and RCDP3 (AGPS/alkyl-DHAP synthase) - lying
      downstream of peroxisomal import. They converge on the same lesion (cellular plasmalogen
      deficiency) and phenocopy RCDP1, but because they act below the PTS2 import step,
      phytanic-acid alpha-oxidation is preserved (normal phytanic acid) - the key biochemical
      discriminator from the two import-receptor forms.
    gene:
      preferred_term: GNPAT
      term:
        id: hgnc:4416
        label: GNPAT
  - description: >-
      RCDP3 arises from loss of AGPS (alkylglycerone-phosphate synthase), the enzyme that
      forms the ether bond in plasmalogen biosynthesis, converging on the same
      plasmalogen-deficiency lesion as the GNPAT (RCDP2) defect with preserved phytanic-acid
      oxidation.
    gene:
      preferred_term: AGPS
      term:
        id: hgnc:327
        label: AGPS
- member: X-linked Chondrodysplasia Punctata 2
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      X-linked dominant, male-lethal deficiency of the delta8-delta7 sterol isomerase EBP,
      accumulating 8(9)-cholestenol and 8-dehydrocholesterol. Uniquely in this grouping the
      phenotype is a *mosaic* readout of the enzymopathy: random X inactivation makes the
      heterozygous female a patchwork of competent and deficient clones, so the disease is
      written on the body in that geometry - blaschkolinear ichthyosis and follicular
      atrophoderma, asymmetric rhizomelic shortening, sectorial cataract. The autosomal
      recessive members have no counterpart to this.
    gene:
      preferred_term: EBP
      term:
        id: hgnc:3133
        label: EBP
- member: X-linked Chondrodysplasia Punctata 1
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      X-linked recessive, affecting hemizygous males, with the brachytelephalangic pattern -
      distal phalangeal shortening and nasomaxillary hypoplasia - rather than rhizomelia. It
      is the only member whose biochemical lesion is unsolved: ARSL's physiological substrate
      has never been identified, so there is no metabolite assay and molecular testing is the
      only confirmatory test. What is known is that the enzyme is warfarin-sensitive, which is
      why maternal coumarin exposure, and probably early-gestation vitamin K deficiency,
      produce phenocopies indistinguishable on examination.
    gene:
      preferred_term: ARSL
      term:
        id: hgnc:719
        label: ARSL
- member: CHILD Syndrome
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      X-linked dominant, male-lethal deficiency of NSDHL, the C4-demethylation-complex enzyme
      acting one step above EBP in the same post-squalene pathway. Like CDPX2 it is a mosaic
      disorder, but its lesions are strictly lateralized with a sharp body-midline boundary
      rather than following Blaschko lines, and it adds ipsilateral limb reduction defects.
      It is also the one member with a pathogenesis-based therapy: topical cholesterol
      combined with a statin clears the skin, whereas cholesterol replacement alone does not.
    gene:
      preferred_term: NSDHL
      term:
        id: hgnc:13398
        label: NSDHL
- member: Greenberg Dysplasia
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      Autosomal recessive, prenatally lethal deficiency of the sterol C14 reductase activity
      carried by LBR, accumulating cholesta-8,14-dien-3-beta-ol. The mechanistic interest is
      that LBR also has a structural role tethering heterochromatin at the inner nuclear
      membrane, and the two functions were separated experimentally: Greenberg-causing
      missense alleles abolish the reductase while leaving nuclear structure intact, so this
      is a cholesterol-synthesis enzymopathy and not a laminopathy. Heterozygous
      structural-domain variants in the same gene give the benign Pelger-Huet anomaly instead.
    gene:
      preferred_term: LBR
      term:
        id: hgnc:6518
        label: LBR
- member: Keutel Syndrome
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      The mechanistic inverse of every other member. Autosomal recessive loss of matrix Gla
      protein, a vitamin-K-dependent extracellular inhibitor of mineralization secreted by
      chondrocytes and vascular smooth muscle - so cartilage does not fail to mineralize
      correctly, it fails to *stop*. Cartilage that should stay uncalcified (larynx,
      tracheobronchial tree, ears, nose, ribs) calcifies, and the same lesion in the vessel
      wall produces the peripheral pulmonary artery stenoses that determine prognosis. It is
      also the only member whose dominant clinical problem is cardiovascular rather than
      skeletal.
    gene:
      preferred_term: MGP
      term:
        id: hgnc:7060
        label: MGP
- member: Chondrodysplasia Punctata, Tibial-metacarpal Type
  member_type: DISEASE
  differentiating_mechanisms:
  - description: >-
      A non-rhizomelic CDP subtype defined by neonatal calcific stippling with short tibiae,
      short central metacarpals, and coronal cleft vertebrae. Unlike every other member it
      has no established molecular cause and no biochemical lesion: sterol,
      very-long-chain-fatty-acid, and phytanic-acid profiles are normal, and the ISDS row for
      it carries blank gene and inheritance columns. Distinguished clinically by the
      tibia-plus-metacarpal shortening pattern and generally preserved cognition.
notes: >-
  Umbrella -> Grouping model over the clinically defined chondrodysplasia punctata family
  (MONDO:0019701); the members are curated as distinct Disease entries, so no duplicate
  Disease root is created. Membership was expanded in August 2026 from three members to nine,
  bringing the grouping into alignment with ISDS group 23 of the 2023 nosology: CDPX2, CDPX1,
  Greenberg dysplasia, Keutel syndrome, and RCDP5 were curated as new entries, and CHILD
  syndrome - already curated but previously untagged - was added. The grouping now covers
  every group-23 row, with one lumping decision: RCDP2, RCDP3, and RCDP4 are three separate
  nosology rows but one dismech entry, because the three genes are consecutive steps of a
  single biosynthetic pathway with nothing gene-specific to distinguish them mechanistically.
  RCDP5 is by contrast kept separate from RCDP1 despite sharing its mechanism node, because
  there the gene *is* the story - an isoform-selective allele is what makes PEX5 cause two
  unrelated diseases.

  Two things are deliberately excluded. Acquired phenocopies (maternal warfarin embryopathy,
  early-gestation vitamin K deficiency, maternal autoimmune disease) reach the same
  radiographic endpoint without a germline lesion; they are recorded as differential diagnoses
  on the CDPX1 entry rather than as members, and the HAS_CLASSIFICATION criterion is what
  formally keeps them out. Dappled diaphyseal dysplasia and Astley-Kendall dysplasia have been
  argued to be allelic with Greenberg dysplasia but are not 2023 nosology rows and are not
  members.

  The first membership criterion changed in the same revision. It was previously stated as
  HAS_PHENOTYPE at HP:0010655 (Epiphyseal stippling) alone, which the expanded membership
  broke: CHILD syndrome annotates the finding as HP:0002764 (Stippled chondral calcification),
  a sibling term rather than a descendant, so the audit would have reported it as failing a
  criterion it in fact satisfies. The phenotype criterion is now anchored at their common
  ancestor HP:0010766 (Ectopic calcification), and the ISDS classification criterion carries
  the work of fixing scope.