Anauxetic dysplasia

Mendelian MONDO:0011773 Pathograph 27 Show in embeddings browser osteochondrodysplasia autosomal recessive disease

Anauxetic dysplasia (AD) is the most severe phenotype of the cartilage-hair hypoplasia to anauxetic dysplasia (CHH-AD) spectrum, a group of autosomal recessive ribosomopathies caused by loss of function in the RNase MRP endoribonuclease complex. It is defined by extreme disproportionate short-limb short stature recognizable at birth, with atlantoaxial instability, joint hypermobility and, at this end of the spectrum, possible cognitive deficiency. Its mechanistic interest is a clean two-substrate dissociation: RNase MRP cleaves both ribosomal RNA and messenger RNA, and which of those two functions a given variant impairs predicts which half of the syndrome the patient gets. Hair, immune, haematologic, gastrointestinal, and malignancy associations are retained below as conditional CHH-AD spectrum risks rather than assumed characteristics of pure AD. In particular, the latest ANXD3 series explicitly lacked immune and gastrointestinal involvement while expanding that subtype with craniofacial, sensory, ophthalmologic, renal, and foot findings; all of these observations remain based on very small numbers of individuals.

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1
Inheritance
7
Pathophys.
25
Phenotypes
4
Gaps
27
Pathograph
3
Genes
7
Medical Actions
3
Subtypes
2
Differentials
2
Models
9
References
1
Deep Research
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Classifications

ISDS Skeletal Nosology
metaphyseal dysplasias
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Inheritance

1
Autosomal recessive inheritance HP:0000007
Anauxetic dysplasia is autosomal recessive, arising from biallelic variants in RMRP or, in the genetically distinct forms, POP1 or NEPRO.
Autosomal recessive inheritance
Show evidence (3 references)
PMID:17701897 SUPPORT Human Clinical
"Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
Establishes autosomal recessive inheritance and places anauxetic dysplasia at the severe end of the RMRP spectrum.
PMID:22420014 SUPPORT Human Clinical
"If both parents are known to be heterozygous for an RMRP pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."
GeneReviews recurrence risks used in counselling families.
PMID:22420014 SUPPORT Human Clinical
"carrier testing for at-risk relatives and molecular genetic prenatal and preimplantation genetic testing for CHH-AD spectrum disorders are possible"
Documents the reproductive testing options available once the familial variants are known.
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Subtypes

3
Anauxetic dysplasia 1 (RMRP-related) MONDO:0054560
RMRP hgnc:10031 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in RMRP (hgnc:10031). hgnc:10031 is a gene from the HUGO Gene Nomenclature Committee.
Caused by biallelic RMRP variants, the non-coding RNA component of RNase MRP. This is the form contiguous with cartilage-hair hypoplasia, and the one in which the two-substrate genotype-phenotype correlation was established.
Show evidence (1 reference)
PMID:17701897 SUPPORT Human Clinical
"Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
Establishes RMRP as the gene of the original anauxetic dysplasia form at the severe end of the CHH spectrum.
Anauxetic dysplasia 2 (POP1-related) MONDO:0054561
POP1 hgnc:30129 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in POP1 (hgnc:30129). hgnc:30129 is a gene from the HUGO Gene Nomenclature Committee.
Caused by biallelic POP1 variants, a protein subunit of the same holoenzyme. Patient material shows markedly reduced RMRP abundance with accumulation of unprocessed pre-5.8S rRNA, which is the direct in-patient counterpart of the in vitro cleavage data from the RMRP arm.
Show evidence (1 reference)
PMID:28067412 SUPPORT Human Clinical
"Markedly reduced abundance of RMRP and elevated levels of pre5.8s rRNA was observed."
Patient-derived evidence that a POP1 lesion destabilizes the RNA component and blocks rRNA processing, converging on the same mechanism as RMRP loss.
Anauxetic dysplasia 3 (NEPRO-related) MONDO:0030019
NEPRO hgnc:24496 HUGO Gene Nomenclature Committee (hgnc) Relation: this subtype is caused by variation in this gene This subtype is caused by variation in NEPRO (hgnc:24496). hgnc:24496 is a gene from the HUGO Gene Nomenclature Committee.
Caused by biallelic NEPRO variants. NEPRO interacts with multiple RNase MRP protein subunits rather than being part of the core complex, and this arm adds prominent skin laxity and joint dislocations to the skeletal core.
Show evidence (2 references)
PMID:31250547 SUPPORT Human Clinical
"Nucleolus and neural progenitor protein (NEPRO), encoded by NEPRO (C3orf17), is known to interact with multiple protein subunits of RMRP."
Establishes NEPRO as an RNase MRP interactor and the basis of the third genetic form.
PMID:41982866 SUPPORT Human Clinical
"This study reports three new ANXD3 cases from a consanguineous Iranian family, carrying the homozygous pathogenic variant Chr3:113014014G>A; exon3; c.280C>T; p.Arg94Cys in the NEPRO gene."
Adds three independently ascertained ANXD3 cases with molecular and segregation confirmation of the recurrent NEPRO p.Arg94Cys variant.
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Discussions and Knowledge Gaps

4
Is anauxetic dysplasia genuinely a disorder of ribosome biogenesis, or does the rRNA-cleavage correlation track something else that RNase MRP does?
KNOWLEDGE GAP OPEN gap_anauxetic_is_it_really_a_ribosomopathy
Attached to
pathophysiology#Impaired rRNA Cleavage in Ribosome Assembly pathophysiology#RNase MRP Complex Loss of Function
The ribosomopathy framing rests on a correlation between residual rRNA cleavage activity and skeletal severity, and it is how this entry and most of the literature describe the disorder. But that assumption has been questioned directly in the POP1 literature, and RNase MRP has at least four known activities beyond 5.8S rRNA processing: Cyclin B2 mRNA cleavage, mitochondrial RNA processing, and complex formation with hTERT. A correlation with rRNA cleavage does not establish that reduced ribosome output is the effector, since the same alleles may degrade a co-varying activity. This matters because it determines whether anauxetic dysplasia belongs mechanistically alongside the other ribosomopathies or forms its own class.
Proposed experiments
Direct measurement of ribosome output against skeletal severity across CHH-AD alleles
exp_anauxetic_ribosome_output_vs_severity
Measure ribosome biogenesis output directly, by polysome profiling and nascent 5.8S rRNA quantification, in patient chondrocytes or chondroprogenitors across an allelic series spanning CHH to anauxetic dysplasia, and test whether ribosome output rather than cleavage-assay activity predicts skeletal severity. Measure Cyclin B2 turnover and mitochondrial RNA processing in the same cells as co-varying candidates.
Decision criterion
If ribosome output predicts skeletal severity better than the other activities do, the ribosomopathy label is earned; if a co-varying activity predicts it as well or better, it is not.
Supporting outcome
  • Reduced ribosome output is the effector and the disorder is a true ribosomopathy
Refuting outcome
  • A co-varying RNase MRP activity predicts skeletal severity equally well, so the ribosomopathy label is an artefact of assay choice
Show evidence (2 references)
PMID:28067412 SUPPORT Human Clinical
"Although CHH and other skeletal dysplasias caused by mutations in RMRP or POP1 are commonly cited as ribosomal biogenesis disorders, recent studies question this assumption."
Direct published challenge to the ribosomopathy framing this entry otherwise adopts.
PMID:21396580 SUPPORT Human Clinical
"processing the mitochondrial RNA, and forming a complex with hTERT suggesting a possible involvement in expression regulation by siRNA synthesis"
Documents the additional RNase MRP activities that could co-vary with rRNA cleavage and confound the correlation.
How does a single ribonucleoprotein enzyme partition its two substrates so that a variant can impair ribosomal RNA cleavage while largely sparing messenger RNA cleavage, or the reverse?
KNOWLEDGE GAP OPEN gap_anauxetic_substrate_dissociation
Attached to
pathophysiology#Impaired rRNA Cleavage in Ribosome Assembly pathophysiology#mRNA Cleavage-Dependent Spectrum Modulation
The in vitro data show a clean double dissociation: rRNA cleavage loss tracks bone severity, mRNA cleavage loss tracks hair, immune and haematological involvement and cancer risk. That means the two activities are separable by single-nucleotide changes in one non-coding RNA, which implies substrate selection depends on local structural elements rather than on global enzyme activity. Which elements, and whether a therapeutic or prognostic assay could read out the two activities independently in a patient sample, is unresolved. A clinically useful consequence would be predicting cancer and immune risk from a functional assay rather than waiting for the phenotype.
Proposed experiments
Structure-function mapping of RNase MRP substrate selection across CHH-AD alleles
exp_anauxetic_substrate_specificity_map
Reconstitute RNase MRP with a panel of patient RMRP alleles spanning the CHH-AD spectrum plus POP1 and NEPRO variants, and measure rRNA and mRNA cleavage independently against solved secondary structure, to identify which structural elements confer substrate selection and whether the two activities can be predicted from sequence.
Decision criterion
Identification of distinct structural determinants for the two substrates that predict the clinical dissociation would establish a prognostic assay.
Supporting outcome
  • Separable structural elements govern the two activities, so allele-level functional testing can predict immune and cancer risk
Refuting outcome
  • Both activities degrade together and the clinical dissociation reflects tissue-specific thresholds instead
Why does a defect in a ubiquitously required ribosome assembly step strike the growth plate so much harder than other proliferating tissues?
KNOWLEDGE GAP OPEN gap_anauxetic_chondrocyte_selectivity
Attached to
pathophysiology#Growth Plate Chondrocyte Differentiation Failure pathophysiology#Extreme Disproportionate Short-Limb Short Stature
This is the general paradox of the ribosomopathies, and anauxetic dysplasia is an unusually clean instance of it because the same enzyme lesion produces a graded skeletal phenotype across the spectrum. Whether growth plate chondrocytes are simply the most ribosome-hungry cells in the developing body, or whether there is a chondrocyte-specific client transcript whose translation fails first, is not established, and the answer determines whether any tissue-directed intervention is conceivable. The question is posed explicitly in the chondrocyte literature, and the observation that RNase MRP expression is itself regulated across chondrogenic differentiation raises a third possibility: that the growth plate is not merely the most demanding tissue but one that actively modulates this complex.
Proposed experiments
Comparative translatome profiling across tissues in an RMRP hypomorphic model
exp_anauxetic_chondrocyte_translatome
Profile ribosome occupancy and nascent translation in growth plate chondrocytes alongside lymphoid progenitors, erythroid progenitors and hair follicle keratinocytes in a graded RMRP hypomorphic background, to test whether chondrocytes show disproportionate loss of translational output or selective loss of specific transcripts.
Decision criterion
Disproportionate global translational collapse in chondrocytes supports a demand model; selective transcript loss supports a client-specific model.
Supporting outcome
  • Growth plate chondrocytes have the highest ribosome demand and fail first on a purely quantitative basis
Refuting outcome
  • Specific chondrocyte transcripts are selectively lost, implicating a targeted client rather than global demand
Show evidence (1 reference)
PMID:28743979 SUPPORT In Vitro
"However, it is not clear why mutations in RMRP RNA lead to skeletal dysplasia."
The chondrocyte literature states the question of this gap directly as unresolved.
What are the subtype-specific natural history, complication rates, and treatment outcomes of anauxetic dysplasia?
KNOWLEDGE GAP OPEN gap_anauxetic_natural_history_and_therapy
Attached to
phenotypes#Severe short stature phenotypes#Atlantoaxial dislocation phenotypes#Thoracolumbar kyphoscoliosis
Published evidence consists mainly of single cases, small families, and mechanism studies across the broader CHH-AD spectrum. There are no reliable ANXD-specific prevalence, penetrance, survival, quality-of-life, or treatment-response estimates, and no disease-specific interventional trial was identified. The 2026 ANXD3 report adds three cases and new systemic findings but remains too small to establish frequency or causality for each manifestation. A longitudinal, genotype-stratified registry is needed to distinguish reproducible subtype features from family-specific observations and to evaluate orthopedic and surveillance outcomes.
Proposed experiments
Genotype-stratified international ANXD natural-history registry
exp_anauxetic_longitudinal_registry
Enroll molecularly confirmed RMRP-, POP1-, and NEPRO-related cases with harmonized skeletal imaging, cervical stability, mobility, pain, development, hearing, ophthalmology, renal, dental, surgical, and patient-reported outcomes assessed longitudinally.
Decision criterion
Replication of each manifestation in unrelated families and stable subtype-specific incidence estimates would distinguish core findings from family-specific observations and provide endpoints for future trials.
Supporting outcome
  • The recently reported systemic ANXD3 findings are reproducible subtype features
  • Defined imaging and functional measures can serve as natural-history and trial endpoints
Refuting outcome
  • The systemic findings remain confined to single families and are not reproducible ANXD3 associations
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"This study reports three new ANXD3 cases from a consanguineous Iranian family"
The latest family series illustrates both ongoing phenotype discovery and the very small evidence base that prevents frequency estimation.
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Pathophysiology

7
RNase MRP Complex Loss of Function
RMRP encodes the untranslated RNA component of RNase MRP, a ribonucleoprotein endoribonuclease. Pathogenic variants either alter evolutionarily conserved nucleotides or disrupt the secondary structure by mispairing within stem regions, so the lesion is one of RNA folding and catalysis rather than of a protein coding sequence. The genetically distinct forms hit protein members of the same complex (POP1) or an interacting nucleolar partner (NEPRO), which is why they converge on one phenotype.
RMRP hgnc:10031 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves RMRP (hgnc:10031). hgnc:10031 is a gene from the HUGO Gene Nomenclature Committee. POP1 hgnc:30129 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves POP1 (hgnc:30129). hgnc:30129 is a gene from the HUGO Gene Nomenclature Committee. NEPRO hgnc:24496 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves NEPRO (hgnc:24496). hgnc:24496 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Impaired rRNA Cleavage in Ribosome Assembly Loss of RNase MRP activity on its ribosomal RNA substrate compromises ribosome biogenesis.
mRNA Cleavage-Dependent Spectrum Modulation Variant-specific impairment of messenger-RNA cleavage determines whether CHH-like hair, immune, and haematologic features overlap the skeletal phenotype; those features are not assumed to be part of pure ANXD.
Show evidence (2 references)
PMID:17701897 SUPPORT Human Clinical
"The RMRP gene encodes the untranslated RNA component of the mitochondrial RNA-processing ribonuclease, RNase MRP."
Identifies the gene product as a non-coding RNA component of the RNase MRP complex.
PMID:17701897 SUPPORT In Vitro
"disease-causing mutations either affect evolutionarily conserved nucleotides or are likely to alter secondary structure through mispairing in stem regions"
Defines the two structural mechanisms by which variants in a non-coding RNA gene impair function.
Impaired rRNA Cleavage in Ribosome Assembly
The first of the two substrate arms. RNase MRP participates in ribosomal RNA processing during ribosome assembly, and the magnitude of the rRNA cleavage defect correlates directly with the degree of bone dysplasia. Anauxetic dysplasia sits at the severe end because its allele combinations produce the greatest loss of this specific activity. The ribosomopathy label is the conventional reading of that correlation, but it is contested; see the knowledge gap attached to this node.
rRNA processing GO:0006364 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased rRNA processing (GO:0006364). GO:0006364 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Rmrp-deficient ATDC5 chondrogenic cell model CELL LINE Measures pre-rRNA processing and mature rRNA abundance after Rmrp interference.
Variant-specific RNase MRP substrate-cleavage assay OTHER Quantifies variant-specific loss of rRNA cleavage against bone-dysplasia severity.
Downstream
Growth Plate Chondrocyte Differentiation Failure Reduced RNase MRP activity disrupts growth-plate chondrocyte differentiation, with the strongest experimental effect at hypertrophy.
Show evidence (3 references)
PMID:17701897 SUPPORT In Vitro
"In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
Establishes the quantitative link between loss of rRNA cleavage and skeletal severity, the basis for the substrate dissociation.
PMID:21396580 SUPPORT Human Clinical
"This complex is involved in the ribosome assembly by cleavage of 5.8S rRNA, cell cycle control by Cyclin B2 mRNA cleavage at the end of mitosis, processing the mitochondrial RNA, and forming a complex with hTERT suggesting a possible involvement in expression regulation by siRNA synthesis."
Names the specific substrates, 5.8S rRNA for the ribosome arm and Cyclin B2 mRNA for the cell-cycle arm, rather than leaving them generic.
PMID:28067412 SUPPORT Human Clinical
"Markedly reduced abundance of RMRP and elevated levels of pre5.8s rRNA was observed."
In-patient confirmation that the rRNA processing step is blocked, which the rest of this node rests on in vitro reconstitution for.
mRNA Cleavage-Dependent Spectrum Modulation
The second substrate arm is a modifier of position within the CHH-AD spectrum rather than an obligatory ANXD lesion. Reduced cleavage of RNase MRP messenger-RNA targets impairs cell-cycle regulation, and the degree of that impairment predicts hair hypoplasia, immunodeficiency and haematological abnormality rather than bone severity. Pure ANXD can therefore combine profound skeletal dysplasia with relative preservation of these extraskeletal systems. The concrete substrate is Cyclin B2 mRNA, cleaved at the end of mitosis.
regulation of cell cycle GO:0051726 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased regulation of cell cycle (GO:0051726). GO:0051726 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Variant-specific RNase MRP substrate-cleavage assay OTHER Quantifies variant-specific mRNA cleavage against extraskeletal spectrum features.
Downstream
Conditional Immune and Haematopoietic Spectrum Involvement When messenger-RNA cleavage is sufficiently impaired, immune and erythroid progenitor dysfunction can overlap the skeletal phenotype.
Fine hair Hair hypoplasia tracks the messenger-RNA-cleavage arm across the spectrum.
Show evidence (3 references)
PMID:17701897 SUPPORT In Vitro
"reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
Establishes that the mRNA-cleavage arm, not the rRNA arm, determines the extraskeletal phenotype including cancer risk.
PMID:21396580 SUPPORT Human Clinical
"The degree of skeletal dysplasia correlates mainly with the rRNA cleavage activity, whereas significantly diminished mRNA cleavage activity is a prerequisite for immunodeficiency."
Independent statement of the two-substrate dissociation, and stronger than correlation for the immune arm: diminished mRNA cleavage is described as a prerequisite.
PMID:17701897 SUPPORT In Vitro
"We recently demonstrated that mutations may affect both messenger RNA (mRNA) and ribosomal RNA (rRNA) cleavage and thus cell-cycle regulation and protein synthesis."
States the dual-substrate nature of the enzyme that underlies the dissociation.
Conditional Immune and Haematopoietic Spectrum Involvement
Immunodeficiency, defective erythrogenesis, and malignancy risk belong to the CHH-AD spectrum and track the messenger-RNA-cleavage arm. They are retained as conditional overlap risks that require baseline assessment, not as expected manifestations of pure ANXD; the 2026 ANXD3 series explicitly reported no immune involvement.
Downstream
Immunodeficiency Conditional immune-cell dysfunction manifests clinically as immunodeficiency.
Anemia Conditional erythroid dysfunction manifests clinically as anemia.
Neoplasm The cell-cycle and immune arm provides the spectrum-level route to malignancy risk.
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
Establishes these as spectrum findings; PARTIAL reflects that they are not assumed characteristics of the pure ANXD phenotype.
PMID:41982866 REFUTE Human Clinical
"Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
Direct negative evidence for immune involvement in ANXD3, scoped to a three-person family and therefore not generalized to every ANXD subtype.
Growth Plate Chondrocyte Differentiation Failure
Chondrocytes in the proliferative zone of the growth plate are among the most biosynthetically demanding cells in the developing skeleton, which is why a generalized ribosome assembly defect strikes them hardest. Experimentally the step most affected is hypertrophic differentiation rather than proliferation alone, and RNase MRP is itself expressed in the growth plate with expression tracking chondrocyte hypertrophy. The result is metaphyseal dysplasia and a failure of endochondral bone elongation that is already evident at birth.
chondrocyte CL:0000138 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves chondrocyte (CL:0000138). CL:0000138 is a cell type from the Cell Ontology.
chondrocyte differentiation GO:0002062 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased chondrocyte differentiation (GO:0002062). GO:0002062 is a biological process from the Gene Ontology. ↓ DECREASED chondrocyte hypertrophy GO:0003415 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased chondrocyte hypertrophy (GO:0003415). GO:0003415 is a biological process from the Gene Ontology. ↓ DECREASED endochondral ossification GO:0001958 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased endochondral ossification (GO:0001958). GO:0001958 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Rmrp-deficient ATDC5 chondrogenic cell model CELL LINE Measures differentiation and hypertrophy after Rmrp interference.
Downstream
Extreme Disproportionate Short-Limb Short Stature Failure of endochondral elongation in the limbs produces disproportionate dwarfism.
Severe short stature Connects the tissue mechanism to the ontology-bound clinical phenotype.
Atlantoaxial Instability The same dysplastic process affects the upper cervical vertebrae and their ligamentous stabilization.
Atlantoaxial dislocation Connects cervical instability to the ontology-bound clinical phenotype.
Brachydactyly Abnormal endochondral development shortens the metacarpals and phalanges.
Ovoid vertebral bodies Disordered vertebral ossification produces the characteristic ovoid vertebral morphology.
Hypoplastic ilia Pelvic endochondral growth failure produces underdeveloped iliac bones.
Metaphyseal irregularity Growth-plate disorganization produces irregular metaphyseal contours.
Thoracolumbar kyphoscoliosis Progressive vertebral dysplasia produces combined thoracolumbar kyphosis and scoliosis.
Show evidence (3 references)
PMID:22420014 SUPPORT Human Clinical
"CHH-AD spectrum disorders are characterized by severe disproportionate (short-limb) short stature that is usually recognized in the newborn, and occasionally prenatally because of the short extremities."
Establishes the short-limb growth failure and its recognition at or before birth, consistent with a prenatal growth plate defect.
PMID:28743979 SUPPORT In Vitro
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
Direct chondrocyte evidence: knocking down Rmrp deranges chondrogenic differentiation and pre-rRNA processing together, which is what this node otherwise had to infer from the clinical phenotype.
PMID:28743979 SUPPORT Model Organism
"Expression of Rmrp RNA and RNase MRP protein subunits was detected in the murine growth plate and during the course of chondrogenic differentiation of ATDC5 cultures, where Rmrp RNA expression was found to be correlated with chondrocyte hypertrophy."
Localizes RNase MRP expression to the growth plate itself and ties it to the hypertrophic step, supporting tissue specificity rather than a purely quantitative demand argument.
Extreme Disproportionate Short-Limb Short Stature
Anauxetic dysplasia carries the most pronounced skeletal phenotype of the spectrum. The name itself means without growth, and adult stature is at the extreme end of human short stature.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"The most severe phenotype, AD, has the most pronounced skeletal phenotype"
Positions anauxetic dysplasia as the most skeletally severe phenotype of the spectrum.
Atlantoaxial Instability
Atlantoaxial subluxation may be present in the newborn and is largely specific to the anauxetic end of the spectrum. It is the feature with the most immediate clinical consequence, because it converts routine general anaesthesia into a cervical cord risk and may require surgical fusion.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"may be associated with atlantoaxial subluxation in the newborn"
Establishes atlantoaxial subluxation as a neonatal feature specific to the anauxetic phenotype.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Anauxetic dysplasia Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

25
Blood 1
Anemia HP:0001903 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Anemia (HP:0001903). HP:0001903 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:17701897 SUPPORT Human Clinical
"This clinical spectrum includes different degrees of short stature, hair hypoplasia, defective erythrogenesis, and immunodeficiency."
The source explicitly scopes defective erythrogenesis to the spectrum, so the association is PARTIAL for the ANXD entry.
Digestive 1
Malabsorption HP:0002024 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Malabsorption (HP:0002024). HP:0002024 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:21396580 SUPPORT Human Clinical
"variable additional features including predisposition to cancer, anemia, immunodeficiency, and gastrointestinal malabsorption and Hirschsprung's disease"
The publication calls this a variable additional spectrum feature, hence PARTIAL for ANXD.
PMID:41982866 REFUTE Human Clinical
"Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
Refutes gastrointestinal involvement in the reported ANXD3 family only.
Ear 1
Hearing impairment HP:0000365 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hearing impairment (HP:0000365). HP:0000365 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
Reports hearing impairment among the newly recognized systemic ANXD3 features.
Eye 1
Cataract HP:0000518 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cataract (HP:0000518). HP:0000518 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
Reports cataracts among the newly recognized systemic ANXD3 features.
Head and Neck 3
Dental anomalies Abnormality of the dentition HP:0000164 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dental anomalies, annotated with Abnormality of the dentition (HP:0000164). HP:0000164 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
DOI:10.1002/ajmg.a.63316 SUPPORT Human Clinical
"Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
Directly documents dental anomalies in an individual with molecularly confirmed anauxetic dysplasia.
DOI:10.1002/ajmg.a.63316 SUPPORT Human Clinical
"Greater awareness of the possibility of atlantoaxial subluxation, dental anomalies, and craniosynostosis may lead to more timely diagnosis and treatment."
The authors' own framing of dental anomalies as a feature clinicians should actively look for in this disorder.
Craniosynostosis HP:0001363 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Craniosynostosis (HP:0001363). HP:0001363 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
DOI:10.1002/ajmg.a.63316 SUPPORT Human Clinical
"Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
Documents sagittal craniosynostosis in a molecularly confirmed ANXD3 patient; single case, so recorded without a frequency claim.
Microcephaly HP:0000252 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Microcephaly (HP:0000252). HP:0000252 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"Microcephaly was observed in our patients, same as previously reported cases, underscoring the phenotypic variability of ANXD3."
Directly documents microcephaly in the new family and earlier ANXD3 cases.
Immune 1
Immunodeficiency HP:0002721 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Immunodeficiency (HP:0002721). HP:0002721 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
Lists immunodeficiency for the whole spectrum, so it is PARTIAL for ANXD.
PMID:41982866 REFUTE Human Clinical
"Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
Negative subtype-specific evidence from three related ANXD3 cases; it counters, but cannot exclude, spectrum overlap in other ANXD genotypes.
Integument 1
Hyperextensible skin HP:0000974 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperextensible skin (HP:0000974). HP:0000974 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31250547 SUPPORT Human Clinical
"All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
Reports skin laxity in all five individuals of the NEPRO series.
Limbs 5
Brachydactyly HP:0001156 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Brachydactyly (HP:0001156). HP:0001156 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31250547 SUPPORT Human Clinical
"All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
Reports brachydactyly in all five individuals of the NEPRO series.
Metaphyseal irregularity HP:0003025 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Metaphyseal irregularity (HP:0003025). HP:0003025 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Directly identifies metaphyseal irregularity in the radiographic ANXD3 pattern.
Talipes equinovarus HP:0001762 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Talipes equinovarus (HP:0001762). HP:0001762 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
Reports clubfoot among the newly recognized systemic ANXD3 features.
Coxa vara HP:0002812 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Coxa vara (HP:0002812). HP:0002812 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22528854 SUPPORT Human Clinical
"Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
Directly documents severe coxa vara in a molecularly untyped clinical ANXD case.
Genu valgum HP:0002857 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Genu valgum (HP:0002857). HP:0002857 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22528854 SUPPORT Human Clinical
"Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
Directly documents genu valgum in a clinical ANXD case.
Musculoskeletal 2
Joint hypermobility HP:0001382 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Joint hypermobility (HP:0001382). HP:0001382 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"Other findings include joint hypermobility, fine, silky hair"
Lists joint hypermobility among the characteristic findings of the spectrum.
PMID:31250547 SUPPORT Human Clinical
"All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
Confirms joint hypermobility and dislocations across all reported NEPRO-related individuals.
Hypoplastic ilia HP:0000946 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoplastic ilia (HP:0000946). HP:0000946 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Directly identifies hypoplastic ilia in the radiographic ANXD3 pattern.
Nervous System 1
Intellectual disability HP:0001249 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Intellectual disability (HP:0001249). HP:0001249 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"The most severe phenotype, AD, has the most pronounced skeletal phenotype, may be associated with atlantoaxial subluxation in the newborn, and may include cognitive deficiency."
Establishes cognitive deficiency as a feature of the anauxetic phenotype specifically.
Growth 1
Severe short stature VERY_FREQUENT HP:0003510 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Severe short stature (HP:0003510). HP:0003510 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"severe disproportionate (short-limb) short stature that is usually recognized in the newborn"
Establishes severe short-limb short stature as the cardinal, near-universal feature.
Neoplasm 1
Neoplasm HP:0002664 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Neoplasm (HP:0002664). HP:0002664 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
Documents malignancy risk for the spectrum; PARTIAL avoids assigning an unquantified risk to every ANXD patient.
Other 6
Atlantoaxial dislocation HP:0003414 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Atlantoaxial dislocation (HP:0003414). HP:0003414 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"may be associated with atlantoaxial subluxation in the newborn"
Documents atlantoaxial subluxation as a neonatal feature of anauxetic dysplasia.
DOI:10.1002/ajmg.a.63316 SUPPORT Human Clinical
"Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
Extends atlantoaxial subluxation, previously documented at the RMRP/POP1 end, to the NEPRO-related form.
Fine hair HP:0002213 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fine hair (HP:0002213). HP:0002213 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
Documents fine hair at spectrum level; PARTIAL avoids assigning it to all individuals with ANXD.
Ovoid vertebral bodies HP:0003300 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ovoid vertebral bodies (HP:0003300). HP:0003300 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Directly identifies ovoid vertebrae in the radiographic ANXD3 pattern.
Thoracolumbar kyphoscoliosis HP:0003423 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Thoracolumbar kyphoscoliosis (HP:0003423). HP:0003423 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"A comparative analysis with previously reported ANXD3 cases revealed shared characteristics, including short stature, brachydactyly, and thoracolumbar kyphoscoliosis"
Identifies thoracolumbar kyphoscoliosis as a shared ANXD3 characteristic.
Urolithiasis HP:0034368 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Urolithiasis (HP:0034368). HP:0034368 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
Reports urolithiasis among the newly recognized systemic ANXD3 features.
Aganglionic megacolon HP:0002251 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Aganglionic megacolon (HP:0002251). HP:0002251 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:21396580 SUPPORT Human Clinical
"gastrointestinal malabsorption and Hirschsprung's disease"
Names Hirschsprung disease within a sentence describing variable additional spectrum features, so the ANXD association is PARTIAL.
🧬

Genetic Associations

3
RMRP (Pathogenic Variants)
Gene: RMRP hgnc:10031 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is RMRP (hgnc:10031). hgnc:10031 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:17701897 SUPPORT Human Clinical
"a novel patient with anauxetic dysplasia who was compound heterozygous for the null mutation g.254_263delCTCAGCGCGG and the mutation g.195C-->T, which was previously described in patients with milder phenotypes"
Illustrates how allele combination rather than allele identity places a patient at the anauxetic end of the spectrum.
POP1 (Pathogenic Variants)
Gene: POP1 hgnc:30129 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is POP1 (hgnc:30129). hgnc:30129 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (1 reference)
PMID:31250547 SUPPORT Human Clinical
"Cartilage hair hypoplasia (CHH), anauxetic dysplasia 1, and anauxetic dysplasia 2 are rare metaphyseal dysplasias caused by biallelic pathogenic variants in RMRP and POP1, which encode the components of RNAse-MRP endoribonuclease complex (RMRP) in ribosomal biogenesis pathway."
Establishes POP1 as the cause of anauxetic dysplasia 2 and places both genes in the RNase MRP complex.
NEPRO (Pathogenic Variants)
Gene: NEPRO hgnc:24496 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is NEPRO (hgnc:24496). hgnc:24496 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (3 references)
PMID:31250547 SUPPORT Human Clinical
"Nucleolus and neural progenitor protein (NEPRO), encoded by NEPRO (C3orf17), is known to interact with multiple protein subunits of RMRP."
Establishes NEPRO as an interactor of the RNase MRP complex, explaining mechanistic convergence.
PMID:31250547 SUPPORT Computational
"Protein modeling and stability prediction showed that the mutant protein has decreased stability. Both the reported variants are in the same domain of the protein."
In silico evidence for the mechanism and domain clustering of the NEPRO variants.
PMID:41982866 SUPPORT Human Clinical
"Diagnostic whole-exome sequencing, supported by Sanger validation, confirmed the autosomal recessive inheritance pattern."
Orthogonally validated segregation evidence from three additional ANXD3 cases.
💊

Medical Actions

7
Cervical spine stabilization and anaesthetic precautions
Action: orthopedic surgical procedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is orthopedic surgical procedure (NCIT:C16186). NCIT:C16186 is a clinical intervention from the NCI Thesaurus. Ontology label: Orthopedic Surgical Procedure NCIT:C16186
Where cervical spinal instability is present, special care is required during general anaesthesia and surgical fusion of unstable cervical vertebrae may be needed. This is the highest-stakes management point in anauxetic dysplasia, because the risk is realized during otherwise routine procedures.
Mechanism Target:
INHIBITS Atlantoaxial Instability — Fusion stabilizes the unstable segment; anaesthetic precautions avoid precipitating cord injury.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"If cervical spinal instability is identified in a person with AD, special care is required during general anesthesia; surgery may be needed to fuse unstable cervical vertebrae"
GeneReviews management guidance specific to the anauxetic phenotype.
Kyphoscoliosis and limb deformity surgery
Action: orthopedic surgical procedureNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is orthopedic surgical procedure (NCIT:C16186). NCIT:C16186 is a clinical intervention from the NCI Thesaurus. Ontology label: Orthopedic Surgical Procedure NCIT:C16186
Surgery may be needed for progressive kyphoscoliosis compromising lung function, and corrective osteotomies for progressive varus deformity of the lower extremities.
Mechanism Target:
INHIBITS Thoracolumbar kyphoscoliosis — Corrective spinal surgery treats progressive deformity when it compromises pulmonary function.
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"surgery may be needed to fuse unstable cervical vertebrae and/or to treat progressive kyphoscoliosis that compromises lung function in AD; corrective osteotomies may be required for progressive varus deformity of the lower extremities"
Specifies the spinal and limb surgical interventions recommended in anauxetic dysplasia.
PMID:22528854 SUPPORT Human Clinical
"Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
Direct ANXD case evidence for combined osteotomy and guided-growth correction.
Spinal surveillance
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Annual clinical and radiographic examination of the spine is specific to anauxetic dysplasia, reflecting the cervical instability and progressive kyphoscoliosis risks.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"annual clinical and radiographic examination of the spine in individuals with AD"
Specifies the AD-specific spinal surveillance interval.
Baseline and conditional immune-haematologic assessment
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Establish baseline immune and haematologic status rather than inferring it from skeletal severity, then tailor surveillance to the initial results and clinical infection or anemia history. This is a spectrum-overlap safeguard, not an assertion that pure ANXD is immunodeficient.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"laboratory assessment of immune function with frequency based on initial lab results"
Supports initial immune assessment followed by result-dependent surveillance across the CHH-AD spectrum.
Avoidance of live vaccines with abnormal immune function
Action: supportive careNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is supportive care (NCIT:C15747). NCIT:C15747 is a clinical intervention from the NCI Thesaurus. Ontology label: Supportive Care NCIT:C15747
Do not administer live vaccines when abnormal immunologic function or SCID is present. The restriction is explicitly conditional on demonstrated immune dysfunction and does not imply routine vaccine avoidance in pure ANXD.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"Agents/circumstances to avoid: Administration of live vaccines when signs of abnormal immunologic function or SCID are present."
Preserves the highest-consequence GeneReviews safety guidance while retaining its explicit immune-status condition.
Conditional infection management and immune support
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
If clinically significant spectrum-overlap immunodeficiency is identified, manage infections by type and severity, use immediate high-dose intravenous acyclovir for varicella, and consider antibiotic prophylaxis or immunoglobulin replacement. These measures do not apply without immune dysfunction.
Mechanism Target:
MODULATES Conditional Immune and Haematopoietic Spectrum Involvement — Anti-infective and replacement therapy compensates for an overlapping immune defect without correcting RNase MRP dysfunction.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"immediate high-dose intravenous acyclovir for varicella infection; consideration of prophylactic antibiotic therapy and/or immunoglobulin replacement therapy"
GeneReviews spectrum management, retained as conditional because immune involvement is not an expected pure-ANXD feature.
Conditional haematopoietic stem cell transplantation
Action: haematopoietic cell transplantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is haematopoietic cell transplantation, annotated with Hematopoietic Cell Transplantation (NCIT:C15431). NCIT:C15431 is a clinical intervention from the NCI Thesaurus. Ontology label: Hematopoietic Cell Transplantation NCIT:C15431
Recurrent severe infections, SCID, or severely depressed erythropoiesis may warrant transplantation when these CHH-AD spectrum manifestations overlap an ANXD diagnosis. Transplantation addresses the haematopoietic complication and does not correct the skeletal dysplasia.
Mechanism Target:
INHIBITS Conditional Immune and Haematopoietic Spectrum Involvement — Replaces the affected haematopoietic compartment in severe conditional overlap disease.
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"recurrent severe infections, severe combined immunodeficiency (SCID), and/or severely depressed erythropoiesis may warrant hematopoietic stem cell transplantation"
Retains the spectrum indication but marks it PARTIAL for an ANXD-specific entry because it requires documented extraskeletal overlap.
🔬

Diagnosis

2
Clinical and radiographic diagnosis
Diagnosis is established in a proband with the characteristic clinical and radiographic findings, with molecular testing reserved for inconclusive cases and for family studies.
skeletal radiography NCIT:C38101 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:22420014 SUPPORT Human Clinical
"Diagnosis of a CHH-AD spectrum disorder is established in a proband with characteristic clinical and radiographic findings."
States the clinical and radiographic basis of diagnosis.
Molecular genetic testing
Identification of biallelic causal variants confirms the molecular subtype and enables family studies. Testing must cover the non-coding RMRP gene as well as POP1 and NEPRO; exome-based testing can diagnose the protein-coding forms, with Sanger confirmation and segregation analysis.
molecular genetic testing NCIT:C19770 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:22420014 SUPPORT Human Clinical
"identification of biallelic pathogenic variants in RMRP by molecular genetic testing can confirm the diagnosis and allow for family studies"
Specifies the role of molecular testing relative to clinical diagnosis.
PMID:41982866 SUPPORT Human Clinical
"Diagnostic whole-exome sequencing, supported by Sanger validation, confirmed the autosomal recessive inheritance pattern."
Demonstrates exome diagnosis, orthogonal confirmation, and segregation for ANXD3.
🩻

Imaging Findings

3
Ovoid vertebral bodies on skeletal radiography
Ovoid vertebral bodies form part of the characteristic generalized skeletal radiographic pattern of ANXD3.
Xray AD3
Ovoid vertebral bodies HP:0003300 Human Phenotype Ontology (HP) Ovoid vertebral bodies HP:0003300 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Defines ovoid vertebral morphology as a distinct radiographic ANXD3 finding.
Hypoplastic ilia on skeletal radiography
Pelvic radiographs show hypoplastic ilia together with narrow acetabular angles in ANXD3.
Xray AD3
Hypoplastic ilia HP:0000946 Human Phenotype Ontology (HP) Hypoplastic ilia HP:0000946 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Defines hypoplastic ilia as a distinct radiographic ANXD3 finding.
Irregular metaphyses on skeletal radiography
Irregular metaphyses are the long-bone radiographic correlate of the growth-plate differentiation defect.
Xray AD3
Metaphyseal irregularity HP:0003025 Human Phenotype Ontology (HP) Metaphyseal irregularity HP:0003025 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:41982866 SUPPORT Human Clinical
"distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
Defines irregular metaphyses as a distinct radiographic ANXD3 finding.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Anauxetic dysplasia:

Cartilage-hair hypoplasia MONDO:0009595
Overlapping Features RMRP-related cartilage-hair hypoplasia lies on the same molecular spectrum and shares disproportionate short stature, but its skeletal dysplasia is generally less severe and hair, immune, and haematologic involvement is more characteristic.
Distinguishing Features
  • Less severe skeletal dysplasia than anauxetic dysplasia.
  • Hair hypoplasia, immunodeficiency, and defective erythrogenesis favor cartilage-hair hypoplasia.
Show evidence (2 references)
PMID:17701897 SUPPORT Human Clinical
"Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
Establishes CHH as a milder RMRP-spectrum disorder overlapping ANXD.
PMID:17701897 SUPPORT In Vitro
"reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
Identifies the extraskeletal features that distinguish CHH-like overlap from pure ANXD.
Metaphyseal dysplasia without hypotrichosis Not Yet Curated MONDO:0009601
Overlapping Features A milder RMRP-spectrum skeletal dysplasia that can share metaphyseal changes and short stature but lacks the extreme spondyloepimetaphyseal severity of ANXD.
Distinguishing Features
  • Milder metaphyseal-predominant skeletal dysplasia.
  • Absence of hypotrichosis, as reflected in the disease definition.
  • Does not show the extreme skeletal phenotype that defines ANXD.
Show evidence (1 reference)
PMID:17701897 SUPPORT Human Clinical
"Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
Places MDWH and ANXD at the mild and severe ends of the same RMRP spectrum.
🧫

Experimental Models

2
Rmrp-deficient ATDC5 chondrogenic cell model CELL_LINE
Rmrp interference in ATDC5 cells models the growth-plate differentiation defect and couples impaired pre-rRNA processing to a particularly strong defect in chondrocyte hypertrophy. It is a two-dimensional mouse-derived model and does not reproduce the multisite human skeletal phenotype.
Rmrp knockdown Control chondrogenic differentiation
chondrocyte CL:0000138 Cell Ontology (CL) Relation: this experimental model uses this cell type This experimental model uses chondrocyte (CL:0000138). CL:0000138 is a cell type from the Cell Ontology.
Organism
mouse NCBITaxon:10090 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in mouse, annotated with Mus musculus (NCBITaxon:10090). NCBITaxon:10090 is an organism from the NCBI Taxonomy.
Cell source
Mouse ATDC5 chondrogenic cell line
Culture
Monolayer chondrogenic differentiation culture with Rmrp RNA interference
Publication
PMID:28743979
Pathograph links
Impaired rRNA Cleavage in Ribosome Assembly Measures pre-rRNA processing and mature rRNA abundance after Rmrp interference.
Show evidence (1 reference)
PMID:28743979 SUPPORT In Vitro
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
Directly links Rmrp loss to altered rRNA processing in the model.
Growth Plate Chondrocyte Differentiation Failure Measures differentiation and hypertrophy after Rmrp interference.
Show evidence (1 reference)
PMID:28743979 SUPPORT In Vitro
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
Directly demonstrates the differentiation and hypertrophy defect.
Findings
Rmrp interference deregulates chondrogenic differentiation, with the strongest effect on hypertrophy.
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
Show evidence (1 reference)
PMID:28743979 SUPPORT In Vitro
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
The experimental result is quoted directly from the publication abstract.
Show evidence (1 reference)
PMID:28743979 SUPPORT In Vitro
"Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
Establishes the model, perturbation, molecular readout, and cellular phenotype.
Variant-specific RNase MRP substrate-cleavage assay OTHER
Variant-specific cleavage assays separate the rRNA activity that tracks skeletal severity from the mRNA activity that tracks CHH-like hair, immune, and haematologic manifestations. The assays support substrate-specific genotype-phenotype correlation but do not model growth-plate architecture.
Thirteen disease-associated RMRP variants Wild-type RNase MRP activity comparator
Organism
human NCBITaxon:9606 NCBI Taxonomy (NCBITaxon) Relation: this experimental model is built in this organism This experimental model is built in human, annotated with Homo sapiens (NCBITaxon:9606). NCBITaxon:9606 is an organism from the NCBI Taxonomy.
Cell source
Reconstituted human RNase MRP complexes carrying patient RMRP variants
Culture
In vitro messenger-RNA and ribosomal-RNA cleavage assays
Publication
PMID:17701897
Pathograph links
Impaired rRNA Cleavage in Ribosome Assembly Quantifies variant-specific loss of rRNA cleavage against bone-dysplasia severity.
Show evidence (1 reference)
PMID:17701897 SUPPORT In Vitro
"In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
Directly reports the assay and the rRNA-cleavage severity correlation.
mRNA Cleavage-Dependent Spectrum Modulation Quantifies variant-specific mRNA cleavage against extraskeletal spectrum features.
Show evidence (1 reference)
PMID:17701897 SUPPORT In Vitro
"reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
Directly reports the substrate-specific extraskeletal correlation.
Show evidence (1 reference)
PMID:17701897 SUPPORT In Vitro
"In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
Establishes the model and its principal genotype-function result.
{ }

Source YAML

click to show 
name: Anauxetic dysplasia
creation_date: "2026-08-01T05:14:29Z"
description: >-
  Anauxetic dysplasia (AD) is the most severe phenotype of the cartilage-hair
  hypoplasia to anauxetic dysplasia (CHH-AD) spectrum, a group of autosomal
  recessive ribosomopathies caused by loss of function in the RNase MRP
  endoribonuclease complex. It is defined by extreme disproportionate short-limb
  short stature recognizable at birth, with atlantoaxial instability, joint
  hypermobility and, at this end of the spectrum, possible cognitive deficiency.
  Its mechanistic interest is a clean two-substrate dissociation: RNase MRP
  cleaves both ribosomal RNA and messenger RNA, and which of those two functions
  a given variant impairs predicts which half of the syndrome the patient gets.
  Hair, immune, haematologic, gastrointestinal, and malignancy associations are
  retained below as conditional CHH-AD spectrum risks rather than assumed
  characteristics of pure AD. In particular, the latest ANXD3 series explicitly
  lacked immune and gastrointestinal involvement while expanding that subtype
  with craniofacial, sensory, ophthalmologic, renal, and foot findings; all of
  these observations remain based on very small numbers of individuals.
category: Mendelian
parents:
- osteochondrodysplasia
- autosomal recessive disease
synonyms:
- AD
- spondyloepimetaphyseal dysplasia, anauxetic type
disease_term:
  preferred_term: anauxetic dysplasia
  term:
    id: MONDO:0011773
    label: anauxetic dysplasia
inheritance:
- name: Autosomal recessive inheritance
  description: >-
    Anauxetic dysplasia is autosomal recessive, arising from biallelic variants
    in RMRP or, in the genetically distinct forms, POP1 or NEPRO.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
    explanation: >-
      Establishes autosomal recessive inheritance and places anauxetic dysplasia
      at the severe end of the RMRP spectrum.
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If both parents are known to be heterozygous for an RMRP pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier."
    explanation: >-
      GeneReviews recurrence risks used in counselling families.
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "carrier testing for at-risk relatives and molecular genetic prenatal and preimplantation genetic testing for CHH-AD spectrum disorders are possible"
    explanation: >-
      Documents the reproductive testing options available once the familial
      variants are known.
classifications:
  isds_skeletal_category:
  - classification_value: metaphyseal_dysplasias
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (Unger,
      Ferreira, Mortier et al., PMID:36779427), Table 1 group 11 "Metaphyseal
      dysplasias". This entry lumps two listed rows of that group, both renamed
      under the 2023 dyadic scheme: NOS 11-0030 "Metaphyseal dysplasia with
      short stature (CHH-like), POP1-related" (MIM 617396, anauxetic dysplasia
      2) and NOS 11-0040 "Metaphyseal dysplasia with short stature (CHH-like),
      NEPRO-related" (MIM 618853, anauxetic dysplasia 3). The RMRP-related
      severe end of the spectrum described here belongs to the same group's
      NOS 11-0020 row (cartilage-hair hypoplasia), which is tagged on the
      separate Cartilage-hair hypoplasia entry.
has_subtypes:
- name: AD1
  display_name: Anauxetic dysplasia 1 (RMRP-related)
  subtype_term:
    preferred_term: anauxetic dysplasia 1
    term:
      id: MONDO:0054560
      label: anauxetic dysplasia 1
  description: >-
    Caused by biallelic RMRP variants, the non-coding RNA component of RNase MRP.
    This is the form contiguous with cartilage-hair hypoplasia, and the one in
    which the two-substrate genotype-phenotype correlation was established.
  genes:
  - preferred_term: RMRP
    term:
      id: hgnc:10031
      label: RMRP
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
    explanation: >-
      Establishes RMRP as the gene of the original anauxetic dysplasia form at
      the severe end of the CHH spectrum.
- name: AD2
  display_name: Anauxetic dysplasia 2 (POP1-related)
  subtype_term:
    preferred_term: anauxetic dysplasia 2
    term:
      id: MONDO:0054561
      label: anauxetic dysplasia 2
  description: >-
    Caused by biallelic POP1 variants, a protein subunit of the same
    holoenzyme. Patient material shows markedly reduced RMRP abundance with
    accumulation of unprocessed pre-5.8S rRNA, which is the direct in-patient
    counterpart of the in vitro cleavage data from the RMRP arm.
  genes:
  - preferred_term: POP1
    term:
      id: hgnc:30129
      label: POP1
  evidence:
  - reference: PMID:28067412
    reference_title: "Broadening the phenotypic spectrum of POP1-skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Markedly reduced abundance of RMRP and elevated levels of pre5.8s rRNA was observed."
    explanation: >-
      Patient-derived evidence that a POP1 lesion destabilizes the RNA component
      and blocks rRNA processing, converging on the same mechanism as RMRP loss.
- name: AD3
  display_name: Anauxetic dysplasia 3 (NEPRO-related)
  subtype_term:
    preferred_term: anauxetic dysplasia 3
    term:
      id: MONDO:0030019
      label: anauxetic dysplasia 3
  description: >-
    Caused by biallelic NEPRO variants. NEPRO interacts with multiple RNase MRP
    protein subunits rather than being part of the core complex, and this arm
    adds prominent skin laxity and joint dislocations to the skeletal core.
  genes:
  - preferred_term: NEPRO
    term:
      id: hgnc:24496
      label: NEPRO
  evidence:
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nucleolus and neural progenitor protein (NEPRO), encoded by NEPRO (C3orf17), is known to interact with multiple protein subunits of RMRP."
    explanation: >-
      Establishes NEPRO as an RNase MRP interactor and the basis of the third
      genetic form.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study reports three new ANXD3 cases from a consanguineous Iranian family, carrying the homozygous pathogenic variant Chr3:113014014G>A; exon3; c.280C>T; p.Arg94Cys in the NEPRO gene."
    explanation: >-
      Adds three independently ascertained ANXD3 cases with molecular and
      segregation confirmation of the recurrent NEPRO p.Arg94Cys variant.
pathophysiology:
- name: RNase MRP Complex Loss of Function
  biological_scale: MOLECULAR
  description: >-
    RMRP encodes the untranslated RNA component of RNase MRP, a
    ribonucleoprotein endoribonuclease. Pathogenic variants either alter
    evolutionarily conserved nucleotides or disrupt the secondary structure by
    mispairing within stem regions, so the lesion is one of RNA folding and
    catalysis rather than of a protein coding sequence. The genetically distinct
    forms hit protein members of the same complex (POP1) or an interacting
    nucleolar partner (NEPRO), which is why they converge on one phenotype.
  genes:
  - preferred_term: RMRP
    term:
      id: hgnc:10031
      label: RMRP
  - preferred_term: POP1
    term:
      id: hgnc:30129
      label: POP1
  - preferred_term: NEPRO
    term:
      id: hgnc:24496
      label: NEPRO
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The RMRP gene encodes the untranslated RNA component of the mitochondrial RNA-processing ribonuclease, RNase MRP."
    explanation: >-
      Identifies the gene product as a non-coding RNA component of the RNase MRP
      complex.
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "disease-causing mutations either affect evolutionarily conserved nucleotides or are likely to alter secondary structure through mispairing in stem regions"
    explanation: >-
      Defines the two structural mechanisms by which variants in a non-coding RNA
      gene impair function.
  downstream:
  - target: Impaired rRNA Cleavage in Ribosome Assembly
    description: >-
      Loss of RNase MRP activity on its ribosomal RNA substrate compromises
      ribosome biogenesis.
  - target: mRNA Cleavage-Dependent Spectrum Modulation
    description: >-
      Variant-specific impairment of messenger-RNA cleavage determines whether
      CHH-like hair, immune, and haematologic features overlap the skeletal
      phenotype; those features are not assumed to be part of pure ANXD.
- name: Impaired rRNA Cleavage in Ribosome Assembly
  biological_scale: MOLECULAR
  description: >-
    The first of the two substrate arms. RNase MRP participates in ribosomal RNA
    processing during ribosome assembly, and the magnitude of the rRNA cleavage
    defect correlates directly with the degree of bone dysplasia. Anauxetic
    dysplasia sits at the severe end because its allele combinations produce the
    greatest loss of this specific activity. The ribosomopathy label is the
    conventional reading of that correlation, but it is contested; see the
    knowledge gap attached to this node.
  biological_processes:
  - preferred_term: rRNA processing
    term:
      id: GO:0006364
      label: rRNA processing
    modifier: DECREASED
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
    explanation: >-
      Establishes the quantitative link between loss of rRNA cleavage and
      skeletal severity, the basis for the substrate dissociation.
  - reference: PMID:21396580
    reference_title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This complex is involved in the ribosome assembly by cleavage of 5.8S rRNA, cell cycle control by Cyclin B2 mRNA cleavage at the end of mitosis, processing the mitochondrial RNA, and forming a complex with hTERT suggesting a possible involvement in expression regulation by siRNA synthesis."
    explanation: >-
      Names the specific substrates, 5.8S rRNA for the ribosome arm and Cyclin
      B2 mRNA for the cell-cycle arm, rather than leaving them generic.
  - reference: PMID:28067412
    reference_title: "Broadening the phenotypic spectrum of POP1-skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Markedly reduced abundance of RMRP and elevated levels of pre5.8s rRNA was observed."
    explanation: >-
      In-patient confirmation that the rRNA processing step is blocked, which
      the rest of this node rests on in vitro reconstitution for.
  downstream:
  - target: Growth Plate Chondrocyte Differentiation Failure
    description: >-
      Reduced RNase MRP activity disrupts growth-plate chondrocyte
      differentiation, with the strongest experimental effect at hypertrophy.
- name: mRNA Cleavage-Dependent Spectrum Modulation
  biological_scale: MOLECULAR
  description: >-
    The second substrate arm is a modifier of position within the CHH-AD
    spectrum rather than an obligatory ANXD lesion. Reduced cleavage of RNase
    MRP messenger-RNA targets impairs cell-cycle regulation, and the degree of
    that impairment predicts hair hypoplasia, immunodeficiency and
    haematological abnormality rather than bone severity. Pure ANXD can
    therefore combine profound skeletal dysplasia with relative preservation of
    these extraskeletal systems. The concrete substrate is Cyclin B2 mRNA,
    cleaved at the end of mitosis.
  biological_processes:
  - preferred_term: regulation of cell cycle
    term:
      id: GO:0051726
      label: regulation of cell cycle
    modifier: DECREASED
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
    explanation: >-
      Establishes that the mRNA-cleavage arm, not the rRNA arm, determines the
      extraskeletal phenotype including cancer risk.
  - reference: PMID:21396580
    reference_title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The degree of skeletal dysplasia correlates mainly with the rRNA cleavage activity, whereas significantly diminished mRNA cleavage activity is a prerequisite for immunodeficiency."
    explanation: >-
      Independent statement of the two-substrate dissociation, and stronger than
      correlation for the immune arm: diminished mRNA cleavage is described as a
      prerequisite.
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "We recently demonstrated that mutations may affect both messenger RNA (mRNA) and ribosomal RNA (rRNA) cleavage and thus cell-cycle regulation and protein synthesis."
    explanation: >-
      States the dual-substrate nature of the enzyme that underlies the
      dissociation.
  downstream:
  - target: Conditional Immune and Haematopoietic Spectrum Involvement
    description: >-
      When messenger-RNA cleavage is sufficiently impaired, immune and erythroid
      progenitor dysfunction can overlap the skeletal phenotype.
  - target: Fine hair
    description: >-
      Hair hypoplasia tracks the messenger-RNA-cleavage arm across the spectrum.
- name: Conditional Immune and Haematopoietic Spectrum Involvement
  biological_scale: ORGANISM
  description: >-
    Immunodeficiency, defective erythrogenesis, and malignancy risk belong to
    the CHH-AD spectrum and track the messenger-RNA-cleavage arm. They are
    retained as conditional overlap risks that require baseline assessment, not
    as expected manifestations of pure ANXD; the 2026 ANXD3 series explicitly
    reported no immune involvement.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
    explanation: >-
      Establishes these as spectrum findings; PARTIAL reflects that they are not
      assumed characteristics of the pure ANXD phenotype.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
    explanation: >-
      Direct negative evidence for immune involvement in ANXD3, scoped to a
      three-person family and therefore not generalized to every ANXD subtype.
  downstream:
  - target: Immunodeficiency
    description: >-
      Conditional immune-cell dysfunction manifests clinically as
      immunodeficiency.
  - target: Anemia
    description: >-
      Conditional erythroid dysfunction manifests clinically as anemia.
  - target: Neoplasm
    description: >-
      The cell-cycle and immune arm provides the spectrum-level route to
      malignancy risk.
- name: Growth Plate Chondrocyte Differentiation Failure
  biological_scale: TISSUE
  description: >-
    Chondrocytes in the proliferative zone of the growth plate are among the most
    biosynthetically demanding cells in the developing skeleton, which is why a
    generalized ribosome assembly defect strikes them hardest. Experimentally the
    step most affected is hypertrophic differentiation rather than proliferation
    alone, and RNase MRP is itself expressed in the growth plate with expression
    tracking chondrocyte hypertrophy. The result is
    metaphyseal dysplasia and a failure of endochondral bone elongation that is
    already evident at birth.
  cell_types:
  - preferred_term: chondrocyte
    term:
      id: CL:0000138
      label: chondrocyte
  biological_processes:
  - preferred_term: chondrocyte differentiation
    term:
      id: GO:0002062
      label: chondrocyte differentiation
    modifier: DECREASED
  - preferred_term: chondrocyte hypertrophy
    term:
      id: GO:0003415
      label: chondrocyte hypertrophy
    modifier: DECREASED
  - preferred_term: endochondral ossification
    term:
      id: GO:0001958
      label: endochondral ossification
    modifier: DECREASED
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "CHH-AD spectrum disorders are characterized by severe disproportionate (short-limb) short stature that is usually recognized in the newborn, and occasionally prenatally because of the short extremities."
    explanation: >-
      Establishes the short-limb growth failure and its recognition at or before
      birth, consistent with a prenatal growth plate defect.
  - reference: PMID:28743979
    reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
    explanation: >-
      Direct chondrocyte evidence: knocking down Rmrp deranges chondrogenic
      differentiation and pre-rRNA processing together, which is what this node
      otherwise had to infer from the clinical phenotype.
  - reference: PMID:28743979
    reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Expression of Rmrp RNA and RNase MRP protein subunits was detected in the murine growth plate and during the course of chondrogenic differentiation of ATDC5 cultures, where Rmrp RNA expression was found to be correlated with chondrocyte hypertrophy."
    explanation: >-
      Localizes RNase MRP expression to the growth plate itself and ties it to
      the hypertrophic step, supporting tissue specificity rather than a purely
      quantitative demand argument.
  downstream:
  - target: Extreme Disproportionate Short-Limb Short Stature
    description: >-
      Failure of endochondral elongation in the limbs produces disproportionate
      dwarfism.
  - target: Severe short stature
    description: >-
      Connects the tissue mechanism to the ontology-bound clinical phenotype.
  - target: Atlantoaxial Instability
    description: >-
      The same dysplastic process affects the upper cervical vertebrae and their
      ligamentous stabilization.
  - target: Atlantoaxial dislocation
    description: >-
      Connects cervical instability to the ontology-bound clinical phenotype.
  - target: Brachydactyly
    description: >-
      Abnormal endochondral development shortens the metacarpals and phalanges.
  - target: Ovoid vertebral bodies
    description: >-
      Disordered vertebral ossification produces the characteristic ovoid
      vertebral morphology.
  - target: Hypoplastic ilia
    description: >-
      Pelvic endochondral growth failure produces underdeveloped iliac bones.
  - target: Metaphyseal irregularity
    description: >-
      Growth-plate disorganization produces irregular metaphyseal contours.
  - target: Thoracolumbar kyphoscoliosis
    description: >-
      Progressive vertebral dysplasia produces combined thoracolumbar kyphosis
      and scoliosis.
- name: Extreme Disproportionate Short-Limb Short Stature
  biological_scale: ORGANISM
  description: >-
    Anauxetic dysplasia carries the most pronounced skeletal phenotype of the
    spectrum. The name itself means without growth, and adult stature is at the
    extreme end of human short stature.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most severe phenotype, AD, has the most pronounced skeletal phenotype"
    explanation: >-
      Positions anauxetic dysplasia as the most skeletally severe phenotype of
      the spectrum.
- name: Atlantoaxial Instability
  biological_scale: ORGANISM
  description: >-
    Atlantoaxial subluxation may be present in the newborn and is largely
    specific to the anauxetic end of the spectrum. It is the feature with the
    most immediate clinical consequence, because it converts routine general
    anaesthesia into a cervical cord risk and may require surgical fusion.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "may be associated with atlantoaxial subluxation in the newborn"
    explanation: >-
      Establishes atlantoaxial subluxation as a neonatal feature specific to the
      anauxetic phenotype.
phenotypes:
- name: Severe short stature
  category: Growth
  description: >-
    Extreme disproportionate short-limb short stature, recognizable in the
    newborn and sometimes prenatally.
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Severe short stature
    term:
      id: HP:0003510
      label: Severe short stature
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "severe disproportionate (short-limb) short stature that is usually recognized in the newborn"
    explanation: >-
      Establishes severe short-limb short stature as the cardinal, near-universal
      feature.
- name: Atlantoaxial dislocation
  category: Skeletal
  description: >-
    Atlantoaxial subluxation, present from the newborn period at the anauxetic
    end of the spectrum, carrying cervical cord risk during anaesthesia.
  phenotype_term:
    preferred_term: Atlantoaxial dislocation
    term:
      id: HP:0003414
      label: Atlantoaxial dislocation
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "may be associated with atlantoaxial subluxation in the newborn"
    explanation: >-
      Documents atlantoaxial subluxation as a neonatal feature of anauxetic
      dysplasia.
  - reference: DOI:10.1002/ajmg.a.63316
    reference_title: "Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
    explanation: >-
      Extends atlantoaxial subluxation, previously documented at the RMRP/POP1
      end, to the NEPRO-related form.
- name: Joint hypermobility
  category: Skeletal
  description: >-
    Generalized joint hypermobility, with joint dislocations reported in the
    NEPRO-related form. Frequency is omitted: the available snippets establish
    the association but not a band.
  phenotype_term:
    preferred_term: Joint hypermobility
    term:
      id: HP:0001382
      label: Joint hypermobility
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other findings include joint hypermobility, fine, silky hair"
    explanation: >-
      Lists joint hypermobility among the characteristic findings of the
      spectrum.
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
    explanation: >-
      Confirms joint hypermobility and dislocations across all reported
      NEPRO-related individuals.
- name: Fine hair
  category: Integumentary
  description: >-
    Fine, silky hair is a CHH-AD spectrum association that tracks the
    messenger-RNA-cleavage arm. It is retained as a differential clue rather
    than an assumed feature of pure ANXD.
  phenotype_term:
    preferred_term: Fine hair
    term:
      id: HP:0002213
      label: Fine hair
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
    explanation: >-
      Documents fine hair at spectrum level; PARTIAL avoids assigning it to all
      individuals with ANXD.
- name: Immunodeficiency
  category: Immunologic
  description: >-
    SPECTRUM-LEVEL: immunodeficiency, including SCID, is established across the
    CHH-AD spectrum but is not assumed in pure ANXD. Because the consequence of
    missing overlap is high, baseline immune assessment and conditional safety
    measures remain appropriate. The latest three-person ANXD3 family reported
    no immunological involvement.
  phenotype_term:
    preferred_term: Immunodeficiency
    term:
      id: HP:0002721
      label: Immunodeficiency
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
    explanation: >-
      Lists immunodeficiency for the whole spectrum, so it is PARTIAL for ANXD.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
    explanation: >-
      Negative subtype-specific evidence from three related ANXD3 cases; it
      counters, but cannot exclude, spectrum overlap in other ANXD genotypes.
- name: Anemia
  category: Hematologic
  description: >-
    SPECTRUM-LEVEL: defective erythrogenesis is documented across CHH-AD but is
    not assumed in pure ANXD. It remains relevant to baseline assessment because
    the molecular and phenotypic boundaries overlap.
  phenotype_term:
    preferred_term: Anemia
    term:
      id: HP:0001903
      label: Anemia
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This clinical spectrum includes different degrees of short stature, hair hypoplasia, defective erythrogenesis, and immunodeficiency."
    explanation: >-
      The source explicitly scopes defective erythrogenesis to the spectrum, so
      the association is PARTIAL for the ANXD entry.
- name: Intellectual disability
  category: Neurologic
  description: >-
    Cognitive deficiency is specific to the anauxetic end of the spectrum rather
    than a general CHH-AD feature, and GeneReviews recommends developmental and
    cognitive assessment throughout childhood in these individuals.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The most severe phenotype, AD, has the most pronounced skeletal phenotype, may be associated with atlantoaxial subluxation in the newborn, and may include cognitive deficiency."
    explanation: >-
      Establishes cognitive deficiency as a feature of the anauxetic phenotype
      specifically.
- name: Dental anomalies
  category: Craniofacial
  description: >-
    Extensive dental anomalies documented on detailed evaluation of an
    NEPRO-related (ANXD3) patient, in whom they had not previously been
    described. The MONDO definition of anauxetic dysplasia names hypodontia
    specifically, but no source cited here states reduced tooth number directly,
    so the phenotype is curated at the level of granularity the literature
    supports rather than at the level the ontology definition implies.
  phenotype_term:
    preferred_term: Dental anomalies
    term:
      id: HP:0000164
      label: Abnormality of the dentition
  evidence:
  - reference: DOI:10.1002/ajmg.a.63316
    reference_title: "Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
    explanation: >-
      Directly documents dental anomalies in an individual with molecularly
      confirmed anauxetic dysplasia.
  - reference: DOI:10.1002/ajmg.a.63316
    reference_title: "Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Greater awareness of the possibility of atlantoaxial subluxation, dental anomalies, and craniosynostosis may lead to more timely diagnosis and treatment."
    explanation: >-
      The authors' own framing of dental anomalies as a feature clinicians
      should actively look for in this disorder.
- name: Craniosynostosis
  category: Craniofacial
  description: >-
    Sagittal suture craniosynostosis producing scaphocephaly, reported in a
    single NEPRO-related individual and not previously described in this
    disorder. A single-case observation, so no frequency is asserted.
  phenotype_term:
    preferred_term: Craniosynostosis
    term:
      id: HP:0001363
      label: Craniosynostosis
  evidence:
  - reference: DOI:10.1002/ajmg.a.63316
    reference_title: "Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient presented with clinically relevant features not previously described in ANXD3: atlantoaxial subluxation, extensive dental anomalies, and a sagittal suture craniosynostosis resulting in scaphocephaly."
    explanation: >-
      Documents sagittal craniosynostosis in a molecularly confirmed ANXD3
      patient; single case, so recorded without a frequency claim.
- name: Brachydactyly
  category: Skeletal
  description: >-
    Short digits with short metacarpals and broad middle phalanges, reported in
    all individuals of the NEPRO-related series.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
  evidence:
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
    explanation: >-
      Reports brachydactyly in all five individuals of the NEPRO series.
- name: Hyperextensible skin
  category: Integumentary
  description: >-
    Skin laxity accompanies the joint hypermobility, and is most prominent in
    the NEPRO-related form.
  phenotype_term:
    preferred_term: Hyperextensible skin
    term:
      id: HP:0000974
      label: Hyperextensible skin
  evidence:
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "All the five affected individuals have severe short stature, brachydactyly, skin laxity, joint hypermobility, and joint dislocations."
    explanation: >-
      Reports skin laxity in all five individuals of the NEPRO series.
- name: Ovoid vertebral bodies
  category: Skeletal
  subtype: AD3
  description: >-
    Ovoid vertebral morphology is part of the characteristic radiographic
    pattern of NEPRO-related anauxetic dysplasia.
  phenotype_term:
    preferred_term: Ovoid vertebral bodies
    term:
      id: HP:0003300
      label: Ovoid vertebral bodies
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Directly identifies ovoid vertebrae in the radiographic ANXD3 pattern.
- name: Hypoplastic ilia
  category: Skeletal
  subtype: AD3
  description: >-
    Underdevelopment of the iliac bones is a characteristic pelvic radiographic
    feature of ANXD3.
  phenotype_term:
    preferred_term: Hypoplastic ilia
    term:
      id: HP:0000946
      label: Hypoplastic ilia
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Directly identifies hypoplastic ilia in the radiographic ANXD3 pattern.
- name: Metaphyseal irregularity
  category: Skeletal
  subtype: AD3
  description: >-
    Irregular metaphyseal contours reflect the growth-plate and endochondral
    ossification defect.
  phenotype_term:
    preferred_term: Metaphyseal irregularity
    term:
      id: HP:0003025
      label: Metaphyseal irregularity
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Directly identifies metaphyseal irregularity in the radiographic ANXD3 pattern.
- name: Thoracolumbar kyphoscoliosis
  category: Skeletal
  description: >-
    Combined thoracolumbar kyphosis and scoliosis is shared across previously
    reported and newly described ANXD3 cases.
  phenotype_term:
    preferred_term: Thoracolumbar kyphoscoliosis
    term:
      id: HP:0003423
      label: Thoracolumbar kyphoscoliosis
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A comparative analysis with previously reported ANXD3 cases revealed shared characteristics, including short stature, brachydactyly, and thoracolumbar kyphoscoliosis"
    explanation: >-
      Identifies thoracolumbar kyphoscoliosis as a shared ANXD3 characteristic.
- name: Microcephaly
  category: Craniofacial
  subtype: AD3
  description: >-
    Microcephaly was present in the 2026 Iranian family and in earlier ANXD3
    cases, with variable head size across reported individuals.
  phenotype_term:
    preferred_term: Microcephaly
    term:
      id: HP:0000252
      label: Microcephaly
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Microcephaly was observed in our patients, same as previously reported cases, underscoring the phenotypic variability of ANXD3."
    explanation: >-
      Directly documents microcephaly in the new family and earlier ANXD3 cases.
- name: Talipes equinovarus
  category: Skeletal
  subtype: AD3
  description: >-
    Clubfoot was newly reported in the 2026 ANXD3 family; its frequency and
    subtype specificity remain unknown.
  phenotype_term:
    preferred_term: Talipes equinovarus
    term:
      id: HP:0001762
      label: Talipes equinovarus
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
    explanation: >-
      Reports clubfoot among the newly recognized systemic ANXD3 features.
- name: Cataract
  category: Ophthalmologic
  subtype: AD3
  description: >-
    Cataracts were reported in the 2026 ANXD3 family and require confirmation
    in additional unrelated families.
  phenotype_term:
    preferred_term: Cataract
    term:
      id: HP:0000518
      label: Cataract
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
    explanation: >-
      Reports cataracts among the newly recognized systemic ANXD3 features.
- name: Urolithiasis
  category: Genitourinary
  subtype: AD3
  description: >-
    Urolithiasis was reported in the 2026 ANXD3 family; the causal route and
    recurrence risk are not yet established.
  phenotype_term:
    preferred_term: Urolithiasis
    term:
      id: HP:0034368
      label: Urolithiasis
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
    explanation: >-
      Reports urolithiasis among the newly recognized systemic ANXD3 features.
- name: Hearing impairment
  category: Ear
  subtype: AD3
  description: >-
    Hearing impairment was reported in the 2026 ANXD3 family without a defined
    conductive or sensorineural subtype.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "unique features such as microcephaly, clubfoot, cataracts, urolithiasis, and hearing impairments"
    explanation: >-
      Reports hearing impairment among the newly recognized systemic ANXD3 features.
- name: Coxa vara
  category: Skeletal
  description: >-
    Severe coxa vara can produce progressive lower-limb malalignment requiring
    corrective osteotomy.
  phenotype_term:
    preferred_term: Coxa vara
    term:
      id: HP:0002812
      label: Coxa vara
  evidence:
  - reference: PMID:22528854
    reference_title: "Axial correction of the lower limb deformities in a girl with anauxetic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
    explanation: >-
      Directly documents severe coxa vara in a molecularly untyped clinical ANXD case.
- name: Genu valgum
  category: Skeletal
  description: >-
    Valgus knee deformity can accompany coxa vara and require guided-growth or
    osteotomy-based correction.
  phenotype_term:
    preferred_term: Genu valgum
    term:
      id: HP:0002857
      label: Genu valgum
  evidence:
  - reference: PMID:22528854
    reference_title: "Axial correction of the lower limb deformities in a girl with anauxetic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
    explanation: >-
      Directly documents genu valgum in a clinical ANXD case.
- name: Malabsorption
  category: Gastrointestinal
  description: >-
    SPECTRUM-LEVEL: gastrointestinal malabsorption is a variable additional
    CHH-AD feature rather than an expected manifestation of pure ANXD. ANXD3
    negative evidence is retained as a counterweight.
  phenotype_term:
    preferred_term: Malabsorption
    term:
      id: HP:0002024
      label: Malabsorption
  evidence:
  - reference: PMID:21396580
    reference_title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "variable additional features including predisposition to cancer, anemia, immunodeficiency, and gastrointestinal malabsorption and Hirschsprung's disease"
    explanation: >-
      The publication calls this a variable additional spectrum feature, hence
      PARTIAL for ANXD.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: "Unlike other CHH-AD subtypes, ANXD3 lacks immunological or gastrointestinal involvement."
    explanation: >-
      Refutes gastrointestinal involvement in the reported ANXD3 family only.
- name: Aganglionic megacolon
  category: Gastrointestinal
  description: >-
    SPECTRUM-LEVEL: Hirschsprung disease is a variable additional CHH-AD feature
    and is retained for differential and conditional management awareness, not
    as an expected feature of pure ANXD.
  phenotype_term:
    preferred_term: Aganglionic megacolon
    term:
      id: HP:0002251
      label: Aganglionic megacolon
  evidence:
  - reference: PMID:21396580
    reference_title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "gastrointestinal malabsorption and Hirschsprung's disease"
    explanation: >-
      Names Hirschsprung disease within a sentence describing variable
      additional spectrum features, so the ANXD association is PARTIAL.
- name: Neoplasm
  category: Oncologic
  description: >-
    SPECTRUM-LEVEL: malignancy risk is established chiefly in CHH cohorts and
    tracks the messenger-RNA-cleavage arm. No risk estimate exists for pure
    ANXD, whose case count is too small to exclude or quantify predisposition.
  phenotype_term:
    preferred_term: Neoplasm
    term:
      id: HP:0002664
      label: Neoplasm
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Other findings include joint hypermobility, fine, silky hair, immunodeficiency, anemia, increased risk for malignancy, gastrointestinal dysfunction, and impaired spermatogenesis."
    explanation: >-
      Documents malignancy risk for the spectrum; PARTIAL avoids assigning an
      unquantified risk to every ANXD patient.
genetic:
- name: RMRP
  gene_term:
    preferred_term: RMRP
    term:
      id: hgnc:10031
      label: RMRP
  association: Pathogenic Variants
  relationship_type: CAUSATIVE
  notes: >-
    Encodes the non-coding RNA component of RNase MRP. Biallelic variants cause
    the whole CHH-AD spectrum; anauxetic dysplasia arises from combinations
    producing the greatest loss of rRNA cleavage activity, for example a null
    allele in trans with a hypomorphic allele otherwise seen in milder disease.
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a novel patient with anauxetic dysplasia who was compound heterozygous for the null mutation g.254_263delCTCAGCGCGG and the mutation g.195C-->T, which was previously described in patients with milder phenotypes"
    explanation: >-
      Illustrates how allele combination rather than allele identity places a
      patient at the anauxetic end of the spectrum.
- name: POP1
  gene_term:
    preferred_term: POP1
    term:
      id: hgnc:30129
      label: POP1
  association: Pathogenic Variants
  relationship_type: CAUSATIVE
  notes: >-
    Encodes a protein subunit of the RNase MRP complex. Biallelic variants cause
    anauxetic dysplasia 2, so the disease can be reached by disabling either the
    RNA or the protein half of the same holoenzyme.
  evidence:
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cartilage hair hypoplasia (CHH), anauxetic dysplasia 1, and anauxetic dysplasia 2 are rare metaphyseal dysplasias caused by biallelic pathogenic variants in RMRP and POP1, which encode the components of RNAse-MRP endoribonuclease complex (RMRP) in ribosomal biogenesis pathway."
    explanation: >-
      Establishes POP1 as the cause of anauxetic dysplasia 2 and places both
      genes in the RNase MRP complex.
- name: NEPRO
  gene_term:
    preferred_term: NEPRO
    term:
      id: hgnc:24496
      label: NEPRO
  association: Pathogenic Variants
  relationship_type: CAUSATIVE
  notes: >-
    Nucleolus and neural progenitor protein, which interacts with multiple RNase
    MRP protein subunits. Biallelic variants cause a third, emerging form with
    the same skeletal core plus prominent skin laxity and joint dislocations.
    Reported variants cluster in one protein domain and reduce protein stability.
  evidence:
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Nucleolus and neural progenitor protein (NEPRO), encoded by NEPRO (C3orf17), is known to interact with multiple protein subunits of RMRP."
    explanation: >-
      Establishes NEPRO as an interactor of the RNase MRP complex, explaining
      mechanistic convergence.
  - reference: PMID:31250547
    reference_title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Protein modeling and stability prediction showed that the mutant protein has decreased stability. Both the reported variants are in the same domain of the protein."
    explanation: >-
      In silico evidence for the mechanism and domain clustering of the NEPRO
      variants.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnostic whole-exome sequencing, supported by Sanger validation, confirmed the autosomal recessive inheritance pattern."
    explanation: >-
      Orthogonally validated segregation evidence from three additional ANXD3 cases.
imaging_findings:
- name: Ovoid vertebral bodies on skeletal radiography
  modality: XRAY
  imaging_finding_term:
    preferred_term: Ovoid vertebral bodies
    term:
      id: HP:0003300
      label: Ovoid vertebral bodies
  phenotype_term:
    preferred_term: Ovoid vertebral bodies
    term:
      id: HP:0003300
      label: Ovoid vertebral bodies
  subtype: AD3
  description: >-
    Ovoid vertebral bodies form part of the characteristic generalized skeletal
    radiographic pattern of ANXD3.
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Defines ovoid vertebral morphology as a distinct radiographic ANXD3 finding.
- name: Hypoplastic ilia on skeletal radiography
  modality: XRAY
  imaging_finding_term:
    preferred_term: Hypoplastic ilia
    term:
      id: HP:0000946
      label: Hypoplastic ilia
  phenotype_term:
    preferred_term: Hypoplastic ilia
    term:
      id: HP:0000946
      label: Hypoplastic ilia
  subtype: AD3
  description: >-
    Pelvic radiographs show hypoplastic ilia together with narrow acetabular
    angles in ANXD3.
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Defines hypoplastic ilia as a distinct radiographic ANXD3 finding.
- name: Irregular metaphyses on skeletal radiography
  modality: XRAY
  imaging_finding_term:
    preferred_term: Metaphyseal irregularity
    term:
      id: HP:0003025
      label: Metaphyseal irregularity
  phenotype_term:
    preferred_term: Metaphyseal irregularity
    term:
      id: HP:0003025
      label: Metaphyseal irregularity
  subtype: AD3
  description: >-
    Irregular metaphyses are the long-bone radiographic correlate of the
    growth-plate differentiation defect.
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "distinct radiographic findings such as ovoid vertebrae, hypoplastic ilia, narrow acetabular angles, and irregular metaphyses"
    explanation: >-
      Defines irregular metaphyses as a distinct radiographic ANXD3 finding.
diagnosis:
- name: Clinical and radiographic diagnosis
  description: >-
    Diagnosis is established in a proband with the characteristic clinical and
    radiographic findings, with molecular testing reserved for inconclusive cases
    and for family studies.
  diagnosis_term:
    preferred_term: skeletal radiography
    term:
      id: NCIT:C38101
      label: X-Ray Imaging
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnosis of a CHH-AD spectrum disorder is established in a proband with characteristic clinical and radiographic findings."
    explanation: >-
      States the clinical and radiographic basis of diagnosis.
- name: Molecular genetic testing
  description: >-
    Identification of biallelic causal variants confirms the molecular subtype
    and enables family studies. Testing must cover the non-coding RMRP gene as
    well as POP1 and NEPRO; exome-based testing can diagnose the protein-coding
    forms, with Sanger confirmation and segregation analysis.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "identification of biallelic pathogenic variants in RMRP by molecular genetic testing can confirm the diagnosis and allow for family studies"
    explanation: >-
      Specifies the role of molecular testing relative to clinical diagnosis.
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Diagnostic whole-exome sequencing, supported by Sanger validation, confirmed the autosomal recessive inheritance pattern."
    explanation: >-
      Demonstrates exome diagnosis, orthogonal confirmation, and segregation for ANXD3.
treatments:
- name: Cervical spine stabilization and anaesthetic precautions
  description: >-
    Where cervical spinal instability is present, special care is required during
    general anaesthesia and surgical fusion of unstable cervical vertebrae may be
    needed. This is the highest-stakes management point in anauxetic dysplasia,
    because the risk is realized during otherwise routine procedures.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: orthopedic surgical procedure
    term:
      id: NCIT:C16186
      label: Orthopedic Surgical Procedure
  target_mechanisms:
  - target: Atlantoaxial Instability
    treatment_effect: INHIBITS
    description: >-
      Fusion stabilizes the unstable segment; anaesthetic precautions avoid
      precipitating cord injury.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "If cervical spinal instability is identified in a person with AD, special care is required during general anesthesia; surgery may be needed to fuse unstable cervical vertebrae"
    explanation: >-
      GeneReviews management guidance specific to the anauxetic phenotype.
- name: Kyphoscoliosis and limb deformity surgery
  description: >-
    Surgery may be needed for progressive kyphoscoliosis compromising lung
    function, and corrective osteotomies for progressive varus deformity of the
    lower extremities.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: orthopedic surgical procedure
    term:
      id: NCIT:C16186
      label: Orthopedic Surgical Procedure
  target_mechanisms:
  - target: Thoracolumbar kyphoscoliosis
    treatment_effect: INHIBITS
    description: >-
      Corrective spinal surgery treats progressive deformity when it compromises
      pulmonary function.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "surgery may be needed to fuse unstable cervical vertebrae and/or to treat progressive kyphoscoliosis that compromises lung function in AD; corrective osteotomies may be required for progressive varus deformity of the lower extremities"
    explanation: >-
      Specifies the spinal and limb surgical interventions recommended in
      anauxetic dysplasia.
  - reference: PMID:22528854
    reference_title: "Axial correction of the lower limb deformities in a girl with anauxetic dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia."
    explanation: >-
      Direct ANXD case evidence for combined osteotomy and guided-growth correction.
- name: Spinal surveillance
  description: >-
    Annual clinical and radiographic examination of the spine is specific to
    anauxetic dysplasia, reflecting the cervical instability and progressive
    kyphoscoliosis risks.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "annual clinical and radiographic examination of the spine in individuals with AD"
    explanation: >-
      Specifies the AD-specific spinal surveillance interval.
- name: Baseline and conditional immune-haematologic assessment
  description: >-
    Establish baseline immune and haematologic status rather than inferring it
    from skeletal severity, then tailor surveillance to the initial results and
    clinical infection or anemia history. This is a spectrum-overlap safeguard,
    not an assertion that pure ANXD is immunodeficient.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "laboratory assessment of immune function with frequency based on initial lab results"
    explanation: >-
      Supports initial immune assessment followed by result-dependent
      surveillance across the CHH-AD spectrum.
- name: Avoidance of live vaccines with abnormal immune function
  description: >-
    Do not administer live vaccines when abnormal immunologic function or SCID
    is present. The restriction is explicitly conditional on demonstrated
    immune dysfunction and does not imply routine vaccine avoidance in pure
    ANXD.
  treatment_term:
    preferred_term: supportive care
    term:
      id: NCIT:C15747
      label: Supportive Care
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Agents/circumstances to avoid: Administration of live vaccines when signs of abnormal immunologic function or SCID are present."
    explanation: >-
      Preserves the highest-consequence GeneReviews safety guidance while
      retaining its explicit immune-status condition.
- name: Conditional infection management and immune support
  description: >-
    If clinically significant spectrum-overlap immunodeficiency is identified,
    manage infections by type and severity, use immediate high-dose intravenous
    acyclovir for varicella, and consider antibiotic prophylaxis or
    immunoglobulin replacement. These measures do not apply without immune
    dysfunction.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  target_mechanisms:
  - target: Conditional Immune and Haematopoietic Spectrum Involvement
    treatment_effect: MODULATES
    description: >-
      Anti-infective and replacement therapy compensates for an overlapping
      immune defect without correcting RNase MRP dysfunction.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "immediate high-dose intravenous acyclovir for varicella infection; consideration of prophylactic antibiotic therapy and/or immunoglobulin replacement therapy"
    explanation: >-
      GeneReviews spectrum management, retained as conditional because immune
      involvement is not an expected pure-ANXD feature.
- name: Conditional haematopoietic stem cell transplantation
  description: >-
    Recurrent severe infections, SCID, or severely depressed erythropoiesis may
    warrant transplantation when these CHH-AD spectrum manifestations overlap
    an ANXD diagnosis. Transplantation addresses the haematopoietic complication
    and does not correct the skeletal dysplasia.
  therapeutic_modality: CELL_THERAPY
  treatment_term:
    preferred_term: haematopoietic cell transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  target_mechanisms:
  - target: Conditional Immune and Haematopoietic Spectrum Involvement
    treatment_effect: INHIBITS
    description: >-
      Replaces the affected haematopoietic compartment in severe conditional
      overlap disease.
  evidence:
  - reference: PMID:22420014
    reference_title: "Cartilage-Hair Hypoplasia – Anauxetic Dysplasia Spectrum Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "recurrent severe infections, severe combined immunodeficiency (SCID), and/or severely depressed erythropoiesis may warrant hematopoietic stem cell transplantation"
    explanation: >-
      Retains the spectrum indication but marks it PARTIAL for an ANXD-specific
      entry because it requires documented extraskeletal overlap.
differential_diagnoses:
- name: Cartilage-hair hypoplasia
  disease_term:
    preferred_term: cartilage-hair hypoplasia
    term:
      id: MONDO:0009595
      label: cartilage-hair hypoplasia
  description: >-
    RMRP-related cartilage-hair hypoplasia lies on the same molecular spectrum
    and shares disproportionate short stature, but its skeletal dysplasia is
    generally less severe and hair, immune, and haematologic involvement is more
    characteristic.
  distinguishing_features:
  - Less severe skeletal dysplasia than anauxetic dysplasia.
  - Hair hypoplasia, immunodeficiency, and defective erythrogenesis favor cartilage-hair hypoplasia.
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
    explanation: >-
      Establishes CHH as a milder RMRP-spectrum disorder overlapping ANXD.
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
    explanation: >-
      Identifies the extraskeletal features that distinguish CHH-like overlap from pure ANXD.
- name: Metaphyseal dysplasia without hypotrichosis
  disease_term:
    preferred_term: metaphyseal dysplasia without hypotrichosis
    term:
      id: MONDO:0009601
      label: metaphyseal dysplasia without hypotrichosis
  description: >-
    A milder RMRP-spectrum skeletal dysplasia that can share metaphyseal changes
    and short stature but lacks the extreme spondyloepimetaphyseal severity of
    ANXD.
  distinguishing_features:
  - Milder metaphyseal-predominant skeletal dysplasia.
  - Absence of hypotrichosis, as reflected in the disease definition.
  - Does not show the extreme skeletal phenotype that defines ANXD.
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in the RMRP gene lead to a wide spectrum of autosomal recessive skeletal dysplasias, ranging from the milder phenotypes metaphyseal dysplasia without hypotrichosis and cartilage hair hypoplasia (CHH) to the severe anauxetic dysplasia (AD)."
    explanation: >-
      Places MDWH and ANXD at the mild and severe ends of the same RMRP spectrum.
experimental_models:
- name: Rmrp-deficient ATDC5 chondrogenic cell model
  experimental_model_type: CELL_LINE
  organism:
    preferred_term: mouse
    term:
      id: NCBITaxon:10090
      label: Mus musculus
  cell_types:
  - preferred_term: chondrocyte
    term:
      id: CL:0000138
      label: chondrocyte
  cell_source: Mouse ATDC5 chondrogenic cell line
  culture_system: Monolayer chondrogenic differentiation culture with Rmrp RNA interference
  conditions:
  - Rmrp knockdown
  - Control chondrogenic differentiation
  publication: PMID:28743979
  description: >-
    Rmrp interference in ATDC5 cells models the growth-plate differentiation
    defect and couples impaired pre-rRNA processing to a particularly strong
    defect in chondrocyte hypertrophy. It is a two-dimensional mouse-derived
    model and does not reproduce the multisite human skeletal phenotype.
  modeled_mechanisms:
  - target: Impaired rRNA Cleavage in Ribosome Assembly
    description: Measures pre-rRNA processing and mature rRNA abundance after Rmrp interference.
    evidence:
    - reference: PMID:28743979
      reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
      explanation: >-
        Directly links Rmrp loss to altered rRNA processing in the model.
  - target: Growth Plate Chondrocyte Differentiation Failure
    description: Measures differentiation and hypertrophy after Rmrp interference.
    evidence:
    - reference: PMID:28743979
      reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
      explanation: >-
        Directly demonstrates the differentiation and hypertrophy defect.
  findings:
  - statement: Rmrp interference deregulates chondrogenic differentiation, with the strongest effect on hypertrophy.
    supporting_text: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
    evidence:
    - reference: PMID:28743979
      reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
      explanation: >-
        The experimental result is quoted directly from the publication abstract.
  evidence:
  - reference: PMID:28743979
    reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels."
    explanation: >-
      Establishes the model, perturbation, molecular readout, and cellular phenotype.
- name: Variant-specific RNase MRP substrate-cleavage assay
  experimental_model_type: OTHER
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  cell_source: Reconstituted human RNase MRP complexes carrying patient RMRP variants
  culture_system: In vitro messenger-RNA and ribosomal-RNA cleavage assays
  conditions:
  - Thirteen disease-associated RMRP variants
  - Wild-type RNase MRP activity comparator
  publication: PMID:17701897
  description: >-
    Variant-specific cleavage assays separate the rRNA activity that tracks
    skeletal severity from the mRNA activity that tracks CHH-like hair, immune,
    and haematologic manifestations. The assays support substrate-specific
    genotype-phenotype correlation but do not model growth-plate architecture.
  modeled_mechanisms:
  - target: Impaired rRNA Cleavage in Ribosome Assembly
    description: Quantifies variant-specific loss of rRNA cleavage against bone-dysplasia severity.
    evidence:
    - reference: PMID:17701897
      reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
      explanation: >-
        Directly reports the assay and the rRNA-cleavage severity correlation.
  - target: mRNA Cleavage-Dependent Spectrum Modulation
    description: Quantifies variant-specific mRNA cleavage against extraskeletal spectrum features.
    evidence:
    - reference: PMID:17701897
      reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "reduced mRNA cleavage, and thus cell-cycle impairment, predicts the presence of hair hypoplasia, immunodeficiency, and hematological abnormalities and thus increased cancer risk"
      explanation: >-
        Directly reports the substrate-specific extraskeletal correlation.
  evidence:
  - reference: PMID:17701897
    reference_title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In vitro testing of RNase MRP multiprotein-specific mRNA and rRNA cleavage of different mutations revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia"
    explanation: >-
      Establishes the model and its principal genotype-function result.
discussions:
- discussion_id: gap_anauxetic_is_it_really_a_ribosomopathy
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is anauxetic dysplasia genuinely a disorder of ribosome biogenesis, or does
    the rRNA-cleavage correlation track something else that RNase MRP does?
  attaches_to:
  - pathophysiology#Impaired rRNA Cleavage in Ribosome Assembly
  - pathophysiology#RNase MRP Complex Loss of Function
  rationale: >-
    The ribosomopathy framing rests on a correlation between residual rRNA
    cleavage activity and skeletal severity, and it is how this entry and most
    of the literature describe the disorder. But that assumption has been
    questioned directly in the POP1 literature, and RNase MRP has at least four
    known activities beyond 5.8S rRNA processing: Cyclin B2 mRNA cleavage,
    mitochondrial RNA processing, and complex formation with hTERT. A
    correlation with rRNA cleavage does not establish that reduced ribosome
    output is the effector, since the same alleles may degrade a co-varying
    activity. This matters because it determines whether anauxetic dysplasia
    belongs mechanistically alongside the other ribosomopathies or forms its own
    class.
  proposed_experiments:
  - experiment_id: exp_anauxetic_ribosome_output_vs_severity
    name: Direct measurement of ribosome output against skeletal severity across CHH-AD alleles
    description: >-
      Measure ribosome biogenesis output directly, by polysome profiling and
      nascent 5.8S rRNA quantification, in patient chondrocytes or
      chondroprogenitors across an allelic series spanning CHH to anauxetic
      dysplasia, and test whether ribosome output rather than cleavage-assay
      activity predicts skeletal severity. Measure Cyclin B2 turnover and
      mitochondrial RNA processing in the same cells as co-varying candidates.
    decision_criterion: >-
      If ribosome output predicts skeletal severity better than the other
      activities do, the ribosomopathy label is earned; if a co-varying activity
      predicts it as well or better, it is not.
    supporting_outcome:
    - Reduced ribosome output is the effector and the disorder is a true ribosomopathy
    refuting_outcome:
    - A co-varying RNase MRP activity predicts skeletal severity equally well, so the ribosomopathy label is an artefact of assay choice
  evidence:
  - reference: PMID:28067412
    reference_title: "Broadening the phenotypic spectrum of POP1-skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although CHH and other skeletal dysplasias caused by mutations in RMRP or POP1 are commonly cited as ribosomal biogenesis disorders, recent studies question this assumption."
    explanation: >-
      Direct published challenge to the ribosomopathy framing this entry
      otherwise adopts.
  - reference: PMID:21396580
    reference_title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "processing the mitochondrial RNA, and forming a complex with hTERT suggesting a possible involvement in expression regulation by siRNA synthesis"
    explanation: >-
      Documents the additional RNase MRP activities that could co-vary with rRNA
      cleavage and confound the correlation.
- discussion_id: gap_anauxetic_substrate_dissociation
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    How does a single ribonucleoprotein enzyme partition its two substrates so
    that a variant can impair ribosomal RNA cleavage while largely sparing
    messenger RNA cleavage, or the reverse?
  attaches_to:
  - pathophysiology#Impaired rRNA Cleavage in Ribosome Assembly
  - pathophysiology#mRNA Cleavage-Dependent Spectrum Modulation
  rationale: >-
    The in vitro data show a clean double dissociation: rRNA cleavage loss tracks
    bone severity, mRNA cleavage loss tracks hair, immune and haematological
    involvement and cancer risk. That means the two activities are separable by
    single-nucleotide changes in one non-coding RNA, which implies substrate
    selection depends on local structural elements rather than on global enzyme
    activity. Which elements, and whether a therapeutic or prognostic assay could
    read out the two activities independently in a patient sample, is unresolved.
    A clinically useful consequence would be predicting cancer and immune risk
    from a functional assay rather than waiting for the phenotype.
  proposed_experiments:
  - experiment_id: exp_anauxetic_substrate_specificity_map
    name: Structure-function mapping of RNase MRP substrate selection across CHH-AD alleles
    description: >-
      Reconstitute RNase MRP with a panel of patient RMRP alleles spanning the
      CHH-AD spectrum plus POP1 and NEPRO variants, and measure rRNA and mRNA
      cleavage independently against solved secondary structure, to identify
      which structural elements confer substrate selection and whether the two
      activities can be predicted from sequence.
    decision_criterion: >-
      Identification of distinct structural determinants for the two substrates
      that predict the clinical dissociation would establish a prognostic assay.
    supporting_outcome:
    - Separable structural elements govern the two activities, so allele-level functional testing can predict immune and cancer risk
    refuting_outcome:
    - Both activities degrade together and the clinical dissociation reflects tissue-specific thresholds instead
- discussion_id: gap_anauxetic_chondrocyte_selectivity
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why does a defect in a ubiquitously required ribosome assembly step strike
    the growth plate so much harder than other proliferating tissues?
  attaches_to:
  - pathophysiology#Growth Plate Chondrocyte Differentiation Failure
  - pathophysiology#Extreme Disproportionate Short-Limb Short Stature
  rationale: >-
    This is the general paradox of the ribosomopathies, and anauxetic dysplasia
    is an unusually clean instance of it because the same enzyme lesion produces
    a graded skeletal phenotype across the spectrum. Whether growth plate
    chondrocytes are simply the most ribosome-hungry cells in the developing
    body, or whether there is a chondrocyte-specific client transcript whose
    translation fails first, is not established, and the answer determines
    whether any tissue-directed intervention is conceivable. The question is
    posed explicitly in the chondrocyte literature, and the observation that
    RNase MRP expression is itself regulated across chondrogenic differentiation
    raises a third possibility: that the growth plate is not merely the most
    demanding tissue but one that actively modulates this complex.
  evidence:
  - reference: PMID:28743979
    reference_title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "However, it is not clear why mutations in RMRP RNA lead to skeletal dysplasia."
    explanation: >-
      The chondrocyte literature states the question of this gap directly as
      unresolved.
  proposed_experiments:
  - experiment_id: exp_anauxetic_chondrocyte_translatome
    name: Comparative translatome profiling across tissues in an RMRP hypomorphic model
    description: >-
      Profile ribosome occupancy and nascent translation in growth plate
      chondrocytes alongside lymphoid progenitors, erythroid progenitors and hair
      follicle keratinocytes in a graded RMRP hypomorphic background, to test
      whether chondrocytes show disproportionate loss of translational output or
      selective loss of specific transcripts.
    decision_criterion: >-
      Disproportionate global translational collapse in chondrocytes supports a
      demand model; selective transcript loss supports a client-specific model.
    supporting_outcome:
    - Growth plate chondrocytes have the highest ribosome demand and fail first on a purely quantitative basis
    refuting_outcome:
    - Specific chondrocyte transcripts are selectively lost, implicating a targeted client rather than global demand
- discussion_id: gap_anauxetic_natural_history_and_therapy
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    What are the subtype-specific natural history, complication rates, and
    treatment outcomes of anauxetic dysplasia?
  rationale: >-
    Published evidence consists mainly of single cases, small families, and
    mechanism studies across the broader CHH-AD spectrum. There are no reliable
    ANXD-specific prevalence, penetrance, survival, quality-of-life, or
    treatment-response estimates, and no disease-specific interventional trial
    was identified. The 2026 ANXD3 report adds three cases and new systemic
    findings but remains too small to establish frequency or causality for each
    manifestation. A longitudinal, genotype-stratified registry is needed to
    distinguish reproducible subtype features from family-specific observations
    and to evaluate orthopedic and surveillance outcomes.
  attaches_to:
  - phenotypes#Severe short stature
  - phenotypes#Atlantoaxial dislocation
  - phenotypes#Thoracolumbar kyphoscoliosis
  evidence:
  - reference: PMID:41982866
    reference_title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This study reports three new ANXD3 cases from a consanguineous Iranian family"
    explanation: >-
      The latest family series illustrates both ongoing phenotype discovery and
      the very small evidence base that prevents frequency estimation.
  proposed_experiments:
  - experiment_id: exp_anauxetic_longitudinal_registry
    name: Genotype-stratified international ANXD natural-history registry
    description: >-
      Enroll molecularly confirmed RMRP-, POP1-, and NEPRO-related cases with
      harmonized skeletal imaging, cervical stability, mobility, pain,
      development, hearing, ophthalmology, renal, dental, surgical, and
      patient-reported outcomes assessed longitudinally.
    decision_criterion: >-
      Replication of each manifestation in unrelated families and stable
      subtype-specific incidence estimates would distinguish core findings from
      family-specific observations and provide endpoints for future trials.
    supporting_outcome:
    - The recently reported systemic ANXD3 findings are reproducible subtype features
    - Defined imaging and functional measures can serve as natural-history and trial endpoints
    refuting_outcome:
    - The systemic findings remain confined to single families and are not reproducible ANXD3 associations
references:
- reference: PMID:22420014
  title: "Cartilage-Hair Hypoplasia - Anauxetic Dysplasia Spectrum Disorders"
  tags:
  - GeneReviews
- reference: PMID:17701897
  title: "Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum"
- reference: PMID:21396580
  title: "The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum"
- reference: PMID:31250547
  title: "An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO"
- reference: PMID:28067412
  title: "Broadening the phenotypic spectrum of POP1-skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia"
- reference: PMID:28743979
  title: "Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation"
- reference: DOI:10.1002/ajmg.a.63316
  title: "Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report"
- reference: PMID:41982866
  title: "Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant"
- reference: PMID:22528854
  title: "Axial correction of the lower limb deformities in a girl with anauxetic dysplasia"
📚

References & Deep Research

References

9
PMID:22420014
Cartilage-Hair Hypoplasia - Anauxetic Dysplasia Spectrum Disorders
No top-level findings curated for this source.
PMID:17701897
Type and level of RMRP functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum
No top-level findings curated for this source.
PMID:21396580
The molecular basis of the cartilage-hair hypoplasia-anauxetic dysplasia spectrum
No top-level findings curated for this source.
PMID:31250547
An emerging ribosomopathy affecting the skeleton due to biallelic variations in NEPRO
No top-level findings curated for this source.
PMID:28067412
Broadening the phenotypic spectrum of POP1-skeletal dysplasias: identification of POP1 mutations in a mild and severe skeletal dysplasia
No top-level findings curated for this source.
PMID:28743979
Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation
No top-level findings curated for this source.
DOI:10.1002/ajmg.a.63316
Expanding the phenotype of anauxetic dysplasia caused by biallelic <scp><i>NEPRO</i></scp> mutations: A case report
No top-level findings curated for this source.
PMID:41982866
Expanding the Phenotypic Spectrum of Anauxetic Dysplasia Type 3: Reporting an Iranian Family With Unique Systemic Features and NEPRO Gene Variant
No top-level findings curated for this source.
PMID:22528854
Axial correction of the lower limb deformities in a girl with anauxetic dysplasia
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Anauxetic Dysplasia: Disease-Characteristics Research Report
Edison Scientific Literature 25 citations 2026-08-01T13:19:23.234207

Anauxetic Dysplasia: Disease-Characteristics Research Report

Executive summary

Anauxetic dysplasia (ANXD) is an ultra-rare, congenital, autosomal-recessive skeletal dysplasia at the severe end of the cartilage-hair hypoplasia–anauxetic dysplasia (CHH–AD) spectrum. Three molecular forms are recognized: ANXD1—RMRP, ANXD2—POP1, and ANXD3—NEPRO/C3orf17. The shared phenotype comprises extreme disproportionate short stature, brachydactyly, ligamentous laxity, joint hypermobility/dislocation, and severe spondylo-epi-metaphyseal abnormalities. Unlike classic cartilage-hair hypoplasia, “pure” ANXD usually lacks hypotrichosis, anemia, clinically important immunodeficiency, intestinal dysmotility, and established cancer predisposition, although the boundary is a spectrum and isolated extraskeletal findings require continued surveillance. (remmelzwaal2023expandingthephenotype pages 1-2, thiel2007typeandlevel pages 1-2)

The best-supported causal chain is biallelic disruption of an RNase-MRP component or interactor → defective pre-rRNA processing/ribosome biogenesis → impaired growth-plate chondrocyte differentiation and hypertrophy → disorganized endochondral ossification → severe short-limb dwarfism and skeletal deformity. This mechanism is strongest for RMRP and POP1; the precise function of NEPRO remains less resolved. No disease-modifying therapy, approved targeted drug, or ANXD-specific interventional trial was identified. Current care is supportive, orthopedic, rehabilitative, dental, and surveillance-based.

Subtype Causal gene / product OMIM disease ID Inheritance Defining phenotype Representative variants Key evidence / limitations
ANXD1 RMRP / noncoding RNA component of RNase MRP 607095 Autosomal recessive; ultra-rare Most severe end of the CHH-AD spectrum; prenatal-onset extreme disproportionate short stature, severe spondyloepimetaphyseal dysplasia, brachydactyly, joint laxity, hypodontia; typically lacks the immunodeficiency/anemia/malignancy predisposition more characteristic of CHH (thiel2007typeandlevel pages 1-2, remmelzwaal2023expandingthephenotype pages 1-2) g.111_112insACTGTAGACATTCCT, g.90_91AG>GC, g.254C>G; severe case with g.195C>T plus null g.254_263delCTCAGCGCGG (thiel2007typeandlevel pages 5-6, thiel2007typeandlevel pages 3-4, thiel2007typeandlevel pages 1-2, thiel2007typeandlevel pages 6-8) Best mechanistic evidence among ANXD subtypes: RMRP mutations impair RNase MRP-mediated pre-rRNA cleavage, correlating with bone-dysplasia severity; reduced cyclin B2 mRNA cleavage tracks more with hair/immuno-hematologic features than with ANXD itself (thiel2007typeandlevel pages 1-2, thiel2007typeandlevel pages 6-8). Limitation: much evidence derives from the broader CHH-AD spectrum rather than large ANXD1 cohorts.
ANXD2 POP1 / hPOP1 protein, shared subunit of RNase MRP and RNase P complexes 617396 Autosomal recessive; ultra-rare ANXD-like skeletal dysplasia spanning mild to severe presentations, including severe short stature and extensive skeletal abnormalities; considered part of the RNase-MRP–related skeletal dysplasia spectrum (barrazagarcia2017broadeningthephenotypic pages 1-2, remmelzwaal2023expandingthephenotype pages 1-2) p.Pro582Ser, p.Glu870fs*5, p.Asp511Tyr (biallelic) (barrazagarcia2017broadeningthephenotypic pages 1-2) Human evidence shows markedly reduced RMRP abundance and elevated pre-5.8S rRNA in at least one proband, supporting disturbed ribosome/RNase-MRP biology (barrazagarcia2017broadeningthephenotypic pages 1-2). Limitation: very small number of reported families/patients; phenotypic boundaries between mild POP1 skeletal dysplasia and ANXD2 remain incompletely defined.
ANXD3 NEPRO (C3orf17) / NEPRO protein, reported to interact with RNase MRP subunits 618853 Autosomal recessive; ultra-rare Severe short stature, brachydactyly, skin laxity, joint hypermobility/dislocations, platyspondyly/ovoid vertebrae, hypoplastic ilia/acetabulae, small femoral epiphyses, irregular metaphyses; 2023 case expanded phenotype to atlantoaxial subluxation, dental anomalies, and sagittal craniosynostosis/scaphocephaly (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 4-4, remmelzwaal2023expandingthephenotype pages 3-4) Homozygous c.280C>T, p.Arg94Cys (apparent recurrent/founder variant in several reported patients) (remmelzwaal2023expandingthephenotype pages 4-4, remmelzwaal2023expandingthephenotype pages 1-2) Recent direct evidence is strongest at the case-report level: before the 2023 report, only five ANXD3 patients had been described; the 2023 paper added one more and broadened the recognized phenotype (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 4-4). Limitation: mechanism is less resolved than for RMRP; patient numbers remain extremely small.
Cross-subtype summary RMRP / POP1 / NEPRO ANXD1 607095; ANXD2 617396; ANXD3 618853 All currently recognized ANXD subtypes are autosomal recessive and ultra-rare Shared core picture: severe prenatal/early-childhood growth failure with marked skeletal dysplasia; subtype-specific extraskeletal findings are limited and evidence is mostly from individual case reports or tiny series (remmelzwaal2023expandingthephenotype pages 1-2, thiel2007typeandlevel pages 1-2) Subtype-defining variants are heterogeneous except for recurrent NEPRO p.Arg94Cys in ANXD3 and multiple recurrent RMRP alleles in the CHH-AD spectrum (remmelzwaal2023expandingthephenotype pages 4-4, thiel2007typeandlevel pages 2-3, thiel2007typeandlevel pages 1-2) Knowledge base should treat ANXD as an ultra-rare Mendelian skeletal dysplasia with sparse epidemiology: prevalence/incidence, penetrance, survival, and genotype-specific prognosis are not well quantified in current literature (remmelzwaal2023expandingthephenotype pages 1-2, barrazagarcia2017broadeningthephenotypic pages 1-2).

Table: This table summarizes the three recognized anauxetic dysplasia subtypes by gene, OMIM identifier, inheritance, phenotype, representative variants, and evidence strength. It is useful as a compact knowledge-base overview while highlighting that all forms are autosomal recessive and exceptionally rare.

1. Disease information

Definition and classification

ANXD is a Mendelian skeletal disorder characterized by prenatal-onset growth failure and severe spondyloepimetaphyseal dysplasia. A 2023 primary report describes it as “a rare autosomal recessive skeletal disorder at the severe end” of the CHH–AD spectrum and recognizes three types. (remmelzwaal2023expandingthephenotype pages 1-2)

Recognized molecular types and identifiers

  • ANXD1: OMIM #607095, caused by biallelic RMRP variants.
  • ANXD2: OMIM #617396, caused by biallelic POP1 variants.
  • ANXD3: OMIM #618853, caused by biallelic NEPRO, formerly C3orf17, variants. (remmelzwaal2023expandingthephenotype pages 1-2)

A definitive MONDO identifier was not established in the retrieved primary literature and should be verified directly against the current MONDO release before database ingestion. Likewise, no dedicated MeSH, ICD-10, or ICD-11 code was demonstrated. In routine coding, ANXD will generally fall under broader congenital osteochondrodysplasia/skeletal-dysplasia categories; such parent codes should not be represented as disease-specific identifiers.

Synonyms: anauxetic dysplasia; anauxetic dysplasia type 1/2/3; ANXD/AD; RMRP-related anauxetic dysplasia; POP1-related skeletal dysplasia/anauxetic dysplasia; NEPRO-related anauxetic dysplasia; severe end of the cartilage-hair hypoplasia–anauxetic dysplasia spectrum. “AD” is ambiguous with autosomal dominant inheritance and should be avoided in knowledge-base displays.

Source granularity: OMIM/nosology-style statements are aggregated disease-level assertions, whereas much of the phenotype and natural-history evidence comes from individual patients or very small families. The 2023 ANXD3 publication was a single-patient case report; only five ANXD3 patients had been reported previously. (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 4-4)

2. Etiology

Causal factors

ANXD is genetic. All recognized forms result from germline biallelic variants in genes connected to RNase MRP/ribosome biology:

  1. RMRP: encodes the untranslated RNA component of RNase MRP.
  2. POP1: encodes a protein subunit shared by RNase MRP and RNase P and involved in complex assembly/stability.
  3. NEPRO: encodes an RNase-MRP-associated protein; its disease mechanism is incompletely defined. (remmelzwaal2023expandingthephenotype pages 1-2, barrazagarcia2017broadeningthephenotypic pages 1-2, steinbusch2017expressionofrmrp pages 1-2)

Genetic risk

The principal risk factor is inheriting one pathogenic allele from each carrier parent. Consanguinity increases the chance that both parents carry the same rare allele. The recurrent homozygous NEPRO c.280C>T, p.(Arg94Cys) allele was found in several consanguineous Arabic families and was characterized as an apparent founder mutation. (remmelzwaal2023expandingthephenotype pages 4-4)

No validated susceptibility loci, polygenic-risk scores, or modifier genes are established. Variable manifestations with similar RMRP genotypes suggest possible nonallelic modifiers, but these remain unidentified. (thiel2007typeandlevel pages 6-8)

Environmental, infectious, lifestyle, and protective factors

No toxin, infection, radiation exposure, diet, smoking behavior, or other environmental factor is known to cause ANXD. No genetic or environmental protective factor has been validated. Environmental circumstances may modify complications—falls or high-risk neck movement could worsen atlantoaxial instability—but do not cause the disorder. Gene–environment interaction studies specific to ANXD were not identified.

3. Phenotypes

Core phenotype

The common phenotype comprises severe or extreme disproportionate short stature, short limbs, brachydactyly, skin laxity, ligamentous/joint laxity, joint hypermobility or dislocations, and extensive axial and appendicular skeletal dysplasia. (remmelzwaal2023expandingthephenotype pages 1-2)

Manifestation Type, onset, course, and impact Suggested HPO term
Disproportionate short stature Clinical sign; prenatal/congenital; severe and progressive relative growth deficit; major mobility and accessibility burden Disproportionate short stature, HP:0003498; Short stature, HP:0004322
Short limbs/long-bone shortening Sign; prenatal or neonatal; lifelong Rhizomelia, HP:0008905, or mesomelia, HP:0003027, where anatomically documented
Brachydactyly; short broad/bullet-shaped phalanges Physical/radiographic sign; childhood; persistent Brachydactyly, HP:0001156
Metaphyseal irregularity/widening Radiographic sign; childhood and progressive during growth Metaphyseal abnormality, HP:0000944
Epiphyseal hypoplasia/premature fusion Radiographic sign; childhood; can drive growth arrest and joint deformity Small epiphyses, HP:0010585; premature epiphyseal fusion where supported
Spondyloepimetaphyseal dysplasia/vertebral abnormalities Radiographic sign; congenital/childhood; scoliosis may progress Platyspondyly, HP:0000926; Abnormal vertebral morphology, HP:0003468
Scoliosis/kyphosis/gibbus Sign; often progressive Scoliosis, HP:0002650; Kyphosis, HP:0002808
Coxa vara, hip dysplasia/ankylosis Sign; childhood; may impair walking and cause pain Coxa vara, HP:0002812; Hip dysplasia, HP:0001385
Joint hypermobility/laxity/dislocation Sign; congenital/childhood; functional instability and pain Joint hypermobility, HP:0001382; Joint dislocation, HP:0001373
Hypodontia/dental anomalies Sign; childhood as dentition develops; impacts mastication and dental care Hypodontia, HP:0000668; Microdontia, HP:0000691; Enamel hypoplasia, HP:0006297
Atlantoaxial instability/subluxation Potentially severe complication; risk of cervical myelopathy and anesthesia-related injury Atlantoaxial instability, HP:0003467
Craniosynostosis/scaphocephaly Rare/newly expanded ANXD3 phenotype Craniosynostosis, HP:0001363; Scaphocephaly, HP:0030799
Developmental delay/intellectual impairment Not universal; mild delay reported in some cases Global developmental delay, HP:0001263; Intellectual disability, HP:0001249

In an RMRP-related 11-year-old, short limbs were visible by prenatal ultrasound at approximately 17 weeks. Birth length was 39 cm, below −5 SD; height at nine years was 83 cm, approximately −8 SD. She developed progressive scoliosis and lower-limb joint pain but had normal hair and psychomotor development. Radiographs showed shortened tubular bones, widened irregular metaphyses, small epiphyses, premature growth-plate fusion, brachydactyly, coxa vara, and dysplastic femoral heads. (thiel2007typeandlevel pages 2-3, thiel2007typeandlevel pages 3-4)

Historical descriptions place adult height below approximately 85 cm in severe RMRP-associated ANXD, but this is based on very small samples rather than a population estimate. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4)

ANXD3 phenotype expansion in 2023

A seven-year-old homozygous for NEPRO p.Arg94Cys had atlantoaxial subluxation, sagittal-suture craniosynostosis with scaphocephaly, Madelung deformity, and extensive dental abnormalities, including agenesis, microdontia, short roots, taurodontism, enamel hypoplasia, and abnormal crowns. The authors’ abstract states: “Greater awareness of the possibility of atlantoaxial subluxation, dental anomalies, and craniosynostosis may lead to more timely diagnosis and treatment.” (remmelzwaal2023expandingthephenotype pages 4-4, remmelzwaal2023expandingthephenotype pages 3-4)

Motor/cognitive delay and recurrent airway infections occurred in that patient, but congenital ichthyosis was attributable to a separate homozygous ALOX12B variant; therefore, those findings should not automatically be assigned to ANXD3. (remmelzwaal2023expandingthephenotype pages 4-4)

Frequency and quality of life

Reliable percentages are unavailable because cohorts are exceptionally small. Severe short stature and skeletal abnormalities are defining and expected to be common; craniosynostosis, atlantoaxial subluxation, and detailed dental anomalies currently have case-level evidence. No ANXD-specific EQ-5D, SF-36, PROMIS, or disease-specific quality-of-life study was identified. Likely burdens include restricted mobility, pain, spinal and hip deformity, need for adapted environments, dental morbidity, repeated imaging/surgery, and cervical-safety concerns.

4. Genetic and molecular information

Genes and representative variants

  • RMRP: noncoding RNA gene on chromosome 9p13. Representative severe alleles include g.111_112insACTGTAGACATTCCT, g.90_91AG>GC, g.254C>G, and the null deletion g.254_263delCTCAGCGCGG. A severe patient was compound heterozygous for g.195C>T and g.254_263delCTCAGCGCGG; both were absent from 378 control chromosomes. (thiel2007typeandlevel pages 5-6, thiel2007typeandlevel pages 3-4, thiel2007typeandlevel pages 1-2)
  • POP1: reported ANXD-spectrum variants include compound-heterozygous p.Pro582Ser/p.Glu870fs*5 and homozygous p.Asp511Tyr. The former combines a missense and frameshift allele; the latter is missense. (barrazagarcia2017broadeningthephenotypic pages 1-2)
  • NEPRO: homozygous NM_015412.4:c.280C>T, p.(Arg94Cys) is the best-documented recurrent ANXD3 allele. (remmelzwaal2023expandingthephenotype pages 4-4)

These are germline variants. There is no evidence that somatic mutation is relevant. Current population allele frequencies were not available in the retrieved papers and should be queried directly in gnomAD by transcript/build before ingestion. Given recessive severe disease and very small case numbers, causal alleles are expected to be rare, but absence from a population database alone is not proof of pathogenicity.

Functional consequences

The RMRP deletion g.254_263delCTCAGCGCGG was undetectable by RT-PCR and interpreted as an unstable-RNA/null allele. Disease-causing RMRP changes cluster in conserved nucleotides or disrupt stem pairing, affecting RNA structure, protein binding, RNA stability, or transcription. (thiel2007typeandlevel pages 5-6, thiel2007typeandlevel pages 6-8)

In POP1-associated disease, p.Pro582Ser/p.Glu870fs*5 was associated with markedly reduced RMRP abundance and increased pre-5.8S rRNA, supporting impaired RNase-MRP function. (barrazagarcia2017broadeningthephenotypic pages 1-2)

ClinVar classifications must be checked at accession level and date of use. The retrieved literature describes the RMRP and recurrent NEPRO alleles as pathogenic/disease-causing, while a 2024 broader CHH-spectrum case illustrates that WES can return a pathogenic allele paired with a VUS; such combinations require phenotype, segregation, and functional review rather than automatic confirmation. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4)

No validated ANXD modifier gene, disease-specific epigenetic signature, recurrent chromosomal abnormality, methylation abnormality, or structural-variant mechanism was established.

5. Environmental information

ANXD is not an infectious, toxic, occupational, lifestyle, or nutritional disease. No causal infectious agent or preventable exposure is known. Standard nutrition and activity adapted to orthopedic limitations support general health but do not reverse the molecular defect. Cervical instability warrants avoidance of unassessed high-impact activities and careful airway/neck positioning, especially during anesthesia. (remmelzwaal2023expandingthephenotype pages 3-4)

6. Mechanism and pathophysiology

Upstream molecular defect

RNase MRP is a ribonucleoprotein endoribonuclease containing RMRP lncRNA and protein subunits including POP1. It participates in ITS1 pre-rRNA cleavage and has reported roles in cyclin-B2 mRNA cleavage and cell-cycle regulation. (steinbusch2017expressionofrmrp pages 1-2)

For RMRP disease, functional testing of 13 variants found a strong negative correlation between bone-dysplasia severity and rRNA-cleavage activity (R = −0.8346, P = .0008). Impaired mRNA cleavage correlated with immunologic/hematologic abnormalities (R = −0.8429, P = .0007) and hair hypoplasia (R = −0.8115, P = .001). Thus, severe impairment of rRNA processing primarily predicts ANXD’s skeletal phenotype, whereas impaired mRNA/cell-cycle regulation better predicts CHH-like extraskeletal findings. (thiel2007typeandlevel pages 5-6, thiel2007typeandlevel pages 1-2)

A key direct statement from the landmark paper is: “the impairment of rRNA cleavage by RMRP mutations is the leading cause of bone dysplasia in patients with features in the CHH-AD spectrum.” (thiel2007typeandlevel pages 6-8)

Cellular and tissue cascade

  1. Biallelic RMRP/POP1/NEPRO dysfunction alters RNase-MRP-associated biology.
  2. Pre-rRNA processing and ribosome production become abnormal; RMRP instability or reduced abundance may worsen the defect.
  3. Highly proliferative growth-plate chondrocytes fail to execute normal proliferative-to-hypertrophic differentiation.
  4. Columnization, matrix production/mineralization, and endochondral ossification are disrupted.
  5. Longitudinal bone growth fails, producing severe metaphyseal, epiphyseal, vertebral, pelvic, and digital abnormalities.

Histologic description in ANXD includes few dispersed chondrocytes, almost absent columnization, and irregular osteochondral ossification. (thiel2007typeandlevel pages 1-2)

In ATDC5 chondrocytes, Rmrp knockdown increased RNase-MRP substrates and an ITS1 processing intermediate, reduced 18S and 5.8S rRNA, and decreased Sox9, Col2a1, Runx2, Col10a1, and Alpl, with particularly strong effects on hypertrophic differentiation. (steinbusch2017expressionofrmrp pages 7-9)

Rmrp promoter activity responded experimentally to developmental mediators: PTHrP −18%, FGF2 −35%, TGF-β3 +40%, BMP2 +105%, dorsomorphin −76%, WNT3A +45%, and WNT5A +26%. These data show pathway responsiveness, not that any of these factors is an established therapy. (steinbusch2017expressionofrmrp pages 7-9)

Suggested ontology annotations

  • GO biological process: rRNA processing (GO:0006364); ribosome biogenesis (GO:0042254); chondrocyte differentiation (GO:0002062); chondrocyte hypertrophy (GO:0003415); endochondral ossification (GO:0001958); regulation of cell cycle (GO:0051726).
  • GO cellular component: RNase MRP complex (GO:0000172); nucleolus (GO:0005730); nucleus (GO:0005634).
  • Cell Ontology: chondrocyte (CL:0000138); hypertrophic chondrocyte and osteoblast should be mapped to the current CL release.

No ANXD-specific single-cell, spatial-transcriptomic, proteomic, metabolomic, lipidomic, epigenomic, organoid, or multi-omics atlas was found. The available molecular profiling is targeted and preclinical.

7. Anatomical structures affected

Primary system: musculoskeletal/connective-tissue system, particularly growth plates and endochondrally formed skeleton.

Primary sites: vertebral column, metaphyses and epiphyses of long bones, pelvis/ilia/acetabula, proximal femur and femoral neck, knees, ankles, radius/ulna, metacarpals, phalanges, hips, and craniovertebral junction. Dentition and cranial sutures can be involved, especially in reported ANXD3. (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 3-4, thiel2007typeandlevel pages 3-4)

Suggested UBERON mappings include growth plate cartilage (UBERON:0003986), cartilage tissue (UBERON:0002418), vertebral column (UBERON:0001130), pelvis (UBERON:0001270), femur (UBERON:0000981), hand skeleton, tooth, and cranial suture; exact release-specific identifiers should be validated.

At tissue level, proliferative and hypertrophic growth-plate chondrocytes and their extracellular matrix are central. Downstream osteoblast/osteoclast remodeling is likely affected through abnormal cartilage scaffolding, but direct ANXD cell-specific evidence is limited. At subcellular level, the nucleolus/nucleus and RNase-MRP ribonucleoprotein complex are implicated. Findings are generally bilateral/generalized rather than unilateral; leg-length discrepancy can be asymmetric in individual patients. (remmelzwaal2023expandingthephenotype pages 3-4, steinbusch2017expressionofrmrp pages 1-2)

8. Temporal development

ANXD begins prenatally or congenitally and follows a chronic lifelong course. Short limbs may be recognized on second-trimester ultrasound, and extreme short length is present at birth. Skeletal disproportionality, scoliosis, joint pain, deformity, and premature growth-plate fusion become more apparent during childhood. (thiel2007typeandlevel pages 2-3, thiel2007typeandlevel pages 3-4)

There is no validated stage system. A practical clinical framework is:

  • Prenatal/neonatal: short limbs and marked birth-length deficit.
  • Early childhood: progressive growth failure, metaphyseal/epiphyseal changes, brachydactyly and laxity.
  • Later childhood/adolescence: increasing scoliosis/kyphosis, hip and limb deformity, joint pain, premature physeal fusion, and possible cervical instability.
  • Adulthood: lifelong extreme short stature and orthopedic disability; robust adult natural-history data are lacking.

There is no spontaneous remission. Growth-plate development is the key vulnerability window, but no proven molecular intervention exists during that period.

9. Inheritance and population

Inheritance is autosomal recessive. For two confirmed carrier parents, each pregnancy has a 25% probability of an affected child, 50% probability of an unaffected carrier, and 25% probability of inheriting neither familial allele.

Penetrance is presumed high for individuals with two severe pathogenic alleles, but it has not been quantified. Expressivity is variable, especially across RMRP and POP1 allelic combinations. Anticipation is not expected. Germline mosaicism has not been established; standard counseling should acknowledge a small residual recurrence risk after an apparently de novo result, although true de novo biallelic ANXD would be unusual.

ANXD-specific prevalence, incidence, carrier frequency, sex ratio, and survival distribution are unknown. ANXD3 had only five published patients before the 2023 case, underscoring its extreme rarity. (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 4-4)

Broader CHH-spectrum statistics must not be misassigned to ANXD: a 2024 review/case report cited CHH-spectrum prevalence of approximately 1:23,000 in Finland with carrier frequency 1:76, and 1–2:1,000 in Amish populations with carrier frequency about 1:10. Those figures reflect RMRP-associated CHH enrichment, not demonstrated ANXD prevalence. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 1-2)

No consistent sex bias exists for an autosomal-recessive disorder. Reported patients occur in multiple ancestries; apparent geographic clustering may reflect founder alleles, consanguinity, ascertainment, and publication bias.

10. Diagnostics

Clinical and radiographic diagnosis

Suspect ANXD in prenatal or congenital extreme short stature with severe disproportion, brachydactyly, joint laxity/dislocation, and a generalized spondylo-epi-metaphyseal radiographic pattern. A skeletal survey should assess the spine, pelvis/hips, long bones, hands/feet, and—given the 2023 ANXD3 findings—the craniovertebral junction when clinically appropriate. (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 3-4)

Characteristic findings include ovoid or foreshortened vertebral bodies/platyspondyly, scoliosis, hypoplastic ilia and acetabula, coxa vara, short femoral necks, small/dysplastic epiphyses, irregular widened metaphyses, shortened tubular bones, short broad metacarpals/phalanges, and premature physeal fusion. (remmelzwaal2023expandingthephenotype pages 1-2, thiel2007typeandlevel pages 3-4)

Suggested baseline assessments are:

  • Height, weight, body proportions, head circumference, joint range of motion, neurologic examination, and developmental assessment.
  • Skeletal survey and serial targeted radiography; dynamic cervical imaging or MRI if instability is suspected.
  • Dental examination and panoramic imaging.
  • CBC with differential and immune evaluation to distinguish ANXD from CHH and detect spectrum overlap.
  • Gastrointestinal history for Hirschsprung disease/chronic diarrhea; respiratory history and pulmonary assessment if recurrent infection occurs.

No specific serum enzyme assay, metabolite biomarker, electrophysiologic signature, or diagnostic biopsy is established.

Molecular testing

  1. Preferred: skeletal-dysplasia panel including RMRP, POP1, and NEPRO, with sequence and copy-number analysis and adequate coverage of the noncoding RMRP transcript and proximal promoter.
  2. Phenotype-directed testing: RMRP sequencing for classic severe CHH–AD-spectrum radiology; POP1/NEPRO if RMRP is negative or subtype clues support them.
  3. WES: useful for POP1/NEPRO and blended phenotypes, as demonstrated by ANXD3 diagnosis; standard exome pipelines may inadequately capture/promote interpretation of noncoding RMRP variants. (remmelzwaal2023expandingthephenotype pages 4-4, park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4)
  4. WGS: potentially advantageous for RMRP promoter/noncoding, copy-number, and structural variants, although ANXD-specific incremental-yield studies are absent.
  5. Confirm candidate variants by orthogonal testing and perform parental segregation.

CMA and karyotyping are useful when the phenotype suggests a chromosomal syndrome but are not first-line confirmatory tests for typical ANXD. FISH, mitochondrial-DNA testing, repeat-expansion testing, liquid biopsy, and routine diagnostic transcriptomics/proteomics/metabolomics are not indicated unless another diagnosis is suspected.

Differential diagnosis

Important differentials include cartilage-hair hypoplasia and metaphyseal dysplasia without hypotrichosis; other spondyloepimetaphyseal dysplasias; Schmid metaphyseal chondrodysplasia; achondroplasia/hypochondroplasia; pseudoachondroplasia; diastrophic dysplasia; and severe prenatal skeletal dysplasias. CHH is distinguished by hypotrichosis, anemia, immune deficiency, Hirschsprung disease, and cancer susceptibility; MDWH has milder metaphyseal disease without hair or immune abnormalities. RMRP-associated ANXD has more severe vertebral, pelvic, and epiphyseal involvement. (thiel2007typeandlevel pages 1-2)

No population or newborn screening program exists. Cascade testing is appropriate after familial variants are identified.

11. Outcome and prognosis

No reliable five- or ten-year survival, life-expectancy, mortality, hospitalization, or quality-of-life statistics are available. Published RMRP ANXD patients can survive through childhood and likely adulthood; however, the literature is too sparse to define survival distributions.

Major morbidity is orthopedic: profound short stature, scoliosis/kyphosis, hip dysplasia or ankylosis, coxa vara, limb bowing/inequality, pain, dislocations, and restricted mobility. Atlantoaxial instability can cause cervical myelopathy and creates procedural/anesthetic risk. Dental and craniosynostosis morbidity may occur in ANXD3. (remmelzwaal2023expandingthephenotype pages 3-4, remmelzwaal2023expandingthephenotype pages 4-5)

Unlike CHH, classic ANXD is generally not associated with clinically significant immunodeficiency, anemia, gastrointestinal manifestations, or established malignancy predisposition. Nevertheless, because molecular and phenotypic boundaries overlap, baseline CBC/immune assessment is prudent rather than assuming their absence. (remmelzwaal2023expandingthephenotype pages 1-2, thiel2007typeandlevel pages 5-6)

Prognosis is likely influenced by genotype/functional severity, spinal and cervical instability, hip disease, pain and mobility, access to orthopedic care, and any spectrum-overlap features. No validated prognostic biomarker or calculator exists.

12. Treatment

There is no curative or disease-modifying ANXD therapy and no evidence-based pharmacologic algorithm. Growth hormone has not been shown to correct the primary growth-plate ribosome-biogenesis defect; broader CHH-spectrum cases have normal stimulated GH responses, and treatment was not attempted in the 2024 Korean report. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4)

Current management

  • Orthopedic/spine care: surveillance for scoliosis, kyphosis, hip dysplasia, coxa vara, limb deformity, contractures, dislocation, and pain; individualized bracing or corrective surgery.
  • Cervical care: evaluate suspected atlantoaxial instability; consider immobilization or surgical fixation according to neurosurgical/orthopedic assessment; use cervical and airway precautions during anesthesia. (remmelzwaal2023expandingthephenotype pages 3-4)
  • Rehabilitation: physical and occupational therapy, mobility aids, adaptive equipment, environmental modification, and low-impact activity adapted to joint/spine status.
  • Dental/craniofacial care: preventive dentistry, orthodontic/prosthodontic planning, and craniofacial/neurosurgical assessment for craniosynostosis.
  • Symptomatic care: pain management and monitoring for neurologic compromise.
  • Spectrum surveillance: CBC, immune function, infection history, pulmonary status, and gastrointestinal symptoms when indicated.

Suggested NCIT intervention concepts include Physical Therapy, Occupational Therapy, Orthopedic Surgery, Spinal Fusion, Dental Care, Genetic Counseling, Pain Management, and Surveillance; exact NCIT codes should be validated against the current release.

No gene replacement, CRISPR therapy, cell therapy, ASO/siRNA therapy, targeted small molecule, or immunotherapy is clinically available. Modulating BMP/WNT/TGF-β based solely on promoter-reporter findings would be premature and potentially unsafe. (steinbusch2017expressionofrmrp pages 7-9)

The retrieved ClinicalTrials.gov record NCT00001754, “Clinical and Molecular Manifestations of Human Skeletal Dysplasias and Short Stature,” was a completed NIH observational study enrolling 600 participants across many skeletal disorders, including cartilage-hair hypoplasia. It evaluated phenotype, natural history, and genotype–phenotype relationships; it was not an ANXD treatment trial. URL: https://clinicaltrials.gov/study/NCT00001754. (NCT00001754 chunk 1)

13. Prevention

Primary prevention by lifestyle change, vaccination, or environmental control is not possible. Relevant prevention is reproductive and complication-directed:

  • Genetic counseling and familial-variant confirmation.
  • Carrier testing for adult relatives.
  • Prenatal diagnosis by chorionic-villus sampling or amniocentesis once familial variants are known.
  • Preimplantation genetic testing for monogenic disease where available.
  • Early prenatal ultrasound can detect limb shortening but is not molecularly specific.
  • Cascade testing in at-risk relatives.
  • Tertiary prevention through early orthopedic, cervical, dental, respiratory, and rehabilitation surveillance.

No vaccine, prophylactic medication, or population screening program prevents ANXD. Standard immunizations remain appropriate unless an individual has immune dysfunction requiring specialist guidance.

14. Other species and natural disease

No naturally occurring veterinary disorder clearly equivalent to human ANXD was established in the retrieved evidence. There is no zoonotic potential or cross-species transmission because ANXD is inherited, not infectious.

Orthologues of RMRP, POP1, and NEPRO are evolutionarily conserved. RMRP sequences were compared across human, mouse, rat, rabbit, dog, armadillo, elephant, opossum, and frog; disease-associated nucleotides frequently mapped to conserved structural regions. (thiel2007typeandlevel pages 4-5, thiel2007typeandlevel pages 1-2)

Suggested taxa for comparative work include Homo sapiens (NCBI Taxon 9606), Mus musculus (10090), Rattus norvegicus (10116), and Xenopus tropicalis (8364). Species-specific NCBI Gene IDs and any OMIA/VBO entries should be verified directly before database loading.

15. Model organisms and experimental systems

Cellular and mouse-derived models

  • ATDC5 mouse chondrogenic cells: Rmrp RNAi causes accumulation of RNase-MRP substrates and ITS1 pre-rRNA intermediates, reduction of 18S/5.8S rRNA, and impaired chondrocyte differentiation—especially hypertrophy. This recapitulates a plausible cellular mechanism but not the full multisite human skeletal phenotype. (steinbusch2017expressionofrmrp pages 7-9)
  • MCT chondrocytes: temperature-induced hypertrophy increases Rmrp expression; PTHrP suppresses both hypertrophy and Rmrp expression. (steinbusch2017expressionofrmrp pages 7-9)
  • Murine growth plate: Rmrp and RNase-MRP proteins are expressed during growth-plate differentiation, supporting biological relevance. (steinbusch2017expressionofrmrp pages 1-2)
  • Human fibroblast assays: transient expression of mutant RMRP constructs quantified ITS1/5.8S rRNA and cyclin-B2 mRNA cleavage; functional impairment correlated with clinical severity. These are strong genotype-function assays but do not recreate three-dimensional growth-plate architecture. (thiel2007typeandlevel pages 1-2, thiel2007typeandlevel pages 6-8)
  • Patient fibroblast chondrogenic transdifferentiation: broader CHH evidence showed impaired hypertrophic differentiation and supports the same disease spectrum mechanism. (steinbusch2017expressionofrmrp pages 1-2)

No validated ANXD-specific knock-in mouse, zebrafish model, patient-derived iPSC growth-plate organoid, or in-vivo therapeutic-rescue model was demonstrated in the retrieved evidence. These constitute important research gaps. Priority applications include defining NEPRO function, resolving subtype-specific mechanisms, testing whether restoration of RNase-MRP activity rescues chondrocyte maturation, and developing preclinical cervical/spinal and growth-plate outcome measures.

Recent developments and expert interpretation

The most consequential recent direct ANXD development was the 2023 expansion of ANXD3 to include atlantoaxial subluxation, extensive dental anomalies, and sagittal craniosynostosis. Its practical implication is that ANXD3 evaluation should extend beyond stature and limb radiographs to the craniovertebral junction, dentition, and cranial sutures. (remmelzwaal2023expandingthephenotype pages 1-2, remmelzwaal2023expandingthephenotype pages 3-4)

The 2023 skeletal-disorder nosology adopted gene–phenotype dyadic naming across 771 entities and 552 genes, an approach especially useful for ANXD because numbered subtypes can obscure distinct causal genes and overlapping phenotypes. URL: https://doi.org/10.1002/ajmg.a.63132; published February 2023. The preferred knowledge-base labels are therefore RMRP-related anauxetic dysplasia, POP1-related anauxetic dysplasia, and NEPRO-related anauxetic dysplasia.

The 2024 Korean report reinforces that extremely short stature from birth should prompt CHH–AD-spectrum testing even without hair or immune abnormalities and that WES plus RMRP-aware analysis can resolve atypical cases. Its cases were MDWH/CHH rather than pure ANXD, so their immune and anemia frequencies must not be generalized to ANXD. URL: https://doi.org/10.1097/MD.0000000000037247; received November 13, 2023, accepted January 23, 2024, published May 2024. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4, park2024cartilagehairhypoplasia–anauxeticdysplasia pages 1-2)

Principal evidence and exact abstract quotations

  1. Remmelzwaal et al., 2023, AJMG Part A. DOI: https://doi.org/10.1002/ajmg.a.63316. Abstract: “The cartilage hair hypoplasia and anauxetic dysplasia (CHH-AD) spectrum encompasses a group of rare skeletal disorders, with anauxetic dysplasia (ANXD) at the most severe end of the spectrum.” It also states, “Thus far, only five patients with type 3 anauxetic dysplasia (ANXD3) have been reported.” This is direct human, single-case evidence. (remmelzwaal2023expandingthephenotype pages 1-2)
  2. Thiel et al., 2007, American Journal of Human Genetics. DOI: https://doi.org/10.1086/521034. Abstract: “In vitro testing…revealed a strong correlation between the decrease in rRNA cleavage in ribosomal assembly and the degree of bone dysplasia.” Direct human genotype–phenotype data plus in-vitro functional assays. (thiel2007typeandlevel pages 1-2)
  3. Barraza-García et al., 2017, Clinical Genetics. DOI: https://doi.org/10.1111/cge.12964. Human POP1 cases plus molecular assays; reduced RMRP abundance and increased pre-5.8S rRNA supported RNase-MRP dysfunction. (barrazagarcia2017broadeningthephenotypic pages 1-2)
  4. Steinbusch et al., 2017, Scientific Reports. DOI: https://doi.org/10.1038/s41598-017-06809-5. Abstract: “Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels.” This is preclinical cellular/mouse-derived evidence, not a clinical treatment study. (steinbusch2017expressionofrmrp pages 1-2)

Evidence limitations

ANXD evidence is dominated by individual cases, a few families, and mechanistic studies spanning the broader CHH–AD spectrum. Consequently, phenotype percentages, penetrance, prevalence, life expectancy, treatment-response rates, and genotype-specific prognosis cannot currently be estimated reliably. Recent 2023–2024 reports improve phenotypic recognition but do not provide population-level natural history or therapeutic evidence. Assertions imported from cartilage-hair hypoplasia—especially immunodeficiency, anemia, Hirschsprung disease, and malignancy risk—must be explicitly labeled as spectrum-level evidence rather than assumed characteristics of pure ANXD.

References

  1. (remmelzwaal2023expandingthephenotype pages 1-2): P. Christian Remmelzwaal, Martijn V. Verhagen, Jan D. H. Jongbloed, Peter C. van den Akker, Hermine E. Veenstra‐Knol, and Marrit M. Hitzert. Expanding the phenotype of anauxetic dysplasia caused by biallelic nepro mutations: a case report. American Journal of Medical Genetics Part A, 191:2440-2445, Jun 2023. URL: https://doi.org/10.1002/ajmg.a.63316, doi:10.1002/ajmg.a.63316. This article has 5 citations.

  2. (thiel2007typeandlevel pages 1-2): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

  3. (thiel2007typeandlevel pages 5-6): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

  4. (thiel2007typeandlevel pages 3-4): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

  5. (thiel2007typeandlevel pages 6-8): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

  6. (barrazagarcia2017broadeningthephenotypic pages 1-2): J. Barraza-García, J. Barraza-García, J. Barraza-García, C. I. Rivera-Pedroza, C. I. Rivera-Pedroza, A. Hisado-Oliva, A. Hisado-Oliva, A. Hisado-Oliva, A. Belinchón-Martínez, A. Belinchón-Martínez, A. Belinchón-Martínez, L. Sentchordi-Montané, L. Sentchordi-Montané, Emma L Duncan, G. R. Clark, A. D. Pozo, A. D. Pozo, K. Ibáñez-Garikano, A. Offiah, P. Prieto-Matos, V. Cormier-Daire, K. E. Heath, K. E. Heath, and K. E. Heath. Broadening the phenotypic spectrum of pop1‐skeletal dysplasias: identification of pop1 mutations in a mild and severe skeletal dysplasia. Clinical Genetics, 92:91-98, Feb 2017. URL: https://doi.org/10.1111/cge.12964, doi:10.1111/cge.12964. This article has 24 citations and is from a peer-reviewed journal.

  7. (remmelzwaal2023expandingthephenotype pages 4-4): P. Christian Remmelzwaal, Martijn V. Verhagen, Jan D. H. Jongbloed, Peter C. van den Akker, Hermine E. Veenstra‐Knol, and Marrit M. Hitzert. Expanding the phenotype of anauxetic dysplasia caused by biallelic nepro mutations: a case report. American Journal of Medical Genetics Part A, 191:2440-2445, Jun 2023. URL: https://doi.org/10.1002/ajmg.a.63316, doi:10.1002/ajmg.a.63316. This article has 5 citations.

  8. (remmelzwaal2023expandingthephenotype pages 3-4): P. Christian Remmelzwaal, Martijn V. Verhagen, Jan D. H. Jongbloed, Peter C. van den Akker, Hermine E. Veenstra‐Knol, and Marrit M. Hitzert. Expanding the phenotype of anauxetic dysplasia caused by biallelic nepro mutations: a case report. American Journal of Medical Genetics Part A, 191:2440-2445, Jun 2023. URL: https://doi.org/10.1002/ajmg.a.63316, doi:10.1002/ajmg.a.63316. This article has 5 citations.

  9. (thiel2007typeandlevel pages 2-3): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

  10. (steinbusch2017expressionofrmrp pages 1-2): Mandy M. F. Steinbusch, Marjolein M. J. Caron, Don A. M. Surtel, Franziska Friedrich, Ekkehart Lausch, Ger J. M. Pruijn, Wouter Verhesen, Blanche L. M. Schroen, Lodewijk W. van Rhijn, Bernhard Zabel, and Tim J. M. Welting. Expression of rmrp rna is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation. Scientific Reports, Jul 2017. URL: https://doi.org/10.1038/s41598-017-06809-5, doi:10.1038/s41598-017-06809-5. This article has 56 citations and is from a peer-reviewed journal.

  11. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 2-4): Ju Heon Park, Minji Im, Yae-Jean Kim, Ja-Hyun Jang, Sae-Mi Lee, Min-Sun Kim, and Sung Yoon Cho. Cartilage-hair hypoplasia–anauxetic dysplasia spectrum disorders harboring rmrp mutations in two korean children: a case report. Medicine, 103:e37247, May 2024. URL: https://doi.org/10.1097/md.0000000000037247, doi:10.1097/md.0000000000037247. This article has 4 citations and is from a peer-reviewed journal.

  12. (steinbusch2017expressionofrmrp pages 7-9): Mandy M. F. Steinbusch, Marjolein M. J. Caron, Don A. M. Surtel, Franziska Friedrich, Ekkehart Lausch, Ger J. M. Pruijn, Wouter Verhesen, Blanche L. M. Schroen, Lodewijk W. van Rhijn, Bernhard Zabel, and Tim J. M. Welting. Expression of rmrp rna is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation. Scientific Reports, Jul 2017. URL: https://doi.org/10.1038/s41598-017-06809-5, doi:10.1038/s41598-017-06809-5. This article has 56 citations and is from a peer-reviewed journal.

  13. (park2024cartilagehairhypoplasia–anauxeticdysplasia pages 1-2): Ju Heon Park, Minji Im, Yae-Jean Kim, Ja-Hyun Jang, Sae-Mi Lee, Min-Sun Kim, and Sung Yoon Cho. Cartilage-hair hypoplasia–anauxetic dysplasia spectrum disorders harboring rmrp mutations in two korean children: a case report. Medicine, 103:e37247, May 2024. URL: https://doi.org/10.1097/md.0000000000037247, doi:10.1097/md.0000000000037247. This article has 4 citations and is from a peer-reviewed journal.

  14. (remmelzwaal2023expandingthephenotype pages 4-5): P. Christian Remmelzwaal, Martijn V. Verhagen, Jan D. H. Jongbloed, Peter C. van den Akker, Hermine E. Veenstra‐Knol, and Marrit M. Hitzert. Expanding the phenotype of anauxetic dysplasia caused by biallelic nepro mutations: a case report. American Journal of Medical Genetics Part A, 191:2440-2445, Jun 2023. URL: https://doi.org/10.1002/ajmg.a.63316, doi:10.1002/ajmg.a.63316. This article has 5 citations.

  15. (NCT00001754 chunk 1): Study of Skeletal Disorders and Short Stature. National Human Genome Research Institute (NHGRI). 1998. ClinicalTrials.gov Identifier: NCT00001754

  16. (thiel2007typeandlevel pages 4-5): Christian T. Thiel, Geert Mortier, Ilkka Kaitila, André Reis, and Anita Rauch. Type and level of rmrp functional impairment predicts phenotype in the cartilage hair hypoplasia-anauxetic dysplasia spectrum. American journal of human genetics, 81 3:519-29, Sep 2007. URL: https://doi.org/10.1086/521034, doi:10.1086/521034. This article has 114 citations and is from a highest quality peer-reviewed journal.

Artifacts