Acromesomelic Dysplasia Maroteaux Type

Mendelian MONDO:0011275 Pathograph 29 Show in embeddings browser Skeletal Dysplasia

Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare autosomal recessive skeletal dysplasia caused by biallelic loss-of-function variants in NPR2, which encodes natriuretic peptide receptor B (NPR-B). Allele-specific defects in RNA processing, receptor trafficking, or catalytic activity reduce C-type natriuretic peptide (CNP)-stimulated cGMP signaling in growth-plate chondrocytes. The resulting impairment of proliferative and hypertrophic growth-plate zones reduces endochondral longitudinal bone growth. AMDM causes disproportionate short-limb short stature, acromesomelic shortening, brachydactyly, short hands and feet, and characteristic vertebral and epiphyseal radiographic findings. Growth is often normal at birth and decelerates during the first two years. Mild and variable frontal prominence or a depressed nasal bridge may occur; intelligence is generally reported as normal.

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1
Inheritance
9
Pathophys.
18
Phenotypes
3
Hypotheses
5
Gaps
29
Pathograph
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Genes
2
Medical Actions
6
Differentials
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Models
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Deep Research
🏷

Classifications

ISDS Skeletal Nosology
acromesomelic dysplasias
👪

Inheritance

1
Autosomal Recessive HP:0000007
AMDM results from biallelic NPR2 loss of function. Heterozygous relatives may have reduced mean stature at a group level, but individual carriers can be phenotypically normal and do not have the full recessive skeletal dysplasia. Carrier status is not uniform across alleles: some AMDM missense alleles are expressed normally and act as dominant negatives on the wild-type subunit, and in a family carrying two such alleles the heterozygous children's height z-scores fell progressively with age while their wild-type siblings' did not.
Autosomal recessive inheritance
Show evidence (4 references)
PMID:15146390 SUPPORT Human Clinical
"The autosomal recessive skeletal dysplasia known as "acromesomelic dysplasia, type Maroteaux" (AMDM) maps to an interval that contains NPR2."
The landmark study explicitly identifies AMDM as autosomal recessive.
PMID:40551241 SUPPORT Human Clinical
"Sanger sequencing confirmed that the variants were inherited from his phenotypically normal parents. The proband is compound heterozygous, while both parents are heterozygous carriers, indicating an autosomal recessive pattern of inheritance."
A recent family demonstrates an affected compound heterozygote with phenotypically normal carrier parents.
PMID:15146390 SUPPORT Human Clinical
"We also found that obligate carriers of NPR2 mutations have heights that are below the mean for matched controls."
The landmark family series supports reduced mean stature among obligate carriers while not implying that every carrier is short.
+ 1 more reference
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Mechanistic Hypotheses

3
Chondrocyte cGMP-Deficit Convergence Model
chondrocyte_cgmp_deficit_convergence CANONICAL
Evidence balance 2 support
The unit that matters for growth-plate output is chondrocyte cGMP, and AMDM is one of several ways to lower it. Achondroplasia lowers it from above by activating FGFR3; AMDM lowers it by disabling the cyclase that makes it; the PRKG2 disorder leaves it intact but removes the kinase that reads it. The model earns its keep by being predictive rather than descriptive: it is why a CNP analogue developed for achondroplasia was expected to help NPR2 deficiency, and a 2026 basket trial found that it does in heterozygous NPR2 carriers.
Show evidence (2 references)
PMID:33986191 SUPPORT Model Organism
"Activating mutations in fibroblast growth factor receptor 3 (FGFR3) and inactivating mutations in the natriuretic peptide receptor 2 (NPR2) guanylyl cyclase both result in decreased production of cyclic GMP in chondrocytes and severe short stature"
States the convergence of two different genetic lesions on one biochemical deficit.
PMID:41967490 SUPPORT Human Clinical
"Vosoritide led to marked increases in growth velocity in children with RASopathies, ACAN, and NPR2 deficiency"
The convergence model's therapeutic prediction holds across several genetic causes. Support is partial for AMDM specifically because the NPR2 arm enrolled heterozygous carriers, not biallelic disease.
NPR-B Phosphoregulation Modifier Model
npr_b_phosphoregulation_modifier EMERGING
Evidence balance 2 support
CNP can only activate NPR-B when the receptor is phosphorylated on several serines and threonines, and FGFR3 signalling drives a PPP-family phosphatase that strips those sites. This makes the receptor's phosphorylation state a second, variant-independent determinant of how much cGMP an AMDM growth plate makes, and predicts two things worth testing: that FGF tone modifies severity in patients carrying residual-activity alleles, and that a phosphatase inhibitor should raise output from those same alleles. Both predictions currently rest on mouse achondroplasia models. Nothing has been measured in an NPR2-mutant background, where the relevant question is whether a partially active mutant receptor is still subject to the same regulation.
Show evidence (2 references)
PMID:33986191 SUPPORT Model Organism
"because FGFR3 signaling decreases NPR2 activity by dephosphorylating the NPR2 protein"
States the regulatory relationship the model rests on.
PMID:15869918 SUPPORT In Vitro
"We found that FGFs inhibited CNP-stimulated cGMP production by disrupting the signaling pathway through GC-B while CNP antagonized the activation of the MAPK cascade by FGFs."
Independently documents the reciprocal cross-talk in chondrocytes, with FGF suppressing CNP-driven cGMP production.
Dominant-Negative Allele Model of Carrier Short Stature
allele_dominant_negative_model EMERGING
Evidence balance 2 support
Carrier short stature has usually been read as haploinsufficiency, but at least some AMDM missense alleles produce a normally expressed receptor that poisons the wild-type subunit within the homodimer. On that reading a carrier's residual activity is below fifty percent, which would explain both why heterozygous relatives are short and why their height z-scores drift downward with age rather than tracking a fixed deficit. The prediction that separates this from haploinsufficiency is that truncating alleles should give milder carrier phenotypes than dominant-negative missense alleles; that comparison has not been made systematically.
Show evidence (2 references)
PMID:32720985 SUPPORT In Vitro
"Both mutant ANPRB proteins were normally expressed in HEK293T cells and exhibited dominant negative effects on wild-type ANPRB catalytic activity."
Demonstrates a dominant-negative effect for two AMDM-causing missense alleles.
PMID:32720985 SUPPORT Human Clinical
"Height z-scores progressively and significantly decreased as NPR2-heterozygous children matured, while remaining constant in their wild-type siblings."
The progressive carrier phenotype within one family is the clinical observation the model is meant to explain.
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Discussions and Knowledge Gaps

5
Does vosoritide help AMDM, where both NPR2 alleles are damaged, given that it works by agonising NPR-B?
KNOWLEDGE GAP OPEN vosoritide_in_biallelic_npr2_disease
Attached to
treatments# pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP mechanistic_hypotheses#chondrocyte_cgmp_deficit_convergence
A 2026 phase 2 basket trial reported a large growth-velocity gain in children with NPR2 deficiency, but that arm enrolled heterozygous carriers, who retain one wild-type receptor for the drug to act on. AMDM is the harder case, because the drug's target is the damaged protein itself. Whether it helps should depend on residual activity: alleles with partial catalytic function might be drivable by supraphysiological CNP, whereas a receptor that cannot bind ligand or reach the membrane offers nothing to agonise. That makes this a question about allele class, not about the disease as a whole, and the existing entry already records that AMDM alleles differ in trafficking and catalytic behaviour. The safety signal from the trial is also relevant to a population already prone to skeletal complications.
Show evidence (3 references)
PMID:41967490 SUPPORT Human Clinical
"Carriers of heterozygous pathogenic/likely pathogenic variants in NPR2"
Identifies the trial population as heterozygous carriers, which is why its result does not transfer directly to AMDM.
PMID:41967490 SUPPORT Human Clinical
"5 subjects discontinued medication due to adverse events, including 3 slipped capital femoral epiphyses and 4 cases of genu valgum"
Records the longer-term safety signal that would need weighing in a skeletal dysplasia population.
PMID:41967490 SUPPORT Human Clinical
"There are no currently approved treatments for either NPR2 or ACAN deficiency."
Confirms that no approved NPR2-directed therapy exists, so this remains an open question rather than a care gap.
Is stature a continuous readout of NPR-B activity, with AMDM and the NPR2 overgrowth syndrome as its two ends?
KNOWLEDGE GAP OPEN npr2_activity_dose_mirror
Attached to
pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP phenotypes#Severe Disproportionate Short-Limb Short Stature
Gain-of-function NPR2 alleles and CNP overproduction cause tall stature with macrodactyly and slipped capital femoral epiphysis, mirroring the AMDM picture in the opposite direction, and the reported gain-of-function receptor is overactive both at baseline and with ligand. If activity maps onto stature continuously, then measured receptor activity should predict height across the whole allelic range, which would give AMDM a quantitative severity model it currently lacks. The competing possibility is that the relationship saturates or is buffered at the top of the range, so that the overgrowth phenotype is not simply AMDM run backwards. No study has plotted measured NPR-B activity against stature across loss- and gain-of-function alleles together.
Show evidence (2 references)
PMID:24259409 SUPPORT Human Clinical
"Loss of function mutations at NPR2 cause acromesomelic dysplasia, type Maroteaux, while overproduction of CNP by chromosomal translocation and a gain-of-function mutation at NPR2 have been reported to be responsible for an overgrowth syndrome in three cases and one family, respectively."
States the two-directional relationship between NPR2 activity and stature.
PMID:24259409 SUPPORT In Vitro
"In vitro transfection assay of the mutant NPR2 revealed overactivity of the mutant receptor at baseline as well as with the ligand."
Provides the measured activity at the gain-of-function end that a continuous activity-to-stature model would need.
Which NPR2 allele-specific functional defects and residual activities predict AMDM skeletal severity?
KNOWLEDGE GAP OPEN genotype_functional_severity
Attached to
pathophysiology#Variant-Specific NPR-B Biogenesis and Catalytic Failure pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
NPR2 missense variants differ in trafficking and catalytic behavior, and clinically mild AMDM is recognized, but no validated genotype-to-severity rule is available. Comparable functional assays linked to standardized longitudinal phenotypes are needed.
Show evidence (2 references)
PMID:38078000 SUPPORT In Vitro
"Conversely, variants p.Arg318Gly, p.Arg495Cys, and p.Arg557His seem to display a non-statistically significant behavior that is slightly comparable to WT-NPR2."
The heterogeneous in-vitro behavior motivates a standardized variant-function study.
PMID:34178199 SUPPORT Human Clinical
"although to date there are no reported genotype-phenotype correlations."
The clinical report explicitly identifies the unresolved genotype-phenotype relationship.
Why does NPR-B deficiency preferentially shorten middle and distal limb segments while producing milder axial involvement?
KNOWLEDGE GAP OPEN regional_acromesomelic_patterning
Attached to
pathophysiology#Impaired Endochondral Longitudinal Bone Growth pathophysiology#Acromesomelic Limb Elongation Deficit
Reduced growth-plate signaling explains impaired longitudinal growth, but it does not by itself explain the reproducible regional acromesomelic pattern. Spatial developmental studies are needed to define segment-specific CNP, NPR-B, cGKII, and downstream signaling dependencies.
Show evidence (1 reference)
PMID:34162036 SUPPORT Human Clinical
"It is a rare type of dwarfism characterized by shortening of the middle and distal segments of the limbs with spondylar dysplasia."
The consistent regional phenotype defines the pattern that remains mechanistically unexplained.
Which AMDM genotypes, if any, predict benefit from somatropin or future NPR-B/cGMP-pathway therapies?
KNOWLEDGE GAP OPEN genotype_stratified_growth_response
Attached to
pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP treatments#Somatropin Therapy
Somatropin evidence is limited to uncontrolled cases with variable response. Complete NPR-B loss and residual-function alleles may differ in their response to CNP-pathway strategies, while MEK inhibition remains confined to a fetal mouse tibia explant model.
Show evidence (2 references)
PMID:34178199 SUPPORT Human Clinical
"Some individuals with AMDM have been treated with recombinant human growth hormone therapy with a variable response"
Variable reported response motivates prospective genotype-stratified study.
PMID:23065701 SUPPORT In Vitro
"Treatment of fetal tibiae explants with mitogen activated protein kinase 1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth defect, providing a promising foundation for skeletal dysplasia therapeutics."
The rescue is preclinical and defines a pathway hypothesis rather than a human treatment.
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Pathophysiology

9
Biallelic NPR2 Loss of Function
Pathogenic variants on both NPR2 alleles reduce NPR-B receptor function. The alleles span truncating, splice-altering, and missense classes and initiate the shared AMDM mechanism.
NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Variant-Specific NPR-B Biogenesis and Catalytic Failure Individual NPR2 alleles directly impair transcript processing, receptor trafficking, or guanylyl-cyclase activity.
Show evidence (1 reference)
PMID:15146390 SUPPORT Human Clinical
"We sequenced DNA from 21 families affected by AMDM and found 4 nonsense mutations, 4 frameshift mutations, 2 splice-site mutations, and 11 missense mutations."
Multiple biallelic variant classes were identified across 21 affected families.
Variant-Specific NPR-B Biogenesis and Catalytic Failure
NPR2 variants use several proximal routes to receptor failure. Some cause aberrant transcripts or premature truncation; some missense receptors are retained in the endoplasmic reticulum; and functional assays of other missense alleles show markedly deficient guanylyl-cyclase activity. These are convergent allelic mechanisms, not competing disease hypotheses.
NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee.
Aberrant pre-mRNA splicing of NPR2 GO:0008380 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Aberrant pre-mRNA splicing of NPR2, annotated with RNA splicing (GO:0008380). GO:0008380 is a biological process from the Gene Ontology. ⚠ ABNORMAL Receptor delivery to the plasma membrane GO:0072659 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Receptor delivery to the plasma membrane, annotated with protein localization to plasma membrane (GO:0072659). GO:0072659 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP The diverse proximal receptor defects converge directly on reduced or absent CNP-stimulated cGMP production, with residual activity depending on the allele.
Show evidence (2 references)
PMID:38078000 SUPPORT In Vitro
"Our results indicate that variants p.Leu51Pro, p.Gly123Val, p.Leu314Arg, p.Arg388Gln have defective cellular trafficking, being sequestered within the endoplasmic reticulum (ER), and consequently impaired cGMP production ability."
Functional testing demonstrates ER retention as one allele-specific route to receptor failure.
PMID:15146390 SUPPORT In Vitro
"Three missense mutations were tested in a functional assay and were found to have markedly deficient guanylyl cyclase activity."
Functional assays in the landmark AMDM study establish deficient catalytic activity as a convergent consequence of missense alleles.
Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
NPR-B is a homodimeric receptor guanylyl cyclase that produces cytoplasmic cGMP after CNP binding. AMDM variants reduce or abolish this response rather than universally eliminating all activity.
NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee.
receptor guanylyl cyclase signaling pathway GO:0007168 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased receptor guanylyl cyclase signaling pathway (GO:0007168). GO:0007168 is a biological process from the Gene Ontology. ↓ DECREASED cGMP biosynthetic process GO:0006182 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cGMP biosynthetic process (GO:0006182). GO:0006182 is a biological process from the Gene Ontology. ↓ DECREASED Activating phosphorylation of the NPR-B kinase-homology domain GO:0018105 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves Activating phosphorylation of the NPR-B kinase-homology domain, annotated with peptidyl-serine phosphorylation (GO:0018105). GO:0018105 is a biological process from the Gene Ontology. NPR-B dephosphorylation by a PPP-family phosphatase GO:0006470 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves NPR-B dephosphorylation by a PPP-family phosphatase, annotated with protein dephosphorylation (GO:0006470). GO:0006470 is a biological process from the Gene Ontology.
guanylate cyclase activity GO:0004383 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased guanylate cyclase activity (GO:0004383). GO:0004383 is a molecular function from the Gene Ontology. ↓ DECREASED natriuretic peptide receptor activity GO:0016941 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased natriuretic peptide receptor activity (GO:0016941). GO:0016941 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Growth-Plate Proliferative and Hypertrophic Zone Dysfunction Reduced NPR-B/cGMP signaling alters downstream cGKII and MEK/ERK control, reducing proliferative and hypertrophic growth-plate zones.
Show evidence (4 references)
PMID:33986191 SUPPORT Model Organism
"Because CNP activation of NPR2 requires that the receptor is phosphorylated on multiple serines and threonines (28, 29), FGF-induced NPR2 dephosphorylation lowers cGMP and opposes bone growth."
Receptor phosphorylation state is a second determinant of NPR-B output alongside the variant itself, which is why this node carries both the activating phosphorylation and the opposing dephosphorylation.
PMID:33986191 SUPPORT Model Organism
"Measurements of cGMP production in chondrocytes of living tibias, and of NPR2 phosphorylation in primary chondrocytes, showed that LB-100 counteracted FGF-induced dephosphorylation and inactivation of NPR2."
Direct measurement of the phosphorylation-to-cGMP relationship in chondrocytes, and the demonstration that it is pharmacologically addressable.
PMID:15146390 SUPPORT In Vitro
"Three missense mutations were tested in a functional assay and were found to have markedly deficient guanylyl cyclase activity."
The landmark functional assays directly show deficient receptor catalytic activity.
+ 1 more reference
Growth-Plate Proliferative and Hypertrophic Zone Dysfunction
NPR2 deficiency reduces both proliferative and hypertrophic zones of the growth plate. Model evidence indicates altered zone organization without a generalized mineralization defect.
growth plate cartilage chondrocyte CL:1000217 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves growth plate cartilage chondrocyte (CL:1000217). CL:1000217 is a cell type from the Cell Ontology. columnar chondrocyte CL:0000744 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves columnar chondrocyte (CL:0000744). CL:0000744 is a cell type from the Cell Ontology. hypertrophic chondrocyte CL:0000743 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves hypertrophic chondrocyte (CL:0000743). CL:0000743 is a cell type from the Cell Ontology.
chondrocyte proliferation GO:0035988 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased chondrocyte proliferation (GO:0035988). GO:0035988 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 growth plate cartilage development GO:0003417 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves dysregulated growth plate cartilage development (GO:0003417). GO:0003417 is a biological process from the Gene Ontology. ↕ DYSREGULATED CNP-dependent restraint of the ERK1/2 cascade GO:0070373 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased CNP-dependent restraint of the ERK1/2 cascade, annotated with negative regulation of ERK1 and ERK2 cascade (GO:0070373). GO:0070373 is a biological process from the Gene Ontology. ↓ DECREASED Fibroblast growth factor receptor signaling pathway GO:0008543 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Fibroblast growth factor receptor signaling pathway (GO:0008543). GO:0008543 is a biological process from the Gene Ontology. ⚠ ABNORMAL
growth plate cartilage UBERON:0004129 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in growth plate cartilage (UBERON:0004129). UBERON:0004129 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Impaired Endochondral Longitudinal Bone Growth Reduced proliferative and hypertrophic zones directly limit longitudinal elongation of endochondral skeletal elements.
Show evidence (3 references)
PMID:23065701 SUPPORT Model Organism
"We determined that the loss of Npr2 causes a reduction in the hypertrophic and proliferative zones of the growth plate, but mineralization of skeletal elements is normal."
The mouse model directly demonstrates reduced growth-plate zones with preserved mineralization.
PMID:15869918 SUPPORT In Vitro
"CNP and 8-bromo-cGMP strongly and dose-dependently inhibited the induction of ERK phosphorylation by FGF2 and FGF18 without changing the level of FGFR-3"
Establishes the CNP-cGMP arm as a restraint on FGF-driven ERK activation in chondrocytes, the restraint that AMDM removes.
PMID:15869918 SUPPORT In Vitro
"In the organ-cultured fetal mouse tibias, CNP and FGF18 counteracted on the longitudinal bone growth, and both the size and number of hypertrophic chondrocytes."
Shows the two arms acting in opposition on hypertrophic chondrocyte number and size in intact tibia, the growth-plate variables this node concerns.
Impaired Endochondral Longitudinal Bone Growth
Growth-plate-zone dysfunction impairs endochondral bone elongation rather than skeletal mineralization. This produces severe short-limb stature and regionally patterned appendicular and axial dysplasia.
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 Growth plate cartilage development GO:0003417 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Growth plate cartilage development (GO:0003417). GO:0003417 is a biological process from the Gene Ontology. ⚠ ABNORMAL endochondral bone growth GO:0003416 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased endochondral bone growth (GO:0003416). GO:0003416 is a biological process from the Gene Ontology. ↓ DECREASED
growth plate cartilage UBERON:0004129 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in growth plate cartilage (UBERON:0004129). UBERON:0004129 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Severe Disproportionate Short-Limb Short Stature Reduced longitudinal growth of the limbs produces disproportionate short-limb stature.
Acromesomelic Limb Elongation Deficit The longitudinal-growth defect is regionally greatest in middle and distal limb segments.
Hand and Foot Epiphyseal and Tubular-Bone Dysplasia Growth failure of distal tubular bones and epiphyses produces the characteristic hand and foot pattern.
Vertebral Growth Dysplasia Impaired vertebral endochondral growth produces characteristic body shape and pedicle spacing.
Long-Bone Modeling Deformity Uneven longitudinal and modeling growth contributes to radial and other long-bone bowing.
Frontal Bossing Frontal bossing is associated with AMDM, but the intervening craniofacial mechanism is unresolved.
Depressed Nasal Bridge A depressed nasal bridge is associated with AMDM, but its mechanistic path is unresolved.
Joint Hypermobility Joint hypermobility is associated with AMDM, but no specific connective-tissue mechanism is established.
Show evidence (1 reference)
PMID:25319082 SUPPORT Model Organism
"The cn/cn dwarf mouse is caused by a loss-of-function mutation in the natriuretic peptide receptor 2 (NPR-2) gene which helps positively regulate endochondral longitudinal bone growth."
The Npr2 model directly links receptor loss to endochondral longitudinal bone growth.
Acromesomelic Limb Elongation Deficit
The middle and distal limb segments are preferentially shortened, producing the defining acromesomelic distribution.
Limb morphogenesis GO:0035108 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Limb morphogenesis (GO:0035108). GO:0035108 is a biological process from the Gene Ontology. ⚠ ABNORMAL Endochondral bone growth GO:0003416 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Endochondral bone growth (GO:0003416). GO:0003416 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Acromesomelic Limb Shortening Preferential middle- and distal-segment growth failure directly produces acromesomelia.
Short Forearms Mesomelic growth failure directly shortens the forearms.
Show evidence (1 reference)
PMID:34162036 SUPPORT Human Clinical
"It is a rare type of dwarfism characterized by shortening of the middle and distal segments of the limbs with spondylar dysplasia."
The nine-patient series defines the segmental pattern.
Hand and Foot Epiphyseal and Tubular-Bone Dysplasia
Abnormal distal tubular-bone growth produces short broad metacarpals, metatarsals and phalanges, with cone-shaped phalangeal epiphyses and short broad hands and feet.
Bone morphogenesis GO:0060349 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Bone morphogenesis (GO:0060349). GO:0060349 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Brachydactyly Short phalanges and metacarpals directly produce brachydactyly.
Cone-Shaped Epiphyses Epiphyseal dysplasia directly manifests as cone-shaped phalangeal epiphyses.
Short Metacarpals Tubular-bone growth failure directly shortens and broadens the metacarpals.
Short Feet Distal tubular-bone growth failure directly produces short broad feet.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Imaging of the upper limbs revealed mild mesomelic shortening, short and broad phalanges and metacarpals with typical cone shaped epiphyses."
The radiographic description defines this distal skeletal branch.
Vertebral Growth Dysplasia
Vertebral endochondral growth is mildly affected, producing flattened or pear-shaped bodies, posterior-anterior height differences, and failure of normal widening of lumbar interpedicular distances.
Endochondral bone growth GO:0003416 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Endochondral bone growth (GO:0003416). GO:0003416 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Platyspondyly Vertebral growth dysplasia directly flattens vertebral bodies.
Lumbar Interpedicular Narrowing Abnormal lumbar vertebral and pedicle growth directly prevents normal caudal widening.
Ovoid Vertebral Bodies Altered vertebral body growth produces an ovoid or pear-shaped contour.
Scoliosis Scoliosis is associated with vertebral dysplasia, but its specific AMDM intermediates are unresolved.
Kyphosis Kyphosis is associated with AMDM vertebral dysplasia, but its causal intermediates are unresolved.
Hyperlordosis Hyperlordosis is associated with AMDM, but its causal intermediates are unresolved.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Lateral (D) and anteroposterior (E) radiographs of the lower spine with pear shaped vertebral bodies with shorter posterior than anterior heights and failure of widening of the lumbar interpedicular distances with some shortening of the pedicles."
The spinal radiographs define the vertebral branch.
Long-Bone Modeling Deformity
Regionally uneven long-bone growth and metaphyseal modeling contribute to radial and generalized long-bone bowing.
Bone morphogenesis GO:0060349 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal Bone morphogenesis (GO:0060349). GO:0060349 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Downstream
Radial Bowing Abnormal radial modeling directly produces radial bowing.
Bowing of Long Bones Abnormal long-bone modeling manifests as bowing beyond the radius in some affected individuals.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius"
The radiographic comparison documents the long-bone modeling pattern.
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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 Acromesomelic Dysplasia Maroteaux Type 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

18
Head and Neck 2
Frontal Bossing FREQUENT HP:0002007 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Frontal bossing (HP:0002007). HP:0002007 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0002007 | Frontal bossing | Frequent (79-30%)"
Orphanet lists frontal bossing as frequent.
Depressed Nasal Bridge FREQUENT HP:0005280 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Depressed nasal bridge (HP:0005280). HP:0005280 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0005280 | Depressed nasal bridge | Frequent (79-30%)"
Orphanet lists depressed nasal bridge as frequent.
Limbs 8
Acromesomelic Limb Shortening FREQUENT Acromesomelia HP:0003086 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Acromesomelia (HP:0003086). HP:0003086 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34162036 SUPPORT Human Clinical
"It is a rare type of dwarfism characterized by shortening of the middle and distal segments of the limbs with spondylar dysplasia."
A nine-patient series directly describes the acromesomelic pattern.
ORPHA:40 SUPPORT Other
"HP:0003086 | Acromesomelia | Frequent (79-30%)"
Orphanet supplies the frequency classification for acromesomelia.
Brachydactyly FREQUENT 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 (2 references)
PMID:32694885 SUPPORT Human Clinical
"She had acromesomelic shortening of limbs and severe brachydactyly."
The molecularly confirmed case directly documents severe brachydactyly.
ORPHA:40 SUPPORT Other
"HP:0001156 | Brachydactyly | Frequent (79-30%)"
Orphanet supplies the frequency classification for brachydactyly.
Cone-Shaped Epiphyses Cone-shaped epiphyses of the phalanges of the hand HP:0010230 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cone-shaped epiphyses of the phalanges of the hand (HP:0010230). HP:0010230 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"DP left hand (A) with broadening and shortening of the bones, and significant coned appearance of the epiphyses"
The hand radiograph directly demonstrates coned epiphyses.
Short Metacarpals HP:0010049 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short metacarpal (HP:0010049). HP:0010049 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32694885 SUPPORT Human Clinical
"Radiological examination showed that her metacarpals and phalanges were short and wide"
Radiographs directly document short, broad metacarpals.
Short Feet Short foot HP:0001773 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short foot (HP:0001773). HP:0001773 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Photographs showing brachydactyly with broad fingers (A) and short, broad toes and feet (B)."
Clinical photographs directly document short broad toes and feet.
Radial Bowing HP:0002986 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Radial bowing (HP:0002986). HP:0002986 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius"
The clinical radiographic comparison directly lists radial bowing.
Short Forearms HP:0005773 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short forearm (HP:0005773). HP:0005773 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:30359775 SUPPORT Human Clinical
"Acromesomelic dysplasia type Maroteaux (AMDM) is characterized by extreme shortening of the forelimbs and disproportionate short stature."
The patient series directly describes extreme forelimb shortening.
Bowing of Long Bones FREQUENT Bowing of the long bones HP:0006487 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bowing of the long bones (HP:0006487). HP:0006487 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0006487 | Bowing of the long bones | Frequent (79-30%)"
Orphanet lists bowing of the long bones as frequent.
Musculoskeletal 5
Platyspondyly HP:0000926 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Platyspondyly (HP:0000926). HP:0000926 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:32694885 SUPPORT Human Clinical
"Her vertebral bodies were mildly flattened"
The confirmed case directly documents mild vertebral flattening.
Scoliosis FREQUENT HP:0002650 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Scoliosis (HP:0002650). HP:0002650 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0002650 | Scoliosis | Frequent (79-30%)"
Orphanet lists scoliosis as frequent.
Kyphosis FREQUENT HP:0002808 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Kyphosis (HP:0002808). HP:0002808 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0002808 | Kyphosis | Frequent (79-30%)"
Orphanet lists kyphosis as frequent.
Hyperlordosis FREQUENT HP:0003307 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperlordosis (HP:0003307). HP:0003307 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"HP:0003307 | Hyperlordosis | Frequent (79-30%)"
Orphanet lists hyperlordosis as frequent.
Joint Hypermobility FREQUENT 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 (1 reference)
ORPHA:40 SUPPORT Other
"HP:0001382 | Joint hypermobility | Frequent (79-30%)"
Orphanet lists joint hypermobility as frequent.
Growth 1
Severe Disproportionate Short-Limb Short Stature HP:0008873 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Disproportionate short-limb short stature (HP:0008873). HP:0008873 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35368703 SUPPORT Human Clinical
"Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare skeletal dysplasia characterized by severe disproportionate short stature, short hands and feet, normal intelligence, and facial dysmorphism."
The clinical report identifies severe disproportionate stature as a defining phenotype.
Other 2
Lumbar Interpedicular Narrowing HP:0008486 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lumbar interpedicular narrowing (HP:0008486). HP:0008486 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"failure of widening of the lumbar interpedicular distances with some shortening of the pedicles."
The spinal radiographs directly demonstrate the lumbar finding.
Ovoid Vertebral Bodies FREQUENT 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 (2 references)
PMID:34178199 SUPPORT Human Clinical
"Pear shaped vertebral bodies with a shorter posterior versus anterior height"
The direct radiographic description supports altered vertebral shape.
ORPHA:40 SUPPORT Other
"HP:0003300 | Ovoid vertebral bodies | Frequent (79-30%)"
Orphanet supplies the frequency classification for ovoid vertebral bodies.
🧬

Genetic Associations

1
Biallelic NPR2 Loss-of-Function Variants (Causative)
Gene: NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:15146390 SUPPORT Human Clinical
"We sequenced DNA from 21 families affected by AMDM and found 4 nonsense mutations, 4 frameshift mutations, 2 splice-site mutations, and 11 missense mutations."
The landmark family series establishes the allelic spectrum of causative NPR2 variants.
PMID:42442044 SUPPORT In Vitro
"Functional analysis using patient-derived leukocyte RNA revealed aberrant splicing leading to partial exon truncation, frameshift, and premature termination of NPR2"
Patient-derived RNA establishes a synonymous splice-altering loss-of-function mechanism.
💊

Medical Actions

2
Somatropin Therapy
Category: Therapeutic 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
Agent: Somatropin NCIT:C837 NCI Thesaurus (NCIT) Relation: this treatment uses this therapeutic agent This treatment uses Somatropin (NCIT:C837). NCIT:C837 is a therapeutic agent from the NCI Thesaurus.
Recombinant human growth hormone has been reported in two long-term-treated siblings and isolated short-term cases. Some height gain occurred, but responses are variable and the uncontrolled evidence is too limited to establish a standard AMDM regimen or expected final-height benefit.
Target Phenotypes: Disproportionate short-limb short stature HP:0008873 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Disproportionate short-limb short stature (HP:0008873). HP:0008873 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:33238275 SUPPORT Human Clinical
"Final heights after 8.5 years of GH treatment were 130.5 cm (-6.57 SDS, Pt-A) and 134 cm (-4.58 SDS, Pt-B)."
Two siblings reached the reported final heights after prolonged treatment, without a control group.
PMID:35368703 SUPPORT Human Clinical
"Furthermore, rhGH therapy in patient 1 increased the patient's height by 0.6SDS over 15 months without adversely affecting the trunk-leg proportion."
One short-term case showed a 0.6-SDS gain; this does not establish general efficacy.
PMID:34178199 SUPPORT Human Clinical
"Some individuals with AMDM have been treated with recombinant human growth hormone therapy with a variable response"
The review explicitly characterizes response as variable.
Genetic Counseling
Category: Counseling / Informational Action: genetic counselingNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is genetic counseling (NCIT:C15240). NCIT:C15240 is a clinical intervention from the NCI Thesaurus. Ontology label: Genetic Counseling NCIT:C15240
Genetic counseling is appropriate after molecular confirmation to explain autosomal recessive inheritance and to support testing of relatives for the known familial variants. Carrier stature is variable and should not be used as a substitute for molecular testing.
Show evidence (2 references)
PMID:40551241 SUPPORT Human Clinical
"Sanger sequencing confirmed that the variants were inherited from his phenotypically normal parents. The proband is compound heterozygous, while both parents are heterozygous carriers, indicating an autosomal recessive pattern of inheritance."
The family demonstrates the recessive carrier relationships relevant to counseling and familial testing.
PMID:40551241 SUPPORT Human Clinical
"Genetic diagnosis is also useful to provide adequate counselling to family memebers, including the formulation of the proper recurrence risk"
The report directly supports using molecular diagnosis to provide family counseling about recurrence risk.
🔬

Diagnosis

3
Characteristic Physical Examination
Examination identifies disproportionate short-limb stature with acromesomelic shortening, brachydactyly, and short broad hands and feet. Craniofacial findings are mild and variable; normal intelligence is typical.
physical examination NCIT:C20989 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:35368703 SUPPORT Human Clinical
"Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare skeletal dysplasia characterized by severe disproportionate short stature, short hands and feet, normal intelligence, and facial dysmorphism."
The clinical description supports the characteristic examination pattern.
Skeletal Radiographic Evaluation
Skeletal radiographs assess mesomelic shortening, short broad metacarpals and phalanges, cone-shaped epiphyses, vertebral flattening or pear shape, lumbar interpedicular narrowing, and long-bone bowing. The pattern can support diagnosis even when stature is only mildly affected.
radiograph imaging procedure NCIT:C38101 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Given these findings, a diagnosis of AMDM should be considered in individuals with characteristic radiological findings, even if stature is only modestly affected."
The report directly supports diagnostic use of the radiographic pattern.
Biallelic NPR2 Molecular Confirmation
Molecular genetic testing confirms the diagnosis by identifying pathogenic or likely pathogenic variants affecting both NPR2 alleles. Transcript-level analysis can resolve suspected splice effects, including synonymous variants.
molecular genetic testing NCIT:C19770 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:15146390 SUPPORT Human Clinical
"We sequenced DNA from 21 families affected by AMDM and found 4 nonsense mutations, 4 frameshift mutations, 2 splice-site mutations, and 11 missense mutations."
The landmark study establishes biallelic NPR2 variant detection as the molecular basis of AMDM.
PMID:42442044 SUPPORT In Vitro
"Functional analysis using patient-derived leukocyte RNA revealed aberrant splicing leading to partial exon truncation, frameshift, and premature termination of NPR2"
Patient-derived RNA demonstrates the value of transcript analysis for a splice-altering synonymous allele.
🩻

Imaging Findings

6
Cone-Shaped Phalangeal Epiphyses on Hand Radiographs
Hand radiographs show cone-shaped epiphyses with broadening and shortening of the phalanges.
Xray
Cone-shaped epiphyses of the phalanges of the hand HP:0010230 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"DP left hand (A) with broadening and shortening of the bones, and significant coned appearance of the epiphyses"
The hand radiograph directly demonstrates the finding.
Short and Broad Metacarpals and Phalanges on Hand Radiographs
Hand radiographs show marked shortening and broadening of metacarpals and phalanges.
Xray
Short metacarpal HP:0010049 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:32694885 SUPPORT Human Clinical
"Radiological examination showed that her metacarpals and phalanges were short and wide"
The case directly documents the hand-radiograph finding.
Platyspondyly on Spine Radiographs
Lateral spine radiographs can show mild vertebral-body flattening.
Xray
Platyspondyly HP:0000926 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:32694885 SUPPORT Human Clinical
"Her vertebral bodies were mildly flattened"
The lateral-spine finding directly supports platyspondyly.
Lumbar Interpedicular Narrowing on Spine Radiographs
Anteroposterior lumbar radiographs show failure of normal interpedicular widening and shortened pedicles.
Xray
Lumbar interpedicular narrowing HP:0008486 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"failure of widening of the lumbar interpedicular distances with some shortening of the pedicles."
The spinal radiographs directly document this finding.
Radial Bowing on Limb Radiographs
Limb radiographs can show radial bowing with metaphyseal flaring or distal radial hypoplasia.
Xray
Radial bowing HP:0002986 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius"
The clinical radiographic comparison directly lists radial bowing.
Ovoid or Pear-Shaped Vertebral Bodies on Spine Radiographs
Vertebral bodies may be ovoid or pear-shaped with shorter posterior than anterior height.
Xray
Ovoid vertebral bodies HP:0003300 Human Phenotype Ontology (HP)
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Pear shaped vertebral bodies with a shorter posterior versus anterior height"
The direct radiographic description supports the finding.
📈

Progression

3
Birth
Age: Neonatal period
Birth weight, length, and head circumference may be within normal ranges, so absence of marked shortening at birth does not exclude AMDM.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"At birth, children with AMDM generally have weight, length and head circumference measurements within the normal range."
The clinical review describes generally normal anthropometric measurements at birth.
Early postnatal growth deceleration
Age: Infancy through two years
Disproportionate limb-growth failure becomes clinically apparent during the first two years of life.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Limb length at birth may be normal but decreased growth becomes obvious in the first 2 years of life."
This directly defines the typical timing of postnatal growth deceleration.
Childhood to adulthood
Age: Childhood through skeletal maturity
Reduced postnatal skeletal growth accumulates into severe adult short stature, although residual severity varies and mild molecularly confirmed cases occur.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"Postnatal skeletal growth is reduced and final height is usually below 120 cm"
The review describes the usual longitudinal growth outcome while allowing milder cases.
📊

Prevalence

1
Worldwide
Point Prevalence ≤0.1 per 100,000 <1 in 1,000,000
Orphanet reports a worldwide point prevalence below one per million. This is a broad rare-disease estimate rather than a population-based AMDM registry measurement.
Show evidence (1 reference)
ORPHA:40 SUPPORT Other
"<1 / 1 000 000 | Worldwide | Point prevalence | ORPHANET"
The structured Orphanet record supplies the prevalence class and geographic scope.
🔀

Differential Diagnoses

6

Conditions with similar clinical presentations that must be differentiated from Acromesomelic Dysplasia Maroteaux Type:

Acromesomelic Dysplasia, Hunter-Thompson Type Not Yet Curated MONDO:0008717
Overlapping Features Hunter-Thompson acromesomelic dysplasia belongs to the GDF5/BMPR1B spectrum and overlaps AMDM in distal limb shortening and brachydactyly.
Distinguishing Features
  • Craniofacial and axial skeleton are generally unaffected, unlike the vertebral and mild craniofacial findings in AMDM.
  • Lower limbs are more severely affected; square phalanges, a single fifth-digit phalanx, ankle dislocation, or radial-head dislocation can occur.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"In AMDH the lower limbs are more severely affected, phalanges tend to square and there may be a single phalangeal bone in the fifth digit. Ankle dislocation is common and radial head dislocation may be present"
The review supplies the distinguishing Hunter-Thompson radiographic pattern.
Acromesomelic Dysplasia, Grebe Type MONDO:0008703
Overlapping Features Grebe-type acromesomelic dysplasia is a severe GDF5/BMPR1B-spectrum limb dysplasia that overlaps AMDM but has much more destructive appendicular involvement.
Distinguishing Features
  • Severe micromelia with absent or fused carpal, metacarpal, tarsal, metatarsal, or phalangeal bones favors Grebe type.
  • Postaxial polydactyly and major femoral, tibial, fibular, ulnar, or radial abnormalities are not typical AMDM findings.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"AMDG is characterized by severe micromelia. Fusion of the carpals and/or metacarpals and tarsals and/or metatarsals maybe present. Metacarpal, metatarsal or proximal and/or middle phalanges may be absent. Postaxial polydactyly has also been reported."
The review provides the severe appendicular findings that distinguish Grebe type.
Acromesomelic Dysplasia, Du Pan Type MONDO:0009231
Overlapping Features Du Pan type is a milder GDF5/BMPR1B-spectrum acromesomelic dysplasia that can overlap AMDM in limb shortening and brachydactyly.
Distinguishing Features
  • Fibular hypoplasia with complex brachydactyly favors Du Pan type; molecular testing distinguishes GDF5/BMPR1B-spectrum disease from NPR2-related AMDM.
Show evidence (1 reference)
PMID:34178199 SUPPORT Human Clinical
"A milder form with fibular hypoplasia and complex brachydactyly (acromesomelic dysplasia, du Pan type) has also been reported"
The review identifies the characteristic Du Pan pattern.
Acromesomelic Dysplasia, Demirhan Type MONDO:0012274
Overlapping Features The BMPR1B-related, receptor-side member of the GDF5/BMPR1B half of ISDS group 16. Its Grebe-like limb phenotype overlaps AMDM in acromesomelic shortening and brachydactyly.
Distinguishing Features
  • Biallelic BMPR1B variants, rather than biallelic NPR2 variants, establish this diagnosis.
  • Genital anomalies with hypergonadotrophic hypogonadism were present in the index patient and are not a feature of AMDM.
Show evidence (2 references)
PMID:15805157 SUPPORT Human Clinical
"In addition, she presented with hypoplasia of the uterus and ovarian dysfunction resulting in hypergonadotrophic hypogonadism."
Identifies the extraskeletal feature that separates the BMPR1B disorder from AMDM.
PMID:15805157 SUPPORT Human Clinical
"Mutation analysis of BMPR1B revealed a homozygous 8 bp deletion (del359-366)."
The molecular finding distinguishes this receptor-side disorder from NPR2-related AMDM.
🐁

Animal Models

2
Npr2(cn/cn) loss-of-function Mus musculus
The cn/cn mouse has Npr2 loss of function and recapitulates disproportionate dwarfism with a shortened physeal hypertrophic zone. Chondrocyte ultrastructure is preserved, supporting a growth-plate-zone defect rather than a primary matrix-synthesis abnormality.
Species
Mus musculus
Genotype
Npr2(cn/cn) loss-of-function
Genes
NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this experimental model concerns this gene This experimental model concerns NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:25319082 SUPPORT Model Organism
"The cn/cn dwarf mouse is caused by a loss-of-function mutation in the natriuretic peptide receptor 2 (NPR-2) gene which helps positively regulate endochondral longitudinal bone growth."
The study establishes cn/cn as an Npr2 loss-of-function skeletal model.
Npr2(pwe/pwe) 4-bp deletion Mus musculus
The peewee mouse carries a truncating Npr2 deletion and models AMDM skeletal growth failure. Increased activated ERK1/2 in mutant tibiae and rescue of fetal tibia explants by MEK inhibitors provide preclinical pathway evidence; they do not establish a human AMDM treatment.
Species
Mus musculus
Genotype
Npr2(pwe/pwe) 4-bp deletion
Genes
NPR2 hgnc:7944 HUGO Gene Nomenclature Committee (hgnc) Relation: this experimental model concerns this gene This experimental model concerns NPR2 (hgnc:7944). hgnc:7944 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (2 references)
PMID:23065701 SUPPORT Model Organism
"The Npr2(pwe/pwe) mouse is a model for the human skeletal dysplasia acromesomelic dysplasia, Maroteaux type (AMDM)."
The publication explicitly identifies the peewee mouse as an AMDM model.
PMID:23065701 SUPPORT In Vitro
"Treatment of fetal tibiae explants with mitogen activated protein kinase 1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth defect, providing a promising foundation for skeletal dysplasia therapeutics."
The fetal-tibia explant result is preclinical evidence for MEK/ERK pathway modulation.
{ }

Source YAML

click to show 
name: Acromesomelic Dysplasia Maroteaux Type
creation_date: "2026-04-02T12:00:00Z"
category: Mendelian
description: >-
  Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare autosomal recessive
  skeletal dysplasia caused by biallelic loss-of-function variants in NPR2,
  which encodes natriuretic peptide receptor B (NPR-B). Allele-specific defects
  in RNA processing, receptor trafficking, or catalytic activity reduce C-type
  natriuretic peptide (CNP)-stimulated cGMP
  signaling in growth-plate chondrocytes. The resulting impairment of
  proliferative and hypertrophic growth-plate zones reduces endochondral
  longitudinal bone growth. AMDM causes disproportionate short-limb short
  stature, acromesomelic shortening, brachydactyly, short hands and feet, and
  characteristic vertebral and epiphyseal radiographic findings. Growth is
  often normal at birth and decelerates during the first two years. Mild and
  variable frontal prominence or a depressed nasal bridge may occur;
  intelligence is generally reported as normal.
disease_term:
  preferred_term: acromesomelic dysplasia, Maroteaux type
  term:
    id: MONDO:0011275
    label: acromesomelic dysplasia 1, Maroteaux type
parents:
- Skeletal Dysplasia
classifications:
  isds_skeletal_category:
  - classification_value: acromesomelic_dysplasias
    notes: >-
      ISDS Nosology of Genetic Skeletal Disorders, 2023 revision (Unger et al.,
      PMID:36779427), group 16 "Acromesomelic dysplasias"; listed under dyadic
      naming as the NPR2-linked Maroteaux type (OMIM 602875). The 2019 revision
      (Mortier et al., PMID:31633310) placed the same entity in group 16 as
      "Acromesomelic dysplasia type Maroteaux (AMDM)", so the group assignment is
      unchanged across the two revisions.
    evidence:
    - reference: PMID:39441036
      reference_title: "Acromesomelic Dysplasia With Homozygosity for a Likely Pathogenic BMPR1B Variant: Postaxial Polydactyly as a Novel Clinical Finding."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        To date, four disease genes and seven distinct ACD subtypes with varying
        severity are recognised according to the 2023 revision of the nosology
        and classification of genetic skeletal disorders
      explanation: >-
        This is the sentence that ties the enumeration below to the 2023 ISDS
        nosology revision. It is quoted separately because the enumeration
        itself names diseases and OMIM numbers without repeating the nosology
        attribution, so on its own it would not support a group assignment.
    - reference: PMID:39441036
      reference_title: "Acromesomelic Dysplasia With Homozygosity for a Likely Pathogenic BMPR1B Variant: Postaxial Polydactyly as a Novel Clinical Finding."
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        The remaining three ACD types encompass NPR2-linked Maroteaux type (OMIM
        #602875), the PRKG2-linked ACD type (OMIM #619636) and Osebold-Remondini
        type, which is not yet associated with a genomic locus (OMIM #112910).
      explanation: >-
        A 2024 report enumerating the seven acromesomelic chondrodysplasia types
        recognised by the 2023 nosology revision places the NPR2-linked Maroteaux
        type inside that group.
prevalence:
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: BELOW_1_IN_1000000
  rate_high: 0.1
  notes: >-
    Orphanet reports a worldwide point prevalence below one per million. This
    is a broad rare-disease estimate rather than a population-based AMDM
    registry measurement.
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "<1 / 1 000 000 | Worldwide | Point prevalence | ORPHANET"
    explanation: The structured Orphanet record supplies the prevalence class and geographic scope.
progression:
- phase: Birth
  age_range: Neonatal period
  notes: >-
    Birth weight, length, and head circumference may be within normal ranges,
    so absence of marked shortening at birth does not exclude AMDM.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At birth, children with AMDM generally have weight, length and head
      circumference measurements within the normal range.
    explanation: The clinical review describes generally normal anthropometric measurements at birth.
- phase: Early postnatal growth deceleration
  age_range: Infancy through two years
  notes: >-
    Disproportionate limb-growth failure becomes clinically apparent during the
    first two years of life.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Limb length at birth may be normal but decreased growth becomes obvious
      in the first 2 years of life.
    explanation: This directly defines the typical timing of postnatal growth deceleration.
- phase: Childhood to adulthood
  age_range: Childhood through skeletal maturity
  notes: >-
    Reduced postnatal skeletal growth accumulates into severe adult short
    stature, although residual severity varies and mild molecularly confirmed
    cases occur.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Postnatal skeletal growth is reduced and final height is usually below 120 cm
    explanation: The review describes the usual longitudinal growth outcome while allowing milder cases.
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    AMDM results from biallelic NPR2 loss of function. Heterozygous relatives may
    have reduced mean stature at a group level, but individual carriers can be
    phenotypically normal and do not have the full recessive skeletal dysplasia.
    Carrier status is not uniform across alleles: some AMDM missense alleles are
    expressed normally and act as dominant negatives on the wild-type subunit,
    and in a family carrying two such alleles the heterozygous children's height
    z-scores fell progressively with age while their wild-type siblings' did
    not.
  evidence:
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The autosomal recessive skeletal dysplasia known as "acromesomelic
      dysplasia, type Maroteaux" (AMDM) maps to an interval that contains NPR2.
    explanation: The landmark study explicitly identifies AMDM as autosomal recessive.
  - reference: PMID:40551241
    reference_title: "A novel variant in NPR2: C.2291T > C (p.Leu764Pro) identified in a patient with acromesomelic dysplasia Maroteaux type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sanger sequencing confirmed that the variants were inherited from his
      phenotypically normal parents. The proband is compound heterozygous, while
      both parents are heterozygous carriers, indicating an autosomal recessive
      pattern of inheritance.
    explanation: A recent family demonstrates an affected compound heterozygote with phenotypically normal carrier parents.
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We also found that obligate carriers of NPR2 mutations have heights that
      are below the mean for matched controls.
    explanation: The landmark family series supports reduced mean stature among obligate carriers while not implying that every carrier is short.
  - reference: PMID:32720985
    reference_title: Short Stature is Progressive in Patients with Heterozygous NPR2 Mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Both mutant ANPRB proteins were normally expressed in HEK293T cells and
      exhibited dominant negative effects on wild-type ANPRB catalytic activity.
    explanation: >-
      Shows that carrier phenotype depends on allele class, since a
      dominant-negative allele leaves a heterozygote with less than half of
      normal receptor activity.
genetic:
- name: Biallelic NPR2 Loss-of-Function Variants
  gene_term:
    preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: >-
    Causative alleles include nonsense, frameshift, splice-site, synonymous
    splice-altering, and missense variants. Functional consequences are
    allele-specific and include abnormal splicing, endoplasmic-reticulum
    retention, and deficient guanylyl-cyclase activity.
  evidence:
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We sequenced DNA from 21 families affected by AMDM and found 4 nonsense
      mutations, 4 frameshift mutations, 2 splice-site mutations, and 11
      missense mutations.
    explanation: The landmark family series establishes the allelic spectrum of causative NPR2 variants.
  - reference: PMID:42442044
    reference_title: A synonymous NPR2 variant causes acromesomelic dysplasia through aberrant pre-mRNA splicing.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Functional analysis using patient-derived leukocyte RNA revealed
      aberrant splicing leading to partial exon truncation, frameshift, and
      premature termination of NPR2
    explanation: Patient-derived RNA establishes a synonymous splice-altering loss-of-function mechanism.
pathophysiology:
- name: Biallelic NPR2 Loss of Function
  description: >-
    Pathogenic variants on both NPR2 alleles reduce NPR-B receptor function.
    The alleles span truncating, splice-altering, and missense classes and
    initiate the shared AMDM mechanism.
  genes:
  - preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  evidence:
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We sequenced DNA from 21 families affected by AMDM and found 4 nonsense
      mutations, 4 frameshift mutations, 2 splice-site mutations, and 11
      missense mutations.
    explanation: Multiple biallelic variant classes were identified across 21 affected families.
  downstream:
  - target: Variant-Specific NPR-B Biogenesis and Catalytic Failure
    causal_link_type: DIRECT
    description: >-
      Individual NPR2 alleles directly impair transcript processing, receptor
      trafficking, or guanylyl-cyclase activity.
    evidence:
    - reference: PMID:42442044
      reference_title: A synonymous NPR2 variant causes acromesomelic dysplasia through aberrant pre-mRNA splicing.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Functional analysis using patient-derived leukocyte RNA revealed
        aberrant splicing leading to partial exon truncation, frameshift, and
        premature termination of NPR2
      explanation: A synonymous NPR2 allele directly produces an abnormal transcript and premature termination.
- name: Variant-Specific NPR-B Biogenesis and Catalytic Failure
  description: >-
    NPR2 variants use several proximal routes to receptor failure. Some cause
    aberrant transcripts or premature truncation; some missense receptors are
    retained in the endoplasmic reticulum; and functional assays of other
    missense alleles show markedly deficient guanylyl-cyclase activity. These
    are convergent allelic mechanisms, not competing disease hypotheses.
  genes:
  - preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  biological_processes:
  - preferred_term: Aberrant pre-mRNA splicing of NPR2
    term:
      id: GO:0008380
      label: RNA splicing
    modifier: ABNORMAL
  - preferred_term: Receptor delivery to the plasma membrane
    term:
      id: GO:0072659
      label: protein localization to plasma membrane
    modifier: DECREASED
  evidence:
  - reference: PMID:38078000
    reference_title: "Unveiling the pathogenic mechanisms of NPR2 missense variants: insights into the genotype-associated severity in acromesomelic dysplasia and short stature."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Our results indicate that variants p.Leu51Pro, p.Gly123Val, p.Leu314Arg,
      p.Arg388Gln have defective cellular trafficking, being sequestered within
      the endoplasmic reticulum (ER), and consequently impaired cGMP production
      ability.
    explanation: Functional testing demonstrates ER retention as one allele-specific route to receptor failure.
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Three missense mutations were tested in a functional assay and were found
      to have markedly deficient guanylyl cyclase activity.
    explanation: Functional assays in the landmark AMDM study establish deficient catalytic activity as a convergent consequence of missense alleles.
  downstream:
  - target: Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
    causal_link_type: DIRECT
    description: >-
      The diverse proximal receptor defects converge directly on reduced or
      absent CNP-stimulated cGMP production, with residual activity depending on
      the allele.
    evidence:
    - reference: PMID:38078000
      reference_title: "Unveiling the pathogenic mechanisms of NPR2 missense variants: insights into the genotype-associated severity in acromesomelic dysplasia and short stature."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Our results indicate that variants p.Leu51Pro, p.Gly123Val,
        p.Leu314Arg, p.Arg388Gln have defective cellular trafficking, being
        sequestered within the endoplasmic reticulum (ER), and consequently
        impaired cGMP production ability.
      explanation: The trafficking-defective variants directly show impaired cGMP production.
- name: Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
  description: >-
    NPR-B is a homodimeric receptor guanylyl cyclase that produces cytoplasmic
    cGMP after CNP binding. AMDM variants reduce or abolish this response rather
    than universally eliminating all activity.
  genes:
  - preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  molecular_functions:
  - preferred_term: guanylate cyclase activity
    term:
      id: GO:0004383
      label: guanylate cyclase activity
    modifier: DECREASED
  - preferred_term: natriuretic peptide receptor activity
    term:
      id: GO:0016941
      label: natriuretic peptide receptor activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: receptor guanylyl cyclase signaling pathway
    term:
      id: GO:0007168
      label: receptor guanylyl cyclase signaling pathway
    modifier: DECREASED
  - preferred_term: cGMP biosynthetic process
    term:
      id: GO:0006182
      label: cGMP biosynthetic process
    modifier: DECREASED
  - preferred_term: Activating phosphorylation of the NPR-B kinase-homology domain
    term:
      id: GO:0018105
      label: peptidyl-serine phosphorylation
  - preferred_term: NPR-B dephosphorylation by a PPP-family phosphatase
    term:
      id: GO:0006470
      label: protein dephosphorylation
  evidence:
  - reference: PMID:33986191
    reference_title: Phosphatase inhibition by LB-100 enhances BMN-111 stimulation of bone growth.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Because CNP activation of NPR2 requires that the receptor is
      phosphorylated on multiple serines and threonines (28, 29), FGF-induced
      NPR2 dephosphorylation lowers cGMP and opposes bone growth.
    explanation: >-
      Receptor phosphorylation state is a second determinant of NPR-B output
      alongside the variant itself, which is why this node carries both the
      activating phosphorylation and the opposing dephosphorylation.
  - reference: PMID:33986191
    reference_title: Phosphatase inhibition by LB-100 enhances BMN-111 stimulation of bone growth.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Measurements of cGMP production in chondrocytes of living tibias, and of
      NPR2 phosphorylation in primary chondrocytes, showed that LB-100
      counteracted FGF-induced dephosphorylation and inactivation of NPR2.
    explanation: >-
      Direct measurement of the phosphorylation-to-cGMP relationship in
      chondrocytes, and the demonstration that it is pharmacologically
      addressable.
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Three missense mutations were tested in a functional assay and were found
      to have markedly deficient guanylyl cyclase activity.
    explanation: The landmark functional assays directly show deficient receptor catalytic activity.
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Cells expressing HA-R388Q-NPRB showed negligible cGMP responses to C-type
      natriuretic peptide (CNP) stimulation, indicating that the mutation led
      to severe loss-of-function.
    explanation: A patient-associated receptor shows a negligible CNP-stimulated cGMP response.
  downstream:
  - target: Growth-Plate Proliferative and Hypertrophic Zone Dysfunction
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Reduced cGMP-dependent protein kinase II signaling
    - MEK/ERK disinhibition in the NPR2-deficient growth plate
    description: >-
      Reduced NPR-B/cGMP signaling alters downstream cGKII and MEK/ERK control,
      reducing proliferative and hypertrophic growth-plate zones.
    evidence:
    - reference: PMID:23065701
      reference_title: "A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Mutant tibiae have increased levels of the activated form of ERK1/2,
        consistent with the idea that natriuretic peptide receptor type 2
        (NPR2) signaling inhibits the activation of the MEK/ERK mitogen
        activated protein kinase pathway.
      explanation: The Npr2-deficient mouse connects receptor loss to ERK activation in tibiae.
    - reference: PMID:33106379
      reference_title: Biallelic cGMP-dependent type II protein kinase gene (PRKG2) variants cause a novel acromesomelic dysplasia.
      supports: SUPPORT
      evidence_source: OTHER
      snippet: >-
        C-type natriuretic peptide (CNP), its endogenous receptor, natriuretic
        peptide receptor-B (NPR-B), as well as its downstream mediator, cyclic
        guanosine monophosphate (cGMP) dependent protein kinase II (cGKII), have
        been shown to play a pivotal role in chondrogenic differentiation and
        endochondral bone growth.
      explanation: The PRKG2 study identifies cGKII as the downstream mediator linking NPR-B/cGMP to chondrogenic growth.
- name: Growth-Plate Proliferative and Hypertrophic Zone Dysfunction
  description: >-
    NPR2 deficiency reduces both proliferative and hypertrophic zones of the
    growth plate. Model evidence indicates altered zone organization without a
    generalized mineralization defect.
  cell_types:
  - preferred_term: growth plate cartilage chondrocyte
    term:
      id: CL:1000217
      label: growth plate cartilage chondrocyte
  - preferred_term: columnar chondrocyte
    term:
      id: CL:0000744
      label: columnar chondrocyte
  - preferred_term: hypertrophic chondrocyte
    term:
      id: CL:0000743
      label: hypertrophic chondrocyte
  biological_processes:
  - preferred_term: chondrocyte proliferation
    term:
      id: GO:0035988
      label: chondrocyte proliferation
    modifier: DECREASED
  - preferred_term: chondrocyte hypertrophy
    term:
      id: GO:0003415
      label: chondrocyte hypertrophy
    modifier: DECREASED
  - preferred_term: growth plate cartilage development
    term:
      id: GO:0003417
      label: growth plate cartilage development
    modifier: DYSREGULATED
  - preferred_term: CNP-dependent restraint of the ERK1/2 cascade
    term:
      id: GO:0070373
      label: negative regulation of ERK1 and ERK2 cascade
    modifier: DECREASED
  - preferred_term: Fibroblast growth factor receptor signaling pathway
    term:
      id: GO:0008543
      label: fibroblast growth factor receptor signaling pathway
    modifier: ABNORMAL
  locations:
  - preferred_term: growth plate cartilage
    term:
      id: UBERON:0004129
      label: growth plate cartilage
  evidence:
  - reference: PMID:23065701
    reference_title: "A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We determined that the loss of Npr2 causes a reduction in the hypertrophic
      and proliferative zones of the growth plate, but mineralization of
      skeletal elements is normal.
    explanation: The mouse model directly demonstrates reduced growth-plate zones with preserved mineralization.
  - reference: PMID:15869918
    reference_title: Complementary antagonistic actions between C-type natriuretic peptide and the MAPK pathway through FGFR-3 in ATDC5 cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      CNP and 8-bromo-cGMP strongly and dose-dependently inhibited the induction
      of ERK phosphorylation by FGF2 and FGF18 without changing the level of
      FGFR-3
    explanation: >-
      Establishes the CNP-cGMP arm as a restraint on FGF-driven ERK activation
      in chondrocytes, the restraint that AMDM removes.
  - reference: PMID:15869918
    reference_title: Complementary antagonistic actions between C-type natriuretic peptide and the MAPK pathway through FGFR-3 in ATDC5 cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In the organ-cultured fetal mouse tibias, CNP and FGF18 counteracted on
      the longitudinal bone growth, and both the size and number of hypertrophic
      chondrocytes.
    explanation: >-
      Shows the two arms acting in opposition on hypertrophic chondrocyte number
      and size in intact tibia, the growth-plate variables this node concerns.
  downstream:
  - target: Impaired Endochondral Longitudinal Bone Growth
    causal_link_type: DIRECT
    description: >-
      Reduced proliferative and hypertrophic zones directly limit longitudinal
      elongation of endochondral skeletal elements.
    evidence:
    - reference: PMID:25319082
      reference_title: "The cn/cn dwarf mouse. Histomorphometric, ultrastructural, and radiographic study in mutants corresponding to human acromesomelic dysplasia Maroteaux type (AMDM)."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The disorder causes a shortened physeal hypertrophic zone but normal
        ultrastructure of cn/cn chondrocytes points to abnormality primarily
        affecting the hypertrophic zone rather than a structural cell or matrix
        synthesis problem.
      explanation: The physeal-zone defect provides the direct cellular basis for reduced longitudinal growth.
- name: Impaired Endochondral Longitudinal Bone Growth
  description: >-
    Growth-plate-zone dysfunction impairs endochondral bone elongation rather
    than skeletal mineralization. This produces severe short-limb stature and
    regionally patterned appendicular and axial dysplasia.
  biological_processes:
  - preferred_term: Endochondral ossification
    term:
      id: GO:0001958
      label: endochondral ossification
    modifier: DECREASED
  - preferred_term: Growth plate cartilage development
    term:
      id: GO:0003417
      label: growth plate cartilage development
    modifier: ABNORMAL
  - preferred_term: endochondral bone growth
    term:
      id: GO:0003416
      label: endochondral bone growth
    modifier: DECREASED
  locations:
  - preferred_term: growth plate cartilage
    term:
      id: UBERON:0004129
      label: growth plate cartilage
  evidence:
  - reference: PMID:25319082
    reference_title: "The cn/cn dwarf mouse. Histomorphometric, ultrastructural, and radiographic study in mutants corresponding to human acromesomelic dysplasia Maroteaux type (AMDM)."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The cn/cn dwarf mouse is caused by a loss-of-function mutation in the
      natriuretic peptide receptor 2 (NPR-2) gene which helps positively
      regulate endochondral longitudinal bone growth.
    explanation: The Npr2 model directly links receptor loss to endochondral longitudinal bone growth.
  downstream:
  - target: Severe Disproportionate Short-Limb Short Stature
    causal_link_type: DIRECT
    description: Reduced longitudinal growth of the limbs produces disproportionate short-limb stature.
    evidence:
    - reference: PMID:35368703
      reference_title: "Novel Loss-of-Function Mutations in NPR2 Cause Acromesomelic Dysplasia, Maroteaux Type."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare skeletal
        dysplasia characterized by severe disproportionate short stature, short
        hands and feet, normal intelligence, and facial dysmorphism.
      explanation: The human clinical series identifies severe disproportionate stature as a core consequence.
  - target: Acromesomelic Limb Elongation Deficit
    causal_link_type: DIRECT
    description: The longitudinal-growth defect is regionally greatest in middle and distal limb segments.
    evidence:
    - reference: PMID:34162036
      reference_title: "Acromesomelic dysplasia-Maroteaux type, nine patients with two novel NPR2 variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        It is a rare type of dwarfism characterized by shortening of the middle
        and distal segments of the limbs with spondylar dysplasia.
      explanation: A nine-patient series directly defines the acromesomelic distribution.
  - target: Hand and Foot Epiphyseal and Tubular-Bone Dysplasia
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Region-specific growth-plate and epiphyseal development
    description: Growth failure of distal tubular bones and epiphyses produces the characteristic hand and foot pattern.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Imaging of the upper limbs revealed mild mesomelic shortening, short and
        broad phalanges and metacarpals with typical cone shaped epiphyses.
      explanation: Human radiographs document the distal tubular-bone and epiphyseal pattern.
  - target: Vertebral Growth Dysplasia
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Region-specific vertebral endochondral growth
    description: Impaired vertebral endochondral growth produces characteristic body shape and pedicle spacing.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Vertebral bodies were pear shaped with a shorter posterior versus
        anterior height.
      explanation: Human radiographs directly document vertebral growth dysplasia.
  - target: Long-Bone Modeling Deformity
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Region-specific metaphyseal and diaphyseal modeling
    description: Uneven longitudinal and modeling growth contributes to radial and other long-bone bowing.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius
      explanation: The clinical radiographic comparison documents long-bone modeling abnormalities.
  - target: Frontal Bossing
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Frontal bossing is associated with AMDM, but the intervening craniofacial mechanism is unresolved.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002007 | Frontal bossing | Frequent (79-30%)"
      explanation: Orphanet supports association of frontal bossing without establishing a direct mechanism.
  - target: Depressed Nasal Bridge
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: A depressed nasal bridge is associated with AMDM, but its mechanistic path is unresolved.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0005280 | Depressed nasal bridge | Frequent (79-30%)"
      explanation: Orphanet supports the phenotype association without establishing causation.
  - target: Joint Hypermobility
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Joint hypermobility is associated with AMDM, but no specific connective-tissue mechanism is established.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0001382 | Joint hypermobility | Frequent (79-30%)"
      explanation: Orphanet supports the association while the causal intermediates remain unknown.
- name: Acromesomelic Limb Elongation Deficit
  description: >-
    The middle and distal limb segments are preferentially shortened, producing
    the defining acromesomelic distribution.
  biological_processes:
  - preferred_term: Limb morphogenesis
    term:
      id: GO:0035108
      label: limb morphogenesis
    modifier: ABNORMAL
  - preferred_term: Endochondral bone growth
    term:
      id: GO:0003416
      label: endochondral bone growth
    modifier: DECREASED
  evidence:
  - reference: PMID:34162036
    reference_title: "Acromesomelic dysplasia-Maroteaux type, nine patients with two novel NPR2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is a rare type of dwarfism characterized by shortening of the middle
      and distal segments of the limbs with spondylar dysplasia.
    explanation: The nine-patient series defines the segmental pattern.
  downstream:
  - target: Acromesomelic Limb Shortening
    causal_link_type: DIRECT
    description: Preferential middle- and distal-segment growth failure directly produces acromesomelia.
    evidence:
    - reference: PMID:34162036
      reference_title: "Acromesomelic dysplasia-Maroteaux type, nine patients with two novel NPR2 variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        It is a rare type of dwarfism characterized by shortening of the middle
        and distal segments of the limbs with spondylar dysplasia.
      explanation: The observed shortening directly supports the phenotype edge.
  - target: Short Forearms
    causal_link_type: DIRECT
    description: Mesomelic growth failure directly shortens the forearms.
    evidence:
    - reference: PMID:30359775
      reference_title: Novel variants in natriuretic peptide receptor 2 in unrelated patients with acromesomelic dysplasia type Maroteaux.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Acromesomelic dysplasia type Maroteaux (AMDM) is characterized by
        extreme shortening of the forelimbs and disproportionate short stature.
      explanation: The clinical series directly describes extreme forelimb shortening.
- name: Hand and Foot Epiphyseal and Tubular-Bone Dysplasia
  description: >-
    Abnormal distal tubular-bone growth produces short broad metacarpals,
    metatarsals and phalanges, with cone-shaped phalangeal epiphyses and short
    broad hands and feet.
  biological_processes:
  - preferred_term: Bone morphogenesis
    term:
      id: GO:0060349
      label: bone morphogenesis
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Imaging of the upper limbs revealed mild mesomelic shortening, short and
      broad phalanges and metacarpals with typical cone shaped epiphyses.
    explanation: The radiographic description defines this distal skeletal branch.
  downstream:
  - target: Brachydactyly
    causal_link_type: DIRECT
    description: Short phalanges and metacarpals directly produce brachydactyly.
    evidence:
    - reference: PMID:32694885
      reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: She had acromesomelic shortening of limbs and severe brachydactyly.
      explanation: The molecularly confirmed case directly documents brachydactyly.
  - target: Cone-Shaped Epiphyses
    causal_link_type: DIRECT
    description: Epiphyseal dysplasia directly manifests as cone-shaped phalangeal epiphyses.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        DP left hand (A) with broadening and shortening of the bones, and
        significant coned appearance of the epiphyses
      explanation: The radiograph directly shows coned epiphyses.
  - target: Short Metacarpals
    causal_link_type: DIRECT
    description: Tubular-bone growth failure directly shortens and broadens the metacarpals.
    evidence:
    - reference: PMID:32694885
      reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Radiological examination showed that her metacarpals and phalanges were
        short and wide
      explanation: The case directly documents short, wide metacarpals.
  - target: Short Feet
    causal_link_type: DIRECT
    description: Distal tubular-bone growth failure directly produces short broad feet.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Photographs showing brachydactyly with broad fingers (A) and short, broad toes and feet (B).
      explanation: Clinical photographs directly document the short broad foot phenotype.
- name: Vertebral Growth Dysplasia
  description: >-
    Vertebral endochondral growth is mildly affected, producing flattened or
    pear-shaped bodies, posterior-anterior height differences, and failure of
    normal widening of lumbar interpedicular distances.
  biological_processes:
  - preferred_term: Endochondral bone growth
    term:
      id: GO:0003416
      label: endochondral bone growth
    modifier: DECREASED
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Lateral (D) and anteroposterior (E) radiographs of the lower spine with
      pear shaped vertebral bodies with shorter posterior than anterior heights
      and failure of widening of the lumbar interpedicular distances with some
      shortening of the pedicles.
    explanation: The spinal radiographs define the vertebral branch.
  downstream:
  - target: Platyspondyly
    causal_link_type: DIRECT
    description: Vertebral growth dysplasia directly flattens vertebral bodies.
    evidence:
    - reference: PMID:32694885
      reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Her vertebral bodies were mildly flattened
      explanation: A confirmed case directly documents flattened vertebral bodies.
  - target: Lumbar Interpedicular Narrowing
    causal_link_type: DIRECT
    description: Abnormal lumbar vertebral and pedicle growth directly prevents normal caudal widening.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: failure of widening of the lumbar interpedicular distances with some shortening of the pedicles.
      explanation: The radiographic report directly documents the lumbar finding.
  - target: Ovoid Vertebral Bodies
    causal_link_type: DIRECT
    description: Altered vertebral body growth produces an ovoid or pear-shaped contour.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Pear shaped vertebral bodies with a shorter posterior versus anterior height
      explanation: The case provides a direct vertebral-shape description.
  - target: Scoliosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Scoliosis is associated with vertebral dysplasia, but its specific AMDM intermediates are unresolved.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002650 | Scoliosis | Frequent (79-30%)"
      explanation: Orphanet supports the phenotype association.
  - target: Kyphosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Kyphosis is associated with AMDM vertebral dysplasia, but its causal intermediates are unresolved.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0002808 | Kyphosis | Frequent (79-30%)"
      explanation: Orphanet supports the phenotype association.
  - target: Hyperlordosis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: Hyperlordosis is associated with AMDM, but its causal intermediates are unresolved.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0003307 | Hyperlordosis | Frequent (79-30%)"
      explanation: Orphanet supports the phenotype association.
- name: Long-Bone Modeling Deformity
  description: >-
    Regionally uneven long-bone growth and metaphyseal modeling contribute to
    radial and generalized long-bone bowing.
  biological_processes:
  - preferred_term: Bone morphogenesis
    term:
      id: GO:0060349
      label: bone morphogenesis
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius
    explanation: The radiographic comparison documents the long-bone modeling pattern.
  downstream:
  - target: Radial Bowing
    causal_link_type: DIRECT
    description: Abnormal radial modeling directly produces radial bowing.
    evidence:
    - reference: PMID:34178199
      reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius
      explanation: The report directly documents radial bowing.
  - target: Bowing of Long Bones
    causal_link_type: DIRECT
    description: Abnormal long-bone modeling manifests as bowing beyond the radius in some affected individuals.
    evidence:
    - reference: ORPHA:40
      reference_title: Acromesomelic dysplasia, Maroteaux type
      supports: SUPPORT
      evidence_source: OTHER
      snippet: "HP:0006487 | Bowing of the long bones | Frequent (79-30%)"
      explanation: Orphanet directly associates long-bone bowing with AMDM.
mechanistic_hypotheses:
- hypothesis_group_id: chondrocyte_cgmp_deficit_convergence
  hypothesis_label: Chondrocyte cGMP-Deficit Convergence Model
  status: CANONICAL
  description: >-
    The unit that matters for growth-plate output is chondrocyte cGMP, and AMDM
    is one of several ways to lower it. Achondroplasia lowers it from above by
    activating FGFR3; AMDM lowers it by disabling the cyclase that makes it; the
    PRKG2 disorder leaves it intact but removes the kinase that reads it. The
    model earns its keep by being predictive rather than descriptive: it is why
    a CNP analogue developed for achondroplasia was expected to help NPR2
    deficiency, and a 2026 basket trial found that it does in heterozygous NPR2
    carriers.
  evidence:
  - reference: PMID:33986191
    reference_title: Phosphatase inhibition by LB-100 enhances BMN-111 stimulation of bone growth.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Activating mutations in fibroblast growth factor receptor 3 (FGFR3) and
      inactivating mutations in the natriuretic peptide receptor 2 (NPR2)
      guanylyl cyclase both result in decreased production of cyclic GMP in
      chondrocytes and severe short stature
    explanation: States the convergence of two different genetic lesions on one biochemical deficit.
  - reference: PMID:41967490
    reference_title: A phase II basket trial of vosoritide in children with RASopathies, ACAN, and NPR2 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Vosoritide led to marked increases in growth velocity in children with
      RASopathies, ACAN, and NPR2 deficiency
    explanation: >-
      The convergence model's therapeutic prediction holds across several
      genetic causes. Support is partial for AMDM specifically because the NPR2
      arm enrolled heterozygous carriers, not biallelic disease.
- hypothesis_group_id: npr_b_phosphoregulation_modifier
  hypothesis_label: NPR-B Phosphoregulation Modifier Model
  status: EMERGING
  description: >-
    CNP can only activate NPR-B when the receptor is phosphorylated on several
    serines and threonines, and FGFR3 signalling drives a PPP-family phosphatase
    that strips those sites. This makes the receptor's phosphorylation state a
    second, variant-independent determinant of how much cGMP an AMDM growth
    plate makes, and predicts two things worth testing: that FGF tone modifies
    severity in patients carrying residual-activity alleles, and that a
    phosphatase inhibitor should raise output from those same alleles. Both
    predictions currently rest on mouse achondroplasia models. Nothing has been
    measured in an NPR2-mutant background, where the relevant question is
    whether a partially active mutant receptor is still subject to the same
    regulation.
  evidence:
  - reference: PMID:33986191
    reference_title: Phosphatase inhibition by LB-100 enhances BMN-111 stimulation of bone growth.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      because FGFR3 signaling decreases NPR2 activity by dephosphorylating the
      NPR2 protein
    explanation: States the regulatory relationship the model rests on.
  - reference: PMID:15869918
    reference_title: Complementary antagonistic actions between C-type natriuretic peptide and the MAPK pathway through FGFR-3 in ATDC5 cells.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We found that FGFs inhibited CNP-stimulated cGMP production by disrupting
      the signaling pathway through GC-B while CNP antagonized the activation of
      the MAPK cascade by FGFs.
    explanation: >-
      Independently documents the reciprocal cross-talk in chondrocytes, with
      FGF suppressing CNP-driven cGMP production.
- hypothesis_group_id: allele_dominant_negative_model
  hypothesis_label: Dominant-Negative Allele Model of Carrier Short Stature
  status: EMERGING
  description: >-
    Carrier short stature has usually been read as haploinsufficiency, but at
    least some AMDM missense alleles produce a normally expressed receptor that
    poisons the wild-type subunit within the homodimer. On that reading a
    carrier's residual activity is below fifty percent, which would explain both
    why heterozygous relatives are short and why their height z-scores drift
    downward with age rather than tracking a fixed deficit. The prediction that
    separates this from haploinsufficiency is that truncating alleles should
    give milder carrier phenotypes than dominant-negative missense alleles; that
    comparison has not been made systematically.
  evidence:
  - reference: PMID:32720985
    reference_title: Short Stature is Progressive in Patients with Heterozygous NPR2 Mutations.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Both mutant ANPRB proteins were normally expressed in HEK293T cells and
      exhibited dominant negative effects on wild-type ANPRB catalytic activity.
    explanation: Demonstrates a dominant-negative effect for two AMDM-causing missense alleles.
  - reference: PMID:32720985
    reference_title: Short Stature is Progressive in Patients with Heterozygous NPR2 Mutations.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Height z-scores progressively and significantly decreased as
      NPR2-heterozygous children matured, while remaining constant in their
      wild-type siblings.
    explanation: >-
      The progressive carrier phenotype within one family is the clinical
      observation the model is meant to explain.
phenotypes:
- category: Skeletal
  name: Severe Disproportionate Short-Limb Short Stature
  description: >-
    Severe short stature is disproportionate, with the limbs more affected than
    the trunk and the middle and distal limb segments most affected. Final
    height is usually below 120 cm, although milder cases occur.
  phenotype_term:
    preferred_term: Disproportionate short-limb short stature
    term:
      id: HP:0008873
      label: Disproportionate short-limb short stature
  evidence:
  - reference: PMID:35368703
    reference_title: "Novel Loss-of-Function Mutations in NPR2 Cause Acromesomelic Dysplasia, Maroteaux Type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare skeletal
      dysplasia characterized by severe disproportionate short stature, short
      hands and feet, normal intelligence, and facial dysmorphism.
    explanation: The clinical report identifies severe disproportionate stature as a defining phenotype.
- category: Skeletal
  name: Acromesomelic Limb Shortening
  frequency: FREQUENT
  description: >-
    Limb shortening predominantly affects the middle and distal segments,
    including the forearms, lower legs, hands, and feet.
  phenotype_term:
    preferred_term: Acromesomelia
    term:
      id: HP:0003086
      label: Acromesomelia
  evidence:
  - reference: PMID:34162036
    reference_title: "Acromesomelic dysplasia-Maroteaux type, nine patients with two novel NPR2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is a rare type of dwarfism characterized by shortening of the middle
      and distal segments of the limbs with spondylar dysplasia.
    explanation: A nine-patient series directly describes the acromesomelic pattern.
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003086 | Acromesomelia | Frequent (79-30%)"
    explanation: Orphanet supplies the frequency classification for acromesomelia.
- category: Skeletal
  name: Brachydactyly
  frequency: FREQUENT
  description: >-
    Short broad phalanges and metacarpals produce marked brachydactyly, which
    can remain recognizable even in relatively mild AMDM.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
  evidence:
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: She had acromesomelic shortening of limbs and severe brachydactyly.
    explanation: The molecularly confirmed case directly documents severe brachydactyly.
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001156 | Brachydactyly | Frequent (79-30%)"
    explanation: Orphanet supplies the frequency classification for brachydactyly.
- category: Skeletal
  name: Cone-Shaped Epiphyses
  description: >-
    Cone-shaped epiphyses of the phalanges are a characteristic hand
    radiographic finding.
  phenotype_term:
    preferred_term: Cone-shaped epiphyses of the phalanges of the hand
    term:
      id: HP:0010230
      label: Cone-shaped epiphyses of the phalanges of the hand
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      DP left hand (A) with broadening and shortening of the bones, and
      significant coned appearance of the epiphyses
    explanation: The hand radiograph directly demonstrates coned epiphyses.
- category: Skeletal
  name: Short Metacarpals
  description: The metacarpals are characteristically short and broad.
  phenotype_term:
    preferred_term: Short metacarpal
    term:
      id: HP:0010049
      label: Short metacarpal
  evidence:
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiological examination showed that her metacarpals and phalanges were
      short and wide
    explanation: Radiographs directly document short, broad metacarpals.
- category: Skeletal
  name: Short Feet
  description: The feet and toes are characteristically short and broad.
  phenotype_term:
    preferred_term: Short foot
    term:
      id: HP:0001773
      label: Short foot
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Photographs showing brachydactyly with broad fingers (A) and short, broad toes and feet (B).
    explanation: Clinical photographs directly document short broad toes and feet.
- category: Skeletal
  name: Platyspondyly
  description: Mild vertebral-body flattening is part of the axial skeletal involvement.
  phenotype_term:
    preferred_term: Platyspondyly
    term:
      id: HP:0000926
      label: Platyspondyly
  evidence:
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Her vertebral bodies were mildly flattened
    explanation: The confirmed case directly documents mild vertebral flattening.
- category: Skeletal
  name: Lumbar Interpedicular Narrowing
  description: >-
    The normal caudal widening of lumbar interpedicular distances may fail, with
    associated pedicle shortening.
  phenotype_term:
    preferred_term: Lumbar interpedicular narrowing
    term:
      id: HP:0008486
      label: Lumbar interpedicular narrowing
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: failure of widening of the lumbar interpedicular distances with some shortening of the pedicles.
    explanation: The spinal radiographs directly demonstrate the lumbar finding.
- category: Skeletal
  name: Radial Bowing
  description: Radial bowing can accompany distal radial hypoplasia and metaphyseal flaring.
  phenotype_term:
    preferred_term: Radial bowing
    term:
      id: HP:0002986
      label: Radial bowing
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius
    explanation: The clinical radiographic comparison directly lists radial bowing.
- category: Skeletal
  name: Short Forearms
  description: Forearm shortening reflects the mesomelic component of AMDM.
  phenotype_term:
    preferred_term: Short forearm
    term:
      id: HP:0005773
      label: Short forearm
  evidence:
  - reference: PMID:30359775
    reference_title: Novel variants in natriuretic peptide receptor 2 in unrelated patients with acromesomelic dysplasia type Maroteaux.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acromesomelic dysplasia type Maroteaux (AMDM) is characterized by
      extreme shortening of the forelimbs and disproportionate short stature.
    explanation: The patient series directly describes extreme forelimb shortening.
- category: Craniofacial
  name: Frontal Bossing
  frequency: FREQUENT
  description: >-
    Frontal prominence is a mild and variable craniofacial feature rather than
    a required diagnostic finding.
  phenotype_term:
    preferred_term: Frontal bossing
    term:
      id: HP:0002007
      label: Frontal bossing
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002007 | Frontal bossing | Frequent (79-30%)"
    explanation: Orphanet lists frontal bossing as frequent.
- category: Craniofacial
  name: Depressed Nasal Bridge
  frequency: FREQUENT
  description: A depressed nasal bridge can occur as a mild and variable craniofacial feature.
  phenotype_term:
    preferred_term: Depressed nasal bridge
    term:
      id: HP:0005280
      label: Depressed nasal bridge
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0005280 | Depressed nasal bridge | Frequent (79-30%)"
    explanation: Orphanet lists depressed nasal bridge as frequent.
- category: Skeletal
  name: Scoliosis
  frequency: FREQUENT
  description: Lateral spinal curvature occurs in association with the axial skeletal dysplasia.
  phenotype_term:
    preferred_term: Scoliosis
    term:
      id: HP:0002650
      label: Scoliosis
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002650 | Scoliosis | Frequent (79-30%)"
    explanation: Orphanet lists scoliosis as frequent.
- category: Skeletal
  name: Kyphosis
  frequency: FREQUENT
  description: Increased thoracic curvature is among the reported spinal features.
  phenotype_term:
    preferred_term: Kyphosis
    term:
      id: HP:0002808
      label: Kyphosis
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0002808 | Kyphosis | Frequent (79-30%)"
    explanation: Orphanet lists kyphosis as frequent.
- category: Skeletal
  name: Hyperlordosis
  frequency: FREQUENT
  description: Increased lumbar lordosis is among the reported spinal features.
  phenotype_term:
    preferred_term: Hyperlordosis
    term:
      id: HP:0003307
      label: Hyperlordosis
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003307 | Hyperlordosis | Frequent (79-30%)"
    explanation: Orphanet lists hyperlordosis as frequent.
- category: Skeletal
  name: Ovoid Vertebral Bodies
  frequency: FREQUENT
  description: Vertebral bodies may have an ovoid or pear-shaped contour with reduced posterior height.
  phenotype_term:
    preferred_term: Ovoid vertebral bodies
    term:
      id: HP:0003300
      label: Ovoid vertebral bodies
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Pear shaped vertebral bodies with a shorter posterior versus anterior height
    explanation: The direct radiographic description supports altered vertebral shape.
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0003300 | Ovoid vertebral bodies | Frequent (79-30%)"
    explanation: Orphanet supplies the frequency classification for ovoid vertebral bodies.
- category: Skeletal
  name: Bowing of Long Bones
  frequency: FREQUENT
  description: Long-bone bowing is a frequent radiographic feature.
  phenotype_term:
    preferred_term: Bowing of the long bones
    term:
      id: HP:0006487
      label: Bowing of the long bones
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0006487 | Bowing of the long bones | Frequent (79-30%)"
    explanation: Orphanet lists bowing of the long bones as frequent.
- category: Skeletal
  name: Joint Hypermobility
  frequency: FREQUENT
  description: Joint hypermobility is reported, but its tissue-level mechanism is not established.
  phenotype_term:
    preferred_term: Joint hypermobility
    term:
      id: HP:0001382
      label: Joint hypermobility
  evidence:
  - reference: ORPHA:40
    reference_title: Acromesomelic dysplasia, Maroteaux type
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "HP:0001382 | Joint hypermobility | Frequent (79-30%)"
    explanation: Orphanet lists joint hypermobility as frequent.
imaging_findings:
- name: Cone-Shaped Phalangeal Epiphyses on Hand Radiographs
  modality: XRAY
  description: Hand radiographs show cone-shaped epiphyses with broadening and shortening of the phalanges.
  imaging_finding_term:
    preferred_term: Cone-shaped epiphyses of the phalanges of the hand
    term:
      id: HP:0010230
      label: Cone-shaped epiphyses of the phalanges of the hand
  diagnostic: false
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      DP left hand (A) with broadening and shortening of the bones, and
      significant coned appearance of the epiphyses
    explanation: The hand radiograph directly demonstrates the finding.
- name: Short and Broad Metacarpals and Phalanges on Hand Radiographs
  modality: XRAY
  description: Hand radiographs show marked shortening and broadening of metacarpals and phalanges.
  imaging_finding_term:
    preferred_term: Short metacarpal
    term:
      id: HP:0010049
      label: Short metacarpal
  diagnostic: false
  evidence:
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Radiological examination showed that her metacarpals and phalanges were
      short and wide
    explanation: The case directly documents the hand-radiograph finding.
- name: Platyspondyly on Spine Radiographs
  modality: XRAY
  description: Lateral spine radiographs can show mild vertebral-body flattening.
  imaging_finding_term:
    preferred_term: Platyspondyly
    term:
      id: HP:0000926
      label: Platyspondyly
  diagnostic: false
  evidence:
  - reference: PMID:32694885
    reference_title: "A novel NPR2 mutation (p.Arg388Gln) in a patient with acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Her vertebral bodies were mildly flattened
    explanation: The lateral-spine finding directly supports platyspondyly.
- name: Lumbar Interpedicular Narrowing on Spine Radiographs
  modality: XRAY
  description: Anteroposterior lumbar radiographs show failure of normal interpedicular widening and shortened pedicles.
  imaging_finding_term:
    preferred_term: Lumbar interpedicular narrowing
    term:
      id: HP:0008486
      label: Lumbar interpedicular narrowing
  diagnostic: false
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: failure of widening of the lumbar interpedicular distances with some shortening of the pedicles.
    explanation: The spinal radiographs directly document this finding.
- name: Radial Bowing on Limb Radiographs
  modality: XRAY
  description: Limb radiographs can show radial bowing with metaphyseal flaring or distal radial hypoplasia.
  imaging_finding_term:
    preferred_term: Radial bowing
    term:
      id: HP:0002986
      label: Radial bowing
  diagnostic: false
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Radial bowing, flared metaphysis and occasional hypoplasia of the distal radius
    explanation: The clinical radiographic comparison directly lists radial bowing.
- name: Ovoid or Pear-Shaped Vertebral Bodies on Spine Radiographs
  modality: XRAY
  description: Vertebral bodies may be ovoid or pear-shaped with shorter posterior than anterior height.
  imaging_finding_term:
    preferred_term: Ovoid vertebral bodies
    term:
      id: HP:0003300
      label: Ovoid vertebral bodies
  diagnostic: false
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Pear shaped vertebral bodies with a shorter posterior versus anterior height
    explanation: The direct radiographic description supports the finding.
animal_models:
- species: Mus musculus
  genotype: Npr2(cn/cn) loss-of-function
  description: >-
    The cn/cn mouse has Npr2 loss of function and recapitulates disproportionate
    dwarfism with a shortened physeal hypertrophic zone. Chondrocyte
    ultrastructure is preserved, supporting a growth-plate-zone defect rather
    than a primary matrix-synthesis abnormality.
  genes:
  - preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  evidence:
  - reference: PMID:25319082
    reference_title: "The cn/cn dwarf mouse. Histomorphometric, ultrastructural, and radiographic study in mutants corresponding to human acromesomelic dysplasia Maroteaux type (AMDM)."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The cn/cn dwarf mouse is caused by a loss-of-function mutation in the
      natriuretic peptide receptor 2 (NPR-2) gene which helps positively
      regulate endochondral longitudinal bone growth.
    explanation: The study establishes cn/cn as an Npr2 loss-of-function skeletal model.
- species: Mus musculus
  genotype: Npr2(pwe/pwe) 4-bp deletion
  description: >-
    The peewee mouse carries a truncating Npr2 deletion and models AMDM skeletal
    growth failure. Increased activated ERK1/2 in mutant tibiae and rescue of
    fetal tibia explants by MEK inhibitors provide preclinical pathway evidence;
    they do not establish a human AMDM treatment.
  genes:
  - preferred_term: NPR2
    term:
      id: hgnc:7944
      label: NPR2
  evidence:
  - reference: PMID:23065701
    reference_title: "A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The Npr2(pwe/pwe) mouse is a model for the human skeletal dysplasia
      acromesomelic dysplasia, Maroteaux type (AMDM).
    explanation: The publication explicitly identifies the peewee mouse as an AMDM model.
  - reference: PMID:23065701
    reference_title: "A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Treatment of fetal tibiae explants with mitogen activated protein kinase
      1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth
      defect, providing a promising foundation for skeletal dysplasia
      therapeutics.
    explanation: The fetal-tibia explant result is preclinical evidence for MEK/ERK pathway modulation.
diagnosis:
- name: Characteristic Physical Examination
  description: >-
    Examination identifies disproportionate short-limb stature with
    acromesomelic shortening, brachydactyly, and short broad hands and feet.
    Craniofacial findings are mild and variable; normal intelligence is typical.
  diagnosis_term:
    preferred_term: physical examination
    term:
      id: NCIT:C20989
      label: Physical Examination
  evidence:
  - reference: PMID:35368703
    reference_title: "Novel Loss-of-Function Mutations in NPR2 Cause Acromesomelic Dysplasia, Maroteaux Type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acromesomelic dysplasia, Maroteaux type (AMDM) is a rare skeletal
      dysplasia characterized by severe disproportionate short stature, short
      hands and feet, normal intelligence, and facial dysmorphism.
    explanation: The clinical description supports the characteristic examination pattern.
- name: Skeletal Radiographic Evaluation
  description: >-
    Skeletal radiographs assess mesomelic shortening, short broad metacarpals
    and phalanges, cone-shaped epiphyses, vertebral flattening or pear shape,
    lumbar interpedicular narrowing, and long-bone bowing. The pattern can
    support diagnosis even when stature is only mildly affected.
  diagnosis_term:
    preferred_term: radiograph imaging procedure
    term:
      id: NCIT:C38101
      label: X-Ray Imaging
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Given these findings, a diagnosis of AMDM should be considered in
      individuals with characteristic radiological findings, even if stature is
      only modestly affected.
    explanation: The report directly supports diagnostic use of the radiographic pattern.
- name: Biallelic NPR2 Molecular Confirmation
  description: >-
    Molecular genetic testing confirms the diagnosis by identifying pathogenic
    or likely pathogenic variants affecting both NPR2 alleles. Transcript-level
    analysis can resolve suspected splice effects, including synonymous
    variants.
  diagnosis_term:
    preferred_term: molecular genetic testing
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:15146390
    reference_title: "Mutations in the transmembrane natriuretic peptide receptor NPR-B impair skeletal growth and cause acromesomelic dysplasia, type Maroteaux."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We sequenced DNA from 21 families affected by AMDM and found 4 nonsense
      mutations, 4 frameshift mutations, 2 splice-site mutations, and 11
      missense mutations.
    explanation: The landmark study establishes biallelic NPR2 variant detection as the molecular basis of AMDM.
  - reference: PMID:42442044
    reference_title: A synonymous NPR2 variant causes acromesomelic dysplasia through aberrant pre-mRNA splicing.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Functional analysis using patient-derived leukocyte RNA revealed
      aberrant splicing leading to partial exon truncation, frameshift, and
      premature termination of NPR2
    explanation: Patient-derived RNA demonstrates the value of transcript analysis for a splice-altering synonymous allele.
differential_diagnoses:
- name: PRKG2-Related Acromesomelic Dysplasia
  description: >-
    Biallelic PRKG2 loss causes a downstream cGMP-pathway skeletal dysplasia with
    severe short stature, acromesomelia, brachydactyly, platyspondyly, and
    progressive metaphyseal changes, closely overlapping NPR2-related AMDM.
  distinguishing_features:
  - Biallelic PRKG2 variants, rather than biallelic NPR2 variants, establish this diagnosis.
  - Progressively increasing metaphyseal long-bone alterations were prominent in the initial PRKG2 cases.
  evidence:
  - reference: PMID:33106379
    reference_title: Biallelic cGMP-dependent type II protein kinase gene (PRKG2) variants cause a novel acromesomelic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Exome sequencing was performed in two girls with severe short stature due
      to acromesomelic limb shortening, brachydactyly, mild to moderate
      platyspondyly and progressively increasing metaphyseal alterations of the
      long bones.
    explanation: The founding PRKG2 series documents the overlapping phenotype and progressive metaphyseal pattern.
  - reference: PMID:33106379
    reference_title: Biallelic cGMP-dependent type II protein kinase gene (PRKG2) variants cause a novel acromesomelic dysplasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: Two homozygous PRKG2 variants, a nonsense and a frameshift, were identified.
    explanation: The genetic finding distinguishes this downstream-pathway disorder from NPR2-related AMDM.
- name: Acromesomelic Dysplasia, Hunter-Thompson Type
  disease_term:
    preferred_term: acromesomelic dysplasia 2C, Hunter-Thompson type
    term:
      id: MONDO:0008717
      label: acromesomelic dysplasia 2C, Hunter-Thompson type
  description: >-
    Hunter-Thompson acromesomelic dysplasia belongs to the GDF5/BMPR1B spectrum
    and overlaps AMDM in distal limb shortening and brachydactyly.
  distinguishing_features:
  - Craniofacial and axial skeleton are generally unaffected, unlike the vertebral and mild craniofacial findings in AMDM.
  - Lower limbs are more severely affected; square phalanges, a single fifth-digit phalanx, ankle dislocation, or radial-head dislocation can occur.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In AMDH the lower limbs are more severely affected, phalanges tend to
      square and there may be a single phalangeal bone in the fifth digit. Ankle
      dislocation is common and radial head dislocation may be present
    explanation: The review supplies the distinguishing Hunter-Thompson radiographic pattern.
- name: Acromesomelic Dysplasia, Grebe Type
  disease_term:
    preferred_term: acromesomelic dysplasia 2A
    term:
      id: MONDO:0008703
      label: acromesomelic dysplasia 2A
  description: >-
    Grebe-type acromesomelic dysplasia is a severe GDF5/BMPR1B-spectrum limb
    dysplasia that overlaps AMDM but has much more destructive appendicular
    involvement.
  distinguishing_features:
  - Severe micromelia with absent or fused carpal, metacarpal, tarsal, metatarsal, or phalangeal bones favors Grebe type.
  - Postaxial polydactyly and major femoral, tibial, fibular, ulnar, or radial abnormalities are not typical AMDM findings.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      AMDG is characterized by severe micromelia. Fusion of the carpals and/or
      metacarpals and tarsals and/or metatarsals maybe present. Metacarpal,
      metatarsal or proximal and/or middle phalanges may be absent. Postaxial
      polydactyly has also been reported.
    explanation: The review provides the severe appendicular findings that distinguish Grebe type.
- name: Acromesomelic Dysplasia, Du Pan Type
  disease_term:
    preferred_term: acromesomelic dysplasia 2B
    term:
      id: MONDO:0009231
      label: acromesomelic dysplasia 2B
  description: >-
    Du Pan type is a milder GDF5/BMPR1B-spectrum acromesomelic dysplasia that can
    overlap AMDM in limb shortening and brachydactyly.
  distinguishing_features:
  - Fibular hypoplasia with complex brachydactyly favors Du Pan type; molecular testing distinguishes GDF5/BMPR1B-spectrum disease from NPR2-related AMDM.
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A milder form with fibular hypoplasia and complex brachydactyly
      (acromesomelic dysplasia, du Pan type) has also been reported
    explanation: The review identifies the characteristic Du Pan pattern.
- name: Acromesomelic Dysplasia, Demirhan Type
  disease_term:
    preferred_term: acromesomelic dysplasia, Demirhan type
    term:
      id: MONDO:0012274
      label: acromesomelic dysplasia 3
  description: >-
    The BMPR1B-related, receptor-side member of the GDF5/BMPR1B half of ISDS
    group 16. Its Grebe-like limb phenotype overlaps AMDM in acromesomelic
    shortening and brachydactyly.
  distinguishing_features:
  - Biallelic BMPR1B variants, rather than biallelic NPR2 variants, establish this diagnosis.
  - >-
    Genital anomalies with hypergonadotrophic hypogonadism were present in the
    index patient and are not a feature of AMDM.
  evidence:
  - reference: PMID:15805157
    reference_title: A homozygous BMPR1B mutation causes a new subtype of acromesomelic chondrodysplasia with genital anomalies.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition, she presented with hypoplasia of the uterus and ovarian
      dysfunction resulting in hypergonadotrophic hypogonadism.
    explanation: Identifies the extraskeletal feature that separates the BMPR1B disorder from AMDM.
  - reference: PMID:15805157
    reference_title: A homozygous BMPR1B mutation causes a new subtype of acromesomelic chondrodysplasia with genital anomalies.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mutation analysis of BMPR1B revealed a homozygous 8 bp deletion
      (del359-366).
    explanation: The molecular finding distinguishes this receptor-side disorder from NPR2-related AMDM.
- name: TRPV4-Related Spondyloepimetaphyseal Dysplasia, Maroteaux Type
  disease_term:
    preferred_term: spondyloepimetaphyseal dysplasia, Maroteaux type
    term:
      id: MONDO:0008473
      label: spondyloepimetaphyseal dysplasia, Maroteaux type
  description: >-
    This autosomal dominant TRPV4 skeletal dysplasia shares the Maroteaux eponym
    but is distinct from autosomal recessive NPR2-related acromesomelic
    dysplasia. Both can cause short stature, brachydactyly, spinal deformity,
    and long-bone involvement.
  distinguishing_features:
  - A heterozygous pathogenic TRPV4 variant establishes the TRPV4-related disorder rather than NPR2-related AMDM.
  - The broader TRPV4 spectrum includes progressive spinal deformity and long-bone and pelvic involvement.
  evidence:
  - reference: PMID:24830047
    reference_title: Autosomal Dominant TRPV4-Related Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The five autosomal dominant skeletal dysplasias are (from mildest to most
      severe) familial digital arthropathy with brachydactyly, brachyolmia,
      spondylometaphyseal dysplasia (Kozlowski type), spondyloepimetaphyseal
      dysplasia (Maroteaux type), and metatropic dysplasia.
    explanation: GeneReviews identifies the separate autosomal dominant TRPV4 disorder sharing the Maroteaux eponym.
  - reference: PMID:24830047
    reference_title: Autosomal Dominant TRPV4-Related Disorders.
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The diagnosis of an autosomal dominant TRPV4-related disorder is
      established in a proband who has characteristic clinical and
      neurophysiologic findings, radiographic findings in the skeletal
      dysplasias, and a heterozygous TRPV4 pathogenic variant identified by
      molecular genetic testing.
    explanation: Heterozygous TRPV4 molecular confirmation distinguishes this eponymic differential.
treatments:
- name: Somatropin Therapy
  action_category: THERAPEUTIC
  description: >-
    Recombinant human growth hormone has been reported in two long-term-treated
    siblings and isolated short-term cases. Some height gain occurred, but
    responses are variable and the uncontrolled evidence is too limited to
    establish a standard AMDM regimen or expected final-height benefit.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: Somatropin
      term:
        id: NCIT:C837
        label: Somatropin
  target_phenotypes:
  - preferred_term: Disproportionate short-limb short stature
    term:
      id: HP:0008873
      label: Disproportionate short-limb short stature
  evidence:
  - reference: PMID:33238275
    reference_title: "Acromesomelic Dysplasia, Type Maroteaux: Impact of Long-Term (8 Years) High-Dose Growth Hormone Treatment on Growth Velocity and Final Height in 2 Siblings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Final heights after 8.5 years of GH treatment were 130.5 cm (-6.57 SDS,
      Pt-A) and 134 cm (-4.58 SDS, Pt-B).
    explanation: Two siblings reached the reported final heights after prolonged treatment, without a control group.
  - reference: PMID:35368703
    reference_title: "Novel Loss-of-Function Mutations in NPR2 Cause Acromesomelic Dysplasia, Maroteaux Type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, rhGH therapy in patient 1 increased the patient's height by
      0.6SDS over 15 months without adversely affecting the trunk-leg
      proportion.
    explanation: One short-term case showed a 0.6-SDS gain; this does not establish general efficacy.
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Some individuals with AMDM have been treated with recombinant human
      growth hormone therapy with a variable response
    explanation: The review explicitly characterizes response as variable.
- name: Genetic Counseling
  action_category: COUNSELING_INFORMATIONAL
  description: >-
    Genetic counseling is appropriate after molecular confirmation to explain
    autosomal recessive inheritance and to support testing of relatives for the
    known familial variants. Carrier stature is variable and should not be used
    as a substitute for molecular testing.
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:40551241
    reference_title: "A novel variant in NPR2: C.2291T > C (p.Leu764Pro) identified in a patient with acromesomelic dysplasia Maroteaux type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sanger sequencing confirmed that the variants were inherited from his
      phenotypically normal parents. The proband is compound heterozygous, while
      both parents are heterozygous carriers, indicating an autosomal recessive
      pattern of inheritance.
    explanation: The family demonstrates the recessive carrier relationships relevant to counseling and familial testing.
  - reference: PMID:40551241
    reference_title: "A novel variant in NPR2: C.2291T > C (p.Leu764Pro) identified in a patient with acromesomelic dysplasia Maroteaux type."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic diagnosis is also useful to provide adequate counselling to family memebers, including the formulation of the proper recurrence risk"  # codespell:ignore-line
    explanation: The report directly supports using molecular diagnosis to provide family counseling about recurrence risk.
clinical_trials: []
datasets: []
discussions:
- discussion_id: vosoritide_in_biallelic_npr2_disease
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Does vosoritide help AMDM, where both NPR2 alleles are damaged, given that
    it works by agonising NPR-B?
  rationale: >-
    A 2026 phase 2 basket trial reported a large growth-velocity gain in
    children with NPR2 deficiency, but that arm enrolled heterozygous carriers,
    who retain one wild-type receptor for the drug to act on. AMDM is the
    harder case, because the drug's target is the damaged protein itself.
    Whether it helps should depend on residual activity: alleles with partial
    catalytic function might be drivable by supraphysiological CNP, whereas a
    receptor that cannot bind ligand or reach the membrane offers nothing to
    agonise. That makes this a question about allele class, not about the
    disease as a whole, and the existing entry already records that AMDM alleles
    differ in trafficking and catalytic behaviour. The safety signal from the
    trial is also relevant to a population already prone to skeletal
    complications.
  attaches_to:
  - treatments#
  - pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
  - mechanistic_hypotheses#chondrocyte_cgmp_deficit_convergence
  evidence:
  - reference: PMID:41967490
    reference_title: A phase II basket trial of vosoritide in children with RASopathies, ACAN, and NPR2 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Carriers of heterozygous pathogenic/likely pathogenic variants in NPR2
    explanation: >-
      Identifies the trial population as heterozygous carriers, which is why its
      result does not transfer directly to AMDM.
  - reference: PMID:41967490
    reference_title: A phase II basket trial of vosoritide in children with RASopathies, ACAN, and NPR2 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      5 subjects discontinued medication due to adverse events, including 3
      slipped capital femoral epiphyses and 4 cases of genu valgum
    explanation: >-
      Records the longer-term safety signal that would need weighing in a
      skeletal dysplasia population.
  - reference: PMID:41967490
    reference_title: A phase II basket trial of vosoritide in children with RASopathies, ACAN, and NPR2 deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: There are no currently approved treatments for either NPR2 or ACAN deficiency.
    explanation: Confirms that no approved NPR2-directed therapy exists, so this remains an open question rather than a care gap.
- discussion_id: npr2_activity_dose_mirror
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is stature a continuous readout of NPR-B activity, with AMDM and the NPR2
    overgrowth syndrome as its two ends?
  rationale: >-
    Gain-of-function NPR2 alleles and CNP overproduction cause tall stature with
    macrodactyly and slipped capital femoral epiphysis, mirroring the AMDM
    picture in the opposite direction, and the reported gain-of-function
    receptor is overactive both at baseline and with ligand. If activity maps
    onto stature continuously, then measured receptor activity should predict
    height across the whole allelic range, which would give AMDM a quantitative
    severity model it currently lacks. The competing possibility is that the
    relationship saturates or is buffered at the top of the range, so that the
    overgrowth phenotype is not simply AMDM run backwards. No study has plotted
    measured NPR-B activity against stature across loss- and gain-of-function
    alleles together.
  attaches_to:
  - pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
  - phenotypes#Severe Disproportionate Short-Limb Short Stature
  evidence:
  - reference: PMID:24259409
    reference_title: Overgrowth syndrome associated with a gain-of-function mutation of the natriuretic peptide receptor 2 (NPR2) gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Loss of function mutations at NPR2 cause acromesomelic dysplasia, type
      Maroteaux, while overproduction of CNP by chromosomal translocation and a
      gain-of-function mutation at NPR2 have been reported to be responsible for
      an overgrowth syndrome in three cases and one family, respectively.
    explanation: States the two-directional relationship between NPR2 activity and stature.
  - reference: PMID:24259409
    reference_title: Overgrowth syndrome associated with a gain-of-function mutation of the natriuretic peptide receptor 2 (NPR2) gene.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      In vitro transfection assay of the mutant NPR2 revealed overactivity of
      the mutant receptor at baseline as well as with the ligand.
    explanation: >-
      Provides the measured activity at the gain-of-function end that a
      continuous activity-to-stature model would need.
- discussion_id: genotype_functional_severity
  prompt: Which NPR2 allele-specific functional defects and residual activities predict AMDM skeletal severity?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    NPR2 missense variants differ in trafficking and catalytic behavior, and
    clinically mild AMDM is recognized, but no validated genotype-to-severity
    rule is available. Comparable functional assays linked to standardized
    longitudinal phenotypes are needed.
  attaches_to:
  - pathophysiology#Variant-Specific NPR-B Biogenesis and Catalytic Failure
  - pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
  evidence:
  - reference: PMID:38078000
    reference_title: "Unveiling the pathogenic mechanisms of NPR2 missense variants: insights into the genotype-associated severity in acromesomelic dysplasia and short stature."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Conversely, variants p.Arg318Gly, p.Arg495Cys, and p.Arg557His seem to
      display a non-statistically significant behavior that is slightly
      comparable to WT-NPR2.
    explanation: The heterogeneous in-vitro behavior motivates a standardized variant-function study.
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: although to date there are no reported genotype-phenotype correlations.
    explanation: The clinical report explicitly identifies the unresolved genotype-phenotype relationship.
- discussion_id: regional_acromesomelic_patterning
  prompt: Why does NPR-B deficiency preferentially shorten middle and distal limb segments while producing milder axial involvement?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    Reduced growth-plate signaling explains impaired longitudinal growth, but it
    does not by itself explain the reproducible regional acromesomelic pattern.
    Spatial developmental studies are needed to define segment-specific CNP,
    NPR-B, cGKII, and downstream signaling dependencies.
  attaches_to:
  - pathophysiology#Impaired Endochondral Longitudinal Bone Growth
  - pathophysiology#Acromesomelic Limb Elongation Deficit
  evidence:
  - reference: PMID:34162036
    reference_title: "Acromesomelic dysplasia-Maroteaux type, nine patients with two novel NPR2 variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is a rare type of dwarfism characterized by shortening of the middle
      and distal segments of the limbs with spondylar dysplasia.
    explanation: The consistent regional phenotype defines the pattern that remains mechanistically unexplained.
- discussion_id: genotype_stratified_growth_response
  prompt: Which AMDM genotypes, if any, predict benefit from somatropin or future NPR-B/cGMP-pathway therapies?
  kind: KNOWLEDGE_GAP
  status: OPEN
  rationale: >-
    Somatropin evidence is limited to uncontrolled cases with variable response.
    Complete NPR-B loss and residual-function alleles may differ in their
    response to CNP-pathway strategies, while MEK inhibition remains confined to
    a fetal mouse tibia explant model.
  attaches_to:
  - pathophysiology#Reduced CNP-Stimulated Guanylyl Cyclase Activity and cGMP
  - treatments#Somatropin Therapy
  evidence:
  - reference: PMID:34178199
    reference_title: "A mild case of acromesomelic dysplasia, type Maroteaux with novel natriuretic peptide receptor B (NPR2) variants."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Some individuals with AMDM have been treated with recombinant human
      growth hormone therapy with a variable response
    explanation: Variable reported response motivates prospective genotype-stratified study.
  - reference: PMID:23065701
    reference_title: "A novel loss-of-function mutation in Npr2 clarifies primary role in female reproduction and reveals a potential therapy for acromesomelic dysplasia, Maroteaux type."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Treatment of fetal tibiae explants with mitogen activated protein kinase
      1 and 2 inhibitors U0126 and PD325901 rescues the Npr2(pwe/pwe) growth
      defect, providing a promising foundation for skeletal dysplasia
      therapeutics.
    explanation: The rescue is preclinical and defines a pathway hypothesis rather than a human treatment.
notes: >-
  AMDM is an NPR2 loss-of-function disorder. It is distinct from the allelic
  NPR2 gain-of-function Miura overgrowth phenotype and from the autosomal
  dominant TRPV4-related spondyloepimetaphyseal dysplasia that also uses the
  Maroteaux eponym. Npr2-deficient mouse models show normal skeletal
  mineralization despite reduced growth-plate proliferative and hypertrophic
  zones; AMDM should therefore not be described as a generalized
  mineralization failure.
📚

References & Deep Research

Deep Research

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Pathophysiology of Acromesomelic Dysplasia, Maroteaux Type (AMDM)
o3-deep-research-2025-06-26 80 citations 2026-04-02T22:53:50.576643

Pathophysiology of Acromesomelic Dysplasia, Maroteaux Type (AMDM)

Disease Name: Acromesomelic Dysplasia, Maroteaux Type
MONDO ID: MONDO:0014401
Category: Mendelian (autosomal recessive skeletal dysplasia)

Core Pathophysiology

Acromesomelic dysplasia Maroteaux type (AMDM) is caused by loss-of-function mutations in the NPR2 gene (natriuretic peptide receptor 2), leading to impaired C-type natriuretic peptide signaling in the growth plate (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Under normal conditions, the C-type natriuretic peptide (CNP) binds to the NPR2 receptor (also known as NPR-B) on chondrocytes, activating its guanylate cyclase domain to produce cyclic GMP (cGMP; CHEBI:16356) inside the cell (pmc.ncbi.nlm.nih.gov). The increase in cGMP activates cGMP-dependent protein kinase II (PKG2), which promotes endochondral bone growth by stimulating chondrocyte proliferation and hypertrophic differentiation (pmc.ncbi.nlm.nih.gov) (www.frontiersin.org). In essence, CNP/NPR2 signaling is a positive regulator of growth plate cartilage homeostasis and longitudinal bone growth (www.frontiersin.org).

In AMDM, biallelic NPR2 mutations abolish this CNP–NPR2–cGMP pathway, removing a crucial proliferative signal in the growth plate (pmc.ncbi.nlm.nih.gov). A key consequence is the loss of NPR2’s antagonism of the fibroblast growth factor receptor 3 (FGFR3) pathway. Normally, CNP-induced PKG activity inhibits the FGFR3-triggered MAPK cascade in chondrocytes, which in turn relieves FGFR3’s brake on cell proliferation (pmc.ncbi.nlm.nih.gov). When NPR2 is nonfunctional, FGFR3 (HGNC:3690) signaling via RAS/MAPK is unchecked, leading to reduced chondrocyte proliferation, premature hypertrophic differentiation, and shortened columns of growth plate cartilage (pmc.ncbi.nlm.nih.gov). This mechanism parallels the pathophysiology of achondroplasia (caused by FGFR3 overactivation), except in AMDM the defect is a loss of the positive natriuretic peptide signal rather than a gain of negative FGFR3 signal (pmc.ncbi.nlm.nih.gov). The end result is severely stunted endochondral ossification: long bones cannot elongate normally because chondrocytes fail to divide and mature adequately. Histologically, growth plates in NPR2-related dysplasia show narrowing of the proliferative zone and an early transition to hypertrophy, similar to the effect of constitutive FGFR3 activity (pmc.ncbi.nlm.nih.gov). This core disturbance – a failure of endochondral ossification (GO:0001958) due to disrupted cGMP signaling – underlies all downstream manifestations of the disease.

At the cellular level, NPR2 mutations cause chondrocyte dysfunction in several ways. Many mutations are truncating or inactivating, resulting in no functional receptor at the cell surface. Missense mutations can produce a protein that misfolds and is retained in the endoplasmic reticulum (ER) rather than reaching the plasma membrane (www.frontiersin.org). For example, a 2022 study showed a missense change (p.Arg371Gln) in the NPR2 extracellular domain prevented the receptor from dimerizing and binding its ligand, effectively abolishing CNP signaling (pmc.ncbi.nlm.nih.gov). Recent cellular studies in 2023 have confirmed that certain NPR2 missense variants lead to ER retention and defective glycosylation of the receptor, thereby eliminating its activity at the cell surface (www.frontiersin.org) (www.frontiersin.org). Other pathogenic mutations in NPR2 that do reach the membrane may still disrupt the guanylyl cyclase function or CNP-binding interface, resulting in little or no cGMP production (pmc.ncbi.nlm.nih.gov). The lack of intracellular cGMP means that pivotal targets like PKG2 and downstream effectors are not activated in growth plate chondrocytes. Notably, one downstream pathway recently elucidated is that NPR2/PKG signaling opens BK channels and triggers Ca²⁺ influx via TRPM7 channels, activating CaMKII and enhancing chondrocyte hypertrophic differentiation (pubmed.ncbi.nlm.nih.gov). Loss of NPR2 likely abolishes this Ca²⁺-mediated signaling cascade as well, further impairing the orderly progression of chondrocytes through proliferation and hypertrophy. In summary, the core pathophysiology is a failure of growth plate signaling: without functional NPR2, growth plate chondrocytes (CL:0000138) cannot properly proliferate or mature, leading to drastic shortening of bones and dwarfism.

Key Molecular Players

  • Gene and Protein: The causative gene is NPR2 (HGNC:7944), which encodes the natriuretic peptide receptor B (a transmembrane guanylate cyclase). NPR2 functions as a homodimeric receptor that, upon binding C-type natriuretic peptide, generates cGMP from GTP at its intracellular domain (pmc.ncbi.nlm.nih.gov). NPR2 is highly expressed in growth plate chondrocytes and is essential for longitudinal bone growth (www.frontiersin.org). Homozygous or compound-heterozygous loss-of-function mutations in NPR2 cause the AMDM phenotype (pmc.ncbi.nlm.nih.gov). (By contrast, heterozygous NPR2 mutations cause milder short stature without full dysplasia (pmc.ncbi.nlm.nih.gov), and gain-of-function mutations in NPR2 lead to tall stature (epiphyseal overgrowth, Miura type) (pmc.ncbi.nlm.nih.gov).) Another gene in this pathway is NPPC (HGNC:7941), encoding the ligand C-type natriuretic peptide (CNP). Rare mutations in NPPC have been reported to cause autosomal dominant short stature, highlighting the importance of CNP ligand availability (pmc.ncbi.nlm.nih.gov). In the context of AMDM, NPPC is usually normal; however, without functional NPR2, CNP cannot exert its effects. Key downstream targets include PRKG2 (cGMP-dependent protein kinase II), which mediates many intracellular effects of cGMP in chondrocytes (pmc.ncbi.nlm.nih.gov). Notably, recessive mutations in PRKG2 (HGNC:9392) have been identified in another form of acromesomelic dysplasia, underscoring that disruption of the NPR2–cGMP–PKG signaling axis at any point leads to similar skeletal pathology (pmc.ncbi.nlm.nih.gov). Additionally, FGFR3 is a crucial interacting protein: though not mutated in AMDM, its signaling is antagonized by NPR2 in normal physiology (pmc.ncbi.nlm.nih.gov). FGFR3’s pathway becomes overactive when NPR2 is absent, contributing to the growth plate impairment. Other genes that cause clinically overlapping acromesomelic dysplasias include GDF5 (for Grebe type) and BMPR1B (for Hunter-Thompson type) (pmc.ncbi.nlm.nih.gov), but those operate in the bone morphogenetic protein pathway rather than the CNP/NPR2 pathway.

  • Chemical Entities: The primary biochemical players are the natriuretic peptides and second messengers involved in growth plate signaling. C-Type Natriuretic Peptide (CNP) is the ligand for NPR2; it is produced by chondrocytes and perichondrial cells as a local paracrine factor. CNP binding to NPR2 induces production of cyclic guanosine monophosphate (cGMP), a second messenger (CHEBI:16356) that mediates downstream effects (pmc.ncbi.nlm.nih.gov). Guanosine triphosphate (GTP) is the substrate for the guanylate cyclase activity of NPR2, and is converted to cGMP upon receptor activation (pmc.ncbi.nlm.nih.gov). Elevated cGMP then activates PKGII (encoded by PRKG2) to phosphorylate target proteins that drive chondrocyte proliferation and matrix synthesis. The MAPK signaling molecules (RAF/MEK/ERK) are also indirectly involved: in the absence of cGMP/PKG signals, MAPK activity remains high due to FGFR3, which suppresses chondrocyte growth (pmc.ncbi.nlm.nih.gov). No exogenous toxins or metabolites are known to be involved in this genetic condition; however, therapeutic hormones have been tried. For instance, recombinant human growth hormone (rhGH) is a drug that has been administered to some AMDM patients to stimulate IGF-1 and growth plate activity (pmc.ncbi.nlm.nih.gov). Insulin-like growth factor 1 (IGF-1) is the downstream effector of GH and is a general promoter of chondrogenesis; in NPR2-deficient chondrocytes IGF-1 can still signal, though NPR2 absence may blunt the maximal response (some GH resistance is observed clinically (pubmed.ncbi.nlm.nih.gov)). It’s worth noting that analogs of CNP (such as vosoritide, an analog of CNP approved for treating achondroplasia) require a functional NPR2 receptor to work – thus such therapies are not effective in AMDM, since NPR2 is nonfunctional.

  • Cell Types: The primary cells affected are growth plate chondrocytes (cartilage cells of the epiphyseal plates; cell ontology: chondrocyte). These include proliferative zone chondrocytes, which normally divide and form columns, and hypertrophic chondrocytes, which terminally differentiate and prepare the cartilage matrix for ossification. NPR2 is expressed in both these chondrocyte populations, and its loss impairs their proliferation and hypertrophy (www.frontiersin.org). Consequently, the osteoblasts and osteoclasts that normally remodel the calcified cartilage into bone are secondarily affected – there is less scaffold for them to ossify. (Indeed, CNP/NPR2 signaling has been shown to promote not only chondrocyte growth but also the activity of osteoblasts and osteoclasts in the growth plate environment (pmc.ncbi.nlm.nih.gov).) However, the primary defect resides in the cartilage cells. Other cell types in the body are largely unaffected, which explains the lack of extraskeletal symptoms. For example, neurons and other cell types do express natriuretic peptide receptors (NPR1/NPR2 in certain tissues), but no neurological deficits are seen in AMDM – likely because NPR2’s role in the central nervous system is minor or redundant. Similarly, visceral organs are normal. Therefore, growth plate chondrocytes (CL:0000138) are the critical cellular players whose dysfunction drives the disease.

  • Anatomical Locations: The pathology is most pronounced in the long bones of the appendicular skeleton (UBERON:0011363), especially the forearms (radius and ulna) and lower legs (tibia and fibula), as well as the bones of the hands and feet (www.malacards.org) (www.malacards.org). These are the skeletal elements that undergo endochondral ossification and normally grow significantly during childhood. In AMDM, the middle segments of limbs (mesomelic segments: e.g. forearm, lower leg) and distal segments (acromelic: hands, feet) are disproportionately shortened (www.malacards.org). The vertebral column (axial skeleton) is also involved – patients have reduced vertebral body height and some vertebral wedging, leading to a shortened trunk (www.malacards.org). This indicates NPR2 signaling is important in vertebral growth plates as well. Notably, regions of the skeleton that grow by intramembranous ossification (such as most of the skull vault and facial bones) are not significantly affected – consistent with the fact that CNP/NPR2 mainly influences endochondral growth. Apart from bone, the growth plate cartilage (anatomically, the epiphyseal plate cartilage of long bones) is the central site of pathology. This cartilage is found at the ends of long bones (e.g. distal femur, proximal tibia, distal radius/ulna, etc.), and in AMDM these plates are abnormally thin. In summary, the disease is localized to the skeletal system – particularly the limb bones (UBERON:0002495) and spine (vertebrae, UBERON:0002412) – and does not significantly involve other organs.

Disrupted Biological Processes (GO Terms)

AMDM fundamentally disrupts the biological process of endochondral ossification (bone development from a cartilage template) (www.frontiersin.org). The endochondral ossification (GO:0001958) pathway involves chondrocyte proliferation, hypertrophic differentiation, matrix mineralization, and replacement of cartilage by bone; all these steps are impaired to varying degrees in AMDM. A hallmark of the condition is inadequate chondrocyte proliferation in the growth plate. Normally, CNP/NPR2 signaling positively regulates chondrocyte proliferation and progression through the cell cycle (pmc.ncbi.nlm.nih.gov). In AMDM, this positive regulation is lost, so there is a failure of growth plate cartilage chondrocyte proliferation (related to GO:0003419) and a premature growth arrest of chondrocyte columns. Another affected process is chondrocyte hypertrophic differentiation (part of GO:0003417). Without NPR2 signals, the maturation of chondrocytes is abnormal – in some growth plates, hypertrophic differentiation may initiate early (due to FGFR3’s influence), but the quality of hypertrophy and matrix production is poor. The hypertrophic zone may be truncated, with chondrocytes not reaching normal size or failing to properly mineralize the cartilage matrix. Thus, cartilage matrix organization and mineralization are secondarily disturbed. The overall longitudinal bone growth (GO:0060012) process is severely reduced, leading to dwarfism.

On a molecular signaling level, several GO-defined pathways are perturbed: The FGF receptor signaling pathway (GO:0008543) is overactive in the absence of NPR2’s check. NPR2 normally elicits a signal that inhibits the MAPK cascade (GO:0000165) in chondrocytes (pmc.ncbi.nlm.nih.gov); this inhibition is lifted in AMDM, resulting in excessive MAPK/ERK activity which suppresses proliferation. Therefore, one can describe AMDM as featuring a relative upregulation of FGFR3-MAPK signaling and a loss of cGMP-mediated signaling (GO:0019934) in cartilage. The cGMP biosynthetic process (GO:0006182) that would normally occur in response to CNP is essentially absent in growth plates of these patients. Genes downstream of cGMP/PKG that drive cell cycle progression, matrix synthesis, and chondrocyte survival are likely underexpressed or dysregulated (for example, NPR2 signaling induces expression of cartilage matrix genes and cell-cycle regulators in normal growth plates, so in AMDM these would be reduced).

Key biological processes directly affected include: cartilage development (GO:0051216) – the growth and maintenance of cartilage tissue is abnormal, as evidenced by disorganized chondrocyte columns and reduced extracellular matrix deposition. Bone morphogenesis (GO:0060349) is also affected, since the shape and size of bones are altered (bones are shorter and can be abnormally shaped due to early growth plate fusion or bowing). The process of ossification (GO:0001503) is delayed or diminished in the sense that less bone tissue is produced from the cartilage template. It’s important to note that the intrinsic ability of osteoblasts to form bone may be normal, but because the cartilage scaffold is deficient, ossification is quantitatively reduced. Additionally, signal transduction processes at the growth plate are perturbed: the natriuretic peptide signaling pathway (part of GO:0030802) is inactive, and thus all downstream biological responses that it normally coordinates (cell proliferation, hypertrophy, angiogenesis in the growth plate, etc.) are blunted. In summary, AMDM interferes with the normal sequence of growth plate maturation: proliferation → hypertrophy → matrix mineralization → vascular invasion → ossification. By halting proliferation early and altering differentiation, it effectively curtails longitudinal bone growth and leads to the classical dwarfism phenotype.

Cellular Components Involved

The pathogenic process of AMDM can be mapped to specific cellular compartments where NPR2 and its signaling partners localize:

  • Plasma Membrane (GO:0005887): NPR2 is an integral membrane protein of the plasma membrane on chondrocytes (pmc.ncbi.nlm.nih.gov). The functional NPR2 receptor is a homodimer embedded in the cell membrane, with an extracellular ligand-binding domain and an intracellular catalytic domain (pmc.ncbi.nlm.nih.gov). In healthy chondrocytes, NPR2 is present on the cell surface of growth plate chondrocytes, poised to bind circulating or locally produced CNP.

  • Extracellular Region (GO:0005576): C-type natriuretic peptide (CNP) is a secreted factor that operates in the extracellular space of the growth plate cartilage. CNP diffuses through the cartilage matrix and binds to NPR2 on chondrocyte membranes (pmc.ncbi.nlm.nih.gov). Thus, the ligand-receptor interaction occurs in the extracellular matrix environment of the growth plate. In AMDM, CNP may still be produced by the cells, but it accumulates or is degraded in the extracellular space without effect, since NPR2 is non-functional or absent on the membrane.

  • Cytosol (GO:0005829): The intracellular signaling events downstream of NPR2 take place in the cytosol of chondrocytes. When NPR2 is activated in normal cells, its guanylyl cyclase domain (located on the cytosolic side of the receptor) converts GTP to cGMP inside the cytoplasm (pmc.ncbi.nlm.nih.gov). The rise in cGMP occurs in the cytosol, where it binds and activates PKG2. PKG2 is a cytosolic kinase that then phosphorylates target proteins, some of which may be cytoskeletal or nuclear. For instance, PKG2 activation can lead to opening of BK potassium channels on the plasma membrane and modulation of Ca²⁺ influx, as well as regulation of transcription factors via CaMKII signaling (pubmed.ncbi.nlm.nih.gov). In AMDM chondrocytes, because NPR2 is not generating cGMP, the cytosolic second messenger (cGMP) is greatly reduced. Essentially, the cytosolic signaling cascades that normally promote growth are silent in these cells.

  • Endoplasmic Reticulum (GO:0005783): Many missense mutations in NPR2 lead to misfolded proteins that are trapped in the endoplasmic reticulum. Cellular studies of several AMDM-associated NPR2 variants show that instead of trafficking to the plasma membrane, the mutant proteins remain in the ER where they undergo ER-associated degradation (www.frontiersin.org) (www.frontiersin.org). The ER is thus a key compartment in the pathology of certain NPR2 mutations: the quality control system in the ER recognizes the mutated receptor as misfolded and prevents it from reaching the cell surface. This not only deprives the cell surface of NPR2 but can also induce ER stress if misfolded protein accumulates (though chronic ER stress has not been specifically reported in AMDM, it is a theoretical concern in cells with high mutant protein load). Proper folding and glycosylation of NPR2 in the ER and Golgi are required for it to become a mature receptor; in some milder mutations, a fraction of NPR2 makes it to the membrane while another fraction is stuck in the ER, resulting in partial residual activity (www.frontiersin.org) (www.frontiersin.org).

  • Other Organelles: While not specific to NPR2, the downstream effects eventually influence the nucleus (e.g. altered gene transcription due to changes in signaling). For example, without NPR2, there may be reduced expression of cartilage matrix genes like COL2A1 and Aggrecan because the pathways that normally enhance their transcription (through Sox9 and other factors) are underactive. However, these nuclear effects are secondary. The primary subcellular locations of dysfunction are the membrane (where signaling fails to initiate) and the cytosol (where cGMP is lacking). Additionally, the extracellular matrix (ECM) of cartilage can be considered here: in AMDM, the ECM of the growth plate is often under-mineralized and thin, reflecting the reduced output of mature chondrocytes. Collagen X and other hypertrophic markers in the ECM might be decreased. But again, this is a downstream result of the intracellular signaling defect.

In summary, the key cellular components in AMDM pathophysiology include the chondrocyte plasma membrane (site of NPR2 and CNP interaction), the ER (site of mutant protein retention), the cytosol (where cGMP and PKG normally act), and the extracellular cartilage matrix (where CNP is present and where the lack of effective chondrocyte activity manifests as poor matrix expansion).

Disease Progression

Initiation (Genetic Trigger): The disease process is initiated by the presence of biallelic NPR2 mutations from conception. Because this is a constitutive genetic disorder, abnormal skeletal development begins in utero. Fetuses with AMDM may have shorter long bones detectable by prenatal ultrasound in the late second or third trimester, although the condition is less dramatic than lethal chondrodysplasias. The initial trigger for the pathophysiological cascade is the absence of functional NPR-B receptors in growth plate chondrocytes starting from embryonic cartilage formation. This leads to an early deficit in chondrocyte proliferation during limb bud development.

Neonatal and Infant Phase: At birth, infants with AMDM often have noticeable shortening of the limbs (micromelia), but birth length might be near the lower end of normal range since fetal growth has multiple inputs. However, within the first months to 2 years of life, a clear growth divergence emerges (www.malacards.org). The middle and distal segments of the limbs fail to grow at the expected rate. Parents or physicians typically observe that the child’s arms and legs remain very short relative to the trunk. By age 2, disproportionate short stature becomes obvious, with both the appendicular and axial skeleton affected (www.malacards.org). There are no distinct “crisis” phases; rather, it is a continuous growth failure evident in serial measurements. During infancy, motor development may be slightly delayed due to short limbs (e.g. delayed walking), but cognitive development is normal.

Childhood Phase: Throughout childhood, linear growth is severely impaired. Growth velocity (height gain per year) is well below the mean for age, despite normal endocrine function (normal growth hormone and thyroid levels, etc.). This progressive deviation leads to a height far below peers. Importantly, the growth pattern in AMDM can be considered a form of dwarfism that is present from early life and non-progressive in a degenerative sense – the condition doesn’t worsen due to ongoing damage, but the relative difference from normal height increases as the child ages because normal children continue to grow. There are no staged “flairs” or regressions, just persistently slow growth. In this phase, distinct clinical management issues arise: the limbs being very short can cause mechanical axes misalignment. For example, the radius/ulna discrepancy can lead to subluxation of the radial head or restricted elbow motion; bowed legs can lead to early knee joint stress. The spine, having abnormal vertebrae, might start developing kyphosis or lordosis once the child begins standing and walking (due to uneven growth of posterior vs anterior vertebral elements). Often by late childhood, patients exhibit lumbar hyperlordosis or thoracolumbar kyphosis, and sometimes bowing of the legs or forearms, which may progress with weight-bearing (www.malacards.org) (www.malacards.org).

Hormonal Therapy Effects: During mid-childhood (around ages 5–10), some patients are started on growth hormone (GH) therapy in hopes of maximizing height. There is evidence of partial GH resistance in AMDM (pubmed.ncbi.nlm.nih.gov). Low-dose GH tends to have minimal effect on growth, but high-dose GH over multiple years can modestly increase growth velocity (pubmed.ncbi.nlm.nih.gov). For instance, an 8-year high-dose GH treatment in two siblings was reported to improve height SDS (standard deviation score) by overcoming the GH resistance to some extent (pubmed.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). GH mainly acts via IGF-1, which still can stimulate chondrocytes even if NPR2 is absent. In practice, GH treatment might accelerate growth by a few centimeters per year more than untreated, improving final height somewhat (one study noted an improvement of +0.6 SD in height over 15 months with GH (pmc.ncbi.nlm.nih.gov)). However, GH does not completely normalize stature and therapy needs to be aggressive (higher doses than used in GH deficiency). This indicates that NPR2-independent pathways (GH/IGF1) can partially compensate if strongly stimulated, but the growth plate remains intrinsically less responsive.

Adolescence and Growth Cessation: Typically, puberty in AMDM occurs at a roughly normal age and can even be slightly early because short stature can be associated with early growth plate fusion in some skeletal dysplasias. As adolescence progresses, the epiphyseal growth plates gradually fuse (cap closure). By the end of puberty, longitudinal growth ceases, and the final adult height is usually extremely short (often under 120 cm, or < –6 SD from the mean) (www.malacards.org). Females might end up in the range of ~110–120 cm and males similarly, as reported in case series (www.malacards.org). Once growth plates are fused, no further height increase is possible. At this point, the disease has “progressed” to its final stature outcome, but again, this is the expected culmination of the developmental process rather than a pathological deterioration.

Adulthood Phase: In adulthood, individuals with AMDM do not experience ongoing metabolic or neurological decline – in that sense, the disease is not progressive. The concerns in adulthood are largely orthopedic sequelae of the skeletal deformities. Many adults suffer from chronic joint pain or early-onset osteoarthritis due to abnormal load distribution (for example, knee degeneration from bowed legs, or back pain from lordosis). Spinal canal narrowing (stenosis) can occasionally occur if the interpedicular distances are very short, potentially leading to nerve compression – though serious neurological complications are less common in AMDM compared to other dwarfisms. Orthopedic interventions may be needed in this phase: spinal surgery for severe kyphosis, osteotomies to correct limb bowing, or even limb-lengthening procedures. Limb lengthening (distraction osteogenesis) has been attempted in some short-stature conditions and could be considered in AMDM after growth completion to improve stature, though this is a serious undertaking.

Throughout all phases, intelligence and other organ systems remain normal, so the progression is purely orthopedic in nature (www.malacards.org). Patients typically adapt to their short stature with appropriate modifications. Lifespan is generally normal; there is no evidence that AMDM itself shortens life expectancy, apart from potential complications (e.g., cervical spine issues or thoracic cage restriction in some skeletal dysplasias, but AMDM is not usually associated with severe chest restriction). In summary, the “disease progression” in AMDM is characterized by an early-onset static growth failure manifesting in infancy and a persistent growth impairment through childhood, culminating in a profoundly short adult stature. After skeletal maturity, the condition’s focus shifts to managing the long-term consequences (spinal curvature, joint issues), as the active growth disturbance has already run its course.

Phenotypic Manifestations

Skeletal Proportions: Acromesomelic dysplasia (Maroteaux type) presents with severe disproportionate short stature. Adult height is typically below 120 cm (approximately <–10 SD), classifying as extreme dwarfism (www.malacards.org). The hallmark is shortening of the mesomelic (middle) and acromelic (distal) segments of the limbs, meaning the forearms, lower legs, hands, and feet are especially underdeveloped (www.malacards.org). This yields a characteristic body disproportion: the trunk is somewhat short, but the limbs (particularly the forearms and hands, and the lower legs and feet) are even more markedly short. For example, the upper arms and thighs (rhizomelic segments) are short as well, but not to the same degree as the forearms and lower legs. As a result, the arm span is much shorter than height, and the sitting height/standing height ratio is elevated (indicating relatively long trunk vs. limbs, a diagnostic clue) (www.malacards.org).

Limb Abnormalities: The hands and feet are very small. Patients often have brachydactyly (short fingers and toes – HP:0001156) with unique features such as “knob-like” appearances of the fingers due to nearly absent middle phalanges (www.malacards.org). The fingers are short and broad, sometimes described as stubby. The feet are also short and broad; on X-ray, the metacarpals and metatarsals are shortened. The forearm bones are disproportionate: the radius is often bowed outward and the ulna is disproportionately short and may have a hypoplastic distal end (www.malacards.org). This can result in limited forearm rotation (pronation/supination) and an increased carrying angle at the elbow. The legs show shortening of the tibiae and fibulae; in some cases, bowing of the lower legs is present. Mesomelic shortening (HP:0003027) is evident as the forearm and lower leg segments are much shorter relative to the upper arm and thigh. Despite the drastic reduction in length, all major skeletal elements are present (there are no missing bones, just very short ones) (www.malacards.org). Radiologically, epiphyses might be small and irregular. Cone-shaped epiphyses and delayed bone age can be seen in childhood. Joint mobility is typically normal in childhood (aside from mechanical limits due to bone length), though early-onset arthritis can restrict mobility later.

Axial Skeleton: The spine is also affected, though less visibly than the limbs. Patients have a short trunk due to decreased vertebral body height (platyspondyly – HP:0000926) and wedge-shaped vertebrae in some regions (www.malacards.org). The interpedicular distances in the lumbar spine fail to increase normally with growth (a common feature in chondrodysplasias), which can contribute to spinal canal narrowing. Clinically, the short trunk may not be as extreme as in some other dwarfisms, but standing height is further compromised by mild vertebral compression. Lumbar lordosis is frequently exaggerated – partly as a compensatory mechanism for balance due to short limbs, and partly from structural vertebral changes. Some individuals also develop thoracolumbar kyphosis. Scoliosis is not a dominant feature but can occur secondary to vertebral anomalies. The ribcage is generally normal-sized (which is important for lung function), distinguishing AMDM from some lethal skeletal dysplasias that have small thoracic cages.

Craniofacial and Other Systems: A notable aspect of AMDM is that facial appearance is typically normal (www.malacards.org). There may be subtle features – some reports mention a relatively large head size (dolichocephaly) or mild midface retrusion – but unlike many skeletal dysplasias, no coarse facies or dysmorphism is pronounced. The skull and face bones largely develop through intramembranous ossification which is not dependent on NPR2, explaining the normal facial features. Teeth and jaw development are normal. Intelligence is entirely normal in AMDM (www.malacards.org); the disorder does not affect the brain or cognitive development. There is no primary neurological involvement and no increase in intellectual disability compared to the general population. The absence of neurologic deficits is an important clinical distinction between pure skeletal dysplasias like AMDM and other conditions that might involve the skeleton and central nervous system.

Joint and Functional Manifestations: Although joint formation is anatomically normal, the extreme shortness of limbs can lead to mechanical strain. Some patients have limited elbow and wrist extension due to bone shape. Knee alignment can be abnormal (genu varum or valgum) requiring bracing or surgery in childhood. Physical function in terms of muscle strength and coordination is otherwise normal; children with AMDM learn to walk, run, and perform fine motor tasks, just with adaptations for their stature. In adulthood, osteoarthritis may occur early in weight-bearing joints.

Quality of Life and Secondary Phenotypes: Psychosocially, individuals have short stature and may face challenges related to height, but intelligence and life activities (education, work) are not inherently limited aside from accommodations for height. There are no metabolic or cardiac abnormalities intrinsic to AMDM. Hearing and vision are normal (in contrast to some other chondrodysplasias that have sensorineural issues – NPR2 is not known to affect those systems). Endocrine function is normal; patients go through normal puberty and can be fertile. Indeed, AMDM is often diagnosed via genetic testing or radiographic review in childhood due to short stature rather than by the presence of systemic illness.

In summary, the phenotype of AMDM is focused on skeletal anomalies: short stature (HP:0004322) that is disproportionate (HP:0003521) with mesomelic and acromesomelic limb shortening, brachydactyly (HP:0001156) of hands and feet, and mild axial skeletal involvement. All these clinical features flow from the underlying failure of endochondral growth. The disproportion (limbs << trunk) directly reflects that growth plates in the limbs have severely reduced activity, whereas the trunk (spine) and cranial bones are less affected. The normal intelligence and lack of other organ involvement underscore that NPR2’s role is highly specific to the growth plate cartilage. This tight correlation between the molecular pathology (NPR2-mediated bone growth) and the phenotype (isolated short limbs) is a classic feature of acromesomelic dysplasia. Every major clinical feature can be traced back to the growth plate dysfunction: for instance, short hands and feet result from early closure or underactivity of phalangeal growth plates, and bowed forearms result from uneven growth in radius vs. ulna due to the same signaling defect. The phenotypic spectrum can have mild variability (some individuals are a bit taller or have more moderate shortening if they have hypomorphic mutations), but generally it is consistent. Importantly, AMDM is distinguished from related conditions by the absence of hand/foot malformations like extra digits (no polydactyly in pure AMDM), and by normal reproductive development (unlike some other acromesomelic syndromes, there are no genital anomalies in Maroteaux type). The phenotypic description here aligns with the documented cases in literature (www.malacards.org) (www.malacards.org) and is encapsulated by the HPO terms such as “disproportionate short stature”, “mesomelic limb shortening”, “short hand” (HP:0004279), “short foot” (HP:0001773), and “platyspondyly”, among others. Each of these clinical signs is a manifestation of the disrupted molecular and cellular processes in the growth plate, providing a clear link between genotype, pathophysiology, and phenotype.

Evidence: The above statements are supported by multiple clinical and research studies. For example, a 2022 report by Wu et al. described AMDM patients with NPR2 mutations and noted “severe disproportionate short stature, short hands and feet, normal intelligence” (pmc.ncbi.nlm.nih.gov). A comprehensive review in 2017 explained that loss of CNP/NPR2 signaling “increases the proliferation and differentiation of chondrocytes” under normal conditions and that homozygous mutations cause this profound skeletal dysplasia (pmc.ncbi.nlm.nih.gov). Detailed case series (e.g. Kılıç et al., 2021) document the radiographic features like mesomelic limb shortening and vertebral changes. Malacards and Orphanet summaries confirm the key clinical features and their genetic cause (www.malacards.org) (www.malacards.org). Furthermore, functional studies (Miyazaki et al., eLife 2022) have elucidated the chondrocyte signaling pathways affected (pubmed.ncbi.nlm.nih.gov). Taken together, these authoritative sources paint a consistent picture of AMDM pathophysiology linking NPR2 mutations to impaired endochondral ossification and resultant acromesomelic dwarfism. (pmc.ncbi.nlm.nih.gov) (www.malacards.org)