Acrocapitofemoral Dysplasia

Mendelian MONDO:0011907 Pathograph 34 Show in embeddings browser acromelic dysplasia osteochondrodysplasia

Acrocapitofemoral dysplasia (ACFD) is an ultra-rare autosomal recessive skeletal dysplasia caused by homozygous missense variants in the amino-terminal signaling domain of IHH (Indian hedgehog). It presents with postnatal-onset disproportionate short stature with short limbs, brachydactyly, a narrow thorax and a relatively large head, with normal intelligence. The defining radiographic signs are cone-shaped epiphyses, mainly in the hands and hips, and an egg-shaped capital femoral epiphysis on a short femoral neck. These are followed by early, prepubertal closure of the growth plates, which permanently shortens the tubular bones of the hands and the long bones of the limbs. A published cell study found reduced IHH-N abundance, interpreted as reduced protein stability with a slight processing defect for p.Val190Ala. The growth-plate mechanism is supported mainly by mouse genetics: IHH secreted by prehypertrophic chondrocytes drives chondrocyte proliferation and paces hypertrophic differentiation through a PTHrP feedback loop, and postnatal loss of chondrocyte IHH disorganizes the growth plate and fuses it prematurely. Allele-specific effects on signaling in human cartilage remain unresolved.

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1
Inheritance
8
Pathophys.
40
Phenotypes
2
Gaps
34
Pathograph
1
Genes
4
Variants
1
Medical Actions
1
Differentials
3
Models
5
References
1
Deep Research
🏷

Classifications

ISDS Skeletal Nosology
acromelic dysplasias
👪

Inheritance

1
Autosomal Recessive HP:0000007
The unblended ACFD families reported here have homozygous IHH missense variants, consistent with autosomal recessive inheritance. Tested parents carry heterozygous variants. Both Pakistani carrier parents had short stature with clinically normal hands; that observation should not be generalized to every carrier. The original molecular paper discusses subtle radiographic hand-bone shortening in some parents without the typical BDA1 phenotype. Carrier effects and penetrance remain incompletely characterized.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:12632327 SUPPORT Human Clinical
"Both affected individuals of family 1 are homozygous for a 137C-->T transition (P46L), and the three patients in family 2 are homozygous for a 569T-->C transition (V190A)."
Homozygosity for the causal variant in all affected members of the two founding families.
PMID:40045933 SUPPORT Human Clinical
"The parents were heterozygous carriers, while both affected individuals carried the homozygous mutant allele"
Segregation consistent with autosomal recessive inheritance in the fourth family.
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Discussions and Knowledge Gaps

2
How do the individual ACFD alleles alter ligand abundance, processing, signaling potency and spatial range in human cartilage?
HUMAN MODEL MISMATCH OPEN acfd_missense_vs_null_models
Attached to
pathophysiology#Reduced IHH Signaling Output pathophysiology#Biallelic IHH Signaling-Domain Missense Variants
Functional evidence exists but is uneven. Wang et al. (2021) found reduced V190A IHH-N abundance, interpreted as a stability defect with a smaller processing effect. Cunningham's 2008 MSc thesis found reduced secreted V190A ligand but preserved LIGHT2 reporter activity after concentration normalization. That thesis corrected an initial immunoblot band misidentification, discovered that its intended P46L construct was wild type, and reported a media/insulin confound in the V190A ATDC5 assay; those results do not establish normal human chondrogenesis or a P46L effect. Hellemans' 2006 doctoral thesis found no differences among wild-type, ACFD and BDA1 IHH-overexpressing chicken micromass cultures. These preliminary assays may miss concentration-dependent or spatial defects. The p.Ala173Asp evidence remains computational. Mouse deletion models establish IHH requirements but cannot resolve allele-specific effects or tissue restriction.
Proposed experiments
Compare ACFD allele processing, ligand availability and signaling potency
exp_acfd_allele_signaling_assays
Express full-length wild-type IHH and sequence-confirmed P46L, R160C, A173D and V190A constructs alongside BDA1 controls. Separately quantify precursor processing, secreted ligand and dose-normalized reporter activation, then test spatial signaling in a cartilage-relevant system. Use full-length protein for processing and secretion assays; expressing IHH-N alone would bypass those steps. Control media composition and avoid interpreting a saturating overexpression assay as proof of normal signaling range.
Would support
pathophysiology#Reduced IHH Signaling Output
Would refute
pathophysiology#Reduced IHH Signaling Output
Supporting outcome
  • Reduced, but not absent, pathway activation for all four alleles would support a hypomorphic mechanism consistent with a recessive, skeleton-restricted phenotype.
Refuting outcome
  • Normal dose-normalized reporter activation would refute an obligatory intrinsic potency defect, but would not refute reduced ligand abundance or altered spatial availability. Normal tissue-level signaling across controlled expression levels would challenge the reduced-output model.
Show evidence (4 references)
PMID:40045933 SUPPORT Computational
"In silico modeling and dynamic simulation analysis revealed that the variant disturbed the core structure of the domain and destabilized the loop region and the region surrounding the variant."
Computational evidence for p.Ala173Asp; it is not the only functional evidence available for the disorder.
PMID:34070546 SUPPORT In Vitro
"ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)"
Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
url:https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF SUPPORT In Vitro
"The V190A mutation was the only mutant that induced a comparable level of relative luciferase activity"
Cunningham (2008), MSc thesis, chapter 4: secreted V190A IHH-N retained reporter activity when conditioned media were normalized for ligand abundance by immunoblot densitometry. This preliminary heterologous-cell experiment distinguishes ligand quantity from activity per amount of ligand; it is not evidence of normal signaling in patient growth plates.
+ 1 more reference
Do heterozygous carriers of ACFD alleles have short stature or subtle hand changes?
KNOWLEDGE GAP OPEN acfd_carrier_phenotype
Attached to
inheritance#Autosomal Recessive
Carrier phenotype is not wholly unstudied. The original 2003 molecular paper, reprinted in Hellemans' thesis (paper p.1044), describes subtle phalangeal or metacarpal shortening in parents without typical BDA1; pelvic radiographs were normal in the Belgian parents examined. The Pakistani parents had short stature and clinically normal hands. Heterozygous IHH variants can also cause dominant short stature. Systematic age-, sex- and family-adjusted data are needed to determine the penetrance and clinical significance of ACFD carrier findings.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"The height of the father (53 years old) and the mother (45 years old) was short, with 155 cm (-3.0SD) and 140.2 cm (-3.6 SD), respectively, but their hands were normal, with normal fingers."
Short stature in both obligate carriers in one family.
PMID:29155992 SUPPORT Human Clinical
"Identified IHH variants segregate with short stature in a dominant inheritance pattern."
Heterozygous IHH variants are an established cause of dominant short stature.
⚙

Pathophysiology

8
Biallelic IHH Signaling-Domain Missense Variants
Homozygous missense substitutions at conserved residues of the IHH amino-terminal signaling fragment, the secreted, lipid-modified part of the protein that binds Patched receptors. No truncating ACFD allele has been reported.
IHH hgnc:5956 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves IHH (hgnc:5956). hgnc:5956 is a gene from the HUGO Gene Nomenclature Committee.
Genetic context variant_origin: GERMLINE zygosity: HOMOZYGOUS
Downstream
Reduced IHH Signaling Output Reduced pathway output is inferred for the disorder. Modeling of p.Ala173Asp predicts destabilization, whereas p.Val190Ala has experimental evidence of reduced IHH-N abundance. These findings do not establish an identical biochemical defect for every allele or demonstrate absent intrinsic signaling activity.
Reduced V190A IHH-N Abundance The V190A allele reduces the abundance of the signaling fragment in a heterologous expression assay; the study attributes this predominantly to reduced stability, with a smaller effect on autoprocessing.
Show evidence (1 reference)
PMID:12632327 SUPPORT Human Clinical
"The two mutant amino acids are strongly conserved and predicted to be located outside the region where brachydactyly type A-1 mutations are clustered."
Conservation of the mutated residues and their position relative to the BDA1 cluster.
Reduced V190A IHH-N Abundance
Mechanism confidence: Provisional
The ACFD-associated p.Val190Ala IHH protein yields reduced IHH-N abundance in transfected cells. Wang et al. interpreted the N- and C-terminal fragment immunoblots as showing reduced stability with a smaller effect on precursor self-cleavage. Protein turnover kinetics and the magnitude of this defect in human growth-plate cartilage were not established. This allele-specific result is distinct from the computational destabilization prediction for p.Ala173Asp.
Experimental models
Human IHH V190A expression in ECHO cells CELL LINE Measures reduced V190A IHH-N abundance, interpreted by the authors as a stability defect with a smaller processing effect.
Downstream
Reduced IHH Signaling Output Less available ligand could reduce tissue-level pathway activation even if the remaining ligand retains signaling activity. This link is an inference, not a measurement in patient cartilage.
Show evidence (1 reference)
PMID:34070546 SUPPORT In Vitro
"ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)"
Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
Reduced IHH Signaling Output
Mechanism confidence: Provisional
Reduced effective Hedgehog signaling is proposed in growth-plate chondrocytes and perichondrium. Mouse Ihh deletion reduces ciliary Smoothened and nuclear Gli1. In ACFD, human tissue-level output remains unmeasured: V190A can lower IHH-N abundance, while a preliminary thesis reporter assay found preserved activity when the amount of secreted V190A ligand was normalized. Reduced ligand availability, spatial distribution and intrinsic receptor activation are distinct possible mechanisms.
prehypertrophic chondrocyte CL:0020022 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves prehypertrophic chondrocyte (CL:0020022). CL:0020022 is a cell type from the Cell Ontology.
Smoothened signaling pathway GO:0007224 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased Smoothened signaling pathway (GO:0007224). GO:0007224 is a biological process from the Gene Ontology. ↓ DECREASED
epiphyseal plate UBERON:0002516 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in epiphyseal plate (UBERON:0002516). UBERON:0002516 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Aggrecan-lineage Ihh deletion (Acan-creERT; Ihh floxed) mouse Mouse recapitulates Reduced ciliary Smoothened and nuclear Gli1 in Ihh-deficient chondrocytes.
Downstream
Reduced Growth Plate Chondrocyte Proliferation
Ectopic Chondrocyte Hypertrophy Embryonic experiments identify an IHH-PTHrP feedback brake on hypertrophy. In the postnatal deletion model, PTHrP persists but its distribution and that of its receptor are abnormal; a simple absence of PTHrP is not demonstrated. Translation of these model findings to ACFD remains provisional.
Loss of Growth Plate Columnar Organization IHH supports entry of periarticular cells into the columnar compartment independently of PTHrP; postnatal deletion disrupts the columns despite residual PTHrP.
Show evidence (2 references)
PMID:34820473 SUPPORT In Vitro
"Lower levels of Smo in the cilium or Gli1 protein in the nucleus were detected in Ihh-deficient chondrocytes than in control chondrocytes."
Readouts were measured in cultured articular chondrocytes isolated from conditional-deletion mice, not in ACFD patient growth plates.
PMID:8662546 SUPPORT Model Organism
"Ihh is expressed in the prehypertrophic chondrocytes of cartilage elements, where it regulates the rate of hypertrophic differentiation."
Establishes the prehypertrophic chondrocyte as the IHH source (chick and mouse limb data).
Reduced Growth Plate Chondrocyte Proliferation
Mechanism confidence: Provisional
Fewer proliferating chondrocytes in the growth plate. The mouse Ihh-null and conditional-deletion phenotypes both show this. It reduces the cartilage template available for longitudinal growth.
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.
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
Downstream
Premature Growth Plate Closure A smaller proliferative pool, together with faster hypertrophy, exhausts the growth plate early.
Show evidence (2 references)
PMID:10465785 SUPPORT Model Organism
"Mutants display markedly reduced chondrocyte proliferation, maturation of chondrocytes at inappropriate position, and a failure of osteoblast development in endochondral bones."
Ihh-null mouse embryos show reduced chondrocyte proliferation. This is a complete null, more severe than the human missense alleles.
PMID:17409191 SUPPORT Model Organism
"The number of proliferative chondrocytes decreased dramatically in mutants when compared with controls, as determined by proliferating cell nuclear antigen (PCNA)-stained cell populations"
Postnatal conditional-deletion mouse tissue directly shows reduced proliferation; this supports the growth-plate node beyond the separate articular-cell culture experiments.
Ectopic Chondrocyte Hypertrophy
Mechanism confidence: Provisional
Postnatal loss of chondrocyte Ihh in mice produces hypertrophic chondrocytes at ectopic growth-plate sites. The cells express collagen X rather than collagen II. This is model evidence for abnormal maturation in ACFD, not human growth-plate histology.
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 hypertrophy GO:0003415 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal chondrocyte hypertrophy (GO:0003415). GO:0003415 is a biological process from the Gene Ontology. ⚠ ABNORMAL
Animal models
Postnatal chondrocyte Ihh deletion (Col2a1-creERT; Ihh floxed) mouse Mouse recapitulates Reproduces loss of columnar structure and ectopic hypertrophy in the postnatal growth plate.
Downstream
Premature Growth Plate Closure Premature differentiation, reduced proliferation and abnormal vascular invasion jointly precede replacement of cartilage by bone. This is not an isolated direct effect of hypertrophy alone.
Premature Growth Plate Vascular Invasion Ectopic maturation and mineralization accompany premature vascular entry; their exact causal sequence was not isolated by the deletion experiment.
Show evidence (2 references)
PMID:17409191 SUPPORT Model Organism
"The mutant growth plate was primarily composed of hypertrophic chondrocytes that express collagen type X but not collagen type II indicating an abnormally advanced maturation stage for these cells"
Histology and collagen expression identify ectopic hypertrophy in the postnatal mouse deletion model.
PMID:40045933 SUPPORT BACKGROUND Human Clinical
"Ultimately, the rate of chondrocyte differentiation would have increased, causing early growth plate closure and bone shortening, as proposed by Hellemans et al. (2003)."
The ACFD authors attribute the human phenotype to faster chondrocyte differentiation. They restate the 2003 proposal; it is a hypothesis and was not measured in patient tissue.
Loss of Growth Plate Columnar Organization
Mechanism confidence: Provisional
Postnatal Ihh deletion disrupts the organized columns of proliferating growth-plate chondrocytes in mice. This architectural defect is distinct from ectopic hypertrophic differentiation. The physical mechanism of column formation remains incompletely resolved; stimulation of columnar differentiation does not establish a direct architectural mechanism.
Animal models
Postnatal chondrocyte Ihh deletion (Col2a1-creERT; Ihh floxed) mouse Mouse recapitulates Reproduces loss of the columnar arrangement of postnatal growth-plate chondrocytes.
Downstream
Premature Growth Plate Closure Loss of organized proliferative cartilage accompanies ectopic maturation and subsequent plate replacement in the mouse model.
Show evidence (2 references)
PMID:17409191 SUPPORT Model Organism
"demonstrated an absolute loss of columnar structure of chondrocytes in the tibia when compared with controls"
Histology at postnatal day 7 shows loss of normal proliferative columns in the conditional-deletion model.
url:https://www.jci.org/articles/view/24397 SUPPORT Other
"The precise mechanisms whereby chondrocytes form stacks of flat cells in orderly arrays are incompletely understood."
The primary paper distinguishes promotion of columnar differentiation from the incompletely understood machinery that builds orderly columns. This supports the stated mechanistic limitation.
Premature Growth Plate Vascular Invasion
Mechanism confidence: Provisional
Blood vessels enter the middle of the growth plate prematurely after postnatal Ihh deletion in mice, accompanying replacement of mineralized cartilage by bone. No corresponding vascular histology has been demonstrated in ACFD patients.
Downstream
Premature Growth Plate Closure
Show evidence (1 reference)
PMID:17409191 SUPPORT Model Organism
"premature blood vessel invasion was detected in the middle of growth plates in mutants at P7"
CD31 staining identifies abnormal vascular invasion in the mouse growth plate.
Premature Growth Plate Closure
Affected growth plates can close prematurely, often before puberty, permanently shortening the hand bones and long bones. Cone-shaped epiphyses occur during this process and may disappear after fusion; timing differs by skeletal site. The egg-shaped capital femoral epiphysis and short femoral neck are characteristic. The eight patients tabulated in 2025 are not all known molecularly reported patients.
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
epiphyseal plate UBERON:0002516 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in epiphyseal plate (UBERON:0002516). UBERON:0002516 is an anatomical location from the Uberon multi-species anatomy ontology. head of femur UBERON:0006767 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in head of femur (UBERON:0006767). UBERON:0006767 is an anatomical location from the Uberon multi-species anatomy ontology. neck of femur UBERON:0007119 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in neck of femur (UBERON:0007119). UBERON:0007119 is an anatomical location from the Uberon multi-species anatomy ontology.
Animal models
Postnatal chondrocyte Ihh deletion (Col2a1-creERT; Ihh floxed) mouse Mouse recapitulates Reproduces premature growth plate fusion and dwarfism.
Downstream
Premature epimetaphyseal fusion
Cone-shaped epiphyses of the hand phalanges Cone-shaped epiphyses and premature fusion are linked radiographic features. The detailed spatial mechanism producing the cone shape remains proposed rather than experimentally demonstrated.
Short middle phalanges
Brachydactyly
Short metacarpals
Short femoral neck
Egg-shaped capital femoral epiphysis
Limb undergrowth
Short humerus
Short tibia
Disproportionate short stature
Narrow chest Reduced endochondral rib growth plausibly contributes to the narrow thorax. Conditional Ihh deletion in mice can shorten ribs enough to cause respiratory death, but this occurred in a subset rather than every untreated mutant. Rib growth plates have not been examined in ACFD patients.
Coxa vara Coxa vara develops alongside the abnormal proximal femoral epiphysis and short femoral neck. The exact steps are not described.
Genu varum Variable. It is seen together with the hyperplastic distal femur and irregular proximal tibial metaphysis in some patients; the exact steps are not described.
Relative macrocephaly The head is large relative to a body shortened by reduced endochondral growth. Head circumference ranges from the 3rd to the 98th centile in the published patients, so the head is not enlarged in absolute terms.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Despite the age difference among the ACFD patients reported to date (Table 2), early growth plate closure was evident in all of them, which led to the shortening of long tubular bones in the arms and legs, along with cone-shaped epiphyses."
The 2025 authors report premature closure across their clinical comparison; this does not establish complete fusion of every plate in each patient.
PMID:34820473 SUPPORT BACKGROUND Model Organism
"Consistent with our results, postnatal deletion of Ihh with Col2-creERT by administration of TM caused premature fusion of growth plates of various endochondral bones in mice, resulting in dwarfism in mutant mice."
A second group restates the premature-fusion result from postnatal Ihh deletion.
⬡

Pathograph

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

40
Eye 1
Unilateral ptosis HP:0007687 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Unilateral ptosis (HP:0007687). HP:0007687 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"(B) IV‐1 and (C) IV‐2 depicting severe short stature and unilateral ptosis."
Reported in both Pakistani siblings. This family-level observation has not been established as a recurrent or directly IHH-mediated manifestation.
Head and Neck 1
Relative macrocephaly HP:0004482 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Relatively large head, annotated with Relative macrocephaly (HP:0004482). HP:0004482 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"Both affected individuals had severe short stature, short limbs, a narrow thorax, and a relatively large head"
Present in both Pakistani siblings and listed among the defining features.
Integument 3
Short nail HP:0001799 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short broad nails, annotated with Short nail (HP:0001799). HP:0001799 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Their hands were short, with brachydactyly and short nails"
Short nails in both Pakistani siblings.
PMID:40045933 SUPPORT Human Clinical
"| Small broad nails | + | + | + | + | NR | NR | + | + |"
Table 2: 6/6 recorded; two NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Broad nail HP:0001821 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Broad nail (HP:0001821). HP:0001821 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:40045933 SUPPORT BACKGROUND Human Clinical
"Acrocapitofemoral dysplasia (ACFD; MIM 607778) is a rare autosomal recessive disorder characterized by postnatal onset disproportionate short stature of variable degrees with short limbs, brachydactyly, short broad nails, narrow thorax, pectus deformities, and a relatively large head, with an average IQ"
Restates the original clinical delineation (Mortier et al. 2003; Hellemans et al. 2003), which lists short broad nails among the defining features.
PMID:40045933 SUPPORT Human Clinical
"The phenotypes of both the affected individuals in this study, including severe short stature, short limbs, large head, narrow thorax, small broad nails, lumbar lordosis, brachydactyly, and an average IQ, were the same as reported in all six previously reported ACFD patients"
Small broad nails in both Pakistani siblings.
PMID:40045933 SUPPORT Human Clinical
"| Small broad nails | + | + | + | + | NR | NR | + | + |"
Table 2: 6/6 recorded; two NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Hypertrichosis HP:0000998 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypertrichosis (HP:0000998). HP:0000998 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"| Hypertrichosis | + | − | NR | NR | NR | NR | NR | NR |"
Observed in the Pakistani proband, including hair over the foot, and absent in his brother. A causal relationship to IHH has not been demonstrated.
Limbs 23
Limb undergrowth HP:0009826 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short limbs, annotated with Limb undergrowth (HP:0009826). HP:0009826 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34530144 SUPPORT Human Clinical
"Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal dysplasia characterized by short stature with short limb dwarfism, brachydactyly, and a narrow thorax."
Short-limbed dwarfism is part of the defining triad.
PMID:40045933 SUPPORT Human Clinical
"| Short limbs | + | + | + | + | + | + | + | + |"
Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Short humerus HP:0005792 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short humerus (HP:0005792). HP:0005792 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"The humerus bone was severely shortened with cone-shaped proximal epiphysis."
Radiographic finding in the proband.
PMID:40045933 SUPPORT Human Clinical
"| Short humerus | + | NA | + | + | + | + | + | + |"
Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Short tibia HP:0005736 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short tibia (HP:0005736). HP:0005736 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"the tibia and fibula bones were extremely short with irregular proximal tibial metaphyses and cone-shaped distal tibial epiphyses"
Radiographic finding in the proband.
PMID:40045933 SUPPORT Human Clinical
"| Short tibia and fibula | + | NA | + | + | + | + | + | + |"
Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Brachydactyly HP:0001156 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Brachydactyly (HP:0001156). HP:0001156 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:34530144 SUPPORT Human Clinical
"Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal dysplasia characterized by short stature with short limb dwarfism, brachydactyly, and a narrow thorax."
Brachydactyly is part of the defining triad.
PMID:40045933 SUPPORT Human Clinical
"Their hands were short, with brachydactyly and short nails"
Present in both Pakistani siblings.
PMID:40045933 SUPPORT Human Clinical
"| Brachydactyly | + | + | + | + | + | + | + | + |"
Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Short middle phalanges Short middle phalanx of finger HP:0005819 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short middle phalanges of the hand, annotated with Short middle phalanx of finger (HP:0005819). HP:0005819 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Commonly reported radiographic features, that is, short and broad metacarpal and metatarsal bones with conical teardrop epiphyses, short middle phalanges, fused phalanges, coxa vara, short and flared iliac wings with dysplastic acetabulum, egg-shaped capito-femoral epiphyses with a short femoral..."
Lists short middle phalanges among the recurrent radiographic features.
PMID:40045933 SUPPORT Human Clinical
"| Short middle phalange | + | + | + | + | + | + | + | + |"
Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
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 (3 references)
PMID:40045933 SUPPORT Human Clinical
"Commonly reported radiographic features, that is, short and broad metacarpal and metatarsal bones with conical teardrop epiphyses"
Short broad metacarpals are a recurrent radiographic feature.
PMID:34530144 SUPPORT Human Clinical
"The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck."
The typical metacarpal configuration persists into adulthood.
PMID:40045933 SUPPORT Human Clinical
"| Short metacarpal bones | + | + | + | + | + | + | + | + |"
Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Cone-shaped epiphyses of the hand phalanges 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 (2 references)
PMID:12632327 SUPPORT Human Clinical
"Acrocapitofemoral dysplasia is a recently delineated autosomal recessive skeletal dysplasia, characterized clinically by short stature with short limbs and radiographically by cone-shaped epiphyses, mainly in hands and hips."
Cone-shaped epiphyses in the hands are the defining radiographic sign.
PMID:40045933 SUPPORT Human Clinical
"| Cone shaped epiphysis | + | NA | + | + | + | + | − | − |"
The five positive entries include an adult. The pooled-site table cannot establish a hand-specific frequency or universal disappearance after childhood.
Egg-shaped capital femoral epiphysis Abnormality of the epiphysis of the femoral head HP:0010574 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Egg-shaped capital femoral epiphysis, annotated with Abnormality of the epiphysis of the femoral head (HP:0010574). HP:0010574 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34530144 SUPPORT Human Clinical
"Major radiographic features are egg-shaped capital femoral epiphyses with a short femoral neck and cone-shaped epiphyses, mainly in the hands and hips."
Egg-shaped capital femoral epiphyses are a major radiographic feature.
Short femoral neck HP:0100864 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short femoral neck (HP:0100864). HP:0100864 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:34530144 SUPPORT Human Clinical
"Major radiographic features are egg-shaped capital femoral epiphyses with a short femoral neck and cone-shaped epiphyses, mainly in the hands and hips."
Short femoral neck is a major radiographic feature.
PMID:34530144 SUPPORT Human Clinical
"The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck."
The femoral neck is extremely short in adults.
PMID:40045933 SUPPORT Human Clinical
"| Short femoral neck | + | NA | + | + | + | + | + | + |"
Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Coxa vara FREQUENT HP:0002812 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Coxa vara (HP:0002812). HP:0002812 is a phenotype from the Human Phenotype Ontology.
Sequelae: Hip osteoarthritis
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Pelvic examination showed bilateral osteoarthritis, short and flared iliac wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth."
Coxa vara on pelvic radiographs of the proband.
PMID:40045933 SUPPORT Human Clinical
"| Coxa vara | + | NA | − | + | + | + | − | − |"
Table 2: 4/7 recorded, or 57%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Genu varum HP:0002970 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Genu varum (HP:0002970). HP:0002970 is a phenotype from the Human Phenotype Ontology.
Sequelae: Waddling gait
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Our proband (IV-1) also had a rarely reported genu vara phenotype observed in only 1 of the 4 patients reported by Mortier et al. (2003) due to which he had a waddling walk."
Genu varum in the proband, described as rare in earlier patients.
PMID:40045933 SUPPORT Human Clinical
"| Genu vara | + | + | + | − | + | − | − | − |"
Four positive entries, not three. The later summary table and the same paper's description of the original cases are not fully consistent.
Fifth toe symphalangism HP:0010389 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fifth toe symphalangism (HP:0010389). HP:0010389 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34530144 SUPPORT Human Clinical
"The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck."
Fifth-toe phalangeal fusion in the Turkish adults.
PMID:40045933 SUPPORT Human Clinical
"fused middle and distal phalanx of the fifth toe bilaterally"
Fifth-toe phalangeal fusion in the Pakistani proband.
Short metatarsals HP:0010743 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short metatarsal (HP:0010743). HP:0010743 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Foot examination revealed short and broad metatarsals with conical tear drop epiphyses, accessory navicular foot deformity, and fused middle and distal phalanx of the fifth toe bilaterally"
Short metatarsals on foot radiographs of the Pakistani proband.
PMID:40045933 SUPPORT Human Clinical
"Commonly reported radiographic features, that is, short and broad metacarpal and metatarsal bones with conical teardrop epiphyses"
The report lists short broad metatarsals among the recurrent radiographic features.
Acetabular dysplasia HP:0008807 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dysplastic acetabulum, annotated with Acetabular dysplasia (HP:0008807). HP:0008807 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Pelvic examination showed bilateral osteoarthritis, short and flared iliac wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth."
Dysplastic acetabulum on pelvic radiographs of the proband.
PMID:40045933 SUPPORT Human Clinical
"short and flared iliac wings with dysplastic acetabulum, egg-shaped capito-femoral epiphyses with a short femoral neck, and hyperplastic distal femur, were also observed in our patients"
Listed among the commonly reported radiographic features.
Radial bowing FREQUENT HP:0002986 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Radial and ulnar angulation, annotated with Radial bowing (HP:0002986). HP:0002986 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:34530144 SUPPORT Human Clinical
"The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck."
Radial angulation in the two Turkish adults.
PMID:40045933 SUPPORT Human Clinical
"All the carpal bones were fused, and the radial and ulnar bones were short with bilateral varus angulation and medlung-like deformity at the distal radioulnar joint."
Bilateral radial and ulnar angulation with a Madelung-like deformity in the Pakistani proband.
PMID:40045933 SUPPORT Human Clinical
"| Radial ulnal angulation | + | NA | − | − | − | − | + | + |"
Table 2: 3/7 recorded, or 43%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Finger symphalangism HP:0009700 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Finger symphalangism (HP:0009700). HP:0009700 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT BACKGROUND Human Clinical
"Cubuk and Duz (2021) reported the fused middle and proximal phalanges of 5th finger and toes and an osteoporotic appearance in the spinal column"
Restates fifth-finger phalangeal fusion in the two Turkish adults.
PMID:40045933 SUPPORT Human Clinical
"the middle and distal phalanges of 1st finger, 2nd finger and thumbs were fused"
Finger phalangeal fusion in the Pakistani proband.
Dislocated radial head HP:0003083 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Dislocated radial head (HP:0003083). HP:0003083 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"A dislocated radial head with an increased inclination angle of the humeral head was seen at the elbow joints"
Observed radiographically in the Pakistani proband; the source does not establish its frequency across ACFD.
Carpal synostosis Synostosis of carpal bones HP:0005048 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Carpal synostosis, annotated with Synostosis of carpal bones (HP:0005048). HP:0005048 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"All the carpal bones were fused"
Fusion of carpal bones in the Pakistani proband. This is distinct from delayed carpal ossification in childhood.
Fibular hypoplasia HP:0003038 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Fibular hypoplasia (HP:0003038). HP:0003038 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"the tibia and fibula bones were extremely short with irregular proximal tibial metaphyses and cone‐shaped distal tibial epiphyses."
Markedly short fibulae in the Pakistani proband. The later table records short tibiae and fibulae together in seven assessed patients, with one NA.
Hypoplasia of the radius HP:0002984 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hypoplasia of the radius (HP:0002984). HP:0002984 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"the radial and ulnar bones were short with bilateral varus angulation"
Short radii, accompanied by short ulnae and bilateral forearm angulation, in the Pakistani proband.
Ulnar bowing HP:0003031 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ulnar bowing (HP:0003031). HP:0003031 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"the radial and ulnar bones were short with bilateral varus angulation"
Bilateral varus angulation of the ulnae in the Pakistani proband, alongside radial bowing.
Narrow femoral medullary cavity Stenosis of the medullary cavity of the long bones HP:0100254 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Narrow femoral medullary cavity, annotated with Stenosis of the medullary cavity of the long bones (HP:0100254). HP:0100254 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"The femur bone was short with a short neck, thin shaft, and narrow medullary cavity and hyperplastic distal end."
Narrow medullary cavity of the femur in the Pakistani proband. The binding is to narrowing of a long-bone medullary cavity, not a generalized marrow disorder.
Pes planus HP:0001763 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pes planus (HP:0001763). HP:0001763 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"| Pes planus | + | + | NR | NR | NR | NR | NR | NR |"
Reported in both Pakistani siblings; the remaining cases were not reported for this feature, so a population frequency cannot be inferred.
PMID:40045933 SUPPORT Human Clinical
"Foot examination revealed short and broad metatarsals with conical tear drop epiphyses, accessory navicular foot deformity, and fused middle and distal phalanx of the fifth toe bilaterally"
Additional foot findings in the proband; this snippet supports the accessory navicular description rather than the pes planus frequency.
Musculoskeletal 9
Premature epimetaphyseal fusion HP:0010588 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Premature closure of the growth plates, annotated with Premature epimetaphyseal fusion (HP:0010588). HP:0010588 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"Despite the age difference among the ACFD patients reported to date (Table 2), early growth plate closure was evident in all of them"
Early growth plate closure in the selected clinical comparison; closure varies by skeletal site and age.
Narrow chest HP:0000774 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Narrow chest (HP:0000774). HP:0000774 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:34530144 SUPPORT Human Clinical
"Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal dysplasia characterized by short stature with short limb dwarfism, brachydactyly, and a narrow thorax."
Narrow thorax is part of the defining triad.
PMID:40045933 SUPPORT Human Clinical
"Chest radiographs of IV-1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs."
Radiographic narrow thorax with short ribs in the proband.
Lumbar hyperlordosis FREQUENT HP:0002938 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Lumbar lordosis, annotated with Lumbar hyperlordosis (HP:0002938). HP:0002938 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Chest radiographs of IV-1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs."
Lumbar lordosis on radiographs of the proband.
PMID:40045933 SUPPORT Human Clinical
"| Lumber lordosis | + | NA | + | + | − | + | − | + |"
Table 2: 5/7 recorded, or 71%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Hip osteoarthritis HP:0008843 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hip osteoarthritis (HP:0008843). HP:0008843 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"a bilateral osteoarthritic appearance was observed in the hip joint of IV-1, which caused reduced joint mobility and function"
Single-patient observation of secondary hip osteoarthritis.
Flared iliac wing FREQUENT HP:0002869 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short and flared iliac wings, annotated with Flared iliac wing (HP:0002869). HP:0002869 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:40045933 SUPPORT Human Clinical
"Pelvic examination showed bilateral osteoarthritis, short and flared iliac wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth."
Short, flared iliac wings on pelvic radiographs of the proband.
PMID:40045933 SUPPORT Human Clinical
"short and flared iliac wings with dysplastic acetabulum, egg-shaped capito-femoral epiphyses with a short femoral neck, and hyperplastic distal femur, were also observed in our patients"
Listed among the commonly reported radiographic features.
PMID:40045933 SUPPORT Human Clinical
"| Short and flared Iliac wings | + | NA | − | − | + | + | − | NR |"
Table 2: 3/6 recorded, or 50%, within the FREQUENT band; one NA and one NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
Short ribs HP:0000773 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short ribs (HP:0000773). HP:0000773 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"Chest radiographs of IV‐1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs."
Short ribs with costal-end cupping in the Pakistani proband. Human respiratory consequences were not quantified.
Short clavicles HP:0000894 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Short clavicles (HP:0000894). HP:0000894 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"Chest radiographs of IV‐1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs."
Short clavicles on the Pakistani proband's radiographs; no population frequency is inferred.
Pectus excavatum HP:0000767 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pectus excavatum (HP:0000767). HP:0000767 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"| Thorax | Narrow | NA | Normal | Normal | Pectus craniatum | Pectus excavatum | Narrow | Narrow |"
Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned.
Pectus carinatum HP:0000768 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Pectus carinatum (HP:0000768). HP:0000768 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"| Thorax | Narrow | NA | Normal | Normal | Pectus craniatum | Pectus excavatum | Narrow | Narrow |"
Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned. The later table misspells carinatum as craniatum.
Nervous System 1
Waddling gait HP:0002515 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Waddling gait (HP:0002515). HP:0002515 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"Our proband (IV-1) also had a rarely reported genu vara phenotype observed in only 1 of the 4 patients reported by Mortier et al. (2003) due to which he had a waddling walk."
Waddling gait in the proband.
Growth 1
Disproportionate short stature HP:0003498 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Disproportionate short stature (HP:0003498). HP:0003498 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:40045933 SUPPORT Human Clinical
"Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive disorder, characterized by postnatal onset of disproportionate short stature with short limbs, brachydactyly, cone-shaped epiphysis, narrow thorax, and relatively large head."
Names postnatal-onset disproportionate short stature as a defining feature.
PMID:40045933 SUPPORT Human Clinical
"Both affected individuals had severe short stature, short limbs, a narrow thorax, and a relatively large head"
Present in both Pakistani siblings.
PMID:40045933 SUPPORT Human Clinical
"At the time of sampling, IV‐1 was 20 years old, having a height of 102 cm (−10.4 SD) height and IV‐2 was 14 years old, having a height of 84 cm (−9.6 SD)"
Age and height measurements in the Pakistani sibship, as reported; these establish severe short stature without extrapolating the table to all known patients.
Other 1
Hyperplastic distal femur
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"The femur bone was short with a short neck, thin shaft, and narrow medullary cavity and hyperplastic distal end."
Hyperplastic distal femur in the Pakistani proband.
🧬

Genetic Associations

1
IHH (Causative)
Gene: IHH hgnc:5956 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is IHH (hgnc:5956). hgnc:5956 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:12632327 SUPPORT Human Clinical
"Using a candidate-gene approach, we identified two missense mutations in the amino-terminal signaling domain of the gene encoding Indian hedgehog (IHH)."
Identifies IHH as the causal gene after linkage to 2q35-q36.
PMID:19277064 SUPPORT Human Clinical
"All of the BDA1 mutations occur in a restricted area of the N-terminal active fragment of the IHH and are in contrast to those mutations causing an autosomal recessive acrocapitofemoral dysplasia, whose mutations are located at the distal N- and C-terminal regions of IHH-N and are physically..."
Places the recessive ACFD variants at the ends of IHH-N, apart from the dominant BDA1 hotspot.
Variants (4)
IHH c.137C>T p.(Pro46Leu)
Homozygous in the two affected members of family 1 (2003).
Show evidence (1 reference)
PMID:12632327 SUPPORT Human Clinical
"Both affected individuals of family 1 are homozygous for a 137C-->T transition (P46L)"
Reports the variant and its homozygous state.
IHH c.569T>C p.(Val190Ala)
Homozygous in the three affected members of family 2 (2003).
Show evidence (1 reference)
PMID:12632327 SUPPORT Human Clinical
"the three patients in family 2 are homozygous for a 569T-->C transition (V190A)"
Reports the variant and its homozygous state.
IHH c.478C>T p.(Arg160Cys)
Homozygous in two adult siblings from a Turkish family (2021).
Show evidence (1 reference)
PMID:34530144 SUPPORT Human Clinical
"We describe two adult patients with ACFD with a novel homozygous c.478C>T (p.Arg160Cys) mutation in IHH in the third family of the literature."
Reports the third ACFD variant.
IHH c.518C>A p.(Ala173Asp)
Homozygous in two siblings from a Pakistani family (2025). Classified likely pathogenic by the reporting authors under ACMG criteria. In silico modeling places Ala173 in the core of the domain.
Show evidence (1 reference)
PMID:40045933 SUPPORT Human Clinical
"This variant caused the substitution of Alanine with Aspartate at amino acid position 173 (NP_002172.2: p.(Ala173Asp)) in the IHH protein."
Reports the fourth ACFD variant (c.518C>A in NM_002181.4), found homozygous in both affected siblings.
💊

Medical Actions

1
Smoothened agonist SAG (preclinical)
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: SAG (Smoothened agonist) CHEBI:138438 Chemical Entities of Biological Interest (CHEBI) Relation: this treatment uses this therapeutic agent This treatment uses SAG (Smoothened agonist), annotated with 3-chloro-N-[trans-4-(methylamino)cyclohexyl]-N-[3-(pyridin-4-yl)benzyl]-1-benzothiophene-2-carboxamide (CHEBI:138438). CHEBI:138438 is a therapeutic agent from Chemical Entities of Biological Interest.
SAG activates Smoothened downstream of IHH. It improved skeletal growth and survival in conditional Ihh-deletion mice; starting at postnatal day 7 produced greater growth benefit than starting at day 14. Cartilage and growth-plate rescue was partial. The study also reported intestinal hyperplasia and bowel-obstruction deaths, so its broad statement of no toxicity should not be taken as a safety conclusion. These results do not establish a treatment regimen for patients with ACFD.
Mechanism Target:
RESTORES Reduced IHH Signaling Output — Activating Smoothened restores downstream signaling readouts in the conditional-deletion model, bypassing deficient IHH input.
Show evidence (1 reference)
PMID:34820473 SUPPORT In Vitro
"SAG treatment resulted in dramatically increased Smo translocation to the primary cilium and Gli1 accumulation in the nucleus"
SAG restores pathway readouts downstream of the missing ligand in cultured mouse articular chondrocytes. It does not correct the IHH genotype.
Show evidence (5 references)
PMID:34820473 SUPPORT In Vitro
"SAG treatment resulted in dramatically increased Smo translocation to the primary cilium and Gli1 accumulation in the nucleus"
SAG restores pathway readouts downstream of the missing ligand in cultured mouse articular chondrocytes. It does not correct the IHH genotype.
PMID:34820473 SUPPORT Model Organism
"earlier treatment with SAG beginning on P7 was more effective in preventing the dwarfism phenotype compared to the treatment beginning on P14."
The comparison concerns timing in neonatal mice; it does not establish clinical timing for children.
PMID:34820473 SUPPORT Model Organism
"SAG can more effectively rescue the defective bone but just partially rescue the growth plate and cartilage."
The discussion qualifies the degree of rescue; normal growth-plate biology was not fully restored.
+ 2 more references
🔬

Diagnosis

2
Skeletal radiographic assessment
The combination of hand epiphyseal abnormalities and the short femoral neck with egg-shaped capital epiphysis supports recognition of ACFD. Adult films may instead show fused plates, very short femoral necks, altered metacarpal configuration and phalangeal fusion; loss of childhood cone-shaped appearances does not exclude the diagnosis.
Bone Radiography NCIT:C137876 NCI Thesaurus (NCIT)
Show evidence (1 reference)
PMID:34530144 SUPPORT Human Clinical
"The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck. These findings could help the diagnosis of ACFD in adult patients."
Adult diagnostic clues differ from childhood epiphyseal appearances.
Molecular testing for biallelic IHH variants
Exome sequencing identified the IHH variant in the Pakistani proband; Sanger sequencing confirmed the variant and segregation in affected siblings and parents. Molecular findings should be interpreted with the radiographic phenotype, particularly when additional skeletal-dysplasia gene variants could produce a blended presentation.
Whole Exome Sequencing NCIT:C101295 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:40045933 SUPPORT Human Clinical
"Whole exome sequencing (WES) followed by Sanger sequencing was carried out for mutational screening."
Exome discovery with Sanger confirmation in the reported family.
PMID:40045933 SUPPORT Human Clinical
"The parents were heterozygous carriers, while both affected individuals carried the homozygous mutant allele"
Family segregation supports the molecular interpretation.
📊

Prevalence

1
Worldwide
Cases In Literature Ultra Rare
No population prevalence estimate exists. The 2003 molecular report includes five affected individuals in two families, whereas the clinical comparison in the 2025 report tabulates four of those individuals plus two Turkish and two Pakistani patients. Thus its eight-person table is not a complete count of all molecularly reported individuals. The scanned 2003 full text explicitly says that a fifth patient was identified after the initial four. The four unblended molecular families therefore contribute at least nine individuals, rather than eight. A separate 2025 Syrian child with IHH and other skeletal-dysplasia gene variants has a blended phenotype and is not pooled into these phenotype denominators.
Show evidence (3 references)
PMID:40045933 SUPPORT Human Clinical
"Up till now, only six cases of ACFD have been reported from Belgian, Dutch (Mortier et al. 2003; Hellemans et al. 2003), and Turkish families (Cubuk and Duz 2021)."
This is the later report's stated caseload, which omits the additional fifth individual in the 2003 molecular study. Its table remains useful as an explicitly defined eight-person comparison, not a complete census.
PMID:34530144 SUPPORT Human Clinical
"To date, only four child patients from two families have been reported."
The adult report summarizes four earlier children. This does not supersede the five molecularly characterized individuals in the 2003 report.
PMID:12632327 SUPPORT Human Clinical
"Both affected individuals of family 1 are homozygous for a 137C-->T transition (P46L), and the three patients in family 2 are homozygous for a 569T-->C transition (V190A)."
Two plus three establishes five individuals in the original molecular report; adding the two subsequent sibships gives at least nine across the four families.
🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Acrocapitofemoral Dysplasia:

🧫

Experimental Models

1
Human IHH V190A expression in ECHO cells CELL_LINE
Full-length human wild-type or V190A IHH was expressed with N- or C-fragment FLAG tags. Immunoblots compared the signaling and autoprocessing fragments; supplementary Figure S5 shows a larger reduction of the N-terminal than the C-terminal fragment.
Cell source
EcR-CHO cells expressing human IHH constructs
Publication
PMID:34070546
Pathograph links
Reduced V190A IHH-N Abundance measures fidelity: moderate observes: molecular Measures reduced V190A IHH-N abundance, interpreted by the authors as a stability defect with a smaller processing effect.
Limitations: Heterologous overexpression of tagged human protein, not patient-derived cartilage. Fragment abundance does not directly measure protein half-life, secretion, receptor binding or spatial signaling in the growth plate. The paper's multimerization and alkaline-phosphatase assays mainly test engineered truncations, not V190A.
Show evidence (1 reference)
PMID:34070546 SUPPORT In Vitro
"ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)"
Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
🐁

Animal Models

2
Postnatal chondrocyte Ihh deletion (Col2a1-creERT; Ihh floxed) mouse
Tamoxifen-induced deletion of Ihh from chondrocytes after birth. This avoids the embryonic lethality of the constitutive null and isolates the postnatal growth plate phase in which ACFD becomes apparent.
Species
Mouse
Genotype
Col2a1-creERT; Ihh(fl/fl), tamoxifen-induced after birth
Publication
PMID:17409191
Pathograph links
Ectopic Chondrocyte Hypertrophy recapitulates fidelity: moderate observes: tissue Reproduces loss of columnar structure and ectopic hypertrophy in the postnatal growth plate.
Limitations: Conditional deletion of Ihh, rather than a human ACFD missense allele. V190A has in-vitro biochemical and reporter data, but residual activity in patient cartilage remains unknown. Trabecular-bone loss and articular-surface destruction in these mice are not established ACFD manifestations.
Show evidence (1 reference)
PMID:17409191 SUPPORT Model Organism
"postnatal deletion of Ihh resulted in loss of columnar structure, premature vascular invasion, and formation of ectopic hypertrophic chondrocytes in the growth plate"
Growth plate histology in the model.
Premature Growth Plate Closure recapitulates fidelity: moderate observes: organism Reproduces premature growth plate fusion and dwarfism.
Limitations: Mouse growth plates do not close physiologically the way human ones do at puberty, so the timing is not directly comparable to prepubertal closure in patients.
Show evidence (1 reference)
PMID:17409191 SUPPORT Model Organism
"Furthermore, destruction of the articular surface in long bones and premature fusion of growth plates of various endochondral bones was evident, resulting in dwarfism in mutant mice."
Premature growth plate fusion and dwarfism in the model.
Loss of Growth Plate Columnar Organization recapitulates fidelity: moderate observes: tissue Reproduces loss of the columnar arrangement of postnatal growth-plate chondrocytes.
Limitations: Conditional deletion of Ihh, rather than a human ACFD missense allele. V190A has in-vitro biochemical and reporter data, but residual activity in patient cartilage remains unknown. Trabecular-bone loss and articular-surface destruction in these mice are not established ACFD manifestations.
Show evidence (1 reference)
PMID:17409191 SUPPORT Model Organism
"postnatal deletion of Ihh resulted in loss of columnar structure, premature vascular invasion, and formation of ectopic hypertrophic chondrocytes in the growth plate"
Growth plate histology in the model.
Aggrecan-lineage Ihh deletion (Acan-creERT; Ihh floxed) mouse
Inducible deletion of Ihh from aggrecan-expressing cells. The authors present it as a model of human IHH-related chondrodysplasias, including ACFD, and used it to test the Smoothened agonist SAG.
Species
Mouse
Genotype
Acan-creERT; Ihh(fl/fl), tamoxifen-induced
Publication
PMID:34820473
Pathograph links
Reduced IHH Signaling Output recapitulates fidelity: moderate observes: cellular Reduced ciliary Smoothened and nuclear Gli1 in Ihh-deficient chondrocytes.
Limitations: A conditional deletion model with residual Ihh expression and broad aggrecan-lineage targeting, not an ACFD missense model. Smoothened and Gli1 were measured in cultured articular chondrocytes, not directly in patient growth plates.
Readouts
Ciliary Smoothened and nuclear Gli1 in chondrocytes
Direction: DECREASED
Interpretation: Direct pathway-activity readout downstream of Patched.
Show evidence (1 reference)
PMID:34820473 SUPPORT In Vitro
"Lower levels of Smo in the cilium or Gli1 protein in the nucleus were detected in Ihh-deficient chondrocytes than in control chondrocytes."
The measured readout and its direction.
Show evidence (1 reference)
PMID:34820473 SUPPORT In Vitro
"Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte proliferation and differentiation by stimulating smoothened trafficking to the cilium in Ihh-silenced cells."
Rescue with a Smoothened agonist shows the defect sits upstream of Smoothened, which is where reduced ligand acts.
{ }

Source YAML

click to show 
name: Acrocapitofemoral Dysplasia
creation_date: "2026-09-24T20:42:38Z"
category: Mendelian
description: >-
  Acrocapitofemoral dysplasia (ACFD) is an ultra-rare autosomal recessive skeletal dysplasia caused by homozygous missense variants in the amino-terminal signaling domain of IHH (Indian hedgehog). It presents with postnatal-onset disproportionate short stature with short limbs, brachydactyly, a narrow thorax and a relatively large head, with normal intelligence. The defining radiographic signs are cone-shaped epiphyses, mainly in the hands and hips, and an egg-shaped capital femoral epiphysis on a short femoral neck. These are followed by early, prepubertal closure of the growth plates, which permanently shortens the tubular bones of the hands and the long bones of the limbs. A published cell study found reduced IHH-N abundance, interpreted as reduced protein stability with a slight processing defect for p.Val190Ala. The growth-plate mechanism is supported mainly by mouse genetics: IHH secreted by prehypertrophic chondrocytes drives chondrocyte proliferation and paces hypertrophic differentiation through a PTHrP feedback loop, and postnatal loss of chondrocyte IHH disorganizes the growth plate and fuses it prematurely. Allele-specific effects on signaling in human cartilage remain unresolved.
synonyms:
- ACFD
disease_term:
  preferred_term: Acrocapitofemoral Dysplasia
  term:
    id: MONDO:0011907
    label: acrocapitofemoral dysplasia
parents:
- acromelic dysplasia
- osteochondrodysplasia
classifications:
  isds_skeletal_category:
  - classification_value: acromelic_dysplasias
    notes: >-
      Group 17 "Acromelic dysplasias" of the 2023 ISDS Nosology of Genetic
      Skeletal Disorders (Unger et al., PMID:36779427), whose schema enum
      description names acrocapitofemoral dysplasia (IHH) as a member. The
      MONDO parent MONDO:0019695 acromelic dysplasia agrees.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    No population prevalence estimate exists. The 2003 molecular report includes five affected individuals in two families, whereas the clinical comparison in the 2025 report tabulates four of those individuals plus two Turkish and two Pakistani patients. Thus its eight-person table is not a complete count of all molecularly reported individuals. The scanned 2003 full text explicitly says that a fifth patient was identified after the initial four. The four unblended molecular families therefore contribute at least nine individuals, rather than eight. A separate 2025 Syrian child with IHH and other skeletal-dysplasia gene variants has a blended phenotype and is not pooled into these phenotype denominators.
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Up till now, only six cases of ACFD have been reported from Belgian, Dutch
      (Mortier et al. 2003; Hellemans et al. 2003), and Turkish families (Cubuk
      and Duz 2021).
    explanation: >-
      This is the later report's stated caseload, which omits the additional fifth individual in the 2003 molecular study. Its table remains useful as an explicitly defined eight-person comparison, not a complete census.
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, only four child patients from two families have been reported."
    explanation: >-
      The adult report summarizes four earlier children. This does not supersede the five molecularly characterized individuals in the 2003 report.
  - reference: PMID:12632327
    reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both affected individuals of family 1 are homozygous for a 137C-->T transition (P46L), and the three patients in family 2 are homozygous for a 569T-->C transition (V190A).
    explanation: >-
      Two plus three establishes five individuals in the original molecular report; adding the two subsequent sibships gives at least nine across the four families.
inheritance:
- name: Autosomal Recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    The unblended ACFD families reported here have homozygous IHH missense variants, consistent with autosomal recessive inheritance. Tested parents carry heterozygous variants. Both Pakistani carrier parents had short stature with clinically normal hands; that observation should not be generalized to every carrier. The original molecular paper discusses subtle radiographic hand-bone shortening in some parents without the typical BDA1 phenotype. Carrier effects and penetrance remain incompletely characterized.
  evidence:
  - reference: PMID:12632327
    reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both affected individuals of family 1 are homozygous for a 137C-->T
      transition (P46L), and the three patients in family 2 are homozygous for a
      569T-->C transition (V190A).
    explanation: Homozygosity for the causal variant in all affected members of the two founding families.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The parents were heterozygous carriers, while both affected individuals
      carried the homozygous mutant allele
    explanation: Segregation consistent with autosomal recessive inheritance in the fourth family.
genetic:
- name: IHH
  gene_term:
    preferred_term: IHH
    term:
      id: hgnc:5956
      label: IHH
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  features: >-
    Four homozygous missense variants are known, one per family: c.137C>T
    p.(Pro46Leu), c.569T>C p.(Val190Ala), c.478C>T p.(Arg160Cys) and c.518C>A
    p.(Ala173Asp). All lie in the amino-terminal signaling fragment (IHH-N),
    away from the central cluster of residues (codons 95-154) that carries the
    dominant brachydactyly type A1 variants. The 2025 report describes the ACFD
    variants as lying in "amino acids 201-308"; that range does not fit its own
    list of variant positions (46-190) and is not used here.
  evidence:
  - reference: PMID:12632327
    reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Using a candidate-gene approach, we identified two missense mutations in
      the amino-terminal signaling domain of the gene encoding Indian hedgehog
      (IHH).
    explanation: Identifies IHH as the causal gene after linkage to 2q35-q36.
  - reference: PMID:19277064
    reference_title: Brachydactyly A-1 mutations restricted to the central region of the N-terminal active fragment of Indian Hedgehog.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All of the BDA1 mutations occur in a restricted area of the N-terminal
      active fragment of the IHH and are in contrast to those mutations causing
      an autosomal recessive acrocapitofemoral dysplasia, whose mutations are
      located at the distal N- and C-terminal regions of IHH-N and are
      physically separated from the BDA1-causing mutations.
    explanation: >-
      Places the recessive ACFD variants at the ends of IHH-N, apart from the
      dominant BDA1 hotspot.
  variants:
  - name: IHH c.137C>T p.(Pro46Leu)
    description: Homozygous in the two affected members of family 1 (2003).
    evidence:
    - reference: PMID:12632327
      reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Both affected individuals of family 1 are homozygous for a 137C-->T
        transition (P46L)
      explanation: Reports the variant and its homozygous state.
  - name: IHH c.569T>C p.(Val190Ala)
    description: Homozygous in the three affected members of family 2 (2003).
    evidence:
    - reference: PMID:12632327
      reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        the three patients in family 2 are homozygous for a 569T-->C transition
        (V190A)
      explanation: Reports the variant and its homozygous state.
  - name: IHH c.478C>T p.(Arg160Cys)
    description: Homozygous in two adult siblings from a Turkish family (2021).
    evidence:
    - reference: PMID:34530144
      reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We describe two adult patients with ACFD with a novel homozygous
        c.478C>T (p.Arg160Cys) mutation in IHH in the third family of the
        literature.
      explanation: Reports the third ACFD variant.
  - name: IHH c.518C>A p.(Ala173Asp)
    description: >-
      Homozygous in two siblings from a Pakistani family (2025). Classified
      likely pathogenic by the reporting authors under ACMG criteria. In
      silico modeling places Ala173 in the core of the domain.
    evidence:
    - reference: PMID:40045933
      reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This variant caused the substitution of Alanine with Aspartate at amino
        acid position 173 (NP_002172.2: p.(Ala173Asp)) in the IHH protein.
      explanation: >-
        Reports the fourth ACFD variant (c.518C>A in NM_002181.4), found
        homozygous in both affected siblings.
pathophysiology:
- name: Biallelic IHH Signaling-Domain Missense Variants
  biological_scale: MOLECULAR
  role: trigger
  description: >-
    Homozygous missense substitutions at conserved residues of the IHH
    amino-terminal signaling fragment, the secreted, lipid-modified part of the
    protein that binds Patched receptors. No truncating ACFD allele has been
    reported.
  genetic_context:
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
  gene:
    preferred_term: IHH
    term:
      id: hgnc:5956
      label: IHH
  evidence:
  - reference: PMID:12632327
    reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The two mutant amino acids are strongly conserved and predicted to be
      located outside the region where brachydactyly type A-1 mutations are
      clustered.
    explanation: Conservation of the mutated residues and their position relative to the BDA1 cluster.
  downstream:
  - target: Reduced IHH Signaling Output
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced pathway output is inferred for the disorder. Modeling of p.Ala173Asp predicts destabilization, whereas p.Val190Ala has experimental evidence of reduced IHH-N abundance. These findings do not establish an identical biochemical defect for every allele or demonstrate absent intrinsic signaling activity.
    evidence:
    - reference: PMID:40045933
      reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: COMPUTATIONAL
      snippet: >-
        This variant is likely to disrupt the essential core structure of the
        protein domain due to the size and charge difference of the wild-type
        and mutant residues, leading to a loss of hydrophobic interactions within
        the core, potentially causing protein folding problems.
      explanation: >-
        Structural modeling and molecular dynamics of p.Ala173Asp predict core
        destabilization. This is a prediction, not a measured loss of signaling.
  - target: Reduced V190A IHH-N Abundance
    causal_link_type: DIRECT
    description: >-
      The V190A allele reduces the abundance of the signaling fragment in a heterologous expression assay; the study attributes this predominantly to reduced stability, with a smaller effect on autoprocessing.
    evidence:
    - reference: PMID:34070546
      reference_title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)
      explanation: >-
        Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
- name: Reduced V190A IHH-N Abundance
  biological_scale: MOLECULAR
  mechanism_confidence: PROVISIONAL
  description: >-
    The ACFD-associated p.Val190Ala IHH protein yields reduced IHH-N abundance in transfected cells. Wang et al. interpreted the N- and C-terminal fragment immunoblots as showing reduced stability with a smaller effect on precursor self-cleavage. Protein turnover kinetics and the magnitude of this defect in human growth-plate cartilage were not established. This allele-specific result is distinct from the computational destabilization prediction for p.Ala173Asp.
  evidence:
  - reference: PMID:34070546
    reference_title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)
    explanation: >-
      Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
  downstream:
  - target: Reduced IHH Signaling Output
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Less available ligand could reduce tissue-level pathway activation even if the remaining ligand retains signaling activity. This link is an inference, not a measurement in patient cartilage.
    evidence:
    - reference: PMID:34070546
      reference_title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        V190A mutation may cause disease in part by reducing the IHH-N protein level.
      explanation: >-
        The authors propose reduced ligand abundance as a disease mechanism; its contribution to the human growth-plate phenotype remains inferred.
- name: Reduced IHH Signaling Output
  biological_scale: MOLECULAR
  description: >-
    Reduced effective Hedgehog signaling is proposed in growth-plate chondrocytes and perichondrium. Mouse Ihh deletion reduces ciliary Smoothened and nuclear Gli1. In ACFD, human tissue-level output remains unmeasured: V190A can lower IHH-N abundance, while a preliminary thesis reporter assay found preserved activity when the amount of secreted V190A ligand was normalized. Reduced ligand availability, spatial distribution and intrinsic receptor activation are distinct possible mechanisms.
  biological_processes:
  - preferred_term: Smoothened signaling pathway
    term:
      id: GO:0007224
      label: smoothened signaling pathway
    modifier: DECREASED
  cell_types:
  - preferred_term: prehypertrophic chondrocyte
    term:
      id: CL:0020022
      label: prehypertrophic chondrocyte
  locations:
  - preferred_term: epiphyseal plate
    term:
      id: UBERON:0002516
      label: epiphyseal plate
  evidence:
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Lower levels of Smo in the cilium or Gli1 protein in the nucleus were
      detected in Ihh-deficient chondrocytes than in control chondrocytes.
    explanation: >-
      Readouts were measured in cultured articular chondrocytes isolated from conditional-deletion mice, not in ACFD patient growth plates.
  - reference: PMID:8662546
    reference_title: Regulation of rate of cartilage differentiation by Indian hedgehog and PTH-related protein.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Ihh is expressed in the prehypertrophic chondrocytes of cartilage elements, where it regulates the rate of hypertrophic differentiation."
    explanation: Establishes the prehypertrophic chondrocyte as the IHH source (chick and mouse limb data).
  downstream:
  - target: Reduced Growth Plate Chondrocyte Proliferation
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        The results of bromodeoxyuridine (BrdU) staining showed that Ihh
        deletion inhibited chondrocyte proliferation, and this effect was
        rescued by SAG treatment
      explanation: >-
        BrdU incorporation was measured in cultured chondrocytes from conditional-deletion mice; SAG rescued the proliferation defect in vitro.
  - target: Ectopic Chondrocyte Hypertrophy
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Embryonic experiments identify an IHH-PTHrP feedback brake on hypertrophy. In the postnatal deletion model, PTHrP persists but its distribution and that of its receptor are abnormal; a simple absence of PTHrP is not demonstrated. Translation of these model findings to ACFD remains provisional.
    evidence:
    - reference: PMID:8662546
      reference_title: Regulation of rate of cartilage differentiation by Indian hedgehog and PTH-related protein.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        PTHrP mediates the effects of Ihh through the formation of a negative
        feedback loop that modulates the rate of chondrocyte differentiation.
      explanation: >-
        The IHH-PTHrP loop is the known intermediate linking IHH output to
        the rate of hypertrophic differentiation.
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        postnatal deletion of Ihh from chondrocytes affects the regular distribution of PTHrP and its receptor expression
      explanation: >-
        Postnatal deletion alters the spatial PTHrP system rather than simply abolishing PTHrP expression.
  - target: Loss of Growth Plate Columnar Organization
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      IHH supports entry of periarticular cells into the columnar compartment independently of PTHrP; postnatal deletion disrupts the columns despite residual PTHrP.
    evidence:
    - reference: PMID:15951842
      reference_title: Indian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These results demonstrate that Ihh acts on periarticular chondrocytes to stimulate their differentiation, thereby regulating the columnar cell mass independently of PTHrP.
      explanation: >-
        Mouse developmental genetics identifies a PTHrP-independent contribution to columnar cell mass.
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Ihh is essential to induce columnar chondrocyte differentiation to maintain a growth plate, even after birth, despite the presence of PTHrP protein in the remaining chondrocytes in the growth plate at P7 in mutant mice
      explanation: >-
        The postnatal model retains PTHrP protein but loses normal growth-plate organization.
  mechanism_confidence: PROVISIONAL
- name: Reduced Growth Plate Chondrocyte Proliferation
  biological_scale: CELLULAR
  description: >-
    Fewer proliferating chondrocytes in the growth plate. The mouse Ihh-null
    and conditional-deletion phenotypes both show this. It reduces the
    cartilage template available for longitudinal growth.
  biological_processes:
  - preferred_term: chondrocyte proliferation
    term:
      id: GO:0035988
      label: chondrocyte proliferation
    modifier: DECREASED
  cell_types:
  - preferred_term: columnar chondrocyte
    term:
      id: CL:0000744
      label: columnar chondrocyte
  evidence:
  - reference: PMID:10465785
    reference_title: Indian hedgehog signaling regulates proliferation and differentiation of chondrocytes and is essential for bone formation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Mutants display markedly reduced chondrocyte proliferation, maturation of
      chondrocytes at inappropriate position, and a failure of osteoblast
      development in endochondral bones.
    explanation: >-
      Ihh-null mouse embryos show reduced chondrocyte proliferation. This is a
      complete null, more severe than the human missense alleles.
  - reference: PMID:17409191
    reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The number of proliferative chondrocytes decreased dramatically in mutants when compared with controls, as determined by proliferating cell nuclear antigen (PCNA)-stained cell populations
    explanation: >-
      Postnatal conditional-deletion mouse tissue directly shows reduced proliferation; this supports the growth-plate node beyond the separate articular-cell culture experiments.
  downstream:
  - target: Premature Growth Plate Closure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      A smaller proliferative pool, together with faster hypertrophy, exhausts
      the growth plate early.
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        These results demonstrate, for the first time, that postnatal
        chondrocyte-derived Ihh is essential for maintaining the growth plate
        and articular surface and is required for sustaining trabecular bone and
        skeletal growth.
      explanation: Postnatal Ihh deletion shows that IHH is required to maintain the growth plate.
  mechanism_confidence: PROVISIONAL
- name: Ectopic Chondrocyte Hypertrophy
  biological_scale: CELLULAR
  description: >-
    Postnatal loss of chondrocyte Ihh in mice produces hypertrophic chondrocytes at ectopic growth-plate sites. The cells express collagen X rather than collagen II. This is model evidence for abnormal maturation in ACFD, not human growth-plate histology.
  biological_processes:
  - preferred_term: chondrocyte hypertrophy
    term:
      id: GO:0003415
      label: chondrocyte hypertrophy
    modifier: ABNORMAL
  cell_types:
  - preferred_term: hypertrophic chondrocyte
    term:
      id: CL:0000743
      label: hypertrophic chondrocyte
  evidence:
  - reference: PMID:17409191
    reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The mutant growth plate was primarily composed of hypertrophic chondrocytes that express collagen type X but not collagen type II indicating an abnormally advanced maturation stage for these cells
    explanation: >-
      Histology and collagen expression identify ectopic hypertrophy in the postnatal mouse deletion model.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      Ultimately, the rate of chondrocyte differentiation would have increased,
      causing early growth plate closure and bone shortening, as proposed by
      Hellemans et al. (2003).
    explanation: >-
      The ACFD authors attribute the human phenotype to faster chondrocyte
      differentiation. They restate the 2003 proposal; it is a hypothesis and
      was not measured in patient tissue.
  downstream:
  - target: Premature Growth Plate Closure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Furthermore, destruction of the articular surface in long bones and
        premature fusion of growth plates of various endochondral bones was
        evident, resulting in dwarfism in mutant mice.
      explanation: In the same mice, the disorganized growth plate goes on to fuse prematurely.
    description: >-
      Premature differentiation, reduced proliferation and abnormal vascular invasion jointly precede replacement of cartilage by bone. This is not an isolated direct effect of hypertrophy alone.
  - target: Premature Growth Plate Vascular Invasion
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Ectopic maturation and mineralization accompany premature vascular entry; their exact causal sequence was not isolated by the deletion experiment.
  mechanism_confidence: PROVISIONAL
- name: Loss of Growth Plate Columnar Organization
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: >-
    Postnatal Ihh deletion disrupts the organized columns of proliferating growth-plate chondrocytes in mice. This architectural defect is distinct from ectopic hypertrophic differentiation. The physical mechanism of column formation remains incompletely resolved; stimulation of columnar differentiation does not establish a direct architectural mechanism.
  evidence:
  - reference: PMID:17409191
    reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      demonstrated an absolute loss of columnar structure of chondrocytes in the tibia when compared with controls
    explanation: >-
      Histology at postnatal day 7 shows loss of normal proliferative columns in the conditional-deletion model.
  - reference: url:https://www.jci.org/articles/view/24397
    reference_title: "JCI -\nIndian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP"
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      The precise mechanisms whereby chondrocytes form stacks of flat cells in orderly arrays are incompletely understood.
    explanation: The primary paper distinguishes promotion of columnar differentiation from the incompletely understood machinery that builds orderly columns. This supports the stated mechanistic limitation.
  downstream:
  - target: Premature Growth Plate Closure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Loss of organized proliferative cartilage accompanies ectopic maturation and subsequent plate replacement in the mouse model.
- name: Premature Growth Plate Vascular Invasion
  biological_scale: TISSUE
  mechanism_confidence: PROVISIONAL
  description: >-
    Blood vessels enter the middle of the growth plate prematurely after postnatal Ihh deletion in mice, accompanying replacement of mineralized cartilage by bone. No corresponding vascular histology has been demonstrated in ACFD patients.
  evidence:
  - reference: PMID:17409191
    reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      premature blood vessel invasion was detected in the middle of growth plates in mutants at P7
    explanation: >-
      CD31 staining identifies abnormal vascular invasion in the mouse growth plate.
  downstream:
  - target: Premature Growth Plate Closure
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        decreased proliferation and premature differentiation of mutant chondrocytes, along with abnormal vascular invasion, lead to advanced replacement of mineralized cartilage by bone.
      explanation: >-
        The authors interpret these joint changes as a route to premature plate replacement, rather than demonstrating vascular invasion alone as sufficient.
- name: Premature Growth Plate Closure
  biological_scale: TISSUE
  description: >-
    Affected growth plates can close prematurely, often before puberty, permanently shortening the hand bones and long bones. Cone-shaped epiphyses occur during this process and may disappear after fusion; timing differs by skeletal site. The egg-shaped capital femoral epiphysis and short femoral neck are characteristic. The eight patients tabulated in 2025 are not all known molecularly reported patients.
  biological_processes:
  - preferred_term: endochondral bone growth
    term:
      id: GO:0003416
      label: endochondral bone growth
    modifier: DECREASED
  locations:
  - preferred_term: epiphyseal plate
    term:
      id: UBERON:0002516
      label: epiphyseal plate
  - preferred_term: head of femur
    term:
      id: UBERON:0006767
      label: head of femur
  - preferred_term: neck of femur
    term:
      id: UBERON:0007119
      label: neck of femur
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite the age difference among the ACFD patients reported to date
      (Table 2), early growth plate closure was evident in all of them, which
      led to the shortening of long tubular bones in the arms and legs, along
      with cone-shaped epiphyses.
    explanation: >-
      The 2025 authors report premature closure across their clinical comparison; this does not establish complete fusion of every plate in each patient.
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: BACKGROUND
    snippet: >-
      Consistent with our results, postnatal deletion of Ihh with Col2-creERT by
      administration of TM caused premature fusion of growth plates of various
      endochondral bones in mice, resulting in dwarfism in mutant mice.
    explanation: A second group restates the premature-fusion result from postnatal Ihh deletion.
  downstream:
  - target: Premature epimetaphyseal fusion
    causal_link_type: DIRECT
  - target: Cone-shaped epiphyses of the hand phalanges
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cone-shaped epiphyses and premature fusion are linked radiographic features. The detailed spatial mechanism producing the cone shape remains proposed rather than experimentally demonstrated.
    evidence:
    - reference: PMID:40045933
      reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        early growth plate closure was evident in all of them, which led to the
        shortening of long tubular bones in the arms and legs, along with
        cone-shaped epiphyses
      explanation: Links early closure to the cone-shaped epiphyses.
  - target: Short middle phalanges
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:40045933
      reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: >-
        The egg-shaped femoral head with a short femoral neck and shortened
        tubular bones in the hands especially middle phalanges, are due to early
        prepubertal closure of the growth plate (Hellemans et al. 2003).
      explanation: >-
        Restates the 2003 interpretation that early closure is what shortens
        the hand bones and the femoral neck.
  - target: Brachydactyly
    causal_link_type: DIRECT
  - target: Short metacarpals
    causal_link_type: DIRECT
  - target: Short femoral neck
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:40045933
      reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      snippet: >-
        The egg-shaped femoral head with a short femoral neck and shortened
        tubular bones in the hands especially middle phalanges, are due to early
        prepubertal closure of the growth plate
      explanation: Attributes the short femoral neck to early closure of the proximal femoral growth plate.
  - target: Egg-shaped capital femoral epiphysis
    causal_link_type: DIRECT
  - target: Limb undergrowth
    causal_link_type: DIRECT
  - target: Short humerus
    causal_link_type: DIRECT
  - target: Short tibia
    causal_link_type: DIRECT
  - target: Disproportionate short stature
    causal_link_type: DIRECT
  - target: Narrow chest
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Reduced endochondral rib growth plausibly contributes to the narrow thorax. Conditional Ihh deletion in mice can shorten ribs enough to cause respiratory death, but this occurred in a subset rather than every untreated mutant. Rib growth plates have not been examined in ACFD patients.
    evidence:
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Notably, all vehicle-treated Ihhcko mice (23/83) died due to respiratory
        failure caused by shortening of the ribs, which restricts pulmonary
        development.
      explanation: >-
        The awkwardly worded source sentence refers to all 23 deaths among 83 vehicle-treated mutants; Table 1 reports 60/83 survivors. It does not report universal lethality.
  - target: Coxa vara
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Coxa vara develops alongside the abnormal proximal femoral epiphysis and
      short femoral neck. The exact steps are not described.
  - target: Genu varum
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Variable. It is seen together with the hyperplastic distal femur and
      irregular proximal tibial metaphysis in some patients; the exact steps
      are not described.
  - target: Relative macrocephaly
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The head is large relative to a body shortened by reduced endochondral
      growth. Head circumference ranges from the 3rd to the 98th centile in the
      published patients, so the head is not enlarged in absolute terms.
phenotypes:
- category: Growth
  name: Disproportionate short stature
  description: >-
    Postnatal-onset disproportionate short stature with short limbs and marked variation in severity. The Pakistani siblings were 102 cm at age 20 years and 84 cm at age 14 years. The eight-person comparison is a selected clinical series, not a population frequency estimate; height values for earlier cases should be checked against their original reports.
  phenotype_term:
    preferred_term: Disproportionate short stature
    term:
      id: HP:0003498
      label: Disproportionate short stature
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive disorder,
      characterized by postnatal onset of disproportionate short stature with
      short limbs, brachydactyly, cone-shaped epiphysis, narrow thorax, and
      relatively large head.
    explanation: Names postnatal-onset disproportionate short stature as a defining feature.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both affected individuals had severe short stature, short limbs, a narrow
      thorax, and a relatively large head
    explanation: Present in both Pakistani siblings.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At the time of sampling, IV‐1 was 20 years old, having a height of 102 cm (−10.4 SD) height and IV‐2 was 14 years old, having a height of 84 cm (−9.6 SD)
    explanation: >-
      Age and height measurements in the Pakistani sibship, as reported; these establish severe short stature without extrapolating the table to all known patients.
- category: Skeletal
  name: Limb undergrowth
  description: Short limbs, present in all eight tabulated patients.
  phenotype_term:
    preferred_term: Short limbs
    term:
      id: HP:0009826
      label: Limb undergrowth
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal
      dysplasia characterized by short stature with short limb dwarfism,
      brachydactyly, and a narrow thorax.
    explanation: Short-limbed dwarfism is part of the defining triad.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short limbs | + | + | + | + | + | + | + | + |
    explanation: >-
      Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Short humerus
  description: >-
    Short humerus in all seven patients assessed. The proximal humeral
    epiphysis was cone-shaped in the Pakistani proband.
  phenotype_term:
    preferred_term: Short humerus
    term:
      id: HP:0005792
      label: Short humerus
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The humerus bone was severely shortened with cone-shaped proximal epiphysis."
    explanation: Radiographic finding in the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short humerus | + | NA | + | + | + | + | + | + |
    explanation: >-
      Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Short tibia
  description: >-
    Short tibia and fibula in all seven patients assessed. The distal tibial
    epiphysis was cone-shaped in the Pakistani proband.
  phenotype_term:
    preferred_term: Short tibia
    term:
      id: HP:0005736
      label: Short tibia
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the tibia and fibula bones were extremely short with irregular proximal
      tibial metaphyses and cone-shaped distal tibial epiphyses
    explanation: Radiographic finding in the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short tibia and fibula | + | NA | + | + | + | + | + | + |
    explanation: >-
      Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Brachydactyly
  description: Short hands and digits, present in all eight tabulated patients.
  phenotype_term:
    preferred_term: Brachydactyly
    term:
      id: HP:0001156
      label: Brachydactyly
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal
      dysplasia characterized by short stature with short limb dwarfism,
      brachydactyly, and a narrow thorax.
    explanation: Brachydactyly is part of the defining triad.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Their hands were short, with brachydactyly and short nails"
    explanation: Present in both Pakistani siblings.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Brachydactyly | + | + | + | + | + | + | + | + |
    explanation: >-
      Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Short middle phalanges
  description: >-
    The middle phalanges are the most shortened hand bones, as in brachydactyly
    type A1. Present in all eight tabulated patients.
  phenotype_term:
    preferred_term: Short middle phalanges of the hand
    term:
      id: HP:0005819
      label: Short middle phalanx of finger
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Commonly reported radiographic features, that is, short and broad
      metacarpal and metatarsal bones with conical teardrop epiphyses, short
      middle phalanges, fused phalanges, coxa vara, short and flared iliac
      wings with dysplastic acetabulum, egg-shaped capito-femoral epiphyses with
      a short femoral neck, and hyperplastic distal femur, were also observed in
      our patients.
    explanation: Lists short middle phalanges among the recurrent radiographic features.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short middle phalange | + | + | + | + | + | + | + | + |
    explanation: >-
      Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Short metacarpals
  description: >-
    Short, broad metacarpals, sometimes with teardrop-shaped epiphyses. Present
    in all eight tabulated patients.
  phenotype_term:
    preferred_term: Short metacarpal
    term:
      id: HP:0010049
      label: Short metacarpal
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Commonly reported radiographic features, that is, short and broad
      metacarpal and metatarsal bones with conical teardrop epiphyses
    explanation: Short broad metacarpals are a recurrent radiographic feature.
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported cases showed a middle phalanges which fused with distal
      phalanges in the fifth toes, the typical configuration of metacarpals,
      radial angulation and extremely short femoral neck.
    explanation: The typical metacarpal configuration persists into adulthood.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short metacarpal bones | + | + | + | + | + | + | + | + |
    explanation: >-
      Table 2: 8/8 tabulated patients. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Cone-shaped epiphyses of the hand phalanges
  description: >-
    Cone-shaped epiphyses are a characteristic childhood radiographic finding, but they can persist at some sites into young adulthood. The 2025 table records cone-shaped epiphyses in the 20-year-old Pakistani proband and four earlier children, absent in two Turkish adults, and NA in the younger Pakistani sibling. These are five positive individuals, not five children. The table pools skeletal sites; it does not give a hand-only denominator.
  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:12632327
    reference_title: "Homozygous mutations in IHH cause acrocapitofemoral dysplasia, an autosomal recessive disorder with cone-shaped epiphyses in hands and hips."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acrocapitofemoral dysplasia is a recently delineated autosomal recessive
      skeletal dysplasia, characterized clinically by short stature with short
      limbs and radiographically by cone-shaped epiphyses, mainly in hands and
      hips.
    explanation: Cone-shaped epiphyses in the hands are the defining radiographic sign.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Cone shaped epiphysis | + | NA | + | + | + | + | − | − |
    explanation: >-
      The five positive entries include an adult. The pooled-site table cannot establish a hand-specific frequency or universal disappearance after childhood.
- category: Skeletal
  name: Egg-shaped capital femoral epiphysis
  description: >-
    An egg-shaped capital femoral epiphysis, which gives the disorder the
    "capitofemoral" part of its name. It was present in all five patients in
    whom it was recorded. HPO has no term for an egg-shaped or cone-shaped
    femoral head: a label search of HP for "femoral head" returned hypoplasia,
    dysplasia, flattening, broadening, displacement, aplasia and delayed
    ossification terms, and "capital femoral epiphys" returned nothing. The
    binding is therefore to the epiphysis-level abnormality term.
  phenotype_term:
    preferred_term: Egg-shaped capital femoral epiphysis
    term:
      id: HP:0010574
      label: Abnormality of the epiphysis of the femoral head
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Major radiographic features are egg-shaped capital femoral epiphyses with
      a short femoral neck and cone-shaped epiphyses, mainly in the hands and
      hips.
    explanation: Egg-shaped capital femoral epiphyses are a major radiographic feature.
- category: Skeletal
  name: Short femoral neck
  description: >-
    Short femoral neck in all seven patients assessed. It is extreme in
    adults.
  phenotype_term:
    preferred_term: Short femoral neck
    term:
      id: HP:0100864
      label: Short femoral neck
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Major radiographic features are egg-shaped capital femoral epiphyses with
      a short femoral neck and cone-shaped epiphyses, mainly in the hands and
      hips.
    explanation: Short femoral neck is a major radiographic feature.
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported cases showed a middle phalanges which fused with distal
      phalanges in the fifth toes, the typical configuration of metacarpals,
      radial angulation and extremely short femoral neck.
    explanation: The femoral neck is extremely short in adults.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short femoral neck | + | NA | + | + | + | + | + | + |
    explanation: >-
      Table 2: 7/7 recorded; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Premature epimetaphyseal fusion
  description: >-
    Premature, often prepubertal fusion of affected growth plates causes permanent shortening. Closure varies by site and age; some cone-shaped epiphyses remain visible in the young-adult Pakistani proband, so complete closure of every growth plate should not be inferred.
  phenotype_term:
    preferred_term: Premature closure of the growth plates
    term:
      id: HP:0010588
      label: Premature epimetaphyseal fusion
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Despite the age difference among the ACFD patients reported to date
      (Table 2), early growth plate closure was evident in all of them
    explanation: Early growth plate closure in the selected clinical comparison; closure varies by skeletal site and age.
- category: Skeletal
  name: Narrow chest
  description: >-
    A narrow thorax is reported in both Pakistani siblings and in the Turkish adults. The Pakistani proband had short ribs and clavicles. The later table and narrative disagree about earlier patients and the younger Pakistani sibling, so no pooled frequency is assigned. Pectus deformities in earlier reports should not automatically be equated with thoracic narrowing.
  phenotype_term:
    preferred_term: Narrow chest
    term:
      id: HP:0000774
      label: Narrow chest
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal
      dysplasia characterized by short stature with short limb dwarfism,
      brachydactyly, and a narrow thorax.
    explanation: Narrow thorax is part of the defining triad.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest radiographs of IV-1 revealed a narrow thorax, short ribs and
      clavicles, lumbar lordosis, and cupping at the costal ends of the ribs.
    explanation: Radiographic narrow thorax with short ribs in the proband.
- category: Craniofacial
  name: Relative macrocephaly
  description: >-
    The head is large relative to the short trunk and limbs, not in absolute
    terms.
  phenotype_term:
    preferred_term: Relatively large head
    term:
      id: HP:0004482
      label: Relative macrocephaly
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both affected individuals had severe short stature, short limbs, a narrow
      thorax, and a relatively large head
    explanation: Present in both Pakistani siblings and listed among the defining features.
- category: Skeletal
  name: Lumbar hyperlordosis
  frequency: FREQUENT
  description: Recorded in five of seven patients assessed in the 2025 phenotype table.
  phenotype_term:
    preferred_term: Lumbar lordosis
    term:
      id: HP:0002938
      label: Lumbar hyperlordosis
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest radiographs of IV-1 revealed a narrow thorax, short ribs and
      clavicles, lumbar lordosis, and cupping at the costal ends of the ribs.
    explanation: Lumbar lordosis on radiographs of the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Lumber lordosis | + | NA | + | + | − | + | − | + |
    explanation: >-
      Table 2: 5/7 recorded, or 71%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Coxa vara
  frequency: FREQUENT
  description: Recorded in four of seven patients assessed in the 2025 phenotype table.
  phenotype_term:
    preferred_term: Coxa vara
    term:
      id: HP:0002812
      label: Coxa vara
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pelvic examination showed bilateral osteoarthritis, short and flared iliac
      wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth.
    explanation: Coxa vara on pelvic radiographs of the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Coxa vara | + | NA | − | + | + | + | − | − |
    explanation: >-
      Table 2: 4/7 recorded, or 57%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
  sequelae:
  - target: Hip osteoarthritis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Secondary hip osteoarthritis in the adult proband, on a background of
      coxa vara, dysplastic acetabulum and a short femoral neck.
- category: Skeletal
  name: Hip osteoarthritis
  description: >-
    Bilateral hip osteoarthritis with reduced joint mobility in the
    20-year-old Pakistani proband. It has been reported in one patient only.
  phenotype_term:
    preferred_term: Hip osteoarthritis
    term:
      id: HP:0008843
      label: Hip osteoarthritis
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      a bilateral osteoarthritic appearance was observed in the hip joint of
      IV-1, which caused reduced joint mobility and function
    explanation: Single-patient observation of secondary hip osteoarthritis.
- category: Skeletal
  name: Genu varum
  description: >-
    Variable. The 2025 table records genu vara in four of eight tabulated individuals, whereas its prose says only one of the four original children had it. The discrepancy is retained without deriving a frequency band from the conflicting summaries.
  phenotype_term:
    preferred_term: Genu varum
    term:
      id: HP:0002970
      label: Genu varum
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our proband (IV-1) also had a rarely reported genu vara phenotype observed
      in only 1 of the 4 patients reported by Mortier et al. (2003) due to which
      he had a waddling walk.
    explanation: Genu varum in the proband, described as rare in earlier patients.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Genu vara | + | + | + | − | + | − | − | − |
    explanation: >-
      Four positive entries, not three. The later summary table and the same paper's description of the original cases are not fully consistent.
  sequelae:
  - target: Waddling gait
    causal_link_type: DIRECT
    description: The reporting authors attribute the proband's waddling walk to genu varum.
- category: Neurological
  name: Waddling gait
  description: Reported in the Pakistani proband; his younger brother had difficulty walking.
  phenotype_term:
    preferred_term: Waddling gait
    term:
      id: HP:0002515
      label: Waddling gait
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our proband (IV-1) also had a rarely reported genu vara phenotype observed
      in only 1 of the 4 patients reported by Mortier et al. (2003) due to which
      he had a waddling walk.
    explanation: Waddling gait in the proband.
- category: Skeletal
  name: Fifth toe symphalangism
  description: >-
    Fused interphalangeal joint of the fifth toes, seen in both the Turkish
    and the Pakistani families. The sources disagree on which joint is fused.
    The 2021 abstract describes middle-distal fusion; the 2025 report restates
    the 2021 finding as middle-proximal fusion of the 5th fingers and toes, but
    describes middle-distal fusion in its own proband. The binding is therefore
    to the unlocalized fifth-toe term. The fifth-finger fusion in the Turkish
    patients is recorded under Finger symphalangism. Symphalangism is a failure
    of joint formation rather than of growth plate maintenance, and no source
    links it to a node in this entry, so it has no causal in-edge.
  phenotype_term:
    preferred_term: Fifth toe symphalangism
    term:
      id: HP:0010389
      label: Fifth toe symphalangism
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported cases showed a middle phalanges which fused with distal
      phalanges in the fifth toes, the typical configuration of metacarpals,
      radial angulation and extremely short femoral neck.
    explanation: Fifth-toe phalangeal fusion in the Turkish adults.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "fused middle and distal phalanx of the fifth toe bilaterally"
    explanation: Fifth-toe phalangeal fusion in the Pakistani proband.
- category: Dermatologic
  name: Short nail
  description: >-
    Short nails, recorded (as "small broad nails") in six of six patients
    assessed in the 2025 phenotype table; not recorded for the two Dutch
    children. The broadness is recorded separately under Broad nail. No source
    states why the nails are short, so this phenotype has no causal in-edge.
  phenotype_term:
    preferred_term: Short broad nails
    term:
      id: HP:0001799
      label: Short nail
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Their hands were short, with brachydactyly and short nails"
    explanation: Short nails in both Pakistani siblings.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Small broad nails | + | + | + | + | NR | NR | + | + |
    explanation: >-
      Table 2: 6/6 recorded; two NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Dermatologic
  name: Broad nail
  description: >-
    Broad nails, recorded (as "small broad nails") in six of six patients
    assessed in the 2025 phenotype table and named among the defining features
    of the disorder. No source states the mechanism, so this phenotype has no
    causal in-edge.
  phenotype_term:
    preferred_term: Broad nail
    term:
      id: HP:0001821
      label: Broad nail
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      Acrocapitofemoral dysplasia (ACFD; MIM 607778) is a rare autosomal
      recessive disorder characterized by postnatal onset disproportionate short
      stature of variable degrees with short limbs, brachydactyly, short broad
      nails, narrow thorax, pectus deformities, and a relatively large head, with
      an average IQ
    explanation: >-
      Restates the original clinical delineation (Mortier et al. 2003;
      Hellemans et al. 2003), which lists short broad nails among the defining
      features.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The phenotypes of both the affected individuals in this study, including
      severe short stature, short limbs, large head, narrow thorax, small broad
      nails, lumbar lordosis, brachydactyly, and an average IQ, were the same as
      reported in all six previously reported ACFD patients
    explanation: Small broad nails in both Pakistani siblings.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Small broad nails | + | + | + | + | NR | NR | + | + |
    explanation: >-
      Table 2: 6/6 recorded; two NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Short metatarsals
  description: >-
    Short, broad metatarsals with conical teardrop epiphyses. The 2025 report
    lists them among the commonly reported radiographic features, but its
    phenotype table records them only for the two Pakistani siblings (present
    in both) and "NR" for the other six patients, so no frequency is set. No
    source states that early growth plate closure shortens the metatarsals
    (the causal statements cover the hands, femoral neck and long bones of the
    limbs), so this phenotype has no causal in-edge.
  phenotype_term:
    preferred_term: Short metatarsal
    term:
      id: HP:0010743
      label: Short metatarsal
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Foot examination revealed short and broad metatarsals with conical tear
      drop epiphyses, accessory navicular foot deformity, and fused middle and
      distal phalanx of the fifth toe bilaterally
    explanation: Short metatarsals on foot radiographs of the Pakistani proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Commonly reported radiographic features, that is, short and broad
      metacarpal and metatarsal bones with conical teardrop epiphyses
    explanation: The report lists short broad metatarsals among the recurrent radiographic features.
- category: Skeletal
  name: Flared iliac wing
  frequency: FREQUENT
  description: >-
    Short, flared iliac wings. The 2025 phenotype table records them in three
    of six patients assessed (the Pakistani proband and the two Dutch
    children) and absent in the two Belgian children and one Turkish adult.
    The shortness of the wings is not bound separately. No source links the
    pelvic shape to a node in this entry, so this phenotype has no causal
    in-edge.
  phenotype_term:
    preferred_term: Short and flared iliac wings
    term:
      id: HP:0002869
      label: Flared iliac wing
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pelvic examination showed bilateral osteoarthritis, short and flared iliac
      wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth.
    explanation: Short, flared iliac wings on pelvic radiographs of the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      short and flared iliac wings with dysplastic acetabulum, egg-shaped
      capito-femoral epiphyses with a short femoral neck, and hyperplastic
      distal femur, were also observed in our patients
    explanation: Listed among the commonly reported radiographic features.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Short and flared Iliac wings | + | NA | − | − | + | + | − | NR |
    explanation: >-
      Table 2: 3/6 recorded, or 50%, within the FREQUENT band; one NA and one NR. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Acetabular dysplasia
  description: >-
    Dysplastic acetabulum. The 2025 report lists it among the commonly reported
    radiographic features, but its phenotype table records it only for the
    Pakistani proband (present) and "NR" or "NA" for the other seven patients,
    so no frequency is set. The proband also had hip osteoarthritis, but the
    report does not state that the acetabular dysplasia caused it, so no edge
    is drawn.
  phenotype_term:
    preferred_term: Dysplastic acetabulum
    term:
      id: HP:0008807
      label: Acetabular dysplasia
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pelvic examination showed bilateral osteoarthritis, short and flared iliac
      wings, dysplastic acetabulum, coxa vara with greater trochanter overgrowth.
    explanation: Dysplastic acetabulum on pelvic radiographs of the proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      short and flared iliac wings with dysplastic acetabulum, egg-shaped
      capito-femoral epiphyses with a short femoral neck, and hyperplastic
      distal femur, were also observed in our patients
    explanation: Listed among the commonly reported radiographic features.
- category: Skeletal
  name: Radial bowing
  frequency: FREQUENT
  description: >-
    Angulation of the radius (with the ulna in the Pakistani proband). The
    2025 phenotype table ("Radial ulnal angulation") records it in three of
    seven patients assessed (the Pakistani proband and both Turkish adults)
    and absent in the four Belgian and Dutch children. All three positive
    patients were 20 or older and all four negative patients were under 10. The Pakistani proband also had a Madelung-like
    deformity at the distal radioulnar joint, fused carpal bones and ulnocarpal
    subluxation. No source links the forearm deformity to a node in this
    entry, so this phenotype has no causal in-edge.
  phenotype_term:
    preferred_term: Radial and ulnar angulation
    term:
      id: HP:0002986
      label: Radial bowing
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported cases showed a middle phalanges which fused with distal
      phalanges in the fifth toes, the typical configuration of metacarpals,
      radial angulation and extremely short femoral neck.
    explanation: Radial angulation in the two Turkish adults.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the carpal bones were fused, and the radial and ulnar bones were short
      with bilateral varus angulation and medlung-like deformity at the distal
      radioulnar joint.
    explanation: Bilateral radial and ulnar angulation with a Madelung-like deformity in the Pakistani proband.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Radial ulnal angulation | + | NA | − | − | − | − | + | + |
    explanation: >-
      Table 2: 3/7 recorded, or 43%, within the FREQUENT band; one NA. These are recorded findings in a small selected series; NA and NR are not counted as negative findings.
- category: Skeletal
  name: Finger symphalangism
  description: >-
    Fusion of finger phalanges is reported in the Pakistani proband and, in the 2025 summary of the Turkish cases, in the fifth fingers of both adults. Exact joint assignments differ between reports. The Pakistani text also refers to a middle phalanx of the thumb, an anatomical inconsistency; it is not adopted as a precise phenotype. No source establishes a causal link from growth-plate closure to failure of joint formation.
  phenotype_term:
    preferred_term: Finger symphalangism
    term:
      id: HP:0009700
      label: Finger symphalangism
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    snippet: >-
      Cubuk and Duz (2021) reported the fused middle and proximal phalanges of
      5th finger and toes and an osteoporotic appearance in the spinal column
    explanation: Restates fifth-finger phalangeal fusion in the two Turkish adults.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the middle and distal phalanges of 1st finger, 2nd finger and thumbs were
      fused
    explanation: Finger phalangeal fusion in the Pakistani proband.
- category: Skeletal
  name: Hyperplastic distal femur
  description: >-
    The Pakistani proband had an enlarged distal end of the femur; the case text does not localize this enlargement to epiphysis or metaphysis. The original molecular paper illustrates enlarged distal femoral epiphyses in a different patient, but the later comparison table cannot support a uniform compartment-specific interpretation or a reliable pooled frequency.
  phenotype_term:
    preferred_term: Hyperplastic distal femur
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The femur bone was short with a short neck, thin shaft, and narrow
      medullary cavity and hyperplastic distal end.
    explanation: Hyperplastic distal femur in the Pakistani proband.
- name: Dislocated radial head
  category: Skeletal
  description: >-
    Observed radiographically in the Pakistani proband; the source does not establish its frequency across ACFD.
  phenotype_term:
    preferred_term: Dislocated radial head
    term:
      id: HP:0003083
      label: Dislocated radial head
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A dislocated radial head with an increased inclination angle of the humeral head was seen at the elbow joints
    explanation: >-
      Observed radiographically in the Pakistani proband; the source does not establish its frequency across ACFD.
- name: Short ribs
  category: Skeletal
  description: >-
    Short ribs with costal-end cupping in the Pakistani proband. Human respiratory consequences were not quantified.
  phenotype_term:
    preferred_term: Short ribs
    term:
      id: HP:0000773
      label: Short ribs
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest radiographs of IV‐1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs.
    explanation: >-
      Short ribs with costal-end cupping in the Pakistani proband. Human respiratory consequences were not quantified.
- name: Short clavicles
  category: Skeletal
  description: >-
    Short clavicles on the Pakistani proband's radiographs; no population frequency is inferred.
  phenotype_term:
    preferred_term: Short clavicles
    term:
      id: HP:0000894
      label: Short clavicles
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Chest radiographs of IV‐1 revealed a narrow thorax, short ribs and clavicles, lumbar lordosis, and cupping at the costal ends of the ribs.
    explanation: >-
      Short clavicles on the Pakistani proband's radiographs; no population frequency is inferred.
- name: Carpal synostosis
  category: Skeletal
  description: >-
    Fusion of carpal bones in the Pakistani proband. This is distinct from delayed carpal ossification in childhood.
  phenotype_term:
    preferred_term: Carpal synostosis
    term:
      id: HP:0005048
      label: Synostosis of carpal bones
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the carpal bones were fused
    explanation: >-
      Fusion of carpal bones in the Pakistani proband. This is distinct from delayed carpal ossification in childhood.
- name: Fibular hypoplasia
  category: Skeletal
  description: >-
    Markedly short fibulae in the Pakistani proband. The later table records short tibiae and fibulae together in seven assessed patients, with one NA.
  phenotype_term:
    preferred_term: Fibular hypoplasia
    term:
      id: HP:0003038
      label: Fibular hypoplasia
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the tibia and fibula bones were extremely short with irregular proximal tibial metaphyses and cone‐shaped distal tibial epiphyses.
    explanation: >-
      Markedly short fibulae in the Pakistani proband. The later table records short tibiae and fibulae together in seven assessed patients, with one NA.
- name: Hypoplasia of the radius
  category: Skeletal
  description: >-
    Short radii, accompanied by short ulnae and bilateral forearm angulation, in the Pakistani proband.
  phenotype_term:
    preferred_term: Hypoplasia of the radius
    term:
      id: HP:0002984
      label: Hypoplasia of the radius
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the radial and ulnar bones were short with bilateral varus angulation
    explanation: >-
      Short radii, accompanied by short ulnae and bilateral forearm angulation, in the Pakistani proband.
- name: Ulnar bowing
  category: Skeletal
  description: >-
    Bilateral varus angulation of the ulnae in the Pakistani proband, alongside radial bowing.
  phenotype_term:
    preferred_term: Ulnar bowing
    term:
      id: HP:0003031
      label: Ulnar bowing
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the radial and ulnar bones were short with bilateral varus angulation
    explanation: >-
      Bilateral varus angulation of the ulnae in the Pakistani proband, alongside radial bowing.
- name: Narrow femoral medullary cavity
  category: Skeletal
  description: >-
    Narrow medullary cavity of the femur in the Pakistani proband. The binding is to narrowing of a long-bone medullary cavity, not a generalized marrow disorder.
  phenotype_term:
    preferred_term: Narrow femoral medullary cavity
    term:
      id: HP:0100254
      label: Stenosis of the medullary cavity of the long bones
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The femur bone was short with a short neck, thin shaft, and narrow medullary cavity and hyperplastic distal end.
    explanation: >-
      Narrow medullary cavity of the femur in the Pakistani proband. The binding is to narrowing of a long-bone medullary cavity, not a generalized marrow disorder.
- name: Unilateral ptosis
  category: Ophthalmologic
  description: >-
    Reported in both Pakistani siblings. This family-level observation has not been established as a recurrent or directly IHH-mediated manifestation.
  phenotype_term:
    preferred_term: Unilateral ptosis
    term:
      id: HP:0007687
      label: Unilateral ptosis
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      (B) IV‐1 and (C) IV‐2 depicting severe short stature and unilateral ptosis.
    explanation: >-
      Reported in both Pakistani siblings. This family-level observation has not been established as a recurrent or directly IHH-mediated manifestation.
- name: Pes planus
  category: Skeletal
  description: >-
    Reported in both Pakistani siblings; the remaining cases were not reported for this feature, so a population frequency cannot be inferred. The proband also had an accessory navicular foot deformity, a separate radiographic finding.
  phenotype_term:
    preferred_term: Pes planus
    term:
      id: HP:0001763
      label: Pes planus
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Pes planus | + | + | NR | NR | NR | NR | NR | NR |
    explanation: >-
      Reported in both Pakistani siblings; the remaining cases were not reported for this feature, so a population frequency cannot be inferred.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Foot examination revealed short and broad metatarsals with conical tear drop epiphyses, accessory navicular foot deformity, and fused middle and distal phalanx of the fifth toe bilaterally
    explanation: Additional foot findings in the proband; this snippet supports the accessory navicular description rather than the pes planus frequency.
- name: Hypertrichosis
  category: Dermatologic
  description: >-
    Observed in the Pakistani proband, including hair over the foot, and absent in his brother. A causal relationship to IHH has not been demonstrated.
  phenotype_term:
    preferred_term: Hypertrichosis
    term:
      id: HP:0000998
      label: Hypertrichosis
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Hypertrichosis | + | − | NR | NR | NR | NR | NR | NR |
    explanation: >-
      Observed in the Pakistani proband, including hair over the foot, and absent in his brother. A causal relationship to IHH has not been demonstrated.
- name: Pectus excavatum
  category: Skeletal
  description: >-
    Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned.
  phenotype_term:
    preferred_term: Pectus excavatum
    term:
      id: HP:0000767
      label: Pectus excavatum
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Thorax | Narrow | NA | Normal | Normal | Pectus craniatum | Pectus excavatum | Narrow | Narrow |
    explanation: >-
      Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned.
- name: Pectus carinatum
  category: Skeletal
  description: >-
    Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned. The later table misspells carinatum as craniatum.
  phenotype_term:
    preferred_term: Pectus carinatum
    term:
      id: HP:0000768
      label: Pectus carinatum
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      | Thorax | Narrow | NA | Normal | Normal | Pectus craniatum | Pectus excavatum | Narrow | Narrow |
    explanation: >-
      Reported in an original affected child. Later summaries differ in patient assignment, so no specific patient number or pooled frequency is assigned. The later table misspells carinatum as craniatum.
differential_diagnoses:
- name: Brachydactyly Type A1 (IHH-related)
  description: >-
    The dominant allelic disorder. Heterozygous IHH variants cause shortened or
    absent middle phalanges, often with mild short stature, but without the
    proximal femoral changes or generalized early growth plate closure of ACFD.
    The two disorders map to separate regions of IHH-N.
  evidence:
  - reference: PMID:19277064
    reference_title: Brachydactyly A-1 mutations restricted to the central region of the N-terminal active fragment of Indian Hedgehog.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All of the BDA1 mutations occur in a restricted area of the N-terminal
      active fragment of the IHH and are in contrast to those mutations causing
      an autosomal recessive acrocapitofemoral dysplasia
    explanation: Distinguishes the two allelic IHH disorders by variant location.
animal_models:
- name: Postnatal chondrocyte Ihh deletion (Col2a1-creERT; Ihh floxed) mouse
  species: Mouse
  genotype: Col2a1-creERT; Ihh(fl/fl), tamoxifen-induced after birth
  publication: PMID:17409191
  description: >-
    Tamoxifen-induced deletion of Ihh from chondrocytes after birth. This
    avoids the embryonic lethality of the constitutive null and isolates the
    postnatal growth plate phase in which ACFD becomes apparent.
  modeled_mechanisms:
  - target: Ectopic Chondrocyte Hypertrophy
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Reproduces loss of columnar structure and ectopic hypertrophy in the
      postnatal growth plate.
    limitations: >-
      Conditional deletion of Ihh, rather than a human ACFD missense allele. V190A has in-vitro biochemical and reporter data, but residual activity in patient cartilage remains unknown. Trabecular-bone loss and articular-surface destruction in these mice are not established ACFD manifestations.
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        postnatal deletion of Ihh resulted in loss of columnar structure,
        premature vascular invasion, and formation of ectopic hypertrophic
        chondrocytes in the growth plate
      explanation: Growth plate histology in the model.
  - target: Premature Growth Plate Closure
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: Reproduces premature growth plate fusion and dwarfism.
    limitations: >-
      Mouse growth plates do not close physiologically the way human ones do at
      puberty, so the timing is not directly comparable to prepubertal closure
      in patients.
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Furthermore, destruction of the articular surface in long bones and
        premature fusion of growth plates of various endochondral bones was
        evident, resulting in dwarfism in mutant mice.
      explanation: Premature growth plate fusion and dwarfism in the model.
  - target: Loss of Growth Plate Columnar Organization
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: TISSUE
    description: >-
      Reproduces loss of the columnar arrangement of postnatal growth-plate chondrocytes.
    limitations: >-
      Conditional deletion of Ihh, rather than a human ACFD missense allele. V190A has in-vitro biochemical and reporter data, but residual activity in patient cartilage remains unknown. Trabecular-bone loss and articular-surface destruction in these mice are not established ACFD manifestations.
    evidence:
    - reference: PMID:17409191
      reference_title: Indian Hedgehog produced by postnatal chondrocytes is essential for maintaining a growth plate and trabecular bone.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        postnatal deletion of Ihh resulted in loss of columnar structure,
        premature vascular invasion, and formation of ectopic hypertrophic
        chondrocytes in the growth plate
      explanation: Growth plate histology in the model.
- name: Aggrecan-lineage Ihh deletion (Acan-creERT; Ihh floxed) mouse
  species: Mouse
  genotype: Acan-creERT; Ihh(fl/fl), tamoxifen-induced
  publication: PMID:34820473
  description: >-
    Inducible deletion of Ihh from aggrecan-expressing cells. The authors
    present it as a model of human IHH-related chondrodysplasias, including
    ACFD, and used it to test the Smoothened agonist SAG.
  modeled_mechanisms:
  - target: Reduced IHH Signaling Output
    relationship: RECAPITULATES
    fidelity: MODERATE
    model_scale: CELLULAR
    description: Reduced ciliary Smoothened and nuclear Gli1 in Ihh-deficient chondrocytes.
    limitations: >-
      A conditional deletion model with residual Ihh expression and broad aggrecan-lineage targeting, not an ACFD missense model. Smoothened and Gli1 were measured in cultured articular chondrocytes, not directly in patient growth plates.
    readouts:
    - name: Ciliary Smoothened and nuclear Gli1 in chondrocytes
      target: Reduced IHH Signaling Output
      direction: DECREASED
      interpretation: Direct pathway-activity readout downstream of Patched.
      evidence:
      - reference: PMID:34820473
        reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          Lower levels of Smo in the cilium or Gli1 protein in the nucleus were
          detected in Ihh-deficient chondrocytes than in control chondrocytes.
        explanation: The measured readout and its direction.
    evidence:
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte
        proliferation and differentiation by stimulating smoothened trafficking
        to the cilium in Ihh-silenced cells.
      explanation: >-
        Rescue with a Smoothened agonist shows the defect sits upstream of
        Smoothened, which is where reduced ligand acts.
  - target: Narrow chest
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    model_scale: ORGANISM
    description: >-
      The mice have short stature, a short spine and a narrow thorax. Respiratory failure attributed to rib shortening caused the 23 deaths among 83 vehicle-treated mutants; 60 survived to the study endpoint.
    limitations: >-
      The mouse model includes lethal thoracic restriction in a subset. This is not established as a typical ACFD outcome; human respiratory manifestations and animal mortality should not be equated.
    evidence:
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The results showed that the phenotype of Ihh-deficient mice (Ihhcko)
        closely mimicked that of humans with Ihh gene mutation-related skeletal
        dysplasia defects, including short stature with short spine and trunk,
        narrow thorax
      explanation: Thoracic and stature phenotype of the model.
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Ihhcko mice treated with vehicle, which had a survival rate of 72.3% (60/83)
      explanation: >-
        The explicit denominator corrects a misleading reading of the same paper as showing universal mortality.
discussions:
- discussion_id: acfd_missense_vs_null_models
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#Reduced IHH Signaling Output
  - pathophysiology#Biallelic IHH Signaling-Domain Missense Variants
  prompt: >-
    How do the individual ACFD alleles alter ligand abundance, processing, signaling potency and spatial range in human cartilage?
  rationale: >-
    Functional evidence exists but is uneven. Wang et al. (2021) found reduced V190A IHH-N abundance, interpreted as a stability defect with a smaller processing effect. Cunningham's 2008 MSc thesis found reduced secreted V190A ligand but preserved LIGHT2 reporter activity after concentration normalization. That thesis corrected an initial immunoblot band misidentification, discovered that its intended P46L construct was wild type, and reported a media/insulin confound in the V190A ATDC5 assay; those results do not establish normal human chondrogenesis or a P46L effect. Hellemans' 2006 doctoral thesis found no differences among wild-type, ACFD and BDA1 IHH-overexpressing chicken micromass cultures. These preliminary assays may miss concentration-dependent or spatial defects. The p.Ala173Asp evidence remains computational. Mouse deletion models establish IHH requirements but cannot resolve allele-specific effects or tissue restriction.
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: >-
      In silico modeling and dynamic simulation analysis revealed that the
      variant disturbed the core structure of the domain and destabilized the
      loop region and the region surrounding the variant.
    explanation: >-
      Computational evidence for p.Ala173Asp; it is not the only functional evidence available for the disorder.
  - reference: PMID:34070546
    reference_title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)
    explanation: >-
      Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
  - reference: url:https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF
    reference_title: "https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF"
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The V190A mutation was the only mutant that induced a comparable level of relative luciferase activity
    explanation: >-
      Cunningham (2008), MSc thesis, chapter 4: secreted V190A IHH-N retained reporter activity when conditioned media were normalized for ligand abundance by immunoblot densitometry. This preliminary heterologous-cell experiment distinguishes ligand quantity from activity per amount of ligand; it is not evidence of normal signaling in patient growth plates.
  - reference: url:https://backoffice.biblio.ugent.be/download/472261/1879896
    reference_title: "https://backoffice.biblio.ugent.be/download/472261/1879896"
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Comparison of the cultures infected with wild-type IHH, ACFD-IHH or BDA1-IHH did not reveal any differences.
    explanation: >-
      Hellemans (2006), doctoral thesis, general discussion: chicken limb-bud micromass cultures overexpressing IHH variants showed no detected differences. The experiment included c.137C>T and c.569T>C equivalents of the ACFD alleles. Overexpression and a coarse differentiation readout may miss quantitative or spatial defects; this was preliminary thesis work.
  proposed_experiments:
  - experiment_id: exp_acfd_allele_signaling_assays
    name: Compare ACFD allele processing, ligand availability and signaling potency
    description: >-
      Express full-length wild-type IHH and sequence-confirmed P46L, R160C, A173D and V190A constructs alongside BDA1 controls. Separately quantify precursor processing, secreted ligand and dose-normalized reporter activation, then test spatial signaling in a cartilage-relevant system. Use full-length protein for processing and secretion assays; expressing IHH-N alone would bypass those steps. Control media composition and avoid interpreting a saturating overexpression assay as proof of normal signaling range.
    would_support:
    - pathophysiology#Reduced IHH Signaling Output
    supporting_outcome:
    - >-
      Reduced, but not absent, pathway activation for all four alleles would
      support a hypomorphic mechanism consistent with a recessive,
      skeleton-restricted phenotype.
    would_refute:
    - pathophysiology#Reduced IHH Signaling Output
    refuting_outcome:
    - >-
      Normal dose-normalized reporter activation would refute an obligatory intrinsic potency defect, but would not refute reduced ligand abundance or altered spatial availability. Normal tissue-level signaling across controlled expression levels would challenge the reduced-output model.
- discussion_id: acfd_carrier_phenotype
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - inheritance#Autosomal Recessive
  prompt: >-
    Do heterozygous carriers of ACFD alleles have short stature or subtle hand
    changes?
  rationale: >-
    Carrier phenotype is not wholly unstudied. The original 2003 molecular paper, reprinted in Hellemans' thesis (paper p.1044), describes subtle phalangeal or metacarpal shortening in parents without typical BDA1; pelvic radiographs were normal in the Belgian parents examined. The Pakistani parents had short stature and clinically normal hands. Heterozygous IHH variants can also cause dominant short stature. Systematic age-, sex- and family-adjusted data are needed to determine the penetrance and clinical significance of ACFD carrier findings.
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The height of the father (53 years old) and the mother (45 years old) was
      short, with 155 cm (-3.0SD) and 140.2 cm (-3.6 SD), respectively, but
      their hands were normal, with normal fingers.
    explanation: Short stature in both obligate carriers in one family.
  - reference: PMID:29155992
    reference_title: IHH Gene Mutations Causing Short Stature With Nonspecific Skeletal Abnormalities and Response to Growth Hormone Therapy.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Identified IHH variants segregate with short stature in a dominant
      inheritance pattern.
    explanation: Heterozygous IHH variants are an established cause of dominant short stature.
notes: >-
  Phenotype counts refer to the explicitly tabulated patients and exclude NA/NR from assessed denominators; the small series does not establish universal population frequencies. Unilateral ptosis, pes planus and hypertrichosis are reported family-level findings with uncertain attribution to IHH. No disease-specific interventional study was identified in ClinicalTrials.gov as of 2026-09-27. Growth-hormone responses reported for heterozygous IHH-related short stature are not established treatment evidence for biallelic ACFD.
references:
- reference: PMID:12624140
  title: "Acrocapitofemoral dysplasia: an autosomal recessive skeletal dysplasia with cone shaped epiphyses in the hands and hips."
  findings: []
- reference: PMID:34070546
  title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
  findings: []
- reference: url:https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF
  title: "https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF"
  findings: []
- reference: url:https://backoffice.biblio.ugent.be/download/472261/1879896
  title: "https://backoffice.biblio.ugent.be/download/472261/1879896"
  findings: []
- reference: url:https://www.jci.org/articles/view/24397
  title: "JCI -\nIndian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP"
  findings: []
diagnosis:
- name: Skeletal radiographic assessment
  description: >-
    The combination of hand epiphyseal abnormalities and the short femoral neck with egg-shaped capital epiphysis supports recognition of ACFD. Adult films may instead show fused plates, very short femoral necks, altered metacarpal configuration and phalangeal fusion; loss of childhood cone-shaped appearances does not exclude the diagnosis.
  evidence:
  - reference: PMID:34530144
    reference_title: "Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck. These findings could help the diagnosis of ACFD in adult patients.
    explanation: >-
      Adult diagnostic clues differ from childhood epiphyseal appearances.
  diagnosis_term:
    preferred_term: Bone Radiography
    term:
      id: NCIT:C137876
      label: Bone Radiography
- name: Molecular testing for biallelic IHH variants
  description: >-
    Exome sequencing identified the IHH variant in the Pakistani proband; Sanger sequencing confirmed the variant and segregation in affected siblings and parents. Molecular findings should be interpreted with the radiographic phenotype, particularly when additional skeletal-dysplasia gene variants could produce a blended presentation.
  diagnosis_term:
    preferred_term: Whole Exome Sequencing
    term:
      id: NCIT:C101295
      label: Whole Exome Sequencing
  evidence:
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Whole exome sequencing (WES) followed by Sanger sequencing was carried out for mutational screening.
    explanation: >-
      Exome discovery with Sanger confirmation in the reported family.
  - reference: PMID:40045933
    reference_title: A Novel Biallelic Variant in IHH Causing Acrocapitofemoral Dysplasia in a Pakistani Family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The parents were heterozygous carriers, while both affected individuals carried the homozygous mutant allele
    explanation: >-
      Family segregation supports the molecular interpretation.
treatments:
- name: Smoothened agonist SAG (preclinical)
  action_category: THERAPEUTIC
  context: Experimental treatment in conditional Ihh-deletion mice and cultured mouse chondrocytes; no established human ACFD efficacy
  description: >-
    SAG activates Smoothened downstream of IHH. It improved skeletal growth and survival in conditional Ihh-deletion mice; starting at postnatal day 7 produced greater growth benefit than starting at day 14. Cartilage and growth-plate rescue was partial. The study also reported intestinal hyperplasia and bowel-obstruction deaths, so its broad statement of no toxicity should not be taken as a safety conclusion. These results do not establish a treatment regimen for patients with ACFD.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: SAG (Smoothened agonist)
      term:
        id: CHEBI:138438
        label: 3-chloro-N-[trans-4-(methylamino)cyclohexyl]-N-[3-(pyridin-4-yl)benzyl]-1-benzothiophene-2-carboxamide
  target_mechanisms:
  - target: Reduced IHH Signaling Output
    treatment_effect: RESTORES
    description: >-
      Activating Smoothened restores downstream signaling readouts in the conditional-deletion model, bypassing deficient IHH input.
    evidence:
    - reference: PMID:34820473
      reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        SAG treatment resulted in dramatically increased Smo translocation to the primary cilium and Gli1 accumulation in the nucleus
      explanation: >-
        SAG restores pathway readouts downstream of the missing ligand in cultured mouse articular chondrocytes. It does not correct the IHH genotype.
  evidence:
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      SAG treatment resulted in dramatically increased Smo translocation to the primary cilium and Gli1 accumulation in the nucleus
    explanation: >-
      SAG restores pathway readouts downstream of the missing ligand in cultured mouse articular chondrocytes. It does not correct the IHH genotype.
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      earlier treatment with SAG beginning on P7 was more effective in preventing the dwarfism phenotype compared to the treatment beginning on P14.
    explanation: >-
      The comparison concerns timing in neonatal mice; it does not establish clinical timing for children.
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      SAG can more effectively rescue the defective bone but just partially rescue the growth plate and cartilage.
    explanation: >-
      The discussion qualifies the degree of rescue; normal growth-plate biology was not fully restored.
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      a few animals treated with SAG had intestinal hyperplasia, showing increased thickness of the smooth muscle layer, which raises the possibility of bowel obstruction.
    explanation: >-
      The full-text toxicity observations materially qualify the abstract's reassurance.
  - reference: PMID:34820473
    reference_title: SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      none of the animals in the vehicle-treated wild-type group died (0/83), while one animal died from bowel obstruction in the SAG-treated wild-type group (1/41).
    explanation: >-
      A reported adverse outcome in treated wild-type animals. The paper's other mortality totals are not fully consistent, so they are not pooled into an additional safety estimate.
experimental_models:
- name: Human IHH V190A expression in ECHO cells
  experimental_model_type: CELL_LINE
  cell_source: EcR-CHO cells expressing human IHH constructs
  publication: PMID:34070546
  description: >-
    Full-length human wild-type or V190A IHH was expressed with N- or C-fragment FLAG tags. Immunoblots compared the signaling and autoprocessing fragments; supplementary Figure S5 shows a larger reduction of the N-terminal than the C-terminal fragment.
  modeled_mechanisms:
  - target: Reduced V190A IHH-N Abundance
    relationship: MEASURES
    fidelity: MODERATE
    model_scale: MOLECULAR
    description: >-
      Measures reduced V190A IHH-N abundance, interpreted by the authors as a stability defect with a smaller processing effect.
    limitations: >-
      Heterologous overexpression of tagged human protein, not patient-derived cartilage. Fragment abundance does not directly measure protein half-life, secretion, receptor binding or spatial signaling in the growth plate. The paper's multimerization and alkaline-phosphatase assays mainly test engineered truncations, not V190A.
    evidence:
    - reference: PMID:34070546
      reference_title: Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        ACFD-associated mutation V190A ... which is closed to the KSEH in the C-terminus of IHH-N, affected the self-cleavage slightly but reduced protein stability obviously (Figure S5)
      explanation: >-
        Wang et al. tested the disease-associated V190A substitution in an IHH expression system. They interpreted the fragment immunoblots as a slight processing defect and a larger stability defect. This does not establish the effects of the other ACFD alleles or quantify signaling in patient cartilage.
📚

References & Deep Research

References

5
PMID:12624140
Acrocapitofemoral dysplasia: an autosomal recessive skeletal dysplasia with cone shaped epiphyses in the hands and hips.
No top-level findings curated for this source.
PMID:34070546
Highly Conserved C-Terminal Region of Indian Hedgehog N-Fragment Contributes to Its Auto-Processing and Multimer Formation.
No top-level findings curated for this source.
url:https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF
https://www.collectionscanada.gc.ca/obj/thesescanada/vol2/002/MR48445.PDF
No top-level findings curated for this source.
url:https://backoffice.biblio.ugent.be/download/472261/1879896
https://backoffice.biblio.ugent.be/download/472261/1879896
No top-level findings curated for this source.
url:https://www.jci.org/articles/view/24397
JCI - Indian hedgehog stimulates periarticular chondrocyte differentiation to regulate growth plate length independently of PTHrP
No top-level findings curated for this source.

Deep Research

1

Deep research results are used as seeds for research; they do not undergo the same validation as the main records and may contain errors. How we use deep research.

Evaluations and curation notes (2)

Review Acrocapitofemoral Dysplasia against clinical and functional full texts · 2026-09-27T00:31:02Z · View source

Reviewed the complete disorder entry, CREATE/EDIT history and matching Perplexity deep-research report/citations against primary sources. Eligible Mendelian IHH disorder with no prior REVIEW; infectious and environmental/poisoning entries are excluded from this sweep. Full-text consumption: read the 2025 Pakistani report (PMID:40045933), including Table 2 and methods; Wang 2021 (PMID:34070546), including methods and the downloaded supplement, with Figure S5 visually inspected; Maeda 2007 (PMID:17409191), including results, discussion and methods; Kobayashi 2005 (PMID:15951842) in its generated JCI URL cache, including results/discussion and methods; and the substantive mouse/cell results, discussion and methods of Huang 2021 (PMID:34820473). Visually read all seven pages of the Hellemans 2003 molecular article (PMID:12632327) in the scanned reprint within the fetched 2006 doctoral thesis; also read the thesis discussion of chicken micromass experiments. Read the relevant in-vitro methods, results, corrections and discussion in Cunningham's 2008 MSc thesis. The unrelated zebrafish chapter was not used. Abstract-only sources include PMID:34530144, PMID:40771183, PMID:10465785, PMID:8662546, PMID:19277064 and PMID:29155992. The original Mortier clinical letter (PMID:12624140) remained unavailable as usable cached text after multiple fetch attempts; no invented quotation or full-text claim is made for it. The scanned Hellemans article did not extract into the text cache, so new exact quotations from those scanned pages are not supplied. All committed reference caches were generated with just fetch-reference. Corrected the claim that no ACFD allele had been experimentally studied: Wang's V190A fragment immunoblots support reduced IHH-N abundance, interpreted as reduced stability with a smaller processing defect, not a directly measured half-life. Added a provisional allele-specific mechanism and expression model. Thesis reporter results distinguish ligand abundance from normalized intrinsic activity; documented the corrected band identification, wild-type contamination of the intended P46L construct and media/insulin confounding in the ATDC5 assay. Computational A173D findings remain separate. Split hypertrophy, loss of columnar organization and vascular invasion; qualified inferred causal edges and postnatal PTHrP redistribution. Corrected cultured-cell versus animal evidence classifications and universal-lethality misreading (60/83 vehicle-treated mutants survived). Reconciled five original molecular patients versus four selected in later tables, giving at least nine unblended individuals across four families. Qualified carrier hand findings using the original molecular paper. Corrected age/count/anatomical overstatements and removed population-frequency claims inferred from small selected series. Added 13 phenotypes, case-specific additional foot findings, radiographic diagnosis and molecular testing. Kept uncertain family-level manifestations without inventing mechanistic links. Added preclinical SAG treatment with pathway target and partial efficacy, alongside intestinal hyperplasia and bowel-obstruction death; no clinical regimen or human efficacy is inferred. Heterozygous-IHH growth-hormone data are not treated as biallelic ACFD treatment evidence. Completeness checklist: phenotype coverage adequate after the additions and denominator corrections; subtypes N/A (one discrete IHH-related disorder, blended Syrian case not pooled); pathophysiology adequate with explicit human/model limitations; treatment/trials adequate for available evidence (SAG experimental only; ClinicalTrials.gov condition query returned zero studies on 2026-09-27); genetics adequate for reported variants and incompletely characterized carriers; biomarkers/diagnostics adequate with radiography and sequencing, no validated biochemical biomarker identified; references adequate after recovering missed functional work and full texts. No applicable GeneReviews chapter was identified by the repository check including online query. Non-blocking limits are inaccessible original clinical text, inconsistent later summary tables and unresolved allele-specific human-cartilage mechanisms, not omitted established treatment or subtype evidence. New evidence and publication titles were checked against generated caches and claim relevance. Validation: just validate-disorders passes schema, ontology and reference checks (132 snippets, 137 titles, none unavailable); two scoped data tests pass. Internal entity links, causal targets, coarse phenotype bindings and source-defect checks pass. Final snippet/title gates and commit hooks are recorded in the PR after completion.

Create: Acrocapitofemoral_Dysplasia · 2026-09-24T21:15:50Z · View source

New entry for acrocapitofemoral dysplasia (MONDO:0011907, IHH). Curated from the Perplexity deep-research report (research/Acrocapitofemoral_Dysplasia-deep-research-perplexity.md) plus a PubMed search for acrocapitofemoral[TIAB] and for the mouse Ihh growth-plate literature. The report's reference validation resolved all 7 references; all were read before use. Its term validation flagged 17 mislabelled and 3 obsolete CURIEs (CL:0000133 offered as chondrocyte is neurectodermal cell; UBERON:0001465 offered as hip joint is knee; every NCIT treatment CURIE named an unrelated concept; HP:0002355 obsolete; HP:0001249, offered for normal intelligence, is Intellectual disability). None of the report's CURIEs was copied; every binding came from runoak (ols:) or cache/<prefix>/terms.csv. just preflight-dr returned PASS (IHH mentioned 94 times; the extra OMIM 112500 is BDA1, mentioned as the allelic disorder). The report misattributes the 2025 Pakistani family paper to 'Khalid et al.' (authors are Saeed et al., PMID:40045933), repeats that paper's inconsistent 'amino acids 201-308' domain range, calls several features universal that the 2025 phenotype table shows as variable, and proposes a treatment section with no human data; none of this was carried over. Frequencies come from the 2025 Table 2 counts (8 patients), recorded in phenotype descriptions. The mechanism chain (missense variants -> reduced IHH signaling -> reduced chondrocyte proliferation and accelerated hypertrophy -> premature growth plate closure -> phenotypes) is graded MODEL_ORGANISM wherever it rests on mouse Ihh deletion. The one allele-level datum is computational and is graded COMPUTATIONAL. A HUMAN_MODEL_MISMATCH discussion records that no ACFD allele has been functionally assayed, and a KNOWLEDGE_GAP records the short carrier parents in the Pakistani family. No GeneReviews chapter (just check-genereviews --online: NO_CHAPTER). Mortier 2003 (PMID:12624140) has no abstract and is listed under references only. Validation: just validate, validate-terms, count-verified-snippets (63/63), check-entity-refs, check-causal-targets, check-duplicate-keys, check-qualifier-terms, check-enum-values and validate-disorders run on the entry. Three phenotypes (lumbar hyperlordosis, fifth toe symphalangism, short nail) are left without a causal in-edge because no source states their mechanism.

Perplexity ▸
1. Disease Information
sonar-deep-research 20 citations 2026-09-24T20:49:21.474930

1. Disease Information

1.1 Definition and Concise Overview

Acrocapitofemoral dysplasia is a rare, monogenic skeletal dysplasia that affects endochondral bone growth, leading to disproportionate short stature with striking involvement of the hands (“acro-”) and capital femoral epiphyses (“-capitofemoral”).[1][3][11] The condition was formally delineated in the early 2000s based on clinical and radiographic characterization of two consanguineous families, in whom all affected individuals exhibited short limbs and brachydactyly associated with cone-shaped epiphyses in hands and hips.[2][7][11] In the original description, the authors emphasized that affected individuals had normal intelligence and no associated malformations outside the skeletal system, suggesting that ACFD represents a relatively “pure” disorder of cartilage and bone growth rather than a multisystem syndrome.[11][19] Subsequent case reports and small series have confirmed the core phenotype while broadening the age range of documented patients, with the first adult cases reported from a Turkish family harboring a novel homozygous IHH variant and a more recent Pakistani family expanding the mutational spectrum.[4][6] Orphanet and MedGen describe ACFD as a postnatal-onset disproportionate short stature with short limbs, brachydactyly, small broad nails, narrow thorax, lumbar lordosis, and characteristic radiographic features of egg-shaped capital femoral epiphyses and cone-shaped epiphyses, mainly in the hands and hips.[3][5]

From a nosologic standpoint, ACFD is classified as a skeletal dysplasia arising from disordered endochondral ossification and is grouped within the hedgehog-signaling-related chondrodysplasias, alongside brachydactyly type A1 and other phenotypes associated with monoallelic IHH variants.[1][10][14] The Online Mendelian Inheritance in Man (OMIM) database assigns ACFD the entry number 607778 and notes that the disorder is caused by homozygous missense mutations in IHH at chromosome 2q35, outside the region where brachydactyly type A1 mutations cluster.[1][7] MedGen associates ACFD with the concept ID C1843096 and cross-references OMIM 607778, Orphanet ORPHA:63446, and MONDO:0011907, establishing ACFD as a distinct disease entity in multiple biomedical ontologies.[5] The National Organization for Rare Disorders (NORD) similarly recognizes ACFD as a recently delineated skeletal dysplasia with short stature, short limbs, brachydactyly, and a narrow thorax.[8]

1.2 Key Identifiers and Ontology Mapping

The disease is represented in several major disease classification and ontology systems. OMIM lists acrocapitofemoral dysplasia under entry 607778 and links it to IHH (gene entry 600726).[1] Orphanet assigns the identifier ORPHA:63446 and categorizes ACFD as a “rare skeletal dysplasia,” with a prevalence of less than 1 per 1,000,000 individuals and an autosomal recessive inheritance pattern.[3] MedGen gives the concept ID C1843096 and associates ACFD with SNOMED CT concept 720416007, reflecting its inclusion in standardized clinical terminology used in electronic health records.[5] The Monarch Initiative and MONDO ontology identify ACFD as MONDO:0011907, situating it within a unified cross-species disease ontology and supporting computational disease modeling and data integration.[5][8] Additional identifiers include UMLS CUI (concept unique identifier) C1843096 and DO (Disease Ontology) term DOID:0050604, which collectively facilitate interoperability across clinical, research, and informatics environments.[1][5]

These identifiers can be linked to relevant phenotype, anatomy, and intervention ontologies. Suggested Human Phenotype Ontology (HPO) terms include short stature (HP:0004322), disproportionate short stature (HP:0003498), brachydactyly (HP:0001156), cone-shaped epiphyses (HP:0003221), short femoral neck (HP:0002823), narrow thorax (HP:0000773), lumbar lordosis (HP:0002938), and small broad nails (HP:0001800).[5][11][17] At the disease level, ACFD maps to the MONDO term for acrocapitofemoral dysplasia (MONDO:0011907), and at the anatomical level, primary sites of involvement include long bones of the limbs (UBERON:0002260), proximal femur (UBERON:0001460), phalanges of hand (UBERON:0001443), and vertebral column (UBERON:0001130).[11][12][17]

1.3 Synonyms and Alternative Names

The term “acrocapitofemoral dysplasia” is itself descriptive, combining “acro-” (extremities) and “capitofemoral” (capital femoral epiphysis) to highlight the characteristic involvement of the distal phalanges and proximal femoral epiphyses.[11][19] Common synonyms include “ACFD” as an acronym, which appears in MedGen, Orphanet, NORD, and clinical literature.[3][5][8] In some contexts, particularly within radiologic and genetic texts, the disease is referred to as “acrocapitofemoral skeletal dysplasia” or “Indian hedgehog–related acrocapitofemoral dysplasia,” emphasizing its pathophysiologic basis in Ihh signaling.[1][9][10] However, no widely used alternative names exist that fundamentally differ from “acrocapitofemoral dysplasia,” reflecting the relatively recent and specific delineation of the entity. Differential diagnostic terms—such as brachydactyly type A1 or other cone-shaped epiphysis syndromes—are related but distinct and should not be considered synonyms.[9][10]

1.4 Data Sources: Individual Patients Versus Aggregated Resources

Information on ACFD is derived from a combination of individual patient data and aggregated disease-level resources. The foundational descriptions by Mortier et al. (J Med Genet 2003, PMID 12624140) and Hellemans et al. (Am J Hum Genet 2003, PMID 12632327) are based on detailed clinical and radiographic evaluation of four affected children from two consanguineous families, coupled with genomewide homozygosity mapping and candidate gene sequencing.[2][7][11][19] More recent reports, such as the Turkish adult siblings described by Ozyavuz Cubuk and Düz (Eur J Med Genet 2021, PMID 34530144) and the Pakistani family studied by Khalid et al. (Mol Genet Genomic Med 2025, PMID 40045933), expand the dataset to a small number of additional individuals but still represent case-based evidence rather than large cohorts.[4][6]

Aggregated resources including OMIM, Orphanet, MedGen, NORD, and clinical genetics panel databases synthesize these case reports into structured disease entries that summarize etiology, inheritance, clinical features, and radiographic hallmarks.[1][3][5][8][10] These resources typically rely on expert curation and literature review rather than direct extraction from electronic health records, reflecting the rarity of the disease and the predominance of published case reports over routine clinical coding. As of current knowledge, there are no population-based registries or large-scale epidemiologic datasets specific to ACFD; thus, most information remains anchored in high-detail descriptions of a few families complemented by mechanistic insights from model organism studies.[6][11][12][16]

2. Etiology

2.1 Primary Causal Factors: Genetic Basis in IHH

Acrocapitofemoral dysplasia is unequivocally a genetic disease caused by biallelic pathogenic variants in the Indian hedgehog (IHH) gene, located on chromosome 2q35.[1][3][5][7] Hellemans et al. performed genomewide homozygosity mapping in two consanguineous families and localized the disease locus to 2q35–q36 with a maximum two-point LOD score of 8.02 at marker D2S2248; subsequent candidate-gene sequencing identified two distinct homozygous missense mutations in the amino-terminal signaling domain of IHH.[7][11][19] In family 1, affected individuals were homozygous for a c.137C>T transition resulting in a p.Pro46Leu substitution, while in family 2, patients carried a c.569T>C transition encoding p.Val190Ala; both residues are highly conserved and lie outside the cluster of residues associated with brachydactyly type A1.[7][11][15] Functional studies and structural modeling indicate that these mutations alter the signaling capacity of the hedgehog protein, leading to impaired chondrocyte proliferation and abnormal epiphyseal development.[7][12][13]

Later work confirmed the genetic etiology and further delineated the mutational spectrum. Orphanet and OMIM report that homozygous mutations in IHH outside the brachydactyly A1 cluster cause ACFD, reinforcing the concept of allelic heterogeneity at the IHH locus with distinct phenotypic consequences depending on variant type and zygosity.[1][3] The 2021 report by Ozyavuz Cubuk and Düz described two adult siblings with ACFD who carried a novel homozygous missense variant c.478C>T (p.Arg160Cys) in exon 2, again within the N-terminal signaling domain and likely affecting the protein’s ability to bind and signal through Patched and Smoothened receptors.[4] In 2025, Khalid et al. identified a novel homozygous missense variant c.518C>A (p.Ala173Asp) in exon 2 of IHH in a Pakistani family, representing the fourth distinct missense mutation associated with ACFD and expanding both phenotypic and genotypic spectra.[6] Collectively, these findings support a model in which ACFD is caused by biallelic missense mutations in the signaling domain of IHH that reduce hedgehog pathway activity, particularly in growth plate chondrocytes.[1][6][7][12]

Environmental, infectious, or purely mechanistic non-genetic causes have not been implicated in ACFD. All reported families exhibit consanguinity or a clear pattern of autosomal recessive inheritance, and no cases have been described without identifiable IHH variants.[4][6][7] Moreover, the convergence of human phenotypes with those observed in Ihh knockout or conditional knockout mice underscores the central role of IHH deficiency in driving the disorder, rather than complex gene–environment interactions or polygenic susceptibility.[12][13][16]

2.2 Genetic Risk Factors Beyond Primary Causal Variants

The principal genetic risk factor for ACFD is the presence of biallelic pathogenic missense variants in IHH, inherited in an autosomal recessive fashion from carrier parents.[1][3][7] As of the most recent literature, four distinct missense variants have been definitively associated with ACFD: p.Pro46Leu (c.137C>T), p.Val190Ala (c.569T>C), p.Arg160Cys (c.478C>T), and p.Ala173Asp (c.518C>A).[4][6][7][15] These variants cluster in the N-terminal signaling domain but are located outside the region associated with brachydactyly type A1, suggesting that they perturb specific aspects of IHH signaling required for growth plate maintenance and cone-shaped epiphysis formation.[1][7][10] ClinVar lists the c.569T>C (p.Val190Ala) variant as pathogenic for acrocapitofemoral dysplasia (RCV000009421), with OMIM as the primary submitter and literature-only evidence based on the original Am J Hum Genet report.[7][15]

Monoallelic heterozygous variants in IHH are known to cause brachydactyly type A1 (BDA1, OMIM 112500), and more recently, familial short stature with non-classical brachydactyly has been described in families with heterozygous frameshift or missense IHH variants.[10][14][18] A 2022 case report detailed a novel heterozygous frameshift insertion c.387_388insC (p.Thr130Hisfs18) in IHH* in two siblings and their mother, all of whom exhibited short stature combined with non-classical BDA1; the variant is predicted to cause nonsense-mediated RNA decay and haploinsufficiency.[18] These observations highlight that even partial reduction of IHH dosage can impair skeletal growth, but in ACFD, complete loss or severe attenuation of signaling due to biallelic missense variants appears necessary to produce the characteristic acrocapitofemoral phenotype.[1][6][7][10]

At present, no modifier genes have been conclusively identified that alter the severity or expressivity of ACFD, and genome-wide association studies are nonexistent due to the extreme rarity of the condition.[6][7] It is possible that common variants in components of the hedgehog pathway, Wnt signaling, or cartilage extracellular matrix could modulate phenotypic variability, but such hypotheses remain untested. Population databases such as gnomAD or ExAC may contain low-frequency missense variants in IHH, but specific allele frequencies for the known ACFD variants have not been reported in the accessible literature, likely reflecting their very low frequency and occurrence mainly within consanguineous pedigrees.[6][15]

2.3 Environmental and Lifestyle Risk Factors

No specific environmental or lifestyle risk factors have been associated with acrocapitofemoral dysplasia. The disorder manifests in early childhood in individuals with biallelic IHH mutations and does not appear to depend on exposures such as toxins, nutritional deficiencies, or mechanical stress.[3][7][11] Orphanet and NORD emphasize its genetic, autosomal recessive nature and do not mention environmental contributors.[3][8] Likewise, primary clinical reports do not identify any consistent environmental triggers or modifiers; in the Belgian and Dutch families described by Mortier and Hellemans, children were born at term without perinatal complications, and growth abnormalities emerged postnatally as cone-shaped epiphyses developed.[2][11] In the Turkish and Pakistani families, there is no indication of relevant environmental exposures beyond typical living conditions.[4][6]

Given that the hedgehog pathway is a central developmental morphogenetic system and that IHH functions during prenatal and postnatal bone growth, one might hypothesize that factors affecting hedgehog signaling, such as certain teratogens, could modulate disease expression.[12][13] However, there is no direct evidence that exogenous hedgehog inhibitors (for example, some small-molecule drugs used in oncology) have been used in these patients or that their prenatal or postnatal exposures differ significantly from unaffected siblings.[6][11] Thus, it is most accurate to regard ACFD as a primarily genetic disease with minimal documented contribution from environmental risk factors.

2.4 Protective Factors and Gene–Environment Interactions

Specific genetic or environmental protective factors that reduce risk or mitigate severity in ACFD have not been reported. No protective variants in IHH have been identified that confer resilience to pathogenic missense mutations, and there are no data on modifier alleles in hedgehog pathway genes that ameliorate skeletal phenotypes.[6][7] Experimental hedgehog pathway activation with Smoothened agonists—such as SAG—in mouse models does suggest that pharmacologic enhancement of hedgehog signaling can partially rescue the consequences of Ihh deficiency, including impaired chondrocyte proliferation and enchondroma formation.[16] In Ihh conditional knockout mice, SAG treatment beginning at postnatal day 7 or 14 improved body length and weight and reduced mortality, indicating a potential therapeutic “protective” strategy, but this remains at the level of preclinical research and does not represent a naturally occurring protective factor.[16]

Gene–environment interactions are similarly poorly characterized. In principle, mechanical loading, nutritional status, endocrine milieu (e.g., growth hormone and IGF-1 levels), or exposure to hedgehog-modulating compounds could interact with reduced IHH signaling to influence growth plate dynamics.[12][13][16] However, human data are lacking, and the small number of reported ACFD cases precludes robust analysis of gene–environment interplay. The study of heterozygous IHH variants causing familial short stature showed that growth hormone therapy over four years yielded a meaningful increase in height in affected siblings, implying that endocrine interventions can modify growth outcomes in the context of partial Ihh deficiency.[18] Nonetheless, this evidence pertains to heterozygous non-ACFD phenotypes, and extrapolation to ACFD must be cautious.[18]

Overall, current evidence supports a model in which ACFD is driven almost entirely by biallelic IHH mutations, with minimal documented influence of external risk or protective factors. Future investigation in larger cohorts or registries, and in animal models exposed to varying environmental conditions, will be needed to detect subtle modifying influences.

3. Phenotypes

3.1 Clinical and Radiographic Phenotypes: Core Features

The clinical phenotype of acrocapitofemoral dysplasia is characterized by disproportionate short stature with short limbs, brachydactyly, relatively large head, and a narrow thorax often associated with pectus deformities and lumbar lordosis.[1][3][5][11] Affected individuals show short stature of variable degree, with postnatal onset, suggesting that prenatal skeletal growth may be relatively spared and that disease manifestations emerge as cone-shaped epiphyses develop in childhood.[11][19] Hands and feet demonstrate brachydactyly with shortening of the tubular bones, especially the middle phalanges; nails tend to be small and broad.[1][3][5] The thorax is described as narrow, and some patients exhibit pectus excavatum or carinatum; lumbar lordosis is common, reflecting spinal involvement and altered posture.[1][5][11]

Radiographically, ACFD is defined by cone-shaped epiphyses and related epiphyseal configurations involving multiple skeletal sites.[11][19] In the hands, cone-shaped epiphyses are prominent in the middle phalanges, and the configuration leads to premature fusion of the growth plate before puberty, resulting in permanent shortening of the digits.[11] In the hips, the capital femoral epiphyses are egg-shaped, and the femoral neck is strikingly short, producing a characteristic appearance that inspired the name “acrocapitofemoral.”[11][17][19] Similar epiphyseal changes can be observed to varying degrees in the shoulders, knees, and ankles, although the hands and hips are most consistently affected.[11][19] The cone-shaped epiphyses appear early in childhood and later disappear as the growth plate fuses; radiographs of older individuals thus show shortened bones but fewer overt cone-shaped epiphyses.[11][19]

Importantly, affected individuals do not exhibit congenital anomalies outside the skeleton and are of normal intelligence, distinguishing ACFD from many syndromic skeletal dysplasias that involve neurodevelopmental or visceral abnormalities.[1][11] The absence of associated malformations suggests that Ihh deficiency in ACFD primarily targets cartilage and bone tissues with limited impact on other hedgehog-dependent developmental processes, perhaps because the disease-causing mutations selectively reduce IHH function in growth plate chondrocytes rather than producing global hedgehog pathway failure.[7][12][13]

3.2 Age of Onset, Severity, and Progression

Orphanet states that acrocapitofemoral dysplasia has neonatal or infantile onset, reflecting the early emergence of growth abnormalities and skeletal changes.[3] However, more detailed clinical descriptions emphasize that the disproportionate short stature is postnatal in onset, with height deficiency and limb shortening becoming apparent in early childhood, often after the first year of life.[1][5][11] Cone-shaped epiphyses appear early in childhood and are radiographically detectable by late infancy or toddlerhood, depending on the timing of epiphyseal ossification.[11][19] The process of epiphyseal dysmorphogenesis and premature growth plate fusion occurs before puberty, such that final adult stature and limb proportions are largely determined by growth patterns in the first decade of life.[11][19]

Symptom severity varies among individuals and families, ranging from moderate short stature with mild limb shortening to more severe dwarfism with pronounced brachydactyly and proximal femoral deformity.[1][4][6][11] Mortier and Hellemans noted variability in height and limb length among affected siblings, suggesting that even within a single family harboring a defined IHH mutation, expressivity can be variable.[2][7][11] The Turkish adult siblings described in 2021 exhibited extremely short femoral necks and distinctive hand configurations, indicating that radiographic severity can be substantial.[4] The Pakistani family reported in 2025 similarly showed classic phenotypes but with some differences in thoracic and vertebral involvement.[6]

The disease course is broadly progressive in the sense that growth plate fusion leads to irreversible skeletal shortening, but once epiphyseal fusion has occurred, radiographic changes become stable and no further progression of bone deformity is expected.[11][19] Symptoms such as disproportionate stature and brachydactyly are lifelong features, but there is no evidence of episodic exacerbations, relapsing-remitting patterns, or degenerative joint disease specific to ACFD beyond the mechanical consequences of altered bone geometry.[4][6][11] Because intelligence is normal and visceral organ function appears preserved, quality of life impact is largely related to physical limitations, cosmetic concerns, and potential musculoskeletal pain, especially in the hips and lower back.[8][11]

3.3 Frequency of Phenotypes and Quality of Life Impact

Given the small number of documented cases, quantitative estimates of phenotype frequencies (e.g., percentage of patients with a given feature) are not available. Nonetheless, descriptive data indicate that short stature with short limbs, brachydactyly, and narrow thorax are consistently present in all reported individuals, making them core features.[1][3][4][6][11] Cone-shaped epiphyses in the hands and hips and an egg-shaped femoral head attached to a short femoral neck are likewise universal radiographic hallmarks.[7][11][19] Lumbar lordosis, relatively large head, and small broad nails are frequently mentioned but may be somewhat more variable.[1][5] Fusion of the middle phalanges with distal phalanges in the fifth toes was noted in the Turkish adult siblings, suggesting that specific digital anomalies may vary across families.[4]

Quality of life impact has not been formally assessed using instruments such as SF-36 or EQ-5D in ACFD patients. However, extrapolation from similar chondrodysplasias suggests that short stature and limb shortening can affect daily functioning, mobility, and psychosocial well-being, particularly in societies that place practical and social demands on height and physical capabilities.[8][16][18] Hip deformities and short femoral necks may predispose to altered gait, limited range of motion, and early-onset degenerative joint changes, potentially leading to pain and functional impairment.[4][11][17] Narrow thorax and pectus deformities could theoretically restrict pulmonary mechanics, but respiratory function has not been systematically studied in ACFD and no overt respiratory failure has been reported.[1][3][11]

From an ontology perspective, HPO terms capturing quality of life relevant phenotypes include reduced mobility (HP:0002355), abnormal gait (HP:0001288), back pain (HP:0003418), and hip pain (HP:0003375).[4][11] Quality of life instruments could be mapped to ontology terms in PROMIS or NCIT for patient-reported outcomes, but specific data for ACFD are lacking. Future research might employ standardized measures to quantify functional limitations and psychosocial burden, thereby enabling more precise integration into disease burden frameworks such as the Global Burden of Disease (GBD) study.

3.4 Suggested HPO Phenotype Terms

Based on current clinical and radiographic descriptions, key suggested HPO terms for acrocapitofemoral dysplasia include short stature (HP:0004322), disproportionate short stature (HP:0003498), short limb (HP:0002113), brachydactyly (HP:0001156), cone-shaped epiphyses (HP:0003221), short femoral neck (HP:0002823), egg-shaped femoral head (captured as abnormal femoral head morphology, HP:0002822), narrow thorax (HP:0000773), pectus deformity (HP:0000766), lumbar lordosis (HP:0002938), broad nails (HP:0001800), normal intelligence (HP:0001249), and absence of non-skeletal anomalies (implicitly mapping to lack of specific HPO terms).[1][3][5][11][17] These terms collectively provide a structured phenotype profile suitable for integration into DECIPHER, ClinVar, and other clinical variant interpretation platforms where ACFD may be considered in differential diagnosis for patients with similar skeletal features.

4. Genetic and Molecular Information

4.1 Causal Gene: IHH (Indian Hedgehog)

The causal gene for acrocapitofemoral dysplasia is IHH (Indian hedgehog), a member of the hedgehog family of secreted signaling proteins that regulate cartilage and bone development.[1][7][12] OMIM lists IHH under entry 600726 and describes its involvement in several phenotypes, including ACFD (607778), brachydactyly type A1 (112500), and syndromic craniosynostosis.[1][14] MedGen and panelapp resources confirm that IHH is located at chromosome 2q35 and highlight its role in skeletal dysplasia panels, with mode of inheritance specified as both monoallelic and biallelic, autosomal or pseudoautosomal, depending on the phenotype.[5][10][14] The hedgehog signaling pathway, in which IHH participates, is a highly conserved developmental pathway that coordinates chondrocyte proliferation, differentiation, and osteoblast development during endochondral ossification.[12][13]

The IHH gene encodes a preproprotein that undergoes autocatalytic cleavage into an N-terminal signaling domain and a C-terminal processing domain; the N-terminal domain is modified by cholesterol and palmitate and serves as the active ligand for Patched receptors, initiating downstream Smoothened activation and GLI transcription factor regulation.[7][12][13] The signaling domain extends roughly from amino acids 25 to 198, and the known ACFD-causing missense variants cluster within this region (P46L, R160C, A173D, V190A).[4][6][7] UniProt (Q14623) and structural data indicate that these residues contribute to the protein’s folding and receptor interaction surfaces, although fine-grained structural consequences of each variant have not been fully resolved.[7][12]

4.2 Pathogenic Variants: Types, Classification, and Frequency

Pathogenic variants causing ACFD are missense substitutions in the N-terminal signaling domain of IHH, and all reported cases involve homozygous variants inherited from heterozygous carrier parents.[4][6][7][15] The initial variants described by Hellemans et al.—c.137C>T (p.Pro46Leu) and c.569T>C (p.Val190Ala)—were identified in Belgian and Dutch families, respectively; both were absent in control chromosomes and affected highly conserved residues, supporting their pathogenic classification.[7][11][19] ClinVar lists c.569T>C (p.Val190Ala) as pathogenic for acrocapitofemoral dysplasia, with OMIM as the submitter and literature-only evidence based on the 2003 Am J Hum Genet report.[7][15] The c.137C>T variant is also recognized in OMIM but is not separately cataloged in ClinVar in the retrieved data.[1][7][15]

Ozyavuz Cubuk and Düz reported a novel homozygous missense variant c.478C>T (p.Arg160Cys) in two adult siblings with ACFD from a Turkish family, representing the third family and third missense variant associated with the disorder.[4] Khalid et al. subsequently described a novel homozygous missense variant c.518C>A (p.Ala173Asp) in a Pakistani family, expanding the catalog to four pathogenic missense variants and the fourth family.[6] Notably, Khalid et al. emphasized that all three previously described mutants (P46L, R160C, V190A) reside within amino acids 201–308 in the signaling domain, although the exact numbering may differ depending on isoform, and that the newly identified A173D variant broadens the phenotypic and genotypic spectrum.[6] All variants are predicted to alter protein function rather than cause complete loss-of-function via nonsense or frameshift mechanisms, suggesting that a specific level of residual activity may be compatible with the ACFD phenotype but insufficient for normal growth plate dynamics.[6][7][12]

Allele frequency data from gnomAD or other large population databases are not explicitly reported for these variants in the accessible literature, but their occurrence in consanguineous families and absence in control cohorts strongly suggests that they are extremely rare.[6][7][15] Given the rarity of ACFD and the absence of reported heterozygous phenotypes associated with these specific variants, penetrance appears to be complete in homozygotes and negligible in heterozygotes, consistent with autosomal recessive inheritance.[1][3][7] No somatic variants in IHH have been implicated in ACFD, and somatic IHH mutations are more relevant to oncologic contexts such as chondrosarcomas, which lie outside the scope of this disease.[12][16]

4.3 Functional Consequences: Loss of Signaling Function

Functional consequences of ACFD-associated IHH variants can be inferred from the role of IHH in growth plate biology and from the phenotypes of Ihh-deficient mouse models. Indian hedgehog produced by prehypertrophic and hypertrophic chondrocytes is essential for chondrocyte and osteoblast proliferation and differentiation during prenatal and postnatal endochondral bone formation; it maintains the growth plate and trabecular bone and regulates periarticular chondrocyte differentiation independently of parathyroid hormone–related protein (PTHrP).[12][13] In conditional Ihh knockout mice, loss of Ihh expression in postnatal chondrocytes leads to growth plate disorganization, reduced chondrocyte proliferation, diminished trabecular bone, and altered osteoblast development, resulting in dwarfism and skeletal dysplasia reminiscent of human hedgehog-related chondrodysplasias.[12][16]

ACFD-associated missense variants likely impair the ability of IHH to bind Patched, form active ligand-receptor complexes, and signal effectively to target cells in the growth plate and perichondrium.[7][12][13] Hellemans et al. suggested that the P46L and V190A substitutions, both at strongly conserved positions, affect the structure of the signaling domain and disrupt interactions with receptor or extracellular matrix components, thereby reducing hedgehog pathway activation.[7][11] While direct biochemical assays for these specific variants are limited, the convergence of clinical phenotypes with Ihh-deficient mice supports a loss-of-function mechanism in which IHH signaling is quantitatively reduced rather than qualitatively altered to a gain-of-function or dominant-negative state.[12][13][16] The recessive inheritance and absence of phenotype in heterozygous carriers further support a loss-of-function model.[1][3][7]

Frameshift and nonsense variants in IHH have been described in heterozygous form in families with short stature and non-classical brachydactyly A1, indicating that complete loss of one allele can reduce hedgehog signaling sufficiently to impair growth but produce a milder phenotype than ACFD.[18] This suggests a dosage-sensitive relationship between IHH function and skeletal outcomes, with full biallelic loss or severe signaling-domain disruption yielding ACFD, partial loss yielding brachydactyly and short stature, and normal dosage supporting typical skeletal development.[10][14][18] From a gene ontology standpoint, IHH participates in biological processes such as “regulation of chondrocyte proliferation” (GO:0032330), “endochondral ossification” (GO:0001958), and “bone morphogenesis” (GO:0060349), and ACFD can be conceptualized as a disorder arising from perturbation of these processes.[12][13]

4.4 Modifier Genes, Epigenetics, and Chromosomal Abnormalities

No modifier genes have been identified that specifically alter the severity or expression of ACFD. The limited number of families and the lack of extensive genomic characterization beyond IHH sequencing constrain the ability to detect modulators.[6][7] In other hedgehog-related conditions, variants in genes encoding Patched (PTCH1), Smoothened (SMO), GLI transcription factors, or interacting pathways (such as Wnt or BMP) can influence phenotype, but such interactions have not been documented in ACFD.[12][13][16] Similarly, epigenetic changes affecting IHH expression, such as promoter methylation or chromatin remodeling, have not been investigated in patients with ACFD, and there is no evidence that epigenetic dysregulation plays a primary etiologic role.[6][7]

Chromosomal abnormalities such as duplications at 2q35 have been implicated in syndromic craniosynostosis and other phenotypes involving IHH and neighboring genes, but these structural variants produce distinct clinical presentations and do not cause ACFD.[14] Panelapp notes “chr2q35dup syndrome (185900)” as a phenotype associated with IHH, highlighting that copy-number changes can perturb hedgehog signaling, but no microdeletions, duplications, translocations, or inversions have been reported in ACFD patients.[10][14] Thus, ACFD appears to be strictly associated with point mutations (missense) in IHH rather than larger chromosomal lesions.

5. Environmental Information

5.1 Non-Genetic Contributing Factors

As discussed earlier, acrocapitofemoral dysplasia is fundamentally a genetic disorder with no documented non-genetic primary causes. Environmental factors such as toxins, radiation, pollution, or occupational exposures have not been linked to the development of ACFD in the available literature.[3][7][11] The age of onset, pattern of inheritance, and clustering in consanguineous families argue strongly against environmental etiology and support a Mendelian recessive model.[1][3][7] Clinical reports do not describe any consistent environmental exposures or events preceding the onset of growth abnormalities, nor do they suggest that environmental variation explains phenotypic differences between affected siblings.[2][4][6][11]

In the broader context of skeletal development, environmental influences such as nutrition, endocrine status, and mechanical loading can modulate growth plate dynamics, but these act on a background of genetic programming and are unlikely to create ACFD-like phenotypes in the absence of IHH mutations.[12][13][16] For example, malnutrition or chronic illness may cause proportional or mild disproportionate short stature but do not produce cone-shaped epiphyses and egg-shaped femoral heads characteristic of ACFD.[11][19] Therefore, non-genetic factors should be considered secondary modifiers at most, and current evidence does not support any specific environmental contributors.

5.2 Lifestyle Factors and Infectious Agents

Lifestyle factors such as smoking, diet, exercise, and alcohol consumption have not been implicated in ACFD pathogenesis or progression. Because ACFD manifests in childhood and reflects developmental abnormalities in the growth plate, adult lifestyle choices are unlikely to influence the emergence of core skeletal features.[3][11] No studies have examined whether differences in childhood physical activity or nutrition modulate disease severity, but the rarity of ACFD and the small number of reported cases make such analyses challenging.[6][7]

No infectious agents, including bacteria, viruses, fungi, or parasites, have been associated with acrocapitofemoral dysplasia. The disease is not infectious, not transmissible, and shows no evidence of inflammation, autoimmunity, or post-infectious phenomena.[1][3][11] Basic science studies in hedgehog signaling have explored viral and chemical modulators, but these experiments address developmental biology rather than ACFD specifically.[12][13] Thus, infectious and lifestyle factors can be considered negligible in the etiologic framework for ACFD.

6. Mechanism and Pathophysiology

6.1 Ordered Causal Chain from Mutation to Clinical Phenotype

1) Biallelic pathogenic missense variants in IHH reduce the signaling capacity of the Indian hedgehog protein in growth plate chondrocytes, leading to impaired activation of downstream hedgehog pathway components.[1][6][7]

2) Reduced Ihh signaling from prehypertrophic and hypertrophic chondrocytes leads to deficient stimulation of periarticular chondrocyte differentiation and decreased chondrocyte proliferation in the columnar growth plate region, thereby shortening growth plate columns.[12][13]

3) Impaired Ihh signaling results in premature hypertrophic differentiation and early growth plate fusion, particularly in the epiphyses of the tubular bones of the hands and the capital femoral epiphyses, leading to cone-shaped epiphyses and egg-shaped femoral heads.[11][12][19]

4) Premature fusion and altered epiphyseal morphogenesis lead to permanent shortening of involved skeletal elements, manifesting clinically as brachydactyly, short limbs, and short femoral necks.[11][17][19]

5) Global reduction in endochondral bone growth leads to disproportionate postnatal short stature with relatively preserved cranial growth, resulting in a relatively large head compared to body size and a narrow thorax with pectus deformities.[1][3][11]

6) Altered spinal and pelvic mechanics due to limb and hip deformities contribute to lumbar lordosis and potential gait abnormalities, as downstream biomechanical consequences of the primary skeletal changes.[4][11]

7) Despite profound effects on skeletal tissues, Ihh deficiency in ACFD does not significantly affect brain development or visceral organogenesis, leading to normal intelligence and absence of major non-skeletal anomalies, likely because the mutations selectively impair skeletal-specific aspects of hedgehog signaling.[1][11][12]

This causal chain integrates experimental evidence from mouse models with human radiographic and clinical data, acknowledging that some steps—particularly the tissue-specific selectivity—are inferred rather than fully demonstrated in ACFD patients.[11][12][13][16]

6.2 Molecular Pathways: Hedgehog and Downstream Cascades

Indian hedgehog is a key ligand in the hedgehog signaling pathway, which regulates endochondral ossification through both PTHrP-dependent and PTHrP-independent mechanisms.[12][13] In the growth plate, Ihh is secreted by prehypertrophic and hypertrophic chondrocytes and binds to the Patched (PTCH) receptor on periarticular chondrocytes and perichondrial cells, relieving PTCH-mediated inhibition of Smoothened (SMO) and allowing activation of GLI transcription factors.[12][13] Activated GLI proteins induce expression of target genes that promote chondrocyte proliferation, delay hypertrophic differentiation, and stimulate bone collar formation and osteoblast development.[12][13] Ihh also upregulates PTHrP production in the periarticular region, which in turn acts on PTH/PTHrP receptors in columnar chondrocytes to maintain their proliferative state and prevent premature hypertrophy, creating a negative feedback loop that maintains growth plate length.[13]

Studies in mouse models demonstrate that Ihh has PTHrP-independent actions as well. In a JCI study, mosaic ablation of the PTH/PTHrP receptor led to upregulation of Ihh action, increased PTHrP, acceleration of periarticular chondrocyte differentiation, and elongation of the columnar region.[13] Overexpression of Ihh in transgenic mice caused PTHrP upregulation, elongated growth plate columns, and increased chondrocyte proliferation.[13] These findings show that Ihh directly stimulates periarticular chondrocyte differentiation to columnar chondrocytes, thereby regulating the mass of proliferating cells independently of PTHrP.[13] In conditional Ihh knockout mice, hedgehog signaling is diminished, leading to decreased chondrocyte proliferation, shortened columns, and premature depletion of the growth plate.[12][16]

In ACFD, pathogenic IHH missense variants are predicted to reduce ligand-receptor interactions and downstream hedgehog pathway activation. This leads to decreased GLI-mediated transcription of genes necessary for chondrocyte proliferation and survival, diminished PTHrP signaling, and failure to maintain normal growth plate architecture.[7][12][13] At the pathway level, this implicates hedgehog signaling (Reactome R-HSA-5358351), PTHrP signaling, Wnt pathway activation (which can be downstream of hedgehog in bone), and BMP/TGF-β interactions in the pathophysiology.[12][13][16] Suggested GO terms for involved processes include “hedgehog signaling pathway” (GO:0007224), “regulation of chondrocyte proliferation” (GO:0032330), “endochondral ossification” (GO:0001958), and “osteoblast differentiation” (GO:0001649).[12][13]

6.3 Cellular Processes: Chondrocyte and Osteoblast Dysregulation

At the cellular level, ACFD reflects dysregulation of chondrocyte proliferation, differentiation, and survival in the growth plate, as well as altered osteoblast development in adjacent bone.[11][12][16] In normal growth plates, periarticular chondrocytes proliferate and differentiate into flat, columnar chondrocytes that undergo rapid proliferation while forming columns; eventually, these columnar cells exit the cell cycle and become hypertrophic chondrocytes, which orchestrate matrix calcification and vascular invasion, followed by replacement with bone.[13] Ihh is produced by prehypertrophic and hypertrophic chondrocytes and acts on periarticular and perichondrial cells to regulate proliferative and differentiative transitions.[12][13]

In Ihh-deficient mice, the growth plate is disorganized, with reduced proliferation in the columnar region and premature hypertrophic differentiation, leading to thin growth plates and early growth cessation.[12][16] Osteoblast development is impaired because Ihh signals from chondrocytes to osteoblast precursors are diminished, resulting in reduced trabecular bone formation and skeletal fragility.[12][16] These cellular processes are mirrored in ACFD, where cone-shaped epiphyses and premature fusion of the growth plate indicate abnormal spatial and temporal patterns of chondrocyte differentiation.[11][19] The cone-shaped morphology reflects localized alterations in proliferation and hypertrophy, likely due to uneven distribution of Ihh signaling across the epiphyseal cartilage.[11][12][13]

Osteoblasts and perichondrial cells are also affected. In Ihh conditional knockouts, osteoblast markers are reduced and bone collar formation is impaired, emphasizing Ihh’s role in osteoblast development.[12] In ACFD, hip and femoral neck deformities suggest that both chondrocyte and osteoblast activities are perturbed during proximal femur development, leading to abnormal bone geometry.[11][17][19] Suggested cell ontology (CL) terms include “growth plate chondrocyte” (CL:0000133), “periarticular chondrocyte” (a subset of chondrocytes in articular cartilage), and “osteoblast” (CL:0000062).[12][13][16]

6.4 Protein Dysfunction and Biochemical Abnormalities

Indian hedgehog protein dysfunction in ACFD stems from missense variants in the signaling domain that likely impair folding, processing, or receptor binding. Hedgehog proteins undergo autocatalytic cleavage and cholesterol modification; their N-terminal domains must adopt a specific conformation to interact with Patched receptors and form multimolecular signaling complexes.[7][12] Missense substitutions such as P46L, R160C, A173D, and V190A may destabilize the N-terminal domain, reduce its affinity for Patched, alter its diffusion properties in the extracellular matrix, or impair its ability to be properly processed and secreted.[7][12] While detailed biochemical characterization of these variants is limited, their strong conservation across species and the severe phenotypic consequences of homozygous mutations suggest that they significantly reduce IHH function.[7][11]

Biochemically, hedgehog signaling involves post-translational modifications such as palmitoylation and cholesterylation of the N-terminal domain, as well as interactions with heparan sulfate proteoglycans in the extracellular matrix that shape morphogen gradients.[12][13] Disruption of these processes can diminish the effective concentration and gradient of IHH across the growth plate, producing localized regions of insufficient signaling and abnormal epiphyseal shaping.[12][13] Suggested GO terms for molecular functions include “hedgehog receptor binding” (GO:0005101) and “morphogen activity” (GO:0016015).[12]

No metabolic or systemic biochemical abnormalities (e.g., in serum calcium, phosphate, alkaline phosphatase, or endocrine parameters) have been specifically associated with ACFD, and routine laboratory testing in reported patients has been generally unremarkable.[2][4][6][11] This again underscores that ACFD is a localized developmental disorder of cartilage and bone rather than a systemic metabolic bone disease like rickets or osteogenesis imperfecta.

6.5 Immune System and Tissue Damage Mechanisms

The immune system does not play a primary role in acrocapitofemoral dysplasia. There is no evidence of autoimmunity, chronic inflammation, or immune-mediated tissue damage in the growth plate or bone in ACFD patients.[1][3][11] Histopathologic examination has not been reported in detail for human cases, but mouse models of Ihh deficiency do not show inflammatory infiltrates; rather, they show decreased proliferation, altered differentiation, and impaired bone formation.[12][16] Tissue damage mechanisms are therefore developmental and biomechanical rather than inflammatory or degenerative.

Over time, altered bone geometry, particularly in the hips and spine, may predispose to secondary tissue damage such as cartilage wear, osteoarthritis, or mechanical back pain, but these are common consequences of many dysplasias and not unique to ACFD.[4][11] If present, such complications would involve processes like cartilage degeneration, osteophyte formation, and secondary inflammation, but data in ACFD are too limited to specify these mechanisms. Suggested GO terms—if needed—might include “mechanical stimulus response” (GO:0009612) and “cartilage development” (GO:0051216), but they relate to broader skeletal biology rather than a distinct immune mechanism.[12][13]

6.6 Epigenetic and Omics Considerations

Epigenetic changes have not been studied in ACFD patients, and there are no transcriptomic, proteomic, metabolomic, or lipidomic profiling data specific to this disorder. Nonetheless, hedgehog signaling and growth plate biology have been extensively investigated in model systems, revealing patterns of gene expression and signaling that underpin endochondral ossification.[12][13][16] For instance, Ihh modulates expression of cyclin D and other cell cycle regulators in chondrocytes, and increased hedgehog signaling correlates with increased chondrocyte proliferation and cyclin D upregulation.[13] Ihh also interacts with Wnt signaling, influencing osteoblast differentiation and trabecular bone formation.[12][16]

In Ihh-deficient mouse models, RNA expression profiling could reveal downregulation of hedgehog target genes and upregulation of markers of premature hypertrophy, but such data are not directly cited in the retrieved literature.[12][16] Proteomic or metabolomic signatures specific to Ihh deficiency have not been reported. Likewise, single-cell analysis and spatial transcriptomics of growth plate chondrocytes in ACFD are not yet available, although these technologies are emerging in skeletal biology research. As a result, multi-omics integration for ACFD remains a theoretical possibility rather than a currently realized resource.

7. Anatomical Structures Affected

7.1 Organ-Level Involvement

Acrocapitofemoral dysplasia primarily affects the skeletal system, specifically bones formed by endochondral ossification, including long bones of the limbs, proximal femora, vertebral bodies, and phalanges.[1][3][11] The most prominent anatomical structures involved are the hands and hips, reflecting the “acro-” and “capitofemoral” components of the disorder.[11][19] In the hands, cone-shaped epiphyses in the middle phalanges lead to brachydactyly and shortening of the fingers.[11] In the hips, egg-shaped femoral heads attached to very short femoral necks produce characteristic deformity that can influence joint biomechanics.[11][17][19]

Secondary involvement includes the thorax and spine. The thorax is narrow, often with pectus excavatum or carinatum, suggesting altered growth of ribs and sternum.[1][3][11] The lumbar spine exhibits lordosis, reflecting changes in vertebral alignment and possibly compensatory mechanisms to maintain posture in the presence of shortened limbs.[11] However, there is no evidence of primary pathology in visceral organs such as heart, lungs, gastrointestinal tract, or nervous system; these systems are generally normal in ACFD.[1][11]

From an anatomical ontology perspective, primary organ-level terms include “skeletal system” (UBERON:0001434), “appendicular skeleton” (UBERON:0001474), “hip joint” (UBERON:0001465), “hand” (UBERON:0002398), “thoracic cage” (UBERON:0002385), and “vertebral column” (UBERON:0001130).[11][12][17] The involvement is bilateral and symmetric in hands and hips, as expected from a genetic developmental disorder.[11][19]

7.2 Tissue and Cell-Level Involvement

At the tissue level, acrocapitofemoral dysplasia affects hyaline cartilage in the growth plate and articular surfaces, as well as cancellous and cortical bone derived from endochondral ossification.[11][12][16] Growth plate cartilage at the distal ends of long bones and in the proximal femur is particularly affected, with altered columnar organization, cone-shaped epiphyseal cartilage, and early fusion.[11][19] Articular cartilage at the hip may also be secondarily affected because of abnormal load distribution arising from egg-shaped femoral heads and short necks.[11][17]

The primary cell types involved include periarticular chondrocytes (round cells at the articular surface), columnar chondrocytes (flat, proliferating cells in the growth plate), hypertrophic chondrocytes (terminally differentiated cells that orchestrate calcification), and osteoblasts (bone-forming cells) in the primary spongiosa and bone collar.[12][13][16] Ihh is produced by prehypertrophic and hypertrophic chondrocytes and acts on periarticular chondrocytes and perichondrial osteoblast progenitors.[12][13] In ACFD, Ihh-expressing chondrocytes carry dysfunctional IHH protein, and their signaling to target cells is impaired, affecting both chondrocyte and osteoblast populations.[7][12][16]

Suggested cell ontology terms include “chondrocyte” (CL:0000133), “hypertrophic chondrocyte” (a subtype of CL:0000133), “periarticular chondrocyte” (a location-specific chondrocyte), and “osteoblast” (CL:0000062).[12][13][16] Connective tissue structures such as bone marrow, periosteum, and perichondrium also participate indirectly, but their primary pathology arises from altered signaling rather than intrinsic defects.

7.3 Subcellular Structures and Localization

Subcellular structures relevant to IHH signaling include the primary cilium, plasma membrane, secretory pathway compartments (endoplasmic reticulum and Golgi apparatus), and extracellular matrix where hedgehog ligands diffuse.[12][16] Hedgehog signaling requires trafficking of Smoothened to the primary cilium, where it transduces the signal to GLI transcription factors; disruptions in ligand-receptor interactions or ciliary trafficking can impair signal transduction.[12][16] The SAG therapy study in Ihh-deficient mice highlighted that the Smoothened agonist SAG promotes Hh activity by stimulating Smoothened trafficking to the cilium in Ihh-silenced cells, rescuing chondrocyte proliferation and differentiation.[16] This underscores the importance of ciliary localization and subcellular dynamics in hedgehog pathway function.

In ACFD, IHH protein produced by chondrocytes may be misfolded or less efficiently processed, potentially leading to retention in the ER or Golgi or reduced secretion to the extracellular space.[7][12] While these subcellular defects have not been experimentally documented for ACFD variants, they represent plausible mechanisms given the nature of missense substitutions in a secreted signaling protein.[7][12] Suggested GO cellular component terms include “primary cilium” (GO:0005929), “plasma membrane” (GO:0005886), “extracellular space” (GO:0005615), and “growth plate cartilage” (captured indirectly through tissue ontology rather than GO).[12][16]

7.4 Localization and Lateralization

The skeletal abnormalities in acrocapitofemoral dysplasia are bilateral and relatively symmetric. Cone-shaped epiphyses occur in multiple digits of both hands, and egg-shaped femoral heads with short necks are present in both hips.[11][19] The thoracic and spinal deformities, such as narrow thorax and lumbar lordosis, also affect bilateral structures and the midline spine.[1][3][11] There is no evidence of lateralization (left versus right predominance) or segmental involvement; this pattern fits the systemic nature of a genetic developmental disorder affecting all growth plates rather than focal lesions.

Localization to particular skeletal sites, such as hands and hips, is more a matter of prominence than exclusivity. Cone-shaped epiphyses have been observed to a variable degree in shoulders, knees, and ankles, but these sites may show less dramatic changes.[11][19] The predominance of hand and hip involvement may reflect differences in growth plate dynamics and mechanical loading, but the underlying Ihh deficiency is systemic.[12][13][16]

8. Temporal Development

8.1 Onset Patterns

Acrocapitofemoral dysplasia exhibits a postnatal onset pattern with infantile or early childhood manifestation of growth abnormalities. Orphanet notes “Infancy, Neonatal” as age of onset, indicating that clinical features may be apparent in early infancy, but more detailed reports emphasize that disproportionate short stature becomes evident as the child grows and that cone-shaped epiphyses appear early in childhood.[3][11][19] The original descriptions reported that cone-shaped epiphyses are observed in childhood and disappear with premature fusion of the growth plate before puberty, implying that radiographic changes begin within the first few years of life and progress through middle childhood.[11][19]

At birth, affected infants may have near-normal length and proportions, although systematic data on birth metrics are limited.[2][11] As postnatal growth proceeds, the growth plates of hands and hips exhibit abnormal morphology and premature fusion, leading to a divergence from population growth curves and the emergence of disproportionate short stature.[11][19] Thus, onset is insidious rather than acute, and the disorder is chronic and developmental, with the primary window of pathogenesis in early childhood when growth plates are most active.[11][12][13]

8.2 Disease Progression and Course

The progression of ACFD follows the life cycle of endochondral growth plates. In early childhood, Ihh deficiency leads to cone-shaped epiphyseal cartilage and altered growth plate organization; as the child approaches puberty, growth plates fuse prematurely, and bone lengths are fixed.[11][19] During this period, stature and limb proportions deviate increasingly from normal, and brachydactyly and hip deformities become pronounced.[11] Once growth plates have fused, the skeletal features become stable, and there is no further progression of bone shortening, although secondary degenerative changes may emerge later.[4][11]

The progression rate is relatively slow and spans several years, corresponding to the length of childhood growth. There are no discrete “stages” defined for ACFD, but one could conceptualize an early stage (cone-shaped epiphyses present, growth plate open), an intermediate stage (ongoing premature fusion), and a late stage (post-fusion skeletal configuration).[11][19] The disease course pattern is therefore progressive through childhood and then stable in adulthood, without episodes of remission or relapse.[11]

Disease duration is lifelong in the sense that skeletal changes and short stature remain present throughout life. However, the active pathogenic process—abnormal growth plate activity—occurs predominantly in childhood and early adolescence.[11][12] Critical periods of vulnerability or opportunity for intervention likely coincide with early childhood, when hedgehog signaling can still influence growth plate behavior; this is supported by SAG therapy timing data in Ihh-deficient mice, where earlier treatment (starting postnatal day 7) was more effective in preventing dwarfism than later treatment (starting day 14).[16]

8.3 Remission and Critical Periods

Spontaneous remission does not occur in acrocapitofemoral dysplasia. Once growth plates have fused and skeletal deformities are established, they do not reverse, although adaptive processes may improve functional outcomes.[11][19] Treatment-induced modification of phenotype is possible in theory, as suggested by experimental hedgehog agonist therapy or growth hormone treatment in heterozygous IHH mutation carriers, but such interventions do not produce true remission; they modify growth patterns and outcomes but do not remove the underlying genetic defect.[16][18]

Critical periods for potential intervention include the early postnatal and childhood years when growth plates are open and Ihh signaling can influence chondrocyte proliferation and differentiation.[12][16] The SAG therapy study in mice showed that the timing of Smoothened agonist administration affected efficacy, with earlier treatment more effective at preventing dwarfism.[16] Extrapolating cautiously, pharmacologic or endocrine interventions in human ACFD would likely need to be instituted early in life to achieve meaningful impact on final stature and skeletal proportions.[12][16] Once growth plates are fused, interventions shift from growth modulation to orthopedic management of deformities and pain, representing a tertiary prevention strategy.[4][11]

9. Inheritance and Population

9.1 Epidemiology: Prevalence and Incidence

Orphanet classifies acrocapitofemoral dysplasia as a “rare disease” with an estimated prevalence of less than 1 per 1,000,000 individuals.[3] This estimate reflects its extreme rarity and is based on the small number of reported families rather than systematic population-based data. Incidence (new cases per year) has not been formally quantified, but given that only three to four families have been described worldwide over more than two decades, the incidence is likely far below one per million births.[4][6][7][11]

No national registries, large cohort studies, or Global Burden of Disease analyses have focused specifically on ACFD. The condition is absent from common epidemiologic databases such as SEER or CDC registries, reflecting both its rarity and its benign mortality profile.[3][8] As a result, the epidemiologic characterization of ACFD relies on case reports and curated rare disease databases rather than systematic surveillance.

9.2 Inheritance Pattern, Penetrance, and Expressivity

Acrocapitofemoral dysplasia follows an autosomal recessive inheritance pattern. All reported cases occur in children born to heterozygous carrier parents, often with consanguinity, and segregation analysis supports recessive transmission.[1][3][4][6][7] OMIM, Orphanet, MedGen, and NORD all describe ACFD as autosomal recessive.[1][3][5][8] Panelapp indicates that IHH has both monoallelic and biallelic modes of inheritance depending on phenotype, noting that biallelic mutations cause a more severe disease form—namely ACFD—while monoallelic mutations tend to cause brachydactyly and mild skeletal hand defects.[10][14]

Penetrance of ACFD-associated IHH variants appears to be complete in homozygous individuals; all reported homozygotes exhibit the characteristic phenotype.[4][6][7][11] Expressivity is variable, with differences in the degree of short stature, limb shortening, thoracic deformity, and hip involvement among affected individuals, even within the same family.[2][4][6][11] This suggests that other genetic or environmental factors may modulate phenotypic severity, but the core features are consistently present. There is no evidence of genetic anticipation, as the severity does not progressively increase across generations; rather, the phenotype depends on zygosity and variant type.[1][7]

Germline mosaicism has not been reported in ACFD, likely because the recessive inheritance and consanguineous context reduce the probability of mosaic parent carriers; nonetheless, mosaicism cannot be completely excluded in sporadic cases.[6][7] Founder effects may exist within specific populations where consanguineous marriages are common, such as certain regions of Turkey or Pakistan, but the limited number of families prevents firm conclusions.[4][6] Carrier frequency in the general population is unknown but presumably extremely low; in communities with reported families, carrier frequency may be higher due to local founder variants.[6][7]

9.3 Population Demographics and Geographic Distribution

Reported families with acrocapitofemoral dysplasia originate from various geographic and ethnic backgrounds. The initial families studied by Mortier and Hellemans were Belgian and Dutch, indicating occurrence in European populations.[2][7][11] The third family, described by Ozyavuz Cubuk and Düz, was Turkish, suggesting presence in Anatolian populations.[4] The fourth family, reported by Khalid et al., was Pakistani, marking the first documented case from South Asia and broadening the geographic scope.[6] These data demonstrate that ACFD is not confined to a single ethnic group or region but can occur wherever consanguinity and rare pathogenic IHH variants coexist.[3][6][7]

Sex distribution appears roughly equal, with both male and female patients reported, and no sex-specific differences in phenotype have been described.[2][4][6][11] Age distribution covers children and adults, with some families documented only in childhood and others, such as the Turkish siblings, followed into adulthood.[4][6][11] However, no systematic data exist on the proportion of patients diagnosed at various ages or on gender ratios, due to the small sample size.

Geographic distribution of specific variants shows some clustering. The P46L and V190A variants were identified in Belgian and Dutch families, the R160C variant in a Turkish family, and the A173D variant in a Pakistani family.[4][6][7] Whether these represent founder mutations or independent occurrences is unclear, but the presence of distinct variants in different populations suggests multiple mutational events rather than a single global founder.[6][7]

10. Diagnostics

10.1 Clinical and Radiographic Evaluation

Diagnosis of acrocapitofemoral dysplasia relies on a combination of clinical assessment and radiographic imaging. Clinically, disproportionate postnatal short stature, short limbs, brachydactyly, narrow thorax, and lumbar lordosis raise suspicion for a skeletal dysplasia involving endochondral ossification.[1][3][11] Routine physical examination can document height, limb lengths, finger and toe proportions, thoracic shape, spinal curvature, and nail morphology.[1][5][11] Laboratory tests such as serum calcium, phosphate, alkaline phosphatase, and endocrine parameters (growth hormone, IGF-1) are typically normal, helping distinguish ACFD from metabolic bone diseases.[2][18]

Radiography is central to diagnosis. Hand radiographs show cone-shaped epiphyses in the tubular bones, especially the middle phalanges, which appear as triangular or conical ossification centers tapering toward the growth plate.[11][19] Hip radiographs reveal egg-shaped capital femoral epiphyses attached to very short femoral necks, producing a distinctive configuration that is nearly pathognomonic for ACFD.[11][17][19] Radiographs of shoulders, knees, and ankles may show similar epiphyseal changes to a variable degree.[11][19] In older patients, cone-shaped epiphyses may no longer be visible because of premature fusion, but residual shortening of bones and deformity of femoral heads and necks persist.[4][11]

Advanced imaging modalities such as CT and MRI are not routinely required for diagnosis but may be useful to assess hip joint morphology and cartilage thickness in complex cases.[4][11] There are no specific histopathologic criteria, and bone biopsy is not routinely performed. Pathology, if examined, would likely show disorganized growth plate cartilage with altered hypertrophic zone thickness and early fusion, similar to Ihh-deficient mouse models.[12][16]

10.2 Genetic Testing Strategies

Genetic confirmation of acrocapitofemoral dysplasia involves sequencing of the IHH gene to identify biallelic pathogenic variants. Single-gene testing of IHH can be performed when clinical and radiographic features strongly suggest ACFD or another IHH-related skeletal dysplasia; this approach is efficient given the strong genotype–phenotype correlation.[1][7][10] Alternatively, targeted skeletal dysplasia panels that include IHH and other growth plate-related genes can be used, especially in patients with atypical phenotypes or in settings where comprehensive panel testing is standard.[10][14] Panelapp resources note that IHH is included in multiple skeletal dysplasia and craniosynostosis panels, with well-established evidence supporting its role in Acrocapitofemoral dysplasia (MIM#607778) and brachydactyly type A1 (MIM#112500).[10][14]

Whole exome sequencing (WES) and whole genome sequencing (WGS) can also identify IHH variants, particularly in undiagnosed skeletal dysplasia cases where phenotype may be complex or overlapping.[6][18] In the Pakistani family reported by Khalid et al., WES was used to detect the c.518C>A (p.Ala173Asp) variant in IHH, and segregation analysis confirmed its recessive inheritance.[6] In the family with heterozygous frameshift IHH mutation and short stature plus non-classical brachydactyly, WES, targeted sequencing, or gene panel testing were used to identify the c.387_388insC variant.[18]

Chromosomal microarray (CMA), karyotyping, FISH, mitochondrial DNA testing, and repeat expansion testing are not typically relevant for ACFD, as the disease arises from point mutations in IHH rather than structural or cytogenetic abnormalities.[1][7][14] ClinVar provides variant-specific information for at least one pathogenic ACFD-associated IHH mutation (p.Val190Ala), supporting clinical interpretation according to ACMG/AMP guidelines.[15] Suggested NCIT terms for genetic interventions include “Genetic Testing” (NCIT:C33211) and “DNA Sequencing” (NCIT:C18537).

10.3 Differential Diagnosis and Clinical Criteria

Standardized diagnostic criteria for acrocapitofemoral dysplasia have not been published in the form of society guidelines, but implicit criteria can be inferred from descriptive and radiographic data.[1][11][19] Key elements include disproportionate postnatal-onset short stature, brachydactyly with cone-shaped epiphyses in the hands, egg-shaped femoral heads with short femoral necks, absence of extra-skeletal anomalies, and autosomal recessive inheritance or consanguinity.[1][3][7][11] Genetic confirmation of biallelic missense variants in IHH outside the brachydactyly A1 cluster supports diagnosis.[1][6][7]

Differential diagnosis encompasses several conditions. Brachydactyly type A1, caused by heterozygous IHH variants clustered in a specific region, presents with shortened middle phalanges and variable cone-shaped epiphyses but usually lacks the hip deformities and autosomal recessive inheritance of ACFD.[10][14][18] Other cone-shaped epiphysis syndromes, such as hereditary multiple epiphyseal dysplasia or isolated cone-shaped epiphyses, may show similar hand radiographic features but differ in pattern, associated findings, and genetic etiology.[9][11] Spondyloepiphyseal dysplasias and other chondrodysplasias may produce short stature and epiphyseal abnormalities, but their genetic bases involve different genes (e.g., COL2A1, TRPV4) and they often have additional axial skeletal involvement or extraskeletal manifestations.[9][11]

Because ACFD is extremely rare, differential diagnosis often begins with more common skeletal dysplasias and then narrows as radiographic and genetic clues accumulate. Pattern recognition of the acrocapitofemoral combination—hands and hips with cone-shaped epiphyses and short femoral necks—is particularly valuable.[11][19]

10.4 Screening and Omics-Based Diagnostics

Routine population screening for acrocapitofemoral dysplasia is not conducted, given its rarity and relatively benign mortality profile.[3][8] Newborn screening programs focus on metabolic and endocrine disorders; skeletal dysplasias are diagnosed clinically rather than through biochemical screening.[8][11] Carrier screening for IHH variants could be considered in families with known ACFD history or in communities with high consanguinity, but no standardized programs exist.[3][6][7]

Omics-based diagnostics beyond gene sequencing—such as RNA sequencing, proteomics, or metabolomics—have not been applied to ACFD in clinical care. Nonetheless, WES and WGS represent omics-level interventions, and their utility has been demonstrated in identifying novel IHH variants in rare skeletal dysplasia cases.[6][18] Liquid biopsy, epigenomics, and multi-omics integration have no current role in diagnosing ACFD, although they may contribute to broader understanding of skeletal development and hedgehog pathway biology.

11. Outcome and Prognosis

11.1 Survival and Mortality

Acrocapitofemoral dysplasia does not appear to significantly reduce life expectancy. Affected individuals in reported families have survived into adolescence and adulthood without evidence of life-threatening complications directly attributable to the disorder.[4][6][11] No data on 5-year or 10-year survival or mortality rates are available, but absence of reported early death suggests that survival is near-normal.[3][8][11] Orphanet and NORD describe ACFD as a skeletal dysplasia without mention of increased mortality, indirectly supporting a favorable survival prognosis.[3][8]

Mortality databases such as CDC WONDER or SEER do not list ACFD as a distinct cause of death, and disease-specific mortality analyses are unavailable.[3][8] Deaths in individuals with ACFD, if they occur, are likely due to unrelated causes or to complications common to the general population rather than to the dysplasia itself.

11.2 Morbidity, Disability, and Quality of Life

Morbidity associated with acrocapitofemoral dysplasia arises primarily from physical disability, including short stature, limb shortening, brachydactyly, and hip deformities that may limit mobility and function.[4][11] Short stature can affect daily living (for example, reaching objects, navigating environments designed for average height), while brachydactyly and small broad nails may impair fine motor tasks requiring long fingers.[8][11] Hip deformities and short femoral necks can cause altered gait, reduced hip range of motion, pain, and possibly increased risk of early osteoarthritis, although longitudinal data on joint outcomes are lacking.[4][11][17]

Quality of life impacts have not been formally measured using standardized instruments such as EQ-5D or SF-36 in ACFD patients, but analogies with other skeletal dysplasias suggest that psychosocial effects (self-image, social interactions) and functional limitations (mobility, work capacity) may be significant.[8][16] Nonetheless, preserved intelligence and lack of major visceral involvement allow many individuals with ACFD to lead independent lives, albeit with adaptations.[1][11] Disability classification frameworks such as the International Classification of Functioning (ICF) would categorize functional impairments mainly as limitations in physical mobility and manual dexterity, with variable impact on participation depending on environmental support.

11.3 Disease Course and Complications

The disease course of acrocapitofemoral dysplasia is characterized by childhood progression of skeletal deformities followed by a relatively stable adult phenotype. Once growth plates fuse and final stature and bone lengths are fixed, progression of the primary skeletal abnormalities ceases.[11][19] However, secondary complications may arise over time. Altered hip and spine mechanics can predispose to chronic pain, degenerative joint changes, and functional impairment, particularly if deformities are severe.[4][11] Narrow thorax and pectus deformities may affect respiratory mechanics, but overt respiratory failure has not been reported, and pulmonary complications appear minor.[1][3][11]

Recovery in the sense of reversal of skeletal abnormalities is not possible; however, functional recovery and compensation may occur through physical therapy, orthopedic interventions, and environmental adaptations.[4][11] Prognostic factors likely include severity of skeletal deformities, presence of degenerative joint changes, and access to supportive care and orthopedic management, but these have not been systematically studied in ACFD due to its rarity.[4][6][11]

Prognostic biomarkers specific to ACFD do not exist. However, identification of the underlying IHH variant may provide some insight into expected severity based on genotype–phenotype correlations, as certain variants may be associated with more pronounced hip deformities or thoracic involvement.[4][6][7] Experimental data in Ihh-deficient mice suggest that early hedgehog agonist therapy can modify disease course, but translational application to humans remains speculative.[16]

12. Treatment

12.1 Pharmacotherapy and Endocrine Interventions

No approved pharmacologic therapy currently exists specifically for acrocapitofemoral dysplasia. Management is largely supportive and orthopedic, focusing on symptom relief and functional optimization rather than disease modification.[3][8][11] Human growth hormone (GH) therapy has been used in some skeletal dysplasias, including heterozygous IHH mutation–associated short stature, but its efficacy in ACFD is unknown.[16][18] A case report of two siblings with short stature and non-classical brachydactyly type A1 due to a heterozygous IHH frameshift mutation showed that four years of GH therapy led to significant improvement in height, with a good safety profile.[18] The authors concluded that “continuous use of growth hormone therapy may provide long-term benefits and have a high safety for height growth” in this context.[18] However, differences in zygosity and phenotype between ACFD and heterozygous short stature limit extrapolation; biallelic loss of Ihh signaling may constrain the capacity of GH to stimulate growth plate activity.[12][16][18]

Experimental pharmacotherapy in Ihh-deficient mouse models has shown promising results with Smoothened agonist (SAG) therapy. SAG enhances hedgehog pathway activity by promoting Smoothened trafficking to the primary cilium, thereby rescuing downstream signaling in Ihh-silenced cells.[16] In Ihh conditional knockout mice, SAG treatment increased chondrocyte proliferation and differentiation, corrected stature, decreased mortality, and reduced incidence of enchondroma-like lesions near growth plates, without evident toxicity.[16] Treatment timing was critical: earlier administration (starting postnatal day 7) was more effective than later (day 14) in preventing dwarfism.[16] These findings suggest that hedgehog agonists could represent a potential pharmacologic approach for human Ihh-related skeletal dysplasias, including ACFD, although clinical trials have not yet been conducted.[16]

If translated to human therapy, SAG or similar hedgehog agonists would be categorized under NCIT terms such as “Targeted Therapy” (NCIT:C15632) or “Signal Transduction Inhibitor/Agonist,” with more specific terms reflecting hedgehog pathway modulation. Careful evaluation of off-target effects and oncogenic risks would be necessary, as hedgehog activation can promote tumorigenesis in some contexts.[12][16]

12.2 Surgical and Orthopedic Interventions

Surgical management in acrocapitofemoral dysplasia primarily addresses orthopedic deformities, particularly hip abnormalities and severe thoracic or spinal deformities. Short femoral necks and egg-shaped femoral heads can predispose to impingement, reduced range of motion, and degenerative changes; orthopedic procedures such as osteotomy, hip reconstruction, or eventually arthroplasty may be considered to improve function and reduce pain.[4][11][17] However, detailed surgical outcomes in ACFD are not reported in the literature, and management parallels that of other hip dysplasias rather than being disease-specific.[11]

Thoracic deformities such as pectus excavatum or carinatum may be treated surgically if they produce significant respiratory compromise or cosmetic concern, using standard procedures like Nuss or Ravitch techniques.[1][3][11] Lumbar lordosis and spinal alignment issues may be managed with physical therapy, bracing, or, in severe cases, spinal surgery, although again no ACFD-specific data exist.[4][11] NCIT terms for such interventions include “Orthopedic Surgery” (NCIT:C15973), “Hip Arthroplasty” (NCIT:C80117), and “Thoracic Surgery” (NCIT:C25761).

12.3 Supportive and Rehabilitative Care

Supportive care for acrocapitofemoral dysplasia focuses on optimizing function and quality of life. Physical therapy can improve strength, flexibility, and gait mechanics, helping individuals adapt to limb and hip deformities and reduce pain.[4][11] Occupational therapy may assist with fine motor tasks and activities of daily living affected by brachydactyly and hand anomalies.[8][11] Pain management strategies, including pharmacologic analgesia and non-pharmacologic approaches, can address chronic musculoskeletal discomfort.[4][11] Psychosocial support and counseling may help individuals and families cope with the challenges of living with a rare skeletal dysplasia.[8][11]

NCIT terms applicable to these interventions include “Physical Therapy” (NCIT:C15273), “Occupational Therapy” (NCIT:C15272), “Pain Management” (NCIT:C49236), and “Psychosocial Support” (NCIT:C20464). While these measures do not alter the pathophysiology of ACFD, they constitute tertiary prevention by reducing complications and enhancing participation.

12.4 Experimental and Advanced Therapeutics

Aside from SAG therapy in mice, no advanced therapeutics such as gene therapy, cell therapy, or RNA-based interventions have been tested specifically for ACFD. In principle, gene therapy delivering functional IHH to growth plate chondrocytes could correct Ihh deficiency, but technical challenges—including targeting, timing, safety, and scaling—are substantial.[12][16] CRISPR-based gene editing to repair IHH mutations in chondrocyte precursors is conceptually possible but far from clinical application.[12][16]

Cell-based approaches such as stem cell transplantation or chondrocyte/osteoblast replacement have not been explored in ACFD. Given that the primary defect lies in signaling rather than cell survival per se, cell therapy would need to restore appropriate hedgehog signaling, which complicates design.[12][16] RNA-based therapies such as antisense oligonucleotides or siRNA are more typically used to reduce expression of pathogenic genes; in ACFD, expression of wild-type IHH would need to be increased or mutant protein function enhanced, making RNA-based strategies less straightforward.[12][16]

ClinicalTrials.gov does not list ACFD-specific interventional studies in the retrieved literature, and experimental treatments remain confined to preclinical models. However, Ihh-deficient chondrodysplasias more broadly may attract interest as candidates for hedgehog agonist therapy, and future clinical trials could include ACFD patients.[16] Any such trial would need rigorous monitoring for adverse events, particularly potential tumorigenic effects of hedgehog activation.

12.5 Treatment Outcomes and Personalized Strategies

Because no disease-specific pharmacologic treatments are currently available for acrocapitofemoral dysplasia, outcome data focus mainly on natural history and supportive care. Surgical and orthopedic interventions can improve function and reduce pain, but quantitative outcomes (e.g., improvement percentages, complication rates) have not been reported in ACFD.[4][11] Personalized treatment strategies would involve tailoring orthopedic and rehabilitative interventions to the individual’s phenotype, considering severity of hip and hand deformities, thoracic shape, and spinal alignment.[4][11]

Given the strong genotype–phenotype correlation with IHH variants, precision medicine approaches could emerge if hedgehog agonist therapies are developed. For instance, variant-specific sensitivity to hedgehog agonists or differential residual signaling activity could inform dosing and timing.[6][7][16] Pharmacogenomic considerations might also involve metabolism and distribution of hedgehog agonists, but such data are hypothetical at this stage.

13. Prevention

13.1 Primary, Secondary, and Tertiary Prevention

Primary prevention of acrocapitofemoral dysplasia involves preventing the occurrence of homozygous pathogenic IHH variants in offspring. This can be achieved through genetic counseling, carrier testing, and informed reproductive choices in families with known ACFD history or in high-consanguinity communities where carrier frequency may be elevated.[3][6][7] Preimplantation genetic diagnosis (PGD) and prenatal testing could allow selection of embryos without IHH mutations, but specific guidelines for ACFD are not published; general Mendelian disease prevention frameworks apply.[3][6][7] NCIT terms for these interventions include “Genetic Counseling” (NCIT:C17189), “Prenatal Genetic Testing” (NCIT:C18243), and “Preimplantation Genetic Diagnosis” (NCIT:C18488).

Secondary prevention focuses on early detection and intervention to mitigate severity. In ACFD, early diagnosis through careful clinical and radiographic evaluation and genetic testing can identify affected children while growth plates are still active.[1][3][11] If hedgehog agonist or growth-promoting therapies are developed, early initiation could improve outcomes, as suggested by timing effects in mouse SAG therapy.[16] Early orthopedic assessment can also inform timely interventions to prevent or reduce secondary complications such as joint contractures or spinal deformities.[4][11]

Tertiary prevention aims to prevent complications and optimize function in individuals with established disease. This includes orthopedic surgery, physical and occupational therapy, pain management, and psychosocial support to reduce disability and enhance quality of life.[4][11] These interventions do not prevent the disease itself but mitigate its impact.

13.2 Screening, Risk Stratification, and Counseling

Population-wide screening for ACFD is not feasible or justified given its rarity. However, targeted carrier screening may be appropriate in families with known mutations or in communities with identified founder variants.[6][7] Risk stratification based on consanguinity and family history can identify couples at increased risk of having affected children, enabling tailored counseling.[3][6][7] ACMG and NSGC guidelines for autosomal recessive disorders provide general frameworks for such counseling, although ACFD-specific documents are lacking.

Genetic counseling should explain the autosomal recessive inheritance pattern, carrier risks (25% chance of an affected child if both parents are carriers), and available reproductive options.[3][6][7] Counseling can also address psychosocial aspects of living with a rare skeletal dysplasia and the potential benefits and limitations of existing treatments. For heterozygous IHH variant carriers with short stature and non-classical brachydactyly, counseling may cover GH therapy and its risks and benefits.[18]

13.3 Public Health and Environmental Interventions

Because acrocapitofemoral dysplasia is a rare genetic disorder, public health interventions at the population level—such as vaccination, sanitation, or environmental cleanup—do not directly prevent the disease.[3][8] Nonetheless, public health policies promoting access to genetic counseling and reducing stigmatization of consanguinity may indirectly affect disease incidence by encouraging informed reproductive decisions.[3][6][7] Environmental interventions have no specific role in ACFD prevention, as environmental exposures do not cause the disease.

13.4 Prophylaxis

No prophylactic medications or procedures exist to prevent acrocapitofemoral dysplasia in genetically at-risk individuals. Prophylaxis in this context refers primarily to reproductive-level interventions such as PGD and prenatal testing. In the future, if hedgehog agonist therapies are shown to prevent progression of skeletal abnormalities when administered early, they might be considered prophylactic against severe deformity in genetically affected infants, but evidence for such strategies in humans is currently absent.[16]

14. Other Species and Natural Disease

14.1 Species and Orthologous Genes

Indian hedgehog (Ihh) is conserved across vertebrate species, including humans (IHH), mice (Ihh), and other mammals.[12][13] NCBI Gene lists orthologous Ihh genes and supports comparative functional studies. In mice, Ihh plays a similar role in growth plate biology as in humans, and Ihh-deficient phenotypes provide strong mechanistic analogues for human ACFD.[12][13][16] Zebrafish, chickens, and other model organisms also express hedgehog pathway components, but specific orthologous Ihh functions differ somewhat by species and have been more extensively studied in general developmental contexts than in skeletal dysplasias.[12][13]

14.2 Natural Disease in Animals and Comparative Pathology

Naturally occurring acrocapitofemoral dysplasia has not been reported in companion animals or livestock. OMIA (Online Mendelian Inheritance in Animals) and veterinary literature do not list ACFD as a recognized entity in animals, although numerous skeletal dysplasias with short limbs and epiphyseal abnormalities occur in dogs, cattle, and other species.[12][16] These animal disorders generally involve different genes or broad developmental processes and are not known to involve Ihh-specific mutations analogous to human ACFD.[12][16]

However, comparative pathology is informative. Ihh-deficient mouse models recapitulate key features of human Ihh-related chondrodysplasias, including short stature, short limbs, narrow thorax, and abnormal growth plates.[12][16] The SAG therapy study demonstrated that hedgehog pathway activation can rescue skeletal phenotypes in Ihh-deficient mice, providing a preclinical platform for therapeutic translation.[16] Comparative studies of hedgehog signaling across species highlight evolutionary conservation of growth plate regulation and the central role of Ihh in endochondral ossification.[12][13]

14.3 Transmission and Zoonotic Potential

Acrocapitofemoral dysplasia is a non-infectious genetic disorder and has no zoonotic potential. Transmission occurs solely through inheritance of pathogenic IHH variants and is limited to human familial contexts.[1][3][7] Cross-species susceptibility is relevant only in terms of experimental models, where gene knockout or transgenic techniques reproduce Ihh deficiency in animals; these are not natural transmissions but induced genetic changes.[12][16]

15. Model Organisms

15.1 Types and Genetic Models

Mouse models represent the primary experimental systems for studying Ihh-related skeletal dysplasias analogous to acrocapitofemoral dysplasia. Conditional Ihh knockout mice, in which Ihh is specifically ablated in chondrocytes, have been generated to examine postnatal roles of Ihh in growth plate maintenance and bone formation.[12][16] These models allow tissue-specific and temporal control of Ihh deletion, illuminating effects on chondrocyte proliferation, differentiation, and osteoblast development without causing early embryonic lethality.[12][16]

In one PNAS study, Ihh expression was conditionally eliminated in postnatal chondrocytes, demonstrating that Ihh is essential for maintaining the growth plate and articular surface and for sustaining trabecular bone after birth.[12] The authors showed that loss of Ihh signaling from the growth plate altered chondrocyte differentiation and affected osteoblast development, leading to diminished trabecular bone and dwarfism.[12] In another study, mosaic ablation of the PTH/PTHrP receptor in the growth plate allowed investigation of Ihh’s PTHrP-independent roles, demonstrating that Ihh stimulates periarticular chondrocyte differentiation and regulates columnar cell mass.[13] These models collectively recapitulate key human features of Ihh deficiency.

15.2 Phenotype Recapitulation and Limitations

Ihh-deficient mouse models reproduce many aspects of human ACFD and related chondrodysplasias, including short stature, short limbs, narrow thorax, and abnormal growth plates.[12][16] Radiographically and histologically, mice show shortened long bones, reduced growth plate thickness, disorganized hypertrophic zones, and impaired bone collar and trabecular bone formation.[12][16] However, specific features of human ACFD, such as cone-shaped epiphyses and egg-shaped femoral heads, have not been described in detail in mice, likely due to species differences in epiphyseal morphology and growth plate structure.[11][12][19]

Mouse models lack the exact hand and hip configurations seen in human ACFD, but they provide mechanistic insight into Ihh’s role in growth plate dynamics and endochondral ossification.[12][13][16] Limitations include differences in skeletal anatomy, growth patterns, and lifespan, which affect translation of therapeutic timing and dosing from mice to humans.[12][16] Additionally, global or conditional knockouts may produce more severe phenotypes than missense variants in humans, complicating direct comparison.

15.3 Applications and Resources

Model organism studies of Ihh deficiency are invaluable for examining mechanistic questions, testing pharmacologic interventions, and exploring gene–environment interactions. SAG therapy in Ihh conditional knockout mice demonstrated that boosting hedgehog signaling can rescue skeletal phenotypes, suggesting potential therapeutic pathways for human diseases.[16] These models also allow assessment of long-term effects and toxicity of hedgehog agonists, which is critical for translational planning.[16]

Resources such as the Mouse Genome Informatics (MGI) database and the International Mouse Phenotyping Consortium (IMPC) catalog Ihh knockout and conditional models, although specific ACFD-like phenotypes may not be explicitly annotated.[12][16] These resources facilitate access to model lines, phenotypic data, and experimental protocols for researchers studying hedgehog-related skeletal disorders. Other model systems, such as zebrafish and organoid cultures of growth plate cartilage, could be developed to provide complementary insights but are not yet documented for ACFD.

16. Conclusion

Acrocapitofemoral dysplasia is a rare but mechanistically well-understood Mendelian skeletal dysplasia caused by biallelic missense variants in the Indian hedgehog gene (IHH), which selectively disrupt hedgehog signaling in growth plate chondrocytes and perichondrial cells.[1][3][6][7] Clinically, ACFD presents with disproportionate postnatal-onset short stature, short limbs, brachydactyly, narrow thorax, lumbar lordosis, and small broad nails, with normal intelligence and absence of major non-skeletal malformations.[1][3][5][11] Radiographically, the disorder is defined by cone-shaped epiphyses in the hands and hips, egg-shaped femoral heads attached to markedly short femoral necks, and variable epiphyseal involvement at shoulders, knees, and ankles; these features arise from abnormal growth plate architecture and premature fusion linked to Ihh deficiency.[11][17][19]

Genetically, ACFD exemplifies allelic heterogeneity at the IHH locus, with at least four distinct homozygous missense variants (P46L, V190A, R160C, A173D) causing similar phenotypes in families of Belgian, Dutch, Turkish, and Pakistani origin.[4][6][7] The autosomal recessive inheritance and consistent penetrance in homozygotes, coupled with variable expressivity, underscore the importance of both pathogenic variants and potential modifiers, although specific modifier genes are not yet identified.[1][3][6][7] Diagnostic confirmation relies on clinical and radiographic pattern recognition and genetic testing of IHH, typically via single-gene sequencing or inclusion in skeletal dysplasia panels.[1][7][10][14]

Mechanistically, acrocapitofemoral dysplasia illuminates the critical role of Ihh in maintaining the growth plate and coordinating chondrocyte proliferation, differentiation, and osteoblast development. Experimental studies in conditional Ihh knockout mice demonstrate that postnatal chondrocyte-derived Ihh is essential for growth plate integrity, articular surface maintenance, and trabecular bone formation, and that its absence leads to dwarfism, skeletal dysplasia, and enchondroma-like lesions.[12][16] JCI work reveals that Ihh stimulates periarticular chondrocyte differentiation and regulates columnar cell mass independently of PTHrP, highlighting complex pathway dynamics that are perturbed in ACFD.[13] These insights provide a robust causal chain from IHH mutation to clinical phenotype, bridging molecular genetics, developmental biology, and orthopedic manifestations.

Therapeutically, management of ACFD currently centers on supportive and orthopedic care, including physical and occupational therapy, pain management, and surgical interventions for severe hip or thoracic deformities.[4][11] Pharmacologic therapies such as growth hormone have shown benefit in heterozygous IHH mutation–related short stature but have not been systematically assessed in ACFD; hedgehog agonists like SAG have demonstrated striking efficacy in rescuing skeletal phenotypes in Ihh-deficient mice, suggesting a potential future avenue for disease-modifying treatment.[16][18] Prevention focuses on genetic counseling, carrier testing, and reproductive planning in families with known mutations, as environmental or infectious prevention strategies are irrelevant for this genetic disorder.[3][6][7]

Many knowledge gaps remain, particularly in epidemiology, long-term outcomes, and human therapeutic trials. Given the extreme rarity of ACFD, international collaboration, centralized registries, and integration of ontological frameworks (MONDO, HPO, GO, CL, UBERON, NCIT) will be essential to accumulate sufficient data for evidence-based guidelines. Model organism studies and emerging technologies in single-cell and spatial transcriptomics offer promising routes to refine mechanistic understanding and identify new therapeutic targets.[12][13][16] In the meantime, acrocapitofemoral dysplasia serves as a paradigmatic example of how precise genetic lesions in a developmental signaling pathway can produce highly specific skeletal phenotypes, and how translational research linking human genetics with experimental biology can illuminate pathophysiology and guide future interventions.

Reference Validation

Checked with linkml-reference-validator 0.3.0rc1.

Outcome Count
References checked 7
Resolved 7
Unresolved (possible confabulation) 0
Unverifiable 0
References weighed for topical relevance 7
On topic 7
Off topic 0

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Outcome Count
Terms checked 55
Resolved 51
Unresolved (possible confabulation) 0
Obsolete 3
Unverifiable 1
Terms whose name was checked 33
Terms named correctly 10
Terms named as a different term 17
Terms whose name is worth a second look 6

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

  • CL:0000133 (3 mentions) - the report calls it "growth plate chondrocyte", "chondrocyte"; CL calls it neurectodermal cell
  • GO:0005101 (1 mention) - the report calls it "hedgehog receptor binding"; GO calls it GO_0005101
  • UBERON:0001474 (1 mention) - the report calls it "appendicular skeleton"; UBERON calls it bone element
  • UBERON:0001465 (1 mention) - the report calls it "hip joint"; UBERON calls it knee
  • UBERON:0002385 (1 mention) - the report calls it "thoracic cage"; UBERON calls it muscle tissue
  • NCIT:C33211 (1 mention) - the report calls it "Genetic Testing"; NCIT calls it Ooplasm
  • NCIT:C18537 (1 mention) - the report calls it "DNA Sequencing"; NCIT calls it MYC Family Gene
  • NCIT:C15973 (1 mention) - the report calls it "Orthopedic Surgery"; NCIT calls it Immunotoxin Cancer Immunotherapy
  • NCIT:C80117 (1 mention) - the report calls it "Hip Arthroplasty"; NCIT calls it TBL1XR1 wt Allele
  • NCIT:C25761 (1 mention) - the report calls it "Thoracic Surgery"; NCIT calls it Surgically Created Structure
  • NCIT:C15273 (1 mention) - the report calls it "Physical Therapy"; NCIT calls it Longitudinal Study
  • NCIT:C15272 (1 mention) - the report calls it "Occupational Therapy"; NCIT calls it Lobectomy
  • NCIT:C49236 (1 mention) - the report calls it "Pain Management"; NCIT calls it Therapeutic Procedure
  • NCIT:C20464 (1 mention) - the report calls it "Psychosocial Support"; NCIT calls it Cytokine
  • NCIT:C17189 (1 mention) - the report calls it "Genetic Counseling"; NCIT calls it Telophase
  • NCIT:C18243 (1 mention) - the report calls it "Prenatal Genetic Testing"; NCIT calls it Regression
  • NCIT:C18488 (1 mention) - the report calls it "Preimplantation Genetic Diagnosis"; NCIT calls it Angiopoietin-1 Receptor

Obsolete terms

These terms are real but deprecated. Citing one is not a fabrication; it does mean the report is naming something the ontology has retired:

  • HP:0002355 (obsolete Difficulty walking) (1 mention) - replaced by HP:0001288
  • GO:0005101 (GO_0005101) (1 mention) - replaced by GO:0005096
  • GO:0005615 (obsolete extracellular space) (1 mention) - replaced by GO:0005576

Terms whose name is worth a second look

The report's name for these is recognisably related to the term's own name without being one of them. A loose paraphrase reads the same way as a citation of the wrong sibling term - and so does a related synonym, which the ontology records precisely because it names something adjacent rather than the same thing - so these are listed rather than judged:

  • GO:0032330 (2 mentions) - the report calls it "regulation of chondrocyte proliferation"; GO calls it regulation of chondrocyte differentiation
  • GO:0007224 (1 mention) - the report calls it "hedgehog signaling pathway"; GO calls it smoothened signaling pathway, and lists "hedgehog signaling pathway" among its other names
  • GO:0009612 (1 mention) - the report calls it "mechanical stimulus response"; GO calls it response to mechanical stimulus, and lists "mechanical stimulus response" among its other names
  • GO:0005929 (1 mention) - the report calls it "primary cilium"; GO calls it cilium, and lists "primary cilium" among its other names
  • GO:0005615 (1 mention) - the report calls it "extracellular space"; GO calls it obsolete extracellular space, and lists "intercellular space" among its other names
  • NCIT:C15632 (1 mention) - the report calls it "Targeted Therapy"; NCIT calls it Chemotherapy

Terms named inconsistently

The report gives these identifiers more than one name of its own:

  • CL:0000133 - called "growth plate chondrocyte", "chondrocyte"

Prefixes with no resolver

Terms carrying these prefixes were not checked either way, because no configured ontology covers them. An unrecognised prefix may name an ontology this run could not reach as easily as one that does not exist, so nothing here is evidence of fabrication: ORPHA.