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Inheritance

2

Autosomal recessive HP:0000007

Homozygosity for the HOXA2 homeodomain missense p.Q186K in a consanguineous Iranian family, mapped by genome-wide linkage to 7p14.3-p15.3.

Autosomal recessive inheritance

Show evidence (1 reference)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Recessive segregation in a consanguineous pedigree establishes the biallelic mode for this subtype.

Autosomal dominant HP:0000006

Heterozygous truncating HOXA2 variants segregate with bilateral microtia in multigeneration pedigrees. Hearing impairment is variable, so auricular morphology and audiology both contribute to family assessment.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:23775976 SUPPORT Human Clinical

"The HOXA2 variant was segregated with microtia and hearing loss in the family and was not seen in 6,500 individuals sequenced by the NHLBI Exome Sequencing Project or in 218 control individuals sequenced in this study."

Co-segregation with the trait plus absence from large control sets supports the dominant allele's causality.

PMID:27503514 SUPPORT Human Clinical

"In our family, sequence analysis detected a heterozygous protein truncating nonsense variant"

Full segregation of a second heterozygous truncating allele in an independent family.

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Subtypes

2

Autosomal recessive microtia, hearing impairment and cleft palate (HOXA2 p.Q186K)

HOXA2 hgnc:5103

The original consanguineous Iranian family has homozygous p.Gln186Lys with bilateral microtia, prelingual severe to profound mixed hearing impairment and partial cleft palate. Three examined relatives had marked canal stenosis and ossicular abnormalities; one had unilateral inner-ear agenesis. These observations do not establish universal features of all biallelic HOXA2 variants.

Show evidence (1 reference)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Defines the recessive subtype's three-component phenotype in the family the disease concept is named for.

Autosomal dominant nonsyndromic bilateral microtia (HOXA2 haploinsufficiency)

HOXA2 hgnc:5103

Heterozygous truncating HOXA2 variants segregate with dominant bilateral microtia. Hearing varies among families: the p.Gln235* family studied by Brown and colleagues includes mild to severe mixed loss, whereas the examined p.Glu224* family members had normal hearing. The characterized dominant families do not show the cleft-palate presentation of the original recessive family. Haploinsufficiency is proposed; transcript decay and an exact reduction in patient protein abundance were not measured in these reports.

Show evidence (2 references)

PMID:23775976 SUPPORT Human Clinical

"Our data extend these conclusions and define HOXA2 haploinsufficiency as the first genetic cause for autosomal-dominant nonsyndromic microtia."

Establishes the dominant, haploinsufficiency-driven subtype.

PMID:27503514 SUPPORT Human Clinical

"Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."

A second, independent dominant family in which the microtia is isolated.

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Discussions and Knowledge Gaps

3

Why does complete Hoxa2 loss kill mice at birth with a full second-to-first arch homeotic transformation, while human HOXA2 loss-of-function alleles produce a viable, largely isolated ear malformation?

HUMAN MODEL MISMATCH hoxa2_mouse_null_lethality_vs_human_viability

Attached to

pathophysiology#Homeotic Transformation of Second-Arch Skeletal Derivatives animal_models#Hoxa2 null mouse (Rijli 1993) animal_models#Hoxa-2 null mouse (Gendron-Maguire 1993)

The complete mouse null is perinatally lethal with extensive skeletal homeosis, whereas characterized human heterozygous truncating and homozygous p.Gln186Lys genotypes are viable. Dose, developmental timing and species differences may contribute. Mouse hypomorphic alleles establish dose sensitivity, but residual activity of the human missense allele was not measured in the founding study. Human ossicular dysplasia therefore should not be described as proven partial homeotic duplication.

Show evidence (3 references)

PMID:7903600 SUPPORT Model Organism

"Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."

The lethal mouse null phenotype at one end of the mismatch.

PMID:27503514 SUPPORT Human Clinical

"Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."

A five-generation pedigree of viable, isolated human disease at the other end of the mismatch.

PMID:24067355 SUPPORT Model Organism

"In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."

Shows that timing of Hoxa2 loss alone spans much of the severity gap, which is part of the candidate resolution.

What explains the sensorineural component of hearing loss in HOXA2-affected ears without demonstrated inner-ear agenesis?

KNOWLEDGE GAP hoxa2_sensorineural_component_unexplained

Attached to

phenotypes#Mixed Hearing Impairment

The original recessive family includes one left inner-ear agenesis confirmed by CT and MRI, while two other examined relatives had normal inner-ear structures despite mixed hearing loss. Mixed loss also occurs in the p.Gln235* dominant family. Thus the gap is not absence of any human inner-ear characterization: the unresolved question is why sensorineural dysfunction occurs in other ears, and how it relates to HOXA2 development.

Show evidence (3 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"The inner-ear structures were normal in patients V: 2 and V: 3, but there were no inner-ear structures on the left side for IV: 3."

Unilateral inner-ear agenesis in one recessive-family member, with normal inner-ear anatomy in the other two imaged relatives.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral mixed hearing loss (Fig. 1C)."

Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one relative, so not every tested ear had both components.

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"All four affected family individuals showed bilateral symmetric severe to profound mixed hearing impairment affecting all frequencies and leading to a flat audiometric shape."

The four affected members of the original recessive family; this severity should not be transferred to all dominant cases.

Is the Hoxa2-associated cleft palate secondary to abnormal tongue musculature, intrinsic to the palatal shelves, or both?

CONTROVERSY hoxa2_cleft_palate_tongue_versus_intrinsic_palate

Attached to

pathophysiology#Abnormal Tongue Posture Obstructing Palatal Shelf Closure pathophysiology#Intrinsic Palatal Shelf Fusion Defect phenotypes#Cleft Palate

Two mouse accounts are on record and they are not the same claim. Barrow and Capecchi report that mis-attachment of the hyoglossus correlates exactly with cleft palate in Hoxa2 mutants and suggest that the resulting tongue posture blocks the shelves, with a genetic rescue in Hoxa1/Hoxa2 double mutants as support. Smith and colleagues report Hoxa2 expression in the palate itself and reduced fusion of Hoxa2-null shelves cultured without a tongue, and conclude explicitly that the cleft is not solely due to the tongue musculature. The two are compatible - a mechanical obstruction and a shelf-intrinsic fusion defect could both contribute - but their relative contribution has not been quantified, and neither has been examined in a HOXA2-mutant patient, in whom the cleft is partial rather than complete. Until that is settled, this entry carries both nodes and asserts neither as the mechanism of the human cleft.

Show evidence (3 references)

PMID:10529419 SUPPORT Model Organism

"We suggest that the hyoglossus, whose function is to depress the lateral edges of the tongue, when unable to make its proper attachment to the greater horn of the hyoid, forces the tongue to adopt an abnormal posture which blocks closure of the palatal shelves."

The tongue-musculature position, in its authors' own hedged wording.

PMID:19653318 SUPPORT BACKGROUND Model Organism

"The cleft palate exhibited by Hoxa2 null murine embryos has been described as being secondary to abnormalities of tongue musculature, and Hoxa2 was presumed to not play a direct role in palate development."

The second group's statement of the prior position, which is what they set out to test.

PMID:19653318 SUPPORT Model Organism

"These results demonstrate the cleft palate phenotype of Hoxa2 null embryos is not solely due to abnormal tongue musculature, and indicate a direct role of Hoxa2 in regulating murine palatogenesis."

The palate-intrinsic position, stated as a conclusion.

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Pathophysiology

9

HOXA2 Loss of Function

Disease-associated alleles include heterozygous truncating variants p.Lys213*, p.Glu224* and p.Gln235*, and the recessive homeodomain missense p.Gln186Lys. Dominant haploinsufficiency is inferred from segregation and variant class, with impaired enhancer activation measured for two truncating alleles. The p.Gln186Lys DNA-binding effect is a homology-model prediction; the founding study did not measure residual protein activity or show functional complementation.

HOXA2 hgnc:5103

anterior/posterior pattern specification GO:0009952 ⚠ ABNORMAL

DNA-binding transcription factor activity GO:0003700 ⇓ LOSS OF FUNCTION

Downstream

Impaired Transactivation of the Long-Range HMX1 Enhancer The p.Lys213* and p.Gln235* variants impair activation of the long-range HMX1 enhancer in a dual-luciferase assay; the abstract does not establish complete abolition of activity.

Loss of Second Pharyngeal Arch Neural Crest Identity HOXA2 is the selector gene that assigns second-arch identity to the cranial neural crest cells populating that arch; without it they adopt first-arch identity.

Intrinsic Palatal Shelf Fusion Defect A route that does not run through the pharyngeal arches at all. Hoxa2 is expressed in the palate itself, and knocking it down there reduces the rate at which the shelves fuse. The intermediates the authors name - increased cell proliferation, and de-repression of the Hoxa2 targets Msx1, Bmp4, Barx1 and Ptx1 - are candidates they identify but do not trace to the fusion failure.

External Auditory Canal Stenosis The HOXA2 genotype segregates with canal narrowing in the recessive family; the specific developmental intermediates remain unresolved.

Unilateral Inner-Ear Aplasia The inner-ear malformation co-occurs with homozygous p.Gln186Lys in one relative. Its developmental relation to HOXA2 remains uncertain and should not be attributed to ossicular homeosis.

Unilateral Facial Paresis Facial weakness was observed in one homozygous relative; a specific neural developmental mechanism was not established.

Show evidence (3 references)

PMID:23775976 SUPPORT Human Clinical

"Exome sequencing of affected family members detected only seven shared, rare, heterozygous, nonsynonymous variants, including one protein truncating variant, a HOXA2 nonsense change (c.703C>T, p.Q235*)."

Identifies the truncating allele class underlying the dominant form.

PMID:18394579 SUPPORT Human Clinical

"Subsequent DNA sequence analysis of the HOXA1 and HOXA2 homeobox genes from the candidate region identified an interesting HOXA2 homeodomain variant: a change in a highly conserved amino acid (p.Q186K)."

Identifies the recessive homeodomain missense allele.

PMID:18394579 SUPPORT INDIRECT Computational

"In the model of the mutant homeodomain, the position of the mutant lysine side chain is consistently farther away from a nearby phosphate group; this altered position results in the loss of a hydrogen bond and affects the DNA-binding activity."

The DNA-binding consequence of p.Q186K is a homology-modelling prediction, not a measurement; recorded as computational and indirect.

Impaired Transactivation of the Long-Range HMX1 Enhancer

The p.Lys213* and p.Gln235* variants impair activation of a long-range HMX1 enhancer in dual-luciferase assays. Prior mouse work places Hoxa2 upstream of Hmx1 in ear development. The assay links these patient variants to a candidate effector, but does not measure the entire developmental pathway in human auricular tissue.

HOXA2 hgnc:5103

ear morphogenesis GO:0042471 ⚠ ABNORMAL

Experimental models

HOXA2 variant HMX1 enhancer reporter assay OTHER

Downstream

Failed Auricular Morphogenesis Reduced HMX1 activation is the candidate route from the HOXA2 alleles to the external ear defect; the link to the human auricle phenotype is inferred, not measured in patient tissue.

Show evidence (2 references)

PMID:32649979 SUPPORT BACKGROUND Model Organism

"In mouse, Hoxa2 can bind to a long-range enhancer and regulate expression of the Hmx1 gene, which is a crucial transcription factor in eye and ear development."

Establishes the HOXA2-HMX1 enhancer relationship; demonstrated in mouse.

PMID:32649979 SUPPORT DIRECT In Vitro

"Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of the long-range enhancer of HMX1."

Direct reporter result for p.Lys213* and p.Gln235*; impairment is not equivalent to a proven null effect.

Loss of Second Pharyngeal Arch Neural Crest Identity

Hoxa2-null mouse embryos retain rhombomeric and neural crest segmentation but lose normal second-arch mesenchymal identity, producing first-arch-like skeletal derivatives. This supports an identity-assignment role. The cited abstract does not separately demonstrate normal migration, cell number or survival, and the complete-null result should not be equated with every human HOXA2 allele.

second-arch neural crest cell CL:0011012

neural crest cell development GO:0014032 ⚠ ABNORMAL pharyngeal system development GO:0060037 ⚠ ABNORMAL

second pharyngeal arch UBERON:0003066

Animal models

Hoxa2 null mouse (Rijli 1993) Mouse recapitulates The model defines the identity-assignment lesion this node represents.

Hoxa2 hypomorphic dosage-series mouse Mouse perturbs

Downstream

Homeotic Transformation of Second-Arch Skeletal Derivatives Mis-specified second-arch crest builds first-arch structures instead of second-arch ones.

Failed Auricular Morphogenesis Hoxa2-expressing second-arch mesenchyme supplies the auricular territory examined in the mouse fate-mapping study. Its loss disrupts that territory; the result should not be generalized to every human external-ear structure.

Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles The same rhombencephalic neural crest that builds the craniofacial skeleton also patterns the craniofacial muscles, and Hoxa2 mutants have abnormal attachments and trajectories of the extrinsic tongue and hyoid muscles. How the arch-identity lesion produces that particular mis-routing was not worked out, so the intermediates are recorded as unknown.

Middle-Ear Ossicular Dysplasia The relationship of second-arch patterning to human ossicular dysplasia is inferred from developmental models and family anatomy; the intervening human developmental steps have not been measured.

Show evidence (2 references)

PMID:7903601 SUPPORT Model Organism

"While rhombomeric and neural crest cell (NCC) segmentation was not affected, mesenchymal NCC derivatives of the second arch were lacking, and second arch mesenchymal NCC identity was changed to first arch identity, resulting in homeotic transformation of second to first arch skeletal elements."

Direct mouse evidence for preserved segmentation with changed second-arch identity; migration and survival were not separately established by this quotation.

url:https://pmc.ncbi.nlm.nih.gov/articles/4143470/ SUPPORT DIRECT REVIEW SYNTHESIS Other

"By definition, the pinna encompasses all external structures of the ear, including the tragus and root."

This review qualifies the terminology of the mouse lineage claim; it is not a new lineage-tracing experiment.

Homeotic Transformation of Second-Arch Skeletal Derivatives

Hoxa2-null mice lose second-arch skeletal elements and develop duplicated first-arch structures, including middle-ear ossification centers and a second Meckel cartilage beside the otic capsule. This is a model-organism developmental phenotype. Human imaging and surgery establish ossicular dysplasia and fixation, but do not demonstrate this complete homeotic duplication. This node has no downstream human-phenotype links because the complete homeotic transformation is documented only in mice.

neural crest cell CL:0011012

embryonic cranial skeleton morphogenesis GO:0048701 ⚠ ABNORMAL embryonic skeletal system morphogenesis GO:0048704 ⚠ ABNORMAL

auditory ossicle UBERON:0001686

Animal models

Hoxa-2 null mouse (Gendron-Maguire 1993) Mouse recapitulates Defines the complete-null mouse skeletal homeosis, including duplicated middle-ear ossification centers.

Show evidence (2 references)

PMID:7903600 SUPPORT Model Organism

"Analysis of stained skeletons revealed that homozygous mutant animals contained multiple cranial skeletal defects, including a duplication of the ossification centers of the bones of the middle ear."

Documents the middle-ear skeletal consequence of the second-arch transformation.

PMID:7903600 SUPPORT Model Organism

"Skeletal elements normally derived from the second arch were absent in the mutants."

Confirms loss, not merely mis-shaping, of the second-arch skeletal derivatives.

Middle-Ear Ossicular Dysplasia

Malformed or fixed ossicles are documented directly in both recessive and dominant HOXA2 families. Recessive cases had a malformed chain apparently fixed by an incomplete atretic plate; dominant cases included abnormal stapes crura, absent stapedial tendon and a rigid chain. These observations support a conductive deficit without assuming mouse-like duplication in humans.

auditory ossicle bone UBERON:0001686

Downstream

Hearing Impairment Ossicular malformation and fixation impair sound transmission and can account for the conductive component. This mechanism does not explain a sensorineural component.

Mixed Hearing Impairment Ossicular malformation and fixation impair sound transmission and can account for the conductive component. This mechanism does not explain a sensorineural component.

Abnormal Middle-Ear Ossicles The structural abnormality is the directly observed phenotype.

Show evidence (3 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate."

CT findings in the three examined members of the recessive family; fixation was described as apparent on imaging.

PMID:23775976 SUPPORT DIRECT Human Clinical

"In individual II.2, the stapes was noted to have a thickened posterior crus and an absent anterior crus, and the stapedial tendon was absent."

Operative observation in one dominant-family member.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Individual II.4 had a rigid ossicular chain."

Operative observation in another member of the same dominant family.

Failed Auricular Morphogenesis

The auricle fails to form normally. Timing determines severity in the mouse: early Hoxa2 inactivation abolishes the auricle and duplicates the external auditory canal, while late inactivation leaves a hypomorphic auricle resembling the human phenotype. Hoxa2 acts on pinna morphogenesis partly through BMP signalling and Eya1 expression.

ear morphogenesis GO:0042471 ⚠ ABNORMAL face morphogenesis GO:0060325 ⚠ ABNORMAL

auricle UBERON:0001757

Animal models

Conditional Hoxa2 inactivation mouse (Minoux 2013) Mouse recapitulates Late inactivation produces auricular hypoplasia resembling the human phenotype. Fate mapping defines the Hoxa2-expressing territory examined in the mouse study.

Downstream

Bilateral Microtia Failure of pinna morphogenesis presents clinically as bilateral microtia.

Thickened Helices Abnormal auricular morphogenesis includes the thickened helices observed in the dominant family.

Underdeveloped Antitragus Antitragal underdevelopment is one component of the documented auricular dysplasia.

Show evidence (2 references)

PMID:24067355 SUPPORT Model Organism

"In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."

Establishes both the auricular defect and its dependence on the timing of Hoxa2 loss.

PMID:24067355 SUPPORT Model Organism

"Hoxa2 partly controls the morphogenesis of the pinna through the BMP signalling pathway and expression of Eya1, which in humans is involved in branchio-oto-renal syndrome."

Names the downstream effectors through which HOXA2 shapes the pinna; the authors qualify this as partial control.

Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles

In Hoxa2 mutant mice the attachments and trajectories of the extrinsic tongue and hyoid muscles are abnormal. The abnormal trajectory of two of them, the styloglossus and the stylohyoideus, blocks the attachment of the hyoglossus to the greater horn of the hyoid, and that blocked attachment correlated exactly with the presence of cleft palate in those animals. The node is mouse-derived; no comparable observation has been reported in HOXA2-mutant patients, in whom tongue and hyoid muscle anatomy has not been described.

muscle attachment GO:0016203 ⚠ ABNORMAL

extrinsic muscle of tongue UBERON:0001575 hyoglossus muscle UBERON:0001572 hyoid bone greater horn UBERON:0003997

Animal models

Hoxa1/Hoxa2 double mutant mouse (Barrow 1999) Mouse rescues Loss of Hoxa1 on the Hoxa2-mutant background restores normal attachment of the hyoglossus to the greater horn of the hyoid.

Downstream

Abnormal Tongue Posture Obstructing Palatal Shelf Closure Barrow and Capecchi's interpretation of the correlation: the hyoglossus, unable to reach the greater horn, cannot depress the lateral edges of the tongue. Support for the link is the rescue arm - restoring the attachment in Hoxa1/Hoxa2 double mutants restores palatal closure over a flattened tongue - rather than direct observation of tongue posture in the single mutants.

Show evidence (2 references)

PMID:10529419 SUPPORT Model Organism

"We also uncovered multiple defects in the attachments and trajectories of the extrinsic tongue and hyoid muscles in Hoxa2 mutants."

Records the muscle attachment and trajectory defects this node represents, in Hoxa2 mutants.

PMID:10529419 SUPPORT Model Organism

"the abnormal trajectory of two of these muscles, the styloglossus and the stylohyoideus, blocked the attachment of the hyoglossus to the greater horn of the hyoid, which in turn correlated exactly with the presence of cleft palate in Hoxa2 mutants"

Names the specific muscles involved and reports the exact correlation between the blocked hyoglossus attachment and cleft palate, which is the observation - as distinct from the interpretation on the next node.

Abnormal Tongue Posture Obstructing Palatal Shelf Closure

The proposed mechanical consequence, stated by its authors as a suggestion rather than an observation: with the hyoglossus unable to depress the lateral edges of the tongue, the tongue adopts an abnormal posture that blocks closure of the palatal shelves. It is not the only published account of the Hoxa2 cleft - see the hoxa2_cleft_palate_tongue_versus_intrinsic_palate discussion and the Intrinsic Palatal Shelf Fusion Defect node - and neither account has been tested in a human patient.

secondary palate development GO:0062009 ⚠ ABNORMAL

tongue UBERON:0001723 secondary palatal shelf UBERON:0005619

Downstream

Cleft Palate Shelves that do not close leave a cleft. In Hoxa1/Hoxa2 double mutants, where the hyoglossus attachment is restored, the penetrance of cleft palate falls sharply - the experimental result that ties the obstruction to the cleft.

Show evidence (1 reference)

PMID:10529419 SUPPORT Model Organism

"We suggest that the hyoglossus, whose function is to depress the lateral edges of the tongue, when unable to make its proper attachment to the greater horn of the hyoid, forces the tongue to adopt an abnormal posture which blocks closure of the palatal shelves."

The proposal this node represents, quoted in full so that its status as the authors' suggestion is visible in the evidence itself.

Intrinsic Palatal Shelf Fusion Defect

A second, independent route to the same cleft. Hoxa2 is expressed in the developing palate itself between E12.5 and E15.5, and Hoxa2-null palatal shelves cultured in the absence of the tongue fuse at lower rates than heterozygous or wild-type shelves, as do shelves in which Hoxa2 is knocked down with antisense constructs. Null palates show an overall increase in cell proliferation, and Hoxa2 represses Msx1, Bmp4, Barx1 and Ptx1 within the palate. On the authors' reading the mouse cleft is therefore not solely secondary to the tongue. Whether either route operates in HOXA2-mutant humans is unknown.

secondary palate development GO:0062009 ⚠ ABNORMAL

secondary palatal shelf UBERON:0005619

Experimental models

Tongue-free Hoxa2 mutant palate organ culture OTHER

Downstream

Cleft Palate The explant and mouse findings support a palate-intrinsic contribution to clefting, but do not establish its quantitative contribution or demonstrate the corresponding intermediate in affected humans.

Show evidence (3 references)

PMID:19653318 SUPPORT Model Organism

"we detected Hoxa2 expression in the developing palate at both the mRNA and protein levels between embryonic day (E) 12.5 and E15.5"

Hoxa2 is expressed in the palate itself, the precondition for a route that does not run through the tongue.

PMID:19653318 SUPPORT In Vitro

"Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures."

Palatal shelves fuse less well without Hoxa2 even when the tongue is removed from the system - explant culture, hence IN_VITRO.

PMID:19653318 SUPPORT Model Organism

"These results demonstrate the cleft palate phenotype of Hoxa2 null embryos is not solely due to abnormal tongue musculature, and indicate a direct role of Hoxa2 in regulating murine palatogenesis."

The authors' own conclusion that the tongue route is not the whole account, which is why this node is curated alongside it rather than instead of it.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

10

Ear 8

Bilateral Microtia HP:0008551

Laterality: BILATERAL

Pedigree observations do not supply a population-level penetrance or frequency estimate.

Show evidence (5 references)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Bilateral microtia in the recessive family.

PMID:23775976 SUPPORT Human Clinical

"We ascertained a three-generation family with bilateral microtia and hearing loss segregating as an autosomal dominant trait."

Bilateral microtia in the first dominant family.

PMID:27503514 SUPPORT Human Clinical

"Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."

Bilateral microtia in a second dominant family.

+ 2 more references

Hearing Impairment HP:0000365

Normal hearing in an affected family member does not exclude dominant HOXA2-related microtia.

Show evidence (4 references)

PMID:23775976 SUPPORT Human Clinical

"We ascertained a three-generation family with bilateral microtia and hearing loss segregating as an autosomal dominant trait."

Hearing loss co-segregating in a dominant family.

PMID:32649979 SUPPORT BACKGROUND Human Clinical

"To date, only four HOXA2 mutations were reported in families with autosomal-recessive or dominant microtia, with or without hearing impairment."

The literature summary records hearing impairment as a variable rather than constant feature of HOXA2-related microtia.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral mixed hearing loss (Fig. 1C)."

Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one relative, so not every tested ear had both components.

+ 1 more reference

Mixed Hearing Impairment HP:0000410

Laterality: BILATERAL

The dominant-family figure also documents a conductive-only ear; severity and audiological subtype should be assessed per ear.

Show evidence (3 references)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Specifies the mixed, symmetrical, severe-to-profound character of the recessive subtype's hearing loss.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral mixed hearing loss (Fig. 1C)."

Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one relative, so not every tested ear had both components.

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"All four affected family individuals showed bilateral symmetric severe to profound mixed hearing impairment affecting all frequencies and leading to a flat audiometric shape."

The four affected members of the original recessive family; this severity should not be transferred to all dominant cases.

External Auditory Canal Stenosis Stenosis of the external auditory canal HP:0000402

Laterality: BILATERAL

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"The results of high-resolution CT scanning confirmed that the external auditory canal was severely narrowed bilaterally in the cartilaginous part of the auditory canal and almost atretic in part of the bony portion in all patients."

CT in the three examined recessive-family members, not every person with HOXA2-related disease.

Abnormal Middle-Ear Ossicles Abnormality of the middle ear ossicles HP:0004452

Show evidence (3 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate."

CT findings in the three examined members of the recessive family; fixation was described as apparent on imaging.

PMID:23775976 SUPPORT DIRECT Human Clinical

"In individual II.2, the stapes was noted to have a thickened posterior crus and an absent anterior crus, and the stapedial tendon was absent."

Operative observation in one dominant-family member.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Individual II.4 had a rigid ossicular chain."

Operative observation in another member of the same dominant family.

Unilateral Inner-Ear Aplasia Aplasia of the inner ear HP:0011372

Laterality: LEFT

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"The inner-ear structures were normal in patients V: 2 and V: 3, but there were no inner-ear structures on the left side for IV: 3."

Unilateral inner-ear agenesis in one recessive-family member, with normal inner-ear anatomy in the other two imaged relatives.

Thickened Helices HP:0000391

Show evidence (1 reference)

PMID:23775976 SUPPORT DIRECT Human Clinical

"All five affected family members had small, malformed ears with a thickened helix and a superficial postauricular sulcus (Fig. 1B)."

Clinical morphology in five enrolled affected members of the p.Gln235* family.

Underdeveloped Antitragus HP:0011251

Show evidence (1 reference)

url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf SUPPORT DIRECT Human Clinical

"underdeveloped antitragus, serpiginous antihelix stem, deep incisura between tragus and antitragus with a laterally dislocated hypoplastic lobe."

Proband morphology from the author thesis describing the same p.Glu224* pedigree later reported in PMID:27503514; this is not an additional family.

Head and Neck 2

Cleft Palate HP:0000175

The subtype association is based on a small number of characterized pedigrees; it is not a universal genotype-phenotype rule.

Show evidence (3 references)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Partial cleft palate in the recessive family.

PMID:27503514 SUPPORT BACKGROUND Human Clinical

"HOXA2 biallelic mutations were also described in an inbreed family with autosomal recessive microtia, hearing impairment and incomplete cleft palate."

The later article summarizes the same recessive family; it does not provide independent replication of its cleft phenotype.

PMID:7903600 SUPPORT Model Organism

"Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."

Cleft palate in the homozygous mouse null provides model evidence for developmental relevance; the abstract does not supply a penetrance denominator.

Unilateral Facial Paresis Unilateral facial palsy HP:0012799

Laterality: RIGHT

Show evidence (1 reference)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"Individual number V: 2 also had a paresis on the right side of the face."

Single affected relative; facial-nerve hypoplasia was suspected clinically but was not confirmed by brain MRI.

🧬

Genetic Associations

1

HOXA2 pathogenic variants (Causal)

Gene: HOXA2 hgnc:5103 relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:18394579 SUPPORT Human Clinical

"Genome-wide linkage analysis localized the responsible gene to chromosome 7p14.3-p15.3 with a maximum multi-point LOD score of 4.17."

Linkage to the HOXA cluster interval is the mapping evidence that identified the gene.

PMID:32649979 SUPPORT Human Clinical

"Next generation sequencing identified two heterozygous nonsense HOXA2 mutations, one in each family."

Two independent families carrying heterozygous nonsense alleles; p.Gln235* recurs from an earlier pedigree.

Variants (4)

p.Q186K homeodomain missense (recessive) Pathogenic

Homozygous homeodomain missense p.Gln186Lys segregated in the original recessive family and was absent from the reported control panels. The founding paper predicts altered DNA binding by homology modeling but does not measure residual function. Protein notation avoids conflating historical nucleotide numbering with a normalized transcript-specific HGVS description.

Show evidence (1 reference)

PMID:18394579 SUPPORT Human Clinical

"The variant was not found in 231 Iranian and 109 Belgian control samples."

Control-panel absence supporting pathogenicity of p.Q186K.

p.Q235* nonsense (dominant) Pathogenic

A recurrent heterozygous nonsense allele, found independently in a three-generation US family and in one of the two Chinese families.

Show evidence (1 reference)

PMID:32649979 SUPPORT Human Clinical

"One mutation (c.637A > T, p.Lys213*) is newly reported, while the other one (c.703C > T,p.Gln235*) is consistent with a previous report."

Documents recurrence of p.Gln235* across unrelated families.

p.E224* nonsense (dominant) Pathogenic

A heterozygous truncating allele segregating in all affected members of a five-generation Italian family and absent from public databases.

Show evidence (2 references)

PMID:27503514 SUPPORT Human Clinical

"In our family, sequence analysis detected a heterozygous protein truncating nonsense variant"

Defines the allele and its segregation.

url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf SUPPORT DIRECT Human Clinical

"Sanger analysis of the index patient (V:1) identified a previously unreported heterozygous variant ... NM_006735.3: c.670G>T, p.(Glu224*) ... in the second exon of the HOXA2 gene (Figure 17a)."

Primary thesis data identifying p.Glu224* in the same Italian pedigree as the journal article.

p.Lys213* nonsense (dominant) Pathogenic

Heterozygous p.Lys213* was found in one Chinese family; a dual-luciferase assay showed impaired HMX1 enhancer activation. The result supports loss of activity without establishing patient transcript decay.

Show evidence (2 references)

PMID:32649979 SUPPORT Human Clinical

"One mutation (c.637A > T, p.Lys213*) is newly reported, while the other one (c.703C > T,p.Gln235*) is consistent with a previous report."

Identifies the newly reported p.Lys213* allele and distinguishes it from recurrent p.Gln235*.

PMID:32649979 SUPPORT DIRECT In Vitro

"Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of the long-range enhancer of HMX1."

Direct reporter result for p.Lys213* and p.Gln235*; impairment is not equivalent to a proven null effect.

💊

Medical Actions

6

Auricular Reconstruction

Action: auricular reconstruction Ontology label: Reconstructive Surgery NCIT:C25351

Platform: Surgery

Discuss observation, an external prosthesis, autologous cartilage reconstruction and alloplastic reconstruction according to the individual goals and anatomy. Reconstruction is elective; coordinate its sequence with any hearing implant or canal surgery. The recommendations come from general microtia care, not a HOXA2 outcome series.

Mechanism Target:

BYPASSES Bilateral Microtia — Reconstruction changes the visible auricular manifestation; it does not reverse the prenatal HOXA2 patterning defect.

Show evidence (1 reference)

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"In discussing the spectrum of reconstructive options, observation should be presented with associated bene ﬁts and drawbacks."

General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment effect is measured.

Show evidence (1 reference)

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"In discussing the spectrum of reconstructive options, observation should be presented with associated bene ﬁts and drawbacks."

General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment effect is measured.

Cleft Palate Repair

Action: cleft palate repair Ontology label: Palatorrhaphy NCIT:C168380

Platform: Surgery

For patients with cleft palate, craniofacial-team assessment determines whether and when palatoplasty is indicated. General ACPA guidance places primary repair commonly at 9–14 months and ideally by 18 months, with individual readiness and airway risk considered. The source supplies general care recommendations, not genotype-specific efficacy.

Mechanism Target:

BYPASSES Cleft Palate — Palatoplasty restores palatal continuity and function after the congenital cleft has formed; it does not correct the embryonic HOXA2 mechanism.

Show evidence (1 reference)

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"The goal of cleft palate surgery is to obtain normal function for speech and swallowing, as well as to optimize airway and dental facial relations."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes.

Show evidence (2 references)

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"The goal of cleft palate surgery is to obtain normal function for speech and swallowing, as well as to optimize airway and dental facial relations."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes.

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Primary surgery of cleft palate often occurs between 9-14 months of age. The timing should take into account the patient and/or family readiness (physically and emotionally). Ideally, the cleft palate should be closed by the age of 18 months."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes. Timing is individualized, rather than an outcome established for this genotype.

Hearing Amplification

Action: hearing amplification Ontology label: Supportive Care NCIT:C15747

Platform: Device

Provide early hearing rehabilitation according to per-ear thresholds, canal anatomy and cochlear reserve. General bilateral microtia/atresia guidance recommends amplification by four months and early intervention by three to six months. Worn bone-conduction devices can bypass a narrowed or atretic canal; patients with patent canals may use conventional amplification if appropriate. Mixed loss requires assessment of the sensorineural component and device limits, rather than assuming normal cochlear function.

Mechanism Target:

BYPASSES Hearing Impairment — Amplification improves access to sound within the usable cochlear reserve. Bone conduction bypasses canal and middle-ear transmission abnormalities but does not repair inner-ear agenesis or restore intrinsic cochlear function.

Show evidence (1 reference)

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Diagnostic audiological assessment should be completed by 2 – 3 months of age and the infant provided with hearing ampli ﬁcation by 4 months of age and enrolled in early intervention (EI) by 3 – 6 months of age to optimize speech and language development."

General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment effect is measured. The timing recommendation is for bilateral microtia with atresia.

Show evidence (2 references)

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Diagnostic audiological assessment should be completed by 2 – 3 months of age and the infant provided with hearing ampli ﬁcation by 4 months of age and enrolled in early intervention (EI) by 3 – 6 months of age to optimize speech and language development."

General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment effect is measured. The timing recommendation is for bilateral microtia with atresia.

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Clinicians should encourage early use of these worn bone conduction devices for infants with CHL."

General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment effect is measured.

Speech and Language Therapy

Action: speech and language therapy Ontology label: Speech Language Therapy NCIT:C159273

Platform: Behavioral / lifestyle

Assess speech and language development in either subtype when hearing impairment or a palatal defect is present. Coordinate early intervention, educational support and targeted therapy. Speech therapy can address learned articulation errors; structural velopharyngeal dysfunction requires a separate surgical or prosthetic assessment.

Show evidence (1 reference)

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"The need for speech and/or language therapy for patients with a CL/P and/or other craniofacial difference, as well as the recommended nature of that therapy, should be based on results of a formal speech and language assessment and current best practices."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Platform: Behavioral / lifestyle

Discuss the identified genotype and variable phenotype with the family. When both parents carry a recessive pathogenic allele, each pregnancy has a 25% probability of an affected child; a heterozygous parent with a dominant pathogenic allele has a 50% transmission probability. These are Mendelian expectations conditional on parental genotypes, not empirically measured penetrance. Severity and hearing status cannot be predicted from transmission probability alone.

Show evidence (2 references)

PMID:23775976 SUPPORT INDIRECT Human Clinical

"Our data extend these conclusions and define HOXA2 haploinsufficiency as the first genetic cause for autosomal-dominant nonsyndromic microtia."

Supports the inheritance mode. The stated recurrence probability is the Mendelian consequence of the specified parental genotype, rather than a measured outcome in this pedigree.

PMID:18394579 SUPPORT INDIRECT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

Supports the inheritance mode. The stated recurrence probability is the Mendelian consequence of the specified parental genotype, rather than a measured outcome in this pedigree.

Feeding and nutrition support for cleft palate

Action: Supportive Care NCIT:C15747

Platform: Other

Assess feeding technique, intake, growth and hydration when cleft palate is present. A cleft team can select an appropriate specialized feeding system and monitor weight gain. This addresses the general functional risk of a cleft; a HOXA2-specific rate of feeding failure is not established.

Mechanism Target:

BYPASSES Cleft Palate — A specialized feeding system compensates for impaired suction without closing the cleft.

Show evidence (1 reference)

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Because infants with cleft palate cannot sustain the suction needed to maintain nutrition exclusively from the breast or standard bottle, they typically require specialized feeding systems to achieve adequate nutrition and hydration."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes. Feeding difficulty is a care risk, not an additional measured HOXA2 phenotype frequency.

Show evidence (1 reference)

url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Because infants with cleft palate cannot sustain the suction needed to maintain nutrition exclusively from the breast or standard bottle, they typically require specialized feeding systems to achieve adequate nutrition and hydration."

General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific outcomes. Feeding difficulty is a care risk, not an additional measured HOXA2 phenotype frequency.

🔬

Diagnosis

3

Clinical and audiological examination

Inspect both auricles, ear canals, palate and facial movement, and obtain age-appropriate air- and bone-conduction hearing thresholds. Mixed loss can occur in either inheritance subtype, and a normal hearing result does not exclude dominant HOXA2 microtia. General microtia guidance recommends diagnostic ABR by two to three months, followed by behavioral assessment as development permits.

Show evidence (3 references)

PMID:18394579 SUPPORT Human Clinical

"We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."

The clinical and audiological characterisation that defines the presentation.

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"A diagnostic ABR should be performed as early as possible."

General microtia diagnostic guidance, extrapolated to affected infants.

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"Air conduction and bone conduction testing should performed."

The source recommends testing both pathways; the quotation preserves its grammatical omission.

HOXA2 sequencing

Identify a phenotype-compatible HOXA2 variant through targeted sequencing, a relevant hearing/craniofacial panel or exome analysis, and test segregation where feasible. Interpret variant class, zygosity and family phenotype together; a rare missense finding alone is not diagnostic. Heterozygous truncating alleles and the original homozygous p.Gln186Lys allele have different inheritance and clinical associations.

Show evidence (2 references)

PMID:23775976 SUPPORT Human Clinical

"Exome sequencing of affected family members detected only seven shared, rare, heterozygous, nonsynonymous variants, including one protein truncating variant, a HOXA2 nonsense change (c.703C>T, p.Q235*)."

Exome sequencing as the diagnostic route in a dominant family.

PMID:23775976 SUPPORT DIRECT Human Clinical

"Both of these nonsynonymous changes affect leucine residues with high evolutionary conservation; however, each of these variants was also found in one control, indicating that either these variants are benign or that these variants in combination with another undetected HOXA2 variant (possibly..."

The study itself did not establish causality for every rare missense variant; the proposed second-variant explanation was untested.

Temporal-bone imaging when clinically indicated

CT characterizes canal narrowing, atretic plates and ossicles; MRI can assess inner-ear and neural anatomy. The original recessive family had both ossicular abnormalities and one unilateral inner-ear agenesis. General microtia guidance reserves routine reconstructive CT for surgical planning or suspected cholesteatoma rather than the newborn period; unusual mixed loss or neurologic findings require individualized specialist assessment.

Show evidence (2 references)

url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/ SUPPORT DIRECT Human Clinical

"The MRI of the auditory system in individual V: 3 was unremarkable for the inner ear and cerebellopontine angle, but an MRI confirmed the inner-ear agenesis on the left side of individual IV: 3 as seen on CT-images."

Human diagnostic imaging, with both normal and abnormal findings.

DOI:10.3389/fsurg.2022.944223 SUPPORT INDIRECT REVIEW SYNTHESIS Human Clinical

"A CT scan of the temporal bone is not recommended in the newborn period."

General microtia imaging guidance; this does not preclude individualized imaging for a specific diagnostic concern.

📊

Prevalence

1

Worldwide

Cases In Literature

Published evidence consists of a small number of pedigrees. No HOXA2-specific population prevalence is established by these reports; all-cause microtia birth prevalence should not be assigned to this molecular disorder.

Show evidence (1 reference)

PMID:32649979 SUPPORT BACKGROUND Human Clinical

"To date, only four HOXA2 mutations were reported in families with autosomal-recessive or dominant microtia, with or without hearing impairment."

A time-specific literature summary illustrates sparse pedigree evidence; it does not establish a current worldwide family count or population prevalence.

🔀

Differential Diagnoses

1

Conditions with similar clinical presentations that must be differentiated from Bilateral Microtia-Deafness-Cleft Palate Syndrome:

🧫

Experimental Models

2

HOXA2 variant HMX1 enhancer reporter assay OTHER

Dual-luciferase assays compare enhancer activation by p.Lys213* and p.Gln235* variants. The accessible abstract does not specify the host-cell identity, so no cell-line or tissue origin is inferred.

Pathograph links

Impaired Transactivation of the Long-Range HMX1 Enhancer measures observes: molecular

Limitations: An isolated reporter does not reproduce human auricular development or quantify clinical penetrance.

Show evidence (1 reference)

PMID:32649979 SUPPORT DIRECT In Vitro

"Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of the long-range enhancer of HMX1."

Variant-specific reporter assay for p.Lys213* and p.Gln235*.

Show evidence (1 reference)

PMID:32649979 SUPPORT DIRECT In Vitro

"Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of the long-range enhancer of HMX1."

Variant-specific reporter assay for p.Lys213* and p.Gln235*.

Tongue-free Hoxa2 mutant palate organ culture OTHER

Null palatal shelves cultured without a tongue have reduced fusion; antisense Hoxa2 knockdown also reduces fusion. This demonstrates an intrinsic component in the mouse system alongside the separate tongue-mechanics hypothesis.

Pathograph links

Intrinsic Palatal Shelf Fusion Defect partially recapitulates observes: tissue

Limitations: Explant fusion rates do not quantify in-vivo penetrance or establish the relative mechanism of the human partial cleft.

Show evidence (1 reference)

PMID:19653318 SUPPORT DIRECT In Vitro

"Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures."

Tongue-free mouse organ culture isolates a palate-intrinsic contribution.

Show evidence (1 reference)

PMID:19653318 SUPPORT DIRECT In Vitro

"Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures."

Tongue-free mouse organ culture isolates a palate-intrinsic contribution.

🐁

Animal Models

5

Hoxa2 null mouse (Rijli 1993)

Homozygous targeted disruption causes perinatal death and loss of normal second-arch mesenchymal identity despite preserved rhombomeric and neural crest segmentation. The source supports an identity defect; normal migration and survival are not separately demonstrated by the cached abstract.

Species

Mouse

Genotype

Hoxa2 homozygous null (targeted disruption)

Publication

PMID:7903601

Pathograph links

Loss of Second Pharyngeal Arch Neural Crest Identity recapitulates fidelity: high The model defines the identity-assignment lesion this node represents.

Limitations: A complete homozygous null differs from human heterozygous truncating alleles and homozygous p.Gln186Lys. Residual function of the human missense allele has not been measured in the cited family study.

Readouts

Second-arch neural crest identity

Direction: ALTERED

Interpretation: Second-arch crest adopts first-arch identity, the defining readout of the selector-gene lesion.

Show evidence (1 reference)

PMID:7903601 SUPPORT Model Organism

"While rhombomeric and neural crest cell (NCC) segmentation was not affected, mesenchymal NCC derivatives of the second arch were lacking, and second arch mesenchymal NCC identity was changed to first arch identity, resulting in homeotic transformation of second to first arch skeletal elements."

The identity-change readout behind this link.

Show evidence (1 reference)

PMID:7903601 SUPPORT Model Organism

"The ground pattern program appears to be modified in the mouse first arch by a Hox-independent process, whereas Hoxa-2 acts as a selector gene in the second arch."

Establishes the model as informative for HOXA2's second-arch selector function.

Hoxa-2 null mouse (Gendron-Maguire 1993)

An independent null allele reported simultaneously. Homozygotes are born with cleft palate and die within 24 hours, with duplicated middle-ear ossification centres and a second Meckel's cartilage beside the otic capsule.

Species

Mouse

Genotype

Hoxa-2 (Hox 1.11) homozygous targeted mutation

Publication

PMID:7903600

Pathograph links

Homeotic Transformation of Second-Arch Skeletal Derivatives recapitulates fidelity: moderate Defines the complete-null mouse skeletal homeosis, including duplicated middle-ear ossification centers.

Limitations: The perinatally lethal complete-null phenotype is more extensive than the observed human ossicular dysplasia. Human imaging and surgery do not establish an equivalent homeotic duplication.

Readouts

Middle-ear ossification centre duplication

Direction: INCREASED

Interpretation: Duplicated ossification centres are the skeletal signature of second-to-first arch transformation.

Show evidence (1 reference)

PMID:7903600 SUPPORT Model Organism

"Analysis of stained skeletons revealed that homozygous mutant animals contained multiple cranial skeletal defects, including a duplication of the ossification centers of the bones of the middle ear."

The skeletal readout behind this link.

Show evidence (1 reference)

PMID:7903600 SUPPORT Model Organism

"Skeletal elements normally derived from the second arch were absent in the mutants."

Establishes the model as informative for loss of second-arch skeletal derivatives.

Hoxa1/Hoxa2 double mutant mouse (Barrow 1999)

A single allele disrupting both linked genes, analysed against the single mutants. Some double-mutant craniofacial defects are additive combinations of the single-mutant ones and others appear only in the double mutant. The result that matters here is a rescue: compensatory defects associated with loss of Hoxa1 restore the hyoglossus attachment that is blocked in Hoxa2 mutants, and the penetrance of cleft palate falls sharply.

Species

Mouse

Genotype

Compound targeted allele disrupting both of the linked genes Hoxa1 and Hoxa2

Publication

PMID:10529419

Pathograph links

Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles rescues fidelity: moderate Loss of Hoxa1 on the Hoxa2-mutant background restores normal attachment of the hyoglossus to the greater horn of the hyoid.

Limitations: The rescue is by a second mutation rather than by restoring Hoxa2 or by any treatment, so it establishes that the palate depends on the attachment without showing how the attachment is normally specified. It is also a mouse result with no human counterpart.

Readouts

Hyoglossus attachment to the greater horn of the hyoid

Direction: RESTORED

Interpretation: The attachment blocked in Hoxa2 single mutants is made again in the double mutants.

Show evidence (1 reference)

PMID:10529419 SUPPORT Model Organism

"We show that two compensatory defects, associated with the loss of Hoxa1 function, restore normal attachment of the hyoglossus to the greater horn thereby allowing the palatal shelves to lift and fuse above the flattened tongue."

The attachment readout behind this link.

Show evidence (1 reference)

PMID:10529419 SUPPORT Model Organism

"To understand how these two genes function together in craniofacial development, an allele was generated that disrupts both of these linked genes."

Identifies the compound allele that makes this model informative for the muscle-attachment node.

Conditional Hoxa2 inactivation mouse (Minoux 2013)

Stage-specific conditional inactivation separates the auricular phenotype from the lethal null. Early inactivation abolishes the auricle and duplicates the external auditory canal; late inactivation yields a hypomorphic auricle that the authors take to mimic the human HOXA2 mutant condition. The reciprocal gain-of-function experiment - ectopic Hoxa2 in first-arch crest - duplicates the pinna and eliminates the canal.

Species

Mouse

Genotype

Conditional Hoxa2 inactivation at early versus late gestational stages, plus conditional ectopic Hoxa2 in first-arch neural crest

Publication

PMID:24067355

Pathograph links

Failed Auricular Morphogenesis recapitulates fidelity: high Late inactivation produces auricular hypoplasia resembling the human phenotype. Fate mapping defines the Hoxa2-expressing territory examined in the mouse study.

Limitations: Mouse and human pinna morphology differ substantially, and the model's resemblance to the human condition is the authors' assessment rather than a quantified comparison.

Readouts

Auricle size and presence by stage of Hoxa2 inactivation

Direction: DECREASED

Interpretation: Auricular severity tracks the developmental stage at which Hoxa2 is removed, from complete absence to hypoplasia.

Show evidence (1 reference)

PMID:24067355 SUPPORT Model Organism

"In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."

The stage-dependent auricular readout behind this link.

Pinna lineage by genetic fate mapping

Direction: ALTERED

Interpretation: The investigators trace the auricular territory they call pinna to second-arch mesenchyme; the review literature notes that including the tragus and root changes the anatomical scope.

Show evidence (1 reference)

PMID:24067355 SUPPORT Model Organism

"By genetic fate mapping we found that the mouse auricle (or pinna) derives from the Hoxa2-expressing neural crest-derived mesenchyme of the second pharyngeal arch, and not from a composite of first and second arch mesenchyme as previously proposed based on morphological observation of human embryos."

The lineage readout behind this link.

Show evidence (1 reference)

PMID:24067355 SUPPORT Model Organism

"Thus, Hoxa2 loss- and gain-of-function approaches in mice provide a suitable model to investigate the molecular aetiology of microtia and auricle duplication."

The authors' own statement that the model is suitable for the human aetiology this node represents.

Hoxa2 hypomorphic dosage-series mouse

An allele with about 45% of wild-type transcriptional activity was combined with normal and null alleles to create a dosage series. Second-arch development was more sensitive than hindbrain patterning, and proximal-caudal arch regions were more sensitive than rostro-distal regions. This supports regional dose sensitivity without assigning a residual activity to a human variant.

Species

Mouse

Genotype

Hypomorphic Hoxa2 allele combined with wild-type or null alleles

Publication

PMID:11578867

Pathograph links

Loss of Second Pharyngeal Arch Neural Crest Identity perturbs observes: tissue

Limitations: An engineered transcriptional-dose series does not measure patient missense function or distinguish every cause of human-mouse phenotypic divergence.

Show evidence (2 references)

PMID:11578867 SUPPORT DIRECT Model Organism

"Analysis of these embryos indicates that in general the hindbrain is more resistant to Hoxa2 deficiencies than the second branchial arch."

Different embryonic regions respond differently to experimental Hoxa2 dose.

+ 1 more reference

Show evidence (2 references)

PMID:11578867 SUPPORT DIRECT Model Organism

"We have created a Hoxa2 allele that is about 45% as active in transcription as its wild-type counterpart."

Engineered mouse allele, not a measured residual level in a patient.

PMID:11578867 SUPPORT DIRECT Model Organism

"Analysis of these embryos indicates that in general the hindbrain is more resistant to Hoxa2 deficiencies than the second branchial arch."

Different embryonic regions respond differently to experimental Hoxa2 dose.

{ }

Source YAML

click to show

name: Bilateral Microtia-Deafness-Cleft Palate Syndrome
creation_date: "2026-09-03T00:00:00Z"
category: Mendelian
description: >-
  HOXA2-related bilateral microtia is a developmental ear-malformation spectrum with autosomal recessive and
  dominant presentations. A homozygous homeodomain p.Gln186Lys allele in an Iranian family is associated with
  grade II bilateral microtia, severe to profound mixed hearing impairment and partial cleft palate. Heterozygous
  truncating alleles cause dominant bilateral microtia with variable hearing impairment; mixed loss is documented
  in a dominant family, whereas examined members of another family had normal hearing. These allelic presentations
  are retained as separate subtypes of the same entry.

  HOXA2 assigns second-pharyngeal-arch identity and supports auricular and middle-ear development. Mouse null
  and conditional experiments establish dose- and timing-sensitive developmental functions, but do not demonstrate
  that human ossicular malformations reproduce the complete homeotic transformation of a mouse null. Most of
  the auricle is linked to second-arch mesenchyme; descriptions that include the tragus and auricular root
  require first-arch contributions to be considered. Haploinsufficiency is an inferred mechanism for dominant
  truncating alleles, with impaired HMX1 enhancer activation shown in reporter assays for p.Lys213* and p.Gln235*.
  Residual function of p.Gln186Lys and the relative contributions of tongue mechanics and intrinsic palatal
  fusion to the human cleft remain unresolved.
disease_term:
  preferred_term: bilateral microtia-deafness-cleft palate syndrome
  term:
    id: MONDO:0012854
    label: bilateral microtia-deafness-cleft palate syndrome
parents:
- congenital malformation of the ear
- neurocristopathy
- hereditary disease
synonyms:
- microtia, hearing impairment, and cleft palate
- microtia with or without hearing impairment
- HOXA2-related microtia
- MHIC
references:
- reference: PMID:18394579
  title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
- reference: PMID:23775976
  title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
- reference: PMID:27503514
  title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
- reference: PMID:32649979
  title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.

- reference: DOI:10.3389/fsurg.2022.944223
  title: Integrated microtia and aural atresia management
- reference: PMID:10529419
  title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
- reference: PMID:11578867
  title: Different levels of Hoxa2 are required for particular developmental processes.
- reference: PMID:19653318
  title: Hoxa2 plays a direct role in murine palate development.
- reference: PMID:24067355
  title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
- reference: PMID:7903600
  title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
- reference: PMID:7903601
  title: A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene.
- reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
  title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
- reference: url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
  title: https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
- reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
  title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
- reference: url:https://pmc.ncbi.nlm.nih.gov/articles/4143470/
  title: 'The genetics of auricular development and malformation: new findings in model systems driving future directions for microtia research - PMC'
has_subtypes:
- name: AR-MHIC
  display_name: Autosomal recessive microtia, hearing impairment and cleft palate (HOXA2 p.Q186K)
  description: >-
    The original consanguineous Iranian family has homozygous p.Gln186Lys with bilateral microtia, prelingual
    severe to profound mixed hearing impairment and partial cleft palate. Three examined relatives had marked
    canal stenosis and ossicular abnormalities; one had unilateral inner-ear agenesis. These observations do
    not establish universal features of all biallelic HOXA2 variants.
  genes:
  - preferred_term: HOXA2
    term:
      id: hgnc:5103
      label: HOXA2
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: >-
      Defines the recessive subtype's three-component phenotype in the family
      the disease concept is named for.
- name: AD-Microtia
  display_name: Autosomal dominant nonsyndromic bilateral microtia (HOXA2 haploinsufficiency)
  description: >-
    Heterozygous truncating HOXA2 variants segregate with dominant bilateral microtia. Hearing varies among
    families: the p.Gln235* family studied by Brown and colleagues includes mild to severe mixed loss, whereas
    the examined p.Glu224* family members had normal hearing. The characterized dominant families do not show
    the cleft-palate presentation of the original recessive family. Haploinsufficiency is proposed; transcript
    decay and an exact reduction in patient protein abundance were not measured in these reports.
  genes:
  - preferred_term: HOXA2
    term:
      id: hgnc:5103
      label: HOXA2
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our data extend these conclusions and define HOXA2 haploinsufficiency as the first genetic cause for autosomal-dominant nonsyndromic microtia."
    explanation: Establishes the dominant, haploinsufficiency-driven subtype.
  - reference: PMID:27503514
    reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."
    explanation: >-
      A second, independent dominant family in which the microtia is isolated.

inheritance:
- name: Autosomal recessive
  description: >-
    Homozygosity for the HOXA2 homeodomain missense p.Q186K in a consanguineous
    Iranian family, mapped by genome-wide linkage to 7p14.3-p15.3.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: >-
      Recessive segregation in a consanguineous pedigree establishes the
      biallelic mode for this subtype.
- name: Autosomal dominant
  description: >-
    Heterozygous truncating HOXA2 variants segregate with bilateral microtia in multigeneration pedigrees.
    Hearing impairment is variable, so auricular morphology and audiology both contribute to family assessment.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The HOXA2 variant was segregated with microtia and hearing loss in the family and was not seen in 6,500 individuals sequenced by the NHLBI Exome Sequencing Project or in 218 control individuals sequenced in this study."
    explanation: >-
      Co-segregation with the trait plus absence from large control sets
      supports the dominant allele's causality.
  - reference: PMID:27503514
    reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In our family, sequence analysis detected a heterozygous protein truncating nonsense variant"
    explanation: >-
      Full segregation of a second heterozygous truncating allele in an
      independent family.

pathophysiology:
- name: HOXA2 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Disease-associated alleles include heterozygous truncating variants p.Lys213*, p.Glu224* and p.Gln235*,
    and the recessive homeodomain missense p.Gln186Lys. Dominant haploinsufficiency is inferred from segregation
    and variant class, with impaired enhancer activation measured for two truncating alleles. The p.Gln186Lys
    DNA-binding effect is a homology-model prediction; the founding study did not measure residual protein
    activity or show functional complementation.
  genes:
  - preferred_term: HOXA2
    term:
      id: hgnc:5103
      label: HOXA2
  molecular_functions:
  - preferred_term: DNA-binding transcription factor activity
    modifier: LOSS_OF_FUNCTION
    term:
      id: GO:0003700
      label: DNA-binding transcription factor activity
  biological_processes:
  - preferred_term: anterior/posterior pattern specification
    modifier: ABNORMAL
    term:
      id: GO:0009952
      label: anterior/posterior pattern specification
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Exome sequencing of affected family members detected only seven shared, rare, heterozygous, nonsynonymous variants, including one protein truncating variant, a HOXA2 nonsense change (c.703C>T, p.Q235*)."
    explanation: Identifies the truncating allele class underlying the dominant form.
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Subsequent DNA sequence analysis of the HOXA1 and HOXA2 homeobox genes from the candidate region identified an interesting HOXA2 homeodomain variant: a change in a highly conserved amino acid (p.Q186K)."
    explanation: Identifies the recessive homeodomain missense allele.
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    directness: INDIRECT
    snippet: "In the model of the mutant homeodomain, the position of the mutant lysine side chain is consistently farther away from a nearby phosphate group; this altered position results in the loss of a hydrogen bond and affects the DNA-binding activity."
    explanation: >-
      The DNA-binding consequence of p.Q186K is a homology-modelling prediction,
      not a measurement; recorded as computational and indirect.
  downstream:
  - target: Impaired Transactivation of the Long-Range HMX1 Enhancer
    description: >-
      The p.Lys213* and p.Gln235* variants impair activation of the long-range HMX1 enhancer in a dual-luciferase
      assay; the abstract does not establish complete abolition of activity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of the long-range enhancer of HMX1."
      explanation: >-
        The reporter assay directly measures impaired enhancer activation by these two variants, rather than
        proving complete absence of activity in patients.
  - target: Loss of Second Pharyngeal Arch Neural Crest Identity
    description: >-
      HOXA2 is the selector gene that assigns second-arch identity to the
      cranial neural crest cells populating that arch; without it they adopt
      first-arch identity.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:7903601
      reference_title: "A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The ground pattern program appears to be modified in the mouse first arch by a Hox-independent process, whereas Hoxa-2 acts as a selector gene in the second arch."
      explanation: >-
        Establishes HOXA2's selector-gene role in the second arch, the step this
        edge represents.
  - target: Intrinsic Palatal Shelf Fusion Defect
    description: >-
      A route that does not run through the pharyngeal arches at all. Hoxa2 is
      expressed in the palate itself, and knocking it down there reduces the
      rate at which the shelves fuse. The intermediates the authors name -
      increased cell proliferation, and de-repression of the Hoxa2 targets
      Msx1, Bmp4, Barx1 and Ptx1 - are candidates they identify but do not
      trace to the fusion failure.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:19653318
      reference_title: Hoxa2 plays a direct role in murine palate development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "Knocking down Hoxa2 expression with antisense retroviral constructs resulted in decreased fusion rates than corresponding controls."
      explanation: >-
        Loss of Hoxa2 in the palate reduces shelf fusion, the step this edge
        represents; the experiment is a knockdown in palate culture.
      directness: INDIRECT
    - reference: PMID:19653318
      reference_title: Hoxa2 plays a direct role in murine palate development.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Hoxa2 also repressed the expression of its downstream targets Msx1, Bmp4, Barx1, and Ptx1 within the palate."
      explanation: >-
        Altered target-gene expression provides candidates, but the study does not trace a complete causal
        chain from any one target to failed fusion.

      directness: INDIRECT
  - target: External Auditory Canal Stenosis
    description: >-
      The HOXA2 genotype segregates with canal narrowing in the recessive family; the specific developmental
      intermediates remain unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        The results of high-resolution CT scanning confirmed that the external auditory canal was severely
        narrowed bilaterally in the cartilaginous part of the auditory canal and almost atretic in part of
        the bony portion in all patients.
      explanation: >-
        CT in the three examined recessive-family members, not every person with HOXA2-related disease.
  - target: Unilateral Inner-Ear Aplasia
    description: >-
      The inner-ear malformation co-occurs with homozygous p.Gln186Lys in one relative. Its developmental relation
      to HOXA2 remains uncertain and should not be attributed to ossicular homeosis.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        The inner-ear structures were normal in patients V: 2 and V: 3, but there were no inner-ear structures
        on the left side for IV: 3.
      explanation: >-
        Unilateral inner-ear agenesis in one recessive-family member, with normal inner-ear anatomy in the
        other two imaged relatives.
  - target: Unilateral Facial Paresis
    description: >-
      Facial weakness was observed in one homozygous relative; a specific neural developmental mechanism was
      not established.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        Individual number V: 2 also had a paresis on the right side of the face.
      explanation: >-
        Single affected relative; facial-nerve hypoplasia was suspected clinically but was not confirmed by
        brain MRI.
- name: Impaired Transactivation of the Long-Range HMX1 Enhancer
  biological_scale: MOLECULAR
  description: >-
    The p.Lys213* and p.Gln235* variants impair activation of a long-range HMX1 enhancer in dual-luciferase
    assays. Prior mouse work places Hoxa2 upstream of Hmx1 in ear development. The assay links these patient
    variants to a candidate effector, but does not measure the entire developmental pathway in human auricular
    tissue.
  genes:
  - preferred_term: HOXA2
    term:
      id: hgnc:5103
      label: HOXA2
  biological_processes:
  - preferred_term: ear morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0042471
      label: ear morphogenesis
  evidence:
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In mouse, Hoxa2 can bind to a long-range enhancer and regulate expression of the Hmx1 gene, which is a crucial transcription factor in eye and ear development."
    explanation: >-
      Establishes the HOXA2-HMX1 enhancer relationship; demonstrated in mouse.
    quote_role: BACKGROUND
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: >-
      Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of
      the long-range enhancer of HMX1.
    explanation: >-
      Direct reporter result for p.Lys213* and p.Gln235*; impairment is not equivalent to a proven null effect.
  downstream:
  - target: Failed Auricular Morphogenesis
    description: >-
      Reduced HMX1 activation is the candidate route from the HOXA2 alleles to
      the external ear defect; the link to the human auricle phenotype is
      inferred, not measured in patient tissue.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "In mouse, Hoxa2 can bind to a long-range enhancer and regulate expression of the Hmx1 gene, which is a crucial transcription factor in eye and ear development."
      explanation: >-
        Supports HMX1 as an ear-development effector downstream of HOXA2;
        the connection to the human auricle is an inference from this.

      directness: INDIRECT
      quote_role: BACKGROUND
- name: Loss of Second Pharyngeal Arch Neural Crest Identity
  biological_scale: CELLULAR
  conforms_to: "pharyngeal_arch_patterning_serial_homology#Cranial Neural Crest and Pharyngeal Arch Program Perturbation"
  description: >-
    Hoxa2-null mouse embryos retain rhombomeric and neural crest segmentation but lose normal second-arch mesenchymal
    identity, producing first-arch-like skeletal derivatives. This supports an identity-assignment role. The
    cited abstract does not separately demonstrate normal migration, cell number or survival, and the complete-null
    result should not be equated with every human HOXA2 allele.
  cell_types:
  - preferred_term: second-arch neural crest cell
    term:
      id: CL:0011012
      label: neural crest cell
  biological_processes:
  - preferred_term: neural crest cell development
    modifier: ABNORMAL
    term:
      id: GO:0014032
      label: neural crest cell development
  - preferred_term: pharyngeal system development
    modifier: ABNORMAL
    term:
      id: GO:0060037
      label: pharyngeal system development
  locations:
  - preferred_term: second pharyngeal arch
    term:
      id: UBERON:0003066
      label: pharyngeal arch 2
  evidence:
  - reference: PMID:7903601
    reference_title: "A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "While rhombomeric and neural crest cell (NCC) segmentation was not affected, mesenchymal NCC derivatives of the second arch were lacking, and second arch mesenchymal NCC identity was changed to first arch identity, resulting in homeotic transformation of second to first arch skeletal elements."
    explanation: >-
      Direct mouse evidence for preserved segmentation with changed second-arch identity; migration and survival
      were not separately established by this quotation.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/4143470/
    reference_title: 'The genetics of auricular development and malformation: new findings in model systems driving future directions for microtia research - PMC'
    supports: SUPPORT
    evidence_source: OTHER
    directness: DIRECT
    snippet: >-
      By definition, the pinna encompasses all external structures of the ear, including the tragus and root.
    explanation: >-
      This review qualifies the terminology of the mouse lineage claim; it is not a new lineage-tracing experiment.
    quote_role: REVIEW_SYNTHESIS
  downstream:
  - target: Homeotic Transformation of Second-Arch Skeletal Derivatives
    description: >-
      Mis-specified second-arch crest builds first-arch structures instead of
      second-arch ones.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:7903600
      reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Histological analysis suggested that this duplication resulted from the transformation of skeletal elements derived from the second branchial arch into more anterior structures, resulting in a duplication of Meckel's cartilage adjacent to the otic capsule."
      explanation: >-
        Independently documents the transformation of second-arch skeletal
        elements toward anterior (first-arch) structures.
  - target: Failed Auricular Morphogenesis
    description: >-
      Hoxa2-expressing second-arch mesenchyme supplies the auricular territory examined in the mouse fate-mapping
      study. Its loss disrupts that territory; the result should not be generalized to every human external-ear
      structure.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24067355
      reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "By genetic fate mapping we found that the mouse auricle (or pinna) derives from the Hoxa2-expressing neural crest-derived mesenchyme of the second pharyngeal arch, and not from a composite of first and second arch mesenchyme as previously proposed based on morphological observation of human embryos."
      explanation: >-
        Mouse fate mapping supports a major second-arch contribution. The extent depends on how the auricle
        is defined; the tragus and root require separate consideration.
  - target: Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles
    description: >-
      The same rhombencephalic neural crest that builds the craniofacial
      skeleton also patterns the craniofacial muscles, and Hoxa2 mutants have
      abnormal attachments and trajectories of the extrinsic tongue and hyoid
      muscles. How the arch-identity lesion produces that particular
      mis-routing was not worked out, so the intermediates are recorded as
      unknown.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10529419
      reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The rhombencephalic neural crest play several roles in craniofacial development. They give rise to the cranial sensory ganglia and much of the craniofacial skeleton, and are vital for patterning of the craniofacial muscles."
      explanation: >-
        States that craniofacial muscle patterning depends on the same neural
        crest population whose identity is lost at this node.

  - target: Middle-Ear Ossicular Dysplasia
    description: >-
      The relationship of second-arch patterning to human ossicular dysplasia is inferred from developmental
      models and family anatomy; the intervening human developmental steps have not been measured.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
      explanation: >-
        CT findings in the three examined members of the recessive family; fixation was described as apparent
        on imaging.
- name: Homeotic Transformation of Second-Arch Skeletal Derivatives
  biological_scale: TISSUE
  conforms_to: "pharyngeal_arch_patterning_serial_homology#Disrupted Pharyngeal-Arch Patterning and Neural-Crest Skeletogenesis"
  description: >-
    Hoxa2-null mice lose second-arch skeletal elements and develop duplicated first-arch structures, including
    middle-ear ossification centers and a second Meckel cartilage beside the otic capsule. This is a model-organism
    developmental phenotype. Human imaging and surgery establish ossicular dysplasia and fixation, but do not
    demonstrate this complete homeotic duplication. This node has no downstream human-phenotype links because
    the complete homeotic transformation is documented only in mice.
  cell_types:
  - preferred_term: neural crest cell
    term:
      id: CL:0011012
      label: neural crest cell
  biological_processes:
  - preferred_term: embryonic cranial skeleton morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0048701
      label: embryonic cranial skeleton morphogenesis
  - preferred_term: embryonic skeletal system morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0048704
      label: embryonic skeletal system morphogenesis
  locations:
  - preferred_term: auditory ossicle
    term:
      id: UBERON:0001686
      label: auditory ossicle bone
  evidence:
  - reference: PMID:7903600
    reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Analysis of stained skeletons revealed that homozygous mutant animals contained multiple cranial skeletal defects, including a duplication of the ossification centers of the bones of the middle ear."
    explanation: >-
      Documents the middle-ear skeletal consequence of the second-arch
      transformation.
  - reference: PMID:7903600
    reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Skeletal elements normally derived from the second arch were absent in the mutants."
    explanation: >-
      Confirms loss, not merely mis-shaping, of the second-arch skeletal
      derivatives.
- name: Middle-Ear Ossicular Dysplasia
  description: >-
    Malformed or fixed ossicles are documented directly in both recessive and dominant HOXA2 families. Recessive
    cases had a malformed chain apparently fixed by an incomplete atretic plate; dominant cases included abnormal
    stapes crura, absent stapedial tendon and a rigid chain. These observations support a conductive deficit
    without assuming mouse-like duplication in humans.
  biological_scale: TISSUE
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
    explanation: >-
      CT findings in the three examined members of the recessive family; fixation was described as apparent
      on imaging.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      In individual II.2, the stapes was noted to have a thickened posterior crus and an absent anterior crus,
      and the stapedial tendon was absent.
    explanation: >-
      Operative observation in one dominant-family member.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Individual II.4 had a rigid ossicular chain.
    explanation: >-
      Operative observation in another member of the same dominant family.
  downstream:
  - target: Hearing Impairment
    description: >-
      Ossicular malformation and fixation impair sound transmission and can account for the conductive component.
      This mechanism does not explain a sensorineural component.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
      explanation: >-
        CT findings in the three examined members of the recessive family; fixation was described as apparent
        on imaging.
  - target: Mixed Hearing Impairment
    description: >-
      Ossicular malformation and fixation impair sound transmission and can account for the conductive component.
      This mechanism does not explain a sensorineural component.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
      explanation: >-
        CT findings in the three examined members of the recessive family; fixation was described as apparent
        on imaging.
  - target: Abnormal Middle-Ear Ossicles
    description: >-
      The structural abnormality is the directly observed phenotype.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: DIRECT
      snippet: >-
        In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
      explanation: >-
        CT findings in the three examined members of the recessive family; fixation was described as apparent
        on imaging.
  locations:
  - preferred_term: auditory ossicle bone
    term:
      id: UBERON:0001686
      label: auditory ossicle bone
- name: Failed Auricular Morphogenesis
  biological_scale: TISSUE
  conforms_to: "pharyngeal_arch_patterning_serial_homology#Serially Homologous Craniofacial Malformation Across Arch Derivatives"
  description: >-
    The auricle fails to form normally. Timing determines severity in the mouse:
    early Hoxa2 inactivation abolishes the auricle and duplicates the external
    auditory canal, while late inactivation leaves a hypomorphic auricle
    resembling the human phenotype. Hoxa2 acts on pinna morphogenesis partly
    through BMP signalling and Eya1 expression.
  biological_processes:
  - preferred_term: ear morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0042471
      label: ear morphogenesis
  - preferred_term: face morphogenesis
    modifier: ABNORMAL
    term:
      id: GO:0060325
      label: face morphogenesis
  locations:
  - preferred_term: auricle
    term:
      id: UBERON:0001757
      label: pinna
  evidence:
  - reference: PMID:24067355
    reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."
    explanation: >-
      Establishes both the auricular defect and its dependence on the timing of
      Hoxa2 loss.
  - reference: PMID:24067355
    reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Hoxa2 partly controls the morphogenesis of the pinna through the BMP signalling pathway and expression of Eya1, which in humans is involved in branchio-oto-renal syndrome."
    explanation: >-
      Names the downstream effectors through which HOXA2 shapes the pinna;
      the authors qualify this as partial control.
  downstream:
  - target: Bilateral Microtia
    description: >-
      Failure of pinna morphogenesis presents clinically as bilateral microtia.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:24067355
      reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Thus, Hoxa2 loss- and gain-of-function approaches in mice provide a suitable model to investigate the molecular aetiology of microtia and auricle duplication."
      explanation: >-
        The authors position the Hoxa2 auricular phenotype as the model of human
        microtia aetiology.

    - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
      reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: DIRECT
      snippet: >-
        Based on the abnormalities observed in this family, the disease was categorized as microtia grade II.
      explanation: >-
        Direct clinical classification of the original family.
  - target: Thickened Helices
    description: >-
      Abnormal auricular morphogenesis includes the thickened helices observed in the dominant family.
    causal_link_type: DIRECT
    evidence:
    - reference: PMID:23775976
      reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: DIRECT
      snippet: >-
        All five affected family members had small, malformed ears with a thickened helix and a superficial
        postauricular sulcus (Fig. 1B).
      explanation: >-
        Clinical morphology in five enrolled affected members of the p.Gln235* family.
  - target: Underdeveloped Antitragus
    description: >-
      Antitragal underdevelopment is one component of the documented auricular dysplasia.
    causal_link_type: DIRECT
    evidence:
    - reference: url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
      reference_title: https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: DIRECT
      snippet: >-
        underdeveloped antitragus, serpiginous antihelix stem, deep incisura between tragus and antitragus
        with a laterally dislocated hypoplastic lobe.
      explanation: >-
        Proband morphology from the author thesis describing the same p.Glu224* pedigree later reported in
        PMID:27503514; this is not an additional family.
- name: Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles
  biological_scale: TISSUE
  description: >-
    In Hoxa2 mutant mice the attachments and trajectories of the extrinsic
    tongue and hyoid muscles are abnormal. The abnormal trajectory of two of
    them, the styloglossus and the stylohyoideus, blocks the attachment of the
    hyoglossus to the greater horn of the hyoid, and that blocked attachment
    correlated exactly with the presence of cleft palate in those animals. The
    node is mouse-derived; no comparable observation has been reported in
    HOXA2-mutant patients, in whom tongue and hyoid muscle anatomy has not been
    described.
  biological_processes:
  - preferred_term: muscle attachment
    modifier: ABNORMAL
    term:
      id: GO:0016203
      label: muscle attachment
  locations:
  - preferred_term: extrinsic muscle of tongue
    term:
      id: UBERON:0001575
      label: extrinsic muscle of tongue
  - preferred_term: hyoglossus muscle
    term:
      id: UBERON:0001572
      label: hyoglossus muscle
  - preferred_term: hyoid bone greater horn
    term:
      id: UBERON:0003997
      label: hyoid bone greater horn
  evidence:
  - reference: PMID:10529419
    reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We also uncovered multiple defects in the attachments and trajectories of the extrinsic tongue and hyoid muscles in Hoxa2 mutants."
    explanation: >-
      Records the muscle attachment and trajectory defects this node
      represents, in Hoxa2 mutants.
  - reference: PMID:10529419
    reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "the abnormal trajectory of two of these muscles, the styloglossus and the stylohyoideus, blocked the attachment of the hyoglossus to the greater horn of the hyoid, which in turn correlated exactly with the presence of cleft palate in Hoxa2 mutants"
    explanation: >-
      Names the specific muscles involved and reports the exact correlation
      between the blocked hyoglossus attachment and cleft palate, which is the
      observation - as distinct from the interpretation on the next node.
  downstream:
  - target: Abnormal Tongue Posture Obstructing Palatal Shelf Closure
    description: >-
      Barrow and Capecchi's interpretation of the correlation: the hyoglossus,
      unable to reach the greater horn, cannot depress the lateral edges of the
      tongue. Support for the link is the rescue arm - restoring the attachment
      in Hoxa1/Hoxa2 double mutants restores palatal closure over a flattened
      tongue - rather than direct observation of tongue posture in the single
      mutants.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10529419
      reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We show that two compensatory defects, associated with the loss of Hoxa1 function, restore normal attachment of the hyoglossus to the greater horn thereby allowing the palatal shelves to lift and fuse above the flattened tongue."
      explanation: >-
        The rescue: restoring the hyoglossus attachment restores both the
        flattened tongue and palatal shelf fusion, tying this node to the next.

      directness: INDIRECT
- name: Abnormal Tongue Posture Obstructing Palatal Shelf Closure
  biological_scale: TISSUE
  description: >-
    The proposed mechanical consequence, stated by its authors as a suggestion
    rather than an observation: with the hyoglossus unable to depress the
    lateral edges of the tongue, the tongue adopts an abnormal posture that
    blocks closure of the palatal shelves. It is not the only published account
    of the Hoxa2 cleft - see the
    hoxa2_cleft_palate_tongue_versus_intrinsic_palate discussion and the
    Intrinsic Palatal Shelf Fusion Defect node - and neither account has been
    tested in a human patient.
  biological_processes:
  - preferred_term: secondary palate development
    modifier: ABNORMAL
    term:
      id: GO:0062009
      label: secondary palate development
  locations:
  - preferred_term: tongue
    term:
      id: UBERON:0001723
      label: tongue
  - preferred_term: secondary palatal shelf
    term:
      id: UBERON:0005619
      label: secondary palatal shelf
  evidence:
  - reference: PMID:10529419
    reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We suggest that the hyoglossus, whose function is to depress the lateral edges of the tongue, when unable to make its proper attachment to the greater horn of the hyoid, forces the tongue to adopt an abnormal posture which blocks closure of the palatal shelves."
    explanation: >-
      The proposal this node represents, quoted in full so that its status as
      the authors' suggestion is visible in the evidence itself.
  downstream:
  - target: Cleft Palate
    description: >-
      Shelves that do not close leave a cleft. In Hoxa1/Hoxa2 double mutants,
      where the hyoglossus attachment is restored, the penetrance of cleft
      palate falls sharply - the experimental result that ties the obstruction
      to the cleft.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:10529419
      reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Unexpectedly, in Hoxa1/Hoxa2 double mutants, the penetrance of cleft palate is dramatically reduced."
      explanation: >-
        Restoring the attachment sharply reduces the cleft, which is what makes
        this edge causal rather than merely correlative.

      directness: INDIRECT
- name: Intrinsic Palatal Shelf Fusion Defect
  biological_scale: TISSUE
  description: >-
    A second, independent route to the same cleft. Hoxa2 is expressed in the
    developing palate itself between E12.5 and E15.5, and Hoxa2-null palatal
    shelves cultured in the absence of the tongue fuse at lower rates than
    heterozygous or wild-type shelves, as do shelves in which Hoxa2 is knocked
    down with antisense constructs. Null palates show an overall increase in
    cell proliferation, and Hoxa2 represses Msx1, Bmp4, Barx1 and Ptx1 within
    the palate. On the authors' reading the mouse cleft is therefore not solely
    secondary to the tongue. Whether either route operates in HOXA2-mutant
    humans is unknown.
  biological_processes:
  - preferred_term: secondary palate development
    modifier: ABNORMAL
    term:
      id: GO:0062009
      label: secondary palate development
  locations:
  - preferred_term: secondary palatal shelf
    term:
      id: UBERON:0005619
      label: secondary palatal shelf
  evidence:
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "we detected Hoxa2 expression in the developing palate at both the mRNA and protein levels between embryonic day (E) 12.5 and E15.5"
    explanation: >-
      Hoxa2 is expressed in the palate itself, the precondition for a route
      that does not run through the tongue.
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures."
    explanation: >-
      Palatal shelves fuse less well without Hoxa2 even when the tongue is
      removed from the system - explant culture, hence IN_VITRO.
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results demonstrate the cleft palate phenotype of Hoxa2 null embryos is not solely due to abnormal tongue musculature, and indicate a direct role of Hoxa2 in regulating murine palatogenesis."
    explanation: >-
      The authors' own conclusion that the tongue route is not the whole
      account, which is why this node is curated alongside it rather than
      instead of it.
  downstream:
  - target: Cleft Palate
    description: >-
      The explant and mouse findings support a palate-intrinsic contribution to clefting, but do not establish
      its quantitative contribution or demonstrate the corresponding intermediate in affected humans.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:19653318
      reference_title: Hoxa2 plays a direct role in murine palate development.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "These results demonstrate the cleft palate phenotype of Hoxa2 null embryos is not solely due to abnormal tongue musculature, and indicate a direct role of Hoxa2 in regulating murine palatogenesis."
      explanation: >-
        The authors' own conclusion that the tongue route is not the whole
        account, which is why this node is curated alongside it rather than
        instead of it.
      directness: INDIRECT
phenotypes:
- name: Bilateral Microtia
  category: Craniofacial
  description: >-
    Bilateral auricular malformation is the characteristic feature in recessive and dominant pedigrees. The
    original recessive family was classified as grade II microtia, with recognizable helix, tragus and antitragus.
    Severity and detailed morphology differ between families.
  phenotype_term:
    preferred_term: Bilateral microtia
    term:
      id: HP:0008551
      label: Microtia
    laterality: BILATERAL
  notes: >-
    Pedigree observations do not supply a population-level penetrance or frequency estimate.
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: Bilateral microtia in the recessive family.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a three-generation family with bilateral microtia and hearing loss segregating as an autosomal dominant trait."
    explanation: Bilateral microtia in the first dominant family.
  - reference: PMID:27503514
    reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."
    explanation: Bilateral microtia in a second dominant family.
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here, we collect two Chinese families with non-syndromic bilateral microtia."
    explanation: Bilateral microtia in two further dominant families.

  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Based on the abnormalities observed in this family, the disease was categorized as microtia grade II.
    explanation: >-
      Clinical grade in the original recessive family, not a universal grade for dominant microtia.
- name: Hearing Impairment
  category: Auditory
  description: >-
    Hearing impairment varies across HOXA2 families. The original recessive family had prelingual severe to
    profound mixed loss; the p.Gln235* dominant family had mild to severe mixed loss with one illustrated conductive-only
    ear. In the p.Glu224* pedigree, the proband had normal otoacoustic emissions and the examined mother and
    grandfather had normal audiometry.
  phenotype_term:
    preferred_term: Hearing impairment
    term:
      id: HP:0000365
      label: Hearing impairment
  notes: >-
    Normal hearing in an affected family member does not exclude dominant HOXA2-related microtia.
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a three-generation family with bilateral microtia and hearing loss segregating as an autosomal dominant trait."
    explanation: Hearing loss co-segregating in a dominant family.
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, only four HOXA2 mutations were reported in families with autosomal-recessive or dominant microtia, with or without hearing impairment."
    explanation: >-
      The literature summary records hearing impairment as a variable rather
      than constant feature of HOXA2-related microtia.

    quote_role: BACKGROUND
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral
      mixed hearing loss (Fig. 1C).
    explanation: >-
      Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one
      relative, so not every tested ear had both components.
  - reference: url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
    reference_title: https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      In both relatives audiometric testing had unremarkable results, as well as intraoral examination.
    explanation: >-
      Normal audiometry in the proband mother and maternal grandfather in the p.Glu224* pedigree; the thesis
      and journal article describe the same family.
- name: Mixed Hearing Impairment
  category: Auditory
  description: >-
    Mixed hearing impairment occurs in both recessive and dominant HOXA2 disease. It was symmetric and severe
    to profound in the original recessive family and mild to severe in the tested p.Gln235* dominant relatives.
    Ossicular abnormalities explain a conductive component. Unilateral inner-ear agenesis explains an anatomic
    substrate in one recessive ear, but does not resolve the sensorineural component in other ears with normal
    or unreported imaging.
  phenotype_term:
    preferred_term: Mixed hearing impairment
    term:
      id: HP:0000410
      label: Mixed hearing impairment
    laterality: BILATERAL
  notes: >-
    The dominant-family figure also documents a conductive-only ear; severity and audiological subtype should
    be assessed per ear.
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: >-
      Specifies the mixed, symmetrical, severe-to-profound character of the
      recessive subtype's hearing loss.

  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral
      mixed hearing loss (Fig. 1C).
    explanation: >-
      Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one
      relative, so not every tested ear had both components.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      All four affected family individuals showed bilateral symmetric severe to profound mixed hearing impairment
      affecting all frequencies and leading to a flat audiometric shape.
    explanation: >-
      The four affected members of the original recessive family; this severity should not be transferred to
      all dominant cases.
- name: Cleft Palate
  category: Craniofacial
  subtype: AR-MHIC
  description: >-
    Partial cleft palate is documented in the original homozygous p.Gln186Lys family. Examined members of the
    p.Gln235* and p.Glu224* dominant pedigrees had an intact palate or unremarkable intraoral examination.
    Mouse null clefting supports developmental relevance but does not establish the specific mechanism of the
    human cleft.
  phenotype_term:
    preferred_term: Cleft palate
    term:
      id: HP:0000175
      label: Cleft palate
  notes: >-
    The subtype association is based on a small number of characterized pedigrees; it is not a universal genotype-phenotype
    rule.
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: Partial cleft palate in the recessive family.
  - reference: PMID:27503514
    reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HOXA2 biallelic mutations were also described in an inbreed family with autosomal recessive microtia, hearing impairment and incomplete cleft palate."
    explanation: >-
      The later article summarizes the same recessive family; it does not provide independent replication of
      its cleft phenotype.
    quote_role: BACKGROUND
  - reference: PMID:7903600
    reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."
    explanation: >-
      Cleft palate in the homozygous mouse null provides model evidence for developmental relevance; the abstract
      does not supply a penetrance denominator.

- name: External Auditory Canal Stenosis
  description: >-
    Three imaged recessive relatives had severe bilateral canal narrowing, with near-atresia of portions of
    the bony canal. Canals were normally formed in the characterized p.Gln235* dominant family.
  phenotype_term:
    preferred_term: Stenosis of the external auditory canal
    term:
      id: HP:0000402
      label: Stenosis of the external auditory canal
    laterality: BILATERAL
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      The results of high-resolution CT scanning confirmed that the external auditory canal was severely narrowed
      bilaterally in the cartilaginous part of the auditory canal and almost atretic in part of the bony portion
      in all patients.
    explanation: >-
      CT in the three examined recessive-family members, not every person with HOXA2-related disease.
  subtype: AR-MHIC
- name: Abnormal Middle-Ear Ossicles
  description: >-
    Ossicular malformation and apparent fixation were imaged in three recessive relatives. Dominant-family
    surgery documented abnormal stapes crura, absent stapedial tendon or a rigid ossicular chain.
  phenotype_term:
    preferred_term: Abnormality of the middle ear ossicles
    term:
      id: HP:0004452
      label: Abnormality of the middle ear ossicles
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      In all three patients the malformed ossicular chain seemed fixated by an incomplete atretic plate.
    explanation: >-
      CT findings in the three examined members of the recessive family; fixation was described as apparent
      on imaging.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      In individual II.2, the stapes was noted to have a thickened posterior crus and an absent anterior crus,
      and the stapedial tendon was absent.
    explanation: >-
      Operative observation in one dominant-family member.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Individual II.4 had a rigid ossicular chain.
    explanation: >-
      Operative observation in another member of the same dominant family.
- name: Unilateral Inner-Ear Aplasia
  description: >-
    Left inner-ear agenesis was confirmed by CT and MRI in one member of the recessive family. The other two
    imaged relatives had normal inner-ear structures.
  phenotype_term:
    preferred_term: Aplasia of the inner ear
    term:
      id: HP:0011372
      label: Aplasia of the inner ear
    laterality: LEFT
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      The inner-ear structures were normal in patients V: 2 and V: 3, but there were no inner-ear structures
      on the left side for IV: 3.
    explanation: >-
      Unilateral inner-ear agenesis in one recessive-family member, with normal inner-ear anatomy in the other
      two imaged relatives.
  subtype: AR-MHIC
- name: Unilateral Facial Paresis
  description: >-
    Right facial paresis occurred in one examined member of the recessive family. Right facial-nerve hypoplasia
    was suspected clinically; brain MRI was normal and did not confirm that explanation.
  phenotype_term:
    preferred_term: Unilateral facial palsy
    term:
      id: HP:0012799
      label: Unilateral facial palsy
    laterality: RIGHT
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Individual number V: 2 also had a paresis on the right side of the face.
    explanation: >-
      Single affected relative; facial-nerve hypoplasia was suspected clinically but was not confirmed by brain
      MRI.
  subtype: AR-MHIC
- name: Thickened Helices
  description: >-
    The five enrolled affected members of the p.Gln235* dominant family had thickened helices and a superficial
    postauricular sulcus.
  phenotype_term:
    preferred_term: Thickened helices
    term:
      id: HP:0000391
      label: Thickened helices
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      All five affected family members had small, malformed ears with a thickened helix and a superficial postauricular
      sulcus (Fig. 1B).
    explanation: >-
      Clinical morphology in five enrolled affected members of the p.Gln235* family.
  subtype: AD-Microtia
- name: Underdeveloped Antitragus
  description: >-
    The p.Glu224* proband had an underdeveloped antitragus as part of complex auricular dysplasia, including
    a serpiginous antihelix and laterally displaced hypoplastic lobe. These detailed observations come from
    the author thesis on the same published pedigree.
  phenotype_term:
    preferred_term: Underdeveloped antitragus
    term:
      id: HP:0011251
      label: Underdeveloped antitragus
  evidence:
  - reference: url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
    reference_title: https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      underdeveloped antitragus, serpiginous antihelix stem, deep incisura between tragus and antitragus with
      a laterally dislocated hypoplastic lobe.
    explanation: >-
      Proband morphology from the author thesis describing the same p.Glu224* pedigree later reported in PMID:27503514;
      this is not an additional family.
  subtype: AD-Microtia
genetic:
- name: HOXA2 pathogenic variants
  association: Causal
  relationship_type: CAUSATIVE
  presence: Pathogenic
  gene_term:
    preferred_term: HOXA2
    term:
      id: hgnc:5103
      label: HOXA2
  notes: >-
    HOXA2 lies in the HOXA cluster at 7p15.2. Linkage and segregation established the recessive family; exome
    or targeted sequencing identified dominant truncating alleles. The curated variants are examples, not an
    exhaustive or current worldwide allele count. Haploinsufficiency is inferred, and the cited family studies
    did not measure patient nonsense-mediated decay or a precise 50% protein reduction.
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genome-wide linkage analysis localized the responsible gene to chromosome 7p14.3-p15.3 with a maximum multi-point LOD score of 4.17."
    explanation: >-
      Linkage to the HOXA cluster interval is the mapping evidence that
      identified the gene.
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Next generation sequencing identified two heterozygous nonsense HOXA2 mutations, one in each family."
    explanation: >-
      Two independent families carrying heterozygous nonsense alleles; p.Gln235* recurs from an earlier pedigree.
  variants:
  - name: p.Q186K homeodomain missense (recessive)
    description: >-
      Homozygous homeodomain missense p.Gln186Lys segregated in the original recessive family and was absent
      from the reported control panels. The founding paper predicts altered DNA binding by homology modeling
      but does not measure residual function. Protein notation avoids conflating historical nucleotide numbering
      with a normalized transcript-specific HGVS description.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:18394579
      reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The variant was not found in 231 Iranian and 109 Belgian control samples."
      explanation: Control-panel absence supporting pathogenicity of p.Q186K.
  - name: p.Q235* nonsense (dominant)
    description: >-
      A recurrent heterozygous nonsense allele, found independently in a
      three-generation US family and in one of the two Chinese families.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "One mutation (c.637A > T, p.Lys213*) is newly reported, while the other one (c.703C > T,p.Gln235*) is consistent with a previous report."
      explanation: Documents recurrence of p.Gln235* across unrelated families.
  - name: p.E224* nonsense (dominant)
    description: >-
      A heterozygous truncating allele segregating in all affected members of a
      five-generation Italian family and absent from public databases.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:27503514
      reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "In our family, sequence analysis detected a heterozygous protein truncating nonsense variant"
      explanation: Defines the allele and its segregation.

    - reference: url:https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
      reference_title: https://fair.unifg.it/retrieve/de2a638f-fc40-8577-e053-3705fe0aa5f3/tesi%20definitiva.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: DIRECT
      snippet: >-
        Sanger analysis of the index patient (V:1) identified a previously unreported heterozygous variant
        ... NM_006735.3: c.670G>T, p.(Glu224*) ... in the second exon of the HOXA2 gene (Figure 17a).
      explanation: >-
        Primary thesis data identifying p.Glu224* in the same Italian pedigree as the journal article.
  - name: p.Lys213* nonsense (dominant)
    description: >-
      Heterozygous p.Lys213* was found in one Chinese family; a dual-luciferase assay showed impaired HMX1
      enhancer activation. The result supports loss of activity without establishing patient transcript decay.
    clinical_significance: PATHOGENIC
    evidence:
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "One mutation (c.637A > T, p.Lys213*) is newly reported, while the other one (c.703C > T,p.Gln235*) is consistent with a previous report."
      explanation: >-
        Identifies the newly reported p.Lys213* allele and distinguishes it from recurrent p.Gln235*.
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      directness: DIRECT
      snippet: >-
        Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation
        of the long-range enhancer of HMX1.
      explanation: >-
        Direct reporter result for p.Lys213* and p.Gln235*; impairment is not equivalent to a proven null effect.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  notes: >-
    Published evidence consists of a small number of pedigrees. No HOXA2-specific population prevalence is
    established by these reports; all-cause microtia birth prevalence should not be assigned to this molecular
    disorder.
  evidence:
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To date, only four HOXA2 mutations were reported in families with autosomal-recessive or dominant microtia, with or without hearing impairment."
    explanation: >-
      A time-specific literature summary illustrates sparse pedigree evidence; it does not establish a current
      worldwide family count or population prevalence.
    quote_role: BACKGROUND
diagnosis:
- name: Clinical and audiological examination
  description: >-
    Inspect both auricles, ear canals, palate and facial movement, and obtain age-appropriate air- and bone-conduction
    hearing thresholds. Mixed loss can occur in either inheritance subtype, and a normal hearing result does
    not exclude dominant HOXA2 microtia. General microtia guidance recommends diagnostic ABR by two to three
    months, followed by behavioral assessment as development permits.
  evidence:
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: >-
      The clinical and audiological characterisation that defines the
      presentation.
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      A diagnostic ABR should be performed as early as possible.
    explanation: >-
      General microtia diagnostic guidance, extrapolated to affected infants.
    quote_role: REVIEW_SYNTHESIS
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Air conduction and bone conduction testing should performed.
    explanation: >-
      The source recommends testing both pathways; the quotation preserves its grammatical omission.
    quote_role: REVIEW_SYNTHESIS
- name: HOXA2 sequencing
  description: >-
    Identify a phenotype-compatible HOXA2 variant through targeted sequencing, a relevant hearing/craniofacial
    panel or exome analysis, and test segregation where feasible. Interpret variant class, zygosity and family
    phenotype together; a rare missense finding alone is not diagnostic. Heterozygous truncating alleles and
    the original homozygous p.Gln186Lys allele have different inheritance and clinical associations.
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Exome sequencing of affected family members detected only seven shared, rare, heterozygous, nonsynonymous variants, including one protein truncating variant, a HOXA2 nonsense change (c.703C>T, p.Q235*)."
    explanation: Exome sequencing as the diagnostic route in a dominant family.

  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Both of these nonsynonymous changes affect leucine residues with high evolutionary conservation; however,
      each of these variants was also found in one control, indicating that either these variants are benign
      or that these variants in combination with another undetected HOXA2 variant (possibly in a noncoding
      portion of the gene) are responsible for microtia in these patients.
    explanation: >-
      The study itself did not establish causality for every rare missense variant; the proposed second-variant
      explanation was untested.
- name: Temporal-bone imaging when clinically indicated
  description: >-
    CT characterizes canal narrowing, atretic plates and ossicles; MRI can assess inner-ear and neural anatomy.
    The original recessive family had both ossicular abnormalities and one unilateral inner-ear agenesis. General
    microtia guidance reserves routine reconstructive CT for surgical planning or suspected cholesteatoma rather
    than the newborn period; unusual mixed loss or neurologic findings require individualized specialist assessment.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      The MRI of the auditory system in individual V: 3 was unremarkable for the inner ear and cerebellopontine
      angle, but an MRI confirmed the inner-ear agenesis on the left side of individual IV: 3 as seen on CT-images.
    explanation: >-
      Human diagnostic imaging, with both normal and abnormal findings.
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      A CT scan of the temporal bone is not recommended in the newborn period.
    explanation: >-
      General microtia imaging guidance; this does not preclude individualized imaging for a specific diagnostic
      concern.
    quote_role: REVIEW_SYNTHESIS
treatments:
- name: Auricular Reconstruction
  description: >-
    Discuss observation, an external prosthesis, autologous cartilage reconstruction and alloplastic reconstruction
    according to the individual goals and anatomy. Reconstruction is elective; coordinate its sequence with
    any hearing implant or canal surgery. The recommendations come from general microtia care, not a HOXA2
    outcome series.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: auricular reconstruction
    term:
      id: NCIT:C25351
      label: Reconstructive Surgery
  target_mechanisms:
  - target: Bilateral Microtia
    treatment_effect: BYPASSES
    description: >-
      Reconstruction changes the visible auricular manifestation; it does not reverse the prenatal HOXA2 patterning
      defect.
    evidence:
    - reference: DOI:10.3389/fsurg.2022.944223
      reference_title: Integrated microtia and aural atresia management
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        In discussing the spectrum of reconstructive options, observation should be presented with associated
        bene ﬁts and drawbacks.
      explanation: >-
        General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment
        effect is measured.
      quote_role: REVIEW_SYNTHESIS
  notes: >-
    Observation is a legitimate choice. Choice and timing of reconstruction should account for the patient
    wishes, hearing rehabilitation and surgical risks.
  evidence:
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      In discussing the spectrum of reconstructive options, observation should be presented with associated
      bene ﬁts and drawbacks.
    explanation: >-
      General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment
      effect is measured.
    quote_role: REVIEW_SYNTHESIS
- name: Cleft Palate Repair
  description: >-
    For patients with cleft palate, craniofacial-team assessment determines whether and when palatoplasty is
    indicated. General ACPA guidance places primary repair commonly at 9–14 months and ideally by 18 months,
    with individual readiness and airway risk considered. The source supplies general care recommendations,
    not genotype-specific efficacy.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: cleft palate repair
    term:
      id: NCIT:C168380
      label: Palatorrhaphy
  target_mechanisms:
  - target: Cleft Palate
    treatment_effect: BYPASSES
    description: >-
      Palatoplasty restores palatal continuity and function after the congenital cleft has formed; it does
      not correct the embryonic HOXA2 mechanism.
    evidence:
    - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
      reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        The goal of cleft palate surgery is to obtain normal function for speech and swallowing, as well as
        to optimize airway and dental facial relations.
      explanation: >-
        General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report
        HOXA2-specific outcomes.
      quote_role: REVIEW_SYNTHESIS
  notes: >-
    Relevant to the cleft phenotype documented in AR-MHIC. Assess feeding, speech and the airway before and
    after surgery; neither mouse cleft mechanism defines the surgical approach.
  evidence:
  - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      The goal of cleft palate surgery is to obtain normal function for speech and swallowing, as well as to
      optimize airway and dental facial relations.
    explanation: >-
      General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific
      outcomes.
    quote_role: REVIEW_SYNTHESIS
  - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Primary surgery of cleft palate often occurs between 9-14 months of age. The timing should take into
      account the patient and/or family readiness (physically and emotionally). Ideally, the cleft palate should
      be closed by the age of 18 months.
    explanation: >-
      General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific
      outcomes. Timing is individualized, rather than an outcome established for this genotype.
    quote_role: REVIEW_SYNTHESIS
- name: Hearing Amplification
  description: >-
    Provide early hearing rehabilitation according to per-ear thresholds, canal anatomy and cochlear reserve.
    General bilateral microtia/atresia guidance recommends amplification by four months and early intervention
    by three to six months. Worn bone-conduction devices can bypass a narrowed or atretic canal; patients with
    patent canals may use conventional amplification if appropriate. Mixed loss requires assessment of the
    sensorineural component and device limits, rather than assuming normal cochlear function.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: hearing amplification
    term:
      id: NCIT:C15747
      label: Supportive Care
    qualifiers:
    - predicate:
        preferred_term: medical device
        term:
          id: NCIT:C16830
          label: Medical Device
      value:
        preferred_term: hearing aid
        term:
          id: NCIT:C183182
          label: Hearing Aid
  target_mechanisms:
  - target: Hearing Impairment
    treatment_effect: BYPASSES
    description: >-
      Amplification improves access to sound within the usable cochlear reserve. Bone conduction bypasses canal
      and middle-ear transmission abnormalities but does not repair inner-ear agenesis or restore intrinsic
      cochlear function.
    evidence:
    - reference: DOI:10.3389/fsurg.2022.944223
      reference_title: Integrated microtia and aural atresia management
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        Diagnostic audiological assessment should be completed by 2 – 3 months of age and the infant provided
        with hearing ampli ﬁcation by 4 months of age and enrolled in early intervention (EI) by 3 – 6 months
        of age to optimize speech and language development.
      explanation: >-
        General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment
        effect is measured. The timing recommendation is for bilateral microtia with atresia.
      quote_role: REVIEW_SYNTHESIS
  notes: >-
    Do not delay early hearing support while deciding on cosmetic ear reconstruction. Device and implant selection
    requires current specialist assessment; historical regulatory age cutoffs in the 2022 guidance are not
    generalized here.
  evidence:
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Diagnostic audiological assessment should be completed by 2 – 3 months of age and the infant provided
      with hearing ampli ﬁcation by 4 months of age and enrolled in early intervention (EI) by 3 – 6 months
      of age to optimize speech and language development.
    explanation: >-
      General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment
      effect is measured. The timing recommendation is for bilateral microtia with atresia.
    quote_role: REVIEW_SYNTHESIS
  - reference: DOI:10.3389/fsurg.2022.944223
    reference_title: Integrated microtia and aural atresia management
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Clinicians should encourage early use of these worn bone conduction devices for infants with CHL.
    explanation: >-
      General microtia/atresia guidance applied to the relevant HOXA2 phenotype; no HOXA2-specific treatment
      effect is measured.
    quote_role: REVIEW_SYNTHESIS
- name: Speech and Language Therapy
  description: >-
    Assess speech and language development in either subtype when hearing impairment or a palatal defect is
    present. Coordinate early intervention, educational support and targeted therapy. Speech therapy can address
    learned articulation errors; structural velopharyngeal dysfunction requires a separate surgical or prosthetic
    assessment.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech and language therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  evidence:
  - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      The need for speech and/or language therapy for patients with a CL/P and/or other craniofacial difference,
      as well as the recommended nature of that therapy, should be based on results of a formal speech and
      language assessment and current best practices.
    explanation: >-
      General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific
      outcomes.
    quote_role: REVIEW_SYNTHESIS
- name: Genetic Counseling
  description: >-
    Discuss the identified genotype and variable phenotype with the family. When both parents carry a recessive
    pathogenic allele, each pregnancy has a 25% probability of an affected child; a heterozygous parent with
    a dominant pathogenic allele has a 50% transmission probability. These are Mendelian expectations conditional
    on parental genotypes, not empirically measured penetrance. Severity and hearing status cannot be predicted
    from transmission probability alone.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our data extend these conclusions and define HOXA2 haploinsufficiency as the first genetic cause for autosomal-dominant nonsyndromic microtia."
    explanation: >-
      Supports the inheritance mode. The stated recurrence probability is the Mendelian consequence of the
      specified parental genotype, rather than a measured outcome in this pedigree.

    directness: INDIRECT
  - reference: PMID:18394579
    reference_title: A mutation in HOXA2 is responsible for autosomal-recessive microtia in an Iranian family.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We ascertained a consanguineous Iranian family segregating with autosomal-recessive bilateral microtia, mixed symmetrical severe to profound hearing impairment, and partial cleft palate."
    explanation: >-
      Supports the inheritance mode. The stated recurrence probability is the Mendelian consequence of the
      specified parental genotype, rather than a measured outcome in this pedigree.
    directness: INDIRECT
- name: Feeding and nutrition support for cleft palate
  description: >-
    Assess feeding technique, intake, growth and hydration when cleft palate is present. A cleft team can select
    an appropriate specialized feeding system and monitor weight gain. This addresses the general functional
    risk of a cleft; a HOXA2-specific rate of feeding failure is not established.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: Supportive Care
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Cleft Palate
    treatment_effect: BYPASSES
    description: >-
      A specialized feeding system compensates for impaired suction without closing the cleft.
    evidence:
    - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
      reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      directness: INDIRECT
      snippet: >-
        Because infants with cleft palate cannot sustain the suction needed to maintain nutrition exclusively
        from the breast or standard bottle, they typically require specialized feeding systems to achieve adequate
        nutrition and hydration.
      explanation: >-
        General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report
        HOXA2-specific outcomes. Feeding difficulty is a care risk, not an additional measured HOXA2 phenotype
        frequency.
      quote_role: REVIEW_SYNTHESIS
  evidence:
  - reference: url:https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    reference_title: https://acpacares.org/wp-content/uploads/2025/02/2024-ACPA_ParametersOfCare_Final.pdf
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: INDIRECT
    snippet: >-
      Because infants with cleft palate cannot sustain the suction needed to maintain nutrition exclusively
      from the breast or standard bottle, they typically require specialized feeding systems to achieve adequate
      nutrition and hydration.
    explanation: >-
      General cleft-palate guidance applied when a HOXA2 patient has a cleft; this source does not report HOXA2-specific
      outcomes. Feeding difficulty is a care risk, not an additional measured HOXA2 phenotype frequency.
    quote_role: REVIEW_SYNTHESIS
animal_models:
- name: Hoxa2 null mouse (Rijli 1993)
  species: Mouse
  genotype: Hoxa2 homozygous null (targeted disruption)
  publication: PMID:7903601
  description: >-
    Homozygous targeted disruption causes perinatal death and loss of normal second-arch mesenchymal identity
    despite preserved rhombomeric and neural crest segmentation. The source supports an identity defect; normal
    migration and survival are not separately demonstrated by the cached abstract.
  modeled_mechanisms:
  - target: Loss of Second Pharyngeal Arch Neural Crest Identity
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      The model defines the identity-assignment lesion this node represents.
    limitations: >-
      A complete homozygous null differs from human heterozygous truncating alleles and homozygous p.Gln186Lys.
      Residual function of the human missense allele has not been measured in the cited family study.
    readouts:
    - name: Second-arch neural crest identity
      target: Loss of Second Pharyngeal Arch Neural Crest Identity
      direction: ALTERED
      interpretation: >-
        Second-arch crest adopts first-arch identity, the defining readout of
        the selector-gene lesion.
      evidence:
      - reference: PMID:7903601
        reference_title: "A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "While rhombomeric and neural crest cell (NCC) segmentation was not affected, mesenchymal NCC derivatives of the second arch were lacking, and second arch mesenchymal NCC identity was changed to first arch identity, resulting in homeotic transformation of second to first arch skeletal elements."
        explanation: The identity-change readout behind this link.
    evidence:
    - reference: PMID:7903601
      reference_title: "A homeotic transformation is generated in the rostral branchial region of the head by disruption of Hoxa-2, which acts as a selector gene."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "The ground pattern program appears to be modified in the mouse first arch by a Hox-independent process, whereas Hoxa-2 acts as a selector gene in the second arch."
      explanation: >-
        Establishes the model as informative for HOXA2's second-arch selector
        function.
- name: Hoxa-2 null mouse (Gendron-Maguire 1993)
  species: Mouse
  genotype: Hoxa-2 (Hox 1.11) homozygous targeted mutation
  publication: PMID:7903600
  description: >-
    An independent null allele reported simultaneously. Homozygotes are born
    with cleft palate and die within 24 hours, with duplicated middle-ear
    ossification centres and a second Meckel's cartilage beside the otic
    capsule.
  modeled_mechanisms:
  - target: Homeotic Transformation of Second-Arch Skeletal Derivatives
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Defines the complete-null mouse skeletal homeosis, including duplicated middle-ear ossification centers.
    limitations: >-
      The perinatally lethal complete-null phenotype is more extensive than the observed human ossicular dysplasia.
      Human imaging and surgery do not establish an equivalent homeotic duplication.
    readouts:
    - name: Middle-ear ossification centre duplication
      target: Homeotic Transformation of Second-Arch Skeletal Derivatives
      direction: INCREASED
      interpretation: >-
        Duplicated ossification centres are the skeletal signature of
        second-to-first arch transformation.
      evidence:
      - reference: PMID:7903600
        reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Analysis of stained skeletons revealed that homozygous mutant animals contained multiple cranial skeletal defects, including a duplication of the ossification centers of the bones of the middle ear."
        explanation: The skeletal readout behind this link.
    evidence:
    - reference: PMID:7903600
      reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Skeletal elements normally derived from the second arch were absent in the mutants."
      explanation: >-
        Establishes the model as informative for loss of second-arch skeletal
        derivatives.
  - target: Cleft Palate
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      The mouse null has cleft palate, providing a phenotypic correspondence to the original recessive human
      family.
    limitations: >-
      The complete-null mouse is perinatally lethal, whereas the original human recessive family has a partial
      cleft and viable affected relatives. This does not establish normal long-term survival for every possible
      human genotype.
    readouts:
    - name: Palatal closure
      target: Cleft Palate
      direction: ABOLISHED
      interpretation: >-
        Homozygous null mice were reported with cleft palate; the cached abstract does not provide a denominator
        for penetrance.
      evidence:
      - reference: PMID:7903600
        reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."
        explanation: The palatal readout behind this link.
    evidence:
    - reference: PMID:7903600
      reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."
      explanation: >-
        Establishes the model as informative for the palatal phenotype of the
        recessive subtype.
- name: Hoxa1/Hoxa2 double mutant mouse (Barrow 1999)
  species: Mouse
  genotype: Compound targeted allele disrupting both of the linked genes Hoxa1 and Hoxa2
  publication: PMID:10529419
  description: >-
    A single allele disrupting both linked genes, analysed against the single
    mutants. Some double-mutant craniofacial defects are additive combinations
    of the single-mutant ones and others appear only in the double mutant. The
    result that matters here is a rescue: compensatory defects associated with
    loss of Hoxa1 restore the hyoglossus attachment that is blocked in Hoxa2
    mutants, and the penetrance of cleft palate falls sharply.
  modeled_mechanisms:
  - target: Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles
    relationship: RESCUES
    fidelity: MODERATE
    description: >-
      Loss of Hoxa1 on the Hoxa2-mutant background restores normal attachment
      of the hyoglossus to the greater horn of the hyoid.
    limitations: >-
      The rescue is by a second mutation rather than by restoring Hoxa2 or by
      any treatment, so it establishes that the palate depends on the
      attachment without showing how the attachment is normally specified. It
      is also a mouse result with no human counterpart.
    readouts:
    - name: Hyoglossus attachment to the greater horn of the hyoid
      target: Mis-Attachment of the Extrinsic Tongue and Hyoid Muscles
      direction: RESTORED
      interpretation: >-
        The attachment blocked in Hoxa2 single mutants is made again in the
        double mutants.
      evidence:
      - reference: PMID:10529419
        reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "We show that two compensatory defects, associated with the loss of Hoxa1 function, restore normal attachment of the hyoglossus to the greater horn thereby allowing the palatal shelves to lift and fuse above the flattened tongue."
        explanation: The attachment readout behind this link.
    evidence:
    - reference: PMID:10529419
      reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "To understand how these two genes function together in craniofacial development, an allele was generated that disrupts both of these linked genes."
      explanation: >-
        Identifies the compound allele that makes this model informative for
        the muscle-attachment node.
  - target: Cleft Palate
    relationship: RESCUES
    fidelity: MODERATE
    description: >-
      Restoring the hyoglossus attachment sharply reduces the penetrance of
      cleft palate, which is the experimental support for treating the muscle
      defect as causal rather than coincidental.
    limitations: >-
      Penetrance falls but the abstract does not report how far, and the rescue
      is genetic. It also does not exclude the palate-intrinsic route reported
      by Smith and colleagues, which was measured in explant culture rather
      than in this model.
    readouts:
    - name: Cleft palate penetrance
      target: Cleft Palate
      direction: DECREASED
      interpretation: >-
        The cleft that Hoxa2 single mutants show is much less penetrant once
        the attachment is restored; the abstract does not give the figures.
      evidence:
      - reference: PMID:10529419
        reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Unexpectedly, in Hoxa1/Hoxa2 double mutants, the penetrance of cleft palate is dramatically reduced."
        explanation: The palatal readout behind this link.
    evidence:
    - reference: PMID:10529419
      reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "We show that two compensatory defects, associated with the loss of Hoxa1 function, restore normal attachment of the hyoglossus to the greater horn thereby allowing the palatal shelves to lift and fuse above the flattened tongue."
      explanation: >-
        Ties the restored attachment to restored palatal closure, which is what
        makes the model informative for the cleft.
- name: Conditional Hoxa2 inactivation mouse (Minoux 2013)
  species: Mouse
  genotype: Conditional Hoxa2 inactivation at early versus late gestational stages, plus conditional ectopic Hoxa2 in first-arch neural crest
  publication: PMID:24067355
  description: >-
    Stage-specific conditional inactivation separates the auricular phenotype
    from the lethal null. Early inactivation abolishes the auricle and
    duplicates the external auditory canal; late inactivation yields a
    hypomorphic auricle that the authors take to mimic the human HOXA2 mutant
    condition. The reciprocal gain-of-function experiment - ectopic Hoxa2 in
    first-arch crest - duplicates the pinna and eliminates the canal.
  modeled_mechanisms:
  - target: Failed Auricular Morphogenesis
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Late inactivation produces auricular hypoplasia resembling the human phenotype. Fate mapping defines
      the Hoxa2-expressing territory examined in the mouse study.
    limitations: >-
      Mouse and human pinna morphology differ substantially, and the model's
      resemblance to the human condition is the authors' assessment rather than
      a quantified comparison.
    readouts:
    - name: Auricle size and presence by stage of Hoxa2 inactivation
      target: Failed Auricular Morphogenesis
      direction: DECREASED
      interpretation: >-
        Auricular severity tracks the developmental stage at which Hoxa2 is
        removed, from complete absence to hypoplasia.
      evidence:
      - reference: PMID:24067355
        reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."
        explanation: The stage-dependent auricular readout behind this link.
    - name: Pinna lineage by genetic fate mapping
      target: Failed Auricular Morphogenesis
      direction: ALTERED
      interpretation: >-
        The investigators trace the auricular territory they call pinna to second-arch mesenchyme; the review
        literature notes that including the tragus and root changes the anatomical scope.
      evidence:
      - reference: PMID:24067355
        reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "By genetic fate mapping we found that the mouse auricle (or pinna) derives from the Hoxa2-expressing neural crest-derived mesenchyme of the second pharyngeal arch, and not from a composite of first and second arch mesenchyme as previously proposed based on morphological observation of human embryos."
        explanation: The lineage readout behind this link.
    evidence:
    - reference: PMID:24067355
      reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Thus, Hoxa2 loss- and gain-of-function approaches in mice provide a suitable model to investigate the molecular aetiology of microtia and auricle duplication."
      explanation: >-
        The authors' own statement that the model is suitable for the human
        aetiology this node represents.

- name: Hoxa2 hypomorphic dosage-series mouse
  species: Mouse
  genotype: Hypomorphic Hoxa2 allele combined with wild-type or null alleles
  publication: PMID:11578867
  description: >-
    An allele with about 45% of wild-type transcriptional activity was combined with normal and null alleles
    to create a dosage series. Second-arch development was more sensitive than hindbrain patterning, and proximal-caudal
    arch regions were more sensitive than rostro-distal regions. This supports regional dose sensitivity without
    assigning a residual activity to a human variant.
  modeled_mechanisms:
  - target: Loss of Second Pharyngeal Arch Neural Crest Identity
    relationship: PERTURBS
    model_scale: TISSUE
    limitations: >-
      An engineered transcriptional-dose series does not measure patient missense function or distinguish every
      cause of human-mouse phenotypic divergence.
    evidence:
    - reference: PMID:11578867
      reference_title: Different levels of Hoxa2 are required for particular developmental processes.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      directness: DIRECT
      snippet: >-
        Analysis of these embryos indicates that in general the hindbrain is more resistant to Hoxa2 deficiencies
        than the second branchial arch.
      explanation: >-
        Different embryonic regions respond differently to experimental Hoxa2 dose.
    - reference: PMID:11578867
      reference_title: Different levels of Hoxa2 are required for particular developmental processes.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      directness: DIRECT
      snippet: >-
        We have created a Hoxa2 allele that is about 45% as active in transcription as its wild-type counterpart.
      explanation: >-
        Engineered mouse allele, not a measured residual level in a patient.
  evidence:
  - reference: PMID:11578867
    reference_title: Different levels of Hoxa2 are required for particular developmental processes.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: DIRECT
    snippet: >-
      We have created a Hoxa2 allele that is about 45% as active in transcription as its wild-type counterpart.
    explanation: >-
      Engineered mouse allele, not a measured residual level in a patient.
  - reference: PMID:11578867
    reference_title: Different levels of Hoxa2 are required for particular developmental processes.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    directness: DIRECT
    snippet: >-
      Analysis of these embryos indicates that in general the hindbrain is more resistant to Hoxa2 deficiencies
      than the second branchial arch.
    explanation: >-
      Different embryonic regions respond differently to experimental Hoxa2 dose.
discussions:
- discussion_id: hoxa2_mouse_null_lethality_vs_human_viability
  kind: HUMAN_MODEL_MISMATCH
  prompt: >-
    Why does complete Hoxa2 loss kill mice at birth with a full second-to-first
    arch homeotic transformation, while human HOXA2 loss-of-function alleles
    produce a viable, largely isolated ear malformation?
  attaches_to:
  - pathophysiology#Homeotic Transformation of Second-Arch Skeletal Derivatives
  - animal_models#Hoxa2 null mouse (Rijli 1993)
  - animal_models#Hoxa-2 null mouse (Gendron-Maguire 1993)
  rationale: >-
    The complete mouse null is perinatally lethal with extensive skeletal homeosis, whereas characterized human
    heterozygous truncating and homozygous p.Gln186Lys genotypes are viable. Dose, developmental timing and
    species differences may contribute. Mouse hypomorphic alleles establish dose sensitivity, but residual
    activity of the human missense allele was not measured in the founding study. Human ossicular dysplasia
    therefore should not be described as proven partial homeotic duplication.
  evidence:
  - reference: PMID:7903600
    reference_title: Hoxa-2 mutant mice exhibit homeotic transformation of skeletal elements derived from cranial neural crest.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Mice homozygous for a targeted mutation of the Hoxa-2 (Hox 1.11) gene are born with cleft palates and die within 24 hr of birth."
    explanation: The lethal mouse null phenotype at one end of the mismatch.
  - reference: PMID:27503514
    reference_title: Identification of a second HOXA2 nonsense mutation in a family with autosomal dominant non-syndromic microtia and distinctive ear morphology.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Here we describe a five-generation family with isolated bilateral microtia segregating as an autosomal dominant trait."
    explanation: >-
      A five-generation pedigree of viable, isolated human disease at the other
      end of the mismatch.
  - reference: PMID:24067355
    reference_title: Mouse Hoxa2 mutations provide a model for microtia and auricle duplication.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "In mice, Hoxa2 inactivation at early gestational stages results in external auditory canal (EAC) duplication and absence of the auricle, whereas its late inactivation results in a hypomorphic auricle, mimicking the human HOXA2 mutant condition."
    explanation: >-
      Shows that timing of Hoxa2 loss alone spans much of the severity gap,
      which is part of the candidate resolution.
- discussion_id: hoxa2_sensorineural_component_unexplained
  kind: KNOWLEDGE_GAP
  prompt: >-
    What explains the sensorineural component of hearing loss in HOXA2-affected ears without demonstrated inner-ear
    agenesis?
  attaches_to:
  - phenotypes#Mixed Hearing Impairment
  rationale: >-
    The original recessive family includes one left inner-ear agenesis confirmed by CT and MRI, while two other
    examined relatives had normal inner-ear structures despite mixed hearing loss. Mixed loss also occurs in
    the p.Gln235* dominant family. Thus the gap is not absence of any human inner-ear characterization: the
    unresolved question is why sensorineural dysfunction occurs in other ears, and how it relates to HOXA2
    development.
  evidence:
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      The inner-ear structures were normal in patients V: 2 and V: 3, but there were no inner-ear structures
      on the left side for IV: 3.
    explanation: >-
      Unilateral inner-ear agenesis in one recessive-family member, with normal inner-ear anatomy in the other
      two imaged relatives.
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      Audiometric testing was performed on three of the affected family members and showed mild to severe bilateral
      mixed hearing loss (Fig. 1C).
    explanation: >-
      Direct dominant-family audiology. The figure caption includes a mild conductive-only left ear in one
      relative, so not every tested ear had both components.
  - reference: url:https://pmc.ncbi.nlm.nih.gov/articles/2427268/
    reference_title: A Mutation in HOXA2 Is Responsible for Autosomal-Recessive Microtia in an Iranian Family - PMC
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      All four affected family individuals showed bilateral symmetric severe to profound mixed hearing impairment
      affecting all frequencies and leading to a flat audiometric shape.
    explanation: >-
      The four affected members of the original recessive family; this severity should not be transferred to
      all dominant cases.
- discussion_id: hoxa2_cleft_palate_tongue_versus_intrinsic_palate
  kind: CONTROVERSY
  prompt: >-
    Is the Hoxa2-associated cleft palate secondary to abnormal tongue
    musculature, intrinsic to the palatal shelves, or both?
  attaches_to:
  - pathophysiology#Abnormal Tongue Posture Obstructing Palatal Shelf Closure
  - pathophysiology#Intrinsic Palatal Shelf Fusion Defect
  - phenotypes#Cleft Palate
  rationale: >-
    Two mouse accounts are on record and they are not the same claim. Barrow
    and Capecchi report that mis-attachment of the hyoglossus correlates
    exactly with cleft palate in Hoxa2 mutants and suggest that the resulting
    tongue posture blocks the shelves, with a genetic rescue in Hoxa1/Hoxa2
    double mutants as support. Smith and colleagues report Hoxa2 expression in
    the palate itself and reduced fusion of Hoxa2-null shelves cultured without
    a tongue, and conclude explicitly that the cleft is not solely due to the
    tongue musculature. The two are compatible - a mechanical obstruction and a
    shelf-intrinsic fusion defect could both contribute - but their relative
    contribution has not been quantified, and neither has been examined in a
    HOXA2-mutant patient, in whom the cleft is partial rather than complete.
    Until that is settled, this entry carries both nodes and asserts neither as
    the mechanism of the human cleft.
  evidence:
  - reference: PMID:10529419
    reference_title: Compensatory defects associated with mutations in Hoxa1 restore normal palatogenesis to Hoxa2 mutants.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "We suggest that the hyoglossus, whose function is to depress the lateral edges of the tongue, when unable to make its proper attachment to the greater horn of the hyoid, forces the tongue to adopt an abnormal posture which blocks closure of the palatal shelves."
    explanation: The tongue-musculature position, in its authors' own hedged wording.
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The cleft palate exhibited by Hoxa2 null murine embryos has been described as being secondary to abnormalities of tongue musculature, and Hoxa2 was presumed to not play a direct role in palate development."
    explanation: >-
      The second group's statement of the prior position, which is what they
      set out to test.
    quote_role: BACKGROUND
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "These results demonstrate the cleft palate phenotype of Hoxa2 null embryos is not solely due to abnormal tongue musculature, and indicate a direct role of Hoxa2 in regulating murine palatogenesis."
    explanation: The palate-intrinsic position, stated as a conclusion.

notes: >-
  This entry covers the recessive microtia-hearing impairment-cleft palate presentation and dominant HOXA2-related
  microtia as allelic subtypes of one developmental disorder. Cleft palate is documented in the original recessive
  family, but phenotype breadth and hearing severity require individual assessment. Pedigree-based observations
  do not support population frequency bands. General microtia/atresia and cleft-palate care recommendations
  are extrapolated to the relevant manifestations; HOXA2-specific treatment outcomes have not been established
  by the cited sources.

  Source identification: American Cleft Palate Craniofacial Association, 2024 Parameters
  of Care. Feeding, speech and palatal-surgery recommendations are general craniofacial guidance extrapolated
  to the relevant HOXA2 phenotype. Francesca Piceci Sparascio, Study of molecular basis of Oculo-Auricolo-Vertebral-Spectrum,
  Università di Foggia doctoral dissertation, academic year 2015–2016. The HOXA2 section on pages 68–71 describes
  the p.Glu224* pedigree also reported in PMID:27503514. Full text of Alasti et al. 2008 (PMID:18394579; PMCID:PMC2427268).
  The PMID cache supplies the abstract; this linked PMC cache supplies the clinical and imaging passages quoted
  here. Full text of Cox et al. 2014 (PMID:24880027; PMCID:PMC4143470), used for the auricular lineage and
  anatomical terminology discussion.

datasets: []
experimental_models:
- name: HOXA2 variant HMX1 enhancer reporter assay
  experimental_model_type: OTHER
  description: >-
    Dual-luciferase assays compare enhancer activation by p.Lys213* and p.Gln235* variants. The accessible
    abstract does not specify the host-cell identity, so no cell-line or tissue origin is inferred.
  modeled_mechanisms:
  - target: Impaired Transactivation of the Long-Range HMX1 Enhancer
    relationship: MEASURES
    model_scale: MOLECULAR
    limitations: >-
      An isolated reporter does not reproduce human auricular development or quantify clinical penetrance.
    evidence:
    - reference: PMID:32649979
      reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
      supports: SUPPORT
      evidence_source: IN_VITRO
      directness: DIRECT
      snippet: >-
        Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation
        of the long-range enhancer of HMX1.
      explanation: >-
        Variant-specific reporter assay for p.Lys213* and p.Gln235*.
  evidence:
  - reference: PMID:32649979
    reference_title: Identification of loss-of-function HOXA2 mutations in Chinese families with dominant bilateral microtia.
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: >-
      Using dual luciferase reporter assays, we showed that both HOXA2 mutations have impaired activation of
      the long-range enhancer of HMX1.
    explanation: >-
      Variant-specific reporter assay for p.Lys213* and p.Gln235*.
- name: Tongue-free Hoxa2 mutant palate organ culture
  experimental_model_type: OTHER
  description: >-
    Null palatal shelves cultured without a tongue have reduced fusion; antisense Hoxa2 knockdown also reduces
    fusion. This demonstrates an intrinsic component in the mouse system alongside the separate tongue-mechanics
    hypothesis.
  modeled_mechanisms:
  - target: Intrinsic Palatal Shelf Fusion Defect
    relationship: PARTIALLY_RECAPITULATES
    model_scale: TISSUE
    limitations: >-
      Explant fusion rates do not quantify in-vivo penetrance or establish the relative mechanism of the human
      partial cleft.
    evidence:
    - reference: PMID:19653318
      reference_title: Hoxa2 plays a direct role in murine palate development.
      supports: SUPPORT
      evidence_source: IN_VITRO
      directness: DIRECT
      snippet: >-
        Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion
        rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures.
      explanation: >-
        Tongue-free mouse organ culture isolates a palate-intrinsic contribution.
  evidence:
  - reference: PMID:19653318
    reference_title: Hoxa2 plays a direct role in murine palate development.
    supports: SUPPORT
    evidence_source: IN_VITRO
    directness: DIRECT
    snippet: >-
      Organ cultures of Hoxa2(-/-) palates maintained in the absence of the tongue showed decreased fusion
      rates than either Hoxa2(+/-) or Hoxa2(+/+) palate cultures.
    explanation: >-
      Tongue-free mouse organ culture isolates a palate-intrinsic contribution.
differential_diagnoses:
- name: FGF3-related labyrinthine aplasia, microtia and microdontia
  disease_term:
    preferred_term: deafness with labyrinthine aplasia, microtia, and microdontia
    term:
      id: MONDO:0012541
      label: deafness with labyrinthine aplasia, microtia, and microdontia
  description: >-
    FGF3-related disease can share microtia and inner-ear agenesis. Microdontia and the broader pattern of
    inner-ear malformation help distinguish it; molecular testing separates the disorders.
  distinguishing_features:
  - FGF3-associated microdontia and inner-ear agenesis contrast with variable inner-ear findings in HOXA2 families.
  evidence:
  - reference: PMID:23775976
    reference_title: HOXA2 haploinsufficiency in dominant bilateral microtia and hearing loss.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    directness: DIRECT
    snippet: >-
      FGF3 (congenital deafness, inner ear agenesis, microtia, microdontia; MIM  # 164950)
    explanation: >-
      Background clinical differential in the primary HOXA2 report.
    quote_role: BACKGROUND

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References & Deep Research