PAX1-Related Otofaciocervical Syndrome

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Inheritance

1

Autosomal recessive inheritance HP:0000007

OTFCS2 is autosomal recessive, with homozygous variants in consanguineous families and confirmed heterozygous carrier parents. This is the point of departure from the EYA1-related otofaciocervical phenotype, which is autosomal dominant.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:37924468 SUPPORT Human Clinical

"The novel homozygous variant c.1212dup (p.Gly405Argfs*51) in the PAX1 gene was identified by whole exome sequencing (WES), and family segregation confirmed the heterozygous status of the mutation in the parents using the Sanger sequencing."

Homozygosity in the proband with heterozygous parents establishes autosomal recessive inheritance.

PMID:37924468 SUPPORT Human Clinical

"Otofaciocervical syndrome (OTFCS) is a rare genetic disorder of both autosomal recessive and autosomal dominant patterns of inheritance. It is caused by biallelic or monoallelic mutations in PAX1 or EYA1 genes, respectively."

States the inheritance split between the PAX1 and EYA1 forms, which is the basis for curating them separately.

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Pathophysiology

4

Loss of PAX1 Transcription Factor Function

Biallelic PAX1 variants abolish or reduce the DNA-binding and transcriptional activity of a paired-box transcription factor. Both mechanisms are documented: hypofunctional missense alleles in the conserved paired-box domain reduce transactivation of PAX1 target promoters, while frameshift and nonsense alleles remove the protein. PAX1 sits within the PAX-SIX-EYA-DACH network that also contains EYA1 and SIX1, which is why the PAX1 and EYA1 disorders share a branchial-arch phenotype despite differing in inheritance and in the thymic component.

PAX1 hgnc:8615

Genetic context variant_origin: GERMLINE zygosity: HOMOZYGOUS functional_impact_category: LOSS_OF_FUNCTION

Biallelic germline PAX1 alleles, typically homozygous in consanguineous families. Two classes are reported and they are not equivalent: the hypofunctional paired-box missense c.497G>T (p.G166V), which retains partial transactivation, and null alleles such as the frameshift c.1212dup (p.Gly405Argfs*51). A heterozygous PAX1 null allele causes a milder, dominantly inherited oculo-auriculo-vertebral phenotype rather than this syndrome.

PAX1-mediated repression of canonical Wnt signaling GO:0090090 ↓ DECREASED

DNA-binding transcription factor activity GO:0003700 ↓ DECREASED

Downstream

Impaired Pharyngeal Pouch and Thymic Epithelial Development PAX1 directly drives the transcriptional programme of pharyngeal pouch-derived tissue, of which the thymic epithelium is the principal product.

Impaired Sclerotome-Derived Skeletal Patterning PAX1 is expressed in the sclerotome and is required for vertebral column and shoulder girdle patterning, the non-immune half of the phenotype.

Show evidence (5 references)

PMID:23851939 SUPPORT In Vitro

"We observed a significantly reduced transactivation in HEK293T cells overexpressing Pax1(G157V) in comparison to Pax1(WT) expressing cells, indicating a reduced DNA-binding affinity of the mutant protein."

Functional assay showing the missense allele is hypofunctional at the level of DNA binding and transactivation.

PMID:23851939 SUPPORT Human Clinical

"Taken together, our results show that the strategy of pooling DNA is a powerful, cost-effective application for WES in consanguineous families and establish PAX1 as a new disease-causing gene for OFCS and as part of the EYA-DACH-SIX-PAX network, important in early embryogenesis."

Establishes PAX1 causality and places it in the PAX-SIX-EYA-DACH network shared with EYA1.

PMID:32111619 SUPPORT In Vitro

"We demonstrated that these mutant PAX1 proteins have an altered conformation and flexibility of the paired box domain and reduced transcriptional activity."

Independently confirms reduced transcriptional activity across a further set of patient alleles.

+ 2 more references

Impaired Pharyngeal Pouch and Thymic Epithelial Development

Failure of the PAX1-dependent transcriptional programme in the third pharyngeal pouch produces thymic aplasia or hypoplasia. The lesion is in the thymic epithelial stroma, not in the haematopoietic progenitors that would normally seed it.

thymic epithelial cell CL:0002293

thymus development GO:0048538 ↓ DECREASED pharyngeal system development GO:0060037 ↓ DECREASED

Experimental models

Patient-derived iPSC thymic epithelial progenitor cells IPSC DERIVED MODEL Human, patient-genotype cells differentiated into the exact lineage whose failure causes the immunodeficiency.

Animal models

Pax1-deficient mouse Mouse partially recapitulates Reproduces thymic hypoplasia, but to a variable degree rather than the aplasia seen at the severe end of the human phenotype.

Downstream

Thymic Aplasia or Hypoplasia Failure of the PAX1-dependent pharyngeal pouch programme is what leaves the thymus absent or hypoplastic.

Primary Hypoparathyroidism The parathyroid glands derive from the same third and fourth pharyngeal pouches as the thymus, so the same field defect produces hypoparathyroidism.

Congenital Heart Defect Cardiac malformation accompanies the pharyngeal field defect, as it does in DiGeorge syndrome, but the intermediate steps from PAX1 loss to the cardiac phenotype have not been established.

Failure of Thymic T Cell Development Without thymic epithelium there is no niche for T cell development, so T cells fail to mature regardless of progenitor availability.

Show evidence (1 reference)

PMID:28657137 SUPPORT Model Organism

"The mouse model strongly supports the hypothesis that PAX1 depletion in our patients caused thymus aplasia responsible for SCID."

Attributes the immunodeficiency to thymic aplasia rather than an intrinsic lymphocyte defect.

Failure of Thymic T Cell Development

Absent or severely reduced T cell output producing a syndromic severe combined immunodeficiency. The stromal locus of the defect is therapeutically decisive: allogeneic haematopoietic stem cell transplantation supplies progenitors but not the epithelial niche they require, so T cell reconstitution fails even after successful engraftment.

T cell CL:0000084

T cell differentiation in thymus GO:0033077 ↓ DECREASED

Downstream

Severe Combined Immunodeficiency Absent thymic T cell output is the immunodeficiency.

Recurrent Infections Absent T cell immunity produces recurrent infection.

Show evidence (2 references)

PMID:32111619 SUPPORT Human Clinical

"We investigated the molecular and cellular basis of severe combined immunodeficiency (SCID) in six patients with otofaciocervical syndrome type 2 who failed to attain T cell reconstitution after allogeneic hematopoietic stem cell transplantation, despite successful engraftment in three of them."

The engraftment-without-reconstitution result is the direct clinical demonstration that the defect is stromal rather than haematopoietic.

PMID:37689091 SUPPORT In Vitro

"Normal ex vivo differentiation of PAX1-deficient CD34+ cells into mature T cells demonstrated the absence of a hematopoietic cell-intrinsic defect."

Directly excludes a haematopoietic-intrinsic defect by showing patient CD34+ cells differentiate normally outside the patient's thymus, which localises the lesion to the stroma.

Impaired Sclerotome-Derived Skeletal Patterning

Loss of PAX1 in the sclerotome disrupts vertebral column and shoulder girdle development, producing the vertebral anomalies, sloping shoulders and winged, hypoplastic scapulae that give the syndrome its name.

somite development GO:0061053 ↓ DECREASED

Animal models

Pax1-deficient mouse Mouse recapitulates Reproduces the vertebral column anomalies that follow sclerotome-derived patterning failure.

Downstream

Vertebral Anomalies Sclerotome-derived vertebral patterning fails, producing the segmentation and morphological anomalies of the spine.

Scapular Winging The shoulder girdle anomalies accompany the axial skeletal defect, but the specific requirement for PAX1 in scapular and clavicular patterning has not been separately demonstrated.

Show evidence (1 reference)

PMID:37924468 SUPPORT Model Organism

"Experimentally, mice with PAX1 deficiency showed vertebral column anomalies and different degrees of thymic hypoplasia"

The mouse phenotype pairs vertebral and thymic involvement, matching the two human expression domains.

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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

15

Cardiovascular 2

Thymic Aplasia or Hypoplasia FREQUENT Aplasia of the thymus HP:0005359

Show evidence (3 references)

PMID:28657137 SUPPORT Model Organism

"The mouse model strongly supports the hypothesis that PAX1 depletion in our patients caused thymus aplasia responsible for SCID."

Attributes the immunodeficiency to thymic aplasia. This is the paper's own mouse-model inference, so it is graded MODEL_ORGANISM and does not stand alone for this human phenotype.

PMID:37689091 SUPPORT Human Clinical

"The most severe cases displayed a T−B+NK+ severe combined immunodeficiency (SCID)-like phenotype secondary to thymic aplasia due to impaired differentiation of thymic epithelial cells"

Direct human evidence for thymic aplasia in PAX1-deficient patients, and it names the epithelial differentiation defect that causes it.

PMID:37689091 SUPPORT Human Clinical

"Thymic aplasia and hypoplasia were associated with impaired T cell immunity."

Reports both the aplastic and hypoplastic ends of the thymic phenotype in the patient cohort.

Congenital Heart Defect OCCASIONAL Abnormal heart morphology HP:0001627

Show evidence (1 reference)

PMID:37689091 SUPPORT Human Clinical

"New overlapping features with DiGeorge syndrome included primary hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line with PAX1 expression during early embryogenesis."

Reports congenital heart defects in two of six patients.

Ear 2

Low-Set Ears VERY_FREQUENT HP:0000369

Show evidence (1 reference)

PMID:41300719 SUPPORT Human Clinical

"ear abnormalities (e.g., low-set, cup-shaped ears with prominent conchae and a hypoplastic tragus and lobe) often associated with hearing loss"

Describes the characteristic ear morphology of the syndrome.

Hearing Impairment VERY_FREQUENT Conductive hearing impairment HP:0000405

Show evidence (2 references)

PMID:35595062 SUPPORT Human Clinical

"Otofaciocervical syndrome (OTFCS) is a rare condition associated with short stature, abnormal facial features and conductive hearing loss."

Specifies the hearing loss as conductive, which is what the binding to the conductive term rests on.

PMID:28657137 SUPPORT Human Clinical

"Otofaciocervical syndrome (OFCS) is a rare disorder characterized by facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing loss, branchial defects, skeletal anomalies, and mild intellectual disability."

Lists hearing loss among the defining features. Graded PARTIAL because it does not itself specify the conductive character.

Endocrine 1

Primary Hypoparathyroidism FREQUENT HP:0000829

Show evidence (1 reference)

PMID:37689091 SUPPORT Human Clinical

"New overlapping features with DiGeorge syndrome included primary hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line with PAX1 expression during early embryogenesis."

Reports primary hypoparathyroidism in five of six patients in the cohort that first characterised it in PAX1 deficiency.

Head and Neck 3

Facial Dysmorphism VERY_FREQUENT Abnormal facial shape HP:0001999

Show evidence (1 reference)

PMID:29681087 SUPPORT Human Clinical

"The major clinical features of OTFCS include ear malformations (external/middle/inner ear), facial dysmorphism, shoulder girdle abnormalities, vertebral anomalies, and mild intellectual disability."

Lists facial dysmorphism among the major clinical features.

Preauricular Pit FREQUENT HP:0004467

Show evidence (1 reference)

PMID:28657137 SUPPORT Human Clinical

"Otofaciocervical syndrome (OFCS) is a rare disorder characterized by facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing loss, branchial defects, skeletal anomalies, and mild intellectual disability."

Lists preauricular fistulae among the defining features.

Branchial Defects FREQUENT Branchial anomaly HP:0009794

Show evidence (1 reference)

PMID:28657137 SUPPORT Human Clinical

"Otofaciocervical syndrome (OFCS) is a rare disorder characterized by facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing loss, branchial defects, skeletal anomalies, and mild intellectual disability."

Lists branchial defects among the defining features of the syndrome.

Immune 2

Severe Combined Immunodeficiency FREQUENT HP:0004430

Show evidence (2 references)

PMID:32111619 SUPPORT Human Clinical

"These results identify biallelic, loss-of-function PAX1 mutations as the cause of a syndromic form of SCID due to altered thymus development."

Establishes syndromic SCID as a consequence of biallelic PAX1 loss.

PMID:37924468 SUPPORT Human Clinical

"However, more severe expanded features, including thymus aplasia, T-cell immunodeficiency, and recurrent infections, were observed in other successive studies"

Places the immunodeficiency as a feature of some but not all reported families. Graded PARTIAL because this paper's own patient lacked immunodeficiency, so it supports variable rather than constant expression.

Recurrent Infections OCCASIONAL HP:0002719

Show evidence (1 reference)

PMID:37924468 SUPPORT Human Clinical

"However, more severe expanded features, including thymus aplasia, T-cell immunodeficiency, and recurrent infections, were observed in other successive studies"

Reports recurrent infections among the severe end of the reported spectrum.

Limbs 1

Scapular Winging VERY_FREQUENT HP:0003691

Show evidence (1 reference)

PMID:41300719 SUPPORT Human Clinical

"shoulder girdle anomalies (sloping shoulders, low-set clavicles, winged scapulae, and trapezius hypoplasia)"

Describes the shoulder girdle anomaly complex including scapular winging.

Musculoskeletal 1

Vertebral Anomalies FREQUENT Abnormal vertebral morphology HP:0003468

Show evidence (1 reference)

PMID:29681087 SUPPORT Human Clinical

"The major clinical features of OTFCS include ear malformations (external/middle/inner ear), facial dysmorphism, shoulder girdle abnormalities, vertebral anomalies, and mild intellectual disability."

Lists vertebral anomalies among the major clinical features.

Nervous System 2

Intellectual Disability FREQUENT HP:0001249

Show evidence (1 reference)

PMID:29681087 SUPPORT Human Clinical

"The major clinical features of OTFCS include ear malformations (external/middle/inner ear), facial dysmorphism, shoulder girdle abnormalities, vertebral anomalies, and mild intellectual disability."

Lists mild intellectual disability among the major clinical features.

Delayed Language Development FREQUENT Delayed speech and language development HP:0000750

Show evidence (1 reference)

PMID:37924468 SUPPORT Human Clinical

"She manifested facial dysmorphism, hearing loss, intellectual disability (ID), and delayed language development (DLD) as the main clinical phenotype."

Documents delayed language development as a main clinical feature.

Growth 1

Short Stature FREQUENT HP:0004322

Show evidence (1 reference)

PMID:35595062 SUPPORT Human Clinical

"Otofaciocervical syndrome (OTFCS) is a rare condition associated with short stature, abnormal facial features and conductive hearing loss."

Names short stature as one of three defining associations of the syndrome.

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Genetic Associations

1

PAX1

Gene: PAX1 hgnc:8615 relationship_type: CAUSATIVE

Show evidence (2 references)

PMID:23851939 SUPPORT Human Clinical

"Filtering for variants with a percentage of alternate reads ≥ 90 % and a coverage of at least five reads identified only a single novel homozygous variant, c.497G>T, located in PAX1 that co-segregated with the disease in the family."

Cosegregation of the homozygous PAX1 variant in a large consanguineous family establishes causality.

PMID:32111619 SUPPORT Human Clinical

"We identified rare biallelic PAX1 rare variants in all patients."

Confirms biallelic PAX1 variants across an independent six-patient cohort.

Variants (2)

PAX1 c.497G>T (p.G166V)

Hypofunctional missense substitution in the conserved paired-box domain. Retains partial transactivation rather than abolishing it, and was the allele in the first reported OTFCS2 family, in whom no immunodeficiency was reported. The source is internally inconsistent about that family: the comparison table in PMID:37924468 records its immune status as no data, while the same paper's discussion reports it as free of SCID with no history of immunodeficiency. Neither statement is a documented negative from immune testing; the documented negative is the c.1212dup family below.

PAX1 c.1212dup (p.Gly405Argfs*51)

Frameshift null allele, homozygous in a consanguineous family. Reported with facial dysmorphism, hearing loss, intellectual disability and delayed language but without immunodeficiency, which is the clearest evidence that immune severity is not predictable from allele class alone.

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Medical Actions

3

Cultured Thymus Tissue Transplantation

Action: cultured thymus tissue transplantation Ontology label: Organ Transplantation NCIT:C15289

Platform: Cell therapy

Transplantation of cultured allogeneic thymus tissue supplies the epithelial niche that PAX1-deficient patients lack, and is the rational corrective therapy for the immunodeficiency. Reported PAX1-deficient patients recovered T cell immunity substantially better after thymus transplantation than after allogeneic HSCT. This is the same approach used for congenital athymia in complete DiGeorge syndrome and FOXN1 deficiency.

Mechanism Target:

Failure of Thymic T Cell Development — Replaces the missing thymic epithelial niche so that the patient's own normal haematopoietic progenitors can complete T cell development.

Show evidence (1 reference)

PMID:37689091 SUPPORT Human Clinical

"Hematopoietic stem cell transplantation resulted in poor immune reconstitution with absent naïve T cells, contrasting with the superior recovery of T cell immunity after thymus transplantation."

Directly contrasts the two interventions against the same node and establishes thymus transplantation as the one that works.

Show evidence (5 references)

PMID:37689091 SUPPORT Human Clinical

"Corrective treatment was required in 4/6 patients."

Establishes that corrective immune therapy is needed in the majority of reported patients.

PMID:33815417 SUPPORT Human Clinical

"This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire."

States both the failure of HSCT and the success of cultured thymus tissue for this class of disorder, of which OTFCS2 is named a member.

PMID:33815417 SUPPORT Human Clinical

"Immune reconstitution after the current treatment is usually incomplete with relatively common inflammatory and autoimmune complications, emphasizing the importance for improving strategies for thymus replacement therapy"

Qualifies the benefit: reconstitution is usually incomplete and carries inflammatory and autoimmune complications. Graded PARTIAL because it tempers rather than supports the therapy's efficacy.

+ 2 more references

Supportive Management of Hypoparathyroidism

Action: Pharmacotherapy NCIT:C15986

Platform: Small molecule

Calcium and active vitamin D replacement for the primary hypoparathyroidism, which is present in most reported patients and required corrective treatment in the majority of the characterised cohort. Curated as standard management of the curated hypoparathyroidism phenotype rather than as a PAX1-specific therapy.

Show evidence (1 reference)

PMID:37689091 SUPPORT Human Clinical

"New overlapping features with DiGeorge syndrome included primary hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line with PAX1 expression during early embryogenesis."

Establishes the hypoparathyroidism that this management addresses. Graded PARTIAL because the paper documents the endocrine phenotype without reporting the replacement regimen or its outcome.

Haematopoietic Stem Cell Transplantation

Action: hematopoietic cell transplantation Ontology label: Hematopoietic Cell Transplantation NCIT:C15431

Platform: Cell therapy

Allogeneic HSCT has been attempted for the immunodeficiency but does not restore T cell immunity in PAX1 deficiency, because the block is in the thymic epithelial niche rather than in the haematopoietic progenitors. Reported patients failed T cell reconstitution despite successful donor engraftment. Recorded here as a documented therapeutic failure, which is itself clinically actionable.

Show evidence (1 reference)

PMID:32111619 REFUTE Human Clinical

"We investigated the molecular and cellular basis of severe combined immunodeficiency (SCID) in six patients with otofaciocervical syndrome type 2 who failed to attain T cell reconstitution after allogeneic hematopoietic stem cell transplantation, despite successful engraftment in three of them."

Refutes HSCT as effective therapy for the T cell defect in this disease; graded REFUTE because the outcome measured was failure of the intervention to achieve its goal.

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Diagnosis

3

Newborn TREC screening for T cell lymphopenia

Absent or greatly reduced T-cell receptor excision circles on standard newborn screening is the first signal of the thymic defect, and it is what makes timely recognition possible. Timing is not incidental here: because the corrective therapy is thymus transplantation rather than HSCT, and because mortality after transplant is driven mainly by infections acquired before it, early detection changes the outcome rather than merely the label.

newborn screening NCIT:C81178

Show evidence (2 references)

PMID:32431714 SUPPORT Human Clinical

"Thymic hypoplasia/aplasia is first suggested by absence or significantly reduced numbers of recent thymic emigrants, revealed in standard-of-care newborn screens for T cell receptor excision circles (TRECs)."

Establishes TREC screening as the first-line detection route for the thymic defect.

PMID:33815417 SUPPORT Human Clinical

"Mortality after this treatment usually occurs before immune reconstitution and is mainly associated with infections most often acquired pre-transplantation."

Explains why early detection is decisive: the deaths happen before reconstitution, from infections acquired before transplant.

Distinguishing a thymic stromal defect from a haematopoietic one

Once T-cell lymphopenia is found, the diagnostic question that determines treatment is whether the defect is in the thymic stroma or in the haematopoietic compartment. PAX1 deficiency is on the stromal side, so the distinction routes the patient to thymus transplantation rather than to HSCT.

Show evidence (2 references)

PMID:33815417 SUPPORT Human Clinical

"It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects."

Names otofaciocervical syndrome type 2 explicitly among the congenital athymia causes to be recognised as thymic rather than haematopoietic.

PMID:33815417 SUPPORT Human Clinical

"This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire."

States the therapeutic consequence of the stromal-versus-haematopoietic distinction, which is why it is a diagnostic priority.

Molecular diagnosis by trio or gene-agnostic exome sequencing

Biallelic PAX1 variants confirm the diagnosis. Rapid gene-agnostic trio exome analysis has produced diagnoses in patients whose earlier panel-based testing was negative.

genetic testing NCIT:C15709

Show evidence (1 reference)

PMID:35595062 SUPPORT Human Clinical

"it further highlights the clinical utility of a rapid gene-agnostic trio exome analysis in identifying a genetic diagnosis in patients who previously underwent genomic testing by gene panel analysis"

Documents gene-agnostic trio exome succeeding where panel testing had failed.

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Prevalence

1

Worldwide

Cases In Literature Ultra Rare

Fourteen affected individuals from six families had been documented as of the 2023 report.

Show evidence (1 reference)

PMID:37924468 SUPPORT Human Clinical

"To date, only fourteen affected individuals with OTFCS2 from six different families have been documented."

Gives the reported case count supporting the ultra-rare band.

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Differential Diagnoses

5

Conditions with similar clinical presentations that must be differentiated from PAX1-Related Otofaciocervical Syndrome:

22q11.2 deletion syndrome MONDO:0018923

Overlapping Features The commonest cause of congenital athymia and the closest clinical mimic, sharing thymic hypoplasia, hypoparathyroidism and cardiac defects. Distinguished by the deletion itself, and by the absence of the shoulder girdle and vertebral anomalies that name otofaciocervical syndrome.

Show evidence (1 reference)

PMID:32431714 SUPPORT Human Clinical

"22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions in humans that can result in hypoplasia and occasionally, aplasia of the thymus."

Groups the four conditions as distinct causes of the same thymic phenotype, which is the differential this entry has to resolve.

CHARGE syndrome MONDO:0008965

Overlapping Features Another CHD7-related cause of thymic hypoplasia with ear anomalies and hearing loss. Distinguished by coloboma, choanal atresia and semicircular canal hypoplasia.

Show evidence (1 reference)

PMID:32431714 SUPPORT Human Clinical

"22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions in humans that can result in hypoplasia and occasionally, aplasia of the thymus."

Names CHARGE syndrome as a distinct condition producing the same thymic phenotype.

Oculo-auriculo-vertebral syndrome (monoallelic PAX1)

Overlapping Features The same gene at a different dose. A heterozygous PAX1 null allele produces a mild, dominantly inherited OAVS phenotype with variable expressivity of facial and ear features, and without the thymic, immunological or vertebral disease of the biallelic form. Recorded because it is the allelic boundary of this entry rather than a diagnostic confusion.

Show evidence (2 references)

PMID:35879406 SUPPORT Human Clinical

"Our findings indicate there can be monoallelic and biallelic disorders associated with PAX1, and further implicate the PSED network in OAVS."

States the monoallelic/biallelic split that bounds this entry's scope.

PMID:35879406 SUPPORT Human Clinical

"Biallelic homozygous nonsense or hypomorphic missense mutations in PAX1 cause otofaciocervical syndrome type 2 (OTFCS2), a similar but more severe multi-system disorder that can be accompanied by severe combined immunodeficiency due to thymic aplasia."

Contrasts the biallelic disorder curated here against the monoallelic phenotype.

FOXN1 deficiency (Nude SCID) MONDO:0011132

Overlapping Features The other monogenic thymic-stromal athymia, and the closest mechanistic parallel: like PAX1 deficiency it is corrected by thymus transplantation rather than HSCT. Distinguished by congenital alopecia and nail dystrophy, and by the absence of the branchial, shoulder girdle and vertebral anomalies.

Show evidence (1 reference)

PMID:33815417 SUPPORT Human Clinical

"It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects."

Pairs Nude SCID with otofaciocervical syndrome type 2 as the two rare monogenic thymic-stromal causes of athymia.

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Experimental Models

1

Patient-derived iPSC thymic epithelial progenitor cells IPSC_DERIVED_MODEL

Induced pluripotent stem cells reprogrammed from OTFCS2 patients and differentiated into thymic epithelial progenitor cells, allowing the transcriptional consequence of biallelic PAX1 loss to be read out directly in the affected human lineage.

Publication

PMID:32111619

Pathograph links

Impaired Pharyngeal Pouch and Thymic Epithelial Development recapitulates fidelity: moderate Human, patient-genotype cells differentiated into the exact lineage whose failure causes the immunodeficiency.

Limitations: Thymic epithelial progenitor cells in culture lack the three-dimensional thymic architecture and the haematopoietic crosstalk required for actual thymopoiesis, so the model reports a transcriptional phenotype rather than a functional T cell developmental defect.

Readouts

Thymic epithelial progenitor transcriptional profile

Direction: ALTERED

Interpretation: Altered expression of thymus and pharyngeal pouch developmental genes, the molecular correlate of the thymic aplasia.

Show evidence (1 reference)

PMID:32111619 SUPPORT In Vitro

"We generated patient-derived induced pluripotent stem cells and differentiated them into thymic epithelial progenitor cells and found that they have an altered transcriptional profile, including for genes involved in the development of the thymus and other tissues derived from pharyngeal pouches."

Reports the transcriptional measurement behind this readout.

Show evidence (1 reference)

PMID:32111619 SUPPORT In Vitro

"We demonstrated that these mutant PAX1 proteins have an altered conformation and flexibility of the paired box domain and reduced transcriptional activity."

Supports the model as informative for the transcriptional defect upstream of thymic epithelial failure.

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Animal Models

1

Pax1-deficient mouse

Mouse carrying PAX1 deficiency, showing both arms of the human phenotype - vertebral column anomalies and thymic hypoplasia.

Species

Mouse

Genotype

Pax1 loss of function

Publication

PMID:37924468

Pathograph links

Impaired Sclerotome-Derived Skeletal Patterning recapitulates fidelity: moderate Reproduces the vertebral column anomalies that follow sclerotome-derived patterning failure.

Limitations: Mouse axial skeletal patterning does not map onto the human shoulder girdle phenotype (sloping shoulders, winged scapulae) that is the most distinctive skeletal feature of the human syndrome, so the model covers the vertebral arm only.

Show evidence (1 reference)

PMID:37924468 SUPPORT Model Organism

"Experimentally, mice with PAX1 deficiency showed vertebral column anomalies and different degrees of thymic hypoplasia"

Reports the vertebral phenotype in the Pax1-deficient mouse.

Impaired Pharyngeal Pouch and Thymic Epithelial Development partially recapitulates fidelity: moderate Reproduces thymic hypoplasia, but to a variable degree rather than the aplasia seen at the severe end of the human phenotype.

Limitations: The mouse shows "different degrees of thymic hypoplasia" rather than consistent aplasia, so it models the milder end of the human thymic spectrum and cannot be used to argue that a given human genotype produces athymia.

Show evidence (1 reference)

PMID:37924468 SUPPORT Model Organism

"Experimentally, mice with PAX1 deficiency showed vertebral column anomalies and different degrees of thymic hypoplasia"

Reports thymic hypoplasia of variable degree, which is why this link is PARTIALLY_RECAPITULATES rather than RECAPITULATES.

{ }

Source YAML

click to show

name: PAX1-Related Otofaciocervical Syndrome
creation_date: "2026-08-29T00:00:00Z"
description: >-
  PAX1-related otofaciocervical syndrome (otofaciocervical syndrome type 2,
  OTFCS2) is an autosomal recessive disorder caused by biallelic
  loss-of-function variants in PAX1, a paired-box transcription factor expressed
  during development of the sclerotome, pharyngeal pouches, thymus and
  parathyroid glands. The constant features are craniofacial dysmorphism with
  low-set cup-shaped ears and preauricular pits, hearing loss, shoulder girdle
  anomalies (sloping shoulders, winged and hypoplastic scapulae), vertebral
  anomalies and mild intellectual disability with delayed language.

  The distinguishing feature relative to every other otofaciocervical phenotype
  is thymic: PAX1 is required for human thymic epithelial development, so
  biallelic null alleles produce thymic aplasia or hypoplasia and a syndromic
  form of severe combined immunodeficiency. This has a direct therapeutic
  consequence — the block is in the thymic stroma rather than the haematopoietic
  compartment, so affected patients fail to reconstitute T cells after
  allogeneic haematopoietic stem cell transplantation even when donor engraftment
  succeeds. Immunological severity varies across reported families, and at least
  one biallelic truncating genotype has been reported without immunodeficiency,
  so an immune phenotype should not be assumed from genotype alone.
category: Mendelian
parents:
- hereditary disease
- Inborn Errors of Immunity
synonyms:
- OTFCS2
- otofaciocervical syndrome 2
- otofaciocervical syndrome type 2
- PAX1 deficiency
disease_term:
  preferred_term: otofaciocervical syndrome 2
  term:
    id: MONDO:0014254
    label: otofaciocervical syndrome 2
inheritance:
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    OTFCS2 is autosomal recessive, with homozygous variants in consanguineous
    families and confirmed heterozygous carrier parents. This is the point of
    departure from the EYA1-related otofaciocervical phenotype, which is
    autosomal dominant.
  evidence:
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The novel homozygous variant c.1212dup (p.Gly405Argfs*51) in the PAX1 gene
      was identified by whole exome sequencing (WES), and family segregation
      confirmed the heterozygous status of the mutation in the parents using the
      Sanger sequencing.
    explanation: >-
      Homozygosity in the proband with heterozygous parents establishes
      autosomal recessive inheritance.
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OTFCS) is a rare genetic disorder of both
      autosomal recessive and autosomal dominant patterns of inheritance. It is
      caused by biallelic or monoallelic mutations in PAX1 or EYA1 genes,
      respectively.
    explanation: >-
      States the inheritance split between the PAX1 and EYA1 forms, which is the
      basis for curating them separately.
pathophysiology:
- name: Loss of PAX1 Transcription Factor Function
  biological_scale: MOLECULAR
  description: >-
    Biallelic PAX1 variants abolish or reduce the DNA-binding and transcriptional
    activity of a paired-box transcription factor. Both mechanisms are
    documented: hypofunctional missense alleles in the conserved paired-box
    domain reduce transactivation of PAX1 target promoters, while frameshift and
    nonsense alleles remove the protein. PAX1 sits within the PAX-SIX-EYA-DACH
    network that also contains EYA1 and SIX1, which is why the PAX1 and EYA1
    disorders share a branchial-arch phenotype despite differing in inheritance
    and in the thymic component.
  genes:
  - preferred_term: PAX1
    term:
      id: hgnc:8615
      label: PAX1
  genetic_context:
    variant_origin: GERMLINE
    zygosity: HOMOZYGOUS
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Biallelic germline PAX1 alleles, typically homozygous in consanguineous
      families. Two classes are reported and they are not equivalent: the
      hypofunctional paired-box missense c.497G>T (p.G166V), which retains
      partial transactivation, and null alleles such as the frameshift
      c.1212dup (p.Gly405Argfs*51). A heterozygous PAX1 null allele causes a
      milder, dominantly inherited oculo-auriculo-vertebral phenotype rather
      than this syndrome.
  molecular_functions:
  - preferred_term: DNA-binding transcription factor activity
    term:
      id: GO:0003700
      label: DNA-binding transcription factor activity
    modifier: DECREASED
  biological_processes:
  - preferred_term: PAX1-mediated repression of canonical Wnt signaling
    term:
      id: GO:0090090
      label: negative regulation of canonical Wnt signaling pathway
    modifier: DECREASED
  evidence:
  - reference: PMID:23851939
    reference_title: A hypofunctional PAX1 mutation causes autosomal recessively inherited otofaciocervical syndrome.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We observed a significantly reduced transactivation in HEK293T cells
      overexpressing Pax1(G157V) in comparison to Pax1(WT) expressing cells,
      indicating a reduced DNA-binding affinity of the mutant protein.
    explanation: >-
      Functional assay showing the missense allele is hypofunctional at the
      level of DNA binding and transactivation.
  - reference: PMID:23851939
    reference_title: A hypofunctional PAX1 mutation causes autosomal recessively inherited otofaciocervical syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Taken together, our results show that the strategy of pooling DNA is a
      powerful, cost-effective application for WES in consanguineous families
      and establish PAX1 as a new disease-causing gene for OFCS and as part of
      the EYA-DACH-SIX-PAX network, important in early embryogenesis.
    explanation: >-
      Establishes PAX1 causality and places it in the PAX-SIX-EYA-DACH network
      shared with EYA1.
  - reference: PMID:32111619
    reference_title: PAX1 is essential for development and function of the human thymus.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      We demonstrated that these mutant PAX1 proteins have an altered
      conformation and flexibility of the paired box domain and reduced
      transcriptional activity.
    explanation: >-
      Independently confirms reduced transcriptional activity across a further
      set of patient alleles.
  - reference: PMID:38664733
    reference_title: PAX1 represses canonical Wnt signaling pathway and plays dual roles during endoderm differentiation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Mechanically, PAX1 competes with SUMO E3 ligase PIASy to bind to TCF7L2,
      thus perturbing TCF7L2 SUMOylation level, further reducing its
      transcriptional activity and protein stability.
    explanation: >-
      Identifies the molecular mechanism by which PAX1 acts, competition with
      PIASy for TCF7L2 binding, which is what the disease alleles disrupt.
  - reference: PMID:38664733
    reference_title: PAX1 represses canonical Wnt signaling pathway and plays dual roles during endoderm differentiation.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Importantly, our data show PAX1 mutations found in SCID patients
      significantly compromise the suppressing ability of PAX1 on Wnt signaling.
    explanation: >-
      Connects the patient alleles specifically to loss of Wnt repression,
      making this the proximate molecular defect.
  downstream:
  - target: Impaired Pharyngeal Pouch and Thymic Epithelial Development
    causal_link_type: DIRECT
    description: >-
      PAX1 directly drives the transcriptional programme of pharyngeal
      pouch-derived tissue, of which the thymic epithelium is the principal
      product.
    evidence:
    - reference: PMID:32111619
      reference_title: PAX1 is essential for development and function of the human thymus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We generated patient-derived induced pluripotent stem cells and
        differentiated them into thymic epithelial progenitor cells and found
        that they have an altered transcriptional profile, including for genes
        involved in the development of the thymus and other tissues derived from
        pharyngeal pouches.
      explanation: >-
        Patient-derived cells show the transcriptional consequence directly in
        the relevant lineage.
  - target: Impaired Sclerotome-Derived Skeletal Patterning
    causal_link_type: DIRECT
    description: >-
      PAX1 is expressed in the sclerotome and is required for vertebral column
      and shoulder girdle patterning, the non-immune half of the phenotype.
    evidence:
    - reference: PMID:37924468
      reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        PAX1 encodes a transcription factor protein specifically expressed
        during the development of the skeleton, thymus, and parathyroid glands
      explanation: >-
        States the expression domains that partition the phenotype into skeletal
        and thymic components.
- name: Impaired Pharyngeal Pouch and Thymic Epithelial Development
  biological_scale: TISSUE
  description: >-
    Failure of the PAX1-dependent transcriptional programme in the third
    pharyngeal pouch produces thymic aplasia or hypoplasia. The lesion is in the
    thymic epithelial stroma, not in the haematopoietic progenitors that would
    normally seed it.
  cell_types:
  - preferred_term: thymic epithelial cell
    term:
      id: CL:0002293
      label: epithelial cell of thymus
  biological_processes:
  - preferred_term: thymus development
    term:
      id: GO:0048538
      label: thymus development
    modifier: DECREASED
  - preferred_term: pharyngeal system development
    term:
      id: GO:0060037
      label: pharyngeal system development
    modifier: DECREASED
  evidence:
  - reference: PMID:28657137
    reference_title: A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The mouse model strongly supports the hypothesis that PAX1 depletion in
      our patients caused thymus aplasia responsible for SCID.
    explanation: >-
      Attributes the immunodeficiency to thymic aplasia rather than an intrinsic
      lymphocyte defect.
  downstream:
  - target: Thymic Aplasia or Hypoplasia
    causal_link_type: DIRECT
    description: >-
      Failure of the PAX1-dependent pharyngeal pouch programme is what leaves
      the thymus absent or hypoplastic.
    evidence:
    - reference: PMID:37689091
      reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The most severe cases displayed a T−B+NK+ severe combined
        immunodeficiency (SCID)-like phenotype secondary to thymic aplasia due
        to impaired differentiation of thymic epithelial cells
      explanation: >-
        States the epithelial differentiation defect as the cause of the thymic
        aplasia.
  - target: Primary Hypoparathyroidism
    causal_link_type: DIRECT
    description: >-
      The parathyroid glands derive from the same third and fourth pharyngeal
      pouches as the thymus, so the same field defect produces
      hypoparathyroidism.
    evidence:
    - reference: PMID:37689091
      reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        New overlapping features with DiGeorge syndrome included primary
        hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line
        with PAX1 expression during early embryogenesis.
      explanation: >-
        Attributes the hypoparathyroidism to PAX1 expression during early
        embryogenesis, the same developmental window as the thymic defect.
  - target: Congenital Heart Defect
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      Cardiac malformation accompanies the pharyngeal field defect, as it does
      in DiGeorge syndrome, but the intermediate steps from PAX1 loss to the
      cardiac phenotype have not been established.
    evidence:
    - reference: PMID:37689091
      reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        New overlapping features with DiGeorge syndrome included primary
        hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line
        with PAX1 expression during early embryogenesis.
      explanation: >-
        Reports the association in two of six patients. Graded PARTIAL because
        the paper establishes co-occurrence and a plausible developmental window
        rather than a mechanism.
  - target: Failure of Thymic T Cell Development
    causal_link_type: DIRECT
    description: >-
      Without thymic epithelium there is no niche for T cell development, so
      T cells fail to mature regardless of progenitor availability.
    evidence:
    - reference: PMID:32111619
      reference_title: PAX1 is essential for development and function of the human thymus.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        These results identify biallelic, loss-of-function PAX1 mutations as the
        cause of a syndromic form of SCID due to altered thymus development.
      explanation: >-
        States the causal chain from PAX1 loss through thymus development to
        SCID.
- name: Failure of Thymic T Cell Development
  biological_scale: CELLULAR
  description: >-
    Absent or severely reduced T cell output producing a syndromic severe
    combined immunodeficiency. The stromal locus of the defect is
    therapeutically decisive: allogeneic haematopoietic stem cell
    transplantation supplies progenitors but not the epithelial niche they
    require, so T cell reconstitution fails even after successful engraftment.
  cell_types:
  - preferred_term: T cell
    term:
      id: CL:0000084
      label: T cell
  biological_processes:
  - preferred_term: T cell differentiation in thymus
    term:
      id: GO:0033077
      label: T cell differentiation in thymus
    modifier: DECREASED
  evidence:
  - reference: PMID:32111619
    reference_title: PAX1 is essential for development and function of the human thymus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We investigated the molecular and cellular basis of severe combined
      immunodeficiency (SCID) in six patients with otofaciocervical syndrome
      type 2 who failed to attain T cell reconstitution after allogeneic
      hematopoietic stem cell transplantation, despite successful engraftment in
      three of them.
    explanation: >-
      The engraftment-without-reconstitution result is the direct clinical
      demonstration that the defect is stromal rather than haematopoietic.
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Normal ex vivo differentiation of PAX1-deficient CD34+ cells into mature T
      cells demonstrated the absence of a hematopoietic cell-intrinsic defect.
    explanation: >-
      Directly excludes a haematopoietic-intrinsic defect by showing patient
      CD34+ cells differentiate normally outside the patient's thymus, which
      localises the lesion to the stroma.
  downstream:
  - target: Severe Combined Immunodeficiency
    causal_link_type: DIRECT
    description: >-
      Absent thymic T cell output is the immunodeficiency.
    evidence:
    - reference: PMID:32111619
      reference_title: PAX1 is essential for development and function of the human thymus.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        These results identify biallelic, loss-of-function PAX1 mutations as the
        cause of a syndromic form of SCID due to altered thymus development.
      explanation: >-
        States the causal chain from altered thymus development to SCID.
  - target: Recurrent Infections
    causal_link_type: DIRECT
    description: >-
      Absent T cell immunity produces recurrent infection.
    evidence:
    - reference: PMID:37924468
      reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        However, more severe expanded features, including thymus aplasia, T-cell
        immunodeficiency, and recurrent infections, were observed in other
        successive studies
      explanation: >-
        Places recurrent infections downstream of the T-cell immunodeficiency in
        the severe end of the spectrum.
  notes: >-
    Immunological severity is variable across reported families and is not
    predictable from genotype: a biallelic truncating PAX1 variant has been
    reported in a patient without immunodeficiency. Do not infer SCID from a
    PAX1 genotype alone.
- name: Impaired Sclerotome-Derived Skeletal Patterning
  biological_scale: TISSUE
  description: >-
    Loss of PAX1 in the sclerotome disrupts vertebral column and shoulder girdle
    development, producing the vertebral anomalies, sloping shoulders and
    winged, hypoplastic scapulae that give the syndrome its name.
  biological_processes:
  - preferred_term: somite development
    term:
      id: GO:0061053
      label: somite development
    modifier: DECREASED
  evidence:
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Experimentally, mice with PAX1 deficiency showed vertebral column
      anomalies and different degrees of thymic hypoplasia
    explanation: >-
      The mouse phenotype pairs vertebral and thymic involvement, matching the
      two human expression domains.
  downstream:
  - target: Vertebral Anomalies
    causal_link_type: DIRECT
    description: >-
      Sclerotome-derived vertebral patterning fails, producing the segmentation
      and morphological anomalies of the spine.
    evidence:
    - reference: PMID:37924468
      reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Experimentally, mice with PAX1 deficiency showed vertebral column
        anomalies and different degrees of thymic hypoplasia
      explanation: >-
        Links PAX1 deficiency directly to vertebral column anomalies.
  - target: Scapular Winging
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      The shoulder girdle anomalies accompany the axial skeletal defect, but the
      specific requirement for PAX1 in scapular and clavicular patterning has
      not been separately demonstrated.
    evidence:
    - reference: PMID:41300719
      reference_title: "Otofaciocervical Syndrome and Its Overlap with Branchiootorenal Spectrum: An Integrated Literature Analysis of EYA1-Related Disorders, Including a Novel Case with an 8q13.2q13.3 Deletion."
      supports: SUPPORT
      directness: INDIRECT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        shoulder girdle anomalies (sloping shoulders, low-set clavicles, winged
        scapulae, and trapezius hypoplasia)
      explanation: >-
        Documents the shoulder girdle anomaly complex. Graded INDIRECT because it
        establishes the phenotype without demonstrating the sclerotome route to
        it.
phenotypes:
- category: Craniofacial
  name: Facial Dysmorphism
  description: >-
    Long triangular face with broad forehead, narrow nose and mandible, and high
    arched palate.
  phenotype_term:
    preferred_term: Abnormal facial shape
    term:
      id: HP:0001999
      label: Abnormal facial shape
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:29681087
    reference_title: Autosomal recessive otofaciocervical syndrome type 2 with novel homozygous small insertion in PAX1 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The major clinical features of OTFCS include ear malformations
      (external/middle/inner ear), facial dysmorphism, shoulder girdle
      abnormalities, vertebral anomalies, and mild intellectual disability.
    explanation: >-
      Lists facial dysmorphism among the major clinical features.
- category: Auditory
  name: Low-Set Ears
  description: Low-set, cup-shaped ears with prominent conchae and hypoplastic tragus.
  phenotype_term:
    preferred_term: Low-set ears
    term:
      id: HP:0000369
      label: Low-set ears
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:41300719
    reference_title: "Otofaciocervical Syndrome and Its Overlap with Branchiootorenal Spectrum: An Integrated Literature Analysis of EYA1-Related Disorders, Including a Novel Case with an 8q13.2q13.3 Deletion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ear abnormalities (e.g., low-set, cup-shaped ears with prominent conchae
      and a hypoplastic tragus and lobe) often associated with hearing loss
    explanation: >-
      Describes the characteristic ear morphology of the syndrome.
- category: Auditory
  name: Preauricular Pit
  description: Preauricular fistulae/pits, a branchial-arch derived feature.
  phenotype_term:
    preferred_term: Preauricular pit
    term:
      id: HP:0004467
      label: Preauricular pit
  frequency: FREQUENT
  evidence:
  - reference: PMID:28657137
    reference_title: A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OFCS) is a rare disorder characterized by
      facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing
      loss, branchial defects, skeletal anomalies, and mild intellectual
      disability.
    explanation: >-
      Lists preauricular fistulae among the defining features.
- category: Auditory
  name: Hearing Impairment
  description: >-
    Hearing loss, reported with external, middle and inner ear malformation.
  phenotype_term:
    preferred_term: Conductive hearing impairment
    term:
      id: HP:0000405
      label: Conductive hearing impairment
  frequency: VERY_FREQUENT
  evidence:
  - reference: PMID:35595062
    reference_title: Dysmorphism and immunodeficiency - One of the differential diagnoses is PAX1 related otofaciocervical syndrome type 2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OTFCS) is a rare condition associated with
      short stature, abnormal facial features and conductive hearing loss.
    explanation: >-
      Specifies the hearing loss as conductive, which is what the binding to the
      conductive term rests on.
  - reference: PMID:28657137
    reference_title: A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OFCS) is a rare disorder characterized by
      facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing
      loss, branchial defects, skeletal anomalies, and mild intellectual
      disability.
    explanation: >-
      Lists hearing loss among the defining features. Graded PARTIAL because it
      does not itself specify the conductive character.
- category: Branchial
  name: Branchial Defects
  description: >-
    Branchial cysts or fistulae of the neck, the "cervical" component of the
    syndrome name.
  phenotype_term:
    preferred_term: Branchial anomaly
    term:
      id: HP:0009794
      label: Branchial anomaly
  frequency: FREQUENT
  evidence:
  - reference: PMID:28657137
    reference_title: A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OFCS) is a rare disorder characterized by
      facial anomalies, cup-shaped low-set ears, preauricular fistulas, hearing
      loss, branchial defects, skeletal anomalies, and mild intellectual
      disability.
    explanation: >-
      Lists branchial defects among the defining features of the syndrome.
- category: Growth
  name: Short Stature
  description: Reduced stature, reported as a consistent feature of the syndrome.
  phenotype_term:
    preferred_term: Short stature
    term:
      id: HP:0004322
      label: Short stature
  frequency: FREQUENT
  evidence:
  - reference: PMID:35595062
    reference_title: Dysmorphism and immunodeficiency - One of the differential diagnoses is PAX1 related otofaciocervical syndrome type 2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Otofaciocervical syndrome (OTFCS) is a rare condition associated with
      short stature, abnormal facial features and conductive hearing loss.
    explanation: >-
      Names short stature as one of three defining associations of the syndrome.
- category: Skeletal
  name: Scapular Winging
  description: >-
    Winged, low and laterally set scapulae with sloping shoulders and trapezius
    hypoplasia — the shoulder girdle anomaly that names the syndrome.
  phenotype_term:
    preferred_term: Scapular winging
    term:
      id: HP:0003691
      label: Scapular winging
  frequency: VERY_FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:41300719
    reference_title: "Otofaciocervical Syndrome and Its Overlap with Branchiootorenal Spectrum: An Integrated Literature Analysis of EYA1-Related Disorders, Including a Novel Case with an 8q13.2q13.3 Deletion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      shoulder girdle anomalies (sloping shoulders, low-set clavicles, winged
      scapulae, and trapezius hypoplasia)
    explanation: >-
      Describes the shoulder girdle anomaly complex including scapular winging.
- category: Skeletal
  name: Vertebral Anomalies
  description: Segmentation and morphological anomalies of the vertebral column.
  phenotype_term:
    preferred_term: Abnormal vertebral morphology
    term:
      id: HP:0003468
      label: Abnormal vertebral morphology
  frequency: FREQUENT
  evidence:
  - reference: PMID:29681087
    reference_title: Autosomal recessive otofaciocervical syndrome type 2 with novel homozygous small insertion in PAX1 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The major clinical features of OTFCS include ear malformations
      (external/middle/inner ear), facial dysmorphism, shoulder girdle
      abnormalities, vertebral anomalies, and mild intellectual disability.
    explanation: >-
      Lists vertebral anomalies among the major clinical features.
- category: Neurologic
  name: Intellectual Disability
  description: Mild intellectual disability.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  frequency: FREQUENT
  evidence:
  - reference: PMID:29681087
    reference_title: Autosomal recessive otofaciocervical syndrome type 2 with novel homozygous small insertion in PAX1 gene.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The major clinical features of OTFCS include ear malformations
      (external/middle/inner ear), facial dysmorphism, shoulder girdle
      abnormalities, vertebral anomalies, and mild intellectual disability.
    explanation: >-
      Lists mild intellectual disability among the major clinical features.
- category: Neurologic
  name: Delayed Language Development
  description: Delayed speech and language development.
  phenotype_term:
    preferred_term: Delayed speech and language development
    term:
      id: HP:0000750
      label: Delayed speech and language development
  frequency: FREQUENT
  evidence:
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      She manifested facial dysmorphism, hearing loss, intellectual disability
      (ID), and delayed language development (DLD) as the main clinical
      phenotype.
    explanation: >-
      Documents delayed language development as a main clinical feature.
- category: Immunologic
  name: Thymic Aplasia or Hypoplasia
  description: >-
    Absent or severely hypoplastic thymus, the feature that separates OTFCS2
    from every other otofaciocervical phenotype.
  phenotype_term:
    preferred_term: Aplasia of the thymus
    term:
      id: HP:0005359
      label: Aplasia of the thymus
  frequency: FREQUENT
  diagnostic: true
  evidence:
  - reference: PMID:28657137
    reference_title: A novel PAX1 null homozygous mutation in autosomal recessive otofaciocervical syndrome associated with severe combined immunodeficiency.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The mouse model strongly supports the hypothesis that PAX1 depletion in
      our patients caused thymus aplasia responsible for SCID.
    explanation: >-
      Attributes the immunodeficiency to thymic aplasia. This is the paper's own
      mouse-model inference, so it is graded MODEL_ORGANISM and does not stand
      alone for this human phenotype.
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The most severe cases displayed a T−B+NK+ severe combined immunodeficiency
      (SCID)-like phenotype secondary to thymic aplasia due to impaired
      differentiation of thymic epithelial cells
    explanation: >-
      Direct human evidence for thymic aplasia in PAX1-deficient patients, and
      it names the epithelial differentiation defect that causes it.
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thymic aplasia and hypoplasia were associated with impaired T cell
      immunity.
    explanation: >-
      Reports both the aplastic and hypoplastic ends of the thymic phenotype in
      the patient cohort.
- category: Immunologic
  name: Severe Combined Immunodeficiency
  description: >-
    Syndromic SCID from failed thymic T cell development. Severity varies: at
    least one biallelic truncating genotype has been reported without
    immunodeficiency.
  phenotype_term:
    preferred_term: Severe combined immunodeficiency
    term:
      id: HP:0004430
      label: Severe combined immunodeficiency
  frequency: FREQUENT
  evidence:
  - reference: PMID:32111619
    reference_title: PAX1 is essential for development and function of the human thymus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These results identify biallelic, loss-of-function PAX1 mutations as the
      cause of a syndromic form of SCID due to altered thymus development.
    explanation: >-
      Establishes syndromic SCID as a consequence of biallelic PAX1 loss.
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, more severe expanded features, including thymus aplasia, T-cell
      immunodeficiency, and recurrent infections, were observed in other
      successive studies
    explanation: >-
      Places the immunodeficiency as a feature of some but not all reported
      families. Graded PARTIAL because this paper's own patient lacked
      immunodeficiency, so it supports variable rather than constant expression.
- category: Immunologic
  name: Recurrent Infections
  description: Recurrent infection secondary to T cell deficiency.
  phenotype_term:
    preferred_term: Recurrent infections
    term:
      id: HP:0002719
      label: Recurrent infections
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, more severe expanded features, including thymus aplasia, T-cell
      immunodeficiency, and recurrent infections, were observed in other
      successive studies
    explanation: >-
      Reports recurrent infections among the severe end of the reported
      spectrum.
- category: Endocrine
  name: Primary Hypoparathyroidism
  description: >-
    Primary hypoparathyroidism from failed parathyroid development, a
    third/fourth pharyngeal pouch derivative like the thymus. Recognised only
    recently as part of the PAX1 phenotype and one of the features that makes
    the syndrome DiGeorge-like.
  phenotype_term:
    preferred_term: Hypoparathyroidism
    term:
      id: HP:0000829
      label: Hypoparathyroidism
  frequency: FREQUENT
  evidence:
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      New overlapping features with DiGeorge syndrome included primary
      hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line
      with PAX1 expression during early embryogenesis.
    explanation: >-
      Reports primary hypoparathyroidism in five of six patients in the cohort
      that first characterised it in PAX1 deficiency.
- category: Cardiovascular
  name: Congenital Heart Defect
  description: >-
    Congenital cardiac malformation, part of the DiGeorge-like pharyngeal field
    phenotype.
  phenotype_term:
    preferred_term: Congenital heart defect
    term:
      id: HP:0001627
      label: Abnormal heart morphology
  frequency: OCCASIONAL
  evidence:
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      New overlapping features with DiGeorge syndrome included primary
      hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line
      with PAX1 expression during early embryogenesis.
    explanation: >-
      Reports congenital heart defects in two of six patients.
genetic:
- name: PAX1
  gene_term:
    preferred_term: PAX1
    term:
      id: hgnc:8615
      label: PAX1
  relationship_type: CAUSATIVE
  variants:
  - name: PAX1 c.497G>T (p.G166V)
    description: >-
      Hypofunctional missense substitution in the conserved paired-box domain.
      Retains partial transactivation rather than abolishing it, and was the
      allele in the first reported OTFCS2 family, in whom no immunodeficiency
      was reported. The source is internally inconsistent about that family:
      the comparison table in PMID:37924468 records its immune status as no
      data, while the same paper's discussion reports it as free of SCID with
      no history of immunodeficiency. Neither statement is a documented
      negative from immune testing; the documented negative is the c.1212dup
      family below.
  - name: PAX1 c.1212dup (p.Gly405Argfs*51)
    description: >-
      Frameshift null allele, homozygous in a consanguineous family. Reported
      with facial dysmorphism, hearing loss, intellectual disability and delayed
      language but without immunodeficiency, which is the clearest evidence that
      immune severity is not predictable from allele class alone.
  notes: >-
    Biallelic PAX1 variants cause otofaciocervical syndrome type 2. Reported
    alleles include the hypofunctional paired-box missense p.G166V, nonsense
    alleles and frameshift insertions. PAX1 lies at 20p11.22 and encodes a
    534-amino-acid paired-box transcription factor whose conserved 128-residue
    paired domain carries the DNA-binding activity.
  evidence:
  - reference: PMID:23851939
    reference_title: A hypofunctional PAX1 mutation causes autosomal recessively inherited otofaciocervical syndrome.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Filtering for variants with a percentage of alternate reads ≥ 90 % and a
      coverage of at least five reads identified only a single novel homozygous
      variant, c.497G>T, located in PAX1 that co-segregated with the disease in
      the family.
    explanation: >-
      Cosegregation of the homozygous PAX1 variant in a large consanguineous
      family establishes causality.
  - reference: PMID:32111619
    reference_title: PAX1 is essential for development and function of the human thymus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We identified rare biallelic PAX1 rare variants in all patients.
    explanation: >-
      Confirms biallelic PAX1 variants across an independent six-patient cohort.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: ULTRA_RARE
  notes: >-
    Fourteen affected individuals from six families had been documented as of
    the 2023 report.
  evidence:
  - reference: PMID:37924468
    reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      To date, only fourteen affected individuals with OTFCS2 from six different
      families have been documented.
    explanation: >-
      Gives the reported case count supporting the ultra-rare band.
animal_models:
- name: Pax1-deficient mouse
  species: Mouse
  genotype: Pax1 loss of function
  publication: PMID:37924468
  description: >-
    Mouse carrying PAX1 deficiency, showing both arms of the human phenotype -
    vertebral column anomalies and thymic hypoplasia.
  modeled_mechanisms:
  - target: Impaired Sclerotome-Derived Skeletal Patterning
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces the vertebral column anomalies that follow sclerotome-derived
      patterning failure.
    limitations: >-
      Mouse axial skeletal patterning does not map onto the human shoulder
      girdle phenotype (sloping shoulders, winged scapulae) that is the most
      distinctive skeletal feature of the human syndrome, so the model covers
      the vertebral arm only.
    evidence:
    - reference: PMID:37924468
      reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Experimentally, mice with PAX1 deficiency showed vertebral column
        anomalies and different degrees of thymic hypoplasia
      explanation: >-
        Reports the vertebral phenotype in the Pax1-deficient mouse.
  - target: Impaired Pharyngeal Pouch and Thymic Epithelial Development
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces thymic hypoplasia, but to a variable degree rather than the
      aplasia seen at the severe end of the human phenotype.
    limitations: >-
      The mouse shows "different degrees of thymic hypoplasia" rather than
      consistent aplasia, so it models the milder end of the human thymic
      spectrum and cannot be used to argue that a given human genotype produces
      athymia.
    evidence:
    - reference: PMID:37924468
      reference_title: A Novel Truncating Mutation in PAX1 Gene Causes Otofaciocervical Syndrome Without Immunodeficiency.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Experimentally, mice with PAX1 deficiency showed vertebral column
        anomalies and different degrees of thymic hypoplasia
      explanation: >-
        Reports thymic hypoplasia of variable degree, which is why this link is
        PARTIALLY_RECAPITULATES rather than RECAPITULATES.
experimental_models:
- name: Patient-derived iPSC thymic epithelial progenitor cells
  experimental_model_type: IPSC_DERIVED_MODEL
  description: >-
    Induced pluripotent stem cells reprogrammed from OTFCS2 patients and
    differentiated into thymic epithelial progenitor cells, allowing the
    transcriptional consequence of biallelic PAX1 loss to be read out directly
    in the affected human lineage.
  publication: PMID:32111619
  modeled_mechanisms:
  - target: Impaired Pharyngeal Pouch and Thymic Epithelial Development
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Human, patient-genotype cells differentiated into the exact lineage whose
      failure causes the immunodeficiency.
    limitations: >-
      Thymic epithelial progenitor cells in culture lack the three-dimensional
      thymic architecture and the haematopoietic crosstalk required for actual
      thymopoiesis, so the model reports a transcriptional phenotype rather than
      a functional T cell developmental defect.
    readouts:
    - name: Thymic epithelial progenitor transcriptional profile
      target: Impaired Pharyngeal Pouch and Thymic Epithelial Development
      direction: ALTERED
      interpretation: >-
        Altered expression of thymus and pharyngeal pouch developmental genes,
        the molecular correlate of the thymic aplasia.
      evidence:
      - reference: PMID:32111619
        reference_title: PAX1 is essential for development and function of the human thymus.
        supports: SUPPORT
        evidence_source: IN_VITRO
        snippet: >-
          We generated patient-derived induced pluripotent stem cells and
          differentiated them into thymic epithelial progenitor cells and found
          that they have an altered transcriptional profile, including for genes
          involved in the development of the thymus and other tissues derived
          from pharyngeal pouches.
        explanation: >-
          Reports the transcriptional measurement behind this readout.
    evidence:
    - reference: PMID:32111619
      reference_title: PAX1 is essential for development and function of the human thymus.
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        We demonstrated that these mutant PAX1 proteins have an altered
        conformation and flexibility of the paired box domain and reduced
        transcriptional activity.
      explanation: >-
        Supports the model as informative for the transcriptional defect
        upstream of thymic epithelial failure.
treatments:
- name: Cultured Thymus Tissue Transplantation
  description: >-
    Transplantation of cultured allogeneic thymus tissue supplies the epithelial
    niche that PAX1-deficient patients lack, and is the rational corrective
    therapy for the immunodeficiency. Reported PAX1-deficient patients recovered
    T cell immunity substantially better after thymus transplantation than after
    allogeneic HSCT. This is the same approach used for congenital athymia in
    complete DiGeorge syndrome and FOXN1 deficiency.
  treatment_term:
    preferred_term: cultured thymus tissue transplantation
    term:
      id: NCIT:C15289
      label: Organ Transplantation
  therapeutic_modality: CELL_THERAPY
  target_mechanisms:
  - target: Failure of Thymic T Cell Development
    description: >-
      Replaces the missing thymic epithelial niche so that the patient's own
      normal haematopoietic progenitors can complete T cell development.
    evidence:
    - reference: PMID:37689091
      reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Hematopoietic stem cell transplantation resulted in poor immune
        reconstitution with absent naïve T cells, contrasting with the superior
        recovery of T cell immunity after thymus transplantation.
      explanation: >-
        Directly contrasts the two interventions against the same node and
        establishes thymus transplantation as the one that works.
  evidence:
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Corrective treatment was required in 4/6 patients.
    explanation: >-
      Establishes that corrective immune therapy is needed in the majority of
      reported patients.
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This group of disorders cannot be corrected by hematopoietic stem cell
      transplantation, but upon timely recognition as thymic defects, can
      successfully be treated by thymus transplantation using cultured postnatal
      thymic tissue with the generation of naïve T-cells showing a diverse
      repertoire.
    explanation: >-
      States both the failure of HSCT and the success of cultured thymus tissue
      for this class of disorder, of which OTFCS2 is named a member.
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Immune reconstitution after the current treatment is usually incomplete
      with relatively common inflammatory and autoimmune complications,
      emphasizing the importance for improving strategies for thymus replacement
      therapy
    explanation: >-
      Qualifies the benefit: reconstitution is usually incomplete and carries
      inflammatory and autoimmune complications. Graded PARTIAL because it
      tempers rather than supports the therapy's efficacy.
  - reference: PMID:34362576
    reference_title: Experience with cultured thymus tissue in 105 children.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our aims were to study 105 patients treated with cultured thymus tissue
      (CTT), and in this report, to focus on the outcomes of 95 patients with
      treatment-naive congenital athymia.
    explanation: >-
      The outcome dataset for this therapy, 105 treated children. Graded PARTIAL
      because the cohort is congenital athymia of all causes rather than PAX1
      deficiency specifically, so it establishes the therapy's track record
      rather than its effect in this disease.
  - reference: PMID:34362576
    reference_title: Experience with cultured thymus tissue in 105 children.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Currently, there are no approved therapies to treat congenital athymia, a
      condition of immune deficiency resulting in high early mortality due to
      infection and immune dysregulation.
    explanation: >-
      States the clinical stakes - congenital athymia is untreated by any
      approved therapy and carries high early mortality - which is why timely
      recognition matters. Graded PARTIAL because it establishes the need for
      this therapy rather than supporting its efficacy, and sits on the very
      treatment it says is unapproved.
- name: Supportive Management of Hypoparathyroidism
  description: >-
    Calcium and active vitamin D replacement for the primary hypoparathyroidism,
    which is present in most reported patients and required corrective treatment
    in the majority of the characterised cohort. Curated as standard management
    of the curated hypoparathyroidism phenotype rather than as a
    PAX1-specific therapy.
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  therapeutic_modality: SMALL_MOLECULE
  evidence:
  - reference: PMID:37689091
    reference_title: Expanding the clinical and immunological phenotypes of PAX1-deficient SCID and CID patients.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      New overlapping features with DiGeorge syndrome included primary
      hypoparathyroidism (n = 5) and congenital heart defects (n = 2), in line
      with PAX1 expression during early embryogenesis.
    explanation: >-
      Establishes the hypoparathyroidism that this management addresses. Graded
      PARTIAL because the paper documents the endocrine phenotype without
      reporting the replacement regimen or its outcome.
- name: Haematopoietic Stem Cell Transplantation
  description: >-
    Allogeneic HSCT has been attempted for the immunodeficiency but does not
    restore T cell immunity in PAX1 deficiency, because the block is in the
    thymic epithelial niche rather than in the haematopoietic progenitors.
    Reported patients failed T cell reconstitution despite successful donor
    engraftment. Recorded here as a documented therapeutic failure, which is
    itself clinically actionable.
  treatment_term:
    preferred_term: hematopoietic cell transplantation
    term:
      id: NCIT:C15431
      label: Hematopoietic Cell Transplantation
  therapeutic_modality: CELL_THERAPY
  evidence:
  - reference: PMID:32111619
    reference_title: PAX1 is essential for development and function of the human thymus.
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We investigated the molecular and cellular basis of severe combined
      immunodeficiency (SCID) in six patients with otofaciocervical syndrome
      type 2 who failed to attain T cell reconstitution after allogeneic
      hematopoietic stem cell transplantation, despite successful engraftment in
      three of them.
    explanation: >-
      Refutes HSCT as effective therapy for the T cell defect in this disease;
      graded REFUTE because the outcome measured was failure of the intervention
      to achieve its goal.
diagnosis:
- name: Newborn TREC screening for T cell lymphopenia
  diagnosis_term:
    preferred_term: newborn screening
    term:
      id: NCIT:C81178
      label: Newborn Screening
  description: >-
    Absent or greatly reduced T-cell receptor excision circles on standard
    newborn screening is the first signal of the thymic defect, and it is what
    makes timely recognition possible. Timing is not incidental here: because
    the corrective therapy is thymus transplantation rather than HSCT, and
    because mortality after transplant is driven mainly by infections acquired
    before it, early detection changes the outcome rather than merely the label.
  evidence:
  - reference: PMID:32431714
    reference_title: Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thymic hypoplasia/aplasia is first suggested by absence or significantly
      reduced numbers of recent thymic emigrants, revealed in standard-of-care
      newborn screens for T cell receptor excision circles (TRECs).
    explanation: >-
      Establishes TREC screening as the first-line detection route for the
      thymic defect.
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Mortality after this treatment usually occurs before immune reconstitution
      and is mainly associated with infections most often acquired
      pre-transplantation.
    explanation: >-
      Explains why early detection is decisive: the deaths happen before
      reconstitution, from infections acquired before transplant.
- name: Distinguishing a thymic stromal defect from a haematopoietic one
  description: >-
    Once T-cell lymphopenia is found, the diagnostic question that determines
    treatment is whether the defect is in the thymic stroma or in the
    haematopoietic compartment. PAX1 deficiency is on the stromal side, so the
    distinction routes the patient to thymus transplantation rather than to
    HSCT.
  evidence:
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is also found in rare cases of T-cell lymphopenia due to Nude SCID and
      Otofaciocervical Syndrome type 2, or in the context of genetically
      undefined defects.
    explanation: >-
      Names otofaciocervical syndrome type 2 explicitly among the congenital
      athymia causes to be recognised as thymic rather than haematopoietic.
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This group of disorders cannot be corrected by hematopoietic stem cell
      transplantation, but upon timely recognition as thymic defects, can
      successfully be treated by thymus transplantation using cultured postnatal
      thymic tissue with the generation of naïve T-cells showing a diverse
      repertoire.
    explanation: >-
      States the therapeutic consequence of the stromal-versus-haematopoietic
      distinction, which is why it is a diagnostic priority.
- name: Molecular diagnosis by trio or gene-agnostic exome sequencing
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: >-
    Biallelic PAX1 variants confirm the diagnosis. Rapid gene-agnostic trio
    exome analysis has produced diagnoses in patients whose earlier panel-based
    testing was negative.
  evidence:
  - reference: PMID:35595062
    reference_title: Dysmorphism and immunodeficiency - One of the differential diagnoses is PAX1 related otofaciocervical syndrome type 2.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      it further highlights the clinical utility of a rapid gene-agnostic trio
      exome analysis in identifying a genetic diagnosis in patients who
      previously underwent genomic testing by gene panel analysis
    explanation: >-
      Documents gene-agnostic trio exome succeeding where panel testing had
      failed.
differential_diagnoses:
- name: EYA1-related branchiootorenal spectrum, including EYA1-related otofaciocervical syndrome
  disease_term:
    preferred_term: otofaciocervical syndrome
    term:
      id: MONDO:0008163
      label: otofaciocervical syndrome
  description: >-
    The other otofaciocervical phenotype. It is autosomal dominant, EYA1-related,
    lacks the thymic and immunological features, and a 2025 integrated analysis
    of all published EYA1-related cases concluded it forms a single continuum
    with branchiootorenal spectrum disorder rather than a separate entity. It is
    curated in dismech as kb/disorders/EYA1-Related_Branchiootorenal_Spectrum.yaml.
  evidence:
  - reference: PMID:41300719
    reference_title: "Otofaciocervical Syndrome and Its Overlap with Branchiootorenal Spectrum: An Integrated Literature Analysis of EYA1-Related Disorders, Including a Novel Case with an 8q13.2q13.3 Deletion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We conclude that BORSD and OTFCS constitute a single EYA1-related
      diagnostic continuum.
    explanation: >-
      States the conclusion that the EYA1-related otofaciocervical phenotype is
      not a separate entity from branchiootorenal spectrum disorder.
  - reference: PMID:41300719
    reference_title: "Otofaciocervical Syndrome and Its Overlap with Branchiootorenal Spectrum: An Integrated Literature Analysis of EYA1-Related Disorders, Including a Novel Case with an 8q13.2q13.3 Deletion."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Crucially, all reported OTFCS patients with EYA1 variants had renal
      anomalies, a feature previously considered a hallmark of BORSD.
    explanation: >-
      Removes the renal-sparing criterion that had been used to separate the
      EYA1 otofaciocervical phenotype from branchiootorenal spectrum disorder.
- name: 22q11.2 deletion syndrome
  disease_term:
    preferred_term: 22q11.2 deletion syndrome
    term:
      id: MONDO:0018923
      label: 22q11.2 deletion syndrome
  description: >-
    The commonest cause of congenital athymia and the closest clinical mimic,
    sharing thymic hypoplasia, hypoparathyroidism and cardiac defects.
    Distinguished by the deletion itself, and by the absence of the shoulder
    girdle and vertebral anomalies that name otofaciocervical syndrome.
  evidence:
  - reference: PMID:32431714
    reference_title: Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and
      otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions
      in humans that can result in hypoplasia and occasionally, aplasia of the
      thymus.
    explanation: >-
      Groups the four conditions as distinct causes of the same thymic
      phenotype, which is the differential this entry has to resolve.
- name: CHARGE syndrome
  disease_term:
    preferred_term: CHARGE syndrome
    term:
      id: MONDO:0008965
      label: CHARGE syndrome
  description: >-
    Another CHD7-related cause of thymic hypoplasia with ear anomalies and
    hearing loss. Distinguished by coloboma, choanal atresia and semicircular
    canal hypoplasia.
  evidence:
  - reference: PMID:32431714
    reference_title: Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and
      otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions
      in humans that can result in hypoplasia and occasionally, aplasia of the
      thymus.
    explanation: >-
      Names CHARGE syndrome as a distinct condition producing the same thymic
      phenotype.
- name: Oculo-auriculo-vertebral syndrome (monoallelic PAX1)
  description: >-
    The same gene at a different dose. A heterozygous PAX1 null allele produces
    a mild, dominantly inherited OAVS phenotype with variable expressivity of
    facial and ear features, and without the thymic, immunological or vertebral
    disease of the biallelic form. Recorded because it is the allelic boundary
    of this entry rather than a diagnostic confusion.
  evidence:
  - reference: PMID:35879406
    reference_title: "Extending the PAX1 spectrum: a dominantly inherited variant causes oculo-auriculo-vertebral syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings indicate there can be monoallelic and biallelic disorders
      associated with PAX1, and further implicate the PSED network in OAVS.
    explanation: >-
      States the monoallelic/biallelic split that bounds this entry's scope.
  - reference: PMID:35879406
    reference_title: "Extending the PAX1 spectrum: a dominantly inherited variant causes oculo-auriculo-vertebral syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Biallelic homozygous nonsense or hypomorphic missense mutations in PAX1
      cause otofaciocervical syndrome type 2 (OTFCS2), a similar but more severe
      multi-system disorder that can be accompanied by severe combined
      immunodeficiency due to thymic aplasia.
    explanation: >-
      Contrasts the biallelic disorder curated here against the monoallelic
      phenotype.
- name: FOXN1 deficiency (Nude SCID)
  disease_term:
    preferred_term: T-cell immunodeficiency, congenital alopecia, and nail dystrophy
    term:
      id: MONDO:0011132
      label: T-cell immunodeficiency, congenital alopecia, and nail dystrophy
  description: >-
    The other monogenic thymic-stromal athymia, and the closest mechanistic
    parallel: like PAX1 deficiency it is corrected by thymus transplantation
    rather than HSCT. Distinguished by congenital alopecia and nail dystrophy,
    and by the absence of the branchial, shoulder girdle and vertebral
    anomalies.
  evidence:
  - reference: PMID:33815417
    reference_title: Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is also found in rare cases of T-cell lymphopenia due to Nude SCID and
      Otofaciocervical Syndrome type 2, or in the context of genetically
      undefined defects.
    explanation: >-
      Pairs Nude SCID with otofaciocervical syndrome type 2 as the two rare
      monogenic thymic-stromal causes of athymia.
notes: >-
  Scope decision, and it departs from the stub. The stub proposed lumping the
  two numbered otofaciocervical forms into one entry on the grounds that both
  sit on the EYA1-SIX1-PAX1 branchial developmental axis. Curating against the
  literature does not support that packaging:

  - The EYA1 form is autosomal dominant, and a 2025 integrated analysis of every
    published EYA1-related case concluded it and branchiootorenal spectrum
    disorder are one diagnostic continuum (PMID:41300719), notably because all
    reported EYA1 otofaciocervical patients had renal anomalies. dismech already
    curates that continuum as EYA1-Related_Branchiootorenal_Spectrum.yaml, where
    MONDO:0008163 is recorded as a differential.
  - The PAX1 form is autosomal recessive and adds thymic aplasia and a syndromic
    SCID that the EYA1 form does not have.

  Lumping them would have produced one entry carrying two mechanisms with
  opposite inheritance, which is the pattern the curation guidance warns against.
  So this entry is scoped to the PAX1 form at MONDO:0014254, and the EYA1 form is
  recorded as a differential pointing at the existing entry. The parent term
  MONDO:0008163 is deliberately not claimed by any single disorder entry.

  A further nuance worth preserving: PAX1 is not otofaciocervical-specific, and
  the allelic relationship runs by zygosity. A heterozygous PAX1 frameshift
  segregates with a mild oculo-auriculo-vertebral phenotype in a
  multi-generational family (PMID:35879406), which is cited on the OAVS
  differential; PAX1 has also been reported in Klippel-Feil syndrome. Those
  phenotypes are out of scope for this entry, which covers the biallelic
  form.

PAX1-Related Otofaciocervical Syndrome

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