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Inheritance

1

Autosomal recessive HP:0000007

All reported ECTD9 families segregate biallelic HOXC13 variants, most often homozygous alleles in consanguineous kindreds. Heterozygous carriers are clinically unaffected.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:23063621 SUPPORT Human Clinical

"Taken together, our results demonstrate that loss-of-function mutations in HOXC13 cause autosomal-recessive PHNED and further highlight the importance of HOXC13 in hair and nail development."

The discovery paper's conclusion establishes autosomal recessive inheritance for HOXC13-related PHNED.

PMID:28297138 SUPPORT Human Clinical

"We describe a homozygous novel missense mutation in the HOXC13 gene that resulted in autosomal recessive PHNED in a Hispanic child."

Independent confirmation of autosomal recessive inheritance in a North American family, showing the mode is not an artifact of the consanguineous pedigrees through which the gene was discovered.

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Discussions and Knowledge Gaps

1

Which Hoxc13-null animal model, if any, faithfully represents human ECTD9, and does the mouse's skeletal phenotype mean HOXC13 loss has consequences in humans that dermatology-ascertained pedigrees have never looked for?

HUMAN MODEL MISMATCH OPEN hoxc13_model_fidelity_disagreement

Attached to

pathophysiology#HOXC13 Transcription Factor Loss of Function pathophysiology#Impaired Hair Follicle Differentiation

Three species carry Hoxc13 nulls and the literature does not agree on which one models the human disease. The mouse reproduces hair and nail defects but adds skeletal defects, progressive weight loss, and low viability that no human patient shows, and the pig paper concludes flatly that mouse models cannot faithfully mimic human ED-9. That same paper reports its own knockouts matching ED-9 patients with a normal skeleton and normal growth. The later rabbit paper contradicts it, asserting that Hoxc13-mutated mice and pigs do not faithfully recapitulate hypotrichosis, and proposing a hair-follicle/sebaceous-gland imbalance - never shown in human skin - as the real mechanism. Two questions remain open. First, which model to trust for mechanistic inference about human hypotrichosis. Second, whether the absence of human skeletal involvement is real or an ascertainment artifact: human ECTD9 is caused chiefly by homeodomain missense alleles that reduce DNA binding or protein stability rather than by complete nulls, so allele hypomorphism is a plausible explanation that has never been tested against systematic imaging. A third question comes from the fourth model, the Naked (N) mouse, and it is the sharpest of the three because the mismatch is mechanistic rather than phenotypic. N is a terminal truncation whose transcript escapes nonsense-mediated decay; the truncated protein persists in follicles and heterozygotes are affected, which the authors read as semi-dominant and dominant-negative. Human ECTD9 is uniformly recessive and no dominant-negative HOXC13 allele has been reported. So the model that is most practically usable - the Hoxc13 knockout is poorly viable, and the Naked allele is offered explicitly as the more tractable alternative - is also the one whose mode of action is furthest from the human disease. Any mechanistic inference drawn from N/+ animals is inference about a dominant-negative truncation, not about the loss of function that causes the human condition.

Proposed experiments

Systematic skeletal imaging in molecularly confirmed ECTD9 patients

hoxc13_patient_skeletal_imaging

Spine and long-bone imaging in a cohort of biallelic-HOXC13 patients to establish whether subclinical vertebral anomalies are present but unreported in dermatology-ascertained pedigrees. A negative result would make allele hypomorphism or species divergence the explanation; a positive result would reclassify ECTD9 as less "pure" than its name implies.

Knock-in mouse carrying a human homeodomain missense allele

hoxc13_missense_knockin_mouse

Generate a mouse carrying the orthologous p.Arg311Trp or p.Asn310Thr substitution and compare its skeletal, growth, and appendage phenotype with the complete null, testing directly whether allele class rather than species explains the divergence.

Sebaceous gland quantification in human ECTD9 scalp biopsies

hoxc13_human_skin_sebaceous_histology

Quantify hair follicle and sebaceous gland number and size in archived ECTD9 scalp specimens to test whether the rabbit model's proposed follicle/sebaceous imbalance occurs in human disease.

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Pathophysiology

4

HOXC13 Transcription Factor Loss of Function

Biallelic HOXC13 variants deplete the functional pool of HOXC13 protein in hair follicle and nail matrix nuclei. Three demonstrated routes converge here in human disease: truncating and whole-exon deletion alleles that trigger nonsense-mediated decay or yield a cytoplasmically mislocalized protein; homeodomain missense alleles that impair sequence-specific DNA binding; and at least one homeodomain missense allele that destabilizes the folded protein. The shared endpoint is reduced nuclear HOXC13 activity. A fourth route exists in the mouse but does not belong to this node. The Naked (N) allele is a terminal truncation whose transcript escapes nonsense-mediated decay, leaving a persistent truncated protein that is pathogenic in heterozygotes - a dominant-negative mechanism rather than a depletion of functional protein. No such allele has been reported in humans, and every human ECTD9 pedigree is recessive. The mouse allele is curated under `animal_models` and its divergence is one of the questions in the `hoxc13_model_fidelity_disagreement` discussion; it is deliberately not folded into this loss-of-function node, which would misdescribe it.

DNA-binding transcription factor activity, RNA polymerase II-specific GO:0000981 ⇓ LOSS OF FUNCTION

Animal models

Naked (N) mouse (Hoxc13 terminal truncation) Mouse partially recapitulates N/N homozygotes reproduce the cardinal ECTD9 appendage phenotype (generalized alopecia with abnormal nails), and the allele is a better practical model than the poorly viable Hoxc13 knockout.

Downstream

Reduced Transactivation of Hair and Nail Differentiation Genes

Show evidence (3 references)

PMID:23063621 SUPPORT Human Clinical

"We examined HOXC13 expression in scalp specimen obtained from the index individual of the Chinese family and detected dramatically reduced mRNA levels in skin tissue and nearly absent protein staining in hair follicles, suggesting a mechanism of nonsense-mediated mRNA decay."

Direct patient-tissue demonstration that a truncating allele depletes HOXC13 transcript and protein in the affected appendage.

PMID:23315978 SUPPORT In Vitro

"Expression studies in cultured cells revealed that the mutant HOXC13 protein mislocalized within the cytoplasm, and failed to upregulate the promoter activities of its target genes."

Functional demonstration that a truncating allele both mislocalizes the protein and abolishes transactivation.

PMID:40225922 SUPPORT Human Clinical

"Previously reported biallelic HOXC13 pathogenic variants led to PHNED by either disrupting protein expression through nonsense-mediated decay or altering the DNA-binding affinity of the homeobox domain of HOXC13."

Summarizes the two previously established molecular routes to HOXC13 loss of function that this node aggregates.

Reduced Transactivation of Hair and Nail Differentiation Genes

HOXC13 drives the terminal differentiation program of hair- and nail-forming keratinocytes, including hair keratin genes. Reported HOXC13 target genes whose expression falls when HOXC13 is lost include KRT35, KRT85, and FOXN1. Loss of this transcriptional output deprives differentiating keratinocytes of the structural proteins needed to build a normal hair shaft or nail plate. Notably, KRT85 is itself the gene mutated in ECTD4, so the HOXC13 and keratin forms of PHNED are linked as regulator and target within one pathway rather than being merely phenocopies.

Hair follicle cell CL:0002559

regulation of transcription by RNA polymerase II GO:0006357 ↓ DECREASED keratinization GO:0031424 ↓ DECREASED

Animal models

Hoxc13 knockout pig Pig recapitulates Loss of Hoxc13 expression with measured downregulation of the FOXN1, KRT85, and KRT35 target genes, directly reproducing the transcriptional step of the human mechanism.

Downstream

Impaired Hair Follicle Differentiation

Impaired Nail Matrix Differentiation

Show evidence (3 references)

PMID:23063621 SUPPORT Human Clinical

"We also observed markedly decreased expression of four HOXC13 target genes in the specimen."

Patient scalp tissue shows reduced target-gene expression, the defining step of this node, in vivo rather than only in reporter assays.

PMID:23315978 SUPPORT In Vitro

"failed to upregulate the promoter activities of its target genes"

Promoter-reporter assays confirm that mutant HOXC13 cannot transactivate its downstream targets.

PMID:28011715 SUPPORT Model Organism

"Hoxc13 was not expressed in pigs with all three mutation types, and the expression levels of Hoxc13-regulated genes, namely, Foxn1, Krt85 and Krt35, were decreased."

Names the specific downstream targets (FOXN1, KRT85, KRT35) whose expression falls on HOXC13 loss, in a large-animal model whose skin phenotype closely matches the human disease.

Impaired Hair Follicle Differentiation

Without the HOXC13-dependent structural gene program, hair follicle keratinocytes fail to assemble a normal cortex and cuticle. Affected scalp skin shows reduced follicle numbers and disorganized hair shafts lacking normal layered architecture, producing hair that is sparse, fragile, or entirely absent from birth.

Hair follicle cell CL:0002559

hair follicle development GO:0001942 ⚠ ABNORMAL

Animal models

Hoxc13 knockout pig Pig recapitulates Reduced follicle number and disarrayed hair follicle architecture with no normal hair anywhere on the body, matching the human follicular defect.

Hoxc13-null mouse Mouse partially recapitulates Hoxc13-null mice develop hair and nail defects closely resembling human PHNED, which is what identified HOXC13 as the candidate gene.

Hoxc13-null rabbit Rabbit recapitulates Reproduces regional hypotrichosis and proposes a specific cellular mechanism for it: a disrupted hair-follicle/sebaceous-gland balance.

Downstream

Hypotrichosis and Alopecia

Abnormal Hair Shaft Morphology

Show evidence (2 references)

PMID:28011715 SUPPORT Model Organism

"The hair follicles displayed various abnormal phenotypes, such as reduced number of follicles and disarrayed hair follicle cable without normal hair all over the body."

Direct histological characterization of the follicular defect caused by Hoxc13 loss, in the animal model that best matches the human phenotype.

PMID:28297138 SUPPORT Human Clinical

"Our findings illustrate the critical role of HOXC13 in human hair and nail development."

Supports HOXC13-dependence of human hair follicle development, the substrate of this node.

Impaired Nail Matrix Differentiation

HOXC13 is also required in nail-forming epithelium, where the same target-gene program supplies the keratins of the nail plate. Loss of HOXC13 activity yields a structurally defective nail plate, clinically evident as nail dystrophy typically involving all twenty nails. Mouse genetics places this requirement at the level of the whole HoxC cluster: deleting the cluster in the limb ectoderm abolishes nails entirely.

Nail matrix keratinocyte CL:4052064

keratinization GO:0031424 ↓ DECREASED

Downstream

Nail Dystrophy

Show evidence (2 references)

PMID:28403827 SUPPORT Human Clinical

"Affected members exhibited PHNED phenotypes with involvement of complete hair loss and nail dysplasia."

Documents nail dysplasia alongside hair loss as the paired consequence of HOXC13 loss of function.

PMID:33199643 SUPPORT Model Organism

"deletion of the HoxC cluster led to mice lacking nails (anonychia), a condition stronger than the previously reported loss of function of Hoxc13, which is the causative gene of the ectodermal dysplasia 9 (ECTD9) in human patients"

Establishes HoxC-cluster dependence of nail formation and positions Hoxc13 loss as a partial version of that requirement, consistent with nail dystrophy rather than anonychia in ECTD9 patients.

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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

7

Head and Neck 1

Hypodontia Absent EXCLUDED HP:0000668

∅ ABSENT

Show evidence (1 reference)

PMID:28297138 SUPPORT Human Clinical

"Pure hair and nail ectodermal dysplasia (PHNED) is a rare disorder that presents with hypotrichosis and nail dystrophy while sparing other ectodermal structures such as teeth and sweat glands."

Explicitly states that teeth are spared in PHNED, the claim this excluded phenotype records.

Integument 4

Hypotrichosis and Alopecia OBLIGATE HP:0001596

`frequency: OBLIGATE` is justified by hair involvement being definitional for the "pure hair and nail" entity, not by a counted cohort. No ECTD9 case series large enough to estimate a frequency band has been published; see docs/frequency-evidence-guidelines.md.

Show evidence (2 references)

PMID:23063621 SUPPORT Human Clinical

"Pure hair and nail ectodermal dysplasia (PHNED) is a congenital condition characterized by hypotrichosis and nail dystrophy."

Establishes hypotrichosis as a defining, congenital feature of the entity in the paper that identified HOXC13 as its cause.

PMID:23315978 SUPPORT Human Clinical

"we have analyzed a consanguineous Syrian family with an affected girl having complete alopecia and nail dystrophy since birth"

Documents the severe end of the range, congenital complete alopecia, in a molecularly confirmed HOXC13 case.

Nail Dystrophy OBLIGATE HP:0008404

`frequency: OBLIGATE` reflects that nail involvement is definitional for PHNED, not a measured proportion.

Show evidence (1 reference)

PMID:23063621 SUPPORT Human Clinical

"Pure hair and nail ectodermal dysplasia (PHNED) is a congenital condition characterized by hypotrichosis and nail dystrophy."

Establishes nail dystrophy as the second cardinal, congenital feature of the entity.

Abnormal Hair Shaft Morphology HP:0003328

Light microscopy of scalp skin in an affected individual showed disorganized hair shafts lacking the normal layered structure (PMID:40225922 introduction; not present in the cached abstract).

Show evidence (1 reference)

PMID:40225922 SUPPORT Human Clinical

"Pure hair and nail ectodermal dysplasia (PHNED) is a congenital disorder characterized by reduced or absent hair and dystrophic nails."

Supports congenitally abnormal hair. Marked PARTIAL because the quoted sentence establishes reduced or absent hair rather than the specific microscopic shaft abnormality, which is recorded in `notes`.

Hypohidrosis Absent EXCLUDED HP:0000966

∅ ABSENT

Curated with `frequency: EXCLUDED` plus `modifier: ABSENT`, following the convention used in Osteogenesis_Imperfecta_Type_V and Epilepsy_with_Generalized_Tonic-Clonic_Seizures_Alone. `frequency: EXCLUDED` is what the HPOA exporter reads to emit a NOT-qualified row; `modifier: ABSENT` documents intent.

Show evidence (1 reference)

PMID:28297138 SUPPORT Human Clinical

"Pure hair and nail ectodermal dysplasia (PHNED) is a rare disorder that presents with hypotrichosis and nail dystrophy while sparing other ectodermal structures such as teeth and sweat glands."

Explicitly states that sweat glands are spared in PHNED, the claim this excluded phenotype records.

Other 2

Lacrimal Duct Obstruction VERY_RARE Abnormal lacrimal duct morphology HP:0011481

Reported in PMID:29278420 (Humbatova et al., Br J Dermatol 2018) and restated in the introduction of PMID:40225922. Neither source has a cached abstract containing a quotable sentence for this claim (PMID:29278420 caches as a Letter with `content_type: unavailable`), so this phenotype is curated without an evidence block per the evidence SOP rather than with a fabricated snippet. The Edison report independently reached the same conclusion, noting the retrieved full text was insufficient to establish frequency or reproducibility.

Skeletal Involvement Absent EXCLUDED Abnormal axial skeleton morphology HP:0009121

∅ ABSENT

Show evidence (1 reference)

PMID:28011715 SUPPORT Model Organism

"Ectodermal dysplasia-9 (ED-9) is a congenital condition characterized by hypotrichosis and nail dystrophy without other disorders, and Hoxc13 is a pathogenic gene for ED-9."

States that ED-9 is hypotrichosis and nail dystrophy "without other disorders", which is the assertion that skeletal and systemic involvement is absent in the human disease. Evidence source is MODEL_ORGANISM because the citing paper reports an animal model, although this particular sentence describes the human condition being modeled.

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Genetic Associations

1

HOXC13 Biallelic Loss-of-Function Variants

Gene: HOXC13 hgnc:5125 relationship_type: CAUSATIVE

Show evidence (1 reference)

PMID:23063621 SUPPORT Human Clinical

"Autosomal-recessive PHNED has previously been mapped to chromosomal region 12q12-q14.1, which contains the type II hair keratin and HOXC clusters."

Explains why HOXC13 and the type II hair keratin genes (KRT85, KRT74) are all PHNED candidates: they share the same 12q linkage interval. This is also why ECTD4, ECTD7, and ECTD9 are readily confused in the literature.

Variants (6)

c.390C>A (p.Tyr130*) nonsense

NONSENSE

Homozygous nonsense allele identified by whole-exome sequencing in a consanguineous Chinese family, the first HOXC13 variant reported in PHNED. Scalp tissue from the index case showed dramatically reduced HOXC13 mRNA and nearly absent protein in hair follicles, indicating nonsense-mediated decay.

Show evidence (1 reference)

PMID:23063621 SUPPORT Human Clinical

"We performed whole-exome sequencing in a consanguineous Chinese family affected by PHNED and identified a homozygous nonsense mutation"

Identifies the nonsense allele and its homozygous state in all affected members of the discovery family. The quote is trimmed before the bracketed HGVS span `[p.Tyr130(∗)]`, which the reference validator strips before matching.

27.6 kb microdeletion of HOXC13 exon 1

DELETION

Homozygous 27.6 kb deletion removing the first exon of HOXC13, found in an affected female from a consanguineous Afghan family. A predicted null allele, and the reason deletion analysis belongs in the diagnostic strategy alongside sequencing.

Show evidence (1 reference)

PMID:23063621 SUPPORT Human Clinical

"In an additional affected female from a consanguineous Afghan family, we found a 27.6 kb homozygous microdeletion involving the first exon of HOXC13."

Documents a whole-exon deletion allele, establishing that copy-number loss as well as point mutation causes ECTD9.

c.355delC (p.Leu119Trpfs*20) frameshift

FRAMESHIFT

Homozygous single-nucleotide deletion in a consanguineous Syrian family. Expression studies showed the truncated protein mislocalizes to the cytoplasm and cannot transactivate target-gene promoters, giving direct functional evidence for loss of function.

Show evidence (1 reference)

PMID:23315978 SUPPORT Human Clinical

"Sequencing of another candidate gene HOXC13 within the linkage interval identified a homozygous frameshift mutation (c.355delC; p.Leu119Trpfs*20)."

Identifies the frameshift allele and its homozygous state in the affected Syrian kindred.

c.812A>G (p.Gln271Arg) homeodomain missense

MISSENSE

Homozygous missense variant in the DNA-binding homeodomain, reported in a Hispanic child and the first missense HOXC13 allele described in PHNED. Pathogenicity support for this allele is familial cosegregation plus in silico prediction (PolyPhen-2, SIFT); no direct functional assay was performed.

Show evidence (1 reference)

PMID:28297138 SUPPORT Human Clinical

"The mutation c.812A>G (p.Gln271Arg) is located within the DNA-binding domain of the HOXC13 gene, cosegregates within the family, and is predicted to be maximally damaging."

Localizes the missense allele to the DNA-binding domain and reports familial cosegregation.

c.929A>C (p.Asn310Thr) homeodomain missense

MISSENSE

Homozygous missense variant in the homeobox DNA-binding domain identified in a four-generation consanguineous Pakistani family mapped to the ECTD9 locus at 12q13.13. Homology modeling predicted loss of hydrogen bonding within the homeodomain fold.

Show evidence (2 references)

PMID:28403827 SUPPORT Human Clinical

"Mutation screening revealed a novel missense mutation (c.929A > C; p.Asn310Thr) in homeobox DNA binding domain of HOXC13 gene in affected members of the family."

Reports the homeodomain missense allele segregating in the ECTD9-mapped Pakistani family.

PMID:28403827 SUPPORT Computational

"Due to mutation, loss of hydrogen bonding and difference in potential energy occurs, which may resulting in alteration of protein function."

Structural modeling supporting a functional consequence. Marked PARTIAL and COMPUTATIONAL because the prediction is in silico rather than an experimental assay.

c.931C>T (p.Arg311Trp) protein-destabilizing missense

MISSENSE

Homozygous homeodomain missense variant that, unlike other homeodomain alleles, acts by reducing HOXC13 protein stability rather than by abolishing DNA binding, establishing a third molecular route to the same phenotype.

Show evidence (2 references)

PMID:40225922 SUPPORT Human Clinical

"Here, we report a case of HOXC13-related PHNED with a rare homozygous variant, c.931C>T, p.Arg311Trp."

Identifies the variant and its homozygous state in the affected individual.

PMID:40225922 SUPPORT In Vitro

"in vitro overexpression assays revealed that the p.Arg311Trp variant decreases HOXC13 protein stability"

Functional assay establishing reduced protein stability as this allele's mechanism, distinct from impaired DNA binding.

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Medical Actions

2

Symptomatic and Supportive Management

Action: Symptomatic Therapy NCIT:C170740

No disease-modifying therapy exists. Management is supportive: gentle hair care avoiding traction and harsh chemical or heat treatment, protective care of dystrophic and fragile nails, and cosmetic measures such as wigs or hairpieces. Because sweating and dentition are normal, the thermoregulatory precautions and extensive dental rehabilitation required in hypohidrotic ectodermal dysplasia are not needed - a direct management consequence of the excluded phenotypes recorded above.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Counseling for autosomal recessive inheritance with a 25% sibling recurrence risk, carrier testing for at-risk relatives, and prenatal or preimplantation diagnosis where the familial biallelic HOXC13 variants are known. Consanguinity is common in reported pedigrees and is directly relevant to recurrence-risk discussion.

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Diagnosis

1

Molecular Genetic Testing with Exon-Level Copy-Number Analysis

Suspect ECTD9 when congenital generalized hypotrichosis or alopecia co-occurs with dystrophy or hypoplasia of most or all twenty nails while teeth and sweating are normal. Confirmation is molecular: a hereditary hypotrichosis / ectodermal-dysplasia panel containing HOXC13, KRT74, and KRT85, or targeted HOXC13 sequencing when the phenotype is highly specific, followed by trio or family-based exome/genome sequencing if the panel is negative. The step that changes management is copy-number analysis. A 27.6 kb homozygous deletion removing HOXC13 exon 1 is an established cause of this disease, and a sequence-only assay will not see it. Any panel or exome used to exclude ECTD9 must therefore include exon-level CNV calling; a negative sequencing-only result is not a negative test. Chromosomal microarray is a poor substitute at this scale unless probe coverage over HOXC13 happens to be adequate.

No diagnostic blood chemistry, circulating protein, metabolite, imaging study, electrophysiologic test, or enzyme assay is established. Hair microscopy and skin biopsy may show abnormal follicular differentiation but are not specific enough to replace molecular testing. Karyotyping, FISH, mitochondrial sequencing, and repeat-expansion testing are not indicated by the known mechanism. There is no population or newborn screening programme; cascade carrier testing, prenatal diagnosis, and preimplantation genetic testing become available once the familial biallelic variants are known.

Show evidence (1 reference)

PMID:23063621 SUPPORT Human Clinical

"In an additional affected female from a consanguineous Afghan family, we found a 27.6 kb homozygous microdeletion involving the first exon of HOXC13."

Establishes that a whole-exon deletion is a real ECTD9 mechanism, which is what makes exon-level copy-number analysis necessary rather than optional.

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Prevalence

1

Worldwide

Cases In Literature <1 in 1,000,000

HOXC13-related PHNED is ultra-rare and known only from individual families of multiple ancestries (Chinese, Afghan, Syrian, Pakistani, Hispanic North American, UK). As of the 2024 report of the p.Arg311Trp allele, nine families had been described worldwide; that count appears in the paper's introduction rather than its abstract. The umbrella Orphanet entry for pure hair and nail ectodermal dysplasia (ORPHA:69084, the source of MONDO:0019071's definition) records fewer than 20 reported cases across all molecular forms. No population-based registry or denominator-based study exists, so no rate is asserted here.

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Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from HOXC13-Related Pure Hair-Nail Ectodermal Dysplasia:

Hypohidrotic and hidrotic ectodermal dysplasias

Overlapping Features Normal teeth and sweating are the discriminator. Hypohidrosis with hypodontia or conical teeth points to the EDA/EDAR/EDARADD forms, curated as the `Hypohidrotic_Ectodermal_Dysplasias` grouping, not to ECTD9. This is the positive diagnostic use of the two EXCLUDED phenotypes curated above.

Other hereditary hypotrichoses and acquired alopecias

Overlapping Features Congenital onset, generalized hair involvement including eyebrows and eyelashes, accompanying nail dystrophy, and biallelic HOXC13 findings favour ECTD9 over an acquired alopecia or a hair-only hereditary hypotrichosis.

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Animal Models

4

Hoxc13 knockout pig

CRISPR/Cas9 and somatic-cell nuclear transfer were used to generate cloned piglets carrying three classes of biallelic Hoxc13 mutation. The animals lose Hoxc13 expression, downregulate the Foxn1/Krt85/Krt35 target program, and show abnormal hair follicles with no normal hair, while skin structure, skeleton, weight gain, and growth remain normal. That combination is what makes the pig a closer match to human ECTD9 than the mouse.

Species

Pig

Genotype

Hoxc13 biallelic knockout (c.396C>A homozygous and related alleles)

Publication

PMID:28011715

Pathograph links

Reduced Transactivation of Hair and Nail Differentiation Genes recapitulates fidelity: high Loss of Hoxc13 expression with measured downregulation of the FOXN1, KRT85, and KRT35 target genes, directly reproducing the transcriptional step of the human mechanism.

Limitations: Target-gene readout is bulk expression in pig skin, not human follicular tissue, and the alleles are engineered nulls rather than the homeodomain missense alleles that predominate in human patients.

Readouts

Foxn1, Krt85 and Krt35 expression in skin

Direction: DECREASED

Interpretation: Confirms that the HOXC13 target-gene program is the transcriptional output lost in this disease.

Show evidence (1 reference)

PMID:28011715 SUPPORT Model Organism

"Hoxc13 was not expressed in pigs with all three mutation types, and the expression levels of Hoxc13-regulated genes, namely, Foxn1, Krt85 and Krt35, were decreased."

Reports the measurement behind this readout.

Show evidence (1 reference)

PMID:28011715 SUPPORT Model Organism

"The phenotypes of Hoxc13 mutation in pigs were similar to those in ED-9 patients."

Supports treating this model as informative for the human mechanism.

Impaired Hair Follicle Differentiation recapitulates fidelity: high Reduced follicle number and disarrayed hair follicle architecture with no normal hair anywhere on the body, matching the human follicular defect.

Limitations: Pig hair-follicle density and cycling differ from human scalp, so severity is not directly transferable. A later study of Hoxc13-null rabbits argues that neither mice nor pigs faithfully recapitulate human hypotrichosis; see the HUMAN_MODEL_MISMATCH discussion on this entry.

Readouts

Hair follicle number and architecture

Direction: DECREASED

Interpretation: Structural correlate of the follicular differentiation node.

Show evidence (1 reference)

PMID:28011715 SUPPORT Model Organism

"The hair follicles displayed various abnormal phenotypes, such as reduced number of follicles and disarrayed hair follicle cable without normal hair all over the body."

Reports the histological measurement behind this readout.

Hoxc13-null mouse

The founding animal model, whose hair and nail defects motivated HOXC13 as a PHNED candidate gene within the 12q linkage interval. It also produces skeletal defects, progressive weight loss, and low viability that are not part of the human phenotype.

Species

Mouse

Genotype

Hoxc13 homozygous null

Publication

PMID:23063621

Pathograph links

Impaired Hair Follicle Differentiation partially recapitulates fidelity: moderate Hoxc13-null mice develop hair and nail defects closely resembling human PHNED, which is what identified HOXC13 as the candidate gene.

Limitations: The null mouse additionally shows skeletal defects, progressive weight loss, and low viability, none reported in human ECTD9 patients, so the model over-represents the systemic consequences of HOXC13 loss. Human disease is also caused chiefly by homeodomain missense alleles rather than by a complete null.

Show evidence (2 references)

PMID:23063621 SUPPORT Model Organism

"Hoxc13-null mice are known to develop hair and nail defects very similar to those seen in human PHNED."

Supports treating the null mouse as informative for the human appendage phenotype.

+ 1 more reference

Hoxc13-null rabbit

Hoxc13-ablated rabbits show complete hair loss on head and dorsum with hypotrichosis of limbs and tail, and - the model's distinctive contribution - a shifted balance between hair follicles and sebaceous glands, with reduced follicles but enlarged and more numerous sebaceous glands.

Species

Rabbit

Genotype

Hoxc13-/-

Publication

PMID:30125135

Pathograph links

Impaired Hair Follicle Differentiation recapitulates fidelity: moderate Reproduces regional hypotrichosis and proposes a specific cellular mechanism for it: a disrupted hair-follicle/sebaceous-gland balance.

Limitations: The sebaceous-gland expansion has not been demonstrated in human ECTD9 skin, so the proposed mechanism for hypotrichosis remains model-derived. The authors' claim that mice and pigs do not faithfully recapitulate hypotrichosis conflicts with the pig paper's own conclusion; see the HUMAN_MODEL_MISMATCH discussion.

Readouts

Hair follicle and sebaceous gland number

Direction: ALTERED

Interpretation: Reduced hair follicles with enlarged and increased sebaceous glands, proposed as the cellular basis of Hoxc13-related hypotrichosis.

Show evidence (1 reference)

PMID:30125135 SUPPORT Model Organism

"In addition, reduced hair follicles (HFs) while the enlarged and increased number of sebaceous glands (SGs) were also found in the Hoxc13-/- rabbits"

Reports the measurement behind this readout.

Show evidence (1 reference)

PMID:30125135 SUPPORT Model Organism

"our findings demonstrate that Hoxc13-/- rabbits can be used as a model for human ECTD-9, especially to understand the pathologic mechanism of hypotrichosis"

Supports treating the rabbit as informative for the human hypotrichosis mechanism.

Naked (N) mouse (Hoxc13 terminal truncation)

A spontaneous mouse mutation characterized as a terminal truncation of Hoxc13 and independently recreated by CRISPR/Cas9. It is the mechanistic outlier among the Hoxc13 animal models: the truncated transcript escapes nonsense-mediated decay, the truncated protein is present in follicles, and heterozygotes are affected - a semi-dominant, apparently dominant-negative behaviour unlike the recessive human pattern and unlike the heterozygous Hoxc13 knockout, which is unaffected.

Species

Mouse

Genotype

Hoxc13 Naked (N) terminal truncation, N/N and N/+

Publication

DOI:10.1111/exd.14469

Pathograph links

HOXC13 Transcription Factor Loss of Function partially recapitulates fidelity: moderate N/N homozygotes reproduce the cardinal ECTD9 appendage phenotype (generalized alopecia with abnormal nails), and the allele is a better practical model than the poorly viable Hoxc13 knockout.

Limitations: The mechanism is not the human one. Human ECTD9 alleles act by nonsense-mediated decay, impaired DNA binding, or reduced protein stability, all recessive; the Naked allele instead escapes NMD and yields a persistent truncated protein that is pathogenic in heterozygotes. It therefore models the phenotype without modeling the loss-of-function route, and no dominant-negative HOXC13 allele has been reported in humans. N/N mice also have a short lifespan, which human patients do not.

Readouts

Coat and nail phenotype in homozygotes

Direction: ALTERED

Interpretation: Homozygous phenotype matching the human appendage presentation.

Show evidence (1 reference)

DOI:10.1111/exd.14469 SUPPORT Model Organism

"homozygous N/N mice exhibit generalized alopecia with abnormal nails and a short lifespan"

Reports the homozygous coat and nail phenotype together with the reduced lifespan that human patients do not share.

Heterozygote phenotype and truncated protein persistence

Direction: ALTERED

Interpretation: Heterozygous involvement plus retained truncated protein is the signature of a dominant-negative allele rather than haploinsufficiency.

Show evidence (2 references)

DOI:10.1111/exd.14469 SUPPORT Model Organism

"N/+ mice show generalized or partial alopecia, associated with loss of hair fibres, along with normal lifespan and fertility"

Establishes that heterozygotes are affected, in contrast to heterozygous Hoxc13 knockout mice and to human ECTD9 carriers.

+ 1 more reference

Show evidence (1 reference)

DOI:10.1111/exd.14469 SUPPORT Model Organism

"Considering the low viability of the Hoxc13 KO mice, the Naked mutation provides an attractive new model for studying ECTD9 disease mechanisms."

The authors propose the allele as an ECTD9 model, which is the claim this link records; the limitations field carries the mechanistic caveat.

{ }

Source YAML

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name: HOXC13-Related Pure Hair-Nail Ectodermal Dysplasia
creation_date: "2026-08-17T00:00:00Z"
description: >-
  Ectodermal dysplasia 9, hair/nail type (ECTD9) is a rare autosomal recessive
  pure hair and nail ectodermal dysplasia caused by biallelic loss-of-function
  variants in HOXC13, a homeodomain transcription factor expressed in hair
  follicle and nail-forming epithelium that transactivates the terminal
  differentiation program of those appendages, including hair keratin genes.
  Affected individuals have congenital hypotrichosis ranging to complete
  alopecia of scalp, eyebrows, and eyelashes, together with nail dystrophy that
  typically involves all twenty nails. The diagnostically decisive feature is
  what is not involved: unlike the hypohidrotic ectodermal dysplasias, sweat
  gland function and dentition are preserved, restricting the phenotype to hair
  and nail appendages. Reported alleles converge on reduced HOXC13 target-gene
  transactivation by three routes - nonsense-mediated decay of truncating and
  deletion alleles, impaired DNA binding by homeodomain missense alleles, and
  reduced protein stability.
category: Genetic
parents:
- Ectodermal Dysplasia
disease_term:
  preferred_term: ectodermal dysplasia 9, hair/nail type
  term:
    id: MONDO:0013976
    label: ectodermal dysplasia 9, hair/nail type
inheritance:
- name: Autosomal recessive
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    All reported ECTD9 families segregate biallelic HOXC13 variants, most often
    homozygous alleles in consanguineous kindreds. Heterozygous carriers are
    clinically unaffected.
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Taken together, our results demonstrate that loss-of-function mutations in
      HOXC13 cause autosomal-recessive PHNED and further highlight the
      importance of HOXC13 in hair and nail development.
    explanation: >-
      The discovery paper's conclusion establishes autosomal recessive
      inheritance for HOXC13-related PHNED.
  - reference: PMID:28297138
    reference_title: "A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We describe a homozygous novel missense mutation in the HOXC13 gene that
      resulted in autosomal recessive PHNED in a Hispanic child.
    explanation: >-
      Independent confirmation of autosomal recessive inheritance in a North
      American family, showing the mode is not an artifact of the consanguineous
      pedigrees through which the gene was discovered.
genetic:
- name: HOXC13 Biallelic Loss-of-Function Variants
  gene_term:
    preferred_term: HOXC13
    term:
      id: hgnc:5125
      label: HOXC13
  relationship_type: CAUSATIVE
  variants:
  - name: c.390C>A (p.Tyr130*) nonsense
    description: >-
      Homozygous nonsense allele identified by whole-exome sequencing in a
      consanguineous Chinese family, the first HOXC13 variant reported in PHNED.
      Scalp tissue from the index case showed dramatically reduced HOXC13 mRNA
      and nearly absent protein in hair follicles, indicating nonsense-mediated
      decay.
    type: NONSENSE
    evidence:
    - reference: PMID:23063621
      reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We performed whole-exome sequencing in a consanguineous Chinese family
        affected by PHNED and identified a homozygous nonsense mutation
      explanation: >-
        Identifies the nonsense allele and its homozygous state in all affected
        members of the discovery family. The quote is trimmed before the
        bracketed HGVS span `[p.Tyr130(∗)]`, which the reference validator
        strips before matching.
  - name: 27.6 kb microdeletion of HOXC13 exon 1
    description: >-
      Homozygous 27.6 kb deletion removing the first exon of HOXC13, found in an
      affected female from a consanguineous Afghan family. A predicted null
      allele, and the reason deletion analysis belongs in the diagnostic
      strategy alongside sequencing.
    type: DELETION
    evidence:
    - reference: PMID:23063621
      reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        In an additional affected female from a consanguineous Afghan family, we
        found a 27.6 kb homozygous microdeletion involving the first exon of
        HOXC13.
      explanation: >-
        Documents a whole-exon deletion allele, establishing that copy-number
        loss as well as point mutation causes ECTD9.
  - name: c.355delC (p.Leu119Trpfs*20) frameshift
    description: >-
      Homozygous single-nucleotide deletion in a consanguineous Syrian family.
      Expression studies showed the truncated protein mislocalizes to the
      cytoplasm and cannot transactivate target-gene promoters, giving direct
      functional evidence for loss of function.
    type: FRAMESHIFT
    evidence:
    - reference: PMID:23315978
      reference_title: "A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Sequencing of another candidate gene HOXC13 within the linkage interval
        identified a homozygous frameshift mutation (c.355delC;
        p.Leu119Trpfs*20).
      explanation: >-
        Identifies the frameshift allele and its homozygous state in the
        affected Syrian kindred.
  - name: c.812A>G (p.Gln271Arg) homeodomain missense
    description: >-
      Homozygous missense variant in the DNA-binding homeodomain, reported in a
      Hispanic child and the first missense HOXC13 allele described in PHNED.
      Pathogenicity support for this allele is familial cosegregation plus in
      silico prediction (PolyPhen-2, SIFT); no direct functional assay was
      performed.
    type: MISSENSE
    evidence:
    - reference: PMID:28297138
      reference_title: "A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The mutation c.812A>G (p.Gln271Arg) is located within the DNA-binding
        domain of the HOXC13 gene, cosegregates within the family, and is
        predicted to be maximally damaging.
      explanation: >-
        Localizes the missense allele to the DNA-binding domain and reports
        familial cosegregation.
  - name: c.929A>C (p.Asn310Thr) homeodomain missense
    description: >-
      Homozygous missense variant in the homeobox DNA-binding domain identified
      in a four-generation consanguineous Pakistani family mapped to the ECTD9
      locus at 12q13.13. Homology modeling predicted loss of hydrogen bonding
      within the homeodomain fold.
    type: MISSENSE
    evidence:
    - reference: PMID:28403827
      reference_title: "A novel mutation in homeobox DNA binding domain of HOXC13 gene underlies pure hair and nail ectodermal dysplasia (ECTD9) in a Pakistani family."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Mutation screening revealed a novel missense mutation (c.929A > C;
        p.Asn310Thr) in homeobox DNA binding domain of HOXC13 gene in affected
        members of the family.
      explanation: >-
        Reports the homeodomain missense allele segregating in the ECTD9-mapped
        Pakistani family.
    - reference: PMID:28403827
      reference_title: "A novel mutation in homeobox DNA binding domain of HOXC13 gene underlies pure hair and nail ectodermal dysplasia (ECTD9) in a Pakistani family."
      supports: SUPPORT
      evidence_source: COMPUTATIONAL
      snippet: >-
        Due to mutation, loss of hydrogen bonding and difference in potential
        energy occurs, which may resulting in alteration of protein function.
      explanation: >-
        Structural modeling supporting a functional consequence. Marked PARTIAL
        and COMPUTATIONAL because the prediction is in silico rather than an
        experimental assay.
  - name: c.931C>T (p.Arg311Trp) protein-destabilizing missense
    description: >-
      Homozygous homeodomain missense variant that, unlike other homeodomain
      alleles, acts by reducing HOXC13 protein stability rather than by
      abolishing DNA binding, establishing a third molecular route to the same
      phenotype.
    type: MISSENSE
    evidence:
    - reference: PMID:40225922
      reference_title: "Homozygous HOXC13 Variant Causes Pure Hair and Nail Ectodermal Dysplasia via Reduction in Protein Stability."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Here, we report a case of HOXC13-related PHNED with a rare homozygous
        variant, c.931C>T, p.Arg311Trp.
      explanation: >-
        Identifies the variant and its homozygous state in the affected
        individual.
    - reference: PMID:40225922
      reference_title: "Homozygous HOXC13 Variant Causes Pure Hair and Nail Ectodermal Dysplasia via Reduction in Protein Stability."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        in vitro overexpression assays revealed that the p.Arg311Trp variant
        decreases HOXC13 protein stability
      explanation: >-
        Functional assay establishing reduced protein stability as this allele's
        mechanism, distinct from impaired DNA binding.
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autosomal-recessive PHNED has previously been mapped to chromosomal region
      12q12-q14.1, which contains the type II hair keratin and HOXC clusters.
    explanation: >-
      Explains why HOXC13 and the type II hair keratin genes (KRT85, KRT74) are
      all PHNED candidates: they share the same 12q linkage interval. This is
      also why ECTD4, ECTD7, and ECTD9 are readily confused in the literature.
  notes: >-
    HOXC13-related PHNED is exceptionally rare. The 2024 report describing
    p.Arg311Trp identifies its family as the ninth reported worldwide; that
    count appears in the paper's introduction rather than its abstract, so it is
    recorded as a note rather than a quoted evidence snippet. Two further
    published families (PMID:23461661, Ali et al. 2013; PMID:29278420,
    Humbatova et al. 2018) are not cited with evidence blocks here because both
    cache as Letters with no retrievable abstract text. PMID:41714886 (Sharma &
    Vinay 2026, "Pure Hair-Nail Ectodermal Dysplasia: Expanding the HOXC13
    Genotypic Spectrum") is cached by this entry's research pass for the same
    reason and likewise carries no quotable content - it caches with
    `content_type: unavailable` and an empty body - so it too is recorded here
    rather than cited. It is listed explicitly so a later curator does not read
    its presence in `references_cache/` as an uncited oversight.
pathophysiology:
- name: HOXC13 Transcription Factor Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Biallelic HOXC13 variants deplete the functional pool of HOXC13 protein in
    hair follicle and nail matrix nuclei. Three demonstrated routes converge
    here in human disease: truncating and whole-exon deletion alleles that
    trigger nonsense-mediated decay or yield a cytoplasmically mislocalized
    protein; homeodomain missense alleles that impair sequence-specific DNA
    binding; and at least one homeodomain missense allele that destabilizes the
    folded protein. The shared endpoint is reduced nuclear HOXC13 activity.

    A fourth route exists in the mouse but does not belong to this node. The
    Naked (N) allele is a terminal truncation whose transcript escapes
    nonsense-mediated decay, leaving a persistent truncated protein that is
    pathogenic in heterozygotes - a dominant-negative mechanism rather than a
    depletion of functional protein. No such allele has been reported in
    humans, and every human ECTD9 pedigree is recessive. The mouse allele is
    curated under `animal_models` and its divergence is one of the questions in
    the `hoxc13_model_fidelity_disagreement` discussion; it is deliberately not
    folded into this loss-of-function node, which would misdescribe it.
  molecular_functions:
  - preferred_term: DNA-binding transcription factor activity, RNA polymerase II-specific
    term:
      id: GO:0000981
      label: DNA-binding transcription factor activity, RNA polymerase II-specific
    modifier: LOSS_OF_FUNCTION
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We examined HOXC13 expression in scalp specimen obtained from the index
      individual of the Chinese family and detected dramatically reduced mRNA
      levels in skin tissue and nearly absent protein staining in hair
      follicles, suggesting a mechanism of nonsense-mediated mRNA decay.
    explanation: >-
      Direct patient-tissue demonstration that a truncating allele depletes
      HOXC13 transcript and protein in the affected appendage.
  - reference: PMID:23315978
    reference_title: "A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Expression studies in cultured cells revealed that the mutant HOXC13
      protein mislocalized within the cytoplasm, and failed to upregulate the
      promoter activities of its target genes.
    explanation: >-
      Functional demonstration that a truncating allele both mislocalizes the
      protein and abolishes transactivation.
  - reference: PMID:40225922
    reference_title: "Homozygous HOXC13 Variant Causes Pure Hair and Nail Ectodermal Dysplasia via Reduction in Protein Stability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Previously reported biallelic HOXC13 pathogenic variants led to PHNED by
      either disrupting protein expression through nonsense-mediated decay or
      altering the DNA-binding affinity of the homeobox domain of HOXC13.
    explanation: >-
      Summarizes the two previously established molecular routes to HOXC13 loss
      of function that this node aggregates.
  downstream:
  - target: Reduced Transactivation of Hair and Nail Differentiation Genes
    causal_link_type: DIRECT
- name: Reduced Transactivation of Hair and Nail Differentiation Genes
  biological_scale: MOLECULAR
  description: >-
    HOXC13 drives the terminal differentiation program of hair- and nail-forming
    keratinocytes, including hair keratin genes. Reported HOXC13 target genes
    whose expression falls when HOXC13 is lost include KRT35, KRT85, and FOXN1.
    Loss of this transcriptional output deprives differentiating keratinocytes
    of the structural proteins needed to build a normal hair shaft or nail
    plate. Notably, KRT85 is itself the gene mutated in ECTD4, so the HOXC13 and
    keratin forms of PHNED are linked as regulator and target within one pathway
    rather than being merely phenocopies.
  biological_processes:
  - preferred_term: regulation of transcription by RNA polymerase II
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
    modifier: DECREASED
  - preferred_term: keratinization
    term:
      id: GO:0031424
      label: keratinization
    modifier: DECREASED
  cell_types:
  - preferred_term: Hair follicle cell
    term:
      id: CL:0002559
      label: hair follicle cell
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We also observed markedly decreased expression of four HOXC13 target genes
      in the specimen.
    explanation: >-
      Patient scalp tissue shows reduced target-gene expression, the defining
      step of this node, in vivo rather than only in reporter assays.
  - reference: PMID:23315978
    reference_title: "A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      failed to upregulate the promoter activities of its target genes
    explanation: >-
      Promoter-reporter assays confirm that mutant HOXC13 cannot transactivate
      its downstream targets.
  - reference: PMID:28011715
    reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Hoxc13 was not expressed in pigs with all three mutation types, and the
      expression levels of Hoxc13-regulated genes, namely, Foxn1, Krt85 and
      Krt35, were decreased.
    explanation: >-
      Names the specific downstream targets (FOXN1, KRT85, KRT35) whose
      expression falls on HOXC13 loss, in a large-animal model whose skin
      phenotype closely matches the human disease.
  downstream:
  - target: Impaired Hair Follicle Differentiation
    causal_link_type: DIRECT
  - target: Impaired Nail Matrix Differentiation
    causal_link_type: DIRECT
- name: Impaired Hair Follicle Differentiation
  biological_scale: CELLULAR
  description: >-
    Without the HOXC13-dependent structural gene program, hair follicle
    keratinocytes fail to assemble a normal cortex and cuticle. Affected scalp
    skin shows reduced follicle numbers and disorganized hair shafts lacking
    normal layered architecture, producing hair that is sparse, fragile, or
    entirely absent from birth.
  cell_types:
  - preferred_term: Hair follicle cell
    term:
      id: CL:0002559
      label: hair follicle cell
  biological_processes:
  - preferred_term: hair follicle development
    term:
      id: GO:0001942
      label: hair follicle development
    modifier: ABNORMAL
  evidence:
  - reference: PMID:28011715
    reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      The hair follicles displayed various abnormal phenotypes, such as reduced
      number of follicles and disarrayed hair follicle cable without normal hair
      all over the body.
    explanation: >-
      Direct histological characterization of the follicular defect caused by
      Hoxc13 loss, in the animal model that best matches the human phenotype.
  - reference: PMID:28297138
    reference_title: "A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our findings illustrate the critical role of HOXC13 in human hair and nail
      development.
    explanation: >-
      Supports HOXC13-dependence of human hair follicle development, the
      substrate of this node.
  notes: >-
    Scalp histology from an affected individual shows a reduced number of hair
    follicles with disorganized hair shafts lacking the normal layered
    structure. That description appears in the introduction of PMID:40225922
    rather than in any cached abstract, so it is recorded here as a note rather
    than as a quoted snippet.
  downstream:
  - target: Hypotrichosis and Alopecia
    causal_link_type: DIRECT
  - target: Abnormal Hair Shaft Morphology
    causal_link_type: DIRECT
- name: Impaired Nail Matrix Differentiation
  biological_scale: CELLULAR
  description: >-
    HOXC13 is also required in nail-forming epithelium, where the same
    target-gene program supplies the keratins of the nail plate. Loss of HOXC13
    activity yields a structurally defective nail plate, clinically evident as
    nail dystrophy typically involving all twenty nails. Mouse genetics places
    this requirement at the level of the whole HoxC cluster: deleting the
    cluster in the limb ectoderm abolishes nails entirely.
  cell_types:
  - preferred_term: Nail matrix keratinocyte
    term:
      id: CL:4052064
      label: nail matrix keratinocyte
  biological_processes:
  - preferred_term: keratinization
    term:
      id: GO:0031424
      label: keratinization
    modifier: DECREASED
  evidence:
  - reference: PMID:28403827
    reference_title: "A novel mutation in homeobox DNA binding domain of HOXC13 gene underlies pure hair and nail ectodermal dysplasia (ECTD9) in a Pakistani family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Affected members exhibited PHNED phenotypes with involvement of complete
      hair loss and nail dysplasia.
    explanation: >-
      Documents nail dysplasia alongside hair loss as the paired consequence of
      HOXC13 loss of function.
  - reference: PMID:33199643
    reference_title: "Mammalian-specific ectodermal enhancers control the expression of Hoxc genes in developing nails and hair follicles."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      deletion of the HoxC cluster led to mice lacking nails (anonychia), a
      condition stronger than the previously reported loss of function of
      Hoxc13, which is the causative gene of the ectodermal dysplasia 9 (ECTD9)
      in human patients
    explanation: >-
      Establishes HoxC-cluster dependence of nail formation and positions Hoxc13
      loss as a partial version of that requirement, consistent with nail
      dystrophy rather than anonychia in ECTD9 patients.
  downstream:
  - target: Nail Dystrophy
    causal_link_type: DIRECT
phenotypes:
- category: Dermatologic
  name: Hypotrichosis and Alopecia
  description: >-
    Congenital sparse hair, ranging from partial hypotrichosis of the scalp,
    eyebrows, and eyelashes to complete alopecia present from birth. Severity
    varies between families and does not map cleanly onto allele class.
  phenotype_term:
    preferred_term: Alopecia
    term:
      id: HP:0001596
      label: Alopecia
  frequency: OBLIGATE
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pure hair and nail ectodermal dysplasia (PHNED) is a congenital condition
      characterized by hypotrichosis and nail dystrophy.
    explanation: >-
      Establishes hypotrichosis as a defining, congenital feature of the entity
      in the paper that identified HOXC13 as its cause.
  - reference: PMID:23315978
    reference_title: "A homozygous frameshift mutation in the HOXC13 gene underlies pure hair and nail ectodermal dysplasia in a Syrian family."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we have analyzed a consanguineous Syrian family with an affected girl
      having complete alopecia and nail dystrophy since birth
    explanation: >-
      Documents the severe end of the range, congenital complete alopecia, in a
      molecularly confirmed HOXC13 case.
  notes: >-
    `frequency: OBLIGATE` is justified by hair involvement being definitional
    for the "pure hair and nail" entity, not by a counted cohort. No ECTD9 case
    series large enough to estimate a frequency band has been published; see
    docs/frequency-evidence-guidelines.md.
- category: Dermatologic
  name: Nail Dystrophy
  description: >-
    Dystrophic nail plates from birth, described across families as nail
    dysplasia, hypoplastic or irregular nails, brittleness, and distal
    onycholysis, usually involving all twenty nails.
  phenotype_term:
    preferred_term: Nail dystrophy
    term:
      id: HP:0008404
      label: Nail dystrophy
  frequency: OBLIGATE
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pure hair and nail ectodermal dysplasia (PHNED) is a congenital condition
      characterized by hypotrichosis and nail dystrophy.
    explanation: >-
      Establishes nail dystrophy as the second cardinal, congenital feature of
      the entity.
  notes: >-
    `frequency: OBLIGATE` reflects that nail involvement is definitional for
    PHNED, not a measured proportion.
- category: Dermatologic
  name: Abnormal Hair Shaft Morphology
  description: >-
    Where hair is present, shafts are structurally abnormal and disorganized,
    lacking the normal layered cortex and cuticle architecture.
  phenotype_term:
    preferred_term: Abnormal hairshaft morphology
    term:
      id: HP:0003328
      label: Abnormal hairshaft morphology
  evidence:
  - reference: PMID:40225922
    reference_title: "Homozygous HOXC13 Variant Causes Pure Hair and Nail Ectodermal Dysplasia via Reduction in Protein Stability."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pure hair and nail ectodermal dysplasia (PHNED) is a congenital disorder
      characterized by reduced or absent hair and dystrophic nails.
    explanation: >-
      Supports congenitally abnormal hair. Marked PARTIAL because the quoted
      sentence establishes reduced or absent hair rather than the specific
      microscopic shaft abnormality, which is recorded in `notes`.
  notes: >-
    Light microscopy of scalp skin in an affected individual showed disorganized
    hair shafts lacking the normal layered structure (PMID:40225922
    introduction; not present in the cached abstract).
- category: Ophthalmologic
  name: Lacrimal Duct Obstruction
  description: >-
    Nasolacrimal duct obstruction reported in a single HOXC13-related PHNED
    family. It is not a feature of most reported kindreds and should be treated
    as a single-report phenotypic expansion rather than part of the core ECTD9
    phenotype.
  phenotype_term:
    preferred_term: Abnormal lacrimal duct morphology
    term:
      id: HP:0011481
      label: Abnormal lacrimal duct morphology
  frequency: VERY_RARE
  notes: >-
    Reported in PMID:29278420 (Humbatova et al., Br J Dermatol 2018) and
    restated in the introduction of PMID:40225922. Neither source has a cached
    abstract containing a quotable sentence for this claim (PMID:29278420 caches
    as a Letter with `content_type: unavailable`), so this phenotype is curated
    without an evidence block per the evidence SOP rather than with a fabricated
    snippet. The Edison report independently reached the same conclusion, noting
    the retrieved full text was insufficient to establish frequency or
    reproducibility.
- category: Dermatologic
  name: Hypohidrosis Absent
  frequency: EXCLUDED
  diagnostic: true
  description: >-
    A defining exclusion. Eccrine sweat gland function is preserved in pure hair
    and nail ectodermal dysplasia. Its absence is what separates ECTD9 from the
    hypohidrotic ectodermal dysplasias (EDA, EDAR, EDARADD), in which
    hypohidrosis and heat intolerance are cardinal and carry the principal
    morbidity.
  phenotype_term:
    preferred_term: Hypohidrosis
    term:
      id: HP:0000966
      label: Hypohidrosis
    modifier: ABSENT
  evidence:
  - reference: PMID:28297138
    reference_title: "A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pure hair and nail ectodermal dysplasia (PHNED) is a rare disorder that
      presents with hypotrichosis and nail dystrophy while sparing other
      ectodermal structures such as teeth and sweat glands.
    explanation: >-
      Explicitly states that sweat glands are spared in PHNED, the claim this
      excluded phenotype records.
  notes: >-
    Curated with `frequency: EXCLUDED` plus `modifier: ABSENT`, following the
    convention used in Osteogenesis_Imperfecta_Type_V and
    Epilepsy_with_Generalized_Tonic-Clonic_Seizures_Alone. `frequency: EXCLUDED`
    is what the HPOA exporter reads to emit a NOT-qualified row; `modifier:
    ABSENT` documents intent.
- category: Dental
  name: Hypodontia Absent
  frequency: EXCLUDED
  diagnostic: true
  description: >-
    The second defining exclusion. Dentition is normal in pure hair and nail
    ectodermal dysplasia. Tooth agenesis, conical teeth, and oligodontia belong
    to the hypohidrotic and TP63-related ectodermal dysplasias, and their
    presence should prompt reconsideration of the ECTD9 diagnosis.
  phenotype_term:
    preferred_term: Hypodontia
    term:
      id: HP:0000668
      label: Hypodontia
    modifier: ABSENT
  evidence:
  - reference: PMID:28297138
    reference_title: "A Novel Homozygous Missense Mutation in HOXC13 Leads to Autosomal Recessive Pure Hair and Nail Ectodermal Dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Pure hair and nail ectodermal dysplasia (PHNED) is a rare disorder that
      presents with hypotrichosis and nail dystrophy while sparing other
      ectodermal structures such as teeth and sweat glands.
    explanation: >-
      Explicitly states that teeth are spared in PHNED, the claim this excluded
      phenotype records.
- category: Skeletal
  name: Skeletal Involvement Absent
  frequency: EXCLUDED
  diagnostic: true
  description: >-
    A third exclusion, and the one that separates the human disease from its
    founding animal model. Hoxc13-null mice develop skeletal defects,
    progressive weight loss, and low viability; reported human ECTD9 patients
    have none of these. This exclusion is therefore also the anchor of the
    human/model mismatch discussion recorded on this entry.

    Term-scope caveat: the bound term HP:0009121 is *Abnormal axial skeleton
    morphology*, which is narrower than the node name. The absence being
    asserted covers the skeleton generally - the murine phenotype is vertebral,
    so the axial term is the closest available match to the specific finding
    that is missing in humans, but it does not by itself exclude appendicular
    involvement. HP:0009121 was chosen over a broader skeletal term because it
    names what the mouse literature actually reports; read the exclusion as
    scoped to that.
  phenotype_term:
    preferred_term: Abnormal axial skeleton morphology
    term:
      id: HP:0009121
      label: Abnormal axial skeleton morphology
    modifier: ABSENT
  evidence:
  - reference: PMID:28011715
    reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Ectodermal dysplasia-9 (ED-9) is a congenital condition characterized by
      hypotrichosis and nail dystrophy without other disorders, and Hoxc13 is a
      pathogenic gene for ED-9.
    explanation: >-
      States that ED-9 is hypotrichosis and nail dystrophy "without other
      disorders", which is the assertion that skeletal and systemic involvement
      is absent in the human disease. Evidence source is MODEL_ORGANISM because
      the citing paper reports an animal model, although this particular
      sentence describes the human condition being modeled.
diagnosis:
- name: Molecular Genetic Testing with Exon-Level Copy-Number Analysis
  description: >-
    Suspect ECTD9 when congenital generalized hypotrichosis or alopecia
    co-occurs with dystrophy or hypoplasia of most or all twenty nails while
    teeth and sweating are normal. Confirmation is molecular: a hereditary
    hypotrichosis / ectodermal-dysplasia panel containing HOXC13, KRT74, and
    KRT85, or targeted HOXC13 sequencing when the phenotype is highly specific,
    followed by trio or family-based exome/genome sequencing if the panel is
    negative.

    The step that changes management is copy-number analysis. A 27.6 kb
    homozygous deletion removing HOXC13 exon 1 is an established cause of this
    disease, and a sequence-only assay will not see it. Any panel or exome used
    to exclude ECTD9 must therefore include exon-level CNV calling; a negative
    sequencing-only result is not a negative test. Chromosomal microarray is a
    poor substitute at this scale unless probe coverage over HOXC13 happens to
    be adequate.
  evidence:
  - reference: PMID:23063621
    reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In an additional affected female from a consanguineous Afghan family, we
      found a 27.6 kb homozygous microdeletion involving the first exon of
      HOXC13.
    explanation: >-
      Establishes that a whole-exon deletion is a real ECTD9 mechanism, which is
      what makes exon-level copy-number analysis necessary rather than optional.
  notes: >-
    No diagnostic blood chemistry, circulating protein, metabolite, imaging
    study, electrophysiologic test, or enzyme assay is established. Hair
    microscopy and skin biopsy may show abnormal follicular differentiation but
    are not specific enough to replace molecular testing. Karyotyping, FISH,
    mitochondrial sequencing, and repeat-expansion testing are not indicated by
    the known mechanism. There is no population or newborn screening programme;
    cascade carrier testing, prenatal diagnosis, and preimplantation genetic
    testing become available once the familial biallelic variants are known.
differential_diagnoses:
- name: KRT74- and KRT85-related PHNED
  description: >-
    The two sibling PHNED forms present identically and are separated only by
    the causal gene - which is why the recommended first-line test is a panel
    covering all three rather than single-gene HOXC13 sequencing. All three are
    collected in the `Pure_Hair_and_Nail_Ectodermal_Dysplasias` grouping.
- name: Hypohidrotic and hidrotic ectodermal dysplasias
  description: >-
    Normal teeth and sweating are the discriminator. Hypohidrosis with
    hypodontia or conical teeth points to the EDA/EDAR/EDARADD forms, curated as
    the `Hypohidrotic_Ectodermal_Dysplasias` grouping, not to ECTD9. This is the
    positive diagnostic use of the two EXCLUDED phenotypes curated above.
- name: Isolated nail disorders, including RSPO4-related anonychia
  description: >-
    Nail-only presentations without the congenital generalized hair involvement
    fall outside ECTD9; hair and nail involvement together is required.
- name: Other hereditary hypotrichoses and acquired alopecias
  description: >-
    Congenital onset, generalized hair involvement including eyebrows and
    eyelashes, accompanying nail dystrophy, and biallelic HOXC13 findings favour
    ECTD9 over an acquired alopecia or a hair-only hereditary hypotrichosis.
prevalence:
- population: Worldwide
  measure_type: CASES_IN_LITERATURE
  prevalence_class: BELOW_1_IN_1000000
  notes: >-
    HOXC13-related PHNED is ultra-rare and known only from individual families
    of multiple ancestries (Chinese, Afghan, Syrian, Pakistani, Hispanic North
    American, UK). As of the 2024 report of the p.Arg311Trp allele, nine
    families had been described worldwide; that count appears in the paper's
    introduction rather than its abstract. The umbrella Orphanet entry for pure
    hair and nail ectodermal dysplasia (ORPHA:69084, the source of
    MONDO:0019071's definition) records fewer than 20 reported cases across all
    molecular forms. No population-based registry or denominator-based study
    exists, so no rate is asserted here.
treatments:
- name: Symptomatic and Supportive Management
  description: >-
    No disease-modifying therapy exists. Management is supportive: gentle hair
    care avoiding traction and harsh chemical or heat treatment, protective care
    of dystrophic and fragile nails, and cosmetic measures such as wigs or
    hairpieces. Because sweating and dentition are normal, the thermoregulatory
    precautions and extensive dental rehabilitation required in hypohidrotic
    ectodermal dysplasia are not needed - a direct management consequence of the
    excluded phenotypes recorded above.
  treatment_term:
    preferred_term: Symptomatic Therapy
    term:
      id: NCIT:C170740
      label: Symptomatic Therapy
  therapeutic_modality: OTHER
- name: Genetic Counseling
  description: >-
    Counseling for autosomal recessive inheritance with a 25% sibling recurrence
    risk, carrier testing for at-risk relatives, and prenatal or preimplantation
    diagnosis where the familial biallelic HOXC13 variants are known.
    Consanguinity is common in reported pedigrees and is directly relevant to
    recurrence-risk discussion.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  therapeutic_modality: BEHAVIORAL
animal_models:
- name: Hoxc13 knockout pig
  species: Pig
  genotype: Hoxc13 biallelic knockout (c.396C>A homozygous and related alleles)
  publication: PMID:28011715
  description: >-
    CRISPR/Cas9 and somatic-cell nuclear transfer were used to generate cloned
    piglets carrying three classes of biallelic Hoxc13 mutation. The animals
    lose Hoxc13 expression, downregulate the Foxn1/Krt85/Krt35 target program,
    and show abnormal hair follicles with no normal hair, while skin structure,
    skeleton, weight gain, and growth remain normal. That combination is what
    makes the pig a closer match to human ECTD9 than the mouse.
  modeled_mechanisms:
  - target: Reduced Transactivation of Hair and Nail Differentiation Genes
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Loss of Hoxc13 expression with measured downregulation of the FOXN1,
      KRT85, and KRT35 target genes, directly reproducing the transcriptional
      step of the human mechanism.
    limitations: >-
      Target-gene readout is bulk expression in pig skin, not human follicular
      tissue, and the alleles are engineered nulls rather than the homeodomain
      missense alleles that predominate in human patients.
    readouts:
    - name: Foxn1, Krt85 and Krt35 expression in skin
      target: Reduced Transactivation of Hair and Nail Differentiation Genes
      direction: DECREASED
      interpretation: >-
        Confirms that the HOXC13 target-gene program is the transcriptional
        output lost in this disease.
      evidence:
      - reference: PMID:28011715
        reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          Hoxc13 was not expressed in pigs with all three mutation types, and
          the expression levels of Hoxc13-regulated genes, namely, Foxn1, Krt85
          and Krt35, were decreased.
        explanation: Reports the measurement behind this readout.
    evidence:
    - reference: PMID:28011715
      reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        The phenotypes of Hoxc13 mutation in pigs were similar to those in ED-9
        patients.
      explanation: >-
        Supports treating this model as informative for the human mechanism.
  - target: Impaired Hair Follicle Differentiation
    relationship: RECAPITULATES
    fidelity: HIGH
    description: >-
      Reduced follicle number and disarrayed hair follicle architecture with no
      normal hair anywhere on the body, matching the human follicular defect.
    limitations: >-
      Pig hair-follicle density and cycling differ from human scalp, so severity
      is not directly transferable. A later study of Hoxc13-null rabbits argues
      that neither mice nor pigs faithfully recapitulate human hypotrichosis;
      see the HUMAN_MODEL_MISMATCH discussion on this entry.
    readouts:
    - name: Hair follicle number and architecture
      target: Impaired Hair Follicle Differentiation
      direction: DECREASED
      interpretation: Structural correlate of the follicular differentiation node.
      evidence:
      - reference: PMID:28011715
        reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          The hair follicles displayed various abnormal phenotypes, such as
          reduced number of follicles and disarrayed hair follicle cable without
          normal hair all over the body.
        explanation: Reports the histological measurement behind this readout.
- name: Hoxc13-null mouse
  species: Mouse
  genotype: Hoxc13 homozygous null
  publication: PMID:23063621
  description: >-
    The founding animal model, whose hair and nail defects motivated HOXC13 as a
    PHNED candidate gene within the 12q linkage interval. It also produces
    skeletal defects, progressive weight loss, and low viability that are not
    part of the human phenotype.
  modeled_mechanisms:
  - target: Impaired Hair Follicle Differentiation
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Hoxc13-null mice develop hair and nail defects closely resembling human
      PHNED, which is what identified HOXC13 as the candidate gene.
    limitations: >-
      The null mouse additionally shows skeletal defects, progressive weight
      loss, and low viability, none reported in human ECTD9 patients, so the
      model over-represents the systemic consequences of HOXC13 loss. Human
      disease is also caused chiefly by homeodomain missense alleles rather than
      by a complete null.
    evidence:
    - reference: PMID:23063621
      reference_title: "Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Hoxc13-null mice are known to develop hair and nail defects very similar
        to those seen in human PHNED.
      explanation: >-
        Supports treating the null mouse as informative for the human appendage
        phenotype.
    - reference: PMID:28011715
      reference_title: "Generation of Hoxc13 knockout pigs recapitulates human ectodermal dysplasia-9."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        However, mice carrying Hoxc13 mutation present several other serious
        disorders, such as skeletal defects, progressive weight loss and low
        viability. Mouse models cannot faithfully mimic human ED-9.
      explanation: >-
        States the limitation directly: the mouse carries extra phenotypes not
        seen in patients. Marked PARTIAL because it qualifies rather than
        supports the model's fidelity.
- name: Hoxc13-null rabbit
  species: Rabbit
  genotype: Hoxc13-/-
  publication: PMID:30125135
  description: >-
    Hoxc13-ablated rabbits show complete hair loss on head and dorsum with
    hypotrichosis of limbs and tail, and - the model's distinctive contribution
    - a shifted balance between hair follicles and sebaceous glands, with
    reduced follicles but enlarged and more numerous sebaceous glands.
  modeled_mechanisms:
  - target: Impaired Hair Follicle Differentiation
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces regional hypotrichosis and proposes a specific cellular
      mechanism for it: a disrupted hair-follicle/sebaceous-gland balance.
    limitations: >-
      The sebaceous-gland expansion has not been demonstrated in human ECTD9
      skin, so the proposed mechanism for hypotrichosis remains model-derived.
      The authors' claim that mice and pigs do not faithfully recapitulate
      hypotrichosis conflicts with the pig paper's own conclusion; see the
      HUMAN_MODEL_MISMATCH discussion.
    readouts:
    - name: Hair follicle and sebaceous gland number
      target: Impaired Hair Follicle Differentiation
      direction: ALTERED
      interpretation: >-
        Reduced hair follicles with enlarged and increased sebaceous glands,
        proposed as the cellular basis of Hoxc13-related hypotrichosis.
      evidence:
      - reference: PMID:30125135
        reference_title: "The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          In addition, reduced hair follicles (HFs) while the enlarged and
          increased number of sebaceous glands (SGs) were also found in the
          Hoxc13-/- rabbits
        explanation: Reports the measurement behind this readout.
    evidence:
    - reference: PMID:30125135
      reference_title: "The disrupted balance between hair follicles and sebaceous glands in Hoxc13-ablated rabbits."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        our findings demonstrate that Hoxc13-/- rabbits can be used as a model
        for human ECTD-9, especially to understand the pathologic mechanism of
        hypotrichosis
      explanation: >-
        Supports treating the rabbit as informative for the human hypotrichosis
        mechanism.
- name: Naked (N) mouse (Hoxc13 terminal truncation)
  species: Mouse
  genotype: Hoxc13 Naked (N) terminal truncation, N/N and N/+
  publication: DOI:10.1111/exd.14469
  description: >-
    A spontaneous mouse mutation characterized as a terminal truncation of
    Hoxc13 and independently recreated by CRISPR/Cas9. It is the mechanistic
    outlier among the Hoxc13 animal models: the truncated transcript escapes
    nonsense-mediated decay, the truncated protein is present in follicles, and
    heterozygotes are affected - a semi-dominant, apparently dominant-negative
    behaviour unlike the recessive human pattern and unlike the heterozygous
    Hoxc13 knockout, which is unaffected.
  modeled_mechanisms:
  - target: HOXC13 Transcription Factor Loss of Function
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      N/N homozygotes reproduce the cardinal ECTD9 appendage phenotype
      (generalized alopecia with abnormal nails), and the allele is a better
      practical model than the poorly viable Hoxc13 knockout.
    limitations: >-
      The mechanism is not the human one. Human ECTD9 alleles act by
      nonsense-mediated decay, impaired DNA binding, or reduced protein
      stability, all recessive; the Naked allele instead escapes NMD and yields
      a persistent truncated protein that is pathogenic in heterozygotes. It
      therefore models the phenotype without modeling the loss-of-function
      route, and no dominant-negative HOXC13 allele has been reported in humans.
      N/N mice also have a short lifespan, which human patients do not.
    readouts:
    - name: Coat and nail phenotype in homozygotes
      target: HOXC13 Transcription Factor Loss of Function
      direction: ALTERED
      interpretation: >-
        Homozygous phenotype matching the human appendage presentation.
      evidence:
      - reference: DOI:10.1111/exd.14469
        reference_title: "Naked (N) mutant mice carry a nonsense mutation in the homeobox of <i>Hoxc13</i>"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          homozygous N/N mice exhibit generalized alopecia with abnormal nails
          and a short lifespan
        explanation: >-
          Reports the homozygous coat and nail phenotype together with the
          reduced lifespan that human patients do not share.
    - name: Heterozygote phenotype and truncated protein persistence
      target: HOXC13 Transcription Factor Loss of Function
      direction: ALTERED
      interpretation: >-
        Heterozygous involvement plus retained truncated protein is the
        signature of a dominant-negative allele rather than haploinsufficiency.
      evidence:
      - reference: DOI:10.1111/exd.14469
        reference_title: "Naked (N) mutant mice carry a nonsense mutation in the homeobox of <i>Hoxc13</i>"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          N/+ mice show generalized or partial alopecia, associated with loss of
          hair fibres, along with normal lifespan and fertility
        explanation: >-
          Establishes that heterozygotes are affected, in contrast to
          heterozygous Hoxc13 knockout mice and to human ECTD9 carriers.
      - reference: DOI:10.1111/exd.14469
        reference_title: "Naked (N) mutant mice carry a nonsense mutation in the homeobox of <i>Hoxc13</i>"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: >-
          the presence of the truncated mutant protein in N/N and N/+ hair
          follicles
        explanation: >-
          Demonstrates that the truncated product persists rather than being
          cleared, the basis of the dominant-negative interpretation.
  evidence:
  - reference: DOI:10.1111/exd.14469
    reference_title: "Naked (N) mutant mice carry a nonsense mutation in the homeobox of <i>Hoxc13</i>"
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Considering the low viability of the Hoxc13 KO mice, the Naked mutation
      provides an attractive new model for studying ECTD9 disease mechanisms.
    explanation: >-
      The authors propose the allele as an ECTD9 model, which is the claim this
      link records; the limitations field carries the mechanistic caveat.
discussions:
- discussion_id: hoxc13_model_fidelity_disagreement
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Which Hoxc13-null animal model, if any, faithfully represents human ECTD9,
    and does the mouse's skeletal phenotype mean HOXC13 loss has consequences in
    humans that dermatology-ascertained pedigrees have never looked for?
  attaches_to:
  - pathophysiology#HOXC13 Transcription Factor Loss of Function
  - pathophysiology#Impaired Hair Follicle Differentiation
  rationale: >-
    Three species carry Hoxc13 nulls and the literature does not agree on which
    one models the human disease. The mouse reproduces hair and nail defects but
    adds skeletal defects, progressive weight loss, and low viability that no
    human patient shows, and the pig paper concludes flatly that mouse models
    cannot faithfully mimic human ED-9. That same paper reports its own
    knockouts matching ED-9 patients with a normal skeleton and normal growth.
    The later rabbit paper contradicts it, asserting that Hoxc13-mutated mice
    and pigs do not faithfully recapitulate hypotrichosis, and proposing a
    hair-follicle/sebaceous-gland imbalance - never shown in human skin - as the
    real mechanism. Two questions remain open. First, which model to trust for
    mechanistic inference about human hypotrichosis. Second, whether the absence
    of human skeletal involvement is real or an ascertainment artifact: human
    ECTD9 is caused chiefly by homeodomain missense alleles that reduce DNA
    binding or protein stability rather than by complete nulls, so allele
    hypomorphism is a plausible explanation that has never been tested against
    systematic imaging.

    A third question comes from the fourth model, the Naked (N) mouse, and it is
    the sharpest of the three because the mismatch is mechanistic rather than
    phenotypic. N is a terminal truncation whose transcript escapes
    nonsense-mediated decay; the truncated protein persists in follicles and
    heterozygotes are affected, which the authors read as semi-dominant and
    dominant-negative. Human ECTD9 is uniformly recessive and no
    dominant-negative HOXC13 allele has been reported. So the model that is most
    practically usable - the Hoxc13 knockout is poorly viable, and the Naked
    allele is offered explicitly as the more tractable alternative - is also the
    one whose mode of action is furthest from the human disease. Any mechanistic
    inference drawn from N/+ animals is inference about a dominant-negative
    truncation, not about the loss of function that causes the human condition.
  proposed_experiments:
  - experiment_id: hoxc13_patient_skeletal_imaging
    name: Systematic skeletal imaging in molecularly confirmed ECTD9 patients
    description: >-
      Spine and long-bone imaging in a cohort of biallelic-HOXC13 patients to
      establish whether subclinical vertebral anomalies are present but
      unreported in dermatology-ascertained pedigrees. A negative result would
      make allele hypomorphism or species divergence the explanation; a positive
      result would reclassify ECTD9 as less "pure" than its name implies.
  - experiment_id: hoxc13_missense_knockin_mouse
    name: Knock-in mouse carrying a human homeodomain missense allele
    description: >-
      Generate a mouse carrying the orthologous p.Arg311Trp or p.Asn310Thr
      substitution and compare its skeletal, growth, and appendage phenotype
      with the complete null, testing directly whether allele class rather than
      species explains the divergence.
  - experiment_id: hoxc13_human_skin_sebaceous_histology
    name: Sebaceous gland quantification in human ECTD9 scalp biopsies
    description: >-
      Quantify hair follicle and sebaceous gland number and size in archived
      ECTD9 scalp specimens to test whether the rabbit model's proposed
      follicle/sebaceous imbalance occurs in human disease.
notes: >-
  Entry scope: this file covers only the HOXC13 (ECTD9, MONDO:0013976) form of
  pure hair and nail ectodermal dysplasia. The KRT85 (ECTD4, MONDO:0011177) and
  KRT74 (ECTD7, MONDO:0013975) forms are separate Disease entries. The
  MONDO:0019071 umbrella "pure hair and nail ectodermal dysplasia" is modeled as
  the `Pure_Hair_and_Nail_Ectodermal_Dysplasias` Grouping rather than as a
  subtyped Disease, following the precedent set by
  `Hypohidrotic_Ectodermal_Dysplasias`.

  Named Entity Confusion risk: ECTD4, ECTD7, and ECTD9 share the clinical label
  "pure hair and nail ectodermal dysplasia" and all three genes sit in the same
  12q linkage interval, so literature and deep-research reports mix them freely.
  The Edison report backing this entry passed `just preflight-dr` against
  MONDO:0013976 (HOXC13 mentioned 49 times against KRT85 5 and KRT74 3).

📚

References & Deep Research

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Disease Characteristics Research Template

Edison Scientific Literature 19 citations 2026-08-17T13:50:46.970072

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on: 1. Key concepts and definitions with current understanding 2. Recent developments and latest research (prioritize 2023-2024 sources) 3. Current applications and real-world implementations 4. Expert opinions and analysis from authoritative sources 5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available. Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Disease Characteristics Research Template

Target Disease

Disease Name: HOXC13-Related Pure Hair-Nail Ectodermal Dysplasia
MONDO ID: (if available)
Category: Genetic

Research Objectives

Please provide a comprehensive research report on HOXC13-Related Pure Hair-Nail Ectodermal Dysplasia covering all of the disease characteristics listed below. This report will be used to populate a disease knowledge base entry. Be thorough and cite primary literature (PMID preferred) for all claims.

For each section, suggested databases/resources are listed. These are the first places you should search for information on each topic.

1. Disease Information

Search first: OMIM, Orphanet, ICD-10/ICD-11, MeSH, PubMed

What is the disease? Provide a concise overview.
What are the key identifiers? (OMIM, Orphanet, ICD-10/ICD-11, MeSH, Mondo)
What are the common synonyms and alternative names?
Is the information derived from individual patients (e.g., EHR) or aggregated disease-level resources?

2. Etiology

Disease Causal Factors: What are the primary causes? (genetic, environmental, infectious, mechanistic)
Risk Factors:

Search first: PubMed, Cochrane Library, UpToDate, clinical guidelines, ClinVar, ClinGen, GWAS Catalog, PheGenI, CTD, CDC, WHO, epidemiological databases
Genetic risk factors (causal variants, susceptibility loci, modifier genes)
Environmental risk factors (toxins, lifestyle, occupational exposures, age, sex, family history)
Protective Factors:

Search first: PubMed, Cochrane Library, clinical trial databases, GWAS Catalog, gnomAD, WHO, CDC, nutrition databases
Genetic protective factors (protective variants, modifier alleles)
Environmental protective factors (diet, lifestyle, exposures that reduce risk)
Gene-Environment Interactions: How do genetic and environmental factors interact to influence disease?

Search first: CTD, PubMed, PheGenI, GxE databases

3. Phenotypes

Search first: HPO (Human Phenotype Ontology), OMIM, Orphanet, PubMed, clinicaltrials.gov, MedDRA, SNOMED CT, DECIPHER, LOINC

For each phenotype, provide: - Phenotype type: symptoms, clinical signs, physical manifestations, behavioral changes, or laboratory abnormalities

For symptoms/signs: HPO, OMIM, Orphanet, PubMed For behavioral changes: HPO, DSM, RDoC (Research Domain Criteria), PubMed For laboratory abnormalities: LOINC, SNOMED CT, LabTests Online, PubMed - Phenotype characteristics: Search first: OMIM, Orphanet, HPO, PubMed - Age of symptom onset (neonatal, childhood, adult-onset, late-onset) - Symptom severity (mild, moderate, severe, variable) - Symptom progression (stable, progressive, episodic, fluctuating) - Frequency among affected individuals (percentage or qualitative) - Quality of life impact: Effects on daily functioning and well-being (per-phenotype when possible) Search first: EQ-5D database, SF-36, WHO QOL databases, PubMed - Suggest HPO (Human Phenotype Ontology) terms for each phenotype

4. Genetic/Molecular Information

Causal Genes: Gene mutations or chromosomal abnormalities responsible for disease (gene symbols, OMIM IDs)

Search first: OMIM, ClinVar, HGMD, Ensembl, NCBI Gene
Pathogenic Variants:
Affected genes (gene symbols, HGNC IDs) > Search first: OMIM, NCBI Gene, Ensembl, HGNC, UniProt, GeneCards
Variant classification (pathogenic, likely pathogenic, VUS per ACMG/AMP guidelines) > Search first: ClinVar, ClinGen, ACMG/AMP guidelines, VarSome
Variant type/class (missense, frameshift, nonsense, splice-site, structural)
Allele frequency in population databases > Search first: gnomAD, 1000 Genomes, ExAC, TOPMed, dbSNP
Somatic vs germline origin > Search first: COSMIC (somatic), ClinVar, ICGC, TCGA
Functional consequences (loss of function, gain of function, dominant negative)
Modifier Genes: Genes that modify disease severity or expression
Epigenetic Information: DNA methylation, histone modifications, chromatin changes affecting disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Chromosomal Abnormalities: Large-scale genetic changes (aneuploidy, translocations, inversions)

Search first: DECIPHER, ClinVar, ECARUCA, UCSC Genome Browser

5. Environmental Information

Environmental Factors: Non-genetic contributing factors (toxins, radiation, pollution, occupational exposure)

Search first: CTD (Comparative Toxicogenomics Database), TOXNET, PubMed, EPA databases
Lifestyle Factors: Behavioral factors (smoking, diet, exercise, alcohol consumption)

Search first: CDC databases, WHO, PubMed, NHANES
Infectious Agents: If applicable, pathogens causing or triggering disease (bacteria, viruses, fungi, parasites)

Search first: NCBI Taxonomy, ViPR, BV-BRC, MicrobeDB, GIDEON

6. Mechanism / Pathophysiology

Molecular Pathways: Specific signaling cascades or biochemical pathways involved (Wnt, MAPK, mTOR, PI3K-AKT, etc.)

Search first: KEGG, Reactome, WikiPathways, PathBank, BioCyc
Cellular Processes: Cell-level mechanisms (apoptosis, autophagy, cell cycle dysregulation, inflammation, etc.)

Search first: Gene Ontology (GO), Reactome, KEGG, PubMed
Protein Dysfunction: How protein structure or function is altered (misfolding, aggregation, loss of function, gain of function)

Search first: UniProt, PDB (Protein Data Bank), InterPro, Pfam, AlphaFold
Metabolic Changes: Alterations in metabolic processes (energy metabolism, lipid metabolism, amino acid metabolism)

Search first: KEGG, BioCyc, HMDB (Human Metabolome Database), BRENDA
Immune System Involvement: Role of immune response (autoimmunity, immunodeficiency, chronic inflammation)

Search first: ImmPort, Immunome Database, IEDB, Gene Ontology
Tissue Damage Mechanisms: How tissues/ are injured (oxidative stress, ischemia, fibrosis, necrosis)

Search first: PubMed, Gene Ontology, Reactome
Biochemical Abnormalities: Specific molecular defects (enzyme deficiencies, receptor dysfunction, ion channel defects)

Search first: BRENDA, UniProt, KEGG, OMIM, PubMed
Epigenetic Changes: DNA methylation, histone modifications affecting gene expression in disease

Search first: ENCODE, Roadmap Epigenomics, MethBase, DiseaseMeth
Molecular Profiling (if available):
Transcriptomics/gene expression changes > Search first: GEO (Gene Expression Omnibus), ArrayExpress, GTEx, Human Cell Atlas, SRA
Proteomics findings > Search first: PRIDE, ProteomeXchange, Human Protein Atlas, STRING, BioGRID
Metabolomics signatures > Search first: MetaboLights, Metabolomics Workbench, HMDB, METLIN
Lipidomics alterations > Search first: LIPID MAPS, SwissLipids, LipidHome, Metabolomics Workbench
Genomic structural features > Search first: UCSC Genome Browser, Ensembl, NCBI, dbVar, DGV
Advanced Technologies (if applicable):
Single-cell analysis findings (cell-type specific mechanisms, cellular heterogeneity) > Search first: Human Cell Atlas, Single Cell Portal, GEO, CELLxGENE
Spatial transcriptomics findings > Search first: GEO, Spatial Research, Vizgen, 10x Genomics data
Multi-omics integration results > Search first: TCGA, ICGC, cBioPortal, LinkedOmics, PubMed
Functional genomics screens (CRISPR, RNAi) > Search first: DepMap, GenomeRNAi, PubMed, BioGRID ORCS

For each mechanism, describe: - The causal chain from initial trigger to clinical manifestation - Which mechanisms are upstream vs downstream - What cell types and biological processes are involved - Suggest GO terms for biological processes and CL terms for cell types

7. Anatomical Structures Affected

Organ Level:
Primary organs directly affected
Secondary organ involvement (complications, secondary effects)
Body systems involved (cardiovascular, nervous, digestive, respiratory, endocrine, etc.)

Search first: Uberon, FMA (Foundational Model of Anatomy), OMIM, HPO, ICD-11, MeSH, SNOMED CT
Tissue and Cell Level:
Specific tissue types affected (epithelial, connective, muscle, nervous)
Specific cell populations targeted (with Cell Ontology terms)

Search first: Uberon, Human Protein Atlas, Cell Ontology, Human Cell Atlas, CellMarker, PanglaoDB
Subcellular Level:
Cellular compartments involved (mitochondria, nucleus, ER, lysosomes) (with GO Cellular Component terms)

Search first: Gene Ontology (Cellular Component), UniProt, Human Protein Atlas
Localization:
Specific anatomical sites (with UBERON terms) > Search first: FMA, Uberon, NeuroNames (for brain), SNOMED CT
Lateralization (unilateral, bilateral, asymmetric) > Search first: HPO, clinical literature, imaging databases

8. Temporal Development

Onset:
Typical age of onset (congenital, pediatric, adult, geriatric)
Onset pattern (acute, subacute, chronic, insidious)

Search first: OMIM, Orphanet, HPO, PubMed
Progression:
Disease stages (early, intermediate, advanced, end-stage) > Search first: Cancer Staging Manual (AJCC), WHO classifications, PubMed
Progression rate (rapid, slow, variable)
Disease course pattern (episodic, relapsing-remitting, progressive, stable)
Disease duration (self-limited, chronic lifelong)

Search first: Disease registries, longitudinal cohort databases, natural history studies, PubMed, Orphanet, OMIM
Patterns:
Remission patterns (spontaneous, treatment-induced) > Search first: Clinical trial databases, disease registries, PubMed
Critical periods (time windows of vulnerability or opportunity for intervention) > Search first: PubMed, developmental biology databases, clinical guidelines

9. Inheritance and Population

Epidemiology:
Prevalence (cases per 100,000 at given time)
Incidence (new cases per 100,000 per year)

Search first: Orphanet, CDC, WHO, GBD (Global Burden of Disease), national registries, SEER, disease registries
For Genetic Etiology:
Inheritance pattern (AD, AR, X-linked, mitochondrial, multifactorial, polygenic) > Search first: OMIM, Orphanet, ClinVar, GTR (Genetic Testing Registry)
Penetrance (complete, incomplete, age-dependent) > Search first: ClinVar, OMIM, PubMed, ClinGen
Expressivity (variable, consistent) > Search first: OMIM, ClinVar, PubMed
Genetic anticipation (increasing severity in successive generations) > Search first: OMIM, PubMed (especially for repeat expansion disorders)
Germline mosaicism > Search first: ClinVar, OMIM, genetic counseling literature, PubMed
Founder effects (population-specific mutations) > Search first: gnomAD, population genetics databases, PubMed
Consanguinity role > Search first: OMIM, population studies, genetic counseling resources
Carrier frequency > Search first: gnomAD, carrier screening databases, GeneReviews, GTR
Population Demographics:
Affected populations (ethnic or demographic groups with higher prevalence) > Search first: gnomAD, 1000 Genomes, PAGE Study, PubMed, population registries
Geographic distribution (endemic areas, regional variation) > Search first: WHO, CDC, GBD, Orphanet, geographic epidemiology databases
Geographic distribution of specific variants
Sex ratio (male:female) > Search first: Disease registries, OMIM, PubMed, epidemiological databases
Age distribution of affected individuals > Search first: CDC, disease registries, SEER, Orphanet

10. Diagnostics

Clinical Tests:
Laboratory tests (blood, urine, tissue chemistry, specific enzyme assays) > Search first: LOINC, LabTests Online, PubMed
Biomarkers (proteins, metabolites, genetic markers, circulating biomarkers) > Search first: FDA Biomarker List, BEST (Biomarkers, EndpointS, and other Tools), PubMed
Imaging studies (X-ray, CT, MRI, PET, ultrasound) > Search first: RadLex, DICOM, Radiopaedia, imaging databases
Functional tests (pulmonary function, cardiac stress tests) > Search first: LOINC, clinical guidelines, PubMed
Electrophysiology (EEG, EMG, ECG, nerve conduction studies) > Search first: LOINC, clinical neurophysiology databases, PubMed
Biopsy findings (histopathology, immunohistochemistry) > Search first: SNOMED CT, College of American Pathologists resources, PubMed
Pathology findings (microscopic examination) > Search first: SNOMED CT, Digital Pathology databases, PubMed
Genetic Testing:

Search first: GTR (Genetic Testing Registry), GeneReviews, ClinGen
Overview of recommended genetic testing approach
Whole genome sequencing (WGS) utility > Search first: GTR, ClinVar, GEL (Genomics England), gnomAD
Whole exome sequencing (WES) utility > Search first: GTR, ClinVar, OMIM, GeneMatcher
Gene panels (which panels, which genes) > Search first: GTR, ClinVar, laboratory-specific databases
Single gene testing > Search first: GTR, ClinVar, OMIM, GeneReviews
Chromosomal microarray (CMA) > Search first: DECIPHER, ClinVar, dbVar, ECARUCA
Karyotyping > Search first: Chromosome Abnormality Database, ClinVar, cytogenetics resources
FISH > Search first: ClinVar, cytogenetics databases, PubMed
Mitochondrial DNA testing > Search first: MITOMAP, MSeqDR, ClinVar, GTR
Repeat expansion testing > Search first: GTR, ClinVar, repeat expansion databases, PubMed
Omics-Based Diagnostics (if applicable):
RNA sequencing / transcriptomics > Search first: GEO, ArrayExpress, GTEx, RNA-seq databases
Proteomics > Search first: PRIDE, ProteomeXchange, FDA Biomarker database
Metabolomics > Search first: MetaboLights, Metabolomics Workbench, HMDB
Epigenomics > Search first: GEO, ENCODE, Roadmap Epigenomics, MethBase
Liquid biopsy > Search first: COSMIC, ClinVar, liquid biopsy databases, PubMed
Clinical Criteria:
Standardized diagnostic criteria (DSM, ICD, society guidelines) > Search first: DSM-5, ICD-11, clinical society guidelines, UpToDate
Differential diagnosis (other conditions to rule out, with distinguishing features) > Search first: DynaMed, UpToDate, clinical decision support systems
Screening:
Screening methods for asymptomatic individuals (newborn screening, carrier screening, cascade screening) > Search first: ACMG recommendations, CDC newborn screening, GTR

11. Outcome/Prognosis

Survival and Mortality:
Survival rate (5-year, 10-year, overall) > Search first: SEER, cancer registries, disease-specific registries, PubMed
Life expectancy (with and without treatment if applicable) > Search first: Orphanet, disease registries, actuarial databases, PubMed
Mortality rate > Search first: CDC, WHO, GBD, national mortality databases
Disease-specific mortality (deaths directly attributable to disease) > Search first: Disease registries, CDC Wonder, GBD, PubMed
Morbidity and Function:
Morbidity (disease-related disability and health impacts) > Search first: GBD, WHO, disability databases, PubMed
Disability outcomes (long-term functional impairments) > Search first: ICF (International Classification of Functioning), disability registries
Quality of life measures (EQ-5D, SF-36, PROMIS, disease-specific tools) > Search first: EQ-5D database, SF-36, PROMIS, PubMed
Disease Course:
Complications (secondary problems: infections, organ failure, etc.) > Search first: ICD codes, disease registries, clinical databases, PubMed
Recovery potential (likelihood and extent of recovery, with vs without treatment) > Search first: Natural history studies, rehabilitation databases, PubMed
Prediction:
Prognostic factors (age, disease severity, biomarkers, treatment response) > Search first: Prognostic models databases, clinical calculators, PubMed
Prognostic biomarkers (molecular markers predicting disease course) > Search first: FDA Biomarker database, PubMed, cancer prognostic databases

12. Treatment

Pharmacotherapy:
Pharmacological treatments (drug names, drug classes, mechanisms of action) > Search first: DrugBank, RxNorm, ATC classification, DailyMed, FDA databases
Pharmacogenomics (how genetic variants affect drug metabolism, efficacy, toxicity) > Search first: PharmGKB, CPIC (Clinical Pharmacogenetics), FDA Table of PGx Biomarkers
Advanced Therapeutics:
Gene therapy (viral vectors, CRISPR, gene replacement, gene editing) > Search first: ClinicalTrials.gov, FDA gene therapy database, ASGCT resources
Cell therapy (stem cell transplant, CAR-T, cellular therapeutics) > Search first: ClinicalTrials.gov, FDA cell therapy database, FACT standards
RNA-based therapies (ASOs, siRNA, mRNA therapies) > Search first: ClinicalTrials.gov, FDA approvals, PubMed
Targeted therapies (treatments directed at specific molecular targets) > Search first: My Cancer Genome, OncoKB, ClinicalTrials.gov, FDA approvals
Immunotherapies (checkpoint inhibitors, monoclonal antibodies) > Search first: Cancer Immunotherapy Database, FDA approvals, ClinicalTrials.gov
Surgical and Interventional:
Surgical interventions (types of surgery, timing, outcomes) > Search first: CPT codes, surgical registries, clinical guidelines, PubMed
Supportive and Rehabilitative:
Supportive care (symptom management, pain control, nutrition) > Search first: Clinical guidelines, Cochrane Library, PubMed
Rehabilitation (physical therapy, occupational therapy, speech therapy) > Search first: Rehabilitation medicine databases, clinical guidelines, PubMed
Experimental:
Experimental treatments in clinical trials (with NCT identifiers if available) > Search first: ClinicalTrials.gov, EU Clinical Trials Register, WHO ICTRP
Treatment Outcomes:
Treatment response rates > Search first: Clinical trial databases, FDA reviews, systematic reviews, PubMed
Side effects and adverse events > Search first: FDA Adverse Event Reporting System (FAERS), MedWatch, PubMed
Treatment Strategy:
Treatment algorithms (clinical pathways, decision trees) > Search first: Clinical practice guidelines, NCCN Guidelines, UpToDate
Combination therapies > Search first: ClinicalTrials.gov, treatment guidelines, PubMed
Personalized medicine approaches (genotype-guided treatment) > Search first: My Cancer Genome, CIViC, PharmGKB, precision medicine databases

For each treatment, suggest NCIT (NCI Thesaurus) clinical-intervention terms where applicable.

13. Prevention

Prevention Levels:
Primary prevention (preventing disease occurrence: vaccination, risk factor modification) > Search first: CDC, WHO, USPSTF recommendations, Cochrane Library
Secondary prevention (early detection and treatment: screening programs, early intervention) > Search first: USPSTF, CDC screening guidelines, WHO
Tertiary prevention (preventing complications in those with disease) > Search first: Clinical guidelines, disease management protocols, PubMed
Immunization: Vaccine strategies (if applicable)

Search first: CDC vaccine schedules, WHO immunization, FDA vaccine database
Screening and Early Detection:
Screening programs (population-based: newborn screening, cancer screening) > Search first: CDC screening programs, USPSTF, cancer screening databases
Genetic screening (carrier screening, preimplantation genetic diagnosis, prenatal testing) > Search first: ACMG recommendations, ACOG guidelines, GTR
Risk stratification (identifying high-risk individuals for targeted prevention) > Search first: Risk prediction models, clinical calculators, PubMed
Behavioral Interventions: Lifestyle modifications to reduce risk

Search first: CDC, WHO, behavioral intervention databases, Cochrane Library
Counseling: Genetic counseling (risk assessment, family planning guidance)

Search first: NSGC resources, ACMG guidelines, GeneReviews
Public Health:
Public health interventions (sanitation, vector control, health education) > Search first: CDC, WHO, public health databases, PubMed
Environmental interventions (reducing environmental risk factors) > Search first: EPA databases, WHO environmental health, PubMed
Prophylaxis: Preventive medications or procedures

Search first: Clinical guidelines, FDA approvals, PubMed

14. Other Species / Natural Disease

Taxonomy: Species affected (with NCBI Taxon identifiers)

Search first: NCBI Taxonomy
Breed: Specific breeds affected (with VBO identifiers if applicable)

Search first: VBO (Vertebrate Breed Ontology)
Gene: Orthologous genes in other species (with NCBI Gene IDs)

Search first: NCBI Gene
Natural Disease:
Naturally occurring disease in other species (companion animals, wildlife) > Search first: OMIA (Online Mendelian Inheritance in Animals), VetCompass, PubMed
Veterinary relevance and importance in animal health > Search first: OMIA, veterinary databases, PubMed
Comparative Biology:
Comparative pathology (similarities and differences across species) > Search first: OMIA, comparative pathology databases, PubMed
Evolutionary conservation of disease mechanisms > Search first: HomoloGene, OrthoMCL, Alliance of Genome Resources
Transmission (if applicable):
Zoonotic potential > Search first: CDC zoonotic diseases, WHO zoonoses, GIDEON
Cross-species susceptibility > Search first: NCBI Taxonomy, veterinary databases, PubMed

15. Model Organisms

Model Types:
Model organism type (mammalian, invertebrate, cellular, in vitro) > Search first: Alliance of Genome Resources, model organism databases
Specific model systems (mouse, rat, zebrafish, Drosophila, C. elegans, yeast, cell lines, organoids, iPSCs) > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, SGD, ATCC, Cellosaurus
Induced models (drug treatment, surgical intervention, environmental manipulation) > Search first: MGI, model organism databases, PubMed
Genetic Models:
Types available (knockout, knock-in, transgenic, conditional, humanized) > Search first: MGI, IMPC, KOMP, EuMMCR, IMSR
Model Characteristics:
Phenotype recapitulation (how well model reproduces human disease features) > Search first: Model organism databases, comparative studies, PubMed
Model limitations (aspects of human disease not captured) > Search first: Model organism databases, PubMed, review articles
Applications:
Research applications (what aspects of disease can be studied) > Search first: Model organism databases, PubMed
Resources:
Model databases > Search first: MGI, RGD, ZFIN, FlyBase, WormBase, IMSR, EMMA, MMRRC

Citation Requirements

Cite primary literature (PMID preferred) for all mechanistic and clinical claims
Prioritize recent reviews and landmark papers
Include direct quotes from abstracts where possible to support key statements
Distinguish evidence source types: human clinical, model organism, in vitro, computational

Output Format

Structure your response as a comprehensive narrative organized by the sections above. For each section, provide: - Factual content with specific details (numbers, percentages, gene names, variant nomenclature) - Ontology term suggestions (HPO, GO, CL, UBERON, CHEBI, NCIT, MONDO) where applicable - Evidence citations with PMIDs - Direct quotes from abstracts to support key claims - Clear indication when information is not available or not applicable for this disease

This report will be used to populate a disease knowledge base entry with: - Pathophysiology descriptions with causal chains - Gene/protein annotations (HGNC, GO terms) - Phenotype associations (HP terms) with frequencies - Cell type involvement (CL terms) - Anatomical locations (UBERON terms) - Chemical entities (CHEBI terms) - Treatment annotations (NCIT terms) - Evidence items with PMIDs and exact abstract quotes - Epidemiology, prognosis, diagnostic, and prevention information - Animal model descriptions with phenotype recapitulation details

HOXC13-Related Pure Hair–Nail Ectodermal Dysplasia

Executive summary

HOXC13-related pure hair–nail ectodermal dysplasia is an ultra-rare, congenital, usually autosomal-recessive genodermatosis in which biallelic HOXC13 variants disrupt terminal differentiation of hair follicles and nail-forming epithelium. The characteristic combination is generalized hypotrichosis or complete alopecia plus dystrophy/hypoplasia of all fingernails and toenails, with teeth, sweating, skeleton, and neurodevelopment generally spared. This restricted distribution distinguishes the disorder from multisystem ectodermal dysplasias. The evidence base consists chiefly of individual families and experimental models; there are no reliable prevalence estimates, formal clinical guidelines, disease-modifying treatments, or registered disease-specific interventional trials in the retrieved evidence. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)

domain	best-supported finding	evidence type	key citation metadata (author/year/PMID/DOI)	evidence limitation
Disease identity	HOXC13-related pure hair-nail ectodermal dysplasia corresponds to ectodermal dysplasia 9 (ECTD9/PHNED), a congenital disorder primarily affecting hair and nails. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)	Human clinical genetics	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	Context does not provide MONDO/Orphanet/ICD identifiers; disease nomenclature varies across papers.
Core phenotype	The most consistent phenotype is congenital hypotrichosis to complete alopecia with dystrophy of finger- and toenails, while teeth, sweating, skeleton, and nervous system are typically normal. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)	Human clinical observations	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	Small number of reported families; severity range across cases is not well quantified.
Variant: c.390C>A (p.Tyr130*)	A homozygous nonsense HOXC13 variant c.390C>A (p.Tyr130*) was identified in affected individuals and supports loss of function. (lin2012lossoffunctionmutationsin pages 1-2)	Human molecular genetics	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029	Family-level evidence; allele frequency and ClinVar classification are not given in context.
Variant: 27.6-kb deletion	A homozygous 27.6-kb microdeletion involving HOXC13 exon 1/intron 1 was reported in an affected family, consistent with a null allele. (lin2012lossoffunctionmutationsin pages 3-4)	Human molecular genetics	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029	Exact HGVS genomic nomenclature beyond coordinates is not fully standardized in the context.
Variant: c.812A>G (p.Gln271Arg)	A homozygous missense variant c.812A>G (p.Gln271Arg) in the DNA-binding domain was reported in a North American/Hispanic proband with classic PHNED. (li2017anovelhomozygous pages 1-3)	Human clinical genetics	Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	Single-family report; functional assay data are limited in the context to in silico predictions.
Variant: c.929A>C (p.Asn310Thr)	A homozygous missense variant c.929A>C (p.Asn310Thr) in the homeobox DNA-binding domain was identified in a consanguineous Pakistani family. (khan2017anovelmutation pages 3-5)	Human clinical genetics + computational structural analysis	Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y	Functional evidence is primarily bioinformatic/modeling in the cited context.
Inheritance	Reported human HOXC13-related PHNED cases are best supported as autosomal recessive, often in consanguineous families; heterozygous carriers are generally unaffected in human reports. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, perez2022naked(n)mutant pages 13-14)	Human pedigree analysis	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Perez et al., 2022, PMID not provided in context, DOI: 10.1111/exd.14469	Mouse data suggest possible semi-dominant effects for a specific mutant allele, which may not generalize to humans.
Mechanism/targets	HOXC13 acts as a transcription factor required for hair/nail differentiation; reported downstream or associated targets include hair keratins (e.g., KRT35, KRT85), FOXN1, DSG4, CRISP1, and FOXQ1, with reduced expression in HOXC13-deficient tissue. (lin2012lossoffunctionmutationsin pages 3-4, khan2017anovelmutation pages 3-5, perez2022naked(n)mutant pages 11-13)	Human tissue expression, mouse functional studies, in vitro/in silico interpretation	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Perez et al., 2022, PMID not provided in context, DOI: 10.1111/exd.14469	Direct target status is stronger for some genes than others; pathway map remains incomplete.
Model organisms	Hoxc13-deficient or mutant mice show alopecia and nail defects; additional engineered pig and rabbit knockout models recapitulate major hair/nail abnormalities and support conserved function. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 13-14, perez2022naked(n)mutant pages 11-13)	Mouse, pig, rabbit models	Perez et al., 2022, PMID not provided in context, DOI: 10.1111/exd.14469; supporting cited models in Perez et al.: Han et al., 2017, PMID 28011715; Deng et al., 2019, PMID 30125135	Animal models may show extra phenotypes (e.g., short lifespan, vertebral findings) not typical of reported human disease.
Epidemiology	The disorder is ultra-rare and described through a small number of families from multiple ancestries; robust prevalence or incidence estimates are not available in the retrieved evidence. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)	Aggregated inference from case reports	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	No population-based registries or denominator-based studies were identified in context.
Diagnostics	Diagnosis is primarily clinical suspicion based on congenital hair/nail findings followed by confirmatory genetic testing of HOXC13; sequencing and deletion analysis are both relevant because both SNVs and a multi-kb deletion have been reported. (lin2012lossoffunctionmutationsin pages 1-2, lin2012lossoffunctionmutationsin pages 3-4, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)	Human diagnostic genetics	Lin et al., 2012, PMID 23063621, DOI: 10.1016/j.ajhg.2012.08.029; Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	No disease-specific formal diagnostic guideline or validated biomarker beyond genotype was identified.
Treatment/trial status	No disease-modifying therapy or disease-specific interventional clinical trial was identified in the retrieved evidence; management appears supportive/cosmetic and genetics-based counseling is relevant. (khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)	Evidence gap from literature/trial search	Khan et al., 2017, PMID 28403827, DOI: 10.1186/s12881-017-0402-y; Li et al., 2017, PMID not provided in context, DOI: 10.1111/pde.13074	Absence of evidence is not proof of absence globally; no trial identifiers were available in context.

Table: This table summarizes the strongest available evidence for HOXC13-related pure hair-nail ectodermal dysplasia across disease definition, variants, mechanism, models, diagnostics, and treatment gaps. It is designed as a compact reference for building a disease knowledge base entry without overstating unavailable epidemiology or therapeutic evidence.

1. Disease information

Definition and nomenclature

The preferred knowledge-base label is HOXC13-related pure hair–nail ectodermal dysplasia. Common names include:

Pure hair and nail ectodermal dysplasia, HOXC13-related
Pure hair–nail ectodermal dysplasia, autosomal recessive
Ectodermal dysplasia 9, hair/nail type
ECTD9
PHNED

The phenotype belongs to the genetically heterogeneous PHNED group: similar hair–nail disease can also arise from genes such as KRT74 and KRT85, so “PHNED” alone does not specify HOXC13 etiology. (lin2012lossoffunctionmutationsin pages 3-4, lin2012lossoffunctionmutationsin pages 4-6)

Identifiers

OMIM phenotype: Ectodermal dysplasia 9, hair/nail type, MIM 614931 is used in the HOXC13-specific literature; the broader PHNED phenotype has also been cited as MIM 602032. These identifiers should not be treated as interchangeable without checking the current OMIM record. (lin2012lossoffunctionmutationsin pages 1-2, li2017anovelhomozygous pages 1-3)
HOXC13 gene: OMIM 142976 is reported in the literature.
MONDO: a dedicated HOXC13-specific MONDO identifier was not verified from the retrieved primary sources; it should be curated directly from the current MONDO release rather than inferred.
Orphanet, MeSH, ICD-10, ICD-11: no specific code was established by the retrieved evidence. In routine coding, the disorder may be grouped under ectodermal dysplasia or congenital hair/nail abnormalities, but a broad code loses molecular specificity.

The source evidence is mostly patient/family-level primary literature, supplemented by aggregated disease nomenclature and experimental animal work—not EHR-derived population data.

2. Etiology

Causal factor

The established cause is a biallelic germline pathogenic or likely pathogenic variant in HOXC13, encoding a homeobox transcription factor required for hair-shaft and nail differentiation. Nonsense, frameshift, missense, and deletion alleles have been reported. The strongest mechanistic class is loss of function through absent transcript/protein, impaired DNA binding, or reduced protein stability. (lin2012lossoffunctionmutationsin pages 1-2, lin2012lossoffunctionmutationsin pages 3-4, khan2017anovelmutation pages 3-5, perez2022naked(n)mutant pages 13-14)

Risk factors

Genetic: having two pathogenic HOXC13 alleles is the primary risk determinant.
Family history/consanguinity: several reported families were consanguineous, increasing the probability that both parents carry the same rare allele. A Pakistani report described three affected siblings born to healthy first-cousin parents. (khan2017anovelmutation pages 3-5)
Sex: both males and females are affected; no credible sex-specific risk has been demonstrated.
Environmental, lifestyle, infectious, occupational, or age-related risk: none is established.

Protective factors and gene–environment interaction

No protective HOXC13 alleles, modifier genes, diets, exposures, or validated gene–environment interactions have been reported. Heterozygosity for conventional human loss-of-function alleles appears clinically protective because carriers in the foundational families had normal hair and nails, but this is carrier status rather than a true protective factor. (lin2012lossoffunctionmutationsin pages 1-2)

3. Phenotypes

The available literature is too small and ascertainment-biased for defensible percentages. “Typical,” “reported,” and “variable” below therefore refer to repeated case observations, not population frequencies.

Core manifestations

Congenital generalized hypotrichosis or alopecia—often complete absence of scalp and body hair, including eyebrows, eyelashes, beard, axillary hair, and pubic hair. Onset is congenital/neonatal, severity ranges from sparse/brittle hair to complete alopecia, and the condition is chronic. Suggested HPO terms: Hypotrichosis (HP:0001006), Alopecia (HP:0001596), Sparse scalp hair (HP:000 hair-subterm; verify current identifier), Sparse eyebrows (HP:0045075), and Sparse eyelashes (HP:0000653). (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)
Nail dystrophy involving fingers and toes—reported findings include micronychia, hypoplastic or irregular nails, brittleness, and distal onycholysis. It is congenital or evident in infancy, persistent, and may be severe across all 20 nails. Suggested HPO terms: Nail dystrophy (HP:0008404), Micronychia (HP:0001800), Hypoplastic nails (HP:0001803), and Onycholysis (HP:0001806; verify current HPO release). (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)
Hair-shaft differentiation abnormality—histologic/mechanistic evidence suggests abnormal shafts may fail to emerge through the epidermis. Suggested HPO: Abnormality of hair texture (HP:0010719) or a more specific hair-shaft term after microscopic confirmation. (lin2012lossoffunctionmutationsin pages 3-4)

Usually absent findings

Reported patients generally had normal teeth, sweat glands, nervous system, skeleton, eyes, and sebaceous glands. These negative findings are diagnostically important because they support a “pure” hair–nail phenotype. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3)

A lacrimal-duct obstruction phenotype has been reported in association with an insertion allele in the broader literature, but the retrieved full-text evidence was insufficient to establish its frequency or whether it is a reproducible HOXC13 manifestation. It should be represented as a single-report phenotypic expansion, not a defining feature.

Quality of life

No disease-specific EQ-5D, SF-36, PROMIS, or validated dermatologic quality-of-life series was found. Likely burdens include cosmetic visibility, stigma, psychosocial distress, difficulty protecting the scalp, and functional/cosmetic effects of fragile nails. These are clinically plausible consequences but have not been quantified specifically for HOXC13-related disease.

4. Genetic and molecular information

Gene

Gene: HOXC13, homeobox C13
Location: chromosome 12q13 region; one report gives 12q13.13.
Protein: a 330-amino-acid nuclear homeobox transcription factor; its C-terminal homeodomain mediates sequence-specific DNA binding. (khan2017anovelmutation pages 3-5)
Suggested annotations: GO:0003677 DNA binding, GO:0003700 DNA-binding transcription-factor activity, GO:0006355 regulation of DNA-templated transcription, and GO:0005634 nucleus.

Reported pathogenic variants

c.390C>A (p.Tyr130*), homozygous nonsense: associated with nonsense-mediated decay, markedly reduced HOXC13 RNA, absent protein, and reduced target-gene expression. (lin2012lossoffunctionmutationsin pages 1-2)
27.6-kb homozygous deletion, reported at approximately chr12:54,308,194–54,335,815 in the source assembly, involving exon 1 and part of intron 1: a predicted null allele. Coordinates must be remapped before use in a current reference build. (lin2012lossoffunctionmutationsin pages 3-4)
c.812A>G (p.Gln271Arg), homozygous missense in the DNA-binding domain: found in a 5-month-old Hispanic boy; both consanguineous parents were heterozygous. PolyPhen-2 and SIFT predicted severe functional impact, but those predictions are not substitutes for a direct functional assay. (li2017anovelhomozygous pages 1-3)
c.929A>C (p.Asn310Thr), homozygous missense in the homeodomain: segregated with disease in three Pakistani siblings, was absent from 102 ethnically matched controls and referenced databases, and computational modeling predicted altered hydrogen bonding and stability. (khan2017anovelmutation pages 3-5)
Additional human frameshift and consanguineous-family alleles are documented in the literature: Farooq et al. 2013, PMID 23315978, and Ali et al. 2013, PMID 23461661. (perez2022naked(n)mutant pages 13-14)

All are reported as germline. No somatic HOXC13 etiology is established for this disorder. Current ClinVar assertions, ACMG classifications, dbSNP identifiers, transcript accession numbers, and gnomAD/TOPMed allele frequencies should be rechecked variant by variant against the current genome build; the retrieved sources do not support assigning exact contemporary frequencies. Given the severe recessive phenotype and rarity, causative alleles are expected to be absent or exceptionally rare in population databases, but that expectation is not itself frequency evidence.

Modifiers, epigenetics, and structural abnormalities

No validated human modifier gene, disease-specific methylation signature, pathogenic chromatin state, aneuploidy, or recurrent translocation has been identified. Mammalian-specific enhancers upstream of the HoxC cluster regulate Hoxc expression in developing hair and nail ectoderm in mice, showing that quantitative cis-regulation is biologically important, but no human enhancer variant has yet been established as a cause of ECTD9. The enhancer study is indexed by PMID 33199643. (perez2022naked(n)mutant pages 13-14)

5. Environmental information

This is a monogenic developmental disorder. No toxin, radiation exposure, pollutant, occupation, smoking pattern, diet, exercise behavior, alcohol exposure, or infectious agent is known to initiate it. Environmental measures may protect exposed scalp or dystrophic nails from secondary injury, but they do not alter the underlying molecular defect. The disease is not contagious or zoonotic.

6. Mechanism and pathophysiology

Causal chain

Upstream: biallelic HOXC13 loss-of-function or function-impairing missense variant → reduced transcript/protein, reduced protein stability, or impaired homeodomain-mediated DNA binding.

Intermediate: failure to activate the terminal differentiation program of hair- and nail-forming keratinocytes. Reported direct or downstream targets include KRT35, KRT85, FOXN1, DSG4, CRISP1, and FOXQ1. Human affected follicles showed sharply reduced or absent expression of several targets. (lin2012lossoffunctionmutationsin pages 3-4, khan2017anovelmutation pages 3-5)

Downstream: defective keratin/intermediate-filament and adhesion programs → malformed hair shafts that break or fail to emerge, plus defective nail-plate formation → congenital hypotrichosis/alopecia and nail dystrophy. (lin2012lossoffunctionmutationsin pages 1-2, lin2012lossoffunctionmutationsin pages 3-4)

A useful expert interpretation is that ECTD9 is principally a terminal epithelial differentiation disorder, not an inflammatory alopecia, metabolic disease, or generalized ectodysplasin-signaling syndrome. HOXC13 has also been linked experimentally to FOXN1 and hair-cycle/TGF-β–SMAD2 regulation, but the relative importance of these branches in human ECTD9 has not been quantified. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 11-13)

Cells and ontology suggestions

Affected populations are differentiating epithelial cells of the hair follicle and nail unit:

Hair matrix/cortical-medullary lineage keratinocytes—suggested CL:0000312 keratinocyte, with a more specific follicular keratinocyte term if available.
Inner and outer root-sheath epithelial cells—CL mapping should be verified because granularity varies.
Nail-matrix keratinocytes—suggested CL:0000312 plus anatomical context.

Suggested biological-process terms include GO:0031069 hair follicle morphogenesis, GO:0042633 hair cycle, GO:0008544 epidermis development, GO:0030216 keratinocyte differentiation, and GO:0031424 keratinization. Suggested cellular components are GO:0005634 nucleus, GO:0005882 intermediate filament, and GO:0045095 keratin filament.

Omics and advanced technologies

The foundational human work used targeted expression analysis rather than modern disease-scale multi-omics. No validated ECTD9 transcriptomic signature, proteomic biomarker, metabolomic/lipidomic profile, patient single-cell atlas, spatial-transcriptomic study, or patient-derived CRISPR screen was found. A 2023 integrated single-cell scalp study provides a general reference atlas but was not retrieved as direct evidence from ECTD9 patients. Therefore, such data should not be represented as disease-specific.

Abstract-supported statements

The 2017 BMC study states: “Affected members exhibited PHNED phenotypes with involvement of complete hair loss and nail dysplasia.” It further reports: “Mutation screening revealed a novel missense mutation (c.929A > C; p.Asn310Thr) in homeobox DNA binding domain of HOXC13 gene.” These are human family and computational-structural evidence, respectively—not randomized or population-level findings. (khan2017anovelmutation pages 3-5)

7. Anatomical structures affected

Primary sites

Hair follicle and hair shaft—suggested UBERON:0002073 hair follicle; verify exact current UBERON term.
Scalp hair and body hair, including eyebrow, eyelash, beard, axillary, and pubic hair.
Nail matrix, nail bed, nail plate, and hyponychium of all digits—use current UBERON terms for nail, nail matrix, and nail bed after ontology validation.
System: integumentary system; tissue class: keratinized stratified squamous epithelium.

HOXC13 expression has been localized to postnatal follicular bulb, medulla, cortex, cuticle, and parts of the root sheath. (lin2012lossoffunctionmutationsin pages 3-4, lin2012lossoffunctionmutationsin pages 4-6)

Secondary involvement and lateralization

No consistent internal-organ involvement is established. Findings are generalized and bilateral rather than unilateral. Reported skeletal, neural, dental, ocular, and sweat-gland sparing argues against a systemic developmental syndrome in typical cases. (lin2012lossoffunctionmutationsin pages 1-2)

8. Temporal development

The condition is congenital, with absent/sparse hair and abnormal nails evident at birth or in early infancy. It follows a chronic lifelong course. Hair growth may remain absent or severely impaired; nail dystrophy persists. No accepted stage system, episodic pattern, remission phenotype, or spontaneous recovery rate exists. The biologically critical period is embryonic/postnatal differentiation of hair and nail ectoderm, although diagnosis and family counseling remain useful at any age. (lin2012lossoffunctionmutationsin pages 1-2, li2017anovelhomozygous pages 1-3)

9. Inheritance and population

Inheritance

The established human pattern is autosomal recessive. For two heterozygous parents, each pregnancy has a theoretical 25% probability of an affected child, 50% probability of a heterozygous carrier, and 25% probability of an unaffected non-carrier. Reported heterozygous human carriers were generally clinically normal. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5)

Penetrance among reported biallelic individuals appears high, but it cannot be estimated precisely. Expressivity varies from sparse/brittle hair to complete alopecia and from nail hypoplasia to severe dystrophy. There is no evidence of anticipation. Germline mosaicism has not been documented but cannot be excluded in apparently de novo cases. Consanguinity is recurrent in reports; no single global founder allele is established.

Epidemiology

No prevalence, incidence, carrier-frequency, or sex-ratio estimate based on a population denominator was found. Cases have been reported in Chinese Hui, Afghan, Pakistani, Syrian, Hispanic/North American, and other families, indicating multi-ancestry distribution rather than a single endemic region. The published sample is too small to infer ancestry-specific risk. (lin2012lossoffunctionmutationsin pages 1-2, khan2017anovelmutation pages 3-5, li2017anovelhomozygous pages 1-3, perez2022naked(n)mutant pages 13-14)

10. Diagnostics

Clinical recognition

Suspect HOXC13-related disease when congenital generalized hypotrichosis/alopecia co-occurs with dystrophy or hypoplasia of most or all nails while teeth and sweating are normal. Examination should document scalp/body-hair distribution, eyebrows/eyelashes, all 20 nails, teeth, sweating, skin, eyes/lacrimal symptoms, and developmental/skeletal findings.

No diagnostic blood chemistry, circulating protein, metabolite, imaging study, electrophysiologic test, or enzyme assay is established. Hair microscopy or skin biopsy may show abnormal follicular differentiation, but neither is specific enough to replace molecular testing.

Genetic testing strategy

Use a hereditary hypotrichosis/ectodermal-dysplasia panel containing HOXC13, KRT74, KRT85, and other phenotype-overlapping genes.
Alternatively, sequence HOXC13 when the phenotype is highly specific.
Include exon-level copy-number analysis because a 27.6-kb deletion has been reported; sequence-only assays may miss it. (lin2012lossoffunctionmutationsin pages 3-4)
If panel testing is negative, use trio or family-based exome/genome sequencing with CNV and noncoding review.
Confirm the variant and segregation by an orthogonal method where appropriate.

CMA has low expected yield unless the causal deletion is large enough and probe coverage is adequate. Karyotyping and FISH are not first-line. Mitochondrial DNA and repeat-expansion testing are not indicated by the known mechanism. RNA analysis may help resolve splice or suspected loss-of-function alleles but is not a standard diagnostic requirement.

Differential diagnosis

Major alternatives include KRT74- or KRT85-related PHNED, other hereditary hypotrichoses, hidrotic ectodermal dysplasia, hypohidrotic ectodermal dysplasia, isolated nail disorders such as RSPO4-related anonychia, and acquired alopecias. Normal teeth and sweating, congenital onset, generalized hair involvement, and biallelic HOXC13 findings favor ECTD9. (lin2012lossoffunctionmutationsin pages 3-4, lin2012lossoffunctionmutationsin pages 4-6)

Screening

There is no population or newborn screening program. Appropriate strategies are cascade testing of relatives, targeted carrier testing for a known familial variant, prenatal diagnosis, and preimplantation genetic testing after molecular confirmation in the family.

11. Outcome and prognosis

Human disease appears to affect morbidity and appearance rather than survival. No reduction in life expectancy, disease-specific mortality, internal-organ failure, or malignant transformation has been established. There are no 5- or 10-year survival statistics. Functional burdens may include nail fragility, secondary trauma/infection, scalp exposure, and psychosocial impact, but formal disability and quality-of-life measures are absent.

The phenotype does not ordinarily recover because the causal developmental/transcriptional defect persists. Prognostic biomarkers beyond genotype are unknown, and genotype–severity correlations remain too weak for individual prediction. Short lifespan observed in some Hoxc13-null or mutant animals should not be extrapolated to humans. (perez2022naked(n)mutant pages 9-11)

12. Treatment

Current management

There is no approved disease-modifying pharmacotherapy. Management is individualized and supportive:

Wigs, hair prostheses, eyebrow/eyelash cosmetics, and psychological support.
Sun, cold, and mechanical protection for exposed scalp.
Nail trimming, emollients, protective gloves/footwear, and prompt treatment of secondary bacterial or fungal infection.
Dermatology, clinical genetics, and genetic-counseling follow-up.
Assessment of lacrimal symptoms if present.

Potential NCIt intervention concepts include Supportive Care, Genetic Counseling, Prosthetic Device, and Psychosocial Intervention; exact NCIt codes should be validated against the current release.

No evidence supports minoxidil, immunosuppressants, biologics, keratin supplements, surgery, stem-cell treatment, RNA therapy, gene replacement, or CRISPR editing for this disorder. Because the defect acts during specialized epithelial differentiation and likely throughout follicular cycling, durable gene restoration would require safe delivery to relevant follicular and nail progenitors. This remains preclinical speculation.

The clinical-trial search found no disease-specific interventional study or NCT identifier. Consequently, response rates, treatment-related adverse-event data, pharmacogenomic guidance, and combination-treatment algorithms are unavailable.

13. Prevention

The genotype cannot be prevented by lifestyle or vaccination. Appropriate prevention is genetic and complication-focused:

Primary/reproductive: carrier testing in at-risk relatives, genetic counseling, preimplantation testing, and prenatal diagnosis where desired.
Secondary: early molecular diagnosis avoids inappropriate immune-directed alopecia treatment and enables family testing.
Tertiary: protect exposed scalp and fragile nails; monitor for trauma or infection; provide psychosocial support.

For a known familial biallelic condition, risk assessment follows autosomal-recessive inheritance. No prophylactic drug, vaccine, environmental intervention, or population screening program is indicated.

14. Other species and natural disease

HOXC13 function is evolutionarily conserved across mammals. Experimental loss or mutation affects pelage/wool and related keratinized appendages:

Mouse, Mus musculus (NCBI Taxon 10090): spontaneous Naked and engineered Hoxc13 alleles cause generalized or partial alopecia and abnormal nails. A p.Ser298Ter-like truncation escaped nonsense-mediated decay and behaved semi-dominantly/dominant-negatively in mice, unlike the predominantly recessive human pattern. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 11-13)
Pig, Sus scrofa (Taxon 9823): engineered knockout animals showed complete hair loss, abnormal nails, reduced follicles, and abnormal hair sheaths; relevant report PMID 28011715. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 13-14)
Rabbit, Oryctolagus cuniculus (Taxon 9986): engineered knockout produced regional hair loss, reduced follicles, approximately 15% survival to adulthood, and increased caudal vertebrae; report PMID 30125135. These extra findings limit direct human extrapolation. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 13-14)
Sheep, Ovis aries (Taxon 9940): a 2024 study found Hoxc13 expression in dermal papillae and inner/outer root sheaths during anagen and catagen; genotypes/haplotypes associated with wool length, supporting conserved control of fiber production rather than documenting an exact natural counterpart of human ECTD9. Published January 2024, DOI: https://doi.org/10.3390/ijms25031594. (sun2024moleculargeneticcharacteristics pages 13-14)

No zoonotic transmission is possible because this is a genetic disorder.

15. Model organisms

Principal models

Hoxc13-null mouse: reproduces alopecia and nail abnormalities and demonstrates reduced hair-keratin/FOXN1 pathway activity. Strength: extensive molecular tools and close phenotypic match. Limitation: some null mice have low viability or additional features absent from humans. (lin2012lossoffunctionmutationsin pages 1-2, lin2012lossoffunctionmutationsin pages 4-6)
Naked mouse: spontaneous Hoxc13S298X truncation; CRISPR recreation reproduced the phenotype, strongly confirming causality. Heterozygotes can be affected, making it especially useful for studying dominant-negative action but less representative of typical recessive human ECTD9. Published October 2022, DOI: https://doi.org/10.1111/exd.14469. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 11-13)
Knockout pig: closely models human hair/nail anatomy and recapitulates major appendage abnormalities; useful for delivery and translational studies, but expensive and less genetically tractable. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 13-14)
Knockout rabbit: useful for follicle–sebaceous-gland balance and hair-pattern studies, although incomplete spatial recapitulation, high mortality, and vertebral findings complicate interpretation. (perez2022naked(n)mutant pages 9-11)

No validated patient-derived organoid, iPSC, or standardized HOXC13-deficient human nail model was found. Such systems would be valuable for separating primary epithelial effects from species-specific systemic phenotypes and for testing allele-specific rescue.

Recent developments and evidence assessment

The most directly relevant 2023–2024 development is a 2024 report that a homozygous HOXC13 variant causes PHNED through reduced protein stability; however, the retrievable source record did not provide sufficient full-text variant and assay detail for independent extraction, so it should be curated from the original article before database deposition. The 2024 sheep study further refined the conserved spatiotemporal expression of Hoxc13 and related expression to wool length, but it is comparative biology—not human therapeutic evidence. (sun2024moleculargeneticcharacteristics pages 13-14)

Overall, expert interpretation remains anchored in the 2012 human loss-of-function study and subsequent family reports. The evidence is compelling for gene–disease causality and the HOXC13→FOXN1/keratin differentiation axis, but weak for phenotype frequencies, genotype–phenotype correlations, epidemiology, prognosis metrics, and treatment efficacy.

Key primary references

Lin Z et al. Loss-of-function mutations in HOXC13 cause pure hair and nail ectodermal dysplasia. American Journal of Human Genetics. Published November 2012. PMID 23063621. DOI/URL: https://doi.org/10.1016/j.ajhg.2012.08.029. (lin2012lossoffunctionmutationsin pages 1-2, lin2012lossoffunctionmutationsin pages 3-4)
Farooq M et al. Homozygous HOXC13 frameshift report. Published 2013. PMID 23315978. (perez2022naked(n)mutant pages 13-14)
Ali RH et al. Novel mutations in HOXC13 underlying pure hair and nail ectodermal dysplasia in consanguineous families. Published August 2013. PMID 23461661. DOI/URL: https://doi.org/10.1111/bjd.12302. (perez2022naked(n)mutant pages 13-14)
Li X et al. A novel homozygous missense mutation in HOXC13 leads to autosomal recessive pure hair and nail ectodermal dysplasia. Pediatric Dermatology. Published March 2017. PMID 28297138. DOI/URL: https://doi.org/10.1111/pde.13074. (li2017anovelhomozygous pages 1-3, perez2022naked(n)mutant pages 13-14)
Khan AK et al. A novel mutation in homeobox DNA binding domain of HOXC13 gene underlies pure hair and nail ectodermal dysplasia (ECTD9) in a Pakistani family. BMC Medical Genetics. Published April 2017. PMID 28403827. DOI/URL: https://doi.org/10.1186/s12881-017-0402-y. (khan2017anovelmutation pages 3-5)
Potter CS et al. The nude mutant gene Foxn1 is a HOXC13 regulatory target during hair follicle and nail differentiation. Journal of Investigative Dermatology. Published April 2011. DOI/URL: https://doi.org/10.1038/jid.2010.391. (perez2022naked(n)mutant pages 11-13)
Fernandez-Guerrero M et al. Mammalian-specific ectodermal enhancers control the expression of Hoxc genes in developing nails and hair follicles. PNAS. Published November 2020. PMID 33199643. DOI/URL: https://doi.org/10.1073/pnas.2011078117. (perez2022naked(n)mutant pages 13-14)
Perez CJ et al. Naked (N) mutant mice carry a nonsense mutation in the homeobox of Hoxc13. Experimental Dermatology. Published October 2022. DOI/URL: https://doi.org/10.1111/exd.14469. (perez2022naked(n)mutant pages 9-11, perez2022naked(n)mutant pages 11-13)
Sun H et al. Molecular Genetic Characteristics of the Hoxc13 Gene and Association Analysis of Wool Traits. International Journal of Molecular Sciences. Published January 2024. DOI/URL: https://doi.org/10.3390/ijms25031594. (sun2024moleculargeneticcharacteristics pages 13-14)

Knowledge-base caution: ontology identifiers marked for verification, contemporary ClinVar classifications, transcript-specific HGVS nomenclature, genome-build coordinates, and population allele frequencies should be checked against live ontology and genomic databases before production import. The primary literature securely supports the disease concept, congenital hair/nail phenotype, autosomal-recessive inheritance, and HOXC13 loss-of-function mechanism, but not precise epidemiologic or treatment estimates.

References

(lin2012lossoffunctionmutationsin pages 1-2): Zhimiao Lin, Quan Chen, Lei Shi, Mingyang Lee, Kathrin A. Giehl, Zhanli Tang, Huijun Wang, Jie Zhang, Jinghua Yin, Lingshen Wu, Ruo Xiao, Xuanzhu Liu, Lanlan Dai, Xuejun Zhu, Ruoyu Li, Regina C. Betz, Xue Zhang, and Yong Yang. Loss-of-function mutations in hoxc13 cause pure hair and nail ectodermal dysplasia. American journal of human genetics, 91 5:906-11, Nov 2012. URL: https://doi.org/10.1016/j.ajhg.2012.08.029, doi:10.1016/j.ajhg.2012.08.029. This article has 88 citations and is from a highest quality peer-reviewed journal.
(khan2017anovelmutation pages 3-5): Anwar Kamal Khan, Noor Muhammad, Abdul Aziz, Sher Alam Khan, Khadim Shah, Abdul Nasir, Muzammil Ahmad Khan, and Saadullah Khan. A novel mutation in homeobox dna binding domain of hoxc13 gene underlies pure hair and nail ectodermal dysplasia (ectd9) in a pakistani family. BMC Medical Genetics, Apr 2017. URL: https://doi.org/10.1186/s12881-017-0402-y, doi:10.1186/s12881-017-0402-y. This article has 17 citations and is from a peer-reviewed journal.
(li2017anovelhomozygous pages 1-3): Xiaoxiao Li, Meredith Lee Orseth, J. Michael Smith, Mary Abigail Brehm, Nnenna Gebechi Agim, and Donald Alexander Glass. A novel homozygous missense mutation in hoxc13 leads to autosomal recessive pure hair and nail ectodermal dysplasia. Pediatric Dermatology, 34:172-175, Mar 2017. URL: https://doi.org/10.1111/pde.13074, doi:10.1111/pde.13074. This article has 10 citations and is from a peer-reviewed journal.
(lin2012lossoffunctionmutationsin pages 3-4): Zhimiao Lin, Quan Chen, Lei Shi, Mingyang Lee, Kathrin A. Giehl, Zhanli Tang, Huijun Wang, Jie Zhang, Jinghua Yin, Lingshen Wu, Ruo Xiao, Xuanzhu Liu, Lanlan Dai, Xuejun Zhu, Ruoyu Li, Regina C. Betz, Xue Zhang, and Yong Yang. Loss-of-function mutations in hoxc13 cause pure hair and nail ectodermal dysplasia. American journal of human genetics, 91 5:906-11, Nov 2012. URL: https://doi.org/10.1016/j.ajhg.2012.08.029, doi:10.1016/j.ajhg.2012.08.029. This article has 88 citations and is from a highest quality peer-reviewed journal.
(perez2022naked(n)mutant pages 13-14): Carlos J. Perez, Lars Mecklenburg, Almudena Fernandez, Marta Cantero, Tiago Antonio de Souza, Kevin Lin, Sharon Y. R. Dent, Lluis Montoliu, Alexander Awgulewitsch, and Fernando Benavides. Naked (n) mutant mice carry a nonsense mutation in the homeobox of hoxc13. Oct 2022. URL: https://doi.org/10.1111/exd.14469, doi:10.1111/exd.14469. This article has 3 citations and is from a domain leading peer-reviewed journal.
(perez2022naked(n)mutant pages 11-13): Carlos J. Perez, Lars Mecklenburg, Almudena Fernandez, Marta Cantero, Tiago Antonio de Souza, Kevin Lin, Sharon Y. R. Dent, Lluis Montoliu, Alexander Awgulewitsch, and Fernando Benavides. Naked (n) mutant mice carry a nonsense mutation in the homeobox of hoxc13. Oct 2022. URL: https://doi.org/10.1111/exd.14469, doi:10.1111/exd.14469. This article has 3 citations and is from a domain leading peer-reviewed journal.
(perez2022naked(n)mutant pages 9-11): Carlos J. Perez, Lars Mecklenburg, Almudena Fernandez, Marta Cantero, Tiago Antonio de Souza, Kevin Lin, Sharon Y. R. Dent, Lluis Montoliu, Alexander Awgulewitsch, and Fernando Benavides. Naked (n) mutant mice carry a nonsense mutation in the homeobox of hoxc13. Oct 2022. URL: https://doi.org/10.1111/exd.14469, doi:10.1111/exd.14469. This article has 3 citations and is from a domain leading peer-reviewed journal.
(lin2012lossoffunctionmutationsin pages 4-6): Zhimiao Lin, Quan Chen, Lei Shi, Mingyang Lee, Kathrin A. Giehl, Zhanli Tang, Huijun Wang, Jie Zhang, Jinghua Yin, Lingshen Wu, Ruo Xiao, Xuanzhu Liu, Lanlan Dai, Xuejun Zhu, Ruoyu Li, Regina C. Betz, Xue Zhang, and Yong Yang. Loss-of-function mutations in hoxc13 cause pure hair and nail ectodermal dysplasia. American journal of human genetics, 91 5:906-11, Nov 2012. URL: https://doi.org/10.1016/j.ajhg.2012.08.029, doi:10.1016/j.ajhg.2012.08.029. This article has 88 citations and is from a highest quality peer-reviewed journal.
(sun2024moleculargeneticcharacteristics pages 13-14): Hongxian Sun, Zhaohua He, Fangfang Zhao, Jiang Hu, Jiqing Wang, Xiu Liu, Zhidong Zhao, Mingna Li, Yuzhu Luo, and Shaobin Li. Molecular genetic characteristics of the hoxc13 gene and association analysis of wool traits. International Journal of Molecular Sciences, 25:1594, Jan 2024. URL: https://doi.org/10.3390/ijms25031594, doi:10.3390/ijms25031594. This article has 3 citations.

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4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Citation Requirements

Output Format

HOXC13-Related Pure Hair–Nail Ectodermal Dysplasia

Executive summary

1. Disease information

Definition and nomenclature

Identifiers

2. Etiology

Causal factor

Risk factors

Protective factors and gene–environment interaction

3. Phenotypes

Core manifestations

Usually absent findings

Quality of life

4. Genetic and molecular information

Gene

Reported pathogenic variants

Modifiers, epigenetics, and structural abnormalities

5. Environmental information

6. Mechanism and pathophysiology

Causal chain

Cells and ontology suggestions

Omics and advanced technologies

Abstract-supported statements

7. Anatomical structures affected

Primary sites

Secondary involvement and lateralization

8. Temporal development

9. Inheritance and population

Inheritance

Epidemiology

10. Diagnostics

Clinical recognition

Genetic testing strategy

Differential diagnosis

Screening

11. Outcome and prognosis

12. Treatment

Current management

13. Prevention

14. Other species and natural disease

15. Model organisms

Principal models

Recent developments and evidence assessment

Key primary references