KRT85-Related Pure Hair-Nail Ectodermal Dysplasia

1. Disease Information

1.1 Overview (current understanding)

KRT85-related pure hair–nail ectodermal dysplasia (PHNED; also written PHNEC) is a congenital genetic disorder characterized primarily by hypotrichosis/atrichia (ranging from sparse fragile hair to complete alopecia) and nail dystrophy, with other ectodermal structures (e.g., teeth and sweating) typically spared (“pure” hair–nail involvement). (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

1.2 Key identifiers and nomenclature

Evidence-supported identifiers and names from the retrieved literature are summarized in the table artifact below.

Table: This table summarizes the core identifiers, synonyms, historical nomenclature, and locus information for KRT85-related pure hair and nail ectodermal dysplasia. It is useful as a normalization artifact for a disease knowledge base entry, with evidence-linked terminology and source URLs.

Notes on disease identifiers not recovered from tools: * Disease-specific MONDO, Orphanet, MeSH, and ICD-10/ICD-11 codes were not present in the retrieved full-text excerpts; only a broad Open Targets disease label (“ectodermal dysplasia syndrome”, MONDO_0019287) was returned and should not be treated as disease-specific for KRT85-PHNED. (artifact-00)

1.3 Evidence source type

The KRT85-related entity is supported mainly by (i) human family-based linkage and candidate-gene sequencing studies and (ii) subsequent NGS-panel diagnosis reports. (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

2. Etiology

2.1 Disease causal factors

Primary cause: biallelic pathogenic variants in KRT85 (historical name KRTHB5/hHb5; OMIM gene MIM 602767) disrupt hard-keratin intermediate filament biology in hair and nail. (shimomura2010mutationsinthe pages 1-2, naeem2006amutationin pages 1-2)

Mode of inheritance: most documented KRT85 cases are autosomal recessive, often in consanguineous families. (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2)

2.2 Risk factors

Genetic risk factors: consanguinity/familial carrier status increases risk of homozygosity for pathogenic alleles (as illustrated by large consanguineous Pakistani pedigrees). (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2)

Environmental risk factors: no disease-specific environmental triggers have been established in the retrieved primary literature. One report noted worsening of alopecia after febrile episodes in affected siblings with compound heterozygous KRT85 variants; this observation does not establish causality but suggests symptoms can fluctuate with systemic stressors. (amico2019compoundheterozygosityfor pages 1-3)

2.3 Protective factors

No genetic or environmental protective factors were identified in the retrieved evidence.

2.4 Gene–environment interactions

No validated gene–environment interaction studies specific to KRT85-PHNED were identified in the retrieved evidence.

3. Phenotypes

3.1 Core phenotypic spectrum

Across reported KRT85-PHNED families, phenotypes include: * Congenital hypotrichosis/atrichia: scalp, facial (including eyebrows/eyelashes), and body hair can be sparse to absent; some families show complete alopecia. (naeem2006amutationin pages 2-3, shimomura2010mutationsinthe pages 1-2) * Hair-shaft fragility and structural abnormalities: scanning electron microscopy (SEM) demonstrated inconsistent hair-shaft thickness (not periodic like monilethrix) in one family; clinically hair is thin/fragile and breaks easily. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3) * Nail dystrophy: irregularly shaped, fragile nails; can include micronychia, koilonychia, distal onycholysis; severe nail deformities reported in severe cases. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3) * Relative sparing of other ectodermal structures: normal teeth and normal sweating are repeatedly reported in KRT85-PHNED families. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

Visual evidence

Pedigrees, clinical photos, and SEM hair images supporting these features are shown in Shimomura et al. 2010 (Figure 1), and the KRT85 variant evidence is shown in their Figure 2. (shimomura2010mutationsinthe media b5f82a0b, shimomura2010mutationsinthe media a9ef3a76)

3.2 Phenotype onset, progression, and severity

• Onset: typically since birth for both hair and nail findings in multiple families. (shimomura2010mutationsinthe pages 1-2)
• Severity: variable even across families; one family showed sparse hair and mild nail fragility while another showed complete alopecia with severe nail deformities. (shimomura2010mutationsinthe pages 1-2)
• Course: at least one sibling pair showed partial improvement (normalization of hair growth) after puberty, suggesting possible age-related modulation in some individuals. (amico2019compoundheterozygosityfor pages 1-3)

3.3 Suggested HPO terms (non-exhaustive)

• Hypotrichosis (HP:0001006)
• Alopecia (HP:0001596)
• Atrichia (HP:0001598)
• Abnormal hair shaft morphology (HP:0011354)
• Onychodystrophy (HP:0001806)
• Koilonychia (HP:0001805)
• Micronychia (HP:0001800)
• Onycholysis (HP:0001804)
• Keratosis pilaris (HP:0000964) / follicular papules (if present)

3.4 Quality-of-life impact

No disease-specific quantitative QoL instruments (e.g., DLQI, SF-36) were identified in the retrieved primary literature; given visible alopecia and nail fragility, psychosocial and functional impacts are plausible but not evidenced quantitatively here.

4. Genetic / Molecular Information

4.1 Causal gene

KRT85 encodes a type II hair keratin expressed in hair matrix/precortex/cuticle cells; impaired availability of functional type II hair keratin to pair with type I partners is proposed to underlie the abnormal hair phenotype. (amico2019compoundheterozygosityfor pages 1-3)

4.2 Pathogenic variants (human)

Pathogenic/likely pathogenic variants reported in retrieved primary/clinical literature include: * c.233G>A (p.Arg78His), exon 1: homozygous in a large consanguineous Pakistani pedigree with complete alopecia and nail dystrophy; absent in 100 unrelated controls (200 chromosomes). (naeem2006amutationin pages 3-4) * c.1448_1449delCT (p.Pro483Argfs*18), exon 9: homozygous frameshift predicted to truncate the protein; reported in consanguineous Pakistani families and absent from 100 healthy Pakistani controls in one study. (shimomura2010mutationsinthe pages 1-2) * c.502_525del (p.del168_175) (in-frame deletion) and c.886A>G (p.Lys296Glu) (missense): compound heterozygosity in two sisters from a non-consanguineous French family; both reported absent from gnomAD. (amico2019compoundheterozygosityfor pages 1-3)

Variant classes: missense, frameshift, and in-frame deletion are represented among reported alleles. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

Population frequency statements: * c.233G>A was not detected in 100 unrelated controls in the original linkage/candidate gene report. (naeem2006amutationin pages 3-4) * The 2019 report states both compound heterozygous variants were absent from gnomAD. (amico2019compoundheterozygosityfor pages 1-3)

Somatic vs germline: all reported variants are germline and segregate with disease in families. (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

4.3 Modifier genes / epigenetics / chromosomal abnormalities

No validated modifier genes, epigenetic signatures, or chromosomal abnormalities specific to KRT85-PHNED were identified in the retrieved evidence.

5. Mechanism / Pathophysiology

5.1 Causal chain (gene → cell → tissue → phenotype)

A coherent mechanism supported by available evidence is: 1. Biallelic KRT85 variants (frameshift or missense) alter K85 structure/function. (shimomura2010mutationsinthe pages 1-2) 2. K85 dysfunction is proposed to impair intermediate filament assembly/heterodimer formation in hard-keratinizing structures (hair shaft and nails), consistent with keratin biology and with a truncation predicted to alter the C-terminal tail (loss of cysteine residues) and thus disrupt keratin interactions. (shimomura2010mutationsinthe pages 1-2) 3. The result is abnormal hair-shaft formation and fragility and nail dystrophy, manifesting clinically as hypotrichosis/alopecia and dystrophic nails. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

5.2 Pathways and processes (ontology suggestions)

Suggested GO Biological Process terms (examples): * keratinization (GO:0031424) * hair follicle development (GO:0001942) * hair cycle process (GO:0022405) * intermediate filament organization (GO:0045109)

Suggested GO Cellular Component terms: * intermediate filament (GO:0005882) * keratin filament (GO:0045095)

Suggested Cell Ontology (CL) terms (examples): * keratinocyte (CL:0000312) * hair follicle keratinocyte (more specific subtypes vary by ontology version)

6. Environmental Information

No specific environmental, lifestyle, or infectious contributors were identified for KRT85-PHNED in the retrieved evidence. One family reported symptom worsening after febrile episodes. (amico2019compoundheterozygosityfor pages 1-3)

7. Anatomical Structures Affected

7.1 Organ/tissue level

Primary structures affected are hair follicles (hair shaft production) and nail unit (nail matrix/plate). KRT85 is described as a hair keratin expressed in hair matrix/precortex/cuticle; clinical findings are limited to hair and nails without broader ectodermal involvement in the cases described. (amico2019compoundheterozygosityfor pages 1-3, shimomura2010mutationsinthe pages 1-2)

7.2 Suggested UBERON terms

• hair follicle (UBERON:0002070)
• nail (UBERON:0001700)
• nail matrix (UBERON:0001524)

8. Temporal Development

• Typical onset: congenital/early life, with hair and nail dystrophy present since birth. (shimomura2010mutationsinthe pages 1-2)
• Course: appears lifelong, but some individuals may show partial improvement after puberty. (amico2019compoundheterozygosityfor pages 1-3)

No formal staging systems or longitudinal natural history cohorts were identified.

9. Inheritance and Population

9.1 Inheritance

Human reports support autosomal recessive inheritance for KRT85-PHNED. (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2)

9.2 Epidemiology

No prevalence or incidence estimates specific to KRT85-PHNED were available in the retrieved evidence. A contemporary ectodermal dysplasia classification review highlights that many EDs are ultra-rare with missing prevalence data and may be underdiagnosed, while providing prevalence estimates for hypohidrotic ED as context (not for KRT85-PHNED). (peschel2022molecularpathwaybasedclassification pages 1-2)

9.3 Founder effects / carrier frequency

No carrier frequency estimates, founder effects, or population-based prevalence statistics for KRT85 pathogenic variants were identified in the retrieved evidence.

10. Diagnostics

10.1 Clinical diagnosis

Diagnosis is suspected clinically based on the combination of congenital hypotrichosis/alopecia and nail dystrophy with normal teeth and sweating and no major additional ectodermal findings. (shimomura2010mutationsinthe pages 1-2, amico2019compoundheterozygosityfor pages 1-3)

10.2 Genetic testing approaches (real-world implementations)

Evidence-supported approaches include: * Linkage mapping + candidate gene Sanger sequencing in large pedigrees (historical approach). (naeem2006amutationin pages 1-2, shimomura2010mutationsinthe pages 1-2) * Targeted next-generation sequencing (NGS) panel testing: a “gene chip-based next-generation sequencing” panel of 22 hypotrichosis genes was used to identify compound heterozygous KRT85 variants in siblings, enabling rapid molecular confirmation and informing genetic counseling. (amico2019compoundheterozygosityfor pages 1-3)

Differential diagnosis (evidence-informed): other “pure” hair–nail ectodermal dysplasias due to HOXC13 or KRT74, and other congenital alopecia/hair-shaft disorders (e.g., monilethrix) are relevant considerations; within PHNED, genetic heterogeneity is emphasized. (amico2019compoundheterozygosityfor pages 1-3, lin2012lossoffunctionmutationsin pages 1-2)

11. Outcome / Prognosis

No mortality signal or systemic organ involvement is described in the retrieved KRT85-focused families; affected individuals are described as otherwise healthy with normal intelligence and normal routine lab tests in at least one large pedigree. (naeem2006amutationin pages 2-3)

Quantitative prognosis metrics (survival, morbidity indices) are not available from the retrieved evidence.

12. Treatment

12.1 Disease-modifying therapy

No disease-modifying pharmacologic, gene, or cell therapies were identified in the retrieved evidence for KRT85-PHNED.

12.2 Supportive care (evidence limits)

The retrieved primary literature and brief reports did not provide detailed management algorithms. The strongest evidence-based “intervention” discussed is genetic counseling enabled by molecular diagnosis. (amico2019compoundheterozygosityfor pages 1-3)

Suggested MAXO terms (as knowledge-base annotations; not asserted as evidence-based efficacy): * genetic counseling (MAXO:0000747) * molecular genetic testing (MAXO:0000059) * wig/hair prosthesis use (supportive) * nail care / protective measures (supportive)

13. Prevention

No primary prevention exists because the disorder is monogenic. Secondary/tertiary prevention is primarily through: * Carrier testing and cascade testing in families once a pathogenic variant is identified (supported indirectly by segregation and counseling emphasis). (amico2019compoundheterozygosityfor pages 1-3)

14. Other Species / Natural Disease

No naturally occurring veterinary disease analogs for KRT85-PHNED were identified in the retrieved evidence.

15. Model Organisms

Direct KRT85 disease models were not identified in the retrieved evidence. However, the broader PHNED genetic landscape includes HOXC13-related models (e.g., Hoxc13 mutant mice) used to study hair/nail biology; these inform shared pathway biology but are not KRT85-specific. (lin2012lossoffunctionmutationsin pages 1-2)

16. Recent Developments (prioritizing 2023–2024)

• 2023–2024 primary human KRT85-PHNED reports: A 2023 European Journal of Dermatology report (“Two homozygous KRT85 mutations in a Chinese patient…”, DOI: 10.1684/ejd.2023.4416) was surfaced by search but was not obtainable via the current toolchain, so its details cannot be verified/cited here.
• Recent authoritative synthesis: A 2022 expert-panel update on ectodermal dysplasia classification underscores the growing role of exome/genome analysis in improving diagnostic accuracy and notes that many EDs remain ultra-rare and underdiagnosed (contextual but not KRT85-specific). (peschel2022molecularpathwaybasedclassification pages 1-2)
• Real-world diagnostic implementation trend: The 2019 KRT85 compound heterozygosity report illustrates deployment of an NGS hypotrichosis gene panel in clinical practice to confirm diagnosis and guide counseling. (amico2019compoundheterozygosityfor pages 1-3)

17. Direct abstract-supported quotes (from retrieved evidence)

Because several key KRT85-PHNED papers were retrieved as full-text pages without clearly captured abstract fields, direct abstract quotations are limited. One available direct abstract quote relevant to “pure hair and nail ectodermal dysplasia” definition (not specific to KRT85 but defining PHNED) is: * “Pure hair and nail ectodermal dysplasia (PHNED) comprises a heterogeneous group of rare heritable disorders characterized by brittle hair, hypotrichosis, onychodystrophy and micronychia.” (Raykova et al., 2014; KRT74-related PHNED subtype) (lin2012lossoffunctionmutationsin pages 1-2)

18. Key statistics/data points from primary studies

• Linkage strength in the original KRTHB5/KRT85 pedigree: maximum multipoint LOD reported as 8.2 (chromosome 12q12–q14.1 region). (naeem2006amutationin pages 1-2)
• Control screening: the KRT85/KRTHB5 R78H change was absent from 100 unrelated controls (200 chromosomes) in the original report; the c.1448_1449delCT variant was absent from 100 healthy Pakistani controls in a later report. (naeem2006amutationin pages 3-4, shimomura2010mutationsinthe pages 1-2)
• Population database check: two novel KRT85 variants in compound heterozygosity were reported absent from gnomAD. (amico2019compoundheterozygosityfor pages 1-3)

19. Expert opinion / authoritative analysis

An expert-panel ectodermal dysplasia classification update emphasizes that ED diagnosis based on phenotype alone is challenging and that exome/genome analysis improves diagnostic accuracy—supporting the shift toward molecular confirmation in rare EDs. (peschel2022molecularpathwaybasedclassification pages 1-2)

Key References (with URLs and publication dates)

• Naeem M, et al. J Med Genet. 2006-08. “A mutation in the hair matrix and cuticle keratin KRTHB5 gene causes ectodermal dysplasia of hair and nail type.” https://doi.org/10.1136/jmg.2005.033381 (naeem2006amutationin pages 1-2)
• Shimomura Y, et al. J Invest Dermatol. Published online 2009-10-29; print 2010-03. “Mutations in the keratin 85 (KRT85/hHb5) gene underlie pure hair and nail ectodermal dysplasia.” https://doi.org/10.1038/jid.2009.341 (shimomura2010mutationsinthe pages 1-2)
• Amico S, et al. JEADV. 2019-07. “Compound heterozygosity for novel KRT85 variants associated with pure hair and nail ectodermal dysplasia.” https://doi.org/10.1111/jdv.15777 (amico2019compoundheterozygosityfor pages 1-3)
• Peschel N, et al. Genes (Basel). 2022-12-10. “Molecular Pathway-Based Classification of Ectodermal Dysplasias: First Five-Yearly Update.” https://doi.org/10.3390/genes13122327 (peschel2022molecularpathwaybasedclassification pages 1-2)

Evidence limitations

• The tool-retrieved excerpts did not include PMIDs for key KRT85 papers; therefore, this report cites DOIs/URLs and the tool-provided context IDs.
• Several potentially relevant 2023–2024 KRT85 case reports were discovered but not obtainable in full text via tools, so they are not cited for factual claims.
• Prevalence/incidence, standardized diagnostic criteria, and treatment outcome statistics are not available from the retrieved disease-specific evidence.

References

1. (shimomura2010mutationsinthe pages 1-2): Yutaka Shimomura, Muhammad Wajid, Mazen Kurban, Nobuyuki Sato, and Angela M. Christiano. Mutations in the keratin 85 (krt85/hhb5) gene underlie pure hair and nail ectodermal dysplasia. The Journal of investigative dermatology, 130 3:892-5, Mar 2010. URL: https://doi.org/10.1038/jid.2009.341, doi:10.1038/jid.2009.341. This article has 50 citations.

2. (amico2019compoundheterozygosityfor pages 1-3): S. Amico, C. Ged, A. Taïeb, and F. Morice‐Picard. Compound heterozygosity for novel krt85 variants associated with pure hair and nail ectodermal dysplasia. Journal of the European Academy of Dermatology and Venereology, Jul 2019. URL: https://doi.org/10.1111/jdv.15777, doi:10.1111/jdv.15777. This article has 7 citations and is from a domain leading peer-reviewed journal.

3. (naeem2006amutationin pages 1-2): M. Naeem, M. Wajid, K. Lee, S. Leal, and W. Ahmad. A mutation in the hair matrix and cuticle keratin krthb5 gene causes ectodermal dysplasia of hair and nail type. Journal of Medical Genetics, 43:274-279, Aug 2006. URL: https://doi.org/10.1136/jmg.2005.033381, doi:10.1136/jmg.2005.033381. This article has 72 citations and is from a domain leading peer-reviewed journal.

4. (naeem2006amutationin pages 3-4): M. Naeem, M. Wajid, K. Lee, S. Leal, and W. Ahmad. A mutation in the hair matrix and cuticle keratin krthb5 gene causes ectodermal dysplasia of hair and nail type. Journal of Medical Genetics, 43:274-279, Aug 2006. URL: https://doi.org/10.1136/jmg.2005.033381, doi:10.1136/jmg.2005.033381. This article has 72 citations and is from a domain leading peer-reviewed journal.

5. (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 87 citations and is from a highest quality peer-reviewed journal.

6. (naeem2006amutationin pages 2-3): M. Naeem, M. Wajid, K. Lee, S. Leal, and W. Ahmad. A mutation in the hair matrix and cuticle keratin krthb5 gene causes ectodermal dysplasia of hair and nail type. Journal of Medical Genetics, 43:274-279, Aug 2006. URL: https://doi.org/10.1136/jmg.2005.033381, doi:10.1136/jmg.2005.033381. This article has 72 citations and is from a domain leading peer-reviewed journal.

7. (shimomura2010mutationsinthe media b5f82a0b): Yutaka Shimomura, Muhammad Wajid, Mazen Kurban, Nobuyuki Sato, and Angela M. Christiano. Mutations in the keratin 85 (krt85/hhb5) gene underlie pure hair and nail ectodermal dysplasia. The Journal of investigative dermatology, 130 3:892-5, Mar 2010. URL: https://doi.org/10.1038/jid.2009.341, doi:10.1038/jid.2009.341. This article has 50 citations.

8. (shimomura2010mutationsinthe media a9ef3a76): Yutaka Shimomura, Muhammad Wajid, Mazen Kurban, Nobuyuki Sato, and Angela M. Christiano. Mutations in the keratin 85 (krt85/hhb5) gene underlie pure hair and nail ectodermal dysplasia. The Journal of investigative dermatology, 130 3:892-5, Mar 2010. URL: https://doi.org/10.1038/jid.2009.341, doi:10.1038/jid.2009.341. This article has 50 citations.

9. (peschel2022molecularpathwaybasedclassification pages 1-2): Nicolai Peschel, John T. Wright, Maranke I. Koster, Angus J. Clarke, Gianluca Tadini, Mary Fete, Smail Hadj-Rabia, Virginia P. Sybert, Johanna Norderyd, Sigrun Maier-Wohlfart, Timothy J. Fete, Nina Pagnan, Atila F. Visinoni, and Holm Schneider. Molecular pathway-based classification of ectodermal dysplasias: first five-yearly update. Genes, 13:2327, Dec 2022. URL: https://doi.org/10.3390/genes13122327, doi:10.3390/genes13122327. This article has 61 citations.