CDSN

Corneodesmosin (CDSN) is a secreted glycoprotein that serves as a major adhesive component of corneodesmosomes in the upper epidermis and inner root sheath of hair follicles, where it is essential for intercellular cohesion and epidermal barrier integrity. Full-length CDSN is required for corneodesmosome structural integrity; truncating or loss-of-function mutations produce non-functional protein and result in shortened, sparse corneodesmosomes, impaired cell–cell adhesion, abnormal desquamation, and secondary Th2-driven inflammation involving IL-4/IL-13 and JAK1 signaling (PMID:12754508, PMID:23957618, PMID:39377561). Loss-of-function CDSN mutations cause hypotrichosis simplex of the scalp and peeling skin disease type B (PMID:12754508, PMID:22146835). Genetic epistasis experiments place CDSN upstream of the desquamation-initiating serine protease KLK5, demonstrating that CDSN loss disrupts the fine protease balance required for controlled stratum corneum shedding (PMID:40943523).

1. 2003 High

   Establishing that CDSN is a disease gene: identification of nonsense mutations in CDSN as the cause of hereditary hypotrichosis simplex of the scalp demonstrated that this corneodesmosomal glycoprotein is required for normal hair follicle adhesion and physiology.

   Evidence Genetic sequencing of multiple affected families with immunohistochemical and Western blot detection of truncated CDSN aggregates in dermis and hair follicle periphery

   PMID:12754508

   Open questions at the time

   • Mechanism by which truncated CDSN aggregates in the dermis rather than being degraded was unknown
   • Whether CDSN loss also affects interfollicular epidermal adhesion was not tested
   • Structural basis of CDSN adhesive function remained unresolved
2. 2011 Medium

   Extending CDSN deficiency from hair loss to generalized skin disease: homozygous loss-of-function CDSN mutations were shown to cause peeling skin syndrome type B, establishing that corneodesmosin is essential for cell–cell adhesion across the entire upper epidermis and that its absence triggers inflammatory barrier disruption.

   Evidence PCR and direct sequencing identifying frameshift mutations; clinical, histological, and immunohistochemical phenotyping across multiple independent reports

   PMID:22146835 PMID:23957618 PMID:24116970 PMID:24372652

   Open questions at the time

   • The molecular mechanism linking barrier disruption to the inflammatory response was not defined
   • Whether residual truncated CDSN retains partial function was unclear
3. 2013 Medium

   Resolving whether truncated CDSN is functional: detection of a stable 16-kDa truncated corneodesmosin (p.Gly142*) in patient epidermis demonstrated that partial CDSN expression is insufficient and that full-length protein is required for adhesive function.

   Evidence Western blot and immunohistochemistry of patient skin biopsies combined with DNA sequencing and real-time PCR

   PMID:23957618

   Open questions at the time

   • Which specific domains of full-length CDSN mediate adhesion was not mapped
   • No in vitro reconstitution of CDSN adhesive activity was performed
4. 2014 Low

   Linking CDSN mutation to corneodesmosome ultrastructure: electron microscopy of a missense CDSN mutant revealed structurally shortened and sparse corneodesmosomes, directly connecting CDSN protein to the structural integrity of these junctions.

   Evidence Electron microscopy with morphometric analysis in a single patient with homozygous CDSN missense mutation

   PMID:25473393

   Open questions at the time

   • Single case from one laboratory without replication
   • No biochemical characterization of how the missense mutation alters CDSN folding or incorporation
   • Whether the ultrastructural defect is a direct or indirect consequence of the mutation was not resolved
5. 2024 Low

   Identifying the downstream inflammatory pathway: CDSN-deficient skin showed elevated Th2 cytokines IL-4 and IL-13 and JAK1-dependent signaling, and JAK1 inhibition alleviated symptoms, linking CDSN loss mechanistically to a specific inflammatory axis.

   Evidence Whole exome sequencing, immunohistochemistry for CDSN and cytokines, and clinical response to JAK1 inhibitor (upadacitinib) in a single patient

   PMID:39377561

   Open questions at the time

   • Mechanistic inference from single case without in vitro reconstitution or controlled trial
   • Whether JAK1-Th2 signaling is a direct consequence of barrier disruption or involves additional intermediaries is unknown
   • Reproducibility across patients not established
6. 2025 High

   Positioning CDSN in the desquamation protease hierarchy: genetic epistasis showed that KLK5 deletion aggravates rather than rescues the CDSN-null phenotype, revealing that CDSN functions upstream of a finely tuned protease balance required for controlled stratum corneum shedding.

   Evidence Double-knockout (Cdsn/Klk5) mouse model and shRNA knockdown in human epidermal equivalents with electron microscopy and barrier permeability assays

   PMID:40943523

   Open questions at the time

   • Identity of compensatory proteases that become hyperactive upon combined CDSN/KLK5 loss is unknown
   • Whether CDSN directly inhibits or modulates protease access to corneodesmosomes versus acting purely as a structural substrate remains unresolved

• Key open question: the structural basis of CDSN adhesive function — which domains mediate homophilic or heterophilic corneodesmosomal interactions, and how CDSN mechanistically controls protease accessibility within the desquamation cascade — remains undefined.
• No crystal or cryo-EM structure of CDSN or CDSN-containing corneodesmosome complexes exists
• Direct binding partners of CDSN within the corneodesmosome (e.g., desmoglein 1, desmocollin 1) have not been biochemically reconstituted
• Mechanism by which CDSN loss triggers compensatory protease upregulation is unknown