Desmosomal Adhesion Failure Module

Module desmosomal_adhesion_failure 9 disorders Pathograph 5

A conserved cell-adhesion module for the desmosomal diseases. Desmosomes are the high-tensile intercellular junctions of tissues that bear mechanical stress, and they work by coupling desmosomal cadherins across the intercellular space to the intermediate filament cytoskeleton of both partner cells through an armadillo-and-plakin plaque. Three mechanistically distinct routes converge on the loss of that coupling: germline loss of a desmosomal structural component, autoantibody blockade of a desmosomal cadherin ectodomain, and loss of the keratinocyte calcium compartmentalization that desmosome assembly requires. Adhesion loss then manifests in whichever desmosome-dependent tissue is affected - acantholysis in epidermis, a fragile beaded or woolly hair shaft, and myocyte detachment with fibrofatty replacement in myocardium. This cross-organ reach is why a single desmosomal gene can produce a cardiocutaneous syndrome. Disorder entries reference these nodes via conforms_to and substitute their own route into the trigger.

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Pathophysiology Nodes

5 shared nodes are defined in this module.

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Cell Types

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Biological Processes

Notes

This is a shared mechanism module, not a disease. Three substitutable routes into the trigger node, which are NOT interchangeable and should be curated as the specific route the disorder takes: 1. Structural gene loss - DSP (Carvajal syndrome, striate palmoplantar keratoderma, arrhythmogenic cardiomyopathy), JUP/plakoglobin (Naxos disease), DSG1 (striate palmoplantar keratoderma type 1, SAM syndrome), PKP1 (ectodermal dysplasia-skin fragility syndrome), PKP2 and DSC2 and DSG2 (arrhythmogenic right ventricular cardiomyopathy). 2. Autoantibody blockade - IgG against the DSG3 and/or DSG1 ectodomain in pemphigus vulgaris and pemphigus foliaceus. The target protein is the same as in route 1; only the mechanism of its removal differs, which is why an acquired disease conforms to a module otherwise populated by Mendelian entries. 3. Calcium-handling failure - ATP2A2/SERCA2 (Darier disease) and ATP2C1/SPCA1 (Hailey-Hailey disease). These are not desmosomal proteins; they are the ER and Golgi calcium pumps whose activity the post-translational processing and assembly of desmosomal proteins depends on, so the desmosomal defect here is secondary. Curate the calcium lesion as the trigger and the desmosomal consequence downstream of it - do not assert a primary desmosomal protein defect in Darier or Hailey-Hailey disease. Dose-sensitivity is a real and curatable feature of route 1: DSP haploinsufficiency alone is sufficient for striate palmoplantar keratoderma, whereas the cardiocutaneous syndromes generally require a more severe or recessive allele. A conforming entry should preserve that distinction rather than describing every desmosomal lesion as equivalent. Scope boundary with `keratin_intermediate_filament_fragility`. Both modules end in a mechanically fragile keratinocyte, but the failing element differs: there the filament network itself collapses, here the network is intact and its anchorage to the junction is lost. A DSP entry belongs here; a KRT5 entry does not. Scope boundary with `cardiomyopathy_maladaptive_remodeling`. The cardiocutaneous entries reach ventricular remodeling and should keep conforming to that module for the heart-failure arm; this module supplies the upstream adhesion lesion that module takes as given. Not an Xogenesis module: acantholysis is the dissolution of intercellular adhesion, not the formation of a pathological anatomical entity. Conformance requires evidence of lost desmosomal adhesion - acantholysis, reduced or malformed desmosomes, or intermediate filament retraction from the plaque. Expression of a desmosomal gene in the affected tissue is not sufficient.

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Used By Disorder Entries

Carvajal Syndrome via Biallelic DSP Deficiency — Desmosome-IF Uncoupling → Desmosomal Component Loss or Blockade , Keratinocyte Adhesion Failure → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues , Cardiomyocyte Desmosomal Uncoupling → Loss of Desmosomal Intercellular Adhesion

Darier Disease via ATP2A2 Haploinsufficiency and Loss of SERCA2 Pump Activity → Desmosomal Component Loss or Blockade , Disturbed Endoplasmic Reticulum Calcium Signalling in Keratinocytes → Failure of Desmosome Assembly and Intermediate Filament Anchorage , Suprabasal Acantholysis → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Hailey-Hailey Disease via ATP2C1 Haploinsufficiency and Loss of Golgi SPCA1 Pump Activity → Desmosomal Component Loss or Blockade , Disturbed Keratinocyte Calcium Handling and the Epidermal Calcium Gradient → Failure of Desmosome Assembly and Intermediate Filament Anchorage , Suprabasal Acantholysis Sparing the Adnexal Epithelia → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Naxos disease via Plakoglobin loss-of-function → Desmosomal Component Loss or Blockade , Intercalated-disc desmosome failure → Loss of Desmosomal Intercellular Adhesion , Cutaneous and hair-follicle desmosome failure → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Paraneoplastic Pemphigus via Autoantibody Binding to Desmosomal Plakins and Desmogleins → Desmosomal Component Loss or Blockade , Desmosome Disruption and Keratinocyte Acantholysis → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Pemphigus Erythematosus via Desmosomal Autoantibody-Mediated Acantholysis → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Pemphigus Vulgaris via Anti-Desmoglein Autoantibodies → Desmosomal Component Loss or Blockade , Acantholysis and Blister Formation → Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

Skin Fragility-Woolly Hair Syndrome via DSP Compound Heterozygous Loss-of-Function → Desmosomal Component Loss or Blockade , Desmosome-Keratin Detachment → Failure of Desmosome Assembly and Intermediate Filament Anchorage

Striate Palmoplantar Keratoderma Type 2 via DSP Premature Termination Codons Triggering Nonsense-Mediated Decay → Desmosomal Component Loss or Blockade , Defective Desmosomal Plaque Assembly → Failure of Desmosome Assembly and Intermediate Filament Anchorage , Keratin Intermediate Filament Network Disruption → Failure of Desmosome Assembly and Intermediate Filament Anchorage , Suprabasal Keratinocyte Adhesion Failure in Mechanical Stress Sites → Loss of Desmosomal Intercellular Adhesion

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Pathograph

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Pathophysiology

Desmosomal Component Loss or Blockade

trigger

A structural component of the desmosome becomes unavailable to the junction. It may be absent because the gene encoding it carries a loss-of-function variant, functionally blocked because autoantibody has bound its adhesive ectodomain, or unable to be assembled because the calcium compartmentalization required for its processing has failed.

keratinocyte CL:0000312

intracellular calcium ion homeostasis GO:0006874 ABNORMAL

desmosome GO:0030057

Used by disorders

Carvajal Syndrome as Biallelic DSP Deficiency — Desmosome-IF Uncoupling

Darier Disease as ATP2A2 Haploinsufficiency and Loss of SERCA2 Pump Activity

Hailey-Hailey Disease as ATP2C1 Haploinsufficiency and Loss of Golgi SPCA1 Pump Activity

Naxos disease as Plakoglobin loss-of-function

Paraneoplastic Pemphigus as Autoantibody Binding to Desmosomal Plakins and Desmogleins

Pemphigus Vulgaris as Anti-Desmoglein Autoantibodies

Skin Fragility-Woolly Hair Syndrome as DSP Compound Heterozygous Loss-of-Function

Striate Palmoplantar Keratoderma Type 2 as DSP Premature Termination Codons Triggering Nonsense-Mediated Decay

Downstream

Failure of Desmosome Assembly and Intermediate Filament Anchorage Without an available component, desmosomes are reduced in number or size and the intermediate filament network is no longer tethered to the plaque.

Failure of Desmosome Assembly and Intermediate Filament Anchorage

amplifier

Desmosomes are assembled in reduced numbers, are structurally abnormal, or lose their cytoskeletal connection. The plakin-family plaque proteins, desmoplakin foremost among them, are what link the intermediate filament network to the junctional membrane, so their loss uncouples the cytoskeleton from the adhesive surface even when cadherins are present. The junction is then no longer a load-bearing element of the tissue.

keratinocyte CL:0000312

desmosome organization GO:0002934 ABNORMAL intermediate filament organization GO:0045109 ABNORMAL

desmosome GO:0030057

Used by disorders

Darier Disease as Disturbed Endoplasmic Reticulum Calcium Signalling in Keratinocytes

Hailey-Hailey Disease as Disturbed Keratinocyte Calcium Handling and the Epidermal Calcium Gradient

Skin Fragility-Woolly Hair Syndrome as Desmosome-Keratin Detachment

Striate Palmoplantar Keratoderma Type 2 as Defective Desmosomal Plaque Assembly

Striate Palmoplantar Keratoderma Type 2 as Keratin Intermediate Filament Network Disruption

Downstream

Loss of Desmosomal Intercellular Adhesion Junctions that are absent, malformed, or uncoupled from the cytoskeleton cannot hold adjacent cells together under load.

Loss of Desmosomal Intercellular Adhesion

central effector

Adjacent cells lose the high-tensile adhesion desmosomes provide. This is the rate-limiting, disorder-agnostic node of the module: the structural, autoimmune, and calcium-handling routes all converge here, and conformance should be declared against it.

keratinocyte CL:0000312

cell-cell adhesion GO:0098609 DECREASED

Used by disorders

Carvajal Syndrome as Cardiomyocyte Desmosomal Uncoupling

Naxos disease as Intercalated-disc desmosome failure

Striate Palmoplantar Keratoderma Type 2 as Suprabasal Keratinocyte Adhesion Failure in Mechanical Stress Sites

Downstream

Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues Cells separate from their neighbours under the mechanical load their tissue normally carries.

Acantholysis and Mechanical Failure of Desmosome-Dependent Tissues

effector

Cells detach from one another in whichever desmosome-dependent tissue is affected. In epidermis this is acantholysis - suprabasal separation producing blisters, erosions, or the acantholytic dyskeratosis of Darier disease - and the palmoplantar epidermis, which bears the greatest shear, responds with keratoderma. In the hair shaft it yields a structurally abnormal woolly or fragile hair. In myocardium, myocyte detachment at the intercalated disc permits cell death and fibrofatty replacement, the substrate for arrhythmogenic cardiomyopathy.

keratinocyte CL:0000312 cardiac muscle cell CL:0000746 hair follicle cell CL:0002559

cell-cell adhesion GO:0098609 DECREASED

Used by disorders

Carvajal Syndrome as Keratinocyte Adhesion Failure

Darier Disease as Suprabasal Acantholysis

Hailey-Hailey Disease as Suprabasal Acantholysis Sparing the Adnexal Epithelia

Naxos disease as Cutaneous and hair-follicle desmosome failure

Paraneoplastic Pemphigus as Desmosome Disruption and Keratinocyte Acantholysis

Pemphigus Erythematosus as Desmosomal Autoantibody-Mediated Acantholysis

Pemphigus Vulgaris as Acantholysis and Blister Formation

Downstream

Cutaneous, Appendageal and Cardiac Manifestations Tissue-level adhesion failure produces the organ-level syndrome, whose composition depends on where the affected component is expressed.

Cutaneous, Appendageal and Cardiac Manifestations

consequence

The organ-level endpoint. Cutaneously this ranges from focal or striate palmoplantar keratoderma through generalized acantholytic blistering; the hair may be woolly or fragile; and where the affected component is also expressed in myocardium the syndrome includes cardiomyopathy with ventricular arrhythmia and a risk of sudden death that can substantially precede any cardiac symptom. The cardiac arm is the reason a dermatological diagnosis in this group carries a cardiological obligation.

cell-cell adhesion GO:0098609 DECREASED