Robin A.J. Eady

The classification of inherited epidermolysis bullosa (EB): Report of the Third International Consensus Meeting on Diagnosis and Classification of EB

BACKGROUND Since publication in 2000 of the Second International Consensus Report on Diagnosis and Classification of Epidermolysis Bullosa, many advances have been made to our understanding of this group of diseases, both clinically and molecularly. At the same time, new epidermolysis bullosa (EB) subtypes have been described and similarities with some other diseases have been identified. OBJECTIVE We sought to arrive at a new consensus of the classification of EB subtypes. RESULTS We now present a revised classification system that takes into account the new advances, as well as encompassing other inherited diseases that should also be included within the EB spectrum, based on the presence of blistering and mechanical fragility. Current recommendations are made on the use of specific diagnostic tests, with updates on the findings known to occur within each of the major EB subtypes. Electronic links are also provided to informational and laboratory resources of particular benefit to clinicians and their patients. LIMITATIONS As more becomes known about this disease, future modifications may be needed. The classification system has been designed with sufficient flexibility for these modifications. CONCLUSION This revised classification system should assist clinicians in accurately diagnosing and subclassifying patients with EB.

Revised clinical and laboratory criteria for subtypes of inherited epidermolysis bullosa: A consensus report by the Subcommittee on Diagnosis and Classification of the National Epidermolysis Bullosa Registry

Inherited epidermolysis bullosa encompasses a number of diseases, with the common finding of blister formation after minor mechanical trauma to the skin. In some forms significant, if not eventually fatal, extracutaneous disease activity may occur. In recent years application of newer technologies has contributed substantially to an overall understanding of this collection of inherited diseases. Concurrently, many new phenotypes have been recognized, in part the result of ongoing prospective patient registries in the United States and abroad. Unfortunately, this has resulted in a massive literature that may appear to be confounded by seemingly excessive or arbitrary subdivision of epidermolysis bullosa variants. With these concerns in mind a subcommittee was established by the National Epidermolysis Bullosa Registry to summarize the current literature and to make recommendations as to the best clinical and laboratory criteria for the practical diagnosis and subclassification of patients with inherited epidermolysis bullosa.

Plectin deficiency results in muscular dystrophy with epidermolysis bullosa.

We report that mutation in the gene for plectin, a cytoskeleton–membrane anchorage protein, is a cause of autosomal recessive muscular dystrophy associated with skin blistering (epidermolysis bullosa simplex). The evidence comes from absence of plectin by antibody staining in affected individuals from four families, supportive genetic analysis (localization of the human plectin gene to chromosome 8q24.13–qter and evidence for disease segregation with markers in this region) and finally the identification of a homozygous frameshift mutation detected in plectin cDNA. Absence of the large multifunctional cytoskeleton protein plectin can simultaneously account for structural failure in both muscle and skin.

Mutations in the plakophilin 1 gene result in ectodermal dysplasia/skin fragility syndrome

Members of the armadillo protein gene family, which includes plakoglobin and β-catenin, have important functions in cytoskeleton/cell membrane interactions1,2. These proteins may act as linker molecules at adherens junctions and desmosomes at the plasma membrane3; in addition, they may have pivotal roles in signal transduction pathways and significant effects on cell behaviour during development4–7. Here, we describe the first human mutations in one of these dual function proteins, plakophilin 1 (band-6 protein; refs 8–10). The affected individual has a complete absence of immunostaining for plakophilin 1 in the skin and is a compound heterozygote for autosomal-recessively inherited premature termination codons of translation on both alleles of the plakophilin 1 gene (PKP1). Clinically, there are features of both cutaneous fragility and congenital ectodermal dysplasia affecting skin, hair and nails. There is no evidence of significant abnormalities in other epithelia or tissues. Desmosomes in the skin are small and poorly formed with widening of keratinocyte intercellular spaces and perturbed desmosome/keratin intermediate filament interactions. The molecular findings and clinical observations in this patient attest to the dual importance of plakophilin 1 in both cutaneous cell–cell adhesion and epidermal morphogenesis.

Epidermolysis bullosa complicated by squamous cell carcinoma : report of 10 cases

Epidermolysis bullosa (KB) refers to a group of hereditary mechano‐bullous conditions, many of which arc associated with chronic scarring. Several forms of (he disease have been reported in association with cutaneous malignancy. We present a series of 10 EB patients (eight generalised recessive dystrophic EB, one dominant dystrophic EB, one non‐lethal junctional EB) aged 24–25 years with a total of 29 squamous cell carcinomas (SCC). Three patients died from metastatic disease associated with invasive, poorly differentiated SCC. Six cases had multiple primary SCG, including three patients with simultaneous multifocal disease. Twenty‐eight of the 29 SCC arose on the limbs. I Histology revealed that most of the SCC were well or moderately differentiated (22/29). Unusual histological findings included two verrucous SCC, as well as a spindle cell (angiosarcoma‐like) SCC. Most of the SCC developed in areas of chronic non‐healing ulceration (10/29) or longstanding hyperkeratotic crusting (14/29). The dermis around or beneath the carcinomas was densely scarred, more so than in non‐malignant areas. In some cases it was difficult to distinguish the clinical appearances of certain areas of chronic ulceration, scarring, and crusting typical of dystrophic EB from many of the SCC. This study underlines the need for constant vigilance for the development of carcinomas in this group of patients, the occasional diagnostic difficulty, and the potential for metastasis.

Epidermolysis bullosa pruriginosa: dystrophic epidermolysis bullosa with distinctive clinicopathological features

Summary We report a study of eight unrelated adult patients with a highly distinctive phenotype of dystrophic epidermolysis bullosa. It is characterized clinically by pruritus, lichenified or nodular prurigo‐like lesions, violaceous linear scarring, occasional trauma‐induced blistering, excoriations, milia, Nail dystrophy and, in some cases, albopapuloid lesions on the trunk, The scarring is most evident on the limbs, particularly on the shins, with relative sparing elsewhere. Intact blisters are rarely seen. Physical signs were present at birth in three patients, but in the others skin manifestations were first noticed between 6 months and 10 years of age. Five cases are sporadic, but three of the eight patients have a history of familial involvement, with autosomal dominant inheritance in two cases and recessive transmission in the other case. Studies of the dermal‐epidermal junction showed alterations in the number and ultrastructure of anchoring fibrils in lesional, perilesional and non‐lesional skin, consistent with a diagnosis of dominant or localized recessive dystrophic epidermolysis bullosa. These patients represent an unusual, poorly recognized form or expression of dystrophic epidermolysis bullosa which has features in common with a variety of acquired inflammatory dermatoses.

Lack of plakophilin 1 increases keratinocyte migration and reduces desmosome stability

Ablation of the desmosomal plaque component plakophilin 1 underlies the autosomal recessive genodermatosis, skin fragility-ectodermal dysplasia syndrome (OMIM 604536). Skin from affected patients is thickened with increased scale, and there is loss of adhesion between adjacent keratinocytes, which exhibit few small, poorly formed desmosomes. To investigate further the influence of plakophilin 1 on keratinocyte adhesion and desmosome morphology, we compared plakophilin 1-deficient keratinocytes (vector controls) with those expressing recombinant plakophilin 1 introduced by retroviral transduction. We found that plakophilin 1 increases desmosomal protein content within the cell rather than enhancing transcriptional levels of desmosomal genes. Re-expression of plakophilin 1 in null cells retards cell migration but does not alter keratinocyte cell growth. Confluent sheets of plakophilin 1-deficient keratinocytes display fewer calcium-independent desmosomes than do plakophilin 1-deficient keratinocytes expressing recombinant plakophilin 1 or keratinocytes expressing endogenous plakophilin 1. In addition electron microscopy studies show that re-expression of plakophilin 1 affects desmosome size and number. Collectively, these results demonstrate that restoration of plakophilin 1 function in our culture system influences the transition of desmosomes from a calcium-dependent to a calcium-independent state and this correlates with altered keratinocyte migration in response to wounding. Thus, plakophilin 1 has a key role in increasing desmosomal protein content, in desmosome assembly, and in regulating cell migration.

Abnormal binding of an anti-amnion antibody to epidermal basement membrane provides a novel diagnostic probe for junctional epidermolysis bullosa

AA3 is a novel antibody raised against human amnion, which reacts with the basement membrane of various epithelia of ectodermal origin. We use AA3 to examine the epidermal basement membrane zone in normal skin and different genetically determined types of epidermolysis bullosa (EB), by indirect immunofluorescence. AA3 staining was normal in dystrophic and simplex EB, but was markedly reduced in lesional and non‐blistered skin in severe forms of junctional EB. In non‐lethal junctional EB, the intensity of staining was variable and appeared to be inversely associated with disease severity, but did not correlate with demonstrable abnormalities of hemidesmosomes. AA3 binding was not reduced in pemphigoid lesions or normal suction blisters. It appeared to localize to the lamina lucida, but with different characteristics compared with antibodies to laminin and bullous pemphigoid antigen. These findings suggest that AA3 recognizes an antigen (or antigens) which may be involved in a primary biochemical defect in junctional EB. Moreover, this antibody may act as a new probe for this potentially lethal mechano‐bullous disease.

Desmosomal proteins, including desmoglein 3, serve as novel negative markers for epidermal stem cell-containing population of keratinocytes

No single method has been universally adopted for identifying and isolating epidermal stem/progenitor cells, and the emergence of new markers of stem cell populations is worth exploring. Here we report, for the first time, that clusters of basal keratinocytes at the tips of the rete ridges in human palm, previously recognised as a major repository of stem cells, had very low levels of desmoplakin protein and mRNA expression, compared with cells at the sides of the ridges or above the dermal papillae. We found that in populations of palm keratinocytes, selected by their ability to adhere rapidly to type IV collagen, there were significantly reduced levels of desmoplakin and other major desmosome proteins. We then showed that a low desmoglein 3 (Dsg3) expression on the cell surface could be used to enrich for a cell population with high clonogenecity, colony forming efficiency and enhanced proliferative potential, but with a low ability to form the abortive clones, compared with populations with a higher Dsg3 expression. Moreover, stringent sorting of populations showing both β1 integrin-bright and Dsg3-dull expression enabled even further enrichment of a population containing the putative epidermal stem cells. These findings provide the basis for a new strategy for epidermal stem/progenitor cell enrichment, and encourage further study of the role of desmosomes in stem cell biology.

Immunoelectron microscopic analysis of cornified cell envelope formation in normal and psoriatic epidermis

The cornified cell envelope (CE) is an insoluble, highly resistant structure formed beneath the plasma membrane of differentiating keratinocytes. It consists of various crosslinked precursor proteins, including involucrin and loricrin. However, neither the normal assembly process of CE nor its alteration in skin disorders has been fully characterized. In this study we analyzed CE formation in normal skin and in lesional psoriatic skin by immunoelectron microscopy. In the superficial granular cells of normal epidermis, involucrin labeling was detected along the plasma membrane, whereas loricrin staining was mostly distributed diffusely within the cells, occasionally with some additional granular aggregates within the cytoplasm and nucleus. Loricrin was also present predominantly on the desmosomal attachment plaques, colocalizing with desmoglein. In the cornified cells, involucrin labeling was reduced, whereas loricrin labeling was retained and continuously decorated the CEs, with relative sparing of the desmosomal areas. In typical psoriatic epidermis, involucrin staining was very intense but loricrin labeling was markedly reduced. The involucrin-positive CEs were formed precociously and further maturation of CE did not occur. These results suggest that formation of CE occurs sequentially, initially involving involucrin deposition and subsequently involving loricrin incorporation. Psoriatic epidermis demonstrates a lack of proper CE maturation.