Epidermolysis bullosa: a spectrum of clinical phenotypes explained by molecular heterogeneity

Synergy between Laminin-Derived Elastin-like Polypeptides (LELPs) Optimizes Cell Spreading

A major component of the extracellular matrix (ECM), laminins, modulates cells via diverse receptors. Their fragments have emerging utility as components of "ECM-mimetics" optimized to promote cell-based therapies. Recently, we reported that a bioactive laminin peptide known as A99 enhanced cell binding and spreading via fusion to an elastin-like polypeptide (ELP). The ELP "handle" serves as a rapid, noncovalent strategy to concentrate bioactive peptide mixtures onto a surface. We now report that this strategy can be further generalized across an expanded panel of additional laminin-derived elastin-like polypeptides (LELPs). A99 (AGTFALRGDNPQG), A2G80 (VQLRNGFPYFSY), AG73 (RKRLQVQLSIRT), and EF1m (LQLQEGRLHFMFD) all promote cell spreading while showing morphologically distinct F-actin formation. Equimolar mixtures of A99:A2G80-LELPs have synergistic effects on adhesion and spreading. Finally, three of these ECM-mimetics promote the neurite outgrowth of PC-12 cells. The evidence presented here demonstrates the potential of ELPs to deposit ECM-mimetics with applications in regenerative medicine, cell therapy, and tissue engineering.

A type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), suppresses skin injury induced by sulfur mustard

Sulfur mustard (SM) is a highly toxic blistering agent thought to mediate its action, in part, by activating matrix metalloproteinases (MMPs) in the skin and disrupting components of the basement membrane zone (BMZ). Type IV collagenases (MMP-9) degrade type IV collagen in the skin, a major component of the BMZ at the dermal-epidermal junction. In the present studies, a type IV collagenase inhibitor, N-hydroxy-3-phenyl-2-(4-phenylbenzenesulfonamido) propanamide (BiPS), was tested for its ability to protect the skin against injury induced by SM in the mouse ear vesicant model. SM induced inflammation, epidermal hyperplasia and microblistering at the dermal/epidermal junction of mouse ears 24-168 h post-exposure. This was associated with upregulation of MMP-9 mRNA and protein in the skin. Dual immunofluorescence labeling showed increases in MMP-9 in the epidermis and in the adjacent dermal matrix of the SM injured skin, as well as breakdown of type IV collagen in the basement membrane. Pretreatment of the skin with BiPS reduced signs of SM-induced cutaneous toxicity; expression of MMP-9 mRNA and protein was also downregulated in the skin by BiPS. Following BiPS pretreatment, type IV collagen appeared intact and was similar to control skin. These results demonstrate that inhibiting type IV collagenases in the skin improves basement membrane integrity after exposure to SM. BiPS may hold promise as a potential protective agent to mitigate SM induced skin injury.

Expression of Laminin γ2 Proteolytic Fragments in Murine Skin Following Exposure to Sulfur Mustard

Laminin-332 is a basement membrane protein composed of three genetically distinct polypeptide chains that actively promote both skin epidermal cell adhesion and migration. Proteolytic fragments of the laminin γ2 chain stimulate migration and scattering of keratinocytes and cancer cells. Sulfur mustard (SM) is a bifunctional alkylating agent that induces separation of basal keratinocytes from the dermal-epidermal junction and invokes a strong inflammatory response leading to delayed wound repair. In the present studies, the role of laminin γ2 in SM-induced skin injury and wound repair was investigated using the mouse ear vesicant model. We found that laminin γ2 chain mRNA was preferentially upregulated in mouse ear skin exposed to SM. In situ hybridization confirmed overexpression of laminin γ2 transcript. Western blot analysis showed increased protein expression of the full-length proform of laminin γ2 and smaller processed fragments of laminin γ2 in skin exposed to SM. Dual immunofluorescence labeling indicated that laminin γ2 fragments are prevalent in suprabasal keratinocytes behind the leading edge in areas of hyperplasia in injured skin. In addition, co-expression of laminin γ2 and the senescent marker, p16^-INK4a was found to overlap with the hyperplastic migratory epithelial sheet. This observation is similar to hypermotile keratinocytes reported in invasive carcinoma cells. Overall, our studies indicate that laminin γ2 is preferentially expressed in skin post SM exposure and that protein expression appears to become progressively more fragmented. The laminin γ2 fragments may play a role in regulating SM-induced skin wound repair. Anat Rec, 2020. © 2020 American Association for Anatomy.

Long-term outcome after superficial keratectomy in an infant with epidermolysis bullosa

A 5-month-old boy presented with a congenital whitish raised lesion in the central cornea of the left eye. The child had a tendency to develop bullous eruptions on the skin with trivial trauma. The patient's father had a similar history of skin lesions. Because the lesion was in the central visual axis, a superficial anterior keratectomy with an amniotic membrane grafting was performed. The lesion healed well, restoring the corneal transparency and resulting in good visual acuity. When the boy was 4 years of age, his cornea was clear, and best-corrected visual acuity in the left eye was 20/60. There was no recurrence of the lesion.

Combining GWAS and RNA-Seq Approaches for Detection of the Causal Mutation for Hereditary Junctional Epidermolysis Bullosa in Sheep

In this study, we demonstrate the use of a genome-wide association mapping together with RNA-seq in a reduced number of samples, as an efficient approach to detect the causal mutation for a Mendelian disease. Junctional epidermolysis bullosa is a recessive genodermatosis that manifests with neonatal mechanical fragility of the skin, blistering confined to the lamina lucida of the basement membrane and severe alteration of the hemidesmosomal junctions. In Spanish Churra sheep, junctional epidermolysis bullosa (JEB) has been detected in two commercial flocks. The JEB locus was mapped to Ovis aries chromosome 11 by GWAS and subsequently fine-mapped to an 868-kb homozygous segment using the identical-by-descent method. The ITGB4, which is located within this region, was identified as the best positional and functional candidate gene. The RNA-seq variant analysis enabled us to discover a 4-bp deletion within exon 33 of the ITGB4 gene (c.4412_4415del). The c.4412_4415del mutation causes a frameshift resulting in a premature stop codon at position 1472 of the integrin β4 protein. A functional analysis of this deletion revealed decreased levels of mRNA in JEB skin samples and the absence of integrin β4 labeling in immunohistochemical assays. Genotyping of c.4412_4415del showed perfect concordance with the recessive mode of the disease phenotype. Selection against this causal mutation will now be used to solve the problem of JEB in flocks of Churra sheep. Furthermore, the identification of the ITGB4 mutation means that affected sheep can be used as a large mammal animal model for the human form of epidermolysis bullosa with aplasia cutis. Our approach evidences that RNA-seq offers cost-effective alternative to identify variants in the species in which high resolution exome-sequencing is not straightforward.

From marrow to matrix: novel gene and cell therapies for epidermolysis bullosa

Epidermolysis bullosa encompasses a group of inherited connective tissue disorders that range from mild to lethal. There is no cure, and current treatment is limited to palliative care that is largely ineffective in treating the systemic, life-threatening pathology associated with the most severe forms of the disease. Although allogeneic cell- and protein-based therapies have shown promise, both novel and combinatorial approaches will undoubtedly be required to totally alleviate the disorder. Progress in the development of next-generation therapies that synergize targeted gene-correction and induced pluripotent stem cell technologies offers exciting prospects for personalized, off-the-shelf treatment options that could avoid many of the limitations associated with current allogeneic cell-based therapies. Although no single therapeutic avenue has achieved complete success, each has substantially increased our collective understanding of the complex biology underlying the disease, both providing mechanistic insights and uncovering new hurdles that must be overcome.

Advances in understanding and treating dystrophic epidermolysis bullosa

Epidermolysis bullosa is a group of inherited disorders that can be both systemic and life-threatening. Standard treatments for the most severe forms of this disorder, typically limited to palliative care, are ineffective in reducing the morbidity and mortality due to complications of the disease. Emerging therapies—such as the use of allogeneic cellular therapy, gene therapy, and protein therapy—have all shown promise, but it is likely that several approaches will need to be combined to realize a cure. For recessive dystrophic epidermolysis bullosa, each particular therapeutic approach has added to our understanding of type VII collagen (C7) function and the basic biology surrounding the disease. The efficacy of these therapies and the mechanisms by which they function also give us insight into developing future strategies for treating this and other extracellular matrix disorders.

Molecular identification of collagen 17a1 as a major genetic modifier of laminin gamma 2 mutation-induced junctional epidermolysis bullosa in mice

Epidermolysis Bullosa (EB) encompasses a spectrum of mechanobullous disorders caused by rare mutations that result in structural weakening of the skin and mucous membranes. While gene mutated and types of mutations present are broadly predictive of the range of disease to be expected, a remarkable amount of phenotypic variability remains unaccounted for in all but the most deleterious cases. This unexplained variance raises the possibility of genetic modifier effects. We tested this hypothesis using a mouse model that recapitulates a non-Herlitz form of junctional EB (JEB) owing to the hypomorphic jeb allele of laminin gamma 2 (Lamc2). By varying normally asymptomatic background genetics, we document the potent impact of genetic modifiers on the strength of dermal-epidermal adhesion and on the clinical severity of JEB in the context of the Lamc2(jeb) mutation. Through an unbiased genetic approach involving a combination of QTL mapping and positional cloning, we demonstrate that Col17a1 is a strong genetic modifier of the non-Herlitz JEB that develops in Lamc2(jeb) mice. This modifier is defined by variations in 1-3 neighboring amino acids in the non-collagenous 4 domain of the collagen XVII protein. These allelic variants alter the strength of dermal-epidermal adhesion in the context of the Lamc2(jeb) mutation and, consequentially, broadly impact the clinical severity of JEB. Overall the results provide an explanation for how normally innocuous allelic variants can act epistatically with a disease causing mutation to impact the severity of a rare, heritable mechanobullous disorder.

The expanding significance of keratin intermediate filaments in normal and diseased epithelia

Intermediate filaments are assembled from a diverse group of evolutionary conserved proteins and are specified in a tissue-dependent, cell type-dependent, and context-dependent fashion in the body. Genetic mutations in intermediate filament proteins account for a large number of diseases, ranging from skin fragility conditions to cardiomyopathies and premature aging. Keratins, the epithelial-specific intermediate filaments, are now recognized as multi-faceted effectors in their native context. In this review, we emphasize the recent progress made in defining the role of keratins towards the regulation of cytoarchitecture, cell growth and proliferation, apoptosis, and cell motility during embryonic development, in normal adult tissues, and in select diseases such as cancer.

Fibroblast-based cell therapy strategy for recessive dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is a severe skin fragility disorder associated with trauma-induced blistering, progressive soft tissue scarring, and increased risk of skin cancer. DEB is caused by mutations in the COL7A1 gene which result in reduced, truncated, or absent type VII collagen, and anchoring fibrils at the dermal-epidermal junction (DEJ). Because no topical wound-healing agents have shown unequivocal benefit in the treatment of DEB, alternative approaches are needed. The purpose of cell therapy for recessive DEB is to increase the amount of collagen VII in the basement membrane zone in order to heal wounds and prevent further wound formation. Fibroblast-based cell therapy is safe and easy to work with, has few side effects, can dramatically restore stable collagen VII at the DEJ, and can normalize the substructure changes of DEB for at least a few months. Even though the mechanism and the duration of newly produced collagen VII at the DEJ are still unknown, this form of cell therapy provides a new effective approach to the treatment of recessive DEB.

The laminin binding integrin alpha6beta1 in prostate cancer perineural invasion

Metastasizing prostate tumor cells invade along nerves innervating the encapsulated human prostate gland in a process known as perineural invasion. The extracellular matrix laminin class of proteins line the neural route and tumor cells escaping from the gland express the laminin binding integrin alpha6beta1 as a prominent cell surface receptor. Integrin alpha6beta1 promotes aggressive disease and supports prostate tumor cell metastasis to bone. Laminins and their integrin receptors are necessary for the development and maintenance of the peripheral nervous system, indicating the potential role for integrin receptors in directing prostate tumor cell invasion on nerves during perineural invasion.

A mouse model of generalized non-Herlitz junctional epidermolysis bullosa

Epidermolysis bullosa (EB) is a class of intractable, rare, genetic disorders characterized by fragile skin and blister formation as a result of dermal-epidermal mechanical instability. EB presents with considerable clinical and molecular heterogeneity. Viable animal models of junctional EB (JEB), that both mimic the human disease and survive beyond the neonatal period, are needed. We identified a spontaneous, autosomal recessive mutation (Lamc2(jeb)) due to a murine leukemia virus long terminal repeat insertion in Lamc2 (laminin gamma2 gene) that results in a hypomorphic allele with reduced levels of LAMC2 protein. These mutant mice develop a progressive blistering disease validated at the gross and microscopic levels to closely resemble generalized non-Herlitz JEB. The Lamc2(jeb) mice display additional extracutaneous features such as loss of bone mineralization and abnormal teeth, as well as a respiratory phenotype that is recognized but not as well characterized in humans. This model faithfully recapitulates human JEB and provides an important preclinical tool to test therapeutic approaches.

Skin pathology induced by snake venom metalloproteinase: acute damage, revascularization, and re-epithelization in a mouse ear model

Viperid snakebite envenomation induces blistering and dermonecrosis. The pathological alterations induced by a snake venom metalloproteinase in the skin were investigated in a mouse ear model. Metalloproteinase BaP1, from Bothrops asper, induced rapid edema, hemorrhage, and blistering; the latter two effects were abrogated by preincubation with the metalloproteinase inhibitor batimastat. Neutrophils did not play a role in the pathology, as depletion of these cells resulted in a similar histological picture. Blisters are likely to result from the direct proteolytic activity of BaP1 of proteins at the dermal-epidermal junction, probably at the lamina lucida, as revealed by immunostaining for type IV collagen and laminin. Widespread apoptosis of keratinocytes was detected by the TUNEL assay, whereas no apoptosis of capillary endothelial cells was observed. BaP1 induced a drastic reduction in the microvessel density, revealed by immunostaining for the endothelial marker vascular endothelial growth factor receptor-2. This was followed by a rapid angiogenic response, leading to a partial revascularization. Skin damage was followed by inflammation and granulation tissue formation. Then, a successful re-epithelization process occurred, and the skin of the ear regained its normal structure by 2 weeks. Venom metalloproteinase-induced skin damage reproduces the pathological changes described in snakebitten patients.

Pathophysiology of acute wound healing

Wound healing is a complex process that can be divided into at least 3 continuous and overlapping processes: an inflammatory reaction, a proliferative process leading to tissue restoration, and, eventually, tissue remodeling. Wound healing processes are strictly regulated by multiple growth factors and cytokines released at the wound site. Although the desirable final result of coordinated healing would be the formation of tissue with a similar structure and comparable functions as with intact skin, regeneration is uncommon (with notable exceptions such as early fetal healing); healing however results in a structurally and functionally satisfactory but not identical outcome. Alterations that disrupt controlled healing processes would extend tissue damage and repair. The pathobiologic states may lead to chronic or nonhealing wounds or excessive fibrosis.

Overexpression of laminin-8 in human dermal microvascular endothelial cells promotes angiogenesis-related functions

This study examined the effects of endogenous overexpression of laminin-8 on angiogenesis and wound healing in primary human dermal microvascular endothelial cells (HDMECs). HDMECs expressed laminin-8 and laminin-10, but no other laminins, as determined by radioimmunoprecipitation assay using a panel of antibodies to individual laminin chains. To study laminin-8 function, full-length human laminin alpha4 cDNA was retrovirally transferred to HDMEC, and specific overexpression of laminin-8 was verified by Western blot. Laminin-8 overexpression promoted endothelial cell spreading and migration in scratch assays and accelerated angiogenic tubule formation in collagen gel overlay assays. Strong inhibitory effect of beta1 integrin and weak inhibition by alphavbeta3 integrin antibodies were observed in laminin-8-stimulated cell migration, but only beta1 integrin antibodies affected tubule formation. These studies suggest that laminin-8 overexpression may prove to be a useful method to engineer HDMECs to promote angiogenesis and wound repair.

[Junctional epidermolysis bullosa. Identification of a new mutation in two Lebanese families]

BACKGROUND

Junctional epidermolysis bullosa (JEB) represents a genetically heterozygous group of bullous disorders characterized by dermo-epidermal separation resulting from mutations affecting the main dermo-epidermal adhesion factor, laminin-5, its cellular receptor, integrin alpha6B4, or collagen XVII. We report the identification of a new mutation of LAMA3, encoding laminin-5 alpha3 subunit in two unrelated Lebanese families.

PATIENTS AND METHODS

Two female newborn, descending from 1st degree consanguineous marriages, presented a lethal form of EBJ-Herlitz. Histologic, ultrastructural and immunofluorescence studies were performed in order to ascertain the diagnosis and to direct genetic analysis. Mutation search was conducted through direct DNA sequencing of patients and ascendants.

RESULTS

Immunohistology of frozen skin samples revealed an extremely reduced immunoreactivity for the alpha3 laminin-5 subunit. The two patients were homozygous carriers (parents heterozygous) of a new missense mutation of LAMA3 gene (exon 32: 4300 insA) encoding the alpha3 subunit of laminin-5. Resulting messenger RNA, rapidly degraded, induced an extremely reduced synthesis of alpha3-polypeptide, truncated in its Cterminal domain.

DISCUSSION

LAMB3 gene recurrent mutations R636X and R42X account for about 50p. 100 of EBJ cases affecting Caucasians while mutation Q1083X, affecting the same gene, is recurrent in Arab populations. The newly identified mutation results in extremely reduced synthesis of alpha3 chain and truncation of its C-terminal domain, which is crucial for the intermolecular interactions of laminin-5. Our data are in accordance with recent reports suggesting geographical specificity of EBJ mutations linked to founder effects which are amplified by consanguineous marriages in genetically isolated populations. Otherwise, the observation of other unexplored cases of bullous dermatoses with early demise originating from the same region of the two families herein reported highlights the need for the implementation of a prenatal and postnatal diagnostic strategy regarding these genodermatoses. These studies should target LAMA3 and other genes involved in JEB too.

Plectin gene mutations can cause epidermolysis bullosa with pyloric atresia

Epidermolysis bullosa with pyloric atresia (EB-PA), manifesting with neonatal blistering and gastric anomalies, is known to be caused by mutations in the hemidesmosomal genes ITGA6 and ITGB4, which encode the alpha6 and beta4 integrin polypeptides, respectively. As part of our molecular diagnostics program, we have now encountered four families with EB-PA in which no mutations could be identified in these two genes. Instead, PCR amplification followed by heteroduplex scanning and/or direct nucleotide sequencing revealed homozygous mutations in the plectin gene (PLEC1), encoding another hemidesmosomal protein previously linked to EB with muscular dystrophy. Our findings provide evidence for additional molecular heterogeneity in EB, and emphasize the importance of screening EB-PA patients not only for alpha6beta4 integrin but also for plectin deficiency.

Dilemmas in distinguishing between dominant and recessive forms of dystrophic epidermolysis bullosa

BACKGROUND

Dystrophic epidermolysis bullosa (DEB) is a heterogeneous inherited blistering skin disorder. The mode of inheritance may be autosomal dominant or recessive but all forms of DEB result from mutations in the gene encoding the anchoring fibril protein, type VII collagen, COL7A1. Consequently, in spite of careful clinical and skin biopsy examination, it may be difficult to distinguish mild recessive cases from de novo dominant disease in families with clinically normal parents and no other affected siblings; this distinction has significant implications for the accuracy of genetic counselling.

OBJECTIVES

To assess whether COL7A1 mutation analysis might help determine mode of inheritance in mild to moderate DEB.

METHODS

We performed COL7A1 screening using heteroduplex analysis and direct nucleotide sequencing in four individuals with mild to moderate "sporadic" DEB and clinically unaffected parents.

RESULTS

In each patient, we identified a heterozygous glycine substitution within the type VII collagen triple helix. However, in two cases these mutations had been inherited in trans with a non-sense mutation on the other allele (i.e. autosomal recessive DEB). In the other two cases, no additional mutation was identified and neither mutation was present in parental DNA (i.e. de novo dominant disease).

CONCLUSIONS

This study highlights the usefulness of DNA sequencing in determining the inherited basis of some sporadic cases of DEB. However, delineation of glycine substitutions should prompt comprehensive COL7A1 gene sequencing in the affected individual, as well as clinical assessment of parents and mutation screening in parental DNA, if the true mode of inheritance is to be established correctly.

Probing the fetal genome: progress in non-invasive prenatal diagnosis

Progress in our understanding of the molecular basis of heritable diseases, through identification of specific mutations, has provided a foundation for the development of DNA-based prenatal diagnosis. Genetic analysis of fetal DNA is now routinely performed from chorionic villus samples obtained as early as the tenth week of gestation or by amniocentesis from week 15 onwards. However, both of these approaches involve invasive procedures with increased risk of fetal loss. To avoid such complications, attempts have been made to develop non-invasive tests through the identification, characterization and isolation of fetal cells or free fetal DNA from the maternal circulation. Recently, progress has been made towards the development of novel strategies that are expected to provide non-invasive means for early prenatal diagnosis in pregnancy.

Epidermolysis bullosa: new and emerging trends

Epidermolysis bullosa is a family of inherited blistering skin disorders characterized by blister formation in response to mechanical trauma. Major types of epidermolysis bullosa include epidermolysis bullosa simplex, hemidesmosomal epidermolysis bullosa, junctional epidermolysis bullosa, and dystrophic epidermolysis bullosa. Current treatment for epidermolysis bullosa consists of supportive care for skin and other organ systems and entails a combination of wound management, infection support for chronic wounds, surgical management as needed, nutritional support, and preventative screening for squamous cell carcinoma in recessive dystrophic epidermolysis bullosa. The regimen must be tailored specifically to the severity and extent of skin and systemic involvement in each case. Recent studies have identified specific protein and genetic abnormalities for most epidermolysis bullosa subtypes. These new advancements in the understanding of molecular pathophysiology have provided much of the basis for current efforts to develop effective gene and protein therapy for epidermolysis bullosa.

Junctional epidermolysis bullosa in the Middle East: clinical and genetic studies in a series of consanguineous families

BACKGROUND

Junctional epidermolysis bullosa (JEB) is a group of inherited blistering diseases characterized by epidermal-dermal separation resulting from mutations that affect the function of critical components of the basement membrane zone. This group of autosomal recessive diseases is especially prevalent in regions where consanguinity is common, such as the Middle East. However, the clinical and genetic epidemiology of JEB in this region remains largely unexplored.

OBJECTIVE

The aim of the present study was to assess a series of consanguineous JEB families originating from the Middle East.

METHODS

We identified 7 families referred to us between 1998 and 1999 and originating from the United Arab Emirates, Saudi Arabia, Sudan, Yemen, and Israel. Histologic, immunofluorescence, and electron microscopy studies were performed to direct the subsequent molecular analysis. DNA obtained from all family members was amplified by means of polymerase chain reaction and analyzed by conformation-sensitive gel electrophoresis with subsequent direct sequencing.

RESULTS

In 6 families presenting with the clinical and histologic features distinctive for JEB, mutations in genes encoding 1 of the 3 subunit polypeptides of laminin-5 were identified. Two families each had mutations in LAMB3, 2 in LAMA3, and 2 in LAMC2. Out of 7 distinct mutations, 5 were novel and 2 were recurrent. No relationship was found between the presence of nonsense/frameshift mutations in laminin-5 genes and perinatal mortality, contradicting a major genotype-phenotype correlation previously reported in the European and US literature. Similarly, none of the recurrent LAMB3 hot spot mutations previously described in other populations was found in our series. Finally, in a family with the clinical diagnosis of generalized atrophic benign epidermolysis bullosa, a homozygous non-sense mutation in Col17A1 gene (encoding the BPAG2 antigen) was identified.

CONCLUSION

The present report suggests (1) the existence of a unique spectrum of mutations in the Middle East populations and (2) the need for the implementation of a diagnostic strategy tailored to the genetic features of JEB in this region.

Disease model: heritable skin blistering

Hereditary skin blistering disorders comprise a group of genodermatoses whose common primary feature is the formation of blisters following minor trauma. Examples of such conditions include epidermolysis bullosa and several bullous forms of ichthyosis. Distinct mutations in various genes encoding intra- and extra-cellular structural components of the skin reflect the clinical heterogeneity of these disorders. Several animal models are currently used to study the role of these molecules in the disease process. Some of these models will find their place in evaluating new therapeutic strategies for this devastating group of diseases.

In vivo restoration of laminin 5 beta 3 expression and function in junctional epidermolysis bullosa

The blistering disorder, lethal junctional epidermolysis bullosa (JEB), can result from mutations in the LAMB3 gene, which encodes laminin 5 beta3 (beta3). Appropriate expression of LAMbeta3 in JEB skin tissue could potentially ameliorate the symptoms of the underlying disease. To explore the utility of this therapeutic approach, primary keratinocytes from six unrelated JEB patients were transduced with a retroviral vector encoding beta3 and used to regenerate human skin on severe combined immunodeficient (SCID) mice. Tissue regenerated from beta3-transduced JEB keratinocytes produced phenotypically normal skin characterized by sustained beta3 expression and the formation of hemidesmosomes. Additionally, beta3 gene transfer corrected the distribution of a number of important basement membrane zone proteins including BPAG2, integrins beta4/beta1, and laminins alpha3/gamma2. Skin produced from beta3-negative (beta3[-]) JEB cells mimicked the hallmarks of the disease state and did not exhibit any of the aforementioned traits. Therefore, by effecting therapeutic gene transfer to beta3-deficient primary keratinocytes, it is possible to produce healthy, normal skin tissue in vivo. These data support the utility of gene therapy for JEB and highlight the potential for gene delivery in the treatment of human genetic skin disease.

Recent advances in the molecular basis of inherited skin diseases

Over the last few years the molecular basis of several inherited skin diseases has been delineated. Some discoveries have stemmed from a candidate gene approach using clinical, biochemical, immunohistochemical, and ultrastructural clues, while others have arisen from genetic linkage and positional cloning analyses. Notable advances have included elucidation of specific gene pathology in the major forms of inherited skin fragility, ichthyosis, and keratoderma. These findings have led to a better understanding of the significance of individual structural proteins and regulatory enzymes in keratinocyte adhesion and differentiation. From a clinical perspective, the advances have led to better genetic counseling in many disorders, the development of DNA-based prenatal diagnosis, and a foundation for planning newer forms of treatment, including somatic gene therapy, in selected conditions.

Investigation into the mechanism of the loss of laminin 5 (alpha3beta3gamma2) expression in prostate cancer

Laminin 5 is a pivotal hemidesmosomal protein involved in cell stability, migration, and anchoring filament formation. Protein and gene expression of the alpha3, beta3, and gamma2 chains of laminin 5 were investigated in normal and invasive prostate carcinoma using immunohistochemistry, Northern analysis, and in situ hybridization. Laser capture microdissection of normal and carcinomatous glands, in conjunction with RNA amplification and reverse Northern analysis, were used to confirm the gene expression data. Protein and mRNA expression of all three laminin 5 chains were detected in the basal cells of normal glands. In contrast, invasive prostate carcinoma showed a loss of beta3 and gamma2 protein expression with variable expression of alpha3 chains. Despite the loss of protein expression, there was retention of beta3 and gamma2 mRNA expression as detected by in situ hybridization, Northern and reverse Northern analysis. Our findings imply that an altered mechanism of translation of beta3 or gamma2 mRNAs into functional proteins contributes to failure of anchoring filaments and hemidesmosomal formation. The resultant hemidesmosome instability or loss would suggest a less stable epithelial-stromal junction, increased invasion and migration of malignant cells, and disruption of normal integrin signaling pathways.

The genodermatoses: candidate diseases for gene therapy

Tremendous progress has been made in understanding the genetic basis of different forms of genodermatoses, a group of heritable diseases displaying a spectrum of phenotypic manifestations and clinical severity. The information about the underlying mutations in the candidate gene/protein systems has provided the basis for initial development of cutaneous gene therapy, and these heritable conditions appear to serve as appropriate candidate diseases for such efforts. Because of its accessibility and the fact that resident skin cells, such as epidermal keratinocytes and dermal fibroblasts, can be readily propagated in culture, skin serves as an appropriate target tissue for gene therapy. Various strategic considerations, including the use of in vivo or ex vivo approaches, gene replacement versus gene repair, utilization of different delivery systems, etc., require careful prioritization depending on the type of mutations and their pathogenetic consequences at the mRNA and protein levels.

Epidermolysis bullosa, pyloric atresia, and obstructive uropathy: a report of two case reports with molecular correlation and clinical management

The epidermolysis bullosa-pyloric atresia-obstructive uropathy (EB-PA-OU) association is a rare, but well-described multisystem disease. While the prognosis at this time is still poor, an increasing number of patients are surviving to adolescence with aggressive care. It is important to understand this syndrome in order to anticipate medical complications and offer preventive strategies where possible. Prompt and expectant management of obstructive uropathy is crucial in these patients. Evidence of ureterovesicular obstruction may require bowel diversion, as excision of the obstructed ureterovesicular junction with reimplantation is often associated with a high risk of reobstruction. Many newborns succumb to sepsis or dehydration and electrolyte imbalance. Those infants who survive need close monitoring for the development of obstructive uropathy, failure to thrive, protein-losing enteropathy, respiratory compromise, and increased susceptibility to invasive infections. Once a clinical diagnosis is made, mutational analysis can confirm it and facilitate genetic counseling, as recurrence risks are 25% for this autosomal recessive condition. Mutational analysis enables direct genetic testing and accurate prenatal diagnosis. As more patients are studied, genotype/phenotype correlations may be possible.

Epidermolysis bullosa: novel and de novo premature termination codon and deletion mutations in the plectin gene predict late-onset muscular dystrophy

Epidermolysis bullosa (EB) with late-onset muscular dystrophy (EB-MD) is a hemidesmosomal variant of EB due to mutations in the plectin gene (PLEC1). The age of onset of muscle involvement has been noted to vary from infancy to the fourth decade of life. Immunofluorescence of the patients' skin and muscle biopsies is usually negative for staining with antibodies recognizing plectin, a large cytoskeleton-associated anchorage protein. In this study we report novel plectin mutations in two families with EB. In both families, the proband was a newborn with neonatal blistering with no evidence for muscle weakness as yet. Peripheral blood DNA was isolated and examined by heteroduplex scanning strategy, protein truncation test (PTT), and/or direct sequencing of the plectin gene. One of the probands was compound heterozygote for nonsense mutations E2005X/K4460X, and the proband in the second family was compound heterozygote for deletion mutations 5083delG/2745-9del21, the latter mutation extending from -9 to +12 at the intron 22/exon 23 border. The mutations K4460X and 5083delG were not present in either one of the parents, thus being de novo events. In both cases, nonpaternity was excluded by microsatellite marker analysis. The stop codon mutations are predicted to result in the synthesis of a truncated protein lacking the carboxy-terminal globular domain of the protein and possibly causing nonsense-mediated decay of the corresponding mRNA. The 2745-9del21 deletion mutation abolishes the splice site at the intron 22/exon 23 junction, predicting abnormal splicing events. Because plectin deficiency is associated with muscular dystrophy, molecular diagnostics of the plectin gene provides prognostic value in evaluation of these patients who appear to be at risk to develop muscular dystrophy.

A novel mutation in the helix termination motif of keratin K12 in a US family with Meesmann corneal dystrophy

PURPOSE

Meesmann corneal dystrophy is an autosomal dominant disorder characterized by fragility of the anterior corneal epithelium. We have previously demonstrated that this disease can be caused by mutations in the genes encoding keratins K3 or K12, the major intermediate filament proteins expressed in corneal epithelial cells. Here, we have carried out mutation analysis in a United States kindred presenting with typical features of Meesmann corneal dystrophy.

METHODS

Exons 1 and 6 of the K12 gene (KRT12) were polymerase chain reaction amplified from the proband's and control DNA and subjected to direct automated sequencing.

RESULTS

A heterozygous missense mutation 1300A-->G was detected in exon 6 of KRT12, predicting amino acid substitution 1426V in the helix termination motif of the K12 polypeptide. The mutation was confirmed in the proband and excluded from 50 normal individuals by restriction enzyme analysis of polymerase chain reaction products.

CONCLUSION

We report a novel mutation in a critical molecular overlap region of K12 in a United States family with Meesmann corneal dystrophy. The results confirm that mutations in the corneal keratins (K3 or K12) can underlie Meesmann corneal dystrophy.

Reduced anchoring fibril formation and collagen VII immunoreactivity in feline dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa was diagnosed in a cat with juvenile-onset epithelial sloughing of the oral mucosa, footpads, and haired skin. Dermoepidermal separation occurred in the absence of inflammation or cytolysis of basal epidermal cells. Collagen IV-specific immunostaining corroborated the fact that clefting took place below the epidermal basement membrane. Ultrastructural examination revealed that the proband's anchoring fibrils exhibited a filamentous morphology and were decreased in number compared with those in a normal cat. Finally, the attenuated immunoreactivity for collagen VII in our patient led us to suspect that its encoding gene, COL7A1, could be mutated in this case of feline dystrophic epidermolysis bullosa.

Targeted inactivation of the type VII collagen gene (Col7a1) in mice results in severe blistering phenotype: a model for recessive dystrophic epidermolysis bullosa

Dystrophic forms of epidermolysis bullosa (DEB) are associated with mutations in the type VII collagen gene (Col7a1) which encodes the major component of anchoring fibrils. To develop a DEB animal model, type VII collagen deficient mice were generated by targeted homologous recombination. The targeting vector replaced exons 46–69 of Col7a1 with the neomycin-resistance gene, in reverse transcriptional orientation, resulting in elimination of most of the collagenous domain 1. Col7a1 heterozygous (+/-) mice were phenotypically normal. Mating of Col7a1 +/- mice revealed that Col7a1 null (-/-) mice, which were born with extensive cutaneous blistering, died during the first two weeks of life probably due to complications arising from the blistering. Transmission electron microscopy revealed subepidermal blistering below the lamina densa and absence of anchoring fibrils. Immunohistochemical staining with anti-human type VII collagen antibody stained the dermal-epidermal junction in control mice, but did not stain the skin of Col7a1 null mice. Collectively, the DEB mice recapitulate the clinical, genetic, immunohistochemical and ultrastructural characteristics of recessive DEB in humans. These mice provide an animal model to study the pathomechanisms of DEB and serve as a system to test therapeutic approaches, including gene replacement, towards the cure of this devastating skin disease.

Moderation of phenotypic severity in dystrophic and junctional forms of epidermolysis bullosa through in-frame skipping of exons containing non-sense or frameshift mutations

Non-sense mutations on both alleles of either the type VII collagen gene (COL7A1) or the genes encoding laminin 5 (LAMA3, LAMB3, or LAMC2) usually result in clinically severe forms of recessive dystrophic or junctional epidermolysis bullosa, respectively. In this study we assessed two unrelated families whose mutations in genomic DNA predicted severe recessive dystrophic epidermolysis bullosa or junctional epidermolysis bullosa phenotypes but in whom the manifestations were milder than expected. The recessive dystrophic epidermolysis bullosa patients had a homozygous single base-pair frameshift mutation in exon 19 of COL7A1 (2470insG). Clinically, there was generalized blistering but only mild scarring. Skin biopsy revealed positive type VII collagen immunoreactivity and recognizable anchoring fibrils. The junctional epidermolysis bullosa patients were compound heterozygotes for a frameshift/non-sense combination of mutations in exons 3 and 17 of LAMB3 (29insC/Q834X). These patients did not have the lethal form of junctional epidermolysis bullosa but, as adults, displayed the milder generalized atrophic benign epidermolysis bullosa variant. There was undetectable laminin 5 staining at the dermal-epidermal junction using an antibody to the beta3 chain, but faintly positive alpha3 and gamma2 chain labeling, and there was variable hypoplasia of hemidesmosomes. To explain the milder recessive dystrophic epidermolysis bullosa and junctional epidermolysis bullosa phenotypes in these families, reverse transcription-polymerase chain reaction, using RNA extracted from frozen skin, was able to provide evidence for some rescue of mutant mRNA transcripts with restoration of the open- reading frame. In the recessive dystrophic epidermolysis bullosa patients, transcripts containing in-frame skipping of exon 19 of COL7A1 in the cDNA were detected, and in the junctional epidermolysis bullosa patients transcripts with in-frame skipping of exon 17 of LAMB3 were identified. The truncated proteins encoded by these transcripts are expected to lack certain critical domains involved in cell-matrix attachment, but may still be able to contribute to adhesion thereby moderating the severity of the skin blistering. This study shows the limitations in predicting phenotype in epidermolysis bullosa solely based on mutation analysis of genomic DNA and emphasizes the importance of immunohistochemistry, electron microscopy, and mRNA assessment as parallel investigations.

Squamous cell carcinoma in a family with dominant dystrophic epidermolysis bullosa: a molecular genetic study

Squamous cell carcinoma in a family with dominant dystrophic epidermolysis bullosa: a molecular genetic study Squamous cell carcinoma (SCC) is a frequent complication in the severe, recessively inherited forms of dystrophic epidermolysis bullosa (RDEB), however, only rarely reported in dominant DEB. Although the SCCs in RDEB are frequently well-differentiated by histopathology, they often have a poor prognosis due to multicentricity, rapid invasiveness, and development of distant metastases. In this study, we sought to determine the molecular basis of DDEB in a family with the unusual occurrence of SCCs. Specifically, a large DDEB family with 2 individuals being affected with SCC was analyzed for potential mutations in the type VII collagen gene (COL7A1) by heteroduplex scanning and direct nucleotide sequencing of PCR amplified segments of the gene. This mutation detection strategy disclosed a G-->A transition at nucleotide position 6,235 which resulted in substitution of a glycine by arginine within the collagenous region of COL7A1. This study establishes, for the first time, the molecular basis in a family with DDEB/SCC. Clinically, this study reemphasizes the importance of vigilance in surveying DEB patients, not only those with recessive but also with dominant inheritance, for SCC.

Mutation analysis and molecular genetics of epidermolysis bullosa

Cutaneous basement membrane zone (BMZ) consists of a number of attachment structures that are critical for stable association of the epidermis to the underlying dermis. These include hemidesmosomes, anchoring filaments and anchoring fibrils which form an interconnecting network extending from the intracellular milieu of basal keratinocytes across the dermal-epidermal basement membrane to the underlying dermis. Aberrations in this network structure, e.g. due to genetic lesions in the corresponding genes, can result in fragility of the skin at the level of the cutaneous BMZ. The prototype of such diseases is epidermolysis bullosa (EB), a heterogeneous group of genodermatoses characterized by fragility and blistering of the skin, often associated with extracutaneous manifestations, and inherited either in an autosomal dominant or autosomal recessive manner. Based on constellations of the phenotypic manifestations, severity of the disease, and the level of tissue separation within the cutaneous BMZ, EB has been divided into clinically distinct subcategories, including the simplex, hemidesmosomal, junctional and dystrophic variants. Elucidation of BMZ gene/protein systems and development of mutation detection strategies have allowed identification of mutations in 10 different BMZ genes which can explain the clinical heterogeneity of EB. These include mutations in the type VII collagen gene (COL7A1) in the dystrophic (severely scarring) forms of EB; mutations in the laminin 5 genes (LAMA3, LAMB3 and LAMC2) in a lethal (Herlitz) variant of junctional EB; aberrations in the type XVII collagen gene (COL17A1) in non-lethal forms of junctional EB; mutations in the alpha6 and beta4 integrin genes in a distinct hemidesmosomal variant of EB with congenital pyloric atresia; and mutations in the plectin gene (PLEC1) in a form of EB associated with late-onset muscular dystrophy. Identification of mutations in these gene/protein systems attests to their critical importance in the overall stability of the cutaneous BMZ. Furthermore, elucidation of mutations in different variants of EB has direct clinical applications in terms of refined classification, improved genetic counseling, and development of DNA-based prenatal testing in families with EB.

Skin fragility and hypohidrotic ectodermal dysplasia resulting from ablation of plakophilin 1

We report a 2-year-old boy with an unusual autosomal recessively inherited skin disease comprising trauma-induced skin fragility and congenital ectodermal dysplasia affecting hair, nails and sweat glands. Skin biopsy showed widening of intercellular spaces between keratinocytes and ultrastructural findings of small, poorly formed desmosomes with reduced connections to the keratin filament cytoskeleton. Immunohistochemical analysis revealed a complete absence of staining for the accessory desmosomal plaque protein plakophilin 1 (PKP1; band 6 protein). The affected individual was a compound heterozygote for null mutations on both alleles of the PKP1 gene. Both mutations occurred within the amino terminus of PKP1, the domain which normally binds the cytoskeletal keratin filament network to the cell membrane. Apart from its localization within desmosomal plaques, PKP1 may also be present within the cytoplasm and nucleus and has putative roles in signal transduction and regulation of gene activity. The clinicopathological observations in this patient demonstrate the relevance of PKP1 to desmosome formation, cutaneous cell-cell adhesion and epidermal development and demonstrate the specific manifestations of human functional knockout mutations in this gene.

BP180 gene delivery in junctional epidermolysis bullosa

Epidermolysis bullosa (EB) comprises a family of inherited blistering skin diseases for which current therapy is only palliative. Junctional EB (JEB) involves dissociation of the dermal-epidermal junction and results from mutations in a number of genes that encode vital structural proteins, including BP180 (type XVII collagen/BPAG2). In order to develop a model of corrective gene delivery for JEB, we produced a retroviral expression vector for wild-type human BP180 and used it to restore BP180 protein expression to primary keratinocytes from BP180-negative patients with generalized atrophic JEB. Restoration of full-length BP180 protein expression was associated with adhesion parameter normalization of primary JEB keratinocytes in vitro. These cells were then used to regenerate human skin on immune-deficient mice. BP180 gene-transduced tissue demonstrated restoration of BP180 gene expression at the dermal-epidermal junction in vivo while untransduced regenerated JEB skin entirely lacked BP180 expression. These findings provide a basis for future efforts to achieve gene delivery in human EB skin tissue.

The 97 kDa linear IgA bullous dermatosis antigen is not expressed in a patient with generalized atrophic benign epidermolysis bullosa with a novel homozygous G258X mutation in COL17A1

The nature and expression pattern of the 97 kDa linear IgA bullous dermatosis antigen (LAD-1) and its role in epidermolysis bullosa have not been fully elucidated. In this study, we examined the expression of LAD-1 in the skin specimens of 70 patients with the various subtypes of epidermolysis bullosa, including simplex (n = 23), junctional (n = 15), and dystrophic variants (n = 32). For immunolabeling, we used two recently developed monoclonal antibodies to LAD-1 whose epitopes were ultrastructurally localized in the lamina lucida between NC16A and carboxyterminal domains of BPAG2, as well as autoantibodies against LAD-1 from the sera of two patients with linear IgA dermatosis. Among the 70 patients, only one patient with generalized atrophic benign epidermolysis bullosa failed to demonstrate LAD-1 expression. Although other major basement membrane components, including laminin 5, BPAG1, plectin, alpha6 and beta4 integrins, as well as type IV and type VII collagens were normally expressed, BPAG2/type XVII collagen was absent from the skin of this patient. Mutation analysis on COL17A1 using polymerase chain reaction amplification, heteroduplex scanning, and direct nucleotide sequencing revealed that this patient was homozygous for a novel nonsense mutation G258X in exon 11, and her parents were heterozygous carriers for this mutation. This is the first mutation located in the intracellular domain of BPAG2, and resides 817 bp upstream from the N-terminal amino acid sequence of LAD-1. These findings indicate that the absent expression of LAD-1 is observed in a BPAG2-deficient generalized atrophic benign epidermolysis bullosa patient with mutations in both alleles of COL17A1, and not in other epidermolysis bullosa subtypes. These findings also support the notion that LAD-1 is a degradation product of BPAG2.

Novel ITGB4 mutations in lethal and nonlethal variants of epidermolysis bullosa with pyloric atresia: missense versus nonsense

Epidermolysis bullosa with pyloric atresia (EB-PA), an autosomal recessive genodermatosis, manifests with neonatal cutaneous blistering associated with congenital pyloric atresia. The disease is frequently lethal, but nonlethal cases have also been reported. Expression of the alpha6 beta4 integrin is altered at the dermal-epidermal basement-membrane zone; recently, mutations in the corresponding genes (ITGA6 and ITGB4) have been disclosed in a limited number of patients, premature termination codons in both alleles being characteristic of lethal variants. In this study, we have examined the molecular basis of EB-PA in five families, two of them with lethal and three of them with nonlethal variants of the disease. Mutation analysis disclosed novel lesions in both ITGB4 alleles of each proband. One of the patients with lethal EB-PA was a compound heterozygote for premature termination-codon mutations (C738X/4791delCA), whereas the other patient with a lethal variant was homozygous for a missense mutation involving a cysteine residue (C61Y). The three nonlethal cases had missense mutations in both alleles (C562R/C562R, R1281W/R252C, and R1281W/R1281W). Immunofluorescence staining of skin in two of the nonlethal patients and in one of the lethal cases was positive, yet attenuated, for alpha6 and beta4 integrins. These results confirm that ITGB4 mutations underlie EB-PA and show that missense mutations may lead to nonlethal phenotypes.

A recurrent glycine substitution mutation, G2043R, in the type VII collagen gene (COL7A1) in dominant dystrophic epidermolysis bullosa

Dystrophic epidermolysis bullosa (DEB) is caused by mutations in the type VII collagen gene (COL7A1). Nearly all cases of dominant DEB are caused by glycine substitution mutations occurring within the triple helical region of type VII collagen, and most of the mutations are unique to individual families. In this study, we identified a patient of Hispanic-Mexican origin with a mild form of DEB, which resulted from a de novo dominant glycine substitution, G2043R, in exon 73 of COL7A1. We also investigated a Scottish family with a three-generation pedigree of dominant DEB, in whom the same glycine to arginine substitution mutation was demonstrated. This particular mutation has also been detected previously in three other families with dominant DEB: one Italian, one Hungarian and one Norwegian. Given the widespread geographical distribution of this mutation and the demonstration of its occurrence as a de novo event, G2043R therefore represents the first example of a mutational hotspot in dominant DEB. Interestingly, although both the Mexican and Scottish families we studied had some clinical features in keeping with the Pasini form of the disorder, there was considerable interfamilial variability as well as intrafamilial diversity in the affected individuals.

Two-hybrid analysis reveals multiple direct interactions for thrombospondin 1

The yeast two-hybrid system was used to reveal the interactions between proteins residing within the cutaneous basement membrane zone and other gene products expressed in cultured human keratinocytes. The proteins of interest included type VII collagen, the predominant component of anchoring fibrils, and laminin 5, a component of anchoring filaments. Although the two-hybrid system was not able to verify a direct interaction between the type VII collagen NC1 domain and the short arm of Lam(beta)3, the type VII collagen NC1 domain (tVII/NC1) and the laminin 5 beta3 chain globular domain VI (lam5/beta3) cDNAs, when used as baits, detected four overlapping cDNA clones encoding thrombospondin 1 (TSP1). The overlapping region of these cDNAs encodes amino acids 400-459, a segment included within a 70 kDa chymotryptic fragment known to bind type V collagen, laminin-1 and other matrix components. The type VII collagen NC1/TSP1 interaction was confirmed by exchanging the vectors, and the interacting domain was mapped by testing a set of both 5' and 3' deletion constructs. The central region of TSP1, when used as a bait in two-hybrid system, showed strong binding to the fibronectin (FN) type III-like repeats 4-7 of type VII collagen NC1 domain. The TSP1 bait also interacted with laminin 5 beta3 chain domain V/III, and the TSP1/laminin 5 beta3 chain interaction was verified by a GST-fusion protein interaction assay. The transcripts encoding TSP1, TSP2, Lam(beta)3 and type VII collagen were abundant in cultured foreskin keratinocytes, and the expression of TSP1 and TSP2 in a wide variety of adult and fetal tissues was confirmed by PCR analysis of multiple tissue cDNA panels. Furthermore, TSP1 type I repeats showed self interaction, and recognized a clone for extracellular matrix protein fibrillin-2. In addition, clones encoding angiogenesis related protein Jagged1 and a platelet enzyme phospholipase scramblase were identified. Thus, the results indicate several previously undetected interactions of TSP1, which is known to be highly expressed during embryonic development, tissue remodeling and wound healing.

Maternal uniparental meroisodisomy in the LAMB3 region of chromosome 1 results in lethal junctional epidermolysis bullosa

Herlitz junctional epidermolysis bullosa (OMIM#226700) is a lethal, autosomal recessive blistering disorder caused by mutations in one of the three genes LAMA3, LAMB3, or LAMC2, encoding the constitutive polypeptide subunits of laminin 5. In this study, we describe a patient homozygous for a novel nonsense mutation Q936X in exon 19 of LAMB3, which has been mapped to chromosome 1q32. The patient was born with extensive blistering and demonstrated negative immunofluorescence staining for laminin 5, and transmission electron microscopy revealed tissue separation within lamina lucida of the dermal-epidermal junction, diagnostic of Herlitz junctional epidermolysis bullosa. The mother of the proband was found to be a heterozygous carrier for this mutation, whereas the father demonstrated the wild-type LAMB3 allele only. Nonpaternity was excluded by 13 microsatellite markers in six different chromosomes. Genotype analysis using 28 microsatellite markers spanning chromosome 1 revealed that the patient had maternal primary heterodisomy, as well as meroisodisomy within two regions of chromosome 1, one on 1p and the other one on 1q, the latter region containing the maternal LAMB3 mutation. These results suggest that Herlitz junctional epidermolysis bullosa in this patient developed as a result of reduction to homozygosity of the maternal LAMB3 mutation on chromosome 1q32.

Hemidesmosomal variants of epidermolysis bullosa. Mutations in the alpha6beta4 integrin and the 180-kD bullous pemphigoid antigen/type XVII collagen genes

Epidermolysis bullosa (EB), a heterogeneous group of genodermatoses, is characterized by fragility and blistering of the skin, associated with characteristic extracutaneous manifestations. Based on clinical severity, constellation of the phenotypic manifestations, and the level of tissue separation within the cutaneous basement membrane zone, EB has been divided into distinct subcategories. Traditionally, these include the simplex, junctional and dystrophic variants of EB. Recent attention has been drawn to variants of EB demonstrating tissue separation at the level of hemidesmosomes, ultrastructurally recognizable adhesion complexes within the cutaneous basement membrane zone. Clinically, these hemidesmosomal variants manifest either as generalized atrophic benign epidermolysis bullosa (GABEB), EB with pyloric atresia, or EB with late-onset muscular dystrophy. Elucidation of basement membrane zone components by molecular cloning and development of mutation detection strategies have revealed that the hemidesmosomal variants of EB result from mutations in the genes encoding the subunit polypeptides of the 180-kD bullous pemphigoid antigen/type XVII collagen, the alpha6beta4 integrin, or plectin, respectively. Collectively, these data add to the understanding of the molecular complexity of the cutaneous basement membrane zone in EB, as attested by the fact that mutations in 10 different genes can underlie different variants of EB. Elucidation of mutations in different forms of EB has direct application to genetic counseling and DNA-based prenatal testing in families with EB.

cDNA cloning, mRNA expression, and chromosomal mapping of human and mouse periplakin genes

A portion of the intracellular domain of Type XVII collagen, used as a bait in a yeast two-hybrid screen of an epidermal keratinocyte cDNA library, identified overlapping cDNA clones that showed a high degree of homology to envoplakin and other members of the plakin family of intermediate filament connector molecules. Subsequent cloning allowed identification of contiguous cDNA sequences with an open reading frame of 5268 bp encoding a putative polypeptide of 1756 amino acids with a computed molecular mass of 204.7 kDa. Northern analysis using these cDNA clones revealed a prominent band of approximately 6.5 kb in keratinocytes, which was barely detectable in fibroblasts. Multiple tissue RNA analysis showed that this protein is highly expressed in tissues with a prominent component of epithelial cells. This novel member of the plakin family was designated periplakin. The human gene (PPL) was mapped to the interval between D16S510 and D16S509 by radiation hybrid mapping, corresponding to chromosomal band 16p13. Murine ESTs having 97.2% amino acid identity to the human sequence were identified. Interspecific backcross mapping was used to place the murine periplakin gene (Ppl) 0.53 cM distal to marker D16mit32 on the proximal part of murine chromosome 16, close to the locus of mahoganoid (md), a mouse hair mutant. Mapping of this gene in human and mouse will allow evaluation of periplakin as a candidate locus for disorders of epithelial fragility, with or without other phenotypes.