Molecular pathology of the cutaneous basement membrane zone

A practical approach to the evaluation and treatment of an infant with aplasia cutis congenita

Aplasia cutis congenita (ACC) is a term describing absence of skin at birth. ACC is a rare cutaneous finding, often noted with no other physical abnormalities. The etiology of ACC varies, and there are likely several causes for its development. ACC can be located anywhere on the body. Its clinical appearance and location can alert the clinician to other potential abnormalities and associations. This discussion covers the diagnosis of ACC and its subtypes and associations in order to provide a pragmatic, clinically relevant and patient-centered approach to evaluation and treatment.

Epidermolysis bullosa: management of esophageal strictures and enteric access by gastrostomy

Epidermolysis bullosa (EB) is a spectrum of rare, inherited, blistering skin disorders, primarily affecting the skin and pharyngoesophageal mucosa. EB affects approximately 2 to 4 per 100,000 children each year. Blistering and scarring occur in response to even the most minor trauma. In this article, the authors outline the potential management options for patients with EB complicated by feeding difficulties secondary to esophageal strictures as well as those with nutritional deficiencies requiring a gastrostomy tube for supplemental feeding.

cDNA sequence of the horse (Equus caballus)LAMA3gene and characterization of two intronic SNP markers

Laminins are large heterotrimeric basement membrane glycoproteins composed of alpha, beta and gamma chains. The Laminin 5 isoform has an alpha3beta3gamma2 composition and is essential for the adhesion of basal keratinocytes to the underlying epithelial basement membrane where it is mainly located. Mutations in the genes coding for the 3 chains have been associated with a severe skin blistering disease, Herlitz's junctional epidermolysis bullosa (JEB), observed in different species as man, dog, cat and horse. In this study, we report the sequence of the 5.2 kb horse laminin alpha 3 cDNA (LAMA3) as well as the detection of two intronic SNPs. These data will be useful to further identify causal mutations for the disease in this gene.

Kindler syndrome: a focal adhesion genodermatosis

Kindler syndrome (OMIM 173650) is an autosomal recessive genodermatosis characterized by trauma-induced blistering, poikiloderma, skin atrophy, mucosal inflammation and varying degrees of photosensitivity. Although Kindler syndrome is classified as a subtype of epidermolysis bullosa, it has distinct clinicopathological and molecular abnormalities. The molecular pathology of Kindler syndrome involves loss-of-function mutations in a newly recognized actin cytoskeleton-associated protein, now known as fermitin family homologue 1, encoded by the gene FERMT1. This protein mediates anchorage between the actin cytoskeleton and the extracellular matrix via focal adhesions, and thus the structural pathology differs from other forms of epidermolysis bullosa in which there is a disruption of the keratin intermediate filament-hemidesmosome network and the extracellular matrix. In the skin, fermitin family homologue 1 is mainly expressed in basal keratinocytes and binds to the cytoplasmic tails of beta1 and beta3 integrins as well as to fermitin family homologue 2 and filamin-binding LIM protein 1. It also plays a crucial role in keratinocyte migration, proliferation and adhesion. In this report, we review the clinical, cellular and molecular pathology of Kindler syndrome and discuss the role of fermitin family homologue 1 in keratinocyte biology.

Gastrointestinal complications of epidermolysis bullosa in children

BACKGROUND

Epidermolysis bullosa (EB) is a group of inherited disorders characterized by skin and mucous membrane fragility. Gastrointestinal (GI) complications have been described in many types of EB and are responsible for significant morbidity.

OBJECTIVES

To delineate the nature and frequency of GI complications in a large cohort of paediatric patients with EB and to postulate why some complications occur more commonly in some specific subtypes.

METHODS

The case notes of 223 children with EB seen at a national referral centre were examined retrospectively for the presence of GI symptoms, investigations and interventions.

RESULTS

GI complications were present in 130/223 (58%) of all patients. In EB simplex, constipation and gastro-oesophageal reflux (GOR) were frequently observed. In junctional EB, failure to thrive and protein-losing enteropathy (PLE) were the prominent GI manifestations. Constipation was common in patients with dystrophic EB (DEB) requiring laxatives and in some cases fibre supplementation. GOR affected three-quarters of those with recessive DEB, two-thirds also having significant oesophageal strictures. Over half of patients with recessive DEB required gastrostomy insertion. Diarrhoea affected a small but significant proportion of children with recessive DEB with macroscopic and/or microscopic changes of colitis in the majority.

CONCLUSION

GI problems in EB are very common with subtype specificity for some of these complications. The occurrence of diarrhoea, PLE and colitis in the context of EB has not been highlighted previously, and may arise secondarily to antigenic exposure in the gut lumen as a result of mucosal fragility.

The management of general and disease specific ENT problems in children with Epidermolysis Bullosa--a retrospective case note review

OBJECTIVE

Epidermolysis Bullosa encompasses a group of inherited disorders characterized by excessive susceptibility of the skin and mucosa to separate from underlying tissues following mechanical trauma. Information in the literature and guidance on the management of Ear, Nose and Throat problems in such children is scarce. The aim of this study is to report the experience of an Ear, Nose and Throat department in a tertiary paediatric hospital linked to a national Epidermolysis Bullosa unit, describing how children have presented and the care that has been given including a theatre protocol aimed at reducing shearing forces.

METHODS

Retrospective case note review of Epidermolysis Bullosa patients referred to Otolaryngology over an 8-year period.

RESULTS

Reviewing notes of 307 EB patients identified 15 that had been referred to the ENT department. Four children with middle ear effusions were effectively treated by watchful waiting or grommets. Three children with otitis externa had some relief from careful microsuction but reinfection from ulcers on other parts of the children's bodies tended to occur. One child with profound sensorineural hearing loss benefited from cochlear implantation but later passed away from unrelated sepsis. One child with intrinsic rhinitis was treated with steroid and then a salt-water nasal spray. Five children had nasal crusting documented, although this was not a specific reason for referral. When severe this had been treated with topical steroids by the dermatology team. One patient with obstructive sleep aponea had tonsillectomy and examination of the post-nasal space. Of the five patients referred with glottic or supraglottic scarring, the management of four included a tracheostomy. When carried out tracheostomy sites healed well in each case. With repeated endoscopic procedures it was subsequently possible to remove the tracheostomy in the two of the children. Using a special theatre protocol no new ulcers were recorded as being precipitated by any of the procedures children underwent.

CONCLUSIONS

Optimal management depends on the support of a multidisciplinary team, including otolaryngologists, pediatricians, dermatologists, anaesthetists, and specialist nurses. Adherence to a protocol for theatre management can help avoid intraoperative complications.

A comparative study between transmission electron microscopy and immunofluorescence mapping in the diagnosis of epidermolysis bullosa

The classification of epidermolysis bullosa (EB) into 3 main subtypes has been based on transmission electron microscopy (TEM) that is able to directly visualize and quantify specific ultrastructural features. Immunofluorescence antigenic mapping (IFM) is a technique that determines the precise level of skin cleavage by determining binding sites for a series of antibodies. To date, no study has compared the accuracy of these two techniques in diagnosing the major types of EB. A prospective cohort of 33 patients thought to have EB on clinical grounds had TEM, IFM, and genetic testing performed. The sensitivities and specificities of TEM and IFM were calculated compared with the genetic results. Of 33 cases, 30 had a positive EB diagnosis. TEM subclassified EB into its three major forms in 24/30 cases (80%) and IFM in 29/30 cases (97%). Overall, TEM sensitivities and specificities when compared with genetic results were 71% and 81%, respectively. IFM sensitivities and specificities when compared with genetic results were 97% and 100%, respectively. If a patient tested positive for EB by IFM, the likelihood ratio of having a particular type of EB was consistently greater than 20 against the reference standard (compared with a likelihood ratio less than 10 for TEM). Our results indicate that the diagnosis of EB is improved (sometimes substantially) by the use of IFM compared with TEM.

Target proteins in inherited and acquired blistering skin disorders

Maintenance of an intact epidermis depends on secure adhesion between adjacent keratinocytes, and between basal keratinocytes and the underlying epidermal basement membrane. The major adhesion units that achieve this are the hemidesmosomes and desmosomes, but when these structures are disrupted, e.g., by gene mutations or autoantibodies, the resilience of the epidermis is lost and blisters develop. Recently, there have been considerable advances in our knowledge of the proteins and glycoproteins that contribute to maintaining keratinocyte adhesion via hemidesmosomes and desmosomes, as well as new insights into the molecular pathogenesis of several inherited and autoimmune blistering skin diseases. These new basic scientific data are clinically relevant, helping to improve patient management and to provide a rationale for developing better and more specific treatments for patients with inherited or acquired blistering skin diseases. In addition, there have also been improvements in our understanding of the organization and assembly of these adhesion structures, and their involvement in signalling pathways, intricately linked to skin development, wound healing and tumour invasion. This review provides an update on the structure and organization of hemidesmosomes and desmosomes, and on the molecular pathology of their various components that result in bullous skin diseases.

Kindler syndrome

Kindler syndrome is a rare, autosomal recessive skin fragility disorder characterized by blistering in infancy, followed by photosensitivity and progressive poikiloderma. Ultrastructural examination reveals marked basement membrane reduplication and variable levels of cleavage at the dermal-epidermal junction. The molecular pathology underlying Kindler syndrome has recently been shown to involve loss-of-function mutations in a novel gene, KIND1, encoding kindlin-1. Immunofluorescence, gene expression and cell biology studies have shown that kindlin-1 is expressed mainly in basal keratinocytes and plays a role in the attachment of the actin cytoskeleton via focal contacts to the extracellular matrix. Thus, Kindler syndrome is the first genodermatosis caused by a defect in actin-extracellular matrix linkage rather than the classic keratin-extracellular matrix linkage underlying the pathology of other inherited skin fragility disorders such as epidermolysis bullosa. This article reviews the clinical features as well as the molecular and cellular pathology of Kindler syndrome and highlights the importance of the new protein, kindlin-1, in cell-matrix adhesion and its intriguing link to photosensitivity.

Fraser syndrome and mouse blebbed phenotype caused by mutations in FRAS1/Fras1 encoding a putative extracellular matrix protein

Fraser syndrome (OMIM 219000) is a multisystem malformation usually comprising cryptophthalmos, syndactyly and renal defects. Here we report autozygosity mapping and show that the locus FS1 at chromosome 4q21 is associated with Fraser syndrome, although the condition is genetically heterogeneous. Mutation analysis identified five frameshift mutations in FRAS1, which encodes one member of a family of novel proteins related to an extracellular matrix (ECM) blastocoelar protein found in sea urchin. The FRAS1 protein contains a series of N-terminal cysteine-rich repeat motifs previously implicated in BMP metabolism, suggesting that it has a role in both structure and signal propagation in the ECM. It has been speculated that Fraser syndrome is a human equivalent of the blebbed phenotype in the mouse, which has been associated with mutations in at least five loci including bl. As mapping data were consistent with homology of FRAS1 and bl, we screened DNA from bl/bl mice and identified a premature termination of mouse Fras1. Thus, the bl mouse is a model for Fraser syndrome in humans, a disorder caused by disrupted epithelial integrity in utero.

Bone metabolism in children with epidermolysis bullosa

We evaluated bone mineral density, vitamin D status, and biochemical markers of bone turnover in seven children with epidermolysis bullosa (EB). Four had osteopenia (Z score, -1.5) and four 25(OH) vitamin D <34 nmol/L (14 ng/mL), two of which had hyperparathyroidism. Children with severe EB should have evaluation of bone metabolism.

Reduced expression of the epithelial adhesion ligand laminin 5 in the skin causes intradermal tissue separation

Laminin 5, the major keratinocyte adhesion ligand, is found in the lamina lucida subregion of the epidermal basement membrane of the skin, where it colocalizes with the anchoring filaments. Mutations in the genes encoding laminin 5 cause junctional epidermolysis bullosa, an inherited skin blistering disease characterized by abnormal hemidesmosomes and cleavage of the lamina lucida leading to epidermal detachment. In this work we describe the genetic basis of a new subtype of lethal inherited epidermolysis bullosa associated with reduced skin reactivity to laminin 5, presence of mature hemidesmosomes, and intradermal cleavage of the skin. The epidermolysis bullosa patients were heterozygous for a nonsense mutation (Q896X) and a splice site mutation (764-10T-->G) in the gene (LAMC2) for the gamma2 chain of laminin 5. The nonsense mutation causes accelerated decay of the corresponding mRNA, while the splice site mutation results in maturation of a cryptic wild-type gamma2 mRNA leading to reduced expression of wild-type laminin 5. In vitro studies using the probands' keratinocytes showed that secretion of reduced amounts of functional laminin 5 in the patient, although permitting formation of hemidesmosomes, fail to restore efficient cell adhesion. Our results provide the first evidence that laminin 5 contributes to the firm adhesion of the epithelial basement membrane to the underlying stroma. They also show that a low expression level of laminin 5 induces assembly of mature hemidesmosomes in vivo but fails to assure a stable cohesion of the dermal-epidermal junction.

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.

Alpha 6 beta 4 integrin abnormalities in junctional epidermolysis bullosa with pyloric atresia

Junctional epidermolysis bullosa with pyloric atresia (JEB-PA) (MIM 226730) is an autosomal recessive disorder resulting from mutations in the genes encoding alpha 6 beta 4 integrin (ITGA6 and ITGB4). Clinically, it is characterized by mucocutaneous fragility and gastrointestinal atresia, which most commonly affects the pylorus. Additional features of JEB-PA include involvement of the urogenital tract, aplasia cutis and failure to thrive. While most affected individuals have a poor prognosis resulting in death in infancy, others have milder clinical features and a better prognosis. We report two previously undescribed homozygous ITGB4 mutations in two unrelated families, which resulted in severe skin blistering, pyloric atresia and lethality in infancy. Delineation of the mutations was used to undertake DNA-based prenatal diagnosis in subsequent pregnancies at risk for recurrence in both families. We review all previously published ITGA6 and ITGB4 mutation reports to help define genotype--phenotype correlation in this rare genodermatosis.