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Epidermolysis bullosa

In medicine (dermatology) Epidermolysis bullosa (EB) is a rare genetic disease characterized by the presence of extremely fragile skin and recurrent blister formation, resulting from minor mechanical friction or trauma. This condition is not contagious. The condition was brought to public attention in the Channel 4 documentary The Boy Whose Skin Fell Off, chronicling the life and death of English sufferer Jonny Kennedy. more...

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Forms

There are three main forms of inherited EB. These different subtypes are defined by the depth of blister location within the skin layers, and the location of the dissolution of the skin.

EB Simplex (EBS) -- ABOVE the basement membrane

Blister formation of EB simplex is within the basal keratinocyte of the epidermis. Sometimes EB simplex is called epidermolytic. There are four subtypes of EBS:

  1. EBS - Weber-Cockayne (EBS-WC)
  2. EBS - Koebner (EBS-K)
  3. EBS - Dowling-Meara (EBS-DM) -- caused by missense mutation in KRT5 (E477K) or one of two missense mutations in KRT14 (R125C and R125H)
  4. EBS - Mottled Pigmentation (EBS-MP) - caused by one missense mutation in KRT5 (I161S) or by missense mutations in the plectin gene (Koss-Harnes et al., 1997;Koss-Harnes et al., 2002).

Junctional EB (JEB) -- THROUGH the basement membrane

Blister formation in Junctional EB is seen at the level of the lamina lucida within the basement membrane zone.

Dystrophic EB (DEB) -- UNDER the basement membrane

Dystrophic EB (DEB) forms which can lead to scarring occur in a deeper tissue level; the sub-lamina densa region(the beneath the lamina densa) within the upper dermis. The disease DEB is caused by genetic defects (or mutations) within the molecule type VII collagen (collagen VII). Collagen VII is a very large molecule (780 nm) that dimerizes to forms a semicircular looping structure: the anchoring fibril. Anchoring fibrils are thought to form a strucutral link between the epidermal basement membrane and the fibrillar collagens in the upper dermis.

Collagen VII is also present in the epithelial tissue of the esophagus, which leads to chronic scarring, webbing, and obstruction. Affected individuals are often severely malnourished due to trauma to the oral and esophageal mucosa and require feeding tubes for nutrition. They also suffer from iron-deficiency anemia of uncertain origin, which leads to chronic fatigue.

Open wounds on the skin heal slowly and are particularly susceptible to infection. Many individuals bathe in a bleach and water mixture to fight off these infections.

The chronic inflammation leads to errors in the DNA of the affected skin cells, which in turn causes squamous cell carcinoma (SCC). The majority of these patients die before the age of 30, either of SCC or complications related to DEB.

Epidemiology

An estimated 2 out of every 100,000 live births are affected with some type of EB. The disorder occurs in every racial and ethnic group throughout the world and affects both sexes equally.

Read more at Wikipedia.org


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Skin genes underlie blistering disorder - epidermolysis bullosa
From Science News, 9/28/91 by Carol Ezzell

They are often born covered with blisters. Their skin is so sensitive that even a mother's loving touch can raise fluid-filled welts. Children with the most severe form of this rare genetic disorder sometimes even lose fingers and toes to the thick scar tissue that forms as the blisters heal.

Epidermolysis bullosa (EB) afflicts an estimated 50,000 people in the United States. For now, treatment is limited mainly to bandages and antibiotic ointments, which help shield the delicate skin and protect the blisters from infection (SN: 1/26/85, p.58; 5/17/86, p.318). But three research reports, uncovering the genetic defects responsible for two types of EB, may offer clues to new treatments--and perhaps a cure -- for those who inherit this dire disorder.

Scientists have identified 23 types of EB. Two of the new reports focus on EB simplex, blaming it on a genetic defect in keratin -- the key protein in the springy "inner skeletons" of cells. A third report links dominant dystrophic EB, the most severe form, with a damaged gene for collagen, another structural protein.

The new work represents "a tremendous step forward" in understanding EB, says Miriam Feder, executive director of the Dystrophic Epidermolysis Bullosa Research Association of America, based in New York City. "It opens the door to finding a cure," she says.

In the Sept. 20 CELL, researchers report finding similar mutations in the keratin genes of two unrelated EB simplex patients. When they isolated the mutant gene and spliced it into healthy, keratin-producing skin cells called keratinocytes, it disrupted the cells' normal, filamentous internal scaffolding. And when they inserted the gene into bacteria, the microbes produced defective keratin lacking the ability to assemble into long, helical filaments in a test tube.

The investigators, led by Elaine V. Fuchs of the Howard Hughes Medical Institute at the University of Chicago, conclude that the mutant keratin causes blisters by weakening keratinocytes so that they sometimes dissolve when touched. They suggest that the various types of EB arise from "different ... mutations in different regions" of the keratin gene, resulting in proteins with varying degrees of strength.

Another team, lead by Ervin H. Epstein at the University of California, San Francisco, found a similar type of keratin mutation in one family with 10 EB simplex patients. These researchers, whose report has been accepted for publication in SCIENCE, also found that the mutant keratin failed to form helical filaments.

A third research group, directed by Jouni Uitto of Thomas Jefferson University in Philadelphia, found that 20 members of a Finnish family affected by dominant dystrophic EB bore defective genes for collagen. In the October AMERICAN JOURNAL OF HUMAN GENETICS, they report that all 20 patients had blistering lesions where the skin's outer, epidermal layer had separated from the inner, dermal layer. Because collagen makes up the fibrils that anchor the two skin layers together, Uitto's team concludes that dominant dystrophic EB results from the collagen mutation.

Robert A. Briggaman, a dermatologist at the University of North Carolina in Chapel Hill, calls the three reports "absolutely essential" to finding a cure for EB, although he concedes that the search will be tough. Gene therapy may hold promise, but there's a catch, he says. Fuchs' group found that even tiny amounts of mutant keratin can block the normal protein's assembly into healthy filaments -- which means that physicians would need to inactivate a patient's mutant gene as well as insert a healthy gene.

COPYRIGHT 1991 Science Service, Inc.
COPYRIGHT 2004 Gale Group

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