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What is the cause of EB Simplex?
Through research it is now known that the genes that carry the instructions
necessary to produce the proteins in the top layer (keratins) are faulty. This
results in incorrectly formed keratins, deeming them unable to perform their
normal role as a 'scaffolding' for the top most layer of skin. It appears as
though there is a mutation (a change in the genetic material) within Keratin
genes K5 or its partner K14. So as a result, the top layer of skin falls apart,
resulting in a blister. Although EB Simplex is considered a non-scarring form of
EB, secondary infection may cause scarring.
How is EB Simplex Inherited?
EB Simplex is usually inherited as an autosomal dominant condition. One parent
of an affected person will usually also have the condition, though it is
possible for EB simplex to appear 'sporadically' (to appear for the first time
in a person who has no other affected family member). Anyone who has EB simplex
whether male or female, can pass the condition on to his or her children. Each
time a pregnancy occurs, there is a 1 in 2 chance that the child will inherit EB
simplex.
Some precipitating factors that may cause an outbreak of blistering may include
the following:
Physical stress
Emotional stress
Warmer climates
Infections
Sexual maturation
Even though some forms of EB Simplex are localized it is important to know that
all skin cells are affected. Therefore, all skin surfaces are prone to develop
generalized blistering.
Weber-Cockayne Subtype of EB Simplex:
This form is also termed localized EB simplex. This disorder usually presents in
childhood or adolescence. It may also occur in an infant or adult life. In many
instances it presents itself in infancy from friction induced by shoes and
starting to walk.
People with Weber Cockayne EB Simplex develop blisters on their feet and hands,
(usually palms and soles) in response to friction. These wounds usually heal
without scarring. Walking even short distances is often enough to cause
blisters. They may experience thickening of the skin (keratoderma) on the soles
of the feet. This type of EBS usually does not involve nails or mucous
membranes. Most individuals seem to be more prone to blisters in warmer climates
and during periods of strenuous activity such as jogging, marching or walking.
With trauma or friction rarely the blistering can be (generalized) or appear on
other parts of the body.
Mutations are in the genes encoding K5 or K14.
Koebner Subtype of EB Simplex:
This is a form of generalized EB simplex. This disorder usually presents at
birth or infancy. Blisters are noted to be widespread over the body's surface.
Though it is not a common feature of this type of EB to scar on rare occasions
it does happen. There may be mild involvement of mucous membranes. Fingernails
and toenails are sometimes involved. Localized thickening of the skin (keratoderma)
on the soles of the feet and the palms of the hands may occur especially as one
gets older.
Mutations are in the genes encoding K5 or K14.
Dowling Meara Subtype of EB Simplex:
EBS-DM is a generalized form of EB simplex. This type of EB is probably the most
severe form of EB Simplex. Infants are often born with widespread grouping of
blisters on the face, trunk and limbs. Blisters on hands and feet often
eventually cause confluent keratoderma (thickening of the skin). In many cases
these calluses form complete thickening of the palms and soles. If the
thickening is severe enough it may limit the range of motion of a joint. In such
cases, consultation from a surgeon may be necessary to determine the best course
of treatment.
Heat may exacerbate blistering. Milia (tiny cysts on skin) may be present after
blisters have healed. Nail thickening and discoloration is a common feature.
Blistering in Dowling Meara EBS can involve organs including the oral cavity,
gastrointestinal tract and rarely, the upper respiratory tree.
Electron microscopy shows clumps of keratin filaments, which are not seen in
other forms of EB simplex.
Mutations are usually in the genes encoding K5 or K14.
Since EBS-DM is the most severe form of EBS, the widespread blistering may lead
to death in infancy. However, blistering tends to become smaller and less
problematic for most patients as they grow older.
*Since EB varies in severity these manifestations may or may not be experienced
by the individual affected.
Common Manifestations of EBS:
Blisters
Keratoderma - Thickened skin on palms of hands and soles of feet. Confluent
keratoderma in EBS-DM.
Nail dystrophy - The presence of rough, thickened or absent finger or toenails.
Problems with the soft tissue inside the mouth.
Uncommon Manifestations of EBS:
Milia - Tiny skin cysts.
Atrophic scarring - Depressions in skin as a result of thinning in epidermis or
dermis.
Anemia - A reduced amount of red blood cells, volume of red blood cells, amount
of hemoglobin. Hemoglobin is the oxygen carrying portion of the red blood cell.
The heme aspect of hemoglobin, is the iron compound that makes up the pigment
part of the hemoglobin molecule. Anemia is more common in the severely affected
individual.
Growth retardation. This is more common in a severely affected individual.
Gastrointestinal tract - Involvement of the GI tract may include blisters in
mouth, esophagus and/or anal margins.
Rare Manifestations of EBS:
Granulation tissue - The appearance of red fleshy tissue which is capillary
formation during tissue healing This would be a rare occurrence in a person
affected with EBS. This is more commonly seen in a person severely affected with
Junctional EB.
Dental caries (cavities) - This is more common in people affected with RDEB or
JEB however, if mouth care is not performed regularly it will increase chances
of cavities.
Ocular (eye) involvement is more commonly seen in people with RDEB or JEB
however, it has been reported in some forms of EBS.
Pseudosyndactyly - Fusion of fingers and/or toes. This manifestation is more
commonly seen in RDEB. In rare instances it has been reported in EBS-DM.
Enamel hypoplasia - Underdeveloped enamel upon the teeth. This is more prevalent
in patients with JEB.
Respiratory tract involvement. Rare occurrences have been noted in the more
severely affected individual.
Genitourinary tract involvement. Rare occurrences involving the GU tract have
been reported in some forms of EBS. There is no evidence that people with EBS
are at a higher risk for developing squamous cell carcinoma or malignant
melanoma, however, suspicious wounds/lesions should always be evaluated by your
dermatologist.
Other Subtypes of EB Simplex include:
EB Simplex Superficialis, EB Simplex with Mottled Pigmentation and Kallin’s
Syndrome.
There is a recessively inherited simplex that accompanies Muscular Dystrophy
which appears to be a mutation in the Plectin gene.
For additional information about types and subtypes of EBS, you can view the
Revised classification system for inherited epidermolysis bullosa on the NEBR
web-site
http://www.daklex.com/
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