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What Is Epidermolysis Bullosa Simplex?
Epidermolysis bullosa is a group of genetic conditions that cause the skin to be very fragile and to blister easily. Erosions and blisters form in response to minor injury or friction, such as rubbing or scratching. Epidermolysis bullosa simplex (EBS) is one of the major forms of epidermolysis bullosa. The signs and symptoms of this condition vary widely among affected individuals. Blistering primarily may affect the hands and feet in mild cases, and blisters usually heal without leaving scars. Severe cases of this condition involve widespread blistering that can lead to infections, dehydration and other medical problems. Severe cases may be life-threatening in infancy.
Researchers have identified four major types of epidermolysis bullosa simplex. Although the types differ in severity, their features overlap significantly, and they are caused by mutations in the same genes. Most researchers now consider the major forms of this condition to be part of a single disorder with a range of signs and symptoms.
The mildest form of epidermolysis bullosa simplex, known as the Weber-Cockayne type, is characterized by skin blistering that begins anytime between childhood and adulthood and usually is confined to the hands and feet. Later in life, skin on the palms and soles of the feet may thicken and harden (hyperkeratosis). In the Koebner type, blisters appear at birth or in early infancy and are more widespread. Another form of the disorder, called epidermolysis bullosa simplex with mottled pigmentation, is characterized by patches of darker skin on the trunk, arms and legs that fade in adulthood. This form of the disorder also involves skin blistering from early infancy, hyperkeratosis of the palms and soles, and abnormal nail growth. The Dowling-Meara type is the most severe form of epidermolysis bullosa simplex. Extensive, severe blistering can occur anywhere on the body, including the inside of the mouth, and blisters may appear in clusters. Blistering is present from birth and tends to improve with age. Affected individuals also experience abnormal nail growth and hyperkeratosis of the palms and soles.
Researchers have identified another skin condition characteristic of epidermolysis bullosa simplex, which they call Ogna type. It is caused by mutations in a gene that is not associated with the other types of epidermolysis bullosa simplex. It is unclear whether Ogna type is a subtype of epidermolysis bullosa simplex or represents a separate form of epidermolysis bullosa.
How Common Is Epidermolysis Bullosa Simplex?
What Genes Are Related to Epidermolysis Bullosa Simplex?
Mutations in the KRT14 and KRT5 genes cause epidermolysis bullosa simplex.
The PLEC1 gene is associated with epidermolysis bullosa simplex.
Mutations in the KRT5 and KRT14 genes are responsible for the four major types of epidermolysis bullosa simplex. These genes provide instructions for making proteins called keratin 5 and keratin 14. These tough, fibrous proteins work together to provide strength and resiliency to the outer layer of the skin (the epidermis). Mutations in either the KRT5 or KRT14 gene cause cells in the epidermis to become fragile and easily damaged. As a result, the skin is less resistant to friction and minor trauma and blisters easily.
In rare cases of epidermolysis bullosa simplex, no KRT5 or KRT14 mutations have been identified. Mutations in another gene, PLEC1, have been associated with the uncommon Ogna type of the condition. The PLEC1 gene provides instructions for making a protein called plectin, which helps attach the epidermis to underlying layers of skin. Researchers continue to search for PLEC1 mutations in people with epidermolysis bullosa simplex. They also are working to determine how these mutations lead to the major features of the condition.
How Do People Inherit Epidermolysis Bullosa Simplex?
Epidermolysis bullosa simplex is usually inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Some affected people inherit the mutation from one affected parent. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.
In rare cases, epidermolysis bullosa simplex is inherited in an autosomal recessive pattern. Autosomal recessive inheritance means the condition results when two copies of the gene in each cell are altered. The parents of an individual with an autosomal recessive disorder typically each carry one copy of the altered gene but do not show signs and symptoms of the disorder.