Epidermolysis bullosa (EB) is a rare genetic disorder that affects infants and children. The disease affects proteins in the layers of the skin and leads to delicate skin that tears and blisters easily. In some cases, affected children also can have painful blisters appear in their lungs, esophagus, intestines, and mouth.
There are more than 30 distinct subtypes of EB, which vary in severity and are caused by different genetic defects. These subtypes usually are grouped together under four main types by their symptoms and by how they are inherited. These main types are epidermolysis bullosa simplex, junctional epidermolysis bullosa, Kindler syndrome, and dystrophic epidermolysis bullosa.
Autosomal dominant inheritance
The most common form of EB, epidermolysis bullosa simplex (EBS), as well as some forms of dystrophic epidermolysis bullosa (DEB) are inherited in an autosomal dominant pattern. This means that a child will develop the disease if they inherit just one copy of the faulty gene from either parent.
Dominant inheritance seems to be associated with less severe disease. EBS, which affects the cells that produce the keratin protein, is the mildest form of EB, often becoming less severe with age.
The dominant form of DEB, which affects the gene encoding for type 7 collagen, a structural protein that holds the different layers of the skin together, also is the least severe form of DEB, though it still can cause scarring and pain.
Autosomal recessive inheritance
The rarer forms of EB, junctional epidermolysis bullosa (JEB), Kindler syndrome, as well as some forms of DEB, are inherited in an autosomal recessive pattern. This means only an individual with two defective copies of the causative gene will have the disease.
So, for a child to inherit one of these diseases, both parents must either be affected by the disease or both be carriers of a defective copy of the same gene. Carriers may pass the disease onto their children without showing any symptoms themselves. An affected parent and a carrier parent have an equal one-in-two risk of either passing the disease to their children or of having children who also are carriers.
Two carrier parents can have a child who is affected by the disease, or have a child who is neither affected by the disease nor is a carrier. However, they have a one-in-two risk of having children who are non-symptomatic carriers of EB.
Recessive inheritance of EB seems to be associated with not only the rarity of the disease, but also with more severe symptoms. For instance, the recessive form of DEB has more severe blistering and scarring symptoms and also has been associated with an increased risk of skin cancer.
Genetic testing for EB
Because the more severe forms of EB are inherited as recessive traits, people with family histories of JEB, DEB, or Kindler’s syndrome should consider being tested to determine if they are carriers of the disease.
It is important to note that EB also can appear “de novo,” or be the result of a new mutation in the child themselves, not passed on to them from their parents.
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