Epidermolysis bullosa (EB) is caused by an inherited genetic mutation that makes skin more fragile.
A genetic mutation occurs when instructions carried in certain genes become 'scrambled'. This results in some of the body's processes not working in the normal way.
How EB is inherited
All genes in your body come in pairs. You receive one half from your mother and the other half from your father.
Genetic conditions such as EB and the mutations which cause them can be passed down through families in two ways:
- it takes only one mutated gene for you to develop the symptoms of a particular genetic condition. The parent you inherited the mutated gene from will also have symptoms of the condition – this is known as autosomal dominant inheritance
- both genes in the pair need to have the same mutation before you develop symptoms of the condition. You would need to inherit one mutated gene from your mother and another from your father. In this case, neither parent would have any symptoms of the condition as they would only be a carrier of the mutated gene – this is known as autosomal recessive inheritance.
In EB, some variants are autosomal dominant and others are autosomal recessive.
Epidermolysis bullosa simplex
Epidermolysis bullosa simplex (EBS) is an autosomal dominant condition. If you have EBS, one of your parents also has a history of the condition and has passed the mutated gene to you. However, if their symptoms are mild, their condition may not have been diagnosed.
You may be the first in your family to be affected. In these cases, the mutation will have occurred in the womb before you were born. Neither of your parents carries the mutation and you have a new mutation.
If you go on to have children, they'll have a 50% chance of developing EBS.
Junctional epidermolysis bullosa
Junctional epidermolysis bullosa (JEB) is an autosomal recessive condition. If you have JEB, both your parents are carriers of the mutated gene but they don't have symptoms.
Your children are only at risk of developing JEB if your partner is also a carrier of a mutated gene known to be associated with JEB. It's difficult to estimate exactly how many people are carriers of the various JEB mutated genes, but the number is thought to be low.
If you and your partner are both carriers of a JEB mutated gene, your children have a one-in-four chance of developing the condition.
Dystrophic epidermolysis bullosa
Depending on the particular variant, dystrophic epidermolysis bullosa can be either autosomal recessive or dominant.
Dominant DEB is autosomal dominant and the other types are autosomal recessive.
Human skin is made of three layers:
- epidermis – the outer layer of skin
- dermis – the middle layer of skin
- subcutis – the deepest layer of skin, mainly made up of fat
The epidermis and dermis meet at a point known as the basement membrane zone (BMZ). This contains specialised proteins that keep the two layers stuck securely together.
Faulty genes can cause one or more proteins in the BMZ to not work properly. This means trauma or friction to an area of skin could result in the epidermis and dermis becoming unstuck. If the two layers become separated, a space is created which fills with fluid to form a blister.