Junctional EB (JEB) is considered less common than simplex or dystrophic EB and comprises two main subtypes:
Intermediate JEB (previously known as JEB generalized intermediate, non-Herlitz JEB)
Severe JEB (previously known as JEB generalized severe, Herlitz JEB)
What are the common clinical symptoms of these JEB subtypes?
Blistering starts at birth or shortly afterwards and occurs within the basement membrane structure that keeps the upper and lower levels of skin together. Blisters tend to rupture leaving erosions, which can become extensive. Areas of ulcerated skin may be present at birth, most commonly on the lower limbs or top of the feet and ankles. Blisters and ulcers may heal with atrophic (indented or pitted) scarring and variable hypopigmentation (lightening of the skin) or hyperpigmentation (darkening of the skin). The oral mucosa (the mucous membrane lining the inside of the mouth) and eyes are usually affected. Corneal blistering and erosions are common; pannus formation (growth of fine blood vessels onto the clear corneal surface), scarring, and symblepharon (adhesion of the inner eyelid to the outer surface of the eyeball) may follow episodes of blistering. Scarring and non-scarring alopecia (hair loss) and thinning of the hair can also occur. Anaemia is common in severe JEB and, to a lesser extent, in intermediate JEB. Dental enamel is also affected.
Which genes are affected?
The main JEB subtypes are caused by variants in the LAMA3, LAMB3, and LAMC2 genes containing information needed to make laminin 332. Variants in the COL17A1 gene containing information needed to make type XVII collagen can also result in intermediate and, rarely, in severe JEB phenotypes.
How is it inherited?
JEB is inherited in an autosomal recessive manner.
Rare subtypes of JEB
There are a number of rare subtypes of JEB. Click the button below to find out more about the symptoms and affected genes of each.
Blistering is generalised but less severe and does not usually tend to develop chronic granulation tissue (although this can occur in chronic wounds). EB naevi (birthmarks or moles) may occur. Development of cutaneous squamous cell carcinoma (SCC) can happen in adulthood. Nails are usually lost or thick and dystrophic (appear damaged, misshapen, discoloured, and curvy), or with ridging of the nail plate.
There may be few blisters during the first couple weeks of life tending to occur on the buttocks, elbows, and around the nails. From a few weeks to months of age, wounds may become chronic with a bed of friable (highly delicate) granulation tissue, which commonly affects the face, ears, and tips of the fingers and toes. Persistent large wounds on the region of the buttocks are common.Laryngeal mucosa (the mucous membranes of the voice box) is affected with blistering, erosions, granulation tissue, and scarring leading to hoarseness, stridor (high-pitched wheezing), and potentially life-threatening airway obstruction. All nails are lost in the first few months of life with the development of friable granulation tissue and soft tissue swelling of the tips of the fingers and toes. Sadly, severe JEB usually results in death in the first 24 months of life due to failure to thrive, affected airway, or sepsis.
The information above has been sourced from the ‘Consensus reclassification of inherited epidermolysis bullosa and other disorders with skin fragility’ article published in the British Journal of Dermatology https://doi.org/10.1111/bjd.18921