Background
Epidermolysis bullosa (EB) is a group of inherited bullous disorders characterized by blister formation in response to mechanical trauma. Historically, epidermolysis bullosa subtypes have been classified according to skin morphology.[1, 2]
Recent discoveries of the molecular basis of epidermolysis bullosa have resulted in the development of new diagnostic tools, including prenatal and preimplantation testing. Based on a better understanding of the basement membrane zone (BMZ) and the genes responsible for its components, new treatments (eg, gene or protein therapy) may provide solutions to the skin fragility found in patients with epidermolysis bullosa.
Related eMedicine articles include Epidermolysis Bullosa Acquisita and Epidermolysis Bullosa (pediatrics version).
Pathophysiology
Epidermolysis bullosa is classified into 3 major categories, including (1) epidermolysis bullosa simplex (intraepidermal skin separation), (2) junctional epidermolysis bullosa (skin separation in lamina lucida or central BMZ), and (3) dystrophic epidermolysis bullosa (sublamina densa BMZ separation, as in the images below).
Dominantly inherited dystrophic epidermolysis bullosa. The blistering in this disease often is localized and is characterized by scarring and milia in healed blister sites.
Dominantly inherited dystrophic epidermolysis bullosa. This subtype, similar to other dystrophic and junctional epidermolysis bullosa subtypes, can result in nail dystrophy and loss. Researchers have proposed a new category termed hemidesmosomal epidermolysis bullosa, which produces blistering at the hemidesmosomal level in the most superior aspect of the BMZ. Epidermolysis bullosa simplex usually is associated with little or no extracutaneous involvement, while the more severe hemidesmosomal, junctional, and dystrophic forms of epidermolysis bullosa may produce significant multiorgan system involvement.[3, 4]
Significant progress has been achieved in finding specific molecular therapies for epidermolysis bullosa, including protein and gene therapy. Type VII collagen and laminin-5 gene therapy have been proven effective through in vivo models. Type VII collagen protein therapy has similarly been shown to be effective in an in vivo model. Currently, these therapies are being extensively studied at the preclinical stage, in animal models.
Epidemiology
Frequency
United States
Assuming that mild cases of epidermolysis bullosa simplex are reported only 10% of the time, the affected population in the United States is approximately 12,500 persons. According to a National Epidermolysis Bullosa Registry report,[5] 50 epidermolysis bullosa cases occur per 1 million live births. Of these cases, approximately 92% are epidermolysis bullosa simplex, 5% are dystrophic epidermolysis bullosa, 1% are junctional epidermolysis bullosa, and 2% are unclassified. Patients with hemidesmosomal epidermolysis bullosa probably constitute much less than 1% of total epidermolysis bullosa cases.
International
According to the National Epidermolysis Bullosa Registry,[5] the number of epidermolysis bullosa cases in Norway is 54 cases per million live births, in Japan is 7.8 cases per million live births, and in Croatia is 9.6 cases per million live births.
Mortality/Morbidity
Infancy is an especially difficult time for epidermolysis bullosa patients. Generalized blistering caused by any subtype may be complicated by infection, sepsis, and death. Severe forms of epidermolysis bullosa increase the mortality risk during infancy. Patients with the Herlitz or letalis form of junctional epidermolysis bullosa have the highest risk during infancy with an estimated mortality rate of 87% during the first year of life. In patients with epidermolysis bullosa that survive childhood, the most common cause of death is metastatic squamous cell carcinoma (SCC), as in the image below.
Recessively inherited dystrophic epidermolysis bullosa, squamous cell carcinoma This skin cancer occurs specifically in patients with recessively inherited epidermolysis bullosa who most commonly are aged 15-35 years. In contrast, dominantly inherited epidermolysis bullosa simplex and dystrophic epidermolysis bullosa and milder forms of junctional epidermolysis bullosa may not affect a patient's life expectancy adversely.
One study reported that from 1979-2002, the overall age-adjusted annual mortality annual mortality rate from bullous skin diseases 0.103 death per 100,000 population (2000 US standard population).[6]
Age
Onset of epidermolysis bullosa is at birth or shortly after. The exception occurs in mild cases of epidermolysis bullosa simplex, which may remain undetected until adulthood or occasionally remain undiagnosed.
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