MECHANOBULLOUS DISEASE (EPIDERMOLYSIS BULLOSA, 'EB'):

These are due to inherited abnormalities in structural skin proteins which lead to 'skin fragility'. The resultant blistering tends to arise secondary to trauma and often appears at or shortly after birth. These conditions can be a mild inconvenience, severely disabling or fatal but fortunately are very rare. There are three groups of disorders in which the fundamental gene/protein abnormalities have been characterized. This enables prenatal amniocentesis diagnosis.
Epidermolysis bullosa simplex
This is a group of autosomal dominant genodermatoses characterized by 'superficial' blistering owing to mutations of cytoskeleton proteins within the basal layer of the epidermis, e.g. keratin 5 (chromosome 12q) or keratin 14 (chromosome 17q). Most forms of EB simplex show mild disease with intermittent blistering of the hands and feet, especially in hot weather. The teeth and nails are normal and scarring is absent.
Epidermolysis bullosa dystrophica
This group of genodermatoses is characterized by 'deeper' blistering associated with scarring and milia formation. The level of split is deep within the basement membrane and is due to a mutation in the COL-7A1 gene (locus at chromosome 3p21.1) which causes a loss of collagen VII in the anchoring fibrils. Nails, mucosae and even the larynx are often involved. The autosomal dominant variety is milder but the autosomal recessive type produces severe disease with disabling scarring, fusion of digits, joint contractures and dysphagia. Life expectancy is significantly reduced. Repeated scarring results in the development of multiple squamous cell carcinomas and most die from this complication in early adult life. The average life expectancy after the appearance of the first squamous cell carcinoma is 5 years.
Junctional epidermolysis bullosa
This, the most severe form, is characterized by a split in the lamina lucida of the basement membrane and is due to mutations in various proteins, mainly laminin 5 but also α6β4 integrin or the 180 kDa bullous pemphigoid-2 antigen. It presents at birth with widespread blistering and areas of absent skin. Erosions of the central face and hoarseness from laryngeal involvement are common. Nail and teeth abnormalities are also common. Both a lethal and a rarer non-lethal form of junctional EB exist and they show an autosomal recessive inheritance. The lethal form causes death in infancy or early childhood.
Investigation and treatment
Investigation and treatment of EB should be carried out in a specialist centre. Diagnosis at birth on clinical grounds is difficult and should be avoided. Exact diagnosis depends on ultrastructural analysis of induced blisters in the skin and immunohistochemistry. Only then can prognosis and genetic counselling be given accurately to parents. Prenatal diagnosis is available for the more severe forms of EB.

FURTHER READING
Allen J et al. (2003) Linear IgA disease. British Journal of Dermatology 149: 977-985, 1055-1058.
Cooper et al. (2003) Treatment of resistant pemphigus vulgaris with an anti-CD20 monoclonal antibody (rituximab). Clinical and Experimental Dermatology 28: 366-368.
Diaz LA, Giudice GJ (2000) End of the century overview of skin blisters. Archives of Dermatology 136: 106-112.
Fine J-D et al. (2000) Inherited epidermolysis bullosa comes into the new millennium. Journal of the American Academy of Dermatology 43: 135-137.
Harman KE et al. (2003) Guidelines for the management of pemphigus. British Journal of Dermatology 149: 926-937.
Trent JT et al. (2003) Epidermolysis bullosa: identification and treatment. Advances in Skin & Wound Care 16: 284-290.
Wojnarowska F et al. (2002) Guidelines for the management of bullous pemphigoid. British Journal of Dermatology 147: 214-221.