Dermatitis herpetiformis: coeliac disease of the skin.

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Abstract
Dermatitis herpetiformis (DH) is a lifelong, gluten-sensitive, blistering skin disease with pathognomonic immunoglobulin (Ig)A deposits in the papillary dermis. Less than 10% of patients with DH have gastrointestinal symptoms suggestive of coeliac disease, yet they all have gluten-sensitive enteropathy. The rash, too, responds to gluten withdrawal. Therefore, DH provides a unique example of the frequent existence of gastroenterologically 'silent' but dermatologically active coeliac disease. DH and coeliac disease are strictly associated with class II HLA alleles A1*0501 and B1*02 encoding the HLA-DQ2 heterodimer. Coeliac disease segregates in the families of patients with DH, also supporting a shared genetic background. Monozygotic twins, one with DH and the other with coeliac disease, show that environmental, not genetic, factors seem to be responsible for the development of the rash in DH. A clinically silent but immunologically active coeliac disease in the gut could well produce IgA autoantibodies which react also with the connective tissue in the skin. The antigen for deposited IgA and its role, if any, in the blister formation in DH remains, however, to be elucidated.