Type 1 segmental manifestation of Hailey-Hailey disease.

Two types of mosaic manifestations can be distinguished in autosomal dominant skin disorders. A type-1 mosaicism reflects a localized postzygotic mutation in an otherwise normal embryo. This mutation leads to a localized population of heterozygous cells, resulting in segmental disease. In contrast, a type-2 mosaicism represents a postzygotic mutation eliminating the normal allele at a gene locus, for which the embryo carries a dominant heterozygous germline mutation. The corresponding phenotype is characterized by segmental lesions superimposed on "classical" disease. The authors describe the clinical and histopathologic aspects of the first case of type-1 segmental manifestation of Hailey-Hailey disease.