[Segmental type 1 manifestation of Darier disease. An example of cutaneous mosaicism].

A 45-year old man presented with red-brown hyperkeratotic papules that were distributed in an unilateral segmental fashion on the right thorax. Histopathological examination revealed acanthosis and, in particular, acantholysis and dyskeratosis in the basal and suprabasal epidermal layers. Based on the clinical and histopathologic findings we diagnosed a type 1 segmental Darier disease. Darier disease is an autosomal dominant disorder that is caused by mutations in the ATP2A2 gene and is characterized by dysfunctional adhesion between neighboring keratinocytes. The type 1 segmental manifestation reflects a de novo postzygotic somatic mutation in the heterozygous state and as a rule can be found in all autosomal dominantly inherited genodermatoses.