Type 2 segmental Darier disease.

A 45-year-old man had bilateral disseminated involvement of Darier disease, and two of his sisters likewise had lesions suggesting this trait. Remarkably the propositus showed, in addition, a unilateral, systematized, segmental pattern of excessively pronounced Darier lesions. This unusual case can be taken as an example of type 2 segmental Darier disease. In contrast to the type 1 segmental manifestation that develops from a new mutation occurring in an otherwise healthy embryo, the type 2 segmental involvement would originate in a heterozygous embryo from postzygotic loss of the corresponding normal allele, resulting in a cell clone that is either homozygous or hemizygous for the mutation. This concept would explain why the segmental lesions were excessively pronounced and superimposed on the ordinary trait. Future studies may show whether the concept of type 2 segmental Darier disease can be confirmed at the molecular level.