Manifestation of the lines of Blaschko in women heterozygous for X-linked hypohidrotic ectodermal dysplasia.

For the detection of the carrier state of X-linked hypohidrotic ectodermal dysplasia, sweat pore counts on fingertips or palms have been used in the past. The results obtained, however, were sometimes difficult to interpret. We here describe a more reliable method, using the entire back as a test area. We provide evidence that the distribution of sweat pores in carriers is not simply patchy. In four heterozygous women we were able to demonstrate a linear distribution of hypohidrotic areas. This pattern followed the lines of Blaschko, forming a typical V-shape over the spine. Apparently, these lines reflect the dorsoventral outgrowth of two functionally different populations of cells during early embryogenesis.