[How are the Blaschko lines arranged on the scalp?].

Linear inherited or nevoid skin lesions mostly follow a characteristic pattern which was delineated by Blaschko in 1901. The system of lines published by this author covered the entire human body, with the exception of the scalp because of lack of pertinent case reports regarding this area. We here report an observation which enables us to fill the blank area in the atlas of the lines of Blaschko. On the scalp of a girl affected with the oral-facial-digital syndrome, we observed an alopecia distributed in several spiral streaks. The pattern resembled that of the normal vertex, but the direction of the hairless streaks did not correspond completely to the direction of hair growth. As the oral-facial-digital syndrome is inherited as an X-linked dominant trait, the linear alopecia probably reflects functional X-chromosome mosaicism. Arguments are presented in favor of the assumption that the hairless streaks of this child follow the lines of Blaschko.