Transposable elements and the lines of Blaschko: A new perspective

Background: Transposable elements or retrotransposons are particles of retroviral origin that are interspersed in large numbers in the genome of plants and animals. They may affect the activity of adjacent genes by methylation or demethylation, resulting in silencing or activation of gene expression. In animals such as mice or dogs, retrotransposons may give rise to phenotypic variation in the form of variegated coat patterns reminiscent of the lines of Blaschko as observed in human skin. Objective and Methods: Because the human genome does likewise contain large amounts of retrotransposons, it is conceivable that these elements may cause similar skin lesions in human skin. The group of genodermatoses following the lines of Blaschko was therefore screened for phenotypes suggesting such an epigenetic origin. Results: As possible examples, the inflammatory linear verrucous epidermal nevus as well as cases of pigmentary mosaicism arranged in hypermelanotic or hypomelanotic streaks following the lines of Blaschko may be taken into consideration. Such phenotypes usually occur sporadically but may affect, by way of exception, several members of a family. Conclusion: These linear skin disorders would possibly visualize the action of a transposable element that is partly expressed and partly silenced at an early developmental stage. Copyright (C) 2002 S. Karger AG, Basel.