title: Phacomatosis pigmentokeratotica is a "pseudodidymosis".
abstract: In phacomatosis pigmentokeratotica, papular nevus spilus coexists with nevus sebaceus. The disorder was thought to be a didymosis with early postzygotic recombination. In this issue, however, Groesser and co-workers provide a new concept. Both nevi originate from a single heterozygous HRAS mutation in a pluripotent progenitor cell. This new understanding has implications for other proposed examples of didymosis in humans.
authors.affiliation: Department of Dermatology, Freiburg University Medical Center, University of Freiburg, Freiburg, Germany. rudolf.happle@uniklinik-freiburg.de
authors.forename: Rudolf
authors.initials: R
authors.lastname: Happle
mesh_terms: D005260:Female; D006801:Humans; D039902:Multipotent Stem Cells / Q000502:physiology*; D009508:Nevus, Pigmented / Q000235:genetics* / Q000473:pathology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics*; D012878:Skin Neoplasms / Q000235:genetics* / Q000473:pathology*
chemical_list: C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)