Widespread epidermal nevus with a postzygotic FGFR3 mutation

Dear Editor, Epidermal nevus syndrome (ENS) is a congenital disorder characterized by widespread linear epidermal lesions consisting of keratinocytic epidermal nevi (KN) and organoid nevi, and extracutaneous involvements, especially of the central nervous system and skeletal system. ENS is divided into several distinct subtypes according to the responsible genes, including fibroblast growth factor receptor 3 (FGFR3). Here, we report a case of extensive KN caused by a postzygotic missense mutation of FGFR3, but failure to detect systemic involvement. A 9-year-old Japanese girl presented with widespread nevoid lesions along Blaschko’s lines on the left hemilateral aspect of the body (Fig. 1a). Linearly distributed brownish macules had been noted since 6 months of age, and they had gradually changed into verrucous lesions at 6 years of age (Fig. 1b–d). Her family history was unremarkable and mental and skeletal growth was normal (height at 9 years old, 136.0 cm [~75 percentile]). Histopathology showed marked papillomatosis with moderate acanthosis and hyperkeratosis, but without sebaceous hyperplasia (Fig. 1e). The genomic DNA of the epidermis was separately extracted from the verrucous lesion, the macular lesion and the clinically normal area. The direct sequencing following polymerase chain reaction revealed a missense mutation of FGFR3, R248C, in both the verrucous