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Identification of a novel S249C FGFR3 mutation in a keratinocytic epidermal naevus syndrome

MADAM, Epidermal naevi (ENs) are benign skin lesions that usually follow the lines of Blaschko and represent a genetic mosaicism affecting the epidermis. The mosaicism may be more widespread and extend to other organ systems, e.g. skeletal system, eye and central nervous system (CNS), which is then referred to as an EN syndrome. There are several more or less well-defined types of EN syndromes, defined by the phenotype, the molecular findings or a combination of both. The knowledge about the molecular basis of these EN syndromes has expanded over recent years. A particular type of keratinocytic EN associated with abnormalities of other organs has been referred to as ‘fibroblast growth factor receptor 3 EN syndrome’ or ‘Garcı́a–Hafner–Happle syndrome’. Keratinocytic EN is a descriptive umbrella term for nonorganoid, nonepidermolytic ENs that can be classified in different (sub)types by their genetic background. The few reported cases of keratinocytic EN syndrome with FGFR3 mutations all had a p.R248C mutation. We report the first case of a keratinocytic EN syndrome caused by an FGFR3 p.S249C mutation, indicating that other FGFR3 mutations apart from p.R248C can define keratinocytic EN syndrome as well. A 40-year-old woman showed nonsymmetrical skin lesions following the lines of Blaschko (Fig. 1a,b), with streaks of light brownish, papillomatous changes of her skin on the left side of the trunk (sharply demarcated in the midline), the upper arm, the neck, and, less severe, in the face and scalp.