The first indication of the presence of an epidermal genetic mosaic due to Ser252Trp-FGFR2 mutation in the form of acneiform nevus was documented in a 14-year-old teenage boy who presented with sharply bordered acneiform lesions along the lines of Blaschko on the left shoulder and elbow as far as the extensor aspect of the left forearm, with comedones in almost all follicles [64]. The gene discussed is FGFR2; the disease is nevus comedonicus syndrome.