Porokeratosis is a rare skin disorder characterized by one or more annular plaques with a surrounding raised horny border that spreads centrifugally. Variants of porokeratosis have been described that differ in morphologic shapes, distribution, and clinical course (Schamroth et al., 1997). However, as noted by Sybert (2010), several families with expression of more than one variant of porokeratosis among members, and individuals expressing more than one variant, have been reported, suggesting that the distinctions among these variants may be artificial. Mutations in the FDPS gene have been found to cause multiple types of porokeratosis, which have been described as disseminated superficial actinic porokeratosis (DSAP) and nonactinic disseminated superficial porokeratosis (DSP). For a discussion of genetic heterogeneity of porokeratosis, see 174800. [from OMIM]