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 MVD gene have been found to cause multiple types of porokeratosis, which have been described as disseminated superficial actinic porokeratosis (DSAP), nonactinic disseminated superficial porokeratosis (DSP), solar facial porokeratosis, linear porokeratosis, and hyperkeratotic porokeratosis. The preferred title of this entry was formerly 'Porokeratosis 7, Disseminated Superficial Actinic Type; POROK7.' Disseminated superficial actinic porokeratosis (DSAP) is the most common subtype of porokeratosis. It is characterized by multiple small, annular, anhidrotic, keratotic lesions that are located predominantly on sun-exposed areas of the skin, such as the face, neck, and distal limbs. The lesions typically begin to develop in adolescence and reach near-complete penetrance by the third or fourth decade of life (summary by Wu et al., 2004 and Zhang et al., 2012). For a discussion of genetic heterogeneity of porokeratosis, see 175800. [from OMIM]