Porokeratosis 4, Disseminated Superficial Actinic Type

Description

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 as well as individuals expressing more than one variant have been reported, suggesting that the distinctions among these variants may be artificial.

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.

Mapping

Xia et al. (2000) identified a locus at chromosome 12q23.2-q24.1 responsible for DSAP in a large Chinese family (DSAP1). To narrow the candidate region and identify the disease gene, Xia et al. (2002) studied another 3-generation Chinese family, consisting of 37 individuals of whom 16 (9 males and 7 females) were affected and originating from a rural area of Hunan Province. Linkage analysis using markers from chromosome 12 suggested that the disorder in this family was not linked to chromosome 12q. By a genomewide scan and fine mapping with 17 microsatellite markers on chromosome 15, Xia et al. (2002) obtained a maximum 2-point lod score of 6.87 (theta = 0) at marker D15S152. They estimated that the disease gene should be located in a 6.4-cM region flanked by D15S1023 and D15S1030 on chromosome 15q25.1-q26.1.