Porokeratosis 6, Multiple Types

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), reports of several families with expression of more than one variant of porokeratosis among members, and of individuals expressing more than one variant, suggest 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).

Clinical Features

Wei et al. (2004) reported a large 4-generation family from the Anhui province in China with disseminated superficial porokeratosis (DSP). The youngest affected individual was a girl who developed annular brown scaling lesions with central atrophy in a linear array on her right arm at age 10 years, consistent with linear porokeratosis. The lesions slowly increased in size and number, and she later developed lesions on the finger of her right hand and neck. Histopathologic examination showed cornoid lamella with absent granular layers below the parakeratotic column. Examination of family members revealed 10 affected individuals, including the proband's father, all of whom developed 0.3 to 0.5-cm annular lesions initially on their faces at age 20 years or younger. The lesions slowly evolved onto the limbs, chest, and back. As the disease progressed, the lesions grew to 0.5 to 1 cm, with an elevated slightly dark-brown border and slightly atrophic center. Wei et al. (2004) noted that, except for the girl who had linear porokeratosis, all affected family members had lesions in sun-exposed as well as non-sun-exposed areas.

Mapping

By genomewide linkage analysis of a Chinese family with disseminated superficial porokeratosis, Wei et al. (2004) identified an 18.7-cM (5.6-Mb) region on chromosome 18p11.3 between the telomere and D18S391 (maximum 2-point lod score of 4.82 at D18S1138).