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Porokeratosis is a morphologically distinct disorder of keratinization, characterized clinically by hyperkeratotic papules or plaques surrounded by a thread-like elevated border that expands centrifugally. Histologically, a thin column of parakeratotic cells extends throughout the stratum corneum and is seen in all variants. This distinctive histopathologic feature, known as the cornoid lamella, corresponds to the raised hyperkeratotic border evident clinically.
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At least six clinical variants of porokeratosis are recognized; however, the clinical distinction between these morphological variants may not be justified (Box 52-1). Reports of one type of porokeratosis coexisting with other forms and different types developing in multiple members of an affected family suggest more similarities than disparities, particularly in the disseminated forms.1–3
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Porokeratosis is a genetically heterogeneous disorder with multiple loci identified to date; however, the pathogenetic mechanisms remain elusive. Loci at chromosome bands 12q23.2–24.1 and 15q25 (DSAP1 and DSAP2) have been reported in familial disseminated superficial actinic porokeratoses; a further locus has been identified for disseminated superficial porokeratosis (DSP) at 18p11.3.4,5 The locus at DSAP1 corresponds to a candidate gene, SART3 (squamous cell antigen recognized by T cells 3); this encodes a tumor rejection antigen thought to be involved in the regulation of messenger RNA splicing. Fine mapping of the locus at DSAP1 has also revealed mutations in another potential candidate gene, SSH1 (slingshot 1), and a variation in the promoter region of ARPC3, which play a key role in actin dynamics....