Genetic porokeratosis

Genetic porokeratosis refers to a group of inherited disorders of keratinization characterized by the presence of one or more atrophic patches surrounded by a distinctive ridge-like border known as a cornoid lamella, which is a column of tightly stacked parakeratotic cells visible on histopathology. This group encompasses several clinical subtypes, including disseminated superficial actinic porokeratosis (DSAP), porokeratosis of Mibelli, linear porokeratosis, porokeratosis palmaris et plantaris disseminata, and punctate porokeratosis. The skin is the primary organ system affected, with lesions typically appearing as annular or irregular keratotic plaques on sun-exposed or other body areas depending on the subtype. Genetic porokeratosis has been linked to mutations in genes of the mevalonate pathway, including MVK, PMVK, MVD, FDPS, and SLC17A9, which are involved in cholesterol biosynthesis. These mutations lead to accumulation of toxic mevalonate pathway intermediates in keratinocytes, contributing to abnormal cornification. The clinical presentation varies by subtype. Disseminated superficial actinic porokeratosis, the most common hereditary form, presents with numerous small annular lesions on sun-exposed areas, typically worsening with ultraviolet exposure. Porokeratosis of Mibelli tends to present in childhood as a single or few larger plaques, often on the extremities. Linear porokeratosis follows Blaschko lines and may appear in childhood. A significant clinical concern across all subtypes is the potential for malignant transformation, with squamous cell carcinoma and basal cell carcinoma reported to arise within longstanding lesions, estimated at 7–11% of cases in some series. There is no definitive cure for genetic porokeratosis. Treatment is primarily aimed at reducing symptoms, preventing progression, and monitoring for malignant transformation. Therapeutic options include topical agents such as 5-fluorouracil, imiquimod, diclofenac gel, and topical retinoids. Cryotherapy, laser therapy (including CO2 laser), photodynamic therapy, and surgical excision may be used for individual lesions. Sun protection is strongly recommended, particularly for DSAP. Regular dermatologic surveillance is advised due to the risk of malignant transformation. Genetic counseling is recommended for affected families.

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