Linear Porokeratosis Associated with Disseminated Superficial Actinic Porokeratosis: A New Example of Type II Segmental Involvement

: The coexistence of linear porokeratosis (LP) and disseminated superficial actinic porokeratosis (DSAP) in a 3‐year‐old girl with a family history of DSAP is presented. Happle proposed loss of heterozygosity (LOH) to explain the origin of this unusual phenomenon. Homozygosity would explain why lesions in LP are far more pronounced than those of the associated heterozygous DSAP lesions. LOH would also explain the early age of presentation of the linear lesions, the family history of DSAP, and why LP cases are particularly prone to malignant transformation. This case is also important for molecular studies because of the presence of heterozygous and homozygous mutated cells in the same patient and the familial occurrence of the heterozygous form of the disease.