Disadhesion of epidermal keratinocytes: A histologic clue to palmoplantar keratodermas caused by DSG1 mutations

Background: Recent developments in molecular genetics may lead to re-examination of the histopathology of inherited palmoplantar keratodermas (PPKs) based on more precise groupings of the various entities and syndromes. Objective: We sought to characterize the histopathological findings in PPKs associated with mutations in DSG1, which encodes desmoglein 1. Methods: We studied the histopathology of 3 cases of keratosis palmoplantaris striata type T and one case of diffuse PPK, all associated with autosomal-dominant mutations in DSG1. Our cases for comparison included 4 cases with Mal de Meleda PPK associated with autosomal-recessive SLURP1 mutations, one case with pachyonychia congenita type II PPK associated with an autosomal-dominant KRT17 mutation, and one case with focal PPK associated with an autosomal-dominant KRT16 mutation. Results: The distinguishing histopathological features of the 3 keratosis palmoplantaris striata type 1 cases and the diffuse PPK case associated with DSG1 mutation were: varying degrees of widening of the intercellular spaces and partial disadhesion of keratinocytes in the mid and upper epidermal spinous cell layers, often extending to the granular cell layer. These findings, which are associated with haploinsufficiency of desmoglein 1, were not observed in any of the other 6 PPK cases. Mild perinuclear eosinophilic condensations and cytoplasmic vacuolizations were observed in the spinous cell layer keratinocytes of the pachyonychia congenita type II PPK and the nonspecified focal PPK cases. Limitations: There were a limited number of patients and control patients with hereditary PPKs. Conclusion: Widening of the intercellular spaces and disadhesion of epidermal keratinocytes may serve as a histologic clue to PPKs caused by DSG1 mutations. (J Am Acad Dermatol 2010;62:107-13.)