Ectodermal dysplasia-skin fragility syndrome.

Pathogenic mutations have now been described in ten different desmosomal proteins: plakophilin 1 (PKP1) and 2 (PKP2); desmoplakin; plakoglobin; desmoglein 1, 2, and 4; desmocollin 2, and 3 corneodesmosin. Nevertheless, the first report of an inherited desmosomal gene disorder, published in 1997, involved loss-of-function mutations on both alleles of PKP1, the PKP1 gene. Loss of PKP1 expression in human skin leads to skin erosions and crusting, notably with perioral fissuring as well as palmoplantar hyperkeratosis with painful cracking of the skin. Other more variable features include abnormalities of ectodermal development with growth delay, hypotrichosis or alopecia, hypohidrosis, and nail dystrophy. In contrast to some other inherited disorders of desmosomes, there is no cardiac pathology in individuals with PKP1 mutations since it is not expressed in the heart. The collection of clinical features in individuals with PKP1 mutations has been termed ectodermal dysplasia-skin fragility (ED-SF) syndrome. This genodermatosis is classified as a suprabasal form of epidermolysis bullosa simplex and thus far there have been 10 published cases. Skin biopsy shows acanthosis, acantholysis, and a reduced number of small, poorly formed desmosomes. Loss of PKP1 expression results in an integral weakness within the desmosomal plaque, leading to desmosomal detachment and cell-cell separation. Thus, the clinicopathologic features attest to the significant role of PKP1 in stabilization of desmosome structure and function, predominantly in the spinous layers of the epidermis. This article reviews the clinical, structural, and molecular pathology of this genetic disorder of desmosomes.