Keratosis palmoplantaris cum degeneratione granulosaQ82.8

Autosomal-dominantly inherited planar palmoplantar keratosis. Most likely, epidermolytic palmoplantar keratosis type Vörner (EPPK) and palmoplantar keratosis type Unna-Thost represent either clinically and genetically distinguishable variants of the same disease or they are one and the same disease(PPK type Unna-Thost-Vörner) whose clinical expression shows a certain variation due to the 26 possible underlying mutations in the KRT9 gene (17q12-q21).

In this respect, the historical nomenclature possibly only insufficiently differentiates and defines this spectrum of manifestations with regard to the phenotypic-genotypic correlation.

In contrast, keratosis palmoplantaris diffusa circumscripta type Norrbotten(synonyms: Non-epidermolytic palmoplantar keratoderma; autosomal dominant diffuse palmoplantar keratoderma, Norrbotten type;diffuse palmoplantar keratoderma, Bothnian type) as a diffuse palmoplantar keratosis with non-epidermolytic hyperkeratoses and with underlying mutation in the aquaporin-5 gene (AQP5, 12q13.12) occupies a genetically and phenotypically clearly defined special position.

Defective structure of keratin due to point mutations in the gene for keratin 9 (KRT9), which is mapped on chromosome 17q12-q21. Mutations in the KRT1 gene are rarer.

Keratin 9 is expressed in the suprabasal layers of the epidermis and is specific for the skin on the palms of the hands and soles of the feet. Mutations in the keratin 9 gene lead to the breakdown of the keratin filament network and cytolysis of corneocytes.

Diffuse, non-transgenic cornification with sharp edges, red rim and ankle-cushion-like hyperkeratosis on the extensor sides of hands and feet, also watch-glass nails. Occasionally hyperhidrosis palmaris or plantaris.

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