Keratosis palmoplantaris cum degeneratione granulosaQ82.8

The name and description of "keratosis palmoplantaris cum degeneratione granulosa" is only used here for historical reasons. In fact, this autosomal-dominantly inherited flat palmoplantar keratosis is referred to as keratosis palmoplantaris diffusa with mutation in KRT9 . Its clinical variability is explained by 26 mutations in the KRT9 gene (17q12-q21) that have been identified to date. KRT9 is possibly a heterodimer partner for keratin 6C (KRT6C) (Li P et al. 2023). Mutations in KRT6C are associated with a mild form of pachyonychia congenita.

Most likely, epidermolytic palmoplantar keratosis type Vörner (EPPK) and palmoplantar keratosis type Unna-Thost are distinct variants of the same disease. However, it is possible that they are one and the same disease(PPK type Unna-Thost-Vörner).

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 diffuse palmoplantar keratosis with non-epidermolytic hyperkeratoses and with an underlying mutation in the aquaporin 5 gene (AQP5, 12q13.12), it 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.

1. Devos SA et al. (2003) An unusual case of palmoplantar keratoderma. J Eur Acad Dermatol Venereol 17: 68-69
2. Küster W et al (1995) Keratosis palmoplantaris diffusa Vörner. Dermatologist 46: 705-10

3. Li P et al. (2023) Proteomic profiling reveals KRT6C as a probable hereterodimer partner for KRT9: New insights into re-classifying epidermolytic palmoplantar keratoderma (EPPK) and a milder form of pachyonychia congenita (PC-K6c) as a group of genetic cutaneous disorders. J Proteomics 287:104971.

4. Loh TH et al. (2003) Palmar-plantar keratoderma of Unna Thost associated with atopic dermatitis: an underrecognized entity? Pediatr Dermatol 20: 195-198
5. Lucker GPH et al. (1994) Topical calcipotriol in the treatment of epidermolytic palmoplantar keratoma of Vörner. Br J Dermatol 130: 543-5
6. Maruyama R (1999) A case of Unna-Thost disease accompanied by Epidermophyton floccosum infection. J Dermatol 26: 63-66
7. Mofid MZ et al. (1998) Hereditary epidermolytic palmoplantar keratoderma (Vorner type) in a family with Ehlers-Danlos syndrome. J Am Acad Dermatol 38(5 Pt 2): 825-830
8. Reis A et al. (1994) Keratin 9 gene mutations in epidermolytic palmoplantar keratoderma (EPPK). Nat Genet 6: 174-179
9. Thost A (1880) On hereditary ichtyosis palmaris et plantaris cornea. Dissertation (Heidelberg)
10. Unna PG (1883) On the keratoma palmare et plantare hereditarium. Vierteljahrsschr Derm Syph (Vienna) 15: 231
11. Vorner H (1901) Zur Kenntniss des Keratoma hereditarium palmare et plantare. Arch Derm Syph 56: 3-31
12. Yang JM (1998) Mutations in the 1A rod domain segment of the keratin 9 gene in epidermolytic palmoplantar keratoderma. Acta Derm Venereol 78: 412-416