[Pachyonychia congenita. Keratin gene mutations with pleiotropic effect].

Pachyonychia congenita (PC) comprises a heterogeneous group of autosomal dominantly inherited conditions showing characteristic nail thickening and associated signs such as palmoplantar keratoderma, follicular keratoses, and mucosal leukokeratoses. Less frequently epidermal cysts, hairshaft abnormalities, natal teeth and laryngeal involvement may be seen. Phenotypically and genetically two major forms of PC are recognized, pachyonychia congenita Jadassohn-Lewandowsky/PC type I (Medelian inheritance in man-MIM-167200) and pachyonychia congenita Jackson-Lawler/PC type II (MIM 167210). Both conditions show nail deformities, focal palmoplantar keratoderma, and follicular hyperkeratoses. Diagnostically relevant are leukokeratoses of the oral mucosa in patients with PC type I. In contrast individuals affected with PC type II show premature dentition and multiple pilosebaceous cysts predominantly affecting the upper trunk. The latter closely resemble eruptive vellus hair cysts and steatocystoma multiplex. By mutational analysis keratin K6a and K16 gene mutations have been detected in patients with PC type I, and keratin K6b and K17 gene mutations have been shown to be the underlying genetic defect in patients with PC type II.