Pachyonychia congenita (PC) is a group of autosomal dominant skin disorders characterized by hypertrophic nail dystrophy accompanied by other features of ectodermal dysplasia, prominently painful palmoplantar keratoderma. Additional clinical features include follicular hyperkeratosis, leukokeratosis of the oral mucosa, and various cysts (steatocysts and pilosebaceous cysts). It is caused by a mutation in one of four keratin genes KRT6A, KRT6B, KRT16, or KRT17.