Mutations in the keratin 9 gene (KRT9) have been shown to cause epidermolytic palmoplantar keratoderma (EPPK; OMIM 144200), an autosomal dominant genodermatosis characterized clinically by diffuse hyperkeratosis limited to the palms and soles, and histologically by epidermolysis in suprabasal layers of the epidermis.
The epidermis showed hyperkeratosis and acanthosis by histologic studies and stained positively for keratin 9 in all of the suprabasal keratinocyte layers like palmoplantar-type skin.