KRT9 and pachyonychia congenita: Defects in the α-helical rod pattern include autosomal dominant conditions, namely epidermolysis bullosa simplex (mutations in the keratin 5 and keratin 14 genes), epidermolytic ichthyosis (mutations in the keratin 1 and keratin 10 genes), pachyonychia congenita (type 1 involves keratin 6a and 16 mutations; type 2 involves keratin 6b and 17 mutations), and epidermolytic palmoplantar keratoderma (mutations in keratin 9) [51,76,77].