Classical DDD is caused by mutations in the KRT5 gene, encoding for keratin 5 (K5) that is normally paired with keratin 14 (K14) to assemble intermediate filaments; in DDD, K5 is truncated, resulting in abnormal intracellular perinuclear architecture of intermediate filaments [99]. The gene discussed is KRT5; the disease is Dowling-Degos disease 1.