Pachyonychia congenita. Photo by Ali87090 via Wikimedia Commons Pachyonychia congenita (PC) is a rare genetic disorder caused by mutations in one of five keratin genes. PC produces debilitating plantar calluses and a characteristic thickening of the nails, with no approved treatment options. In a paper in Science Translational Medicine , University of Michigan investigators report that a single stress‑induced keratin, keratin 16 (K16), may help explain why the skin’s response