Pachyonychia Congenita (PC) is a rare genetic disorder that primarily affects the skin, nails, and mouth. It is caused by a mutation in any one of four genes that code for keratin proteins. Keratins are proteins that form tough fibers that strengthen skin and things that grow out of the skin, such as hair and finger nails. Although mutations in different keratins can cause many disorders, only mutations in keratins 6a, 6b, 16, and 17 are linked to PC. This disorder does not affect lifespan, but patients do experience constant pain.