tooth and nail syndrome tooth and nail syndrome tooth and nail syndrome (also known as "hypodontia with nail dysgenesis," and "witkop syndrome") is a rare disorder, first described in 1965, characterized by nails that are thin, small, and friable, and which may show koilonychia at birth.: 521 tooth and nail syndromeother nameshypodontia with nail dysgenesisspecialtymedical genetics it is associated with msx1.