A clinical entity that may be called congenital onychodysplasia of the index fingers (COIF) was studied. This clinical entity, proposed by Iso, is characterized by anonychia, micronychia, polyonychia (or "hemionychogryposis") restricted to the index fingers. These changes are more prominent on the medial aspect of the nail than its lateral aspect. Unlike most congenital nail diseases, it is a nonhereditary, nonfamilial disease. Two patients had COIF, with bone anomalies.
Kikuchi I, Horikawa S, Amano F. Congenital Onychodysplasia of the Index Fingers. Arch Dermatol. 1974;110(5):743-746. doi:10.1001/archderm.1974.01630110037008