Similarities between a conjoined nail and the palmar nail syndrome.

The congenital palmar nail syndrome consists of a triad of palmar nail, absent finger flexion and abnormalities of the distal phalanx. There are two main theories about the pathogenesis of this syndrome: the ancestral reversion theory and the duplication theory. In this paper, similarities between a conjoined nail in conjoined twins and the palmar nail syndrome are described to support the duplication theory.