Palmar and plantar pads and flexion creases of genetic polydactyly mice (Pdn)

Attempts to gain a better understanding of the relationship between the epi dermal ridge patterns (dermatoglyphics) and flexion creases on the volar as pects of human hands and feet and specific medical disorders led to a searc h for a suitable animal model, allowing studies of the fetal development of the pertinent structures. A common experimental animal, the rat (Rattus no rvegicus), was found to be an excellent candidate, owing to the strong rese mblance of the volar pads and flexion creases on its palmar and plantar sur faces to those of human subjects. A hereditary preaxial polydactyly mouse ! Pdn) provides an opportunity to study the effects of this malformation on t he surrounding morphological structures and, specifically, on the volar pad s, i.e., the sites over which the dermatoglyphic patterns develop. The hands and feet of the wild-type (+/+) mice show no anomalies, and their major pad and flexion crease configurations correspond to those of normal rats. The heterozygous (Pdn/+) mice, in spite of having a thumb/big toe wit h a duplicated distal phalanx on their hands/feet, did not display any alte rations in palmar/plantar pads. The homozygous (Pdn/Pdn) mice have a protru sion in the thenar area and one to three supernumerary digits on the preaxi al portion of both the hands and feet. The effect of these anomalies was fo und to be limited to the pad and flexion crease configurations in the preax ial areas; the postaxial sites were not affected. The original number of pa ds on the thenar/first interdigital areas of Pdn/Pdn mice was apparently id entical to that of the +/+ and Pdn/+ mice. The preaxial protrusion, however , affected the number, size, and location of the pads observed in the newbo rn mice, resulting in varying pad configurations, such as fused and scatter ed pads or a pad cluster formed by gathering the neighboring pads. These pa d modifications were induced by the preaxial plantar/palmar protrusion only and were not affected by the presence of supernumerary preaxial digits. In view of the similarities in the morphology and fetal development of human and mouse distal limbs, the present study is relevant to human subjects, pa rticularly to the understanding of the significance of dermatoglyphic varia tions in individuals with specific medical disorders. Future studies of nat urally occurring or experimentally induced limb malformations in mice or ra ts should provide valuable insights into the development of human hands and feet and into factors contributing to their congenital anomalies. (C) 1999 Wiley-Liss, Inc.