A POLYDACTYLOUS HUMAN FOOT WITH DOUBLE-DORSAL TOES

A human polydactylous left foot with 9 toes, amputated from an 11-mo-o ld child, was examined by x-ray and magnetic resonance imaging and by gross dissection to identify the digits. The normal sequence of toes f rom medial to lateral is 1, 2, 3, 4, 5. Examination of the morphology of tendons and muscles suggested the toe sequence was 1, 2, 3/4, ?,5 2 , 3/4, 3/4, 5. The 2 toes in the sequence that are underlined were dis placed dorsally and were found to have 2 extensor tendons, no flexor t endons and nails that were conical and situated at their tips. These t oes resembled those described as 'double-dorsal' and which develop in paws of mice in which a gene normally expressed ventrally is functiona lly inactivated (Loomis et al. 1996). Specification of toe formation o ccurs in leg buds early in embryonic development and later there is ro tation of the limb so that the anterior (rostral) part comes to lie me dially, i.e. the hallux which was anterior (rostral) now is on the inn er (medial) side of the foot. A disruption in the patterning of this f oot in both anteroposterior (rostral-caudal) and dorsoventral axes dur ing development could be responsible.