A human polydactylous left foot with 9 toes, amputated from an
11-mo-old child, was examined by x-ray
and magnetic resonance imaging and by gross dissection to identify the
digits. The normal sequence of toes
from 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 displaced
dorsally and were found to have 2 extensor tendons, no flexor tendons
and nails that were conical and
situated at their tips. These toes resembled those described as
‘double-dorsal’ and which develop in paws of
mice in which a gene normally expressed ventrally is functionally
inactivated (Loomis et al. 1996).
Specification of toe formation occurs in leg buds early in embryonic
development and later there is rotation
of the limb so that the anterior (rostral) part comes to lie medially,
i.e. the hallux which was anterior
(rostral) now is on the inner (medial) side of the foot. A disruption
in the patterning of this foot in both
anteroposterior (rostral-caudal) and dorsoventral axes during
development could be responsible.