Ectrodactyly

Terminal transverse defects are a broad category limb dysplasias where there is absence or hypoplasia of the distal limbs with relatively intact proximal structures. More severe forms of terminal transverse defects include hemimelia or amelia.

Ectrodactyly (from the Greek ektroma, abortion and daktylos, finger) is a subcategory of terminal transverse defects that refers to the absence of more distal elements and can include aphalangia (absence of phalange(s)), adactylia (absence of finger(s)), or the entire hand (acheiria). The feet are uncommonly affected.

Split-hand/-foot malformations are a class of ectrodactyly that can present as absence of a central ray resulting in a cleft (as seen in the first case above), or absence of the radial rays with monodactyly of the fifth digit.

The 'lobster claw' deformity is a type of split-hand/-foot malformation, where there is absence of the middle digit with formation of a cleft hand, and syndactyly of the digits on either side of the cleft. This deformity is associated with ectrodactyly-ectodermal dysplasia-cleft palate (EEC, Walker-Clodius) syndrome and autosomal dominant ectrodactyly syndrome.

Ectrodactyly is a rare condition, with sporadic ectrodactyly being more common than syndromic presentations. A notable exception is the Vadoma tribe of Zimbabwe, in whom the condition is more common.

References

• Leung KY, MacLachlan NA, Sepulveda W. Prenatal diagnosis of ectrodactyly: the 'lobster claw' anomaly. Ultrasound Obstet Gynecol. 1995 Dec;6(6):443-6.
• Schwabe GC, Mundlos S. Genetics of congenital hand anomalies. Handchir Mikrochir Plast Chir. 2004 Apr-Jun;36(2-3):85-97.