| A defect in the apical ectodermal ridge (AER) will lead to which of the following types of congenital limb difference? |
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- Transverse deficiency The AER regulates proximal-to-distal limb development. Therefore, a defect in the AER results in a transverse deficiency.
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- Syndactyly Syndactyly occurs as a result of failure of apoptosis in the developing web space.
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- Constriction band syndrome Constriction band syndrome results from an amniotic band wrapping around an appendage in utero. This is a deformation rather than a malformation.
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- Mirror Hand Mirror hand occurs as a result of a duplicated zone of polarizing activity (ZPA) such that both sides of the hand are ulnarized.