The expanding panorama of split hand foot malformation.

The split hand/foot malformation is a developmental defect of the extremities resulting from errors in the initiation and maintenance of the apical ectodermal ridge. The phenotype is genetically heterogeneous, and it can be identified either as an isolated phenotypic manifestation or as a constituent component of a malformation syndrome. This overview describes the clinical phenotype, related animal models, and the evolving genetic heterogeneity of the malformation.