*3.3.1. Polydactyly*

Polydactyly is a limb malformation, characterized by additional digit(s) in the limbs (**Figure 4A** and **B**) [23]. There can be preaxial, postaxial, or median polydactyly, corresponding to extra digits on the radial or tibial sides, ulnar or fibular sides, or in between medial fingers, respectively [24].This malformation is more likely to occur in the hands than in the feet, and can be estimated at CS 16 [25]. The prevalence varies across races, and occurs more frequently in the right hand than the left, among the Japanese. Its frequency on each finger may also vary; the highest to lowest being in the order: thumb, little finger, middle finger, ring finger, and index finger in the Japanese population. Polydactyly is one of the most common hereditary malformations of the extremities, with *GLI3* and *SHH* genes being responsible [23]. The extra digit in preaxial polydactyly may be surgically treated after 8–12 months of birth, whereas that of postaxial polydactyly is dissected shortly after birth.

Ectrodactyly, or oligodactyly refers to malformations of the limb such that there are digits less than 5, arising from either ulnar deficiency, radial deficiency, or median deficiency (cleft hand/foot) [26]. **Figure 4C** shows a cleft hand with four distinct digits, with a large gap in

**Figure 4.** Congenital anomalies of extremities. (A) Polydactyly in hand; (B) polydactyly in foot; (C) cleft hand, (D)

Congenital Anomalies in Human Embryos http://dx.doi.org/10.5772/intechopen.72628 31

The inheritance of cleft hand is autosomal dominant, caused by deletions or mutations in autosomes such as chromosomes 2, 3, 7, and 10. For example, the deletion in chromosome 2 results not only in ectrodactyly, but also in microcephaly, micrognathia, low-set ears, and mental retardation. Although ectrodactyly is often associated with other malformations, a single family has been reported for the inheritance of isolated ectrodactyly resulting from X-linked recessive inheritance [26]. Another well-known syndrome that is associated with this malformation is EEC (ectrodactyly-ectodermal dysplasia-cleft lip/palate) syndrome, which

between the second and third digits, presenting a lobster claw-like feature.

sirenomelia, lateral view, and (E) sirenomelia, anterior view.
