Postaxial Polydactyly

► [Increased number of digits on the ulnar side of the hand]

As already mentioned in the previous section, postaxial hexadactyly (OMIM 174200) is by far the commonest form of Polydactyly, accounting for about 78 % of all Polydactylies. It is often an isolated anomaly, but can also occur in association with several malformation syndromes or with multiple other anomalies that do not clearly fit into well-defined syndromes.

Two phenotypically and possibly genetically different forms of postaxial Polydactyly are recognized (Fig. 6.25 a-c). In postaxial polydactyly type A the supernumerary digit is usually fully developed and functional and articulates with the 5th digit or with an extra metacarpal. Attempts at duplication (bifi-dity, widening) of the 5th metacarpal, rather than complete duplication, are common. With complete duplication, accessory carpals or carpal fusion may

Fig. 6.25 a-c. Chromosome 13 trisomy syndrome. a In a female newborn. A bifid 5th metacarpal is harboring the extra digit (type A of postaxial Polydactyly). b, c In a 21-day-old baby girl. Both hands display a rudimentary (skin tag) extra-digit connected with the middle portion of the 5th finger through soft tissues (type B of postaxial polydactyly).A similar pheno-type was evident in the feet

Fig. 6.25 a-c. Chromosome 13 trisomy syndrome. a In a female newborn. A bifid 5th metacarpal is harboring the extra digit (type A of postaxial Polydactyly). b, c In a 21-day-old baby girl. Both hands display a rudimentary (skin tag) extra-digit connected with the middle portion of the 5th finger through soft tissues (type B of postaxial polydactyly).A similar pheno-type was evident in the feet

Extra Digit Hand Postaxial Type

Fig. 6.26 a,b. Oro-facio-digi-tal (OFD) syndrome, undetermined type in a female infant. a Left and b right hand, showing bilateral postaxial Polydactyly and forked 5th metacarpals. Many features in this girl were consistent with type V OFD syndrome (Thurston syndrome), but the presence of cerebellar anomalies, which is typical of OFD syndrome type VI, militates against this diagnosis. (From Chung et al. 1999)

Fig. 6.26 a,b. Oro-facio-digi-tal (OFD) syndrome, undetermined type in a female infant. a Left and b right hand, showing bilateral postaxial Polydactyly and forked 5th metacarpals. Many features in this girl were consistent with type V OFD syndrome (Thurston syndrome), but the presence of cerebellar anomalies, which is typical of OFD syndrome type VI, militates against this diagnosis. (From Chung et al. 1999)

Greig Cephalo Polydactyly Syndrome

occur. A comparable anomaly occurs in the feet (in isolation, or in combination with the hand defect), often together with syndactyly of toes 4 and 5 (Castilla et al. 1998). This type of postaxial poly-dactyly is inherited as an autosomal dominant trait with marked penetrance, and the responsible gene has been mapped to the centromeric region of 7p (Radhakrishna et al. 1997), in the same region of the GLI3 gene. Disruption of the GLI3 gene is involved in different clinical syndromes. Haploinsufficiency of GLI3 is associated with some cases of Greig cephalo-polysyndactyly syndrome (OMIM 175700) (Petti-grew et al. 1991), whereas GLI3 frameshift mutations cause the Pallister-Hall syndrome (OMIM 146510), a lethal disorder of hypothalamic hamartoblastoma, postaxial polydactyly, and imperforate anus (Kang et al. 1997; Hall et al. 1980). Two additional loci for this disorder have been mapped, one to 13q (postaxial polydactyly type A2, OMIM 602085) (Akarsu et al. 1997) and the other to 19p (postaxial polydactyly type A3, OMIM 607324) (Zhao et al. 2002). Thus, there appears to be genetic heterogeneity for postaxial polydactyly. The second type of postaxial polydactyly, type B, consists of a rudimentary extra digit (pedunculated postminimi), often manifesting in the form of a skin tag. The genetics of this type is more complex. Owing to lack of penetrance, the presence of two dominant genes has been suggested (Walker et al. 1961). Based on the observation that both types A and B of postaxial polydactyly can occur in the same pedigree, it has been suggested that these are genetically identical disorders (Scott-Emuakpor and Madueke 1976; Ventruto et al. 1980). Among the chromosomal syndromes, postaxial polydactyly occurs almost exclusively with chromosome trisomy 13 syndrome (Lewandowski and Yunis 1977). In contrast, deletion of 13q leads to oligodactyly and bony syndactyly of the 4th and 5th metacarpals and metatarsals. Based on a large series of 2,271 cases of isolated (nonsyndromal) postaxial polydactyly ascertained from 1,582,289 births, it was concluded that hand and foot postaxial polydactyly are distinct entities, with different clinical and epi-demiological characteristics and a larger genetic component in the form affecting the hands than in that involving the feet (Castilla et al. 1997). In the same work, postaxial polydactyly of the hand was the most frequent type (76%), followed by foot postaxial polydactyly (15%) and hand and foot postaxial polydactyly (9%). Unlike polydactyly in the hands, which was bilateral in 50 % of cases, polydactyly in the feet was bilateral in only 19% of cases, and was associated with American Indian racial background, parental subfertility, and bleeding in the first trimester of fetal life. Polydactyly in the hands was most frequently located on the left side (77 %) and was associated with African Black ethnicity, male sex, twinning, and parental consanguinity. The variety involving both hands and feet showed the highest frequency of associated congenital defects.

Postaxial Polydactyly is an important manifestation of some types of oro-facio-digital (OFD) syndrome, a heterogeneous group of disorders characterized by anomalies of the face, oral cavity, and digits. Nine different syndromes have been delineated (Jones 1997; Toriello 1993). Bilateral postaxial Polydactyly of hands occurs in the following types: OFD type II (Mohr syndrome, OMIM 252100), an autosomal recessive, together with partial reduplication of hallux, midline cleft of tongue, and conductive deafness (Mohr 1941); OFD type III (Sug-arman syndrome, OMIM 258850), an autosomal recessive, in association with a bulbous nose, extra teeth, eye abnormalities, and bifid uvula (Sugarman et al. 1971); OFD type 7 (Thurston syndrome, OMIM 174300), an autosomal recessive, together with midline cleft lip, and duplicated frenulum (Fig. 6.26 a,b) (Thurston 1909); and OFD type VI (Varadi-Papp syndrome, OMIM 277170), an autosomal recessive, in association with preaxial polysyndactyly of toes, and cerebellar anomalies (Varadi et al. 1980; Munke et al. 1990). Pre- and/or postaxial polydac-tyly of hands and feet occurs in OFD type IV (Burn-Baraitser syndrome, OMIM 258860), an autosomal recessive disorder with short tibias, cerebral atrophy, porencephaly, and short stature (Baraitser et al. 1983); and in OFD type VIII (OFD with retinal abnormalities, OMIM 258865), an X-linked recessive disorder with duplicated halluces, abnormal tibias, short stature, hypoplasia of the epiglottis, absent central incisors, broad/bifid nasal tip, and retino-choroideal lacunae of colobomatous type, similar to those seen in Aicardi syndrome (Gurrieri et al. 1992).

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Responses

  • Ponto Underhill
    Is postaxial polydactyly a form of downsydrome?
    6 years ago
  • JESSICA
    How many cases of isolated dominant tetramelic postaxial oligodactyly?
    5 years ago

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