Polydactyly refers to the occurrence of supernumerary digits and is the most frequent of congenital hand and foot deformities. Based on the location of the extra digits, polydactyly can be classified into preaxial, involving the thumb or great ... Polydactyly refers to the occurrence of supernumerary digits and is the most frequent of congenital hand and foot deformities. Based on the location of the extra digits, polydactyly can be classified into preaxial, involving the thumb or great toe; postaxial, affecting the fifth digit; and central, involving the 3 central digits. Postaxial polydactyly (PAP) is further subclassified into 2 types: in type A, a well-formed extra digit articulates with the fifth or a sixth metacarpal, whereas in type B, a rudimentary, poorly developed extra digit is present (summary by Umm-e-Kalsoom et al., 2012). - Genetic Heterogeneity of Postaxial Polydactyly Other loci for autosomal dominant postaxial polydactyly type A include PAPA2 (602085) on chromosome 13q21, PAPA3 (607324) on chromosome 19p13, and PAPA4 (608562) on chromosome 7q22. An autosomal recessive form of postaxial polydactyly, PAPA5 (263450), has been mapped to chromosome 13q13.
Studies of various pedigrees with postaxial polydactyly indicate that there are 2 phenotypically different forms. In postaxial polydactyly type A, the extra digit is well formed and articulates with the fifth or an extra metacarpal. This type is ... Studies of various pedigrees with postaxial polydactyly indicate that there are 2 phenotypically different forms. In postaxial polydactyly type A, the extra digit is well formed and articulates with the fifth or an extra metacarpal. This type is inherited as a dominant trait with high penetrance. In postaxial polydactyly type B, also known as pedunculated postminimi, the extra digit is not well formed and is frequently in the form of a skin tag (Ventruto et al., 1980). Sverdrup (1922) studied a large affected kindred; he noted the occurrence of types A and B in the same pedigree and discussed the possibility of a genetic difference between the 2 forms. Odiorne (1943) described a large pedigree with postaxial polydactyly. Ventruto et al. (1980) studied an Italian family in which some individuals had both types A and B on different limbs. These findings were consistent with a single dominant gene. Kucheria et al. (1981) observed postaxial polydactyly in 4 generations of an Indian family. The 11 affected males showed type A polydactyly in both hands and feet. The 1 affected female showed polysyndactyly and both types A and B postaxial polydactyly: the left foot showed type A and the right foot type B; the left hand showed type A polydactyly and the right hand showed fusion of otherwise well-formed fifth and sixth fingers and a well-formed seventh finger similar to the usual fifth. The findings suggested a common causal factor for postaxial polydactyly types A and B and polysyndactyly, consistent with an autosomal dominant pattern of inheritance. Furniss et al. (2007) reported a patient with postaxial polydactyly type B affecting both hands. Her father had unilateral PAPB, and an obligate carrier in the family was unaffected, indicating variable expressivity and reduced penetrance.
In an Indian family with PAPA1 linked to chromosome 7p, Radhakrishna et al. (1997) identified a heterozygous in the GLI3 gene (165240.0004).
In a patient with postaxial polydactyly type B of the hands, Furniss et al. ... In an Indian family with PAPA1 linked to chromosome 7p, Radhakrishna et al. (1997) identified a heterozygous in the GLI3 gene (165240.0004). In a patient with postaxial polydactyly type B of the hands, Furniss et al. (2007) identified a heterozygous mutation in the GLI3 gene (165240.0015), which was predicted to result in premature termination and shown to be subject to nonsense-mediated mRNA decay. Furniss et al. (2007) postulated that the relatively mild phenotype may be due to nonsense-mediated mRNA decay that eliminates a toxic dominant-negative effect of a mutant protein. In affected members of a 3-generation nonconsanguineous Saudi Arabian family with broad thumbs, postaxial polydactyly of the hands, and variable cutaneous syndactyly of the hands and feet, Al-Qattan (2012) identified heterozygosity for a 2-bp deletion in the GLI3 gene (165240.0022). Some family members also had broad great toes and PAP of the feet. The PAP was rudimentary in all but 1 family member, who had bilateral PAP type A of both feet. Al-Qattan (2012) noted that although this frameshift predicts truncation in the N-terminal part of the gene with an expected Greig cephalopolysyndactyly (175700) phenotype, none of the family members had craniofacial features.
Postaxial polydactyly is about 10 times more frequent in blacks than in Caucasians (Frazier, 1960).
In Nigeria, Scott-Emuakpor and Madueke (1976) found frequencies of 17.92 and 27.08 per thousand for females and males, respectively. They concluded ... Postaxial polydactyly is about 10 times more frequent in blacks than in Caucasians (Frazier, 1960). In Nigeria, Scott-Emuakpor and Madueke (1976) found frequencies of 17.92 and 27.08 per thousand for females and males, respectively. They concluded that the trait is an autosomal dominant with penetrance of 64.9%.