Polydactyly, Postaxial, Type A7

A number sign (#) is used with this entry because of evidence that postaxial polydactyly type A7 (PAPA7) is caused by homozygous mutation in the IQCE gene (617631) on chromosome 7p22. One such family has been reported.

Description

PAPA7 is characterized by postaxial polydactyly restricted to the feet, with well-developed nails present on the extra digits and attachment of both the fifth and sixth toes to a broad 2-headed fifth metatarsal (Umair et al., 2017).

For a discussion of genetic heterogeneity of postaxial polydactyly, see 174200.

Clinical Features

Umair et al. (2017) studied a large consanguineous family of Pakistani origin in which 5 individuals in 2 sibships had postaxial polydactyly of the feet. Examination of 4 affected individuals showed well-developed nails in the extra toes, and radiography revealed that both the fifth and sixth toes were attached to a 2-headed thick broad fifth metatarsal. Phenotypic variability was observed among the patients, including unilateral involvement in 1 patient, brachymetatarsia of the fifth right toe in 1 patient, and bilateral cutaneous syndactyly of the second and third toes in 1 patient. In addition, x-rays showed radial varus deviation of the fourth and fifth toes bilaterally in 2 patients, whereas another patient had valgus deviation of the right fifth metatarsal with cubitus varus deviation of the right fifth and sixth toes.

Molecular Genetics

In a large consanguineous family of Pakistani origin segregating autosomal recessive postaxial polydactyly of the feet, Umair et al. (2017) performed whole-exome sequencing and identified a homozygous splice site variant in the IQCE gene (617631.0001) that segregated with disease.