Clinical and descriptive genetic study of polydactyly: a Pakistani experience of 313 cases

Polydactyly, a common hereditary condition with additional digits in hands and/or feet, is a very attractive model to appreciate clinical and genetic heterogeneity. In order to get an insight into its phenotypic manifestations, we ascertained a cohort of 313 independent families with polydactyly from Pakistan; 35% cases turned out to be familial while 65% were sporadic. In majority of the index cases, polydactyly was presented as an isolated digit defect. Preaxial polydactyly types were 48.24% and postaxial were 51.8%. Familial polydactylies mainly had bilateral and symmetrical presentations, whereas sporadic cases were mostly unilateral and less often symmetrical. In the 313 index subjects a total of 508 limbs with additional digits were recorded. Variable expression was evident as the involvement of upper limbs was more common than the lower, right hand than the left, and left foot than the right. The present cohort establishes interesting epidemiological attributes of polydactyly in the Pakistani population and highlights its extraordinary clinical heterogeneity. Molecular analyses of this cohort are anticipated to elucidate novel genetic factors involved in the origin of additional digits in the growing limb and may provide clues to the role of stochastic factors in the etiology of phenotypic variability in polydactyly.