Background
Polydactyly is the most common congenital digital anomaly of the hand and foot. It may appear in isolation or in association with other birth defects. Isolated polydactyly is often autosomal dominant or occasionally random, while syndromic polydactyly is commonly autosomal recessive.[1]
Pathophysiology
Polydactyly should not be considered as a single mendelian trait but rather multifactorial. Early theories for polydactyly concerned disorders in the programmed cell death cycle of fetal limb development. Current theories focus on mutations in specific genetic locations that cause limb development to go awry. Mammals have been shown to have genetic clusters identified as homeobox or Hox genes corresponding to 5 domains across the limb bud. According to Muragaki et al,[2] mutations in the HOXD13 gene are associated with synpolydactyly. As limb growth in utero progresses along a preset time line, elongation of the limb, development of soft tissue, and differentiation of digits progresses.
The Medscape Genomic Medicine Research Center may be of interest.
Epidemiology
Frequency
United States
The epidemiologic data on postaxial polydactyly is limited because most birth defect registries do not include them, preferring to focus on defects linked to teratogens. Despite being a common malformation, the true incidence of polydactyly is not fully known.
One study by Finley et al[3] combined data from Jefferson County, Alabama and Uppsala County, Sweden. This study showed incidence of all types of polydactyly to be 2.3 per 1000 in white males, 0.6 per 1000 in white females, 13.5 per 1000 in black males, and 11.1 per 1000 in black females. The Swedish data alone showed polydactyly of all types to have an incidence of 1.0 per 1000, equally distributed between males and females.
While the incidence of preaxial and postaxial polydactylies has been investigated, central polydactyly has not been fully studied.
International
Genetic and ethnic factors greatly influence the nature of polydactyly in the world population. Unfortunately, the knowledge of polydactyly is limited to select studies of certain subpopulations. Preaxial polydactyly is very common in various Asian populations, accounting for 90% of cases in South China, Hong Kong, and Japan. Duplicated thumbs at the metacarpophalangeal level are the usual anomaly.[4, 5]
Race
Postaxial hand polydactyly is a common isolated disorder in African black and African American children, and autosomal dominant transmission is suspected. Postaxial polydactyly is approximately 10 times more frequent in blacks than in whites and is more frequent in male children. In contrast, postaxial polydactyly seen in white children is usually syndromic and associated with an autosomal recessive transmission.
Other factors associated with postaxial hand polydactyly include male sex, twinning, low maternal education, parental consanguinity, and recurrence in first-degree relatives. Postaxial polydactyly is associated with Amerindian, parental subfertility, and bleeding in the first trimester.
Hosalkar HS, Shah H, Gujar P, Kulkarni AD. Crossed polydactyly. J Postgrad Med. Jul-Sep 1999;45(3):90-2. [Medline].
Muragaki Y, Mundlos S, Upton J, Olsen BR. Altered growth and branching patterns in synpolydactyly caused by mutations in HOXD13. Science. Apr 26 1996;272(5261):548-51. [Medline].
Finley WH, Gustavson KH, Hall TM, Hurst DC, Barganier CM, Wiedmeyer JA. Birth defects surveillance: Jefferson County, Alabama, and Uppsala County, Sweden. South Med J. Apr 1994;87(4):440-5. [Medline].
Cohen MS. Thumb duplication. Hand Clin. Feb 1998;14(1):17-27. [Medline].
Hung L, Cheng JC, Bundoc R, Leung P. Thumb duplication at the metacarpophalangeal joint. Management and a new classification. Clin Orthop Relat Res. Feb 1996;31-41. [Medline].
Klaassen Z, Shoja MM, Tubbs RS, Loukas M. Supernumerary and absent limbs and digits of the lower limb: a review of the literature. Clin Anat. Jul 2011;24(5):570-5. [Medline].
Temtamy SA, McKusick VA. The genetics of hand malformations. Birth Defects Orig Artic Ser. 1978;14(3):i-xviii, 1-619. [Medline].
Belthur MV, Linton JL, Barnes DA. The spectrum of preaxial polydactyly of the foot. J Pediatr Orthop. Jun 2011;31(4):435-47. [Medline].
Malik S, Grzeschik KH. Synpolydactyly: clinical and molecular advances. Clin Genet. Feb 2008;73(2):113-20. [Medline].
Tian F, Tian LJ, Zhao W, Li XC, Li B, Ji XL. Plastic repair for a case with synpolydactyly. Arch Orthop Trauma Surg. Jun 2011;131(6):869-73. [Medline].
Jafari D, Sharifi B. A variant of mirror hand. A case report. J Bone Joint Surg Br. Jan 2005;87(1):108-10. [Medline].
Castilla EE, Lugarinho R, da Graça Dutra M, Salgado LJ. Associated anomalies in individuals with polydactyly. Am J Med Genet. Dec 28 1998;80(5):459-65. [Medline].
Bromley B, Shipp TD, Benacerraf B. Isolated polydactyly: prenatal diagnosis and perinatal outcome. Prenat Diagn. Nov 2000;20(11):905-8. [Medline].
Zimmer EZ, Bronshtein M. Fetal polydactyly diagnosis during early pregnancy: clinical applications. Am J Obstet Gynecol. Sep 2000;183(3):755-8. [Medline].
Ban M, Kitajima Y. The number and distribution of Merkel cells in rudimentary polydactyly. Dermatology. 2001;202(1):31-4. [Medline].
Morley SE, Smith PJ. Polydactyly of the feet in children: suggestions for surgical management. Br J Plast Surg. Jan 2001;54(1):34-8. [Medline].
Eskandari MM, Oztuna V, Demirkan F. Late psychosocial effects of congenital hand anomaly. Hand Surg. Dec 2004;9(2):257-9. [Medline].
Al-Aithan B, Al-Blaihed L, Mahmoud S, Hassanain J, Al-Qattan MM. Thumb polydactyly with symphalangism. J Hand Surg [Br]. Aug 2005;30(4):346-9. [Medline].
Castilla EE, da Graca Dutra M, Lugarinho da Fonseca R, Paz JE. Hand and foot postaxial polydactyly: two different traits. Am J Med Genet. Nov 28 1997;73(1):48-54. [Medline].
Cavalcanti DP, Salomão MA. Dandy-Walker malformation with postaxial polydactyly: further evidence for autosomal recessive inheritance. Am J Med Genet. Jul 16 1999;85(2):183-4. [Medline].
Chiang H, Huang SC. Polydactyly of the foot: manifestations and treatment. J Formos Med Assoc. Mar 1997;96(3):194-8. [Medline].
Chung J, Nam IW, Ahn SK, Lee SH, Kim JG, Sung YO. Rudimentary polydactyly. J Dermatol. Jan 1994;21(1):54-5. [Medline].
Cummins H. Spontaneous amputation of human supernumerary digits: pedunculated postminimi. Am J Anat. 1932;51:381-416.
Graham TJ, Ress AM. Finger polydactyly. Hand Clin. Feb 1998;14(1):49-64. [Medline].
Hare PJ. Rudimentary polydactyly. Br J Dermatol. Nov 1954;66(11):402-8. [Medline].
Heras L, Barco J, Cohen A. Unusual complication of ligation of rudimentary ulnar digit. J Hand Surg [Br]. Dec 1999;24(6):750-1. [Medline].
Manske PR. Subclassification of polydactyly. Br J Plast Surg. Mar 1996;49(2):137. [Medline].
Sergi C, Adam S, Kahl P, Otto HF. Study of the malformation of ductal plate of the liver in Meckel syndrome and review of other syndromes presenting with this anomaly. Pediatr Dev Pathol. Nov-Dec 2000;3(6):568-83. [Medline].
Shapiro L, Juhlin EA, Brownstein MH. "Rudimentary polydactyly": an amputation neuroma. Arch Dermatol. Aug 1973;108(2):223-5. [Medline].

