Supernumerary Digit 

  • Author: Carter G Abel, MD; Chief Editor: Dirk M Elston, MD   more...
 
Updated: Nov 23, 2011
 

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]

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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.

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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.

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Contributor Information and Disclosures
Author

Carter G Abel, MD  Clinical Assistant Attending, Department of Dermatology, New York Presbyterian Hospital

Carter G Abel, MD is a member of the following medical societies: American Academy of Dermatology, American College of Mohs Micrographic Surgery and Cutaneous Oncology, American Society for Dermatologic Surgery, and Medical Society of New Jersey

Disclosure: Nothing to disclose.

Coauthor(s)

Denise M McCarthy, MD  Associate Professor, Department of Radiology, Morristown Memorial Hospital

Denise M McCarthy, MD is a member of the following medical societies: American Association for Women Radiologists, American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America

Disclosure: Nothing to disclose.

Specialty Editor Board

Albert C Yan, MD  Section Chief, Associate Professor, Department of Pediatrics, Section of Dermatology, Children's Hospital of Philadelphia and University of Pennsylvania School of Medicine

Albert C Yan, MD is a member of the following medical societies: American Academy of Dermatology, American Academy of Pediatrics, Society for Investigative Dermatology, and Society for Pediatric Dermatology

Disclosure: Nothing to disclose.

Richard P Vinson, MD  Assistant Clinical Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine; Consulting Staff, Mountain View Dermatology, PA

Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association

Disclosure: Nothing to disclose.

Robert A Schwartz, MD, MPH  Professor and Head, Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, University of Medicine and Dentistry of New Jersey-New Jersey Medical School

Robert A Schwartz, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and Sigma Xi

Disclosure: Nothing to disclose.

Glen H Crawford, MD  Assistant Clinical Professor, Department of Dermatology, University of Pennsylvania School of Medicine; Chief, Division of Dermatology, The Pennsylvania Hospital

Glen H Crawford, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, Phi Beta Kappa, and Society of USAF Flight Surgeons

Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD  Director, Ackerman Academy of Dermatopathology, New York

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

References

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