Handbook of Genetic Counseling/Polydactyly and Syndactyly

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Polydactyly and Syndactyly

Medical and Family History[edit | edit source]

  • Medical history
    • How/when did they diagnose the polydactyly/syndactyly?
    • Is it bilateral?
    • Has she had X-rays or other imaging? Is this scheduled?
    • Pregnancy history - teratogen exposures, illness, womb anomalies
    • Birth history - any complications?
    • Hearing screen? Responses to sound?
  • Family history
    • Polydactyly/syndactyly? Other limb anomalies?
    • Cleft lip or palate?
    • Learning difficulties? Mental retardation?
    • Heart defects? Kidney abnormalities?
    • Skeletal abnormalities? Short stature? Other birth defects?

Overview of Hand/Foot Abnormalities[edit | edit source]

    • Presence of more than normal number of fingers or toes
    • Can vary from rudimentary finger or toe to fully developed extra digits
  • Syndactyly
    • Webbing or fusing of two or more fingers or toes
    • Varies from incomplete webbing of skin of two digits to complete funtion of digits or fusion of bones and nails
    • Fusion can be connected by shared skin, bones, nerves, vessels, or nails
  • Polysyndactyly is presence of extra digits that are fused
  • Fetal development of digits
    • Limbs arise from small limb buds
      • Upper limb bud appears 26-27 days after fertilization, lower limb bud 28-30 days
      • Consists of mesenchymal core covered by epithelial tissue
    • Apical ectodermal ridge (AER) forms along anteroposterior surface
      • Longitudinal growth of limb with pattern forming proximodistally and anteroposteriorly
      • Homeobox genes and morphogen (possibly retinoic acid) provide information for cell growth and division
    • Separation of digits occurs due to programmed cell death in interdigital zones
  • Anything that disrupts patterning or programmed cell death can result in limb defect

Syndactylies[edit | edit source]

  • Most are malformations except when associated with amniotic bands
  • Can be classified based on anatomic criteria
    • Syndactyly type I
      • Cutaneous syndactyly of fingers 3 and 4 or toes 2 and 3
      • Can be bilateral in hands (50%) and feet (66%)
      • Syndactyly of toes is four times more common than fingers
      • Can be inherited as autosomal dominant trait
      • About twice as common in males than in females
    • Syndactyly type II (synpolydactyly)
      • Syndactyly of fingers 3 and 4 or toes 4 and 5 with partial or complete duplication of digit
      • Can be variable, hand anomalies can be severe including clinodactyly
      • Extra digit may have fused, forked, or broad metacarpals and metatarsals, complete or partial duplications or digit
      • Incidence is uncertain, some autosomal dominant forms have been reported
    • Syndactyly type III
      • Variable cutaneous or osseous syndactyly of fingers 3 to 5
      • Syndactyly might be complete or partial, nails may be fused
      • Condition is rare
    • Syndactyly type IV (Haas type polysyndactyly)
      • Complete cutaneous syndactyly of fingers and/or thumbs with a degree of polydactyly on radiography and a hypoplastic or triphalangeal thumb
      • Hands often resemble "mitten" deformity
      • Rarely seen as isolated defect, very rare with few families reported
    • Syndactyly type V
      • Metacarpal and metatarsal fusion associated with variable degrees of syndactyly
      • Usually involves digits 4 and 5 but can be variable
      • Can be variable involvement within families
      • Autosomal dominant and X-linked recessive families have been described
      • Rare - only 10 families reported
    • Complete syndactyly
      • Includes digits 2-5 and may include thumb also
      • Usually seen with Apert syndrome (craniosynostosis)
    • Cenani-Lenz syndrome
      • Syndactyly involving all elements of all digits, often with fusion of radius and ulna or tibia and fibula
      • Hands and feet often appear as mass of digits
      • Autosomal recessive inheritance
    • Preaxial syndactyly
      • Failure of separation of preaxial digits of hands and feet
      • Postaxial digits are relatively normal
      • Lack of separation of thumb from finger 2 in hands, similar in feet
      • Only reported in one family
    • Symbrachydactyly
      • Shortening of phalanges and other elements of digits in association with cutaneous syndactyly
      • Usually seen unilaterally, middle phalanges tend to be more severely affected
      • Incidence estimated to be 1/32,000

Polydactylies[edit | edit source]

  • Usually manifest as extra digits or incomplete digits resulting in broad or bifid digit
  • Postaxial polydactyly (80% of cases)
    • Extra digit on ulnar or fibular side of limb
    • Type A postaxial polydactyly
      • Digit usually consists of three phalanges and nail
      • Extra digit is relatively well formed but some or all of elements may be reduced
    • Type B postaxial polydactyly
      • Extra digit is represented by small conical projection or tag containing distal phalanx and nail on fifth digit
      • 10 times more common in African-Americans than Caucasians
      • Unilateral in 2/3 of cases, affects left side twice as commonly as right
      • Autosomal dominant inheritance with reduced penetrance
  • Preaxial polydactyly
    • Preaxial polydactyly type I
      • Complete or partial duplication of a normal biphalangeal thumb
      • Varies from extra phalanx to complete hypoplastic thumb
      • May cause broadening of distal phalanx to triphalangeal thumb
      • More common in males, most often unilateral, usually not familial
      • Part of many malformation syndromes
    • Preaxial polydactyly type II (triphalangeal thumb)
      • Opposable thumb with three phalanges
      • Estimated incidence is 1/25,000
      • Usually sporadic, associated with prenatal hydantoin and thalidomide exposure, can be autosomal dominant
    • Preaxial polydactyly type III (polydactyly of an index finger)
      • Duplication of the index finger with or without an additional biphalangeal or triphalangeal thumb
      • Can be autosomal dominant or associated with genetic syndromes
    • Preaxial polydactyly type IV (polysyndactyly)
      • Duplication of preaxial digits associated with syndactyly of the extra rays
      • May see broadening of thumbs or six or seven toes
      • Autosomal dominant with complete penetrance
      • Sporadic cases occur in 1/10,000 births
    • Mirror hands and feet
      • Polydactyly of hand or foot with appearance of mirror duplication around midline axis of arm or leg in absence of recognizable thumb or great toe
      • Very rare with a few autosomal dominant cases but usually sporadic

Treatment/Management Options[edit | edit source]

  • Diagnosed by external observation, X-ray, or ultrasound
  • Polydactyly
    • Can be corrected surgically to improve appearance and functioning
    • Usually done at 1 year of age so skeletal development is complete and accurate anatomic assessment can be done
    • May require reconstruction of any associated abnormalities in remaining digit
    • Cast and soft dressing may be used until healed
  • Syndactyly
    • Treatment aimed at maintaining and improving function with cosmetic benefits
    • Involves surgery and may require skin graft from groin area
    • Surgery usually done after 1 year and may be delayed as late as 18-24 months

Resources[edit | edit source]

  • MUMS parent to parent matching
Phone: 1-877-336-5333
Email: mums@netnet.net
  • Penn State Health and Disease Information
Web: www.hmc.psu.edu/healthinfo/pq/poly.htm
  • Specific resources and support groups available for genetic conditions

References[edit | edit source]

  • "Hands and Feet." Human Malformations and Related Anomalies (1993). Oxford University Press, NY.
  • Novick, Car***"Polydactyly of the Foot." eMedicin***www.emedicing.com
  • "Polydactyly." Health Library. www.mercksource.com
  • "Polydactyly and Syndactyly." Penn State Health and Disease Information. www.hmc.psu.edu/healthinfo/

Notes[edit | edit source]

The information in this outline was last updated in 2001.