Handbook of Genetic Counseling/Polydactyly and Syndactyly

Polydactyly and Syndactyly

Medical and Family History

• 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

• • 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

• 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

• 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

• 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

• MUMS parent to parent matching

Phone: 1-877-336-5333

Email: mums@netnet.net

Web:www.netnet.net/mums/

• 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

• "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

The information in this outline was last updated in 2001.