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 function 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.