# 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.