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