What is polydactyly?

Risk Factors

Polydactyly can occur spontaneously (familial polydactyly) or in conjunction with a number of genetic disorders. Asphyxiating thoracic dystrophy (Jeune syndrome) is a bone growth disorder. Carpenter syndrome is an acrocephalopolysyndactyly (ACPS) disorder that affects bone growth. Ellis-van Creveld syndrome (chondroectodermal dysplasia) is a bone growth disorder involving growth hormone derficiency; the highest incidence rate of this syndrome occurs in Old Order Amish from Lancaster County, Pennsylvania. Laurence-Moon-Biedl syndrome is a mitochondrial myopathic disorder characterized by intellectual disability and possibly short stature.

Rubinstein-Taybi syndrome is a rare disorder characterized by intellectual diability and short stature. Smith-Lemli-Opitz syndrome is a disorder characterized by microcephaly (small head circumference), hypotonia (weak muscle tonus), and possible organ malformations; the highest incidence of this syndrome occurs in Caucasians of central European ancestry. Trisomy 13 (Patau syndrome) is a usually fatal disorder characterized by multiple structural and developmental abnormalities.

Familial polydactyly may occur independent of any other symptoms or disease. The highest incidence of sixth digit inheritance occurs in African Americans. In those rare instances where polydactylism causality cannot be definitively attributed to genetic abnormality, it is hypothesized that womb abnormality or exposure to toxins may be contributing factors.

Etiology and Genetics

Although it can occur independent of genetic factors, polydactyly is most commonly a heritable, autosomal dominant trait involving a single gene that is capable of causing several variations in expression. Therefore, inheritance is not gender linked and does not require that both parents have the trait. It most likely occurs as the result of duplication of a single embryologic bud.

Incidence rate for polydactyly of the hand is approximately 1 per 1,000 births. It is the most common hand anomaly and occurs most frequently as preaxial (thumb) polydactyly in those of Asian ancestry who have the trait and as postaxial (little finger) polydactyly in those of African ancestry who have the trait. It does not usually occur bilaterally.

Incidence rate for polydactyly of the foot is approximately 1 to 2 per 1,000 births. In approximately 50 percent of all cases, it occurs bilaterally although not necessarily symmetrically. In approximately 33 percent of all cases, it occurs in conjunction with polydactyly of the hand.

Incidence of fused extra digits indicates the concomitant occurrence of polydactyly and syndactyly (fusion of digits) and is termed polysyndactyly.

Symptoms

The only symptom of polydactyly is the presence of one or more extra digits. The presence of other symptoms may indicate the possibility of a concomitant genetic disorder.

Screening and Diagnosis

Screening consists of obtaining a comprehensive medical history and performing chromosome studies. Diagnosis is possibly via fetal sonogram and is immediately apparent at birth. Radiographic evaluation may be necessary to determine the extent of possible skeletal involvement and to confirm that there is no underlying deformity. Other tests that may be used to confirm the diagnosis are enzyme tests and metabolic studies.

Treatment and Therapy

Treatment most often involves surgery, the extent of which is dependent upon the degree of bone, ligament, and tendon involvement. In order to reduce the risk of anesthesia yet allow for the maximum potential for remodeling, surgical excision usually occurs when a baby is approximately one year old.

Standard practice for correction of a “floppy digit,” one attached only by soft tissue, is application of suture ligature while the baby is in the hospital nursery. This practice is not recommended, however, if the extra digit has metacarpal/metatarsal duplication and/or residual cartilage, due to the risk of future deformity.

Extensive surgical intervention may require subsequent stabilization of the joint area via short-term casting and maximization of function via physical therapy. Additional surgery may be required during childhood to prevent or correct growth deformity.

Prevention and Outcomes

There is no known means of prevention for spontaneously occurring polydactyly. Possible prevention of polydactyly that occurs in conjunction with genetic disorders would require genetic screening and counseling of prospective parents. The prognosis for isolated polydactyly is extremely favorable with surgical excision.

Bibliography

Barnhill, Raymond L., and A. Neil Crowson. Textbook of Dermatopathology. 3rd ed. New York: McGraw, 2010. Print.

Holmes, Lewis B. Common Malformations. New York: Oxford UP, 2012. Print.

Hosalkar H. S., Spiegel D. A., and Davidson R. S. “Toe Deformities.” Nelson Textbook of Pediatrics. 19th ed. Ed. R. M. Kliegman, et al. Philadelphia: Saunders, 2011. Print.

Kumar, Praveen, and Barbara K. Burton. Congenital Malformations Evidence-Based Evaluation and Management. New York: McGraw, 2011. Digital file.

Malik, S. "Polydactyly: Phenotypes, Genetics and Classification." Clinical Genetics 85.3 (n.d.): 203–12. Biological Abstracts. Web. 7 Aug. 2014.

McGlamry, Dalton, et al. McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery. 3rd ed. Philadelphia: Lippincott, 2001. Print.

Tickle, C. “Embryology.” The Growing Hand: Diagnosis and Management of the Upper Extremity in Children. Ed. A. Gupta, S. P. J. Kay, and L. R. Scheker. London: Mosby, 2000. Print.