Polydactyly

Polydactyly is a congenital disorder in which an individual is born with one or more extra digits (fingers or toes), which can occur on both the hands and feet. It affects people throughout the world regardless of racial ethnicity or socioeconomic background.

Definition & Facts

Polydactyly is a condition where a person has more than five fingers per hand or five toes per foot. This rare condition occurs in roughly 1 out of 500-1,000 births. Syndactyly is another condition affecting the digits in which the hands or feet have united or webbed digits. There are several variations of polydactyly:

• Ulnar/Post-axial polydactyly – This presents as an extra digit on the ulnar side, or outside, of the hand. This is most common in African-American populations, with post-axial type B polydactyly affecting about 1 in every 143 African-American children.
• Radial/Pre-axial polydactyly – This presents as an extra digit on the radial side (or inside) of the hand.
• Central polydactyly – This is a very rare form of polydactyly, where the extra digit is in the middle of the hand.

Symptoms & Complaints

Polydactyly can have several effects on daily life. It can make shopping for essential clothing like gloves and shoes very difficult, and it can cause psychosocial issues in which a person perceives real or imagined negative reactions from others as a result of their physical difference.

Physically, it can lead to a number of other issues, depending on whether it is present in the hands or feet. For feet, it can make walking more difficult, delaying muscle development and causing additional stress upon the hips and back. For fingers, it can delay fine motor skill development, and make writing, typing, and playing instruments more difficult.

Causes

Some cases of polydactyly are sporadic occurrences, with no other underlying condition. However, there are a number of genetic syndromes that may present with polydactyly as a feature. These include:

• Asphyxiating thoracic dystrophy. This disorder is also known as Jeune syndrome. It is caused by genetic mutations in the IFT80 gene and the DYNC2H1 gene.
• Carpenter syndrome is a type of acrocephalosyndactylia caused by mutations in the RAB23 gene.
• Ellis-van Creveld syndrome. This is caused by mutations in the EVC gene.
• Bardet-Biedl syndrome. This is caused by mutations in the BBS1 gene among other genes.
• Rubinstein-Taybi syndrome. Mutations in the CREBBP  gene and EP300 can cause this genetic disorder. Chromosome abnormality on chromosome 16 may also cause this disorder.
• Smith-Lemli-Opitz syndrome. This is caused by genetic mutations in the 7-dehydrocholesterol reductase gene (DHCR7).
• Trisomy 13 (Patau Syndrome). This is caused by a chromosome abnormality in which a person is born with an additional thirteenth chromosome.

Diagnosis & Tests

Polydactyly on its own is not usually painful for patients, or directly causal of other health concerns. However, due to the relationship between polydactyly and other syndromes, additional testing may be conducted to identify if there are other health concerns that would be related to an underlying genetic disorder.

To investigate syndromes effectively, the doctor may recommend genetic testing which can be conducted through a blood test. There are several tests used to diagnose polydactyly and/or underlying disorders, which include chromosome studies, enzyme tests, X-rays and metabolic studies. Additionally, polydactyly may be diagnosed prenatally through an ultrasound.

During an X-ray, the physician will be looking for the internal structure of extra digits, whether there is only soft tissue, or if additional bone formations are present, and how well developed they are. This will change the treatment options. Each of the forms of polydactyly has several classifications into which they may fall:

• Ulnar polydactyly – This form has up to three different classifications. Type I includes nubbins, or little floating fingers, and is soft-tissue only. Type II Includes duplication of the metacarpophalangeal joint. Type III includes a complete duplication of the digit.
• Radial polydactyly – This is classified with the Wassel classification system. In this system, radial polydactyly has three different classifications, which is based on the underlying level of skeletal duplication.
• Central polydactyly – There are three primary classifications for central polydactyly: Type I is a duplication that is not attached to an adjacent finger and rarely includes bones, joints, cartilage, or tendons. Type II has two subtypes, but is marked by the partial duplication of a digit and is attached to an adjacent digit. Type III is a complete digit duplication, and is not attached to an adjoining digit.

Treatment & Therapy

The treatment for polydactyly depends on the type and classification of the condition, but usually involves surgical intervention. Not all forms of polydactyly interfere with a patient’s ability to function. However, due to social and psychological pressures, treatment may be sought.

• Ulnar polydactyly – The extra digit is often surgically removed, usually between the ages of 6-12 months. If the digit is attached, or there is duplication of bone, ligaments and tendons, a doctor must decide how to join the skeletal structure effectively to preserve one fully functional little finger.
• Radial polydactyly – Treating radial polydactyly is complex due to the skeletal structure of the thumb. A surgeon will need to evaluate the level of duplication, and how the options to correct it surgically while preserving a functional thumb. Treatment for radial polydactyly is often performed between 9-15 months of age.
• Central polydactyly – This has the most variability in treating, depending on the type of duplication present. Oftentimes early treatment is preferred to prevent additional deformities as a result of the extra growth. The concern is the function of the hand, as well as the aesthetic appearance of the hand. Functionally, a full amputation of a digit may be recommended if it will offer four fully functional digits as opposed to restricted function due to a stiff reconstructed finger.

Prevention & Prophylaxis