How is Polydactyly Inherited?

Polydactyly, also referred to as polydactylism, is a condition in which the patient has more than five fingers on his hands or more than five toes on his feet. This anatomical abnormality is a congenital abnormality. Patients will have six or more toes or fingers at birth. It is estimated that every two in one thousand children will be born with this disorder. Certain populations have a higher incidence rate due to the founder effect, such as the Pennsylvania Dutch in the USA. The one question many patients, and parents, ask is “how is polydactyly inherited?

Causes

Inheriting this disorder through familial genetics is the most common cause. However, there are certain developmental and rare inherited disorders in which this disorder may occur. Some of the most common causes include:

• Familial polydactyly.
• Asphyxiating thoracic dystrophy.
• Trisomy 13.
• Carpenter syndrome.
• Smith-Lemli Opitz syndrome.
• Chondroectodermal dysplasia (Ellis-van Creveld syndrome).
• Rubinstein-Taybi syndrome.
• Laurence-Moon-Biedl syndrome.

Diagnosis

Diagnosing this condition is relatively easy. The doctor will make a diagnosis based on medical history, family history, a physical examination, and some diagnostic testing. When assessing the patient’s family medical history the doctor will often asking the following questions:

• Is there a history of other family members, particularly parents, siblings, and grandparents, being born with extra toes or fingers?
• Is there a family history of the disorders associated with this disorder?
• Is the patient experiencing any other medical problems or symptoms?

Diagnostic Tests

• Enzyme tests
• Metabolic studies
• Chromosome studies
• X-rays

How is Polydactyly Inherited?

Polydactyly is inherited genetically as an autosomal dominant trait. Autosomal refers to not being sex-linked, meaning that both females and males have an equal chance of inheriting this trait. Since it is a dominant gene, those who have only one parent with this trait will have a fifty-percent chance of inheriting the trait. This disorder is also associated with more than 100 developmental and rare inherited disorders. In some cases, a genetic defect is responsible.

Types

There are many types of this disorder and they vary in frequency. They include:

• Polydactyly alopecia seborrheic dermatitis.
• Polydactyly visceral anomalies cleft lip palate.
• Polydactyly cleft lip palate psychomotor retardation.
• Polydactyly syndrome middle ray duplication.
• Polydactyly myopia syndrome.
• Polydactyly preaxial type 1.
• Polydactyly postaxial dental and vertebral.
• Polydactyly postaxial.
• Polydactyly postaxial with median cleft of upper lip.

Treatment

This condition is most often treated around the first year of life. Surgical removal is the most common mode of treatment. A surgeon will have the patient prepped for surgery and will remove the partial digit or extra digit is excised. Once it is removed, the surgeon will reconstruct any abnormalities associated with the extra digit or its removal.

Resources

Medline Plus. (2009). Polydactyly. Retrieved on January 25, 2010 from Medline Plus: https://www.nlm.nih.gov/medlineplus/ency/article/003176.htm