Polydactyly is a medical term used to describe extra fingers on the hands or toes on the feet. Since the extra fingers or toes are present at birth, they are called a congenital anomaly. The extra fingers or toes may be small and non-functional, in the case of nubbins or skin tags, or they may be fully formed with bones and skeletal connections. Extra digits can exist in different places on the hands and feet. If they are adjacent to the thumb or big toe, they are called pre-axial digits. If they are adjacent to the pinky finger or toe, they are called post-axial digits. Extra digits can also be centrally located in the hand or foot.
Polydactyly often occurs bilaterally (on both hands or both feet), or it may occur on just one hand or foot. Similarly, a person may have extra digits on just the hands, just the feet, or some other combination.
Polydactyly occurs when the body follows a different set of directions than usual while forming the hands or feet during development. Researchers are still learning about all the genes that cause extra digits. The trait may be passed down in families as an isolated, benign condition, like having a hitchhiker's thumb or being double jointed. This is considered a non-syndromic anomaly. Alternatively, the trait may exist as part of a syndrome, which is a group of several recognizable clinical features that often occur together. Some syndromes that might present with polydactyly include Greig Cephalopolysyndactyly Syndrome (GCPS) or Bardet-Biedl Syndrome (BBS).
The chances vary based on each person's family history. Sometimes extra digits appear to be a strong family trait that does not usually skip generations. In this case, we would consider the gene change to be dominant, so the chance of passing the polydactyly trait on to a child is 50 percent with each pregnancy if one parent has polydactyly. Alternatively a gene change might be recessive, in which case the chance of a person with polydactyly passing that trait onto a child is much smaller, depending on their partner's family history.
When polydactyly does occur as a family trait, it may occur in different combinations. One family member may have extra digits only on their hands, while another family member may have extra digits only on their feet.
Polydactyly can also occur even if there is no family history of extra digits.
There are special exceptions to these rules. Genetic counseling is recommended to understand how these exceptions may apply to your family.
Last Reviewed: April 2, 2012