When polydactyly could be Bardet-Biedl syndrome
Fact-checked by Polydactyly — having extra fingers or toes — is one of the primary features of Bardet-Biedl syndrome (BBS), occurring in most infants born with the disorder. However, BBS is overall an uncommon cause of polydactyly, with most incidents being isolated cases unrelated to an underlying disease.
BBS is a rare, multisystemic genetic disorder in which cellular structures called cilia are defective. This disrupts typical development and can lead to symptoms that affect almost any organ.
Because polydactyly is congenital, meaning it is present at birth, it is often the first obvious sign of BBS. It may also be the only obvious clinical sign at birth, with other symptoms emerging over time. If a child is born with polydactyly and a genetic syndrome like BBS is suspected, doctors may refer families for genetic testing.
What is polydactyly?
Polydactyly is the medical term for being born with extra fingers or toes, also called digits. It can be:
- postaxial: the extra digit appears alongside the littlest (pinky) finger or toe
- preaxial: the extra digit appears alongside the thumb or big toe
- central: the extra digits appear between other fingers, and there may be finger fusion
The extra digit can appear in several ways, including as a small bump or a fully formed and functional finger or toe.
Polydactyly is one of the most common congenital limb abnormalities and sometimes runs in families. It can occur without a known cause or in people with various genetic syndromes, including BBS.
When polydactyly is an isolated finding
In the majority of cases, polydactyly is an isolated finding not associated with a specific disease or other health complications.
When polydactyly is an isolated finding, it may be postaxial, preaxial, or central and could affect one or more limbs. It is typically not accompanied by other hand or foot abnormalities or other congenital disorders. There may or may not be a family history of polydactyly.
When extra fingers or toes may be signs of BBS
More rarely, polydactyly is associated with one of many underlying genetic syndromes, including BBS. Overall, BBS is a rare cause of polydactyly.
Extra digits in BBS are typically postaxial and may be accompanied by webbing or fusion between the fingers or toes (syndactyly) and short, wide, or flat feet.
Polydactyly in BBS can affect the hands, feet, or both. In around 2o% of people, polydactyly is present on all four limbs.
Other signs that may appear alongside polydactyly
The presentation of polydactyly can be variable, so a key way to differentiate isolated polydactyly from BBS-related polydactyly is to identify other core disease symptoms, which may appear and evolve over time.
If a child with polydactyly has BBS, they may also be born with:
- structural defects in the kidneys
- underdeveloped reproductive organs or other structural alterations in the reproductive and urinary tract
As the child grows, other primary signs of BBS may appear, including:
- obesity
- vision loss
- developmental delays
How doctors evaluate a possible genetic syndrome
If a genetic syndrome like BBS is suspected in an infant with polydactyly, imaging and other diagnostic tests may be used to identify additional features of the disease.
The child will likely also be referred for genetic testing to identify mutations that may cause the disease. A geneticist will review family history to see whether any relatives have experienced polydactyly or other BBS-related symptoms.
Questions to ask after birth or diagnosis
If a child is born with polydactyly, a few questions for families to ask include:
- Is this an isolated finding or part of a broader genetic syndrome?
- What additional imaging scans or other tests are needed to confirm this?
- Should we consult with a geneticist or genetic counselor?
- What are some symptoms we should look out for that may indicate a genetic syndrome, even if polydactyly appears isolated now?
- How often should my child be monitored for new disease symptoms? Which specialists should be involved?
- Is surgery recommended? If so, what do the risks and recovery look like?
- How will this affect my child’s daily functioning?
Rare Obesity News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
