Bardet-Biedl syndrome (BBS)

What is Bardet-Biedl syndrome?

Bardet-Biedl syndrome (BBS) is a complex disorder that affects many parts of the body including the retina. Individuals with this syndrome have a retinal degeneration similar to retinitis pigmentosa (RP).

The retina is a thin piece of tissue lining the back of the eye. Rod and cone photoreceptors in the retina convert light into electrical signals that the brain interprets as vision. People with BBS-related RP experience a gradual decline in their vision, because photoreceptors degenerate.

What are the symptoms?

The diagnosis of Bardet-Biedl syndrome is often confirmed in childhood when visual problems due to RP are discovered. The first symptom of RP is night blindness. Night blindness makes it difficult to see in low light levels.

RP then causes a progressive loss of peripheral vision. Peripheral vision loss is often referred to as tunnel vision. Individuals with Bardet-Biedl can also experience central vision loss during childhood or adolescence.

In addition to RP, polydactyly (extra fingers and/or toes) and obesity are defining characteristics of Bardet-Biedl syndrome. The condition is usually first suspected when a child is born with polydactyly. Subsequent RP symptoms and obesity confirm the diagnosis. Extra fingers and toes are usually removed in infancy or early childhood. Slight webbing (extra skin) between fingers and between toes is also common. Most individuals have short, broad feet as well. Obesity may be present by childhood and is usually limited to the trunk of the body. Many individuals are also shorter than average.

About half of all individuals with Bardet-Biedl syndrome experience developmental disabilities ranging from mild impairment or delayed emotional development to intellectual disability. The degree of intellectual disability can range from mild cognitive disability to severe intellectual disability. Individuals may also experience renal (kidney) disease. Renal abnormalities can affect the structure and the function of the kidneys and can lead to severe renal impairment.

How the Disease is Inherited

Bardet-Biedl syndrome is genetically passed through families by the autosomal recessive pattern of Bardet-Biedl Syndrome inheritance. In this type of inheritance both parents, called carriers, have one gene for the syndrome paired with one normal gene. Each of their children then has a 25 percent chance (or 1 chance in 4) of inheriting the two Bardet-Biedl genes (one from each parent) needed to cause the disorder. Carriers are unaffected because they have only one copy of the gene. Researchers have identified 18 genes, when mutated, can each cause BBS.

Living with BBS

There are many services and accommodative and assistive resources available to people and families with BBS. Visit the Foundation’s Low Vision Resources page to learn about many of the vision-related resources. A low vision specialist can help recommend the resources that are right for you or your loved one.

More information on managing BBS-related RP is in the Newly Diagnosed section of this website.

Genetic Testing

Genetic testing is available for BBS. It helps with attaining an accurate diagnosis. It also helps assess the risk of passing the disorder from parent to offspring. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.

Clinical Trials

View a list of current clinical trials, many made possible by Foundation support.

Bardet-Biedl syndrome page at www.ClinicalTrials.gov.

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