What is Bardet-Biedl syndrome?
Bardet-Biedl syndrome 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).
What are the symptoms?
The diagnosis of Bardet-Biedl syndrome is usually 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 (side) vision. Peripheral vision loss is often referred to as tunnel vision. Individuals with Bardet-Biedl also experience central vision loss during childhood or adolescence. RP symptoms progress rapidly and usually lead to severe visual impairment by early adulthood.
In addition to RP, polydactyly (extra fingers and/or toes) and obesity are defining characteristics of Bardet-Biedl syndrome. A diagnosis of Bardet-Biedl syndrome 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.
Approximately half of all individuals with Bardet-Biedl syndrome experience developmental disabilities ranging from mild impairment or delayed emotional development to mental retardation. The degree of mental retardation can range from mild cognitive disability to severe mental retardation. 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.
Upon reaching adulthood, males with Bardet-Biedl syndrome can have small genitalia (testes and penis). Because female sexual organ size is more difficult to assess, it is not known how many women have this characteristic. Females with Bardet-Biedl can experience irregular menstrual cycles.
Is it an inherited disease?
Bardet-Biedl syndrome is genetically passed through families by the autosomal recessive pattern of 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.
What treatment is available?
There are no treatments for all of the characteristics associated with Bardet-Biedl syndrome. As vision worsens, individuals will benefit from the use of low-vision aids and orientation as well as from mobility training. Researchers have identified 12 genes that are linked to Bardet-Biedl syndrome, giving them clear targets for treatment development.
Are there other related syndromes?
Bardet-Biedl syndrome is often confused with Laurence-Moon syndrome. Individuals with Laurence-Moon syndrome almost always experience neurologic problems but rarely polydactyly. Polydactyly is a defining feature of Bardet-Biedl syndrome, while neurologic problems almost never occur. Laurence-Moon syndrome is extremely rare; only a few cases have been documented. Because of the similarity of these syndromes, Bardet-Biedl syndrome is often referred to as Laurence-Moon/Bardet-Biedl syndrome or Laurence-Moon/Biedl syndrome.