What is Bardet-Biedl syndrome?
Bardet-Biedl syndrome is a rare, inherited disorder that causes a number of abnormalities in the way certain parts of the body function. The symptoms vary greatly, and may include some or all of the following:
- vision loss caused by retinal dystrophy
- obesity, usually more pronounced in the area of the torso (truncal obesity)
- extra fingers and/or toes (polydactyly), or minor abnormalities of the hands and feet such as slight webbing or extra skin between the fingers and toes.
- lack or decreased secondary sex characteristics (hypogonadism)
- developmental delay, and
- kidney problems.
On rare occasions there are other symptoms, and these may include a need for eye glasses, heart problems, and hearing deficiency.
Various forms of retinitis pigmentosa (RP) cause the vision loss experienced by individuals with Bardet-Biedl syndrome. Click here to read about RP. In Bardet-Biedl syndrome, central vision may become blurry as the first symptom. Severe visual impairment is often experienced by the teenage years or early adulthood.
Bardet-Biedl syndrome is an autosomal recessive disorder. Most often, it is presumed that both parents are carriers of genes that cause the disease abnormalities. Carriers usually have no abnormalities and no idea that they are carrying the genetic abnormality (in fact, all people carry 6-8 genetic diseases without any knowledge of what diseases these represent).
- one in four chance with EACH pregnancy of having an affected child
- one in two chance with EACH pregnancy that a child will be, like the parents, a carrier, and
- one in four chance with EACH pregnancy that a child will be completely free of the disease-causing gene.
The exact genetic causes of Bardet-Biedl have not been completely explained. Abnormalities on at least five different chromosomes may each cause a form of this syndrome. Presently, there is no way to detect carriers by blood testing. However, some centres may offer blood testing to help continue research into the genetic cause of the syndrome. Scientific research is being directed at locating and identifying the genes that cause this syndrome.
Because Bardet-Biedl can affect more than one of the body's systems, a number of medical specialists may be needed to watch over the health of individuals with this disorder. Depending on the needs of the individual, this may include an ophthalmologist for vision; nephrologists for kidneys; dietician for weight control and cardiologist if heart problems are present.
Problems with the kidney system may pose the most serious health risks in individuals with Bardet-Biedl syndrome. These abnormalities can affect the function of the kidneys and lead to severe renal impairment. A nephrologist (a specialist in diseases of the kidney) should examine individuals with Bardet-Biedl to assess how well the kidneys are working. Some patients will require no treatment, but others may benefit from dietary changes, medications, or even kidney transplantation depending on the nature and severity of the kidney involvement.
There is no treatment for the severe vision impairment associated with Bardet-Biedl syndrome. As vision worsens, individuals may benefit from low vision aids and eventually mobility training.
Related Syndromes
Laurence-Moon-Biedl syndrome is also known as Laurence-Moon syndrome. In individuals with Laurence-Moon syndrome related neurological problems, which are not found in the Bardet-Biedl patient, almost always occur. The most common neurologic abnormality is a spastic diplegia (abnormality in the function of leg muscles). The extra digits, which are common in Bardet-Biedl, are not as common in Laurence-Moon. Laurence-Moon is less common than Bardet-Biedl.
Researchers worldwide are seeking to understand the genetic causes of Bardet-Biedl syndrome. The FFB-C is proud to be funding the research of Dr. Elise Héon at The Hospital for Sick Children in Toronto. To see an overview of Dr. Héon's study click here.
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We would like to keep you updated with the latest news and updates, fill out the registration form to stay in touch.The above information has been reviewed by:
Dr. Alex V. Levin, MHSc., M.D., FRCSC
Ophthalmologis
The Hospital for Sick Children, Toronto
Medical Advisor, The Foundation Fighting Blindness - Canada
This information has been provided by The Foundation Fighting Blindness - Canada and has been reviewed by its medical advisor. It is not intended to replace the advice of a qualified vision care professional. The Foundation urges everyone affected by an eye disorder to seek the best healthcare possible.