Bardet-Biedl Syndrome
Jump to: Causes of BBS | Symptoms | Diagnosis | Treatment and Care | Research | Resources | References
Overview
Bardet-Biedl syndrome, also known as BBS, is a rare genetic condition that impacts many parts of the body including the retina. People with BBS have an eye condition similar to retinitis pigmentosa, which leads to gradual vision loss, starting with night and peripheral (side) vision.
BBS affects between 1 in 140,000 to 1 in 160,000 people in Canada. [1]
Causes of BBS
BBS is a hereditary syndrome caused by mutations or changes in specific genes. Mutations in over 20 genes can cause BBS and these mutations are usually inherited as an autosomal recessive condition. This means that both parents carry one copy of the healthy gene and one copy of a mutated gene. Because they have a copy of the healthy gene the parents will not have BBS. However, if both parents pass on their copy of the mutated gene, their child will be affected by the disease. If both parents are carriers of a BBS-causing gene mutation, there is a 25% chance that their child will have BBS.
About 25% of cases of BBS are caused by mutations in the BBS1 gene and 15% by mutations in the BBS10 gene. Mutations in other genes each account for a smaller percentage of cases. [2]
The genes that are mutated in BBS play a role in the structure and function of primary cilia. Primary cilia are thin, eyelash-like projections that extend from many cells. Primary cilia act like antennae, sensing chemical signals and allowing cells to communicate with each other. Mutations that impact cilia are believed to be responsible for most of the symptoms of BBS.
Symptoms
There are many symptoms of BBS. Every individual is affected by BBS differently and some individuals may experience some but not all the symptoms.
BBS is classified as an inherited retinal disease and vision loss is one of the main symptoms of this syndrome. In BBS, vision loss is caused when the light sensing cells in the retina, called photoreceptor cells, are damaged. Gene mutations change the normal function of cilia in photoreceptor cells making them unable to effectively sense light. This ultimately leads to vision loss. You can learn more about how retinal diseases affect the eye here.
One of the first signs of vision loss in children with BBS is difficulty seeing in the dark. Night blindness is usually followed by a loss of peripheral vision, creating tunnel vision. Most people with BBS will also have blurred central vision and may develop significant vision loss by the time they are teenagers or young adults. Individuals with BBS may also have other eye conditions including cataracts, glaucoma, and strabismus.
Some other key symptoms of BBS are:
- Obesity, especially excess weight in the abdomen and chest. Extra weight gain usually begins in a baby’s first year of life. It can be hard for individuals with BBS to maintain a healthy weight and it can be complicated by diabetes, heart problems and high blood pressure. [3]
- Problems with hands and feet. It is very common for people with BBS to have extra fingers or toes, called polydactyly. People with BBS may also have flat or wide feet, shortened digits and webbing, or extra skin between the fingers and toes.
- Learning disabilities. Mild to moderate learning challenges are common, especially in the context of vision loss
- Kidney problems, including infection and inflammation.
- Abnormalities of genitalia and potential infertility.
Some less common symptoms of BBS are:
- Behavioral problems
- Neurological issues
- Speech problems
- Dental differences
- Loss of sense of smell
- Thyroid problems
- Short stature
- Hearing difficulties
DIAGNOSIS
Diagnosing BBS can be difficult as it affects many parts of the body in different ways. Doctors usually diagnose someone with BBS when several symptoms have been observed together. Childhood vision loss is often one of the first symptoms that leads to a diagnosis. Genetic testing can help confirm a diagnosis of BBS but it is not always definitive.
Treatment and Care
Currently, there is no cure for BBS but there are things that can help. In some cases, certain symptoms of BBS can be treated. For example, mobility issues can be treated with physical therapy, there are medications for obesity and surgery may be an option for some kidney and thyroid issues. Counselling can also be beneficial, especially in childhood and the teenage years.
There are currently no treatments for vision loss caused by BBS, but accessing vision rehabilitation and low vision services can help maintain independence as vision loss progresses.
RESEARCH
Research into treatments for vision loss associated with BBS and other inherited retinal diseases is happening in Canada and around the world.
- Learn more about clinical trials for Bardet Biedel Syndrome. If you are interested in a clinical trial, please read our clinical trials guide and speak with your eye doctor.
- Learn more about innovative treatments including gene therapies, stem cell therapies and optogenetic therapies.
Fighting Blindness Canada is proud to invest in research that may drive treatments and cures for vision loss caused by BBS and other inherited retinal diseases.
- Learn about Dr. Arlene Drack’s research to develop a gene therapy for BBS10
- Learn more about all of Fighting Blindness Canada’s funded research.
Resources
Fighting Blindness Canada has developed resources to help you navigate vision care. Follow the links below to learn more.
- Learn about genetic testing and join our Inherited Retinal Disease Patient Registry to connect with clinical trials and treatments.
- Learn about the latest in vision research with our View Point educational series
- Sign up for our e-newsletter to keep up to date on the latest breakthroughs and community events.
- Contact our Heath Information line by email or phone to ask questions about your eye health.
References
[1] https://ghr.nlm.nih.gov/condition/bardet-biedl-syndrome
[2] https://www.ncbi.nlm.nih.gov/books/NBK1363/
[3] https://rarediseases.org/rare-diseases/bardet-biedl-syndrome/
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Updated on January 2, 2024
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