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Bardet-Biedl syndrome
This syndrome is characterised by a combination of symptoms such as progressive vision loss, obesity, kidney abnormalities, and extra fingers or toes. It is a complex condition that varies significantly among individuals.
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Overview
Bardet-Biedl syndrome is a rare genetic disorder affecting multiple systems within the body. It is classified as a ciliopathy, meaning it arises from defects in cilia - tiny, hair-like structures found on the surface of almost all human cells [PMID:33671239]. Cilia play a crucial role in sensing the environment and cellular communication, impacting many developmental processes.
Individuals with Bardet-Biedl syndrome typically experience a range of symptoms, though the specific features and their severity can differ greatly from person to person. Key characteristics often include progressive vision impairment, obesity that usually begins in childhood, kidney problems, learning difficulties, and extra fingers or toes (polydactyly).
Symptoms & clinical features
The symptoms of Bardet-Biedl syndrome typically appear early in life and can affect many different body systems. Vision loss is a common and often significant symptom, usually beginning in childhood with poor night vision and reduced peripheral (side) vision, gradually progressing to more severe sight impairment [PMID:31809053].
Childhood-onset obesity is another characteristic feature, often developing within the first few years of life. Kidney abnormalities are also common and can range from mild to severe, sometimes requiring dialysis or kidney transplant. Other potential symptoms include learning difficulties, speech and language delays, and developmental delays. Many individuals are born with polydactyly, meaning they have extra fingers or toes.
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Affected organs
Bardet-Biedl syndrome can affect a wide range of organs and body systems due to the widespread importance of cilia. The eyes are particularly affected, leading to retinal degeneration and progressive vision loss. The kidneys are also commonly impacted, with various structural abnormalities and impaired function reported.
Other affected systems can include the brain, contributing to learning difficulties and developmental delays, and the endocrine system, which can play a role in the development of obesity. The skeletal system may be affected, particularly with the presence of polydactyly, and reproductive organs may also show abnormalities.
Risks & severity
The severity of Bardet-Biedl syndrome can vary considerably among individuals, even within the same family. Vision loss typically begins in early childhood and progresses over time, often leading to significant visual impairment by early adulthood [PMID:31809053]. Childhood obesity is a common feature, often leading to associated health concerns such as type 2 diabetes and high blood blood pressure.
Kidney complications are a serious aspect of the condition, and their severity can range from mild abnormalities to severe kidney failure, which may require medical intervention. The estimated prevalence of Bardet-Biedl syndrome in the UK and Europe is approximately 1 in 100,000 to 1 in 160,000 people. Onset of symptoms is generally in childhood, although the progression and specific impact on health can vary over a person's lifetime.
Genetic causes
Bardet-Biedl syndrome is caused by pathogenic variants, or changes, in specific genes. Two such genes are BBS1 and BBS10. These genes provide instructions for making proteins that are vital for the normal function of cilia. Cilia are tiny, hair-like structures on the surface of most cells in the body, which act like antennae, helping cells sense their environment and communicate.
The protein made from the BBS1 gene is a component of a complex called the BBSome, which is essential for building and maintaining healthy cilia [PMID:32766336]. Similarly, the BBS10 gene produces a protein that helps other ciliary proteins fold correctly into their appropriate three-dimensional shapes. When these genes have pathogenic variants, the cilia cannot function properly, leading to the wide range of symptoms seen in Bardet-Biedl syndrome.
- BBS1 Bardet-Biedl syndrome 1The BBS1 gene provides instructions for a protein that is crucial for the formation and function of primary cilia, playing a key role in cellular signalling and various developmental processes.
- BBS10 Bardet-Biedl syndrome 10The BBS10 gene provides instructions for making a protein critical for the proper formation and function of primary cilia, playing a significant role in various cellular processes.
Inheritance pattern
Bardet-Biedl syndrome is inherited in an autosomal recessive pattern. This means that an individual must inherit two altered copies of the same gene - one from each parent - to develop the condition. People who have only one altered copy of the gene are known as carriers; they typically do not show symptoms of the syndrome.
When both parents are carriers of a pathogenic variant in the same gene related to Bardet-Biedl syndrome, there is a 1 in 4 (25%) chance with each pregnancy that their child will inherit two altered copies and develop the condition. There is also a 2 in 4 (50%) chance their child will be a carrier, and a 1 in 4 (25%) chance their child will inherit two normal copies of the gene and not be affected or a carrier.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
Diagnosis & testing
Diagnosing Bardet-Biedl syndrome often begins with a clinical assessment based on the child's symptoms, such as vision problems, polydactyly, and developmental delays. Due to the varied nature of the symptoms, a diagnosis can sometimes take time.
Once a clinical suspicion is raised, a diagnosis is typically confirmed through genetic testing. This involves analysing a blood sample to look for pathogenic variants in the genes known to cause Bardet-Biedl syndrome, such as BBS1 or BBS10. In the UK, genetic testing for suspected inherited conditions may be arranged through the NHS Genomic Medicine Service (GMS) following a referral to a clinical genetics service. This testing falls under relevant R-codes for rare intellectual disability and neurological disorders.
Management & lifestyle
While there is currently no cure for Bardet-Biedl syndrome, management focuses on addressing the specific symptoms and complications experienced by each individual. This often involves a multidisciplinary team of specialists, including ophthalmologists for vision care, nephrologists for kidney monitoring, endocrinologists for obesity management, and paediatricians.
Regular monitoring of kidney function, vision, and weight is crucial. Interventions may include low-vision aids, dietary management, and, in some cases, kidney transplant for severe renal failure. Accessing support services and educational resources can also be beneficial. Individuals and their families are typically supported through NHS care pathways, often coordinated by a genetic counsellor and clinical genetics team, to ensure comprehensive and ongoing care.
UK care pathway
In the UK, individuals with suspected genetic conditions like Bardet-Biedl syndrome are typically referred to a clinical genetics service within the NHS Genomic Medicine Service (GMS). These services provide expert assessment, genetic counselling, and access to advanced genomic testing.
Genetic counsellors are key professionals who offer information and support to individuals and families regarding genetic conditions, inheritance patterns, and the implications of genetic testing results. Diagnostic testing for Bardet-Biedl syndrome may be undertaken through GMS pathways, aligning with specific R-codes for inherited multi-system disorders.
Frequently asked questions
What are cilia and why are they important in Bardet-Biedl syndrome?
Cilia are tiny, hair-like structures found on almost all human cells. They act as sensory antennae, helping cells communicate and respond to their environment. In Bardet-Biedl syndrome, defects in cilia structure or function lead to problems in many different organs, causing the wide range of symptoms.
Is Bardet-Biedl syndrome only inherited from one parent?
No, Bardet-Biedl syndrome is inherited in an autosomal recessive pattern. This means a child must inherit a pathogenic genetic variant from both their mother and their father to develop the condition. If only one parent passes on a variant, the child will be a carrier but generally won't have symptoms.
Can the symptoms of Bardet-Biedl syndrome be managed?
While there isn't a cure, the symptoms of Bardet-Biedl syndrome can be managed. This involves regular monitoring and care from a team of specialists to address specific issues such as vision loss, obesity, and kidney problems, aiming to improve quality of life.
Will someone with Bardet-Biedl syndrome definitely lose their vision?
Vision loss is a very common feature of Bardet-Biedl syndrome, typically starting in childhood with difficulties seeing at night and in dim light, and progressively worsening over time. Most individuals experience significant visual impairment, often leading to severe vision loss by adulthood.
Where can I find support if my family is affected by Bardet-Biedl syndrome?
In the UK, support is available through the NHS clinical genetics services and genetic counsellors. There are also patient support groups and charities dedicated to rare genetic conditions and ciliopathies that can provide valuable resources and connections with other affected families.
References
- Forsythe E, Beales PL. Bardet-Biedl syndrome. European journal of human genetics : EJHG. 2013. PMID: 22713813
- Tsang SH, Aycinena ARP, Sharma T. Ciliopathy: Bardet-Biedl Syndrome. Advances in experimental medicine and biology. 2018. PMID: 30578506
- Keith CG. Bardet-Biedl syndrome. Australian journal of ophthalmology. 1984. PMID: 6487184
- Suspitsin EN, Imyanitov EN. Bardet-Biedl Syndrome. Molecular syndromology. 2016. PMID: 27385962
- Forsythe E, Kenny J, Bacchelli C. Managing Bardet-Biedl Syndrome-Now and in the Future. Frontiers in pediatrics. 2018. PMID: 29487844
- Hondur A, Tsang S, Aycinena ARP. Ciliopathy: Bardet-Biedl Syndrome. Advances in experimental medicine and biology. 2025. PMID: 40736835
- Melluso A, Secondulfo F, Capolongo G. Bardet-Biedl Syndrome: Current Perspectives and Clinical Outlook. Therapeutics and clinical risk management. 2023. PMID: 36741589
- Meyer JR, Krentz AD, Berg RL. Kidney failure in Bardet-Biedl syndrome. Clinical genetics. 2022. PMID: 35112343