What is Bardet-Biedl Syndrome?
Bardet-Biedl Syndrome is a rare, recessively inherited ciliopathy which affects approximately 1 in 100,000 babies born. Features of the syndrome include rod-cone dystrophy, a progressive eye disorder that leads to blindness, characterised by tunnel vision and night blindness; obesity; renal abnormalities; developmental delay; speech and language difficulties; extra fingers and/or toes and learning difficulties. The variability in presentation and severity of the syndrome together with the rarity of the condition can lead to delayed diagnosis and a lack of adequate local health care. There are around 560 affected individuals known to us in the UK.
There is at present no cure for Bardet-Biedl Syndrome. Patients have access to NHS specialised multi-disciplinary clinics held in four centres in London and Birmingham. Bardet-Biedl Syndrome UK are third-sector partners in this service.
Diagnosis
Beales et al (1999 and 2001) suggest that the presence of four primary features or three primary features plus two secondary features is necessary for a clinical diagnosis of Bardet-Biedl Syndrome. Not all of the features are always present in those diagnosed as having BBS and each one can vary in severity and appearance.

Primary Features
- Rod-cone dystrophy
- Polydactyly
- Obesity
- Learning disabilities
- Hypogonadism in males
- Renal anomalies
Secondary Features
- Speech delay/disorder
- Developmental delay
- Brachydactyly
- Polyuria/polydipsia
- Ataxia
- Poor co-ordination
- Diabetes mellitus
- Left ventricular hypertrophy
- Hepatic fibrosis
In most cases of BBS, both parents carry a normal gene and a faulty, recessive gene. Although the parents have one copy of the faulty gene and are called carriers of the disease, they are unaffected by the presence of the faulty gene. For a recessive disease to occur, a child has to inherit two faulty copies of the gene; one from each parent. The child from each pregnancy has a 1 in 4 chance of being affected. If a new born child is not affected then there is a 2 in 3 chance that he/she will be a carrier of the faulty gene for BBS. As the syndrome is rare, a gene carrier is unlikely to have affected children unless their partner is also a carrier. This risk of encountering another carrier increases if people marry close relatives. As some BBS genes are more common than others, there is variation in the frequency with which they are being carried, known or unknown, in the population. For the most common BBS genes, BBS1 and BBS10, the frequency is estimated to be 1 in 250, whereas for a rarer gene such as BBS9, the frequency is closer to 1 in 820.
To date, (2020) mutations in 22 BBS genes have been identified in 85% of BBS patients. It is known that there are still more genes to find since not all patients have an identified mutation in any of these identified BBS genes, indicating that these patients must have mutations in other genes. Some genes are more common than others; a quarter of patients have mutations in BBS1 and another quarter have mutations in BBS10. However, patients who carry mutations in the same BBS gene can display quite different symptoms of the syndrome: one might have extra digits at birth whereas another person with an identical mutation may not have extra digits at all. It is hoped that comprehensive genetic testing will improve predictions about disease progression in the future.