Bardet-Biedl syndrome (BBS) is a genetic disorder that affects different parts of the body.¹ It affects different parts of the body and is characterised by various conditions, such as obesity, vision loss and cognitive impairment.^1,2 The condition is rare and is thought to affect between 1 in 140000 to 1 in 160000 in Europe and North America.² It is thought to be caused by mutations in around 14 genes which are known as BBS genes.² These have an important role in the development of the cell structure, cilia.² The condition itself can become life-threatening as someone with this condition has various organ systems failing to function as they should as well as other progressive symptoms. Read on to find out more about the progression and the long-term outcomes of this condition.

Clinical manifestations of barbet-biedl syndrome

Primary symptoms

Bardet-Biedl syndrome affects various types of the body and mainly affects the function of the organ systems in the body, as well as other primary symptoms. These include:³

• Obesity
• Visual impairment
• Polydactyly (extra digits on feet or hands)
• Renal abnormalities (problems with the kidneys)
• Cognitive impairment
• Problems with male and female genital development

Secondary symptoms

In addition to primary symptoms, there may be other symptoms that may be identified in someone with Bardet-Biedl syndrome. These are known as secondary symptoms:^2,3

• Hypogonadism (problems with hormone secretion)
• Hypertension (high blood pressure)
• Problems with the liver
• Muscle control difficulty
• Poor coordination
• Type 2 diabetes
• Speech problems

Prognosis of bardet-biedl syndrome

Life expectancy 

The disease itself will not cause the life expectancy to reduce, however, a lack of support for the affected parts of the body, such as the kidneys, may cause issues and could be life-threatening if left untreated. Bardet-Biedl syndrome can be identified as early as birth depending on what symptoms are being shown. An early diagnosis means that support can be given sooner for any existing symptoms, as well as any other problems that are expected to arise as the individual ages.⁴ The support given can vary depending on the severity of symptoms and when these are identified. For example, if there is a visual impairment in an individual and they are not showing any other clear symptoms, it would be difficult to diagnose the individual with BBS at birth and would be clearer to diagnose when older when other symptoms are being shown. 

Quality of life 

While the life expectancy of someone with BBS may be normal, the associated symptoms of the syndrome, such as vision impairment and cognitive impairments, would be difficult to live with as it affects daily life, affects the ability to learn and in some cases may cause pain, ranging from mild to severe. Psychologically, an individual with BBS may have a delay in development, and so may have difficulty with speech and motility, for example standing up². This means that an individual may find it difficult to function normally without having support and may have difficulty in socialising and getting around. This can prove to be a challenge as it means that in some cases, depending on the severity of BBS, the individual may be unfit for work, or unable to learn as expected within an educational setting. 

Long-term outcomes in bardet-biedl syndrome

Visual impairment and blindness 

In individuals with BBS, it has been found that there is a degeneration of the retina as the individual ages.⁵ This can first be identified in childhood and the first sign of vision loss is usually night blindness, where an individual has difficulty in being able to see in low light.⁵ This can then develop into a loss of peripheral vision, which is commonly known as ‘tunnel vision’. In some cases, the individual can suffer from central vision loss which means that they only have their peripheral vision remaining. This can severely impact daily life if the individual is unable to see properly and needs extra support from specialists throughout their childhood and as they age.

Renal function and failure 

Another main symptom of BBS is the dysfunction of the kidneys as it affects around 50% of people diagnosed with BBS.⁶ This can be fatal if left untreated as it can develop into serious, chronic complications such as chronic kidney disease and potentially lead to failure of the kidneys.⁶ Dysfunction of the kidneys means that waste and other toxic substances from the blood cannot be filtered out, which can lead to further complications.⁷ The severity of renal dysfunction can vary from mild to severe, and the less severe it is the more manageable and treatable it can be. However, in more severe cases, when renal dysfunction is identified, it may be found that there is malformation of the kidneys.⁶ This can be difficult to manage and may potentially develop into kidney failure such as end-stage renal disease (ESRD) which would require treatments such as dialysis or a kidney transplant as it can be fatal.⁶

Obesity and related complications 

Obesity is another main symptom of BBS, which can be life-threatening if not treated properly. Obesity in individuals with BBS is caused as a result of feeling hungry, despite being full.⁶ This is due to the body being unable to detect that it is full. This is detected in infancy by measuring BMI and weight can be rapidly gained in early childhood. Obesity in those with BBS can be considered dangerous as there is a build-up of adipose tissue in the abdomen and other internal organs.⁶ This can lead to potentially life-threatening health complications such as the development of type 2 diabetes, development of high blood pressure and high cholesterol levels.² The development of high blood pressure and cholesterol levels can lead to the risk of developing cardiovascular diseases which would require treatments, such as statins or stents.

Cognitive and behavioural outcomes 

While it only affects a minority of those with BBS, the condition can also impair the cognitive development of an individual. This can include problems with the development of speech, development of basic skills such as movement and difficulty with controlling emotions.⁶ This can affect the learning of the individual and may be unable to function without support in some severe cases. In other cases, an individual may show symptoms that are similar to those that have autism and attention deficit hyperactivity disorder (ADHD).⁶ These problems may cause the individual to have difficulty with expressing themselves, and difficulty with learning, meaning support would need to be offered within schools or the individual may be referred to a specialist school. Other conditions that are associated, such as autism and ADHD, can be treated with therapy and medication to help relieve associated symptoms.

Reproductive health

BBS can affect both men and women and can affect the reproductive systems. In people assigned male at birth (AMAB), the testes may be smaller, and undescended and their function is impaired, which can cause various complications, such as delayed puberty.⁶ This is due to the reduced level of hormones being produced and in the long-term may cause the individual to become infertile.² In more severe cases, this could potentially develop into testicular cancer if this is left untreated. In people assigned female at birth (AFAB) with BBS, there may also be problems with fertility due to the development of the ovaries, fallopian tubes and/or uterus being impaired which can affect hormone production.⁶ Both cases can be treated with hormone therapy and medication to regulate the production of hormones, which can increase fertility, as well as other associated symptoms, such as depression or anxiety, as a result of hormone imbalance in both sexes.^8,9

Summary

While Bardet-Biedl syndrome itself is not a life-threatening condition, the associated symptoms, such as obesity and vision impairment, can result in the development of further health complications that can range from mild to life-threatening. In most cases, these complications can affect the quality of life as they may be difficult to live with due to the severity of the conditions. However, with the appropriate treatment and support from specialists, some of these symptoms can be relieved, thus improving the quality of life of the individual and reducing the chance of further complications arising.