Bardet-Biedl syndrome

Also known as: Laurence-Moon-Bardet-Biedl syndrome; Laurence-Moon-Biedl syndrome

Background

Bardet-Biedl syndrome (BBS) is a rare inherited (autosomal recessive) condition. It is characterised by vision loss, obesity, additional fingers and/or toes, undeveloped genitals, learning difficulty (see entry Learning Disability), renal (kidney) dysfunction and a range of endocrine problems. BBS is seen in about 1 in 100,000 of the general population but occurs more frequently in populations where there is marriage between family members and children born as a result of that (consanguineous marriage). It is also more common in historically isolated communities, such as Newfoundland.

Credits

Medical text written January 1996 by Dr PL Beales. Last updated April 2018 by Professor PL Beales, Professor of Medical and Molecular Genetics, NIHR Senior Investigator, Consultant in Clinical Genetics, Genetics and Genomic Medicine Programme, Institute of Child Health, London, UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

Primary features:

  • rod/cone dystrophy – a progressive eye condition, which can lead to blindness
  • obesity, childhood-onset with fat distributed particularly around the trunk (middle of body)
  • polydactyly (extra fingers and/or toes)
  • hypogenitalism (underdeveloped genitals)
  • mild-to-severe learning difficulties (see entry Learning Disability)
  • renal abnormalities (such as cysts) and impaired renal function
  • endocrine disturbances that involve pituitary, thyroid, adrenal glands, the ovaries and testes (may lead to subfertility).

Secondary features may include:

  • speech problems
  • developmental delay (see entry Global Developmental Delay)
  • behavioural abnormalities
  • eye abnormalities, including strabismus (cross-eyed), cataracts, and astigmatism (abnormally shaped eyeball)
  • balance disturbance and broad gait (walking)
  • reduced fine motor skills
  • brachydactyly (short fingers and/or thumbs)
  • syndactyly (digits joined together)
  • diabetes mellitus
  • dental and roof of mouth abnormalities (high-arched palate)
  • cardiovascular anomalies (high blood pressure, abnormal heart valves)
  • hepatic (liver) problems
  • olfactory dysfunction (lack of ability to smell)
  • Situs inversus (misplacement of internal organs – eg mirror-image).

In children with BBS, night-blindness usually occurs by seven to eight years of age and total blindness is typical by the third decade.

What are the causes?

Twenty-one genes are known to be associated with BBS. Two mutations in any one of these genes are enough to manifest the syndrome. Not all people (~15%) with BBS have mutations in these known genes, so more remain to be discovered. It is now known that these mutations result in abnormal cilia function. These are finger-like projections that are important for cells to sense their surrounding environment and communicate with one another.

How is it diagnosed?

Diagnosis is made on the basis of clinical features initially. A diagnosis can be confirmed by testing DNA to see if the mutation(s) causing the condition lie in one of the 21 genes already identified.

How is it treated?

There is no cure for BBS. Treatment aims to reduce the symptoms experienced by a person with BBS. Regular eye check-ups by an ophthalmologist will highlight any existing problems. Visual aids and educational programmes can assist with visual difficulties. Obesity is managed with diet, exercise and behavioural therapies. Hypercholesterolemia (high cholesterol) and diabetes mellitus may be treated with the appropriate medications and changes to diet. Early intervention, special education provision and speech and language therapy can help with learning.

In cases of severe renal (kidney) abnormality, renal transplantation may be required. Genital abnormalities, for example hypospadias, may be surgically corrected. Hormone replacement therapy can be initiated for hypogonadism (where sex glands produce little or no sex hormones). Cardiac abnormalities need to be monitored and may be corrected surgically. Surgery to remove extra digits prevents difficulties walking and balancing and poor fitting of footwear.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Inheritance is autosomal recessive (two mutations required to manifest the disease).

Prenatal diagnosis
A number of features (e.g. extra digits, hyperechogenic kidneys) can be determined on high-definition ultrasound scanning of the fetus. This, however, is not a test of exclusion of the condition. If two gene mutations can be identified in a BBS family then a molecular genetic DNA test can be offered prenatally.

Is there support?

Bardet-Biedl Syndrome UK (Formerly LMBBS)

Tel: 07591 206680
Email: [email protected]
Website: bbsuk.org.uk

The charity is a Registered Charity in England and Wales No. 1027384 and in Scotland No. SCO41839. It provides information and support for people with Bardet-Biedl Syndrome and their families and carers throughout the UK. The Charity holds an annual family conference and activities throughout the year and through the BBS UK Clinics provides further support and facilitation services alongside the NHS.

Group details last updated April 2018.

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