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Bardet-Biedl Syndrome Pathophysiology

By Dr Ananya Mandal, MD

Bardet-Biedl Syndrome is a genetically inherited condition. It is the result of inheriting mutations or alterations in the genes. At least 14 different genes have been identified that may be mutated or altered in individuals with this syndrome.

Genetics of Bardet-Biedl syndrome

There are 14 different genes that may be altered or mutated in individuals with Bardet-Biedl syndrome. These are commonly termed BBS genes.

These genes code for proteins that are involved in the maintenance and function of cilia of the cells.

What are cilia?

Cilia are finger-like or hair-like structures that are present on the surfaces of many types of cells. These are involved in movement of the cells and different chemical signalling pathways.

Cilia are also vital in perception of sensory input including sight, smell and hearing.

Deformed cilia

Mutations in BBS genes may lead to deformed cilia. Due to these defects there may be disruptions in important chemical signalling pathways. This leads to impaired sensory perceptions. These defective cilia are the basic pathology of Bardet-Biedl syndrome.

BBS1 and BBS10 gene

Around 25% of all cases of this syndrome result from mutations in the BBS1 gene. Another 20 percent of cases are caused by mutations in the BBS10 gene.

The other BBS genes each account for only a small percentage of all cases of this condition. In a quarter of patients no specific gene or cause is known.

Genetic changes in a specific BBS gene may exist alone or in combination with mutations in other genes that may modify the course of the disease.

These additional changes of genes along with the original changes in the genes are responsible for the variations of signs and symptoms of Bardet-Biedl syndrome.

Inheritance of Bardet-Biedl syndrome

Bardet-Biedl syndrome is inherited in an autosomal recessive pattern. This means for a child to inherit the condition both parents have to have a single copy of the mutated gene.

These parents do not manifest the symptoms of the condition and typically do not show signs and symptoms of the condition.

Associations with other genetic disorders

There are several genetic disorders that may be associated with Bardet-Biedl syndrome. Commonly other cilia related disorders may be associated with this syndrome. This includes Meckel–Gruber syndrome, Alstrom syndrome, nephronophthisis, polycystic kidney, primary ciliary dyskinesia, retinitis pigmentosa and some forms of retinal degeneration.

Reviewed by , BA Hons (Cantab)

Further Reading

Last Updated: Jul 22, 2013

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