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An Overview of Bardet-Biedl Syndrome

written by: Blaise Wellesley•edited by: lrohner•updated: 9/30/2010

Bardet-Biedl syndrome is a rare autosomal recessive disorder that has many striking characteristics. Learn more about this disorder such as causes, signs and symptoms, and more.

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    Bardet-Biedl syndrome, or Laurence-Moon-Biedl-Bardet, is a genetic disorder that has many severe effects on the human body. Its characteristics include mental retardation, renal failure, polydactylism, retinitis pigmentosa, vision loss and hypogonadism. Bardet-Biedl syndrome has a prevelance rate of around 1 in 140,000 to 160,000 newborns in North America and Europe. The onset of Bardet-Biedl syndrome has been known to rise from 14 different genes, often called BBS genes. Bardet-Biedl syndrome is inherited in an autosomal recessive pattern, which is a reason why Bardet-Biedl syndrome is so rare.

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    Signs and Symptoms

    Bardet-Biedl syndrome is a disorder that can have a widespread number of symptoms and variability in affected individuals. The most striking feature of Bardet-Biedl syndrome is a childhood-onset visual loss followed by night blindness. This occurs when the light-sensing portion of the eye begins to irreverisbly deteriorate at a young age. Blind spots can form and eventually lead to tunnel vision, which decreases the total field of view in a patient. Some patients become completely blind by adolesence due the severity of the complications.

    Obesity is another symptom apparent in individuals with Bardet-Biedl syndrome. Irregular weight gain begins during early childhood and continues to be a prominent issue throughout the patient's life. Obesity in the individual can start the onset of other problems, such as diabetes, high blood pressure and high cholesterol levels.

    Other symptoms can include:

    • Speech delay
    • Cardiovascular abnormalities
    • Presence of extra fingers or toes; polydactyly
    • Learning disability
    • Reduced amounts of sex hormones
    • Abnormal genitalia and kidneys
    • Motor skill impairments
    • Lose of smell
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    Bardet-Biedl syndrome can arise from mutations of the 14 Bardet-Biedl syndrome, or BBS genes. These genes have known functions with cell structures called cilia. Cilia are hair-like projections that extend from the surface of many cells in the human body. They have direct involvement of cellular movement and signaling of many pathways. It has been found that cilia is also need from sensory input such as smelling, hearing, and sight. Proteins created from the 14 BBS genes influence the maintenance, upkeep, and functioning of cilia in cells. Mutations in these proteins directly affect the cilia.Defects in the cilia can interrupt cell signaling early through development which can impair the senses.

    It has been found that although the majority of those with Bardet-Biedl syndrome have mutations in one of the 14 BBS genes, some patients can have the syndrome without these mutations, but have defective gene complexes elsewhere. This is one theory that can explain the wide range of variability of symptoms of those with Bardet-Biedl syndrome.

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    Inheritance Patterns

    Bardet-Biedl syndrome is an autosomal recessive pattern. This means that both copies of the mutated BBS genes from both parents are passed through. Unaffected parents that have a child with the disorder may not have symptoms because of the recessive trait of Bardet-Biedl syndrome.

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    Testing includes the sequencing and isolation of the BBS genes of an affected individual. Having these results can confirm or negate the diagnosis of Bardet-Biedl syndrome.

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    As with most rare and severe genetic disorders, there are no known cures or treatmen options for Bardet-Biedl syndrome. However, there are many educational and occupational therapies that are available to the individual with the desire to increase their quality of living. These options exist in hospitals, schools, and other community centers.

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