What Is Bardet-Biedl Syndrome?

Clara Kedrek

Bardet-Biedl syndrome is a rare genetic disease that causes a variety of symptoms. It is considered to be a ciliopathic human genetic disorder because the mutations that cause the syndrome affect the function of cilia, which are tiny hair-like protrusions located on the outside of cells. Symptoms of Bardet-Biedl characteristically include obesity, renal failure, learning disabilities, and low levels of sex hormones. The diagnosis of this condition is often made on the basis of symptoms seen in patients. Treatment of the disease focuses on alleviating symptoms, reducing the risk of developing complications, and providing patients with genetic counseling.

One symptom of Bardet-Biedl syndrome is obesity.
One symptom of Bardet-Biedl syndrome is obesity.

One characteristic of Bardet-Biedl syndrome is that it is inherited in an autosomal recessive pattern, meaning that a person needs to have two abnormal copies of the affected gene in order to develop symptoms. Patients with only one bad copy are typically normal and do not have any symptoms. The condition is considered to be congenital, which means that patients with the syndrome have symptoms from birth.

A diagnosis of Bardet-Biedl syndrome will be made after an examination from a doctor.
A diagnosis of Bardet-Biedl syndrome will be made after an examination from a doctor.

Symptoms of Bardet-Biedl syndrome are typically broken into two categories, the primary features and the secondary features. Primary features such as obesity in the midsection of the body, learning disabilities, malfunctioning kidneys, and an abnormal condition of the eye called retinitis pigmentosa are commonly seen with the syndrome. Another primary feature is polydactyly, which is characterized by having extra fingers or extra toes. Secondary features include abnormalities that are less clearly associated with Bardet-Biedl syndrome, but are still often present in affected patients. Examples include behavioral problems, mental retardation, nonspecific eye abnormalities, delayed speech, poor coordination, diabetes mellitus, and problems with the heart.

The diagnosis of Bardet-Biedl syndrome is made on the basis of an examination performed by a doctor or other health care professional. A number of researchers have proposed different diagnostic criteria that can be used to establish the diagnosis. For example, one group of investigators suggests that a patient must have either four of the primary features or three primary features along with two secondary features. Some researchers are working on creating tests to identify the specific genetic mutations seen in patients. Developing these tests is difficult, however, because mutations in 14 different genes have been identified as causes of the syndrome.

Treatment of Bardet-Biedl syndrome focuses on alleviating the symptoms caused by the condition, as the syndrome does not have a cure. Patients need to follow up regularly with ophthalmologists in order to monitor the development of their eye disease. Often these patients are advised to restrict their caloric intake and perform regular physical activity in an effort to prevent excessive weight gain. Routine laboratory tests to check the function of the kidney are also important in these patients, as involvement of the disease in this organ could be life-threatening.

Patients diagnosed with Bardet-Biedl syndrome can be offered genetic counseling to prevent passing the condition along to their children. If an affected man wants to have a child, his partner can be tested to see whether or not she has one bad copy of the gene. A couple consisting of an affected individual and a partner who has one bad copy of the gene has a 50% chance of having a child with the syndrome.

Bardet-Biedl syndrome is considered a ciliopathic human genetic disorder.
Bardet-Biedl syndrome is considered a ciliopathic human genetic disorder.

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