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Bardet-Biedl Syndrome (BBS)
Monday, 18 August 2003
Tuesday, 23 November 2004

What

Bardet-Biedl syndrome (BBS) is a rare genetic disorder characterized by mental disabilities, retinal dystrophy (visual disturbances, usually appearing in individuals when they are 10 to 20 years of age), malformed extremities, functional and structural kidney problems, small gonads (in males), and obesity. BBS has been known since the early 1920s and was formerly grouped with Laurence-Moon syndrome as the Laurence-Moon-Biedl disease. Bardet-Biedl syndrome is now considered as a separate entity.

Who

BBS seems to occur about once for every 150,000 persons born in the population.

Signs and Symptoms

The following are physical signs and symptoms that parents of children with BBS might notice and seek medical help:

  • Infants and children may display slow development in such areas as sitting, walking, and speaking in contrast with other children of the same age. These early delays can continue on into later years with mild to moderate learning disabilities in school.
  • Progressive visual loss occurs when the retina (back of the eye) undergoes degenerative changes. Cells in the retina, called rods and cones, are essential for the ability to see at night (rods) and to see color (cones). The earliest signs of vision problems are often not apparent until seven to eight years of age and usually start with night blindness. Even this feature may be missed, only becoming apparent to parents in retrospect. Visual acuity, ability to see in the dark and peripheral vision are all affected. Ophthalmological assessment should be sought as soon as possible to determine visual acuity, field deficits, or refractive errors.
  • Deformities of the hands and feet are seen with an extra finger or toe (polydactyly) and short, stubby fingers or toes (brachydactyly), with toes being more commonly affected. ∑ One study found that 71% of patients had structural kidney problems including renal hypoplasia, hydronephrosis, pyelonephritis, and glomerulonephritis. Kidney problems can also cause hypertension, which is very common in these patients. Because a third of patients with Bardet-Biedl syndrome develop renal failure, careful monitoring of kidney function is necessary in all patients. If blood tests are abnormal renal function tests may be warranted.
  • Excessive weight gain leading to obesity and a characteristic “Moon face” is common and usually begins after the age of 1 or 2 years.
  • Other findings are a high pitched nasal and breathy voice; joint pain; small testes in males.

Possible Causes

BBS is a recessively inherited disorder, meaning that both parents would have had to pass along an altered gene to the child. The parents have one altered gene and one normal gene so they are not affected by BBS, but are carriers, and would have no way of knowing when both altered genes are inherited to affect their child. There are currently four known genes that are responsible for BBS in children that are found on chromosomes 3, 11, 15 and 16. Because these genes are not the cause of all BBS cases, there are still more genes to be discovered. The function of these genes is not known.

Diagnosis

The diagnosis of BBS is usually confirmed in childhood when visual problems are found to be due to abnormal pigments in the retina of the eye. The first sign of visual problems is usually night blindness. Because developmental delays can be associated with a multitude of genetic disorders, slowness in achieving milestones and academic learning is not diagnostic. Four of the following features are required to diagnose BBS: rod-cone dystrophy, polydactyly, kidney problems, excessive weight gain, learning disabilities, and small gonads (in males).

Treatment

Because it is currently not known how BBS works, there is no cure. However, the symptoms can be treated. An extra toe or finger can be surgically removed. Obesity can be addressed by diet and exercise regimen, although it is a constant and life long struggle to maintain reasonable weight. Learning difficulties are usually treated at school through special educational programs and parents are often resourceful in finding alternative strategies for their children to learn. Speech therapy is also very useful. The hypogonadism (small gonads) can be evaluated by endocrine specialists who may treat these boys with medication. While being seen by the endocrinologist, the short stature can be also be evaluated for treatment with growth hormone therapy, which has improved ultimate height in some children. No cure exists for the progressive visual loss, but early evaluation of visual acuity helps prepare the child for a future with little or no sight.

Prognosis

The type and severity of the various signs and symptoms of BBS show great variability, even within families. The visual prognosis for children with Bardet-Biedl syndrome is poor. Vision is usually abnormal by age ten years. As early as 17 years, there is very little vision remaining. The mean age at which patients are registered legally blind in the UK is 15.5 years. Thus, the mean time for progression from diagnosis to blindness is approximately seven years. Children with BBS do encounter a number of disabilities that affects his/her life. Of greatest concern is early onset of blindness, complications of obesity and severe kidney impairment (the most frequent cause of early death).

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Genetics Education Center
A website with a comprehensive list of organizations for the disease located worldwide.

Lawrence Moon Baret Biedl Syndrome
A great, easy to use website with educational information as well as links to other sites.

Family Village
A nice site with educational information and links to other sites and support groups.

Google Search for Bardet-Biedl Syndrome (BBS)

References and Sources

UMDS: www.isgrd.umds.ac.uk/laurence/ Foundation of Fighting Blindness: www.blindness.org/visiondisorders/causes.asp?type=9