Bardet-Biedl syndrome, BBS1-related
What Is Bardet-Biedl Syndrome, BBS1-Related?
Bardet-Biedl Syndrome (BBS), BBS1-Related is an inherited disease that affects many different parts of the body. This condition generally causes vision problems, mild obesity, extra fingers or toes, genital and kidney abnormalities, and learning difficulties. Vision problems result from degeneration of the cone cells of the retina. In approximately 90% of individuals, the vision loss begins as night blindness in childhood and progresses to a loss of peripheral vision and eventual blindness by adolescence. Abnormal weight gain begins in early childhood and continues throughout adulthood. As a result, obesity-related diabetes, high blood pressure, and high cholesterol may also develop.
Kidney abnormalities range from a few functional problems to life-threatening kidney failure. Approximately 50% of individuals with the disease have developmental disabilities, which can range from delayed emotional development or mild learning difficulties to more severe intellectual disability. In some cases, these delays are due in part to vision loss, while in other cases they are a direct result of the condition.
Other features of BBS include liver disease, poor balance and coordination, behavioral issues, characteristic physical features (facial features and dental irregularities), and hearing loss. BBS can also affect the heart and reproductive system. These features tend to vary by the BBS type. Some secondary features reported in BBS type 1 are liver disease, diabetes, characteristic facial features, heart defects, dental anomalies, hearing loss, and short fingers that may be webbed or joined together.
There are at least 19 genes that are associated with BBS.
How Common Is Bardet-Biedl Syndrome, BBS1-Related?
The prevalence of BBS in North American and European populations is 1 in 100,000 to 1 in 160,000. Approximately 20% of BBS is caused by mutations in BBS1. However, the incidence varies greatly by region, especially in small, possibly isolated populations. The prevalence of BBS is up to 1 in 13,500 in Kuwaiti Bedouins, up to 1 in 87,000 in Tunisians, and up to 1 in 17,000 in Canadians from Newfoundland. Incidence information specific to BBS type 1 is lacking for these populations. However, BBS associated with BBS1 has been reported in both the Newfoundland and Faroe Islands populations.
How Is Bardet-Biedl Syndrome, BBS1-Related Treated?
There is no cure for BBS. Regular monitoring of vision; weight; blood pressure; thyroid, kidney, and liver function; and development are recommended. Visual aids and education can help with impaired vision. Proper diet and exercise can help with obesity. Behavioral, speech, and educational therapies are also beneficial.
Kidney issues are managed in a standard way, but if they become life-threatening, dialysis or transplantation may be necessary. Surgery can correct some birth defects (extra digits may be removed in childhood and heart or vaginal malformation may be corrected), and an orthodontist may assist with correction of dental anomalies. While hormone therapy can aid sexual development, males can still have fertility issues.
What Is the Prognosis for an Individual with Bardet-Biedl Syndrome, BBS1-Related?
Predicting symptoms and the course of the disease for individuals with BBS can be difficult due to the variable nature of the condition. Symptoms vary, even within families. One of the most consistent features is progressive vision loss, which leads to blindness in about 90% of cases. Kidney disease is also frequent, with about a third of individuals developing kidney failure and about 10% requiring dialysis or transplantation. Kidney failure is a major cause of early death for those with BBS, although complications of obesity, heart disease, and diabetes have also been reported as causes of death. With proper treatment and monitoring, a majority of individuals may have a normal or near-normal life expectancy.