Bardet-Biedl syndrome, BBS2-related

What is Bardet-Biedl Syndrome, BBS2-related?

Bardet-Biedl syndrome (BBS) is an inherited disease that generally causes vision problems, mild obesity, extra fingers or toes, genital and kidney abnormalities, and learning difficulties.

One hallmark of the disease is a vision problem caused by degeneration of the retina. It begins as night blindness in childhood and progresses to a loss of peripheral vision. People with Bardet-Biedl syndrome can also lose central vision during childhood or adolescence. The mean age at which these adolescents become legally blind is 15.5 years. By early adulthood, they are severely visually impaired.

Kidney abnormalities are present in most people with Bardet-Biedl syndrome. The problems caused by these abnormalities can range from few functional problems to life-threatening kidney failure. Around half of people with the disease have developmental disabilities. This can range from mild learning disabilities or delayed emotional development to more severe symptoms. In some cases these delays are due in part to vision loss, while in other cases they are a direct result of the disease.

Less common features include liver disease, diabetes, neurological issues (like poor balance and coordination), behavioral issues, characteristic physical features (facial features and dental irregularities), high blood pressure, defects in the heart or reproductive system, and hearing loss amongst others. These features tend to vary by the type. Some secondary features reported in Bardet-Biedl syndrome, BBS2-related are characteristic facial features, heart defects, and short fingers that may be webbed or joined together.

There are at least 19 genes that are associated with Bardet-Biedl syndrome, and some of these genes have been associated with other syndromes (e.g., Laurence-Moon syndrome, retinitis pigmentosa, Meckel-Gruber syndrome). It is unclear if these represent a spectrum of disease or if BBS is a distinct condition from the other associated syndromes. Mutations in BBS2 have been reported in a few individuals with retinitis pigmentosa (vision loss only) and Meckel-Gruber syndrome (typical features include kidney disease and extra fingers or toes with the addition of brain malformations).

How common is Bardet-Biedl Syndrome, BBS2-related?

Bardet-Biedl syndrome is generally thought to be a rare disorder. A few studies, primarily in Caucasians, have suggested an overall frequency of cases from 1 in 100,000 individuals in North America to 1 in 150,000 in Europe. However, the global frequency of this condition cannot be estimated from these numbers. One reason for this is that the disease frequency varies by population, being higher in populations where marriage between blood relatives (consanguinity) is common or the population was isolated. Examples of populations with a higher frequency of BBS include Kuwaiti Bedouins (1 in 6900), Tunisians (1 in 87,000), and individuals from Newfoundland (1 in 18,000). Populations with higher frequencies of BBS2 have also been reported in Tunisia, a Hutterite population from South Dakota, and the Ashkenazi Jewish. BBS2 only accounts for 7.5-17% of all BBS cases.

How is Bardet-Biedl Syndrome, BBS2-related treated?

There is no cure for Bardet-Biedl syndrome, and symptoms of the condition are managed by a team of specialists. A geneticist is typically involved in the diagnosis and centralized management of an affected child. Management may include monitoring, provision of aids/therapies, or surgery.

Regular monitoring of vision, weight, blood pressure, thyroid/kidney/liver function, and development are recommended. Vision issues will be managed by an ophthalmologist and there may be aids that help improve quality of life. A dietician may help with weight regulation and medications may help with high blood pressure. An endocrinologist may be consulted for diabetes, thyroid disease, and proper pubertal development. Kidney issues are managed in a standard fashion, 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 or heart/vaginal malformation may be corrected), and an orthodontist may assist with correction of dental anomalies. Early intervention and therapies may assist with learning difficulties, and a pediatric neurologist may help monitor the progression of development, if necessary.

What is the prognosis for a person with Bardet-Biedl Syndrome, BBS2-related?

Predicting symptoms and the course of the disease for individuals with BBS can be difficult due to the variable nature of the condition - even within families. One of the most consistent features is progressive vision loss, which frequently leads to blindness. Kidney disease is also frequent, with about a third of patients developing kidney failure and about 10% requiring dialysis or transplantation. Kidney disease is a major cause of early death for people with BBS, though complications of obesity, heart disease, and diabetes have also been reported as causes of death. A majority of individuals may have a normal or near-normal life expectancy though with various impairments.