The DISEASE
Bardet-Biedl Syndrome is a genetic disease caused by a change (mutation) in a gene. To date, there are at least twenty-four different genes that may be responsible for this disease. These are genes BBS1 to BBS24.
Bardet-Biedl most often combines obesity, vision problems, finger abnormalities, and in some cases kidney and genital abnormalities. Learning difficulties are often present. Other malformations (of the heart, for example) may be associated, but more rarely.
Bardet-Biedl Syndrome affects both boys and girls and usually begins at birth and is not contagious. The manifestations and severity of the syndrome vary considerably from person to person.
Bardet-Biedl syndrome is a rare disease whose prevalence (number of people affected in a population at a given time) is between 1 in 100,000 and 1 in 160,000 for the populations of Europe and North America. This syndrome is much more common in certain isolated populations such as the Bedouin populations of Kuwait where the prevalence is estimated at 1 in 13,500.
TRANSMISSION
In most cases of BBS, both parents carry a normal gene and a defective recessive gene. Although the parents have a copy of the defective gene and are called carriers of the disease, they are not affected by the presence of the defective gene.
For a recessive disease to occur, the child must inherit two defective copies of the gene, one from each parent. The child from each pregnancy has a one in four chance of being affected. If a newborn child is not affected, there is a 2 in 3 chance that it will carry the defective BBS gene.
Because the syndrome is rare, it is unlikely that a carrier will have affected children unless their partner is also a carrier.
GENETIC
To date (2022), mutations in 24 BBS genes have been identified in 85% of BBS patients. There are still more genes to be found, as 15% of patients do not have a mutation in one of the identified BBS genes.
Some genes are more common than others: 38% of patients have mutations in the BBS1 gene and in the BBS10 gene. However, patients with mutations in the same BBS gene can have very different symptoms of the syndrome: one person may be born with extra fingers, while another person with the same mutation may not have extra fingers at all.
The genes involved in this syndrome 'control' the production of proteins that play a role in the cilia of cells. Cells have cilia that function like antennae, capturing and transmitting information about the state of their environment. When these cilia are defective (which is the case when genes are mutated), certain functions are also altered.
In particular, cilia play an important role in vision and kidney function, which explains the visual deficit and possible kidney abnormalities in Bardet-Biedl syndrome. Much research is underway to understand the role of the cilia in all manifestations of the disease.
CLINICAL MANIFESTATIONS
The clinical manifestations of Bardet-Biedl syndrome are multiple and vary considerably from person to person. Therefore, not all patients have all of the symptoms described below.
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HOW CAN THE SYMPTOMS
BE EXPLAINED
The genes involved in this syndrome "control" the production of proteins that play a role in the cells' eyelashes. The cells have lashes that function like antennae, capturing and transmitting information about the state of their environment. When these cilia are defective (which is the case when genes are mutated), certain functions are also altered. In particular, cilia play an important role in vision and kidney function, which explains the visual deficit and possible kidney abnormalities in Bardet-Biedl syndrome.
A great deal of research is underway to understand the role of the cilia in all manifestations of the disease.
If left untreated, the various manifestations can worsen, in particular kidney damage and obesity. Obesity, which is resistant to the usual diet and measures, can be complicated by diabetes and excess lipids in the blood (hyperlipidemia), heart and joint problems.In addition, retinal abnormality leads to a severe reduction in vision, and even blindness between the ages of 15 and 30. Indeed, the field of vision gradually reduces and central vision can sometimes end up being reduced. Early treatment can limit the worsening of symptoms.