Bardet-Biedl syndrome is a condition that affects several parts of the body. It runs in families and may severely impair the sufferer.
Symptoms and features of the condition
One of the major features of Bardet-Biedl syndrome is loss of vision. Loss of vision occurs as the retina, that is the light sensing tissue or layer at the back of the eye, fails gradually.
The problems appear initially as difficulty in seeing in the dark. This is seen in childhood as a slow onset condition. This is followed by development of blind spots in vision that leads to falls and knocks initially.
Over time, these blind spots enlarge and turn into a tunnel where only the center is visible. With time the central clear area also clouds.
By the time the child reaches adolescence or early adulthood, he may become legally blind.
Another characteristic feature is obesity. There is typical abdominal obesity that begin in early childhood and continues throughout life. This may give rise to other complications like type 2 diabetes, high blood pressure and abnormally high levels of cholesterol.
Typically there may also be presence of extra fingers and/or toes along with mental retardation, learning problems, and abnormalities of the genital organs.
Bardet-Biedl syndrome epidemiology
This is a rare condition and is seen in 1 in 140,000 to 1 in 160,000 newborns in most of North America and Europe.
The prevalence is slightly higher on the island of Newfoundland (off the east coast of Canada), where it affects an estimated 1 in 17,000 newborns.
Further Bedouin population of Kuwait and Arabs are also more commonly affected with prevalence there being about 1 in 13,500 newborns.
Causes of Bardet-Biedl syndrome
Bardet-Biedl syndrome is a genetically inherited condition. It results from mutations in at least 14 different genes in the body. These are commonly called BBS genes.
It is found that these genes help make the hair like cellular structures called cilia. These cilia are involved in cell movement, different chemical signalling pathways perception of sensory input (such as sight, hearing, and smell) etc.
The BBS genes code for proteins that maintain the functions of the cilia. Defects in these genes lead to defective cilia.
The inheritance of Bardet-Biedl syndrome is autosomal recessive. This means parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene but have no symptoms of the condition (carriers of the gene).