The Bardet-Biedl syndrome is a a syndrome characterized mainly by obesity, pigmentary retinopathy, polydactyly, mental retardation, hypogonadism, and renal failure in fatal cases.

The syndrome is named after Georges Bardet and Arthur Biedl.

Two forms have been identified:

Bardet-Biedl syndrome 1 (BBS1) has no linkage to chromosome 16
Bardet-Biedl syndrome 2 (BBS2) is mapped to markers on chromosome 16.

Laurence-Moon-Biedl syndrome and Laurence-Moon-Biedl-Bardet syndrome are no longer considered as valid terms in that patients of Laurence and Moon had paraplegia but no polydactyly and obesity which are the key elements of the Bardet-Biedl the syndrome. Laurence-Moon syndrome is a separate entity.

Major features

Eyes: Pigmentary retinopathy.
Hand and foot: Polydactyly.
Cardiovascular system: Hypertrophy of interventricular septum and left ventricle and dilated cardiomyopathy.
Gastrointestinal system: Fibrosis.
Urogenital system: Hypogonadism, renal failure, urogenital sinuses, ectopic urethra, uterus duplex, septate vagina, and hypoplasia of the uterus, ovaries, and fallopian tubes.
Growth and development: Mental and growth retardation.
Behavior and performance: Poor visual acuity and blindness.
Heredity: The syndrome is familial and is transmitted as an autosomal recessive trait. chromosome 3 locus appears to be linked to polydactyly of all four limbs, whereas chromosome 15 is associated with early-onset morbid obesity and is mostly confined to the hands, and chromosome 16 represents the "leanest" form.
Additional features: Obesity.

Cause

The detail biochemical mechanism that leads to BBS is still unclear. Recently, eight genes (BBS1 to BBS8) that are responsible for the disease when mutated have been cloned, and most of the gene products encoded by these BBS genes are located in the basal body and cilia of the cell. It has been postulated that these BBS gene products might involve in the cell signaling pathway in the cilia, and these signaling systems play an essential role in the normal development so that a malfunction in these systems causes the diverse pathological effects of the Syndrome.

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Genetic disorder traced to cilia - Obesity - Bardet-Biedl syndrome
From USA Today (Society for the Advancement of Education), 2/1/04

A potential new contributor to obesity--faulty cilia--has been discovered by researchers at Johns Hopkins University, Baltimore, Md. Many a high school biology student has glanced into a microscope to see the planet's smallest animals--paramecium and the like--being propelled by the waving, hair-like projections known as cilia. Yet, cilia also are found in human cells, helping move fluid and mucous around in the brain, lungs, eyes, and kidneys, or sticking out from cells to act like antennae. Studying families with a relatively rare condition called Bardet-Biedl syndrome (BBS), characterized by obesity, learning disabilities, and eye and kidney problems, the researchers uncovered a new gene. Furthermore, the gene's protein, BBS8, is found only at the base of cilia.

Bardet-Biedl syndrome (pronounced BAR-day BEED-el) "is a relatively rare genetic disorder, but it has traits common to many people," declares Nicholas Katsanis, assistant professor in the McKusick-Nathans Institute of Genetic Medicine. "We don't know yet how the ciliary defect might lead to obesity or learning disabilities, but the finding provides a new avenue to studying these genetically murky traits. It is very difficult to translate genetic understanding into a cellular mechanism that explains what is seen in a disease."

Some aspects of BBS have been linked to ciliary defects in other conditions. Cilia are known to play key roles in mammalian development, creating what is known as left-right asymmetry so organs like the heart, lungs, and liver end up in the correct place. In people with BBS, sometimes left-right asymmetry is reversed. Also, malfunctioning cilia in the back of the eye can cause retinal dystrophy and eventual blindness, and ciliary difficulties in the kidney lead to structural complications in the organ.

Even though these primary characteristics of Bardet-Biedl have been tied to ciliary defects, the condition itself and its other traits-extra fingers and diabetes--never have been linked to cilia before. These syndrome characteristics may be caused by defects in the cellular mechanics, but the research finding opens a never-before-pursued channel to understanding these attributes in the general population.

Katsanis says the next step is to figure out exactly what is wrong with the cilia and how those defects affect different tissues. The answer could lie in ciliary movement or in their ability to sense cells' surroundings. "Cilia are very overlooked. The majority of cilia in human cells act as a sort of communication device, which isn't the typical picture of waving, mobile cilia. Cilia can act as cells' private satellite dish."

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