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The Bardet-Biedl syndrome is a human genetic disorder that produces many effects and affects many body systems. It is characterized mainly by obesity, retinitis pigmentosa, polydactyly, mental retardation, hypogonadism, and renal failure in some cases.[1]
Eponym and classificationThe syndrome is named after Georges Bardet and Arthur Biedl.[2] Two forms have been identified:
The first known case was reported by Laurence and Moon in 1866 at the Ophthalmic Hospital in South London. 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 usually considered a separate entity. However, some recent research suggests that the two conditions may not be distinct.[3] Major clinical features
PathophysiologyThe detailed biochemical mechanism that leads to BBS is still unclear. At this moment, twelve genes (BBS1 to BBS12) that are responsible for the disease when mutated, have been cloned. The gene products encoded by these BBS genes, called BBS proteins, are located in the basal body and cilia of the cell.[citation needed] Using the round worm C. elegans as a model system, biologists found that BBS proteins are involved in a process called Intraflagellar transport (IFT), a bi-directional transportation activity within the cilia along the long axis of the ciliary shaft, that are essential for the formation and maintenance of cilia[6]. Recent biochemical analysis of human BBS proteins revealed that BBS proteins are assembled into a multiple protein complex, called "BBSome". BBSome is proposed to be responsible for transporting intracellular vesicles to the base of the cilia and to play an important roles in the ciliary function. Since abnormalities of cilia are known to be related to a wide range of disease symptoms including those commonly seen in BBS patients, it is now widely accepted that mutated BBS genes affect normal cilia functions, which, in turns, cause BBS.[citation needed] Relation to other rare genetic disordersRecent findings in genetic research have suggested that a large number of genetic disorders, both genetic syndromes and genetic diseases, that were not previously identified in the medical literature as related, may be, in fact, highly related in the genetypical root cause of the widely-varying, phenotypically-observed disorders. BBS is one such syndrome that has now been identified to be caused by defects in the cellular ciliary structure. Thus, BBS is a ciliopathy. Other known ciliopathies include primary ciliary dyskinesia, polycystic kidney and liver disease, nephronophthisis, Alstrom syndrome, Meckel-Gruber syndrome and some forms of retinal degeneration[7]. Hereditary characteristicsThe 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.[citation needed] Notes
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