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Its prevalence in Europe is estimated at between 1/125,000 and 1/175,000.

This disorder is characterized by a combination of clinical signs: obesity, pigmentary retinopathy, post-axial polydactyly, polycystic kidneys, hypogenitalism, and learning disabilities, many of which appear several years after disease onset. Clinical expression is variable but most patients manifest the majority of clinical signs during the disease course. Pigmentary retinopathy is the only constant clinical sign after childhood. BBS may also be associated with several other manifestations including diabetes, hypertension, congenital cardiopathy and Hirschsprung disease (see this term).

The wide clinical spectrum observed in BBS is associated with significant genetic heterogeneity. To date, mutations in 12 different genes (BBS1 to BBS12) have been identified as being responsible for this phenotype. These genes code for proteins involved in the development and function of primary cilia. Absence or dysfunction of BBS proteins results in ciliary anomalies in organs such as the kidney or eye. However, the relationship between symptoms and ciliary dysfunction remains obscure for some of the clinical manifestations of BBS.

Recognition of the clinical picture is important as the diagnosis can be confirmed by molecular analysis, allowing appropriate genetic counseling for family members and possible prenatal diagnosis.

The differential diagnosis should include the Alström, McKusick-Kaufmann and Meckel-Gruber syndromes (see these terms).

The disorder is transmitted mainly in an autosomal recessive manner but oligogenic inheritance has been reported in some cases.

Patients with BBS will need multidisciplinary medical care.

The renal abnormalities are the main life-threatening manifestations because they can lead to end-stage renal failure and require renal transplantation. Progressive vision loss due to retinal dystrophy, together with moderate intellectual deficit (when present), behavioral anomalies, hypomimia and obesity will affect the social life of these patients.