Bardet-Biedl syndrome is a rare, genetic multisystem disorder characterized primarily by deterioration of the cells that receive light stimuli (cone and rod cells), in the retina of the eyes (progressive cone-rod dystrophy), an extra finger near the pinky or an extra toe near the fifth toe (postaxial polydactyly), a condition in which fat is disproportionately distributed on the abdomen and chest rather than the arms and legs (truncal obesity), diminished size and decreased function of the gonads (testes), in males (hypgonadism), kidney (renal), ,abnormalities, and learning difficulties. Visual abnormalities usually become progressively worse and may ultimately result in blindness. Kidney (renal) abnormalities may progress to cause life-threatening complications. Learning difficulties are a common finding due, in part, to vision loss. Only a minority of affected individuals have severe mental impairment. Most cases of Bardet-Biedl syndrome are inherited as an autosomal recessive trait.
Bardet-Biedl syndrome shows significant overlap with a disorder called Laurence-Moon syndrome. In fact, in the past, these disorders were considered the same and referred to as Laurence-Bardet-Biedl syndrome. Eventually, researchers decided that the two disorders despite numerous similarities were distinct entities. However, recent research has demonstrated that some individuals with the clinical findings of Laurence-Moon syndrome have had mutations in genes linked to Bardet-Biedl syndrome. This discovery has led some researchers to suggest that little evidence exists to continue to classify these two disorders as distinct entities.