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Genetic Causes of Intellectual Disabilities:Bardet-Biedl Syndrome and Laurence-Moon Syndrome-Taybi Syndrome

Tammy Reynolds, B.A., C.E. Zupanick, Psy.D. & Mark Dombeck, Ph.D.

Bardet-Biedl syndrome

Bardet-Biedl syndrome describes two inherited, genetic disorders. The first type is linked to problems on chromosome 3. Mutations cause polydactyl limbs. Polydactyl means 'many fingers.' It refers to anyone who has more than five fingers.

Symptoms include incomplete development of reproductive organs, kidney and eye abnormalities, and extra fingers or toes. The characteristic most commonly associated with the syndrome is obesity. Fatal cases are marked by renal failure.

Bardet-Biedl syndrome has been closely associated with Laurence Moon syndrome (see below). People with Laurence Moon syndrome have paralysis below the waist. However, they do have extra limbs or obesity as with Bardet-Biedl syndrome. Some authors refer to Laurence-Moon-Biedl-Bardet syndrome. This is inaccurate. The two conditions are distinct.

Laurence-Moon syndrome

Laurence-Moon syndrome is a rare inherited genetic disorder. Some researchers have associated the syndrome with Bardet-Biedl syndrome (see above). This is inaccurate. The two conditions are distinct.

Symptoms include hypogondadism and retinitis pigmentosa. Retinitis pigmentosa is an eye disorder. Eyesight is gradually lost. Hypogondadism means the testes and ovaries do not produce enough sex hormones. In males, this results in the underdevelopment of sexual organs. It also results in reduced sperm count. In addition, there may be low levels of testosterone. Females may have defective egg development and early menopause.

Physical traits are not obvious except some people have paralysis in the lower body. This is similar to Bardet-Biedl Syndrome). The condition is often accompanied by involuntary muscle spasms known as spastic paraplegia. Unlike Bardet-Biedl syndrome, obesity is not an issue.