Williams syndrome

Definition:

A condition of unknown cause characterized by mental retardation, unusual facial appearance, and frequent heart abnormalities.

Causes, incidence, and risk factors:

Williams syndrome is a rare condition whose cause remains undetermined. The most commonly observed findings are mild-to-moderate mental retardation which may be mild to moderate, and abnormal facial features, including prominent lips with an open mouth, a long philtrum (midline of upper lip from lip margin to nose), low nasal bridge, or epicanthal folds. There may be partial absence of the teeth and defective tooth enamel.

Affected people may have heart and blood vessel problems, including supravalvular aortic stenosis, pulmonic stenosis and pulmonary artery stenosis. These abnormalities are thought to be due to a subtle defect in connective tissue. Many affected people may have elevated levels of calcium in their blood (hypercalcemia).

Other minor abnormalities may be present but are not consistent. An irregular star-like pattern in the iris of the eye is often seen. Bony abnormalities include pectus excavatum, an inward bend of the small finger (clinodactyly), and an inward point of the great toe.