Williams syndrome, also known as Williams-Beuren syndrome, is a rare genetic disorder characterized by growth delays before and after birth (prenatal and postnatal growth retardation), short stature, a varying degree of mental deficiency, and distinctive facial features that typically become more pronounced with age. Such characteristic facial features may include a round face, full cheeks, thick lips, a large mouth that is usually held open, and a broad nasal bridge with nostrils that flare forward (anteverted nares). Affected individuals may also have unusually short eyelid folds (palpebral fissures), flared eyebrows, a small lower jaw (mandible), and prominent ears. Dental abnormalities may also occur including abnormally small, underdeveloped teeth (hypodontia) with small, slender roots.
Williams syndrome may also be associated with heart (cardiac) defects, abnormally increased levels of calcium in the blood during infancy (infantile hypercalcemia), musculoskeletal defects, and/or other abnormalities. Cardiac defects may include obstruction of proper blood flow from the lower right chamber (ventricle) of the heart to the lungs (pulmonary stenosis) or abnormal narrowing above the valve in the heart between the left ventricle and the main artery of the body (supravalvular aortic stenosis). Musculoskeletal abnormalities associated with Williams syndrome may include depression of the breastbone (pectus excavatum), abnormal side-to-side or front-to-back curvature of the spine (scoliosis or kyphosis), or an awkward gait. In addition, most affected individuals have mild to moderate mental retardation; poor visual-motor integration skills; a friendly, outgoing, talkative manner of speech; a short attention span; and are easily distracted.
In most individuals with Williams syndrome, the disorder appears to occur spontaneously for unknown reasons (sporadically). However, familial cases have also been reported. Sporadic and familial cases are thought to result from deletion of genetic material from adjacent genes (contiguous genes) within a specific region of chromosome 7 (7q11.23).