Williams syndrome: A genetic disorder characterized by mild mental retardation, unique personality characteristics, unusual facial features, and cardiovascular disease. The level of calcium tends to be high in blood (hypercalcemia) and urine (hypercalciuria).
Mental retardation is the rule and ranges from severe to mild. Personality features include overfriendliness, generalized anxiety, and attention deficit disorder. Facial features include narrow forehead, fullness about the eyes, short nose, flat midface, full lips, wide mouth, small jaw, and prominent earlobes. Supravalvar aortic stenosis (narrowing of the aorta just above the valve) is the most common and important cardiovascular abnormality.
Williams syndrome is inherited in an autosomal dominant manner and is due to a small chromosome deletion. Most cases are new occurrences but parent-to-child transmission is known. The region deleted is from chromosome 7 (band 7q11) and includes the ELN (elastic) gene, a useful molecular marker in tests to detect the deletion. The syndrome is due not merely to the loss of ELN but to contiguous gene deletion, loss of a series of adjacent genes.