Williams-Beuren syndrome.

Copyright © 2010 Massachusetts Medical Society. Williams–Beuren syndrome (also known as Williams’ syndrome; Online Mendelian Inheritance in Man [OMIM] number, 194050), a multi­ system disorder, is caused by deletion of the Williams–Beuren syndrome chromosome region, spanning 1.5 million to 1.8 million base pairs and containing 26 to 28 genes. Exactly how gene loss leads to the characteristic phenotype of Williams–Beuren syndrome is unknown, but hypoexpression of gene products is likely to be involved. Estimated to occur in approximately 1 in 10,000 persons,1 Williams–Beuren syndrome is a microdeletion disorder, or contiguous­gene­deletion disorder, that can serve as a model for the study of genotype–phenotype correlations and potentially reveal genes contributing to diabetes, hypertension, and anxiety. The first cases of Williams–Beuren syndrome were described as two seemingly unrelated disorders. One presentation was characterized by hypercalcemia plus per­ sistent growth failure, characteristic facial appearance, “mental retardation,” heart murmur, and hypertension,2,3 while the other was characterized by supravalvular aortic stenosis (narrowing of the ascending aorta above the aortic valve, involving the sinotubular junction) plus a distinctive facial appearance, “mental retardation,” “friendly” personality, and growth retardation.4,5 Subsequent description of a patient with features common to both phenotypes indicated that these were variations of the same disorder,6 now referred to as Williams–Beuren syndrome.