Williams syndrome (or Williams-Beuren syndrome) is a rare microdeletion anomaly concerning chromosome 7, mostly sporadic, leading to the deletion of several genes among which the ELN gene.

Clinical features: multisystemic neurodevelopmental disorder characterized by a distinct facial appearance, cardiac anomalies (most frequently supravalvular aortic stenosis), cognitive and developmental abnormalities, and connective tissue abnormalities (such as joint laxity).