Williams syndrome (WS or WMS; also Williams–Beuren syndrome or WBS) is a rare neurodevelopmental disorder characterized by a distinctive, "elfin" facial appearance, along with a low nasal bridge; an unusually cheerful demeanor and ease with strangers; developmental delay coupled with strong language skills; and cardiovascular problems, such as supravalvular aortic stenosis and transient hypercalcaemia. It is caused by a deletion of about 26 genes from the long arm of chromosome 7. The syndrome was first identified in 1961 by Dr. J. C. P. Williams of New Zealand and has an estimated prevalence of 1 in 7,500 to 1 in 20,000 births.