NINDS - Williams Syndrome
National Institute of Neurological Disorders and Stroke offers an informational page about WS. Includes a definition, treatment and prognosis.
NLM Archives - Williams Syndrome
The National Library of Medicine offers the alternate names of this disorder, a summary, the major features, and historical references.
NORD - Williams Syndrome
The National Organization for Rare Disorders offers a definition, alternative names, and related organizations.