William syndrome is caused by a deletion of genetic material on one copy of chromosome 7, resulting in the person only having a single copy of the genes on this deleted region (on the other chromosome 7). It usually the result of a random deletion around conception, rather than being inherited from an affected parent.

Epidemiology

1/10,000 births

Clinical Features

Characteristic faces:

• Broad forehead
• Starburst eyes (a star-like pattern on the iris)
• Flattened nasal bridge
• Long philtrum
• Wide mouth with widely spaced teeth
• Small chin
• Very sociable trusting personality
• Mild learning disability

TOM TIP: The distinctive features to remember with William syndrome are the very sociable personality, the starburst eyes and the wide mouth with a big smile. It is worth remembering the association with supravalvular aortic stenosis and hypercalcaemia, as these are unique features that are easy to test in exams.

Internal features

• Supravalvular aortic stenosis (narrowing just above the aortic valve)
• Attention-deficit hyperactivity disorder