"First discovered by John C.P. Williams of New Zealand in 1961, Williams syndrome, also known as Williams-Burnham Syndrome, is a result of a deletion of a specific region on chromosome number seven, containing 26 to 28 genes. Approximately one in 10,000 births are affected by this spontaneous gene deletion."
https://en.wikiquote.org/wiki/The_Mayor%3A_A_Chronicle_of_Williams_Syndrome%2C_with_Josh_Duffy