Williams syndrome is a very interesting condition and may be the origin of elf myths. People who have it are small, cute ("elfin facial appearance"), cheerful, and glib. They have wonderfully fluent speech, but they are also physically weak and mentally retarded, with an average IQ of around 60 and problems with numbers, memory, and visual-spatial perception. A host of other physical characteristics are associated with it.
There are very few genetic differences between Willliamses and normals, so researchers had to look at relatively few genes to find one associated with it, and they found one that is related to its role in intelligence.
I predict that within 50 years, Williams syndrome will be diagnosed and ameliorated in utero. In fact, I predict that within 50 years, a whole string of genetic or congenital mental and physical problems will occur only in people without access to modern medicine. Williams, autism, schizophrenia, depression, bi-polar, spinal bifida, multiple sclerosis--it's hard to think of something you can be born with that shouldn't be fixable in 50 years.
This will be another difference between the US and, say, the Central African Republic. (Or whatever it is named by then; it was optimistically called the Central African Empire when I passed through Bangui in 1983. I'll tell you about that trip some evening over margaritas. I especially liked the airport fire engines that had surface-to-air missiles on top. I doubt that it is any more of a republic now than it was an empire then.)