The cause of William's Syndrome is a hemizygous deletion on chromosome 7.
One of the genes that is deleted is the LIMK1 gene which codes for the LIMK1 protein. The LIMK1 protein is involved in the regulation of actin in the cytoskeleton. The actin structurally helps cells form and maintain their proper shape. It also pulls sister chromatids apart during mitosis and is required for cell locomotion. (www.wehi.edu.au/research/devneur/neuron_miswiring.html). The clinical molecular diagnosis for Williams Syndrome is confirmed by FISH using a WS-specific probe. The probe is detects the elastin gene. A blood sample is taken, usually during childhood, and is then treated with two specific colored markers that fluoresce when exposed to ultra-violet light. One of the markers attaches to each of the two copies of chromosome number seven in a cell. When both copies of the chromosome possess the elastin gene, an additional fluorescence of another color is seen attached at another location to each of the two chromosome 7s.
However, since Williams Syndrome patients have only one copy of the elastin gene, only one spot will fluoresce. The molecular test is 95% accurate, only because 95% of patients show the hemizygous deletion (www.wsf.org).
There does not seem to be an evolutionary benefit to Williams Syndrome. The allele is maintained in the population because people with Williams Syndrome have a 50% chance of passing the disease onto their children since it is a hemizygous deletion. Williams Syndrome is estimated to occur in 1/20,000 births. It affects males and females equally and can occur in all ethnic groups. There is certainly a large financial burden for the family. Also, not all people with Williams Syndrome are capable of living on their own, so it is a social issue of what the best living situation is for these people. Many people...