Williams syndrome is a rare genetic disorder that affects a childs growth, physical appearance, and cognitive development. People who have Williams syndrome are missing genetic material from chromosome 7, including the gene elastin. This genes protein product gives blood vessels the stretchiness and strength required to withstand a lifetime of use. The elastin protein is made only during embryonic development and childhood, when blood vessels are formed. Because they lack the elastin protein, people with Williams Syndrome have disorders of the circulatory system and heart.