Williams syndrome is caused by the deletion of genetic material from the region q11.2 of chromosome 7. The deleted region includes more than 20 genes, and researchers believe that the loss of several of these genes probably contributes to the characteristic features of this disorder. CYLN2, ELN, GTF2I, GTF2IRD1, and LIMK1 are among the genes that are typically deleted in people with Williams syndrome. Researchers have found that loss of the ELN gene, which codes for the protein elastin, is associated with the connective-tissue abnormalities and cardiovascular disease (specifically supravalvular aortic stenosis (SVAS) and supravalvular pulmonary stenosis (SVPS)) found in many people with this disease. Studies suggest that deletion of LIMK1, GTF2I, GTF2IRD1, and perhaps other genes may help explain the characteristic difficulties with visual–spatial tasks. Additionally, there is evidence that the loss of several of these genes, including CYLN2, may contribute to the unique behavioral characteristics, mental retardation, and other cognitive difficulties seen in Williams syndrome.
The relationship between other genes in the deleted region and the signs and symptoms of Williams syndrome is unknown.