The Diagnosis Of Williams Syndrome typically involves a two-pronged approach: clinical evaluation based on a range of distinctive characteristics and a definitive medical confirmation through genetic testing.
Clinical diagnosis is the initial step, relying on the recognition of a specific set of features associated with Williams syndrome. These characteristics, detailed further in resources such as key features of WS, and the overview provided in What is Williams syndrome, guide clinicians towards a potential diagnosis.
Confirmation of Williams syndrome requires a medical genetic test, specifically a DNA test. This test is conducted using a small blood sample from the individual. Crucially, in the vast majority of cases (98-99%), individuals exhibiting the typical clinical features of Williams syndrome will have a deletion in the elastin gene.
From a genetic standpoint, Williams syndrome arises from a deletion in the 7q11.23 region of chromosome 7. This deleted region encompasses 26-28 genes, notably including the elastin gene. The elastin gene serves as a key “marker gene” for Williams syndrome.
Williams syndrome is categorized as a contiguous gene syndrome. This term signifies that all the genes deleted are located consecutively within the Williams syndrome “critical region,” a segment spanning 26-28 genes. Two primary DNA tests are utilized to detect Williams syndrome: the FISH (Fluorescence In Situ Hybridization) test and the Microarray analysis. Both tests are effective in identifying the characteristic genetic deletion.
It is paramount to understand that Williams syndrome is fundamentally a genetic diagnosis. An individual lacking the specific gene deletion does not have Williams syndrome. Therefore, even if a person receives a clinical diagnosis of Williams syndrome based on observed characteristics, but subsequent genetic testing reveals no deletion, the definitive diagnosis is that Williams syndrome is not present.
Important Note: The occurrence of Williams syndrome in multiple family members is exceedingly rare. This is because the genetic deletion responsible for Williams syndrome usually arises spontaneously, with an estimated occurrence rate of only 1 in 7,500 births. However, it is essential to consider that an individual with Williams syndrome has a 50% chance of passing the condition on to each of their children. For individuals with Williams syndrome considering parenthood, consultation with an obstetrician is recommended to discuss prenatal testing options, such as the FISH test, for embryonic cells.
