The chromosomal deletion that causes Williams Syndrome is so small that it cannot be seen in a karyotype. .
WS pg 2.
However, the deletion can be observed using a special technique called fluorescent in situ hybridization, or FISH. This technique allows DNA sequences to be labeled with a fluorescent chemical (called a probe) that lights up when exposed to ultraviolet (UV) light. The Williams Syndrome deletion can be detected by labeling the elastin gene with a fluorescent probe. The gene is will light up under a UV light only if it is present; a lack of signal indicates a deletion (Greer, 1997, p 112). .
The majority of individuals with Williams syndrome have some type of heart or blood vessel problem. Typically, there is narrowing in the aorta (producing supravalvular aortic stenos SVAS), or narrowing in the pulmonary arteries. There is a broad range in the degree of narrowing, ranging from trivial to severe (requiring surgical correction of the defect) (Shulman, 1996, p 12).
Elevations in their blood calcium level is common. The true frequency and cause of this problem is unknown. When hypercalcemia is present, it can cause extreme irritability or "colic-like" symptoms. Occasionally, dietary or medical treatment is needed. In most cases, the problem resolves on its own during childhood ) (Shulman, 1996, p 114).
Lower birth-weight and development is a characteristic of the syndrome. Slow weight gain, especially during the first several years of life, is also a common problem and many children are diagnosed as "failure to thrive". Adult stature is slightly smaller than average.
Many infants and young children have feeding problems. These problems have been linked to low muscle tone, severe gag reflex, poor suck/swallow, tactile defensiveness etc. .
Feeding difficulties tend to resolve as the children get older (Lopez, 1992, p 5).
Slightly small, widely spaced teeth are common in children with Williams syndrome.