Diagnosing Williams Syndrome

The diagnosis of Williams syndrome generally has two parts:

  • Clinical diagnosis is based on a variety of characteristics common to Williams syndrome.  A combination of specific facial characteristics including a stellate pattern in the iris, long philtrum and puffiness around the eyes; cardiovascular disease - especially aortic or pulmonary stenosis; feeding difficulties (in infants) and developmental delays will lead to a blood test to confirm Williams syndrome.
  • There are two tests which can be used to confirm Williams syndrome - FISH test or micro-array analysis.

The FISH test

Fluorescent in situ hybridization (FISH), is a type of specialized chromosome analysis utilizing specially prepared elastin probes. If a patient has 2 copies of the elastin gene (one on each of their chromosomes #7), they probably do not have WS. If the individual only has one copy, the diagnosis of WS will be confirmed.  Virtually all (98-99%) persons with Williams syndome will have a deletion of the elastin gene along with about 26 other genes.  These genes comprise the "Williams syndrome critical area" on Chromosome #7.

In more technical terms:

Williams syndrome is the result of a deletion of the 7q11.23 region of chromosome #7 containing the elastin gene.  It is believed to be a contiguous gene syndrome. Diagnosis of Williams syndrome is confirmed by dual colour FISH analysis using a specific probe and a control probe.

The laboratory will need 5 ml of blood drawn in a Sodium heparin tube. The sample should arrive in the lab the same day it was drawn or on the following day. Results are usually available in 2-4 weeks.

The FISH test is readily available at major hospitals and Cytogenetics laboratories around the country, but it is not a routine test. Therefore not all labs will do FISH-based diagnosis. Families or their physicians should call the lab in advance to make sure they can perform the test.

If you have any doubts that a child may have Williams syndrome, the FISH test will give you a clear cut answer in most cases.

It is important to stress that WS is a genetic diagnosis and an individual who does not have the gene deletion does not have Williams syndrome (i.e. a person who was clinically diagnosed with WS but was later found not be have a deletion in fact, does NOT have WS).

NOTE: the incidence of WS is 1 in 10,000 births.  It is extremely unlikely that any other family member will also have Williams syndrome. However, if the individual with Williams syndrome plans to become a parent, there is a 50/50 chance that his or her child will have Williams syndrome. If such a situation should arise, consult an obstetrician about using the FISH test for prenatal testing of the embryonic cells.