Deletion of genes on the long arm of Chromosome 7 (7q) can cause a characteristic syndrome of abnormal neurodevelopment and malformations (Williams syndrome). This test provides diagnostic information.
In an affected person, an abnormal result is diagnostic of this microdeletion syndrome. Further family studies may clarify the recurrence risk in relatives.
A normal result does not exclude a clinical diagnosis as there are other mutations on Chromosome 7 which can cause the syndrome.
These mutations are usually de novo and do not increase the risk of this disorder in siblings or other relatives. However a parent and other relatives may carry a balanced translocation involving this chromosome region and be at increased risk of having an affected child.
Fluorescent in situ hybridisation (FISH) analysis using probes located on the long arm of Chromosome 7.
Requesting the test
This test is usually requested by a paediatrician or clinical geneticist. A full karyotype is usually requested at the same time.
2-5 mL blood in EDTA and 2-5 mL blood in lithium heparin. Specimens may be collected by the requesting practitioner or at any Sonic Healthcare collection centre (see link below).
To help ensure the quality of the test, a genetic test should be done with a dedicated sample whenever possible i.e. a sample collected specifically for that test rather than a sample that is used for multiple tests.
We recommend that the patient or another adult check the labelling of request forms and sample tubes.
If the clinical diagnosis is uncertain, it may be preferable to request a microarray study rather than this specific FISH test as a microarray screens for microdeletions and duplications across all chromosomes.